脉冲激光制膜过程中等离子体演化规律的研究

利用有限差分法对脉冲激光沉积(PLD)技术制备KTa065Nb035O3(KTN)薄膜过程中等离子体在等温和绝热两个阶段的速度演化进行了模拟，并给出了其中主要粒子在空间的具体演化规律，对等离子体在空间膨胀的物理机制，进行了深入的讨论，给出了相应演化过程的物理图像，并揭示了等离子体羽辉在膨胀过程中呈现椭球外形的内在原因.     

大气压等离子体辅助多晶硅薄膜化学气相沉积参数诊断

本文采用发射光谱法诊断了大气压下Ar气、SiCl₄及H₂气混合气体（Ar/SiCl₄/H₂）射频放电等离子体射流特性.利用Si原子谱线强度计算了电子激发温度并以此估算了Si原子数密度,研究了射频功率及气体流量对电子激发温度和Si原子数密度以及SiCl₄解离率的作用. 关键词： 大气压等离子体射流 发射光谱 电子激发温度 多晶硅薄膜沉积     

大气压等离子体辅助多晶硅薄膜化学气相沉积参数诊断

本文采用发射光谱法诊断了大气压下Ar气、SiCl₄及H₂气混合气体（Ar/SiCl₄/H₂）射频放电等离子体射流特性.利用Si原子谱线强度计算了电子激发温度并以此估算了Si原子数密度,研究了射频功率及气体流量对电子激发温度和Si原子数密度以及SiCl₄解离率的作用.     

Superhydrophobicity of polytetrafluoroethylene thin film fabricated by pulsed laser deposition

Superhydrophobic polytetrafluoroethylene (PTFE) thin films were obtained by pulsed laser deposition (PLD) technique carried out with KrF excimer laser (λ = 248 nm) of about 1 J/cm² at a pressure of 1.33 Pa. The samples exhibit high water contact angle of about 170° and the sliding angle smaller than 2°. From studying the surface morphology of the prepared films, it is believed that the nano-scale surface roughness has enhanced the hydrophobic property of the PTFE. The increase of trapping air and reducing liquid-solid contact area due to the rough surface, as suggested by the Cassie-Baxter's model, should be responsible for superhydrophobicity of the PLD prepared films. This study thus provides a convenient one-step method without using wet-process to produce a superhydrophobic surface with good self-cleaning properties.     

CuGaO2 thin film synthesis using hydrogen-assisted pulsed laser deposition

Phase formation, crystallinity, and orientation of CuGaO₂ thin films is reported in which hydrogen gas is utilized as a reducing reactant during growth to drive the valence state of Cu to +1. At relatively low growth temperatures, the films are a mixture of CuGaO₂, Cu₂O, and CuGa₂O₄. At higher temperatures, the majority phase is CuGaO₂. The use of H₂ during film growth facilitated the formation of the delafossite phase. Phase purity is further improved via high temperature annealing. The formation of the delafossite phase via post-annealing treatment is in agreement with the thermodynamic equilibrium studies of the Cu-Ga-O system, showing that the CuGaO₂ phase is thermodynamically stable under the conditions considered. With the post-annealing process, we achieved phase-pure CuGaO₂ films with p-type resistivity on the order of 30 Ω cm and carrier density of mid-10¹⁷ cm^-3. PACS 71.20.Nr; 73.61.Le; 81.15.-z     

Chalcogenide-based thin film sensors prepared by pulsed laser deposition technique

One advantage of the pulsed laser deposition (PLD) method is the stoichiometric transfer of multi-component target material to a given substrate. This advantage of the PLD determined the choice to prepare chalco-genide-based thin films with an off-axis geometry PLD. Ag-As-S and Cu-Ag-As-Se-Tetargets were used to deposit thin films on Si substrates for an application as a heavy metal sensing device. The films were characterized by means of Rutherford backscattering spectrometry (RBS), transmission electron microscopy (TEM), and electrochemical measurements. The same stoichiometry of the films and the targets was confirmed by RBS measurements. We observed a good long-term stability of more than 60 days and a nearly Nernstian sensitivity towards Pb and Cu, which is comparable to bulk sensors.     

