Fabrication processing effects on the microstructure and morphology of erbium film

The effect of substrate temperature on the microstructure and the morphology of erbium film are systematically investigated using X-ray diffraction (XRD) and scanning electron microscopy (SEM). All the erbium films are grown by electron-beam vapor deposition (EBVD). A novel preparation method for observing the cross-section morphology of the erbium film is developed. The films deposited at 200°C have (002) preferred orientation, and the films deposited at 450°C have a mixed (100) and (101) texture, due to the different growth mechanisms of surface energy minimization and recrystallization, respectively. The peak positions and the full widths at half maximum (FWHMs) of erbium diffraction lines (100), (002), and (101) shift towards higher angles and decrease with the increasing substrate temperature in a largely uniform manner, respectively. Also, the lattice constants decrease with increasing temperature. The transition in the film stresses can be used to interpret the changes in peak positions, FWHMs, and lattice constants. The stress is compressive for the as-growth films, and is counteracted by the tensile stress formed during the process of temperature cooling to room temperature. The tensile stress mainly originates from the difference in the coefficients of thermal expansion of the substrate-film couple.     

Fabrication processing effects on microstructure and morphology of erbium film

The effects of substrate temperature on the microstructure and the morphology of erbium film are systematically investigated by using X-ray diffraction (XRD) and scanning electron microscopy (SEM). All the erbium films are grown by the electron-beam vapor deposition (EBVD). A novel preparation method for observing the cross-section morphology of the erbium film is developed. The films deposited at 200 ℃ have (002) preferred orientation, and the films deposited at 450 ℃ have mixed (100) and (101) texture, which are due to the different growth mechanisms of surface energy minimization and recrystallization, respectively. The peak positions and the full widths at half maximum (FWHMs) of erbium diffraction lines (100), (002), and (101) shift towards higher angles and decrease with the increasing substrate temperature in a largely uniform manner, respectively. Also, the lattice constants decrease with the increasing temperature. The transition in the film stresses can be used to interpret the changes in peak positions, FWHMs, and lattice constants. The stress is compressive for the as-growth films, and is counteracted by the tensile stress formed during the process of temperature cooling down to room temperature. The tensile stress mainly originates from the difference in the coefficients of thermal expansion of substrate--film couple.     

红外薄膜中热应力的研究

由于红外薄膜材料和基板热膨胀系数显著不同,所以在高温基板上镀膜后降温将产生热应力,进而引起边界分层破裂现象,影响薄膜器件的牢固性.对薄膜厚度、杨氏模量和热膨胀系数对薄膜分层破裂的影响进行了研究,同时分析了薄膜设计对减小分层破裂的作用.这对减小红外薄膜系统因热应力引起的分层破裂现象具有实际应用价值. 关键词： 多层介质薄膜 红外 热应力 分层破裂     

Preparation of super-hard coatings by pulsed laser deposition

Amorphous diamond-like carbon (DLC) films and nanocrystalline cubic boron nitride (c-BN) films were prepared by pulsed laser deposition. DLC films with 80 to 85% sp³ bonds prepared at a laser fluence above 6 J/cm² and a substrate temperature below 100 °C show high compressive stresses in the range of 8 to 10 GPa. Those stresses can be completely removed by means of pulsed laser annealing, allowing the preparation of DLC films with several-micrometre thickness. c-BN films were prepared with additional ion-beam bombardment at a substrate temperature of 250 °C. The properties of DLC and c-BN films deposited at high growth rates up to 100 nm/min are presented . PACS 81.15.Fg; 68.60.Bs: 62.40.+i     

Effect of a thermal factor on the concentration-structure ordering in ion-plasma W-Ti-B condensates

Small-angle X-ray scattering is used to study the effect of deposition and annealing conditions on the concentration-structure ordering in ion-plasma W-Ti-B condensates. At a relatively low condensation temperature of a solid solution (up to T _c = 770 K), the formed modulated structure has a uniform volume distribution of its structural elements. A stage-by-stage transition from a volume-modulated to a two-dimensional modulated structure is revealed when the condensation temperature increases from 570 to 1170 K. As the annealing time of the metastable postcondensation state of an ion-plasma condensate increases, the diffusion mobility of metallic atoms (W, Ti) decreases upon the formation of a modulated ordered structure. The action of a radiation factor in a three-electrode ion sputtering scheme enhances the concentration phase separation in a condensate, decreases the transition temperature, and stimulates an increase in concentration ordering wavelength λ_od.     

