Search

The structure-dependent electronic properties of suspended graphene nanoribbon (GNR) have still been important issues. However, these properties have been rarely investigated experimentally due to technical difficulties to produce high-quality suspended GNRs and the identification of atomic structures. Here, we report the electronic properties of suspended GNRs by in situ transmission electron microscopy observations to simultaneously obtain the structural information while measuring the current-voltage (I-V) curves. The suspended GNRs could be obtained by convergent electron beam nanosculpting after careful cleaning by current annealing. The I-V curves were measured for GNRs with a mixture of both zigzag and armchair edges (MGNR) with widths of 3.7 to 1.9 nm and also zigzag edge GNRs (ZGNR) with widths of 1.7 to 1.2 nm. The I-V curves for the ZGNRs were different from those of the MGNRs, as follows. (1) The ZGNRs showed a sharp increase at the threshold voltage in differential conductance-voltage curves. (2) The band gaps measured for ZGNRs were smaller than the band gaps calculated using the GW approximation. (3) The threshold voltage increased with the GNR length. These findings support magnetic-insulator and nonmagnetic-metal nonequilibrium phase transitions as theoretically predicted. Narrow and short ZGNR represents the potential for further nanosized switching devices.

Pt and PtNi alloy nanoparticle-supported multiwalled carbon nanotubes (Pt/MWCNTs and PtNi/MWCNTs) are prepared by a one-pot pyrolysis method with the N,N,N-trimethyl-N-propylammonium bis(trifluorom...

Recently, visualization of lithium ions has brought great benefit for understanding lithium movement in the cathode, electrolyte and anode materials of lithium ion battery. It has been achieved by several methods such as spherical aberration corrected scanning transmission electron microscopy, multivariable analysis, advanced electron holography and so on, which was reviewed by the special issue, 'Challenges for Lithium Detection' in Microscopy (Vol. 66, No. 1, 2017). In this paper, recent research progress in lithium detection is introduced as a follow-up for the special issue.

Graphene nanoribbons (GNRs) are expected in nanodevices and sensors but are degraded by contaminants that adsorb firmly on the surface during the transfer and lithography processes. Current annealing appears to be the most appropriate cleaning method, but its effects have not been quantitatively clarified. To this end, the cleaning processes of suspended monolayer GNRs were observed by in situ transmission electron microscopy. The gradual cleaning processes, which were successfully observed by improving the contact resistance at graphene-metal interface, showed that the GNRs was cleaned on the atomic scale in the current density range of 2.0–5.0 × 1012 A/m2. The corresponding temperature was estimated to be ∼ 700 K by finite element method. To be surprised, clean monolayer and bilayer GNRs withstood current densities of 5.1 × 1012 A/m2 and 1.7 × 1013 A/m2 (current-carrying capacities), respectively, which values were approximately three orders of magnitude higher than those of typical metals. The higher current-carrying capacity of bilayer GNR can be attributed to the formation of closed edges. This study shows that the electrical current is effective for cleaning GNR and boosting the current-carrying capacity.

We propose a self-similar assembly to generate planar orientation of megamolecular polysaccharides on the nanometer scale and submicron scale. Evaporating the aqueous liquid crystalline (LC) solution on a planar air-LC interface induces polymer layering by self-assembly and rational action of macroscopic capillary forces between the layers. To clarify the mechanisms of nanometer- and submicron-scale layering, the polymer films are investigated by electron microscopy.

Atom-scaled ripple structure can be intrinsically formed because of thermal instability or induced stress in graphene or two-dimensional (2D) materials. However, it is difficult to estimate the period, amplitude, and shape of such a ripple structure. In this study, by applying the geometrical phase analysis method to atomically resolved transmission electron microscopy images, we demonstrate that the atom-scaled ripple structure of MoS2 nanosheet can be quantitatively analyzed at the subnanometer scale. Furthermore, by analyzing the observed ripple structure of the MoS2 nanosheet, we established that it is inclined by approximately 7.1° from the plane perpendicular to the incident electron beam; it had 5.5 and 0.3 nm in period and amplitude, respectively. For quantitative estimation of ripple structure, our results provide an effective method that contributes to a better understanding of 2D materials in the sub-nanometre scale.

