Arsenic-terminated silicon and germanium surfaces studied by scanning tunnelling microscopy

The epitaxial growth of As on the (111) and (100) faces of Si and the (111) face of Ge has been studied with vacuum tunnelling microscopy. The (111) faces of both semiconductors display a principally 1×1 termination, but differ with the presence of point defects on the Si(111): As-1×1 surface and trenches separating large (～ 100 Å) domains on the Ge(111): As-1×1 surface. I-V characteristics of the tunnel junction show a surface energy gap of approximately 1·9 eV for the Si(111): As-1×1 surface and 0·9 eV for the Ge(111): As-1×1 surface, in good agreement with recent theoretical calculations for these systems. As deposition on Si(001) results in a nominal 2×1 reconstruction of symmetric As dimers and elimination of missing dimer defects characteristic of the native Si(001) 2×1 surface. Further studies on vicinal, double-stepped substrates shows the orientation of the dimers with respect to the substrate depends critically on the substrate temperature during the growth phase, with destruction of the single principle domain surface order occurring at temperatures in excess of 700°C.     

How the down step edges influence formation of the 7×7 structure

A surface that has wide terraces was fabricated by utilizing the step bunching phenomenon to study the effect of the down step edges on the formation of the 7×7 reconstruction. The surface with wide terraces was quenched through the 1×1–7×7 phase transition, freezing the formation process of the 7×7 reconstruction. On this surface, it became possible to investigate the influence of the down step edges on the formation of the 7×7 reconstruction because the influence of the upper step edge, which is located at the other side of the terrace, did not reach to the down step edge. A considerable decrease in the existence probability of the 7×7 reconstruction was observed near the down step edges. This decrease cannot explained by electromigration and steps advancement caused by the difference in adatom density between the 7×7 and disordered structure. Instead, we propose that the decrease in existence probability at down step edges is well explained by a simple topographic model assuming corner holes as the growth nuclei of the 7×7 domains.     

Metal-induced reconstructions of the silicon(111) surface

We have used scanning tunnelling microscopy (STM) to study changes in the structure of the Si(111) surface induced by deposition of the group III metals In and Ga. For both metals, several different ordered reconstructions are seen as a function of coverage. The STM images provide new structural information on each of these reconstructions. With In metal deposition, we have seen the surface reconstructions √3×, √3, √31× √31, √7×√3 and 4×1 as the coverage increases. In the case of Ga on Si(111), we have studied structures that exist up to 0·7 ML. At 1/3 ML, there is a √3×√3 structure identical to that of In. Above 0·3 ML there is a different phase that may correspond to the (6·3times6·3) RHEED pattern reported in this coverage range. This surface tends to grow as triangular islands at higher coverages.     

Scanning tunnelling microscopy on reconstructed Si(110)

We have prepared clean surfaces of reconstructed Si(110), which showed a distinct 4×5 LEED pattern with particularly high intensity of the diffraction beams corresponding to a 2×1 periodicity of the surface. Images obtained by scanning tunnelling microscopy on the same surfaces are characterized by rows of reconstructed Si atoms along the direction. On high-resolution images, atomic subunits in a 2×5 periodicity of ideal Si(110) have been identified. By using these subunits as building blocks for both the 4×5 and the 2×1 reconstruction, a previously reported phase transition between both reconstructions may be explained by a loss of order along the direction.     

