Indian Journal of Advances in Chemical Science Fabrication of Nanomaterials on Porous Anodic ...

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Indian Journal of Advances in Chemical Science 3(3) (2015) 235-246
Fabrication of Nanomaterials on Porous Anodic Alumina Template Using
Various Techniques
Naveen Verma*, Krishan Chander Singh, Jitender Jindal
Department of Chemistry, Maharshi Dayanand University Rohtak, Rohtak - 124 001, Haryana, India.
Received: 31st March 2015; Revised: 2nd April 2015; Accepted: 11th April 2015
ABSTRACT
Porous anodic aluminum oxide film is a versatile template for the fabrication of nanomaterials. Porous alumina
can be fabricated electrochemically through anodic oxidation of aluminum by self-organization method yielding
highly ordered arrays of nanoholes. Various techniques such as chemical vapor deposition, electrodeposition,
spin coating, dip coating, physical vapor deposition are elaborated for the fabrication of nanomaterials using
porous anodic alumina as template.
Key words: Porous anodic alumina, Chemical vapor deposition, Physical vapor deposition, Spin Coating, Dip
coating, Electrodeposition.
1. INTRODUCTION nanorods, nanotubes, and various other nanomaterials
In today’s world, in the vast and rapidly growing which are useful. Various techniques are used for the
nanotechnology fields, a bottom-up manufacturing production of nanomaterials.
using template materials becomes increasingly
important [1]. One of the best and most widely used 2. CHEMICAL VAPOR DEPOSITION (CVD)
methods to ensure high repeatability and high quality CVD is a chemical process used to produce high-
of produced nanostructures is applications of porous purity, high-performance solid materials. The process
anodic aluminum oxide as a template. Since Masuda is generally used in the semiconductor industry to
and Fukuda [2] have invented the two steps method produce thin films. In this technique, the substrate
for the production of well-ordered anodic aluminum
is exposed to one or more volatile precursors which
oxide (AAO) in 1995. Scientists are working on
react or decompose on the substrate surface to
improving its manufacturing process. Usually, the
produce the desired deposit. CVD is widely used in
highly ordered porous anodic alumina is obtained
the microfabrication processes to deposit materials
as a result of self-organized two-step anodization of
in different forms including mono crystalline,
pure aluminum pieces in various acidic solutions or
polycrystalline and amorphous. CVD of materials in
in some other electrolyte. The most commonly and
nanoporous holes of alumina is a very important and
widely used electrolytes, to produce nanosized pores
challenging topic for researchers. Since it is interesting
in the range of 10-240 nm, are the acidic electrolytes
to investigate the filling of high aspect ratio of holes
like oxalic acid, sulfuric acid, phosphoric acid or
which are contained by porous alumina film. When
their combinations. It has been found that the best
a thin porous alumina film is uniformly coated with
honeycomb-like structure of anodic alumina layers
carbon, the carbon coated film exhibits a bright, and
in which uniform pore arrangement and uniform
tunable interference color with much higher saturation
size distribution obtained is produced in sulfuric acid
electrolyte [3]. However, based on the calculations of than the primary alumina membrane. Chemical vapor
regulatory ratio, the best honeycomb-like structure of synthesis (CVS) is a modified CVD method where the
nanopores is obtained in the oxalic acid solutions [4]. process parameters are adjusted to form nanoparticles
There are various anodizing parameters such as instead of the film. Both in CVD and CVS, precursors
applied voltage, solution temperature, electrolyte are metal organics, carbonyls, hydrides, chlorides, and
concentration affect the control of pore diameter other volatile compounds in gaseous, liquid or solid
of AAO [5-7]. The AAO is used as template for the state. The major limitation of the CVS process is the
growth of self-organized, highly ordered nanodots, availability of appropriate precursor materials.
*Corresponding Author: 235
E-mail: [email protected]
Indian Journal of Advances in Chemical Science 3(3) (2015) 235-246
The energy for the conversion of the reactants into as templates for growing microstructured tungsten
nanoparticles is supplied in hot wall (external furnace), oxide films and macroporous silicon substrates cause
flame (reaction enthalpy), plasma (microwave or radio the growth of “grids” of polycrystalline tungsten
frequency), and laser (photolysis or pyrolysis) reactors. oxide. The effect of interstitial lattice mismatch
The most important process parameters determining upon Hg Cd Te epitaxial layers grown by metal
1-x x
the quality and usability of the nanopowders are the organic CVD (MOCVD) were investigated [11].
