Structural and optical properties of pulsed laser deposited ZnO thin films

Nanocrystalline ZnO thin films were grown by means of pulsed laser deposition. The ablation process was carried out at relatively low background oxygen gas pressure (10 Pa) and by varying the substrate temperature up to 600 °C. Information on the structural and morphological properties of the deposited thin films have been obtained by means of X-ray photoelectron, Raman spectroscopies, X-ray diffraction (XRD) and atomic force microscopy (AFM). The results showed that all the deposited films are sub-stoichiometric in oxygen and with a hexagonal wurtzite crystalline structure, characterized by features of some tens of nanometers in size. An improvement of the films' crystalline quality was observed for the deposition temperature of 300 °C while the further increase of the deposition temperature up to 600 °C induces a worsening of the material's structural properties with the development of a large amount of nanoparticle's clusters. The analysis of the XRD patterns shows a growth crystallographic preferential direction as a function of the deposition temperature, in agreement with the appearance of the only E₂ optical phonon mode in the Raman spectra. Such findings are compatible with the changes observed in the photoluminescent (PL) optical response and was related to the modification of the ZnO thin film structural quality.     

Structural and optical properties of amorphous Sb2S3 thin films deposited by vacuum thermal evaporation method

Sb₂S₃ thin films have been deposited by vacuum thermal evaporation onto glass substrates at various substrate temperatures in the range of 30–240 °C. Crushed powder of the synthesized Sb₂S₃ was used as raw material for the vacuum thermal evaporation. The structural investigation performed by means of X-ray diffraction (XRD) showed that the all as-deposited films present an amorphous structure and all the films were highly resistive. The reflectance and transmittance of the films are measured in the incident wavelength range 300–1800 nm. The absorption coefficient spectral analysis revealed the existence of long and wide band tails of the localized states in the low absorption region. The band tails width is calculated and found to be varying between 0.024 and 0.032 eV. The analysis of the absorption coefficient in the high absorption region revealed two direct forbidden band gaps between 1.78–1.98 eV and 1.86–2.08 eV.     

Electrical and optical properties of Ga doped zinc oxide thin films deposited at room temperature by continuous composition spread

Ga doped ZnO (GZO) thin films were deposited on glass substrates at room temperature by continuous composition spread (CCS) method. CCS is thin films growth method of various Ga_xZn_1−xO(GZO) thin film compositions on a substrate, and evaluating critical properties as a function position, which is directly related to material composition. Various compositions of Ga doped ZnO deposited at room temperature were explored to find excellent electrical and optical properties. Optimized GZO thin films with a low resistivity of 1.46 × 10⁻³ Ω cm and an average transmittance above 90% in the 550 nm wavelength region were able to be formed at an Ar pressure of 2.66 Pa and a room temperature. Also, optimized composition of the GZO thin film which had the lowest resistivity and high transmittance was found at 0.8 wt.% Ga₂O₃ doped in ZnO.     

Electrical and optical properties of Al-doped ZnO thin films by sol-gel process

Al-doped ZnO (AZO) thin films oriented along the (0 0 2) plane have been prepared by the sol-gel process and their electrical and optical properties with post-deposition heating temperature were investigated. The preferred c-axis orientation along the (0 0 2) plane was enhanced with increasing post-deposition heating temperature and the surface of the films showed a uniform and nano-sized microstructure. The electrical resistivity of the films decreased from 73 to 22 Ω cm as the post-deposition heating temperature increased from 500 to 650 °C; however, the film postheated at 700 °C increased greatly to 580 Ω cm. The optical transmittance of the films postheated below 650 °C was over 86%, but it decreased at 700 °C. The electrical and optical properties of the AZO films with post-deposition heating temperature are discussed.     

非化学计量比靶材溅射制备Cu-Al-O薄膜的光学电学性质研究

考虑到铜铝溅射速率的差别,使用铜铝比例为0.9 ∶1的多晶CuAlO₂靶材,用射频磁控溅射法制备Cu-Al-O薄膜.研究不同衬底温度对薄膜光学电学性能的影响.在衬底温度500 ℃附近,薄膜在可见光范围内具有很好的透光性,达到70%,计算拟合得到直接帯隙为3.52 eV,与CuAlO₂相的理论值符合较好.在室温附近,薄膜导电符合半导体热激活机理,在衬底温度为500 ℃附近薄膜电导率达到2.48×10^-3 S·cm^-1. 关键词： Cu-Al-O 衬底温度 透过率 电导率     

