PS Films Research Articles

Effect of porous silicon on the performances of silicon solar cells during the porous silicon-based gettering procedure

In this work we analyse the effect of porous silicon on the performances of multicrystalline silicon (mc-Si) solar cells during the porous silicon-based gettering procedure. This procedure consists of forming PS layers on both front and back sides of the mc-Si wafers followed by an annealing in an infrared furnace under a controlled atmosphere at different temperatures. Three sets of samples (A, B and C) have been prepared; for samples A and B, the PS films were removed before and after annealing, respectively. In order to optimize the annealing temperature, we measure the defect density at a selected grain boundary (GB) using the dark current–voltage ( I– V) characteristics across the GB itself. The annealing temperature was optimized to 1000 °C. The effect of these treatments on the performances of mc-Si solar cells was studied by means of the current–voltage characteristic (at AM 1.5) and the internal quantum efficiency (IQE). The results obtained for cell A and cell B were compared to those obtained on a reference cell (C).

Methods for probing charging properties of polymeric materials using XPS

Various thin polystyrene, PS, and poly(methyl methacrylate), PMMA and PS + PMMA blend films have been examined using the technique of recording X-ray photoelectron spectrum while the sample is subjected to ±10 V d.c. bias, and three different forms of (square-wave (SQW), sinusoidal (SIN) and triangular (TRG)), a.c. pulses. All films exhibit charging shifts as observed in the position of the corresponding C1s peak under d.c. bias. The a.c. pulses convert the single C1s peak to twinned peaks in the case of the square-wave form, and distort severely in the cases of the SIN, and TRG forms, and all three of them exhibit strong frequency dependence. In order to mimic and better understand the behavior of these polymeric materials, an artificial dielectric system consisting of a clean Si-wafer coupled to an external 1 MΩ resistor and 56 nF capacitor is created, and its response to different forms of voltage stimuli, is examined in detail. A simple electrical circuit model is also developed treating the system as consisting of a parallel resistor and a series capacitor. With the help of the model, the response of the artificial system is successfully calculated as judged by comparison with the experimental data. Using one high frequency SQW measurements, the off-set in the charging shift due to the extra low-energy neutralizing electrons is estimated. After correcting the corresponding off-set shifts, the XPS spectra of the three different PS films, one PMMA, and one PS + PMMA blend film are re-examined. As a result of these detailed analysis, there emerges a clear relationship between the thicknesses of the PS films with their charging abilities. In the blend film, PS and PMMA domains are electrically separated, and exhibit different charging shifts, however, the presence of one is felt by the other. Hence, the PS component shifts are larger in the blend, due to the presence of PMMA domains, which has intrinsically a larger R eff, and conversely the PMMA component shifts are smaller due to the presence of PS domains.

Electrical Conductivity in Anisotropic Porous Silicon Films

The electrical transport in free standing porous silicon films formed from heavily boron-doped (110) Si wafers are investigated. The conductivity and photoconductivity of the films are shown to be significantly larger along the [110] in-plane crystallographic direction than that along the [001] one. The conductivity anisotropy decreases with increasing temperature and frequency of the applied voltage. The experimental results are explained by a model, which takes into account potential barriers between anisotropic Si nanocrystals assembling PS films.

Adaptation of polystyrene/multi‐wall carbon nanotube composite properties in respect of its thermal stability

AbstractPolystyrene (PS)/multi‐wall carbon nanotube (MWCNT) nanocomposites were prepared by melt mixing and by coagulation of PS/MWCNT sonicated dispersion. Before mixing and coagulation particles of MWCNT were covered with PS nanospheres by microemulsion polymerization to increase their dispersibility and compatibility with the matrix. Microemulsion polymerization was carried out under sonication in the presence of surfactants and a cross‐linking agent. The structure of modified MWCNT filler was revealed by SEM and TEM microscopy analyses. They show that PS is well grafted onto surface of MWCNT in form of ca 30 nm nanospheres or as ca 3–8 nm PS film layer. Significant changes in properties were recorded mainly for the coagulated sample. Although no shift of Tg was recorded for the melt mixed composite, the coagulated sample shows an increase by 9°C. Also the reinforcing effect of MWCNT was more pronounced for the same method of preparation (further supported by the filler modification). The creep response of this material shifts to longer times not only in the Tg area, but also as low as 70°C below it, which is perceived as an improvement of temperature stability (the same properties kept for a longer time). This was also proved by the increase of creep modulus, and consequently by the prolonged time needed to reach the same tensile creep compliance after aging. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers

