Papers by Jun-ichi Shirakashi
Feedback-controlled electromigration (FCE) has been employed to control metal nanowires with quan... more Feedback-controlled electromigration (FCE) has been employed to control metal nanowires with quantized conductance and to create nanogaps. The setting of the experimental parameters based on experiences is a common practice in FCE. However, tuning the optimization of parameters is intractable because trying all different combinations systematically is practically impossible. Therefore, we proposed an optimization process of the FCE parameters using Ising spin model, which can search for the global optimum in a multidimensional solution space within short calculation time. The FCE parameters were determined through a convergence property of the Ising spin model. This result implies that the proposed method is an effective tool for the process optimization of FCE.
IEICE technical report. Electron devices, Feb 20, 2014
Over the past few decades several experimental methods have been used to fabricate single-electro... more Over the past few decades several experimental methods have been used to fabricate single-electron transistors (SETs). We have reported the method for fabrication of the SETs using field-emission-induced electromigration, which is so-called “activation”. By applying the activation to the nanogap electrodes, it is expected that the moved atoms accumulate within the gaps and play the dual role of reducing the gap width and forming coulomb islands. We applied the activation procedure to the Au nanogaps at room temperature under vacuum. Following the activation, drain current $\pmb{I}_{\mathbf{D}}-$ drain voltage VDcharacteristics of the devices were obtained with the modulation of gate voltage $\pmb{V}_{\mathrm{G}}$ at T=18 K. As a result, $\pmb{I}_{\mathbf{D}}-\pmb{V}_{\mathbf{D}}$ characteristics displayed Coulomb blockade properties, and the Coulomb blockade voltage was clearly modulated by gate voltage $\pmb{V}_{\mathrm{G}}$. These results indicate that this simple technique can make Au nanogap-based SETs easier.
Applied Surface Science, 2012
Japanese Journal of Applied Physics, Mar 1, 1998
Applied Physics Express, Apr 12, 2023
Feedback-controlled electromigration (FCE) is employed to control metal nanowires with quantized ... more Feedback-controlled electromigration (FCE) is employed to control metal nanowires with quantized conductance and create atomic junctions. The FCE scheme is commonly implemented using many experimental parameters, and determining the optimal FCE parameters can be regarded as a combinatorial optimization problem. The D-Wave quantum annealer has attracted attention for its hardware implementation of quantum annealing (QA), which is a heuristic algorithm for solving combinatorial optimization problems. This study developed a QA approach for optimizing the FCE parameters and executed it on a quantum annealer. The results and performance were compared with those of a classical solver.
We report the conduction mechanism of the single-electron transistors (SETs) fabricated by field-... more We report the conduction mechanism of the single-electron transistors (SETs) fabricated by field-emission-induced electromigration, which is so-called “activation”. By applying the activation to Ni nanogaps, we were easily able to fabricate the SETs operating at room temperature. Additionally, strong Coulomb staircases were clearly obtained, and the quasi-periodic current oscillations were also observed at room temperature. These results indicate that the higher charging energy associated with a smaller Ni island structure within the multiple islands causes a bottleneck mechanism in conduction, improving the Coulomb staircase structures.
Nanoscience and Nanotechnology Letters, Oct 1, 2013
Applied Physics A, Mar 1, 1998
2022 IEEE International Conference on Manipulation, Manufacturing and Measurement on the Nanoscale (3M-NANO), Aug 8, 2022
Feedback-controlled electromigration (FCE) has been employed to control metal nanowires with quan... more Feedback-controlled electromigration (FCE) has been employed to control metal nanowires with quantized conductance and to create nanogaps. However, the formation of nanostructures by conventional FCE procedure using a microprocessor-based controller with a general purpose operating system (GPOS) is considerably slow process. Therefore, we proposed an ultrafast FCE method using a field-programmable gate array (FPGA) to immediately and precisely control the channel conductance of Au nanowires. In this report, we study the tuning of quantized conductance of Au nanowires by ultrafast FCE using FPGA-based control system with a constant-voltage (CV) method. First, in the FCE procedure, preset values of quantized conductance of Au nanowires were defined as 25 G0, 15 G0, and 5 G0 (G0 = 2e2/h). The conductance of the Au nanowires during FCE procedure decreased until the conductance reached the preset values within an order of a millisecond. Furthermore, the quantized conductance plateaus of the Au nanowires were precisely controlled by the CV procedure with the preset values of 15 G0 and 5 G0. These results imply that the combination of FCE and CV procedures with FPGA-based control system can precisely and stably tune the channel conductance of Au nanowires with millisecond-scale resolution.
