arXiv subjects

Yuri Barsukov

Publications and source records attributed to Yuri Barsukov.

10 recordsLinked to original sources

arXiv2026

Transition Metal Dichalcogenide MoS${}_2$: oxygen and fluorine functionalization for selective plasma processing

Low-temperature plasma processing is a promising technique for tailoring transition metal dichalcogenides (TMDs). For chalcogen substitution processing, a key challenge is to identify the ion energy window that enables selective chalcogen removal while preserving the metal lattice. Using ab-initio molecular dynamics (AIMD), we demonstrate that oxygen and fluorine functionalization widen the processing window by significantly lowering the sulfur sputtering energy threshold ($E_{\text{sputt,S}}$) of MoS${}_2$ from $\sim 30$ eV to $\sim 10$ eV via formation of sputtering products such as SO${}_2$ and SF${}_n$. Additionally, we show that experimentally relevant cryogenic temperatures strongly affect $E_{\text{sputt,S}}$. The dependence is confirmed via AIMD and also predicted by a mechanistic parameter-free theory, suggesting that $E_{\text{sputt}}(T)$ generalizes to other TMDs, functionalization, and surface impacts in general. Our results highlight oxygen/fluorine functionalization, ionic impact angle, and material temperature to be key control parameters for selective, damage-controlled chalcogen removal in TMD processing.

cond-mat.mtrl-sci↗

arXiv2025

Mechanisms of inductively coupled BCl3-plasma interaction with the GaN surfaceMechanisms of inductively coupled BCl3-plasma interaction with the GaN surface

Consideration is given to inductively coupled BCl3-plasma (ICP) treatment of the GaN surface, which is a promising technique to get the low resistance ohmic contacts in GaN-based transistors. In some cases, BCl3 plasma treatment results in ohmic contact degradation because BClx radicals tend to form a polymer thin film BxCly on the surface. In the present work, the mechanisms of BCl3 plasma interaction with the GaN surface are considered. Threshold ion energies of reactive ion etching for polymer BxCly and semiconductor GaN, respectively, are estimated using numerical plasma modeling. It has been demonstrated that a plasma treatment regime without polymer deposition and reactive etching is possible when an ion energy is in the range ~32-60 eV.

physics.chem-ph↗

arXiv2025

Size-dependent second-order-like phase transitions in Fe nanocluster melting from low-temperature structural isomerization

In this work, the melting phase transitions of $Fe_{n}$ nanoclusters with $10 \leq n \leq 100$ atoms are investigated using classical many-body molecular dynamics simulations. For many cluster sizes, surface melting occurs at much lower temperatures than core melting. Surface and core melting points, and energetic melting points (temperatures of maximum heat capacity, $C_v$) are calculated for all cluster sizes. Melting properties are found to be strong functions of cluster structure. Cluster sizes with closed-shell structures always have first-order-like phase transitions. Almost one-third of cluster sizes in the analyzed range exhibit second-order-like phase transitions due to the presence of multiple structural configurations close in energy. 1-shell clusters with one to a few more atoms than a neighboring closed-shell structure have very low surface melting points and very high energetic melting points compared to their closed-shell counterparts. In clusters above 50 atoms with certain core structures, melting of the surface before the core was observed.

physics.atm-clus↗

arXiv2024

Gibbs free energies of Fe clusters can be approximated by Tolman correction to accurately model cluster nucleation and growth

Accurate Gibbs free energies of Fe clusters are required for predictive modeling of Fe cluster growth during condensation of a cooling vapor. We present a straightforward method of calculating free energies of cluster formation using the data provided by molecular dynamics (MD) simulations. We apply this method to calculate free energies of Fe clusters having from 2 to 100 atoms. The free energies are verified by comparing to an MD-simulated equilibrium cluster size distribution in a sub-saturated vapor. We show that these free energies differ significantly from those obtained with a commonly used spherical cluster approximation - which relies on a surface tension coefficient of a flat surface. The spherical cluster approximation can be improved by using a cluster size-dependent Tolman correction for the surface tension. The values for the Tolman length and effective surface tension were derived, which differ from the commonly used experimentally measured surface tension based on the potential energy. This improved approximation does not account for geometric magic number effects responsible for spikes and troughs in densities of neighbor cluster sizes. Nonetheless, it allows to model cluster formation from a cooling vapor and accurately reproduce the condensation timeline, overall shape of the cluster size distribution, average cluster size, and the distribution width. Using a constant surface tension coefficient resulted in distorted condensation dynamics and inaccurate cluster size distributions. The analytical expression for cluster nucleation rate from classical nucleation theory (CNT) was updated to account for the size-dependence of cluster surface tension.

