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295 Pages·2012·3.69 MB·English

Sunday Afternoon, October 28, 2012
Biomaterials Plenary Session on-off-switching at low intensities I, by resorting to molecular switching
mechanisms that entail low switching thresholds I. An I lower by many
Room: 23 - Session BP+AS-SuA s s
orders of magnitude is provided by reversibly switching the fluorophore to a
long-lived dark (triplet) state2 or between a long-lived ‘fluorescence
Biomaterials Plenary - Bioimaging: In Vacuo, In Vitro, activated’ and ‘deactivated’ state.2,5 These alternative switching
mechanisms entail an I that is several orders of magnitude lower than in
In Vivo s
STED. In imaging applications, STED/RESOLFT enables fast recordings
Moderator: M.R. Alexander, University of Nottingham, and the application to living cells, tissues, and even living animals.6,7
UK Starting from the basic principles of nanoscopy we will discuss recent
developments8,9 with particular attention to RESOLFT and the recent
4:00pm BP+AS-SuA1 NanoBio Imaging for New Biomedical nanoscale imaging of the brain of living mice7 by STED.
Applications, D.W. Moon, Korea Research Institute of Standards and 1 Hell, S. W. & Wichmann, J. Breaking the diffraction resolution limit by
Science INVITED stimulated-emission - stimulated-emission-depletion fluorescence
Surface and interface analysis techniques have been mainly developed to microscopy, 780-782, doi:10.1364/OL.19.000780 (1994).
meet the demands on atomic scale characterization from semiconductor 2 Hell, S. W. Toward fluorescence nanoscopy, 1347-1355 (2003).
industries. KRISS has been trying to meet the surface and interface analysis
3 Hell, S. W., Jakobs, S. & Kastrup, L. Imaging and writing at the
challenges from semiconductor industries and furthermore to extend the
nanoscale with focused visible light through saturable optical transitions,
application scope to biomedical areas. In this presentation, I’d like to report
859-860 (2003).
our recent activities of nanobio imaging for new biomedical applications
such as 1) Coherent Anti-Stokes Raman Scattering (CARS) for 4 Hell, S. W. Far-Field Optical Nanoscopy, 1153-1158 (2007).
atherosclerotic plaque imaging 2) Time-of-flight secondary ion mass 5 Hofmann, M., Eggeling, C., Jakobs, S. & Hell, S. W. Breaking the
spectrometry (TOF-SIMS) for mass imaging of collagen fibrils, diffraction barrier in fluorescence microscopy at low light intensities by
atherosclerotic plaques, and cancer tissues and 3) Surface Plasmon using reversibly photoswitchable proteins, 17565-17569 (2005).
Resonance Imaging Ellipsometry for cell adhesion, migration, and
6 Rankin, B. R. Nanoscopy in a Living Multicellular Organism Expressing
infiltration dynamics for HUVEC, CASMC, and T cells 4) TOF-medium
GFP, L63 - L65 (2011).
energy ion scattering spectroscopy (TOF-MEIS) for nanothin films and
nanoparticles such as CdSe/ZnS quantum dots and calcium hydroxyapatite 7 Berning, S., Willig, K. I., Steffens, H., Dibaj, P. & Hell, S. W. Nanoscopy
nano-size biominerals. Future challenges of nanobio imaging for biomedical in a Living Mouse Brain, 551 (2012).
applications will be discussed. 8 Grotjohann, T. Diffraction-unlimited all-optical imaging and writing with
a photochromic GFP, 204-208 (2011).
4:40pm BP+AS-SuA3 3-D View into Cells by X-ray Nano- 9 Brakemann, T. A reversibly photoswitchable GFP-like protein with
Tomography, G. Schneider, P. Guttmann, S. Werner, K. Henzler, S. fluorescence excitation decoupled from switching, 942-947 (2011).
Rehbein, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH,
Germany INVITED

X-ray imaging offers a new 3-D view into cells. With its ability to penetrate
whole hydrated cells it is ideally suited for pairing fluorescence light
microscopy and nanoscale X-ray tomography. The HZB TXM at the
undulator U41 provides a spectral resolution of 10.000 and a spatial
resolution of 11 nm. For high resolution tomography, we adopted a tilt stage
originally developed for electron tomography. The stage is able to tilt
samples up to ± 80°. Such a large tilt of flat sample holders is impossible
with TXM at bending magnet sources because they require a
monochromator pinhole to be positioned close to the specimen. In our
TXM, the holder geometry is no longer restricted to glass
tubes.Conventional fluorescence images are diffraction-limited to ~200 nm,
whereas current TXM achieve a ten-fold improvement in resolution. Since
fluorescence and X-ray microscopy permit analysis of whole cells, it is
possible to investigate the same cell in both microscopes by correlative
microscopy. These correlative studies are ideally suited to X-ray
microscopy because of its ability to image cells in 3D. In the talk, we
present the cryo TXM and selected applications. In particular, we will show
the internal structures of mammalian cells, i.e. plasma membrane,nuclear
membrane, nuclear pores, nucleoli, endoplasmic reticulum, vesicles,
lysosomes and mitochondria. It is now also possible to resolve internal
organellar structures, such as mitochondrial cristae, the double nuclear
membrane and lysosomal inclusions. In addition, we discuss ways towards
10 nm 3D imaging of cells. Keywords: X-ray microscopy, tomography, cell
organelles, correlative microscopy
References
1. S. Rehbein, S. Heim, P. Guttmann, S. Werner, G. Schneider, Phys. Rev.
Lett. 103, (2009) 110801
2. G. Schneider, P. Guttmann, S. Heim, S. Rehbein, F. Mueller, K.
Nagashima, J.B. Heymann, W.G. Müller, J.G. McNally, Nature Methods 7
(2010), 985-987
3. P. Guttmann, C. Bittencourt, S. Rehbein, P. Umek, X. Ke, G. Van
Tendeloo, C. P. Ewels and G. Schneider, Nature Photonics 6 (2012), 25-29
4. G. Schneider, P. Guttmann, S. Rehbein, S. Werner, R. Follath, J. Struct.
Biol. 177 (2012), 212-223
5:20pm BP+AS-SuA5 Nanoscopy with Focused Light, S.W. Hell, Max-
Planck-Institut für Biophysikalische Chemie, Germany INVITED
In STED microscopy1, fluorescent features are switched off by the STED
beam, which confines the fluorophores to the ground state everywhere in
the focal region except at a subdiffraction area of extent. In RESOLFT
microscopy,2,3 the principles of STED have been expanded to fluorescence
1 Sunday Afternoon, October 28, 2012
Monday Morning, October 29, 2012
Actinides and Rare Earths Focus Topic have also obtained the first direct measurement of Hubbard gap in 5f system
[4].
Room: 6 - Session AC+MI+SS+TF-MoM
The novel femtosecond pump-probe methods provide unique information
about the dynamics of 5f quasiparticles, and open novel possibilities in
Electronic Structure and Spectroscopy of Actinides addressing the long-standing questions about the role of near-Fermi level
Moderator: A.J. Nelson, Lawrence Livermore National band renormalization in establishing the physical properties of correlated
materials.
Laboratory
References
9:00am AC+MI+SS+TF-MoM3 Strong Correlations and the [1] Physical Review B 84, 161101(Rapid Comm.) (2011)
Electronic Structure of the Actinide Dioxides, R.L. Martin, Los Alamos [2] Physical Review B 84, 161103(Rapid Comm.) (2011)
National Laboratory INVITED
[3] Physical Review Letters 106, 207402 (2011)
The series of actinide dioxides (AnO2, An=Pa, ... Cm) are difficult
[4] manuscript in preparation
challenges for electronic structure theory. The early members of the series
are Mott insulators, the band gap corresponding to f-f transitions, while the
later members, beginning with PuO2, are O2p -> An5f charge transfer 11:00am AC+MI+SS+TF-MoM9 Comparison of Spectroscopic Data
insulators. I will review recent experimental results (X-ray absorption, with Cluster Calculations of Plutonium, Plutonium Dioxide and
photoemission and optical band gaps) which now allow us to distinguish Uranium Dioxide, J.G. Tobin, S.W. Yu, B.W. Chung, Lawrence Livermore
among several many-body approximations to their electronic structure, National Laboratory, M.V. Ryzhkov, Russian Academy of Science-
including the SIC, DFT+U, DMFT+U and hybrid DFT (HSE) approaches. Ekaterinburg, A. Mirmelstein, Russian Federation Nuclear Center-
Snezhinsk
9:40am AC+MI+SS+TF-MoM5 Synchrotron Radiation Studies of Using spectroscopic data produced in the experimental investigations of
Actinide Compounds, S.M. Butorin, Uppsala University, Sweden bulk systems, including X-Ray Absorption Spectroscopy (XAS),
INVITED Photoelectron Spectroscopy (PES) and Bremstrahlung Isochromat
Spectroscopy (BIS) [1-5], the theoretical results within for U0 [6], PuO [6]
Core-to-core resonant inelastic x-ray scattering (RIXS) and valence-to-core 2 2
and Pu [7] clusters have been evaluated. The calculations of the electronic
RIXS techniques are two complimentary ways for probing the electronic
structure of the clusters have been performed within the framework of the
structure in actinide systems. Specific cuts of the core-to-core RIXS maps
Relativistic Discrete-Variational Method (RDV). [6,7] The comparisons
around Mβ and Lαlines of actinides represent remarkably improved high-
between the LLNL experimental data and the Russian calculations are quite
resolution x-ray absorption spectra of actinide 3d and 2p edges,
favorable. The cluster calculations may represent a new and useful avenue
respectively, as a result of limited lifetime broadening of core holes present
to address unresolved questions within the field of actinide electron
in shallower levels in the final state of the spectroscopic process. That
structure, particularly that of Pu. Observation of the changes in the Pu
allows for more detailed studies of unoccupied states and better oxidation
electronic structure as a function of size suggests interesting implications
states assignments. In turn, the valence-to-core RIXS spectra are only
for bulk Pu electronic structure.
limited by the instrumental resolution and provide information about
actinide chemical bonding and interactions between valence electrons. Acknowledgements
Lawrence Livermore National Laboratory is operated by Lawrence
Livermore National Security, LLC, for the U.S. Department of Energy,
A comparison of experimental data with results of model calculations
National Nuclear Security Administration under Contract No. DE-AC52-
shows that the resonant spectra of actinide systems recoded at the actinide
07NA27344. JGT and SWY were supported by the DOE Office of Science,
M(3d) and O (5d) thresholds which probe the 5f states can be interpreted
Office of Basic Energy Science, Division of Materials Science and
using the many-body theory, such as the Anderson impurity model, while
Engineering. Work at the RAS and VNIITF was supported in part by
the data obtained at the L3 threshold and representing the 6d states of
Contract B590089 between LLNL and VNIITF. The Advanced Light
actinides can be described within a single-particle approach, such as
Source (ALS) in Berkeley and the Stanford Synchrotron Radiation
LDA+U (local density approximation with supplemented Coulomb
Laboratory are supported by the DOE Office of Science, Office of Basic
interaction U) framework.