Electrical transport and optical properties of Cd_3As_2 thin films

Cd_3As_2, as a three-dimensional(3D) topological Dirac semimetal, has attracted wide attention due to its unique physical properties originating from the 3D massless Dirac fermions. While many efforts have been devoted to the exploration of novel physical phenomena such as chiral anomaly and phase transitions by using bulk crystals, the development of high-quality and large-scale thin films becomes necessary for practical electronic and optical applications. Here, we report our recent progress in developing single-crystalline thin films with improved quality and their optical devices including Cd_3As_2-based heterojunctions and ultrafast optical switches. We find that a post-annealing process can significantly enhance the crystallinity of Cd_3As_2 in both intrinsic and Zn-doped thin films. With excellent characteristics of high mobility and linear band dispersion, Cd_3As_2 exhibits a good optical response in the visible-to-mid-infrared range due to an advantageous optical absorption, which is reminiscent of 3D graphene. It also behaves as an excellent saturable absorber in the mid-infrared regime. Through the delicate doping process in this material system, it may further open up the long-sought parameter space crucial for the development of compact and high-performance mid-infrared ultrafast sources.     

Full X-ray pattern analysis of vacuum deposited pentacene thin films

Pentacene thin films with thicknesses ranging from 10 nm to 180 nm are investigated by specular X-ray diffraction in the reflectivity regime and in the wide angular regime. The results of the reflectivity measurements show a clear shift of the 001 reflection of the thin film phase depending on the layer thickness. It is shown that this shift can be explained by the dynamical scattering theory. The wide angular regime measurements show the 00L of the thin film phase. Williams-Hall plots are used to extract information on the crystallite size and mean micro strain of the thin film phase. The crystallite size is in good agreement with the results obtained by the reflectivity measurements. From this it can be concluded that the thin film phase crystallites are extended over the entire film thickness down to the substrate. Additionally an increase of the micro strain with increasing film thickness is observed.     

近距离升华沉积CdTe掺Cd薄膜的微结构和电学、光学特性

采用近距离升华技术制备了掺杂Cd元素的CdTe多晶薄膜.利用X射线衍射仪和扫描电子显微镜表征其微结构,用霍尔效应测试仪和紫外可见分光光度计分析其电学、光学特性.结果显示,适量的掺杂Cd元素可改善CdTe薄膜晶形,显著提高薄膜的电导特性,由弱的p型电导转变为导电性能良好的n型电导,但对光能隙影响不大. 关键词： 近距离升华 CdTe薄膜 掺杂Cd 电学和光学特性     

Electrical properties of boron-doped diamond-like carbon thin films deposited by femtosecond pulsed laser ablation

We report on electrical measurements and structural characterization performed on boron-doped diamond-like carbon thin films deposited by femtosecond pulsed laser deposition. The resistance has been measured between 77 and 300 K using four probe technique on platinum contacts for different boron doping. Different behaviours of the resistance versus temperature have been evidenced between pure DLC and boron-doped DLC. The a-C:B thin film resistances exhibit Mott variable range hopping signature with temperature. Potential applications of DLC thin films to highly sensitive resistive thermometry is going to be discussed.     

Electrical and optical properties of Sb-doped ZnO thin films synthesized by sol–gel method

Sb-doped ZnO thin films with different values of Sb content （from 0 to 1.1 at.%） are deposited by the sol-gel dip- coating method under different sol concentrations. The effects of Sb-doping content, sol concentration, and annealing ambient on the structural, optical, and electrical properties of ZnO films are investigated. The results of the X-ray diffraction and ultraviolet-visible spectroscopy （UV-VIS） spectrophotometer indicate that each of all the films retains the wurtzite ZnO structure and possesses a preferred orientation along the c axis, with high transmittance （〉 90%） in the visible range. The Hall effect measurements show that the vacuum annealed thin films synthesized in the sol concentration of 0.75 mol/L each have an adjustable n-type electrical conductivity by varying Sb-doping density, and the photoluminescence （PL） spectra revealed that the defect emission （around 450 nm） is predominant. However, the thin films prepared by the sol with a concentration of 0.25 mol/L, despite their poor conductivity, have priority in ultraviolet emission, and the PL peak position shows first a blue-shift and then a red-shift with the increase of the Sb doping content.     