Resonant infrared pulsed laser deposition of thin biodegradable polymer films

Thin films of the biodegradable polymer poly(DL-lactide-co-glycolide) (PLGA) were deposited using resonant infrared pulsed laser deposition (RIR-PLD). The output of a free-electron laser was focused onto a solid target of the polymer, and the films were deposited using 2.90 (resonant with O-H stretch) and 3.40 (C-H) μm light at macropulse fluences of 7.8 and 6.7 J/cm², respectively. Under these conditions, a 0.5-μm thick film can be grown in less than 5 min. Film structure was determined from infrared absorbance measurements and gel permeation chromatography (GPC). While the infrared absorbance spectrum of the films is nearly identical with that of the native polymer, the average molecular weight of the films is a little less than half that of the starting material. Potential strategies for defeating this mass change are discussed. Received: 22 August 2001 / Accepted: 23 August 2001 / Published online: 17 October 2001     

Characterization of polymer thin films obtained by pulsed laser deposition

The development of laser techniques for the deposition of polymer and biomaterial thin films on solid surfaces in a controlled manner has attracted great attention during the last few years. Here we report the deposition of thin polymer films, namely Polyepichlorhydrin by pulsed laser deposition. Polyepichlorhydrin polymer was deposited on flat substrate (i.e. silicon) using an NdYAG laser (266 nm, 5 ns pulse duration and 10 Hz repetition rate).The obtained thin films have been characterized by atomic force microscopy, scanning electron microscopy, Fourier transform infrared spectroscopy and spectroscopic ellipsometry.It was found that for laser fluences up to 1.5 J/cm² the chemical structure of the deposited polyepichlorhydrin polymer thin layers resembles to the native polymer, whilst by increasing the laser fluence above 1.5 J/cm² the polyepichlorohydrin films present deviations from the bulk polymer.Morphological investigations (atomic force microscopy and scanning electron microscopy) reveal continuous polyepichlorhydrin thin films for a relatively narrow range of fluences (1-1.5 J/cm²).The wavelength dependence of the refractive index and extinction coefficient was determined by ellipsometry studies which lead to new insights about the material.The obtained results indicate that pulsed laser deposition method is potentially useful for the fabrication of polymer thin films to be used in applications including electronics, microsensor or bioengineering industries.     

Characterization of a LiCoO2 thin film cathode grown by pulsed laser deposition

A highly (003)-oriented pure LiCoO₂ thin film cathode, without Co₃O₄ impurities, was grown on a stainless steel substrate by pulsed laser deposition and characterized by electrochemical testing, scanning electron microscopy (SEM), ex situ X-ray diffraction (XRD), Raman and X-ray photoelectron spectroscopy (XPS). The initial reversible discharge capacity of the LiCoO₂ thin film cathode reached 52.5?μAh/cm²µm and capacity loss was about 0.18% per cycle at a current density of 12.74?μA/cm². The chemical diffusion coefficient of the Li⁺ ion was estimated to be about 4.7?×?10^?11?cm²/s from cyclic voltammetric (CV) scans. Ex situ XRD revealed that the spacing of crystalline planes expanded about 0.09?Å when charged to 4.2?V, corresponding to Li_0.5CoO₂, lower than the value for composite powder LiCoO₂ electrodes. XPS results showed that the number of low-coordinated oxygen ions increased relative to the removal of Li⁺ ions.     

Matrix assisted pulsed laser deposition of light emitting polymer thin films

Matrix assisted laser processing allows for the deposition of functional and fragile materials with a minimum of breakdown and decomposition. In this communication we report on light emitting thin films of ruthenium tris(bipyridine)-centered star-shaped poly(methyl methacrylate), Ru(bpyPMMA₂)₃(PF₆)₂, grown by matrix assisted pulsed laser deposition. A pulsed excimer laser (KrF) operating at 248 nm was used for all experiments. Due to the absorption at 248 nm and the solubility characteristics of [Ru(bpyPMMA₂)₃](PF₆)₂, dimethoxy-ethane (DME) was used as a solvent [1]. Dilute solutions (2 wt.%) of [Ru(bpyPMMA₂)₃](PF₆)₂ and DME were flash frozen in liquid nitrogen producing a solid target. Thin films ranging from 20 to 100 nm were grown on Si in an Ar atmosphere at 200 mTorr at a laser fluence of 0.04 J/cm². The deposited materials were characterized by proton nuclear magnetic resonance (¹H NMR) and gel permeation chromatography (GPC) equipped with refractive index (RI), and ultraviolet/visible (UV/vis) detection. PACS 81.15.Fg; 79.20.Ds; 78.66.Qn; 42.70.Jk     

