Single wavelength ellipsometry measurements at Brewster's angle provide a powerful technique for characterizing ultrathin polymeric films. By conducting the experiments in different ambient media, multiple incident media (MIM) ellipsometry, simultaneous determinations of a film's thickness and refractive index are possible. Poly(tert-butyl acrylate) (PtBA) films serve as a model system for the simultaneous determination of thickness and refractive index (1.45 at 632 nm). Thickness measurements on films of variable thickness agree with X-ray reflectivity results. The method is also applicable to spincoated films where refractive indices of PtBA, polystyrene and poly(methyl methacrylate) are found to agree with literature values within experimental error. Likewise, MIM ellipsometry is utilized to simultaneously obtain the refractive indices and thicknesses of thin films of trimethylsilylcellulose (TMSC), regenerated cellulose, and cellulose nanocrystals where Langmuir-Blodgett (LB) films of TMSC serve as a model system. Ellipsometry measurements not only provide thickness and optical constants of thin films, but can also detect thermally induced structural changes like surface glass transition temperatures (Tg) and layer deformation in LB-films. Understanding the thermal properties of the polymer thin films is crucial for designing nanoscale coatings, where thermal properties are expected to differ from their corresponding bulk properties because of greater fractional free volume in thin films and residual stresses that remain from film preparation. Polyhedral oligomeric silsesquioxane (POSS) derivatives may be useful as a nanofiller in nanocomposite formulations to enhance thermal properties. As a model system, thin films of trisilanolphenyl-POSS (TPP) and two different molar mass PtBA were prepared as blends by Y-type Langmuir-Blodgett film deposition. For comparison, bulk blends were prepared by solution casting and the samples were characterized via differential scanning calorimetry (DSC). Our observations show that surface Tg is depressed relative to bulk Tg and that magnitude of depression is molar mass dependent for pure PtBA films. By adding TPP as a nanofiller both bulk and surface Tg increase. Whereas, bulk Tg shows comparable increases for both molar masses, the increase in surface Tg for higher molar mass PtBA is greater than for lower molar mass PtBA. These studies show that POSS can serve as a model nanofiller for controlling Tg in nanoscale coatings. / Ph. D.

Thin film bilayers and blends composed of polymers and nanoparticles are increasingly important for technological applications that range from space survivable coatings to novel drug delivery systems. Dewetting or spontaneous hole formation in amorphous polymer films and phase separation in multicomponent polymer films can hinder the stability of these systems at elevated temperatures. Hence, fundamental understanding of dewetting and phase separation in polymer/nanoparticle bilayer and blend films is crucial for controlling transport and thermomechanical properties and surface morphologies of these systems. This dissertation provides studies on morphological evolution driven by phase separation and/or dewetting in model polymer/nanoparticle thin film bilayers and blends at elevated temperatures. Morphological evolution in dewetting bilayers of poly(t-butyl acrylate) (PtBA) or polystyrene (PS) and a polyhedral oligomeric silsesquioxane (POSS), trisilanolphenyl-POSS (TPP) is explored at elevated temperatures. The results demonstrate unique dewetting morphologies in both PtBA/TPP and PS/TPP bilayers that are significantly different from those typically observed in dewetting polymer/polymer bilayers. Upon annealing the PtBA/TPP bilayers at 95°C, a two-step dewetting process is observed. PtBA immediately diffuses into the upper TPP layer leading to hole formation and subsequently the holes merge to form interconnected rim structures in the upper TPP layer. Dewetting of both the TPP and PtBA layers at longer annealing times leads to the evolution of scattered holes containing TPP-rich, fractal aggregates. The fractal dimensions of the TPP-rich, fractal aggregates are ~2.2 suggesting fractal pattern formation via cluster-cluster aggregation. Dewetting in PS/TPP bilayers also proceeds via a two-step process; however, the observed dewetting morphologies are dramatically different from those observed in PtBA/TPP bilayers. Cracks immediately form in the upper TPP layer during annealing of PS/TPP bilayers at 200°C. With increasing annealing times, the cracks in the TPP layer act as nucleation sites for dewetting and aggregation of the TPP layer and subsequent dewetting of the underlying PS layer. Complete dewetting of both the TPP and PS layers results in the formation of TPP encapsulated PS droplets. Phase separation in PtBA/TPP thin film blends is investigated as functions of annealing temperature and time. The PtBA/TPP thin film blend system exhibits an upper critical solution temperature (LCST) phase diagram with a critical composition and temperature of 60 wt% PtBA and ~70°C, respectively. Spinodal decomposition (SD) is observed for 60 wt% PtBA blend films and off-critical SD is seen for 58 and 62 wt% PtBA blend films. The temporal evolution of SD in 60 wt% PtBA blend films is also explored. Power law scaling for the characteristic wavevector with time (q ~ t^n with n = -1/4 to -1/3) during the early stages of phase separation yields to domain pinning at the later stages for films annealed at 75, 85, and 95°C. In contrast, domain growth is instantly pinned for films annealed at 105°C. Our work provides an important first step towards understanding how nanoparticles affect polymer thin film stability and this knowledge may be utilized to fabricate surfaces with tunable morphologies via controlled dewetting and/or phase separation. / Ph. D.

