Solid State Phenomena Vols. 121-123

Abstract: This work describes the combination of photolithography and self-assembly methods for fabrication of 3D photonic crystals (PCs) with well-defined micron-scale line defects embedded in the PCs. Line defects with different dimensions, shapes, and compositions have been introduced into the 3D PCs by choosing different photoresists, masks, and template-directed assembly techniques. Infiltration of carbon using high-temperature chemical vapor deposition (CVD) technique showed that the fabrication procedure offers an ideal approach to functional 3D photonic devices from self-assembled photonic crystals.

Abstract: Highly ordered rods of large-pore periodic mesoporous organosilica (PMO) were successfully synthesized at low acid concentrations and in the presence of inorganic salt using triblock copolymer P123 as template. The roles of inorganic salt, acidity and temperature in the production of highly ordered mesostructure and the morphology control of PMOs were examined and elucidated. It was found that the addition of inorganic salt can dramatically widen the range of the synthesis parameters to produce highly ordered 2D hexagonal pore structure of p6mm symmetry. However, the uniform rods of PMOs can only be synthesized in a narrow range of acid and salt concentrations, which was sensitive to induction time. The results also showed that the optimized salt concentration (1 M) and low acidity (0.167 M) at 40 oC were beneficial to not only the production of highly ordered mesostucture but also the control of rod-like morphology. Highly ordered rods can also be produced at low temperature (35 oC) with high salt amount (1.5 M) or high temperature (45 oC) with low salt concentration (0.5 M).

Abstract: In this paper, the corrosion phenomenon occurred on the polycrystalline gold substrates has been for the first time observed by in situ quartz crystal microbalance (QCM) method for adsorption of alkanethiol monolayers, which may be attributed to thiol-induced dissolution of gold during the adsorption process in the presence of oxygen. It is evident from the image of many corrosive defects or holes produced on the surface of gold grains by using atomic force microscopy (AFM). The kinetic equation on corrosion rate of gold dissolved in the organothiol solution has been obtained. The gold corrosion rate at fast stage can be estimated to be 9.2 × 1011 Au atoms cm-2 s-1.

Abstract: Pentacene channel for organic thin film transistor was deposited on the SiOC film by thermal evaporation. The growth of pentacene is related with the Diels-Alder reaction and the nucleophilic reaction by the thermal induction. The surface is an important factor to control the recursive Diels-Alder reaction for growing of pentacene on SiOC film. The terminal C=C double bond of pentacene molecule was broken easily as a result of attack of the nucleophilic reagents on the surface of SiOC film. The nucleophilic reaction can be accelerated by increasing temperature on surface, and it making pentacene to grow hardly on the SiOC film with a flow rate ratio of O2/(BTMSM+O2)=0.5 due to its inorganic property. The nucleophlic reaction mechanism is SN2 (bimolecular nucleophilic substitution) type.

Abstract: InAs lateral quantum dot molecules (QDMs) are grown on (001)-GaAs substrates. The self-assembled QDMs are formed in one continuous molecular beam epitaxial (MBE) growth via a thin-capping-and-regrowth technique. Lateral QDMs, each with 10-12 dots arranged in a specific pattern, are determined by the shapes of the underlying nanopropeller quantum dots (QDs). The nanopropeller QDs in turn are obtained by regrowth on nano-holes which have been previously created by capping the first InAs QD layer grown on (001)-GaAs substrate with a thin GaAs layer. The length of the propeller directly influences the number of QDs in a QDM. By varying the conditions for thin-capping, shorter or longer propellers can be achieved, allowing the number of QDs in each QDM to be controlled.

Abstract: In this study, the molecular dynamics is employed to simulate the selfassembly of crossed gold nanowires at various temperatures. The nanowires with a multi-shell helical (HMS) structure are different from those of the bulk FCC structure. This work compares the morphology of crossed HMS nanowires with 7-1 structure after self-assembly and investigates the atom motion trajectory on the joint. The structure transform are observed from helical structure to FCC structure by angular correlation function (ACF). The results can be suggested for a nano-scale circuit design.

Abstract: Through self-assembly monolayer surface treatment, metal oxide nanoparticles uniformly dispersed onto carbon nanotubes (CNTs) surface are investigated. At first, oxidation treatment was performed to increase O/C ratio of CNTs surface at 250°C for 1 hr under an oxygen atmosphere. X-ray photoelectron spectroscopy (XPS) analysis shows that O/C ratio is a increasing function of oxidating time. Distribution of oxygen functional groups on CNTs surface, i.e., carboxyl, carbonyl, phenolic groups, can be identified and deconvoluted by a symmetrical Gauss function. Experiments indicate that heat time for 5hr can produce a greater O/C ratio on CNTs surface. It is observed that carboxyl groups acts an important role to link with metal ions via an ionic interaction, thus, forming a monolayer adsorption on CNTs surface. By heating the treated CNTs, a completely composite nanostructure is thus formed. In the present work, we successfully fabricate three kinds of nanoparticles including SnO2, and RuO2, with an average diameter of 5-10 nm coated on the CNTs.

Abstract: Long erbium disilicide nanowires were fabricated through laser ablation and annealing process on the Si (001) surface. The ErSi2 nanowires were along the perpendicular Si <110> directions. The average width of nanowires is less than 10nm and the maximum length is more then 10um. The electrical transport properties of the ErSi2 nanowires were measured and a resistivity value of 1.87×10-6Ωm was acquired. These self-assembled Si-based nanowires could be used for further devices applications.

Abstract: This work explores an estimation of adsorptive surface coverage for carbon tetrachloride onto different carbon nanofibers (CNFs). Two kinds of CNFs with various pore characteristics are fabricated by template-based and thermal chemical vapor deposition methods, respectively. The pore size distributions of these carbons, determined according to the density functional theory model, are found to vary with synthesis methods. The results of adsorption experiments show that CCl4 adsorption isotherms of these CNFs are of Langmuir-type model during the restricted pressure of 0–0.2 atm at 30°C. The surface coverage capable of adsorbing CCl4 molecules onto the CNFs can be determined based on the monolayer adsorption model. Interestingly, the CCl4 capacity of these CNFs does not proportionally increase with their specific surface area, and the CNFs with more micropore fraction facilitate the adsorptive surface coverage. This finding attributes to a fact that micropores in the CNFs have stronger adsorption energies, thus, become a major provider for carbon tetrachloride adsorption.

Abstract: Well-defined block copolymers consisting of a hydrophilic poly (ethylene oxide) (PEO) and lipophobic poly (1H,1H-perfluorooctyl methacrylate) (PFOMA) were synthesized with controlled molecular weight via atom transfer radical polymerization (ATRP). The block copolymers formed stable micelles where PEO is the shell and PFOMA is the core in chloroform. The micellar morphology of PEO5K-b-PFOMA5K was found to be spherical with average diameter of ca. 12 nm, while meandering cylindrical with average diameter of ca. 13 nm was observed for PEO5K-b-PFOMA13K by TEM analysis. The self-assembled structures were reorganized to thermodynamically stable morphologies upon annealing above glass transition temperature (Tg). For example, spherical shape of PEO5K-b-PFOMA5K and cylindrical domain of PFOMA block in PEO5K-b-PFOMA5K became ordered cylindrical and continuous phase, respectively.