Scanning tunnelling microscopy of B/Si(111) √3×√3 R(30°)

The √3 superstructure induced by boron outdiffusion at the surface of highly p doped Si(111) samples is studied by means of Auger, LEED and STM. Simultaneous double imaging at different voltages allows us to probe both filled and empty electronic states. A modification of the T₄ structural model of (Al, In, Ga)/Si(111) √3 is proposed for the B/Si(111) √3 superstructure.     

Electron microscopy of surfaces

Electron beam techniques used to study clean surfaces and surface processes on a microscopic scale are reviewed. Recent experimental examples and possible future developments are discussed. Special emphasis is given to (i) transmission diffraction and microscopy techniques, including atomic imaging; (ii) Auger microscopy on bulk and thin film samples; (iii) secondary electron microscopy, especially low energy secondaries for work-function imaging and photoelectron imaging; and (iv) reflection electron microscopy and diffraction.     

Spin–charge separation and electron pairing instabilities in Hubbard nanoclusters

Electron charge and spin pairing instabilities in various cluster geometries for attractive and repulsive electrons are studied exactly under variation of interaction strength, electron doping and temperature. The exact diagonalization, level crossing degeneracies, spin–charge separation and separate condensation of paired electron charge and opposite spins yield intriguing insights into the origin of magnetism, ferroelectricity and superconductivity seen in inhomogeneous bulk nanomaterials and various phenomena in cold fermionic atoms in optical lattices. Phase diagrams resemble a number of inhomogeneous, coherent and incoherent nanoscale phases found recently in high-_Tc$T_c$ cuprates, manganites and multiferroic nanomaterials probed by scanning tunneling microscopy. Separate condensation of electron charge and spin degrees at various crossover temperatures offers a new route for superconductivity, different from the BCS scenario. The calculated phase diagrams resemble a number of inhomogeneous paired phases, superconductivity, ferromagnetism and ferroelectricity found in Nb and Co nanoparticles. The phase separation and electron pairing, monitored by electron doping and magnetic field surprisingly resemble incoherent electron pairing in the family of doped high-_Tc$T_c$ cuprates, ruthenocuprates, iron pnictides and spontaneous ferroelectricity in multiferroic materials.     

基于选择最优滤光片的多光谱成像系统的研究

研究了基于选择最优滤光片多光谱成像系统优化问题,采用了优化的滤光片组合,组建了一个六通道的多光谱成像系统。利用提出的基向量和多项式组合的方式重构光谱数据,成功重建出博物馆、美术馆等展览馆常用的两种典型光源模拟器D65和A光源下油画的光谱反射率,并以光谱均方误差和色差综合误差评价成像质量。对两种光源下重建结果分析可得,最优滤光片的选取与光照环境密切相关。根据光照环境不同采用选取出的最优滤光片可得到最好光谱成像图,并且能在光谱和色度上都达到较高精度。     

Advantages of CO2 compared to R410a refrigerant of tribologically tested Aluminum 390-T6 surfaces

Carbon dioxide (CO₂) is currently being investigated as a viable alternative refrigerant due to its environmental advantages. Much research is still needed regarding thermodynamic, tribological, and design issues, yet CO₂ is a promising environmentally friendly refrigerant. This study investigates the physical and chemical changes of aluminum alloy disks that occur with increased severity tribotesting in the presence of either R410a or CO₂ refrigerants while submerged in POE lubricant. Visibly and through surface profilometry, this study clearly shows that R410a environment results in increased disk wear compared to CO₂ environment. In addition, Auger Electron Spectroscopy analysis was conducted showing that the oxygen concentration tends to increase with testing duration for both R410a and, to a greater extent, CO₂ tested samples. When Auger data were compared for the R410a submerged in POE, CO₂ submerged in PAG, and CO₂ submerged in POE, the CO₂ tested samples had significantly higher oxygen concentrations. This indicates that CO₂ refrigerant is promoting a strong oxygenated layer, which reduces wear.     

