Takahito Hashimoto

Incipient Space Weathering Observed on the Surface of Itokawa Dust Particles

Laboratory analysis of samples returned from an asteroid establishes a direct link between asteroids and meteorites and provides clues to the complex history of the asteroid and its surface. The reflectance spectra of the most abundant meteorites, ordinary chondrites, are different from those of the abundant S-type (mnemonic for siliceous) asteroids. This discrepancy has been thought to be due to space weathering, which is an alteration of the surfaces of airless bodies exposed to the space environment. Here we report evidence of space weathering on particles returned from the S-type asteroid 25143 Itokawa by the Hayabusa spacecraft. Surface modification was found in 5 out of 10 particles, which varies depending on mineral species. Sulfur-bearing Fe-rich nanoparticles exist in a thin (5 to 15 nanometers) surface layer on olivine, low-Ca pyroxene, and plagioclase, which is suggestive of vapor deposition. Sulfur-free Fe-rich nanoparticles exist deeper inside (<60 nanometers) ferromagnesian silicates. Their texture suggests formation by metamictization and in situ reduction of Fe2+.

Ion-Sensitive Characteristics of an Electrolyte-Solution-Gate ZnO/ZnMgO Heterojunction Field-Effect Transistor as a Biosensing Transducer

Characteristics of an ion-sensitive ZnO/ZnMgO heterojunction field-effect transistor (HFET) with an amine-modified single-crystalline O-polar ZnMgO gate electrode are discussed to develop the application to biosensing transducers. The ion-sensitivity was based on the proton transfer to/from the amino groups on the gate electrode, the amine-modification of which was performed using a silanization technique by immersing the HFET into an aminosilane based solution. Stable operation in electrolyte solution in accordance with the standard FET theory with small hysteresis and small leakage current was confirmed, and the amperometric operation revealed a high pH sensitivity of -20 µA/pH with a reproducible result. A potential application of the ion-sensitive HFET to amperometric biosensing transducers was also demonstrated by immobilizing enzyme molecules of glucose oxidase on the amine-modified gate electrode.

A FIB Micro-Sampling Technique and a Site Specific TEM Specimen Preparation Method

A FIB micro-sampling technique has been developed to facilitate TEM specimen preparation while allowing samples to remain intact. A deep trench is FIB-milled to remove a portion of the sample containing the region of interest. A micromanipulator is employed for the purpose of lifting out a small portion of the sample, i.e., the micro-sample. FIB assisted metal deposition is used to bond the micro-sample to the micromanipulator. The micro-sample is subsequently lifted out and mounted onto an edge of the micro-sample carrier using FIB assisted metal deposition. The micro-sample is then thinned to the thickness of about 0.1µm for TEM observation. All of the above steps are accomplished under vacuum in the same FIB system. This procedure is a reliable TEM specimen preparation technique when the evaluation or failure analysis of a specific site is required. Both cross sectional and plan view TEM specimen preparations are feasible with this technique. In addition, a technique to prepare TEM specimens from a specific site has also been developed. In this technique, an FIB system equipped with a FIB/TEM(STEM) compatible specimen holder is used for thinning of the samples, e.g., a micro-sample. The compatible specimen holder permits repeated alternating FIB milling and TEM(STEM) observation, enabling TEM specimen preparation from a specific site.

Characteristics of Enzyme-Based ZnO/Zn0.7Mg0.3O Heterojunction Field-Effect Transistor as Glucose Sensor

The characteristics of an enzyme-based ZnO/Zn0.7Mg0.3O heterojunction field-effect transistor (HFET) for glucose sensing are reported. The enzyme glucose oxidase (GOD) was immobilized on an amine-modified gate electrode of the ZnO/Zn0.7Mg0.3O HFET, and glucose sensing was performed by detecting biocatalytically yielded protons using an ion-sensitive function of the gate electrode. The chemical bonding states of the amine-modified and GOD-immobilized surfaces were analyzed by X-ray photoemission spectroscopy, and the enzyme activity of GOD was examined by a colorimetric method. In agreement with the promising results of these experiments, this enzyme-based HFET exhibited stable sensing performance with a linear response in a wide range of glucose concentrations from 0 to 4 mgcm-3 and at a short time constant less than 20 s.

