Jun-ichi Shirakashi

Single-electron charging effects in Nb/Nb oxide-based single-electron transistors at room temperature

We have reported the single-electron charging effects in Nb/Nb oxide-based single-electron transistors (SETs) at room temperature (T=298 K). The SETs were first fabricated by a scanning probe microscope based anodic oxidation. Then, the miniaturization of tunnel junctions was performed by thermal oxidation. Ultra-low-capacitance tunnel junctions were easily obtained by utilizing both kinds of oxidation processes, which realizes room-temperature Nb-based SETs.

Electron-beam-induced deposition of carbonaceous microstructures using scanning electron microscopy

Scanning electron microscopy (SEM) was utilized for deposition of carbonaceous microstructures. Conic-, wire- and square-shaped structures were fabricated with various scanning modes. A narrow carbonaceous wire with a width of 30 nm was obtained at an electron-beam current of 15 pA. The conic-structure was successfully applied to a cantilever of an atomic force microscope (AFM) and a planar resolution was extremely improved. Furthermore, the square-shaped structure was also employed as the insulator in a metal-insulator-metal (MIM) diode and a clear non-linear I-V characteristic was observed at room temperature.

Scratching properties of nickel-iron thin film and silicon using atomic force microscopy

Atomic force microscopy (AFM) is well known for its ability for nanopatterning many different materials. The patterning technique using an AFM tip as a scratch tool, known as scratch nanolithography, is used to study the scratch characteristics of 80% Permalloy thin film and silicon, with the emphasis on establishing their scratchability or the nanoscale machinability. The effects of the scratch parameters, including the applied tip force, scratch speed, and number of scratches, on the size of the scratched geometry were specifically evaluated. The primary factors that measure the scratchability were then identified and the governing material properties for scratchability were evaluated. To demonstrate its versatility, the scratching technique was applied to fabricate a NiFe-based nanoconstriction, which is used for many ferromagnetic devices. All results indicated that NiFe thin film has much better scratchability than that of Si and the scratched groove geometry can be accurately correlated with and pre...

Heavily carbon-doped p-type InGaAs by MOMBE

Abstract Carbon-doped In x Ga 1− x As layers ( x =0−0.96) were grown by metalorganic molecular beam epitaxy (MOMBE) using trimethylgallium (TMG), solid arsenic (As 4 ) and solid indium (In) as sources of Ga, As and In, respectively. The carrier concentration is strongly affected by growth temperature and indium beam flux. Heavy p-type doping is obtained for smaller In compositions. The hole concentration decreases with the indium composition from 0 to 0.8, and then the conductivity type changes from p to n at x =0.8. Hole concentrations of 1.0×10 19 and 1.2×10 18 cm -3 are obtained for x =0.3 and 0.54, respectively. These values are significantly higher than those reported on carbon-doped In x Ga 1− x As by MBE. Preliminary results on carbon-doped GaAs/In x Ga 1− x As strained layer superlattices are also discussed.

Scratch Nanolithography on Si Surface Using Scanning Probe Microscopy: Influence of Scanning Parameters on Groove Size

Scanning probe microscope (SPM) scratching with a diamond-coated tip on a Si surface was performed in a low-force regime of less than 9 µN. The influence of various scan parameters on the groove size was investigated. The groove size could be precisely controlled by the applied force, scan direction, and the number of scan cycles. There is no effect of the scan speed on the groove size. It is concluded that high-speed nanolithography can be achieved without the degradation of patterns by SPM scratching. Using this method, more complex nanostructures such as a line and space pattern with a pitch of 30 nm and a dot array of 2.6 ×1010 cm-2 density were successfully fabricated on a Si surface.

Scratch properties of nickel thin films using atomic force microscopy

Experiments using atomic force microscopy (AFM) as a machining tool for scratching patterns on nickel thin films have been conducted with an emphasis on establishing the material scratchability or more general, the nanoscale machinability. The effects of the scratch parameters, including the applied tip force and scratch direction, on the size of the scratched geometry were investigated. The primary factors that measure the scratchability were then assessed. The scratchability of Ni as compared to that of Si was specifically evaluated and discussed. A stress-hardness analysis was also performed to further validate the experimental and correlation results. All results indicate that the Ni thin film possesses excellent scratchability and one order of magnitude higher than that of Si. Based on the correlation formula developed, Ni should be able to be precisely scratched by AFM tip with the required dimension and nanoscale accuracy and precision.

Control of Tunnel Resistance of Nanogaps by Field-Emission-Induced Electromigration

A simple method for controlling the tunnel resistance of nanogap electrodes, based on electromigration induced by field emission current, is presented. In this study, we investigated the controllability of the tunnel resistance of nanogap electrodes by only adjusting the applied current. Initial planar nanogaps of Ni, typically separated by 22–44 nm, were fabricated on SiO2/Si substrates by electron-beam lithography and lift-off process. Then, a current was passed through the nanogaps at room temperature. By increasing the current from about 1 nA to 30 µA, the resistance of the nanogaps decreased, ranging from 100 TΩ to 10 MΩ. This result implies that this technique can simplify the fabrication of planar-type tunnel junction devices.

Fabrication of nanogap electrodes by field-emission-induced electromigration

The authors report a simple and easy technique for the fabrication of nanogaps with separations of less than 10nm. This technique is based on electromigration induced by field emission current. Here, the authors investigated the dependence of tunnel resistance on the shape of nanogap electrodes and initial gap separation. The initial nanogap electrodes having asymmetrical shape with the separation of 30–60nm were fabricated by electron-beam lithography and lift-off process. In the nanogaps with asymmetrical shape, the tunnel resistance was controlled by the magnitude of the preset current during field-emission-induced electromigration and decreased from the order of 100TΩto100kΩ with increasing the preset current from 1nAto150μA. This tendency was quite similar to that of nanogaps with symmetrical shape. Furthermore, the tunnel resistance after the electromigration was less dependent on the initial gap separation and was completely determined by the preset current. This suggests that it is possible to con...

Room Temperature Nb-Based Single-Electron Transistors

Room temperature operation of Nb/Nb oxide-based single-electron transistors (SETs) was successfully achieved and was reported in detail. First, the SETs were fabricated using a scanning probe microscope (SPM)-based anodic oxidation technique and then the junction area was further reduced by thermal oxidation. Ultra-small tunnel junctions were easily obtained by utilizing these two types of oxidation processes, and clear single-electron charging effects were observed through the Nb/Nb oxide-based SETs at room temperature.

P-Type Carbon-Doped InGaAs Grown by Metalorganic Molecular Beam Epitaxy

Carbon-doped InxGa1-xAs layers (x=0~0.96) were grown by metalorganic molecular beam epitaxy (MOMBE) using trimethylgallium (TMG), solid arsenic (As4) and solid indium (In) as sources of Ga, As and In, respectively. The growth temperature and the indium beam flux strongly affect carrier concentration, and the growth temperature also affects the indium molar fraction of the InxGa1-xAs layers grown even with the fixed indium beam flux. The hole concentration decreases with increasing indium molar fraction from 0 to 0.8, and then the conduction type changes from the p to n type at x=0.8. Hole concentrations of 1.0×1019 and 1.2×1018 cm-3 are obtained for x=0.3 and 0.54, respectively. These values are significantly higher than those reported for carbon-doped InxGa1-xAs by MBE.