A novel high power symmetric ZnO/carbon aerogel composite electrode for electrochemical supercapacitor

We present, for the first time, a new material of symmetric electrochemical supercapacitor in which zinc oxide (ZnO) with carbon aerogel (CA) was used as active material. Physical properties of ZnO/CA composite were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). It was found that ZnO has single hexagonal structure and the grain size increases with increase of ZnO compository. The result of cyclic voltammetry indicates that the specific capacitance of ZnO/CA composite in 6 M KOH electrolyte was approximately 25 F/g at 10 mV/s for 2:1 composition. AC impedance analysis reveals that ZnO with carbon aerogel powder enhanced the conductivity by reducing the internal resistance. Galvanostatic charge/discharge measurements were done at various current densities, namely 25, 50, 75, and 100 mA/cm². It was found that the cells have excellent electrochemical reversibility and capacitive characteristics in KOH electrolyte. The maximum capacitance of the ZnO/CA supercapacitor was 500 F/g at 100 mA/cm². It has been observed that the specific capacitance is constant up to 500 cycles at all current densities, which implies that the dendrite formation was controlled.     

Equations describing molecular-motor-assisted transport in dendrites with a non-uniform cross-sectional area

The purpose of this paper is to develop new transport equations describing transport of intracellular organelles by a combined effect of diffusion and molecular-motor-driven transport in dendrites of neuron cells that have a non-uniform cross-sectional area which depends on the distance from the neuron soma. The obtained equations are solved numerically for two types of microtubule (MT) orientations that are experimentally found in dendrites. In one type of dendrites, which is found in cultured rat hippocampal neurons, MTs have a mixed polarity orientation while in the second type, which is found in Drosophila neurons, MTs have the minus-end-out polarity orientation. Simulations show important differences in organelle transport in these two types of dendrites. The conclusion is that the MT orientation has a profound effect on the total rate of organelle transfer toward the growth cone of a dendrite and consequently determines its growth potential and its growth rate.     

Preparation of rod-like Sb2S3 dendrites processed in conventional hydrothermal

Large-scale rod-like antimony sulfide (Sb₂S₃) dendrites have been prepared by hydrothermal method using antimony chloride (SbCl₃), citric acid and thioacetamide as raw materials at 160 °C for 12 h. The powder X-ray diffraction pattern shows the Sb₂S₃ crystals belong to the orthorhombic phase with calculated lattice parameters a = 1.120 nm, b = 1.128 nm and c = 0.3830 nm. The quantification of energy dispersive X-ray spectrometry analysis peaks gives an atomic ratio of 2:3 for Sb:S. Transmission electron microscopy micrograph studies reveal the appearance of the as-prepared Sb₂S₃ is dendrites-like which is composed of nanorods with the typical width of 300-500 nm and length of 5-20 µm. Finally the influences of the reaction conditions are discussed and a possible mechanism for the formation of rod-like Sb₂S₃ dendrites is proposed.     

Investigations on the corrosion of copper patterns in the course of the “post-CMP cleaning” of integrated electronic microcircuits in oxalic acid aqueous solutions

An unknown corrosion process producing dendrites was recently found to take place at copper patterns immersed in oxalic acid aqueous solutions in the course of the post-chemical-mechanical polishing of integrated microcircuits (ICs). We report here investigations of this corrosion phenomenon in ICs using atomic force microscopy (AFM), cyclic voltammetry and Raman spectroscopy. AFM first allowed an accurate morphological characterisation of the copper patterns and their surroundings while cyclic voltammetry was used to identify their electrochemical reactivity in oxalic acid aqueous solutions. In situ AFM experiments carried out in this same aqueous media in open circuit conditions unambiguously showed a progressive and partial dissolution of copper patterns as well as the formation of a ring type structure. Raman spectroscopy was used on gold supported electrogenerated copper films to identify the precipitation or adsorption products resulting from the electrochemistry of the copper/oxalic acid system as a function of the applied potential and the pH of the oxalic acid aqueous solutions. The collected results rather suggest a two-step galvanic corrosion phenomenon involving the tantalum barrier, copper seed layer and electrodeposited copper.     

Dendrite‐Assisted Growth of Silicon Nanowires in Electroless Metal Deposition

This article concerns the detailed investigations on the silver dendrite‐assisted growth of single‐crystalline silicon nanowires, and their possible self‐assembling nanoelectrochemistry growth mechanism. The growth of silicon nanowires was carried out through an electroless metal deposition process in a conventional autoclave containing aqueous HF and AgNO₃ solution near room temperature. In order to explore the mechanism and prove the centrality of silver dendrites in the growth of silicon nanowires, other etching solution systems with different metal species were also investigated in this work. The morphology of etched silicon substrates strongly depends upon the composition of the etching solution, especially the metal species. Our experimental results prove that the simultaneous formation of silver dendrites is a guarantee of the preservation of free‐standing nanoscale electrolytic cells on the silicon substrate, and also assists in the final formation of silicon nanowire arrays on the substrate surface.     

Effect of medium-density direct current on dendrites of directionally solidified Pb–50Sn alloy

This paper investigated the effect of coupling of direct current (DC) and pulling rate on dendrites and cooling behaviours of directionally solidified Pb–50Sn alloy. Experimental results indicated that the secondary dendritic arm spacing (SDAS) decreased and temperature gradient increased as increasing current densities. Moreover, temperature rise and SDAS under positive DC were higher than those under negative DC. It was speculated that Joule heating and electromigration were obviously induced by the present DC. The effect of DC on the microstructure and solidification parameters was weakened as the pulling rate increases. The coarsening rate reduced from tf^1/3 toward a value of tf^0.29 when DC of ±200?A?cm^–2 were applied. The refinement mechanism of SDAS was discussed.     

Pattern formation in solidification

Regular patterns form in many solidification processes. Examples occur during lamella and rod-like eutectic growth and when single-phase cells or dendrites are formed. The scale and regularity of the microstructure can determine the properties of the cast materials and is thus important practically. The purpose of the present paper is to show that common features occur in all processes.

Steady-state analysis indicates that a wide range of possible spacings could occur during eutectic, cellular or dendritic growth. The degree of freedom is removed by considering the mechanism determining the minimum and maximum spacing on a specimen. It is found that the minimum spacing occurs when the array first becomes stable for a lamella or rod-like eutectic, for cell growth and for some dendrites. For low temperature gradient, high-velocity dendrites, the minimum spacing is determined by thespacing when the dendrites irst become near enough to interact. The maximum spacing for eutectics andfor cells is determined by tip splitting. The maximum spacing for dendrites occurs when a tertiary arm becomes a new primary. Good agreement is obtained between theory and experiment using this approachto predict spacing limits. The average spacing on a specimen can approach either limit depending o past history. The two extreme spacings are found to span the spacing of the minimum undercooling foreutectic and cellular growth and this allows an average spacing to be estimated using a single condition.

It is concluded that three conditions are necessary to form regular structures. A mechanism must exist to eliminate members of the array when the spacing is too small. A mechanism must exist to form new members of the array when the spacing is too wide. The structure must be stable to fluctuations in the range of spacing between the two limits.