Lithium ion batteries are encountering ever-growing demand for further increases in energy density. Li-rich layered oxides are considered a feasible solution to meet this demand because their specific capacities often surpass 200 mAh g−1 due to the additional lithium occupation in the transition metal layers. However, this lithium arrangement, in turn, triggers cation mixing with the transition metals, causing phase transitions during cycling and loss of reversible capacity. Here we report a Li-rich layered surface bearing a consistent framework with the host, in which nickel is regularly arranged between the transition metal layers. This surface structure mitigates unwanted phase transitions, improving the cycling stability. This surface modification enables a reversible capacity of 218.3 mAh g−1 at 1C (250 mA g−1) with improved cycle retention (94.1% after 100 cycles). The present surface design can be applied to various battery electrodes that suffer from structural degradations propagating from the surface., Surface modification of high-capacity lithium-rich layered oxides for improved capacity retention is an active area of battery materials research. Here authors demonstrate lithium-rich layered surfaces with a framework matching the host's, but with nickel atoms regularly arranged between layers.

Graphene nanoribbon is an attractive material for nano-electronic devices, as their electrical transport performance can be controlled by their edge structures. However, in most cases, the electrical transport has been investigated only for graphene nanoribbons fabricated on a substrate, which hinders the appearance of intrinsic electrical transport due to screening effects. In this study, we developed special devices based on silicon chips for transmission electron microscopy to observe a monolayer graphene nanoribbon suspended between two gold electrodes. Moreover, with the development of an in-situ transmission electron microscopy holder, the current–voltage characteristics were achieved simultaneously with observing and modifying the structure. We found that the current–voltage characteristics differed between 1.5 nm-wide graphene nanoribbons with armchair and zigzag edge structures. The energy gap of the zigzag edge was more than two-fold larger than that of the armchair edge and exhibited an abrupt jump above a critical bias voltage in the differential conductance curve. Thus, our in-situ transmission electron microscopy method is promising for elucidating the structural dependence of electrical conduction in two-dimensional materials.

Li 2 RuO 3 (001) films with a lithium-rich layered rocksalt structure are epitaxially grown on a Al 2 O 3 (0001) substrate through pulsed laser deposition, followed by stacking of an amorphous Li 3 PO 4 solid electrolyte. A half solid-state battery with a Li 3 PO 4 /Li 2 RuO 3 cathode, liquid electrolyte, and lithium anode exhibits two redox peak pairs at 3.4 and 3.6 V, demonstrating lithium intercalation in the Li 2 RuO 3 through the Li 3 PO 4 solid electrolyte. All-solid-state batteries are fabricated by Li or In metal anode deposition on the Li 3 PO 4 /Li 2 RuO 3 . The Li/Li 3 PO 4 /Li 2 RuO 3 cell delivers an initial discharge capacity of 101 mAh g −1 , which does not fade significantly over 30 cycles. Furthermore, the Li 2 RuO 3 rate capability is comparable to that of a liquid-type battery. Lithium-rich layered materials are available for use as cathodes in all-solid-state batteries.

Fast charge-discharge process has been reported to give a high capacity loss. A nanobattery consisting of a single LiMn2O4 nanowire cathode, ionic liquid electrolyte and lithium titanium oxide anode was developed for in situ transmission electron microscopy. When it was fully charged or discharged within a range of 4 V in less than half an hour (corresponding average C rate: 2.5C), Li-rich and Li-poor phases were observed to be separated by a transition region, and coexisted during whole process. The phase transition region moved reversibly along the nanowire axis which corresponds to the [011] direction, allowing the volume fraction of both phases to change. In the electron diffraction patterns, the Li-rich phase was seen to have the (100) orientation with respect to the incident electron beam, while the Li-poor phase had the (111̅) orientation. The orientation was changed as the transition region moved. However, the nanowire did not fracture. This suggests that a LiMn2O4 nanowire has the advantage of preventing capacity fading at high charge rates.

A through-focus series of annular bright field (ABF) images were observed simultaneously with high-angle annular dark field (HAADF) images of very thin lithium manganese oxide (LiMn 2 O 4 ), a typical cathode material used in lithium ion batteries, using a spherical aberration corrected electron microscope with a 50 pm resolution (R005). The ABF images showed dark dips at the positions of Li and Mn–O atomic columns, which reversed to bright peaks when the defocus sign was changed, as commonly observed in phase contrast images. The optimal defocus for the ABF images was about 2 nm of over-focus, while that for the HAADF images was 2 nm of under-focus for an incident probe with a convergent semi-angle of 30 mrad. These experimental results are interpreted based on a weak-phase-object approximation.