Reaction of tributyl phosphate with oxidized iron: surface chemistry and tribological significance

The chemistry of tributyl phosphate on Fe₃O₄ was studied in ultrahigh vacuum using temperature-programmed desorption (TPD) and Auger spectroscopy. A portion of the tributyl phosphate desorbs intact with an activation energy of ~120 kJ/mol. The remainder decomposes either by P-O bond scission to deposit surface butoxy species or appears to dehydrogenate desorbing C₂ or C₃ compounds and depositing hydrogen and carbon on the surface. The resulting hydrogen reacts either with the oxide to desorb water or with butoxy species yielding 1-butanol. The remaining butoxy species are stable up to ~600 K where they decompose to desorb butanal via hydride elimination where again the hydrogen reacts with butoxy species to form 1-butanol or with the oxide to form water. The carbon deposited onto the surface further reduces the oxide to desorb as CO above ~750 K, although a small amount of carbon is detected on the surface using Auger spectroscopy. Substantially larger amounts of carbon are deposited onto the surface when Fe₃O₄ is exposed to tributyl phosphate at 300 K, where an Auger depth profile reveals that the carbon is located at the surface while the PO_x species formed by tributyl phosphate decomposition diffuse rapidly into the oxide layer, leading to a film structure in which graphitic carbon is deposited onto a phosphorus-containing oxide layer.     

基于滤光轮双相机系统的高光谱分辨率成像

滤光轮光谱成像系统在光谱成像领域应用广泛,空间分辨率高,但是光谱分辨率较低。针对这一问题,提出了基于滤光轮双相机系统的高光谱分辨率成像,设计了一种基于插分补偿的多光谱计算重构方法,实现系统的高光谱分辨率、高空间分辨率成像。首先利用滤光轮双相机成像系统采集多光谱图像以及RGB图像,然后从多光谱图像获取离散的光谱响应曲线,最后根据RGB三通道数据与光谱高维数据之间的映射关系以及能量守恒定理,进行光谱响应曲线的插分补偿并实现高光谱分辨率成像。实验结果表明,本文方法能够在保持空间分辨率的情况下,高效地实现光谱分辨率为5 nm甚至更高光谱分辨率的成像,重建结果与真实值的均方根误差为0.017 1,具有较好的准确性和鲁棒性。     

The fabrication of a multi-spectral lens array and its application in assisting color blindness

This article presents a compact multi-spectral lens array and describes its application in assisting color-blindness. The lens array consists of 9 microlens, and each microlens is coated with a different color filter. Thus, it can capture different light bands, including red, orange, yellow, green, cyan, blue, violet, near-infrared, and the entire visible band. First, the fabrication process is described in detail. Second, an imaging system is setup and a color blindness testing card is selected as the sample. By the system, the vision results of normal people and color blindness can be captured simultaneously. Based on the imaging results, it is possible to be used for helping color-blindness to recover normal vision.     

Variation of roughness parameters on some typical manufactured surfaces

A number of specimen surfaces, including machined surfaces and calibration standards, are examined by a stylus instrument on-line to a microcomputer. For each measuement on each specimen 14 roughness parameters are computed for each of 10 profiles, and the mean and standard deviation of each parameter is calculated. Variations of up to 15% are found even on calibration standards, and 50% variations or larger are found on many machined surfaces. Increasing the range setting and decreasing the cut-off are both found to increase scatter. Using a skid has little effect. Measuring with the lay increases the scatter. Decreasing the sampling interval has no effect on R_a and R_q roughness but increase R_z and similar roughness and makes texture parameters ‘shape’.     

