采用MOCVD方法的GaN薄膜制备试验研究

介绍了使用本实验室自制的MOCVD设备,以蓝宝石材料作为衬底,按照MOCVD方法设计的GaN薄膜制备试验.衬底入炉后先在1150℃的H2气氛下烘烤20min,然后降温至540℃、550℃、560℃、570℃和580℃生长20nm厚的GaN缓冲层,再升温至1100℃生长GaN外延,外延的厚度约为3μm.缓冲层生长温度为570℃时,样品外延的生长质量最好.     

应用于微型成像的氮化镓超透镜设计

为了实现可见光入射时亚波长尺度内的聚焦,设计了以氮化镓(GaN)纳米柱为基本晶胞的超透镜,该透镜能够改进传统成像系统的笨重低效,可应用于微型成像系统。超透镜表面由宽度渐变高度不变的GaN纳米柱阵列构成,分析GaN在亚波长尺度内对相位的调控能力和机理,并基于时域有限差分法模拟仿真了在蓝光波长为460nm入射时透射场的高效率聚焦,对比超透镜尺寸为3.75μm×3.75μm、6.75μm×6.75μm、8.75μm×8.75μm、10.75μm×10.75μm时超透镜的聚焦能力,得出聚焦后透射场焦点处的半峰全宽分别为1,0.8,0.5,0.3μm,给出了强度分布、聚焦光斑等仿真模拟结果,发现实际焦距与设计值存在偏差,且随超透镜尺寸的变化而变化。文中所设计的超透镜能够在微米级别实现聚焦,有效降低了传统成像系统的复杂度。     

微米级H62铜合金箔拉伸时的尺度效应

对不同厚度微米级和宽度的H62黄铜箔进行了拉伸试验,研究试样厚度和宽度与其屈服强度和伸长率的关系。结果表明:随着厚度的减小,合金箔的微拉伸屈服强度先是减小,但当厚度小于250μm后,屈服强度开始增大;随着宽度的减小,其伸长率一直在减小;但随厚度从500μm减小到50μm,伸长率先增大再减小,在厚度为250μm时出现最大值。     

一种压电薄膜微致动器的致动原理分析及有限元模拟

介绍了硬盘磁头中的压电薄膜微致动器,用层合梁理论分析了微致动器的致动原理,得出了致动力与压电薄膜层数成正比.用有限元软件对粘有40 μm、80μm单层薄膜以及单层厚度40μm的二层和三层微致动器进行有限元仿真,其中薄膜厚度为40 μm的单层和双层的微致动器位移分别达到0.850 29μm/20V、0.827 44 μm/20V,满足了低能耗高位移的行业要求,同时比较了压电薄膜不同粘贴方式的致动效果,得出悬臂上下各粘一层薄膜的致动效果比较理想的结论.     

微细电火花铣削影响加工精度的主要因素分析

通过微电火花铣削试验研究,优化电参数、小厚度分层加工等方法分析微小孔加工直线度和圆柱度误差。结果表明:空载电压110V,峰值电流为70A,脉冲宽度为4μs,脉冲间隔为90μs,分层厚度0.15mm,放电间隙0.012mm,微小孔铣削精度最高,其加工尺寸精度±0.005mm,表面粗糙度0.427μm。     

超声表面滚压加工对Ti-6Al-4V合金显微组织及表面完整性的影响

采用"回"字形加工路径对退火态Ti-6Al-4V合金进行超声表面滚压加工(USRP),使用光学显微镜、透射电镜、显微维氏硬度计、X射线残余应力分析仪、表面三维形貌仪等设备对USRP后合金的显微组织和表面完整性进行表征。结果表明:USRP后Ti-6Al-4V合金表面形成了厚度约300μm的塑性变形层,塑性变形层的表面为等轴纳米晶层,次表面为晶粒取向一致的长条状纳米片晶层;USRP后Ti-6Al-4V合金的显微硬度最高达到390 HV,表面粗糙度由0.76μm减小为0.23μm。随着距表面距离的增大,合金的残余压应力先增大后减小。     

