Indium nanowires at the silicon surface

Conductive indium nanowires up to 50 nm in width and up to 10 μm in length are fabricated on the surface of silicon by local resputtering from the probe of an atomic-force microscope. The transfer of indium from the probe of the atomic-force microscope onto the silicon surface is initiated by applying a potential between the probe and the surface as they approach each other to spacings, at which the mutual repulsive force is ~10^–7 N. The conductivity of the nanowires ranges from 7 × 10^–3 to 4 × 10^–2 Ω cm, which is several orders of magnitude lower than that in the case of the alternative technique of heat transfer.     

Nucleation at the lateral surface and the shape of whisker nanocrystals

A theoretical model of nucleation at the lateral surface of whisker nanocrystals during molecular-beam epitaxy and other high-vacuum deposition procedures is suggested. A model solution is obtained, which allows the calculation of the shape of whisker nanocrystals in relation to the diffusion flux of adatoms from the substrate surface to the base of the crystals. The temperature dependence of the nucleation effect is treated theoretically. It is shown that, at lowered surface temperatures, nucleation at the side walls results in the formation of cone-shaped crystals, with the length decreasing with decreasing temperature. The theoretical results are compared, at a qualitative level, with the experimental data for the GaAs whisker nanocrystals grown by molecular beam epitaxy on the Au-activated GaAs(111)As surface in the temperature range 400–600°C.     

Poxvirus virions: their surface ultrastructure and interaction with the surface membrane of host cells

Virions of vaccinia and orf viruses were examined by ultrahigh-resolution scanning electron microscopy using a non-coating method. Intracellular mature particles of vaccinia virus appeared to be covered with a net and ultrastructurally their surface consists of many fine ridges and globules, while the surfaces of orf virus mature particles recovered from infected cells consist of spirally running protrusions. The ridge-like structures of vaccinia virus were presumed to correspond to surface tubules shown by negative staining of this virus, while the spiral protrusions of orf virus were presumed to correspond to spiral threads having a criss-cross appearance by the same staining. Using scanning electron microscopy in which the samples were prepared by the conventional method, we observed: (i) many virions, i.e. one or two hundreds, or occasionally more reaching about one thousand particles, of the IHD strain of vaccinia virus, (ii) many or a moderate number of virions, i.e. about one hundred or fewer particles, of the 58 strain of cowpox virus and (iii) rather few virions, i.e. several tens or fewer particles, of the Iwate strain of orf virus on the free surface of each cell infected with these viruses. It must be noted that the number of virions detected considerably differed in respective cells examined. Virus budding was frequently observed at the cell surface of monolayer cells infected with vaccinia virus but it was never detected with cowpox or orf virus, indicating a difference in the mechanism of virus release between vaccinia and the other two viruses. When whole cells infected with vaccinia virus were examined by a combination of high-voltage and scanning electron microscopies, virions on the cell surface and those inside the cells were clearly differentiated. All virions on the cell surface had an envelope, and some of the envelopes had a slack and/or one or more bulges.     

Capacitance-voltage characteristics of the electrolyte-n-InN surface and electron states at the interface

Dependences of differential capacitance of the system degenerate n-InN-electrolyte on the voltage are measured at a frequency of the probing voltage of 300 Hz. Qualitative analysis of these characteristics is performed based on a one-dimensional model of the metal-insulator-semiconductor structure in the region of bias voltages near the flat-band voltage and depletion. It is shown that the magnitude of capacitance in this voltage region is affected by electron states at the interface. The density and energy distribution of these states are evaluated. The form of the voltage dependence of capacitance in the region of accumulation also indicates the existence of the states at the interface, the energy of which exceeds the energy of the conduction band bottom by several tenths of eV. The density of these states increases as the energy increases.     