Tribological behaviour of the adduct of bis(O,O′-dibutyldithiophosphato)-nickel (II) with isoquinoline

The bis(isoquinoline) adduct of bis(O,O′-dibutyldithiophos-phato)nickel (II), Ni(dtp)₂ · 2IQ, has been prepared; its crystal structure reveals that the nickel atom is bonded to four sulphur atoms of the dithiophosphate molecule, and two nitrogen atoms in the isoquinoline ring, to form a six-coordinated complex. Evaluation of the adduct's properties as an extreme-pressure (EP) and antiwear (AW) additive was conducted using a fourball machine. The results show that Ni(dtp)₂ · 2IQ exhibits better load-carrying capacity than Ni(dtp)₂ and Zn(dtp)₂, but poorer antiwear abilities. SEMs show that a wear scar surface on the ball lubricated with the adduct was much rougher than for those with isooctanol, Ni(dtp)₂ and Zn(dtp)₂, respectively. Further, energy dispersive X-ray (EDX) spectra indicates that the sulphur concentration in the wear scar lubricated with the adduct is much less than that of Ni(dtp)₂, which leads to a lesser wear reducing ability.     

On the Mechanism of Lubrication by Tricresylphosphate (TCP)—The Coefficient of Friction as a Function of Temperature for TCP on M-50 Steel

A pin-on-disk tribometer was used to study the coefficient of friction as a function of temperature for tricresylphosphate (TCP) on CVM M-50 tool steel under the following conditions: TCP was present in a liquid reservoir (bulk lubrication), and TCP was applied as a liquid layer directly to the disk (limited lubrication). Under limited lubrication conditions, experiments were performed in dry (< 100 ppm H₂O) air, dry (< 20 ppm H₂O) nitrogen, dry nitrogen with the disks heated to 700°C, then cooled to room temperature before the TCP was applied and the measurements made (preheated disks), and moist nitrogen using preheated disks. The coefficient of friction decreased at a characteristic temperature, T_r T_r values observed were: 265°C for bulk lubrication conditions in dry air, 225°C for limited lubrication conditions in dry air, and 215°C for limited lubrication conditions in dry nitrogen. The use of preheated disks produced a sharp failure temperature at 218°C which was taken as the temperature about which the behavior of TCP should be judged. X-ray photoelectron spectroscopy confirmed the presence of phosphate on the surface of TCP-lubricated iron pins. Depth profile studies support the suggestion that a chemical reaction occurs between the TCP and the metal surface at T_r.     

A Chitosan-Graphene Electrochemical Sensor for the Determination of Copper(II)

Graphite oxide was prepared by oxidizing graphite powder, reduced to graphene using hydrazine hydrate, and the grapheme was mixed with chitosan to form a composite that was used to modify a glassy carbon electrode for the determination of copper(II). The electrochemical behavior of the modified electrode was studied by cyclic and square wave voltammetries. The morphology and structure of the composite were characterized by infrared spectroscopy, transmission electron microscopy, and scanning electron microscopy. In addition, the proportion of composite material, pH, and adsorption time was optimized. Under the optimized experimental conditions, the sensor showed a linear dynamic range from 1.0 × 10^?9 to 1.5 × 10^?8 mol · L^?1 for copper(II) with a limit of detection of 4.3 × 10^?10 mol · L^?1 at a signal-to-noise ratio of three. The sensor displayed excellent electrochemical response and high sensitivity.     

Water loss at normal enamel histological points during air drying at room temperature

This in vitro study aimed to quantify water loss at histological points in ground sections of normal enamel during air drying at room temperature (25°C) and relative humidity of 50%. From each of 10 ground sections of erupted permanent human normal enamel, three histological points (n = 30) located at 100, 300 and 500 μm from enamel surface and along a transversal following prisms paths were characterized regarding the mineral, organic and water volumes. Water loss during air drying was from 0 to 48 h. Drying occurred with both falling and constant‐drying rates, and drying stabilization times (T_eq) ranged from 0.5 to 11 h with a mean 0.26 (±0.12)% weight loss. In some samples (n = 5; 15 points), T_eq increased as a function of the distance from the enamel surface, and drying occurred at an apparent diffusion rate of 3.47 × 10^?8 cm² s^?1. Our data provide evidence of air drying resulting in air replacing enamel's loosely bound water in prisms sheaths following a unidirectional water diffusion rate of 3.47 × 10^?8 cm² s^?1 (from the original enamel surface inward), not necessarily resulting in water evaporating directly into air, with important implications for transport processes and optical and mechanical properties.     