Energy Science .

References
In course of discussion of the above statements, we present the RIXS data
1. J.G. Tobin and S.-W. Yu, Phys. Rev. Lett, 107, 167406 (2011).
for a number of actinide systems with emphasis on the results contributing
to understanding of the U-O and Pu-O phase diagrams, in particular data for 2. S.-W. Yu,J. G. Tobin, J. C. Crowhurst, S. Sharma, J. K. Dewhurst, P.
UO2+x, U4O9, U3O8 and PuO2+x. The influence of the Coulomb Olalde-Velasco, W. L. Yang, and W. J. Siekhaus, Phys. Rev. B 83, 165102
interaction between 5f electrons on the electronic structure of actinides is (2011).
also discussed. 3. J.G. Tobin, B.W. Chung, R. K. Schulze, J. Terry, J. D. Farr, D. K. Shuh,
K. Heinzelman, E. Rotenberg, G.D. Waddill, and G. Van der Laan, Phys.
10:40am AC+MI+SS+TF-MoM8 Quasiparticle Dynamics in Uranium Rev. B 68, 155109 (2003).
Systems from Ultrafast Spectroscopies, T. Durakiewicz, Los Alamos 4. J.G. Tobin, P. S ö derlind, A. Landa, K.T. Moore, A.J. Schwartz, B.W.
National Laboratory Chung, M.A. Wall, J.M. Wills, R.G. Haire, and A.L. Kutepov, J. Phys.
Every time we add a new dimension to an experimental method, we open a Cond. Matter 20, 125204 (2008) .
window to novel, unexpected and fascinating phenomena. Here we show
5. S.-W. Yu,J. G. Tobin, P. Olalde-Velasco, W. L. Yang,and W. J.
the results of our focused effort of adding time-domain to the powerful Siekhaus,” J. Vac. Sci. Tech. A. 30, 011402 (2012).
experimental techniques of Angle Resolved Photoelectron Spectroscopy
(ARPES) and reflectivity. The novel tools are applied to actinides and help 6. M.V. Ryzhkov and A.Ya. Kupryazhkin, J. Nucl. Materials 384, 226
us understand the details of the electronic structure of the correlated f- (2009).
electron materials. 7. M.V. Ryzhkov, A. Mirmelstein, S.-W. Yu and J.G. Tobin, “Probing
In the hidden order system URuSi we investigate the massive Actinide Electronic Structure through Pu Cluster Calculations,” submitted
2 2
renormalization of the Fermi surface at specific k values. The application of to Phys. Rev. B, Feb 2012.
time-resolved ARPES allowed a direct measurement of the momentum-
resolved quasiparticle lifetime which was shown to increase by an order of
magnitude at the hidden order transition. Time-resolved ARPES together
with the ultrafast reflectivity results provided evidence for forming a
multiple gap structure, including the hybridization gap, pseudogap and HO
gap [1, 2].
Another actinide system of interest is a Mott insulator UO, where we have
2
investigated the complex dynamics of the Hubbard excitons. We have found
that the dynamics can be divided into four distinct processes: instantaneous
hop, picosecond lattice deformation, phonon emission and relaxation, and
the slow relaxation related to the propagation of Hubbard excitons [3]. We
Monday Morning, October 29, 2012 2
Applied Surface Science analysis of angular/energy photoelectron spectra. This is done for standard
AlKα and Mg Kα laboratory sources, but the possibility to gain additional
Room: 20 - Session AS-MoM
information by increasing the photon energy to the hard x-ray regime is also
examined.
Quantitative Surface Chemical Analysis, Technique 1. http://www.nist.gov/srd/nist100.cfm.
Development, and Data Interpretation - Part 1 2. W. Smekal, W. S. M. Werner, and C. J. Powell, Surf. Interface Anal. 37,
Moderator: J.A. Ohlhausen, Sandia National Laboratories, 1059 (2005).
S. Suzer, Bilkent University, Turkey
9:20am AS-MoM4 XPS Characterisation of InP Features Etched in
Cl-Ar and Cl-H Inductively Coupled Plasmas, C. Cardinaud, CNRS,
8:20am AS-MoM1 2012 AVS Albert Nerken Award Lecture: Fra2nce, R. Ch2ans2on, CNRS-IMN, France, S. Bouchoule, CNRS-LPN,
Characterization of Thin-Film Nano-Structures by XPS, S. Tougaard*, France, A. Rhallabi, M.-C. Fernandez, Université de Nantes, France
University of Southern Denmark INVITED
High-aspect-ratio etching of InP-based heterostructures is a critical building
This is a brief summary of the work that was involved in the development block for photonic device fabrication. This study is focused on the chemical
of the technique for quantitative XPS from analysis of the background of characterisation of the bottom and sidewall surfaces of InP ridge patterns
inelastically scattered electrons. About 30 years ago it became evident that etched with Cl2-Ar and Cl2-H2 plasmas using a SiNx mask. Each sample
these electrons must carry valuable information about the depth where the contains five arrays combining various ridge widths (1.5 to 4µm) and space
XPS electrons are excited. Theoretical modeling started and algorithms widths (5 to 16µm) plus four InP and mask open areas. Experiments are
were developed. It was necessary to have an accurate description of the carried out in a Kratos-Axis-Ultra. The direction of analysis is vertical, i.e.
electron energy loss processes which at that time was not available. normal to the sample surface, while the x-rays strike the surface with an
Theoretical calculations of inelastic cross sections based on a dielectric angle of incidence α = 60°. The sample can be rotated in azimuth to align
response description were done and a new experimental method to precisely the arrays, either parallel to or perpendicular to the plane defined
determine this from analysis of reflected electron energy loss spectra by the x-source and the analyser. The first arrangement enables the analysis
(REELS) was also developed. of the bottom (as well as the top of the ridge), whereas the second
To make these procedures for quantitative XPS analysis work in practice it arrangement allows the analysis of the sidewall after tilting the sample. In
is however not possible to use calculations valid only for specific sample this latter case two configurations are used. Taking advantage of the
compositions. Therefore an effort was made early on to find cross sections absorption of the x-rays by the InP ridges (1.8µm of InP absorbs 99% of
which can be used as an approximation for wide classes of materials and AlKα under 60° of angle of incidence), the first configuration consists in
compositions. This resulted in the Universal cross sections which are now tilting the sample opposite to the x-ray source until the bottom is totally
widely used and without which practical use of the formalism would have screened. Simultaneously this brings the sidewall that is irradiated in the
been very limited. The resulting XPS analysis technique was summarized in analyser line of sight. Tilting the sample towards the x-ray source to an
[1]. angle θ = atan(space width / ridge height) allows to shadow the bottom and
observe photoelectrons coming from the sidewall (and the top of the
In the following years, much effort was then centered on applications to
ridges), in this case θ needs to be larger than α to obtain full irradiation of
increasingly finer details of the morphology of nanostructures. This requires
the sidewall that comes in the analyser line of sight.
a careful data analysis since otherwise the uncertainty on the determined
morphology may be large. Sometimes the detailed morphology is however For each array, the intensity of the In, P, N and Si core levels, normalised
not the most important issue for technological applications. Things like with respect to that measured on the mask and InP open spaces, are
speed of analysis, robustness, and automation is often more important in compared to the corresponding ratio calculated from the geometry of the
industrial environments. It was therefore decided to develop a simpler array and the analysis arrangement or configuration. Modelling takes into
algorithm which does not give as detailed information but which is very account the contribution of the various surfaces (mask, InP) in the line of
robust and therefore faster to use and less dependent on a meticulous sight of the analyser, and the rate of irradiation according to the geometry of
analysis procedure. The resulting algorithm [2] has been shown to be very the array and the nature of the materials (InP ridge, mask) the x-rays pass
robust and therefore suitable for automation. It proved also effective in through. This comparison points out the relation between the intensity
generating 3D images of nano-structures where automation is mandatory emitted from the bottom and the aspect ratio of the array. A good agreement
since thousands of spectra (one per pixel) must be analyzed. is obtained when including the analyser acceptance angle to the model.
Concerning the sidewall the discrepancy between experiment and
Throughout, efforts were always exerted to test the validity of each step in
simulation corroborates the presence of a passivation layer. The
the development of algorithms and procedures by designing and performing
presentation will discuss in detail the influence of the plasma chemistry on
critical experiments. This is of utmost importance to ensure progress which
the quantitative composition of the sidewall and the bottom.
does not lead to dead ends.
In this talk I will give an overview of the development of the technique and
9:40am AS-MoM5 Simplified Extrinsic Background for XPS Data
discuss some technological applications.
Fitting, A. Herrera-Gomez, UAM-Azcapotzalco and CINVESTAV-
1. S. Tougaard, J. Vac. Sci. Technol. A14, 1415 (1996) Queretaro, Mexico
2. S. Tougaard, J. Vac. Sci. Technol. A23, 741 (2005) In this presentation it is described a simplified form of the background for
extrinsic scattering in the near-peak regime for X-Ray Photoelectron
9:00am AS-MoM3 Simulation of Electron Spectra for Surface Spectroscopy (XPS) data peak-fitting. It directly accounts for the change on
Analysis (SESSA): (Hard) X-ray Photoelectron Spectra of the slope of the background between the two sides of the core-level peak.
