Bocong Zheng

Beijing Institute of Technology | BIT · School of Physics

This work proves that the sputtering deposition angle has significant effects on the ITO film crystallinity and properties under the assistance of an ion beam at room temperature. The films grown at 30º and 45º are crystalline while the ones produced at 60º and 90º are amorphous in nature. The films’ sheet resistance was observed to be lower at 30º...

Hall thrusters are electric propulsion devices widely used on spacecraft. The stability of Hall thrusters is often disturbed by low-frequency oscillations (LFOs) around 5–100 kHz, known as the ‘breathing mode’, typically observed through fluctuations in channel discharge current and plasma parameters. Experimental studies on Hall thrusters with a w...

Introducing asymmetry in capacitively coupled plasmas (CCPs) is a common strategy for achieving independent control of ion mean energy and flux. Our 1d3v particle-in-cell/Monte Carlo collision simulations reveal that a uniform magnetic field within a specific range can induce spatial asymmetry in low-pressure CCPs, even under perfectly symmetric co...

Effects of N2 admixture on multiple wave modes and transitions were investigated in N2–Ar helicon plasma under fixed input power and magnetic field. The structures of helicon waves were measured by a B-dot probe to verify the different eigenmodes. The experimental results show that the plasma morphology, emission spectrum, and spatial profile chang...

Low magnetic field density peak (LFP) is a typical nonlinear phenomenon in helicon wave discharge, which is characterized by the nonlinear increase in electron density with the magnetic field in lower magnetic fields. In this paper, the characteristics and generation mechanism of LFPs of argon helicon wave plasma excited by m = 0 single-loop antenn...

Scale-invariant breathing oscillations are observed in similar magnetized discharges at different spatiotemporal scales via fully kinetic particle-in-cell simulations. With an increase in the similarity invariant B/p, i.e., the ratio of magnetic field to pressure, breathing oscillations are triggered, leading to an appreciable time-averaged potenti...

Mechanisms of cavity resonance and antenna resonance and their coupling effects on mode transitions in argon helicon plasma excited by a half-helical antenna (14 cm in length) were investigated in this paper. Cavity length was changed to distinguish the effects of cavity and antenna resonances in experiments. Plasma parameters under various dischar...

In this paper, multiple wave modes and transitions of argon helicon plasma excited by a half right-helical in a system without any reflection endplate are investigated experimentally and theoretically at increasing radio frequency (RF) powers and external magnetic fields. Experiments show that above a critical magnetic field strength and pressure (...

This paper presents the quantification of gas breakdown voltages in low-pressure argon capacitive radio frequency (rf) discharges in the presence of an external transverse magnetic field via fully kinetic particle-in-cell/Monte Carlo collision simulations. It is found that as the magnetic field increases, the left branch of the breakdown curve, a d...

We demonstrate similarity-based scaling networks for capacitive radio frequency (RF) plasmas, which extensively correlate discharge characteristics under varied conditions, incorporating the transition from original to similarity states. Based on fully kinetic particle-in-cell simulations, similar RF discharges in argon are demonstrated with three...

We demonstrate similarity rules for inductively coupled plasmas with thermohydrodynamic coupling effects using two-dimensional fluid simulations and theoretical analyses of the gas flow and heat transfer equations. The results confirm the validity of conventional similarity laws, e.g., the similarity relation for electron density, which can be viol...

Resonance mechanisms have been found to be essential for the generation of high-density rf plasmas at low pressures, in which electrons can be continuously accelerated through multiple interactions with the oscillating rf sheaths. In this work, we report the scale-invariant resonance mechanisms, such as bounce resonance heating and plasma series re...

Derived from electric double‐layer capacitors (EDLCs), capacitive deionization (CDI) using symmetric carbon‐based electrodes is an emerging approach to purifying brackish water into drinking water. The deionization performance is mainly determined by the properties of the electrode materials. This work reports a green and efficient plasma treatment...

Similarity laws (SLs) are useful for correlation and prediction of plasma parameters at different scales, which have been verified for geometrically symmetric capacitive radio-frequency (rf) discharges in nonlocal kinetic regimes. In this work, we demonstrate the applicability of SLs to dual-frequency rf discharges and confirm that similarity relat...

A single-beam plasma source was developed and used to deposit hydrogenated amorphous carbon ( a-C:H) thin films at room temperature. The plasma source was excited by a combined radio frequency and direct current power, which resulted in tunable ion energy over a wide range. The plasma source could effectively dissociate the source hydrocarbon gas a...