Area selective atomic layer deposition (ASALD) is demonstrated to be a promising route to perform direct patterned deposition. In particular, methods to modify (or mask) the surface and process parameters to perform selective deposition of titanium dioxide have been developed and investigated in detail. Results indicated that self assembled monolayer based masking methodology posses significant limitations due to challenges associated with obtaining defect free monolayer and absence of traditional patterning techniques. On the other hand, polymer films based masking methodology offer a better alternative to perform ASALD. A number of factors that must be considered in designing a successful ASALD process based on polymer films were identified. These include: reactivity of polymer with ALD precursor, diffusion of ALD precursors through polymer mask and remnant precursor content in the polymer film during ALD cycling. Investigations suggested that ALD nucleation can be successfully blocked on polymer films that do not contain direct OH sites in their backbone. It was observed that sorption of water in the polymer film does not pose a serious limitation however; metal precursor diffusion through the polymer mask was identified as a critical parameter in determining the minimum required masking layer thickness for a successful ASALD process. In addition, a novel ASALD-based top surface imaging (TSI) technique has been developed. The ASALD-TSI process has demonstrated sharp contrast (etch barrier deposition vs exposure dose) and therefore offers the potential to overcome many of the challenges experienced with conventional TSI schemes.

Structure and dynamics of nanoconfined glass-forming oligomers and diblock coplymers (BPCs) are investigated by a combination of infrared transition moment orientational analysis (IR-TMOA), positron annihilation lifetime spectroscopy (PALS), grazing incidence small angle X-ray scattering (GISAXS), atomic force microscopy (AFM), scanning electron microscopy (SEM) and broadband dielectric spectroscopy (BDS). The oligomers probed are the van der Waals type, tris(2-ethyhexyl)phosphate (TEHP) and the self-associating molecules of 2-ethyl-1-hexanol (2E1H). Symmetric and asymmetric poly(styrene-b-1,4-isoprene) P(S-b-I) are studied for the case of BCPs. The samples are confined either in one-dimensional (1D) in form of thin films or in 2D (nanopores) geometrical constraints. The molecular order of TEHP in nanopores as studied by IR-TMOA shows that about 7% of the molecules are preferentially oriented perpendicular to the long axis of the pores due to their interaction with the pore walls. PALS results reveal that 2E1H confined in nanopores exhibit larger free volume with respect to the bulk. In thin films (1D), P(S-b-I) having volume fraction of isoprene blocks f(PI)= 0.55 exhibits randomly oriented lamellae and their thicknesses are directly proportional to the film thickness d(film). For f(PI) = 0.73, perpendicular cylinders with respect to the substrate are observed for d(film)>50 nm but they lie along the substrate plane when d(film) < 50 nm. In AAO pores (2D) with average pore diameter d(pore) of 150 nm, straight nanorods are formed which change to helical structures in 18 nm pores. Molecular dynamics of 2E1H and TEHP constrained in nanopores (2D), is influenced by the interplay between confinement and surface effects. Confinement effects show up as an increase in the structural relaxation rate with decreasing pore sizes at the vicinity of the glass transition temperature. This is attributed to the reduced packing density of the molecules in pores as quantified by PALS results for 2E1H. Whereas the orientation and morphologies of the domains in P(S-b-I) and the chain dynamics of isoprene chains are influenced by the finite--size and dimensionality of confinement, the segmental motion, related to the dynamic glass transition (DGT) of both styrene and isoprene blocks remains unaffected-in its relaxation time-within experimental accuracy. Effects of nanoscale confinement on the molecular dynamics therefore depend on a number of factors: the type of molecules (polymers, low molecular liquids), interfacial interactions and the dimensionality of the constraining geometries.