Nanostructured Surfaces, W.S.M. Werner, W. Smekal, Vienna University With an approach similar to the employed for the Shirley background, it is
of Technology, Austria, C.J. Powell, National Institute of Standards and proposed that the change on the background slope at energy E is
Technology proportional to the integrated signal above E. This functional form can be
reproduced by assuming that the inelastic cross section is proportional to the
The National Institute of Standards and Technology (NIST) Database for
energy loss. As for the Shirley background, and in contrast to the currently
the Simulation of Electron Spectra for Surface Analysis (SESSA) [1,2] has
employed extrinsic background models, the background here introduced
been modified to allow a user to simulate XPS spectra of nanostructured
only employs one parameter. It has some extra advantages for XPS data
surfaces, such as surfaces covered with rectangular islands, pyramids,
spheres, layered spheres, etc. The effect of the nanomorhphology of the peak fitting, such that its functional form is the same regardless of the core
surface on the emitted angular and energy distribution of photoelectrons is level, it account for the finiteness of the peak width in the generation of the
investigated. Comparison with simple models in the literature, which background signal, it can be employed simultaneously with the intrinsic
neglect several aspects of the physics of signal generation, such as elastic Shirley background, and last, but not least, it provides for good fits. Some
electron scattering, the dependence of the inelastic mean free path of the implementations of the method are discussed.
position of the electron in the specimen, the anisotropy of the photoelectric
cross section, etc. gives good agreement when the same model assumptions 10:00am AS-MoM6 Effective Attenuation Lengths for Photoelectrons
are made in the simulations, but show significant deviations for more in Thin Films of Silicon Oxynitride and Hafnium Oxynitride on Silicon,
physically realistic simulations. The extent to which information on the C.J. Powell, National Institute of Standards and Technology, W.S.M.
nanomorphology can be extracted from the photoelectron angular/energy Werner, W. Smekal, G. Tasneem, Vienna University of Technology, Austria
distribution is investigated, in particular the question is addressed whether We have used the National Institute of Standards and Technology (NIST)
the average size of nanostructures on a surface is accessible by means of Database for the Simulation of Electron Spectra for Surface Analysis
(SESSA) [1,2] to simulate photoelectron intensities for thin films of

SiO N and HfO N on silicon with excitation by Al Kα X-rays. We
1.6 0.4 1.9 0.1
* Albert Nerken Award Winner considered Si 2p photoelectrons from SiO N and the substrate and Hf
3/2 1.6 0.4
3 Monday Morning, October 29, 2012
4f photoelectrons from HfO N . The simulations were performed for Spectroscopy (XPS) offers surface-sensitive, quantified chemical state
7/2 1.9 0.1
ranges of film thicknesses and photoelectron emission angles and for two analysis and imaging capabilities. Ultraviolet Photoelectron Spectroscopy
common configurations for X-ray photoelectron spectroscopy (XPS), the (UPS) allows measurement of valence band positions. Reflected Electron
sample-tilting configuration and the Theta Probe configuration. We Energy Loss Spectroscopy (REELS) yields information on the electronic
determined photoelectron effective attenuation lengths (EALs) by two band gap and hydrogen content of a material. These techniques are
methods, one by analyzing photoelectron intensities as a function of film combined for a thorough characterisation of the electronic structure of
thickness for each emission angle (Method 1) and the other by analyzing optoelectronic devices.
photoelectron intensities as a function of emission angle for each film
thickness (Method 2). Our analyses were made with simple expressions that 11:40am AS-MoM11 Chemically Resolved Electrical Characterisation
had been derived with the assumption that elastic-scattering effects were of Working Devices by XPS, S. Suzer, Bilkent University, Turkey
negligible. We found that EALs from both methods were systematically
A noncontact chemical and electrical measurement technique of XPS is
larger for the Theta Probe configuration, by amounts varying between 1 %
performed to investigate a CdS based Photoresistor and a Si-Diode during
and 5 %, than those for the sample-tilting configuration. These differences
their operation. The main aim of the technique is to trace chemical and
were attributed to anisotropy effects in the photoionization cross section
location specified surface potential variations as shifts of the XPS peak
that are expected to occur in the former configuration. Generally similar
positions under operating conditions. For the Photoresistor Cd3d and for the
EALs were found by each method for each film material although larger
Diode (p-n junction) Si2p peaks positions have been recorded, respectively.
EALs were found from Method 2 for film thicknesses less than 1.5 nm.
The variations in the Cd3d peak without and under photoillumination with 4
SESSA is a useful tool for showing how elastic scattering of photoelectrons
different lasers is extracted to yield the location dependent resistance
modifies EALs for particular materials, film thicknesses, and XPS
values, which are represented; (i) two dimensionally for line scans, and (ii)
configurations.
three dimensionally for area measurements. In both cases one of the
[1] http://www.nist.gov/srd/nist100.cfm . dimensions is the binding energy. For the Si p-n junction the variations in
[2] W. Smekal, W. S. M. Werner, and C. J. Powell, Surf. Interface Anal. 37, the Si2p peak position under normal and reverse bias are recorded to
1059 (2005). differentiate and identify the nature of the doping (p- or n-). The main
advantage of the technique is its ability to assess element-specific surface
electrical potentials of devices under operation based on the energy
10:40am AS-MoM8 Valence Band XPS: A Valuable, but
deviation of core level peaks in surface domains/structures. Detection of the
Underexploited, Tool for the Identification of Subtle Differences in
variations in electrical potentials and especially their responses to the
Surface Chemistry, P.M.A. Sherwood, Oklahoma State University
energy of the illuminating source in operando, is also shown to be capable
INVITED
of detecting, locating, and identifying the chemical nature of structural and
Valence band X-ray photoelectron spectroscopy (XPS)1 gives spectral other types of defects.
features (peak positions and peak intensities) that arise from different
physical principles than the core spectral region. This difference leads to the
valence band region providing complimentary information to that of the
Biomaterial Interfaces
core region. In many cases the valence band region can be used to detect
subtle chemical differences that cannot be determined in core XPS studies. Room: 23 - Session BI-MoM
The value of using valence band XPS interpreted by calculation models will
be demonstrated for various systems, and the use of core and valence band
Surfaces to Control Cell Response
XPS for the study of buried interfaces will be discussed. Examples
discussed will include the formation and study of thin (less than 100A) Moderator: A. Rosenhahn, Karlsruhe Institute of
oxide-free phosphate films, polymer films, composite surfaces, and the Technology, Germany
identification of different oxide films (including aluminum oxides) with
similar chemical composition. Studies of shallow buried interfaces will be
discussed. Recent work involving the preparation of hydroxyapatite films 8:20am BI-MoM1 Click Chemistry on Brominated Plasma Polymer
formed on metals which were coated with a thin oxide free film of metal Thin Films for Immobilizing and Patterning Biomolecules and Cells,
etidronate will be reported. The metals studied were stainless steel and B.W. Muir, CSIRO Materials Science and Engineering, Australia, R. Chen,
titanium. The key to adhesion of the hydroxyapatite films is the initial CSIRO Materials Science and Engineering and The University of
formation of a thin, oxide free, etidronate film on the metal. It was not Melbourne, Australia, G.K. Such, The University of Melbourne, Australia,
found possible to prepare the hydroxyapatite films directly on the metal A. Postma, R.A. Evans, K.M. McLean, CSIRO Materials Science and
surfaces. Since hydroxyapatite is a key component of bone and teeth, it is Engineering, Australia, F. Caruso, The University of Melbourne, Australia
likely that the coated metals will have desirable biocompatible properties, The development of versatile and robust strategies for the surface
and that these treated metals may find applications in the production of modification of multiple classes of materials has proven challenging, with
medical implants. few generalized methods. Many available methods have limitation for
1P..M.A. Sherwood, “XPS Valence Bands”, chapter in “Surface Analysis by widespread use due to the need for specific surface chemistries and/or
Auger and X-ray Photoelectron laborious multistep procedures[1]. A protocol to deposit brominated plasma
polymer (Brpp) thin films on a variety of substrate surfaces (silicon wafers,
Spectroscopy” edited by D Briggs and J T Grant, SurfaceSpectra Ltd and glass, gold, Teflon) has been developed. These coatings are highly adherent
IM Publications, Chapter 19, 531-555, and exhibit good stability in aqueous, biphasic and autoclaving conditions.
2003. The Brpp coating was found to be a useful platform for secondary reactions
leading to surfaces with specific chemical properties. Following
nucleophilic exchange, azide functionalized surfaces were developed and
11:20am AS-MoM10 Multitechnique Electron Spectroscopic
the copper catalysed azide alkyne cycloaddition (CuAAC) reaction[2]; a
Characterisation of Optoelectronic Devices, A.E. Wright, P. Mack, R.G.
White, A. Bushell, Thermo Fisher Scientific, UK paradigm of click chemistry, was successful in immobilizing various
acetylenes. A particular highlight is the patterning of cells via selective
Optoelectronic devices, used for inter-conversion of light and electricity
surface functionalisation of PEG-alkyne using a photomask.[3] This is the
(e.g. photovoltaics and displayes), depend upon careful optimisation of
first known example of CuAAC reactions on pp thin films. A detailed
chemical, electronic and structural properties for efficient operation and
physicochemical characterisation study of these films will also be
useful operating lifetime.
presented.
Characterisation of such a device will typically identify the chemical
[1] aH. Lee, S. M. Dellatore, W. M. Miller, P. B. Messersmith, Science
bonding states, valence band positions, band gap and work function for each
2007, 318, 426-430; bD. Y. Ryu, K. Shin, E. Drockenmuller, C. J. Hawker,
component. Lateral and depth resolution may be required to evaluate
T. P. Russell, Science 2005, 308, 236-239.
cell/pixel and multilayer structures.
[2] R. A. Evans, Australian Journal of Chemistry 2007, 60, 384-395.
Electron spectroscopic surface analysis techniques are ideal for the detailed
analysis of the electronic structures of optoelectronic devices. Such [3] Chen, R. T.; Marchesan, S.; Evans, R. A.; Styan, K. E.; Such, G. K.;
techniques allow full quantitative characterisation of materials with Postma, A.; McLean, K. M.; Muir, B. W*.; Caruso, F., Biomacromolecules
chemical state and structural information. Surface specificity of 2012, 13, (3), 889-895.
spectroscopic information ensures that thin films can be analysed without
interference from deeper parts of the sample. Multilayer structures may be
studied with depth profiling techniques, and imaging functionality may be
used to study cell or pixel structures.
The Thermo Scientific Escalab250Xi offers several such spectroscopic
techniques, which have been employed in this study. X-ray Photoelectron
Monday Morning, October 29, 2012 4
8:40am BI-MoM2 Temperature-Induced Electrostatic Assembly of chain transfer agent approach2 and that such coatings can be used for the
Poly (Ethylene Glycol) Co-Polymer for Non-Fouling Biomedical effective control of cell-surface interactions, an essential requirement in a
Applications: How Low Can You Go?, R. Ogaki, O. Zoffmann Andersen, broad range of applications in biomaterials and regenerative medicine. In
K. Kolind, D.C.E. Kraft, M. Foss, Aarhus University, Denmark the expansion of stem cells for therapeutic applications, fully synthetic,
Development of long-term stable surfaces that resist bio-adhesion continues chemically defined materials are a requirement. Polymeric coatings which
to stimulate the field of biomedical and biological research. While contain synthetic cell signalling molecules are key to ongoing progress in
numerous strategies have been developed over the last several decades, the the generation of cells as therapies. Coating characterization was carried out
challenge remains in the creation of surfaces that can provide long-term using X-ray photoelectron spectroscopy (XPS) and colloid probe atomic
‘zero’ bio-adhesion from a variety of biological entities that spans lengths force microscope (AFM). Cell culture studies were carried out using bone
scales from biomolecules to cells. Although the physical and chemical marrow derived human mesenchymal stem cells (hMSCs) using standard
properties of the resisting surface itself are important in achieving this techniques. Differentiation of hMSCs was carried out using standard
ultimate goal, assessing the extent of bio-adhesion must be accompanied by protocols in induction medias and the presence of characteristic cell surface
detailed surface analysis via highly sensitive analytical techniques. markers was determined using flow cytometry. Substrate materials were
silicon wafers or tissue culture polystyrene (TCPS).
