Search

Magnesium oxide (MgO) is generally a wide band-gap oxide unable to conduct electric current in the bulk at room temperature. In this study, MgO nanocubes synthesized by self-burning micro-sized Mg metal powders in air showed electrical conductivity when they were sandwiched between two gold-mesh electrodes and steadily applied a voltage at room temperature (∼25 °C). In addition, a simultaneous light emission caused by the microdischarge of nitrogen molecules occurred adjacent to the cathode. The light emission was observed when traces of water vapor existed in the gas environment. In the case of a voltage pulse produced by switching off, transient emissions of Mg I and Mg II were detected on both sides of the electrodes. However, those steady and transient light emissions were not observed in the commercial MgO nanoparticles devoid of nanocubes. The light emissions shown in the cases of the steady-state might be caused by electron injection into the empty conductive states, which exist along the edges of MgO nanocubes, as a result of the spontaneous dissociation of water vapors at reactive sites of the nanocube surfaces as well as a result of the reduction of the energy barriers between the cathode and MgO nanocubes in contact. For transient emission, electrons trapped in the low coordinate sites were released with voltage pulse and neutralized the nearby Mg+ and Mg2+ ions, driving them into the excited neutral states, Mg I and Mg II.

Improving the stability of perovskite solar cells remains crucial. Here, Ahn et al. show that trapped charges at grain boundaries induce the dissociation of the perovskite compound in the presence of moisture, and explain why degradation is irreversible under illumination and reversible in the dark.

Mn2+ ion doping is used as an electron paramagnetic resonance (EPR) probe to investigate the influence of low-coordination structural defects such as step edges at the surface of terraced (001) MgO nanoparticles on the electronic properties. Beside the well-known hyperfine sextet of Mn2+ ions in the cubic crystal field of MgO, an additional EPR feature with a striking nonmonotonous temperature dependent shift of the g-factor is observed in terraced nanoparticles in the temperature range from 4 K to room temperature. By linking the difference in the temperature dependence of the Mn2+ sextet intensity in cubic and terraced nanoparticles with the possible s-d exchange shift and enhanced Zeeman splitting we conclude that the novel EPR feature originates from the loosely trapped charge-compensating carriers at the abundant structural defects at the surface of terraced nanoparticles due to their exchange interaction with neighboring Mn2+ ions.

We provide a complete classification of possible configurations of mutually pairwise-touching infinite cylinders in Euclidian three-dimensional space. It turns out that there is a maximum number of such cylinders possible in three dimensions independently of the shape of the cylinder cross-sections. We give the explanation of the uniqueness of the non-trivial configuration of seven equal mutually touching round infinite cylinders found earlier. Some results obtained for the chirality matrix, which is equivalent to the Seidel adjacency matrix, may be found useful for the theory of graphs.

Among many attempts to make a decent human motion detector in various engineering fields, a mechanical crack-based sensor that deliberately generates and uses nano-scale cracks on a metal deposited thin film is gaining attention for its high sensitivity. While the metal layer of the sensor must be responsible for its high performance, its effects have not received much academic interest. In this paper, we studied the relationship between the thickness of the metal layer and the characteristics of the sensor by depositing a few nanometers of chromium (Cr) and gold (Au) on the PET film. We found that the sensitivity of the crack sensor improves/increases under the following conditions: (1) when Au is thin and Cr is thick; and (2) when the ratio of Au is lower than that of Cr, which also increases the transmittance of the sensor, along with its sensitivity. As we only need a small amount of Au to achieve high sensitivity of the sensor, we have suggested more efficient and economical fabrication methods. With this crack-based sensor, we were able to successfully detect finger motions and to distinguish various signs of American Sign Language (ASL).

We investigated changes in emission spectra from nitrogen/argon diluted laminar diffusion acetylene and ethylene blue flames irradiated by a powerful cw infrared CO2 laser. The changes in the radical emission bands can be interpreted as an indication of laser-induced decomposition of ethylene (for laser absorbing C2H4 fuel) and of laser-absorbing intermediates (for non-absorbing C2H2 fuel). The results indicate that released active hydrogen plays an important role in addition/abstraction reactions without any participation of oxygen.