Electric field effect in pulsed laser deposition of epitaxial ZnO thin film

We have developed a new system in which thin films can be pulsed laser deposited under an external electric field. Application of 1 kV high voltage to a thin metal wire placed 1 mm above an edge of a 14 mm long substrate distributes electric fields ranging from 4500 V/cm at the left to 50 V/cm at the right side of the substrate. The crystallinity of the ZnO thin film was remarkably improved in the area where the electric field higher than +100 V/cm was applied during the film deposition. Thus, the film growth of ZnO with a strong polarity along the c-axis was verified to depend on an external electric field. PACS 61.10.Nz; 68.55.-a; 72.80.Ga; 78.55.-m; 78.55.-Et     

Combinatorial arc plasma deposition search for Ru-based thin film metallic glass

We have discovered a novel Ru-based thin film metallic glass (TFMG) using combinatorial arc plasma deposition (CAPD). To search for Ru-based TFMG, alloy systems of Ru-Zr-Al, Ru-Zr-Fe and Ru-Zr-Mo were investigated by making libraries. Each library consisted of 1089 CAPD samples deposited on a substrate by CAPD. Composition of each sample is different with each other.The composition and phases of the CAPD samples were measured by energy dispersive X-ray fluorescence spectrometry and X-ray diffractometry, respectively. Results showed the amorphous regions depended on the additive elements Al, Fe or Mo. Compared with the addition of Al, the addition of Fe or Mo exhibited high amorphous forming ability.To evaluate the mechanical properties, the glass transition temperature T_g and the crystallization temperature T_x of the amorphous samples in each Ru-Zr-X alloy, larger samples having the same compositions as the typical amorphous CAPD samples were reproduced by sputtering because the CAPD samples were too small to measure the mechanical properties, T_g and T_x.Ru₆₅Zr₃₀Al₅ and Ru₆₇Zr₂₅Al₈ samples were found to exhibit the better fracture stress and elastic limit than conventional TFMGs, while Ru-Zr-Fe and Ru-Zr-Mo samples were found to be brittle. DSC revealed that the Ru₆₅Zr₃₀Al₅ sample was a TFMG, with a T_g of 902 K and T_x of 973 K.     

脉冲激光气相沉积法制备钴纳米薄膜实验研究

采用脉冲激光沉积技术制备了钴纳米薄膜,分析和讨论了不同背景气压和脉冲频率对钴纳米薄膜表面形貌的影响及纳米微粒的形成机理。实验结果表明：在低背景气压下,等离子体羽辉自身粒子之间的碰撞占主导作用,容易形成液滴;在较高背景气压下,等离子体羽辉边缘粒子和背景气体粒子之间的碰撞占主导作用,容易形成小岛并凝聚成微颗粒;在4Hz的脉冲重复频率和5Pa背景气压下生长出单分散性良好的钴纳米颗粒。     

Nano-structured Fe thin film deposition using plasma focus device

This paper reports the deposition of nano-structured Fe thin films using 3.3 kJ Mather-type plasma focus. The conventional hollow copper anode was replaced by anode fitted with solid Fe top and the deposition was done using different numbers of deposition shots at two different angular positions. Scanning Electron Microscopy shows that the size of nano-phase agglomerate is smaller when the sample is deposited using either lesser number of deposition shots or at higher angular position with respect to anode axis. X-ray Diffraction shows that crystal structure characteristics change with increase in number of deposition shots. Measurements of magnetic properties using Vibrating Sample Magnetometer identify intermediate magnetization and coercivity in Fe thin films deposited at smaller angular position with respect to anode axis. It is concluded that the morphological, structural and magnetic characteristics of Fe thin films deposited using plasma focus device depend not only on the number of focus deposition shots but also on the angular position of the sample.     

