环境气压对激光烧蚀Cu诱导发光机理的影响

利用时间分辨的光谱测量技术,测定了不同氪气压强下脉冲激光烧蚀金属Cu诱导等离子体发光羽的发射光谱及其强度随时间的分布。利用快速同步照相的方法,拍摄了不同氪气压强下的等离子体发光羽的照片。实验结果表明,等离子体发光羽的光谱主要由原子谱线构成,发光羽颜色随环境气压而变化。结合实验结果探讨了环境气压对脉冲激光烧蚀Cu诱导等离子体发光羽的发光机理的影响,认为不同环境气压下等离子体发光羽的发光机理不同,低压下以电子碰撞传能激发辐射为主,中压下以电子与原子碰撞传能激发和电子与一价离子的复合激发辐射为主,高压下以电子与一价离子的复合激发辐射为主,并用此机理定性地解释了所观察到的实验现象。     

Experimental study of enhanced emission of the laser-ablated plume in backing gas

The effects of background gases on the optical emission of the excimer-laser-ablated plume from a brass target have been studied experimentally. It is found that the plume emission can be enhanced significantly in a proper gas ambient. In hydrogen, the highest peak intensity is detected, and in argon, there is a distinctive difference in the pressure-dependent emission between in He and in the other three gases, Ar, N₂ and H₂. Moreover, the monitored line peak intensity remains unchanged in Ar and N₂ and increases in H₂ within a distance above the target surface; but in He, the observed peak intensity decreases with distance like in vacuum. Furthermore, the emissions of several more atomic lines of Cu and Zn atoms from the plume are also found to be enhanced in the same manner in gas ambient. Some physical processes involved in the plume expansion and the possible mechanisms for the enhanced emission of the plume in backing gas are discussed.     

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利用时空分辨的测量技术,测定了XeCl紫外激光烧蚀金属Cu消融粒子的发射光谱随时间与空间的强度分布。通过在不同的氢气压强下拍摄到的XeCl308nm紫外激光烧蚀金属Cu消融粒子的发光羽照片,发现激光消融粒子发光羽的颜色在不同区域有不同的颜色,不同区域的发光羽颜色随环境气压的改变而变化。随环境气压的增大,发光羽不仅逐渐变小,而且逐渐变淡。对激光消融粒子发光羽的机理进行了探讨,激光消融粒子发光羽的发光动力学模式在不同区域有不同的发光模式,且随环境气压的变化而改变。定性地解释了所观察的实验现象。     

Expansion of a laser plume from a silicon wafer in a wide range of ambient gas pressures

Expansion of the laser plume from a silicon wafer into surrounding gas is considered in the range of ambient gas pressure from 0.1 to 1 bar using a kinetic approach. The plume is generated by a nanosecond Gaussian laser pulse. Absorption of laser radiation and heating and melting of the target are described by a two-dimensional thermal model. Axisymmetric flow in the laser plume is calculated by the direct simulation Monte Carlo method. It was found that diffusion of mixture components is significant in the considered time scale, flow is non-equilibrium, and regions of high rarefaction temporally appear in the flow. In atmospheric pressure, the re-deposition of the silicon vapor was observed only in the vicinity of the laser spot.     

脉冲激光诱导Cu靶产生发光羽的特性分析

通过在不同的环境气压下拍摄脉冲激光烧蚀金属Cu诱导产生的发光羽,获取了不同区域具有不同颜色特征的发光羽照片.结果发现:发光羽的颜色随环境气压的改变而变化.采用空间分辨光谱技术,测定了激光诱导金属Cu靶产生发光羽辐射强度的空间分布,以及不同烧蚀环境气压对发光羽辐射强度的影响.研究了脉冲激光烧蚀Cu表面诱导发光的动力学过程,建立了可能的发光羽分区模型,对发光羽的不同区域发光粒子的激发机理进行了探讨,并用之定性地解释了所观察的实验现象.结果分析表明:脉冲激光诱导Cu产生的发光羽可以分为三个区域,不同区域的发光机理不同,Cu原子和Cu离子的激发机理不完全相同.     

