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.
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...
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
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,...
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.
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 ...
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.
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.
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.
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.
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...
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
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,...
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.
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 ...
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.
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.
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