Fast-Response and Flexible Nanocrystal-Based Humidity Sensor for Monitoring Human Respiration and Water Evaporation on Skin

We develop a fast-response and flexible nanocrystal-based humidity sensor for real-time monitoring of human activity: respiration and water evaporation on skin. A silicon-nanocrystal film is formed on a polyimide film by spin-coating the colloidal solution and is used as a flexible and humidity-sensitive material in a humidity sensor. The flexible nanocrystal-based humidity sensor shows a high sensitivity; current through the nanocrystal film changes by 5 orders of magnitude in the relative humidity range of 8–83%. The response/recovery time of the sensor is 40 ms. Thanks to the fast response and recovery time, the sensor can monitor human respiration and water evaporation on skin in real time. Due to the flexibility and the fast response/recovery time, the sensor is promising for application in personal health monitoring as well as environmental monitoring

Fast-Response and Flexible Nanocrystal-Based Humidity Sensor for Monitoring Human Respiration and Water Evaporation on Skin

We develop a fast-response and flexible nanocrystal-based humidity sensor for real-time monitoring of human activity: respiration and water evaporation on skin. A silicon-nanocrystal film is formed on a polyimide film by spin-coating the colloidal solution and is used as a flexible and humidity-sensitive material in a humidity sensor. The flexible nanocrystal-based humidity sensor shows a high sensitivity; current through the nanocrystal film changes by 5 orders of magnitude in the relative humidity range of 8–83%. The response/recovery time of the sensor is 40 ms. Thanks to the fast response and recovery time, the sensor can monitor human respiration and water evaporation on skin in real time. Due to the flexibility and the fast response/recovery time, the sensor is promising for application in personal health monitoring as well as environmental monitoring

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

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