Predicted diffusion rates on fcc (001) metal surfaces for adsorbate/substrate combinations of Ni, Cu, Rh, Pd, Ag, Pt, Au

We investigate the diffusion of a single metal atom on the surface of a fcc (001) metal. Two points concerning the application of kinetic models to diffusion were considered. First, we test the assumption of kinetic models that diffusion occurs via a sequence of uncorrelated jumps. Second, when kinetic models are applicable we predict reasonable values of the kinetic rate constants.

Direct molecular dynamics (MD) simulations were performed for Ag on Ag(001) and Rh on Rh(001) systems. Diffusion was found to obey an Arrhenius-type dependence on temperature in both systems. The barriers and prefactors extracted from the MD results agree with estimates made from transition state theory (TST) and the experimental values for the Rh system. We conclude that kinetic models are applicable to diffusion on fcc (001) surfaces.

Transition state theory was then used to estimate diffusion parameters for all other adsorbate/ substrate combinations of the metals Ni, Cu, Rh, Pd, Ag, Pt, and Au. These results indicate that the characteristics of diffusion are primarily a property of the adsorbate. We also predict Ag atoms to have an anomalously low diffusion barrier on all of the substrates in this study. We use the accurate many-body density functional based MD/MC-CEM potential energy surface which allows us to consistently treat these multi-component systems.     

Plume splitting in pico-second laser-material interaction under the influence of shock wave

In this work, molecular dynamics simulations are conducted to study the physics of plume splitting in pico-second laser material interaction in background gas. The velocity distribution shows a clear split into two distinctive components. Detailed atom trajectory track reveals the behavior of atoms within the peaks and uncovers the mechanisms of peak formation. The observed plume velocity splitting emerges from two distinguished parts of the plume. The front peak of the plume is from the faster moving atoms and smaller particles during laser-material ablation. This region experiences strong constraint from the ambient gas and has substantial velocity attenuation. The second (rear) peak of the plume velocity originates from the larger and slower clusters in laser-material ablation. These larger clusters/particles experience very little constraint from the background, but are affected by the relaxation dynamics of plume and appear almost as a standing wave during the evolution. Density splitting only appears at the beginning of laser-material ablation and quickly disappears due to spread-out of the slower moving clusters. It is found that higher ambient pressure and stronger laser fluence favor earlier plume splitting.     

沿面型介质阻挡放电喷枪的发光特性及气体温度研究

利用氩气作为工作气体,采用正弦电压驱动沿面型等离子体喷枪,在大气压空气环境中产生了均匀的等离子体羽。电学和光学测量结果表明,等离子体羽放电只存在于外加峰值电压的正半周期,并且正半周期的放电脉冲个数随气体流量的增加而增加。通过对正半周期不同位置的发光脉冲信号进行比较,发现等离子体羽均按子弹形式传播,其中每一个发光脉冲均对应一次等离子体子弹传播过程。通过对比放电电流和等离子体羽的发光信号,发现等离子体羽的发光脉冲滞后于放电电流脉冲,且该延迟时间基本服从正态分布。该延迟时间随着外加电压峰值及气体流量的增大而减小。利用光纤测温仪测量了等离子体羽的气体温度,发现气体温度随外加峰值电压的增大而升高,随工作气体流量的增大而降低。通过分析放电过程,对上述现象进行了定性解释。     

Polyol mediated hexadecylamine capped silver allied nanobimetallic particles and their fluxional properties

The syntheses of hexadecylamine seed mediated Ag/M (M=Co, Ni, Pd and Pt) allied nanobimetallic particles were successfully carried out by the successive reduction of ligand capped metal ions with polyols, resulting in concomitant precipitation of some high index faceted hybrid Ag/M bimetal nanoparticles. The optical measurements revealed the existence of surface plasmon band and peak broadening that causes diffusion processes of the metal sols to decrease making it possible to monitor the changes spectrophotometrically. The bimetallic nanoparticles were characterized by X-ray diffraction, X-ray photoelectron spectroscopy and electron microscopy techniques which confirm the formation of alloyed clusters.     

