Interaction of thin gold films with silicon

The study of thin (~ 10 monolayers) films Au on Si(III) after heating using LEED, ELS, AES, TEM, PES methods has been carried out. We came to the conclusion that gold on the silicon surface forms a chemical bond with the semiconductor forming surface phases with different electron structures, depending on the Si and Au concentrations.     

Pulsed laser deposition of NiMnGa thin films on silicon

Thin films of the magnetic shape-memory (MSM) material NiMnGa have been deposited on Si(100) substrates using pulsed laser deposition. The -–200 300nm-thick films were prepared at substrate temperatures ranging from 450 °C to 650 °C and at different background Ar pressures. Large saturation magnetizations, up to 60% of the bulk value, were measured for the films. Only the films deposited in vacuum or at Ar pressures below 10^-3 mbar and at temperatures between 500 °C and 600 °C were ferromagnetic. The films are mainly crystallized in the austenitic phase and they have a smooth surface with a low droplet density (0.01 m^-2). The magnetization and surface quality are sufficient that the films could be utilized in the realization of thin-film MSM devices. PACS 75.70.Ak     

用迈克尔逊干涉仪测量全息干板膜厚度

全息干板膜的厚度是全息干板的重要参数之一。使用迈克尔逊干涉仪和白光光源对2种全息干板膜厚度进行测量，并对测量结果误差进行分析，给出了测量误差与膜厚及折射率之间的关系以及此方法的适用范围。研究结果表明：在膜厚从8μm增至41μm的过程中，测量结果的绝对误差≤2μm且变化很小，相对误差则从14.1%降到了2.2%。随着膜厚的增加，相对误差明显降低；折射率n也参与了误差传递，其值与测量误差呈类似反比关系；当n值在1.5附近时，为保证测量的准确性，所测膜厚≥40μm。最后指出，迈克尔逊干涉仪在测量全息干板膜等较厚的薄膜时，具有测量范围大，结果较准确等优点。     

Chromium carbide thin films deposited by ultra-short pulse laser deposition

Pulsed laser deposition performed by a laser with a pulse duration of 250 fs has been used to deposit films from a Cr₃C₂ target. Due to the different processes involved in the laser ablation when it is performed by an ultra-short pulse source instead of a conventional short pulse one, it has been possible to obtain in vacuum films containing only one type of carbide, Cr₃C₂, as shown by X-ray photoelectron spectroscopy. On the other hand, Cr₃C₂ is not the only component of the films, since a large amount of amorphous carbon is also present. The films, deposited at room temperature, are amorphous and seem to be formed by the coalescence of a large number of particles with nanometric size. The film composition can be explained in terms of thermal evaporation from particles ejected from the target.     

碳化硅薄膜脉冲激光晶化特性研究

采用XeCl准分子激光对非晶碳化硅(a-SiC)薄膜的脉冲激光晶化特性进行了研究.通过原子力显微镜（AFM）和Raman光谱技术对退火前后薄膜样品的形貌、结构及物相特性进行了分析.结果表明，选用合适的激光能量采用激光退火技术能够实现a-SiC薄膜的纳米晶化.退火薄膜中的纳米颗粒大小随着激光能量密度的增加而增大；Raman谱分析结果显示了退火后的薄膜的晶态结构特性并给出了伴随退火过程存在的物相分凝现象.根据以上结果并结合激光退火特性，对a-SiC的脉冲激光晶化机理进行了讨论. 关键词： 激光退火 晶化 碳化硅     

Preliminary result of bunch length measurement using a modified Michelson interferometer

Based on the femtosecond accelerator device which was built at the Shanghai Institute of Applied Physics (SINAP), recently a modified far infrared Michelson interferometer has been developed to measure the length of electron bunches via the optical autocorrelation method.Compared with our former normal Michelson interferometer, we use a hollow retroreflector instead of a flat mirror as the reflective mirror.The experimental setup and results of the bunch length measurement will be described in this paper.     