非线性偏微分方程增强多光谱图像清晰度

多光谱成像系统会改变输出光的波长,这就导致图像在不同波段下形成了不均匀亮度(阴暗图像和高亮度图像),严重影响了特征波段提取与测量。为了提高各波段的有效利用率,引用了一种增强多光谱灰度图像清晰度的有效方法。通过非线性的偏微分方程扩大梯度空间、保留梯度值较大的边缘,增强图像的纹理细节。由于多光谱图像阴暗波段的纹理较弱,不容易辨别其所有信息,为了更好地使增强效果完全体现出来,使用直方图均衡化来调节亮度的不均匀性。最后,通过人眼视觉的定性和客观函数的定量两方面对该组增强图像的清晰度进行了评价。结果表明:该方法能够有效地协调各波段的多光谱图像清晰度,并且图像的增强效果也非常明显。     

THE SCATTER OF SURFACE RESIDUAL STRESSES PRODUCED BY FACE-TURNING AND GRINDING

Conventional studies on residual stresses induced by manufacturing processes have focused on the average residual stress value over the processed surface area. However, what dictates the fatigue life of a manufactured surface is its weakest point. Thus, it is not the average value of the stress but the local extreme that is most relevant for safety considerations. Therefore, it is very important to study the variations of residual stresses over the machined surface. This paper is the continuation of the work [1] investigating the magnitude of surface residual stress scatter between the face-turned and ground samples. The objective of this research is to test the hypotheses that the scatter of surface residual stresses over the faced samples is smaller than that of the ground ones and that the scatter of surface residual stresses varies significantly among ground samples while it does not vary in a statistically significant sense among faced specimens for the given cutting conditions. In order to compare the surface residual stress variations, two sets of the specimens of Ti 6Al-4V bar are ground while the other two sets faced. The residual stresses over a small surface area (5mm × 8 mm) are measured at four locations of each machined sample using an X-ray diffraction technique. Statistical analysis of the measured residual stresses shows that the proposed hypotheses hold. Experimental data also show that a different number of grinding passes may induce a different scatter of microhardness. The possible causes and ramifications of the foregoing results are discussed. It is suggested that the variations of residual stress be included as a surface integrity parameter, joining its average value.     

Two new microscopical variants of thermomechanical modulation: scanning thermal expansion microscopy and dynamic localized thermomechanical analysis

We describe two ways in which thermomechanical modulation may be used in conjunction with scanning thermal microscopy, in order to distinguish between different components of an inhomogeneous sample. The sample is subjected to a modulated mechanical stress, and the heating is supplied locally by the probe itself.
Scanning thermal expansion microscopy is an imaging mode, in which an imposed localized temperature modulation is used to generate thermal expansion, which in turn produces mechanical strain and gives thermal expansion contrast images. We present results using two types of active thermal probe. For polymer/resin samples, the depth of material contributing to the measured thermal expansion is typically a few micrometres. Under certain conditions we observe a reversal in contrast as the frequency of the temperature modulation is increased.
In dynamic localized thermomechanical analysis, the modulated stress is applied directly, and accompanied by a localized temperature change, as used in other forms of localized thermal analysis. The resulting modulated lateral force signals are obtained. The glass transition of polystyrene is detected, and shows a significant variation with frequency. The amplitude or phase signal may be used to obtain image contrast for inhomogeneous samples.     

A technique for the preparation of cross-sectional TEM samples of ZnSe/GaAs heterostructures which eliminates process-induced defects

Cross-sectional transmission electron microscopy (TEM) sample preparation of ZnSe/GaAs epitaxial films is investigated. Conventional argon ion milling is shown to produce a high density (～ 5–8 × 10¹¹/cm²) of small (diameter ～ 60–80 Å) extended defects (stacking faults, microtwins, double positioning twins, etc.). In addition, transmission electron diffraction results indicate a thin ZnO layer can also occasionally form upon ion milling or electron-beam irradiation although the exact conditions for ZnO formation are not well understood. Conventional TEM (amplitude contrast) and high-resolution TEM (phase contrast) imaging in combination with transmission electron diffraction studies were performed to determine the optimum method of removing the ion milling related damage and ZnO layers during sample preparation. HF/HCl, NaOH/H₂O, H₂SO₄/H₂O₂/H₂O and Br₂/CH₃OH etching mixtures as well as low voltage argon or iodine ion milling were studied. A low energy (2 ke V) iodine or argon ion milling step was shown to remove the ZnO layer and reduced the density of the extended defects associated with Ar⁺ ion milling, but was unsuccessful in removing all of the defects. Auger electron spectroscopy results indicate residual iodine was either left on the surface or implanted beneath the surface during iodine ion milling. Etching the XTEM samples in HF/HCl was shown to be effective in removing the ZnO layer but had little or no effect on the ion milling induced defects. Etching the samples in a 0.5% Br₂/CH₃OH solution resulted in complete elimination of the ion milling induced extended defects including the residual defects associated with iodine ion milling. In addition the Br₂/CH₃OH etch produced the best surface morphology. Thus a brief (1–2 seconds) Br₂/CH₃OH etch after conventional preparation (argon ion milling) of cross-sectional ZnSe/GaAs TEM samples appears to be an inexpensive and superior alternative to iodine ion milling.     