热辐射处理制备VC涂层的温度-应力场有限元分析

利用ANSYS有限元软件对热辐射处理制备VC(碳化钒)涂层进行建模,分析了涂层厚度、加热温度及加热时间对VC涂层温度场-应力场的影响规律。结果表明,不同温度下涂层沿x轴方向温度变化的趋势均呈上升趋势;涂层最高温度(837℃)与加热温度(850℃)相差15℃左右,温度差值约1.52%;不同厚度下温度的变化趋势均为递减,当厚度为6μm时,温度递减的趋势较平稳,未出现峰值,当涂层厚度增加时,应力值先增加然后减小,在厚度为6.3μm时发生突变,而后呈递增趋势;考虑应力、厚度因素对涂层性能的影响,涂层最佳厚度应为5～6μm。     

渗氮电压对液相等离子体电解渗氮层组织及耐腐蚀性能的影响

以氨水和KCl的混合溶液为电解液,利用液相等离子体电解渗氮工艺在180,200,220,240V电压下于38CrMoAl钢表面制备了渗氮层,研究了渗氮电压对渗氮层组织与耐腐蚀性能的影响。结果表明:随着渗氮电压升高,渗氮层中白亮层和扩散层的厚度不断增加,当渗氮电压为240V时,白亮层和扩散层的厚度最大,分别为42.9μm和84.9μm;渗氮层表面均呈"火山凸起"微区形貌,随着渗氮电压增大,"火山凸起"微区的落差逐渐增大,孔洞分布均匀性逐渐降低,孔径逐渐增大,渗氮层的峰值硬度先增大后趋于稳定;在200,220,240V电压下制备渗氮层的耐腐蚀性能优于基体的;当渗氮电压为220V时,渗氮层的耐腐蚀性能最好。     

线性摩擦焊AA5083铝合金/T2纯铜异质接头特征研究

对AA5083铝合金/T2纯铜进行不同焊接压力下的线性摩擦焊试验,结果表明:焊接过程主要以铝合金的压缩变形为主,T2变形量较小。焊缝处界限分明,两侧晶粒均明显细化,铝侧细化程度更高且金属流线消失。焊缝界面可观察到明显的孔洞缺陷,且随摩擦压力的增大孔洞逐渐减小直到消失。接头拉伸强度达到T2母材的50%,接头伸长率很低,拉伸断裂均发生在焊缝区,断裂形式均为脆性断裂。微区成分分析可知,Al/Cu界面处存在厚度大约为2μm扩散层;界面附近Al侧出现以Cu粒子与金属间化合物弥散的机械混合组织,厚度在100~500μm浮动。接头强度较低的主要原因是存在界面孔洞缺陷及金属间化合物混合组织。     

大动态范围外延电阻淬灭型硅光电倍增器

外延电阻淬灭型硅光电倍增器(EQR SiPM)的特点是利用硅衬底外延层来制作器件淬灭电阻。为了进一步提高大动态范围EQR SiPM的光子探测效率,并且解决填充因子较低和增益较小等问题,在前期研究工作的基础上研制出微单元尺寸分别为15μm和7μm的EQR SiPM,有源区面积均是1 mm×1 mm。通过改变EQR SiPM的微单元尺寸优化填充因子,有效提高了探测效率与增益;其微单元密度分别是4400个/mm 2和23200个/mm 2,依然保持着较大的动态范围。室温条件下(20℃),工作在5 V过偏压的EQR SiPM至少可分辨13个光电子;15μm和7μm EQR SiPM的增益分别为5.1×105和1.1×105,在400 nm波长下的峰值光探测效率分别达到40%和34%。     

A sample holder for soft x-ray absorption spectroscopy of liquids in transmission mode

A novel sample holder for soft x-ray absorption spectroscopy of liquids in transmission mode based on sample cells with x-ray transparent silicon nitride membranes is introduced. The sample holder allows for a reliable preparation of ultrathin liquid films with an adjustable thickness in the nm-μm range. This enables measurements of high quality x-ray absorption spectra of liquids in transmission mode, as will be shown for the example of liquid H(2)O, aqueous solutions of 3d-transition metal ions and alcohol-water mixtures. The fine structure of the x-ray absorption spectra is not affected by the sample thickness. No effects of the silicon nitride membranes were observed in the spectra. It is shown how an inhomogeneous thickness of the sample affects the spectra and how this can be avoided.     

