Atsushi Muto

Effect of one monolayer of surface gold atoms on the epitaxial growth of InAs nanowhiskers

This letter shows that selective heteroepitaxy of nanometer‐scale InAs whiskers on SiO2‐patterned GaAs substrates [Yazawa, Koguchi, and Hiruma, Appl. Phys. Lett. 58, 1080 (1991)] is induced by surface contamination with Au resulting from the fluorocarbon plasma etching process used to etch the SiO2 mask. We demonstrate that high densities (≂1010/cm2) of InAs nanowhiskers 20–30 nm in diameter can be epitaxially grown on InAs(111)B substrates onto which 1 monolayer of Au atoms had been deposited. This wirelike growth appears to be induced by ultrafine alloy droplets generated by the reactions between Au‐clusters and InAs substrates.

Comparison of Electron Imaging Modes for Dimensional Measurements in the Scanning Electron Microscope.

Dimensional measurements from secondary electron (SE) images were compared with those from backscattered electron (BSE) and low-loss electron (LLE) images. With the commonly used 50% threshold criterion, the lines consistently appeared larger in the SE images. As the images were acquired simultaneously by an instrument with the capability to operate detectors for both signals at the same time, the differences cannot be explained by the assumption that contamination or drift between images affected the SE, BSE, or LLE images differently. Simulations with JMONSEL, an electron microscope simulator, indicate that the nanometer-scale differences observed on this sample can be explained by the different convolution effects of a beam with finite size on signals with different symmetry (the SE signals characteristic peak versus the BSE or LLE signals characteristic step). This effect is too small to explain the >100 nm discrepancies that were observed in earlier work on different samples. Additional modeling indicates that those discrepancies can be explained by the much larger sidewall angles of the earlier samples, coupled with the different response of SE versus BSE/LLE profiles to such wall angles.

Environmentally induced chemical and morphological heterogeneity of zinc oxide thin films

Zinc oxide (ZnO) thin films have been reported to suffer from degradation in electrical properties, when exposed to elevated heat and humidity, often leading to failures of electronic devices containing ZnO films. This degradation appears to be linked to water and oxygen penetration into the ZnO film. However, a direct observation in the ZnO film morphological evolution detailing structural and chemical changes has been lacking. Here, we systematically investigated the chemical and morphological heterogeneities of ZnO thin films caused by elevated heat and humidity, simulating an environmental aging. X-ray fluorescence microscopy, X-ray absorption spectroscopy, grazing incidence small angle and wide angle X-ray scattering, scanning electron microscopy (SEM), ultra-high-resolution SEM, and optical microscopy were carried out to examine ZnO and Al-doped ZnO thin films on two different substrates—silicon wafers and flexible polyethylene terephthalate (PET) films. In the un-doped ZnO thin film, the simulated ...

Correlative Fluorescence and Scanning Electron Microscope Imaging of Cultured Neurons Pretreated with Ionic Liquid

Ionic liquids are organic salts that are liquid at room temperatures; some are non-volatile and have high ionic conductivity. HILEM IL1000 (Hitachi High-Technologies) is an ionic liquid designed for use in electron microscopy (Fig. 1) [1]. It is stable under vacuum, conductive, hydrophilic and hyperosmotic, while also being inert and chemically safe [2]. Furthermore, it has the unique capability to maintain wet samples in a “hydrated” state under vacuum conditions. IL1000 has been applied to biological samples including bacteria, yeast, fungi and hard-shelled organisms such as worms and shrimp for successful imaging of fine morphologies [3, 4]. We now report the application of IL1000 to the traditionally difficult process of SEM imaging of neuronal cultured cells.

Comparison of Secondary, Backscattered and Low Loss Electron Imaging for Dimensional Measurements in the Scanning Electron Microscope

In many research and production environments, a great deal of dimensional metrology, characterization and process control is accomplished using scanning electron microscopes (SEM). The accuracy of these SEM measurements has always been important, but is often overshadowed by two other main measurement drivers: throughput and precision. It is slow and often tedious to achieve accuracy and, so it is often ignored, especially in the production environment. Accuracy of a measurement is becoming more of an abiding concern as sub-10 nm semiconductor structures are routinely produced. Hence, the metrology error budget has shrunk, and has become atomic scale. Clever new measurement and signal collection methods applied to sub-10 nm metrology must be sought for all types of semiconductor nanostructures, nanomaterials and nano-enabled materials to ultimately achieve the needed accurate measurements.

A Study of the Behavior of SE and BSE in UltraLow Landing Voltage Condition

In the study, we set our motivation to consider the mechanism to explain such an interesting phenomena particularly happened at the ultra low voltage situation. At first we gathered a set of SE and BSE images simultaneously at ultra low voltage condition from various kinds of specimen. Second, we compared the SE and BSE image to investigate the difference. A simulation results by CASINO [3] was also applied for the theoretical consideration. In the study the recent cold FE-SEM (Hitachi SU8000) is used. The SEM is offering the SE/BSE filtering capability even at ultra low voltage condition as shown in Fig.1.

A Study of Beam Sensitive Materials Using High Resolution, ULV Scanning Electron Microscopy

Low voltage scanning electron microscopy has become common both for topmost surface imaging and reducing beam damage [1]. Lately, high resolution, ultra-low-voltage (ULV) imaging (less than 500 V) has been realized by beam retarding [2] and/or boosting [3] techniques. In this study, some beam sensitive materials are observed by the Hitachi S-4800, which employs a cold field emission source, snorkel type objective lens and a retarding function [4].

Correlative Characterization of Graphene with the Linkage of SEM and KFM

Graphene has been one of the most attractive and promising materials because of its unique material properties and potential applications. Its properties depend strongly on the number of layers, so the reliable examination method to determine its thickness has been required [1]. ULV (Ultra low voltage) SEM (scanning electron microscopy) is one of the possible methods for determining its thickness by clarifying layer-sensitive images of graphene. To explore further into the mechanism of the SEM contrast on graphene images, it has been explained that the difference of thickness causes the difference of surface potential that can affect the SE (secondary electron) signal intensity [2]. It has also reported that the effect of the thickness of graphene layers on its surface potential was detected by AFM-based technique KFM (Kelvin force microscopy) [3]. In this study, we developed the linkage system of SEM and AFM with compatible sample holder with correlation technology between SEM, AFM, and KFM image at the same area of interest to reveal the relationship between SEM contrast, its height, and surface potential.

Investigation of Image Contrast of Energy-Filtered BSE Image at Ultra Low Voltage

To meet the increasing demands to clarify the compositional differences in advanced composite materials, we reported a new imaging method using energy filtered BSE signals at Ultra Low Voltages (ULV) [1][2]. This method was applied to carbon nanotube (CNT) and polytetrafluoroethylene (PTFE) composite films to confirm its ability to differentiate distribution of CNT and PTFE components at 0.3 kV as shown in Figure 1. We confirmed that the difference of surface potential affects the contrast between CNT and PTFE more strongly than the differences of average atomic number and surface morphology for this specimen. To apply this method to any other materials, it will be necessary to investigate the effect of the difference in average atomic number and surface morphology on the contrast because the signal behavior under ULV condition does not follow the conventional theory used over 1 kV [3]. In this study, we investigated the effect from the difference of average atomic number by fundamental experiments and simulation techniques.