A small scanning tunnelling microscope with large scan range for biological studies

We have developed a scanning tunnelling microscope specially designed for biological applications presenting some new features: the scanner tube is mounted parallel to the surface of the sample which enables a high resolution optical microscope to be brought close to the sample when working in air or liquids. The maximum scan range is 5×20 μm with a vertical range of 20 μm and the total size of the system does not exceed 10×40 mm. The piezo-sensitivity of the scanner tube versus applied voltage was analysed by interferometry measurements and by using scanning tunnelling microscopes. We found a value for the piezoelectric constant d₁₃ of ?1·71 Å/V at low voltages (under a few volts) going up to ?2 Å/V for higher voltages. Large-scale images of a carbon grid showed a surprisingly good linearity of the scanner tube.     

Modification of the sample holder for a variable temperature scanning tunneling microscope (Omicron)

The design of a sample holder for a variable temperature scanning tunneling microscope (VT STM (Omicron)) with a variable sample temperature is described. This design considerably extends the range of investigated materials whose surface structure is sensitive to low concentrations of contaminations. The device is manufactured on the basis of the components of a standard holder with the possibility of heat-treating samples in a temperature range of 100–1500 K. The working capacity of the modified sample holder was demonstrated for an example of obtaining a Si(100)?2 × 1 surface with an ultimately low concentration of structural defects.     

基于柔性MEMS皮肤技术温度传感器阵列的研究

采用MEMS皮肤技术,在聚酰亚胺柔性衬底上成功研制出8×8阵列铂薄膜热敏电阻温度传感器。实验采用热氧化硅片为机械载体,以便于旋涂液态聚酰亚胺柔性衬底上器件的加工。最后用湿法腐蚀方法将柔性器件从载体上释放下来。试验表明聚酰亚胺衬底上的铂薄膜热敏电阻与温度的变化具有良好的线性,其电阻温度系数达0.0023/℃。与固态聚酰亚胺膜衬底相比,采用旋涂液态聚酰亚胺解决了制备中遇到的两大主要困难:其一,消除了涂聚酰亚胺衬底与载体界面之间的气泡,聚酰亚胺衬底表面能保持良好平整度;其二,制备过程中由于热循环而使柔性衬底产生的热膨胀明显减小。这种柔性温度传感器阵列易贴于高曲率物体表面以探测小面积温度场分布。     

X射线椭圆弯晶谱仪实验研究

利用椭圆从一个焦点发射出的光线经椭圆面反射必汇聚于另一焦点的性质,设计了基于620～6200eV的X射线椭圆弯晶谱仪.文中分析了系统原理,完成了谱仪光学色散系统、探测系统及仪器的研制.采用KAP、LiF、PET、MiCa作为色散元件,其2d值在0.4～2.6nm、Bragg角为30°～67.5°,晶体尺寸为120×8×0.2mm,偏心率为0.9586,焦距1350mm,光程长1456mm,分析器基底材料用数控铣床加工.实验在上海"神光Ⅱ"号装置上实施,激光能量为150J,波长为0.35mm,真空度为3×10^-3Pa.为达到光学对准,采用了小点光源以及精密望远镜对中.实验结果显示出金靶在0.63～0.79nm范围,其分辨力(△λ/λ)达到了1/486.谱的分辨力还与晶体特征和激光靶源尺寸有关.谱仪性能良好、使用方便、简单,具有高的收集效率和分辨能力,能够有效获取激光惯性约束聚变中激光等离子体发射光谱的丰富信息.     