Effect of the nanostructuring of a Cu substrate on the fracture of heat-resistant Si-Al-N coatings during uniaxial tension

The effect of the nanostructuring of the surface layers in a Cu substrate on the microstructure, mechanical properties, and fracture mechanisms of heat-resistant Si-Al-N coatings during uniaxial tension is studied. The nanostructuring of a substrate is performed by the following two methods: bombardment by Zr⁺ ion beams and ultrasonic impact treatment. Depending on the state of the substrate, different spallation mechanisms are found to operate in the Si-Al-N coatings during mechanical loading. The maximum shear strength of the coating/substrate interface is shown to be achieved due to ion bombardment of the substrate.     

Effect of substrate temperature on the magnetic properties and internal stresses of CoPt/AlN multilayer deposited by dc magnetron sputtering

Magnetic properties and internal stresses of AlN(20 nm)/[CoPt(2 nm)/AlN(20 nm)]₅ multilayer structure deposited at different substrate temperatures by dc magnetron sputtering have been studied. It is found that with increasing the substrate temperature from room temperature to 400 °C, in-plane magnetic anisotropy field of the film becomes smaller, and the out-of-plane magnetization becomes stronger. Especially when the film is deposited at substrate temperature of 400 °C, the out-of-plane magnetization becomes as strong as the in-plane magnetization. On the other hand, the total in-plane residual stress of the film changes gradually from compressive to tensile. The compressive intrinsic stress is generated during deposition process and decreases with increasing the substrate temperature. After annealing at high temperatures, the films show strong perpendicular magnetic anisotropy. With increasing the annealing temperature, the in-plane thermal stress also increases and becomes dominant, which is considered to result in the perpendicular magnetic anisotropy of the films.     

ZnS和MgF2薄膜的离子辅助淀积

用Ar离子辅助制备了ZnS和MgF_2薄膜,依据滤光片吸潮波长漂移的测量,MgF_2膜的聚集密度大约从未轰击时的0.8上升到轰击后的0.9～0.95,实验发现,高能离子轰击(>1keV),膜层的吸收散射损耗增加,而低能离子轰击(<700eV)可以保持优良的光学性质,并显著地增加膜层的牢固度,这对于温度敏感的基底制备耐久薄膜是一个重要的应用.     

Surface Morphological Evolution of Thin Films Under Stress and Capillary Forces

Holes and hillocks can commonly be observed on the surface of thin films after thermal processing. For films deposited on a substrate with a different coefficient of thermal expansion, strains due to thermal expansion mismatch can produce very large stresses. While capillary forces tend to produce a thermal groove at a grain boundary (GB), compressive and tensile stresses can form, respectively, a ridge or a canal at the GB. These phenomena can strongly influence mobility of a GB. The formation of a canal enhances the potential for pinning the GB, whereas the formation of a ridge tends to repel the GB.After a short overview of the theory, analytical and numerical solutions for surface profiles of static and travelling GBs under stress are presented. The results of the computed profiles are compared to experimental surface morphologies in aluminum thin film.     

Failure of thin films: Optical shearography versus electrochemical impedance spectroscopy

In the present work, the temperature versus thermal deformation (strain) with respect to time, of different coating films, was studied by a non-destructive technique (NDT) known as shearography. An organic coating, i.e., ACE Premium Enamel, on a metallic alloy, i.e., a carbon steel, was investigated at a temperature range simulating the severe weather temperatures in Kuwait, especially between the daylight and the nighttime temperatures, 20-60 °C. The investigation focused on determining the in-plane displacement of the coating, which amounts to the thermal deformation (strain) with respect to the applied temperature range. Furthermore, the investigation focused on determining the thermal expansion coefficients of coatings, the slope of the plot of the thermal deformation (strain) versus the applied temperature range. In other words, one could determine, from the decreasing value of the thermal expansion coefficients of coatings, a critical (steady state) value of the thermal expansion coefficients of coatings, in which the integrity of the coatings can be assessed with respect to time. In fact, determination of the critical (steady state) value of the thermal expansion coefficients of coatings could be accomplished independent of parameters, i.e., ultraviolet (UV) exposure, humidity, and exposure to chemical species, which normally are considered in conventional methods of assessing the integrity of coatings. Furthermore, results of shearography indicate that the technique is a very useful NDT method not only to determine the critical value of the thermal expansion coefficients of different coatings but also to be used as a 2D-microscope for monitoring the deformation of the coatings in real time at a submicroscopic scale. Also, the obtained data of the shearography technique were compared with data obtained by electrochemical impedance spectroscopy (EIS) in an aqueous solution of 3% NaCl.     

