Deposition of GaN nanoparticles on the surface of a copper film under the action of electrostatic field during the femtosecond laser ablation synthesis in ammonia environment

In this article, we show the possibility for obtaining and deposition of gallium nitride nanoparticles under the action of femtosecond laser radiation. Using the developed setup for thermal vacuum deposition of copper on silicon plates, we obtained the thin-film substrates following by the deposition of gallium nitride on them. The gallium nitride was formed by applying the femtosecond laser radiation to the gallium targets in ammonia medium. The controlled collection of ablation products following by their removal from the processing area by means of electrostatic field was used in the setup in order to efficiently collect gallium nitride nanoparticles. The formation of gallium nitride nanoparticles is verified by the results of X-ray diffraction analysis.

Role of base strength, cluster structure and charge in sulfuric-acid-driven particle formation

In atmospheric sulfuric-acid-driven particle formation, bases are able to stabilize the initial molecular clusters and thus enhance particle formation. The enhancing potential of a stabilizing base is affected by different factors, such as the basicity and abundance. Here we use weak (ammonia), medium strong (dimethylamine) and very strong (guanidine) bases as representative atmospheric base compounds, and we systematically investigate their ability to stabilize sulfuric acid clusters. Using quantum chemistry, we study proton transfer as well as intermolecular interactions and symmetry in clusters, of which the former is directly related to the base strength and the latter to the structural effects. Based on the theoretical cluster stabilities and cluster population kinetics modeling, we provide molecular-level mechanisms of cluster growth and show that in electrically neutral particle formation, guanidine can dominate formation events even at relatively low concentrations. However, when ions are involved, charge effects can also stabilize small clusters for weaker bases. In this case the atmospheric abundance of the bases becomes more important, and thus ammonia is likely to play a key role. The theoretical findings are validated by cluster distribution experiments, as well as comparisons to previously reported particle formation rates, showing a good agreement.

Role of Base Strength, Cluster Structure and Charge in Sulfuric Acid-Driven Particle Formation

In atmospheric sulfuric acid-driven particle formation, bases are able to stabilize the initial molecular clusters, and thus enhance particle formation. The enhancing potential of a stabilizing base is affected by different factors, such as the basicity and abundance. Here we use weak (ammonia), medium strong (dimethylamine) and very strong (guanidine) bases as representative atmospheric base compounds, and systematically investigate their ability to stabilize sulfuric acid clusters. Using quantum chemistry, we study proton transfer as well as intermolecular interactions and symmetry in clusters, of which the former is directly related to the base strength and the latter to the structural effects. Based on the theoretical cluster stabilities and cluster population kinetics modeling, we provide molecular-level mechanisms of cluster growth and show that in electrically neutral particle formation, guanidine can dominate formation events even at relatively low concentrations. However, when ions are involved, charge effects can stabilize small clusters also for weaker bases. In this case the atmospheric abundance of the bases becomes more important, and thus ammonia is likely to play a key role. The theoretical findings are validated by cluster distribution experiments, as well as comparisons to previously reported particle formation rates, showing a good agreement.

Modification of Thin-Film Polymer Membranes by Microwave Radiation in Ammonia Medium

In this paper, we aimed to modify thin-film microfiltration membranes of nylon and polytetrafluoroethylene (PTFE) with ultrahigh-frequency (UHF) radiation within the decimeter wave band in ammonia vapor medium. It has been found that the treatment of a nylon membrane in ammonia leads to the membrane capacity decrease from 79% to 70.8% and to membrane weight decrease by 0.52%. And they observed the decrease of membrane weight by 0.24% from the original. In general, the treatment of membranes with microwave radiation in ammonia medium leads to specific productivity increase. They revealed the decrease of emulsion separation degree after the nylon membrane treatment by microwave radiation in ammonia environment. And when the oil emulsion is separated using PTFE-treated membranes, the degree of purification from oil increases by 3.6%, and the size of the separated oil particles also decreases from 118 nm to 49 nm.

Novel Method of Graphite Exfoliation

ABSTRACTThe paper describes a novel method of exfoliated graphite synthesis. The method includes synthesis of graphite intercalation compound in liquid ammonia medium and subsequent intercalate decomposition with graphite exfoliation. Influence of the experimental parameters on the morphology and structure of the exfoliated graphite is shown. Comparison of the developed exfoliation method to the high-temperature oxidation-reduction method used in industrial scale nowadays is presented. A number of application areas for the synthesized exfoliated graphite are described.

A Study of the Initial Stages of Co Deposition on a Silver Electrode in Ammonia Medium Using an Electrochemical Quartz Crystal Microbalance

The early stages of Co deposition on a silver electrode in ammonia medium were studied using cyclic voltammetry and chronoamperometry coupled with quartz crystal microbalance (EQCM) in ammonia solution. The results obtained by means of EQCM showed that during the initial stages of cobalt deposition a monolayer is formed on the substrate both in the underpotential and overpotential region, and this monolayer is formed at −600 mV and −980 mV. Once the cobalt deposition process starts, the growth is very fast making the investigation of the initial stages rather difficult. During this process, cobalt atoms transfer their two electrons through free species and not through cobalt hydroxide species adsorbed on the electrode as CoOH+ or Co(OH)2. In addition, it has been found that at potentials more positive than −600 mV, ammonia adsorption takes place on the substrate surface, and theses species are replaced when the cobalt atoms arrive at potentials more negative than −600 mV.

The Effect of Plastic Deformation on Nitrogen Diffusion in α-Fe

The surface diffusion layers formed in preliminary deformed (350 %) -Fe after nitriding at 853 K in ammonia medium were studied by means of metallography, electron microscopy, microhardness test and X-ray powder diffractometry. The preliminary plastic deformation (PPD) effects non-monotonously on the structure, microhardness and thickness of nitride - and -phases layers formed in -Fe. The narrow intervals of deformations of 3-8 % and 20-30 % were found in which the accelerated formation of nitride - and -phases occurs.