Crystal orientation of epitaxial film deposited on silicon surface.

Direct growth of oxide film on silicon is usually prevented by extensive diffusion or chemical reaction between silicon (Si) and oxide materials. Thermodynamic stability of binary oxides is comprehensively investigated on Si substrates and shows possibility of chemical reaction of oxide materials on Si surface. However, the thermodynamic stability does not include any crystallographic factors, which is required for epitaxial growth. Adsorption energy evaluated by total energy estimated with the density functional theory predicted the orientation of epitaxial film growth on Si surface. For lower computing cost, the adsorption energy was estimated without any structural optimization (simple total of energy method). Although the adsorption energies were different on simple ToE method, the crystal orientation of epitaxial growth showed the same direction with/without the structural optimization. The results were agreed with previous simulations including structural optimization. Magnesium oxide (MgO), as example of epitaxial film, was experimentally deposited on Si substrates and compared with the results from the adsorption evaluation. X-ray diffraction showed cubic on cubic growth [MgO(100)//Si(100) and MgO(001)//Si(001)] which agreed with the results of the adsorption energy.

Diamond-like Carbon Patterning by the Submerged Discharge Plasma Technique via Soft Solution Processing.

Submerged plasma-assisted discharge direct patterning of diamond-like carbon (DLC) onto the silicon substrate in ambient conditions has succeeded as a new and novel soft solution process. In this environmentally benign technique, a copious amount of pure ethanol (ca. 4 mL) was locally activated with a maximum of ca. 0.23 mkWh by an as-electrochemically synthesized ultrasharp tungsten tip. With the assisted submerged plasma, the decomposed ethanol molecules are anodically patterned directly onto the silicon substrate in ambient conditions. The physical nature of DLC patterns was accessed by profilometry, atomic force microscopy, scanning electron microscopy, and transmission electron microscopy analysis. Furthermore, Fourier-transform infrared, Raman, and X-ray photoelectron spectra were analyzed for chemical compositions and structures, such as surface functionalization, carbon-carbon bonding, and sp2-sp3 ratio, respectively. From a Berkovich-configured nanoindentation analysis, Young's modulus and hardness have shown increasing trend with increasing sp3-sp2 ratio in DLC patterns of 68.5 and 2.8 GPa, respectively. From the electrochemical cyclovoltammetry analysis, a maximum areal specific capacitance of 205.5 µF/cm2 has been achieved at a scan rate of 5 mV/s. The one-step, green, and environmentally sustainable approach of rapid formation of DLC patterns is thus a promising technique for various carbon-based electrode fabrication processes.

Carbon clusters on substrate surface for graphene growth- theoretical and experimental approach.

Growth morphology of carbon clusters deposited on different substrates were investigated by theoretical and experimental approach. For theoretical approach, molecular dynamics was employed to evaluate an adsorptive stability of different size of carbon clusters placed on different substrates. The adsorptive stability was estimated by the difference of total energy of supercell designed as carbon cluster placed on a certain crystal plane of substrate. Among the simulations of this study, carbon cluster flatly settled down on the surface of SrTiO[Formula: see text](001). The result was experimentally verified with layer by layer growth of graphene by pulsed laser deposition in carbon dioxide atmosphere. The absorptive stability can be useful reference for screening substrate for any target material other than graphene.

Revisiting the valence stability and preparation of perovskite structure type oxides ABO3 with the use of Madelung electrostatic potential energy and lattice site potential.

Valence stability of aliovalent ions is mostly correlated with lattice site potential in ionic crystals. Madelung electrostatic potential is obtained by adding all the lattice site potentials for all the ions present in a crystal structure. Therefore, valence stability and the stability of a crystal structure can be better understood with consideration of both the lattice site potential and Madelung electrostatic potential. This was first demonstrated more than four decades ago by one of the present authors. We revisit this situation by using re-calculated lattice site potential and Madelung electrostatic potential for perovskite structure type ABO3 compounds using a new computer program VESTA. We show that the formation of a perovskite structure type compound with the general formula ABO3 (where A and B are cations and O is an oxide ion) becomes energetically favorable when it has a higher Madelung electrostatic potential than the combined Madelung electrostatic potential of parent binary compounds AO and B2O3 or BO2. It is further shown that strong lattice site potential results in stability of high valence or high valence ions can be stabilized in a lattice site with strong lattice-site potential. It further follows that certain ions experience maximum lattice site potential at the B ion lattice site of the perovskite structure when compared to other structures such as fluorite BO2, rutile BO2 and corundum B2O3. Therefore, (i) the stability of an ion with a high (and uncommon) valence state at the B site being higher than that at the A site, (ii) occurrence of point defects at A or O sites with weak lattice site potentials, respectively and (iii) instability of perovskite A4+B2+O3, and A5+B1+O3 compounds, respectively can be rationalized by lattice site potential and Madelung electrostatic potential analysis.

