共查询到20条相似文献,搜索用时 140 毫秒
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铀是非常活泼的金属,在大气环境中很容易发生腐蚀,通过磁控溅射方法,在铀表面镀铝可以对铀起到很好的防腐蚀效果,但经过磁控溅射以后,薄膜内会产:生应力,从而影响了铀表面铝镀层的结合强度及使用性能。一般认为,薄膜内的应力来源于两个方面:一是热应力,二是生长应力。热应力是由于薄膜与基体热膨胀系数不同经温度变化引起的,而生长应力则来自于薄膜与基体物理性质的不同,以及薄膜中的结构缺陷。对于一种确定结构的膜基体系,生长应力比较固定,而热应力却可以通过磁控溅射工艺进行一定的调整。文中采用热弹塑性有限元分析方法,对铀表面磁控溅射沉积铝镀层的热应力分布进行了研究。 相似文献
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热膨胀系数异性轴夹角优化分析 总被引:1,自引:0,他引:1
高超声速飞行器需要先进的材料进行热防护,比如增强碳/碳材料.有两种将碳纤维制作成碳/碳球锥外形的工艺,研究表明在每种工艺中,碳/碳块体或碳纤维热膨胀系数异性轴角度对结构热应力影响很大,为此本文发展了一套优化设计方法,对给定的对流加热温度场可以实现球锥热应力的最小化.分析结果表明对于热膨胀系数异性轴角度,存在某些取值点,那时结构热应力分别达到最大和最小值.在异性轴模晕小于同性平面模量的条件下,对于工艺1,如果将球锥对称轴设置成垂直于碳/碳块体的同性平面,可以将热应力减至最小;对于工艺2,如果能将编制面内的碳纤维束异性轴角度取成负值(即指向来流方向),则球锥热应力也可以得到相当程度的减小. 相似文献
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为满足红外探测系统无热化、高质量成像的需求,在非球面硫系玻璃基底制备3.7~4.8 μm波段增透膜.根据试验要求选取黏结层材料,提高基板与薄膜之间的附着力;利用有限元分析法通过多物理场仿真软件,将温度场与热应力场相结合建立三维模型,分析非球面薄膜的应力分布情况.根据模拟结果对沉积工艺进行优化,采用温度梯度烘烤法降低硫系玻璃基底的热应力,并采用真空原位退火法释放沉积薄膜的应力,解决非球面镜的脱膜问题.所制备的薄膜可以通过MIL-C-48497A标准中的附着力、湿度、中度摩擦等测试,并在3.7~4.8 μm波段的平均透过率为99.12%,满足红外探测系统的指标要求. 相似文献
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用有限Hankel积分变换法对轴对称强激光束辐照下平面薄靶(或薄膜)传热及热应力分布进行了解析推导,得到了随时间演变的温度场及相应的热应力场的解析解。对比有关实验,对强激光束辐照窗口材料(例如MgF2晶体、K9玻璃)靶引起其脆性热应力破裂进行了分析,详细讨论了激光强度、激光-靶能量耦合系数、辐照时间及光斑尺寸等因素对靶的破坏的影响。 相似文献
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本文将硅(Si)衬底上外延生长的氮化镓(GaN)基发光二极管(LED)薄膜剥离转移到新的硅基板和紫铜基板上,并获得了垂直结构的LED芯片,对其变温变电流电致发光(EL)特性进行了研究. 结果表明:当环境温度不变时,在13 K低温状态下铜基板芯片的EL波长始终大于硅基板芯片约6 nm,在300 K 状态下随着驱动电流的加大铜基板芯片的EL波长会由大于硅基板芯片3 nm左右而逐渐变为与硅基板芯片重合;当驱动电流不变时,环境温度由13 K升高到320 K,两种基板芯片的EL波长随温度升高呈现S形变化并且波谱逐渐趋于重合;在100 K以下温度时铜基板芯片的Droop效应比硅基板芯片明显,在100 K 以上温度时硅基板芯片的Droop效应比铜基板芯片明显. 可能是由于两种芯片的基板具有不同的热膨胀系数和热导率导致了其变温变电流的EL特性不同.
