Polysilane Films Research Articles

Optical constants and electrical conductivity of polysilanes: Effects of substituents and iodine doping

This work deals with the effect of chemical structure and iodine doping on electro-optical characteristics of different polysilanes in the solid state. The properties of polymethylphenylsilane homopolymer were compared with those of polysilane copolymers containing diphenylsilylene structural units associated with either methylhydrogen- or methylphenylsilylene moieties. Their optical parameters, such as Urbach energy and optical band gap, were evaluated using the method proposed by Tauc. The forbidden gap values for the studied polysilanes are reduced after doping from 3.22–3.46 eV to 2.47–2.64 eV, while the electrical conductivities were found in the range of 6.2 10−11 – 1.2 10−8 S/cm for pristine samples, and increased by 2–3 orders of magnitude following their doping, depending on the nature/content of the organic substituents attached to the silicon main chain. A simple mathematical approach starting from Tauc classical theory was used to establish allowed direct optical transitions for both undoped and doped polysilane samples. The obtained data indicated that the polysilane films with a high content of phenyl side groups presented the best properties for their use in electro-optical applications.

Correlation Between Shear-Flow Rheology and Solution Spreading During Spin Coating of Polysilane Solutions

The effect of side groups on rheological properties of different polysilanes in solution phase is investigated and correlated, with radial uniformity of estimated thickness of wet films. The polymethylphenylsilane homopolymer has shear rate-dependent flow properties in the interval 0.2-0.8 s-1 and relaxation time of 0.53 s. This behavior is changed for the copolymer containing methylphenylsilylene units, which becomes less sensitive to shear deformation as a result of chain reduced mobility, with the highest relaxation time of 1.54 s and flow activation energy of 27.08 kJ/mol, combined with the smallest deviation from constant viscosity (~0.02 Pa·s). Such Newtonian flow leads to higher uniformity of the wet film thickness profile alongthe radial position of the spin-coating wafer, comparatively with the other polysilane solutions. Higher spinning times (>60 s) and lower spinning speeds (<590 rpm) are also favorable, to obtain polysilane films with constant thickness. Molecular modeling was performed to investigate polysilane conformation in solution, and its interaction with toluene molecules. The studied polymer solutions have slightly higher work of adhesion to indium tin oxide, and polyethylene terephthalate (around 143 mN/m) substrates, in regard with glass and silicon (around 140 mN/m).

Effect of the polymer ordering on the optical spectra and thermoluminescence of polygermane and polysilane films and nanocomposites

Comparative study of optical spectra and thermoluminescence of poly(di-n-hexylgermane) (PDHGe) and poly(di-n-hexylsilane) (PDHS) films and nanocomposites with different degrees of ordering have been carried out in the temperature range 5–200 K. The disordering processes, which are essential for PDHGe, lead to the appearance of additional bands in its optical spectra associated with different set of trans- and gauche-conformations of the polymer chain as well as to the broadening of vibrational bands in Raman spectrum. It is shown that polymer chains of confined PDHGe introduced into the nanopores of SBA-15 silica, in contrast to those of PDHS have the gauche-conformation instead of the trans-conformation, as a result of decrease of intermolecular interaction between the polymer chain segments and increase of their mobility. Besides, appearance of discrete levels of the carriers’ activation energy in thermoluminescence of both polymers were observed, energies of which coincide with the optical vibration quanta. Disordering processes cause reduction of the number of observed discrete levels of the activation energy for PDHGe.

Structural Analysis of Ionic Photobase Generators and Lithographic Patterning of Polysilane Films Containing the Photobase Generators

Structural Analysis of Ionic Photobase Generators and Lithographic Patterning of Polysilane Films Containing the Photobase Generators

Behavior of Si-Si Bond Oxidation by Electron Beam Lithography

Lithography using siloxane polymers is reasonable for process reduction compared to mask etching process. Generally, crosslinkable groups, such as acrylates and epoxides, and protecting groups are added to siloxane polymers for lithography. We synthesized polydiphenylsilane without those functional groups, and the thermal behavior of that was observed with TG-DSC-MS. The thermal elimination of phenyl group from polydiphenylsilane was observed and the thermal weight loss until 500 °C was under 3%. The polysilane film was directly imaged with EB nano melting apparatus (ENF-3500) and line width of pattern was 12.9 μm. The film thicknesses before and after development were same. The partial heating by EB irradiation caused oxidation of polydiphenylsilane after elimination reaction of phenyl group and cleavage of Si-Si bond by XPS analysis.