A eletrônica digital desempenha papel essencial no desenvolvimento e manutenção dos padrões de vida em prática hoje no mundo. A peça fundamental para a criação desta era tecnológica é sem dúvidas o transistor. Com o advento de novos materiais, a busca por transistores que oferecem novas oportunidades de processamento e aplicação permitiu que uma nova área fosse criada: a eletrônica orgânica. Transistores de efeito de campo baseados em filmes finos de materiais orgânicos têm recebido grande atenção nas últimas décadas. Apresentamos um estudo experimental e teórico de transistores de efeito de campo a base de filmes finos orgânicos. Foram caracterizados transistores usando um derivado do pentaceno (TMTES-pentaceno) como camada ativa em um dispositivo feito sobre Si/SiO2. Mostramos que a inclusão do semicondutor orgânico em uma matriz polimérica isolante ajuda a manter a estabilidade termo mecânica do dispositivo. Foi desenvolvido um modelo que levasse em conta as resistências parasíticas para explicar o comportamento do transistor em função da temperatura. Também foram construídos e caracterizados transistores usando rr-P3HT como semicondutor e PMMA como isolantes. Apresentamos transistores do tipo Top-Gate e Bottom-Gate com mobilidade máxima de 7 x 10-3 cm2/V.s. Valores de razão ON/OFF de ~ 900 foram encontrados nos transistores otimizados. O comportamento dos transistores é analisado em função da temperatura e os modelos de aproximação de canal gradual e de Vissenberg-Matters foram aplicados para extração dos parâmetros de interesse. Por fim, apresentamos um modelo de corrente de canal baseado na resolução 2D numérica da equação de Poisson usando as idéias de Vissenberg-Matters para a concentração de cargas em função do potencial local. O modelo, embora ainda nos primeiros estágios de desenvolvimento, prevê a saturação da corrente nas curvas de saída simuladas sem limitações de regime de validade. / Digital electronics plays an essential role in the development and maintenance of living standards into practice in the world today. The cornerstone for the creation of this technological age is undoubtedly the transistor. With the advent of new materials, the search for transistors that offer new opportunities in processing and application allowed a new area to be created: the organic electronics. Field effect transistors based on organic thin films have received great attention in recent decades. We report an experimental and theoretical study of field effect transistors based on organic thin films. We characterized transistors manufactured using a derivative of pentacene (TMTES-pentacene) as the active layer in a device and using Si/SiO2 as gate and insulator. We show that the inclusion of the organic semiconductor in an insulating polymeric matrix helps to maintain the termo-mechanical stability of the device. A model was developed that take into account the parasitic resistances and to explain the behavior of the transistor as a function of temperature. We also present the manufacturing and characterization process of transistors using rr-P3HT as semiconductor and PMMA as insulator. We report Top-Gate and Bottom-Gate transistors with maximum mobility of 7 x 10-3 cm2/V.s. The maximun ON/OFF ratio of ~ 900 was found for the optimized transistors. The behavior of the transistors was analyzed as a function of temperature and both gradual channel approximation and Vissenberg-Matters models were applied for extracting the parameters. Finally, we present a channel current model based on the resolution of 2D numerical Poisson equation using the ideas of Vissenberg-Matters to the calculate the concentration of charges due to the local potential. The model, although still in the early stages of development, predicts the saturation current at output simulated curves with no limitation of regime validity.

A eletrônica digital desempenha papel essencial no desenvolvimento e manutenção dos padrões de vida em prática hoje no mundo. A peça fundamental para a criação desta era tecnológica é sem dúvidas o transistor. Com o advento de novos materiais, a busca por transistores que oferecem novas oportunidades de processamento e aplicação permitiu que uma nova área fosse criada: a eletrônica orgânica. Transistores de efeito de campo baseados em filmes finos de materiais orgânicos têm recebido grande atenção nas últimas décadas. Apresentamos um estudo experimental e teórico de transistores de efeito de campo a base de filmes finos orgânicos. Foram caracterizados transistores usando um derivado do pentaceno (TMTES-pentaceno) como camada ativa em um dispositivo feito sobre Si/SiO2. Mostramos que a inclusão do semicondutor orgânico em uma matriz polimérica isolante ajuda a manter a estabilidade termo mecânica do dispositivo. Foi desenvolvido um modelo que levasse em conta as resistências parasíticas para explicar o comportamento do transistor em função da temperatura. Também foram construídos e caracterizados transistores usando rr-P3HT como semicondutor e PMMA como isolantes. Apresentamos transistores do tipo Top-Gate e Bottom-Gate com mobilidade máxima de 7 x 10-3 cm2/V.s. Valores de razão ON/OFF de ~ 900 foram encontrados nos transistores otimizados. O comportamento dos transistores é analisado em função da temperatura e os modelos de aproximação de canal gradual e de Vissenberg-Matters foram aplicados para extração dos parâmetros de interesse. Por fim, apresentamos um modelo de corrente de canal baseado na resolução 2D numérica da equação de Poisson usando as idéias de Vissenberg-Matters para a concentração de cargas em função do potencial local. O modelo, embora ainda nos primeiros estágios de desenvolvimento, prevê a saturação da corrente nas curvas de saída simuladas sem limitações de regime de validade. / Digital electronics plays an essential role in the development and maintenance of living standards into practice in the world today. The cornerstone for the creation of this technological age is undoubtedly the transistor. With the advent of new materials, the search for transistors that offer new opportunities in processing and application allowed a new area to be created: the organic electronics. Field effect transistors based on organic thin films have received great attention in recent decades. We report an experimental and theoretical study of field effect transistors based on organic thin films. We characterized transistors manufactured using a derivative of pentacene (TMTES-pentacene) as the active layer in a device and using Si/SiO2 as gate and insulator. We show that the inclusion of the organic semiconductor in an insulating polymeric matrix helps to maintain the termo-mechanical stability of the device. A model was developed that take into account the parasitic resistances and to explain the behavior of the transistor as a function of temperature. We also present the manufacturing and characterization process of transistors using rr-P3HT as semiconductor and PMMA as insulator. We report Top-Gate and Bottom-Gate transistors with maximum mobility of 7 x 10-3 cm2/V.s. The maximun ON/OFF ratio of ~ 900 was found for the optimized transistors. The behavior of the transistors was analyzed as a function of temperature and both gradual channel approximation and Vissenberg-Matters models were applied for extracting the parameters. Finally, we present a channel current model based on the resolution of 2D numerical Poisson equation using the ideas of Vissenberg-Matters to the calculate the concentration of charges due to the local potential. The model, although still in the early stages of development, predicts the saturation current at output simulated curves with no limitation of regime validity.

