Pulsed laser deposition of Co and growth of CoSi2 on Si(111)

Monolayers of Co were prepared by pulsed laser deposition (PLD) and thermal deposition (TD) on Si(111) substrates. The surface structure and morphology were studied as a function of annealing temperature with scanning tunneling microscopy and low-energy electron diffraction (LEED). Comparing PLD to TD in the monolayer regime, we find surface phases with lower Co content in the top layer for annealing temperatures below 500 °C, indicating an implantation of Co into the Si substrate. The implanted Co leads to an increased intermixing of Co and Si and a higher density of nucleation centers for Co multilayers produced by PLD compared to TD. Multilayer PLD films therefore show an improved film quality, which is detected by an increased intensity of the LEED reflectivity. PACS 68.37.Ef; 61.14.Hg; 68.55.-a     

Physical aspects of the pulsed laser deposition technique: The stoichiometric transfer of material from target to film

The physical processes of pulsed laser deposition (PLD) change strongly from the initial light absorption in a target to the final deposition and growth of a film. One of the primary advantages of PLD is the stoichiometric transfer of material from target to a film on a substrate. Even for a stoichiometric flow of material from a multicomponent target, the simultaneous arrival of the target atoms is not sufficient to ensure a stoichiometric film growth. The laser fluence has to be sufficiently high to induce ablation rather than pure evaporation from target, but a high fluence may lead to preferential (self)sputtering and possibly implantation of the light atoms in the film. A background gas of a sufficiently high pressure may reduce sputtering of the film, but may lead the preferential diffusion of the light component to the substrate. The importance of these processes during the entire PLD process will be discussed.     

Study on the properties of Pb(Zr,Ti)O3 thin films grown alternately by pulsed laser deposition and sol-gel method

In order to prepare good quality Pb(Zr,Ti)O₃ (PZT) thin films, we consider the method of alternately growing PZT thin films on Pt (111)/Ti/SiO₂/Si (100) substrates by pulsed laser deposition (PLD) and sol-gel. In this work, we conducted comparative experiments on different film preparation methods, and 1.0 um thick PZT film was grown on platinized silicon wafers by an alternate PLD and sol-gel method. The microstructure and electrical properties of the films is analyzed. Through the study of X-ray diffraction, SEM, AFM, PFM, and ferroelectric testing, it is found that the alternating growth of a film by the alternate PLD and sol-gel method has good compactness, excellent ferroelectric properties, and smaller leakage current compared to film prepared by the sol-gel method alone.     

Study of laser-deposited metallic thin films by a combination of high-resolution ex situ and time-resolved in situ experiments

Laser-deposited metallic alloys and multilayers were studied in detail by a combination of high-resolution ex situ and time-resolved in situ experiments. The purpose of these experiments is to better understand the special properties of laser-deposited metallic films in comparison with conventionally prepared thin films. During deposition, thickness, resistance, and electron diffraction (THEED) experiments show that the film surface is resputtered, local mixing at the interfaces of multilayers on a nanometre scale occurs, and metastable phases up to large film thicknesses are formed. After deposition, a compressive stress of 1-2 GPa was measured using four-circle diffractometry, and growth defects were observed on an atomic scale by electron microscopy (HRTEM) and field ion microscopy (FIM). The obtained structural details of the metallic films can be explained by an implantation model for the laser deposition process.     

