ABSTRACT
InN has received considerable attentions due to its small band-gap and unique properties in the III-nitride family. Understanding the effects of defects on optoelectronic properties of InN nanowire is essential for exploring its applications in future nanodevices. In this work, we have systematically calculated defect states in InN nanowires based on density-functional theory. Hydrogen passivation and several potential intrinsic point defects are considered in various sizes of nanowires, as well as charged defect states. For small-sized hexagonal nanowires, V N at N-poor condition or N In at N-rich condition is the most stable defect. Whereas for larger-sized nanowires, V N and InN defects are competing when the N chemical potential changes, showing obvious size effect of the defect stability on the nanowire surface. Those defect states change the electronic structure of the nanowires drastically by introducing empty bands or deep level and provide possibility to tailor the optical properties in terms of forming different stable defects.
ABSTRACT
Understanding the structure-property relationships of energetic compounds is challenging. Herein, by including the experimental data, we systematically evaluated the microscopic characteristics of a series of transition metal carbohydrazide perchlorate (TMCP) complexes (MnCP, FeCP, CoCP, NiCP, ZnCP, and CdCP) by first-principles calculations. The calculated properties, i.e., lattice enthalpy, bulk modulus, and electronic structures, were correlated with their thermal decomposition temperatures and impact sensitivities, which indicated that the stability and sensitivity of the TMCP complexes were greatly changed through coordination with different metal ions. The trend was that a large lattice enthalpy indicated a better thermal stability. Complexes with a high impact sensitivity tended to have a smaller bulk modulus and pseudo-gap. The ultra-high impact sensitivity of FeCP may have been related to the unstable spin state with respect to the volume change in the lattice. The calculated bond order and bond dissociation energy did not fully reflect the impact and friction sensitivities in this study. In addition, the combination of crystal properties and local bond information may better describe the sensitivity trend for the TMCP energetic compounds. This analysis can be applied to other energetic compounds and may provide clues for the synthesis and assessment of novel energetic compounds.
ABSTRACT
Tantalum disulfide (TaS2) two-dimensional film material has attracted wide attention due to its unique optical and electrical properties. In this work, we report the preparation of 1 T-TaS2 quantum dots (1 T-TaS2 QDs) by top-down method. Herein, we prepared the TaS2 QDs having a monodisperse grain size of around 3 nm by an effective ultrasonic liquid phase exfoliation method. Optical studies using UV-Vis, PL, and PLE techniques on the as-prepared TaS2 QDs exhibited ultraviolet absorption at 283 nm. Furthermore, we found that dimension reduction of TaS2 has led to a modification of the band gap, namely a transition from indirect to direct band gap, which is explained using first-principle calculations. By using quinine as reference, the fluorescence quantum yield is 45.6%. Therefore, our results suggest TaS2 QDs have unique and extraordinary optical properties. Moreover, the low-cost, facile method of producing high quality TaS2 QDs in this work is ideal for mass production to ensure commercial viability of devices based on this material. TaS2 quantum dots having a monodisperse grain size of around 3 nm have been prepared by an ultrasonic liquid phase exfoliation method, it has been found that the dimension reduction of TaS2 has led to a transition from indirect to direct band gap that results in the unique and extraordinary optical properties (PL QY: 45.6%).