Temperature dependent resistivity of platinum-carbon composite nanowires grown by focused ion beam on SiO2/Si substrate

Experimental studies of the temperature dependent resistivity of platinum nanowires grown on an oxidised silicon wafer by using focused ion beam (FIB) have been made. A series of 4-terminal resistivity measurements were carried out in the temperature range 50-300 K on single nanowires of width and thickness ∼100 nm grown by decomposition of an organometallic precursor using Ga⁺ ions of different accelerating voltages from 10 keV to 30 keV. Energy dispersive X-ray spectroscopy showed the nanowires to be composed of more than 60% by volume of carbon, the remainder being principally platinum and gallium. The exact composition depends on the accelerating voltage of the ions used. There is clear evidence from cross-sectional microscopy that the material is a composite consisting of a metallic phase present in the form of nanoscale clusters, randomly distributed in a matrix of carbon. Electrical measurements are consistent with this, showing a critical volume concentration for conduction, which is typical of electron transport in composites with percolating metal phase. Results show an unexpectedly high sensitivity of the temperature dependence of resistivity near the critical volume concentration, which has been explained to arise from thermal strain effects. The anomalous temperature/strain effects observed in this investigation might be exploited in temperature measurement and strain sensor applications.     

Regional approach to model charges and capacitances of intrinsic carbon nanotube field effect transistors

Estimation of total channel charge (Q _Tot ) of carbon nanotube field effect transistor from the self-consistently computed charge density (Q _Top ) at the top of conduction band subband minima, is found to be inaccurate. A regional approach based on extended ballistic transport theory is proposed to model Q _Tot , and its partitioning into source and drain components. The models for charges and subsequently derived capacitances are validated with the numerically simulated data obtained using semi-classical technique. The model agreement with numerical data shows the superiority of our regional approach compared to ones obtained from only the information of Q _Top .     

A semianalytic meshless approach to the transient Fokker–Planck equation

In this paper, a semianalytic partition of unity finite element method (PUFEM) is presented to solve the transient Fokker–Planck equation (FPE) for high-dimensional nonlinear dynamical systems. Meshless spatial discretization of PUFEM with local p$p$-refinement (discussed in a previous paper) is employed to develop linear ordinary differential equations for the time varying coefficients of local shape functions. A similarity transformation to modal coordinates is shown to reveal numerous spurious modes in the eigenspace of the discretized FPE operator. Identification and elimination of these modes leads to an analytical solution of ODEs obtained from spatial discretization in terms of the remaining admissible modes, and a significant reduction in the size of the discretized transient problem. Initial equation error resulting from the set of admissible modes is shown to be an upper bound for all time, meaning that the reduced admissible set is sufficient for the FPE approximation for all time.     

Finite difference solution for circular plates on elastic foundations

In the present work the authors have developed a finite difference method of analysis for any circular plate with any kind of loading on semi-infinite elastic foundations. No assumption regarding the contact pressure distribution has been made. The equations have been developed in non-dimensional form and also the results have been obtained in non-dimensional form. These results have been compared with the available experimental results and the agreement between them is found to be much better than that of the previous works. The same method with slight modification can be applied for Winkler type foundations and problems of circular plates with varying thickness.     

Improved AMBER torsional parameters for the N-N rotational barrier in diacylhydrazines

The structure and rotational barrier for substituted diacylhydrazines are of significant interest given the role this functionality plays in peptidomimetics and ecdysone agonists, the latter of which have application as extremely selective insecticides. Ab initio calculations show that the lowest energy conformations are typically nonplanar with essentially perpendicular nitrogen lone pairs. Molecular mechanics calculations using the AMBER* force field in MacroModel yield minima and rotational barriers that are both quantitatively and qualitatively inconsistent with the ab initio results. In this work the AMBER* N-N rotational barriers for all configurations of the parent, methyl and di-methyl substituted diformylhydrazines have been fitted to MP2/6-31+G** relative energies. The resulting AMBER* torsional parameters have been validated by calculating the rotational barriers for N-t-butyl substituted diformylhydrazine, dibenzoylhydrazine and an azadipeptide. In each case the new AMBER* rotational barriers compare favorably with the corresponding MP2 calculated rotational barriers.     

Kaolinite–Mullite Reaction Series: The Development and Significance of a Binary Aluminosilicate Phase

The semiquantitative estimations of 980°C exothermic reaction products of kaolinite by quantitative X-ray diffraction (QXRD) and chemical leaching techniques show the formation of a significant amount of amorphous aluminosilicate phase (∼ 30 to 40 wt%). The theoretically expected AlO₄/AlO₆ ratio in the 980°C reaction is in close agreement with the value measured by the X-ray fluorescence (XRF) technique and the experimental radial electron distribution (RED) profile agrees with the suggested 980°C formation of Si-Al spinel with mullite-like composition. Mullitization of kaolinite has been compared with a synthetic Al₂O₃—SiO₂ mixture. In synthetic mixtures development of an intermediate amorphous aluminosilicate phase is an essential step prior to mullitization. Kaolinite forms mullite in two ways: (i) by polymorphic transformation of cubic mullite at 1150° to 1250°C and (ii) by nucleation of mullite in the amorphous aluminosilicate phase and its subsequent growth above 1250°C. Thus chemical continuity is maintained throughout the reaction series and the intermediate spinel phase is silicon bearing and its subsequent transformation to mullite confirms the topotactic concept in the kaolinite transformation.     

Phase Separation and Structural Differences between Alkali Silicate Glasses Prepared by the Sol-Gel and Melt-Quench Methods

Glasses of composition x M₂O:(1- x )SiO₂ [M = Na, Li] with x = 0.15 and 0.2 have been prepared both by the melt-quench and the sol-gel methods. X-ray photoelectron spectroscopy shows that with increasing sintering temperature the structure of gels approaches that of the melt-quench glass but does not become identical even on heating above the glass transition temperature ( T _g). Phase separation occurs in gel much below T _g, and before it evolves into the structure of melt-quench glass. Thus phase separation is achieved more readily in sintered gels than in the corresponding melt-quench glass.