cond-mat.mtrl-sci↗

arXiv2024

Methods for color center preserving hydrogen-termination of diamond

Chemical functionalization of diamond surfaces by hydrogen is an important method for controlling the charge state of near-surface fluorescent color centers, an essential process in fabricating devices such as diamond field-effect transistors and chemical sensors, and a required first step for realizing families of more complex terminations through subsequent chemical processing. In all these cases, termination is typically achieved using hydrogen plasma sources which can etch or damage the diamond as well as deposited materials or embedded colour centers. This work explores alternative methods for lower-damage hydrogenation of diamond surfaces, specifically the annealing of diamond samples in high-purity, non-explosive mixtures of nitrogen and hydrogen gas, and the exposure of samples to microwave hydrogen plasmas in the absence of intentional stage heating. The effectiveness of these methods are characterized by x-ray photoelectron spectroscopy, and comparison of the results to density-functional modelling of the surface hydrogenation energetics implicates surface oxygen ligands as the primary factor limiting the termination quality of annealed samples. Finally, photoluminescence spectroscopy is used to verify that both the annealing and reduced sample temperature plasma methods are non-destructive to near-surface ensembles of nitrogen-vacancy centers, in stark contrast to plasma treatments which use heated sample stages.

cond-mat.mtrl-sci↗

arXiv2024

Quantum Chemistry Model of Surface Reactions and Kinetic Model of Diamond Growth: Effects of CH3 Radicals and C2H2 Molecules at Low-Temperatures CVD

The objective of this study is to explore conditions that facilitate a significant reduction in substrate temperature during diamond growth. The typical temperature for this process is around 1200K; we aim to reduce it to a much lower level. To achieve this, we need to understand processes that limit the diamond growth at low temperatures. Therefore, we developed a detailed chemical kinetic model to analyze diamond growth on the (100) surface. This model accounts for variations in substrate temperature and gas composition. Using an ab initio quantum chemistry, we calculated the reaction rates of all major gas phase reactants with the diamond surface, totaling 91 elemental surface reactions. Consistent with previous studies, the model identifies that CH3 is a major precursor of diamond growth, and the contribution from C2H2 to the growth is significantly smaller. However, C2H2 can also contribute to forming a sp2-phase instead of a sp3-phase, and this process becomes dominant below a critical temperature. As a result, C2H2 flux inhibits diamond growth at low temperatures. To quantify this deleterious process, we developed a new mechanism for sp2-phase nucleation on the (100) surface. Similar to the so-called HACA mechanism for soot formation it involves hydrogen abstraction and C2H2 addition. Consequently, optimal low-temperature CVD growth could be realized in a reactor designed to maximize the CH3 radical production, while minimizing the generation of C2H2 and other sp and sp2 hydrocarbons.

physics.chem-ph↗

arXiv2023

Compact and accurate chemical mechanism for methane pyrolysis with PAH growth

A reliable and compact chemical mechanism of gas-phase methane pyrolysis leading to formation of large polycyclic aromatic hydrocarbon (PAH) molecules has been developed. This model is designed for studies of carbon nanostructure synthesis such as carbon black and graphene flakes, including soot growth kinetics. Methane pyrolysis with carbon nanostructure synthesis is a two-stage process where conversion of CH4 to C2H2 precedes the growth of PAH molecules from acetylene. We present a single chemical mechanism that accurately describes both stages. We have constructed a compact and accurate chemical mechanism capable of modeling both stages of methane pyrolysis based on the ABF mechanism which was expanded with most prominent reaction pathways from the mechanism by Tao for small PAH molecules and HACA pathways for larger PAH molecules, up to 37 aromatic rings. The resulting mechanism was validated through comparison to multiple available sets of experimental data. Good agreement with the experimental data for both processes was obtained. Performance of the mechanism was tested for pyrolysis of methane-rich mixtures under long residence times leading to abundant formation of PAH molecules. It is shown that the inclusion of larger PAH species (up to A37) in the chemical mechanism is important for accurate prediction of the fraction of carbon converted to PAH molecules and, correspondingly, residual fraction of acetylene in the mixture.

physics.chem-ph↗

arXiv2023

Orientation dependent etching of silicon by fluorine molecules: a quantum chemistry computational study