We developed a “nanobattery” consisting of LiMn2O4 nanowires, ionic liquid electrolyte, and Li4Ti5O12 crystals and performed in situ transmission electron microscope observation during charge and discharge cycles. The LiMn2O4 nanowire was found to be changed into the tetragonal phase at the interface region with electrolyte during the discharge process of the 4 V reaction (vs Li/Li+). This result is explained by the lithium accumulation due to the different local lithium diffusion rates: the lithium ions were inserted into the nanowire at a higher rate than they diffused toward the bulk side of the nanowire. We also found that the LiMn2O4 nanowire cathode was restored to be cubic phase without any fracture in the charge process. No fracture during the cubic-tetragonal transition is promising for the long-lifetime battery with LiMn2O4 nanowire cathode.

High-angle annular dark-field scanning transmission electron microscopy was used to investigate the crystallization mechanism of amorphous hafnium dioxide (HfO 2 ) layers in gate stacks (polysilicon/HfO 2 /SiON/Si substrate). A 0.9-nm-thick HfO 2 layer remained amorphous with a uniform thickness on annealing at 1050 °C. In contrast, crystalline islands with a cubic structure formed when a 1.8-nm-thick HfO 2 layer was annealed. These islands had commensurate interfaces with both the silicon substrate and the polysilicon film. These results suggest that crystallization is promoted on a silicon surface.

Distribution of lithium ions in crystals is an important issue for development of advanced lithium ion batteries. Using spherical aberration-corrected electron microscope, lithium columns in crystals have been visualized with heavy element ones by a new method of scanning transmission electron microscopy (STEM) called as annular bright field (ABF) imaging. ABF images are taken by setting an annular detector in bright field disk. It is so powerful that it visualizes not only lithium but also hydrogen columns in battery and storage materials. Some suggested explanations of ABF imaging mechanism, hollow-cone beam illumination method, phase object approximation and s-state channeling model, will be reviewed.

Annular dark-field scanning transmission electron microscope (ADF-STEM) images of an Si (001) crystal were obtained by using an aberration-corrected electron microscope, at 30-mrad convergent probe and cold field-emission gun at 300 kV. The intensity of ADF-STEM images, that is, the number of scattered electrons relative to the incident electrons, obtained for specimen thickness from 10 to 50 nm was compared quantitatively with absorptive multi-slice simulation. The column and background intensities were analyzed by column-by-column two-dimensional Gaussian fitting. These intensities were found to increase linearly with the sample thicknesses. However, the simulated image gave higher column intensity and lower background intensity for all the sample thickness. We found that experimental images were reproduced by the simulation with Gaussian convolution of 70 pm full-width at half-maximum for all the sample thicknesses from 10 to 50 nm. The possible factors accounted for this Gaussian convolution is discussed.

Aberrations up to the fifth-order were successfully measured using an autocorrelation function of the segmental areas of a Ronchigram. The method applied to aberration measurement in a newly developed 300 kV microscope that is equipped with a spherical aberration corrector for probe-forming systems. The experimental Ronchigram agreed well with the simulated Ronchigram that was calculated by using the measured aberrations. The Ronchigram had an infinite magnification area with a half-angle of 50 mrad, corresponding to the convergence angle of a uniform phase.

We investigated the bias voltage polarity dependence of atomically resolved barrier height (BH) images on Si(1 1 1)3 × 1–Ag surfaces. The BH images were very similar to scanning tunneling microscopy (STM) images in both the empty and filled states. This similarity strongly supports the interpretation that the BH image reflects the vertical decay rate of the surface local density of states (LDOS). Differences in contrast and protrusion shapes between BH and STM images were observed. We attributed these differences to the geometric contribution to the STM image and to the improved spatial resolution of the BH image due to the lock-in technique.

A new miniature scanning tunneling microscope (STM) holder was developed in order to simultaneously investigate electronic conductance and structure of nanowires in an ultra high-vacuum electron microscope (UHV–TEM). A thin gold wire held between the STM tip and substrate stage of the specimen holder was stretched to form a suspended gold nanowire. The new TEM–STM system allowed us to measure electronic conductance at intervals of 20 ms, and to record high-resolution TEM images on videotape at 30 fps. Suspended gold nanowires formed from [1 1 0] oriented electrodes were well-elongated. In contrast, [1 0 0] and [1 1 1] electrodes produced nanowires with short necks. Electronic conductance was found to change as nanowire structure changed, with conductance quantization in units of 2 e 2 / h , where e is the electron charge and h is Planck’s constant, only being exhibited for well-elongated nanowires.

