Immobilization of DNA on 11-mercaptoundecanoic acid-modified gold (111) surface for atomic force microscopy imaging

Immobilized DNA on preformed 11-mercaptoundecanoic acids (MUDA) self-assembled monolayers (SAMs) on a gold (111) surface was bound by a divalent cation bridges was imaged by atomic force microscopy (AFM). The DNA immobilization was attributed to the formation of ionic bridges between the carboxylate groups of MUDA and the phosphate groups of DNA. AFM images revealed that DNA molecules could be immobilized strongly enough to permit stable and reproducible imaging. The effect of different bridge cations, such as Mg(2+), Zn(2+) and Cu(2+), and the pH of DNA assembled solution on immobilization and conformation of DNA was studied. Plasmid DNA pBR 322/Pst I molecules were straightened by using a molecular combing technique on the MUDA surface.     

Scanning tunnelling microscopy and spectroscopy on Cu(111) and Au(111)

We have studied Cu(111) and Au(111) by means of scanning tunnelling microscopy and spectroscopy. The constant current topographies showed flat parts as well as regions with a high density of monoatomic steps (in particular on Au(111)). Local I/U characteristics have been determined at a fixed sample-tip distance in the range of ?10 V≤U≤10 V. They show a linear behaviour near the Fermi level and a nearly exponential dependency for larger values of U. Neither an influence of the sp-like surface states or an onset due to d electron contributions of the sample could be observed.     

基于遗传算法的单晶炉热场温度控制系统

介绍了以AT89C51单片机为核心的单晶炉热场温度控制系统的设计与实现方法,提出了一种基于遗传算法的PID参数寻优方法。仿真研究结果表明,系统具有良好的控制性能。     

基于DMC算法的单晶炉热场温度控制系统

介绍了以AT89C51单片机为核心的单晶炉热场温度控制系统的组成及工作原理.研究了动态矩阵控制(DMC)算法在单晶炉热场温度控制系统中的应用.给出了系统的硬件与软件设计的实现方法.研究表明,与PID控制结果相比较,应用动态矩阵控制算法能使系统具有更好的控制性能.     

Large-scale, uniform DNA network on 11-mercaptoundecanoic acid modified gold (111) surface: atomic force microscopy study

Large-scale, uniform plasmid deoxyribonucleic acid (DNA) network has been successfully constructed on 11-mercaptoundecanoic acid modified gold (111) surface using a self-assembly technique. The effect of DNA concentration on the characteristics of the DNA network was investigated by atomic force microscopy. It was found that the size of meshes and the height of fibers in the DNA network could be controlled by varying the concentration of DNA with a constant time of assembly of 24 h.     

High resolution images of a reconstructed surface structure on (111) gold platelets: Interpretation and comparison with theoretical models

Reconstruction of the (111) gold surface has been previously observed, and it has been shown that the surface net is compressed in the <110> direction, as compared with the bulk lattice. We present here some high resolution studies made on this surface reconstruction: the problem was to obtain a structure image corresponding mainly to the uppermost plane which forms the surface. For this, we have formed high resolution images by interferences between the so-called forbidden diffracted beams $\text{1}\text{3}$ (4?22): bulk gold, when observed along the <111> direction, is better described as a stacking of hexagonal two-dimensional layers, and the $\text{1}\text{3}$ (4?22) beams occur as diffracted beams from 1 (or2) hexagonal layers; they nearly disappear every 3 slices. If the top layer is reconstructed, the diffracted beams from the first slice will be different and will not cancel with the diffracted beams from the bulk layers. Hence the image formed with these beams will give some information on the reconstructed top layer. Computed images have been obtained for different models of the reconstructed surface. They show that, indeed, images obtained under these conditions are linked with the topography of the surface. They also show the importance of different experimental parameters, in particular the beam divergence.     

