Gyroid Optical Metamaterials: Solvent Vapour Annealing, Confined Crystallisation, and Optical Anisotropy PDF
Preview Gyroid Optical Metamaterials: Solvent Vapour Annealing, Confined Crystallisation, and Optical Anisotropy
Springer Theses Recognizing Outstanding Ph.D. Research James A. Dolan Gyroid Optical Metamaterials Solvent Vapour Annealing, Confined Crystallisation, and Optical Anisotropy Springer Theses Recognizing Outstanding Ph.D. Research Aims and Scope The series “Springer Theses” brings together a selection of the very best Ph.D. theses from around the world and across the physical sciences. Nominated and endorsed by two recognized specialists, each published volume has been selected foritsscientificexcellenceandthehighimpactofitscontentsforthepertinentfield of research. For greater accessibility to non-specialists, the published versions includeanextendedintroduction,aswellasaforewordbythestudent’ssupervisor explainingthespecialrelevanceoftheworkforthefield.Asawhole,theserieswill provide a valuable resource both for newcomers to the research fields described, and for other scientists seeking detailed background information on special questions. Finally, it provides an accredited documentation of the valuable contributions made by today’s younger generation of scientists. Theses are accepted into the series by invited nomination only and must fulfill all of the following criteria (cid:129) They must be written in good English. (cid:129) ThetopicshouldfallwithintheconfinesofChemistry,Physics,EarthSciences, Engineeringandrelatedinterdisciplinary fields such asMaterials,Nanoscience, Chemical Engineering, Complex Systems and Biophysics. (cid:129) The work reported in the thesis must represent a significant scientific advance. (cid:129) Ifthethesisincludespreviouslypublishedmaterial,permissiontoreproducethis must be gained from the respective copyright holder. (cid:129) They must have been examined and passed during the 12 months prior to nomination. (cid:129) Each thesis should include a foreword by the supervisor outlining the signifi- cance of its content. (cid:129) The theses should have a clearly defined structure including an introduction accessible to scientists not expert in that particular field. More information about this series at http://www.springer.com/series/8790 James A. Dolan Gyroid Optical Metamaterials fi Solvent Vapour Annealing, Con ned Crystallisation, and Optical Anisotropy Doctoral Thesis accepted by the University of Cambridge, Cambridge, UK 123 Author Supervisors Dr. James A.Dolan Prof. Ullrich Steiner University of Cambridge SoftMatterPhysicsGroup,AdolpheMerkle Cambridge, UK Institute University of Fribourg Fribourg, Switzerland Prof. Jeremy J.Baumberg NanoPhotonics Centre, Cavendish Laboratory University of Cambridge Cambridge, UK Prof. Timothy D.Wilkinson CentreofMolecularMaterialsforPhotonics andElectronics,Department of Engineering University of Cambridge Cambridge, UK ISSN 2190-5053 ISSN 2190-5061 (electronic) SpringerTheses ISBN978-3-030-03010-0 ISBN978-3-030-03011-7 (eBook) https://doi.org/10.1007/978-3-030-03011-7 LibraryofCongressControlNumber:2018958933 ©SpringerNatureSwitzerlandAG2018 Thisworkissubjecttocopyright.AllrightsarereservedbythePublisher,whetherthewholeorpart of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission orinformationstorageandretrieval,electronicadaptation,computersoftware,orbysimilarordissimilar methodologynowknownorhereafterdeveloped. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publicationdoesnotimply,evenintheabsenceofaspecificstatement,thatsuchnamesareexemptfrom therelevantprotectivelawsandregulationsandthereforefreeforgeneraluse. The publisher, the authors and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authorsortheeditorsgiveawarranty,expressorimplied,withrespecttothematerialcontainedhereinor for any errors or omissions that may have been made. The publisher remains neutral with regard to jurisdictionalclaimsinpublishedmapsandinstitutionalaffiliations. ThisSpringerimprintispublishedbytheregisteredcompanySpringerNatureSwitzerlandAG Theregisteredcompanyaddressis:Gewerbestrasse11,6330Cham,Switzerland Everything stinks till it’s finished. —Dr. Seuss Dedicated to Douglas William Richard Tate 1934–2005 Engineer, teacher, friend. ’ Supervisor s Foreword The concept of a “left-handed” or negative-index material was first proposed by Victor Veselago in 1968 through his theoretical predictions of the electrodynamic behaviour of materials that simultaneously exhibit negative values of dielectric permittivity and magnetic permeability. Thirty years later, John B. Pendry demonstrated that artificial electromagnetic materials—“metamaterials”—consist- ing,inthiscase,ofinterpenetratedorderedarraysofwiresandsplit-ringresonators could also exhibit similar phenomena. Initially demonstrated for microwave radi- ation, metamaterials have borne out Pendry’s predictions, and the quest since then hasbeentheirimplementationinthevisiblerangeoftheelectromagneticspectrum. Whilst the physical principles are scale-invariant, practical realisation of the sub-wavelength structural elements that constitute an optical