分子动力学模拟C+离子与聚变材料钨的相互作用

采用分子动力学方法模拟不同能量的C+离子与聚变材料钨的相互作用.模拟结果表明:当C+离子入射剂量为3.11×1016 cm-2,入射能量为50eV时,样品表面形成一层碳膜;而入射离子能量为150和250eV时,C+离子入射到样品内与钨原子共同形成碳钨混合层,样品表面没有形成碳膜;碳的沉积率随能量的增大先减小后增加,溅射率随能量的增大先增大后减小;轰击后的样品中,碳原子密度、C-W键密度及C-C键密度分布都随能量的增加逐渐向样品内移动,且C-W键分布厚度随能量的增加而逐渐增加,C-C键分布厚度几乎不随能量变化;在作用过程中极少量的钨原子发生溅射,但引起钨品格损伤严重;碳在轰击后的样品中主要以Csp3杂化形式存在.     

科学家首次发现非线性电子散射现象

正中国科学技术大学合肥微尺度物质科学国家实验室陈向军教授研究组与罗毅教授合作,利用自主研制的扫描探针电子能谱仪,首次发现了非线性电子散射现象,该发现有可能产生出一种革命性的表面单分子探测技术。电子能量损失谱学是分析材料化学组成的一种重要手段,电子打到样品上会损失能量而发生非弹性散射,电子损失的能量取     

介质材料在电子辐射环境中的放电特性

航天器表面介质材料在空间等离子体环境下会产生放电现象,放电诱发的瞬态脉冲会对航天器在轨安全运行产生较大的影响。通过对不同厚度的聚酰亚胺和聚四氟乙烯材料进行电子辐照,对放电诱发的瞬态脉冲进行测量,结果表明:随着电子能量增加,材料的电荷累积速率加快,放电电流的峰值并不随着电子能量的增加而增大,而是一个近似不变的值;放电频率随着电子能量的增加而增大且呈现出正相关的特性;随着介质材料厚度略微增大,表面充电电位增大,累积的电荷量增多,放电峰值增大,放电频率变小。     

板厚对冲裁力影响规律的研究

理论分析和生产实践表明,在一定范围内,间隙对冲裁力的影响是很小的,而板材相对厚度是影响单位厚度上冲裁力的主要因素.当材料性能等其它条件一定时,冲裁力随着板厚的增大而增大,但单位板厚上的冲裁力则随着板厚的增加而减小.在有限元模拟和实验分析的基础上,提出了计算冲裁力的新方法,对揭示剪切加工机理及正确确定冲裁力有理论和实际意义.     

工艺参数对聚甲醛微注塑制品力学性能的影响机理EI北大核心CSCD

基于单因素实验,研究工艺参数对不同厚度聚甲醛(POM)微注塑制品屈服应力、弹性模量、断裂强度和断裂伸长率等力学性能指标的影响,并基于制品形态结构分析工艺参数对制品力学性能的影响机理。实验结果表明,随着注射速度的增大,1.0mm厚微制品的皮层厚度减小,过渡层厚度增加,结晶度增大,综合效应使得屈服应力、断裂强度和弹性模量增大,断裂伸长率减小;0.2mm厚微制品的皮层厚度占主导地位,其力学性能是由皮层的力学性能决定,皮层厚度先增大后减小使得屈服应力、断裂强度和弹性模量先增大后减小,断裂伸长率先减小后增大。随着熔体温度的升高,1.0mm厚微制品的分子链取向度减小,皮层厚度减小,收缩量增大,使得屈服应力、断裂强度和弹性模量减小,断裂伸长率增大;而0.2mm厚微制品的皮层减小,但过渡层增加,结晶度增大,且补料更充分,综合作用使得屈服应力、断裂强度和弹性模量增大,断裂伸长率减小。随着模具温度的升高,1.0mm厚微制品的皮层比例减小,结晶度增大,结晶度影响占主导,使得屈服应力、断裂强度和弹性模量逐渐增大,断裂伸长率减小;而0.2mm厚微制品的皮层厚度占主导,皮层厚度明显减小使得屈服应力、断裂强度和弹性模量减小,断裂伸长率增大。     

CH与聚变材料Be相互作用的分子动力学模拟

采用分子动力学方法模拟了不同能量的CH粒子与聚变材料Be的相互作用。根据托卡马克中的环境,入射粒子CH的模拟入射能量分别设定为低能量(1,5,10,25 eV)和高能量(50,100,150,200 eV),其中碳的沉积率随能量的增大逐渐增加,而氢的沉积率恰好相反。当CH粒子的入射能量为低能量时,Be样品表面形成一层碳氢膜;且其膜厚度越来越薄,并且形成一个厚度逐渐增加中间层;当入射能量为高能量时,样品中的Be原子溅射越来越大,入射粒子在样品中的入射深度越来越深,对样品的破坏越来越大,且会在样品中形成一个C反应层。     