Sol-gel preparation of low oxygen content, high surface area silicon nitride and imidonitride materials.

Reactions of Si(NHMe)4 with ammonia are effectively catalysed by small ammonium triflate concentrations, and can be used to produce free-standing silicon imide gels. Firing at various temperatures produces amorphous or partially crystallised silicon imidonitride/nitride samples with high surface areas and low oxygen contents. The crystalline phase is entirely α-Si3N4 and structural similarities are observed between the amorphous and crystallised materials.

Water-splitting electrocatalysis in acid conditions using ruthenate-iridate pyrochlores.

The pyrochlore solid solution (Na(0.33)Ce(0.67))2(Ir(1-x)Ru(x))2O7 (0≤x≤1), containing B-site Ru(IV) and Ir(IV) is prepared by hydrothermal synthesis and used as a catalyst layer for electrochemical oxygen evolution from water at pH<7. The materials have atomically mixed Ru and Ir and their nanocrystalline form allows effective fabrication of electrode coatings with improved charge densities over a typical (Ru,Ir)O2 catalyst. An in situ study of the catalyst layers using XANES spectroscopy at the Ir L(III) and Ru K edges shows that both Ru and Ir participate in redox chemistry at oxygen evolution conditions and that Ru is more active than Ir, being oxidized by almost one oxidation state at maximum applied potential, with no evidence for ruthenate or iridate in +6 or higher oxidation states.

Escape from the destruction of the galvanic replacement reaction for solid → hollow → solid conversion process in one pot reaction.

Based on the difference in the redox potentials between two metal species, the galvanic replacement reaction is known to create an irreversible process to generate hollow nanostructures in a wide range of shapes. In the context of galvanic replacement reaction, continuing etching leads to the general collapse of the hollow structures because of the excess amount of oxidizing agent. We demonstrate the growth of solid nanostructures from a hollow frame-like architecture in the course of a galvanic replacement reaction without any morphology destruction. We report the successful composition transformation of solid Ag with a wide range of shapes, such as plate, decahedron, rod, prism, sphere, and foil, from as thin as <10 nm up to 5 µm and with an area of ∼4 mm(2), to their solid Au counterparts using straightforward chemical reactions. The successful conversion process relies on a decrease in the reduction rate of the metallic precursor to initiate dissolution of Ag in the first stage (a galvanic replacement reaction), then a subsequent backfilling of Au into the hollowed-out structures. Cetyltrimethylammonium bromide (CTAB) surfactant, a key parameter, interacts with metal salt precursor to form a complex species that retards metal reduction. In addition, we demonstrate conversion of solid nano-Ag to solid nano-Pd as well as of Cu foil (10 µm thick) to shiny Au foil.

Structural, spectroscopic, magnetic and electrical characterization of Ca-doped polycrystalline bismuth ferrite, Bi(1-x)Ca(x)FeO(3-x/2) (x ≤ 0.1).

The crystal structure and physical properties of multiferroic polycrystalline Ca(2+)-doped BiFeO(3) samples have been investigated. The present experimental investigation suggests that Bi(1-x)Ca(x)FeO(3-x/2) (x ≤ 0.1) can be considered as a solid solution between BiFeO(3) and CaFeO(2.5). The oxidation state of Fe in these materials is + 3 and charge balance occurs through the creation of oxygen vacancies. For each composition, two structural phase transitions are revealed as anomalies in the variable-temperature in situ x-ray diffraction data which is consistent with the well-established high-temperature structural transformation in pure BiFeO(3). All compositions studied show antiferromagnetic behaviour along with a ferromagnetic component that increases with Ca(2+) doping. The resistivities of the Bi(1-x)Ca(x)FeO(3-x/2) samples at room temperature are of the order of 10(9) Ω cm and decrease with increasing Ca(2+) content. Arrhenius plots of the resistivity show two distinct linear regions with activation energies in the range of 0.4-0.7 and 0.03-0.16 eV. A correlation has been established between the critical temperatures associated with the structural phase transitions and the multiferroic properties. A composition of x = 0.085 is predicted to show maximum magneto-electric coupling.