total pressure (typical range from 100 to 100000 Pa), HgCdTe was found to be easily affected by lattice
the precursor material (decomposition kinetics and mismatch of less than ± 0.1% [12]. α- Fe O thin
2 3
ligands determining the impurity level), the partial film were fabricated by aerosol assisted CVD using
pressure of the precursor (determining the production a hexanuclear iron precursor (Fe [PhCOO] [acac]
6 10 2
rate and particle size), the temperature or power of the [O] [OH] ).3C H [13] where PhCOO-benzoate and
2 2 7 8
energy source, the carrier gas (mass flow determining acac- 2, 4-pentanedionate). The Si-doped α-Fe O was
2 3
the residence time), and the reactor geometry. The prepared by atmospheric pressure CVD (APCVD)
nanoparticles are extracted from the aerosol by means with iron pentacarbonyl (Fe [CO] ) as iron precursor
5
of filters, thermophoretic collectors, and electrostatic and tetraethoxysilane as the Si precursor at 450°C.
precipitators or scrubbing in a liquid [8,9]. A more A requirement of APCVD process is that the precursor
developed CVD technique called as plasma enhanced material must have high enough vapor pressure [14].
CVD is one of the bright methods for the growth of
carbon nanotubes using porous AAO as template. Silver nanowires were fabricated by deposition in
A controllable method for carbon nanotubes the porous anodic alumina nanochannels with almost
production is plasma enhanced-CVD. The processes 100% efficiency only with small fluctuations in the
involve the growth at low temperature and provide growth rate. The monocrystalline silver nanowires
easy vertical alignment to the nanomaterials. Plasma growth direction is perpendicular to <110> direction
is a partially ionized gas consisting of electrons and and the diameter is varied from 30 nm to 70 nm
ions. Typical ionization fractions of 10−5 to 10−1 depends on how the alumina template is prepared. For
are encountered in process reactors. Plasmas are the fabrication of uniform porous alumina layer pulsed
electrically conductive with the primary charge electrodeposition and a highly conductive electrolyte
carriers being the electrons. The light mass of the are prerequisite conditions [15]. Electrodeposition of
electron allows it to respond much more quickly to ZnO on the porous anodic alumina membrane (PAAM)
changes in the field than the heavier ions. For example, with a sputtered Au electrode yields polycrystalline
the thermal CVD of silicon nitride occurs between ZnO nanotubes. The deposition of particles starts at
700°C and 900°C, the equivalent PECVD process is the Au cathode on the bottom of nanopores and the
accomplished between 250°C and 350°C. The carbon deposition time control the length of ZnO nanotubes.
nanotubes were grown by PECVD on the AAO These technologies provide a new way to fabricate
template at 550°C temperature. The ethylene (C H ) metal oxide nanotube array and have applications in
2 2
is used as a carbon source and the ammonia (NH ) optoelectronics and sensing devices [16].
3
gas used for dilution purpose and as a catalytic gas.
For the growth of CNTs, the thorough hollow porous Few transition metal complexes like iridium (Ir),
membrane was prepared by removing its barrier layer. Platinum (Pt), Rhodium (Rh), or Palladium (Pd) have
Plasma CVD has numerous advantages over thermal a favorable combination of stability, volatility, and
CVD. Obviously the reduced deposition temperature clean decomposition. For this group of metals, the
is a bonus for the semiconductor industry which must rates of deposition are low. So the use of auxiliary
worry about dopant diffusion and metal interconnects energy sources such as plasma or laser to assist CVD
melting at the temperatures required for thermal is a viable route to increase deposition rates [17].
CVD. Furthermore, the low pressures (between 0.1
and 10 Torr) required for sustaining a plasma result in Catalysis is the main part of CVD-CNT technique.
surface kinetics controlling the reaction and therefore With the use of a suitable catalyst; the CVD
greater film uniformity. A disadvantage of plasma CVD temperature can be brought down to room temperature
is that it is often difficult to control stoichiometry due and also possible to control the diameter and chirality
to variations in bond strengths of various precursors. of the resulting CNTs [18].
For example, PECVD films of silicon nitride tend to
be silicon rich because of the relative bond strength Fabrication of CeO -doped Y O -stabilized ZrO films
2 2 3 2
of N relative to the Si-H bond. In addition, some on dense silicon and porous alumina substrates were
2
films may be easily damaged by ion bombardment produced via atmospheric pressure metal organic
from the plasma. Tungsten oxide was deposited on CVD. A toluene solution of the precursors Zr (tfac) ,
4
the PAA template and macroporous silicon substrates Y (hfac) , and Ce (tmhd) was used to deposit films
3 4
via aerosol assisted CVD from the precursor tungsten with thickness around 1 µm. The results show that
hexaphenoxide [10]. The results show that the thin crystalline multicomponent films can be obtained
porous anodic alumina substrates have potential and that solution composition can be manipulated to
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Indian Journal of Advances in Chemical Science 3(3) (2015) 235-246
change film composition. Deposition temperature and directly as catalysts in the synthesis of CNTs. Plasma
precursor concentration have important effects on the enhanced CVD is a suitable method for the synthesis
film morphology and deposition rate [19]. of CNTs and modification of their surface properties.