With the advantages of superior energy density, lithium‐sulfur batteries (LSBs) have been considered as one of the promising next‐generation batteries. However, some key issues, such as the shuttle effect of the intermediate lithium polysulfides, poor conductivity of the sulfur, Li2S and Li2S2, and huge volume variation during charge/discharge proc...

A single-beam ion source was developed and used in combination with magnetron sputtering to modulate the film microstructure. The ion source emits a single beam of ions that interact with the deposited film and simultaneously enhances the magnetron discharge. The magnetron voltage can be adjusted over a wide range, from approximately 240 to 130 V,...

Similarity laws (SL) are essential for correlating the characteristics of plasmas at different dimensional scales, which have been validated for radio frequency (rf) discharges at low pressure but under limited conditions. In this work, we evaluate the effects of nonlinear collisions (e.g., stepwise ionization) on the similarity properties in capac...

We generalize similarity theory based on the scaling and solution invariance of the Boltzmann equation, coupled with the Poisson equation, and demonstrate similarity laws for radio-frequency (rf) discharge plasmas across three nonlinear transitional regimes, namely, the alpha-gamma mode transition, the stochastic-Ohmic-heating mode transition, and...

The theoretical background and historical development of the similarity theory during the past decades are reviewed. We demonstrate similar discharges in local and nonlocal kinetic regimes, taking the low-pressure capacitive radio frequency (rf) discharges and microdischarges as examples. By using fully kinetic particle-in-cell simulations, we veri...

Lithium metal batteries (LMBs) are considered the most promising energy storage devices for applications such as electrical vehicles owing to its tremendous theoretical capacity (3860 mAh g⁻¹). However, the serious safety issues and poor cycling performance caused by the dendritic crystal growth during deposition are concerned for any rechargeable...

We demonstrate the formation and transition behaviors of a microplasma around microstructure arrays at different gas pressures via two-dimensional particle-in-cell/Monte Carlo collision simulations. It is found that the microdischarge occurs outside the cathode microcavities at the lowest pressure and starts penetrating the microcavities with a cur...

We demonstrate a self-consistent and complete description of electron dynamics in a typical electropositive radio frequency magnetron sputtering (RFMS) argon discharge with a dielectric target. The electron dynamics, including the electron power absorption dynamics in one radio frequency (RF) period, is studied via a fully kinetic 2d3v particle-in-...

We demonstrate the transition characteristics and electron kinetics of microdischarges in a microgap with a cathode having microstructures using two-dimensional particle-in-cell/Monte Carlo collision (2d3v) simulations. It is found that the microdischarge is inside the hollow cavity at lower pressures, forming microhollow cathode discharges (MHCDs)...

One-dimensional and two-dimensional particle-in-cell (PIC)/Monte Carlo collision simulations are performed for a balanced direct current magnetron sputtering (DCMS) discharge. The plasma parameters obtained by both simulations above the target racetrack share similar features and magnitudes under similar discharge intensities, i.e., similar local d...

We verify the similarity law (SL) and show a violation of frequency scaling (f-scaling) in low-pressure capacitive radio frequency (rf) plasmas via fully kinetic particle-in-cell simulations. The SL scaling relations for electron density and electron power absorption are first confirmed in similar rf discharges. Based on these results, with only th...

MXene has been considered as a promising electrode materials for energy storage devices. This work reports using an electrophoresis effect to efficiently deposit Ti3C2Tx/rGO composite on flexible substrates, which are subsequently used as the electrodes of all-solid-state supercapacitors. The electrophoresis deposition does not require a binder in...

Similarity transformations are essential for correlating discharges at different scales, which are mostly utilized with local field or local energy approximations. In this work, we report the fully kinetic results from particle-in-cell/Monte Carlo collision simulations that unambiguously demonstrate the similarity of radio frequency (rf) discharges...

This work demonstrates the presence of a small number of high-energy ballistic electrons (HEBEs) that originate from secondary electrons in low-pressure radio-frequency (rf) plasmas. The kinetic behaviors of the HEBEs are illustrated through electron energy probability functions from the fully kinetic particle-in-cell simulations, showing two wavy...

One-dimensional particle-in-cell simulations with Monte Carlo collisions are used to investigate the influence of metastable atoms in low pressure radio-frequency argon discharges with magnetic fields ranging from 0 G to 60 G. Two metastable levels of argon species are included and tracked as particles, enabling multistep ionization and metastable...

Systematic analysis of discharge processes is needed for a good understanding of the physical mechanism that enables optimal coating deposition, especially pulsed discharges sustained by high voltages and large currents. Owing to the temporal and complex characteristics of the discharge process and relatively simplistic analytical methods, the disc...