We have recently discovered that increasing the temperature alone during
the assembly process of poly-l-lysine grafted poly (ethylene glycol) (PLL- In this study, we focus on a surface initiated Radical Addition-
g-PEG) results in the formation of highly dense PLL-g-PEG brush coating. Fragmentation chain Transfer (RAFT) approach and present data
The PLL-g-PEG surfaces prepared at various temperatures (20 to 80 °C) demonstrating that dense polymer brushes can be prepared via surface
have been characterized by X-ray photoelectron spectroscopy (XPS). The immobilized macro-RAFT agents. The brush nature of the coatings was
PLL-g-PEG surfaces prepared at the ‘standard’ temperature of 20 °C are confirmed using a combination of XPS analysis and direct interaction force
found to be comparable to the previously reported literatures. Interestingly, measurements with the AFM colloid probe technique. The properties of the
the surfaces prepared at 80°C have shown the highest surface grafted coatings could be fine tuned using a variety of parameters such as the RAFT
density of PLL-g-PEG, with ~ 4 times denser than those prepared at 20 °C. agent surface density, the polymerisation conditions, the monomer feed
composition and the conjugation of cell attachment motifs such as cyclic
The degree of cell and protein adhesions on these surfaces has been
peptides which interact with cell surface integrins. For example, the
stringently determined using cell culture and serum/blood adsorption assays
combination of a low cell adherent, low protein adsorbing polymer brush
combined with XPS and time of flight secondary ion mass spectrometry
coating containing a conjugated peptide which interacted with alphabeta
(ToF-SIMS). The temperature-induced PLL-g-PEG surfaces have achieved v 3
integrins resulted in a surface which supported the expansion of hMSCs in a
‘zero’ cell adhesions from three different types of mammalian cells for at
xeno-free, chemically defined, serum replacement media. In addition the
least 36 days. In addition, XPS and ToF-SIMS analysis have confirmed
expanded cells expressed cell surface markers typical of undifferentiated
near-zero protein adsorptions from 10% serum/MEM (at least 36 days),
hMSCs and the expanded cells were able to differentiate along adipogenic,
whole undiluted blood (at least 24 hrs) and undiluted serum (at least 24 hrs)
osteogenic and chondrogenic pathways.
with the surfaces being pre-incubated in high ionic strength buffer (2.4 M
NaCl for 24 hrs). 1 Edmond, S., Osborne, V.L. and Huck, W.T.S., Chem. Soc. Rev. 2004, 33,
14.2 Meagher, L., Thissen, H., Pasic, P., Evans, R.A. and Johnson, G.,
The outcome of the rigorous bio-resistance tests presented here highlights
WO2008/019450.
the critical importance of processing temperature on the surface graft
density of electrostatically driven PLL-g-PEG. The temperature induced
assembly process can be effectively and easily implemented for a range of 10:00am BI-MoM6 Binary Colloidal Crystal Structures Combined
biomedical and biotechnological applications. with Chemical Surface Modification to Achieve Superior Control Over
Biointerfacial Interactions, P. Koegler, Swinburne Univ. of Tech.,
Australia, P. Pasic, J. Gardiner, V. Glattauer, CSIRO Materials Science
9:00am BI-MoM3 Spatially and Temporally Coordinated Processes of
and Eng., Australia, A. Clayton, Swinburne Univ. of Tech., Australia, H.
Cells at Molecular to Cellular Scales, J.P. Spatz, Max Planck Institute for
Thissen, CSIRO Materials Science and Eng., Australia, P. Kingshott,
Intelligent Systems & University of Heidelberg, Germany INVITED
Swinburne Univ. of Tech., Australia
Our approach to engineer cellular environments is based on self-organizing
Biointerfacial interactions play a major role in the field of biomedical
spatial positioning of single signaling molecules attached to synthetic
materials and regenerative medicine and are of tremendous importance to in
extracellular matrices, which offers the highest spatial resolution with
vivo and in vitro applications. Cell-material interactions are mediated by
respect to the position of single signaling molecules. This approach allows
surface parameters including the materials surface chemistry and
tuning tissue with respect to its most relevant properties, i.e., viscoelasticity,
topography. Colloidal lithography represents a promising tool to modify
peptide composition, nanotopography and spatial nanopatterning of
surface topographies at the nanoscale with precision and over large areas
signaling molecule. Such materials are defined as “nano-digital materials”
while at the same time not requiring complex instrumental set-ups or
since they enable the counting of individual signaling molecules, separated
rigorous experimental conditions. The creation of nanostructured surfaces in
by a biologically inert background. Within these materials, the regulation of
this way can also be combined with sophisticated surface modification
cellular responses is based on a biologically inert background which does
techniques such as polymer grafting techniques via functional groups
not initiate any cell activation, which is then patterned with specific
(grafting-to) or initiating groups (grafting-from) on the particle surface.
signaling molecules such as peptide ligands in well defined nanoscopic
This platform, which provides control over surface chemistry and
geometries. This approach is very powerful, since it enables the testing of
topography, offers great flexibility in regard to the design of advanced
cellular responses to individual, specific signaling molecules and their
surface coatings.In the current study we have generated highly ordered
spatial ordering. Detailed consideration is also given to the fact that protein
binary colloidal crystal structures using surface functionalized particles.
clusters such as those found at focal adhesion sites represent, to a large
This approach allows precise control over particle size, spacing, and thus
extent, hierarchically-organized cooperativity among various proteins. We
pattern morphology. In order to minimize undesired non-specific protein
found that integrin cluster have a functional packing density which is
adsorption which can mediate cell attachment, graft polymer coatings were
defined by an integrin-integrin spacing of approximately 68 nanometers.
applied to particles using heterobifunctional poly(ethylene glycol) (PEG) to
Such critical spacing values vary as matter of transmembrane receptor
render the surfaces non-fouling. In addition, colloid crystal modified
choice of interest. We have also developed methods which allows the light
surfaces were modified with specific bioactive signals, such as the cyclic
initiated activation of adhesion processes by switching the chemical
RGD peptide (cRGDfK) to promote cell attachment. Surface
composition of the extracellular matrix. This enabled us to identify the
characterization was carried using scanning electron microscopy (SEM),
frequency of leader cell formation in collective cell migration as a matter of
atomic force microscopy (AFM) and X-ray photoelectron spectroscopy
initial cell cluster pattern size and geometry. Moreover, “nano-digital
(XPS). Cell culture experiments were carried out using L929 mouse
supports” such as those described herein are clearly capable of involvement
fibroblasts up to 24 hours.The unprecedented control over the surface
in such dynamic cellular processes as protein ordering at the cell’s
chemistry and topography provided by this simple coating platform is of
periphery which in turn leads to programming cell responses.
significant interest for the study of biointerfacial interactions and the
development of new and improved biomedical devices.
9:40am BI-MoM5 Chemically Defined Synthetic Surfaces for
Mesenchymal Stem Cell Expansion, L. Meagher, H. Thissen, P. Pasic,
11:20am BI-MoM10 Influence of Ca2+ Binding to Titania on Platelet
R.A. Evans, S. Pereira, K. Tsang, V. Glattauer, K. Styan, C.L. Be, D.
Activation Profiles, S. Gupta, I. Reviakine, CIC biomaGUNE, Spain
Haylock, CSIRO Materials Science and Engineering, Australia
Surface properties of implant materials are known to influence biological
Interest in surface initiated polymerisation (SIP) for biomedical applications
responses they elicit. However, complex processes operating at the interface
has increased rapidly recently, particularly the use of “living” free radical
polymerisation mechanisms1 as highly defined coating remain poorly understood. To get an insight into these processes, we
investigated the role played by surface ion equilibrium in defining
properties/architectures can be achieved. Here we demonstrate that
interactions between an implant material (TiO) and components of blood
advanced coatings can be produced using a surface immobilised macro- 2
(in this case, platelets), because blood is the first tissue that foreign
5 Monday Morning, October 29, 2012
materials come into contact with when inserted into the body and because Spectroscopic Ellipsometry Focus Topic
platelet response is crucial in defining the implant’s fate.
Room: 19 - Session EL+TF+AS+EM+SS+PS+EN+NM-
Titanium is a widely used biomaterial. Its success is in part due the
MoM
favorable biocompatibility properties conferred by its oxide, TiO. We have
2
previously shown that Ca2+-TiO interactions affect the distribution of
2
phospholipid phosphatidyl serine (PS) in model lipid membranes prepared Spectroscopic Ellipsometry for Photovoltaics and
on TiO. This allowed us to hypothesize that platelet activation will be
2 Semiconductor Manufacturing
affected by these interactions as well.
Moderator: M. Creatore, Eindhoven University of
Platelets are anuclear cell fragments circulating in blood. Activated at
wound sites, they aggregate and provide a catalytic surface for the Technology, the Netherlands, H. Wormeester, MESA+
formation of a fibrin-based clot that stops the bleeding. Recently, platelets Institute for Nanotechnology, Univeristy of Twente,
have been recognized to participate in inflammation, wound healing, tissue
Enschede, The Netherlands
regeneration, and immune responses. Activation of platelets by foreign
surfaces is detrimental to blood-contacting implants but beneficial for
osteoimplants. Upon activation, platelets expose on their surface and secrete 8:20am EL+TF+AS+EM+SS+PS+EN+NM-MoM1 Multichannel
a number of markers. These include PS, activated form of GPIIb-IIIa, and Spectroscopic Ellipsometry: Applications in I-III-VI Thin Film
2
proteins CD62P and CD63 that are found in the membranes of the Photovoltaics, R.W. Collins, D. Attygalle, P. Aryal, P. Pradhan, N.J.
intracellular α- and dense granules of quiescent platelets. To assess the state Podraza, University of Toledo, V. Ranjan, S. Marsillac, Old Dominion
of platelet activation on TiO, we assayed for the expression of these University INVITED
2
markers. In order to isolate a clear cause-and-effect relationship between Multichannel spectroscopic ellipsometry (SE) has been applied successfully
Ca2+-TiO2 interactions and platelet activation, we focused on purified as an in situ, real time tool for optimizing, monitoring, and controlling
platelets. multi-stage deposition processes in various thin film photovoltaics (PV)
Our main finding is that the platelet activation profile on TiO depends on technologies. A particularly challenging process optimization problem
2
the presence of Ca2+. Furthermore, in the absence of Ca2+, the α- and dense involves the thermal co-evaporation of individual elements of Cu, In, Ga,
granule secretion is differentially regulated on titania. The differential and Se in a three-stage process, which has proven to produce high quality
granule secretion by platelets, as regulated by the surface properties, can be Cu(In1-xGax)Se2 (CIGS) materials and high performance PV devices. This
applied towards controlled release of molecules from platelets by three-stage process provides a high level of flexibility in determining the
nanoparticles or implants in drug delivery applications. phase, composition, and microstructure of the film, but also generates
greater challenges in run-to-run reproducibility of the optimized process.
