Numerical Simulation of Single-Electron Tunneling in Random Arrays of Small Tunnel Junctions Formed by Percolation of Conductive Nanoparticles

We numerically simulated electrical properties, i.e., the resistance and Coulomb blockade threshold, of randomly-placed conductive nanoparticles. In simulation, tunnel junctions were assumed to be formed between neighboring particle-particle and particle-electrode connections. On a plane of triangle 100×100 grids, three electrodes, the drain, source, and gate, were defined. After random placements of conductive particles, the connection between the drain and source electrodes were evaluated with keeping the gate electrode disconnected. The resistance was obtained by use of a SPICE-like simulator, whereas the Coulomb blockade threshold was determined from the current-voltage characteristics simulated using a Monte-Carlo simulator. Strong linear correlation between the resistance and threshold voltage was confirmed, which agreed with results for uniform one-dimensional arrays

One-dimensional array of small tunnel junctions fabricated using 30-nm-diameter gold nanoparticles placed in a 140-nm-wide resist groove

We present percolative arrays of gold nanoparticles (NPs) formed in a resist groove. To enhance the con nection probability, the width of the resist groove (140 nm) was designed to be approximately five times larger than the diameter of gold NPs (30 nm). Two-stage deposition of gold NPs was employed to form bridge connections between the source and drain electrodes. Dithiol molecules coated on surfaces of gold NPs worked as tunnel barriers. 5 of 12 samples exhibited Coulomb blockade characteristics, in one of which the gate response was confirmed

One-step generation of multiple transgenic mouse lines using an improved Pronuclear Injection-based Targeted Transgenesis (i-PITT)

Ohtsuka, M., Miura, H., Mochida, K. et al. One-step generation of multiple transgenic mouse lines using an improved Pronuclear Injection-based Targeted Transgenesis (i-PITT). BMC Genomics 16, 274 (2015). https://doi.org/10.1186/s12864-015-1432-

Equivalent circuit model modified for free-standing bilayer lipid membranes beyond 1 TΩ

A cell is the basic functional unit of living organisms. Bilayer lipid membranes (BLMs), which form cell membranes can be assembled by using artificial methods. The electrochemical characteristics of BLMs are normally investigated using electrochemical impedance spectroscopy (EIS); however, the equivalent circuit need to be modified by the experimental conditions. In this study, we formed plain BLMs to determine the underlying equivalent circuit model of free-standing BLMs, and we measured the electrical characteristics using EIS. To analyze the results of EIS, we proposed equivalent circuit models including electrical double layer (EDL) effects on both sides of a BLM. We also extracted and evaluated the electrochemical parameters; the aperture-suspended BLMs using an Si chip having tapered edge recorded TΩ-order membrane resistances, which were one order higher than those reported in most previous studies. Regarding the capacitances of EDL, we compared the extracted values and the calculated results

Capacitance extraction method for a free-standing bilayer lipid membrane formed over an aperture in a nanofabricated silicon chip

A bilayer lipid membrane (BLM) is the main component of the cell membrane of living organisms, which can be formed artificially. Although the specific capacitance of a BLM is known to be in the range of 0.4–1.0 μF cm^–2, many previous works that formed free-standing BLMs over an aperture in silicon chips reported larger values beyond this typical range, which suggests that equivalent-circuit models are not adequate. In this work, we modified the equivalent-circuit model by adding a resistance element of silicon. To evaluate the validity of the modified model, we applied the model to the results of electrochemical impedance spectroscopy for free-standing BLMs formed over an aperture in nanofabricated silicon chips. The derived specific capacitance values were 0.57 ± 0.08 μF cm^–2, which settles in the typical range

Dielectrophoretic Assembly of Gold Nanoparticle Arrays Evaluated in Terms of Room-Temperature Resistance

Gold nanoparticles (GNPs) are often used as island electrodes of single-electron (SE) devices. One of technical challenges in fabrication of SE devices with GNPs is the placement of GNPs in a nanogap between two lead electrodes. Utilization of dielectrophoresis (DEP) phenomena is one of possible solutions for this challenge, whereas the fabrication process with DEP includes stochastic aspects. In this brief paper, we present our experimental results on electric resistance of GNP arrays assembled by DEP. More than 300 pairs of electrodes were investigated under various DEP conditions by trial and error approach. We evaluated the relationship between the DEP conditions and the electric resistance of assembled GNP arrays, which would indicate possible DEP conditions for fabrication of SE devices

Evaluation of the inter-particle distance of gold nanoparticles dispersed on silane-treated substrates to fabricate dithiol-connected arrays

Small tunnel junctions using gold nanoparticles (GNPs) as electrodes have been studied to fabricate single-electron devices. GNPs connected via dithiol molecules have been used as small tunnel junctions, and a two-stage dispersion method was used to fabricate dithiol-connected GNP arrays. In this process, the GNPs were fixed on silane-treated substrates by immersing the substrate in a colloidal gold solution. For fabricating dithiol-connected arrays, the inter-particle distance of the dispersed GNPs must be smaller than the GNP diameter. Consequently, the inter-particle distance controlled by the immersion time (T IM1) was evaluated. For T IM1 values exceeding 8 h, the inter-particle distance was less than the GNP diameter. A second dispersion of GNPs after treating samples with dithiol realized particle connections. For the GNP arrays produced with T IM1 values greater than 8 h, the I–V characteristics were measured at 77 K, and the yield of devices exhibiting nonlinear I–V curves was 23%