Lim et al. [29] gives the application of PECVD in the
An alternative method for the common use of production and modification of CNTs. PECVD used in
oxalic acid, acetylene pyrolysis in porous alumina several different modes; radiofrequency (RF-PECVD),
template obtained by anodic oxidation in sulfuric acid direct current (DC-PECVD), diffusion (D-PECVD),
solution can produce carbon nanotubes with a higher and microwave (MW-PECVD). Kim and Gangloff
density(~56 × 109 cm2) at 650°C and 550°C. After demonstrated the low temperature (480°C-612°C)
boiling in water, carbon nanofibers can be obtained synthesis of CNTs on different metallic under layers
in the templates anodized in oxalic acid solution by (i.e., Ir, Ag, Pt, W, and Ta) using diffusion PECVD [30].
growing at 650°C through the CVD method which
shows the catalytic activity for anodic alumina. No 3. ELECTRODEPOSITION TECHNIQUE
carbon tubes or carbon nanofibers can be formed if the Electrodeposition is a very versatile tool to fabricate
CVD temperature decreases to 500° [20]. multi-component metal oxide nanotube array
composites. Mainly electrodeposition technique refers
in three processes. Electroplating, a process that uses
Catalytic CVD-either thermal [21] or plasma enhanced
electrical current to reduce dissolved metal cations, so
is the standard method for the CNTs production.
that they form a coherent metal coating on an electrode.
CCVD is an economically executable process on
Electroplating uses an electrical current to finish a
the large scale for the production of pure CNTs. The
contact or component with a thin layer of metal. The
function of the catalyst in the CVD process is the
applications of electroplating deposits have a desired
decomposition of carbon source via either plasma
property like abrasion, wear resistance, corrosion
irradiation (plasma enhanced CVD) or heat (thermal
protection, lubricity or esthetics onto a substrate
CVD) and its new nucleation to form CNTs. The most
lacking the desired property. The electroplating process
frequently used catalysts are transition metals Fe, Co,
is also known as electrodeposition. It is a galvanic or
Ni, and Au [22,23] and mostly some hydrocarbons like
electrochemical cell acting in reverse. The part being
methane, ethane, ethylene, xylene or ethanol are used
plated becomes the cathode of the circuit. With a soluble
as a carbon source in CVD. CNTs growth efficiency
anode, the anode is made of the metal to be placed on
depends upon reactivity and concentration of gas-
the part which dissolves in a chemical solution, like
phase intermediates when gaseous carbon source used
gold or palladium. In a soluble anode, the metal is
for the growth of CNTs. The choice of catalyst is one
actually contained in the solution. Both the anode and
of the most important parameter affecting the CNTs
the part or cathode is submerged in a solution containing
growth.
one or more metal salts in addition to other ions that
enable the flow of electricity throughout the solution.
Flahaut et al. [24] reported that the catalyst was
A rectifier supplies direct current to the cathode causing
prepared by the combustion route using either urea
the metal ions in solution to lose their charge and plate
or citric acid for the synthesis of CNTs by CCVD.
onto the part or cathode within the solution. As the
Xiang et al. prepared CNTs via CCVD of acetylene
electrical current flows through the solution, the anode
on a series of catalysts derived from Co/Fe/Al layered
dissolves in a controlled manner and replenishes the
double hydroxides. Lyu et al. [25] produced high quality
ions in the bath. Electrophoretic deposition, a term for
and high purity DWNTs by catalytic decomposition of
a broad range of industrial processes which includes
benzene as an ideal carbon source and Fe-Mo/Al O as
2 3 electrocoating, e-coating, cathodic electrodeposition,
a catalyst at 900°C. Jiang et al. [26] studied the growth
anodic electrodeposition, and electrophoretic coating,
of CNTs in situ on the pre-treated graphite electrode or electrophoretic painting. Under potential deposition,
via CCVD using Ni(NO3)2 as the catalyst [27]. The a phenomenon of electrodeposition of a species
prepared CNTs had 80 nm and 20 nm in outer and (typically reduction of a metal cation to a solid metal) at
inner diameter, respectively. Feng et al. used acetone a potential less negative than the equilibrium (Nernst)
as a carbon source, ferrocene as a source of Fe catalyst potential for the reduction of this metal.
and thiophene as a promoter to synthesize high-quality
DWNTs thin films through CCVD [27]. Kim et al. [28] Embedded thin layer of titanium between the porous
gives a royal method for the growth of CNTs that uses anodic alumina template which is supported on a Si
three different iron-containing proteins; hemoglobin, substrate, is used for the fabrication of vertical arrays
myoglobin, and cytochrome C in order to control of high aspect ratio (>100) InSb nanowires with
precisely the size and structure of CNTs. These iron- diameters of ~20 nm. SEM results show that the InSb
containing protein source were adsorbed on the amine- nanowires completely fills the channels of the porous
terminated self-assembled monolayer (SAM) surfaces anodic alumina thereby acquiring a wire diameter of
by peptide bonds between the carboxyl groups of the about 20 nm. Raman spectrum of the InSb nanowires
proteins and the amine groups of the SAMs and used indicates high crystal quality [31].