Investigation of the dewetting inhibition mechanism of thin polymer films

The mechanism of inhibition of polymer film dewetting is investigated by adding a star comb-like polymer, four-arm P(S-ran-VB-g-PMMA), to PS film and PMMA film on different substrates. It is found that the mechanism of inhibition of polymer film dewetting is kinetic in nature, and is related to the miscibility between the additional compound and the polymer film. On addition to the miscible system [four-arm P(S-ran-VB-g-PMMA) and PMMA], the star comb-like polymers can increase the resistant force of dewetting with hole growth and inhibit the dewetting process of the thin polymer film by enrichment in the rim. To the immiscible system [four-arm P(S-ran-VB-g-PMMA) and PS], firstly the four-arm P(S-ran-VB-g-PMMA) enriches the solid substrate and forms nanodroplets in the process of spin-coating, and then PS film dewets on these nanodroplets; however, the star comb-like polymer can inhibit the dewetting of the polymer film only when the contact angle θ of the polymer on the additional four-arm P(S-ran-VB-g-PMMA) is smaller than that of the polymer on the substrate.

Formation of low surface energy separators with undercut structures via a full-solution process and its application in inkjet printed matrix of polymer light-emitting diodes

In this paper, low surface energy separators with undercut structures were fabricated through a full-solution process. These low surface energy separators are more suitable for application in inkjet printed passive-matrix displays of polymer light-emitting diodes. A patterned PS film was formed on the P4VP/photoresist film by microtransfer printing firstly. Patterned Au-coated Ni film was formed on the uncovered P4VP/photoresist film by electroless deposition. This metal film was used as mask to pattern the photoresist layer and form undercut structures with the patterned photoresist layer. The surface energy of the metal film also decreased dramatically from 84.6 mJ/m 2 to 21.1 mJ/m 2 by modification of fluorinated mercaptan self-assemble monolayer on Au surface. The low surface energy separators were used to confine the flow of inkjet printed PFO solution and improve the patterning resolution of inkjet printing successfully. Separated PFO stripes, complement with the pattern of the separators, formed through inkjet printing. The separators also realized the patterning of cathodes. A passive-matrix display device was obtained through the assistant patterning of low surface energy separators.

Preparation of Electrically Conductive Polystyrene/Carbon Nanofiber Nanocomposite Films

A simple and effective approach to prepare conductive polystyrene/carbon nanofiber (PS/CNF) nanocomposite films via a solution dispersion method is presented. Inexpensive CNF, which has a structure similar to multi-walled carbon nanotubes, is chosen as a nanofiller in this experiment to achieve conductivity in PS films. A good dispersion is achieved in the PS matrix with ultrasonication. The experiment to prepare PS/CNF system is suitable as a laboratory experiment for college chemistry or material science course. The experiment provides students with a hands-on laboratory experience in nanotechnology and its related fundamental concept.

The Storing Matter technique: Preliminary results on PS and PVC

The Storing Matter technique has been developed recently in SAM to perform quantitative analyses with high sensitivity: the sample to be analysed is sputtered by ion bombardment and up to a sub-monolayer of emitted particles is deposited on a collector. In the present work, this collector is subsequently analysed by static Secondary Ion Mass Spectrometry (SIMS). We concentrate on the conservation of the molecular information throughout the deposition and analysis processes. The experiments are realised on PS and PVC films. The deposits have been clearly identified on the collector. The molecular information is partially conserved throughout the deposition and analysis processes. Higher fragmentation in the mass spectra of the collectors is due to double fragmentation in the sputter-deposition and analysis steps.

