Cathodoluminescence imaging—the study of yttrium aluminates distribution in aluminum nitride

Cathodoluminescence imaging is a technique which may combine a high-resolution spectroscopic method with a high-spatial resolution electron imaging technique to characterize chemical identity as well as physical size, shape, and spatial distribution of the materials which have cathodoluminescence. Cathodoluminescence imaging has been used to characterize yttrium aluminates in aluminum nitride ceramics. By digitally combining cathodoluminescence and backscat-tering electron images, it is possible not only to distinguish between different yttrium aluminates, but also to determine the size, shape, and spatial distribution of these phases. This information provides a route to understanding the local residual oxygen concentration before sintering, the amount of sintering aid to be added, and possible sintering schedule. Furthermore, this information may be related to other properties of aluminum nitride such as residual oxygen concentration and thermal conductivity.     

Processing of hollow micro- and nanostructures using the hydrophilic nature of MgO

We show that covering the water-saturated MgO surface with an Al₂O₃ film using atomic layer deposition and then annealing it at 400 °C leads to plastic deformation of alumina by trapped water vapor with consequent development of hollow structures. This phenomenon is applied to thin films, nanopatterned surfaces and isolated 3D nanostructures.     

Comparative characterization of chemical vapor deposition diamond films by scanning cathodoluminescence microscopy

Thin diamond films grown by chemical vapor deposition (CVD) process on Si substrates under similar deposition conditions in the microwave-excited (MW) and direct current (DC) plasma discharges were taken for comparative examination. Raman spectra, photoluminescence (PL) spectroscopy, and color cathodoluminescence scanning electron microscopy (CCL-SEM) have been used for characterization of the structure and composition features of poly-crystalline diamond films. No essential difference in Raman spectra for the CVD diamond films was detected. A significant difference was revealed in the PL spectra and in CCL-SEM images.     

Light field propagation by metal micro- and nanostructures

The ability to sustain plasmon oscillations gives rise to unique properties of metal nanostructures, which can be exploited for the controlled manipulation of light fields on the nanoscale. In this context we investigate electromagnetic coupling effects within lithographically produced ensembles of gold nanoparticles with a photon scanning tunnelling microscope. To provide an interface between these nano-optical devices and classical far-field optics, we investigate surface plasmon propagation on microstructured metal thin films.     

From quantum-well wires to nanowires as studied by cathodoluminescence imaging and spectroscopy

Cathodoluminescence (CL) imaging and spectroscopy are used to study one-dimensional structures from three different decades. Quantum-well wires were fabricated in the 1980s and CL images are presented here, where the individual wires of a 450 nm grating are resolved. V-grooved quantum wires (QWRs) were fabricated in the 1990s and the structures exhibit a number of emission peaks. CL is used to identify the spatial origin of the various peaks, including the positions of individual impurities in the QWRs. Nanowires from the 2000s show some variations along the length, which are presented here.     

Structural study of titanium oxide films synthesized by ion beam-assisted deposition

The application of titanium dioxide (TiO(2)) films as surgical implant coatings for antibiotic attachment depends crucially on their available surface area and thus their surface morphology and crystallinity. Here, we report our fabrication of high Wenzel ratio TiO(2) films targeted to increase the film surface area using the ion beam-assisted deposition (IBAD) technique at high-deposition temperatures (approximately 610 degrees C). The modulation of the films' surface morphology was accomplished by varying the chemical identity of the concurrent ion beams bombarded on the films during the e-beam evaporation process. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) were employed to investigate the surface morphology of the as-deposited films. X-ray diffractometry (XRD) revealed that these nanocrystalline films primarily consist of anatase phase TiO(2). Wenzel ratio, the ratio of the actual surface area to the projected area, of IBAD films prepared with argon, oxygen, and nitrogen ion beams was measured to be 1.52, 1.31 and 1.49, respectively. The effect of the differences in chemical reactivity and ion size of these three type ion beams are discussed to explain the present results.     

The morphology and composition of cholesterol,protein, and bilirubin deposits in dried human bile: Cathodoluminescence and backscattered electron imaging

This work is the first to deal with the application of color cathodoluminescence scanning electron microscopy (CCL SEM) and a novel version of combined imaging with backscattered electrons (CCL+BSE SEM) for the study of the composition of bile and its precipitation mechanisms. The present study demonstrates cholesterol, protein, and bilirubin distribution in deposits of normal and abnormal humanbile after solution evaporation to full dryness. Qualitative CCL SEM analysis showed that dried bile remnants include different proportions of the above components. Three types of deposits were observed: Arborescent crystals, typical cholesterol crystals, and amorphous bilirubin particles. The selection of crystalline or amorphous precipitate phases is determined by the dehydration/concentration process. The findings may explain key features in lithogenesis.     