Analysis of inherent potential nonuniformities at the extrinsic-semiconductor surface

The concept of an inherent dimensional effect in depleted semiconductor layers (comparability of the characteristic scale of a depleted layer to an average distance between electrically active defects) is introduced. Inherent nonuniformities of an electric field and the potential at the semiconductor surface are determined for intrinsic and impurity surface states. The dependence of these nonuniformities on surface and bulk parameters is considered.     

Analysis of charges and surface states at the interfaces of semiconductor-insulator-semiconductor structures

A method for determining the energy spectrum of charges and surface-state densities at the interfaces of semiconductor-insulator-semiconductor structures was developed; the method is based on the analysis of capacitance-voltage characteristics. The method was experimentally tested with Si-SiO₂-Si structures prepared by direct bonding of both mirror-polished smooth wafers and wafers with a regular mesoscopic relief pattern at the inner surface of the wafers to be bonded. The density of surface states is lower at the surfaces with a regular relief pattern than that at the surfaces without the surface relief.     

Reflection and transmission at the surface of a chiral negative refractive medium

Electromagnetic fields at the surface of a chiral negative refraction medium (the chirality parameter is larger than the refractive index) are analyzed theoretically. For obtaining chirality parameter,the normalized reflected and transmitted powers as a function of the incident angle are given for the perpendicular (TE) and parallel (TM) polarized incident wave.Brewster angle and total internal reflection angle are discussed. Due to the negative refraction of one eigen-wave in the chiral medium, the reflection, transmission and Brewster angle characteristics are very different from those in the normal chiral medium.     

Reflection and transmission at the surface of a chiral negafive refractive medium

Electromagnetic fields at the surface of a chiral negative refraction medium （the chirality parameter is larger than the refractive index） are analyzed theoretically. For obtaining chirality parameter,the normalized reflected and transmitted powers as a function of the incident angle are given for the perpendicular （TE） and parallel （TM） polarized incident wave. Brewster angle and total internal reflection angle are discussed. Due to the negative refraction of one eigen-wave in the chiral medium, the reflection, transmission and Brewster angle characteristics are very different from those in the normal chiral medium.     

Control of electric field at the surface of P-N junctions

Both degradation resulting from ion migration and surface breakdown ofp-njunctions depend strongly on electric field. These problems can be minimized or avoided by designingp-njunction devices so that the electric field at the surface is substantially lower than that within the body of the device. The shape, surface doping, and dielectric constant at the junction-surface interface have an appreciable influence on the electric field of the adjoining space charge layer. Using relaxation methods, solutions of Poisson's equation in two dimensions have been found which permit predictions of the surface fields as a function of surface geometry and dielectric coatings. Measurements of the surface field by probing the junctions are in good agreement with calculated values. This approach has led to the design of very high voltagep-njunction devices which exhibit body breakdown only. With the breakdown confined to the body of the device, the reverse power dissipation capability is not only predictable but significantly greater (typically 30 a at 1200 v for a 100 µsec pulse applied to a large area device) than that achievable with surface limited devices.     

多种肿瘤细胞表面超微结构的原子力显微镜观察及药物对细胞膜表面超微结构影响的初步研究

本文应用原子力显微镜对人胃癌SGC7901、人肝癌HepG2、人肺癌AFFC-A-1、人乳腺癌MCF．7.R和人肺腺癌A549等肿瘤细胞膜表面进行了超微结构的形态学观察和比较。并研究了Nm23-Hl／NDPK-A蛋白对人肺腺癌A549等细胞膜表面超微结构的影响。发现不同肿瘤细胞膜表面超微结构存在较大的差异，药物处理和对照组A549细胞膜的表面超微结构也存在较大差异，药物处理的A549细胞膜表面出现大量的疤痕状集聚物，而药物处理的其它几种肿瘤细胞膜表面未发现明显的变化。说明原子力显微镜具有发展为一种观察和鉴别某些细胞的有力工具的潜力，并有可能应用于病理学或药理学研究，但在这些研究中这种技术只能作为一种辅助手段。     