Solid-phase photocatalytic degradation of polystyrene with TiO2 modified by iron (II) phthalocyanine

A novel photodegradable polystyrene-FePc-TiO2 (PS-FePc-TiO2) nanocomposite was prepared by embedding the FePc-TiO2 into the commercial polystyrene. The TiO2 catalyst was modified by iron (II) phthalocyanine in order to improve its photocatalytic efficiency under the visible light irradiation. Solid-phase photocatalytic degradation of the PS-FePc-TiO2 nanocomposite was carried out in an ambient air at room temperature under ultraviolet lamp and/or sunlight irradiation. The properties of composite films were compared with those of the pure PS films and the polystyrene-TiO2 (PS-TiO2) composite films through performing weight loss monitoring, scanning electron microscope (SEM), FT-IR and UV–vis spectroscopy. The photo-induced degradation of PS-FePc-TiO2 composite films was significantly higher than that of the pure PS films and the PS-TiO2 composite films both under the UV irradiation and under the sunlight irradiation. The weight loss of the PS-FePc-TiO2 composite film reached 35% under the sunlight irradiation. FT-IR analysis and weight loss results indicated that the benzene rings in PS matrix of the composite film were cleaved during UV-light irradiation. The photocatalytic degradation mechanism of the composite films was briefly discussed.

Silver/polystyrene-coated hollow glass waveguides for the transmission of terahertz radiation

We have applied techniques developed for IR waveguides to fabricate Ag/polystyrene (PS) -coated hollow glass waveguides (HGWs) for transmission of terahertz radiation. A loss of 0.95 dB/m at 119 microm (2.5 THz) was obtained for a 2 mm bore, 90 cm long Ag/PS HGW. We found that TE modes are supported in HGWs with thin PS films, while hybrid (HE) modes dominate when PS film thickness increases. The lowest losses are obtained for the thicker PS films and the propagation of the HE modes.

Evaluation of the electrical conductivity of nano-porous silicon from photoluminescence and particle size distribution

This paper aims modelling and determining the electrical conductivity of nano-porous silicon (nano-PS) films. The latter were prepared by electrochemical etching monocrystalline silicon (c-Si) wafers in HF-based solutions for different values of the anodic current. The experimental values of the dc-electrical conductivity of nano-PS films were obtained using the dark current–voltage ( I– V) characteristic of an Al/nano-PS/c-Si/Al type structure. The electrical conductivity of the PS films was theoretically estimated using the Bruggeman effective medium approximation (EMA) theory and by considering quantum size effects in small silicon particles. We give a comparative study between two different approaches. In the first one, we assume the PS layer to be formed of three phases: vacuum, oxide and c-Si nanocrystallites having the same mean size dimension (mean size value). In the second approach, we consider the nanocrystallites as being formed of multiple crystalline phases, depending on their size dimension. As a result, we found that in the case of the first simple approximation (three simple phases), theoretical data fit well the experimental results for small and medium porosities, and a discrepancy appears for porosities greater than 65%. However, in the case of multiple phases, theoretical values fit very well the experimental results for all porosities.

Fabrication of Ni Nanocrystal Flash Memories Using a Polymeric Self-Assembly Approach

Fabrication of nickel nanocrystal flash memories using a polymeric approach is presented. Heat treatment of the poly (styrene-b-methyl methacrylate) block copolymer with a molecular weight of 67 000 g/mol followed by PMMA removal in an organic solvent created a porous PS film with 20-nm-diameter pores and a total pore density of ~6 times 1010 cm-2. A trilayer pattern-transfer approach was employed in order to solve the metal lift-off issue intertwined with the low aspect ratio block copolymer patterns. As a result, a highly uniform self- assembled array of nickel nanocrystals was attained and utilized for flash memory fabrication. The memory devices demonstrated an unchanged memory window for up to 2 times 105 stressing cycles.

