ABSTRACT
The gas sensing properties of pristine Sn3C2monolayer and different transition metal adatom (TM-Sn3C2, where TM = Fe, Co, Ni, Cu, Ru, Rh, Pd and Ag) was investigated using van der Waals corrected density functional theory. The understanding and potential of use of Sn3C2monolayers as sensors or adsorbent for CO, CO2, NO, NO2and SO2gaseous molecules is evaluated by calculating the adsorption and desorption energetics. From the calculated adsorption energies, we found that the pristine Sn3C2monolayer and 3dTM has desirable properties for removal of the considered molecules based on their high adsorption energy, however the 4dTM is applicable as recoverable sensors. We applied an Arrhenius-type equation to evaluate the recovery time for the desorption of the molecules on the pristine and TM adatom on Sn3C2monolayer. We found that the negative adsorption energies from -1 to -2 eV of the molecules resulted in easier recovery of the adsorbed gases at reasonable temperatures compared to adsorption energies in between 0 and -1 eV (weakly physiosorbed) and below -2 eV (strongly chemisorbed). Hence, we obtained that the Rh-Sn3C2, Ru-Sn3C2, Pd-Sn3C2, Pd-Sn3C2, and Rh-Sn3C2monolayers are good recoverable scavengers for the CO, CO2, NO, NO2, and SO2molecules. The current theoretical calculations provide new insight on the effect of TM adatoms on the structural, electronic, and magnetic properties of the Sn3C2monolayer and different transition metal adatom as well as shed light on their application as gas sensors/scavengers.
ABSTRACT
Two dimensional HfS2 is a material with potential applications in the field of photo-catalysis and advanced solid state devices. Density functional theory with the Hubbard U parameter (DFT+U) calculations were carried out to investigate the structural, electronic and optical properties of lanthanide dopant atoms (LN = La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu) in the HfS2 mono-layer. The calculated electronic band gap for a pristine HfS2 mono-layer is 1.30 eV with a non-magnetic ground state. The dopant substitutional energies under both Hf-rich and S-rich conditions were evaluated, with the S-rich condition for the dopant atoms being negative. This implies that the incorporation of these LN dopant atoms in the HfS2 is feasible and experimental realization possible. The introduction of LN dopant atoms in the HfS2 mono-layer resulted in a significant change of the material properties. We found that the presence of LN dopant atoms in the HfS2 mono-layer significantly alters its electronic ground states by introducing defect states as well as changes in the overall density of states profile resulting in a metallic ground state for the doped mono-layers. The doped mono-layers are all magnetic with the exception of La and Lu dopant atoms. We found that LN dopant atoms in the HfS2 mono-layer influence the absorption and reflectivity spectra with the introduction of states in the lower frequency range (<1.30 eV). Furthermore, we showed that the applicability of doped HfS2 mono-layers as photo-catalysts is very different compared with the pristine HfS2 mono-layer.
ABSTRACT
An electron current can move atoms in a nanoscale device with important consequences for the device operation and breakdown. We perform first principles calculations aimed at evaluating the possibility of changing the energy barriers for atom migration in carbon-based systems. In particular, we consider the migration of adatoms and defects in graphene and carbon nanotubes. Although the current-induced forces are large for both the systems, in graphene the force component along the migration path is small and therefore the barrier height is little affected by the current flow. In contrast, the same barrier is significantly reduced in carbon nanotubes as the current increases. Our work also provides a real-system numerical demonstration that current-induced forces within density functional theory are non-conservative.