ZnO nanowall networks grown on DiMPLA pre‐patterned thin gold films

ZnO nanowall networks grown by a high pressure pulsed laser deposition (PLD) technique on a pre‐patterned thin gold film are presented. The thin gold film on a c ‐plane oriented sapphire substrate was structured with diffraction mask projection laser ablation (DiMPLA). It is shown that only areas processed with the laser patterning technique reveal homogeneous growth of ZnO nanowall networks. Photoluminescence measurements prove the higher material quality of the pre‐patterned regions compared to the untreated ones. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Simulation of multilayer Cu/Pd（100） heteroepitaxial growth by pulse laser deposition

The heteroepitaxial growth of multilayer Cu/Pd(100) thin film via pulse laser deposition (PLD) at room temperature is simulated by using kinetic Monte Carlo (KMC) method with realistic physical parameters. The effects of mass transport between interlayers, edge diffusion of adatoms along the islands and instantaneous deposition are considered in the simulation model. Emphasis is placed on revealing the details of multilayer Cu/Pd(100) thin film growth and estimating the Ehrlich--Schwoebel (ES) barrier. It is shown that the instantaneous deposition in the PLD growth gives rise to the layer-by-layer growth mode, persisting up to about 9 monolayers (ML) of Cu/Pd(100). The ES barriers of The heteroepitaxial growth of multilayer Cu/Pd（100） thin film via pulse laser deposition （PLD） at room temperature is simulated by using kinetic Monte Carlo （KMC） method with realistic physical parameters. The effects of mass transport between interlayers, edge diffusion of adatoms along the islands and instantaneous deposition are considered in the simulation model, Emphasis is placed on revealing the details of multilayer Cu/Pd（100） thin film growth and estimating the Ehrlich-Schwoebel （ES） barrier. It is shown that the instantaneous deposition in the PLD growth gives rise to the layer-by-layer growth mode, persisting up to about 9 monolayers （ML） of Cu/Pd（100）. The ES barriers of 0.08 ± 0.01 eV is estimated by comparing the KMC simulation results with the real scanning tunnelling microscopy （STM） measurements,     

AlFe单晶薄膜微结构与热力学性质研究

采用PLD方法,在573 K条件下制备了AlFe单晶合金薄膜.X射线衍射与透射电子衍射表明,AlFe空间点群为PM-3M,晶格常数a =0.297 nm (略大于bcc-Fe的晶格常数,a =0.293 nm),且AlFe晶体结构为bcc-Fe晶格体心Fe原子被Al取代产生的新结构.采用第一性原理与准谐德拜模型研究了AlFe合金的化学势与热力学性能,计算表明AlFe合金具有更低的化学势,导致在生长过程只出现AlFe相.与此同时,AlFe合金具有与bc 关键词： PLD AlFe单晶薄膜 第一性原理 准谐德拜模型     

PLD方法制备的纳米Fe/Al薄膜的结构及应力分析

 采用PLD方法制备了Fe/Al合金薄膜，研究了Fe/Al合金薄膜的物相、结构、应力等。研究表明薄膜的沉积速率随着衬底温度的升高而降低。原子力显微镜（AFM）图像显示，薄膜表面平整、致密且光滑，均方根粗糙度小于1 nm。等离子体发射谱（ICP）表明Fe/Al原子比为1∶1。X射线小角衍射（XRD）分析表明薄膜中的物相是Al_0.5Fe_0.5，Al_0.5Fe_0.5晶体具有简单立方结构(SC)，晶格常数为0.297 nm，平均晶粒尺寸为81.74 nm，平均微畸变为0.007 6。     

Oriented growth of CoPt nanoparticles by pulsed laser deposition

The magnetic nanoparticles of Fe/FeCo/FePt, in the past, in a PLD system were grown by us using argon ambient gas pressure of about 0.1–75.0 mbar, as the ambient gas pressure can be used to tune the energy of the incident plasma plume species, the expansion volume, the growth duration, etc. which can control the particle size. In present paper, we report the direct synthesis of small-sized nanoparticles even when no ambient gas was used, with the experiments being done in higher vacuum of about 10^?5 mbar in PLD chamber. The deposition rate under vacuum condition is significantly higher than the deposition rate at high ambient pressure. The study of inplane and outplane magnetic properties, along with XRD results, confirmed that the as-deposited CoPt nanoparticles thin film has oriented growth. The as-deposited CoPt nanoparticles are in magnetically soft fcc phase and a post deposition annealing at 600°C resulted in phase transition to magnetically hard fct phase.     

