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Shu Seki - One of the best experts on this subject based on the ideXlab platform.
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Confinement of Single Polysilane Chains in Coordination Nanospaces
Journal of the American Chemical Society, 2015Co-Authors: Takashi Kitao, Shu Seki, Silvia Bracco, Angiolina Comotti, Piero Sozzani, Masanobu Naito, Takashi Uemura, Susumu KitagawaAbstract:Understanding the intrinsic properties of single conducting polymer chains is of interest, largely for their applications in molecular devices. In this study, we report the accommodation of single polysilane chains with hole-transporting ability in porous coordination polymers (PCPs), [Al(OH)(L)]n (1a; L = 2,6-naphthalenedicarboxylate, channel size = 8.5 × 8.5 A2, 1b; L = 4,4′-biphenyldicarboxylate, channel size = 11.1 × 11.1 A2). Interestingly, the isolation of single polysilane chains increased the values of carrier mobility in comparison with that in the bulk state due to the elimination of the slow interchain hole hopping. Moreover, even when the chains are isolated one another, the main chain conformation of polysilane could be controlled by changing the pore environment of PCPs, as evidenced by Raman spectroscopy, solid-state NMR measurements, and molecular dynamics simulation. Hence, we succeeded in varying the conducting property of single polysilane chains. Additionally, Polysilanes have a drawba...
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Confinement of Single Polysilane Chains in Coordination Nanospaces
2015Co-Authors: Takashi Kitao, Shu Seki, Silvia Bracco, Angiolina Comotti, Piero Sozzani, Masanobu Naito, Takashi Uemura, Susumu KitagawaAbstract:Understanding the intrinsic properties of single conducting polymer chains is of interest, largely for their applications in molecular devices. In this study, we report the accommodation of single polysilane chains with hole-transporting ability in porous coordination polymers (PCPs), [Al(OH)(L)]n (1a; L = 2,6-naphthalenedicarboxylate, channel size = 8.5 × 8.5 Å2, 1b; L = 4,4′-biphenyldicarboxylate, channel size = 11.1 × 11.1 Å2). Interestingly, the isolation of single polysilane chains increased the values of carrier mobility in comparison with that in the bulk state due to the elimination of the slow interchain hole hopping. Moreover, even when the chains are isolated one another, the main chain conformation of polysilane could be controlled by changing the pore environment of PCPs, as evidenced by Raman spectroscopy, solid-state NMR measurements, and molecular dynamics simulation. Hence, we succeeded in varying the conducting property of single polysilane chains. Additionally, Polysilanes have a drawback, photodegradation under ultraviolet light, which should be overcome for the application of Polysilanes. It is noteworthy that the accommodation of polysilane in the nanopores did not exhibit photodegradation. These results highlight that PCP–polysilane hybrids are promising candidates for further use in the field of molecular electronics
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evidence of electron conductivity in Polysilanes and its implications in design of ultraviolet emitting devices
Journal of Applied Physics, 2010Co-Authors: Niladri Banerjee, Shu SekiAbstract:Polysilanes are thought to be primarily hole conducting. Consequently, poor efficiency of a polysilane based light emitting diode is explained on the basis of propensity of the charge carriers to nonradiatively recombine near the cathode. We fabricated a single layer device based on poly(n-octylphenylsilane) with a calcium cathode. This device, however, cannot be analyzed on the basis of a single carrier (hole) transport and the device, unexpectedly, exhibits an injection limited current, though no barrier to hole injection exists. Simulation based analysis reveals bipolar transport, with electron mobility much greater than the hole mobility. This now also makes polysilane electron transport layers possible. In addition, we establish that the time-of-flight measured mobilities in Polysilanes may not be relevant to electronic devices, which employ much thinner layers. Based on these observations, the basis for device design is revised. Accordingly, a N, N-diphenyl-N, N-bis(1-naphthyl)(1,1-biphenyl)-4,4 dia...
