溅射气压对非晶Hg1-xCdx Te薄膜微观结构和化学组分的影响（英文）

采用射频磁控溅射制备了非晶态结构的Hg1-xCdxTe薄膜,并利用台阶仪、XRD、原子力显微镜、EDS等分析手段对薄膜生长速率、物相、表面形貌、组分比例进行了研究。实验结果表明,溅射气压对薄膜生长速率、微观结构、表面形貌和化学组分有直接影响。随着溅射气压增大,其生长速率逐渐降低。当溅射气压高于1.1 Pa时,薄膜XRD图谱上没有出现任何特征衍射峰,只是在2θ=23°附近出现衍射波包,具有明显的非晶态特征;当溅射气压小于1.1 Pa时,XRD谱表现为多晶结构。另外,随着溅射气压的增加,薄膜表面粗糙度逐渐减小,而且溅射气压对薄膜组成的化学计量比有明显影响,当溅射气压为1.1 Pa时,薄膜中Hg的组分比最低,而Cd组分比最高。     

Swift heavy ion induced modifications in cobalt doped ZnO thin films: Structural and optical studies

Modifications in the structural and optical properties of 100 MeV Ni⁷⁺ ions irradiated cobalt doped ZnO thin films (Zn_1−xCo_xO, x = 0.05) prepared by sol-gel route were studied. The films irradiated with a fluence of 1 × 10¹³ ions/cm² were single phase and show improved crystalline structure with preferred C-axis orientation as revealed from XRD analysis. Effects of irradiation on bond structure of thin films were studied by FTIR spectroscopy. The spectrum shows no change in bonding structure of Zn-O after irradiation. Improved quality of films is further supported by FTIR studies. Optical properties of the pristine and irradiated samples have been determined by using UV-vis spectroscopic technique. Optical absorption spectra show an appreciable red shift in the band gap of irradiated Zn_1−xCo_xO thin film due to sp-d interaction between Co²⁺ ions and ZnO band electrons. Transmission spectra show absorption band edges at 1.8 eV, 2.05 eV and 2.18 eV corresponding to d-d transition of Co²⁺ ions in tetrahedral field of ZnO. The AFM study shows a slight increase in grain size and surface roughness of the thin films after irradiation.     

Formation of nanocrystalline TiO2 by 100 MeV Au

Nanocrystalline TiO₂ structures are formed by irradiation of 100 MeV Au⁸⁺ ion beam on amorphous thin films of TiO₂. Surface morphology of the nanocrystals is studied by Atomic Force Microscopy (AFM). Amorphous to nanocrystalline phase transformation is identified by Glancing Angle X-ray Diffraction (GAXRD) and Raman spectroscopic studies. Optical characterization is carried out by UV-VIS spectroscopy technique. Blue shift observed in absorption band edge indicates the formation of nanophase TiO₂ after irradiation. The impinging swift heavy ion (100 MeV Au⁸⁺) induces nucleation of nanoparticles along the ion trajectory through inelastic collisions of the projectile with electrons of the material. It is observed that the shape and size of nanoparticles formed is dependant on the irradiation fluence.     

Li ION BACKSCATTERING STUDY ON HIGH-Tc YBaCuO AND GdBaCuO SUPERCONDUCTOR FILMS

Rutherford backscattering (RBS) measurements of 4.2 MeV Li and 2.4 MeV He ions were done for YBaCuO and GdBaCuO high-T_c, superconductor films deposited on MgO and SrTiO₃ single crystalline substrates and for their bulk samples. Energy spectra of both ions were calculated using the RBS analysis program rewritten by the authors. Comparisons between these two non-destructive tech-niques showed some advantages in analyzing the layer thickness and composition ratios of those thin films by MeV Li ions backscattering. Estimated errors are within 7 % for the measured elemental con-centrations and l0 % for the layer thickness in our experiments. A brief discussion is also made of the results.     

