Polysilane Films Research Articles

Subgap Absorption Spectra in Polysilane Films

The subgap absorption spectra of polysilane films have been measured by photothermal deflection spectroscopy using the deflection medium 1,4-butanediol. It has been revealed that poly(methylphenylsilane) (PMPS) films have a band tail with an exponential distribution rather than a Gaussian distribution and a low density of states in the midgap. The Urbach energy is estimated to be 30 meV. The photodegradation of PMPS films increases the subgap absorption, indicating defect generation. The defects are generated from the photoscission of σ bonds, which has a stretched exponential time dependence. The doping of C60 to PMPS sensitizes the absorption in the visible region. The absorption increases proportionally to the doping ratio of C60 in a range of three orders of magnitude. The absorption spectrum of the PMPS and C60 mixture shows no interaction between the two ground states.

Nanolithography of Organic Polysilane Films Using Carbon Nanotube Tips

The patterning of polysilane films is performed by means of the contact-mode-Scanning Probe Microscope(SPM) lithography technique. Both a carbon nanotube tip and a gold-coated Si tip are used. The polysilane film is directly patterned or grooved when the tip is negatively biased. It is considered that the grooves are fabricated by the scission of Si-Si bonds and volatilization of the species due to the emanating of electrons from the scanning tip. Compared with gold-coated Si tips, carbon nanotube tips produce narrower grooves with a higher scan speed and have a longer lifetime. The maximum ratio of groove depth to width can be obtained at a speed as high as 20 µm/s when using the carbon nanotube tip.

Photocontrol of Poly(dihexylsilane) Chain Organization using a Photochromic Monolayer

The in-plane orientation of a polysilane film on photochromic monolayer was controlled by irradiation with linearly polarized visible light. The polymer backbone was aligned in the perpendicular direction to the polarization plane of actinic light. In this photoprocess, the orientational order could be controlled by the light exposure dose.

Orientation of Polysilanes along the Film Thickness and their Properties

The method to prepare polysilane films aligning along their thickness has been developed. Oriented polysilane films of (MeSiPh)n and (n-Hex2Si)n with the respective aligning of 84% and 94% of Si chains are demonstrated and their molecular orientations are investigated. The plane of phenyl rings are perpendicular to the aligned Si chains in the oriented (MeSiPh)n film and the plane of trans-planar of n-hexyl side chains is also perpendicular to the aligned Si chains in the oriented (n-Hex2Si)n. The carrier transport measurement indicates that the hole drift mobility is improved in the oriented films of (MeSiPh)n. However, it is not sufficient and its reason is discussed in terms of the energetic and positional disorders of the carrier hopping sites.

Electronic Energy Transfer in Oriented Bilayer Films of Polysilanes

The intermolecular energy transfer was studied in a bilayer film of polysilanes. The highly oriented films of poly(diethylsilylene) (PDES) were prepared by the mechanical deposition technique, which had been originally developed by Wittmann and co-workers. The poorly oriented layer was formed on the highly oriented PDES layer by spin-casting a solution of poly(methyloctadecylsilylene) (PMOdS). The bilayer films were characterized with polarized UV absorption and polarized fluorescence spectroscopy. It was shown that the light absorption in the PMOdS layer contributed to the fluorescence intensity of the PDES layer and that the electronic energy was transferred from the PMOdS layer to the PDES layer. Although the poorly oriented PMOdS layer absorbs both parallel-polarized light and perpendicular-polarized light, the highly oriented PDES layer emits only light polarized parallel to the orientation direction of the silicon main chains. Thus, the bilayer film has a function of rotating the polarization direction and of the isotropic-to-polarized light conversion. The fluorescence intensity of PDES was shown to increase with an increase in the thickness of the PMOdS layer, but the increase in the fluorescence intensity saturates above 500 nm. The saturation is caused by the limitation of the migration distance of excitons. The polarization of the excitation light influenced the emission intensity when the thickness of the PMOdS layer was thinner than 100 nm, suggesting that the excitons move between the sites having similar orientations of transition dipole moments. The possible mechanism of exciton migration was discussed in terms of the segment models, in which the molecular chains are separated into the ordered segments with various lengths.

Photocarrier Generation in Polysilane Films Doped With and Without Fullerene

Photocarrier Generation in Polysilane Films Doped With and Without Fullerene

Langmuir-Blodgett Films of Functional Polysilanes. Modification of Optical Properties in Polysilane Monolayer at the Air/Water Interface

Novel functional polysilanes bearing ethereal groups were prepared and the interfacial behavior of the polysilanes was investigated by using the LB method. It was found that the polysilane monolayers demonstrated a unique chromic effect induced by a specific conformational and orientational change of polymer backbones at the air/water interface.