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dynamics of positive charge carriers on si chains of Polysilanes
Journal of the American Chemical Society, 2004Co-Authors: Shu Seki, Tomoyo Kawaguchi, Yoshiko Koizumi, Hidefumi Habara, Seiichi TagawaAbstract:The transient absorption of radical cations of a variety of substituted Polysilanes is discussed quantitatively in terms of the molar extinction coefficient and oscillator strength by nanosecond pulse radiolysis. Oxygen-saturated polysilane solutions in benzene exhibit a strong transient absorption band ascribed to the polysilane radical cation. The transient species react with N,N,N‘,N‘-tetramethyl-p-phenylene-diamine (TMPD) to produce TMPD radical cations. On the basis of the molar extinction coefficient of the TMPD radical cation, the molar extinction coefficients for the radical cations of Polysilanes are found to increase in the range 3.3 × 104 to 2.0 × 105 M-1 cm-1 with increasing polymer segment length. The stepwise increase in the total oscillator strength with an increase in the number of phenyl rings directly bonded to the Si skeleton suggests the delocalization of the positive polaron state and/or the SOMO state over the phenyl rings, indicating the importance of phenyl rings in intermolecular ...
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Pulse radiolysis study of radical cations of Polysilanes
Chemical Physics Letters, 2003Co-Authors: Tomoyo Kawaguchi, Shu Seki, Kazumasa Okamoto, Akinori Saeki, Yoichi Yoshida, Seiichi TagawaAbstract:Abstract Molar extinction coefficients of radical cations are quantitatively discussed for a variety of substituted Polysilanes by nano-second pulse radiolysis. Polysilane solution in benzene under saturated oxygen exhibits a strong absorption band ascribed to polysilane radical cation in the transient spectra. The transient species react with N,N,N′,N′-tetramethyl-p-phenylene-diamine (TMPD) to produce TMPD radical cations. Using the molar extinction coefficient of TMPD radical cation, the molar extinction coefficients for the radical cations of Polysilanes are found to increase in the range 3.8 × 104–15.0 × 104 M−1 cm−1 with an increase in the segment length of the polymers. This is the first report on the extinction coefficient and oscillator strength of polysilane radical cations.
Masanobu Naito - One of the best experts on this subject based on the ideXlab platform.
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chain dimensions and intermolecular interactions of Polysilanes bearing alkyl side groups over the uv thermochromic temperature
Polymer, 2015Co-Authors: Xinyue Jiang, Masanobu Naito, Ken Terao, Woojung ChungAbstract:Abstract To elucidate temperature change of intermolecular interactions and chain dimensions for poly(dialkylsilane)s with or without thermochromism, synchrotron-radiation small-angle X-ray scattering and UV-absorption measurements were carried out for relatively low-molar mass poly(n-hexylmethyl)silane (PSi-1), poly(n-decylmethyl)silane (PSi-2), and poly(n-hexylpropyl)silane (PSi-3) samples in isooctane over a wide temperature range down to −94 °C. While the dimensional properties for the three Polysilanes were almost irrespective of temperature, the second virial coefficient for PSi-2 and PSi-3 significantly decreased and became negative below the thermochromic temperature at −60 °C and −50 °C, respectively. Analyses in terms of the quasi-two-parameter theory for the wormlike chain showed that conformational change detected by UV-absorption behavior does not cause appreciably the unperturbed chain dimensions of the polysilane samples. Furthermore, aggregates were detected by ultra-small-angle X-ray scattering measurements for high molar mass PSi-3 samples at low temperatures. These results indicate that intermolecular interactions between poly(dialkylsilane) molecules become attractive around the thermochromic temperature.