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Indian Journal of Advances in Chemical Science 3(3) (2015) 235-246
Highly ordered ZnO nanowires array were fabricated compared to other fabrication techniques, namely
by the oxidation of metal Zn that was electrodeposited pulsed laser deposition, vapor liquid solid (VLS)
in the pores of anodic alumina membrane [32]. The method, and CVD [36]. Electrodeposition of copper
ZnO nanowires diameter is in the range from 15 nm nanowires depends on many factors, namely inter-
to 90 nm. Atomic force microscopy, X-ray diffraction electrode spacing, electrolyte composition and pH
(XRD), and transmission electron microscopy (TEM) value, current density and time of deposition. The
characterization shows that the polycrystalline ZnO diameter of copper nanowires nearly matches with the
nanowires array were uniformly assembled into the pore diameter of polycarbonate template, but the wire
hexagonally arranged nanochannels of the anodic growth is not as perfect cylinders. The aspect ratio is
alumina membrane. In this work, the arrays of in the order of 300.
semiconductor ZnO nanowire were synthesized by
oxidizing Zn that was electrodeposited in the pores Electrodeposition of ZnO on the PAAM with a sputtered
of AAMs. As a wide band gap semiconductor, ZnO Au electrode yields polycrystalline ZnO nanotubes.
is of interest for low voltage and short wavelength The deposition of particles starts at the Au cathode
on the bottom of nanopores and the deposition time
electro-optical devices such as light emitting diodes
control the length of ZnO nanotubes. This technology
(LED) and diode lasers. ZnO nanoparticles offer
provides a new way to fabricate metal oxide nanotube
considerable potential as starting material for other
array and have application in optoelectronics and
applications such as transparent ultraviolet protection
sensing devices [16]. Different nanostructures of
films and chemical sensors. The uniform orders of
metal and alloys can be fabricated by electrodeposition
ZnO nanowire arrays make it more practical to apply
technique using anodic alumina membrane as
ZnO in electron devices and chemical sensors.
template. Nickel and copper oxide electrodeposition
resulted in the formation of short metal nanotubes
Zinc telluride is an important semiconductor material
of nickel about 5 µm long and large array of aligned
with a direct optical band gap of 2.2-2.3 eV at room
copper (I) oxide nanowires, respectively. Potential
temperature, which has potential applications in
perturbation and bath composition influence the
optoelectronics and thermoelectric devices [33].
composition and crystallographic nature of Cu O
A plating solution containing cadmium sulfate, 2
nanowires. CeO nanotubes and PbO nanowires
tellurium dioxide, and citric acid was used to obtain thin 2 2
also fabricated by electrodeposition techniques,
films of zinc telluride by electrodeposition into AAM
former from non-aqueous electrolyte and later
pores. From this study, it was possible to establish the
by potentiostatic electrodeposition under anodic
optimal experimental conditions for the preparation
polarization [37]. For the fabrication of Ni nanotubes,
of zinc telluride films with an almost stoichiometric
nickel electroless deposition was carried out in a
atomic composition (50.40% Zn, 49.60% Te). The
bath containing Ni sulfate. Under a square potential
ZnTe nanowires on the AAM membranes with
waveform, Ni NTs were fabricated inside the channels
50 nm of pore diameter were also fabricated through
of anodic alumina membranes and in the trapezoidal
potentiostatic electrodeposition under similar
wave; length of nickel nanowires increased with
conditions.
