Fabrication of key components of a receptor-based biosensor

A three-pronged approach was taken to the development of receptor-based bisensors. First, asymmetric bilayer membranes were developed with one monolayer adaptable to the particular receptor of interest and the other monolayer polymerized to enhance membrane stability. Second, alamethicin and calcium channel complexes were introduced into the stabilized membrane and tested for ion-channel function. Third, a porous support for the receptor-containing membrane was fabricated, which is compatible with silicon technology. Preliminary devices incorporating these components were constructed.     

蒸发诱导自组装法制备多孔二氧化硅光学薄膜

报道采用溶胶—凝胶技术、蒸发诱导自组装法,通过酸/酸二步法控制实验条件,实验中采用表面活性剂十六烷基三甲基溴化氨(CTAB)为模板剂,正硅酸乙酯为硅源,以及二次去离子水,盐酸为催化剂等原料制备前驱体溶胶。加入不同量的1,3,5-三甲基苯(TMB)辅助剂来调整膜的孔径。简单提拉迅速蒸发溶剂制备多孔二氧化硅光学薄膜,利用红外光谱对样品进行结构分析,采用UV-VIS-NIR分光光度计测量了薄膜的透过光谱,原子力显微镜(AFM)观察发现多孔薄膜的表面形貌具有明显的多孔结构、表面光滑、均匀;结果表明所制备的薄膜有好的光学性能、机械性能。     

分散剂对电泳沉积制备碳纳米管薄膜形貌和场发射性能的影响

采用丙酮、异丙醇、丙酮/无水乙醇混合溶液3种不同的分散剂,利用电泳沉积法在硅基底上制备了碳纳米管(CNTs)薄膜;采用超景深光学显微镜和电子显微镜观察了不同薄膜的表面形貌,并在高真空中对碳纳米管薄膜阴极进行了场发射特性测试。结果表明:以异丙醇作分散剂制备的CNTs薄膜表面均匀连续,场发射性能较好,开启电场和阈值电场分别为0.188V.μm-1和2.8V.μm-1。     

Ultraprecision surface flattening of porous silicon by diamond turning

Porous silicon is receiving increasing interest from a wide range of scientific and technological fields due to its excellent material properties. In this study, we attempted ultraprecision surface flattening of porous silicon by diamond turning and investigated the fundamental material removal mechanism. Scanning electron microscopy and laser Raman spectroscopy of the machined surface showed that the mechanisms of material deformation and phase transformation around the pores were greatly different from those of bulk single-crystal silicon. The mechanism of cutting was strongly dependent on the direction of cutting with respect to pore edge orientation. Crack propagation was dominant near specific pore edges due to the release of hydrostatic pressure that was essential for ductile machining. Wax was used as an infiltrant to coat the workpiece before machining, and it was found that the wax not only prevented chips from entering the pores, but also contributed to suppress brittle fractures around the pores. The machined surface showed a nanometric surface flatness with open pores, demonstrating the possibility of fabricating high-precision porous silicon components by diamond turning.     

类金刚石薄膜的光学性能的研究

利用脉冲真空电弧镀的方法,在硅基底上沉积类金刚石薄膜,研究薄膜的光学性能、光学常数和离子能量关系。结果表明:不同的离子能量可以得到不同折射率的薄膜,无氢类金刚石薄膜的折射率在2.5～2.7之间变化;通过改变工艺条件来制备不同折射率的薄膜,和不同折射率的基底材料相互匹配;折射率和光学能隙随离子能量具有相反的变化趋势,和理论预测的趋势相一致;对于硅、锗等红外材料,要求的薄膜应具有1.8～2.1左右的折射率,因此提出一种基于物理汽相沉积和化学汽相沉积两种相互结合的方法,来降低薄膜的折射率,以达到和硅、锗等材料的折射率匹配。     

