First-principles investigation of the physical properties of indium based fluoroperovskites InAF(3) (A = Ca, Cd and Hg)
MATERIALS SCIENCE IN SEMICONDUCTOR PROCESSING
Authors: Khan, Sajid; Ahmad, Rashid; Mehmood, Nasir; Hina, Faryal; Rehman, Alatf Ur; Zaman, Shams U.; Kim, H. J.
The theoretical study is performed to investigate the structural, elastic, electronic and optical properties of Indium based fluoroperovskites InAF(3) (A = Ca, Cd, and Hg) based on the Density Functional Theory (DFT) using the Full-Potential Linearized Augmented Plane Wave (FP-LAPW) method implemented in WIEN2K. Generalized Gradient Approximation (GGA) with Hubbard term (GGA + U) is employed for the incorporation of exchangecorrelation energy. The optimized lattice constants are found in the range of 4.51 angstrom to 4.69 angstrom. The calculated values of elastic constants show that compounds satisfy the stability criteria for a cubic system. It has also been observed that all the compounds are ductile and show anisotropic behavior. Calculated bandgaps of InCaF3 and InCdF3 are 3.66 eV and 3.29 eV, respectively, exhibiting direct band nature. The InHgF3 is found to be an indirect bandgap material having the value of 1.59 eV. The significance of states contributed by each element is inferred from the total and partial density of state plots. The optical characteristics are discussed and analyzed in a broad energy range (with specific range shown 0-30 eV) using important parameters such as optical conductivity and reflectivity, refractive index, extinction coefficient, and absorption coefficient. The results are communicated for the first time for understudy Indium based compounds.
Defect engineering on MoS2 surface with argon ion bombardments and thermal annealing
APPLIED SURFACE SCIENCE
Authors: Lu, Weigang; Birmingham, Blake; Zhang, Zhenrong
Various approaches have been developed to produce MoS2 monolayers and multilayers. Using plasma and thermal thinning, layer-by-layer thinning processes were developed to produce MoS2 monolayer and multilayers. However, an atomic-level understanding of the thinning mechanism and defects created in these processes is not clear. In this paper, we studied the impact on surface structures of bulk MoS2 by argon ion (Art(+)) bombardments and thermal annealing using an ultra-high vacuum (UHV) scanning tunneling microscope (STM). The STM images obtained before and after Ar+ bombardments show that low-energy (50 eV) Ar+ ions can remove single atoms from the surface and fragment the top sulfur layer resulting in single sulfur vacancy point defects and atomic pits on the MoS2 surface. Higher energy (100 eV) Ar+ ions can penetrate deeper and remove the topmost MoS2 trilayer. After bombardment with an Ar+ beam of 500 eV, the MoS2 surface appeared as granulated nanostructures consisting of 1-3 nm nanoparticles. Upon thermal annealing, topmost sulfur atoms were removed through sublimation after heating at 650 degrees C for 5 min and deeper atom sublimation was observed with longer annealing time, resulting in granulated nanostructures on the MoS2 surface.