SARS CoV感染Vero E6的电镜研究

我们用广州地区临床确诊的SARS病人的咽拭子标本感染Vero E6细胞,将感染3天即严重病变的Vero E6细胞进行3％戊二醛和l％锇酸双固定,经乙醇脱水后用Spurt包埋剂包埋。样品进行超薄切片和用醋酸氧铀和柠檬酸铅双染色后即可用透射电子显微镜进行观察。正常的Vero E6细胞也同上操     

Increasing the efficiency of photoelectric cells by nanostructuring their surface

A method of fabrication of nanostructured objects, which increases the efficiency of the photo-electric system used in the conversion of energy of electromagnetic radiation into electric energy is suggested. The method is based on the formation of metal nanodots on the basis of the surface layer of porous silicon, which concentrates the energy of electromagnetic radiation due to localized plasmon modes.     

The base current recombining at the oxidized silicon surface

The recombination of minority carriers at the oxidized silicon interface plays an important role in modelling the base current of bipolar devices. Essential in this process is the quality of the Si/SiO₂ interface, characterized by the fundamental recombination velocity s₀ = √(σ_nσ_p)v_thkTD_it.Measurements of s₀ have been carried out, by measuring the base current of special transistors with an epitaxially grown, low-doped base, and a gate on top of the base oxide. Typical values of s₀ in the range 0.5–2 cm/s have been found. These experiments are extended to graded base transistors, where comparable results are obtained.Independent measurements (QSCV and conductance) have been carried out to calculate s₀ from the interface trap density and the capture cross sections. Using values for σ_n and σ_p of 10^?16 and 3 x 10^?15 cm² respectively, a good correspondence to the base current measurements is obtained.The results shed some light upon the measuring and the modelling of the base current component recombining at the Si/SiO₂ interface in I²L devices.     

Incoherent bistatic scattering from the sea surface at L-band

A bistatic electromagnetic wave scattering model for the sea surface is developed to examine its wind dependence property over a wide range of incident angles along the specular direction. This is done by combining an existing scattering model with a sea spectrum recently reported in the literature. In general, electromagnetic wave scattering from a rough surface is dependent on the Fourier transform of the nth power of its height correlation function which can be computed numerically from the surface spectrum. This transform relation indicates that scattering is sensitive not only to the surface spectrum but also to its convoluted properties. Generally, surface scattering is sensitive only to a portion of the surface correlation measured from the origin. The size of this portion is a function of three variables (the incident angle, the surface height standard deviation, and the exploring wavelength) and the rate of decay of the correlation function. The decay rate near the origin of the sea surface correlation is very small, so much so that at L-band this portion is too wide for a two-term approximation of the correlation function. This is true in spite of the fact that the sea surface has a very large rms height. Thus, a scattering model based on geometric optics is generally not applicable at L-band especially at large angles of incidence. An additional finding is that in specular scattering wind dependence is stronger at larger angles of incidence for incident angles between 0 and 70° over the wind speed range of 4 m/s-20 m/s     

Measurement of surface impedance at microwave frequencies

A technique for measuring the surface impedance of a plane stratified media at microwave frequencies is given, and preliminary tests are made for a variety of situations ranging from capacitive impedances to surfaces, which display a purely inductive reactance. The technique utilises a modulated scatterer to measure the elliptically polarised electric field of a TM wave propagation over the surface.     

Observation of surface charging at the edge of a Schottky contact

Scanning Kelvin probe microscopy was used to detect reverse-bias-induced surface potential changes near the Schottky contact of a GaN Schottky diode. After application of a reverse bias, the surface potential near the Schottky contact gradually decreased with time, indicating an increase of band bending. Surface potential traces recorded after turning off the reverse bias indeed revealed increased band bending near the Schottky contact. A higher reverse bias caused a larger increase of band bending. The authors suggest that a reverse bias facilitates electron tunneling at the edge of the Schottky contact by decreasing the potential barrier width. Capture of these tunneled electrons by surface states causes the observed increase of band bending.