No description available.

No description available.

Binary mixtures of polymers and soft nanocolloids, also called as polymer nanocomposites are well known and studied for their enormous potentials on various technological fronts. In this thesis blends of polystyrene grafted gold nanoparticles (PGNPs) and polystyrene (PS) are studied experimentally, both in bulk and in thin films. This thesis comprises three parts; 1) evolution of microscopic dynamics in the bulk(chapter-3),2) dispersion behavior of PGNPs in thin and ultra thin polymer matrices (chapter-4) 3) effect of dispersion on the glass transition behavior (chapter-5). In first part, the state of art technique, x-ray photon correlation spectroscopy is used to study the temperature and wave vector dependent microscopic dy¬namics of PGNPs and PGNP-PS mixtures. Structural similarities between PGNPs and star polymers (SPs) are shown using small angle x-ray scatter¬ing and scaling relations. We find unexpected (when compared with SPs) non-monotonic dependence of the structural relaxation time of the nanoparticles with functionality (number of arms attached to the surface). Role of core-core attractions in PGNPs is shown and discussed to be the cause of anomalous behavior in dynamics. In PGNP-PS mixtures, we find evidence of melting of the dynamically arrested state of the PGNPs with addition of PS followed by a reentrant slowing down of the dynamics with further increase in polymer frac¬tion, depending on the size ratio(δ)of PS and PGNPs. For higher δ the reen¬trant behavior is not observed with polymer densities explored here. Possible explanation of the observed dynamics in terms of the presence of double-glass phase is provided. The correlation between structure and reentrant vitrifica¬tion in both pristine PGNPs and blends are derived rather qualitatively. In the second part, the focus is shifted to miscibility between PGNPs and polymers under confinement i.e., in thin films. This chapter provide a compre¬hensive study on the different parameters affecting dispersion viz., annealing conditions, fraction of the added particles, polymer-particle interface and more importantly the thickness of the films. Changes in the dispersion behavior with annealing is shown and the need for annealing the films at temperatures higher than the glass transition temperature of the matrix polymers is clearly elucidated. Irrespective of the thickness of the films( 20 and 65 nm) studied, immiscible particle-polymer blends unequivocally prove the presence of gradi¬ent in dynamics along the depth of the films. To our knowledge for the first time, we report results on confinement induced enhancement in the dispersion of the nanoparticles in thin polymer films. The enhanced dispersion is argued to be facilitated by the increased free volume in the polymer due to confinement as shown by others. Based on these results we have proposed a phase diagram for dispersibility of the nanoparticles in polymer films. The phase diagram for ultra thin films highlights an important point: In ultra thin films the particles are dispersed even with grafting molecular weight less than matrix molecular weight. In the third part, we have studied the glass transition of the thin films whose structure has been studied earlier in the earlier part. Non-monotonic variation in glass transition with the fraction of particles in thin films has increased our belief on the gradient in the dynamics of thin polymer films. En¬hanced dispersion with confinement is captured with the enhanced deviation in glass transition temperature of ultra thin films. Effect of miscibility param¬eter on Tgis studied and the results are explained with the subtle interplay of polymer-particle interface and confinement.