Showing papers by "Hiroshi Yamaguchi published in 2006"

NMR Spectroscopic Study of a DNA Duplex with Mercury-Mediated T-T Base Pairs

Abstract: Recently, we reported that T-T mismatches can specifically recognize Hg(II) (T-Hg(II)-T pair formation). In order to understand the properties of the T-Hg(II)-T pair, we recorded NMR spectra for a DNA duplex, d(CGCGTTGTCC).d(GGACTTCGCG), with two successive T-T mismatches (Hg (II)-binding sites). We assigned 1H resonances for mercury-free and di-mercurated duplexes, and performed titration experiments with Hg(II) by using 1D 1H NMR spectra. Because of the above mentioned assignments, we could confirm the existence of mono-mercurated species, because individual components gave independent NMR signals in the titration spectra.

Proposal of Carbon Nanotube Inductors

Abstract: The inductors made of carbon Nanotube (CNT) have been proposed. Though the fabrication of the proposed inductor is still challenging and has many problems, merits of the proposed inductor are following, (i)The magnetic field induced by the current in CNT is about one thousand times larger than that induced by the current in normal copper wire. (ii)The large magnetic field results in the large inductance, according to the relation between magnetic field and inductance. (iii)The inductor made of CNT is smaller than the inductor in IC circuits, because CNT can be bent with small curvature.

Impurity conduction in phosphorus-doped buried-channel silicon-on-insulator field-effect transistors at temperatures between 10 and 295 K

Abstract: We investigate transport in phosphorus-doped buried-channel metal-oxide-semiconductor field-effect transistors at temperatures between 10 and $295\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. We focus on transistors with phosphorus donor concentrations higher than those previously studied, where we expect conduction to rely on donor electrons rather than conduction-band electrons. In a range of doping concentration between around 2.1 and $8.7\ifmmode\times\else\texttimes\fi{}{10}^{17}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}$, we find that a clear peak emerges in the conductance versus gate-voltage curves at low temperature. In addition, temperature dependence measurements reveal that the conductance obeys a variable-range-hopping law up to an unexpectedly high temperature of over $100\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. The symmetric dual-gate configuration of the silicon-on-insulator we use allows us to fully characterize the vertical-bias dependence of the conductance. Comparison to computer simulation of the phosphorus impurity band depth profile reveals how the spatial variation of the impurity-band energy determines the hopping conduction in transistor structures. We conclude that the emergence of the conductance peak and the high-temperature variable-range hopping originate from the band bending and its change by the gate bias. Moreover, the peak structure is found to be strongly related to the density of states (DOS) of the phosphorus impurity band, suggesting the possibility of performing a spectroscopy for the DOS of phosphorus, the dopant of paramount importance in Si technology, through transport experiments.

Carbon Multiprobe on a Si Cantilever for Pseudo-Metal-Oxide-Semiconductor Field-Effect-Transistor

Abstract: A newly developed scanning probe microscopy system with multiple probes has been applied to measurements of local electrical properties of semiconductor films. Carbon multiprobes fabricated by focused ion beam deposition on a Si cantilever were used for source and drain electrodes on a pseudo-silicon-on-insulator (SOI) metal–oxide–semiconductor (MOS) field-effect-transistor (FET) on which the Si substrate and buried oxide (BOX) act as a gate electrode and gate insulator, respectively. The pseudo-MOSFET characteristics of a 10-nm-thick Si layer on an SOI substrate were successfully measured using the multiprobe. Furthermore, a carbon film deposited by electron cyclotron resonance (ECR) plasma sputtering on a Si substrate with an oxide layer was confirmed as a semiconductor for the first time, using the pseudo-FET method with a carbon multiprobe. The results clearly demonstrate that this multiprobe system can be a powerful and widely applicable tool for measuring local device characteristics of electrical materials.

Electron phase modulation in a suspended InAs∕AlGaSb nanomechanical beam

Abstract: The magnetopiezoresistance in a quasi one-dimensional electron system incorporated into an InAs∕AlGaSb nanomechanical suspended beam was measured while the beam was at mechanical resonance. The magnetopiezoresistance showed reproducible highly periodic resistance oscillations which arise via strain induced electron phase modulation. The Fourier transform of the magnetopiezoresistance indicates that mechanical activation of the beam affects only a few electron trajectories and the electron interference in only a single electron loop gives rise to the resistance oscillations in the magnetopiezoresistance.