Information extracted from real time SE measurements includes the
11:40am BI-MoM11 Enhancing the Osseointegration of Titanium
evolution of the bulk layer and one or more surface layer thicknesses, as
Dental Implants by Magnetron-Sputtered Strontium Containing
well as layer dielectric functions. The layer dielectric functions can be
Coatings, O.Z. Andersen, Interdisciplinary Nanoscience Center (iNANO),
analyzed further to extract the phase and alloy compositions and the defect
Aarhus University, Denmark, V. Offermanns, Medizinische Universität
density or grain size, which can assist in understanding the fabrication
Innsbruck, Universitätsklinik für Mund-, Kiefer- und Gesichtschirurgie,
process, in optimizing solar cells, and ultimately in monitoring and
Austria, M. Sillassen, Interdisciplinary Nanoscience Center (iNANO),
controlling the optimized process for improved reproducibility. In this
Aarhus University, Denmark, D.C.E. Kraft, Aarhus School of Dentistry,
study, the focus is on analysis of ellipsometric (ψ, Δ) spectra acquired by
Denmark, J. Bøttiger, F. Besenbacher, Interdisciplinary Nanoscience
real time SE in order to characterize (i) the structural and compositional
Center (iNANO), Aarhus University, Denmark, F. Kloss, Medizinische
evolution in (In,Ga)Se film growth from In, Ga, and Se fluxes in the first
Universität Innsbruck, Universitätsklinik für Mund-, Kiefer- und 2 3
stage, (ii) the transition from Cu-poor to Cu-rich CIGS at the end of the
Gesichtschirurgie, Austria, M. Foss, Interdisciplinary Nanoscience Center
second stage, which occurs under Cu and Se fluxes, and (iii) the transition
(iNANO), Aarhus University, Denmark
from Cu-rich to the desired Cu-poor CIGS, which defines the end of the
Introduction: Strontium (Sr) has been shown to have a beneficial influence
third and final stage, and occurs under a second application of In, Ga, and
on the subsequent remodelling of the bone structure in relation with implant
Se fluxes. After the transition from Cu-poor to Cu-rich material in the
osseointegration. Both decrease of the osteoclast driven bone resorption and
second stage, a Cu Se phase near the surface of the bulk layer is tracked.
enhancement of the osteoblast driven process of bone formation has been 2-x
In the Cu-rich to Cu-poor transition, this Cu Se phase has fully reacted
shown. Furthermore, Sr has proven to have an anti-inflammatory effect. 2-x
with In, Ga, and Se to form CIGS. Studies using a standard Mo substrate
Methods: The coatings used in this study were either prepared on Ti and 2 μm thick CIGS for solar cells have also revealed features in the (ψ, Δ)
implants (rods with diameter = 1.1 mm and length = 6 mm) or on silicon spectra characteristic of the anticipated changes in the near surface phase
wafers. The Sr containing surface modifications were prepared by co- composition as established by detailed modeling on thinner and smoother
sputtering in a setup with a pure Ti and a sintered composite target. The films. Although careful analysis of real time SE is expected to provide
samples were characterized using SEM, AFM, XPS and RBS. ICP-AES quantitative information on the surface properties and their evolution in this
was used to investigate the amount of Sr released from the samples as a case of solar cells, control of the deposition has been successful simply by
function of time. Human dental pulp stem cell (hDPSC) cultures were used monitoring real time changes in the ellipsometric (ψ,Δ) spectra.
to assess the in vitro cellular response: Cell attachment and proliferation
was studied along with the cells ability to mineralize. Quantification of
9:00am EL+TF+AS+EM+SS+PS+EN+NM-MoM3 Contribution of
osteogenic expression markers and specific cytokines was performed via
Plasma Generated Nanoparticles to the Growth of Microcrystalline
RT-PCR. Human blood derived monocyte cultures were carried out to
Silicon Deposited from SiF/H/Argon Gas Mixtures, J.-C. Dornstetter,
investigate the in vitro differentiation of these into osteoclast-like cells in 4 2
S. Kasouit, J.-F. Besnier, Total S.a, France, P. Roca i Cabarrocas, LPICM-
response to Sr. In vivo experiments were carried by inserting implants into CNRS, Ecole Polytechnique, France
the femur of Wistar rats and evaluation was done by assessing bone-to-
Despite the low fabrication cost of thin film silicon solar modules, this type
implant contact and new bone volume.
of technology remains non competitive in main stream markets because of
Results: The amount of Sr incorporated in the surfaces was found to be the high BOS costs, due to the low energy conversion efficiency of this type
between 0 and 8.7 at. %. The Sr release profile showed that the most Sr was of modules (~10%).We have recently shown that microcrystalline silicon
released from samples incorporating 5.5 at. % Sr. In relation with the in films deposited using SiF/H/Argon RF capacitive plasmas have excellent
4 2
vitroexperiments, the hDPSC proliferation and mineralization was found to structural and transport properties, compared to films deposited using
correlate with the surface Sr concentrations. Moreover, the Sr concentration conventional SiH/H mixtures, allowing for a very good carrier collection,
4 2
also affected the differentiation of monocytes into osteoclast-like cells. In even for thick cells, and Voc values of 0.55 V, without device optimization,
relation with the in vivo experiment it was found that the incorporation of Sr thus opening up the path for the realization of high performance solar cells.
had a beneficial effect on implant osseointegration, where an increase in However, little is known so far about the growth mechanism of this type of
direct bone contact and in new bone volume was observed with an materials and the reason for such interesting properties.Studies of silicon
increasing Sr release. thin films deposition from SiF/H mixes, under conditions different from
4 2
Discussion: From the in vitro and in vivo Sr release experiments it was ours, suggested that the growth is due to the deposition of SiF2 radicals,
found that a more dense surface structure developed as the Sr concentration followed by the abstraction of fluorine by hydrogen. Previous work within
were increased. We therefore speculate that the peak in the Sr release our group has also shown that deposition occurs only when particles are
around 5.5 at.% can be ascribed to an optimal correlation between the present in the plasma, and that growth starts from crystallites without any
morphology and the amount of incorporated Sr. The results from the in vitro amorphous phase.We present here a systematic study of the growth of
and in vivo models shows that the coating process we have developed for microcrystalline films, together with the composition of nanoparticles
modifying implants is an interesting candidate in relation with shortening attracted by thermophoresis to cold traps located both on the walls of the
the healing period when inserting osseointegrating implants. plasma chamber and in the fore line as a function of deposition conditions.
Monday Morning, October 29, 2012 6
The composition of the deposit on the traps is found to be amorphous at low responsible physical processes have to be understood. Traditionally, charge-
power/ low hydrogen conditions and becomes crystalline when either of carrier-scattering processes are investigated by combining morphology data
them increases. This correlates well with an increase in atomic hydrogen and Hall measurements. This contribution discusses the extensive optical
concentration in the plasma, as estimated by actinometry. The crystalline modeling of plasma-deposited ZnO and how its interpretation directly
fraction of the deposited film was measured using in-situ ellipsometry and provides insight into the relevant charge-carrier-scattering processes at
was found to correlate with the composition of the deposit on the cold traps. different length scales. The interpretation is generalized to the concept of
Deposition rate is drastically reduced when a water cooled trap is installed frequency-dependent resistivity, which is used to explain the applicability
on the walls of the plasma chamber, and switches off at high H flow rates. of different Drude models.
2
Under these conditions, TEM and AFM images, show that at the initial Thin films (50-1000 nm) of Al-doped and undoped ZnO were deposited
stages of the growth the film is constituted of sparse, hexagonal crystalline using an expanding thermal plasma MOCVD process.1 Conditions of high
particles, having sizes on the order of few tens of nanometers. We interpret
pressure and high diethyl zinc flow allowed for dense films with low
the data above as a result of plasma-generated nanocrystals being a electrical resistivities (e.g., 4×10-4 Ω cm at 300 nm). The films were
significant contribution to the deposited film. This may explain the
analyzed with variable-angle spectroscopic ellipsometry (SE) (0.75 – 5.0
excellent electronic properties of the films, as the particles are formed in the
eV), FTIR reflection spectroscopy (0.04 – 0.86 eV), Four-point-probe
bulk of the plasma region, free from energetic ions bombardment. We will
(FPP), and Hall measurements.
correlate the structural properties and the film growth mechanisms to the
properties of solar cells. The SE and FTIR data were combined and fitted with classical and
extended Drude2 models. The high intensity of the Drude in the FTIR range
resulted in a high sensitivity with which the carrier concentration and
9:20am EL+TF+AS+EM+SS+PS+EN+NM-MoM4 Multichannel
mobility could even be determined for thin (~40 nm) undoped ZnO films.
Spectroscopic Ellipsometry for CdTe Photovoltaics: from Materials
An extended Drude model was needed to correctly model the SE energy
and Interfaces to Full-Scale Modules, P. Koirala, J. Chen, X. Tan, N.J.
range, which was explained by the dominance of ionized impurity scattering
Podraza, The University of Toledo, S. Marsillac, Old Dominion University,
and a reduction of this scattering for higher photon energies. The grain-
R.W. Collins, The University of Toledo
boundary-scattering mobility could be determined by the difference
Real time spectroscopic ellipsometry (RTSE) has been implemented in between optical and Hall mobilities.3 When combined with FPP results, the
studies of the evolution of the semiconductor structural and optical effective mobility can be determined from these optical techniques without
properties during sputter deposition of thin film polycrystalline CdS/CdTe the use of Hall measurements. The optical response above the band gap was
solar cells on transparent conducting oxide (TCO) coated glass substrates. modeled by a PSEMI or Tauc-Lorentz oscillator model, where a broadening
Analysis of the real time optical spectra collected during CdS/CdTe and shift of the transition was seen for increasing carrier concentration.4
deposition requires an optical property database as a function of
These insights and a generalized view of electron scattering in ZnO at
measurement temperature for all substrate components. These include not
different length scales will be presented.
only soda lime glass, but also an SiO layer and three different SnO layers.
2 2
We report optical functions parameterized versus temperature for the glass 1. Ponomarev et al., J. Appl. Phys. Submitted (2012)
substrate and its overlayers starting from room temperature and ending at 2. Ehrmann and Reineke-Koch, Thin Solid Films 519, 1475 (2010)
elevated temperature above which the semiconductor layers are deposited.
