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First-principles calculations are performed to inspect the electronic and transport properties of a Fe-thiacrown molecular device, namely, a Au-Fe(9S3)2-Au junction. It is found that the junction has a low-spin (LS) ground state and a high-spin (HS) metastable state. Further study shows that the HS state is a conducting state while the LS state is a nearly insulating one, which means that a switch between these two spin configurations results in a good electrical switching behavior and can serve as an ON/OFF state for a logic unit. Thus, it may find applications as switches or memories in molecular electronic circuits. [ABSTRACT FROM AUTHOR]

We reported the effect of the deposition time of barrier layers on optical and structural properties of high-efficiency green-light-emitting InGaN/GaN multiple quantum wells (MQWs) by photoluminescence (PL) and high-resolution x-ray diffraction techniques. The MQW samples on (0001)-plane sapphire substrates were prepared with a ramping method by metalorganic chemical deposition. It was found that the structural or interface quality of the MQW system improved as the deposition time of barrier layers increased from 10 to 14 min, but lattice relaxation was still observed. The relaxation degree decreases from 33% to 6% as the deposition time increases. Temperature-dependent PL measurements from 12 to 300 K indicated that the integrated PL intensities start to decay rapidly as temperature rises above 50 K for the sample with the shorter deposition time, and above 100 K for the sample with the longer deposition time. The luminescence thermal quenching of the two samples suggests the two nonradiative recombination centers based on a fit to Arrhenius plot of the normalized integrated PL intensity over the entire temperature range. The first centers at higher temperatures show less difference for the two samples. The second centers at lower temperatures can be attributed to the trapping of carriers at the rough interface for the sample with the shorter deposition time and to the thermal quenching of bound excitons for the sample with the longer deposition time, respectively. [ABSTRACT FROM AUTHOR]

We report first-principles calculations on the electrical transport properties of two kinds of one-dimensional nanowires:  (a) a carbon nanowire (CNW) with alternating single and triple bonds and (b) a boron−nitrogen nanowire (BNNW) with equidistant bonds. We demonstrate the similarity and difference between the carbon nanowire and its boron−nitrogen analogue in the molecular orbital and transport properties, and then explore the potential innovations. The effects of molecular orbitals and nanowire-electrode coupling on the transport properties are analyzed. The cases of the nanowires sandwiched between both nanoscale and bulk electrodes are considered. It suggests that the characteristics of the transmission spectra and the current−voltage characteristics (I−Vcurves) are determined both by the electrodes and by the molecule as well as their coupling. In particular, the negative differential resistance (NDR) phenomenon is more apparent when the nanowires are positioned between two nanoscale electrodes. The tuning of the transport properties is also probed through the changes of nanowire−electrode separation and the inclusion of a gate voltage. These lead to dramatic variations in the equilibrium conductance, which can be understood from the shift and alignment of the molecular orbital relative to the Fermi level of the electrodes. In the analysis of the effects of nanowire−electrode separation, it shows that the equilibrium conductance has the same variation behavior as that of the projected density of states (PDOS) for CNW, while the localized molecular orbitals of BNNW result in its conductance varies differently from its PDOS. The different molecular orbital characteristics near the Fermi level of these two kinds of nanowires underlie their different transport properties. [ABSTRACT FROM AUTHOR]