Structure Of Polymer Thin Films Research Articles

Scaled Production of Functionally Gradient Thin Films Using Slot Die Coating on a Roll-to-Roll System.

Polymer thin films with a cross-web gradient structure is a burgeoning area of research, having received more attention in the last two decades, for improvements in the performance and material properties. Such patterned films have been fabricated using several techniques, but in practice these techniques are non-scalable, material-dependent, wasteful, and not highly efficient. Slot die coating, a well-known scalable manufacturing process, is used to fabricate gradient polymer thin films which will be investigated herein. By incorporating slot die with the custom roll-to-roll imaging system, gradient thin films are successfully fabricated by forcing two fluidic materials into the slot die simultaneously and by manipulating the viscous, diffusive, and inertial forces. The materials will be allowed to intermix, with the aim of having approximately a 50% mix along the centerline of any two contiguous stripes. Moreover, several characterizations such as FTIR, UV-vis spectroscopy, and SEM are performed to assess the quality of the gradient polymer thin films. The gradient structure fabricated using functional and nonfunctional materials has successfully improved the functional properties compared to fully blended two materials. This work will provide an understanding of the mechanisms to obtain gradient polymer thin-film structures that exhibit the desired geometric structure and performance.

Multidirectional Polymer Waveguide Lattices for Enhanced Ultrawide-Angle Light Capture in Silicon Solar Cells.

We report the synthesis and characterization of a polymer thin-film structure consisting of two intersecting broadband optical waveguide lattices, and its performance in wide-angle optical energy collection and conversion in silicon solar cells. The structures are synthetically organized via the concurrent irradiation of photoreactive polymer blends by two arrays of intersecting, microscale optical beams transmitted through the medium. Through optical beam-induced photopolymerization and photopolymerization-induced phase separation, well-organized lattices are produced comprising of cylindrical core–cladding waveguide architectures that intersect one another. The optical waveguide properties of the lattices transform the transmission characteristics of the polymer film so that incident optical energy is collected and transmitted along the waveguide axes, rather than their natural directions dictated by refraction, thereby creating efficient light-collecting capability. The embedded structures collectively impart their wide-angle acceptance ranges to enable the film to efficiently collect and interact with light over a large angular range (±70°). When employed as the encapsulant material for a commercial silicon solar cell, the novel light collection and transmission properties result in greater wide-angle conversion efficiency and electrical current density, compared to a single vertically aligned waveguide array. The sustained and greater conversion of light afforded by the encapsulating optical material promises to increase solar cell performance by enabling ultrawide-angle solar energy conversion.

Neutron Reflectometry Tomography for Imaging and Depth Structure Analysis of Thin Films with In-Plane Inhomogeneity.

Neutron reflectometry (NR) has been used for the depth structure analysis of materials at the surface and interface with a sub-nanometric resolution. Conventional NR provides averaged information for an area larger than several square centimeters; therefore, it cannot be applied to an interface with an in-plane inhomogeneity. In this study, the NR imaging of the in-plane structure of polymer thin films was achieved. The tomographic reconstruction of the spatially resolved NR profiles obtained by a sheet-shaped neutron beam provided a two-dimensional image of the in-plane interface morphology. The depth distribution of the neutron scattering length density was obtained by analyzing the position-dependent NR profile at a local area less than 0.1 mm2. The current NR tomography method enables NR measurements for an interface with an inhomogeneous structure. It also provides information on the three-dimensional distribution of the atomic composition near the surface and interfaces for various materials.

Preparation and Self‐Repairing of Highly Oriented Structures of Ultrathin Polymer Films

AbstractThin and ultrathin polymer films play an important role in a variety of applications, such as electronics, liquid crystal alignment, adhesion, and so on. It is well established that the properties of semicrystalline polymeric materials depend remarkably on their multiscale structures; for example, an increase of more than a factor of 100 has been reported for the electrical conductivity of doped and aligned conjugated macromolecules compared with their nonoriented counterparts. Consequently, sophisticated methods have been developed for preparing highly oriented polymer ultrathin films. It should be pointed out that the highly oriented crystalline structure of polymers can be maintained only at temperatures below their melting points. Otherwise, structure rearrangement will result in the loss of orientation and therefore the properties. Therefore, self‐repairing of highly oriented polymer structures is of great significance for the long‐term application of polymer thin films in some specific fields. In this review paper, the preparation and self‐repair of the highly oriented structure of polymer thin films is described in the hopes that this will afford useful information for further development of polymeric materials for advanced applications.