3. Steinhauser et al., Appl. Phys. Lett. 90, 142107 (2007)
In fact, such a database has additional applications for on-line, through-the-
glass monitoring applications of coated glass at elevated temperature. In the 4. Fujiwara and Kondo, Phys. Rev. B 71, 075109 (2005)
RTSE studies, knowledge of the temperature dependent optical functions of
the substrate components enables an accurate substrate temperature 10:40am EL+TF+AS+EM+SS+PS+EN+NM-MoM8 The Ellipsometric
determination before the onset of deposition and is critical for accurate Response of Single-Crystal Silicon to Doping, H.G. Tompkins,
extraction of the semiconductor layer optical properties. We implement Consultant
RTSE to study the filling process of the surface roughness modulations on
The current wisdom is that for ellipsometry in the UV-vis-NIR spectral
the top-most SnO substrate layer and modification of the optical properties
2 range, doping of single-crystal silicon can be ignored. We study the
of this layer. This modification is further studied post-deposition by infrared
ellipsometric response of silicon doped with arsenic at various levels. We
spectroscopic ellipsometry. In addition to providing information on
also studied the response after implant (before activation) and after the
interface formation to the substrate during film growth, RTSE also provides
activation (anneal). We find that for samples implanted with 1E18
information on the bulk layer CdS growth, its surface roughness evolution,
atoms/cm3, the single-crystal silicon was not amorphized. Implants of 2E19
as well as overlying CdTe interface formation and bulk layer growth.
atoms/cm3 and higher left an amorphous layer on the surface of the wafer
Information from RTSE at a single point during solar cell stack deposition
the thickness of which was about the depth of the implant. Activation of the
assists in the development of a model that can be used for mapping the
sample implanted with 2E19 atoms/cm3 returned the sample to single-
completed cell stack properties, which can then be correlated with device
crystal silicon and the ellipsometric response in the UV-vis-near_IR is
performance. Independent non-uniformities in the layers over the full area
essentially that of undoped silicon. However, the response in the mid-IR is
of the cell stack enable optimization of cell performance combinatorially.
that the extinction coefficient is no longer zero. For samples implanted with
2.5E20 atoms/cm3 and greater, annealing did not return the UV-vis-near_IR
9:40am EL+TF+AS+EM+SS+PS+EN+NM-MoM5 Determination of ellipsometric response to that of single-crystal silicon. Although this
Electronic Band Gaps from Optical Spectra, R.A. Synowicki, J.A. amount of other material (arsenic) is still less that about one tenth of one
Woollam Co., Inc. percent, our conjecture is that the microstructure simply could not be
The band gap of a material Eg is defined theoretically as the lowest energy returned to that of a single crystal. As with the lower doped sample, the
for electronic transition from the valence to conduction bands in a solid. For mid-IR spectral region showed significant increase in the extinction
an ideal material free of defects this is the photon energy or wavelength coefficient.
where the optical properties change from transparent to absorbing.
However, real materials contain defects which cause absorption to begin 11:00am EL+TF+AS+EM+SS+PS+EN+NM-MoM9 The Effect of
below the band gap (i.e. the Urbach Tail) making determination of the true Stress on the Optical Properties Semiconductor Films, A.C. Diebold,
band gap position difficult. For example, in a solar cell the measured G.R. Muthinti, M. Medikonda, T.N. Adam, College of Nanoscale Science
absorption edge represents the onset of transitions first due to defects, then and Engineering, University at Albany, A. Reznicek, B. Doris, IBM
from band to band. Empirical methods used to determine the band gap in Research at Albany Nanotech
real materials with defects include the Tauc plot and the Mott-Davis plot.
Here we review the impact of stress on the complex dielectric function of
More theoretical mathematical dispersion models such as the Tauc-Lorentz,
semiconductor films measured using spectroscopic ellipsometry. Two
Cody-Lorentz, and Herzinger-Johs models have been developed which
relevant examples of stressed semiconductor layers are pseudomorphic
include an adjustable band gap parameter. The various plots and dispersion
epitaxial layers fabricated during semiconductor manufacturing and strained
model methods will be discussed and applied to different materials
silicon on insulator (sSOI) wafers. Stress is known to shift the energies of
measured optically via spectroscopic ellipsometry, intensity transmission,
direct gap critical point transitions in semiconductors. The biaxial stress in
reflection, absorption, or a combination of these methods.
pseudomorphic films grown on silicon wafers can be as high as that used
during opto-elastic studies of bulk semiconductors. The amount of stress in
10:00am EL+TF+AS+EM+SS+PS+EN+NM-MoM6 Optical Modeling un-relaxed, pseudomorphic films of Si Ge on Si (100) reaches 1 GPa for
1-x x
of Plasma-Deposited ZnO: Extended Drude and its Physical alloys with 20% Ge and is more than 3 GPa for films with > 50% Ge. The
Interpretation, H.C.M. Knoops, M.V. Ponomarev, J.W. Weber, N. Leick, bi-axial stress in sSOI is typically ~1 GPa. An elastic theory approach for
B.W.H. van de Loo, Y.G. Melese, W.M.M. Kessels, M. Creatore, Eindhoven the effect of strain on the k*p determined band structure and optical
University of Technology, the Netherlands transition energy is well known. Both low shear stress and high shear stress
High-quality transparent conductive oxides such as ZnO are important due approximations can apply to the shift in transition energy depending on the
to their electrical and optical properties. To improve these properties the magnitude of the spin orbit splitting energy vs the magnitude of the shear
7 Monday Morning, October 29, 2012
stress. Until recently it was difficult to obtain sets of samples that test both density and bulk hole mobility 860cm2/Vs. Optimization of strain in QWs
approximations. Here we discuss results from our recent study of provided the highest Hall mobility of 1020 cm2/Vs at sheet hole density of
pseudomorphic films of Si Ge on Si (100) from x= 0.05 to 0.75 which 1.3x1012/cm2 obtained for In Ga Sb with compressive strain of 1.8%.
1-x x 0.36 0.64
covers both low and high shear regimes. We also present our recent study of Hole mobility in QW channel was benchmarked against the thickness of top
the dielectric function of thinned sSOI which illustrates the impact of stress semiconductor AlGaSb barrier. The effect of interface-related scattering
on the optical transitions for the Si layer on sSOI. All of these samples are hole mobility in the channel was found to be significantly less than e.g. for
examples of new materials being used in semiconductor research. The n-InGaAs, that might be due to stronger localization of holes in QWs.
results of this study are directly transferred into cleanroom spectroscopic
Two approaches to fabricate high-quality III-Sb/high-k interface were
ellipsometry systems used for process control during manufacturing.
studied: all in-situ AlO or HfO gate oxides, and ex-situ atomic layer
2 3 2
deposited (ALD) AlO with InAs top semiconductor capping layer.
2 3
11:20am EL+TF+AS+EM+SS+PS+EN+NM-MoM10 Numerical Interface with in-situ MBE gate oxides was found to improve with in-situ
Ellipsometry: Spectroscopic n-k Plane Analysis of Thin Films Growing deposited a-Si interface passivation layer (IPL). Interfaces with better
on Unknown Layered Substrates, F.K. Urban, D. Barton, Florida thermal stability, reduced interface trap density and hysteresis were
International University observed on both n- and p- type GaSb MOSCaps with the IPL. P-type
Spectroscopic ellipsometry measurements on thin films commonly make MOSFETs with HfO2 showed a maximum drain current of 23 mA/mm for a
use of prior knowledge of the structure and optical properties of the 3μm gate length. Use of a-Si IPL has also resulted in a significant (over an
underlying substrate. However, imprecision in substrate statistics order of magnitude) reduction of the hole density in QWs and
propagates into the solution for the film of interest. Thus it is more accurate corresponding negative flat band voltage shift and drop of mobility which
to have a method for solving for film properties which simultaneously becomes remote Coulomb scattering-limited. An interface with ALD Al2O3
obtains whatever is needed about the substrate. And it makes solutions was improved by a thin 2nm interface layer of InAs which was treated with
possible whether or not book data or previous substrate solutions are HCl or(NH4)2S immediately prior to ALD process. Optimized annealing
available. In this work we apply Complex Analysis in the n-k plane to further improved the C-V characteristics, reduced interface trap density
achieve solutions employing the well-know reflection equations. The down to 1012 cm-2eV-1, leakage current and MOSFET subthreshold slope
method is carried out at each measured wavelength and does not necessitate down to 200 mV/dec. Increasing annealing temperature to and above 450oC
an a-priori assumption of optical property dependencies on wavelength. drastically degraded C-V characteristics due to low thermal budget of
The mean square error has been improved by many orders of magnitude, a antimonides.
selected limit of 10-14 as opposed to 1 to 30 or so for least squares. Thus the
full accuracy of the ellipsometer is now available for more accurate 9:40am EM+TF+OX+GR-MoM5 Interface Study of the Atomic Layer
measurements of film thickness and optical properties. The method requires Deposited AlO on Al Ga N, X. Qin, B. Brennan, H. Dong, R.M.
2 3 0.25 0.75
six measurements during growth. The first is used to determine the Wallace, The University of Texas at Dallas
relationship between Rp and Rs at the film-substrate interface. The
Due to the high two-dimensional electron gas (2-DEG) density,
following four are used to uniquely determine the values of Rp, Rs, and film
AlGaN/GaN high electron mobility transistors (HEMTS) are recognized as
n, k, and d. The final measurement confirms the unique solution. Suitability
key devices for high power and low noise applications. However, the
of the model is tested by comparing measurements at two of more
associated large gate leakage current degrades the performance of AlGaN
wavelengths for self consistency. Results for n and k of the growing film
HEMTs. In order to solve this problem, MOS-HEMTs have been
are examined across the measurement spectrum in comparison with
developed, in which the incorporation of a high-k gate dielectric layer can
parameterizations in common use.
overcome the drawbacks.
In this work, the native and treated Al Ga N surface chemical states and
0.25 0.75
structure of were studied by x-ray photoelectron spectroscopy (XPS), ion
Electronic Materials and Processing
scattering spectroscopy (ISS) and low energy electron diffraction. Different
Room: 9 - Session EM+TF+OX+GR-MoM chemical treatment processes including (NH)OH, (NH)S and HF were
4 42
studied, followed by atomic layer deposition (ALD) AlO layers on
2 3
Al Ga N . The oxidation states of the Al Ga Ninterface and AlO
High-k Dielectrics for MOSFETs I 0.25 0.75 0.25 0.75 2 3
deposition process were studied by in-situ XPS analysis. In addition, ex-situ
Moderator: A.C. Kummel, University of California San atomic force microscopy (AFM) was used to observe the surface
Diego topography before and after the Al2O3 deposition. According to the XPS
results, it is found that chemical treatments could remove the native AlO
2 3
but were not effective to eliminate the Ga oxide, and the growth rate of
8:20am EM+TF+OX+GR-MoM1 Surface Preparation and Dielectric AlO is low on the native and treated Al Ga N samples. The AFM
2 3 0.25 0.75
Growth for Graphene-based Devices, R.M. Wallace, University of Texas images show that there are many pin holes in the surface of Al Ga N.