Consistent indexing of a (set of) single crystal SAED pattern(s) with the ProcessDiffraction program

A computer program called "ProcessDiffraction" helps indexing a set of single crystal selected area electron diffraction (SAED) patterns by determining which of the presumed structures can fit all the measured patterns simultaneously. Distances and angles are measured in the digitalized patterns with a graphical tool by clicking on the two shortest non-collinear vectors (spots), using user-supplied calibration data. Centers of the spots and center of the pattern are optionally refined by the program. Suggested individual indexing solutions (consistent with an assumed unit cell) are listed by the program for each pattern. Simulated patterns are also consulted to check if the shortest calculated distances coincide with measured ones. Common solutions for the set are selected by checking the angles between the suggested zone axes against the angles between the experimental goniometer settings. The indexing process is manually controlled by selecting the candidate structures (one-by-one) for indexing and by specifying the tolerances for d-values, plane angles and zone angles. Patterns of any crystal system can be indexed successfully. Although error bars are larger in electron diffraction than in X-ray diffraction (XRD), frequently, many unrelated indexings are possible for any one electron diffraction pattern (irrespective of the indexing method), a set of SAED patterns can generally be indexed unambiguously, i.e. the three-dimensional reciprocal space can be identified correctly. Two other tools also help planning tilting experiments: zones along a plane can be listed (with their angles extended from a pre-selected zone in that plane) and zones lying at a given angle (specified with a tolerance) from a zone can also be identified (as they are situated between two cones). Another tool searches the XRD database directly either for advice on possible structures for a composition or to help calibration.     

涡盘在气体力和温度载荷作用下的应力及变形分析

采用有限元方法，对涡旋压缩机动涡盘在气体力及温度载荷作用下应力分布特点及变形规律进行了分析。结果表明最大应力发生在齿头根部，对变形的分析中得到气体力主要影响径向及周向变形。而温度载荷主要影响轴向变形。     

Morphological study on thermal treatment and degradation behaviors of solution-grown poly(l-lactide) single crystals

Morphological changes of solution-grown crystals (SGCs) of poly(l-lactide) (PLLA) following thermal treatment and enzymatic degradation were investigated using atomic force microscopy in terms of defects in the crystals. PLLA SGCs were grown from a dilute solution of acetonitrile at 5 degrees C. The obtained solution-grown monolamellar crystals have a lozenge-shaped morphology containing unique dimensions, with one side measuring 12mum. To investigate enzymatic degradation behavior, PLLA SGCs were incubated in buffered solution with proteinase-K at 37 degrees C. The initial stage of enzymatic degradation of PLLA SGCs with proteinase-K occurs in loosely folding chains at the surface of the crystal. Thermally treated PLLA SGCs below the melting temperature showed an increase of the lamellar thickness of the SGCs at the treated temperature and partial surface erosion following enzyme exposure. These results indicate that less ordered chains exist throughout the lamellae and their thermal-induced chain extension makes them more susceptible to enzyme attack.     

Effect of surface contamination on the UHV tribological behavior of the Cu(111)/Cu(111) interface

Friction and adhesion measurements have been made using two Cu(1 11) samples modified by the presence of atomic adsorbates. Copper surfaces with 10–15 Å thick contaminant films resulting from exposure to the atmosphere exhibited a static friction coefficient of _s = 0.75 ± 0.18. A sharp increase in the friction coefficient was observed when the contaminant layer was reduced to submonolayer thickness by sputtering and for the cleanest Cu(111) surfaces studied the static friction coefficient was _s = 4.4 ± 1.3. To further investigate the tribological effect of submonolayer coverages of surface contamination adhesion experiments were performed using surfaces modified with sulfur adsorbed at coverages in the range _s = 0.0–0.39 ML (saturation). The adhesion coefficient of the clean surfaces (_ad = 0.69 ± 0.20) was markedly reduced by the presence of 0.05 ML of sulfur and decreased monotonically with increasing sulfur coverage to a limiting value of _ad = 0.26 ± 0.07 at _s = 0.39.     

Effects of shear plane boundary condition on stress loading in orthogonal machining

The finite element method is used to investigate the effect of shear plane boundary conditions on the stress field in the workpiece during machining. The balances of force and moment on both the shear plane and the tool rake face are used to calculate the unknown boundary condition, i.e. normal stress distribution on the shear plane. The results of finite element analysis show that the normal stress distribution on the shear plane does not significantly affect the value of the stresses in the workpiece under the tool tip. The length of the shear plane is found to be a major parameter governing the stress field in the workpiece in machining, confirming a previous experimental study.     