Study on the orientation of silver films by ion-beam assisted deposition

Low energy ion beam assisted deposition (IBAD) was employed to prepare Ag films on Mo/Si (100) substrate. It was found that Ag films deposited by sputtering method without ion beam bombardment were preferred (111) orientation. When the depositing film was simultaneously bombardment by Ar⁺ beam perpendicular to the film surface at ion/atom arrival ratio of 0.18, the prepared films exhibited weak (111) and (200) mixed orientations. When the direction of Ar⁺ beam was off-normal direction of the film surface, Ag films showed highly preferred (111) orientation. Monte Carlo method was used to calculate the sputtering yields of Ar⁺ ions at various incident and azimuth angles. The effects of channeling and surface free energy on the crystallographic orientation of Ag films were discussed.     

Effect of local curvature of the coating-substrate interface on deformation and fracture of ceramic coatings under uniaxial tension

Scanning electron microscopy and atomic force microscopy have been applied to study the fracture of SiAlN coatings on Cu substrates under uniaxial tension. It is shown that coating spalling occurs in the zones of local curvature of the SiAlN-Cu interface which form due to dislocation glide in the substrate. Preliminary ion bombardment of the substrate suppresses dislocation-induced kinking at the coating-substrate interface and increases the adhesive strength of the coatings, thus preventing their edge delamination. At the same time, the wavy coatingsubstrate interface resulting from ion bombardment gives rise to normal stresses that lead to the buckling and spalling of the coatings in the zones of positive local curvature of the interface.     

New concepts for controlled homoepitaxy

On the basis of a kinetic growth model we discuss new methods to grow atomically flat homoepitaxial layers in a controlled way. The underlying principle of these methods is to change the growth parameters during growth of an atomic layer in such a way that nucleation on top of a growing layer is suppressed, and thus, layer-by-layer growth is achieved. Experimentally, this can be realized by changing the substrate temperature or deposition rate during monolayer growth in a well-defined way. The same can be achieved at constant temperature and deposition rate by simultaneous ion bombardment during the early stages of growth of a monolayer, or by adding suitable surfactants to the system. Model experiments on Ag(111) and on Cu(111) using thermal energy atom scattering and scanning tunneling microscopy demonstrate the success of these methods.     

Influence of Si substrate preparation on surface chemistry and morphology of L-CVD SnO2 thin films studied by XPS and AFM

Results of experimental studies of the influence of substrate preparation on the surface chemistry and surface morphology of the laser-assisted chemical vapour deposition (L-CVD) SnO₂ thin films are presented in this paper. The native Si(1 0 0) substrate cleaned by UHV thermal annealing (TA) as well as thermally oxidized Si(1 0 0) substrate cleaned by ion bombardment (IBA) have been used as the substrates. X-ray photoemission spectroscopy (XPS) has been used for the control of surface chemistry of the substrates as well as of deposited films. Atomic force microscopy (AFM) has been used to control the surface morphology of the L-CVD SnO₂ thin films deposited on differently prepared substrates. Our XPS shows that the L-CVD SnO₂ thin films deposited on thermally oxidized Si(1 0 0) substrate after cleaning with ion bombardment exhibit the same stoichiometry, i.e. ratio [O]/[Sn] = 1.30 as that of the layers deposited on Si(1 0 0) substrate previously cleaned by UHV prolonged heating. AFM shows that L-CVD SnO₂ thin films deposited on thermally oxidized Si(1 0 0) substrate after cleaning with ion bombardment exhibit evidently increasing rough surface topography with respect to roughness, grain size range and maximum grain height as the L-CVD SnO₂ thin films deposited on atomically clean Si substrate at the same surface chemistry (nonstoichiometry) reflect the higher substrate roughness after cleaning with ion bombardment.     

The effect of stresses on self-polarization of thin ferroelectric films

The effect of stresses, appearing due to a difference between the temperature coefficients of linear expansion of a substrate and ferroelectric film, on the self-polarization is discussed using thin films of lead zirconate-titanate PbZr_xTi_1?xO₃ (PZT) of different compositions as an example. It is assumed that the nature of self-polarization is connected with internal polarizing electric fields caused by the different density of charged surface states at the ferroelectric-layer interfaces, while tensile or compressive stresses are able only to change the polarization orientation, which causes the self-polarization to increase or decrease in magnitude. The problem of improving the efficiency of PZT films in infrared radiation detectors and memory devices is considered.     

