Effect of frequency and pulse-on time of high power impulse magnetron sputtering on deposition rate and morphology of titanium nitride using response surface methodology

Titanium nitride thin films were deposited on silicon by high power impulse magnetron sputtering(HiPIMS)method at different frequencies(162-637 Hz)and pulse-on time(60-322μs).Response surface methodology(RSM)was employed to study the simultaneous effect of frequency and pulse-on time on the current waveforms and the crystallographic orientation,microstructure,and in particular,the deposition rate of titanium nitride at constant time and average power equal to 250 W.The crystallographic structure and morphology of deposited films were analyzed using XRD and FESEM,respectively.It is found that the deposition rate of HiPIMS samples is tremendously dependent on pulse-on time and frequency of pulses where the deposition rate changes from 4.5 to 14.5 nm/min.The regression equations and analyses of variance(ANOVA)reveal that the maximum deposition rate(equal to(17±0.8)nm/min)occurs when the frequency is 537 Hz and pulse-on time is 212μs.The experimental measurement of the deposition rate under this condition gives rise to the deposition rate of 16.7 nm/min that is in good agreement with the predicted value.

Saturation Ion Current Densities in Inductively Coupled Hydrogen Plasma Produced by Large-Power Radio Frequency Generator

An experimental investigation of the saturation ion current densities （Jions） in hydrogen inductively coupled plasma （ICP） produced by a large-power （2-32 kW） radio frequency （RF） generator is reported, then some reasonable explanations are given out. With the increase of RF power, the experimental results show three stages： in the first stage （2-14 kW）, the electron temperature will rise with the increase of RF power in the ICP, thus, the Jions increases continually as the electron temperature rises in the ICP. In the second stage （14 20 kW）, as some H- ions lead to the mutual neutralization （MN）, the slope of Jio^s variation firstly decreases then increases. In the third stage （20-32 kW）, both the electronic detachment （ED） and the associative detachment （AD） in the ICP result in the destruction of H- ions, therefore, the increased amplitude of the Jions in the third stage is weaker than the one in the first stage. In addition, with the equivalent transformer model, we successfully Explain that the Jions at different radial locations in ICP has the same rule. Finally, it is found that the Jions has nothing to do with the outer/inner puffing gas pressure ratio, which is attributed to the high-speed movement of hydrogen molecules.

Effect of BCD Plasma on a Bacteria Cell Membrane

Cell membrane rupture is considered to be one of the probable mechanisms for bacterial inactivation using barrier corona discharge （BCD） plasma. In this paper, the effect of the BCD plasma on the Escherichia coli （E. coli） bacteria cell wall was investigated through two analytical methods; Adenosine-5-triphosphate （ATP） assay and Atomic Force Microscopy （AFM）. The ATP assay results indicate an increase in the ATP content of samples which were exposed to the BCD plasma. This implies the bacteria cell rupture. Moreover, AFM images confirm a serious damage of the bacteria cell wall under the influence of the bactericidal agents of the plasma.

The E×B drift instability in Hall thruster using 1D PIC/MCC simulation

The E×B drift instability is studied in Hall thruster using one-dimensional particle in cell(PIC)simulation method.By using the dispersion relation,it is found that unstable modes occur only in discrete bands in k space at cyclotron harmonics.The results indicate that the number of unstable modes increases by increasing the external electric field and decreases by increasing the radial magnetic field.The ion mass does not affect the instability wavelength.Furthermore,the results confirm that there is an instability with short wavelength and high frequency.Finally,it is shown that the electron and ion distribution functions deviate from the initial state and eventually the instability is saturated by ion trapping in the azimuthal direction.Also for light mass ion,the frequency and phase velocity are very high that could lead to high electron mobility in the axial direction.

Numerical Simulation of Self-Pumped Phase Conjugate Plane-Curve Loop Mirror Based on Photorefractive Nonlinearity

We deal with computer simulation of a transient process in a self-pumped phase conjugate plane-curve loop mirror based on BaTiO3. In optimal circumstances the nonlinear reflectivity and fidelity of such a mirror respectively achieve 0.80-0.90 and 0.95-0.98. The generation of conjugate wave-front occurs due to scattering from the dynamic hologram which is produced in the region of self-intersection of forward and backward beams. In such a model the scenario of passing to unstable generation regimes is similar to the self-pumped phase conjugate plane-plane loop mirror and substantially differs from a single-crystal double phase conjugate mirror.