Hard Ti-Al-Si-N coatings are widely used in cutting tools, due to their excellent mechanical properties and superior thermal properties. In this study, Ti-Al-Si-N coatings are deposited by modulated pulsed power magnetron sputtering, with various substrate bias voltages from -35 V to -130V. As the bias voltage goes up, the composition of coatings r...

Cold plasma sterilization offers an efficient way to sterilize medical components and instruments. This paper reports using a magnetized plasma to realize low-temperature sterilization. A radio frequency dielectric barrier discharge is created in a quartz tube using a mixture of argon and oxygen gas. A uniform amount of Escherichia coli is applied...

In low-pressure capacitively coupled discharges, a heating mode transition from a pressure-heating dominated state to an Ohmic-heating dominated state is known by applying a small transverse magnetic field. Here we demonstrate via particle-in-cell simulations and a moment analysis of the Boltzmann equation that the enhancement of Ohmic heating is i...

Solenoid coils with grounded ends positioned on the dielectric window were proposed and numerically studied to reduce the capacitive coupling in conventional inductively coupled plasma (ICP) sources. The capacitive coupling between the plasma and the coils was subsequently suppressed, leading to a significant reduction of the window erosion. To und...

Plasma electrolysis combines the characteristics of electrolysis and plasma discharges, creating high-energy-density plasmas that lead to intensive physical processes and chemical reactions on the working electrode. The authors have found that the physical processes and the chemical reactions could be decoupled under certain conditions, and a textu...

Two dimensional transition metal carbides and nitrides, known as MXenes, are promising materials for energy storage. Although superior capacitance performance has been demonstrated using MXene electrodes in supercapacitors, the relatively high resistance and inefficient separation process limit the materials applications. This work reports an innov...

High-power impulse magnetron sputtering boasts high ionization, large coating density, and good film adhesion but suffers from drawbacks such as low deposition rates, unstable discharge, and different ionization rates for different materials. Herein, a cylindrical cathode in which the special cathode shape introduces the hollow cathode effect to en...

The discharge and deposition characteristics of high power impulse magnetron sputtering (HiPIMS) using various target materials with different sputtering yields (Cu, Cr, Ti and C) were analyzed by a plasma global model. The experimental discharge voltages and currents of various target materials were used as the input parameters of the model. The a...

TiAlSiN nanocomposite coatings were deposited by modulated pulsed power magnetron sputtering (MPPMS) with the varied peak power from 24.8 to 56.8 kW. The coatings had a typical nc-TiAlN/a-Si3N4 nanocomposite structure. The microstructure of the coatings changed from a columnar structure (Zone I in Thornton's Model) at 24.8 kW and 35.2 kW to a dense...

This work presents a concept of using acoustic standing waves to modulate plasmas. A one-dimensional self-consistent fluid model combined with an acoustic standing wave model has been established to investigate the strong coupling effects between acoustic standing waves and capacitively coupled argon plasmas. The modulation effects are revealed by...

Low-temperature growth of microcrystalline silicon (mc-Si) is attractive for many optoelectronic device applications. This paper reports a detailed comparison of optical properties, microstructure, and morphology of amorphous silicon (a-Si) thin films crystallized by furnace annealing and flash lamp annealing (FLA) at temperatures below the softeni...

Activated carbon is widely used for electrodes in supercapacitors. Fabrication of supercapacitors is currently based on hydraulic pressing method, which is a lengthy process (several h) with challenges in controlling the layer thickness and mass. This work reports an electrophoresis method that can efficiently deposit activated biochar onto metal e...

An optically enhanced Fabry-Perot etalon was demonstrated to accurately measure the refractive index of sugar solutions. The etalon consisted of two silver/SiO2 coated glass substrates separated by a spacer. The semi-transparent silver films of ~15 nm thickness greatly enhanced the interference of light. The SiO2 layer coated on the silver created...

A spatially averaged, time-dependent global plasma model has been developed to describe the reactive deposition of a TiAlSiN thin film by modulated pulsed power magnetron sputtering (MPPMS) discharges in Ar/N2 mixture gas, based on the particle balance and the energy balance in the ionization region, and considering the formation and erosion of the...

High-power impulse magnetron sputtering (HiPIMS), a new physical vapor deposition technique which combines the advantages of the high ionization rates of the sputtered materials and control of electromagnetism, has been widely used to deposit high-performance coatings with a large density and high adhesion. However, HiPIMS has some intrinsic disadv...