Modified structural,morphological and photoelectrochemical properties of 120 MeV Ag9+ ion irradiated BaTiO3 thin films

The effects of high electronic energy deposition on the structure, surface topography, optical property and photoelectrochemical behavior of barium titanate thin (BaTiO₃) films have been investigated by irradiating films with 120 MeV Ag⁹⁺ ions at different ion fluences in the range of 1 × 10¹¹–3 × 10¹² ions cm^?2. Barium titanate thin films were deposited on indium tin oxide-coated glass substrate by sol–gel spin coating method. The structure of the film was crystalline with tetragonal phase. Surface topography was studied by atomic force microscopy detailing the values of roughness of the films. Maximum photocurrent density of 1.78 mA cm^?2 at 0.4 V/SCE and applied bias photon-to-current efficiency (ABPE) of 0.91% was observed for BaTiO₃ film irradiated at 1 × 10¹¹ ions cm^?2.     

Growth and studies of Hg1−xCdxTe based low dimensional structures

The band structure of HgTe quantum wells (QWs) has been determined from absorption experiments on superlattices in conjunction with calculations based on an 8×8 k·p model. The band structure combined with self-consistent Hartree calculations has enabled transport results to be quantitatively explained.Rashba spin–orbit, (SO) splitting has been investigated in n-type modulation doped HgTe QWs by means of Shubnikov–de Haas oscillations (SdH) in gated Hall bars. The heavy hole nature of the H1 conduction subband in QWs with an inverted band structure greatly enhances the Rashba SO splitting, with values up to 17 meV.By analyzing the SdH oscillations of a magnetic two-dimensional electron gas (2DEG) in modulation-doped n-type Hg_1−xMn_xTe QWs, we have been able to separate the gate voltage-dependent Rashba SO splitting from the temperature-dependent giant Zeeman splitting, which are of comparable magnitudes. In addition, hot electrons and Mn ions in a magnetic 2DEG have been investigated as a function of current.Nano-scale structures of lower dimensions are planned and experiments on sub-micrometer magneto-transport structures have resulted in the first evidence for ballistic transport in quasi-1D HgTe QW structures.     

Electrons and holes in HgTe and Hg0.82Cd0.18Te with controlled deviations from stoichiometry

The deviations from the stoichiometric composition of HgTe and Hg_0.82Cd_0.18Te crystals have been controlled by heat treatment under Hg vapor pressure. The magnetic field dependence of the Hall coefficient always shows the presence of two different sets of electrons and one set of holes. A low mobility electron is shown to belong to the conduction band. Vapor pressure dependence of hole concentration in HgTe shows that the concentration of nonstoichiometric defects decreases with increasing Hg vapor pressure, but the hole concentration is always higher than the electron concentration. In the case of Hg_0.82Cd_0.18Te, the electron concentration exceeds the hole concentration at high Hg vapor pressures. The dependence of the conduction band electron mobility in HgTe upon carrier density shows that the scattering by holes and impurities is predominant. In Hg_0.82Cd_0.18Te, however, optical phonon scattering is dominant when the deviation from stoichiometry is small and the effect of residual impurities can be neglected, and scattering by holes is dominant when the hole concentration is over $\text{10}{}^{17}\text{cm}{}^3$.     

Swift heavy ion irradiation induced modification of BiFeO3 thin films prepared by sol-gel method

We report the preparation of multiferroic BiFeO₃ thin films on ITO coated glass substrates through sol-gel spin coating method followed by thermal annealing and their modification by swift heavy ion (SHI) irradiation. X-ray diffraction and Raman spectroscopy studies revealed amorphous nature of the as deposited films. Rhombohedral crystalline phase of BiFeO₃ evolved on annealing the films at 550°C. Both XRD and Raman studies indicated that SHI irradiation by 200 MeV Au ions result in fragmentation of particles and progressive amorphization with increasing irradiation fluence. The average crystallite size estimated from the XRD line width decreased from 38 nm in pristine sample annealed at 550°C to 29 nm on irradiating these films by 200 MeV Au ions at 1 × 10¹¹ ions cm⁻². Complete amorphization of the rhombohedral BiFeO₃ phase occurs at a fluence of 1 × 10¹² ions.cm⁻². Irradiation by another ion (200 MeV Ag) had the similar effect. For both the ions, the electronic energy loss exceeds the threshold electronic energy loss for creation of amorphized latent tracks in BiFeO₃.     

