Preparation of Silica Coatings Heavily Doped with Spiropyran Using Perhydropolysilazane as the Silica Source and Their Photochromic Properties

Fine-Structure Analysis of Perhydropolysilazane-Derived Nano Layers in Deep-Buried Condition Using Polarized Neutron Reflectometry

A large background scattering originating from the sample matrix is a major obstacle for fine-structure analysis of a nanometric layer buried in a bulk material. As polarization analysis can decrease undesired scattering in a neutron reflectivity (NR) profile, we performed NR experiments with polarization analysis on a polypropylene (PP)/perhydropolysilazane-derived SiO₂ (PDS)/Si substrate sample, having a deep-buried layer of SiO₂ to elucidate the fine structure of the nano-PDS layer. This method offers unique possibilities for increasing the amplitude of the Kiessig fringes in the higher scattering vector (Q_z) region of the NR profiles in the sample by decreasing the undesired background scattering. Fitting and Fourier transform analysis results of the NR data indicated that the synthesized PDS layer remained between the PP plate and Si substrate with a thickness of approximately 109 Å. Furthermore, the scattering length density of the PDS layer, obtained from the background subtracted data appeared to be more accurate than that obtained from the raw data. Although the density of the PDS layer was lower than that of natural SiO₂, the PDS thin layer had adequate mechanical strength to maintain a uniform PDS layer in the depth-direction under the deep-buried condition.

Dense, uniform, smooth SiO2/TiO2 hard coatings derived from a single precursor source of tetra-n-butyl titanate modified perhydropolysilazane

SiO₂/TiO₂ composite coatings are of great interest due to their optical, photocatalytic, electrical and mechanical properties. There are many methods for preparing SiO₂/TiO₂ composite coatings. Among these, the sol–gel process is eco-friendly and easily implementable for industrial applications. However, it is still a great challenge to prepare dense, uniform and smooth SiO₂/TiO₂ composite coatings with a sol–gel process. In this work, we show a modified sol–gel process for achieving dense, uniform and smooth SiO₂/TiO₂ coatings with tetra-n-butyl titanate modified perhydropolysilazane (PHPS) as a single precursor source, in which PHPS acts as the source for SiO₂ instead of a traditional alkoxylsilane compound. The micro-morphology and composition evolution during the preparation process have been investigated; a smooth surface with a roughness average (S_a) below 4.5 nm and a uniform distribution of Ti elements over the entire coating are shown. These dense, uniform SiO₂/TiO₂ coatings exhibit excellent mechanical robustness, with hardness values as high as 9.45 GPa, excellent optical transparency and hydrophilic properties.

Dense, uniform, smooth SiO₂/TiO₂ hard coatings derived from a single precursor source of tetra n-butyl titanate modified perhydropolysilazane.

Solution-processable LaZrOx/SiO2 gate dielectric at low temperature of 180 °C for high-performance metal oxide field-effect transistors

Although solution-processable high-k inorganic dielectrics have been implemented as a gate insulator for high-performance, low-cost transition metal oxide field-effect transistors (FETs), the high-temperature annealing (>300 °C) required to achieve acceptable insulating properties still limits the facile realization of flexible electronics. This study reports that the addition of a 2-dimetylamino-1-propanol (DMAPO) catalyst to a perhydropolysilazane (PHPS) solution enables a significant reduction of the curing temperature for the resulting SiO2 dielectrics to as low as 180 °C. The hydrolysis and condensation of the as-spun PHPS film under humidity conditions were enhanced greatly by the presence of DMAPO, even at extremely low curing temperatures, which allowed a smooth surface (roughness of 0.31 nm) and acceptable leakage characteristics (1.8 × 10(-6) A/cm(2) at an electric field of 1MV/cm) of the resulting SiO2 dielectric films. Although the resulting indium zinc oxide (IZO) FETs exhibited an apparent high mobility of 261.6 cm(2)/(V s), they suffered from a low on/off current (ION/OFF) ratio and large hysteresis due to the hygroscopic property of silazane-derived SiO2 film. The ION/OFF value and hysteresis instability of IZO FETs was improved by capping the high-k LaZrOx dielectric on a solution-processed SiO2 film via sol-gel processing at a low temperature of 180 °C while maintaining a high mobility of 24.8 cm(2)/(V s). This superior performance of the IZO FETs with a spin-coated LaZrOx/SiO2 bilayer gate insulator can be attributed to the efficient intercalation of the 5s orbital of In(3+) ion in the IZO channel, the good interface matching of IZO/LaZrOx and the carrier blocking ability of PHPS-derived SiO2 dielectric film. Therefore, the solution-processable LaZrOx/SiO2 stack can be a promising candidate as a gate dielectric for low-temperature, high-performance, and low-cost flexible metal oxide FETs.