Surface studies in UHV SEM and STEM

Some recent advances in surface analyses with scanning electron microscopy techniques are reviewed. It is shown that secondary electron microscopy can image monatomic steps, emergent dislocations and the early growth of thin films and oxide nuclei. The chemical composition of inhomogeneous surfaces can, in some cases, be determined with nanometre resolution with Auger signals. Overlayer coverages can occasionally be monitored with the secondary electron signal if the change of work function with coverage has been determined previously. The interpretation of these secondary and Auger signals is discussed. The combination of angular electron spectroscopy with electron microscopy is potentially a powerful technique for determining atomic positions of surface atoms and one method for obtaining the experimental data is described. Several substrate/overlayer systems are used to illustrate the amount of information that can be obtained about surface processes with scanning electron microscopy.     

Comparison of hyperspectral classification methods for the analysis of cerium oxide nanoparticles in histological and aqueous samples

Hyperspectral imaging (HSI) and classification are established methods that are being applied in new ways to the analysis of nanoscale materials in a variety of matrices. Typically, enhanced darkfield microscopy (EDFM)‐based HSI data (also known as image datacubes) are collected in the wavelength range of 400–1000 nm for each pixel in a datacube. Utilising different spectral library (SL) creation methods, spectra from pixels in the datacube corresponding to known materials can be collected into reference spectral libraries (RSLs), which can be used to classify materials in datacubes of experimental samples using existing classification algorithms. In this study, EDFM‐HSI was used to visualise and analyse industrial cerium oxide (CeO₂; ceria) nanoparticles (NPs) in rat lung tissues and in aqueous suspension. Rats were exposed to ceria NPs via inhalation, mimicking potential real‐world occupational exposures. The lung tissues were histologically prepared: some tissues were stained with hematoxylin and eosin (H&E) and some were left unstained. The goal of this study was to determine how HSI and classification results for ceria NPs were influenced by (1) the use of different RSL creation and classification methods and (2) the application of those methods to samples in different matrices (stained tissue, unstained tissue, or aqueous solution). Three different RSL creation methods – particle filtering (PF), manual selection, and spectral hourglass wizard (SHW) – were utilised to create the RSLs of known materials in unstained and stained tissue, and aqueous suspensions, which were then used to classify the NPs in the different matrices. Two classification algorithms – spectral angle mapper (SAM) and spectral feature fitting (SFF) – were utilised to determine the presence or absence of ceria NPs in each sample. The results from the classification algorithms were compared to determine how each influenced the classification results for samples in different matrices. The results showed that sample matrix and sample preparation significantly influenced the NP classification thresholds in the complex matrices. Moreover, considerable differences were observed in the classification results when utilising each RSL creation and classification method for each type of sample. Results from this study illustrate the importance of appropriately selecting HSI algorithms based on specific material and matrix characteristics in order to obtain optimal classification results. As HSI is increasingly utilised for NP characterisation for clinical, environmental and health and safety applications, this investigation is important for further refining HSI protocols while ensuring appropriate data collection and analysis.     

