Texture and columnar structure of evaporated cobalt films: II

The dependence of the columnar structure on the degree of texture was investigated in cobalt films prepared at various evaporation rates. The angle of incidence was 70° and the substrate temperature 200°C. The evaporation rates range from 70 to 11 000 Å min^-1. The texture was analysed by means of pole figures and the columnar structure was observed by replica electron microscopy. The results obtained are as follows. (1) With an increase of the degree of texture the gaps between columnar grains increase but the angle of inclination of the columnar grains decreases. (2) In the film with a high degree of texture bundles of columnar grains exist. On the basis of these results, the correlation between the texture and the columnar structure is briefly discussed.     

High-speed oxide coating by laser chemical vapor deposition and their nano-structure

Oxide thick films, partially yttria-stabilized zirconia (YSZ) and titania (TiO₂), were prepared by laser chemical vapor deposition (LCVD). The assistance of laser tremendously increased the deposition rate for YSZ and TiO₂ films up to 660 and 2500 μm/h, respectively. The increase in the deposition rate was accompanied by plasma formation around the deposition zone, and the plasma was observed over critical values of laser power and substrate pre-heating temperature. A wide variety of morphologies of films from feather-like columnar to dense microstructures were obtained depending on deposition conditions. The columnar structure contained a large amount of nano-pores at columnar boundary and inside grains. These columnar structure and nano-pores were advantageous for applying YSZ films to thermal barrier coatings.     

Effect of filament and substrate temperatures on the structural and electrical properties of SiC thin films grown by the HWCVD technique

The effect of varying filament and substrate temperatures on the structure and electrical conductivity of crystalline SiC films prepared by HWCVD technique are described in this paper. At a constant filament temperature, the electrical conductivity of the SiC films increases with increasing substrate temperature. However, TEM studies show that there is no change in the size of the SiC columnar grains. On the other hand, a significant variation in filament temperature at constant substrate temperature leads to a variation of structure and conductivity. Raman spectroscopy and TEM studies reveal that crystallinity improves with increase in filament temperature. Furthermore, a μc-Si phase exists alongside SiC at low filament temperature (1750 °C).     

Microstructure characterization of sol-gel derived PZT films

The crystallization of sol-gel derived amorphous PZT films deposited on a MgO single-crystal substrate and a SiO₂ glass substrate was examined. The pyrochlore crystallites, 5 nm in size, were homogeneously nucleated in the amorphous films at 350 °C. The nucleation temperature of pyrochlore did not depend on the type of substrate. Fine pyrochlore grains were stable even during annealing at high temperatures up to 600 °C. The perovskite formation temperature was dependent on the substrate, and was about 550 °C on the MgO single-crystal substrate and about 750 °C on the SiO₂ glass substrate. The perovskite was heterogeneously nucleated preferentially at the substrate-film interface. Perovskite nucleation was more difficult at the SiO₂ glass-film interface than at the MgO single crystal-film interface. The ease of nucleation reflected the perovskite formation temperature. Perovskite crystals grew fairly rapidly, once they were nucleated in the films. In the multiple-coated films, the interface between successive layers of PZT films was a favourable nucleation site of perovskite, and the columnar perovskite grains passing through the interface were often developed.     

Temperature dependence of the magnetization of nanostructured Ni films

Ni films were prepared on SiO₂/Si(100) substrates at 300 K by DC magnetron sputter-deposition. The films consist of thin columnar grains grown perpendicularly to the substrate surface. A magnetization dependence on temperature was investigated in the range from 300 to 673 K with the use of a vibrating sample magnetometer. The saturation magnetization of the Ni films decreases markedly with increasing the temperature up to 520 K. However, as the temperature exceeds 520 K, the magnetization begins to increase forming the magnetization minimum at 520 K and then finally falls to zero at 590 K. It is confirmed by field emission scanning electron microscopy and X-ray diffraction that such recovery of the magnetization at the temperature over 520 K is attributed to an improvement of the crystallinity in the film due to the migration and annihilation of vacancies during the magnetization measurement at the higher temperature. In conclusion, the Curie temperature of the Ni films with the thin columnar grains can be determined to be about 520 K appreciably lower than that of the Ni bulk crystal.     

