Effect of ambient gas on the expansion dynamics of plasma plume formed by laser blow off of thin film

A study has been carried out to understand the influence of ambient gases on the dynamics of laser-blow-off plumes of multi-layered LiF–C thin film. Plume images at various time intervals ranging from 100 to 3000 ns have been recorded using an intensified CCD camera. Enhancement in the plume intensity and change in size and shape occurs on introducing ambient gases and these changes are highly dependent on the nature and composition of the ambient gas used. Velocity of the plume was found to be higher in helium ambient whereas intensity enhancement is greater in argon environment. The plume shapes have maximum size at 10⁻² and 10⁻¹ Torr of Ar and He pressures, respectively. As the background pressure increases further (>10⁻² Torr: depending on the nature of gas), the plume gets compressed/focused in the lateral direction. Internal structure formation and turbulences are observed at higher pressures (>10⁻¹ Torr) in both ambient gases.     

Spectroscopic investigations of microwave microplasmas in various gases at atmospheric pressure

In this paper results of the experimental investigations of a coaxial microwave (2.45 GHz) microplasma source (MMS) with graphite or tungsten inner conductor operated in Ar, N₂ and Ar/C₂H₂ mixture at atmospheric pressure are presented. The microwave power absorbed by the microplasmas and the intensity of UV-C emission from the microplasmas were measured. Using optical emission spectroscopy, the electron number density in Ar microplasma, and rotational and vibrational temperatures in N₂ and Ar/C₂H₂ microplasmas were determined. All experiments were performed with a gas flow rate from 0.3 to 8 l/min and absorbed microwave power from 5 to 300 W. The simplicity of the MMS, stability of its operation with atmospheric pressure gases, and parameters of the microplasmas allow concluding that the MMS can be used in various applications.     

激光诱导Al等离子体在背景气体中的流体现象

调Q-YAG脉冲激光（波长1.06μm,脉宽10ns,能量为250mJ/pu1se）烧蚀Al靶,用短焦距照相系统和光学多道分析仪（OMA）记录了等离子体在氩气背景气体及不同压强下所呈现的流体现象及其等离子体辐射的空间分辨光谱。实验发现,当背景气压为400Pa以下时,在靶面上存在一个明亮的发光球体,球体直径远大于激光烧蚀斑的大小,此球体向四周辐射等离子体光谱,只是在垂直靶面的方向辐射相对较强。在气压约为400Pa,等离子体辐射才以较为明显的羽状体形态向前喷散,且随气压增高,喷散的立体角变小。随着背景气压的继续升高,等离子体羽被压缩,成为一个明亮的发光小羽状体,当气压达20～30kPa,发光羽状体开始出现分解的迹象,在羽状体前端形成一个光球。气压继续升高,等离子体羽完全变成一串发光球。离开靶面越远,发光球的半径越大。用光学多道分析系统分析这些发光球的光谱特征,发现在靶面附近主要是Al等离子体的谱线,而较远的发光球,其主要谱线则来自背景气体。在气压为20kPa左右,等离子休羽呈现烧蚀点为明亮的白色亮点,而羽端为鲜艳绿色（氩的514nm）的彩色羽。     

Plasma dynamics from laser ablated solid lithium

Emission plasma plume generated by pulsed laser ablation of a lithium solid target by a ruby laser (694 nm, 20 ns, 3 J) was subjected to optical emission spectroscopy: time and space resolved optical emission was characterised as a function of distance from the target surface. Propagation of the plume was studied through ambient background of argon gas. Spectroscopic observations can, in general, be used to analyse plume structure with respect to an appropriate theoretical plasma model. The plume expansion dynamics in this case could be explained through a shock wave propagation model wherein, the experimental observations made were seen to fit well with the theoretical predictions. Spectral information derived from measurement of peak intensity and line width determined the parameters, electron temperature (T _e) and electron number density (n _e), typically used to characterise laser produced plasma plume emission. These measurements were also used to validate the assumptions underlying the local thermodynamic equilibrium (LTE) model, invoked for the high density laser plasma under study. Some interesting results pertaining to the analysis of plume structure and spatio-temporal behaviour of T _e and n _e along the plume length will be presented and discussed.     

Intensity and line-width measurements of the NO fundamental by infrared molecular absorption spectrometry

The integrated intensity of the fundamental vibration-rotation band of NO and the pressure-broadening parameters of NO with various foreign gases have been determined at room temperature by measuring the resonance absorption of the infrared emission line of the NO fundamental. The Hg photo-sensitized vibrational excitation of NO was utilized to obtain a light source for the NO fundamental. in which the individual rotational lines could be described in terms of the Doppler line profile at room temperature. The total band intensity was found to be 122 ± 6 cm^-2 atm^-1, and the collision-broadened full-widths at half maximum in CO₂, N₂, Ar, H₂ and He gases were 0.10, 0.086, 0.059, 0.086 and 0.078 cm^-1 atm^-1, respectively.     

