Auswahl der wissenschaftlichen Literatur zum Thema „Switchable thin films“

Samarium monosulfide (SmS) is a switchable material, showing a pressure-induced semiconductor to metal transition. As such, it can be used in different applications such as piezoresistive sensors and memory devices. In this work, we present how e-beam sublimation of samarium metal in a reactive atmosphere can be used for the deposition of semiconducting SmS thin films on 150 mm diameter silicon wafers. The deposition parameters influencing the composition and properties of the thin films are evaluated, such as the deposition rate of Sm metal, the substrate temperature and the H2S partial pressure. We then present the changes in the optical, structural and electrical properties of this compound after the pressure-induced switching to the metallic state. The back-switching and stability of SmS thin films are studied as a function of temperature and atmosphere via in-situ X-ray diffraction. The thermally induced back switching initiates at 250 °C, while above 500 °C, Sm2O2S is formed. Lastly, we explore the possibility to determine the valence state of the samarium ions by means of X-ray photoelectron spectroscopy.

ABSTRACTVanadium Oxide has application to infrared bolometers due to high temperature coefficient of resistivity (TCR). It has attracted interest for switchable plasmonic devices due to its metal to insulator transition near room temperature. We report here the properties of vanadium oxide deposited by an aqueous spray process. The films have a ropy surface morphology with ∼70 nm surface roughness. The polycrystalline phase depends on annealing conditions. The films have TCR of ∼2%/deg, which compares well with sputtered films. Only weak evidence is found for an insulator-metal phase transition in these films.

This work analyzes the processing of Pb(Zr,Ti)O3 (PZT) thin films directly on copper-coated polymer films. PZT thin film deposition was performed onto the metallized Kapton® films using a single RF plasma jet. In order to reduce the interaction of PZT and Cu during the initial growth stage, an ultrathin amorphous TiO2-x seeding layer was sputter-deposited prior to PZT deposition. The film texture was a mixture of (111)-oriented perovskite nanocrystals, rutile and pyrochlore. Topography and piezoelectric in-plane and out-of-plane response of the films were evaluated using a commercial AFM adapted for piezoforce measurements. The as-deposited films were self-polarized with polarization pointing at the surface of the sample. Polarization was switchable and a piezoelectric hysteresis was obtained.

Pouvoir aller de la molécule aux dispositifs technologiques est un des enjeux actuels dans le domaine des molécules commutables. Dans ce contexte, les complexes à transition de spin (TS) sont de bons candidats car ils peuvent commuter d'un état bas spin vers un état haut spin de manière réversible sous l'influence de stimuli externes (température, lumière...). Il en résulte une modification importante de leurs propriétés physiques (magnétique, optique, élastique etc.). L'objectif de cette thèse est de synthétiser et de caractériser des films et des nanocomposites de matériaux à transition de spin en vue d'applications dans des dispositifs électroniques, mécaniques et optique. Une première approche synthétique pour obtenir des films minces intégrables consiste à utiliser la technique de sublimation. Dans cette optique des complexes neutres du Fe(II) à base de ligand poly(azolyl)borate ont été synthétisés. L'étude de la corrélation de leurs propriétés de TS et des propriétés structurales a été complétée par une étude synchrotron pour déterminer les paramètres de la dynamique du réseau cristallin. Les films de ces complexes ont pu être intégrés dans des jonctions électriques verticales conférant à ces dernières des nouvelles propriétés de bistabilité et illustrant différents mécanismes de conduction en fonction de l'épaisseur du film de complexe. D'autre part ces films ont aussi été déposés sur des dispositifs électromécaniques micrométriques (MEMS) qui ont présenté des propriétés mécaniques bistables. Une autre approche réside dans l'élaboration de matériaux composites constitués de polymère et de complexe à TS. Ainsi, un papier composite de cellulose à base de complexe à TS a été préparé et l'étude par analyse mécanique dynamique a permis de démontrer une bistabilité de ses propriétés mécaniques. Une preuve de concept de papier ré-inscriptible liée au thermochromisme du complexe est également présentée. D'autre part, un nanocomposite à base de polymère électroactif P(VDF-trFE) (piezo-, pyro- et ferroélectrique) et de nanoparticules à TS a été synthétisé. L'étude des propriétés électromécaniques a révélé la présence de pics de décharge de courant associé à la TS indiquant une synergie entre les deux constituants du composite<br>Nowadays, going from molecules to devices is one of the main challenge in the field of switchable molecular materials. In this context, spin crossover complexes (SCO) are good candidates as they can be reversibly switched from a low spin state to a high spin state with various external stimuli (temperature, light ...). This switch is followed by an important change of their physical properties (magnetic, optical, elastic...). The objective of this Ph.D thesis is to synthetize and characterize films and nanocomposites based on spin crossover materials for applications in electronical and mechanical and optical devices. A first approach to obtain thin film that can be integrated consist in using sublimation technique. To this aim, neutral Fe(II) complexes based on poly(azolyl)borate ligand have been synthetized. Studies of the correlation between spin crossover properties and structural properties have been complemented with synchrotron measurements to determine crystal lattice dynamics parameters. Films of these complexes have been integrated in electrical junction bringing new bistability properties and displaying different conduction mechanisms depending on the SCO film thickness. Films have been also deposited on micro-electromechanical systems (MEMS) which demonstrated mechanical bistability. Another approach reside in elaborating composite materials based on polymer and SCO complexes. Thus, a cellulose composite paper based on SCO complexes has been prepared and studied by dynamic mechanical analysis indicating a bistability of its mechanical properties. A proof of concept of a re-writable composite paper using SCO thermochromism has been presented. In another hand, nanocomposites based on the electroactive polymer P(VDF-trFE) (piezo-, pyro- and ferroelectric), and SCO nanoparticles has been synthetized. A study of their electromechanical properties revealed current discharge peaks associated to the SCO phenomenon highlighting a synergy between the two composites constituents