PBb03 ラビング処理を施した高分子膜上でのポリシラン/液晶混合キャスト膜の配向挙動

PBb03 ラビング処理を施した高分子膜上でのポリシラン/液晶混合キャスト膜の配向挙動

Transparent and fluorescent thin films of polysilane–SiQD nanocomposite: cellulose acetate

Fluorescent and highly transparent free standing thin films have been prepared using polysilane–silicon quantum dots nanocomposite (PSiQD) dispersed within cellulose triacetate (CA). Polysilane acts like a carrier that transports the silicon quantum dots (SiQDs) within the CA matrix. Extremely low, subcatalytic amounts of PSiQD are enough to transfer to CA the optical properties of both polysilane and SiQDs. Thin films obtained by solvent casting are mechanically resistant, highly flexible and show the characteristic high intensity fluorescent emission due to SiQDs. Also, the nanocomposite is UV photosensitive and could be easily converted to a hydrophilic material, compatible with the common paper. The PSiQD carrier is obtained in situ by microwave assisted coupling of chlorosilanes in heterogeneous reaction conditions. ATR-FTIR analysis was used to investigate the chemical structure within the bulk material. The presence of SiQDs and their content within the CA nanocomposite were proved by XPS. These results were further sustained by TEM and SAXS analysis. The wetting properties of the composite were probed before and after UV exposure by contact angle measurements. Thin films of such a nanocomposite material are designed for special opto-electronic applications that require processing by UV patterning and control of surface wetting properties.

The influence of polysilane chemical structure on optical properties, rubbed film morphology and LC alignment

Polysilane films were prepared by the drop casting method and their optical and morphological properties have been analyzed in order to investigate their suitability as alignment layers for nematic molecules. The samples do not absorb the radiations in the visible domain, particularly those containing methylhydrosilyl units, and present a transmittance of about 90% starting from 390 to 1100 nm. The optical band-gap is higher than 3.26 eV for all polysilanes indicating a low probability of optical absorption processes in the visible range. The morphology of the pristine samples shows isotropically distributed granular formations. The polymer surface was oriented by rubbing with two types of velvet: one with short fibers and the other with long fibers. The latter generates higher surface anisotropy, as shown by the reduction of the surface texture direction index values. The presence of methylhydrosilyl units allows a denser packing of the polymer structure and thus finer surface periodicities, leading to better orientation of the nematic molecules on the polysilane surface.

Spectral Changes in Thin Films of Cyclicsilanes and Polysilanes by Heat Treatment

We report the optical properties of the thin films of cyclic and linear and polysilanes containing phenyl groups by heat treatments. We observe the shift to a longer wavelength of the absorption edge in UV-visible absorption spectra of the thin films, when the cyclic and linear polysilane films were heated at 500 °C after UV irradiation. This behavior is interpreted in terms of the formation of network siloxene films by the dissociation of phenyl groups from silicon structures and the accompanying incorporation of oxygen into the silicon structures. It is shown that UV irradiation before heating and substituent groups attached to cyclic and linear polysilanes affect the spectral changes by heat treatment.

Solution-Based Synthesis of Crystalline Silicon from Liquid Silane through Laser and Chemical Annealing

We report a solution process for the synthesis of crystalline silicon from the liquid silane precursor cyclohexasilane (Si(6)H(12)). Polysilane films were crystallized through thermal and laser annealing, with plasma hydrogenation at atmospheric pressure generating further structural changes in the films. The evolution from amorphous to microcrystalline is characterized using scanning electron microscopy (SEM), atomic force microscopy (AFM), Raman spectroscopy and impedance spectroscopy. A four-decade enhancement in the electrical conductivity is attributed to a disorder-order transition in a bonded Si network. Our results demonstrate a potentially attractive approach that employs a solution process coupled with ambient postprocessing to produce crystalline silicon thin films.