电化学制备多孔硅的工艺对其形貌的影响

采用电化学腐蚀方法,将不同比例的乙醇和质量分数为40%的氢氟酸混合,并以此混合液为腐蚀液,在光照条件下,制备了N型轻掺杂的多孔硅。讨论了不同电化学腐蚀条件对多孔硅结构的影响。研究表明,电流密度、腐蚀时间和氢氟酸质量分数越大时,制备的多孔硅越深,孔径也越大,当以上三者数值过大时会导致多孔硅机械强度急速减弱。由表面形貌可知,当多孔层孔径小于500nm时其机械强度良好,当孔径超过这一阈值尤其是大于800nm时,多孔层骨架则极易断裂。     

Tribological Behavior of Hard W/NbN Superlattice Films

Epitaxial W/NbN superlattice films with different modulation periods were deposited by reactive dc magnetron sputtering. The mechanical properties were measured by nanoindentation and ball-on-disk tribometry, worn surface of the films were investigated by atomic force microscopy, scanning electron microscopy, and optical profiler. The superlattice films with a modulation period of 5.6 and 10.4 nm provide superhardness of 42.2 ± 1.6 and 40.4 ± 3.1 GPa, respectively, much higher than the constituent NbN and W monolayers. However, dry rubbing tests of both W/NbN superlattice films exhibit the wear rate higher than that of the NbN film. It is suggested that for superlattice films, hard NbN bilayer flakes off during the wear process due to weak interface bonding and different deformability between the bilayer constitutions. Sharp interface, as well as differences in deformability and wear property of the bilayer constituents is responsible for the wear deterioration of epitaxial W/NbN superlattice films.     

Effect of cation on micro/nano-tribological properties of ultra-thin ionic liquid films

Room temperature ionic liquids (RTILs) have some unique characteristics which meet the requirements as high performance lubricants. In this work, three kinds of RTILs films with the same anion but different cations were prepared on single-crystal silicon wafer by dip-coating method. Thermal stability of the RTILs was evaluated using thermal gravity analysis in a nitrogen atmosphere. The morphology, nano-friction and nano-adhesion properties of the RTILs films were experimentally investigated at nano-scale using AFM/FFM. Chemical compositions of the films were characterized with a multi-functional X-ray photoelectron spectrometer. Micro-tribological properties of RTILs films were investigated using AISI-52100 steel ball in ball-on-plate configuration, and compared with perfluoropolyether. The worn surface morphologies were measured with a 3D optical surface profilometer. Results show that 3-butyl-1-methyl-imidazolium tetrafluoroborate exhibited the best anti-wear ability in comparison with the other three lubricants. RTILs films could be used as a kind of novel lubricant for application in M/NEMS. The corresponding friction-reduction and anti-wear mechanisms of the tested ultra-thin RTILs films under tested condition were proposed based on the experimental observation. The investigation revealed that friction-reduction and anti-wear properties of RTILs were strongly dependent on their chemical structures. For the friction at nano-scale, the flexibility and surface energy of the lubricant played significant role, while for the friction at micro-scale, both the rigid cycle structure and flexible chain of the RTILs played crucial role.     

Silicon Nitride and Carbonitride Films for Waveguide Structures Based on Strained Silicon

Waveguide microstructures based on strained silicon with the use of silicon carbonitride and silicon nitride films as cladding layers are created. A plasma-enhanced chemical vapor deposition technique is developed, which allows obtaining high values of intrinsic mechanical stresses in films (about 700 MPa). The strained waveguide structures are characterized by micro-Raman spectroscopy during a scanning procedure. It is demonstrated that deposition of silicon carbonitride and silicon nitride films induces compressive stresses in the silicon waveguide, which is proved by the shift of the maximum of the main peak of scattering on LO-phonons of silicon toward higher wave numbers. The compressive stresses in the silicon waveguide clad with silicon nitride and carbonitride layers are estimated as 350 and 250 MPa, respectively, which is sufficient for the emergence of nonlinear optical properties of silicon (Pockels effect).     

