脉冲准分子激光淀积薄膜的实验研究

利用两种脉宽 (30ns,5 0 0fs)的KrF准分子激光展开了淀积类金刚石薄膜的实验研究 ,并且成功地制备了大面积不含氢成分的HF DLC薄膜 ,运用时空分辨的等离子体发射光谱诊断系统和离子探针系统研究了等离子体特性对薄膜性能的影响。尝试了利用准分子激光制备非晶硅薄膜 ,研究了实验参数对非晶硅薄膜制备的影响 ,并分析了制备具有良好电学和光学性能的非晶硅薄膜的条件     

Growth and characterization of pulsed laser deposited ZnO thin films

One of the most important and promising materials from metal oxides is ZnO with specific properties for near UV emission and absorption optical devices. The properties of ZnO thin films strongly depend on the deposition method. Among them, pulsed laser deposition (PLD) plays an important role for preparing various kinds of ZnO films, e.g. doped, undoped, monocrystalline, and polycrystalline. Different approaches — ablation of sintered ZnO pellets or pure metallic Zn as target material are described. This contribution is comparing properties of ZnO thin films deposited from pure Zn target in oxygen atmosphere and those deposited from sintered ZnO target. There is a close connection between final thin film properties and PLD conditions. The surface properties of differently grown ZnO thin films are measured by secondary ion mass spectrometry (SIMS), atomic force microscopy (AFM) and scanning electron microscopy (SEM). Furthermore, different approaches — ablation of sintered ZnO pellet or pure metallic Zn as target materials are described. The main results characterize typical properties of ZnO films versus technological parameters are presented. Presented at 5-th International Conference Solid State Surfaces and Interfaces, November 19–24, 2006, Smolenice Castle, Slovakia     

Characterization of pulsed laser deposited chalcogenide thin layers

In this work we report on pulsed laser deposition (PLD) of chalcogenide thin films from the systems (AsSe)_100−xAgI_x and (AsSe)_100−xAg_x for sensing applications. A KrF* excimer laser (λ = 248 nm; τ_FWHM = 25 ns) was used to ablate the targets that had been prepared from the synthesised chalcogenide materials. The films were deposited in either vacuum (4 × 10⁻⁴ Pa) or argon (5 Pa) on silicon and glass substrates kept at room temperature. The basic properties of the films, including their morphology, topography, structure, and composition were characterised by complementary techniques. Investigations by X-ray diffraction (XRD) confirmed the amorphous nature of the films, as no strong diffraction reflections were found. The film composition was studied by energy dispersive X-ray (EDX) spectroscopy. The morphology of the films investigated by scanning electron microscopy (SEM), revealed a particulate-covered homogeneous surface, typical of PLD. Topographical analyses by atomic force microscopy (AFM) showed that the particulate size was slightly larger in Ar than in vacuum. The uniform surface areas were rather smooth, with root mean square (rms) roughness increasing up to several nanometers with the AgI or Ag doping. Based upon the results from the comprehensive investigation of the basic properties of the chalcogenide films prepared by PLD and their dependence on the process parameters, samples with appropriate sorption properties can be selected for possible applications in cantilever gas sensors.     

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.     

Preparation of ZnMgO:Ga thin films on flexible substrates by pulsed laser deposition

Transparent conducting ZnMgO:Ga films were deposited on flexible PET substrates by pulsed laser deposition (PLD). Effects of deposition pressure and time on the structural, electrical and optical properties of ZnMgO:Ga films were investigated. The films showed a low resistivity about 7.68 × 10⁻⁴ Ω cm when deposited at the pressure of 0.03 Pa for 40 min. All the films exhibited a high transmittance over 80% in the visible and near-ultraviolet region. The band gap of as-grown films was about 3.50 eV.     

脉冲激光沉积动力学研究进展

脉冲激光沉积技术是现代常用的先进薄膜材料制备技术之一.文章在简要介绍脉冲激光沉积技术及其进展的基础上,较全面地介绍了脉冲激光沉积动力学的基本物理图像和动力学构架,深入地探讨了激光烧蚀靶材过程、等离子体膨胀过程和薄膜沉积过程的动力学规律,阐述了我国学者在脉冲激光沉积动力学研究方面的贡献,例如包括脉冲激光沉积三个工艺过程自洽的统一模型,等离子体膨胀的冲击波模型,基于局域能量动量守恒定律的新等离子体演化动力学模型,包括热源项、蒸发项、等离子体屏蔽效应和动态物性参数的烧蚀热传导模型,考虑电子碰撞效应和能带结构变化的修正双温模型,能统一描写从纳秒级到飞秒级脉冲激光烧蚀规律的统一双温模型等.     