Cathodoluminescence and transmission electron microscopy of an abrupt lateral junction in algaas grown by molecular beam epitaxy

We present evidence for a novel type of junction, lateral to the growth direction, in AlGaAs grown by molecular beam epitaxy. Cathodoluminescence data show an abrupt change in the bandgap of AlGaAs grown in grooves on a GaAs substrate at the boundary between adjacent facets. Transmission electron microscopy of a cross section of the groove reveals an unexpected quasiperiodic compositional modulation on the (111) facets of the grooves. The transition in the bandgap occurs as a result of abrupt termination of the compositional modulation at the facet boundaries.     

Color cathodoluminescence-scanning electron microscopy study of the 4H-SiC heteroepitaxial layers grown by sublimation “sandwich method”

The color cathodoluminescence scanning electron microscopy (CCL-SEM) technique was used for the study of the 4H-SiC epitaxial layers grown by sublimation “sandwich method” on the 6H- or 21R substrates. Elements of the BIY group were introduced for polytype transformations. The method makes it possible to control the polytype in thin layers (0.1–2 μam). The effect of supersaturation and the growth rate on 4H polytype formation have been studied. It was shown that the probability of polytype transformation depends on the configuration of the substrate surface. At low supersaturation, 4H polytype nuclei arise predominantly on projected areas of the (0001)C substrate surface, which had no growth centers such as screw dislocations.     

空心微纳米结构的制备及应用研究进展

空心微纳米结构材料由于其独特而优异的性质,越来越引起人们的广泛关注,成为材料领域研究的一个热点。本文综述了近年来空心微纳米结构的制备方法,如模板法、水热法、喷雾干燥法、高温溶解法及超声波法等,并介绍了空心微纳米结构的表征手段,如电子显微镜、X射线衍射、X射线光电子能谱及红外光谱等,同时综述了空心微纳米材料在不同领域的应用进展。     

TEM determination of directions of (Ga,Mn)As nanowires grown by MBE on GaAs(001) substrates

The structure of GaMnAs nanowires (NW) with nominal Mn concentration of up to 7 at% was investigated by transmission electron microscopy. The (Ga,Mn)As NW were grown on epiready GaAs(001) n -type wafers by molecular beam epitaxy. The crystal structure of the NW was determined to be zinc-blende. NW with Mn concentrations lower than 5 at% grow along the 〈111〉 direction. NW with higher Mn concentrations grow along the 〈110〉 direction and reveal a branching structure. The main nanowire and branches grow along the 〈110〉 directions belonging to only one {111} plane.     

Nanoscale electrical properties of ZnO nanorods grown by chemical bath deposition

Well‐aligned zinc oxide nanorod arrays (ZNAs) synthesized using chemical bath deposition were fabricated on a gallium‐doped zinc oxide substrate, and the effects of varying the precursor concentrations on the growth and nanoscale electrical properties of the ZNAs were investigated. The as‐synthesized ZNAs were characterized using field‐emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), conducting atomic force microscopy (CAFM), and scanning surface potential microscopy (SSPM). The FESEM and AFM images show that the growth rate in terms of length and diameter is highly sensitive to the precursor concentration. CAFM and SSPM analyses indicate that when concentrations of both the zinc acetate and hexamethylenetetramine solutions were 30 mM, the coverage percentages of the recordable and conducting regions on the ZNA surface were 48.3% and 0.9%, which is suitable for application in resistive random access memory devices.     

半导体激光器高稳定度系统的研究与设计

半导体激光器(LD)随着温度的增加,阈值电流升高,输出功率下降.为了使半导体激光器输出激光功率稳定,设计了激光器高精度稳功率电路,使用功率MOSFET作为电流控制元件,运用负反馈原理调整输出电流,实现对激光器输出功率的控制.试验结果表明,电路设计合理,响应速度快,输出激光功率长期稳定度可以达到0.1%.     

Structural, optical and mechanical properties of nanostructure diamond synthesized by chemical vapor deposition

Nanostructure diamond (NSD) films on Si substrate are prepared by microwave plasma enhanced chemical vapor deposition (MPECVD) using methane and hydrogen as the reactants with two-step negative substrate bias (SB). The dependencies of the NSD film morphology, grains, surface roughness, crystal and bonding structures and hardness on the negative SB at the bias-enhanced growth (BEG) step and substrate temperature during growth have been investigated by conducting atomic force microscopy (CAFM), X-ray diffraction (XRD), Raman spectroscopy and nanoindentation. The hardness of the NSD film is found to be as high as 80 GPa with CAFM average and root mean square roughness of 7 and 9 nm, respectively, under optimal negative SB at the BEG step. From the studies of substrate temperature effect, the hardness of the NSD film is as high as 70 GPa, with average and root mean square CAFM roughness of 9 and 11 nm, respectively, which were obtained at a substrate temperature of 500 °C. In both cases, the film hardness was found to be affected by the size of clusters, which are composed of many small NSD particles, the amount of NSD in an amorphous matrix as well as surface roughness. We also synthesized transparent NSD films by MPECVD under optimized single-step growth conditions on quartz substrates, which are scratched with several micrometers diamond powder. A hardness as high as 60 GPa and a maximum transmittance of 60% in the visible light region are achieved for an NSD coating of 1.0 μm thickness with small surface roughness.     

