高温氨预处理对单晶硅衬底上镍薄膜显微结构的影响

采用K575X高分辨率溅射仪在单晶硅衬底上制备镍纳米催化剂薄膜。研究了高温氨气刻蚀对镍催化剂由连续薄膜转变成纳米颗粒的影响。探讨了预处理时间、温度和催化剂薄膜原始厚度等工艺参数对镍薄膜微结构的影响,得到了镍催化剂薄膜的氨预处理规律,并初步分析了氨气对其形貌变化的影响机理。研究结果表明,获得均匀、细小和高密度过渡镍金属催化剂颗粒的工艺条件是预处理时间、温度和催化剂薄膜原始厚度分别为12min8、00℃和10nm。     

Influence of pulse parameters on the microstructure and microhardness of nickel electrodeposits

Square-wave cathodic current modulation was used to electrodeposit fine-grained nickel from an additive-free and saccharin-containing Watts bath. The influence of pulse on-time, off-time, peak current density and saccharin on the grain size, surface morphology, crystal orientation, and microhardness was determined. The study showed that at constant off-time and peak current density, the crystal size of the deposits was found initially to decrease with pulse on-time before it started to increase with further increase in on-time. The crystal orientation progressively changed from a (111) texture at the on-time of 0.1 ms to a strong (200) texture at an on-time of 8 ms. An increase in the pulse off-time at constant on-time and peak current density resulted in a progressive increase in crystal size. However, the crystal orientation remained unaffected with increasing off-time. An increase in peak current density resulted in considerable refinement in crystal size of the deposits. The crystal orientation progressively changed from an almost random distribution at the lowest peak current density of 0.2 A/m² to a strong (200) texture at a peak current density of 2.0 A/m². The nanocrystalline nickel with grain size in the order of 30 nm can be produced from saccharin-containing Watts' baths. In contrast, when using an organic-free Watts' bath and similar pulse-plating conditions, the grain size can only be refined down to about 80-100 nm. The microhardness of deposits is related with grain size: when the grain size is large, the microhardness is consistent with Hall-Petch law (HPL); when the grain size is ultrafine, “nano-effect” would be generated, the microhardness is against HPL.     

Property enhancement of nickel electrodeposits by anodic current pulses

The yield and tensile strengths of nickel electrodeposits were increased by a factor of three by the periodic imposition of an anodic current pulse. The time periods between pulses were much longer than those used in periodic reversal plating. The increased strength was attributed to grain refinement resulting from nucleation on surfaces which became passivated during the anodic pulses. The reduced adhesion between layers plated between pulses resulted in a reduction in the coefficients of friction.     

Porosity of nickel electrodeposits on mild steel using electrochemical impedance spectroscopy

Abstract

Impedance spectroscopy recorded at the open circuit potential in 1M H₂SO₄ at 293 K is shown to provide a convenient test for detecting the degree of through porosity in electroplated nickel coatings, electrodeposited from a Watts bath, on mild steel. The impedance data can be interpreted in terms of a simple equivalent circuit, and the corrosion resistance provides a reliable guide to the quality of the deposit. The quantitative estimation of porosity from these data is considered.     

Diffusion-elastic phenomena in nickel and cobalt electrodeposits plated on to strip cathodes

A quantitative analysis was made of the post-deposition increase of the internal tensile stress in nickel and cobalt electrodeposits using an approach based on the diffusion-elastic phenomena. Equations were derived for the determination of the amount and the effective diffusion coefficient of hydrogen, which leaves the deposit immediately after plating. The experimental results are processed using these equations and the results are compared with data in the literature. The role played by hydrogen desorption in increasing the tensile stress after the electrodeposition current is switched off was confirmed.     