La recherche continuelle vers de plus petits composants technologiques, à la fois plus puissants et moins énergivores, a conduit à d’importantes recherches dans les domaines de l’électronique moléculaire et, plus récemment, de la spintronique moléculaire. Dans ce contexte, les molécules à conversion de spin (« spin crossover » ou SCO en anglais) sont prometteuses : ces complexes de métaux de transition peuvent être convertis d’un état à l’autre par de multiples stimuli, ce qui induit des changements de propriétés chimiques et physiques, leur donnant de nombreux usages potentiels.Cette thèse présente de nouveaux complexes SCO de fer (II) avec une conversion thermique - et dans quelques cas photoinduite – qui dépend de l’encombrement stérique des ligands. Habituellement, les monocouches montrent une SCO différente de celle observée sur la poudre à cause des interactions entre les molécules et le substrat métallique. Cependant, les molécules présentées dans cette thèse sont l’un des rares exemples dont la SCO n’est pas altérée. Ceci s’explique par la présence d’une chaine alkyle qui sépare la partie SCO du substrat. Le comportement SCO des molécules en poudre a été suivi par de la magnétométrie (VSM et SQUID), de la résonance magnétique nucléaire (NMR) à température variable, de la spectroscopie Raman, et des spectroscopies de photoélectrons induits par rayons X et d’absorption des rayons X (XPS et XAS). Le comportement SCO dans les monocouches a été caractérisé par XPS et par XAS.Grâce à une synthèse flexible, ces molécules sont capables de former aussi bien des monocouches autoassemblées (« self-assembled monolayers » ou SAMs en anglais) que des « break junctions ». Cela dépend du nombre et de la nature des groupements d’ancrage. Des SAMs ont été préparées sur de l’or, de l’argent et du cuivre ultra-plat. La morphologie, la composition chimique et l’arrangement de ces monocouches ont été caractérisés par de la microscopie à force atomique (AFM), de la spectrométrie de masse d’ions secondaires à temps de vol (ToF-SIMS), du XPS semi-quantitatif, de la spectroscopie infrarouge de réflexion-absorption à modulation de polarisation (PM-IRRAS), et de l’électrochimie, complété par des calculs de théorie de la fonctionnelle de la densité (DFT).Pour faire de ces SAMs des dispositifs moléculaires commutables, l’eutectique d’indium et de gallium (eGaIn) a été choisi comme électrode. Cet alliage est un fluide non-newtonien mou et déformable, capable de former des contacts non-destructifs avec des molécules. Les propriétés électroniques de jonctions moléculaires de large taille ont ainsi été mesurées, d’abord à température ambiante, et ensuite au-dessus et en dessous de celle-ci, pour suivre les changements de comportement électronique avec la température. Par ailleurs, des jonctions mono-moléculaires ont aussi été mesurées par deux techniques différentes : par microscopie à effet tunnel (STM) et par nanotubes de carbone simple-feuillet. Les propriétés des jonctions mono-moléculaires ont été mesurées respectivement à température ambiante en solution, et à l’état solide. Bien que les changements de comportement électronique des SAMs en fonction de la température n’ont pas pu être attribué à la SCO de manière concluante, les travaux présentés dans cette thèse démontrent que ces systèmes, avec un peu de réglage, sont de bons candidats pour des composants électroniques commutables.La synthèse flexible de cette famille de molécules leur apporte d’innombrables usages potentiels, et ouvre de nombreux chemins pour des recherches futures. Les jonctions moléculaires présentées peuvent nous conduire à des dispositifs moléculaires stables et moins énergivores, qui sont commutables à l’ambiante<br>The continual quest for ever-smaller technological components has led to massive research efforts in the fields of molecular electronics and, more recently, spintronics. These components should be simultaneously more powerful and less energy-hungry, and in this context, spin crossover (SCO) molecules have far-reaching potential. These transition metal complexes can be switched between two distinct states by a multitude of stimuli, and exhibit substantial changes in their chemical and physical properties upon switching, giving them many prospective applications.This thesis presents several new iron (II) SCO molecules with a thermal - and in some cases photo-induced - switching that is dependent on the degree of steric hindrance of the ligands. Typically, SCO in monolayers is significantly altered due to molecule-substrate interactions, but the molecules presented in this thesis exhibit a rarely observed non-quenched SCO thanks to an alkyl spacer separating the SCO moiety from the coinage metal substrates. The SCO of the molecules in bulk was followed by magnetometry (vibrating sample magnetometry, VSM, and superconducting quantum interference device, or SQUID, magnetometry), variable-temperature nuclear magnetic resonance (NMR) and Raman spectroscopies, as well as X-ray photoelectron and absorption spectroscopies (XPS and XAS, respectively). The SCO behaviour of the monolayers was characterised by XPS and XAS.Thanks to a flexible synthesis route, these novel molecules can form both self-assembled monolayers (SAMs) and break junctions, depending on the number and nature of the anchoring groups. SAMs have been prepared on ultra-flat gold, silver and copper substrates. The morphology, chemical composition, and packing of these monolayers were characterised by atomic force microscopy (AFM), time-of-flight secondary ion mass spectrometry (ToF-SIMS), XPS semi-quantitative analysis, polarisation modulation infrared reflection absorption spectroscopy (PM-IRRAS), and electrochemistry, supported by density functional theory (DFT) calculations.In order to turn these SAMs into switchable devices, eutectic Gallium Indium (eGaIn) was used as a top electrode. This alloy is a soft and deformable non-Newtonian fluid capable of forming non-damaging contacts with molecules. The electrical properties of large-area molecular junctions were thus measured, initially at room temperature, and then above and below, in order to follow the changes in transport behaviour with temperature. Single molecule junctions were formed using two different methods, both at room temperature: scanning tunnelling microscopy (STM) in solution, and single-walled carbon nanotube nanogap junctions in the solid state. Though the changes in electronic behaviour of the SAMs with temperature could not be conclusively assigned to SCO, this thesis shows that, with some fine-tuning, these systems are feasible as switchable components.The easily tuneable synthesis route gives this family of molecules countless potential applications, and opens up numerous different avenues for future research. The presented molecular junction systems help pave the way towards stable, low-power, multi-addressable, and switchable molecular devices that function at ambient conditions