Valence control of cobalt oxide thin films by annealing atmosphere

The cobalt oxide (CoO and Co₃O₄) thin films were successfully prepared using a spin-coating technique by a chemical solution method with CH₃OCH₂CH₂OH and Co(NO₃)₂·6H₂O as starting materials. The grayish cobalt oxide films had uniform crystalline grains with less than 50 nm in diameter. The phase structure is able to tailor by controlling the annealing atmosphere and temperature, in which Co₃O₄ thin film was obtained by annealing in air at 300-600, and N₂ at 300, and transferred to CoO thin film by raising annealing temperature in N₂. The fitted X-ray photoelectron spectroscopy (XPS) spectra of the Co2p electrons are distinguishable from different valence states of cobalt oxide especially for their satellite structure. The valence control of cobalt oxide thin films by annealing atmosphere contributes to the tailored optical absorption property.     

Room temperature ferroelectricity of tetragonally strained SrTiO3 thin films on single crystal Rh substrates

Epitaxial SrTiO₃ thin films were deposited on single crystalline Rh substrates by pulsed laser deposition. The tetragonally stained structure of the SrTiO₃ thin films with a c/a ratio of 1.04 was confirmed by x-ray diffraction experiments. The SrTiO₃ thin films exhibited good ferroelectric properties with a high remanent polarization (2P_r) of 8 μC/cm² and a canonical ferroelectric piezoresponse hysteresis loop at room temperature. We estimated a high activation electric field of about 6.4 MV/cm for domain wall creeping. This activation electric field is higher than that of typical ferroelectric materials such as PbTiO₃.     

Ferromagnetism modulation by phase change in Mn-doped GeTe chalcogenide magnetic materials

In this work, an effective method to modulate the ferromagnetic properties of Mn-doped GeTe chalcogenide-based phase change materials is presented. The microstructure of the phase change magnetic material Ge_1?x Mn _x Te thin films was studied. The X-ray diffraction results demonstrate that the as-deposited films are amorphous, and the crystalline films are formed after annealing at 350 °C for 10 min. Crystallographic structure investigation shows the existence of some secondary magnetic phases. The lattice parameters of Ge_1?x Mn _x Te (x = 0.04, 0.12 and 0.15) thin films are found to be slightly different with changes of Mn compositions. The structural analysis clearly indicates that all the films have a stable rhombohedral face-centered cubic polycrystalline structure. The magnetic properties of the amorphous and crystalline Ge_0.96Mn_0.04Te were investigated. The measurements of magnetization (M) as a function of the magnetic field (H) show that both amorphous and crystalline phases of Ge_0.96Mn_0.04Te thin film are ferromagnetic and there is drastic variation between amorphous and crystalline states. The temperature (T) dependence of magnetizations at zero field cooling (ZFC) and field cooling (FC) conditions of the crystalline Ge_0.96Mn_0.04Te thin film under different applied magnetic fields were performed. The measured data at 100 and 300 Oe applied magnetic fields show large bifurcations in the ZFC and FC curves while on the 5,000 Oe magnetic field there is no deviation.     