Growth of carbon nanotubes on Fe or Ni-coated Si substrate by feeding with carbon from a graphite ablation plume

By feeding with carbon clusters from the ArF excimer laser (=193 nm) ablation of graphite target, carbon nanotubes (CNTs) were grown on Fe and Ni films deposited on SiO₂/Si substrates, which were set inside a quartz tube with Ar gas pressure of 500 Torr operating at 1100 °C. Optical emission spectroscopic observation of the ablation plume of graphite and Ni/Y catalyst was performed in the Ar gas for a pressure range of 0–600 Torr at room temperature and 1000 °C. The emission band intensity of C₃ (ù_u) at the distance of 2 mm from the target increased with increasing Ar gas pressure. PACS 79.20.Ds; 81.07.De; 39.30.+w     

NeMu* chemiluminescence: Radiolysis effects in gases

Near-infrared chemiluminescent emission from NeMu^*, the analogue of the Rydberg molecule NeH, has been observed in Ne, Ar, and Ne/Ar gas mixtures. Three temporally distinct features were observed: First, a large sharp emission peak at time zero, observed in all gases (Ne, He, N₂, Ar), is assigned to scintillation light during muon thermalization, probably caused by spur electrons. Second, a lowintensity broad region observed in all gases is attributed to e⁺ from muon decay. Finally, NeMu in 1–6 atm Ne with 0.1–2 torr Ar appeared as a high intensitydelayed emission, whose width and intensity depended linearly on the Ar concentration. Its wavelength spectrum from 680–960 nm was measured. Although questions remain as to how NeMu^* is formed, the precursor is likely Ne ⁺. Possible electron donors include metastable Ar^* (³ P ₂ or³ P ₀) and long-lived free (spur) electrons.Contribution from CEMAID, Center of Excellence in Molecular and Interfacial Dynamics; the financial support afforded by participation in Canada's National Centers of Excellence program is greatly appreciated.     

Spectroscopic studies of XeCl-laser-induced plasma on Ti targets in nitrogen containing atmospheres

This work deals with the study of a plasma produced by intense XeCl-excimer-laser irradiation of a titanium surface in nitrogen-containing atmospheres. We observed that the optical emission spectra resulting from irradiation of Ti targets in various ambient atmospheres (N₂, NH₃, N₂+H₂ mixtures) contain lines of atomic and ionized species of the irradiated target material only. The spectra are almost independent of the ambient atmosphere. The expansion velocities of atomic and ionic species in the plasma plume were obtained by time-of-flight measurements at different distances from the target. Mass spectrometry measurements are also performed at low background pressure to identify non-emitting species.     

环境气体对激光诱导Al等离子体光谱的影响

调QNd:YAG脉冲激光(波长1.06μm,脉冲宽度10ns,能量42mj/pulse)烧蚀平面Al靶,在垂直靶面方向,利用光学多道分析系统(OMA),测量了激光诱导产生的等离子体发射光谱分别在环境气体为Air,N2和Ar,气压范围分别在10-2Torr,152Torr,304Torr,532Torr和760Torr下的空间分布。实验表明,随着环境气体压强的增大,光谱的空间分布被压缩,且谱线强度的峰值向靶面方向移动;在相同的气压下,Ar环境下产生的光谱强度明显大于在Air和N2环境下产生的光谱强度;在气压为152Torr的不同环境气体下,均发现光谱在离靶面很近的地方(约0.5mm～1.0mm)减小,甚至消失;在Ar环境气体下,谱线396.1nmAlⅠ的空间分布随着与靶面距离的增大,谱线位置向短波方向有约0.03nm(对应OMA探头的一个二极管阵列)的移动,而谱线394.4nmAlⅠ的移动不太明显。     

Effect of dissolved gases in water on acoustic cavitation and bubble growth rate in 0.83 MHz megasonic of interest to wafer cleaning