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Confinement of Single Polysilane Chains in Coordination Nanospaces
Journal of the American Chemical Society, 2015Co-Authors: Takashi Kitao, Shu Seki, Silvia Bracco, Angiolina Comotti, Piero Sozzani, Masanobu Naito, Takashi Uemura, Susumu KitagawaAbstract:Understanding the intrinsic properties of single conducting polymer chains is of interest, largely for their applications in molecular devices. In this study, we report the accommodation of single polysilane chains with hole-transporting ability in porous coordination polymers (PCPs), [Al(OH)(L)]n (1a; L = 2,6-naphthalenedicarboxylate, channel size = 8.5 × 8.5 A2, 1b; L = 4,4′-biphenyldicarboxylate, channel size = 11.1 × 11.1 A2). Interestingly, the isolation of single polysilane chains increased the values of carrier mobility in comparison with that in the bulk state due to the elimination of the slow interchain hole hopping. Moreover, even when the chains are isolated one another, the main chain conformation of polysilane could be controlled by changing the pore environment of PCPs, as evidenced by Raman spectroscopy, solid-state NMR measurements, and molecular dynamics simulation. Hence, we succeeded in varying the conducting property of single polysilane chains. Additionally, Polysilanes have a drawba...
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Confinement of Single Polysilane Chains in Coordination Nanospaces
2015Co-Authors: Takashi Kitao, Shu Seki, Silvia Bracco, Angiolina Comotti, Piero Sozzani, Masanobu Naito, Takashi Uemura, Susumu KitagawaAbstract:Understanding the intrinsic properties of single conducting polymer chains is of interest, largely for their applications in molecular devices. In this study, we report the accommodation of single polysilane chains with hole-transporting ability in porous coordination polymers (PCPs), [Al(OH)(L)]n (1a; L = 2,6-naphthalenedicarboxylate, channel size = 8.5 × 8.5 Å2, 1b; L = 4,4′-biphenyldicarboxylate, channel size = 11.1 × 11.1 Å2). Interestingly, the isolation of single polysilane chains increased the values of carrier mobility in comparison with that in the bulk state due to the elimination of the slow interchain hole hopping. Moreover, even when the chains are isolated one another, the main chain conformation of polysilane could be controlled by changing the pore environment of PCPs, as evidenced by Raman spectroscopy, solid-state NMR measurements, and molecular dynamics simulation. Hence, we succeeded in varying the conducting property of single polysilane chains. Additionally, Polysilanes have a drawback, photodegradation under ultraviolet light, which should be overcome for the application of Polysilanes. It is noteworthy that the accommodation of polysilane in the nanopores did not exhibit photodegradation. These results highlight that PCP–polysilane hybrids are promising candidates for further use in the field of molecular electronics
Seiichi Tagawa - One of the best experts on this subject based on the ideXlab platform.
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dynamics of positive charge carriers on si chains of Polysilanes
Journal of the American Chemical Society, 2004Co-Authors: Shu Seki, Tomoyo Kawaguchi, Yoshiko Koizumi, Hidefumi Habara, Seiichi TagawaAbstract:The transient absorption of radical cations of a variety of substituted Polysilanes is discussed quantitatively in terms of the molar extinction coefficient and oscillator strength by nanosecond pulse radiolysis. Oxygen-saturated polysilane solutions in benzene exhibit a strong transient absorption band ascribed to the polysilane radical cation. The transient species react with N,N,N‘,N‘-tetramethyl-p-phenylene-diamine (TMPD) to produce TMPD radical cations. On the basis of the molar extinction coefficient of the TMPD radical cation, the molar extinction coefficients for the radical cations of Polysilanes are found to increase in the range 3.3 × 104 to 2.0 × 105 M-1 cm-1 with increasing polymer segment length. The stepwise increase in the total oscillator strength with an increase in the number of phenyl rings directly bonded to the Si skeleton suggests the delocalization of the positive polaron state and/or the SOMO state over the phenyl rings, indicating the importance of phenyl rings in intermolecular ...