Transfer and Detection of Single Electrons using Metal-Oxide-Semiconductor Field-Effect-Transistors

Abstract: A single-electron turnstile and electrometer circuit was fabricated on a silicon-on-insulator substrate. The turnstile, which is operated by opening and closing two metal-oxide-semiconductor field-effect transistors (MOSFETs) alternately, allows current quantization at 20 K due to single-electron transfer. Another MOSFET is placed at the drain side of the turnstile to form an electron storage island. Therefore, one-by-one electron entrance into the storage island from the turnstile can be detected as an abrupt change in the current of the electrometer, which is placed near the storage island and electrically coupled to it. The correspondence between the quantized current and the single-electron counting was confirmed.

Structural analyses on the mercuryII-mediated T-T base pair.

Abstract: Recently, it was reported that T-T mismatches can specifically recognize Hg(II), and form T-Hg(II)-T pairs. In order to understand the structure and properties of the T-Hg(II)-T pair, we measured NMR spectra for a DNA duplex, d(CGCGTTGTCC) x d(GGACTTCGCG), with two successive T-T mismatches (Hg(II)-binding sites) in the middle of the duplex. We identified imino proton resonances of the T-T mismatches in mercury-free duplex, and performed titration experiments with Hg(II) by using 1-dimensional (1D) (1)H NMR spectra. From the titration spectra, disappearances of imino proton signals were observed upon the addition of Hg(II). Furthermore, we observed additional signals of transient species, most likely mono-mercurated duplexes. This is an evidence that structural transformations between Hg(II)-free and Hg(II)-bound forms are slow enough for each species to give independent signals. These data strongly suggest that the imino protons of thymine bases were substituted with Hg(II), to form T-Hg(II)-T pairs in which one Hg(II) cross-links two N3 atoms of thymines.

High field magnetization and multi-frequency ESR in the spin-ladder compound Na2Fe2(C2O4)3(H2O)2

Abstract: We have performed high field magnetization and multi-frequency electron spin resonance (ESR) measurements on single crystal and powder samples of Na2Fe2(C2O4)3(H2O)2, abbreviated as SIO. The Fe2+ ions in SIO are bridged by oxalate groups to make two-leg ladders. The temperature dependence of magnetic susceptibilities parallel and perpendicular to the leg direction show very different and anisotropic behavior. Experimental results of the isomorphous compound Na2Co2(C2O4)3(H2O)2 (SCO) are well explained by isolated magnetic dimers with an Ising-type anisotropy. Therefore, we analyze the frequency dependence of the ESR resonance fields by the same model with a fictitious spin 1 as in SCO. The agreement between experiment and calculation is satisfactorily good. Magnetic susceptibility and magnetization curves calculated with the same parameters obtained in the ESR analyses, however, do not agree well with the experimental ones. This indicates the presence of the exchange interaction between the dimers, namely the interaction along the leg.

Micromechanical Quantum Electron Transport

Abstract: We have studied quantum effects on the piezoresistance (PR) of various kinds of low-dimensional heterostructures. The PR is strongly enhanced by electron interference in Q1D electron systems, by Landau qunatization in 2DEG systems, and also by the localizeddelocalized electronic state transition in quantum Hall systems. We have also studied PR for superconductor/semiconductor junctions and found that PR was enhanced at the critical current. In each system, the nonlinear response of device conductance against the change of magnetic field or bias current is responsible for the resistance change against the strain.

Association of Nephrin Gene Polymorphisms With Type 2 Diabetes in a Japanese Population

Abstract: Nephrin is a major component of the glomerular filtration barrier, and its expression was at first thought to be specific to kidney glomerular podocytes (1). However, it was later found in nonrenal tissues, such as the pancreas (2–4), as well. Several studies (2,3,5) have shown the expression of nephrin in human pancreatic islet cells. Therefore, nephrin may play some roles in the pancreatic islet and, thus, may be involved in the pathophysiology leading to diabetes. We here examined the association of the nephrin gene polymorphisms with type 2 diabetes. The associations of three single nucleotide polymorphisms (SNPs) (C294T, −61C/G, and C2289T) of the nephrin gene with diabetes were examined using two (first and second) sample sets (diabetes, n = 72 and 31, respectively; impaired glucose tolerance [IGT], n = 75 and 77, respectively; and normal glucose tolerance [NGT], n = 227 and 244, respectively) from the cohort population of the Funagata Study, a Japanese community-based study (6). The study conditions were the same as those in our previous report (7). Three SNPs in the nephrin gene (C to T at nucleotide position 294 in exon 3 from the translation intitiation codon ATG (C294T) (JSNP database ID: IMS-JST 035656), C to G in intron 5 at nucleotide position 61 upstream from the intron 5/exon 6 splicing site …

