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.

Double-gate single-electron transistors (SETs) were fabricated by chemical assembling using electroless gold-plated nanogap electrodes and chemisorbed chemically synthesized gold nanoparticles. The fabricated SET showed periodic and stable Coulomb oscillations under application of voltages of both gates. The sole SET also exhibited all two-input logic operations-XOR, XNOR, NAND, OR, NOR, and AND-with an on/off ratio of 10(2). This demonstrates the potential of chemical assembling to give highly stable SETs exhibiting all logic operations.

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.

In this review, we describe recent progress made in the study of nanoparticles characterized by scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS). Basic principles of STM measurements and single-electron tunneling phenomena through a single NP are summarized. We highlight the results of electrical and photonic properties on NPs studied by STM and STS. Because nanoparticles are single-digit nanometre in diameter, a single-electron transport on individual nanoparticles such as Coulomb blockade and resonant tunneling through discrete energy levels are investigated. Photon-emission from NPs is also introduced based on STM measurements. Novel single-nanoparticle functions such as stochastic blinking and one-write erasing behaviours are presented. This review provides an overview of nanoparticle characterization methods based on STM and STS that include the detailed understanding of the electrical and photonics properties of nanoparticles.

Sub-2-nm-size basic ligand Au nanoparticles were chemically synthesized and chemisorbed on an acidic self-assembled monolayer/Au(111) substrate by acid–base interaction. Coulomb blockade behaviors with clear Coulomb gaps were observed in current–voltage (I–V) and log I–V curves of the chemisorbed Au nanoparticles by scanning tunneling spectroscopy at room temperature. By fitting the measured I(V) and log I(V) to a Coulomb blockade model, we estimated the charging energy of one electron on the Au nanoparticles to be 10 times greater than the thermal energy k T; the tunneling resistance of the Au core–Au(111) surface was evaluated to be 3.5 GΩ ±15%.

We propose an all-painting process to produce a respiration sensor made from a humiditysensitive nanoparticle (NP) film and a graphite trace. The sensor is fabricated under ambient air with a simple vacuum-free process for green electronics: solely hand-painting on a cellulose acetate film. A humidity-sensitive silica NP film is painted by brush on pencil-trace graphite electrodes. An all-painted humidity sensor using this film shows 10 6 % sensitivity within a 10-93% humidity change. The film is flexible and the humidity sensor operates as a respiration sensor after bending test. We design an all-painted respiration sensor using the humidity sensor

The electrical and optical properties of semiconductor nanocrystals (NCs) can be controlled, in addition to size and shape, by doping. However, such a process is not trivial in NCs due to the high formation energy of dopants there. Nevertheless, it has been shown theoretically that in the case of B and P (acceptor/donor) codoped Si-NCs the formation energy is reduced relative to that of single type doping. Previous comprehensive measurements on ensembles of such codoped Si-NCs have pointed to the presence of donor and acceptor states within the energy gap. However, such a conjecture has not been directly verified previously. Following that, we investigate here the electronic properties of B and P codoped Si-NCs via Scanning Tunneling Spectroscopy. We monitored the quantum confinement effect in this system, for which the energy gap changed from ∼1.4 eV to ∼1.8 eV with the decrease of NC diameter from 8.5 to 3.5 nm. Importantly, all spectra showed two in-gap band-states, one close to the conduction band edge and the other to the valence band edge, which we attribute to the P and B dopant levels, respectively. The energy separation between these dopants states decrease monotonically with increasing NC diameter, in parallel to the decrease of the conduction-to-valence bands separation. A fundamental quantity that is derived directly for these Si-NCs is the intrinsic like position of the Fermi energy, a non-trivial result that is very relevant for understanding the system. Following the above results we suggest an explanation for the character and the origin of the dopants bands.

We report a portable respiration sensor for the analysis of respiration rates, patterns, and phases during exercise. A SiO2 nanoparticle thin film on a flexible substrate is used as a sensor chip (4.1 mm × 5 mm in area of electrodes) to detect respiration. Response and recovery time of the sensor chip are 0.7 and 1.7 s against human respiration. Even when it is covered with water, the response quickly recovers within 1 s after removal of the water. At 5 cm away from a face, a portable respiration sensor can track respiration rates up to 1.7 Hz at rest. The sensor also monitors respiration patterns and phases during exercise noninvasively. The fast-response and portable respiration sensor is usable as a healthcare device.