The molecular dynamic study of anharmonic effects at Cu(111) and Ag(111) surfaces in the presence of Cu- and Ag-trimer island

The molecular dynamics (MD) technique based on semi-empirical potentials, is used to carry out the diffusion of Cu- and Ag-trimer on Cu- and Ag(111) surface at 300, 500 and 700 K temperatures. The constant energy MD simulation elaborates the anharmonic effects at the surface such as fissures, dislocations and vacancy creation, in the presence of island. The fissures and dislocations formed are in the range of 1.5–4 Å and 1–7 Å, respectively, from the island's position. The Cu and Ag islands both diffuse easily on Cu(111) surface, manipulate that the trend of diffusion is faster on Cu surface as compared to Ag surface. The process of breaking and opening of the island has also been observed. Moreover, a surface atom popped-up at 700 K by creating a vacancy near the Cu island on Ag surface. The rate of diffusion increases with the increase in temperature, both for homo- and hetero-cases.     

Single-walled carbon nanotube formation with double laser vaporization technique

Single-walled carbon nanotubes (SWNTs) were prepared with double laser vaporization of a graphite target and a metal/alloy target inside an electric furnace at 1200 ^°C ambient temperature with 500 torr Ar gas atmosphere. Each target was vaporized simultaneously with a different Nd:YAG laser. Several kinds of metal/alloy target (Ni, Co, Fe, and permalloy) were tested in order to see the difference in the resulting SWNT yield and the diameter distribution of them. The Raman spectra of SWNT-containing soot prepared by use of this technique with permalloy/carbon system indicated that permalloy gives almost the same yield as compared with Ni/Co carbon composite rod with single laser vaporization technique, though the diameter distribution of them is slightly different. Also, time-resolved images of the plume by carbon and permalloy nanoparticles after laser vaporization were collected using a high-speed video camera. These images suggest that the hot plumes due to carbon and permalloy nanoparticles do not mix together so extensively, at least in a few hundred microseconds after laser vaporization. The effect of time delay between two laser pulses on the yield and the diameter distribution of SWNTs was also presented and discussed.     

Comparative investigation on decorating carbon nanotubes with different transition metals

The diffusion dynamics and structure evolvement of the transition metal (TM=Ni, Cu, Au, and Pt) atoms decorating carbon nanotubes (CNTs) with differences have been systematically studied by Monte Carlo (MC) simulation. The studies show that TM atoms can be encapsulated inside, aggregated and even wrapped on the surface of the CNT, which depend on the interactions among TM–TM and TM–C during the spontaneous diffusion process. The decorating effect is greatly influenced by the diameters of CNTs, TM atoms tend to be encapsulated inside the tube in the relatively large CNTs, while they are inclined to stack on the surface for the small ones. More interestingly, Au and Pt atoms would wrap around the smaller CNT, whereas Ni and Cu atoms are still clustering outside of the CNTs with the increase of the number of TM atoms. Simulation results indicate that Pt and Au possess a better wetting effect with CNT than Ni and Cu.     

Morphology, optical and electrical properties of Cu-Ni nanoparticles in a-C:H prepared by co-deposition of RF-sputtering and RF-PECVD

We report optical and electrical properties of Cu-Ni nanoparticles in hydrogenated amorphous carbon (Cu-Ni NPs @ a-C:H) with different surface morphology. Ni NPs with layer thicknesses of 5, 10 and 15 nm over Cu NPs @ a-C:H were prepared by co-deposition of RF-sputtering and RF-Plasma Enhanced Chemical Vapor Deposition (RF-PECVD) from acetylene gas and Cu and Ni targets. A nonmetal-metal transition was observed as the thickness of Ni over layer increases. The surface morphology of the sample was described by a two dimensional (2D) Gaussian self-affine fractal, except the sample with 10 nm thickness of Ni over layer, which is in the nonmetal-metal transition region. X-ray diffraction profile indicates that Cu NPs and Ni NPs with fcc crystalline structure are formed in these films. Localized Surface Plasmon Resonance (LSPR) peak of Cu NPs is observed around 600 nm in visible spectra, which is widen and shifted to lower wavelengths as the thickness of Ni over layer increases. The variation of LSPR peak width correlates with conductivity variation of these bilayers. We assign both effects to surface electron delocalization of Cu NPs.     