Structural,electrical and photoluminescence properties of ZnO:Al films grown on MgO(0 0 1) by direct current magnetron sputtering with the oblique target

ZnO:Al films were deposited on MgO(0 0 1) substrates at 300 K and 673 K by direct current magnetron sputtering with the oblique target. The Ar pressure was adjusted to 0.4 Pa and 1.2 Pa, respectively. All the films have a wurtzite structure and a c-axis orientation in the film growth direction. The films deposited at 300 K initially grow with thin columnar grains and subsequently grow with large granular grains on the thin columnar grains. However, the films grown at 673 K consist mainly of dense columnar grains perpendicular to the substrate surface. The ZnO:Al film deposited at 673 K and 0.4 Pa has the lowest resistivity, the highest free electron concentration and Hall's mobility. A temperature dependence of the resistivity within 5–300 K reveals that the films grown at 300 K exhibit a semiconducting behavior and those grown at 673 K show a metal–semiconductor transition. The carrier transport mechanism is Mott's variable range hopping in the temperature range below 90 K for all the films and thermally activated band conduction above 215 K for the films grown at 300 K. Room temperature photoluminescence spectra for wavelengths between 300 nm and 800 nm reveal mainly blue-green emissions centered at 452 nm, 475 nm and 515 nm.     

Effect of thermal annealing on the microstructure and morphology of erbium films

The effects of thermal annealing on the microstructure and morphology of erbium films were investigated by X-ray diffraction and scanning electron microscopy. All the erbium films were fabricated by electron-beam vapor deposition. The columnar grain sizes of as-received erbium films increased with the substrate temperatures and were enlarged by the coalescence and migration of grains during the high temperature annealing. The intrinsic stresses of erbium films, fabricated at a low substrate temperature (200 °C), were relaxed accompanied with the appearance of cracks on the films surface. The films deposited at 200 °C had (002) preferred orientation, and the film deposited at 450 °C had mixed (100) and (101) texture. The peak positions and the full width at half maximum of (100), (002), and (101) diffraction lines of erbium shift towards higher angles and sharply decrease during the annealing process, indicating that the stress inside the film was relaxed.     

La0.7Ca0.3MnO3薄膜微观结构的HRTEM表征

利用透射电子显微镜研究了衬底温度600～800℃条件下采用脉冲激光法在(001)LaAlO3(LAO)衬底上制备的La0.7Ca0.3MnO3(LCMO)薄膜的微观结构。结果表明薄膜由大量柱状晶组成且与LAO衬底形成良好外延关系。LCMO薄膜与LAO衬底的取向关系可以描述为:(ⅰ)(100)f∥(001)s、[011]f∥[100]s;(ⅱ)(011)f∥(001)s、[100]f∥[100]s。LCMO显示层状畴结构,即在衬底上初始生长的薄膜为(ⅱ)型畴,在此之上生长的薄膜为(ⅰ)类和(ⅱ)类型畴的混合体。薄膜中可观察到一些反向畴与孪晶等缺陷。薄膜与衬底界面少见错配位错,薄膜以Stranski-Krastanov模式生长。     

Nanostructural Features and Optical Performance of RF Magnetron Sputtered ZnO Thin Films

Zinc oxide (ZnO) thin films were grown on silicon substrate by RF (radio frequency) magnetron sputtering.Surface topography of these films exhibited a nanostructured granular appearance with the size of individual grains between 50 to 100 nm.Corresponding cross-sectional electron micrographs revealed columnar grains in the form of aggregated nanorods/wires with length of about 500 nm,similar to the thickness of these thin films of ZnO nucleated and grown vertically on the silicon substrate.High resolution l...     

Preparation of cobalt oxide films by plasma-enhanced metalorganic chemical vapour deposition

Co oxide films were prepared on glass substrates at 150–400°C by plasma-enhanced metalorganic chemical vapour deposition using cobalt (II) acetylacetonate as a source material. NaCl-type CoO films were formed at low O₂ flow rate of 7cm³ min^–1 and at a substrate temperature of 150–400°C. The CoO films possessed (100) orientation, independent of substrate temperature. Deposition rates of the CoO films were 40–47 nm min^–1. The CoO film deposited at 400 °C was composed of closely packed columnar grains and average diameter size at film surface was 60 nm. At high O₂ flow rate of 20–50 cm³ min^–1, high crystalline spinel-type Co₃O₄ films were formed at a substrate temperature of 150–400°C. The Co₃O₄ film deposited at 400°C possessed (100) preferred orientation and the film deposited at 150°C possessed (111) preferred orientation. Deposition rates of the Co₃O₄ films were 20–41 nm min^–1. Both Co₃O₄ films with (100) and (111) orientation had columnar structure. The shape and average size of the columnar grains at the film surface were different; a square shape and 35 nm for (100)-oriented Co₃O₄ film and a hexagonal shape and 60 nm for (111)-oriented film, respectively.     