0.25 0.75
at Dallas INVITED Studies of HfO deposition will also be presented.
2
In addition to interesting physics, numerous device applications are under
This work is supported by the AOARD under AFOSR Grant No. FA2386-
investigation for graphene. Many of these devices require an interaction of
11-1-4077
graphene with dielectrics, and require a thorough understanding of the
graphene/dielectric interface. As practical device applications require large
area graphene, CVD methods have been employed to synthesize graphene 10:00am EM+TF+OX+GR-MoM6 Ideal Monolayer Nitridation of
and typically involve a wet chemical transfer process, which can leave Semiconductors using a Nitrogen Radical Generator, A.T. Lucero, J.
Kim, University of Texas at Dallas
residues that impact device behavior. This talk will review recent progress
in the investigation of CVD graphene growth, transfer and dielectric growth Thin silicon nitride films have long been desirable for various applications.
processes with an emphasis on in-situ studies of the surfaces produced by Suggested uses range from surface and interface passivation to ultra-thin
these processes and the resultant electrical behavior. This work is supported dielectric layers. Traditional deposition techniques are low pressure
by the NRI SWAN Center. chemical vapor deposition (LPCVD) and plasma enhanced chemical vapor
deposition (PECVD). High quality LPCVD films require high processing
temperatures, and PECVD exposes the substrate to damaging plasma and
9:00am EM+TF+OX+GR-MoM3 Antimonide-Based P-Channel
electric potentials. While both techniques are suitable for many
MOSFET: Progress and Challenges, S. Oktyabrsky, A. Greene, S.
applications, there are some instances where both processes are too harsh.
Madisetti, P. Nagaiah, M. Yakimov, R. Moore, S. Novak, H. Bakhru, V.
Tokranov, University at Albany-SUNY INVITED In this paper, we report the growth of silicon nitride using a remote nitrogen
Development of p-type MOSFETs using new materials is an important goal radical generator system. Growth temperatures range from room
to provide a further scaling of CMOS circuits. Although Ge is still temperature to 400 °C,and growth time is varied from two minutes to one
considered as a main candidate for novel p-channels due to its superior bulk hour. Film composition is analyzed using x-ray photoelectron spectroscopy
transport properties, recent progress in strained III-Sb channels and MOS (XPS) and morphology is checked using atomic force microscopy. Results
technologies makes it a good competitor in particular for deeply scaled indicate that surface nitrogen saturation can be reached at both low
devices. The materials parameters affecting MOSFET’s figures-of-merit are temperatures and short exposure times,and that the reaction is self limiting,
reviewed with the emphasis on strain in quantum wells (QWs), effective terminating at one monolayer. Film thickness is approximately one
mass, density of states and mobility. Angstrom, as determined by XPS. Results for silicon and III-V passivation
will be discussed.
Progress in development of materials for III-Sb channels is reported.
Optimization of MBE growth of metamorphic buffers and GaSb on lattice- We would like to thank Toshiba Mitsubishi-Electric Industrial Systems
mismatched GaAs substrates has resulted in “step-flow” growth mode of Corporation for providing the nitridation system used in this study.
GaSb with monolayer-high steps on the surface, ~107cm-2 dislocation
Monday Morning, October 29, 2012 8
11:00am EM+TF+OX+GR-MoM9 Characterization of ALD Energy Frontiers Focus Topic
Laminated Gate Dielectrics on GaN MOSCAPs, D. Wei, T. Hossain,
Room: 15 - Session EN+NS-MoM
Kansas State University, N. Nepal, N.Y. Garces, Naval Research
Laboratory, H.M. Meyer III, Oak Ridge National Laboratory, C.R. Eddy,
Jr., Naval Research Laboratory, J.H. Edgar, Kansas State University Nanostructured Solar Cells
To improve the efficiency of GaN based power electronic devices there is Moderator: M.S. Arnold, University of Wisconsin Madison
tremendous and growing interest in employing metal-insulator-
semiconductor (MIS) transistors. As with all compound semiconductors,
there is a significant challenge in forming an electronic quality dielectric- 8:20am EN+NS-MoM1 Doping Control for the Development of Silicon
semiconductor interface. Thus, there is a need to better understand and Quantum Dot Solar Cell, K.J. Kim, J.H. Park, Korea Research Institute of
improve the dielectric-semiconductor interface quality in order to improve Standards and Science (KRISS), Republic of Korea, H.-J. Baek, H.H.
the overall performance of the device. Hwang, University of Science and Technology (UST), Republic of Korea,
J.S. Jang, Chungbuk National University (CBNU), Republic of Korea

Si quantum dots (QDs) imbedded in a SiO matrix is a promising material
This research focuses on the benefits and properties of Al2O3, TiO2 and 2
for the next generation optoelectronic devices, such as solar cells and light
TiO2-Al2O3 nanolaminate thin films deposited on GaN and GaOx/GaN by
emission diodes (LEDs). However, low conductivity of the Si quantum dot
plasma-assisted atomic layer deposition (PA-ALD) for gate dielectric
layer is a great hindrance for the performance of the Si QD-based
development. Correlations were sought between the films’ structure,
optoelectronic devices. The effective doping of the Si QDs by
composition, and electrical properties. The gate dielectrics were
semiconducting elements is one of the most important factors for the
approximately 15nm thick as determined by spectroscopic ellipsometry.
improvement of conductivity. High dielectric constant of the matrix
The interface carbon concentration, as measured by x-ray photoelectron
material SiO is an additional source of the low conductivity.
spectroscopy (XPS) depth profile, was lower for Al2O3/GaN than 2
TiO2/GaN, and the nanolaminate structure did not decrease the carbon Active doping of B in Si nano structures and the effect of internal
concentration. However, carbon was not detected at the interface for the polycrystalline bridge layer were investigated by secondary ion mass
GaN samples pretreated by annealing in O2 for 30 minutes at 800°C. Also, spectroscopy (SIMS) depth profiling analyses. Phosphorous and boron
according to XPS, the Al2O3 films had a better coverage than TiO2. The doped-Si / SiO2 multilayers on Si wafers were fabricated by ion beam
RMS roughness of TiO2 and Al2O3 top layers were ~0.53nm and ~0.20nm sputtering deposition as a model structure for the study of the diffusion
respectively, as determined by atomic force microscopy. The dielectric behavior of the dopants. The distributions of the dopants after annealing at
constant of Al2O3 on GaOx/GaN was greatly increased compared to that of high temperatures were analyzed by SIMS depth profiling analyses.
the TiO2-Al2O3 and pure Al2O3 on GaN substrate. In addition, the Al2O3 In this study, the diffusion behaviors of various dopants in silicon
deposited on the GaOx/GaN showing no hysteresis in capacitance-voltage nanostructures will be discussed and the effects of the various parameters
(C-V) characteristics, which is corresponding with a negligible carbon for the improvement of conversion efficiency in Si quantum dot solar cell
concentration from the XPS depth profile. These results indicate the will be introduced.
promising potential of plasma ALD deposited Al2O3 serving as the gate
oxide on GaOx/GaN based MOS devices.
8:40am EN+NS-MoM2 Photocarrier Generation in Si Quantum-dot
Sensitized Solar Cells, G. Uchida, H. Seo, Y. Wang, K. Kamataki, N.
11:20am EM+TF+OX+GR-MoM10 Passivation of Interfacial Defects Itagaki, K. Koga, M. Shiratani, Kyushu University, Japan
in GaAs and Other III-Vs, J. Robertson, Cambridge University, UK The pressing need for massively scalable carbon-free energy sources has
INVITED focused attention on both increasing the efficiency and decreasing the cost
It has always been harder to make FETs from GaAs than Si, because of of solar cells. Quantum-dot (QD) solar cells employing multiple exciton
‘Fermi level pinning’ and the difficulty of passivating its surfaces. These generation (MEG) have attracted much attention as a candidate for the third
issues were discussed by Spicer et al [1] in the ‘unified defect model’ and generation solar cells, because MEG represents a promising route to
Hasegawa [2] is his ‘Disorder Induced Gap states’ model. Since 1997 it was increased solar conversion efficiencies up to about 44 % in single junction.
possible to make inverted GaAs MOSFETs using the epitaxial Gadolinium Our interest has been concerned with QD sensitized solar cells using Si
gallium oxide [3]. The main impetuous now is to use atomic layer nanoparticles [1]. The main purpose of this study is to discuss the
deposition (ALD) to make scalable FETs [4], as recently achieved by Intel characteristic of the quantum yield in view of the MEG effect.
[5]. The obvious question is why (In)GaAs is much harder to passivate than
QD thin films composed of size-controlled Si nanoparticles were deposited
Si. The early answer was its poor native oxide. But since the advent of good
using double multi-hollow discharge plasma chemical vapour deposition
ALD HfO2 or Al2O3 oxides on Si, this answer is deficient, as they should
(CVD) of a SiH/H and CH or N gas mixture [2]. Short-circuit current
also work on GaAs [6]. The underlying reason for defects is not stress, it 4 2 4 2
density of Si QD sensitized solar cells increases by a factor of 2.5 by
must be chemical. I show that it arises from the polar bonding of GaAs [7],
irradiation of CH or N plasma to Si nanoparticle surface. We also have
and a driving force to keep the surface Fermi level in a gap. The electron 4 2
measured incident photon-to-current conversion efficiency (IPCE) in the
counting rule of Pashley [8] that describes surface reconstructions is shown
near-ultraviolet range using quartz-glass plates as front panels of QD
to be a variant of auto-compensation, and it works more generally [9]. It
sensitized solar cells. IPCE gradually increases by light irradiation in a
leads to a continuous generation of defects if it is not satisfied. So the
wavelength range less than 600 nm around optical band-gap (E) of Si
answer is to deposit oxide layers that meet this rule, and also to break any g
nanoparticle films, and then steeply increases below 280 nm around 2E.
surface reconstructions that may lead to As-As dimers [9]. Diffusion g
This rapid increase of IPCE under the ultraviolet light incidence may be
barriers are also crucial to a good passivant, on GaAs or on Ge .
explained by the theoretically predicted MEG, the creation of two electron-
1. W E Spicer, et al, J Vac Sci Technol 16 1422 (1979); Phys Rev Lett 44 hole pairs from one high-energy photon incidence, in Si nanoparticle QDs.
420 (1980)
[1] G. Uchida, et al., Phys. Status Solidi C 8 (2011) 3021.
2. H Hasegawa, et al, J Vac Sci Technol B 5 1097 (1987)
[2] G. Uchida, et al., Jpn. J. Appl. Phys. 51 (2011) 01AD01-1.