Effect of spin contamination error on surface catalytic reaction: NO reduction by core-shell catalysts

ABSTRACT

The effects of spin contamination errors on the activation barriers of catalytic NO reduction by TiO₂/Ag and ZrO₂/Cu core-shell catalyst models were investigated using an approximate spin projection method and an unrestricted density functional theory calculation with the plane-wave basis set. The estimated barrier of the TiO₂/Ag system increased (0.03?eV), whereas that of the ZrO₂/Cu system decreased (0.04?eV) after the correction of the spin contamination error. This difference in the estimated barriers of the two systems can be attributed to the difference in their surface structures. The error obtained for the TiO₂/Ag system was larger than that obtained for the gas phase, i.e. the spin contamination error was induced by the molecule/surface interaction. Moreover, the error correction also changed the rate-determining step of ZrO₂/Cu. These results demonstrate the importance of the correction of spin contamination errors for the detailed investigation of catalytic reactions.     

Double-pulse laser ablation applied to reactive PLD method for synthesis of carbon nitride film: A second laser shot delay

Carbon nitride films were deposited using ablation of graphite target by second harmonic radiation of Nd:YAG laser in nitrogen atmosphere. To produce high hardness films, the deposited particles should have sufficient kinetic energy to provide their efficient diffusion on a substrate surface for formation of crystal structure. However, a shock wave is arisen in ambient gas as a consequence of laser plasma explosive formation. This shock wave reflected from the substrate interacts with plume particles produced by the first laser pulse and decreases their kinetic energy. This results in decrease of film crystallinity. To improve film quality, two successive laser pulses was proposed to be used. At adjusting time delay, the particles induced by the second pulse wilt serve as a piston, which will push forward both stopped particles ablated by the first pulse and arisen from chemical reactions in ambient gas. An X-ray photoelectron spectroscopy (XPS) analysis of deposited films has shown an increase of content of sp ³ carbon atoms corresponding to crystalline phase, if double-pulse configuration is employed. The luminescence of excited C₂ and CN molecules in laser plume at different distances from the target was studied to optimize the delay between laser pulses.     

Interdiffusion of Al-Ni system enhanced by ultrasonic vibration at ambient temperature

At ambient temperature, Al–1%Si wire of 25 μm diameter was bonded successfully onto the Au/Ni/Cu pad by ultrasonic wedge bonding technology. Physical process of the bond formation and the interface joining essence were investigated. It is found that the wire was softened by ultrasonic vibration, at the same time, pressure was loaded on the wire and plastic flow was generated in the bonding wire, which promoted the diffusion for Ni into Al. Ultrasonic vibration enhanced the interdiffusion that resulted from the inner defects such as dislocations, vacancies, voids and so on, which ascribed to short circuit diffusion.     

Enhanced emission of the laser generated plume in Ar gas

We report an effect of enhanced emission of laser generated plume in gas ambi-ent.Nonreactive argon gas was used in the experiment of UV laser ablation of copper plate.The emission of Cu atoms from the plume was increased more than the times.The emission in-tensity is sensitive to the gas pressure,but in a certain region of gas pressure,the enhanced ef-fect can be controlled stably.For the emission lines from other element,Zn,in the plume,the intensities are subjected to the same factor of increasement.     

Ag-Cu离子注入玻璃后不同气氛退火的光吸收研究

采用MEVVA源（metal vapor vacuum arc ion source）引出的强束流脉冲Ag,Cu离子先后注入到SiO₂玻璃，x射线光电子能谱仪（XPS）分析显示Ag，Cu大多仍为金属态，有部分氧化态Cu存在.透射电镜观察分析和光学吸收谱都表明在衬底中形成了纳米合金颗粒.结合有效媒质理论，得到模拟的光学吸收谱，与实验结果基本符合，较好地验证了以上结论.样品退火后颗粒发生分解，分解的颗粒在氧化气氛下被氧化，且有部分向样品表面蒸发；在还原气氛下氧化态元素被还原并成核生长.故 关键词： 离子注入 纳米颗粒 退火 光学吸收率