Optical Properties of Siloxene Films Prepared by High-Temperature Heat Treatment from Thin Films of Polysilane Containing Anthryl Groups

We report the synthesis of linear and network polysilanes containing anthryl groups and the optical properties of the thin films by heat treatments. We observe the shift to a lower energy of the absorption edge in UV–visible absorption spectra of the thin films, when the polysilane films were heated at 500 °C. This behavior is interpreted in terms of the formation of network siloxene films by the dissociation of anthryl groups from silicon structures and the accompanying incorporation of oxygen into the silicon structures. The addition of UV irradiation before heating enhances the spectral changes caused by heat treatment. It is shown that a vacuum degree during heating and backbone structures of polysilanes affect the formation of the network siloxene structures by heat treatment.

Mach-Zehnder Type Thermo-Optic Switch with Antenna-Coupled Y-Junction Fabricated by Selective Photobleaching of Polysilane Films

The Mach-Zehnder type thermo-optic switch with antenna-coupled Y-junction was demonstrated for the first time. The selective photobleaching of the polysilane films are used for fabrication. The branching angle was 3 deg and the longitudinal length was around 30 mm, which was reduced as around 60 % from the conventional structure. The beam propagation method was used for optimizing the design and the calculated transmission loss was only 0.16 dB. Our experiments showed the ON/OFF ratio of 9.9 dB and the switching power of 11.4 mW.

Mass Spectrometry Characterization of Methylphenylsilane‐Hydrogen RF Plasmas

AbstractThe plasmochemistry of methylphenylsilane diluted with hydrogen in radio frequency discharges during the deposition of thin films of plasmatic polysilane is investigated. The plasma reaction system has been examined under conditions identified from previous studies to give the best material. Mass spectrometry is used to follow the monomer fragmentation and to directly (on‐line) analyze the plasma composition under the static and dynamic regimes. The effect of input power is described. The products of the plasma‐induced reactions are collected in a cryogenic trap and then separated and analyzed by gas chromatography with a mass spectrometry analyzer. Organosilicon precursors for the plasma polymerization of one‐dimensional polysilanes are identified together with prevailing reaction pathways in the plasma. A simple method of monomer conversion efficiency is introduced.magnified image

Polarized Phthalocyanine Electroluminescence Diodes Prepared on Polysilane Films Treated with Polarized UV Light

ABSTRACT Photoalignment ability of poly[methyl(phenyl)silylene] (PMPSi) films makes possible to use them as hole transporting substrates for the preparation of organic oriented films. PMPSi layer prepared by spin coating was after drying irradiated with linearly polarized UV light. Then, water soluble hydroxyaluminium phthalocyaninesulfonate sodium salt [Al(OH)Pc(SO3Na)1–2] was deposited by casting. The cell ITO/PMPSi/Al(OH)Pc(SO3Na)1–2/Al showed non-linear current-voltage characteristics. For applied voltages higher than 20 V, a polarized electroluminescence was observed. Its polarizing anisotropy R EL = Φ⊥/Φ| was ca. 2 and 2.1 for phthalocyanine film prepared from solution and by vacuum evaporation, respectively.

Photoconductivity in fullerene-doped polysilane thin films

Flash photolysis time-resolved microwave conductivity (FP-TRMC) measurements have been performed to study the transport properties of charge carriers in the polysilane films. The effect of C 60 concentrations on photoconductivity of poly(methylphenylsilane) (PMPS) and poly( n-hexylphenylsilane) (PHPS) films has been studied using a variety of excitation light sources. The value of ϕ ∑ μ , which is the product of quantum efficiency of photocarrier generation ( ϕ) and sum of moibilities of the carriers ( ∑ μ ), depends strongly on C 60 concentration upon exposure of 532 nm. The quantum efficiency reaches ∼0.06 with C 60 concentration at 5.7 mol%, and saturates at the higher concentrations. The ϕ ∑ μ value increases considerably upon exposure of 193 nm up to 1.22 × 10 −3 cm 2/Vs without significant dependence on C 60 concentration, suggesting the direct formation of electron-hole pair by 6.39 eV photon absorption with the higher ϕ value at ∼0.12. The present technique gave the estimates of intra-chain mobility of charge carriers in PMPS and PHPS, and one-order magnitude higher intra-chain mobility was observed in PHPS than that in PMPS. This is suggestive of a highly ordered Si backbone conformation in PHPS. The intra-chain mobility in PMPS, however, is at least two orders of magnitude higher than the mobility values estimated by conventional time-of-flight techniques. Thus we conclude that the higher mobility than ∼10 −3 cm 2/Vs ( E ∼ 0) is realizable even with PMPS by precise synthesis and device fabrication free from disordering, defects, impurities, etc.