Process parameter selection for selective laser melting of Ti6Al4V based on temperature distribution simulation and experimental sintering

Considering that the densification level and the attendant quality of selective laser melted Ti6Al4V parts depend strongly on the operating temperature of the melting system, which is mainly controlled by the processing parameters. The processing parameters of selective laser melting were thus investigated in this study to fabricate denser Ti6Al4V parts without post-processes. Temperature distribution calculation was firstly carried out based on a three-dimensional model. It was found that there exists a great temperature gradient from the surface of powder bed to the experimental platform, and the maximum depth of molten powder layer is about 45?μm, very close to the total thickness of powder bed (50?μm) under the condition of laser power of 110?W and scan rate of 0.2?m/s. The Ti6Al4V parts with lower porosity and higher density were then well fabricated by experimental method under the condition of laser power of 110?W and scan rate of 0.2?m/s. The experimental results also indicate that the microstructures exhibit more and more pores and the layer structures are more and more obvious with the increase in the scan rate. Moreover, the microhardness measurement yields different values with increasing scan rate, owing to the increase of α phase and porosity.     

原子力显微镜测量杨木细胞特征参数

在微/纳米尺度下原子力显微镜已成为研究木质材料的重要工具。本文基于原子力显微镜对速生杨木细胞的特征参数进行测量。结果表明:利用原子力显微镜,完全可以在微/纳米尺度下对速生杨木的细胞形态特征进行测量;杨木细胞横截面的导管壁厚平均尺寸为2.230 μ m;木纤维壁厚平均为2.044 μ m,壁长平均为9.498μm;细胞外径平均为19.723 μ m。     

自适应微反射镜阵列制作与性能测试

为了改善微反射镜存在的驱动电压高、驱动力小的缺点,基于双金属效应,制得可调焦微光学自适应阵列。以硅为基底,先后经过热氧化、光刻显影、HF酸刻蚀、KOH湿法刻蚀,溅射铝膜等微加工工艺,制得的4×4阵列,基底厚50μm,硅表面铝膜厚100nm。利用激光数字波面干涉仪对可调焦微反射镜的动态性能进行了测试。实验表明,在0~11V电压范围内,可产生最大7.91μm的连续变形。     

Design of dynamic Hohlraum opacity samples to increase measured sample density on Z

We are attempting to measure the transmission of iron on Z at plasma temperatures and densities relevant to the solar radiation and convection zone boundary. The opacity data published by us to date has been taken at an electron density about a factor of 10 below the 9×10(22)/cm(3) electron density of this boundary. We present results of two-dimensional (2D) simulations of the heating and expansion of an opacity sample driven by the dynamic Hohlraum radiation source on Z. The aim of the simulations is to design foil samples that provide opacity data at increased density. The inputs or source terms for the simulations are spatially and temporally varying radiation temperatures with a Lambertian angular distribution. These temperature profiles were inferred on Z with on-axis time-resolved pinhole cameras, x-ray diodes, and bolometers. A typical sample is 0.3?μm of magnesium and 0.078?μm of iron sandwiched between 10?μm layers of plastic. The 2D LASNEX simulations indicate that to increase the density of the sample one should increase the thickness of the plastic backing.     