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Pulse radiolysis study of radical cations of Polysilanes
Chemical Physics Letters, 2003Co-Authors: Tomoyo Kawaguchi, Shu Seki, Kazumasa Okamoto, Akinori Saeki, Yoichi Yoshida, Seiichi TagawaAbstract:Abstract Molar extinction coefficients of radical cations are quantitatively discussed for a variety of substituted Polysilanes by nano-second pulse radiolysis. Polysilane solution in benzene under saturated oxygen exhibits a strong absorption band ascribed to polysilane radical cation in the transient spectra. The transient species react with N,N,N′,N′-tetramethyl-p-phenylene-diamine (TMPD) to produce TMPD radical cations. Using the molar extinction coefficient of TMPD radical cation, the molar extinction coefficients for the radical cations of Polysilanes are found to increase in the range 3.8 × 104–15.0 × 104 M−1 cm−1 with an increase in the segment length of the polymers. This is the first report on the extinction coefficient and oscillator strength of polysilane radical cations.
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Optical properties of pyrrolyl-substituted Polysilanes
Journal of Organometallic Chemistry, 2000Co-Authors: Shu Seki, Yoshihisa Kunimi, Kazutaka Nishida, Kayo Aramaki, Seiichi TagawaAbstract:Abstract Pyrrolyl-substituted Polysilanes were synthesized in the present study. The pyrrolyl rings directly attached to the Si conjugated main chains with SiN bonds. Poly(alkylpyrrolylsilane) and poly(phenylpyrrolylsilane) showed a chromophore which is attributed to σ–σ* transition in the conjugated system associated with near-UV fluorescence. However, a strong photoluminescence band was observed at 450–500 mn other than the near-UV photoluminescence for the Polysilanes. The luminescence is due to the energy relaxation from σ* to an inter-band level produced by σ–π mixing between main chain σ-conjugated system and pyrrolyl groups as suggested by theoretical calculations. Transient spectroscopy of the Polysilanes was also carried out showing a new chromophore at the vis-IR region (800 nm) other than near-UV (300–400 nm) and IR (∼2000 nm) absorption bands typically observed for alkyl- and phenyl-substituted Polysilanes. It also supports the presence of the mid-gap level in the pyrrolyl-substituted Polysilanes.
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electronic structure of radical anions and cations of Polysilanes with structural defects
Macromolecules, 1999Co-Authors: Shu Seki, Yoichi Yoshida, Seiichi Tagawa, Keisuke AsaiAbstract:The electronic structure of a charged polysilane molecule is studied. The transient absorption spectroscopy was carried out for radical cations and anions of aryl-substituted polysilane molecules with Si-based defects by means of the nanosecond pulse radiolysis technique. Radical cations and anions of Polysilanes displayed near-UV and IR absorption maxima at ca. 3.2−3.4 and 0.5−1 eV, respectively. They are ascribed to interband and subband transitions of polaron states and/or charge resonance states (CR) between σ-conjugated segments. The transition energy of the bands was strongly affected by the defects, showing a remarkable blue shift in IR absorption. The energy of the IR absorption band was interpreted as the degree of electron−phonon coupling. The energy rapidly increased from ca. 0.5 eV with an increase in the defect density and saturated at ca. 0.85 eV for radical cations and 0.95 eV for radical anions. It indicated that excess electrons and holes relatively localized at the defect structures, whe...
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stability of radicals in aryl substituted Polysilanes with linear and planar silicon skeleton structures
Journal of Physical Chemistry B, 1998Co-Authors: Shu Seki, Yoichi Yoshida, Seiichi Tagawa, Keith R Cromack, A D Trifunac, And Keisuke Asai, Kenkichi IshigureAbstract:This paper discusses the stability of radicals produced under γ-irradiation for phenyl-substituted Polysilanes with different backbone structures. Poly(methylphenylsilane) and structural defect-containing phenyl-substituted Polysilanes were irradiated by 60Co γ-rays in the solid state. Temperature dependence of the EPR signal intensity from the radicals induced by radiolysis was measured. The radicals appeared to be more stable as the induced defect density in the backbone structure was increased, indicating that the structure defects on the polymer backbone may play a role in stabilizing silyl radicals. The migration of unpaired electrons was also observed from chain ends to chain center leading to stable radical species. The estimated-branched structures were less than 3.5% in the linear polysilane obtained by conventional Wurtz coupling condensation.