Preparation and characterization of La0.5Sr0.5CoO3 /Al-doped ZnO thin film heterojunctions

In this study, p–n heterojunctions with La_0.5Sr_0.5CoO₃ (LSCO) and Al-doped ZnO (AZO) thin films were fabricated by the radio frequency (r.f.) magnetron sputtering technique. The LSCO/AZO heterojunction was obtained by stacking the p-type LSCO thin film on the annealed n-type AZO thin film under different Ar: O₂ sputter gas ratio atmosphere. The thickness of LSCO and AZO thin films are about 400 nm and 500 nm, respectively. Good crystalline match between LSCO and AZO films was observed from the SEM and XRD analysis. The heterojunction diode clearly demonstrated rectifying behavior in the range of ?8 to +8 V in reverse shape. The turn-on voltage of the diodes is obtained around 1.5 V and is in agreement with the value obtained from the difference in the work functions of LSCO and AZO. The band structure of the heterojunction was proposed based on the results of analysis.     

Hg1-xCdxTe/Cd1-zZnzTe的X射线反射率及半峰全宽的动力学研究

X射线衍射摇摆曲线的计算机模拟是一种获得材料晶体质量参量的有效方法，其中材料本征摇摆曲线的计算是计算机模拟的基础。用X射线动力学理论计算了Hg1-xCdxTe和Cd1-zZnzTe本征反射率曲线，并研究了组分、膜厚分别对本征反射率和半峰全宽的影响。结果表明Hg1-xCdxTe和Cd1-zZnzTe的本征反射率和半峰全宽与材料组分和厚度有明显的依赖关系，且该依赖关系取决于X射线在材料中的散射和吸收的相对强弱。薄膜的厚度也是直接影响本征摇摆曲线峰形、半峰全宽和反射率的重要因素，当薄膜厚度小于穿透深度时，表征本征反射率曲线的各个参量均与薄膜厚度有直接的关系。对于(333)衍射面，碲镉汞材料厚度大于7μm后，本征反射率和半峰全宽将不再发生明显变化。     

The crystalline orientation and ferroelectric properties of Bi3.25La0.75Ti3O12 thin films mediated by the intermediate layer of LaNiO3

c-Axis-oriented and (1 1 7)-oriented Bi_3.25La_0.75Ti₃O₁₂ (BLT) thin films are successfully controlled by the intermediate layer of LaNiO₃ (LNO) with chemical solution deposition (CSD), respectively. X-ray diffraction (XRD) demonstrates that the structure and orientation of LNO thin films have a strong effect on the orientation of BLT thin films. Scanning electron microscopy suggests that BLT thin films on LNO electrode exhibit crack-free, uniform size grains and dense microstructure. A crystalline orientation dependent remanent polarization is observed in BLT thin films, and it is found that the remanent polarization (2P_r) of (1 1 7)-oriented films is larger than that of c-axis-oriented films. Our research directly demonstrates that the vector of the main spontaneous polarization in these layered perovskite materials (BLT) is along a-axis.     

Swift heavy ion irradiation-induced modifications of tris-(8-hydroxyquinoline)aluminum thin films

Tris-(8-hydroxyquinoline)aluminum (Alq₃), one of the most widely used light emitting and electron transport materials in organic luminescent devices, has been synthesized. Alq₃ thin films have been deposited by a thermal evaporation process on glass substrates. The effect of swift heavy ion (SHI) irradiation using 40 MeV Li³⁺ on the Alq₃ thin films has been studied by UV-visible, infrared, photoluminescence (PL) and time-resolved photoluminescence (TRPL) spectroscopy. From TRPL studies, it is found that the PL of Alq₃ thin films arises from two species corresponding to its two geometrical isomers, namely facial and meridional having two different life times. It is also confirmed that the PL and lifetimes of excitons decrease with the increase of ion fluences of SHI of 40 MeV Li³⁺, indicating a transfer of exciton energy to unstable cationic Alq₃ species generated by SHI irradiation.     