Chapter 4 – Hitachi's Development of Cold-Field Emission Scanning Transmission Electron Microscopes

Publisher Summary This chapter describes Hitachis efforts to develop cold-field emission (CFE) technology and scanning transmission electron microscope (STEMs). The chapter introduces cutting-edge application data obtained with the latest CFE-STEMs, highlights Hitachis contributions to field emission (FE) technology development, and shows how the knowledge gained has been passed from generation to generation at Hitachi. The chapter also shows how CFE scanning electron microscopes (SEM)/ STEM technologies were established. The fusion of TEM technology by Hitachi started before World War II, and the CFE technology introduced by Crewe played an important role in Hitachis development of FE-STEMs. These were not fortuities. The very strong enthusiasm of the researchers and designers at Hitachi met the challenge to develop the worlds highest performance STEMs. Their enthusiasm enabled Hitachi to develop various types of STEMs, from the 50-kV STEM in 1975 to the latest HD-2700 dedicated STEM. Along the way, M. Haider and H. Rose developed Cs-correction technology and it was introduced into the HD-2700. The result was elemental and chemical-bonding–state mapping and high-resolution STEM image observation at an atomic order. These microscopes contributed to the fine structure analysis of nano-materials, nano-electronic devices, and nano-biomaterials in various fields. CFESTEMs have become an essential analytical tool in many fields.

Spherical-aberration-free observation of TEM images by defocus-modulation image processing

Abstract Defocus-modulation image processing has been applied to correct the spherical aberration in transmission electron microscopic images. The correction procedure is performed by off-line integration of through-focus images with bipolar weighting functions. An electron microscope with a field emission gun, the HF-2000, was used in this experiment. The Thon diagrams constructed by plotting the power spectra of the processed images as a function of virtual defocus value clearly demonstrate that the spherical aberration was corrected very well, leading to the marked improvement of the resolution from 3.7 to 5.8 nm -1 . As a novel approach to assess the information limit more accurately, we have represented the Thon diagrams for the amplitude and phase components separately. The presented results reveal that this approach is of practical use even for thicker samples which cannot be treated as weak phase objects.

Transmission Electron Microscope Sample Shape Optimization for Energy Dispersive X-Ray Spectroscopy Using the Focused Ion Beam Technique

By utilizing the focused ion beam (FIB) technique, we evaluated signal intensity ratios of analyzed areas and the matrix for energy dispersive X-ray spectroscopy with a transmission electron microscope (TEM-EDX). In the case of conventional FIB samples (H-shape), electrons scattered from the thin film area irradiate the sidewalls of the matrix (Si substrate) under the thin film position and they generate a large number of X-rays. These matrix signals are reduced by making samples as U-shaped and removing the underlying sidewalls. The final matrix (Si) X-ray signal is reduced by 90% compared with the conventional H-shaped samples.

Development of Two Steradian EDX System for the HD-2700 FE-STEM Equipped with Dual X-MaxN 100 TLE Large Area Windowless SDDs

The model HD-2700 [1] 200 kV spherical aberration (Cs) corrected dedicated Scanning Transmission Electron Microscope (STEM) has been used for analyzing nanoto subnano-area targets in the fields of nanoscience and nanotechnology with Energy Dispersive X-ray spectrometry (EDX). The Cs corrector [2] enables the formation of sub-nanometer probe size with several hundred to a thousand pico amperes of probe current, but still EDX detectors with much higher sensitivity are desired. Recent adaptation of Silicon Drift Detector (SDD) technology [3] accelerated the counting rate of detection and enhancement of detector active area. These features are suitable to improve analytical sensitivity. Using a windowless high solid angle SDD, high sensitivity elemental analysis can be achieved [4].

High-precision image-drift-correction method for EM images with a low signal-to-noise ratio.

The phase correlation method (PCM) is well known for high-precision matching between images. However, if the signal-to-noise ratio of an image is low, the method is difficult to apply. To solve this problem, we developed an improved PCM that can match images automatically with sub-pixel matching precision. Using this method, a 0.2-nm crystal lattice spacing was clearly revealed after 10 blurred images were processed in a verification experiment; such a lattice could not be recognized or hardly be recognized in each individual image.

Mineralogy of four Itokawa particles collected from the first touchdown site

Four Itokawa particles collected from the first touchdown site were mineralogically investigated by optical microscopy, micro-Raman (μ-Raman) spectrometry, scanning electron microscopy (SEM), electron microprobe analysis (EPMA), X-ray absorption spectroscopy (XAS), and transmission electron microscopy (TEM). Their mineralogy has an affinity to that of LL6 chondrites based on micro-Raman spectroscopy, EPMA, and XAS analyses. However, the space weathering rims on them are less developed than those observed on the Itokawa particles collected from the second touchdown site. Solar flare tracks are rarely observed in the four particles, whose number densities were lower than those observed in the Itokawa particles from the second touchdown site.