沉积温度对硫化锌(ZnS)薄膜的结晶和光学特性影响研究

对不同温度下沉积的ZnS薄膜的结晶情况和光学特性进行了研究, 结果表明：沉积温度对ZnS薄膜的物理和光学特性有较大影响, 不同的温度沉积的ZnS薄膜具有不同的择优取向, 牢固度也大不相同; 不同沉积温度下, ZnS薄膜的光学常数也不尽相同. 温度为115 ℃和155 ℃时, ZnS薄膜的物理性能和光学性能较差, 不适合空间用光学薄膜的研制使用. 而190 ℃和230 ℃沉积温度下所得薄膜具有较好的物理和光学性能, 适合于不同要求的空间用薄膜器件的研制使用. 关键词： 硫化锌薄膜 沉积温度 表面形貌 光学常数     

Investigation of structural and optical properties of UHV deposited titanium thin films under thermal oxidation

Titanium dioxide thin layers were prepared by annealing method, on glass substrate at different temperatures, 150, 250 and 350 °C, in presence of 5 cm³/s uniform oxygen flow. The structural investigations were performed by means of atomic force microscopy (AFM) and X-ray diffraction (XRD) techniques. Roughness of the films changed due to annealing process. The optical constants of the layers were obtained by Kramers–Kronig analysis of the reflectivity curves. There was a good agreement between structural and optical properties of the layers. Annealing temperature can play an important role in nanostructures of the films.     

球面元件表面AlF3薄膜的光学特性和微观结构表征

在模拟球面元件曲率半径的仿面形夹具上镀制了AlF3单层薄膜,并对不同口径位置上的薄膜进行了比较,以表征球面元件表面镀制薄膜的光学特性和微观结构。首先,采用紫外可见光分光光度计测量了不同口径位置上薄膜样品的透射和反射光谱,反演得出AlF3的折射率和消光系数。然后,使用原子力显微镜观察了样品的表面形貌和表面粗糙度。最后,使用X射线衍射仪对薄膜的内部结构进行了表征。实验结果表明：在球面不同位置镀制的AlF3单层薄膜样品的光学损耗随着所在位置口径的增大而增大。口径为280 mm处的消光系数是中心位置处消光系数的1.8倍,表面粗糙度是中心位置的17.7倍。因此,球面元件需要考虑由蒸汽入射角不同带来的光学损耗的差异。     

Magnetic and optical properties of epitaxial n-type Cu-doped ZnO thin films deposited on sapphire substrates

In this paper, we report on pulsed laser deposition of n-type Cu-doped ZnO thin films on c-plane sapphire substrates at 700°C. XRD and HRTEM were employed to study the epitaxial growth relationship between the Zn_1−x Cu _x O film and sapphire substrate. Absorption measurements showed excitonic nature of the thin films and a decrease in the bandgap energy with increased Cu concentration was observed. Such as-deposited films showed room temperature ferromagnetism with Curie temperature (T _c ) at around 320 K. The moment per Cu atom decreases as the Cu concentration increases. The largest magnetic moment about 0.81μ _B /Cu atom was observed for Zn_0.95Cu_0.05O thin films. The presence of any magnetic second phase was ruled out and the ferromagnetism was attributed to Cu ions substituted directly into the ZnO lattice.     

Interfacial reactions of ultrahigh vacuum deposited ytterbium thin films on silicon

Epitaxial ytterbium silicide thin films were grown on (111)Si by ultrahigh vacuum deposition and subsequent thermal annealing. The epitaxial YbSi(2-x) thin films consist of various kinds of defects such as vacancies, stacking faults, and pinholes. The vacancies were ordered so as to relax the compressive stress in Si sublattice of YbSi(2-x) thin films. The vacancy ordering structure is of an out-of-step structure with higher vacancy concentration after higher temperature annealing so that the compressive stress was further relaxed. A high density of stacking faults was present in the epitaxial YbSi(2-x) thin films. The stacking faults were annihilated by high temperature annealing. Pinholes also formed in the epitaxial YbSi(2-x) thin films and could be avoided by appropriate fabrication process. The epitaxial YbSi(2-x) thin films were thermally stable up to 1000 degrees C.     