Time-domain whole-field fluorescence lifetime imaging with optical sectioning

A whole-field time-domain fluorescence lifetime imaging (FLIM) microscope with the capability to perform optical sectioning is described. The excitation source is a mode-locked Ti:Sapphire laser that is regeneratively amplified and frequency doubled to 415 nm. Time-gated fluorescence intensity images at increasing delays after excitation are acquired using a gated microchannel plate image intensifier combined with an intensified CCD camera. By fitting a single or multiple exponential decay to each pixel in the field of view of the time-gated images, 2-D FLIM maps are obtained for each component of the fluorescence lifetime. This FLIM instrument was demonstrated to exhibit a temporal discrimination of better than 10 ps. It has been applied to chemically specific imaging, quantitative imaging of concentration ratios of mixed fluorophores and quantitative imaging of perturbations to fluorophore environment. Initially, standard fluorescent dyes were studied and then this FLIM microscope was applied to the imaging of biological tissue, successfully contrasting different tissues and different states of tissue using autofluorescence. To demonstrate the potential for real-world applications, the FLIM microscope has been configured using potentially compact, portable and low cost all-solid-state diode-pumped laser technology. Whole-field FLIM with optical sectioning (3D FLIM) has been realized using a structured illumination technique.     

Direct Draw技术在多光谱图像实时显示中的应用

在高分辨率成像光谱仪的工作中,要求在不影响诸如采集、存储等优先级高的工作条件下,实时显示多光谱图像,用传统的GDI是无法实现的。文中提出的DirectDraw理论和实现方法,可实时显示多光谱图像并已应用于863-2高分辨率成像光谱仪系统中。     

A comparative materials study of magnetron ion etched GaAs using Freon-12, SiCl4 and BCl3

Etch characteristics and residual damage incurred via magnetron ion etching of GaAs using three different etch gases, namely, freon-12, SiCl₄ and BCl₃, at two different power levels has been studied. Transmission electron microscopy, scanning electron microscopy, Auger electron spectroscopy, and Schottky diode measurements were employed to determine the suitability of the processed surfaces for device fabrication. Lattice damage was incurred in all processing situations in the form of small dislocation loops. Samples etched in freon-12 at the highest power density exhibited the roughest surface morphology, while those etched in SiCl₄ and BCl₃ resulted in planar surfaces. The Schottky barrier diode characteristics, for all etch gases, degraded with increasing power density. The electrical quality of the BCl₃-etched GaAs at the lowest power density was superior to that of the other etch gases at all power levels. The etched profiles of SiCl₄ and BCl₃ yielded vertical sidewalls, whereas freon-12 yielded a negative undercut. The BCl₃-etched GaAs surfaces were residue-free, while those of freon-12 and SiCl₄ exhibited surface or sidewall contamination. Our results have demonstrated that magnetron ion etching with BCl₃ yields planar residue-free surfaces with minimum material surface damage and superior electrical integrity compared with GaAs etched with freon-12 or SiCl₄.     

Image reconstruction using industrial gamma ray tomograph with different scatter energy windows

Scattered gamma rays have beneficial information for reconstructing an image. Therefore, it is important to count both attenuated and scattered rays. For achieving this aim, an industrial computed tomography (CT) system was designed and developed on the base of a first generation CT system. The CT scanner consists of a 5.08 cm NaI(Tl) detector in diameter and a ¹³⁷Cs (30 mCi) radioactive source. The position of phantom is defined by three motors. The CT scans are taken out by scanning 180° to collect attenuated beams. Several experiments were performed with different widths of scatter energy windows and full absorption peak window. The full peak window was 530–761 keV, Compton scatter window changed, 200–530 and 300–530 keV and total count peak window was 200–761 keV. Finally, the quality of images with different scatter area widths is analyzed and compared by computing the RMS contrast of each image.     

Gas/liquid two-phase flow regime identification by ultrasonic tomography

A gas/liquid two-phase flow is considered as a strongly inhomogeneous medium with respect to high contrast in acoustic impedance distribution. Based upon a binary logic operation and a method of “time-of-propagation along straight path”, an ultrasonic facility for tomographic imaging of gas/liquid two-phase flow was developed. In this paper the principle and construction of this facility are briefly introduced. Emphasis is placed on the evaluation of its performance in flow regime identification and cross-sectional void fraction measurement. Several flow pattern models were used and the corresponding monitoring results given. Finally, limitations and possible future improvements of the system are discussed.