deposition time [38]. Sn-Co nanowires also obtained
by electrochemical deposition which is carried out
Synthesis of silver telluride nanowire arrays were
at −1.0 V (SCE) and 60°C in a solution of 0.005 M
carried out by cathodic electrolysis on the porous
CoSO and 0.01 M SnSO in the presence of 0.2 M
4 4
anodic alumina template from dimethyl sulfoxide
Na SO as supporting electrolyte and 0.2 M sodium
2 4
(DMSO) solutions which contain 0.1 M NaNO ,
3 gluconate as chelating agent [38]. By adjusting the
5.0 mM AgNO3 and 6.0 mM TeCl4 [34]. Synthesized deposition time, nanowires of different composition
Ag2Te nanowires are well crystallized monoclinic and length were formed. Metal oxide nanostructures
that obtained at potentials between -0.55 to -0.65V. like Cu O, CeO and PbO are obtained by template
2 2 2
By the adjustment of the concentration of TeCl4 in electrodeposition. For the fabrication of Cu2O
the solution, the chemical composition of the silver nanostructures, the electrodeposition was carried out
telluride nanowires can be controlled. The method of at 55°C and electrode potential of −0.2 V (SCE). Two
using DMSO as a solvent and TeCl4 as a Te source different electrolyte solutions were used: The first was
could be extended to the synthesis of other metal a 0.01 M cupric acetate/0.1 M sodium acetate bath
telluride by electrodeposition. at pH=6.5 and the 2nd plating bath was prepared by
dissolving 0.4 M CuSO in a 3 M lactic acid solution
4
Fabrication of copper nanowires [35] with diameter with pH=10 [36].
100 nm and 200 nm in an electrochemical cell takes
place through electrodeposition technique based on the Fabrication of uniform and regular arrays of Cu and
principle of electroplating using anodic alumina and Pd nanowires by displacement deposition at room
polycarbonate templates. Electrochemical deposition temperature. For the preparation of Cu nanowires,
route is easy, low cost as well as cumbersome 0.2 M copper sulfate solution was used while a
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Indian Journal of Advances in Chemical Science 3(3) (2015) 235-246
solution containing Pd(NH ) (NO ) was used for the observations due to their different size. The high
3 4 3 2
fabrication of Pd nanowires are straight, dense, and degrees of hydration of lithium have faster silicate
continuous with a uniform diameter through the entire adsorption on the alumina surface than the potassium
length [36,39-41]. of the oxide layer from alkaline dissolution.
4. DIP COATING Maghemite (γ-Fe2O3) with 20 nm diameter
In dip coating techniques, the porous template is nanoparticles were filled by dip-coating process
immersed in a colloidal dispersion of particles which into the aluminum oxide nanotemplate pores with
wets the pores; upon withdrawal from solution and 100 nm diameter and their magnetic properties were
drying, some particles remain within the template [42]. studied [45]. The maghemite nanoparticles were
Assisted dip coating methods have also been reported stabilized by oleic acid. To obtain the multilayer of
where a secondary force is used to aid the infiltration maghemite nanoparticles, the dip-coating procedure is
of particles into the template; for instance, magnetic repeated. The magnetic moment of AAO with particles
stirring can be used to force the liquid to impinge increased in proportion of the number of layers. These
upon the template thereby increasing the number of results demonstrate the possibility of integrating
nanoparticles into nanotemplates and controlling their
infiltrated particles. Dip coating methods, however,
properties. Ti-Al composite oxide film was obtained
achieve at most a modest 3.5 volume percent
between TiO coating and Al substrate by using the
nanoparticle filling [43] rendering them unsuitable for 2
sol-gel dip coating method [46]. In this process, Al
a complete filling of the template with building blocks
specimens were covered with TiO film by sol-gel
and voiding any possibility of obtaining a freestanding 2
dip coating and then anodized in ammonium adipate
structure upon removal of the template.
solution. Characterization studies (TEM, XRD,
electrochemical impedance spectroscopy) shows
Dip Coating is a simple and low-cost method to
that dual layered anodic oxide film formed between
create a thin film on a substrate. In general, it can
TiO coating and aluminum substrate. The dual layer
be separated into five stages- (i) Immersion: The 2
structure consists of Al O as an inner layer and an
substrate is immersed in the solution of the coating 2 3
outer Ti-Al composite oxide layer. With the repetition
material at a constant speed. (ii) Start-up: After the
of sol-gel dip coating, the thickness of inner layer
substrate has remained inside the solution for a while
reduced and outer layer increased. Pore network in
and we start to pull it up. (iii) Deposition: The thin film
TiO coating affect the formation and structure of Al
deposits itself on the substrate while it is pulled up at 2
anodic oxide film. TiO deposited anodic oxide film
a constant speed. The speed determines the thickness 2
has 80% higher capacitance than that without TiO
of the coating. (iv) Drainage: Excess liquid will drain 2
and the resistance decreases with the repetition of dip
from the surface of the substrate. (v) Evaporation: The
coating.
solvent evaporates from the liquid to form the thin film
on the substrate.