Estimation of charge carrier mobility in polymer thin-film structures

In this article, the polymer polydiphenylenphthalide. The estimates of the mobility of charge carriers for FDP films of different thicknesses by the CELIV method are carried out. During the measurements it was concluded that the mobility value does not depend on the thickness of the polymer film within 100-800 nm.

Depth-Resolved Characterization of Perylenediimide Side-Chain Polymer Thin Film Structure Using Grazing-Incidence Wide-Angle X-ray Diffraction with Tender X-rays.

Polymers with a perylenediimide (PDI) side chain (PAc12PDI) consist of two kinds of crystalline structures with various types of orientations in a thin film. Understanding the population of the microcrystalline structure and its orientation along the thickness is strongly desired. Grazing-incidence wide-angle X-ray diffraction (GIWAXD) measurements with hard X-rays, which are generally chosen as λ = 0.1 nm, are a powerful tool to evaluate the molecular aggregation structure in thin films. A depth-resolved analysis for the outermost surface of the polymeric materials using conventional GIWAXD measurements, however, has limitations on depth resolution because the X-ray penetration depth dramatically increases above the critical angle. Meanwhile, tender X-rays (λ = 0.5 nm) have the potential advantage that the penetration depth gradually increases above the critical angle, leading to precise characterization for the population of crystallite distribution along the thickness. The population of the microcrystalline states in the PAc12PDI thin film was precisely characterized utilizing GIWAXD measurements using tender X-rays. The outermost surface of the PAc12PDI thin film is occupied by a monoclinic lattice with a = 2.38 nm, b = 0.74 nm, c = 5.98 nm, and β = 108.13°, while maintaining the c-axis perpendicular to the substrate surface. Additionally, the presence of solid substrate controls the formation of the crystallite with unidirectional orientation.

Spurious electro-optic coefficients inferred from modulation ellipsometry measurements in the presence of an air cavity

This paper describes how thin air gaps in multilayer polymer thin film structures can lead to unexpectedly large signals in modulation ellipsometry experiments, which can then be misinterpreted as the electro-optic effect. The contributions from the electro-optic effect and polarisation on reflection from the air cavity are indistinguishable and the reflection contribution can be on the order of 100 times that of the electro-optic effect. Caution must thus be exercised in any attempt to measure electro-optic coefficients with modulation ellipsometry in the presence of air gaps, to avoid spuriously high results. Thin film multilayer structures containing air gaps may be suitable for some of the same applications as electro-optic reflectance modulators.

Thermal reorganization of alkyl-substituted thienothiophene semiconductors

Controlling the structure of polymer thin films under thermal annealing is vital to realize reproducible transport properties and acceptable device lifetimes needed to fabricate electronic circuits.

New Approach for Analyzing the Vertical Structure of Polymer Thin Films Based on Surface-Enhanced Raman Scattering

We report on a new approach for measuring the chemical composition of the 20 nanometers at the top or bottom of a polymer film. This approach is based on a variation of the surface enhanced Raman scattering effect with laser illumination through a thin gold layer (∼4 nm). We show that the introduction of the thin gold layer has little or no effect on the morphology of the film that is spin coated on top of it. We demonstrate that this technique has better than 20 nanometer vertical resolution by studying bilayers of polyfluorines with varying thicknesses and by showing the existence of top and bottom wetting layers in a polymer blend of the same polymers. We also show that the top wetting layer is thinner than the bottom one. The difference in thicknesses explains how a solar cell with an electron blocking layer at the cathode works.

Polymer thin film structures for ultra-low cost biosensing

Reflectance change due to binding of molecules on thin film structures has been exploited for bio-molecular sensing by several groups due to its potential in the development of sensitive, low cost, easy to fabricate, large area sensors with high multiplexing capabilities. However, all of these sensing platforms have been developed using traditional semiconductor materials and processing techniques, which are expensive. This article presents a method to fabricate disposable thin film reflectance biosensors using polymers, such as polycarbonate, which are 2–3 orders of magnitude cheaper than conventional semiconductor and dielectric materials and can be processed by alternate low cost methods, leading to significant reduction in consumable costs associated with diagnostic biosensing.