Annealing effect on the structural and optical properties of a Cd1−xZnxS thin film for photovoltaic applications

Herein is a report of a study on a Cd_1−xZn_xS thin film grown on an ITO substrate using a chemical bath deposition technique. The as-deposited films were annealed in air at 400 °C for 30 min. The composition, surface morphology and structural properties of the as-deposited and annealed Cd_1−xZn_xS thin films were studied using EDX, SEM and X-ray diffraction techniques. The annealed films have been observed to possess a crystalline nature with a hexagonal structure. The optical absorption spectra were recorded within the range of 350-800 nm. The band gap of the as-deposited thin films varied from 2.46 to 2.62 eV, whereas in the annealed film these varied from 2.42 to 2.59 eV. The decreased band gap of the films after annealing was due to the improved crystalline nature of the material.     

Low dielectric loss Ba0.6Sr0.4TiO3/MgTiO3 composite thin films prepared by a sol–gel process

The dielectric properties of Ba_0.6Sr_0.4TiO₃ (BST)/MgTiO₃ (MT) composite thin films deposited on Pt(1 1 1)/Ti/SiO₂/Si(1 0 0) substrates by the sol–gel method were investigated. The X-ray pattern analysis indicates that the thin films exhibit good crystalline quality with perovskite phase and that insertion of MT layer does not obviously affect the phase structure of BST thin films. The characterization of dielectric properties demonstrates that configuration of BST/MT/BST thin films is an effective approach to obtain low dielectric loss and dielectric tunability of BST thin films. At room temperature, the tunability of pure BST60 films and BST/MT (15 nm)/BST composite thin films is 47% and 36%, respectively, at the frequency of 1 MHz with an applied electric field of 400 kV/cm. For BST/MT/BST composite thin films, considerable reduction in the dielectric loss values is observed, which renders them attractive for tunable microwave device applications.     

体心立方金属W薄膜晶体取向的膜厚尺寸效应及其表面映射

体心立方W膜(110)织构系数T₁₁₀的变化存在非单调的厚度尺寸效应，这依赖于薄膜中晶粒形核和长大时表面能和应变能的相互作用，薄膜表面结构演变反映了两者的竞争过程.应用小波变换结合分形几何描述薄膜表面结构各向异性行为，用此法构建了薄膜织构系数T₁₁₀与表面结构各向异性的关系，表明薄膜晶体取向存在表面映射. 关键词： 金属薄膜 晶体取向 膜厚 表面形貌     

Giant magneto-optical faraday effect in HgTe thin films in the terahertz spectral range

We report the observation of a giant Faraday effect, using terahertz (THz) spectroscopy on epitaxial HgTe thin films at room temperature. The effect is caused by the combination of the unique band structure and the very high electron mobility of HgTe. Our observations suggest that HgTe is a high-potential material for applications as optical isolator and modulator in the THz spectral range.     

Phase transformation in Ni–Mn–Sn ferromagnetic shape memory alloy thin films induced by dense ionization

The effects of 200 MeV Au ions irradiation on the structural and magnetic properties of Ni–Mn–Sn ferromagnetic shape memory alloy (FSMA) thin films have been systematically investigated. In order to understand the role of initial microstructure and phase of the film with respect to high energy irradiation, the two types of Ni–Mn–Sn FSMA films having different phases at room temperature were irradiated, one in martensite phase (Ni_58.9Mn_28.0Sn_13.1) and other in austenite phase (Ni₅₀Mn_35.6Sn_14.4). Transmission electron microscope (TEM) and scanning electron microscope (SEM) images along with the diffraction patterns of X-rays and electrons confirm that martensite phase transforms to austenite phase at a fluence of 6×10¹² ions/cm² and a complete amorphization occurs at a fluence of 3×10¹³ ions/cm², whereas ion irradiation has a minimal effect on the austenitic structure (Ni₅₀Mn_35.6Sn_14.4). Thermo-magnetic measurements also support the above mentioned behaviour of Ni–Mn–Sn FSMA films with increasing fluence of 200 MeV Au ions. The results are explained on the basis of thermal spike model considering the core and halo regions of ion tracks in FSMA materials.