Papers by Masaki Takeguchi
The Japan Society of Applied Physics, Jul 6, 2021
Digest of Papers. Microprocesses and Nanotechnology '99. 1999 International Microprocesses and Nanotechnology Conference
Ge nanoparticles smaller than 4 nm in diameter were deposited on Si TEM samples and directly tran... more Ge nanoparticles smaller than 4 nm in diameter were deposited on Si TEM samples and directly transferred into TEM using a UHV-MBE-TEM system. The structure of some nanoparticles was different from diamond structure. Some Ge nanocrystals even become amorphous and then fluctuate during HRTEM observation.
AIP Advances, 2022
AlN layers were grown on a c-plane sapphire substrate by metal–organic vapor phase epitaxy (MOVPE... more AlN layers were grown on a c-plane sapphire substrate by metal–organic vapor phase epitaxy (MOVPE) at 1350 °C. The structural quality of the grown AlN layers was drastically improved by post-growth annealing in mixed hydrogen, ammonia, and trimethylgallium ambiance at 1350 °C. As a first step, we grew the AlN layers exhibiting a double-domain structure with an in-plane rotation angle of ∼4°. Then, the domain structure was changed from double to single by the post-growth annealing. After 20 min post-growth annealing, the surface possessed an atomically flat step-and-terrace structure with a root-mean-square value of ∼0.11 nm measured across 5 × 5 µm2. The full-width at half maximum values for 0002 and 101̄4 AlN reflections using x-ray diffraction were as small as ∼75 and ∼280 arcsec, respectively. Since this work provides a simple continuous MOVPE growth procedure to improve the structural quality of AlN/sapphire, it is advantageous to the industrial fabrication of AlxGa1−xN-based ul...
Science, 2021
Straining to make a transistor The use of carbon nanotubes (CNTs) as short-channel-length transis... more Straining to make a transistor The use of carbon nanotubes (CNTs) as short-channel-length transistors will require control of their chirality, which determines whether they are semiconducting or metallic and if they form strong, low-resistance contacts. Tang et al . fabricated CNT intramolecular transistors by progressive heating and straining of individual CNTs within a transmission electron microscope. Changes to chirality along sections of the nanotube created metallic-to-semiconducting transitions. A semiconducting nanotube channel was covalently bonded to the metallic nanotube source and drain regions. The resulting CNT intramolecular transistors had channel lengths as short as 2.8 nanometers. —PDS
Journal of Surface Analysis, 2019
The reduction process of the Fe2O3 (α-hematite) by Si was investigated with in-situ transmission ... more The reduction process of the Fe2O3 (α-hematite) by Si was investigated with in-situ transmission electron microscopy (TEM). Hematite and other iron oxides are main component of iron ore and Si is main gangue elements of iron ore. Si reduced hematite and Fe precipitated around 700℃. The electrons due to TEM(=200keV) was not necessary condition of Fe precipitation and grew until run out of Si. The residual Si reacted with precipitated Fe after a certain period of time of electron irradiation. The reaction completed very short time less than one frame of video. One of the reacted material was identified as α-FeSi2. These results indicated that the possibility of new ironmaking without CO2 emission and silicide formation.
The Japan Society of Applied Physics, 2016
Ptychographcal iterative phase retrievalは、回折顕微法(Diffractive imaging)の一種であり、条件 の異なる回折像のセットから反復的な手法... more Ptychographcal iterative phase retrievalは、回折顕微法(Diffractive imaging)の一種であり、条件 の異なる回折像のセットから反復的な手法により位相を回復するもので、回折顕微法で必要とさ れる試料周りの“サポート”と呼ばれる既知領域が不要な事や、複数の回折像から位相回復する ために解の収束性や安定性が高いなどの特徴を持ち、特に X 線を用いた応用例が多く報告されて いる。電子線を用いた場合、X 線とは異なり、走査透過環状暗視野法(ADF-STEM)などにより 実像を得ることが可能である。 本研究では、この像を反復的に位相回復する際の拘束条件の一 つとして用いる事により、Ptychographcal phase retrievalのアーティファクトの低減や収束性の向上 を目的とする。 なお、回折顕微法に於いては、Yamasaki らが、低倍の像を拘束として用いる手 法を提案しており 、本研究はそのアイディアを、Ptychographcal phase retrievalへ応用したもので ある。 図に再構成された位相の例を示す。試料は金を蒸着したカーボン支持膜を用い、5×5点のプ ローブ位置に於いて、回折像を取得し、再構成 を行った。(a)は、ADF-STEM 像であり、再構 成する際の物体の振幅を拘束するために用い た。 (b)は通常の再構成結果であり、(c)は像 による拘束を加えた結果である。 (b)の通常 の再生ではスキャン位置が周期的であること に起因するアーティファクトが真空領域に現 れているが、(c)では、実像拘束によってそれら のアーティファクトが低減されている。
Bulletin of the American Physical Society, 2017
Submitted for the MAR17 Meeting of The American Physical Society Monolayered copper based film. E... more Submitted for the MAR17 Meeting of The American Physical Society Monolayered copper based film. Experimental observation and theoretical investigation.