Numerical analysis of crater formation and ablation depth in thin silicon films heated by ultrashort pulse train lasers

This study numerically investigates the optical and heat transfer characteristics of thin silicon films irradiated by ultrashort (shorter than 10 ps) pulse train lasers. The one-dimensional two-temperature model (1DTTM) is extended to the two-dimensional (2DTTM) model for estimation of crater formation. In addition, the wave interference effects on the optical and energy transfer characteristics are considered to predict accurately the energy absorption rates in thin silicon films irradiated by picosecond-to-femtosecond pulse train lasers. Unlike bulk silicon, a significant change in energy absorption is found to occur in thin silicon films with the variation of film thickness due to the wave interference. The spatial distributions of energy carrier and lattice temperature show quite a different tendency at different pulse durations as well as the number of pulses because of significant changes in the optical and thermal properties. The predicted crater shapes and the ablation depths by 2DTTM are also presented.     

Vacuum ellipsometry as a method for probing glass transition in thin polymer films

A vacuum ellipsometer has been designed for probing the glass transition in thin supported polymer films. The device is based on the optics of a commercial spectroscopic phase-modulated ellipsometer. A custom-made vacuum chamber evacuated by oil-free pumps, variable temperature optical table, and computer-based data acquisition system was described. The performance of the tool has been demonstrated using 20-200 nm thick poly(methyl methacrylate) and polystyrene films coated on silicon substrates at 10(-6)-10(-8) torr residual gas pressure. Both polymers show pronounced glass transitions. The difficulties in assigning in the glass transition temperature are discussed with respect to the experimental challenges of the measurements in thin polymer films. It is found that the experimental curves can be significantly affected by a residual gas. This effect manifests itself at lower temperatures as a decreased or even negative apparent thermal coefficient of expansion, and is related to the uptake and desorption of water by the samples during temperature scans. It is also found that an ionization gauge--the standard accessory of any high vacuum system--can cause a number of spurious phenomena including drift in the experimental data, roughening of the polymer surface, and film dewetting.     

Nanographite analyzer of laser polarization

An optical analyzer of laser polarization has been designed and manufactured. The principle of operation of this analyzer is based on the recording of the polarization-dependent surface photocurrents in nanographite films. The analyzer does not contain additional optical elements and consists of a cylindrical bushing with a gauge of its angular position, a nanographite film grown on a silicon substrate, two parallel measurement electrodes placed on the film surface, and an electrical measuring instrument. The nanographite film is placed on the bushing obliquely so that the measuring electrodes are parallel to the axial cross section of the bushing, which is oriented perpendicular to the film tilt plane. The analyzer can operate in the wavelength range from 266 to 4000 nm.     

Optimum film thickness of thin metallic coatings on silicon substrates for low load sliding applications

The frictional behaviour of thin metallic films on silicon substrates sliding against 52100 steel balls is presented. The motivation of this work is to identify an optimum film thickness that will result in low friction under relatively low loads for various metallic films. Dry sliding friction experiments on silicon substrates with soft metallic coatings (silver, copper, tin and zinc) of various thickness (1–2000 nm) were conducted using a reciprocating pin-on-flat type apparatus under a controlled environment. A thermal vapour deposition technique was used to produce pure and smooth coatings. The morphology of the films was examined using an atomic force microscope, a non-contact optical profilometer and a scanning electron microscope. Following the sliding tests, the sliding tracks were examined by various surface characterization techniques and tools. The results indicate that the frictional characteristics of silicon are improved by coating the surface with a thin metallic film, and furthermore, an optimum film thickness can be identified for silver, copper and zinc coatings. In most cases ploughing marks could be found on the film which suggests that plastic deformation of the film is the dominant mode by which frictional energy dissipation occurred. Based on this observation, the frictional behaviour of thin metallic coatings under low loads is discussed and friction coefficients are correlated with an energy based friction model.     