Robert West - One of the best experts on this subject based on the ideXlab platform.
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Patai's Chemistry of Functional Groups - Polysilanes: Conformations, Chromotropism and Conductivity
PATAI'S Chemistry of Functional Groups, 2009Co-Authors: Robert WestAbstract:1 Introduction 2 Conformations and Electronic Structure 3 Chromotropism 4 Electrical Conductivity 5 Acknowledgements Keywords: Polysilanes - conformations, chromotropism and conductivity; conformations and electronic structure; polysilane thermochromism in solution; polysilane thermochromism as solids; solvatochromism; ionochromism; other chromotropic behavior; pristine Polysilanes and electrical conductivity
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Polysilanes conformations chromotropism and conductivity
Patai's Chemistry of Functional Groups, 2009Co-Authors: Robert WestAbstract:1 Introduction 2 Conformations and Electronic Structure 3 Chromotropism 4 Electrical Conductivity 5 Acknowledgements Keywords: Polysilanes - conformations, chromotropism and conductivity; conformations and electronic structure; polysilane thermochromism in solution; polysilane thermochromism as solids; solvatochromism; ionochromism; other chromotropic behavior; pristine Polysilanes and electrical conductivity
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Inorganic Polymers - Polysilanes and Related Polymers
Inorganic Polymers, 2005Co-Authors: James E. Mark, Harry R. Allcock, Robert WestAbstract:In polysilane polymers, the polymer backbone is made up entirely of silicon atoms. Therefore these materials differ from other important inorganic polymers, the siloxanes and phosphazenes, in which the polymer chain is heteroatomic. Structurally, they are more closely related to homoatomic organic polymers such as the polyolefins. However, because the units in the main chain are all silicon atoms, the Polysilanes exhibit quite unusual properties. The cumulated silicon-silicon bonds in the polymer chain allow extensive electron delocalization to take place, and this delocalization of the sigma electrons in the Si-Si bonds gives the Polysilanes unique optical and electronic properties. Many of the potential technical uses, as well as the remarkable properties, of Polysilanes result from this unusual mobility of the sigma electrons. The Polysilanes can be regarded as one-dimensional analogs to elemental silicon, on which, of course, nearly all of modern electronics is based. The photophysical behavior of Polysilanes is not approached by any other materials, save for the less stable and more costly polygermanes and polystannanes. The remarkable properties of Polysilanes have led to intense interest, and to numerous proposed high-tech applications. But the great promise of Polysilanes as materials has yet to be realized. Their only commercial use at present is as precursors to silicon carbide ceramics, an application which takes no advantage of their optical or electronic properties. Linear polysilane polymers, properly called poly(silylene)s, can be obtained as homopolymers or copolymers. Continuation of the polysilane chain consumes two of the four valences of each silicon atom; the other two are taken up by pendent groups, which may be the same or different. Copolymers, which contain two or more kinds of silicon atoms, can be made up from units. A typical example is the copolymer of Me2Si and PhMeSi units, poly(dimethylsilylene-co-phenylmethylsilylene), which bears the popular name “polysilastyrene.” The pendent groups are typically organic units and can include alkyl, aryl, substituted aryl, hydrogen, Me3Si, ferrocenyl, and so on. An unlimited number of different polymers are possible, and several hundred compositions have been described in the literature.
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Mass Spectroscopy Study on Pyrolysis of Polysilanes.
Journal of Photopolymer Science and Technology, 1998Co-Authors: Lujun Pan, Robert West, Mei Zhang, Kunio Oka, Mikio Aramata, Yoshikazu NakayamaAbstract: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.