We investigated thin film samples of Mg2NiH4 with two intentions. First of all, we wanted to ascertain if the same nanomaterial (Mg2NiH4) prepared by magnetron sputtering and ball milling can exhibit different hydrogen storage properties and to see possible advantages/disadvantages of employing of magnetron sputtering for synthesis of nanometerials for hydrogenstorage. Furthermore, we wanted to see if thin film samples of Mg2NiH4 could be used in a switchable mirror or window device by utilizing the high to low temperature transition at about 510 K. In powder samples, this transition, between a monoclinic conducting low temperature phase to an FCC non-conducting high temperature phase, have been demonstrated in a mechanical reversible conductor–insulator transition [Blomqvist and Nor��us, J. Appl. Phys 91(2002)5141]. The new thin film Mg2NiH4 samples were produced by reacting hydrogen with magnetron sputtered Mg2Ni films on quartz glass or CaF2 substrates. But we could not obtain the monoclinic low temperature phase upon cooling the samples. Instead a cubic phase, related but not identical to the cubic high temperature phase, was formed at temperatures both below and above 510 K. TEM pictures revealed the new cubic phase in the films to have the same cell parameter as the FCC high temperature phase. But the symmetry was lower with similar streaking patterns as observed for the monoclinic low temperature phase. IR-spectroscopy indicated an identical vibrational frequency for... [to full text]<br>Tiriamojo darbo metu magnetroniniu garinimu suformuotos Mg-Ni dangos, kurios hidrintos esant aukštai temperatūrai ir vandenilio slėgiui. Hidrintos dangos ištirtos įvairiais analizės metodais, siekiant nustatyti magnetronio garinimo būdu suformuotos medžiagos (magnio nikelio hidrido) skirtumus nuo rutulinio trynimo metodu gautos analogiškos medžiagos. Darbe išanalizuoti duomenys ir pateiktas aiškinamasis modelis, kuris atskleidžia plonų dangų ypatybes, dėl kurių dangose pilnai neįvyksta dangos relaksacijos procesai. Nustatyta, kad dėl tų pačių priežasčių, dangų panaudojimo „įjungiamiesiems veidrodžiams“ galimybės yra ribotos.