Influence of growth parameters on the microstructures of erbium films deposited on Si(111) substrates

Erbium films were grown on single crystal Si(111) substrates by electron beam vapor deposition. The microstructures of the erbium films were systematically investigated by X-ray diffraction, scanning electron microscopy, and energy dispersive spectroscopy. Results indicate that the surface morphologies and microstructures of the erbium films with Si as substrates are susceptible to the substrate temperatures when the deposition rates are fixed. The pure erbium films with columnar grains were obtained at temperatures below 200 °C, but in the films grown at temperatures higher than 350 °C, some pinholes that are composed of erbium silicides were found. The pinholes have triangular shapes which is in accordance with the geometry of the underlying Si(111) substrate. The films grown at a substrate temperature equal or greater than 450 °C have cracks which would be formed due to the different shrinkage degree of erbium and silicon when the substrate temperature was cooled down to room temperature. The films grown at 200 °C show the (002) preferred orientation, which is consistent to the prediction by the theory of surface energy minimization. The deposition rate and deposition time are considered as factors to affect the reaction of the erbium film and the silicon substrate.     

Electron microscopic study of sputter-deposited Ir films

The microstructural development of iridium (Ir) film deposited on isotropic graphite by a sputtering method was investigated using a transmission electron microscope. A columnar structure was developed in which the diameters of columnar grains were distributed from 3 to 50 nm at the substrate temperature of 330 K. Directions of grains were almost perpendicular to the substrate surface, and grain boundaries were wavy. Grains forming the columnar structure indicated different orientations of a growth direction, though growth orientations of grains showed the weak preferred orientation of a [111] direction. Non coincident related boundaries, as well as low angle grain boundaries and twin boundaries tend to be observed more frequently than coincidence lattice related boundaries.     

石英衬底上柱状多晶硅薄膜的制备

利用射频等离子体增强化学气相沉积法(RF-PECVD)在已经预沉积有非晶硅薄膜的石英衬底上低温沉积了N/I非晶硅薄膜, 对样品进行了两步快速光热(RTP)退火. 采用 Raman、X射线衍射(XRD)、扫描电子显微镜(SEM)和透射电子显微镜(TEM)等测试仪器对样品退火前后的结晶状况和微观形貌进行了分析. 结果表明, 该N/I非晶硅薄膜退火后的晶化率达到了94%左右, 断面形貌为柱状结构, 样品中的平均晶粒尺寸约30nm, 晶粒团簇的尺寸最大约1.5μm.     

Structure and microstructure of EB-PVD yttria thin films grown on Si (111) substrate

Structure and microstructure of yttria thin films grown by electron beam physical vapour deposition on a stationary Si (111) substrate at room temperature (RT), 500° and 700 °C, were investigated by the grazing-incidence X-ray diffraction and scanning electron microscopy, respectively. X-ray photoelectron spectroscopy provided information on the surface contamination from the atmosphere and the Y oxidation state. A strong effect of the deposition temperature and the vapour flux incidence angle was found. The film deposited at RT is polycrystalline with very fine grains of the body-centered cubic (bcc) crystallographic symmetry. An increase of deposition temperature results in a rapid growth of bcc grains with an improved crystalline structure. Moreover, the based-centered monoclinic phase appears for the deposition temperature of 700 °C. Preferred grain orientation (texture) with two main components, (400) and (622), was observed in the films deposited at 500 °C whereas no texture was found for 700 °C. The microstructure exhibits the columnar feather-like structure of different degrees of perfection which can be explained by the shadowing effects caused by an oblique vapour flux incidence angle. Surface morphology of the films is governed by a combination of the triangular and four-sided (square) columns. All films were found to be dense with a little porosity between the columns.     

直流磁控溅射ZnO薄膜的结构和室温PL谱研究

ZnO是一种新型的宽带化合化半导体材料 ,对短波长的光电子器件如UV探测器 ,LED和LD有着巨大的潜在应用。本实验研究采用直流反应磁控溅射法在硅衬底上沉积C轴择优取向的ZnO晶体薄膜 ,薄膜呈柱状结构 ,晶粒大小约为 10 0nm ,晶粒内为结晶性能完整的单晶 ,但晶粒在C轴方向存在较大的张应力。ZnO薄膜在He Cd激光器激发下有较强的紫外荧光发射 ,应力引起ZnO禁带宽度向长波方向移动 ,提高衬底温度有利于降低应力和抑制深能级的绿光发射     

Structural characterization of ZnO thin films deposited by dc magnetron sputtering

In this work we present recent results on ZnO thin films grown by dc magnetron sputtering technique at room temperature (RT), focusing on structural and surface characterization using conventional cross-section transmission electron microscopy (XTEM) and high resolution cross section transmission electron microscopy (HRXTEM) in an attempt to understand the thickness influence on film, mechanical and optical properties as well as photoreduction/oxidation conductivity changes. Films were found to be polycrystalline with a columnar mode of growth. For films with thickness over 100 nm, XTEM and HRTEM analysis evidenced the presence of a small grains transition layer near interface with the substrate, feature which plays an important role in ZnO thin films for gas sensing application. The control of such structural parameters is proved to be critical for the improvement of their gas sensing performance.     