Structural and luminescent characteristics of pulsed laser deposited Eu3+-doped Y2O3 thin films

Thin films of Eu-doped Y₂O₃ were deposited using the pulsed laser ablation technique on amorphous fused silica substrates. The effect of oxygen partial pressure (pO₂) and substrate temperature on the structural and optical characteristics of the deposited films were investigated. All the deposited films were crystalline, showing preferred orientation along the (111) plane, irrespective of oxygen partial pressure and substrate temperature. The film deposited at 0.005?mbar pO₂ exhibited better crystallinity with minimum FWHM at a substrate temperature of 600°C. All the films deposited at various substrate temperatures and different partial pressure (at 600°C) exhibited a red luminescence peak at 615?nm corresponding to the ⁵D₀–⁷F₁ transition in Eu³⁺. Photoluminescence excitation spectra exhibited two bands, one corresponding to band to band excitation (212?nm) of the host and the other to charge transfer band excitation (245?nm). A microstructure analysis revealed that surface roughness of the as-deposited films increases with increase in oxygen partial pressure.     

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.     

Non-stoichiometry-induced metal-to-insulator transition in nickelate thin films grown by pulsed laser deposition

While controlling the cation contents in perovskite rare-earth nickelate thin films, a metal-to-insulator phase transition is reported. Systematic control of cation stoichiometry has been achieved by manipulating the irradiation of excimer laser in pulsed laser deposition. Two rare-earth nickelate bilayer thin-film heterostructures with the controlled cation stoichiometry (i.e. stoichiometric and Ni-excessive) have been fabricated. It is found that the Ni-excessive nickelate film is structurally less dense than the stoichiometric film, albeit both of them are epitaxial and coherent with respect to the underlying substrate. More interestingly, as a temperature decreases, a metal-to-insulator transition is only observed in the Ni-excessive nickelate films, which can be associated with the enhanced disproportionation of the Ni charge valence. Based on our theoretical results, possible origins (e.g. anti-site defects) of the low-temperature insulating state are discussed with the need of future work for deeper understanding. Our work can be utilized to realize unusual physical phenomena (e.g. metal-to-insulator phase transitions) in complex oxide films by manipulating the chemical stoichiometry in pulsed laser deposition.     

Nanostructured silver thin films deposited by pulsed laser ablation

Nanostructured thin films were deposited by excimer laser ablation of silver targets in controlled atmospheres of He and Ar. The film structural properties were investigated by means of scanning electron microscope and transmission electron microscope imaging. The film growth mechanism was identified as the result of coalescence of nanometric clusters formed during plume flight. Cluster formation involves plume confinement as a consequence of the increased collisional rate among plasma species. Fast photography imaging of the laser-generated silver plasma allowed to identify plasma confinement, shock wave formation and plasma stopping.     

Properties of Dy-doped ZnO nanocrystalline thin films prepared by pulsed laser deposition

Highly transparent conductive Dy₂O₃ doped zinc oxide (ZnO)_1-x(Dy₂O₃)_x nanocrystalline thin films with x from 0.5% to 5% have been deposited on glass substrate by pulsed laser deposition technique. The structural, electrical and optical properties of Dy₂O₃ doped thin films were investigated as a function of the x value. The experimental results show that the Dy concentration in Dy-doped ZnO thin films has a strong influence on the material properties especially electrical properties. The resistivity decreased to a minimum value of 5.02 × 10⁻⁴ Ω cm with x increasing from 0.5% to 1.0%, then significantly increased with the further increasing of x value. On the contrary, the optical direct band gap of the (ZnO)_1-x(Dy₂O₃)_x films first increased, then decreased with x increasing. The average transmission of Dy₂O₃ doped zinc oxide films in the visible range is above 90%.     

脉冲激光气相沉积法制备的非晶CH薄膜特性分析

采用脉冲激光气相沉积(PLD)法,研究了氢气压强对非晶CH薄膜性能的影响。原子力显微镜图和白光干涉图显示,薄膜表面平整致密,随着氢气压强增大,粗糙度变大。拉曼光谱分析表明,氢气压强增加,G峰和D峰位置都在向高波数方向移动。傅里叶变换红外光谱分析显示,薄膜中存在sp3—CH2和sp2—CH等基团。最后,采用PLD漂浮法在最优参数氢气压强为0.3 Pa下,成功制备了不同厚度（100~300 nm）、满足一定力学强度、无明显宏观缺陷的自支撑CH薄膜。     

Structural and optical properties of ZnO thin films deposited on quartz glass by pulsed laser deposition

ZnO thin films with typical c-axis (0 0 2) orientation were successfully deposited on quartz glass substrates by pulse laser ablation of Zn target in oxygen atmosphere at a relatively low temperature range of 100-250 °C. The structural and optical properties of the films were studied. In photoluminescence (PL) spectra at room temperature, single ultraviolet emission (without deep-level emission) was obtained from ZnO film deposited at the temperature of 200 °C. This was attributed to its low intrinsic defects.     