Carrier Trapping Centers in Polysilane Film

Anomalous behavior of trapping and release of charge carriers in poly(methylphenylsilane) films has been discovered by thermally stimulated current spectroscopy. The carrier trapping occurs effectively at room temperature but not at 77 K. Trapped carriers are released at some specific temperatures which do not depend on the heating rate in the measurements. No trapped carrier is released at room temperature. Differential scanning calorimetry indicates that the onset temperatures of the carrier release correspond to the endothermic peaks. Such carrier trapping and release are not observed for polysilanes with saturated hydrocarbon side group but with aromatic side group. Theses results suggest that the observed phenomena are related to the motion of the aromatic substituents.

Hole transport in oriented polysilane films

Hole transport in oriented films of poly (di- n-pentylsilane) has been studied in terms of the effect of the orientation and conformation of Si chain on the drift mobility and disorder of hopping sites. The results support the view that (1) the interchain overlap of wave functions for a 7/3 helix is higher than that for a transoid, (2) the hopping sites have higher diagonal and off-diagonal disorder in a 7/3 helix than in a transoid, and (3) the orientation of Si chains significantly enhances the interchain overlap of wave functions and reduces the diagonal (1/1.3) and off-diagonal disorder parameter (1/2.7) in a transoid but has no effect in the case of a 7/3 helix.

Oriented thin films of conjugated polymers: polysilanes and polyphenylenes

In this paper, preparation of uniaxially oriented films of conjugated polymers, polysilanes and poly(p-phenylenes) (PPP) is investigated. Highly oriented thin films of poly(dimethylsilane) (PDMS) were prepared by the friction transfer method. The properties of PDMS films strongly depend on the preparation temperature. At a temperature higher than 210°C, uniform ultrathin films with extremely high orientation were obtained. It is considered that the friction transfer is related to the disorder (hexagonal) phase of PDMS. Other polysilanes, such as poly(diethylsilane) (PDES), poly(di-n-hexylsilane) (PDHS), poly(di-n-butylsilane) and poly(methylphenylsilane) also afforded oriented films by the same method. Oriented films of PPP were prepared by the friction transfer method. The thin films of the polymers were characterized mainly by ultraviolet absorption spectroscopy. The friction-transferred PDMS and PPP had abilities of orienting other materials. The films of polysilanes, such as PDHS, which were cast on the oriented PDMS from solution, were oriented along the PDMS chain direction. Oriented films of some oligophenylenes were obtained by vapor deposition or cast on the friction-transferred PPP. When the friction-transferred PPP film was immersed into the reaction mixture, a newly oriented PPP film were polymerized on the friction-transferred PPP films.

Polysilanes as conducting material producers and their application to metal pattern formation by UV light and electroless metallization

This paper describes a novel method for the deposition of gold, silver and palladium colloids on polysilane films by reducing the corresponding metal salt dissolved in alcohol without the use of any other reductants, and an application of the methodology to the pattern formation of copper and nickel metal by palladium-catalyzed electroless metallization on the surface of poly(methylphenylsilane) film, in combination with UV light lithography at 254 nm without the use of any other photoresists.

Novel Offset Printing without a Developing Process Utilizing the UV-Photodecomposition of Polysilane

Abstract Utilizing a surface modification of polysilane film due to photodecomposition by patterned UV-light irradiation, we have confirmed that polysilanes have a potential application as a material for novel offset printing, which will enable us to skip the alkaline development process required in current offset printing. This has been achieved by a wettability change of photodecomposable polysilane and a modified fountain solution. It has been found that the hydrophilicity in the UV-exposed area is sufficiently maintained by a treatment with tris(2-hydroxyethyl)methylammonium iodide added to the fountain water, which rejects an oil ink in the printing process.

Au Colloid Formation in Polysilane/Au Layered Film and its Application as Novel Optical Recording Media

Vacuum deposited gold thin layer on a ultraviolet (UV) light pre-exposed polysilanc film undergoes colloidal gold formation by heating. This process was found to accompany the degradation of polysilane by catalytic oxidation due to the colloidal gold formed. Incorporating a titanyl phthalocyanine (TiOPc) pigment layer as a photon-thermal energy conversion layer in-between polysilane film and substrate, we have succeeded in demonstrating experimentally the possible application of such phenomenon to a new optical recording system.

Preparation of Substituted Network Polysilanes and Their Electrical Conductivities

The introduction of various substituents, such as alkyl and aryl groups, into the MeO-functionalized network polysilane, [MeSi(OMe)l]m (2) via a substitution reaction using Grignard reagents gave the substituted polysilanes [MeSi(OMe)x(R)y]n (3), which are soluble in common organic solvents. Films of polysilanes bearing the (dialkylamino)phenyl side chain p-R‘2NC6H4 (R‘ = Me, Et, and Pr) exhibited electrical conductivities on the order of 10-3 S·cm-1 when doped with iodine. The electronic absorption bands for the network polysilanes were correlated to their CT complexes associated with the conductivity.