多通道柔性神经微电极加工工艺研究

目的：设计并制作多通道柔性神经微电极,对微电极的加工工艺进行研究。方法：采用一种新型的柔性聚合物材料——聚对二甲苯（parylene C）作为微电极的基底和绝缘材料,借助微细加工技术,制作柔性神经微电极。结果：利用上述方法制作了36通道（按6×6矩阵排列）的柔性神经微电极,微电极的尺寸分别为150m（圆形）和150m×150m（方形）,电极引线线宽为30m。无论微电极为圆形或方形,表面均平整光滑、轮廓清晰。电学性能测试结果表明：1kHz时微电极的阻抗仅为7k左右,且随着频率的增加,阻抗逐渐降低,呈明显高通特性。结论：微电极加工质量较好,电学性能优良。实现了微电极和柔性基底的集成,有利于高效率批量制作。为视觉假体中柔性神经接口的研制奠定基础。     

CERIUM(IV)-BASED CHEMILUMINESCENCE OF FELODIPINE SENSITIZED BY RHODAMINE 6G

A simple, rapid, and sensitive flow injection chemiluminescence (FI-CL) method was proposed for the determination of felodipine. The method was based on the CL-emitting reaction between the studied drug and cerium(IV) in a nitric acid medium and measurement of the CL intensity produced by rhodamine 6G used as a sensitizer. Under the optimum conditions, the proposed procedure had a linear range between 5.0 × 10^?9 and 7.0 × 10^?6 g mL^?1, with a detection limit of 2.0 × 10^?9 g mL^?1. The relative standard deviation was 2.3% for 1.0 × 10^?7 g mL^?1 felodipine solution (n = 11). It was applied to the determination of felodipine in pharmaceutical preparations and biological fluids with satisfactory results. The possible mechanism of the chemiluminescence reaction was also discussed briefly.     

TEM and AES investigations of surface-diffusion-induced aging processes in thin Au films on Ag(111)

Surface-diffusion-induced aging processes have been observed in epitaxial Au films on Ag(111) which were prepared by vapour deposition at 30°C and subsequently annealed at temperatures between 100 and 210°C. In discontinuous Au films (thickness<5 monolayers) at temperatures below 170°C overlayers of Ag substrate material are created on top of the Au films, whereas at temperatures above 170°C the film and substrate materials are intermixed in the surface region. Continuous Au films, however, are completely levelled during annealing. The growth-induced surface roughness disappears, and perfectly flat surfaces develop exhibiting only some 2D islands or pits. The results obtained for the Au-Ag system are expected to be applicable to other systems, too.     

Characterization of 4H-SiC (0001) surface processed by plasma-assisted polishing

For the finishing of some difficult-to-machine materials, such as silicon carbide, diamond, and so on, a novel polishing technique named plasma-assisted polishing (PAP) was proposed, which combined with the irradiation of atmospheric pressure water vapor plasma and polishing using soft abrasives. In this article, application of PAP to 4H-SiC (0001) substrate was conducted. We used helium-based water vapor plasma to modify the mechanical and chemical properties of the SiC surface. The results of X-ray photoelectron spectroscopy measurements indicate that the surface was efficiently oxidized after plasma irradiation, and the main product was SiO₂. CeO₂ was used as the abrasive material in PAP, the hardness of which was near to that of the oxidized surface. The scanning white light interferometer images of the PAP processed surface showed us that scratches disappeared and surface roughness also decreased from 4.410 nm p-v, 0.621 nm root mean square (rms) to 1.889 nm p-v, 0.280 nm rms. From the atomic force microscopy images, step and terrace structure was observed on the surface after PAP, which means an atomically flat surface was obtained. The PAP processed surface was observed using cross-sectional transmission electron microscope, which indicated that almost no crystallographical defects were introduced.     

Study of Au surfaces by scanning tunnelling microscopy

The reconstructions of Au surfaces have been studied by scanning tunnelling microscopy. Topographs of Au(110)-(1×2) as a function of annealing temperature show changes in the long range order, in good agreement with diffraction measurements and theoretical studies. Some insight into the nucleation and growth of the (1×2) reconstruction was obtained by imaging the surface after deposition of Cs or O. A new structural model for Au(100)-(5×20) is proposed with a high resolution topograph. Adsorption of Si clusters on Au(100) will be described.     