溶胶-凝胶法AZO/rGO薄膜的制备研究

采用溶胶-凝胶法制备了掺铝氧化锌/还原氧化石墨烯(AZO/rGO)薄膜,研究了不同还原氧化石墨烯(rGO)的添加量对薄膜结构和光电性能的影响。采用四探针方块电阻仪测量样品的电学性能,XRD检测薄膜晶体结构,SEM研究薄膜表面形貌,U4100分光光度计检测光学透过率。研究发现,热处理温度为500℃时,AZO/rGO薄膜样品的电阻率随着rGO含量的上升,先减小后增大;当添加量为0.04%(wt,质量分数)时,电学性能最优,样品(002)衍射峰强度最大。光学透过率随着rGO增多而减小,但幅度很小。而热处理温度为530℃时,随着rGO含量的增大,薄膜样品的电阻率逐渐增大,可见光透过率同样有所下降。     

GeS_2-Ga_2S_3-AgCl玻璃的光学特性研究

采用熔融-淬冷法制备了摩尔组成为(100-x)(0.85GeS2-0.15Ga2S3)-xAgC l(x=0,5,10,15,20)硫卤玻璃,测试了样品的密度、转变温度、析晶温度、可见到中远红外透过光谱、吸收光谱以及折射率参数,根据Z-扫描测试原理用钛宝石飞秒激光器测试了样品的三阶非线性特性.利用经典的Tauc方程计算了样品光学带隙允许的直接跃迁、允许的间接跃迁及Urbach能量.讨论了玻璃的摩尔折射度、金属标准值、光学带隙、Urbach能量对玻璃样品折射率的影响.结果表明:该系统玻璃具有较宽光谱,从可见到中远红外透过区域(0.46~11.50)μm,可作为潜在的多光谱成像材料.随AgC l含量的增加,玻璃的折射率随着摩尔折射度增大而增大,金属标准值、光学带隙与Urbach能量有减小的趋势,而玻璃的三阶非线性性能得到明显提高.     

分子动力学模拟不同入射能量的SiF2与SiC的相互作用

采用分子动力学模拟方法研究了入射能量对SiF2与SiC样品表面相互作用的影响。本次模拟选择的入射初始能量分别为0.3,1,5,10和25 eV。模拟结果显示SiF2分解率与Si和F原子的沉积率有密切的关系。沉积的Si和F原子在SiC表面形成一层SixFy薄膜。随入射能量的增加,薄膜厚度先增加后减小,薄膜中Si-Si键密度增大。构成薄膜的主要成分SiFx(x=1~4)中主要是SiF和SiF2,随入射能量的增加,薄膜成分由SiF2向SiF转变。     

低能低剂量注水形成SOI结构材料的研究

采用无质量分析器的离子注入机，以低能量低剂量注水的方式替代常规SIMOX注氧制备SOI材料，测试结果表明，此技术成功地制备了界面陡峭，平整，表层硅单晶质量好的SOI结构材料，在剂量一定的条件下，研究不同注入能量对SOI结构形成的影响，使用剖面透射电镜技术（XTEM）和二次离子质谱技术（SIMS）等测试方法对注入样品和退火后样品进行分析，结果表明，表层硅厚度随注入能量增大不断增大；埋层二氧化硅厚度相对独立，仅在超低能（50keV)低剂量情况下厚度出现明显降低；埋层质量（包括界面平整度，硅岛密度等）与注入能量变化相关。     

无碳污染微通道板电子透射膜的工作特性

利用静电贴膜技术在MCP输入面制备了4nm厚Al2O3非晶态电子透射膜,此工艺不造成MCP通道壁内表面碳污染。探讨了贴膜与气体辉光放电的关系,测量了MCP电子透射膜的电子透过特性和离子阻挡特性。实验表明,4nm厚Al2O3非晶态电子透射膜能有效地透过电子,阻止反馈离子。     

电子透射膜的生成及其对微通道板性能的影响

研究采用有机衬底掩膜技术和冷基底直流溅射在多孔微通道板输入面制备非晶态Al2O3电子透射膜的可行性,讨论在微通道板输入面形成连续电子透射膜与气体辉光放电的关系,测量带膜微通道板的电特性。结果表明,微通道板带膜后电子增益下降、体电阻增加、暗电流降低。     

Phonon Mediated Helium Atom Transmission through Superfluid Helium Four

We report results of experiments in which pulses of helium vapor with translational energies of 3 K are directed at a thin film of superfluid helium at a temperature of about 0.2 K suspended over a cesium covered orifice in a platinum film. The response of the superfluid film was detected by a super-conducting titanium bolometer placed on the side of the film opposite to that of the source. For films of approximately 1 mm in thickness we find no response of the bolometer within the limits of our detector. However, for films of less than 100μ thickness, we find a response which is of the same temporal shape, but smaller in amplitude, than that of the orifice when it is not covered with superfluid helium. We interpret these results to mean that we are seeing phonon mediated transmission in the thin films. Roton and condensate mediated transmission amplitudes for these conditions are apparently too small for us to detect in any of the films. This result is consistent with the theoretical results of Sobnack and Inkson [M. B. Sobnack, J. C. Inkson, and J. C. H. Fung, Phys. Rev. B 60, 3465 (1999)] concerning the amplitude of roton to atom and photon to atom conversion as a function of the atomic energy.     