Error analysis and compensation of feature point angular–optical bias in machine vision

Stereolithography was introduced into the net-shape SiC components fabrication process to produce the molds for the preparation of porous carbon preforms. The mixed resin was cast into the molds and then pyrolyzed to produce the porous carbon preforms which had a high porosity of 40.93% and were infiltrated and reacted with molten silicon to get reaction-formed silicon carbide (RFSC) components. To realize the complete infiltration of the thick wall parts, pipelines as the channels for the molten silicon were added into the components. The hierarchical structures of the porous carbon had been attained to realize the controllability of the microstructure and properties of RFSC. The samples had a high linear and volume shrinkage, 24.7% and 57.3%, respectively, during the pyrolysis process. Phase composition had been investigated by optical microscopy and X-ray diffraction analysis. The results indicate that no residual carbon was available in the final RFSC. The net-shape fabrication process for the RFSC components could promote the industry applications where SiC components with complex surface and inner structure were needed.     

用X射线反射测量法表征双层结构中 低原子序数材料的特性

介绍了用X射线反射测量术表征双层薄膜中低原子序数材料特性的方法。由于低原子序数材料的光学常数与Si基板材料的光学常数非常接近,用X射线反射法确定镀制在Si基板上的低原子序数材料膜层结构的变化十分困难,因此,提出了在镀制低原子序数材料前,首先在基板上镀制一层非常薄的金属层的方法。实验中,选用Cr作为金属层材料,制备并测试了三种不同C膜镀制时间的Cr/C双层薄膜。反射率曲线拟合结果表明,C膜密度约为2.25 g/cm³,沉积速率为0.058 nm/s。     

稀氢氟酸处理氢终结化纳米硅制备研究

文中介绍氧终结化纳米硅膜通过超高真空条件下氧氩基硅蒸发沉积法制备,利用稀氢氟酸处理得到氢终结化纳米硅。硅膜的表面状态由红外线测量法测定,结果得出纳米硅膜中的所有Si-O键全部被Si-H键取代。退火处理后样品在光子能量为1.65eV(750nm)和2.2eV(560nm)处表现出很强的光致发光强度。然而经稀氢氟酸处理后样品无这两处光致发光信号,这说明这两处光致发光信号是由Si-O产生。     

微电子机械系统的力学特性与尺度效应

针对微电子机械系统（MEMS）材料的力学特性,工艺过程对力学特性的影响以及微执行器、微机器人的尺度效应等力学问题进行了研究。从力学角度提出了硅和常用的薄膜材料作为MEMS结构材料时应遵循的设计和加工原则,并系统地分析、归纳了静电、电磁、压电、形状记忆合金等各种微执行器的尺度效应特征。通过对机器蚂蚁、微型飞机、微型机器鱼等微机器人在微尺度下的动力学特性分析,得到微机器人在尺寸越小时越容易被驱动的结论,为设计和制作微机器人等复杂微系统提供了理论依据。     

PECVD制备光学氮化硅薄膜均匀性分析研究

采用等离子体增强化学气相沉积(PECVD)技术制备的光学薄膜,其均匀性受到多种工艺参数的影响,在这些参数中,一类是沉积过程的工艺参数;另一类则是设备结构参数,设备结构参数决定着反应腔室内气流分布、以及电场分布等。通过改变沉积过程的工艺参数和一组正交试验,分析各个工艺参数对均匀性的影响,从而改善氮化硅薄膜均匀性。     

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.     

磁控溅射Ni56Mn27Ga17合金薄膜的光学反射特性研究

Ni-Mn-Ga磁性形状记忆合金薄膜是非常有用的多功能材料,为考察其光学反射特性,采用磁控溅射技术在单晶硅衬底上沉积了Ni56Mn27Ga17合金薄膜,并对其表面形貌和光学反射特性进行研究。研究结果表明,薄膜的表面粗糙度随退火温度的升高而增大;在300～800nm波长范围内,薄膜反射率均随波长的减小而降低,且薄膜整体谱线范围内的反射率随退火温度的升高而降低。