3. M Hong et al, Science 283 1897 (1997)
4. P D Ye et al, App Phys Lett 83 180 (2003) 9:00am EN+NS-MoM3 Quantum Dot Solar Cells with External
5. M Radosavljevic, et al, Tech Digest IEDM (2009) p13.1 Quantum Efficiency Exceeding 100% by Multiple Exciton Generation,
J.M. Luther, M.C. Beard, A.J. Nozik, O.E. Semonin, National Renewable
6. C Hinkle, et al, Curr Opin Solid State Mat Sci 15 188 (2011) Energy Laboratory INVITED
7. W Harrison, J Vac Sci Technol 16 1492 (1979) Traditional semiconductors used in photovoltaic devices produce one
8. M D Pashley, Phys Rev B 40 10481 (1989) electron from each absorbed photon. On the other hand, new materials such
as quantum dots, nanorods, carbon nanotubes and graphene can more
9. J Robertson, L Lin, App Phys Letts 99 222906 (2011); 98 082903 (2011)
efficiently convert high-energy photons into multiple electron-hole pairs
through a process titled multiple exciton generation (MEG) provided that
the energy of the photon is at least twice the bandgap of the absorber. This
process has been shown to be more efficient in highly confined quantum
dots than other forms of carrier multiplication (such as impact ionization) in
bulk materials. Photovoltaic devices can benefit greatly from MEG by
producing increased photocurrent from the multiple electrons and thus
allowing a single junction solar cell to yield a theoretical maximum
efficiency as high as 44% compared to 33% for bulk semiconductors. In this
talk, we will present recent findings from incorporating PbSe quantum dots
9 Monday Morning, October 29, 2012
(QDs) into semiconducting arrays that make up the absorber layer in distributions of the electron and hole (i.e. wave-function engineering) in
prototype solar cells. In these devices, MEG is confirmed by demonstrating type II core/shell QDs and nanorods.
the first solar cell with external quantum efficiency (EQE) exceeding 100%
for solar relevant photon energies. The EQE in our device reaches a 11:40am EN+NS-MoM11 Intermediate Band Upconversion for Low-
maximum value of 114% at 380 nm and we have employed an optical Cost, Solution Processed Photovoltaics, J. Lewis, E.J.D. Klem, C.W.
model to determine that the PbSe QD layer produces as many as 1.3 Gregory, G.B. Cunningham, S. Hall, D.S. Temple, RTI International
electrons per photon (on average) for these photons. These findings are
PV devices based on disordered semiconductors such as polymers, organic
compared to ultrafast time resolved measurements of carrier quantum yields
small molecules, and colloidal quantum dots have seen gradually improving
where we find reasonable agreement. We will also discuss future directions
performance in recent years, but are likely to be limited to efficiencies in the
for materials designs that increase the quantum yield through more efficient
range of 10–15%. To increase efficiency further would require the use of
MEG.
tandem cells, which adds complexity and cost. Alternatively one can pursue
devices such as intermediate band solar photovoltaics (IBPV) that can
9:40am EN+NS-MoM5 Quantum-Confined Nanocrystals as Building exceed the Shockley-Queisser efficiency limit. In an IBPV device mid-gap
Blocks for Low-Cost Solution-Processed Multi-Junction Solar Cells, T. states are incorporated into a wider band-gap host, allowing infrared
Hanrath, J.W. Choi, W.N. Wenger, R.S. Hoffman, Cornell University photons to contribute to the photocurrent of the device via sequential
In light of recent advances in synthesis, characterization, and the emerging absorption of two photons. Ideally this occurs without compromising the
understanding of their size-dependent properties, there are many exciting open circuit voltage. We will present the first example of an IBPV solar cell
opportunities for semiconductor nanomaterials to contribute to the using solution processed, low-cost disordered materials. We show that the
development of next-generation energy conversion technologies. nature of the defect states in Pb-salt quantum dots is uniquely suited to
Semiconductor nanocrystal quantum dots are particularly attractive material efficient upconversion at optical power densities that are relevant for
candidates for the efficient capture of solar emission in inexpensive, thin unconcentrated solar illumination. This demonstration provides a path for a
film photovoltaic devices due to their large absorption cross sections, low- step-change in the efficiency of low-cost PV.
cost solution-phase processing and size-tunable energy gaps. The prospect
of exploiting colloidal nanostructures for the creation of low-cost multi-
junction solar cells has garnered immense scientific and technological Graphene and Related Materials Focus Topic
interest. We recently demonstrated demonstrate solution-processed tandem
Room: 13 - Session GR+EM+NS+PS+SS+TF-MoM
solar cells created from nanocrystal quantum dots with size-tuned energy
levels. Bringing this prospect to fruition requires the connection of absorber
layers with cascaded energy gaps subject to stringent electrical and optical Graphene Growth
constraints. We show that interlayers composed of ZnO/Au/PEDOT provide
Moderator: M. Spencer, Cornell University, V.D. Wheeler,
appropriate carrier density and energy-level alignment to resolve this
challenge. With such interlayers we have been able to create nanocrystal U.S. Naval Research Laboratory
quantum dot tandem cells that exhibit IR sensitivity and a open circuit
voltage approaching 1V. These advances provide guidelines for the design
8:20am GR+EM+NS+PS+SS+TF-MoM1 Synthesis Ingredients
of an effective interlayer in tandem cell devices and suggest a promising
Enabling Low Noise Epitaxial Graphene Applications, D.K. Gaskill,
future for solution-processed nanocrystal quantum dot solar cells.
L.O. Nyakiti, V.D. Wheeler, U.S. Naval Research Lab, A. Nath, George
Mason Univ., V.K. Nagareddy, Newcastle University, UK, R.L. Myers-
10:00am EN+NS-MoM6 Improvement of Carrier Transport in PbSe Ward, N.Y. Garces, S.C. Hernández, S.G. Walton, U.S. Naval Research
Quantum Dot-Embedded Polymeric Solar Cells Fabricated by a Laser Lab, M.V. Rao, George Mason Univ., A.B. Horsfall, Newcastle Univ., UK,
Assisted Spray Process, C. Hettiarachchi, D.M. Feliciano, D. Mukherjee, C.R. Eddy, Jr., U.S. Naval Research Lab, J.S. Moon, HRL Labs LLC
P. Mukherjee, S. Witanachchi, University of South Florida
Sensors made from graphene flakes have demonstrated single molecule
PbSe quantum dots (QD) in the size range of 4-8 nm are promising detection [Schedin et al., Nat Mat 6, 652 (2007) ]; this ultra-sensitivity is
candidates for solar energy harvesting as they exhibit multi-exciton likely due to the high crystalline quality of the graphene and the associated
generation with ultraviolet (UV) photon absorption. While generation of relative lack of defects that give rise to noise. The low noise nature of high
multi-excitons has been demonstrated, dissociation of excitons to enhance quality graphene should also facilitate other applications, e.g., low-noise
current densities has not been realized. One of the main bottlenecks has amplifiers. Combined with the unique ambipolar property of graphene field
been the difficulty in removing the surfactants on QDs to form a clear effect transistors (FETs), the low noise character of graphene would
interface between the QD and the polymer matrix. We have developed a significantly advance the performance of frequency multipliers, mixers and
Laser Assisted Spray (LAS) deposition technique to deposit uniform high-speed radiometers. To exploit these applications, high quality,
coatings of surfactant-free QDs on substrates. This technique involves the reproducible wafer-scale epitaxial graphene (EG) with minimal thickness
transient heating of aerosols containing PbSe QDs by a CO2 laser-gas variations and defects are essential requirements. Here, crucial graphene
interaction to burn the organic surfactants. Transmission electron synthesis elements required to achieve the wafer-scale quality goal are
micrographs and absorption spectroscopy show, under optimum conditions, described. Understanding the effect of substrate misorientation as well as
the particles remain as single crystals and maintain quantum confinement. hydrogen etch and Si sublimation conditions for graphene synthesis on the
Growth parameters are optimized by monitoring the degree of surfactant (0001) SiC surface is essential to achieve improved and reproducible wafer-
removal by studying the Fourier Transform Infrared (FTIR) spectra of scale graphene quality. For example, the impact of processing factors such
coatings grown by LAS technique. Two-layer solar cell structures of as temperature control, laminar gas flow and substrate rotation on large area
PbSe/polymer that is sandwiched between ITO and Al electrodes have been EG uniformity are described using examples created in an Aixtron SiC
fabricated. Comparison of the IV characteristics of these cells and cells epitaxy reactor. In addition, managing SiC step formation on the nominal
fabricated by PbSe QDs with ligand-exchange will be presented. (0001) orientation is significant for achieving uniform EG thickness on
terraces and to minimize additional growth at the step edges; this is
10:40am EN+NS-MoM8 Single and Multiple Exciton Dissociation in illustrated using data from atomic force microscopy and scanning electron
Colloidal Nanoheterostructures, T. Lian, Emory University INVITED microscopy images in combination with Raman spectroscopy maps and x-
The ability to control charge transfer dynamics to and from quantum dots ray photoelectron spectroscopy analysis. Managing step formation
(QDs) is essential to many QD-based devices, such as solar cells and light combined with optimal growth leads to the suppression of the Raman defect
emitting diodes. Recent reports of multiple exciton generation (MEG) by “D” band confirming minimal grain boundaries and defects, which are
one absorbed photon in some QDsoffer an exciting new approach to additional sources of electronic noise. Lastly, contactless Lehighton
improve the efficiency of QD-based solar cells and to design novel multi- resistivity maps of 75 mm wafers are used to illustrate the overall
electron/hole photocatalysts. Two major challenges remain. First, the uniformity of optimally synthesized graphene as well as to show the re-
efficiency of MEG process needs to be significantly improved for practical sistance state-of-the-art, with individual wafers exhibiting about a ±3%
applications. Second, the utilization of multi-excitons requires ultrafast relative variation. Examples of the impact of this synthesis approach on
exciton dissociation to compete with the exciton-exciton annihilation chemical sensors devices and FETs will be shown, each exhibiting 1/f noise
process, which occurs on the 10s to 100s ps time scale. In this presentation behavior down to 1 Hz and possessing noise spectral densities similar to
we report a series of studies of exciton dissociation dynamics in QDs and reports from exfoliated graphene. Hence, careful control of EG formation
nanorods by electron transfer to adsorbed electron acceptors. We show that across the wafer results in improved quality which subsequently leads to the
excitons in CdX (X=S, Se, Te) and PbS QDs can be dissociated on the reduction or elimination of additional noise sources from graphene defects
picosecond and and faster timescales and multiple excitons (generated by that would then adversely affect device performance.
multiple photons) per QD can be dissociated by electron transfer to
adsorbed acceptors. We discuss approaches for optimizing the single and
multiple exciton dissociation efficiencies by controlling the spatial
Monday Morning, October 29, 2012 10