Fluoroalkylated Polysilane Film as a Chemosensor for Explosive Nitroaromatic Compounds

The present paper reports a new type of polymer-based chemosensor made of stiff fluoroalkylated polysilane, poly(3,3,3-trifluoropropylmethylsilane) (1), which showed a remarkable sensitivity for explosive nitroaromatic compounds (NACs), such as 2,4,6-trinitrophenol (picric acid), 1,3,5-trinitrobenzene (TNB), 2,4-dinitrotoluene (DNT), and m-dinitrobenzene (DNB), by a decrease in the photoluminescence (PL) intensity in the near-UV region with parts per million concentration of NACs in tetrahydrofuran (THF) solution and in the solid film in water. The PL intensity was completely reversible repeatedly after the removal of NACs from the thin film by rinsing with methanol (or water). A linear Stern−Volmer relationship was observed in all of the cases with high quenching constants. The PL quenching efficiency of 1 (Mn = 3.12 × 104, PDI = 3.6, K = 4.15 × 104 M-1) for picric acid is 198 times better than that of nonfluoroalkylpolysilane, poly(n-propylmethylsilane) (2) (Mn = 2.93 × 104, PDI = 2.1, K = 2.09 × 102 M-1). The weak noncovalent interaction between Si atoms of σ-conjugated polysilane and N and/or O atoms of electron-deficient NACs may be responsible for electron transfer from the excited state of the polysilane to the electron-deficient NACs, resulting in the PL quenching of 1 in solution and in the thin film by NACs.

Study of transport properties in fullerene-doped polysilane films using flash photolysis time-resolved microwave technique

The charge carrier photo generation in fullerene (C 60) doped polysilane (PS) is a multistage process including, photo induced electron transfer between polysilane to 3 C 60 ∗ and relaxation of the charge-transfer state which results in polaron pair (PS + and C 60 - ) formation. To study the mobility of charge carriers in polysilane films (PS1-8) doped with fullerene (C 60), the flash photolysis time-resolved microwave conductivity (FP-TRMC) measurements have been performed. Second harmonic generation (SHG), laser of wavelength 532 nm has been used as excitation source. The highest ϕ∑ μ value (7 × 10 −5 cm 2/V s) obtained for PS6 among all polysilanes due to its highly ordered structure. The photo carrier generation efficiency of polysilane films have increased due to fullerene doping. The fast decay kinetics of TRMC signal is due to backward electron transfer between PS + and C 60 - where as slow decay can be attributed to charge recombination after diffusion process.

紫外光分解を用いたポリシランフィルムの新しい応用展開

紫外光分解を用いたポリシランフィルムの新しい応用展開

UV-Patterned Polysilane Films as a Phase Mask in Optical Correlation System

Entirely transparent polysilane films, which were modified by ultraviolet (UV) light exposure to decrease their refractive index, were used as phase masks. The phase modulation amount of the transmitted laser, which was estimated using a Mach–Zehnder interferometer, can be modified linearly by UV exposure dose, indicating that the polysilane films have a very useful property of controllability by UV light exposure. Optical correlation using the polysilane phase masks as the information-carrying medium was then demonstrated. A matched-filter four-wave-mixing optical correlator using a photorefractive (PR) polymer as a real-time holographic data storage medium was used. A large correlation signal difference of over 3.6-fold was obtained for the striped polysilane phase masks that were arranged orthogonally or in parallel. This is due to the distinct encoded images in the polysilane phasemasks originating from the large refractive index modification in polysilane films of approximately Δn=-0.14 at λ=633 nm. The high transparency in the entire visible region and such large refractive index modification make polysilane films difficult to forge, and allow us to use phase masks in pattern recognition systems for security verification.

Versatile Helical Polymer Films: Chiroptical Inversion Switching and Memory with Re‐Writable (RW) and Write‐Once Read‐Many (WORM) Modes

Solid-state films of chiral polysilanes undergo an optical inversion (see Figure) above a helix–helix transition temperature, determined by the polymer molecular weight and by the thermal processing. These films could be used for re-writable or write-once, read-many data storage, depending on the molecular weight and the transition temperature.