metamaterial is far fromtrivial,asitrequiresperiodicarraysofwell-definedstructuralfeaturesinthree dimensions on the 10–50 nm length scale. Nearly all approaches so far employ some type of lithographic method, which is not well suited for the manufacture of 3D architectures on such small length scales. James Dolan’s thesis makes an important contribution to the quest for optical metamaterials.Asopposedto“top-down”lithographicmethods,histhesisexplores “bottom-up” polymer self-assembly methods for the manufacture of 3D metama- terials in the visible range of the spectrum. This methodology, however, presents the researcher with a new set of challenges. First, macromolecular self-assembly mustbecontrolledwithahithertounprecedentedlevelofprecision.Thisisdifficult not only from a thermodynamic point of view, but also because the outcome of self-assembly is “invisible”. Since molecular self-assembly takes place on the sub-100 nm length scale, the morphologies attained cannot be probed by optical microscopy. WhilstX-ray scattering and electron and atomic force microscopy are all possible, the lack of optical methods is cumbersome for the experimenter. The first part of the thesis addresses these two challenges: the control of polymer self-assembly in thin films and the optical visualisation of its structural perfection. Chapter 4 explores in detail the structural evolution of block copolymer films that are exposed to a solvent atmosphere in the so-called solvent vapour annealing experiment. The results of this chapter provide the thermodynamic basis for the ix x Supervisor’sForeword control over polymer self-assembly that is required to fabricate optical metamate- rials.Thefollowingchapter,Chap. 5,tacklesthe“invisibility”issue.Byexploiting the crystallisation of one of the copolymer blocks, the lateral organisation of the self-assembled morphology gives rise to birefringence. This chapter carefully investigatesthiseffectanddevelopsamodelthatdirectlylinksthebirefringenceto thestructuralorganisation,therebyofferingavaluablenewtooltooptimisepolymer self-assembly for the manufacture of optical metamaterials. This chapter also, for the first time, demonstrates 100 lm large domains of the self-assembled gyroid morphology, from which some of the most interesting metamaterial properties are predicted to arise. The second part of the thesis focuses on the optical properties of metamaterials created by polymer self-assembly. To this end, the copolymer morphologies were partially voided and then replicated into a plasmonic metal (gold). Chapter 6 explores the question of whether long-range order in this optical metamaterial is required. By combining experimental studies, simulations, and analytical calcula- tions, this chapter explores the optical response of locally-ordered gyroid mor- phologies that are disordered on the micrometre-length scale. The finding that the optical spectra of these disordered gyroids are well described by an effective mediummodelillustrates,ontheonehand,thatorderisrequiredtoaccessthemost interesting aspects of optical metamaterials, but also, on the other hand, that these materialshaveinterestingpropertiesintheirownright(e.g.achangeofsigninthe permittivity as afunctionof wavelength). The finalexperimental chapter, Chap. 7, solves a long-standing puzzle in the field of self-assembled optical metamaterials, therebyprovidinganimportantsteppingstoneinmetamaterialresearch.Thepuzzle in question is the strong linear dichroism of gyroid metamaterials, which is unex- pected given the cubic nature of the gyroid unit cell. By combining experimental observations with numerical simulations, this chapter demonstrates that gyroid samples can be considered as a bulk metamaterial terminated by a distinct meta- surface—the 2D equivalent of a metamaterial. It is the symmetry-breaking of the metasurface that induces the strong, experimentally observed linear dichroism. Importantly,thischapteruncoversthatthein-couplingandout-couplingoflightto and from the metamaterial depend extremely sensitively on the specific surface termination of the metamaterial. The control of such terminations will require a manufacturing precision ofaround 1nm,therebysetting ahigh barfor thereliable manufacture of optical metamaterials for visible wavelengths. The scalable manufacture of optical metamaterials with a negative refractive index has the potential for transformative changes in the application of optical materials, utilising, for example, their super-focusing and “cloaking” properties. This thesis demonstrates, on the one hand, that the manufacture of these materials by self-assembly isa promising way forward.On theother hand,the results ofthe Supervisor’sForeword xi four main thesis chapters elucidate the significant challenges in mastering this approach,therebysettingfutureresearchersasetofchallengingtasksthattheywill havetoovercomeonthepathtothedemonstrationanduseofopticalmetamaterial effects visible to the naked eye. Fribourg, Switzerland Prof. Ullrich Steiner October 2018 Soft Matter Physics Group Adolphe Merkle Institute University of Fribourg
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