Morphological study on thermal treatment and degradation behaviors of solution-grown poly(l-lactide) single crystals

Morphological changes of solution-grown crystals (SGCs) of poly(l-lactide) (PLLA) following thermal treatment and enzymatic degradation were investigated using atomic force microscopy in terms of defects in the crystals. PLLA SGCs were grown from a dilute solution of acetonitrile at 5 °C. The obtained solution-grown monolamellar crystals have a lozenge-shaped morphology containing unique dimensions, with one side measuring 12 μm. To investigate enzymatic degradation behavior, PLLA SGCs were incubated in buffered solution with proteinase-K at 37 °C. The initial stage of enzymatic degradation of PLLA SGCs with proteinase-K occurs in loosely folding chains at the surface of the crystal. Thermally treated PLLA SGCs below the melting temperature showed an increase of the lamellar thickness of the SGCs at the treated temperature and partial surface erosion following enzyme exposure. These results indicate that less ordered chains exist throughout the lamellae and their thermal-induced chain extension makes them more susceptible to enzyme attack.     

单晶蓝宝石的延性研磨加工

为实现单晶蓝宝石的延性研磨加工,采用纳米压痕和划痕法测试并分析了单晶蓝宝石(0001)面的微纳力学特性,建立了单颗圆锥状磨粒的压入模型并计算了延性研磨加工的受力临界条件,分析了金刚石磨粒嵌入合成锡研磨盘表面的效果.对单晶蓝宝石进行了延性研磨加工试验,采用NT9800白光干涉仪、扫描电子显微镜(SEM)和透射电子显微镜(TEM)等方法分析了单晶蓝宝石的延性研磨表面特征.试验结果表明:采用纳米压痕和划痕法可以为单晶蓝宝石的延性研磨加工提供工艺参数,单晶蓝宝石的延性堆积的极限深度为100 nm,金刚石磨粒的嵌入及在适当载荷下可以实现蓝宝石的延性研磨加工,实验条件下的最佳载荷为21 kPa,延性研磨后单晶蓝宝石表面划痕深度的分布情况较好,分散性小,研磨后的表面发生了位错滑移变形.     

Atomic Friction Modulation on the Reconstructed Au(111) Surface

Friction between a nanoscale tip and a reconstructed Au(111) surface is investigated both by atomic force microscopy (AFM) and molecular statics calculations. Lateral force AFM images exhibit atomic lattice stick–slip behavior with a superstructure corresponding to the herringbone reconstruction pattern. However, the superstructure contrast is not primarily due to variations in the local frictional dissipation (which corresponds to the local width of the friction loop). Rather, the contrast occurs primarily because the local centerline position of the friction loop is periodically shifted from its usual value of zero. Qualitatively, similar behavior is reproduced in atomistic simulations of an AFM tip sliding on the reconstructed Au(111) substrate. In both simulations and experiments, this centerline modulation effect is not observed on unreconstructed surfaces. Similarly, using a topographically flat surface as a hypothetical control system, the simulations show that the centerline modulation is not caused by variations in the reconstructed surface’s topography. Rather, we attribute it to the long-range variation of the local average value of the tip-sample interaction potential that arises from the surface reconstruction. In other words, surface atoms located at unfavorable sites, i.e., in the transition between face-centered-cubic (FCC) and hexagonal-close-packed (HCP) regions, have a higher surface free energy. This leads to a varying conservative force which locally shifts the centerline position of the friction force. This demonstrates that stick–slip behavior in AFM can serve as a rather sensitive probe of the local energetics of surface atoms, with an attainable lateral spatial resolution of a few nanometers.     

Surface potential study of Au(111) surfaces

The structure of the one-dimensional surface potential barrier of the gold (111) surface has been investigated by the analysis of the deflection of the central spot of a microdiffraction pattern which is easily obtained by using a HB-5 scanning transmission electron microscope. The result shows direct evidence for the existence of this surface barrier potential up to about 25 Å away from surface. From a suggested modified image potential barrier model, the streaking length on the central spot has been obtained from calculation and compared with the experimental measurement. The agreement is good within the limitations of the experimental technique.     

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.