Hafnium oxide thin films deposited from a filtered cathodic vacuum arc

The electrical and structural characteristics of hafnium oxide thin films reactively deposited from a filtered cathodic vacuum arc have been investigated. X-ray photoelectron spectroscopy was used to determine the deposition conditions (Ar/O₂ ratio) which produced stoichiometric HfO₂ films. Cross-sectional transmission electron microscopy showed that the micro-structure of the films was highly disordered with electron-diffraction analysis providing evidence for the presence of sub-nano-metre crystallites of the monoclinic HfO₂ (P2₁/c) phase. Further evidence for the presence of this phase was provided by measuring the O k-edge using electron energy loss spectroscopy and comparing it with calculations performed using FEFF8.2, a multiple scattering code. Surface imaging revealed that local film damage occurred in films deposited with substrate bias voltages exceeding −200 V. The current-leakage characteristics of the HfO₂ films deposited with a bias of approximately −100 V suggest that device grade HfO₂ films can be produced from a filtered cathodic vacuum arc.     

Electrical and magnetic properties of CoFeAlO thin films

Influences of oxygen-partial pressure and annealing on the electrical and magnetic properties of CoFeAlO thin films were systematically investigated by means of resistivity, permeability, magnetization and ferromagnetic resonance (FMR) measurements. It was found that, with increasing oxygen-partial pressure or under annealing, the electrical resistivity of the film increased and the magnetic softness decreased, which is attributed to the microstructural change of the film. Interestingly, an as-deposited Co_45.30Fe_20.65Al_19.34O_14.71 film was found to exhibit an inverted hysteresis loop with negative coercivity, and this peculiar phenomenon disappeared upon effects of oxygen-partial pressure and annealing. It was also found that the as-deposited films owned a narrow FMR line width that increased with increasing oxygen-partial pressure or under annealing.     

Electrical properties and structure of thin chromium films

The temperature dependence of the electrical resistance of thin chromium films produced by vacuum condensation at 1· 10^–4 mm Hg on mica, optical glass, and rock salt substrates is considered. The electrical resistance of chromium films condensed on substrates heated to temperatures below 450 °C increases irreversibly on subsequent heating and cooling. Chromium films condensed on substrates heated to 500–600 °C, however, retain stable electrical properties on repeatedly heating and cooling.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii Fizika, No. 9, pp. 56–60, September, 1971.     

Electrical and optical properties of Jäger-nickel (II)-based molecular-material thin films prepared by the vacuum thermal evaporation technique

Semiconductor molecular-material thin films of [6,13-Ac₂-5,14-Me₂-[14]-4,6,11,13-tetraenato-1,4,8,11-N₄] and the bidentate amines 1,4-diaminebutane, 1,12-diaminedodecane and 2,6-diamineanthraquinone have been prepared by vacuum thermal evaporation on corning glass substrates and crystalline silicon wafers. The films thus obtained were characterized by infrared (FTIR), ultraviolet-visible (UV-VIS) and photoluminescence (PL) spectroscopies. The surface morphology, thickness and structure of these films were analyzed by atomic force microscopy (AFM), ellipsometry and X-ray diffraction (XRD), respectively. IR spectroscopy showed that the molecular-material thin films exhibit the same intra-molecular bonds as the original compounds, which suggests that the thermal evaporation process does not significantly alter their bonds. The effect of temperature on conductivity was also measured in these samples; it was found that the temperature-dependent electric current is always higher for the voluminous amines with large molecular weights and suggests a semiconductor behavior with conductivities in the order of 10⁻⁶-10⁻¹ Ω⁻¹ cm⁻¹. Finally, the optical band gap (E_g) and cubic χ⁽³⁾ non-linear optical (NLO) properties of these amorphous molecular complexes were also evaluated from optical absorption and optical third harmonic generation (THG) measurements, respectively.     

Electrical properties of cerium fluoride thin films

Thin films of ionic conductors have low internal resistance. Hence, it could be used as an electrolyte material in sensors to operate at ambient temperatures. Cerium fluoride, a unipolar fluoride ion conductor, has got a different application in electrochemical sensor. In the present work, cerium fluoride thin films have been prepared by physical vapor deposition method and their electrical properties are studied. X-ray diffraction studies reveal the polycrystalline nature of the prepared thin films and the structure of the material. Scanning electron microscopy (SEM) images show grain-like structures. Conductivity analysis of the thin films has been studied by ac impedance analysis and the maximum conductivity value is found to be 1.04 × 10⁻⁶ S cm⁻¹. The impedance spectra emphasize intergranular conduction in the prepared thin films.