Studies on Polymer Thin Film Structure by X-ray and Neutron Reflectivity and Grazing Incidence Small Angle Scattering

Studies on Polymer Thin Film Structure by X-ray and Neutron Reflectivity and Grazing Incidence Small Angle Scattering

Influence of the thin‐film thickness and crystallization temperature on the spherulitic structure of polymer thin films

AbstractThe spherulitic structure and morphology of poly(3‐hydroxybutyrate) (PHB) thin films crystallized from the melt were observed with a polarizing optical microscope. Depending on the thickness of the PHB thin film and crystallization temperature, banded and nonbanded spherulites could form. Reducing the thin‐film thickness and crystallization temperature was favorable for the formation of the banded structure. The morphology transition from banded spherulites to nonbanded spherulites was related to the ratio of the crystallization rate to the diffusion rate. The formation mechanism of the banded structure was examined with the discontinuity growth theory. A depletion zone was considered to appear periodically at the crystal growth front because of the slow diffusion rate, and this may have resulted in the banded spherulites. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Crystallization behavior of polyethylene on silicon wafers in solution casting processes traced by time-resolved measurements of synchrotron grazing-incidence small-angle and wide-angle X-ray scattering

Crystallization behavior of polyethylene (PE) on silicon wafers in solution casting processes has been successfully traced by time-resolved grazing-incidence small-angle and wide-angle X-ray scattering (GISWAXS) measurements utilizing synchrotron radiation. A p-xylene solution of PE kept at ca. 343 K was dropped on a silicon wafer at ca. 298 K. While the p-xylene evaporated naturally from the dropped solution sample, PE chains crystallized to be a thin film. Raman spectral measurements were performed simultaneously with the GISWAXS measurements to evaluate quantitatively the p-xylene the dropped solution contained. Grazing-incidence wide-angle X-ray scattering (GIWAXS) patterns indicated nucleation and crystal growth in the dropped solution and the following as-cast film. GIWAXS and Raman spectral data revealed that crystallization of PE was enhanced after complete evaporation of the p-xylene from the dropped solution. The [110] and [200] directions of the orthorhombic PE crystal became relatively parallel to the wafer surface with time, which implied that the flat-on lamellae with respect to the wafer surface were mainly formed in the as-cast film. On the other hand, grazing-incidence small-angle X-ray scattering (GISAXS) patterns implied formation of isolated lamellae in the dropped solution. The lamellae and amorphous might alternatively be stacked in the preferred direction perpendicular to the wafer surface. The synchrotron GISWAXS experimental method could be applied for kinetic study on hierarchical structure of polymer thin films.

Specific features of electrical conduction of the poly-[NiSalen] metal-containing polymer thin-film structure

The charge transfer in the oxidized and reduced forms of poly-[NiSalen] metal-containing polymer films is investigated. It is established that the voltage dependence of the differential conductivity for the polymer in the oxidized form exhibits a nonlinear behavior, which indicates a high electrical activity of this state. The microscopic parameters characterizing the charge transfer are calculated within the space-charge-limited current theory. Differences in the surface morphology of two forms of the poly-[NiSalen] films are revealed using atomic-force microscopy.

量子ビームによる高分子研究

Quantum bean is defined as a well-organized beam with both natures of wave and particle such as laser, synchrotron radiation (SR) X-ray and neutron. In this article we review recent progress in polymer researches using quantum beam, including (1)fine structure of polymers using micro-beam, (2) internal structure of polymer thin films by gracing incident small-angle X-ray and neutron scattering, (3) polymer crystallization under flow by time resolved SR X-ray and neutron scattering, and (4) dynamics of polymers by SR X-ray and neutron scattering.

Surfaces and interfaces characterization by neutron reflectometry

Neutron reflectivity allows to characterize surfaces and interfaces of ultra-thin film layered systems down to a nanometric scale (∼2nm). It is a powerful tool for the study of magnetic and polymer thin film structures. The neutron magnetic interaction is of the same order as the nuclear interaction and makes polarised neutron reflectivity a very sensitive tool for probing magnetic multilayers. It allows the determination of magnetic ordering and coupling in artificial magnetic multilayers (either metallic/semi-conducting or oxides). Examples of studies in the field of giant magneto resistive (GMR) sensors used in hard drive and tape read heads are given. The search for efficient spin-injection materials which could be used in spin electronics is also a growing field of activity. Several material candidates are presently evaluated. Recent studies on such materials are presented: oxide materials (Fe2O3–Fe3O4) epitaxial thin films; multilayer systems involving semiconducting materials ((Fe/Si)n–(GaMnAs/GaAs)). Besides the high sensitivity of neutrons to magnetism, the possibility of isotopic labelling (H/D substitution) offers a way to probe polymer and protein thin film structures with great details: polymer interdiffusion or polymer grafting can be studied at the substrate–polymer or liquid–polymer interfaces. A model study of polymer grafting is presented.