KCl ultra-thin films with polar and non-polar surfaces grown on Si(111)7 × 7

Novel Unexpected Reconstructions of (100) and (111) Surfaces of NaCl: Theoretical Prediction

We have predicted stable reconstructions of the (100) and (111) surfaces of NaCl using the global optimization algorithm USPEX. Several new reconstructions, together with the previously reported ones, are found. For the cleaved bare (100) surface, pure Na and pure Cl are the only stable surface phases. Our study of the (111) surface shows that a newly predicted Na₃Cl-(1 × 1) reconstruction is thermodynamically stable in a wide range of chlorine chemical potentials. It has a sawtooth-like profile where each facet reproduces the (100) surface of rock-salt NaCl, hinting on the preferred growth of the (100) surface. We used Bader charge analysis to explain the preferable formation of this sawtooth-like Na₃Cl-(1 × 1) reconstruction of the (111) surface of NaCl. We find that at a very high chemical potential of Na, the polar (and normally absent) (111) surface becomes part of the equilibrium crystal morphology. At both very high and very low chemical potentials of Cl, we predict a large decrease of surface energy and fracture toughness (the Rehbinder effect).

Stabilizing the commensurate charge-density wave in 1T-tantalum disulfide at higher temperatures via potassium intercalation

The 1T phase of tantalum disulfide (1T-TaS2) possesses a variety of charge-density-wave (CDW) orders, and as a result, it attracts an increasing amount of academic and technological interest. Researchers have devoted tremendous efforts towards understanding the impacts of doping, alloying, intercalation or other triggering agents on its charge density wave orders. In this work, we demonstrate that incorporating potassium chloride (KCl) during chemical vapor deposition (CVD) of TaS2 can control the phase (1T, 2H or metal nanowires) via the intercalation of potassium ions (K+) between TaS2 layers. Finally, we demonstrate that K+ not only impacts the structure during synthesis but also strongly impacts the CDW phase transition as a function of temperature, increasing the nearly commensurate (NCCDW) to commensurate (CCDW) transition to just below room temperature.