Changes in the cavitation intensity of gases dissolved in water, including H₂, N₂, and Ar, have been established in studies of acoustic bubble growth rates under ultrasonic fields. Variations in the acoustic properties of dissolved gases in water affect the cavitation intensity at a high frequency (0.83 MHz) due to changes in the rectified diffusion and bubble coalescence rate. It has been proposed that acoustic bubble growth rates rapidly increase when water contains a gas, such as hydrogen faster single bubble growth due to rectified diffusion, and a higher rate of coalescence under Bjerknes forces. The change of acoustic bubble growth rate in rectified diffusion has an effect on the damping constant and diffusivity of gas at the acoustic bubble and liquid interface. It has been suggested that the coalescence reaction of bubbles under Bjerknes forces is a reaction determined by the compressibility and density of dissolved gas in water associated with sound velocity and density in acoustic bubbles. High acoustic bubble growth rates also contribute to enhanced cavitation effects in terms of dissolved gas in water. On the other hand, when Ar gas dissolves into water under ultrasound field, cavitation behavior was reduced remarkably due to its lower acoustic bubble growth rate. It is shown that change of cavitation intensity in various dissolved gases were verified through cleaning experiments in the single type of cleaning tool such as particle removal and pattern damage based on numerically calculated acoustic bubble growth rates.     

等离子体增强化学气相沉积法制备立方氮化硼薄膜过程中的表面生长机理

利用感应耦合等离子体增强化学气相沉积法以Ar，He，N₂和B₂H₆为反应气体制备了高纯立方氮化硼薄膜.用四极质谱仪对等离子体状况进行了系统的分析，发现B₂H₆完全被电离而N₂只是部分被电离.H₂和过量的N₂在等离子体中生成大量中性的H原子和活化的N^*₂，它们与表面的相互作用严重地阻碍了立方 关键词： 立方氮化硼薄膜 等离子体 质谱     

环境气体种类对激光烧蚀粒子速度劈裂的影响

采用蒙特-卡罗(Monte Carlo)方法, 模拟了激光烧蚀粒子输运动力学过程, 在环境气体压强为100 Pa的情况下, 研究了环境气体种类(He, Ne, Ar和假想气体等)对烧蚀粒子速度劈裂的影响. 研究结果表明, 在四种环境气体中传输的烧蚀粒子均出现了速度劈裂现象, 形成速度劈裂所需时间按He, Ne, 假想气体和Ar的次序减小. 还研究了环境气体分子的质量和半径对烧蚀粒子速度劈裂的影响, 形成速度劈裂所需时间随环境气体分子半径(或质量)增大而减小. 在假想气体中, 两速度峰强度相等时的强度最小. 结合欠阻尼振荡模型和惯性流体模型, 对劈裂的形成时间进行了解释. 所得结论可为进一步定量研究纳米晶粒生长机理提供基础.     

Shielding gas influences on laser weldability of tailored blanks of advanced automotive steels

The effects of shielding gas types and flow rates on CO₂ laser weldability of DP600/TRIP700 steel sheets were studied in this work. The evaluated shielding gases were helium (He), argon (Ar) and different mixtures of He and Ar. Weld penetration, tensile strength and formability (Erichsen test) of laser welds were found to be strongly dependent upon the shielding gas types. The ability of shielding gas in removing plasma plume and thus increasing weld penetration is believed to be closely related to ionization potential and atomic weight which determine the period of plasma formation and disappearance. It was found that the higher helium shielding gas flow rate, the deeper weld penetration and the lower weld width.     

Determination of N and O‐atoms and N2 (A) Metastable Molecule Densities in the Afterglows of N2‐H2, Ar‐N2‐H2 and Ar‐N2‐O2 Microwave Discharges

Early afterglows of N₂‐H₂, Ar‐N₂‐H₂ and Ar‐N₂‐O₂ flowing microwave discharges are characterized by optical emission spectroscopy. The N and O atoms and the N₂ (A) metastable molecule densities are determined by optical emission spectroscopy after calibration by NO titration for N and O‐atoms and measurements of NO and N₂ band intensities. If an uncertainty of 30% is estimated on N‐atomic density, an inaccuracy of one order of magnitude is obtained on the O and N₂ (A) densities. In N₂‐(0.05‐2.5%)H₂ and Ar‐(1‐50%)N₂‐(0.05‐2.5%) H₂ gas mixtures, the O‐atoms are coming from O₂ impurities in the discharge. Concentrations of N and O‐atoms and of N₂ (A) densities are compared to the ones obtained in Ar‐(5‐50%)N₂‐(0.2‐2.5%) O₂ gas mixtures in which a controlled amount of O₂ is added. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Spectroscopic diagnostics of barrier discharge plasmas in mixtures of zinc diiodide with inert gases

The spectral characteristics of the emission of gas discharge atmospheric pressure plasmas in mixtures of zinc diiodide vapor with inert gases (He, Ne, Ar, Kr, and Xe) are investigated. The formation of a gas discharge plasma and the excitation of the components of a working mixture were performed in a high-frequency (with a repetition frequency of sinusoidal voltage pulses of 100 kHz) barrier discharge. The gas discharge emission was analyzed in the spectral range 200–900 nm with a resolution of 0.05 nm. Emission bands of ZnI(B-X) exciplex molecules and I₂* excimer molecules, lines of inert gases, and emission bands of XeI* exciplex molecules (in Xe-containing mixtures) were revealed. It is ascertained that the strongest emission of ZnI* molecules is observed in ZnI₂/He(Ne) mixtures. The regularities in the spectral characteristics of the gas discharge plasma emission are considered.     