Multi-millijoule terahertz emission from laser- wakefield-accelerated electrons

High-power terahertz radiation was observed to be emitted from a gas jet irradiated by 100-terawatt-class laser pulses in the laser-wakefield acceleration of electrons.The emitted terahertz radiation was characterized in terms of its spectrum,polarization,and energy dependence on the accompanying electron bunch energy and charge under various gas target conditions.With a nitrogen target,more than 4 mJ of energy Was produced at<10 THz with a laser-to-terahertz conversion efficiency of~0.15%.Such strong terahertz radiation is hypothesized to be produced from plasma electrons accelerated by the ponderomotive force of the laser and the plasma wakefelds on the time scale of the laser pulse duration and plasma period.This model is examined with analytic calculations and particle-in-cell simulations to better understand the generation mechanism of high-energy terahertz radiation in laser-wakefield acceleration.

Adjustable surface plasmon resonance with Au,Ag,and Ag@Au core-shell nanoparticles

We report an experimental study on the synthesis of metal nanoparticles （NPs） with adjustable optical density based on surface plasmon resonance （SPR）. Metal NPs prepared by laser ablation in liquid method and the effect of laser parameters on the size, distribution, wavelength of SPR of Ag, Au, and mixture of Ag-Au, and Ag core/Au shell NPs are investigated. Our results show that the adjustable SPR band can be achieved in each class of NPs which is suitable for adjustable optical window applications.

Design and analysis of superlens based on complex two-dimensional square lattice photonic crystal

We theoretically demonstrate the imaging properties of a complex two-dimensional(2D) face-centered square lattice photonic crystal(PC) made from germanium cylinders in air background. The finitedifference time-domain(FDTD) method is employed to calculate the band structure and simulate image construction. The band diagram of the complex structure is significantly compressed. Negative refraction occurs in the second energy band with negative phase velocity at a frequency of 0.228(2πc/a), which is lower than results from previous studies. Lower negative refraction frequency leads to higher image resolution. Numerical results show that the spatial resolution of the system reaches 0.7296λ, which is lower than the incident wavelength.

Structural and Mechanical Properties of TiN-TiC-TiO System: First Principle Study

Mechanical and structural properties of ternary system of TiN-TiO-TiC are investigated using first principle methods. 70 different compositions of Ti100(NOC)100 with cubic structure are examined in order to illustrate the trend of properties variations. The geometry of compounds is optimized, and then, their chemical stability is assessed. Afterward,shear, bulk and young moduli, Cauchy pressure, Zener ratio, hardness and H3/E2 ratio are computed based on elastic constants. Graphical ternary diagram is used to represent the trend of such properties when the content of nitrogen,oxygen and carbon varies. The results show that incorporation of oxygen into the system decreases the hardness and H^3/E^2 ratio while subsequently ductility increases due to positive Cauchy pressure. It is revealed that the maximum H^3/E^2 ratio occurs when both nitrogen and carbon with a little amount of oxygen are incorporated. Ti_(100) N_(30) C_(70) owns the highest hardness and H^3/E^2 ratio equal to 39.5 and 0.2 GPa, respectively. In addition, the G/B of this compound,which is about 0.9, shows it is brittle. It is also observed that the solid solutions have better mechanical properties with respect to titanium nitride and titanium carbide. The obtained results could be used to enhance monolayer coatings as well as to design multilayers with specific mechanical properties.

Dynamics of ionisation wave propagation in an applied external electric field

This study presents spatio-temporal development of the ionisation waves(IWs)along one dielectric tube with an extra alternating electric field.A pulsed direct current power supply is used for generating the IWs,and another alternating current power supply is used for altering the distribution of electric fields along the dielectric tube.The measurements show that the propagation velocity and density of IWs are strongly affected by the external electric field.The direct relation between external electric field and the velocity of the IWs is demonstrated.Further analysis indicates that the external electric field can be utilised to control the propagation of the IWs,resulting in a change of their density and velocity.