脉冲激光制备薄膜材料的烧蚀机理

研究了脉冲激光烧蚀靶材的整个过程.从包含热源项的导热方程出发，利用适当的动态边界条件，详细研究了靶材在熔融前后的温度分布规律，并且给出了熔融后的固、液分界面的变化规律.熔融后的温度演化规律和固液相界面均以解析表达式的形式给出.还根据能量平衡原理给出烧蚀面位置随时间的变化规律.以硅靶材为例计算模拟了激光烧蚀的整个过程，与实验结果符合较好. 关键词： 脉冲激光 烧蚀面 熔融 温度演化     

Synthesis of heavy fermion CeCoIn5 thin film via pulsed laser deposition

CeCoIn₅ (Co115) thin films have been grown on Al₂O₃ (000l) substrates through the pulsed laser deposition (PLD). The films are grown mainly along the c-axis, with CeIn₃ and In-related alloys. The rock-salt type grains are nucleated, where Co115 grains mixed with excess indium are evenly distributed over the substrate. The electrical resistivity of the films shows a Kondo coherence peak near 47 K and the zero-resistance superconducting state at 1.8 K, which is the first observation in the PLD grown thin films of Co115. The Rietveld refinement of the thin films shows that the c/a ratio (tetragonality) is suppressed to 1.6312 from 1.6374 of single crystals, which is consistent with the linear relationship between the superconducting transition temperature and tetragonality. The good agreement indicates that the PLD could provide an alternative route to tune the 2D character of the critical spin fluctuations to understand the superconducting pairing mechanism of Co115.     

Electroluminescence characteristics of organic thin film pumped by pulsed excitation

The current roll-off in organic light-emitting diodes has been studied by observing the current density versus voltage characteristics and spectra of single-layer and bilayer devices. Pumped by radiation sources of a variety of intensities, the current densities in a single-layer device decrease and spectra were shifted towards blue region. This is a result of the large amount of excess anion radicals that absorb the emitted photons. Using a bilayer device to balance the excess anion radicals is one of the methods to restrain the current roll-off.     

Optical, structural and optoelectronic properties of pulsed laser deposition PbS thin film

Lead sulfide (PbS) nano-structured film has been grown on quartz substrates by the PLD technique. The deposited films were characterized by X-ray diffraction (XRD), selected area electron diffraction (SAED), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Formation of cubic phase of PbS nanocrystals is proven. The absorption and emission spectra were measured for different thicknesses of the films. I–V characteristics and photoconductivity of the deposited film were also measured. The results indicate an efficient performance of the deposited films as an optical detector.     

Observation of multiferroic properties in a CdTe:Mn thin film grown by pulsed laser deposition techniques

We report multiferroic properties in a 3% Mn-doped CdTe (CdTe:Mn or CTM) thin film grown in a co-deposition system constituting pulsed laser deposition and radio frequency (RF) sputtering, in which the Mn concentration was tuned by the sputtering rate of Mn. We observed a clear ferroelectric hysteresis loop in the CTM thin film with remanent polarization of 3.5 μC/cm² and ferromagnetism in the film at a temperature lower than the Curie temperature of 15 K. Both features show direct evidence of multiferroics in the CTM thin film.     

SBN thin films growth by RF plasma beam assisted pulsed laser deposition

SBN thin films were grown on MgO and Silicon substrates by PLD and RF-PLD (radiofrequency assisted PLD) starting from single crystal Sr_0.6Ba_0.4Nb₂O₆ and ceramic Sr_0.5Ba_0.5Nb₂O₆ stoichiometric targets. Morphological and structural analyses were performed on the SBN layers by AFM and XRD and optical properties were measured by spectroellipsometry. The films composition was determined by Rutherford Backscattering Spectrometry. The best set of experimental conditions for obtaining crystalline, c-axis preferential texture and with dominant 31° in-plane orientation relative to the MgO (100) axis is identified.