Influence of additional external pressure on optical emission intensity in liquid-phase laser ablation

We examined the influence of additional external pressure on the optical emission intensity from plasmas produced by laser ablation of a Ti target immersed in distilled water. We adopted two methods for applying the external pressure. When ambient water was pressurized by connecting the ablation chamber to N₂ gas at a pressure range of 0.1-0.9 MPa, we observed the increase in the optical emission intensity with the pressure. This increase was considered to be caused by the change in the amount of dissolved N₂ gas in the water. On the other hand, when an external pressure of 30 MPa was applied to ambient water by using a mechanical pump, we observed the compression of the spatial distribution of the optical emission intensity. These experimental results suggest a possibility that chemical reactions and physical states (pressure and temperature) of liquid-phase laser-ablation plasmas can be controlled by adding external pressure to ambient liquid.     

Temporal and spatial TaO emission generated from UV laser ablation of Ta and Ta2O5 in oxygen ambient

2 O₅ targets in oxygen ambient are presented. Line assignments indicate the presence of the excited Ta(I), Ta(II), and TaO in the plume. At higher oxygen pressure, a single peak appears in the TaO emission spectrum from the laser ablation of Ta while two peaks corresponding to a fast and a slow component of TaO emission are observed from the laser ablation of the Ta₂O₅ target by time-resolved emission spectroscopy. The delay times after laser pulse corresponding to two components of TaO emission from the laser ablation of Ta₂O₅ have been investigated as a function of oxygen pressure, laser fluence, and observation distance from the target surface. The two components of TaO emission could be attributed to different pathways for the generation of excited TaO molecules. A blast wave model is proposed to describe the behavior of the excited TaO in the plume of laser ablation of Ta₂O₅. Received: 1 February 1997/Accepted: 12 March 1997     

A general analytical method for evaluation of the thermodynamic properties of matters using virial coefficients with Morse potential at high temperature

In this paper, we established an analytical formula for the second virial coefficient (SVC) with Morse potential without using any numerical methods, and the obtained formula is applied to the calculation of the speed of sound of some matter at high temperature. This approach is based on the series expansion formula and special functions, which allows the exact evaluations of any thermodynamic properties of matter using the SVC. As an application, the obtained analytical formula is used for evaluation of the SVC with Morse potential for high‐temperature gas and the plasma region of the intermolecular interactions of neutral atom gases of B, Si, Zn, H₂, N₂, O₂, NO, CO, He, Ne, Ar, Kr , and Xe . Based on the obtained formula of SVC, the speed of sound for gases of N₂, Ar , and Zn are also determined analytically. A specific maximum temperature is chosen for every gas to ensure that there are still neutral atoms in the gas, and low temperatures are avoided due to quantum effects. The results are compared with numerical data and another analytical data from the literature. The new analytical solution is shown to be in good agreement with the compared data and is verified to supply proper thermodynamic data.     

The double M-effect induced by noble gases activated with negative ions

The M-effect (monochromatization-effect) is a powerful tool which can give high intensity monochromatic spectra with a certain wavelength depending on the type of used gas mixtures to generate plasma state. The effect consists in the emission of a single spectral line of plasmas ignited in certain gas mixtures. The main condition to obtain the M effect is the presence of an electropositive and an electronegative gas mixture. For example, in the case of Ne+H₂ monochrome radiation was obtained, the wavelength of Ne being 585.3 nm (1s²–2p⁵). In this paper we prove the general character of this effect, i.e. if the optical emission spectra reduced to nearly one line can be observed also in other gas mixture discharges, for example in the case of one electronegative gas and two electropositive gases. Different other mixtures, as Xe+Ne+H₂ and Xe+Ar+H₂ have been studied. In all these cases, the M-effect appeared without doubt.     

Controlling the parameters of ion bombardment in preparing solid-lubrication coatings with improved properties

Features of the expansion of a pulsed laser-initiated plasma-vapor plume containing Se and Watoms in buffer gases of different chemical compositions (Ar and He) is investigated. It is found that gas pressure influences the structure and chemical state of the deposited WSe_x layers. The conditions for preparing coatings with low coefficients of sliding friction and high wear resistance are determined.