turn changes the effective contrast between the alternating polymer and LC rich layers in the structure. This is a simple and flexible system by which photoresponsive photonic crystals can be fabricated in a single-step process. In addition to the one-dimensionally periodic systems such as those presented here, complex two-and three-dimensionally periodic HPDLC photonic materials could be fabricated [13] with the Azo-LC materials to make dynamic photonic crystals of any structure in a one-step process. Future studies will include fabricating novel photo-optic photonic structures, in addition to probing the ultimate response time of the system, as well as the effects of excitation intensity, wavelength, and azobenzene concentration. ExperimentalHolographic-polymer-dispersed liquid crystal structures containing azobenzene-derived liquid crystals were prepared from a standard prepolymer syrup containing 35 % E7, to which was added an additional 3.5 % BMAB. The preparation of a standard syrup can be found in [10] and [11], for example. The BMAB was synthesized according to [14], and can be commercially obtained from BEAMCo Inc, Winter Park, FL. Sample cells were prepared by placing a small amount of syrup to which a small amount of 8 lm glass spherical spacers were added on indium tin oxide (ITO) coated glass. The resulting cell contains approximately an 8±10 lm layer of photo sensitive syrup between two glass plates. Bragg reflection gratings were prepared using two counter propagating beams incident on the sample cell. This produced a one dimensionally periodic holographic structure with a grating vector perpendicular to the surface of the cell. The initial diffraction efficiency of these gratings was probed at normal incidence and ranged from 45 to 55 %. Control gratings prepared from an identical syrup without BMAB showed diffraction efficiencies of 50 to 55 %. Current studies in bulk have shown that 10 % BMAB in E7 is sufficient to induce an isothermal N±I transition at room temperature [15]. In order to minimize the attenuation of the triggering UV light through the thickness of the sample, it is desirable to use as low a concentration of Azo-LC as is sufficient to observe a complete, isothermal N±I transition. Thus approximately 3.5 % of the weight of the syrup in BMAB was added to the syrup, which constitutes roughly 10 % of the liquid crystal content. A convenient wavelength, 540 nm, was selected for holographic recording such that it did not overlap the cis absorption substantially, which provided for an accurate measurement of the diffraction efficiency.Once recorded, the reflection gratings are characterized in an apparatus which allowed for the introduction of both a UV laser beam (up to 80 mW cm ±2 of 365 nm from and Ar+ laser) and a doubled Nd:YVO 4 CW beam of 532 nm (up to 100 mW cm ±2 ) while the visible transmission spectrum and absorbance at 365 nm are simultaneously recorded. The UV beam was near the peak absorption of the trans conformer of the Azo-LC and produced a discernable change in color ...

Phase-separated Al–Si films composed of Al nanocylinders embedded in an amorphous-Si matrix have been prepared by a sputtering method. By controlling the deposition rate, substrate temperature, and film composition, the average diameter of the Al cylinders can be varied systematically from less than 5to13nm with a cylinder density ranging from 1015 to in excess of 1016cylindersm−2. A three-dimensional simulation of phase separation in binary thin films was performed using a modified Cahn-Hilliard [J. Chem. Phys. 28, 258 (1958)] equation to understand the growth mechanism. The simulation studies indicate that the surface diffusion length and film composition are important factors which determine film morphology. Experimental and simulation studies are compared and discussed.

In recent years, there has been great interest in self-organized pattern systems, such as patterned structures of wellaligned rods embedded in a matrix. These systems have been important in many research fields since Turing [1] mathematically demonstrated that such pattern formation in reactiondiffusion systems could account for morphogenesis. Some examples are: the fish-skin textures seen in mathematical biology, [2] concentration patterns like the Belousov-Zhabotinsky reaction in chemical systems, [3] and the phase separation seen during the directional solidification of some inorganic alloy substances.[4] These patterns are created in nonlinear open systems with a diffusion factor, where substance injection and ejection are allowed. Well-aligned structures of phase-separated inorganic materials are particularly attractive for use in new devices and processes. Such materials can be classified into two systems: 1) one-directional solidification into bulk and 2) film growth in vacuum. These are nonlinear open systems as they accompany injection caused by melting or depositing substances, and accompany ejection caused by freezing substances in a plane of solidification. Various well-aligned structures with a micrometer scale like the NiAl-Mo, [5] NaCl-LiF, [6] MgO-CaF 2 , [7] and EuB 6 -ZrB 2 [8] systems have been created by using a one-directional solidification method. However, it is difficult to obtain nanometerscale structures in bulk systems by using this method. Film-growth methods have provided a successful means for synthesizing well-aligned nanometer-scale structures, which are sometimes smaller than that achievable by using lithography techniques. Fe-LaSrFeO 4 , [9] BaTiO 3 -CoFe 2 O 4 , [10] AlSi, [11,12] and Al-Ge [13] systems have already been examined by using conventional physical vapor-deposition (PVD) methods. These deposited films also consist of two phases. One phase forms well-aligned rods normal to the substrate and another phase forms a matrix. Because of the interaction of these two phases, new effects are expected in these nanometer-scale phase-separated materials. In addition, several silicides have been investigated as material candidates for next-generation semiconductor devices. [14] These silicides can create Schottky-barrier and p-n junctions with silicon or other silicides. [14,15,16] It has been reported that iron disilicide, in particular, has an absorption coefficient almost 100 times higher than silicon in the near-infrared region. [17] This indicates that these are promising materials for near-infrared detector devices. Our concept is to fuse the physical properties in each phase of the nanometer-scale phase-separated structures to create new detector devices and to display quantum effects from the interaction of each phase. If a narrow distribution of diameters and spacing of rods in these phase-separated films could be achieved, their physical properties would also be well-defined with low dispersion. In this Communication, we report the well-aligned structure formation in var...

The morphology of a phase-separated binary film during spinodal decomposition, whose evolution is limited on the growth surface, is studied. The temporal evolution of the Cahn-Hilliard equation without the elastic energy term under frozen bulk approximation is solved to investigate the possibility of well-aligned nanostructures. The model simulation showed that the well-aligned phase pattern on the top surface can be formed when surface diffusion length was optimized and film thickness was larger than a certain value. These simulation results highly agree with the experimental observation of phase-separated Al-Si films. An additional simulation study indicated that well-aligned nanowires can be prepared from the initial growth stage when an initial phase pattern given on the substrate matched the periodicity of the phase pattern of deposited films.

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