Enhanced atomic mobility in pulsed laser deposition of Cu films

The growth of Cu films by pulsed laser deposition (PLD) is studied with molecular dynamics simulations. We focus on examining the effects of high momentary deposition rate and energetic particle impact in the PLD process. Simulations show that these two factors can promote surface atomic mobility and lead to 2D smooth growth of films at lower substrate temperature. These features are consistent with experiments.     

The power of in situ pulsed laser deposition synchrotron characterization for the detection of domain formation during growth of Ba0.5Sr0.5TiO3 on MgO

A highly sophisticated pulsed laser deposition (PLD) chamber has recently been installed at the NANO beamline at the synchrotron facility ANKA (Karlsruhe, Germany), which allows for comprehensive studies on the PLD growth process of dielectric, ferroelectric and ferromagnetic thin films in epitaxial oxide heterostructures or even multilayer systems by combining in situ reflective high‐energy diffraction with the in situ synchrotron high‐resolution X‐ray diffraction and surface diffraction methods. The modularity of the in situ PLD chamber offers the opportunity to explore the microstructure of the grown thin films as a function of the substrate temperature, gas pressure, laser fluence and target–substrate separation distance. Ba_0.5Sr_0.5TiO₃ grown on MgO represents the first system that is grown in this in situ PLD chamber and studied by in situ X‐ray reflectivity, in situ two‐dimensional reciprocal space mapping of symmetric X‐ray diffraction and acquisition of time‐resolved diffraction profiles during the ablation process. In situ PLD synchrotron investigation has revealed the occurrence of structural distortion as well as domain formation and misfit dislocation which all depend strongly on the film thickness. The microstructure transformation has been accurately detected with a time resolution of 1 s. The acquisition of two‐dimensional reciprocal space maps during the PLD growth has the advantage of simultaneously monitoring the changes of the crystalline structure as well as the formation of defects. The stability of the morphology during the PLD growth is demonstrated to be remarkably affected by the film thickness. A critical thickness for the domain formation in Ba_0.5Sr_0.5TiO₃ grown on MgO could be determined from the acquisition of time‐resolved diffraction profiles during the PLD growth. A splitting of the diffraction peak into two distinguishable peaks has revealed a morphology change due to modification of the internal strain during growth.     

Pulsed laser deposition of ZnO grown on glass substrates for realizing high-performance thin-film transistors

We report characterization of ZnO thin-film transistors (TFTs) on glass substrates fabricated by pulsed laser deposition (PLD). ZnO films were characterized by X-ray diffraction (XRD), atomic force microscopy and Hall effect measurements. The XRD results showed high c-axis-oriented ZnO(0002) diffraction corresponding to the wurtzite phase. Moreover, the crystallization and the electrical properties of ZnO thin films grown at room temperature are controllable by PLD growth conditions such as oxygen gas pressure. The ZnO films are very smooth, with a root-mean-square roughness of 1 nm. From the Hall effect measurements, we have succeeded in fabricating ZnO films on glass substrates with an electron mobility of 21.7 cm²/V s. By using the ZnO thin film grown by two-step PLD and a HfO₂ high-k gate insulator, a transconductance of 24.1 mS/mm, a drain current on/off ratio of 4.4×10⁶ and a subthreshold gate swing of 0.26 V/decade were obtained for the ZnO TFT.     