限流电阻对FeSiB非晶薄带磁感应效应的影响

采用单辊法制备了宽4．5mm、厚25μm的Fe78Si9B18非晶薄带,并研究了限流电阻对Fe78Si9B13非晶薄带的磁感应效应及磁感应效应变化幅度的影响。结果表明,磁感应效应随着限流电阻的增大而减弱;磁感应效应变化幅度随着限流电阻的增大呈现出先增大后减小的趋势。当正弦交流励磁电压峰值为10V、频率为0．1MHz、限流电阻为800Ω、磁场强度为368A／m时,磁感应效应变化幅度为3．5V。     

Positron Annihilation Studies of Subsurface Zone Created during Friction in Pure Silver

Abstract

Positron lifetime research has been performed on well-annealed pure silver samples after dry sliding, compression, and sandblasting processes. These treatments affect the surface but also have been shown to significantly modify the region adjacent to the surface. A great number of dislocations decorated with monovacancies and jogs are observed in the layer up to 110 µm beneath the surface. In the deeper layer, which extends to a depth of 300?μm, their concentration decreases gradually. Unlike other metals, the total depth of the subsurface zone induced by dry sliding is almost independent of the applied load. A significant increase in the positron lifetime has been observed in the layer 15 µm below the worn surface in the sample exposed to a long duration sliding test. Large clusters that consist of about 12 vacancies are observed in this layer, which can be a tribolayer that occurs as a result of dynamic recrystallization near the surface. This shows that conventional positron techniques can be effective tools in the investigation of defects in tribolayers, whose thickness is about several dozen micrometers. For a sample exposed to sandblasting, the total depth of the subsurface zone is smaller—that is, about 120 µm; however, the depth dependency of the positron lifetime is very similar to that obtained for dry sliding.     

The Annealing Behavior of the Subsurface Zone Induced by Friction in Bismuth Detected by Positron Lifetime Technique

The annealing behavior of the subsurface zone (SZ) in pure bismuth induced by dry sliding was studied using the positron lifetime measurement. This measurement allows us to detect the SZ and its recovery, and recrystallization processes. The comparative measurements of the sample exposed to compression revealed the thermal stability of the SZ. The compressed sample rebuilt its structure due to the recovery and recrystallization processes at the temperature of 60 °C, whereas the sample exposed to dry sliding does it at higher temperature of 260 °C, which is close to the melting point. The isothermal annealing at the temperature of 100 °C confirmed these results. The defect depth profile induced by dry sliding evolves with the annealing temperature in such a way that the concentration of defects at the worn surface gradually decreases, but at the depth between 50 and 170 μm, the generation of new defects takes place at the temperature of 75, 100 and even at 175 °C. At the temperature of 175 °C, the defects still are extended up to the depth of about 60 μm from the worn surface. The results were qualitatively confirmed by the measurements of the Vickers microhardness depth profile. Similar annealing behavior of the SZ was observed in pure magnesium.     

Surface quality improvement of EDMed Ti–6Al–4V alloy using plasma etching and TiN coating

This paper seeks to improve the surface quality of electrical discharge machining (EDM) Ti–6Al–4V using plasma etching treatment and TiN coating. The EDM parameter setting is optimized firstly based on grey-Taguchi method. Four EDM parameters, including current (A), voltage (V), pulse duration (μs), and duty factor (%), are selected for multiple performance of lower electrode wear rate (EWR), higher material removal rate (MRR), and better surface roughness (SR). An orthogonal array, signal-to-noise (S/N) ratios, and analysis of variance (ANOVA) are used to analyze the effects of these EDM parameters. Normality tests show that all the distributions fit normality assumption with p?=?0.276, 0.688, and 0.663, respectively. The EDM process is stable over time monitored by Shewhart control charts. It is observed that there is an EDM damaged layer on the surface consisting of debris, microcracks, molten drops, and solidified metals by scanning electron microscopy. The plasma etching and TiN coating are employed to improve surface quality of the EDMed Ti–6Al–4V alloys. The results demonstrate that using the oxygen plasma etching treatment, the damaged phenomena are decreased, and the mean SR value is reduced from Ra?=?2.91 to Ra?=?2.50 μm. In addition, when the plasma-treated alloy is coated with Ti buffer/TiN coating by physical vapor deposition, the surface morphology exhibits less defects and a better surface finish. The mean SR values are further reduced from Ra?=?2.50 μm to Ra?=?1.48 μm (for 740 nm TiN film) and Ra?=?0.61 μm (for 1450 nm TiN film), respectively.