Helical multishell (HMS) gold nanowires were observed in situ by ultra-high-vacuum electron microscopy. During thinning of the helical nanowire, a junction was formed between two nanowires of different diameter. The structure of the gold junction is proposed in comparison with the multiwall carbon nanotube. The gold junction has a dislocation-like core to accommodate the number difference of the atomic rows that compose the HMS nanowires, while the carbon junction has a pair of five- and seven-membered rings. Thinning of the helical gold nanowire by electron-beam radiation can be caused by the climbing motion of the dislocation-like core along the nanowire.

Growths of Ag islands on Si(1 1 1) 3 × 3 -Ag surface at room temperature were observed by UHV transmission electron microscopy and diffraction. The Ag islands grown after six monolayer deposition had neither (1 0 0) nor (1 1 0) orientation, but had two complex epitaxial orientations dominantly. One was striped islands which gave rise to a diffraction pattern commensurate with the 3 × 3 lattice of the Si(1 1 1) surface. The other was the coagulated islands whose diffraction pattern indicated the Ag(1 −3 4) sheet grown parallel to the Si(1 1 1) surface.

High-resolution electron microscope images of a suspended gold chain were analyzed quantitatively. The images of the suspended gold chain were recorded on videotapes, during in situ observation in an ultra-high-vacuum electron microscope. The chain consisted of four gold atoms free from any substrate. Image simulation verified that the gold chain has a center-top geometry. The simulation also showed that the chain has no glue atoms spinning around the axis of the chain. A spinning gold atom was shown to give 50% of the stationary atom in gray scale. By comparing the noise level of the observed image and the gray scale of single atoms such as C, Si, S, Cu, and Au, we verified that the Si and S atoms have almost twice as large contrast as the noise (peak-to-peak), and C atoms have almost the same contrast as the noise level. The analysis showed it critical to detect a single Si and S atoms.

We studied the atomic structure of the Si(00l)-c(4×12)-Al surface, which appears in scanning tunneling microscopy (STM) images as an array of clusters in the four-fold direction. Transmission electron diffraction (TED) patterns showed ( h /4, k /12) fractional-order spots after depositing about four monolayers of aluminum on clean Si(00l) surfaces at a substrate temperature of 600°C. A model, which accords with the TED intensity and the observed STM images, consists of a periodical terrace-and-trench geometry in the 12-fold direction. In the four-fold direction, an aluminum ad-dimer is adsorbed every 4 a distance ( a =0.384 nm) on the terraces terminated by double-height steps, making up the cluster array corresponding to bright protrusions in STM images. In addition to ad-dimers, rebonded atoms at the double-height step edge and zigzag isolated dimers in the trench are found to be the building blocks of the c(4×12) structure.

A miniaturized scanning tunnelling microscope (STM) was fitted in a side-entry holder of an ultra-high vacuum electron microscope. The clean Si(111)7 x 7 surface was observed by both STM and reflection electron microscopy (REM) at atomic resolution. The tungsten tips were often rounded off upon tip-approach with a constant current, through a gentle touch with the sample surface. The apices of such rounded tips had radii of several tens of granometre with widths of about 3 x 3 nm. Atomically resolved STM of the Si(111)7 x 7 surface was obtainable when an atom or an atomic cluster sits on the tip surface. The rounded tips were used for fabrication of Si nanowires by the touch-and-away operation of the tip. The nanowires grew longer at higher substrate temperature and they reached as long as several tens of nanometre at 700 degrees C. The nanowire had many twins and the (111) twin lamellae were stacked in the direction of the wire axis. In another case, the twin planes were oblique to the wire axis so that the (112) direction was nearly parallel to the wire axis.

A single shell carbon fullerene (SSF) was fabricated from an amorphous carbon agglomerate (a-C agglomerate) suspended between two gold electrodes. As the applied bias voltage to the a-C agglomerate was increased using a transmission electron microscope–scanning tunneling microscope (TEM–STM) system, the transformation into the SSF via a glassy carbon was observed. It was found that the SSF transformation occurred above the bias voltage of 0.6 V without a prominent loss of the number of carbon atoms. The size of the SSFs ranged from C60 to C620 having Ih or I symmetry.