关键词:
GaN
热膨胀系数
内量子效率
热导率 相似文献
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T. Miyazaki R. Inoue K. Nishida T. Kanaya 《The European physical journal. Special topics》2007,141(1):203-206
We have studied thermal expansion of free standing polystyrene thin films using X-ray reflectivity to elucidate the glass
transition temperature and the thermal expansivity. We found that the glass transition temperature Tg decreased with the film thickness, depending on molecular weight. The reduction in the free standing films is much larger
than in the supported films on Si substrate, suggesting that some segmental motions are activated due to free surfaces on
both sides in the free standing films. We also found that the thermal expansivity in the glass and the melt decreased with
the film thickness. This decrease must be attributable to chain confinement effects. 相似文献
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Zhixun Ma Kin Man Yu Wladek Walukiewicz Peter Y. Yu Samuel S. Mao 《Applied Physics A: Materials Science & Processing》2009,96(2):379-384
We have deposited CdTe films by laser-assisted epitaxy approach and investigated the influence of substrate and film thickness
on the film properties. Grown on Si(001), GaAs(001), and quartz substrates; the CdTe films exhibit preferential orientation
along the cubic CdTe(111) direction. When the films are thin (<500 nm), a blueshift of the band gap and splitting of valence
bands were observed. These results are attributed to the existence of residual strains induced by mismatch of the film lattice
constant with that of the substrate, and by their difference in thermal expansion coefficients. The bulk band-gap energy of
1.5 eV was achieved on the surface of thick CdTe films grown on Si(001) substrate, indicating that strain was almost completely
relaxed in this case. Our results demonstrate that by a proper selection of substrate and film thickness it is possible to
grow film semiconductors with band gap approaching those of bulk crystals. 相似文献
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ZnO外延膜与蓝宝石衬底的取向偏差及其弯曲变形 总被引:1,自引:1,他引:0
采用常压MOCVD方法在Al2O3(00.1)衬底上生长出了高质量ZnO单晶薄膜。由ZnO(00.2)面和Al2O3(00.6)面及ZnO(10.2)面和Al2O3(11.6)面X射线双晶(w/2θ衍射曲线的相对峰位,得到ZnO外延膜的晶格常数及外延层和衬底间的取向差异角。结果表明外延层和衬底在应力作用下产生了取向差和晶格畸变,并且取向倾斜方向与衬底的切割倾角方向一致;高温直接生长的样品的取向差比有低温缓冲层样品更大,晶格畸变也更严重。高温直接生长的样品弯曲半径小而应力更大;实验测量的应力值和理论计算的热应力值之间存在差异,原因主要是晶格失配应力的存在。有缓冲层的样品由于能更好地弛豫晶格失配引入的应力,热应力所占整个残余应力的比例相对更大。 相似文献
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François Y. Génin 《Interface Science》2001,9(1-2):83-92
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. 相似文献
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S. Besseghini A. Gambardella V. A. Chernenko M. Hagler C. Pohl P. Müllner M. Ohtsuka S. Doyle 《The European physical journal. Special topics》2008,158(1):179-185
A series of Ni51.4Mn28.3Ga20.3/Si(100) thin film composites with different film thicknesses varying from 0.1 to 5 μm have been prepared by magnetron sputtering
and subsequently annealed. X-ray powder diffraction patterns of the films show the features associated with the lattice-modulated
martensitic phase and/or cubic austenite at room temperature. 220-fiber texture was confirmed by the X-rays measurements made
at 150 °C. While the Curie temperature is almost film thickness independent, the martensitic transformation temperature shows
a strong descended dependence in the submicron range. The substrate curvature measurements demonstrate that the forward and
reverse martensitic transformation in the films is accompanied by the reversible relaxation and accumulation of residual stress,
originally created by the thermal treatment due to the difference in thermal expansion of the film and substrate. The values
of residual stresses measured by both substrate curvature and X-rays diffraction methods at constant temperatures are found
to be dependent on the film thickness. This behavior appears in correlation with the thickness dependence of the transformation
temperature. 相似文献
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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. 相似文献
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A.V. Simakin E.N. Loubnin G.A. Shafeev 《Applied Physics A: Materials Science & Processing》1999,69(7):S267-S269
A novel effect is studied of self-limitation of the diamond-like film thickness during laser irradiation of the interface of transparent substrates with liquid aromatic hydrocarbons. The interface is exposed through the transparent substrate to radiation of a copper vapor laser (wavelength of 510.6 nm, pulse duration of 20 ns). The thickness of diamond-like film increases linearly to 80-100 nm with the number of laser pulses and then saturates, while the substrate is ablated with nearly constant rate. This ablation rate depends on the thermal expansion coefficient of the substrate (glass, fused silica, sapphire, or CaF2). The absorption of extinction coefficient of deposited films measured by ellipsometry is of order of 104 cm-1 and is sufficient to cause the significant heating of the interface. The ablation of the transparent substrates is due to their unequal thermal expansion compared to the diamond-like film having different thermal expansion coefficient. The measured ablation rates scale from 0.2 Å/pulse for glass to 4.5 Å/pulse for CaF2. A 7m spatial resolution of the ablation process has been demonstrated for fused silica. 相似文献
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B. Saftić N. Rašula W. Zinn J. Chevallier 《Journal of magnetism and magnetic materials》1982,28(3):305-312
EuS single crystalline films were grown epitaxially on silicon (111), (100) and (110) crystal substrate planes. By Rutherford backscattering techniques they are shown to achieve the stoichiometric composition and crystal perfection expected with molecular beam epitaxy. The angular dependence of the remagnetization process in the film plane confirms the expected crystal symmetry and magnetic anisotropy. The substantial, but different, reductions in the Curie temperatures of EuS-(111), -(110) and -(100) films by up to 15% have been attributed to the largely different thermal expansion coefficients of Si and EuS. 相似文献
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We study the features of excitation of acoustic waves by high-power microwave pulses in thin metal films bordering on liquid. Aluminum films with thicknesses 1–10 nm deposited onto a quartz substrate were used in experiments. It is shown theoretically that the absorption coefficient of microwaves is maximum for film thickness from 2 to 3 nm and the value of this maximum is determined by the dielectric permittivity of the bordering liquid. Theoretical calculations and experiments are performed for water and ethyl alcohol. The sound generation in a layered system quartz-aluminum film-liquid is analyzed with the help of the step-by-step approach. At the first step, microwave energy is absorbed in the film and heat is released. Then heat almost instantly diffuses into a liquid whose thermal expansion creates an acoustic signal. Profiles of acoustic signals excited in aluminum films by microwave pulses with a 5-ns duration and an energy of up to 1 mJ are experimentally detected. The most efficient transduction was observed for an aluminum film 3.5 nm thick. 相似文献
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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. 相似文献