Preliminary result of bunch length measurement using a modified Michelson interferometer

Based on the femtosecond accelerator device which was built at the Shanghai Institute of Applied Physics （SINAP）, recently a modified far infrared Michelson interferometer has been developed to measure the length of electron bunches via the optical autocorrelation method. Compared with our former normal Michelson interferometer, we use a hollow retroreflector instead of a flat mirror as the reflective mirror. The experimental setup and results of the bunch length measurement will be described in this paper.     

Determining the refractive index of liquids using a modified Michelson interferometer

An accurate method for measuring the refractive index of liquids is proposed, modeled, and experimentally verified. The experimental setup is a modified Michelson interferometer employing a novel liquid chamber that allows the optical pathlength to be continuously varied without moving a mirror. This experiment allows determining the refractive index of a given liquid to high precision, with an accuracy limited only by the normal random variables encountered in interferometric measurements and ultimately the accuracy to which the wavelength of the laser light is known.     

Amorphous-polycrystal transition induced by laser pulse in self-ion implanted silicon

Reflection high energy electron diffraction has been used to investigate the amorphous to polycrystalline structure transition in silicon induced by laser pulse. The power density of the ruby laser pulse, in the free generation mode, has been maintained below the threshold to induce surface damage. Depth analysis has been carried out in 〈100〉 silicon crystal using the channeling effect technique.     

Pulsed laser treatment of gold and black gold thin films fabricated by thermal evaporation

The effect of pulsed laser treatment of metal, and metal blacks, was studied. Gold and black gold thin films were fabricated by thermal evaporation of gold in a vacuum and nitrogen atmosphere respectively. Black gold films were grown in a nitrogen atmosphere at pressures of 200 Pa and 300 Pa. UV pulsed laser radiation (λ = 266 nm, τ = 4 ns), with fluence ranging from 1 mJ·cm⁻² to 250 mJ·cm⁻² was used for the film treatment in a vacuum and nitrogen atmosphere. The nitrogen pressure was varied up to 100 kPa. Surface structure modifications were analyzed by optical microscopy, atomic force microscopy (AFM) and scanning electron microscopy (SEM). Energy dispersive X-ray spectroscopy (EDX) was used for chemical characterization of the samples. A significant dependence of the film optical and structural properties on laser treatment conditions (laser fluence, ambient pressure and number of applied pulses) was found. The threshold for observable damage and initiation of changes of morphology for gold and black gold surfaces was determined. Distinct modifications were observed for fluences greater than 106 mJ·cm⁻² and 3.5 mJ·cm⁻² for the gold and black gold films respectively. Absorbtivity of the black gold film is found to decrease with an increase in the number of laser pulses. Microstructural and nanostructural modifications after laser treatment of the black gold film were observed. EDX analysis revealed that no impurities were introduced into the samples during both the deposition and laser treatment.      

Common path interferometer based on the modified Michelson configuration using a reflective grating

A common-path interferometer using the modified Michelson system with a reflective grating is proposed for quantitative phase imaging. The frequency spectrum of the object beam is split into two beams using a beam splitter. One beam is diffracted into +1, 0, and −1 orders by the reflective grating to act as an object beam, and the other beam is low-filtered and diffracted by a pinhole mirror to act as a reference beam. Three phase-shifted interferograms can be simultaneously captured using the proposed interferometer, and the specimen phase can then be reconstructed from the three interferograms. Experiments are carried out to prove the precision, real-time ability, and stability of the proposed method.     

Reactive pulsed laser deposition of gold nitride thin films

We report on the growth and characterization of gold nitride thin films on Si 〈1 0 0〉 substrates at room temperature by reactive pulsed laser ablation. A pure (99.95%) Au target was ablated with KrF excimer laser pulses in nitrogen containing atmosphere (N₂ or NH₃). The gas ambient pressure was varied in the range 0.1-100 Pa. The morphology of the films was studied by using optical, scanning electron and atomic force microscopy, evidencing compact films with RMS roughness in the range 3.6-35.1 nm, depending on the deposition pressure. Rutherford backscattering spectrometry and energy dispersion spectroscopy (EDS) were used to detect the nitrogen concentration into the films. The EDS nitrogen peak does not decrease in intensity after 2 h annealing at 250 °C. Film resistivity was measured using a four-point probe and resulted in the (4-20) × 10⁻⁸ Ω m range, depending on the ambient pressure, to be compared with the value 2.6 × 10⁻⁸ Ω m of a pure gold film. Indentation and scratch measurements gave microhardness values of 2-3 GPa and the Young's modulus close to 100 GPa. X-ray photoemission spectra clearly showed the N 1s peak around 400 eV and displaced with respect to N₂ phase. All these measurements point to the formation of the gold nitride phase.     