The inner alumina layer grew due to the inward
transport of O−2 anions and the outer Ti-Al composite
The effect of alkali metal cations (namely lithium, oxide layer grown due to the outward transport of Al+3
sodium and potassium) on the silicate/alumina was
cations. TiO film caused the thickness variation of
2
studied in this work [44]. Porous anodic aluminum both layers by inhibiting Al+3 and O−2 ion transport
oxide were silicate treated by dipping in water based
during anodization.
silicate solutions of different monovalent alkali metal
cations (Li+, Na+, K+). Aqueous sodium silicate
Highly ordered TiO nanowires were prepared by
2
solution is widely used as cleaner and corrosion
dipping technique into a porous anodic alumina
inhibitor for aluminum alloys. The alumina oxide template for the application as electrolytic
surface modification during immersion in solution capacitor [47]. Homogenous infiltration of TiO
2
was studied as a function of the type of cation at nanowires were obtained through dipping technique
ratio SiO2/M2O=1 (Here M=Li, Na, K) at different even in the highly acidic solution. The electronic
temperature of the silicate solutions (30°C and 70°C). capacitance of the TiO nanowires were measured
2
Alkali metal cation acting as a coagulating agent and compared with the theoretical calculations using
between the anodized alumina surface and the silicate an effective thickness, which correspond to the mean
anions. Silicate anion coagulation would result in a radius of nanowires.
homogenous adsorption of the silicate on the anodic
oxide surface. Morphological differences were 5. SPIN COATING
observed in alumina surface by changing the type of Spin coating is a procedure used to deposit uniform
alkali metal cation after the immersion in solution. thin films to flat substrates. Usually, a small amount of
The dissolution of oxide layer was faster in potassium coating material is applied on the center of the substrate,
silicate, while the highest protection of the oxide layer which is either spinning at low speed or not spinning
was given by lithium. The three cations show different at all. The substrate is then rotated at high speed in
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Indian Journal of Advances in Chemical Science 3(3) (2015) 235-246
order to spread the coating material by centrifugal 2-6 nm pore size deposited on the anodized disk by
force. Rotation is continued while the fluid spins off dip coating. Later the mesoporous gas separation
the edges of the substrate, until the desired thickness membrane layer is deposited by spin coating,
of the film is achieved. The applied solvent is usually obtaining a defect free mesoporous silica having high
volatile, and simultaneously evaporates. So, the higher selectivity and permittivity [53]. This method can be
the angular speed of spinning, the thinner the film. The used for the development of different type of inorganic
thickness of the film also depends on the viscosity and membranes having the advantage of availability and
concentration of the solution and the solvent. Spin low permittivity resistance of anodic alumina oxide
coating is widely used in microfabrication, where it template.
can be used to create thin films with thicknesses below
10 nm. It is used intensively in photolithography, to Synthesis of single crystalline PbO2 nanowires
deposit layers of photoresist about 1 µm thick. (diameter 42 nm) carried out by a spin-coating process
of putting a lead oxide sol-gel solution into a PAAM.
Uniformly and controlled distribution of Co and Ag Lead oxide has various application and most one is,
nanoparticles on the Si and SiO substrate can be use as active material of lead acid battery [54]. Other
2
investigations show that the PbO is a strong oxidant,
achieved by employing the spin coating method [48]. 2
like ozone, due to its high overpotential for oxygen
The particle density can be controlled by changing
evolution. Electron diffraction analysis and TEM
the molar concentration of nanoparticle colloids
results shows that the synthesized PbO nanowires
with the fixed rotational speed of the spin coater. 2
are single crystalline and orthorhombic with diameter
Co nanoparticles were synthesized by thermal
30 nm to 52 nm. These PbO nanowires are very
decomposition process where 4 ml of 0.5 mol (M) 2
sensitive toward electron beam irradiation in the TEM
Co (CO) toluene solution was injected into hot
2 8
microscope, resulting in the phase transformation
toluene solution with 0.089 g of NaAOT (Sodium
from α PbO to β PbO.
bis[2-ethylhexyl]sulfosuccinate). After refluxing for 2
6 h at 380 K and following centrifuge separation
6. PHYSICAL VAPOR DEPOSITION
process, black colored Co nanoparticle were obtained
PVD is the process involving vaporization of the
in powder form. This AOT stabilized Co nanoparticle
coating material in vacuum, transportation of the vapor
were dispersed in toluene. Ag nanoparticles were
to the substrate and condensation of the vapor on the
obtained by alcohol reduction of silver acetate (AgAc)
substrate surface. Two PVD techniques are used for
in the presence of polyvinyl pyrollidone [49].
depositing wear resistant alumina coatings: Sputtering
is a PVD method utilizing argon ions for bombarding
Alumina membrane based high-quality PbO and
2 a cathodically connected target made of the coating
Pb (Zr, Ti) O metal oxide nanowires with uniform
3 material. Atoms of the target are knocked out by the
diameter and relatively smooth surface are synthesized
high energy ions and deposit on the substrate surface.
