V. N. Nevolin

Ion-assisted deposition of MoSx films from laser-generated plume under pulsed electric field

The thickness profiles and compositional distributions of MoSx films deposited from a plume generated by pulsed laser irradiation of the MoS2 target were investigated at a varying fluence and constant laser pulse energy. It was shown that films with stoichiometric composition were formed at sufficiently low fluence (near the ionization threshold), and increasing fluence caused intricate nonmonotonic variations of the compositional distribution. A substantial deviation of the film composition from stoichiometric and a significant radial gradient of the sulfur concentration over the substrate surface (1<x<3, where x is the ratio of concentrations of S and Mo atoms, x=S/Mo) were found. These phenomena were caused by: (1) the incongruent target evaporation; (2) the mass dependence of the angular distribution of the ablated particles; and (3) the selective sulfur sputtering and desorption induced by energetic particles (ions, excited atoms) of the laser-generated plume. When the laser fluence was low, films of...

Pulsed laser deposition of MoSx films in a buffer gas atmosphere

Abstract The influence of a buffer (inert) gas atmosphere on structure, composition and tribological properties of MoSx films formed by pulsed laser deposition with various laser influence was investigated. The films were deposited at room temperature from an MoS1.8 target under vacuum conditions (4 × 10-4 Pa) and in Ar atmosphere at a gas pressure varying from 0.7 Pa to 4 Pa. Ablation under vacuum conditions using a relatively low laser fluence resulted in the deposition of amorphous films with conservation of stoichiometry. According to XPS analysis data, such films may contain many defects of chemical nature. Deposition at higher laser fluences resulted in substantial sulphur depletion and, under certain conditions, crystallization of the films. These microcrystalline films exhibited a lower friction coefficient than amorphous ones. Ablation at high laser fluences in Ar atmosphere allowed us to deposit MoSx films with various stoichiometries (x ⩽ 2.2) and tribological properties superior to those of the films deposited under vacuum conditions. These films have the amorphous structure and chemistry (according to XPS measurements) inherent in perfect MoS2.

Study and simulation of the growth of solid lubricant MoSe x coatings during pulsed laser deposition

The chemical composition and tribological properties of the thin-film diselenide molybdenum coatings deposited by pulsed laser deposition in vacuum and a rarefied inert gas (argon) atmosphere are studied. Upon deposition in a gas at a pressure of ∼2 Pa, stoichiometric coatings with improved antifriction properties as compared vacuum-deposited coatings form. However, a too strong increase in the argon pressure (to ∼10 Pa) degrades the tribological properties of the coating. Structure formation in the MoSex coatings grown by pulsed laser deposition on an unheated substrate is investigated. Deposition in vacuum or argon at a pressure of 2 Pa leads to formation of rather smooth coatings with a dense amorphous structure containing molybdenum nanoinclusions. Deposition at a high argon pressure results in a developed surface relief and a loose coating structure. A mathematical model is developed using the kinetic Monte Carlo method in order to describe structure formation in the coatings that grow during physical deposition of an atomic flux. A comparative analysis demonstrates satisfactory agreement between the simulated and experimentally studied structures in the coatings created by pulsed laser deposition at various gas pressures.

Energy and dose characteristics of ion bombardment during pulsed laser deposition of thin films under pulsed electric field

Experiments on pulsed laser deposition of Fe films on Si substrates were performed with the aim to analyze the role of factors determining the formation of an energy spectrum and a dose of ions bombarding the film in strong pulsed electric fields. The amplitude of the high-voltage pulse (−40kV) applied to the substrate and the laser fluence at the Fe target were fixed during the deposition. Owing to the high laser fluence (8J∕cm2) at a relatively low power (20mJ), the ionization of the laser plume was high, but the Fe vapor pressure near the substrate was low enough to avoid arcing. Electric signals from a target exposed to laser radiation were measured under different conditions (at different delay times) of application of electric pulses. The Si(100) substrates were analyzed using Rutherford ion backscattering∕channeling spectrometry. The ion implantation dose occurred to be the highest if the high-voltage pulse was applied at a moment of time when the ion component of the plume approached the substrate...