质量分离低能离子束沉积碳膜及离子轰击效应

用质量分离的低能离子束沉积技术得到了非晶碳薄膜,X射线衍射、Raman谱以及俄歇深度谱的线形表明,此种非晶碳膜中镶嵌着金刚石颗粒.碳离子的浅注入是该碳膜SP³形成的主要机理.从一个侧面说明了化学气相沉积法中偏压预处理增加金刚石成核的主要原因是因为离子轰击效应. 关键词： 非晶碳 离子轰击 质量分离低能离子束     

Lattice Boltzmann model for multi-component mass transfer in a solid oxide fuel cell anode with heterogeneous internal reformation and electrochemistry

We have deposited SiC thin films using two different deposition techniques, Pulsed Electron Deposition (PED) and Pulsed Laser Deposition (PLD). The PED technique is a relatively new technique where a pulsed electron flux with high energy directly hits the target surface producing a plasma in a very similar way to PLD, where, instead, a pulsed laser beam is used. These two techniques can give very dense thin films with stoichiometry much closer to the target one’s compared to others physical vapour deposition techniques (sputtering, e-beam). The major drawback of PED is that the thin film surface is affected by the presence of particulate, due to the impact of the high energy electron beam with the target. In the PLD system we used a magnetic field to curve the plasma path in the vacuum and we placed the substrate at 90^○ with respect to the target allowing the deposition of particulate-free samples. The characterization of the films has been made by measuring the optical reflectance vs angle of incidence in the EUV region (from 121.6 nm down to 40.7 nm), taking measurements at different time from deposition. X-ray photoemission measurements have been also carried out to show stoichiometry and the presence of contaminants. Other measurements such as X-ray diffraction, atomic force microscopy and profiling were also carried out to check crystalline domains and surface roughness.     

Growth of thin Fe(0 0 1) films for terahertz emission experiments

The electrical and magnetic properties of thin iron (Fe) films have sparked significant scientific interest. Our interest, however, is in the fundamental interactions between light and matter. We have discovered a novel application for thin Fe films. These films are sources of terahertz (THz) radiation when stimulated by an incident laser pulse. After intense femtosecond pulse excitation by a Ti:sapphire laser, these films emit picosecond, broadband THz frequencies. The terahertz emission provides a direct measure of the induced ultrafast change in magnetization within the Fe film. The THz generation experiments and the growth of appropriate thin Fe films for these experiments are discussed. Several criteria are used to select the substrate and film growth conditions, including that the substrate must permit the epitaxial growth of a continuous, monocrystalline or single crystal film, yet must also be transparent to the emitted THz radiation. An Fe(0 0 1) film grown on the (0 0 1) surface of a magnesium oxide (MgO) substrate makes an ideal sample. The Fe films are grown by physical vapor deposition (PVD) in an ultrahigh vacuum (UHV) system. Low energy electron diffraction (LEED) and Auger electron spectroscopy (AES) are used to characterize the Fe(0 0 1) films. Two substrate surface preparation methods are investigated. Fe(0 0 1) films grown on MgO(0 0 1) substrates that are used as-received and films grown on MgO(0 0 1) substrates that have been UV/ozone-cleaned ex vacuo and annealed in vacuo produce the same results in the THz generation experiments. Either substrate preparation method permits the growth of samples suitable for the THz emission experiments.     

Effects of temperature and oxygen pressure on binary oxide growth using aperture-controlled combinatorial pulsed-laser deposition

In pulsed-laser deposition (PLD), there are many processing parameters that influence film properties such as substrate-target distance, background reactive gas pressure, laser energy, substrate temperature and composition in multi-component systems. By introducing a 12.7-mm diameter circular aperture in front of a 76.2-mm silicon wafer and rotating the substrate while changing conditions during the PLD process, these parameters may be studied in a combinatorial fashion, discretely as a function of processing conditions. We demonstrate the use of the aperture technique to systematically study the effects of oxygen partial pressure on the film stoichiometry and growth rate of VO_x, using Rutherford backscattering spectrometry (RBS). In another example, we discuss the effect of growth temperature on TiO₂ films characterized by X-ray diffraction and Fourier transform far-infrared (Terahertz) absorption spectroscopy. We demonstrate that we have considerable combinatorial control of other processing variables besides composition in our combi-PLD system. These may be used to systematically study film growth and properties.     