Superior properties of silica thin films prepared from perhydropolysilazane solutions at room temperature in comparison with conventional alkoxide-derived silica gel films

Preparation of silica thin films from perhydropolysilazane (PHPS) at room temperature has attracted much attention because it provides a new way to realize silica thin films in a variety of technologies where any high temperature processes should be avoided. Although silica gel films can also be prepared from alkoxides at room temperature by conventional sol-gel method, they are believed to have low mechanical and chemical durability. However, even such alkoxide-derived silica gel films have possibilities to become more durable via condensation reaction and densification when aged at room temperature. In order to clarify whether or not PHPS-derived silica thin films have critical superiority on properties, the hardness and chemical durability were compared between PHPS- and alkoxide-derived silica thin films, where PHPS films were exposed to the vapor from aqueous ammonia at room temperature for PHPS-to-silica conversion. Alkoxide-derived silica gel films were found to be densified and hardened when stored in air at room temperature, which resulted in pencil hardness even higher than 9H on Si(100) substrates. However, the ultra-microindentation tests demonstrated that the PHPS-derived films are definitely harder than the alkoxide-derived ones. The PHPS-derived films were also found to have higher chemical durability in water and in aqueous ammonia. Such higher mechanical and chemical durability of the PHPS-derived films was ascribed to their higher density, i.e., more highly condensed states, which was evidenced in infrared absorption spectra. Hard coating performance on plastic substrates was also studied, and the PHPS-derived films were demonstrated to have much higher adhesive strength on polymethylmethacrylate substrates. The in-plane stress measurement demonstrated that the PHPS-derived films have much lower or even negligible tensile stress, which may be one of the causes for such higher adhesive strength.

Mechanical and Thermal Characteristics of Bio-Nanocomposites Consisting of Poly-L-lactic Acid and Self-Assembling Siloxane Nanoparticles with Three Phases

Biopolymer nanocomposites (bio-nanocomposite) consisting of poly-L-lactic acid (PLLA) and siloxane nanoparticles with three phases, a high-density siloxane phase (plural cores), an elastomeric silicone phase, and a caprolactone oligomer phase, were developed to increase the mechanical properties of PLLA. The nanoparticles, average size of 13 nm, were self-assembled by aggregation and condensation of an organosiloxane with three units: isocyanatepropyltrimethoxysilane (IPTS), polymethylpropyloxysiloxane (PMPS), and a caprolactone oligomer (CLO), which form each phase. The bio-nanocomposite was produced using PLLA and the nanoparticles. Bending and tensile testing showed that the use of these nanoparticles (5 wt% in PLLA) greatly increases the tenacity (breaking strain) of PLLA while maintaining its relatively high breaking (maximum) strength. The elongation of the nanocomposite was more than twice that of PLLA while the elasticity modulus and breaking (maximum) strength were comparable to those of PLLA. The nanoparticles also increased the impact strength of PLLA. The use of the nanoparticles almost did not show adverse affect on the thermal resistance of PLLA. The nanocomposite’s heat resistance indicated by the glass transition temperature and heat distortion temperature was fairly kept. The decomposition temperature of the nanocomposite somewhat increased.

Nanometer-sized domains in Langmuir-Blodgett films for patterning SiO2

In this study, we prepared Langmuir-Blodgett films with domains ranging from 20 to 100 nm in size by using perfluorinated fatty acids. The domain size of the obtained LB films is markedly smaller than the ordinary domain size of hydrocarbons and fluorocarbons on the micrometer scale. The domains were prepared by controlling their growth through the addition of 2-propanol to the subphase of Langmuir monolayers. Furthermore, the prepared domains in the LB films were used as templates for patterning SiO(2) films. The obtained SiO(2) films have completely negative structures compared with those of the domains in the LB films.