Liquid crystal (LC)-based research and its technological output vary from daily-use personal electronics and flat panels to switchable optical devices such as sensors. Optical and dielectric anisotropy is a key attribute of LCs, imparting functionality and broadening the scope of smart film systems to such products. Among LC smart films, the polymer dispersed liquid crystal (PDLC) smart film depicts an electro-optical (EO) composite sandwiched by transparent conductive oxide electrode-coated polyethylene terephthalate (PET) films. LC orientation and optical transparency in the composite are readily tuned by altering the electric field. The competitiveness of such PDLC devices reflects its favorable response time, energy conservation potential, and manufacturing convenience, all attributes that are readily endorsed by smart home appliances and areas of architecture and the automotive industry. In response to unrelenting market demands, sustainable, energy-efficient, and “greener” PDLC variants have appeared. Particularly worthy of mention are systems featuring transparency at zero field (reverse-mode). Others boast very high energy efficiencies (%80). In this chapter, the science and technology of PDLC, reverse-mode PDLC, and related LC smart films will be reviewed with a highlight on fabrication methods and operating principles. Market potential and research prospects compared to non-LC smart film technologies will also be touched upon.

Observation of at least two coexisting switchable ferroic states viz., ferromagnetic, ferroelectric, and/or ferroelastic at room temperature with promising coupling among order parameters, has made BiFeO3 a highly explored material in the field of multiferroics and/or magnetoelectric multiferroics, which creates the possibility for its application in various technological devices such as spintronics, spin-valve, DRAM, actuators, sensors, solar-cells photovoltaic, etc. Intrinsically, its low coupling coefficients, difficulty to prepare in pure phase in bulk, high leakage current, etc. have restricted BiFeO3 from technological reliability. However, the effect of doping with iso- and alio-valent ions, nanostructure, thin-film-form and nanoparticles, etc., has been carried out to improve its physical properties by several research groups over the decades. In this chapter, the structural, luminescence, and dielectric properties of samarium (Sm3+) doped BiFeO3 nanoceramics synthesized using a modified gelcombustion route are discussed in detail. The effect of Sm3+ doping in BiFeO3 is explored using the X-ray diffraction (XRD) technique. The XRD studies exhibit a possible structural phase transition above Sm3+ doping of 15% from rhombohedral (R3c) space group to the orthorhombic (Pbnm) space group. The dielectric study shows interesting behavior accompanied by structural transition. Our study suggests that Sm3+ doping plays an important role in governing the structural, luminescence, and dielectric properties of BiFeO3 samples.

Polyvinyl alcohol (PVA) films with embedded electrically-responsive liquid crystal (LC) ellipsoids were fabricated to develop a membrane coating featuring tunable roughness. Membranes (∼30 microns thick) were placed between opposing pieces of indium-tin oxide (ITO) glass, creating electrodes for creation of a uniform electric field. Applied voltages ranged from 0V–350 V, as films were observed using an optical microscope. Thin-film interference patterns were observed in various regions of each film and were measured. Contour plots of film displacement were created and showed elevations across the observed region. The area of the first dark fringe regions, assumed to be in contact with the top glass surface, were measured as a function of applied voltage. The maximum displacement of the film was estimated to reach 1.5 microns and the area in contacted with the top glass surface increased 127% between 0–350 V. Finite element modelling results illustrate the influence of polarity on the roughness of the film surface.