Nanostructured thin films obtained by ultra-short pulse laser deposition of vanadium carbide

In this paper we will report the results obtained by femtosecond Pulsed Laser Deposition on vanadium carbide. These results, compared with those obtained for another group 5 carbide, tantalum carbide, evidence large analogies between the two systems. Optical emission spectroscopy shows in both cases the presence of particles in the secondary plume and in both cases the films are formed by nanoparticles and present a stoichiometry corresponding to the hemicarbide.     

Thermal behavior of thin metal films irradiated by shaped femtosecond pulse sequences laser

A numerical solution of the two-temperature model has been performed up to the shaped femtosecond pulse sequences heated metal target. The two-temperature model is used to analyze the shaped femtosecond pulse sequences with the following major conclusions. We confirm the distinctly different results on the different shaped femtosecond pulse sequences. As the number of shaped femtosecond pulses increases, the nonequilibrium state between electrons and phonons gradually disappears, the highest transient electron temperature is lowered and the thermolization time is prolonged, the electron heat conductivity remains higher because of the effect of incubation on the electron temperature, which preserves the advantages of ultrashort lasers. The shaped femtosecond pulse sequences can increase the efficiency in ablation and micromachining.     

飞秒激光作用下薄膜破坏的力学过程

提出了等离子体膨胀的力学模型, 在等离子体膨胀过程中考虑了球壳膨胀时的惯性效应，实现了动态特性的模拟.采用能量守恒原理，研究了薄膜中等离子体受限制爆炸的薄膜损伤机理的力学特性,并对薄膜损伤的发展作了初步探讨. 关键词： 等离子体 膨胀 薄膜 激光     

Optical characterization of thin silicon films deposited by CVD and annealed by pulsed laser

Polycrystalline Si layers 100 to 800 nm thick have been deposited on Si single crystal substrates by CVD and annealed with a Q-switched ruby laser at energies up to 1.5 J/cm². The optical characteristics of these layers have been measured by SEM and ellipsometry. The results can be attributed to a change in surface roughness with film thickness and laser energy.     

Microdroplet evolution induced by a laser pulse

Interaction between high-power ultrashort laser pulse and giant clusters (microdroplets) consisting of 10⁹ to 10¹⁰ atoms is considered. The microdroplet size is comparable to the laser wavelength. A model of the evolution of a microdroplet plasma induced by a high-power laser pulse is developed, and the processes taking place after interaction with the pulse are analyzed. It is shown theoretically that the plasma is superheated: its temperature is approximately equal to the ionization potential of an ion having a typical charge. The microdroplet plasma parameters are independent of the pulse shape and duration. The theoretical conclusions are supported by experimental studies of x-ray spectra conducted at JAERI, where a 100-terawatt Ti-sapphire laser system was used to irradiate krypton and xenon microdroplets by laser pulses with pulse widths of 30 to 500 fs and intensities of 6×10¹⁶ to 2×10¹⁹W/cm².     

Synthesis of non-stoichiometric (LaO)CuS thin films by pulse laser deposition

We have attempted to control the photoluminescence spectrum of transparent p-type semiconductor (LaO)CuS to check possibilities of phosphor application using non-stoichiometric thin films prepared by pulse laser deposition method. Two kinds of samples are examined, one is the samples that contain the excess S and the other is the excess Cu. All samples are a single phase without impurities, regardless of heavily doping. Lattice constants for all samples don’t depend on the concentration of excess atoms. Perhaps, this is due to the nature of the layered materials. Introduction of excess atoms leads to change the photoluminescence spectra. The excess S and Cu have much effect on the red and the blue luminescence bands, respectively. We have succeeded in the tuning luminescence band of photoluminescence spectra.