physica status solidi (RRL) – Rapid Research Letters, 2020
Chalcogenide materials play essential roles in modern nonvolatile memory technology in the form o... more Chalcogenide materials play essential roles in modern nonvolatile memory technology in the form of both phase‐change memory (PCM) and selector devices. Herein, Bi–Te binary alloys are explored as an alternative candidate for superlattice (SL) or interfacial PCM (iPCM). GeTe/Bi4Te3 (GT/BT) SL exhibits similar structural features to conventional GeTe/Sb2Te3 (GT/ST) SL, such as highly oriented crystal grains and intermixing. Furthermore, preliminary device measurements show that Ge–Bi–Te (GBT) SL switches in a similar manner to conventional Ge–Sb–Te (GST), suggesting that they may be a promising candidate for memory applications. In addition, Bi2Te3/Sb2Te3 (BT/ST) heterostructure films have been successfully fabricated and show clear interface stacking at the atomic level. Although the BT/ST heterostructure is ostensibly a p–n junction, rectifying behavior is not observed in current (I)–voltage (V) measurements due to the existence of a large number of carriers in both layers. Finally,...
Journal of Surface Analysis, 2019
Japanese Journal of Applied Physics, 2019
The demand for nanoscale strain mapping is increasing with the spread of nanotechnologies. Tradit... more The demand for nanoscale strain mapping is increasing with the spread of nanotechnologies. Traditional macroscale strain measurement methods do not have the required spatial resolution, and well-known transmission electron microscopy methods often encounter difficulties that limit their practical application. We evaluate a stage-scan strain mapping method based on nanosized selected area electron diffraction. Two-dimensional scanning of the sample and simultaneous acquisition of diffraction patterns at fixed beam conditions enable the comparison of interplanar distances measured at different places. Accurate determination of the lattice constant changes becomes possible owing to the two-dimensional Gaussian fitting used to determine the exact position of diffraction spots. The results obtained by stage-scan mapping agree well with the reference X-ray diffraction data, and are not affected by elliptical distortion of the diffraction pattern. The simplicity and stability of the stage-scan strain mapping method make it complementary to other transmission electron microscopy based methods for strain mapping.
Microscopy and Microanalysis, 2017
Scientific Reports, 2017
Direct growth of graphene integrated into electronic devices is highly desirable but difficult du... more Direct growth of graphene integrated into electronic devices is highly desirable but difficult due to the nominal ~1000 °C chemical vapor deposition (CVD) temperature, which can seriously deteriorate the substrates. Here we report a great reduction of graphene CVD temperature, down to 50 °C on sapphire and 100 °C on polycarbonate, by using dilute methane as the source and molten gallium (Ga) as catalysts. The very low temperature graphene synthesis is made possible by carbon attachment to the island edges of pre-existing graphene nuclei islands, and causes no damages to the substrates. A key benefit of using molten Ga catalyst is the enhanced methane absorption in Ga at lower temperatures; this leads to a surprisingly low apparent reaction barrier of ~0.16 eV below 300 °C. The faster growth kinetics due to a low reaction barrier and a demonstrated low-temperature graphene nuclei transfer protocol can facilitate practical direct graphene synthesis on many kinds of substrates down to ...
Superconductor Science and Technology, 2012
ABSTRACT The internal Mg diffusion (IMD) process produces a high-density MgB2 layer with high cri... more ABSTRACT The internal Mg diffusion (IMD) process produces a high-density MgB2 layer with high critical current properties, which makes it an attractive and promising method for fabricating MgB2 wires. We have obtained high critical current properties in our previous research. However, IMD-processed MgB2 wires can have unreacted B particles remain in the reacted layer due to the long Mg diffusion distance in the B layer during heat treatment. A reduction in the amount of unreacted B particles is expected to enhance the critical current properties. In this study, we attempted to disperse Mg powder in the B layer as an additive in order to decrease the Mg diffusion distance. We found that a 6 mol% Mg powder addition to a B layer drastically decreased the amount of unreacted B particles and enhanced the critical current density to twice the value for IMD-processed MgB2 wire with no Mg powder added. An analysis is presented that relates the microstructure to the critical current density.
Microscopy and Microanalysis, 2010
Extended abstract of a paper presented at Microscopy and Microanalysis 2010 in Portland, Oregon, ... more Extended abstract of a paper presented at Microscopy and Microanalysis 2010 in Portland, Oregon, USA, August 1 – August 5, 2010.
Microscopy and Microanalysis, 2010
Extended abstract of a paper presented at Microscopy and Microanalysis 2010 in Portland, Oregon, ... more Extended abstract of a paper presented at Microscopy and Microanalysis 2010 in Portland, Oregon, USA, August 1 – August 5, 2010.
Uploads
Papers by Masaki Takeguchi