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.     

Optical and electrical properties of aluminum-doped ZnO thin films grown by pulsed laser deposition

Transparent aluminum-doped zinc oxide (AZO) thin films were deposited on quartz glass substrates by pulsed laser deposition (PLD) from ablating Zn-Al metallic targets. The structural, electrical and optical properties of these films were characterized as a function of Al concentration (0-8 wt.%) in the target. Films were deposited at a low substrate temperature of 150 °C under 11 Pa of oxygen pressure. It was observed that 2 wt.% of Al in the target (or 1.37 wt.% of Al doped in the AZO film) is the optimum concentration to achieve the minimum film resistivity and strong ultraviolet emission. The presence of Al in the ZnO film changes the carrier concentration and the intrinsic defects.     

Effects of deposition temperature on the structural and morphological properties of thin ZnO films fabricated by pulsed laser deposition

ZnO thin films were grown on Si(1 0 0) substrates using pulsed laser deposition in O₂ gas ambient (10 Pa) and at different substrate temperatures (25, 150, 300 and 400 °C). The influence of the substrate temperature on the structural and morphological properties of the films was investigated using XRD, AFM and SEM. At substrate temperature of T=150 °C, a good quality ZnO film was fabricated that exhibits an average grain size of 15.1 nm with an average RMS roughness of 3.4 nm. The refractive index and the thickness of the thin films determined by the ellipsometry data are also presented and discussed.     

Preparation and characterizations of amorphous nanostructured SiC thin films by low energy pulsed laser deposition

Amorphous silicon carbide (SiC) thin films were deposited on silicon substrates by pulsed laser ablation at room temperature. Thicknesses and surface morphology of the thin films were characterized using optical profilers, atomic force and field emission scanning electron microscopy. Nanohardnes, modulus and scratch resistance properties were determined using XP nanoindenter. The results show that crack free, smooth and nanostructured thin films can be deposited using low laser energy densities.     

Structural characterization of AlN films synthesized by pulsed laser deposition

We obtained AlN thin films by pulsed laser deposition (PLD) from a polycrystalline AlN target using a pulsed KrF* excimer laser source (248 nm, 25 ns, intensity of ∼4 × 10⁸ W/cm², repetition rate 3 Hz, 10 J/cm² laser fluence). The target-Si substrate distance was 5 cm. Films were grown either in vacuum (10⁻⁴ Pa residual pressure) or in nitrogen at a dynamic pressure of 0.1 and 10 Pa, using a total of 20,000 subsequent pulses. The films structure was characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and spectral ellipsometry (SE). Our TEM and XRD studies showed a strong dependence of the film structure on the nitrogen content in the ambient gas. The films deposited in vacuum exhibited a high quality polycrystalline structure with a hexagonal phase. The crystallite growth proceeds along the c-axis, perpendicular to the substrate surface, resulting in a columnar and strongly textured structure. The films grown at low nitrogen pressure (0.1 Pa) were amorphous as seen by TEM and XRD, but SE data analysis revealed ∼1.7 vol.% crystallites embedded in the amorphous AlN matrix. Increasing the nitrogen pressure to 10 Pa promotes the formation of cubic (≤10 nm) crystallites as seen by TEM but their density was still low to be detected by XRD. SE data analysis confirmed the results obtained from the TEM and XRD observations.     

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.     

Excimer laser deposition of thin amorphous carbon films

A new carbon film deposition technique, based upon excimer laser vaporization of graphite in a flowing gas system has been developed. The low temperature vapor (LTV) technique alleviates high temperatures occurring in most other deposition methods. In this technique the UV laser ablation occurs in an inert flowing gas atmosphere. Atoms and molecules evaporated from graphite are cooled by gas entrainment before condensing on a substrate. The resulting films of amorphous carbon or hydrogenated amorphous carbon are free from strain. Measurement of the optical band gap of these films shows that E_g can be controlled by the hydrogen content of the carrier gas.