Surface transmission electron microscopy (TEM) has been used to reveal surface steps and structures by bright and dark field imaging, and high resolution plan view and/or profile view imaging. Dynamic processes on surfaces, such as step motion, surface phase transitions and film growths, are visualized by a TV system attached to the electron microscope. Atom positions can precisely be detected by convergent beam illumination (CBI) of high resolution surface TEM. Imaging of the atomic positions of surfaces with truncation is briefly reviewed in this paper, with recent development of a TEM–STM (scanning tunneling microscope) system.

Metal contacts are regarded as key elements of nanometer-scale electronics. Since gold contacts show quantized conductance even at room temperature, much effort has been devoted to understand their conductance behavior on the nanoscale. However, gold contacts do not always show quantized conductance steps during their thinning process, the reason for which has been an open question. Thus, it is necessary to investigate the relationship between the atomic structure and conductance of gold contacts. We developed a custom-made scanning tunneling microscope combined with an ultra-high vacuum transmission electron microscope to clarify the structural dependence of conductance quantization in gold contacts. We found that [111] and [001] gold contacts with a bottleneck shape showed a gradual decrease in conductance with elastic elongation and successive conductance jumps with periodic plastic deformation. In contrast, [110] gold contacts had a hexagonal prism shape (termed gold [110] nanowires). In the conductance histogram, peaks appeared nearly in steps of the quantum unit. We found that the prominent peaks corresponded to stable gold nanowires with a regular hexagonal cross-section. Following first-principles calculations, we confirmed that very thin gold [110] nanowires were ballistic conductors. The conductance behavior differed depending on the contact shape.

Solid-liquid transition of fine tin particles having diameter of 2–10 nm is studied in-situ by high-resolution transmission electron microscopy under a ultra-high vacuum condition. Melting temperature is confirmed to decrease with the decrease of particle diameter. The particles less than the critical size, 2rc⋍5 nm, are found to have a specific phase between the solid and the liquid phase. The particle in this “pseudo-crystalline” phase contains crystalline embryos in it. Particles larger than the critical size have sharp liquid-solid transition, which completed within the time resolution of our microscope observation, 33 ms upon heating or cooling process. Large solid particles have Wulff's polyhedron, while particles around the critical diameter have rather spherical shape. Structural anomaly at the critical size occurs all over the outer most surface layer slightly below the melting temperature. Origin of the “pseudo-crystalline” phase and surface pre-melting phenomena are discussed.

To achieve 50 pm resolution (R005: Resolution 0.05 nm), we have been developing a 300 kV high-resolution scanning transmission electron microscope (STEM)/transmission electron microscope (TEM) equipped with a cold-field emission gun (FEG) (Fig.1(a))[1]. Energy spread (FWHM) of the cold-FEG was measured to be 0.32 eV (Fig.1(b)). Spherical aberration correction systems have been incorporated into STEM and TEM systems of the microscope. The aberration corrector is based on a hexapole-type correction system, which has asymmetrical dodeca-poles [2]. We developed a method to measure aberrations for a STEM corrector. In the method, the aberrations are obtained from sets of auto-correlation functions on Ronchigram pattern of an amorphous specimen. For the TEM corrector, a diffractogram tableau is used to measure the aberration of image forming system. Aberrations up to the fifth order were measured and the aberrations are automatically adjusted using the newly developed software in both TEM and STEM systems.

The performance of a newly developed high-resolution 300 kV microscope equipped with a spherical aberration corrector for probe-forming systems is reported. This microscope gave the highest resolution for the distance between atomic columns, as determined by a high-angle annular dark field imaging method using a GaN[211] crystalline specimen, where the distance between the neighboring columns of Ga was 63 pm.

Extended abstract of a paper presented at Microscopy and Microanalysis 2013 in Indianapolis, Indiana, USA, August 4 – August 8, 2013.

Gold nanowires were synthesized at 150 K by electron beam thinning of a gold thin foil in an UHV electron microscope. The gold nanowires were found to have a helical multishell structure (HMS). One particular nanowire, which was thinner than the 7-1 HMS nanowire, was found to have a tubular structure. The gold single wall nanotube is composed of five atomic rows that coil about the tube axis. The diameter was 0.4 nm and the pitch was 11 nm. The stability of the $(5,3)$ nanotube was discussed in terms of the shear deformation of the triangular network of gold atoms.