Thermal Hysteresis in UV Absorption of Polysilane Films

UV absorption spectra of poly(methylphenylsilane) films were measured at varying temperatures from 25°C to 200°C and a new thermal hysteresis in UV absorption of the polysilane films was observed. Once a polysilane film was annealed above its glass transition temperature, its UV absorption spectrum greatly and irreversibly changed. In other words, the absorption spectrum intrinsic to a particular polysilane film is obtained only after it is annealed above its Tg. This thermal hysteresis is discussed in relation to the changes in the micrtoscopic free spaces and in the hole transport characteristics between the annealed and non-annealed polysilane films. We concluded that after a polysilane film is annealed above its Tg, there occurs an irreversible re-distribution of the σ-conjugated domains in a way as to increase their average size.

Formation of polysilane film by laser CVD

The laser chemical vapor deposition (CVD) using dichloromethyl phenylsilane as a monomer gave a polysilane film on a substrate. The micropatterns of the polysilane with the resolution of about 300 μm were formed by laser projection CVD through a photomask. The silylene was observed by laser flash photolysis of dichloromethyl phenylsilane as a transient intermediate during the photochemical reaction. The transient absorption spectrum and the molecular orbital (MO) calculation suggest the formation of the methylphenylsilylene by the cleavage of the SiCl bond of the dichloromethylphenylsilane. The elemental composition by XPS spectra showed the higher Si:C ratio of the polysilane film compared to the monomer, which implies the existence of the silicon network structure. The time-resolved emission spectra of the polysilane film were similar to that of the network polysilane. The optical band gap of polysilane film was decreased with increasing laser excitation power.

Photoconduction in Polysilane Film

The photoconduction of poly(methylphenylsilane) doped with and without C60 has been studied in terms of the carrier generation kinetics. The photoconductivity spectrum of polysilane has an onset coincident with the optical absorption edge and this photoconduction is not due to the hole creation from excitons at electrodes but due to photogeneration of holes in the disorder system or photogeneration of charged polarons. The analysis of the disorder model successfully explains the zero temperature photoconductivity. Doping of C60 well sensitizes the photoconductivity of polysilane in the spectral region where C60 has optical absorption. This sensitization is suppressed at lower temperature. In a low temperature region holes accumulate by the photoexcitation of polysilane and the dark and photoconductivities increase. The accumulated holes recombine with electrons in C60 at temperatures higher than 130 K.

Mass Spectroscopy Study on Pyrolysis of Polysilanes.

Pyrolysis of polysilanes with different molecular weights, solid states and substituents has been studied by quadrupole mass spectroscopy. The analysis of kinetics on the gas evolution spectra of a unit of the polysilanes gives their activation energies having Gaussian distributions. The number reduction of the weak Si-Si bonds with the decrease of the chain length of polysilanes results in the increase of activation energy of decomposition. The activation energy is also affected by the kind of solid states of polysilane. Because of the stronger interaction among the molecules, polysilane film has higher activation energies than powder. Due to the photodegradation and oxidation of polysilanes, photooxidized film has higher activation energies of decomposition and a broader distribution of activation energies than the unoxidized film. Furthermore, substituents give intense effects on the activation energies and the order of the decomposition reactions. It is found that the decomposition reactions occur at the low temperature if the substituents are easy to be disconnected from Si.

Oxygen-crosslinked polysilane: the new class of Si-related material for electroluminescent devices

The preparation and optical properties of the novel silicon-related material named oxygen-crosslinked polysilane were investigated. The oxygen-crosslinked polysilane was prepared by the thermal annealing of the precursor polysilane bearing alkoxyl groups. The photoluminescence consisting of a broad visible band at about 440 nm and a relatively sharp band at about 360 nm was observed at room temperature. The relative intensities of the visible emission were changed during the crosslinking. The visible emission was greatly affected by the steric hindrance of the alkoxyl groups of the precursor. The visible electroluminescene (EL) was also observed uniformly from the EL cell consisting of the oxygen-crosslinked polysilane film sandwiched between A1 electrode and indium-tin-oxide (ITO) electrode. The current densities of the EL cell increased with an increase in the oxygen-crosslinking. © 1997 John Wiley & Sons, Ltd.

Colloid Formation from Vacuum Deposited Au Thin Layer on a UV-light Pre-exposed Polysilane Film

Abstract Vacuum deposited gold thin layer on a UV-light pre-exposed polysilane film underwent colloidal gold formation by heating. This process was found to accompany the degradation of polysilane by catalytic oxidation due to the formed colloidal gold. Such a phenomenon occurred in only the combination of polysilane and gold.