by combination f sol-gel processing and spin coating
In the EB-PVD method, the target anode is bombarded
method [50]. The resulting fabricated PbO nanowires
2 in a high vacuum with an electron beam generated by a
have a single crystalline structure with 40 nm diameter
charged tungsten filament. Electron beam evaporation
and 10 µm length and PZT nanowires have diameter
method is much faster than sputtering. According to
50 nm and length 20 µm. Spin coating creates an
the sputtering process [55] takes approximately 50 h
outward radial flow from the center of the disk which
to prepare a 0.24-0.31 mil (6-8 µm) thick alumina
results in the removal of the residual air inside the
film compared to only 20 min needed for the E-beam
nanopores. The air flow can provide a suction effect
evaporation. Typical alumina coating obtained by
for the sol to enter the nanopores, providing the the Electron beam PVD methods has a columnar
coating is the versatile method that is favorable for a structure. Dense fine grain crack-free structure of
wide variety of sol system, regardless of the acidity of PVD deposited alumina coatings does not requires
the solution [51]. post-deposition polishing and provides low wear
rate. The wear characteristics of the foil air bearings
A low-cost inorganic matrix contain terbium doped are greatly improved by applying a protective sputter
yttrium aluminum oxide films were synthesized by deposited Al O coating. AAO template is used for the
2 3
spin coating deposition grown on a silicon wafer and electrodeposition of cuprous oxide (Cu O) nanorods
2
terbium photoluminescence was studied at annealing in alkaline (pH=12) copper sulfate electrolyte TiN
temperature from 400°C to 1100°C on porous anodic coated Si wafer in room temperature [56]. In this work,
alumina [52]. A Tb-doped inorganic matrix on the electrochemical deposition method is used because
basis of PAA as prospective for green terbium emission length of the nanorods can be controlled by changing
within the broad temperature range of applications. electrochemical factors. Cuprous oxide, a p-type
semiconductor, having band gap 2.0-2.2eV has many
For the deposition of microporous silica on anodic applications in hydrogen production, superconductor,
alumina template, a mesoporous silica layer with solar cell and negative electrode material [57-60].
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Indian Journal of Advances in Chemical Science 3(3) (2015) 235-246
The ordered arrays of Ni and Au nanodots with been fabricated by PVD/atmospheric pressure injection
uniform diameter and density of 1.2 × 1010 cm−2 on using porous anodic alumina as a template [62]. PVD
the anodic alumina oxide template were fabricated is a simple and suitable method for the fabrication of
by a three-step method combining PVD, grazing ion special purpose of metal nanotubes and it is applicable
milling and thermal annealing technique [61]. First, only for those metals which are evaporated in vacuum.
deposition of 80 nm Ni film on the AAO template, For fabricating metal nanotubes on AAO templates,
a new method “two-step evaporating method” is
which was prepared by two-step anodization method,
developed. This method includes two evaporation
by ion beam sputter deposition. After that grazing ion
steps. First step is an aluminum evaporating process
milling used for the removal of continuous layer and
for depositing Al on the surface of the porous alumina
lastly spherical nanodot array was formed by thermal
template in vacuum and the second step is a heating
annealing process. Above similar process is used for the
process of Al sample which is deposited on the surface
deposition of Au film and resulting Au nanodot arrays
into the pores under the atmospheric pressure.
are formed. The packing density of nanodots can be
controlled by selecting a template with the desired pore
A modern way for the fabrication of macroporous TiO
2
density. Due to the high uniformity and controllability
oxygen sensors as an etching mask for the production
of the diameters, the nanodots are very stable for the
of macroporous silicon substrate is discussed by chih-
study of their size-related properties. The diameter cheng Lu et al. [63]. For the enhancement of sensor
of the nanodots can be controlled independently of sensitivity and to reduce sensor dimensions, a higher
the packing density which helps for investigating the specific surface area is generating with this method.
coupling between adjacent nanodots [61].
7. APPLICATION OF NANO MATERIALS
Aluminum nanotubes with pore external diameter PAAM is used as universal nanoscale templates due
60 nm, inside diameter 35 nm and length 2 µm, have to its simple preparation technique. It has been widely
a
b c
Schematic diagram for the fabrication of porous anodic alumina (a) Vertical view of porous layer on anodic
aluminum template, (b) Pores formed on alumina layer after anodization, (c) Experimental setup
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Indian Journal of Advances in Chemical Science 3(3) (2015) 235-246
used to fabricate nanotubes and nanowires by filling nanoscale devices [81,82]. Numerous techniques
various materials into the nanopores such as metals, such as VLS growth, laser assisted catalytic growth,
semiconductors, and organic matters [64-66]. CVD, laser ablation, molecular beam epitaxy, e-beam
lithography, Nanosphere lithography – assisted
A porous anodic aluminum oxide template is used techniques have been used to prepare nanowires [83].
for the fabrication of gold nanotube membranes
(GNT). GNTs have various types of applications Carbon nanotubes mainly used as gas sensors due to
because the shape and structure of GNTs are closely their large surface area, high electrical conductivity,
related to their catalytic, electronic, and optical and chemical stability. Gas sensors have various novel
properties [67,68]. Catalytic properties of gold depend applications [84,85]. CNT-based sensors have been
on the size of the particle and the interaction between used for the detection of gases such as H , O , NO ,
2 2 2
gold and the supporting oxide [69]. Gold nanotube CO , and NH [86,87] and organic compounds [88].