A compact ultra-precision air bearing stage with 3-DOF planar motions using electromagnetic motors

We designed a novel surface motor stage supported by air bearings and driven by linear electromagnetic motors. This compact and simple planar stage is proposed for compact-sized precision machine systems, such as micro-machine tools or measurement systems requiring minimum X-Y stage height. Four single-phase linear motors with coils and iron cores are located under the base plate, and air bearings and cores with permanent magnets are attached under the moving table. The hard, non-magnetic alumina-ceramic base plate surface acts as a planar guide for the air bearings. The attractive magnetic force between the magnets and motor cores preload the air bearing to increase vertical stiffness. By simultaneously combining actuations of the motors, linear X and Y motion can be controlled, and angular motions can also be generated. A grid encoder is used to control planar motion, and the system is run by a programmable numerical controller. The thrust and attractive force were calculated using a magnetic circuit model. The designed prototype is 220 (L) × 220 (W) × 66 (H) mm³ in size with a 20 mm × 20 mm range of motion. After fabrication, basic aspects of the prototype, such as vertical stiffness and thrust force, were evaluated. Twenty nanometers of positioning resolution was obtained for the X and Y axes, and the three motions could be controlled independently.     

Micromorphology analysis of TiO2 thin films by atomic force microscopy images: The influence of postannealing

This work describes an analysis of titanium dioxide (TiO₂) thin films prepared on silicon substrates by direct current (DC) planar magnetron sputtering system in O₂/Ar atmosphere in correlation with three‐dimensional (3D) surface characterization using atomic force microscopy (AFM). The samples were grown at temperatures 200, 300, and 400°C on silicon substrate using the same deposition time (30 min) and were distributed into four groups: Group I (as‐deposited samples), Group II (samples annealed at 200°C), Group III (samples annealed at 300°C), and Group IV (samples annealed at 400°C). AFM images with a size of 0.95 μm × 0.95 μm were recorded with a scanning resolution of 256 × 256 pixels. Stereometric analysis was carried out on the basis of AFM data, and the surface topography was described according to ISO 25178‐2:2012 and American Society of Mechanical Engineers (ASME) B46.1‐2009 standards. The maximum and minimum root mean square roughnesses were observed in surfaces of Group II (Sq = 7.96 ± 0.1 nm) and Group IV (Sq = 3.87 ± 0.1 nm), respectively.     

Electron Microscope Studies Of Vpe Gainas Layer Structures Suitable For Use As Infrared Leds

Electron microscope investigations have been carried out on vapour grown (100) GaAs/GaInAs structures designed for use as infrared emitters of wavelength 1·06 μm. The structures consist of a GaAs substrate, a graded layer in which the indium concentration is increased from zero to 17 atomic %, and a constant composition Ga_0·83In_0·17As layer which contains a p-n junction. X-ray microprobe analysis of cross-sections of the slices established the uniformity of the grading. TEM analysis showed a dense and extensive asymmetric network of misfit dislocations (1 × 10¹² m^?2 (10⁸ cm^?2)) in the graded layer, threading dislocations and other anomalous contrast features extending from the graded layer through the p-n junction to the surface (local densities of 1 × 10¹¹–1 × 10¹² m^?2 (10⁷–10⁸ cm^?2)), and a planar network of dislocations just below the surface (spacing 0·2–2 μm). SEM EBIC and CL studies of the layer above the junction revealed dark spots, and a cross-grid of dark lines, which could be correlated with the threading defects, and the dislocation network just below the surface, respectively. The SEM results showed that these defects had a deleterious effect on the luminescent and electrical properties of the material in the vicinity of the p-n junction, and would therefore impair the performance of devices made from these layer structures.