Electron diffraction analysis of antimony films

Antimony films of about 3000 Å thickness are grown on NaCl substrate at various substrate temperatures. The films were subsequently analysed for electron diffraction and for grain size on electron microscope. At lower substrate temperatures, the film showed a single crystalline growth, and the crystal grain size was small. However at higher substrate temperatures a cubic phase along with hcp phase was found to exist and also the enlargement of the grain size was observed.     

Electron Diffraction Using Transmission Electron Microscopy

Electron diffraction via the transmission electron microscope is a powerful method for characterizing the structure of materials, including perfect crystals and defect structures. The advantages of electron diffraction over other methods, e.g., x-ray or neutron, arise from the extremely short wavelength (≈2 pm), the strong atomic scattering, and the ability to examine tiny volumes of matter (≈10 nm³). The NIST Materials Science and Engineering Laboratory has a history of discovery and characterization of new structures through electron diffraction, alone or in combination with other diffraction methods. This paper provides a survey of some of this work enabled through electron microscopy.     

Electron microscopy studies of plasma-polymerized organosilicon thin films

Plasma-polymerized thin films of hexamethylcyclotrisilazane were pyrolysed in vacuum and studied by transmission electron microscopy. Examination of the polymer film after various durations of pyrolysis revealed significant changes in their surface structure and a distinct difference in the thermal stability powder and film phases. The number of powder particles in the surface layer and their size increased with pyrolysis time. The observations showed that powder particles embedded in the film matrix were gradually exposed in the surface layer owing to a decrease in the film thickness during pyrolysis. Good agreement was obtained between the experimental and theoretical distribution curves of particle size. The identical properties of powder particles exposed in the surface of the pyrolysed film and those taken from the interelectrode region indicates that they are primarily formed in the gas phase.     

膜厚对导电氧化锌宽带抗反射涂层的太赫兹传输影响

利用直流磁控溅射方法,在石英基底上制备了可用于太赫兹电磁波频率范围内的宽带抗反射涂层的掺铝氧化锌导电薄膜。在太赫兹时域光谱频率0.1~1.0THz范围内研究不同厚度的氧化锌薄膜的介电响应,得到了与频率相关的电导率、吸收和薄膜折射率,着重研究了膜厚对太赫兹波传输特性的调制作用。实验结果很好地符合了经典的Drude模型,表明可以通过控制氧化锌薄膜的厚度来改变太赫兹波的传输特性,并且导电氧化锌薄膜能够作为太赫兹频段范围的宽带抗反射涂层应用于衬底和光学器件上。     

Optical properties and crystallinity of hydrogenated nanocrystalline silicon (nc-Si:H) thin films deposited by rf-PECVD

Hydrogenated nanocrystalline silicon (nc-Si:H) thin films prepared in a home-built radio-frequency (rf) plasma enhanced chemical vapour deposition (PECVD) system have been studied. The rf powers were fixed in the range of 5 W-80 W. The optical properties and crystallinity of the films were studied by X-ray diffraction (XRD), Micro-Raman scattering spectroscopy, high resolution transmission electron microscope (HRTEM), and optical transmission and reflection spectroscopy. The XRD and Micro-Raman scattering spectra were used to investigate the evidence of crystallinity in order to determine the crystallite sizes and crystalline volume fraction in the films. The HRTEM image of the film was used to correlate with the crystallinity that was determined from XRD and Micro-Raman scattering spectra. Optical constants such as refractive index, optical energy gap, Tauc slope, Urbach energy and ionic constants were obtained from the optical transmission and reflectance spectra. From the results, it was interesting to found that the optical constants showed a good correlation with the crystallinity within the variation of rf power. Also, the ionic constants of the films showed an indication of the degree of crystallinity in the films. The variation of the optical energy gap with the rf power based on structure disorder and the quantum confinement effect is discussed.     

Effect of ion irradiation on internal stress of amorphic carbon films produced by pulsed laser

Amorphic carbon films either 50 or 160 nm thick were deposited on Si(100) and glass substrates at room temperature in a high-vacuum environment using a Q-switched Nd-YAG pulse laser focused on a graphite target. These films were irradiated with Ti⁺ or C⁺ ions having kinetic energies of 35 and 75 keV, and the changes in internal stresses of the films with varying ion influence were investigated by measuring substrate bending using stylus profilometry. The ion energy and the film thickness were chosen such that the ion penetration depth, R_p, corresponded to either the film thickness or one half of the film thickness. The results indicate that there is an optimum ion fluence leading to a stress-free film for a given ion species and energy. Interpretation of the resulting stress behavior from ion irradiation was made based on the relaxation resulting from damage inside the film together with interfacial mixing. The scanning electron microscopy pictures and surface roughness measurements showed a very smooth surface for both as-deposited and ion-irradiated films. The ion-irradiated films had a Vickers hardness greater than 22 GPa, and were adherent to both Si and glass substrates. An investigation of the film characteristics using Raman scattering and electron-energy loss spectra has revealed that high-energy ion irradiation of an intermediate ion fluence can be utilized successfully to deposit an adherent and hard carbon film with controlled internal stress without changing the film structure significantly.