Effect of thin film stress on the elastic strain energy of Cr thin film on substrate

The effect of thin film stress on the elastic strain energy of a coherent Cr thin film on a substrate has been calculated by applying Eshelby's inclusion theory taking into account both the anisotropy and inhomogenity. The elastic strain energy is more significantly influenced by the magnitude of the coherent misfit than by the film orientation, which explains why the (200) Cr texture can develop on the (200) MgO seed layer. The application of compressive stress to a film showing a positive dilatational misfit with a constant magnitude raises the elastic strain energy at all film orientations and causes the (200) Cr orientation to have the smallest elastic strain energy at a sufficiently large compressive stress. This suggests the possibility that a coherent Cr thin film on a substrate can exhibit a (200) texture due to the development of high thin film stress during the early period of sputter deposition. The elastic strain energy of an incoherent Cr thin film on a substrate is mostly determined by that due to the thin film stress itself and is always the smallest at the (200) Cr orientation, unlikely from the coherent thin film. Although this energy is normally negligibly small compared with the elastic strain energy due to a coherent misfit, it can nevertheless attain a critical energy range for a texture change from the (110) to (200) Cr at thin film stresses more than several hundred MPa. This explains why the (200) Cr texture is promoted over the (110) on amorphous NiP coating on applying either a mechanical texturing or a bias of negative voltage during sputter deposition. All of these analyses strongly suggest that the thin film stress developed in a thin film during the early period of sputter deposition plays an important role in determining its texture.     

Effect of substrate temperature on adhesion strength of plasma-sprayed nickel coatings

We plasma-sprayed nickel coatings on stainless steel and cobalt alloy coupons heated to temperatures ranging from room temperature to 650 °C. Temperatures, velocities, and sizes of spray particles were recorded while in-flight and held constant during experiments. We measured coating adhesion strength and porosity, photographed coating microstructure, and determined thickness and composition of surface oxide layers on heated substrates. Coating adhesion strength on stainless steel coupons increased from 10–74 MPa when substrate temperatures were raised from 25–650 °C. Coating porosity was lower on high-temperature surfaces. Surface oxide layers grew thicker when substrates were heated, but oxidation alone could not account for the increase in coating adhesion strength. When a coupon was heated to 650 °C and allowed to cool before plasma-spraying, its coating adhesion strength was much less than that of a coating deposited on a surface maintained at 650 °C. Cobalt alloy coupons, which oxidize much less than stainless steel when heated, also showed improved coating adhesion when heated. Heating the substrate removes surface moisture and other volatile contaminants, delays solidification of droplets so that they can better penetrate surface cavities, and promotes diffusion between the coating and substrate. All of these mechanisms enhance coating adhesion.     

Effect of substrate oxidation on spreading of plasma-sprayed nickel on stainless steel

Plasma-sprayed, molten nickel particles (∼ 60 μm diameter) were photographed during impact on oxidized 304L stainless steel surfaces that were maintained at either room temperature or at 350 °C. Steel coupons were oxidized by heating them at different temperatures. A fast charge-coupled device (CCD) camera captured time-integrated images of the spreading splat. A two-color pyrometer collected thermal radiation from particles and recorded the evolution of their temperature after impact. Molten nickel particles impacting on oxidized steel at room temperature fragmented significantly, while heating the surfaces produced splats with disk-like morphologies. Impact on steel that was highly oxidized induced the formation of finger-like splash projections at the splat periphery. Thermal contact resistance between splats and non-heated oxidized steel was calculated from splat cooling rates and found to decrease as the degree of oxidation increased. On heated, oxidized steel thermal contact resistance was much lower and did not change significantly with the degree of oxidation. It was concluded that thermal contact resistance was largely influenced by adsorbates on the steel surface that evaporated when the surface was heated or oxidized.     