Selective metal deposition in hydrophobic porous cavities of self-organized honeycomb-patterned polymer films by all-wet electroless plating

We report selective metal deposition of self-organized honeycomb-patterned polymer (hp) films possessing hydrophobic surfaces by all-wet electroless plating. Nickel/phosphorus (Ni/P) coated hp films were fabricated as follows. A catalytic nucleus of electroless plating was adsorbed on hp films by immersion in a saturated ethanol solution of palladium(II) chloride (PdCl2). Homogeneous metal deposition on the hydrophobic surface of the hp film was easily carried out by all-wet process. In addition an ultrahydrophobic surface of pincushion-structured polymer (ps) films having periodic pillars which was obtained by peeling off a top layer of the hp film was metal-coated by the same all-wet process. It was found that immersion in the saturated ethanol solution of PdCl2 is suitable for catalyzation on hydrophobic surfaces for metal deposition by all-wet electroless plating. To use differences of wettability of honeycomb structures between inner and outer surfaces of porous cavities, site-selective Ni/P deposition in porous cavities was carried out by immersion in a palladium chloride acid aqueous solution after ethanol treatment.

Effect of molecular weight on the physicochemical modifications induced in the UV laser ablation of doped polymers

This work investigates the effect of polymer molecular weight MW on the UV ablation of iodo-naphthalene- and iodo-phenanthrene-doped poly(methyl methacrylate) PMMA, and polystyrene PS films following irradiation at 248 nm. For irradiation at weakly absorbed wavelengths, the ablation threshold increases with increasing MW. However, at strongly absorbed wavelengths, the difference in the ablation thresholds is much smaller, or minimal. In parallel, bubble formation due to accumulation of gas produced by polymer and dopant decomposition differs depending on MW. For highly absorbing PS, the differences of behaviour show a less dramatic dependence on MW. These results are explained within the framework of the bulk photothermal model, according to which ejection requires that a critical number of bonds is broken. In all, they are of direct importance for the optimisation of laser processing schemes and applications and provide the first indication of explosive boiling in UV ablation of polymers.

Diffusion of one or more components of a silane adhesion-promoting mixture into poly(methyl methacrylate)

The surface-sensitive technique of sum frequency generation (SFG) vibrational spectroscopy has been applied to study the buried interfaces between different polymers including deuterated polystyrene ( d-PS) and deuterated poly(methyl methacrylate) ( d-PMMA) and a two-component silane adhesion-promoting mixture (SAPM) composed of (3-glycidoxypropyl)trimethoxysilane ( γ-GPS) and a methylvinylsiloxanol (MVS). Because of the dissolution of d-PS, no SFG C H stretching signals could be collected from the d-PS/ γ-GPS interface, and SFG signals collected from the d-PS/SAPM interface gradually disappeared over time. SFG results also showed that γ-GPS can diffuse through the d-PMMA film. The diffusion of γ-GPS through the d-PMMA film was confirmed by SFG studies on the interface between γ-GPS and a d-PMMA/PS two-polymer layer system. Initially the SFG signal from the PS layer was detected. However, after γ-GPS diffused through the d-PMMA film, the PS film was dissolved by the silane, and thus the SFG signal from PS was lost. Similar experiments have been carried out at the interface between the SAPM and the d-PMMA/PS two-polymer layer system and it was found that the diffusion time of the γ-GPS in the SAPM through the d-PMMA film was significantly longer. These results were much different to those from previous SFG studies on the analogous PET interfaces and appear consistent with differences in solubility parameters calculated for these systems.

Effect of spreading solvents on Langmuir monolayers and Langmuir–Blodgett films of PS- b-P2VP

Langmuir monolayers of polystyrene- block-poly(2-vinylpyridine) (PS- b-P2VP) diblock copolymers (with the same PS block length and different P2VP block lengths) formed at the air/water interface were characterized with the Langmuir film balance technique. Nonselective and selective solvents were used to spread the samples on the water surface and the spreading solvents showed large effect on the surface pressure–molecular area isotherms. The corresponding Langmuir–Blodgett (LB) films of the samples were characterized with atomic force microscopy. The LB films transferred from the Langmuir monolayers spread with a nonselective solvent only exhibited isolated circular micelles, while those with a selective solvent exhibited quite different morphologies including planar structure, rodlike structure, circular micelles, and labyrinth pattern. As far as we know, the labyrinth pattern appears in the LB films for the first time.

