Electrically Stimulated Synaptic Resistive Switch in Solution-Processed Silicon Nanocrystal Thin Film: Formation Mechanism of Oxygen Vacancy Filament for Synaptic Function

We demonstrate an electrically stimulated synaptic resistive switch in a silicon nanocrystal (Si NC) thin film. A forming-free resistive switching occurs on the surface of natively oxidized Si NCs because of filaments of oxygen vacancies. To show a gradual change of the resistance, we investigate a formation mechanism of an oxygen vacancy filament. This gradual change in the resistance with input voltage pulses corresponds to short-term plasticity (STP) and long-term potentiation (LTP) in biological synapses. We simulate spike-timing-dependent plasticity (STDP) in the resistive switch by voltage pulses

Surface Potential of 1,10-Decanedithiol Molecules Inserted into Octanethiol Self-Assembled Monolayers on Au(111)

We measured the surface potential of 1,10-decanedithiol (C10S2) molecules inserted into 1-octanethiol (C8S) self-assembled monolayers (SAMs) using Kelvin-probe force microscopy (KFM) with noncontact atomic force microscopy (NC-AFM) under ultrahigh-vacuum (UHV) conditions. C8S SAMs on Au(111) were used as host matrices for C10S2 molecular insertion. Molecular insertion was used to orient the inserted C10S2 molecules to form a Au(111) surface−thiol bond at one end, whereas the thiol termini at the other end protruded from the C8S SAMs. The histograms of the surface potential images of the mixed C10S2:C8S SAMs exhibited two Gaussian peaks; however, the histograms of the surface potential images of the C8S SAMs exhibited only one peak. The surface fractions of C10S2 molecules in the mixed C10S2:C8S SAMs were evaluated from the Gaussian peaks. The surface potential of the inserted C10S2 molecules was 11 mV higher than that of the host C8S SAMs. The dipole moment difference between C10S2 molecules and C8S molecules was evaluated as 16 mD

Solution Processing of Hydrogen-Terminated Silicon Nanocrystal for Flexible Electronic Device

We demonstrate solution processing of hydrogen-terminated silicon nanocrystals (H–Si NCs) for flexible electronic devices. To obtain high and uniform conductivity of a solution-processed Si NC film, we adopt a perfectly dispersed colloidal H–Si NC solution. We show a high conductivity (2 × 10^–5 S/cm) of a solution-processed H–Si NC film which is spin-coated in air. The NC film (area: 100 mm²) has uniform conductivity and responds to laser irradiation with 6.8 and 24.1 μs of rise and fall time. By using time-of-flight measurements, we propose a charge transport model in the H–Si NC film. For the proof-of-concept of this study, a flexible photodetector on a polyethylene terephthalate substrate is demonstrated by spin-coating colloidal H–Si NC solution in air. The photodetector can be bent in 5.9 mm bending radius at smallest, and the device properly works after being bent in 2500 cycles

Surface Structure and Current Transport Property of Boron and Phosphorus Co-Doped Silicon Nanocrystals

Silicon (Si) nanocrystals (NCs) with high boron (B) and phosphorus (P) concentration shells are dispersible in polar solvents without organic ligands. In order to understand the mechanism of the solution dispersibility, the surface structure is studied by infrared absorption spectroscopy. It is shown that water molecules are adsorbed at the B–oxygen (O) bond sites on NC surface with high hydrogen bond strength, and thus B and P co-doped Si-NCs are a kind of hydrate containing large amounts of water molecules (Si-NC·<i>x</i>H₂O). The current transport properties of Si-NC films made from the solutions are studied. It is found that the conductivity is very sensitive to the amount of adsorbed water molecules and changes by 8 orders of magnitude. The high affinity of the NC surface with water molecules is considered to be the origin of the high sensitivity

Size-Dependence of Acceptor and Donor Levels of Boron and Phosphorus Codoped Colloidal Silicon Nanocrystals

Size dependence of the boron (B) acceptor and phosphorus (P) donor levels of silicon (Si) nanocrystals (NCs) measured from the vacuum level was obtained in a very wide size range from 1 to 9 nm in diameter by photoemission yield spectroscopy and photoluminescence spectroscopy for B and P codoped Si-NCs. In relatively large Si-NCs, both levels are within the bulk Si band gap. The levels exhibited much smaller size dependence compared to the valence band and conduction band edges. The Fermi level of B and P codoped Si-NCs was also studied. It was found that the Fermi level of relatively large codoped Si-NCs is close to the valence band and it approaches the middle of the band gap with decreasing the size. The results suggest that below a certain size perfectly compensated Si-NCs, that is, Si-NCs with exactly the same number of active B and P, are preferentially grown, irrespective of average B and P concentrations in samples

Ideal Discrete Energy Levels in Synthesized Au Nanoparticles for Chemically Assembled Single-Electron Transistors

Ideal discrete energy levels in synthesized Au nanoparticles (6.2 ± 0.8 nm) for a chemically assembled single-electron transistor (SET) are demonstrated at 300 mK. The spatial structure of the double-gate SET is determined by two gate and drain voltages dependence of the stability diagram, and electron transport to the Coulomb box of a single, nearby Coulomb island of Au nanoparticles is detected by the SET. The SET exhibits discrete energy levels, and the excited energy level spacing of the Coulomb island is evaluated as 0.73 meV, which well corresponds to the expected theoretical value. The discrete energy levels show magnetic field evolution with the Zeeman effect and dependence on the odd–even electron number of a single Au nanoparticle