高气压反射式高能电子衍射仪监控脉冲激光外延氧化物薄膜

在超高真空分子束外延（MBE）生长技术中，反射式高能电子衍射仪（RHEED）能实时显示半导体和金属外延生长过程，给出薄膜表面结构和平整度的信息，成为MBE必备的原位表面分 析仪.为了研究氧化物薄膜如高温超导（YBa₂Cu₃O₇） 、铁电薄膜（Sr_1-xBa_x TiO₃）及它们的同质和异质外延结构的生长机理，获得高质量的符合各种应用 需要的氧化 物多层薄膜结构，在常规的制备氧化 关键词： 高温超导薄膜 RHEED     

Perpendicularly oriented barium ferrite thin films with low microwave loss,prepared by pulsed laser deposition

Barium ferrite(Ba M) thin films are deposited on platinum coated silicon wafers by pulsed laser deposition(PLD).The effects of deposition substrate temperature on the microstructure,magnetic and microwave properties of Ba M thin films are investigated in detail.It is found that microstructure,magnetic and microwave properties of Ba M thin film are very sensitive to deposition substrate temperature,and excellent Ba M thin film is obtained when deposition temperature is 910℃ and oxygen pressure is 300 m Torr(1 Torr = 1.3332×10~2Pa).X-ray diffraction patterns and atomic force microscopy images show that the best thin film has perpendicular orientation and hexagonal morphology,and the crystallographic alignment degree can be calculated to be 0.94.Hysteresis loops reveal that the squareness ratio(M_r/M_s) is as high as 0.93,the saturated magnetization is 4004 Gs(1 Gs = 10~4T),and the anisotropy field is 16.5 kOe(1 Oe = 79.5775 A·m~(-1)).Ferromagnetic resonance measurements reveal that the gyromagnetic ratio is 2.8 GHz/kOe,and the ferromagnetic resonance linewith is108 Oe at 50 GHz,which means that this thin film has low microwave loss.These properties make the Ba M thin films have potential applications in microwave devices.     

Superconductivity of MgB 2 Thin Films Prepared By CoEvaporation and Magnetism of MgB 2 /Fe Multilayers Studied By Mössbauer Spectroscopy

MgB 2 thin films and MgB 2 /Fe multilayers have been prepared by vapor deposition of the elements in vacuum. X-ray diffraction studies of the MgB 2 samples show preferred c -axis growth along the film normal direction. Superconducting transition temperatures of 18 K and 22 K have been measured before and after annealing, respectively, of an MgB 2 film of 1575 Å thickness. Atomic force microscope images show island growth of the films leading to a rough surface. Mössbauer spectroscopy on MgB 2 /Fe/MgB 2 multilayers of various Fe layer thicknesses indicates superparamagnetic behavior. Evidence is provided for the formation of interfacial amorphous (a-) Fe 3 B. The magnetic ordering of Fe and a-Fe 3 B and the size effect in MgB 2 are assumed to be the cause for the destruction of the superconductivity in the as-grown multilayers.     

Thickness influence on surface morphology and ozone sensing properties of nanostructured ZnO transparent thin films grown by PLD

Transparent zinc oxide (ZnO) thin films with a thickness from 10 to 200 nm were prepared by the PLD technique onto silicon and Corning glass substrates at 350 °C, using an Excimer Laser XeCl (308 nm). Surface investigations carried out by atomic force microscopy (AFM) and X-ray diffraction (XRD) revealed a strong influence of thickness on film surface topography. Film roughness (RMS), grain shape and dimensions correlate with film thickness. For the 200 nm thick film, the RMS shows a maximum (13.9 nm) due to the presence of hexagonal shaped nanorods on the surface. XRD measurements proved that the films grown by PLD are c-axis textured. It was demonstrated that the gas sensing characteristics of ZnO films are strongly influenced and may be enhanced significantly by the control of film deposition parameters and surface characteristics, i.e. thickness and RMS, grain shape and dimension.