Solid-phase photocatalytic degradation of polystyrene with modified nano-TiO 2 catalyst

A novel photodegradable polystyrene-grafted-TiO 2 (PS- g-TiO 2) nanocomposite was prepared by embedding the grafted-TiO 2 into the commercial polystyrene. Solid-phase photocatalytic degradation of the PS- g-TiO 2 nanocomposite was carried out in ambient air at room temperature under ultraviolet lamp and/or sunlight irradiation. The properties of composite film were compared with those of the pure PS film by methods such as weight loss measurement, scanning electron microscope (SEM), gel permeation chromatogram (GPC), X-ray photoelectron spectroscopy (XPS), FT-IR spectroscopy, and UV–vis spectroscopy. The results show that the photo-induced degradation of PS- g-TiO 2 composite film is significantly higher than that of pure PS film. The weight loss of composite film reached 31.9%, average molecular weight ( M w) of composite film decreased by 53.1%, and the number average molecular weight ( M n) decreased by 73.2% after 396 h of UV-light irradiation. FT-IR analysis and weight loss indicated that the benzene rings in PS-matrix of composite film were cleaved during UV-light irradiation. The photocatalytic degradation mechanism of the films is briefly discussed.

Elastic Moduli of Ultrathin Amorphous Polymer Films

The elastic moduli of ultrathin poly(styrene) (PS) and poly(methylmethacrylate) (PMMA) films of thickness ranging from 200 nm to 5 nm were investigated using a buckling-based metrology. Below 40 nm, the apparent modulus of the PS and PMMA films decreases dramatically, with an order of magnitude decrease compared to bulk values for the thinnest films measured. We can account for the observed decrease in apparent modulus by applying a composite model based on the film having a surface layer with a reduced modulus and of finite thickness. The observed decrease in the apparent modulus highlights issues in mechanical stability and robustness of sub-40 nm polymer films and features.

Wplyw ciepla na niektore wlasciwosci warstwy wierzchniej folii polimerowych przeznaczonych do formowania prozniowego

The effects of specific energy of activation (Ej - controlled by speed of travel) of PP, PS or PET films, used in vacuum forming processes, on the values of contact angle, surface free energy and oxidation degree of the surface layer (WW) were presented. Contact angles with water, formamide or diiodomethane were measured by goniometer, surface free energy (SEP) was calculated using Owens-Wendt method and oxidation degree (SU) of WW was investigated using X-ray photoelectron spectroscopy (XPS). The measurements were done either after the film activation or after heating of activated film up to temperature about 150 °C and subsequent cooling to temperature about 23 °C. It was found that SEP values (Fig. 1-3) calculated on the basis of contact angles with water and diiodomethane (Table 2-4) were higher than those calculated on the basis of contact angles with formamide and diiodomethane. Heating of the films investigated decreased SEP value in every case and slightly decreased SU of WW of PP or PS (Fig. 4,5) but not in case of PET (Fig. 6).

Pulsed laser deposition of polymers doped with fluorescent molecular sensors

Pulsed laser deposition (PLD) has been used to obtain thin films of poly(methyl-methacrylate), PMMA, and polystyrene, PS, doped with fluorescent probes based in the amino aromatic compounds S6, DMA-2,4, Dans and Acrid-acryl. These compounds, both in solution and inserted in polymeric films, show solvatochromic emission band shifts upon changes of pH, polarity and viscosity in their micro-environment and, prepared in thin films, could prove advantageous for use as sensors of the presence of contaminating environmental agents. Deposits, obtained by irradiating targets consisting in films of doped PMMA and PS with a Ti:sapphire laser (800 nm, 120 fs pulse), were analyzed by optical and environmental scanning electron microscopy, fluorescence microscopy, laser-induced fluorescence, micro-Raman spectroscopy and flow injection analysis-mass spectrometry. Results show the effective transfer of the polymer and the probe to the substrate and the high dependence on film structure on the polymer used in the targets. Irradiation with a KrF laser (248 nm, 20 ns) of Dans-doped targets only produced deposits when using PMMA for target preparation. Results are discussed in terms of the participation of multiphoton processes in the fs IR irradiation, the influence of the linear absorption coefficient of the targets and of the different contributions of thermal and chemical effects in the IR femtosecond and UV nanosecond domains.