Influence of lower current densities on the residual stress and structure of thick nickel electrodeposits

Thick Ni electrodeposits, with thicknesses ranging from 18 to 90 μm, have been produced from sulfamate baths using very low current densities (1.5-5 mA cm⁻²). Increasing grain sizes, with a corresponding decrease in the hardness values, and more columnar grain morphologies were observed with increasing current densities in the deposits. The anisotropy in the mechanical properties of the deposits were found to correlate strongly with the deposit texture, where the change from a < 101> dominated orientation at 1.5 mA cm⁻² to a < 001> orientation at the higher (5 mA cm⁻²) current density led to a corresponding decrease in the indentation modulus values for the respective Ni films. The residual stress values measured in the deposits (75-136 MPa) were found to be comparable to literature values of deposits plated at higher current densities, which rules out any potential advantage from the use of such low current densities for producing lower residual stresses.     

Effect of substrate constraint on spinodal decomposition in an elastically inhomogeneous thin film

Spinodal decomposition in a binary thin film is studied by a three-dimensional (3D) phase field model. A cubic thin film with an (001) orientation is considered. The focus is on the effect of the types of substrate constraint on the morphological evolution during spinodal decomposition as compared to the corresponding bulk. The elastic strain effect is incorporated by solving the elasticity equations for an elastically inhomogeneous thin film with a free surface and constrained by a substrate. Temporal evolution for the composition field, and thus the morphological evolution, is obtained by solving the Cahn-Hilliard equation using a semi-implicit Fourier-spectral method. It is shown that a biaxial substrate constraint has essentially no effect on the spinodally decomposed two-phase morphology which is primarily controlled by the cubically anisotropic elastic interactions. The asymmetry in the strain components along the [100] and [010] directions from the substrate constraint results in the preferential alignment along one of the two directions. In the particular case of a harder phase whose lattice parameter increases with composition, a tensile substrate constraint along the film plane leads to the alignment of two-phase microstructures parallel to the tensile direction. This article is based on a presentation made in the 2003 Korea-Japan symposium on the “Current Issues on Phase Transformations”, held at Marriott Hotel, Busan, Korea, November 21, 2003, which was organized by the Phase Transformation Committee of the Korean Institute of Metals and Materials.     

沉积温度对ZnO薄膜结构及发光性能的影响

利用Nd-YAG激光器(波长为1064nm,频率为10Hz)做光源,采用纯金属锌靶,以Si(111)为基体在有氧的气氛中通过激光烧蚀锌靶表面来制备氧化锌薄膜,研究基体温度对ZnO薄膜结构及发光性能的影响.通过XRD和AFM原子力显微镜来表征氧化锌薄膜的结构和表面形貌,其光学性质由光致发光谱来表征.结果表明:在450-550 ℃的条件下沉积的ZnO薄膜具有c-轴择优取向,500℃时c-轴取向最明显.具有c-轴取向的ZnO薄膜具有强的紫外光发射和弱的绿光发射,发光中心在518nm处的黄绿光发射主要归因于电子从导带底部到氧位错缺陷OZn能级之间的跃迁.     

热丝CVD金刚石涂层硬质合金衬底两步法预处理的研究

研究了引入超声振动后酸碱两步法预处理对硬质合金衬底表面去Co催石墨化作用。采用偏压增强辅助热丝化学气相沉积(HFCVD)法,在硬质合金衬底上沉积了一层均匀、光滑的金刚石薄膜。研究结果表明:在酸碱两步法预处理过程中引入超声振动,能够有效的去除硬质合金衬底表面的Co元素,衬底表面发生了明显的粗化;采用Murakami试剂超声振动20 min腐蚀WC相,再用V(H2SO4)∶V(H2O2)=3∶7混合溶液超声振动30 s去除Co相,金刚石薄膜形核密度高、结晶质量好。这说明了超声酸碱两步法预处理能够有效的抑制钴对金刚石薄膜的不利影响,对提高金刚石薄膜与基体之间的附着力起着非常重要的作用。     

Effect of interfacial segregation on phase decomposition of a thin film on a patterned substrate