Electromigration (EM) method for the fabrication of nanogaps is specifically simple as compared w... more Electromigration (EM) method for the fabrication of nanogaps is specifically simple as compared with other methods because it is achieved by only passing a current through a metal nanowire. However, typical EM procedure induces an abrupt break that yields a nanogap with high tunnel resistance. Hence, various approaches have been reported to address this problem, and feedback-controlled electromigration (FCE) scheme has been successfully employed to make nanogaps safely and reliably. On the other hand, the formation of nanogaps by FCE method using a microprocessor-based controller with a general purpose operating system is considerably slow process. In this study, we designed a new system using field programmable gate array (FPGA). Furthermore, we applied this system to Au μm-wires. Consequently, the FCE experiments using FPGA-based control system were performed at 20 μsec of deterministic loop time. In addition, conductance was precisely controlled and adjusted from 10 mS to less than 77.5 μS for within 1 sec, which is 102-3 times shorter than that of conventional FCE procedure using microprocessor-based control system.
Journal of physics, Dec 1, 2017
Wearable health-monitoring devices have attracted increasing attention in disease diagnosis and h... more Wearable health-monitoring devices have attracted increasing attention in disease diagnosis and health assessment. In many cases, such devices have been prepared by complicated multistep procedures which result in the waste of materials and require expensive facilities. In this study, we focused on pyrolytic graphite sheet (PGS), which is a low-cost, simple, and flexible material, used as wearable devices for monitoring human activity. We investigated wearable devices based on PGSs for the observation of elbow and finger motions. The thin graphite films were fabricated by cutting small films from PGSs. The wearable devices were then made from the thin graphite films assembled on a commercially available rubber glove. The human motions could be observed using the wearable devices. Therefore, these results suggested that the wearable devices based on thin graphite films may broaden their application in cost-effective wearable electronics for the observation of human activity.
Recent advances in the field of natural computing have boosted the hope that complicated problems... more Recent advances in the field of natural computing have boosted the hope that complicated problems can be solved efficiently on the heuristics applying natural phenomena. In particular, it is expected that Ising spin model implemented with CMOS circuits solves combinatorial optimization problems more effectively and conveniently at room temperature, and thus, it is potentially achievable for practical use. So far, we have developed Ising machine that can be implemented with simple logic circuits consisting of XNOR gate utilized as spin decision logics for finding the ground state. In this study, we propose the hybrid-type spin decision logic (HDL), a combination of two conventional methods. HDL can find the global optimal solution of combinatorial optimization problems, that is impossible to solve with conventional spin decision logics.
Combinatorial optimization problems often arise naturally in various fields of research. However,... more Combinatorial optimization problems often arise naturally in various fields of research. However, finding the global optimum solution of these problems remains computationally difficult. Ising spin model is considered to be an effective method to solve combinatorial optimization problems because these problems can be mapped and embedded into the Ising spin model. In general, Ising spin model requires to adjust and tune the spin connection parameters, for example, topology of spin connection and resolution of exchange interaction coefficient values between spins, according to the problems. In this paper, we focus on the number of spin connection, which is one of the spin connection parameters, and perform the calculation experiments through solving max-cut problems with Ising spin computing. As a result, all-to-all connectivity makes Ising spin computing well suited for searching the ground states of complex combinatorial optimization problems.
Materials Science in Semiconductor Processing, Nov 1, 2017
Abstract Using the reducing activity of ballistic hot electrons emitted from a nanocrystalline si... more Abstract Using the reducing activity of ballistic hot electrons emitted from a nanocrystalline silicon (nc-Si) diode, it is demonstrated that thin Si and Ge films can be deposited under a situation that output electrons directly impinge upon a SiCl4 or GeCl4 solution-coated target substrate located in close proximity to the nc-Si emitter. After the electron incidence, uniform deposition of thin Si or Ge films was clearly observed in the irradiated area. In accordance with spectroscopic characterizations, no signs of contaminations were detected in deposited thin Si and Ge films, and those films exhibit features as oxidized nano-clusters. It is also shown that from a thermodynamic viewpoint, the output electron energy of the nc-Si emitter is suitable for promoting preferential reduction of target ions within the penetration depth in solutions followed by the nuclei formation.
Journal of Crystal Growth, May 1, 1992
Carbon-doped In~Ga 1 .~As layers (x = 0-0.96) were grown by metalorganic molecular beam epitaxy (... more Carbon-doped In~Ga 1 .~As 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 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 ton at x = 0.8. Hole concentrations of i.OxiO' 9 and 1.2x 1018 cm3 are obtained for x = 0.3 and 0.54, respectively. These values are significantly higher than those reported on carbon-doped InrGai~As by MBE. Preliminary results on carbon-doped GaAs/In~Ga 1.~Asstrained layer superlattices are also discussed.
CRC Press eBooks, Nov 22, 2017
IEICE Technical Report; IEICE Tech. Rep., May 20, 2021
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Papers by Jun-ichi Shirakashi