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Hole transport in Polysilanes with diverse side-chain substituents
Philosophical Magazine B, 1995Co-Authors: Takaaki Dohmaru, Yoshikazu Nakayama, K. Oka, T. Yajima, M. Miyamoto, Takao Kawamura, Robert WestAbstract:Abstract The hole drift mobilities in Polysilanes with diverse substituents and different molecular weights have been measured by the conventional time-of-flight technique. Depending on the kind of substituents, hole drift mobilities varied by more than one order of magnitude; poly(?henyltrimethyldisilane) gave the highest room temperature hole drift mobility, 6·0 × 10−4cm2V−1s−1 at a field of 2 × 105 V cm−1, of all the Polysilanes reported so far. The electric field and temperature dependences of the hole drift mobilities in Polysilanes were analysed in the framework of Gill's expression and Bassler's consideration. Polysilanes with an aromatic side group exhibited a zero-field activation energy E 0 of ca. 0·35 eV compared to E 0 = 0·22-0·26 eV obtained for Polysilanes with non-aromatic groups, while poly(phenyltrimethyldisilane), with one aromatic side group at every two Si atoms, manifested E 0 = 0·26 eV, a value which may be categorized in the latter group with non-aromatic substituents. The effects o...
Shuzi Hayase - One of the best experts on this subject based on the ideXlab platform.
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Polysilanes for semiconductor fabrication
Progress in Polymer Science, 2003Co-Authors: Shuzi HayaseAbstract:Abstract Polysilanes have various interesting properties and many applications have been proposed. However, low durability at elevated temperature and that toward light exposure on Polysilanes have limited their application fields. The most promising application is lithography for LIS fabrication. The unusual photo-reactivity and high etching durability render Polysilanes the candidate of most promising material for the LSI lithography in future, where new materials have been required in order to fabricate micro-patterns less than 0.2 μm. In this report, application of Polysilanes to semiconductor fabrication, particularly, bilayer resists and anti-reflection layers with high etching properties, is reviewed. This review includes synthesis of new Polysilanes, photo-reactivity, amplification of the photo-reactivity, bilayer resists developable with aqueous solutions, pattern fabrication with all dry process, UV absorptions, anti-reflection properties, durability toward plasma etchings and the pattern transfer.
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Application of Polysilanes to LSI Manufacturing ProcessesTheir Antireflective Properties and Etching Selectivity toward Resists
Chemistry of Materials, 2001Co-Authors: Shuzi Hayase, Y. Nakano, And S.yoshikawa, Hiromichi Ohta, Yasunori Sato, Eishi Shiobara, Seiro Miyoshi, Y. Onishi, M. Abe, And H. MatsuyamaAbstract:Fundamental aspects for a novel LSI pattern fabrication process employing Polysilanes as an antireflective layer (ARL) are discussed. The multilayer is composed of an organic resist, a polysilane layer, and a substrate. The polysilane avoids reflections from the substrate when the resist is exposed to 248-nm light emitted from a KrF excimer laser. It also acts as a pattern transfer layer. The polysilane layer is etched faster than the resist when the etching is carried out with reactive ions by employing Cl 2 gas. Therefore, the resist pattern is transferred to the polysilane layer precisely. The relationship between the structure of the polysilane and its physical properties, namely, the UV absorbance at 248 nm and etching selectivity toward the organic resist, is discussed and the best polysilane structure for this application identified.
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preparation of oriented langmuir blodgett films of Polysilanes bearing hydroxyalkyl or alkoxyalkyl groups
Macromolecules, 1994Co-Authors: Rikako Kani, Chien-hua Yuan, Shuzi Hayase, Yoshihiko Nakano, Yutaka Majima, Robert WestAbstract:Polysilane polymers bearing hydroxyalkyl or alkoxyalkyl groups form monolayers (L films) at an air-water interface. It is possible to transfer all of the L films to hydrophobic substituents to provide Langmuir-Blodgett films. Among these polymers, Polysilanes having more than three alkyl carbons have provided, oriented polysilane thin films in which the silicon main chains align with each other in the direction parallel to the dipping direction of the substrates. The orientations were evaluated by their polarized UV absorptions