Tribological characteristics of gold films deposited on metals by ion plating and vapor deposition

Recent work on the graded interface between an ion-plated film and a substrate is discussed as well as the friction and wear properties of ionplated gold. X-ray photoelectron spectroscopy, depth profiling and microhardness measurements were used to investigate the interface. The friction and wear properties of ion-plated and vapor-deposited gold films were studied both in an ultrahigh vacuum system to maximize adhesion and in oil to minimize adhesion. The results of the investigation indicate that the solubility of gold in the substrate material controls the depth of the graded interface. Thermal and chemical diffusion mechanisms are thought to be involved in the formation of the Au-Ni interface. In the Fe-Au graded inter- face, gold was slightly dispersed in the iron and formed only a physically bonded interface. The hardness of the gold film was influenced by the thickness and was also related to the composition gradient between the gold and the substrate. A graded Ni-Au interface exhibited the highest hardness because of an alloy hardening effect. The effects of film thickness on adhesion and friction were established. A minimum coefficient of friction was found in the thin film region. No graded interfaces were detected in this investigation between vapor-deposited gold films and substrates.     

推拉式小车法制备单层硒化钨薄膜

为了提升单层硒化钨（WSe₂）薄膜的制备质量,在传统化学气相沉积（CVD）法制备的基础上进行改进,通过引入推拉式小车来制备单层WSe₂薄膜,从而构造出可以调控沉积区域、精确控制生长时间,并可实现快速降温的生长方式。采用光学显微镜和原子力显微镜来表征制备材料的尺寸、荧光强度、形貌结构等特性,证明了利用推拉式小车法可成功制备出高质量的单层WSe₂薄膜。推拉式小车法可以稳定制备大面积、高质量、单层的WSe₂薄膜,为其在信息、能源、生物等前沿领域的应用提供参考。     

Method for determination of the displacement field in patterned nanostructures by TEM/CBED analysis of split high-order Laue zone line profiles

A method to extract accurate information on the displacement field distribution from split high‐order Laue zones lines in a convergent‐beam electron diffraction pattern of nanostructures has been developed. Starting from two‐dimensional many beam dynamical simulation of HOLZ patterns, we assembled a recursive procedure to reconstruct the displacement field in the investigated regions of the sample, based on the best fit of a parametrized model. This recursive procedure minimizes the differences between simulated and experimental patterns, taken in strained regions, by comparing the corresponding rocking curves of a number of high‐order Laue zone reflections. Due to its sensitivity to small displacement variations along the electron beam direction, this method is able to discriminate between different models, and can be also used to map a strain field component in the specimen. We tested this method in a series of experimental convergent‐beam electron diffraction patterns, taken in a shallow trench isolation structure. The method presented here is of general validity and, in principle, it can be applied to any sample where not negligible strain gradients along the beam direction are present.     

Measuring the randomness of micro- and nanostructure spatial distributions: Effects of scanning electron microscope image processing and analysis

The quantitative characterisation of the degree of randomness and aggregation of surface micro- and nanostructures is critical to evaluate their effects on targeted functionalities. To this end, the methods of point pattern analysis (PPA), largely used in ecology and medical imaging, seem to provide a powerful toolset. However, the application of these techniques requires the extraction of the point pattern of nanostructures from their microscope images. In this work, we address the issue of the impact that Scanning Electron Microscope (SEM) image processing may have on the fundamental metric of PPA, that is, the Nearest Neighbour Index (NNI). Using typical SEM images of polymer micro- and nanostructures taken from secondary and backscattered electrons, we report the effects of the (a) noise filtering and (b) binarisation threshold on the value of NNI as well as the impact of the image finite size effects. Based on these results, we draw conclusions for the safe choice of SEM settings to provide accurate measurement of nanostructure randomness through NNI estimation.     

Repeatability of linear and radial dimension of ABS replicas fabricated by fused deposition modelling and chemical vapor smoothing process: A case study

In this research work, an effort has been made to study the influence of fused deposition modelling (FDM) and chemical vapor smoothing (CVS) process parameters on the selected linear and radial dimension as well as on repeatability of acrylonitrile butadiene styrene (ABS) replicas as a case study. The study highlights that orientation of parts on FDM build platform, part density (part interior style) and interaction between these two parameters significantly affect the accuracy of selected dimensions. Shrinkage has been observed in the selected radial dimension of the prototypes, but there is a positive deviation in the linear dimension from the desired value. The CVS process reduces both the dimensions slightly due to reflow of the material. Optimum parameter settings that were different for both linear and radial dimensions have been investigated using Taguchi’s L18 orthogonal array. The IT grades of ABS replicas prepared by this combined process were found to be consistent with the permissible range of tolerance grades as per ISO standard UNI EN 20286-I (1995) and DIN 16901 for plastic materials. Finally, optimum level of process parameters that simultaneously minimizes the deviation in both the dimensions have been found out using response optimization module of Minitab 17 software and the results obtained have been verified by performing the confirmation experiments.