Fabrication and characterization of solid oxide fuel cell electrolyte films by electron beam vapor deposition

Thin films of SDC for SOFC electrolyte were prepared using electron beam deposition technique. The influence of annealing temperature, substrate temperature and e-beam gun power on the structure and surface morphology of the thin films was examined. It was found that the SDC thin films annealed at 800 degrees C consisted of a single cubic phase and the main crystal structure of the thin films represented those of evaporated electrolyte powders. The crystal orientation of the SDC films increased with substrate temperature and decreased with e-beam gun power. The higher XRD peak intensity was observed for the SDC films deposited on NiO-YSZ substrate compared with those on SiO2 substrate due to the polycrystalline structure of the NiO-YSZ substrate. A good adhesion to the substrate and a columnar structure were observed by the fractured cross-sectional view of the SDC films on NiO-YSZ anode substrate. Electrical conductivity of SDC film with 5 microm thickness was observed to be 2.31 x 10(-3) Sm(-1) at 800 degrees C.     

Structural characteristics and mechanical properties of Ti(Cr) films produced on Si substrate

A series of nanogranular Ti₉₀Cr₁₀ thin films have been fabricated by pulsed-laser deposition on Si substrates at different temperatures. The crystal structure and mechanical properties of these films were investigated. The X-ray diffraction and transmission electron microscope images with selected area diffraction showed that the structure of as-prepared films is dependent on film thickness and deposition temperature. It was found that the Ti₉₀Cr₁₀ films consisted of fine hexagonal close packed microstructure with columnar grains, while body close-packed cubic structure of Cr films are composed of irregular grains, meanwhile, a chromium disilicide (CrSi₂) layer formed in the interface between the substrate and Cr films which deposited at temperature of greater than 600 °C. The crystalline and columnar grains improved with an increase of the thickness of the films and an optimum microstructure is obtained under the present experimental condition of about 50 nm thickness and deposited temperature of 500 °C for Ti₉₀Cr₁₀ films. Deposited at 300 °C, the Ti₉₀Cr₁₀ films have hardness of 12.7 GPa and elastic modulus of 174.6 GPa. Improved to 600 °C the sample shows higher hardness of 13.1 GPa and higher elastic modulus of 183.2 GPa. Using Benjamin-Weaver model, adhesion shearing force can be calculated as 34.9 MPa for 300 °C Ti₉₀Cr₁₀ film while higher value of 44.4 MPa for higher temperature of 600 °C.     

Pyrite Films Grown by Sulfurizing Precursive Iron of Different Crystallizing Status

Precursive iron films with different grain sizes were prepared by magnetron sputtering on substrates heated at different temperatures. The iron films were sulfurized at 673 K for 20 h to form pyrite films. The structural and electrical characters were determined. High substrate temperatures produce large crystallites in the precursive iron films. The pyrite films are composed of a surface layer with coarse columnar grains and a bottom layer with fine equiaxed grains. With the increase of iron grain scale, the carrier concentration decreases and the carrier mobility increases. The electrical resistivity of the pyrite films increases to a maximum in the precursive iron films with increasing the grain size to about 39 nm. Sufficient formation and growth of iron grains result in improved crystallinity and high continuity of the pyrite films. The crystal defect density, transformation stress level and atom diffusion behavior are responsible for the characteristics of the electrical properties dependent on the crystallinity and continuity of the pyrite films or the crystallizing status of the precursive iron films.     

Characterization and sensing properties of ZnO film prepared by single source chemical vapor deposition

A novel deposition technique has been used to grow ZnO films. Good quality films were obtained on glass substrates by single source chemical vapor deposition (SSCVD), for gas sensing applications. The properties of ZnO films were investigated at different deposition temperatures 300, 350 and 400 °C. X-ray diffraction results show that all deposited films were polycrystalline. The morphological, structural, optical and electrical properties of the films have been investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), cathodoluminescence (CL) and Hall effect techniques. The morphology of the deposited films evolves from columnar grains, to parallel plates as the substrate temperature increases. A significant increase in the relative intensities of the green and red emission with increasing deposition temperature has been observed. Electrical properties, relevant for gas sensing behavior have been investigated as well. In the particular case of CO an operating temperature of 300 °C seems to yield the best sensitivity.