Effect of the pulsed laser deposition conditions on the tribological properties of thin-film nanostructured coatings based on molybdenum diselenide and carbon

The structural state and tribological properties of gradient and composite antifriction coatings produced by pulsed laser codeposition from MoSe₂(Ni) and graphite targets are studied. The coatings are deposited onto steel substrates in vacuum and an inert gas, and an antidrop shield is used to prevent the deposition of micron-size particles from a laser jet onto the coating. The deposition of a laser jet from the graphite target and the application of a negative potential to the substrate ensure additional high-energy atom bombardment of growing coatings. Comparative tribological tests performed at a relative air humidity of ∼50% demonstrate that the “drop-free” deposition of a laser-induced atomic flux in the shield shadow significantly improves the antifriction properties of MoSe _x coatings, decreasing the friction coefficient from 0.07 to 0.04. The best tribological properties, which combine a low friction coefficient and high wear resistance, are detected in drop-free MoSe _x coatings additionally alloyed with carbon (up to ∼55 at %) and subjected to effective bombardment by high-energy atoms during growth. Under these conditions, a dense nanocomposite structure containing the self-lubricating MoSe₂ phase and an amorphous carbon phase with a rather high concentration of diamond bonds forms.     

Development of protective metal coatings on aluminum by magnetron sputtering

Depositions of copper and titanium coatings on aluminum foils and polished aluminum plates for thier protection against corrosion in alkaline media were performed. The coatings were deposited in three different types of magnetron sputtering systems: a direct current (DC) magnetron discharge, a high current impulse magnetron discharge, and a DC magnetron discharge with melted cathode. Only aluminum foils coated with copper films obtained by combined ion-plasma technology, which included preliminarily sputtering of the aluminum surface with an ion beam, deposition of a dense interlayer in the DC magnetron discharge with ion assistance of initial stage of deposition, and deposition of additional layer in the magnetron discharge with melted cathode, were resistant against 30 wt % NaOH solution.     

Effect of temperature on residual stress and mechanical properties of Ti films prepared by both ion implantation and ion beam assisted deposition

Ti films with a thickness of 1.6 μm (group A) and 4.6 μm (group B) were prepared on surface of silicon crystal by metal vapor vacuum arc (MEVVA) ion implantation combined with ion beam assisted deposition (IBAD). Different anneal temperatures ranging from 100 to 500 °C were used to investigate effect of temperature on residual stress and mechanical properties of the Ti films. X-ray diffraction (XRD) was used to measure residual stress of the Ti films. The morphology, depth profile, roughness, nanohardness, and modulus of the Ti films were measured by scanning electron microscopy (SEM), scanning Auger nanoprobe (SAN), atomic force microscopy (AFM), and nanoindentation, respectively. The experimental results suggest that residual stress was sensitive to film thickness and anneal temperature. The critical temperatures of the sample groups A and B that residual stress changed from compressive to tensile were 404 and 428 °C, respectively. The mean surface roughness and grain size of the annealed Ti films increased with increasing anneal temperature. The values of nanohardness and modulus of the Ti films reached their maximum values near the surface, then, reached corresponding values with increasing depth of the indentation. The mechanism of stress relaxation of the Ti films is discussed in terms of re-crystallization and difference of coefficient of thermal expansion between Ti film and Si substrate.     

Ta_2O_5薄膜的低能离子辅助蒸镀

用低能氧离子辅助蒸镀技术,制备了一系列Ta_2O_5薄膜.观测了薄膜的微结构,测量了薄膜的光吸收和光散射.实验指出,离子束轰击和基片加热同时进行,能够制得透明而匀均的Ta_2O_5薄膜.     

K9和石英玻璃基片上Au膜真空紫外反射特性研究

采用离子束溅射法,分别在经过不同前期清洗方法处理过的K9及石英玻璃光学基片上,选择不同的镀膜参量,镀制了多种厚度的Au膜。对镀制的Au膜在真空紫外波段较宽波长范围内的反射率进行了连续测量。测试结果表明:辅助离子源的使用方式、Au膜厚度对反射镜的反射率有重大影响。基片材料、镀前基片表面清洗工艺等对反射率也有一定影响。采用镀前离子轰击,可显著提高Au膜反射率及膜与基底的粘合力;获得最高反射率时的最佳膜厚与基片材料、镀膜工艺密切相关。对经过离子清洗的石英基片,膜厚在30 nm左右反射率最高;比较而言,石英基片可获得更高的反射率;辅助离子源的使用还显著影响获得最高反射率时对应的最佳膜厚值,且对K9基片的影响更显著。