A single-equation approach as an extension to the EKV MOS transistor model, to realize the drain current modeling characteristics for low-voltage MOS circuits is presented. Instead of three sets of separate equations in the triode, saturation, and weak inversion regions, only a single expression which is valid to describe the drain current behavior in all the transistor operation regions can be realized by using hyperbola and interpolation techniques. Since all the terms and the derivatives in this expression are continuous, this single-equation can predict good results for the current, output conductance, and transconductance with continuous and smooth characteristics.

(Received 10 August 2001; revised manuscript received 9 November 2001; published 1 March 2002) A suspended platinum nanowire was observed to have the same helical multishell structure (HMS) that was reported for gold nanowires thinner than 2 nm. The investigation was made in an ultrahigh vacuum high-resolution electron microscope (JEM-2000VF). The platinum nanowire was synthesized by an electron-beam thinning method at elevated temperatures to enhance the Pt atom migration. A platinum multishell nanowire was thinned by migration until it finally snapped. In the meantime, the outer shell was stripped from a 13-6 HMS to partially expose the inner shell. Simulated electron microscope images supported that the exposed inner shell was a single-wall tube having a tunnel at the wire axis.

A sub-50pm resolution electron microscope was applied for in-situ studies of ion transport in lithium ion battery and CO-oxidation catalyst. Lithium ions in LiM2O4 electrodes (M: transition metals) and titanium ions in Au/TiO2 catalyst were enabled us to observe individually by ABF-STEM and TEM. Transport of lithium ions was seen, after in-situ observations, to induce structural transformation of the electrode materials that causes irreversible cycle of the battery reaction. Transport of the interstitial titanium ions results, due to oxygen gas for CO-oxidation, in modification of Au/TiO2 interface structure. In-situ studies, thus, revealed materials' transformation induced locally by ion/electron transport of the battery/catalyst system at high resolution and high contrast.

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 2009 in Richmond, Virginia, USA, July 26 – July 30, 2009

Extended abstract of a paper presented at Microscopy and Microanalysis 2008 in Albuquerque, New Mexico, USA, August 3 – August 7, 2008

We demonstrate that a gold zigzag nanowire changes conductance stepwise between 1 and 2G0 (=2e2/h, e is the elementary charge and h is Planck constant) upon slight stretching or compression at room temperature by a scanning tunneling microscope combined with a transmission electron microscope. The conductance change from 2 to 1G0 and vice versa occurred around the critical atomic distance of 0.32 nm, which is in agreement with theoretical calculations.

We succeeded in sandwiching a single carbon fullerene between two (111) facets and measured the conductance at room temperature using a transmission electron microscope combined with a scanning tunneling microscope. The carbon fullerene prevented to move around at the gap when it was slightly compressed between two facets. In this condition, the C80 and C140 fullerenes had the values of 0.53 and 0.62G0 (=2e2/h), respectively, and sometime showed stepwise conductance change due to rotation. Since current–voltage characteristics showed metallic behavior for the C140 fullerene, the single carbon fullerene is thought to have metallic bonds to gold (111) surface under a slight compression, resulting in keeping the same adsorption site.

Using a transmission electron microscope combined with a scanning tunneling microscope, the relationship between structure and conductance of gold nanowires with axis along the [110] direction is investigated. The conductance histogram shows several high peaks and some subsidiary ones among them. The high peaks correspond to stable gold nanowires with a hexagonal cross section. The conductance peaks including the subsidiary peaks almost appear at integral multiples of the conductance quantum, G 0 (=2 e 2 / h ), which is a direct evidence that these peaks are due to one-by-one evolution of conductance channel.

Nonlinear current-voltage (I‐V) curves of gold quantum point contacts (QPC) were investigated using a transmission electron microscope–scanning tunneling microscope system. The I‐V curves were measured by sweeping the bias voltage from 0 to 0.3 V at room temperature under ultrahigh vacuum. The results revealed that when the QPC formed a short nanowire, a nonlinear I‐V curve was observed, while a long nanowire produced a linear I‐V curve. The nonlinear I‐V curves were found to be caused by a nanowire thickening that occurred during increases of the bias voltage. This thickening resulted from a shortened distance between electrodes.

We studied In2O3 for use as an intermediate layer between the YBCO emitter electrode and the SrTiO3 base region of dielectric-base transistors (DBT). We fabricated and tested a YBCO(001)/In2O3(100)/SrTiO3(110) hetero-structure by using a laser-ablation deposition technique with high-density targets. Our YBCO/In2O3/n-SrTiO3 diode structure showed a current density that was one order of magnitude larger than with an MgO intermediate layer.