Synthesis of Carbon Particles using Laser Ablation in Ethanol

AbstractCarbon particles were synthesized via laser ablation of a bulk graphite in ethanol medium using Nd:YAG laser with a wavelength of 1064nm. The target was irradiated by the laser beam with a pulse energy of 3J, a pulse repetition rate of 2Hz, and a pulse duration of 5ms. Effect of using ethanol as a liquid medium for laser ablation on physical, chemical, and optical properties of resulted carbon particles was reported. SEM images presented that a flake-like morphology of graphite in the target has been transformed into a flower-like cluster after the ablation. Raman measurement showed that G peak position of the graphite flakes and that of the synthesized carbon particles were similar, about 1582cm-1, whereas D peak position and its shape of the synthesized particles was different from those of graphite flakes. UV-visible and fluorescent spectrometers were used to investigate absorption and emission characteristics of the particles, respectively. The carbon particles can absorb a light in the UV range and emit a photoluminescence of bright blue-green color

Raman Spectroscopy of DLC/a-Si Bilayer Film Prepared by Pulsed Filtered Cathodic Arc

DLC/a-Si bilayer film was deposited on germanium substrate. The a-Si layer, a seed layer, was firstly deposited on the substrate using DC magnetron sputtering and DLC layer was then deposited on the a-Si layer using pulsed filtered cathodic arc method. The bilayer films were deposited with different DLC/a-Si thickness ratios, including 2/2, 2/6, 4/4, 6/2, and 9/6. The effect of DLC/a-Si thickness ratios on the sp3 content of DLC was analyzed by Raman spectroscopy. The results show that a-Si layer has no effect on the structure of DLC film. Furthermore, the upper shift in G wavenumber and the decrease in ID/IG inform that sp3 content of the film is directly proportional to DLC thickness. The plot modified from the three-stage model informed that the structural characteristics of DLC/a-Si bilayer films are located close to the tetrahedral amorphous carbon. This information may be important for analyzing and developing bilayer protective films for future hard disk drive

Growth of Silver Nanoparticles by DC Magnetron Sputtering

Silver (Ag) nanoparticles are of great interest for many applications. However, their fabrications have been limited by the synthesis methods in which size, shape, and aggregation are still difficult to control. Here, we reported on using direct current (DC) magnetron sputtering for growing Ag nanoparticles on unheated substrates. Effects of sputtering condition on grain size of Ag nanoparticle were discussed. At constant sputtering current and deposition time, the average sizes of Ag nanoparticles were 5.9 ± 1.8, 5.4 ± 1.3, and 3.8 ± 0.7 nm for the target-substrate distances of 10, 15, and 20 cm, respectively. The morphology evolution from nanoparticles to wormlike networks was also reported. High-resolution transmission electron microscopy image represented clear lattice fringes of Ag nanoparticles with a d-spacing of 0.203 nm, corresponding to the (200) plane. The technique could be applied for growth of nanoparticles that were previously difficult to control over size and size uniformity

Heterogeneous Nucleation of Protein Crystals on Fluorinated Layered Silicate

Here, we describe an improved system for protein crystallization based on heterogeneous nucleation using fluorinated layered silicate. In addition, we also investigated the mechanism of nucleation on the silicate surface. Crystallization of lysozyme using silicates with different chemical compositions indicated that fluorosilicates promoted nucleation whereas the silicates without fluorine did not. The use of synthesized saponites for lysozyme crystallization confirmed that the substitution of hydroxyl groups contained in the lamellae structure for fluorine atoms is responsible for the nucleation-inducing property of the nucleant. Crystallization of twelve proteins with a wide range of pI values revealed that the nucleation promoting effect of the saponites tended to increase with increased substitution rate. Furthermore, the saponite with the highest fluorine content promoted nucleation in all the test proteins regardless of their overall net charge. Adsorption experiments of proteins on the saponites confirmed that the density of adsorbed molecules increased according to the substitution rate, thereby explaining the heterogeneous nucleation on the silicate surface

Confinement increases the lifetimes of hydroxyapatite precursors

The mineral component of bone is a carbonated, nonstoichiometric hydroxyapatite (calcium phosphate) that forms in nanometer confinement within collagen fibrils, the principal organic constituent of bone. We here employ a model system to study the effects of confinement on hydroxyapatite precipitation from solution under physiological conditions. In common with earlier studies of calcium carbonate and calcium sulfate precipitation, we find that confinement significantly prolongs the lifetime of metastable phases, here amorphous calcium phosphate (ACP) and octacalcium phosphate (OCP). The effect occurs at surprisingly large separations of up to 1 μm, and at 0.2 μm the lifetime of ACP is extended by at least an order of magnitude. The soluble additive poly(aspartic acid), which in bulk stabilizes ACP, appears to act synergistically with confinement to give a greatly enhanced stability of ACP. The reason for the extended lifetime appears to be different from that found with CaCO3 and CaSO4, and underscores both the variety of mechanisms whereby confinement affects the growth and transformation of solid phases, and the necessity to study a wide range of crystalline systems to build a full understanding of confinement effects. We suggest that in the case of ACP and OCP the extended lifetime of these metastable phases is chiefly due to a slower transport of ions between a dissolving metastable phase, and the more stable, growing phase. These results highlight the potential importance of confinement on biomineralization processes