Anisotropic etching is a widely used process in semiconductor manufacturing, in particular for micro- and nano-scale texturing of silicon surfaces for black silicon production. The typical process of plasma-assisted etching uses energetic ions to remove material in the vertical direction, creating anisotropic etch profiles. Plasma-less anisotropic etching, considered here, is a less common process that does not use ions and plasma. The anisotropy is caused by the unequal etching rates of different crystal planes; the etching process thus proceeds in a preferred direction. In this paper, we have performed quantum chemistry modeling of gas-surface reactions involved in the etching of silicon surfaces by molecular fluorine. The results confirm that orientation-dependent etch rates are the reason for anisotropy. The modeling of F2 dissociative chemisorption on the F-terminated silicon surfaces show that Si-Si bond breaking is slow for Si(111) surface, while it is fast for the Si(100) and Si(110) surfaces. The Si(100) and Si(110) surfaces incorporate a larger number of fluorine atoms resulting in the Si-Si bonds having a larger amount of positive charge which lowers the reaction barrier of F2 dissociative chemisorption, yielding a higher etch rate for the Si(100) and Si(110) surfaces compared to the Si(111) surfaces. Molecular dynamics modeling of the same reactions has shown that the chosen reactive bond order (REBO) potential does not accurately reproduce the lower reaction barriers for F2 dissociative chemisorption on Si(100) and Si(100) surfaces. Thus, reparameterization is necessary to model the anisotropic etching process that occurs at lower temperatures.

physics.chem-ph↗

arXiv2023

Plasma processes affecting etching and growth of nitride materials

The main goal of this research was to determine the key reagents during the highly Si3N4/SiO2 selective etching. The experiments were conducted, where both Si3N4 and SiO2 samples were etched by NF3/O2 and NF3/O2/N2/H2 plasmas. The sources of the plasmas were removed from the etched sample to exclude a damaging from UV emission and ion bombardment. Optical emission spectroscopy and mass-spectroscopy were used during the etching. The reaction mechanisms were studied using quantum chemistry methods. It was suggested analytical models, which quantitively describe dependence of Si3N4 and SiO2 etch rate on the fluxes of key reactants in NF3/O2 and NF3/O2/N2/H2 downstream plasmas. The densities of the kye reagents were measured and calculated using plasma simulation. Thus, the Si3N4 etch rate curve in NF3/O2 mixture has a peak, where NO density peaks. The high and narrow Si3N4/SiO2 selectivity peaks, which appears in NF3/O2/N2/H2, correlates with high and narrow density peak of vibration excited HF(v1) molecule. Also, this research was aimed to study a mechanism of precursor formation of boron nitride nanotubes growth during high temperature synthesis. It was shown that boron consumption (it is the main impediment to large scale production) occurs through the reactions of N2 dissociative adsorption on small boron clusters (N2 fixation) resulting in generation of B4N4 and B5N4 chains. The liquid boron is only source of the small boron clusters. A subsequent formation of longer chains occurs via collisions of B4N4 and B5N4 with each other. It was also shown that slow gas cooling rate and high pressure enhance liquid boron consumption during the synthesis, creating a good condition to large scale production of high purity and quality BNNT.

physics.chem-ph↗

arXiv2021

Boron nitride nanotube precursor formation during high-temperature synthesis: kinetic and thermodynamic modelling

We performed integrated modelling of the chemical pathways of formation for boron nitride nanotube (BNNT) precursors during high-temperature synthesis in a B/N2 mixture. Modelling includes quantum chemistry, quantum-classical molecular dynamics, thermodynamic, and kinetic approaches. It is shown that BN compounds are formed in the interaction of N2 molecules with small boron clusters (N2 molecule fixation) rather than with less reactive liquid boron. We demonstrate that the transformation and consumption of liquid boron proceeds through the evaporation of clusters, Bm with m less than or equal to 5 and their subsequent conversion into BmNn chains. The production of such chains is crucial to the growth of BNNTs because these chains form the building blocks of bigger and longer BN chains and rings, which are themselves the building blocks of fullborenes and BNNTs. Moreover, kinetic modelling revealed that B4N4 and B5N4 species play a major role in the N2 molecule fixation process. The formation of these species via reactions with B4 and B5 clusters is not adequately described under the assumption of thermodynamic equilibrium because the accumulation of both B4N4 and B5N4 depends on the background gas pressure and the gas cooling rate. Long BN chains and rings, which are precursors of the fullborene and BNNT growth, form via self-assembly of component B4N4 and B5N4. Our modelling results (particularly the increased densities of B4N4 and B5N4 species at higher gas pressures) explain the experimentally observed effect of gas pressure on the yield of high-quality BNNTs. The catalytic role of hydrogen was also studied; it is shown that HBNH molecules can be the main precursor of BNNT synthesis in the presence of hydrogen.

physics.chem-ph↗