Numerical simulations of phase decomposition in thin films on patterned substrates are presented for a binary alloy in order to study the influence of substrate composition on microstructural evolution. For systems with a substrate composition less than the film composition, a preferential segregation ofA to the interface was observed and no phase decomposition occurred within the film. For patterned systems with a substrate composition exceeding the film composition, theB-rich phase was able to grow by a barrierless transformation for a range of film compositions outside the chemical spinodal. The number of precipitates which formed on the mesa, the dihedral angles at the three-phase trijunctions, and the resulting microstructure within the film were shown to be sensitive to the substrate composition. This article is based on a presentation made in the 2002 Korea-US symposium on the “Phase Transformations of Nano-Materials,” organized as a special program of the 2002 Annual Meeting of the Korean Institute of Metals and Materials, held at Yonsel University, Seoul, Korea on October 25–26, 2002.     

Influence of rare earths on shrinkage porosity in thin walled ductile cast iron

Abstract

Ductile cast iron has been cast in test bars with thickness from 2 to 10 mm. The rare earth elements La and Ce have been added to some of the castings to evaluate their influence on microstructure and shrinkage tendency. Both La and Ce increased the graphite nodule count, especially for thickness of 6 mm and below. La gave the best nodule size distribution with many small nodules. La had less shrinkage tendency than Ce in the 10 mm test bars. This tendency was less pronounced for the 6 and 4 mm test bars and other factors may have a large influence at these thicknesses. Increasing the temperature T ₁, which is controlled by the growth of off-eutectic austenite dendrites, increased the shrinkage tendency.     

Effect of substrate temperature on microstructures and dielectric properties of compositionally graded BST thin films

Compositionally graded Ba1-xSrxTiO3 （BST） （x = 0-0.3） thin films were prepared on Pt/Ti/SiO2/Si substrate at different substrate temperatures ranging from 550 ℃ to 650 ℃ by radio-frequency （rf） magnetron sputtering. The effect of substrate temperature on the preferential orientation, microstructures and dielectric properties of compositionally graded BST thin films was investigated by X-ray diffraction, scanning electron microscopy and dielectric frequency spectra, respectively. As the temperature increases, the preferential orientation evolves in the order： randomly orientation→ （111） → highly oriented （111） （α（111）= 60.2%）. The surface roughness of the graded BST thin films varies with the substrate temperatures. No visible internal interface in the compositionally graded thin films can be observed in the cross-sectional SEM images. The graded BST thin films deposited at 650 ℃ possess the highest dielectric constant and dielectric loss, which are 408 and 0.013, respectively.     

Effect of substrate temperature on structural properties and photocatalytic activity of TiO2 thin films

Titanium dioxide （TiO2） films with anatase structure were prepared on quartz glass substrates by pulse laser ablating titanium （99.99%） target under oxygen pressure of 10 Pa at substrate temperature of 500-800 ℃. The structural properties of the films were characterized by X-ray difffactometry（XRD）, X-ray photoelectron spectroscopy（XPS） and field emission scan electron microscopy（FESEM）. The results show that, as the substrate temperature is increased from 600 ℃ to 800 ℃, the anatase structure of the films changes from random growth to （211）-oriented growth. The absorption edge tested by UV-Vis Spectrometer has a blue shift. The photocatalytic activity of the films was tested on the degradation of methyl orange. It is found that the film with random growth structure exhibits better photo-degradation efficiency than that with （211）-oriented growth structure.     

Influence of substrate temperature on the preparation of GaP thin films

Gallium phosphide (GaP) was prepared by treating specpure gallium with AnalaR grade Zn₃P₂ in an argon atmosphere. Thin films of GaP were evaporated onto glass substrates at various substrate temperatures under vacuum. Films evaporated onto substrates at and above 250°C were polycrystalline in nature. Films of various thicknesses were grown. The conductivity of these films in the dark and in white light is presented for the temperature range 100–300 K. Optical absorption spectra for films grown at substrate temperatures T_s = 90, 180 and 250°C were also recorded in the range 0.5–2.5 eV. All the features are attributed to the structural disorder which probably occurs during evaporation onto the glass substrates.