Photochemical removal of organic contaminants from silicon surface at room temperature

Using in situ x‐ray photoelectron spectroscopy we have investigated the possibility of photochemical organic contaminant removal from a silicon surface at room temperature in oxygen and fluorine containing atmospheres (O2, NF3/H 2, O2/NF3/H2). In contrast to UV irradiation in O2 and NF3/H2 reagents, the possibility of complete organic contaminant removal has been observed in O2/NF3/H2 gas mixture.

Peculiarities of Pulsed Ion Implantation from a Laser Plasma Containing Multiply Charged Ions

A mathematical model describing the dynamics of a pulsed laser plasma with multiply charged ions, as well as the formation of the accelerated ion flow in an external magnetic field, is developed. Experimental studies and mathematical simulation by the particle-in-cell method are used to determine the role of multiply charged ions in the process of ion implantation into a silicon substrate from the pulsed plasma containing singly and doubly charged titanium ions. The plasma spreads between parallel-plate electrodes (Ti target and Si substrate) along the normal to the surface of the target. Ions are accelerated by high-voltage negative pulses applied to the substrate. It is found that doubly charged ions effectively participate in the implantation process when an external electric field is applied very soon after the laser action on the target. The application of a high-voltage pulse with an amplitude of 50 kV 0.5 μs after a laser pulse leads to ion implantation with an energy close to 100 keV. With increasing delay in the application of the high-voltage pulse, the upper boundary of the energy spectrum of implanted ions is displaced towards lower energies. Comparison of the depth profiles of titanium distribution in silicon calculated from the results of simulation are compared with the experimental profiles shows that the model developed here correctly describes the formation of the high-energy component of the ion flow, which is responsible for defect formation and doping of deep layers of the substrate.

Combined photochemical processes for silicon technology: substrate cleaning, silicon dioxide deposition and annealing

Abstract A combination of low-pressure mercury lamp radiation-assisted processes for removal of carbon contaminants from the silicon substrate, SiO 2 chemical vapor deposition (CVD) from an Si 2 H 6 /O 2 mixture, and annealing of the deposited layers has been employed to fabricate dielectric-semiconductor structures with sufficiently good properties at low temperature (250°C) using gas-phase techniques only.

Application of Pulsed Laser Deposition in Reactive Gaseous Media to Fabricate an Effective Hybrid MoS x /WO y Catalyst for the Reaction of Hydrogen Evolution

To fabricate an electrocatalyst containing nanostructured layers of WOy and MoSx, a sequential formation of tungsten oxide and molybdenum sulfide thin films is performed by means of the pulsed laser deposition of W and Mo in low-pressure air and hydrogen sulfide media, respectively. The reactive medium pressure and the substrate (glassy carbon) temperature are varied during and after the deposition. WOy thin films of various morphologies and structures determining certain differences in their catalytic properties in the reaction of hydrogen evolution in acidic solutions are obtained. However, the catalytic efficiency of the obtained WOy nanoelements (spheres, needles, and sheets) with amorphous and crystalline structures appears to be insufficient. Additional deposition of MoSx with an amorphous structure results in a significant improvement of the catalytic properties. Sulfur atoms in the MoSx amorphous matrix cause the formation of catalytically active sites, while the developed surface of the WOy stimulates an increase in the catalyst total active area. Penetration of hydrogen effectively formed on MoSx into the bulk of thin films of WOy provides a crucial electrocatalysis condition—low current resistance in the support layer with a large exposed surface area.

The influence of the local atomic packing of thin MoS x films on their electrocatalytic properties in hydrogen reduction

We have studied the characteristics of the structure, composition, and electrocatalytic properties of thin MoSx films obtained by pulsed laser deposition using an Mo target ablated in H2S reactive-gas medium. The laser plume during deposition was directed tangentially and normally to the substrate, which allowed amorphous films to be obtained with different local atomic packings in an amorphous matrix consisting of Mo3–S clusters. It is established that the orientation of Mo3–S clusters influences charge transport in the catalyst and determines the type and surface density of catalytically active sites in the reaction of hydrogen evolution. For small, approximately equal amounts of Mo and Pt (~4 μg/cm2) laser-deposited on glassy carbon substrates, the MoSx films were inferior to a Pt film with respect to hydrogen overvoltage (by about 90 mV) in acid solution, but the efficiency of thin-film MoSx catalysts at elevated cathode potentials exceeded that of a thin Pt film.