Transfer and Detection of Single Electrons using Metal-Oxide-Semiconductor Field-Effect-Transistors(Session 8B Emerging Devices and Technologies II,AWAD2006)

Abstract: A single-electron turnstile and electrometer circuit was fabricated on a silicon-on-insulator substrate. The turnstile, which is operated by opening and closing two metal-oxide-semiconductor field-effect transistors (MOSFETs) alternately, allows current quantization at 20 K due to single-electron transfer. Another MOSFET is placed at the drain side of the turnstile to form an electron storage island. Therefore, one-by-one electron entrance into the storage island from the turnstile can be detected as an abrupt change in the current of the electrometer, which is placed near the storage island and electrically coupled to it. The correspondence between the quantized current and the single-electron counting was confirmed.

Giant magnetopiezoresistance at the localized-extended electronic state transition in a high-mobility 2DEG system

Abstract: A high-mobility two-dimensional electron gas system with a Hall-bar geometry was integrated in a micromechanical cantilever to measure the piezoresistance, i.e., the resistance change induced by the deflection of the cantilever in the quantum Hall regime. The piezoresistance was strongly enhanced at the transition between the localized and extended states, and we obtained a piezoresistive gauge factor as large as 25,000. This “giant magnetopiezoresistance” is caused by the strong strain effect on the electronic state transition and the cantilever will lead to highly sensitive force and displacement sensors at low temperature. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

A piezoresistive cantilever integrating an InAs-based semiconductor–superconductor junction

Abstract: Targeting highly sensitive displacement and force sensors, we fabricated a piezoresistive cantilever that integrates a superconductor–semiconductor–superconductor (S–Sm–S) junction based on an InAs/AlGaSb heterostructure. The S–Sm–S junction is composed of a submicron Nb gap patterned on the InAs thin film, and a deflection of the cantilever is detected as a resistance change at the junction. We confirmed that the resistance change caused by induced strain (i.e., piezoresistance) has a strong dependence on bias current. When the maximum Josephson current ( I c ) is biased to the junction, the resistance change is significantly enhanced by more than a factor of 10 compared to that at the bias current above I c (the resistive state). The resulting maximum resistance change is 3.9 m Ω , which is three orders of magnitude larger than that obtained for our preliminary sample. This large piezoresistance at the S–Sm–S junction will lead to highly sensitive self-detective sensors.

Enhanced emission of single quantum dot formed by interface fluctuations in photonic-crystal microcavities

Abstract: We fabricated photonic-crystal (PhC) microcavities tuned to GaAs quantum dots (QDs) formed by interface fluctuation for the first time and observed the spontaneous emission enhancement in a weak coupling regime A QD is a very thin GaAs quantum well (QW), and its interface steps exhibit quantum dot-like behavior The emission intensity from the PhC cavity was stronger than that from the area where no PhC pattern was fabricated and the overall shape of the photoluminescence (PL) agreed with the cavity mode calculated with the three-dimensional (3D) finite-difference time domain (FDTD) method The spontaneous emission enhancement factor was 10

Device Linearity Comparison of Uniformly Doped

Abstract: fore [5], [6]. However, no paper on the linearity performance of these two kinds of HEMTs has ever been reported. The In0.52Al0.48As/In0.6Ga0.4As MHEMTs with different doping profiles are studied in this letter for device linearity comparison. Fig. 1 shows the two kinds of device structures studied: one with uniform doping in the In0.3Al0.7As layer and another one with δ doping between the In0.3Al0.7As and In0.52Al0.48As layers. These wafers were grown by molecular beam epitaxy (MBE) on 3-in GaAs substrates with a InAlAs-graded metamorphic buffer. The In0.52Ga0.48As layer was used as the cap layer with a doping concentration of 3 × 10 18 cm −3 to get good ohmic contacts. The In0.3Al0.7As Schottky layer has high etch selectivity with the In0.52Ga0.48As cap layer, which provides excellent gate recess uniformity. Dual channels with In0.52Al0.48As spacer layers are designed to increase the current density, provide uniform electron distribution, and improve the device linearity [4], [7].