2 3
membranes have numerous applications including CVD is used in the direct synthesis of CNTs on
selective molecular separation, enzyme reactors, drug substrate or CNT powders were posted on substrates
delivery, biosensing, and electroanalysis [70-72]. The for the fabrication of devices. The use of metallic
excellent catalytic properties (catalytic rate constant nanostructures with high work function is beneficial
K = 0.132 min−1) of the gold nanotube membranes for the electrical properties of the cell. The gold
were demonstrated by testing catalytic conversion of and silver nanodot arrays are prepared on a glass/
4-nitrophenol into 4-aminophenol in the presence of indium tin oxide substrate using AAO lithography.
NaBH as a reductant. This technique is very efficient for the preparation of
4
nanostructures [2,89].
Fabrication of Ni nanowires on AAO template is carried
out by the combined technique of anodic anodization Ultra-sensitive sensing and biosensing devices using
and direct current electrodeposition. Metal nanowires nanomaterial have great interest of study due to
have various applications in high density recording their unique physical and chemical properties. Self-
media [73,74] and optical labels [75], The diameter of ordering electrochemical anodization is used for the
Ni nanowires is about 30 nm which corresponds to the synthesis of the highly ordered vertically aligned
diameter of the pores in the alumina film. Ni nanowires nanoporous and nanotubular structures with well-
exhibit a polycrystalline bamboo-like structure. defined and controllable geometry, which are useful
for the production of such sensing and biosensing
Since 19th century, carbon nanotubes are of great devices [90]. Self-ordering electrochemical
interest of study as the key material for nanotechnology anodization is very simple and advantageous method
because of their semiconducting, electron emitting, including controllable pore structure with high aspect
high strength and other unique properties [76,77]. ratio and cost competitive fabrication. The potential
of nanopores to mimic protein nanochannels in cell
Metal nanowires have various unique electrical, membranes which have single molecule sensitivity
electronic, thermoelectrical, optical, magnetic and and selectivity and selectivity is critical toward the
chemical properties. Morphology of nanowires, development of novel bio-inspired biosensors [91].
diameter dependant band gap and carrier density of Anodic aluminum oxide is an excellent platform for
states are the factors which influence the physical the development of advanced, smart, simple, cost-
properties of MNWs. MNWs and metal nanorods have effecting sensing devices for numerous analytical
unique physical properties [36]. applications. AAO has unique dimensions, geometry,
and chemical composition which show characteristics
Semiconductor nanocrystallites [78,79] have unique responses when interacting with light. AAO is an
electronic, optical, and catalytic properties. These outstanding platform for the fabrication of sensing
are of great interest in optical and photoelectronic devices with optical properties including reflectance,
devices such as optical switches, lasers, and LEDs. transmittance, absorbance, photoluminescence,
The optical properties of nanocrystallites are very chemiluminescence, and wave guiding. AAO
different from the bulk material. In the fabrication chemical sensors and biosensors have been used in a
of semiconductor nanomaterials, the control of the broad range of application from gases, vapors, organic
size, size distribution and arrangement is of great molecules, biomolecules (DNA, protein, antibodies)
importance in nanoelectronics, optoelectronics, and and, cells (viruses, bacteria, cancer cells) in air, water,
catalyst chemistry [80]. Various diameter modulated and biological environment.
metallic nanowires (Ag, Au, Ni, and Ag-Au) were
fabricated by electrodeposition in the pores of For the fabrication of highly ordered nanohole arrays,
anodic alumina membrane. Nanowires made of porous anodic alumina film is used as molds [92-95].
metal; semiconductor and polymer have many novel Al nanodot array is formed at the interface between the
applications ranging from chemical and biological porous alumina film and the SiO film by a breakup of
2
sensors to optical, thermoelectric, and electronic Al film due to completion of anodic oxidation. These
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Indian Journal of Advances in Chemical Science 3(3) (2015) 235-246
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effect devices such as single electron memory nodes 21: 3763-3772.
or quantum cellular automata devices [96]. 13. J. Ohi, (2005) Hydrogen energy cycle: An
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