Structure of a zinc oxide ultra-thin film on Rh(100)

Electronic structure of strain-tunable Janus WSSe–ZnO heterostructures from first-principles

The electronic structure of semiconducting 2D materials such as monolayer transition metal dichalcogenides (TMDs) are known to be tunable via environment and external fields, and van der Waals (vdW) heterostructures consisting of stacks of distinct types of 2D materials offer the possibility to further tune and optimize the electronic properties of 2D materials. In this work, we use density functional theory (DFT) calculations to calculate the structure and electronic properties of a vdW heterostructure of Janus monolayer WSSe with monolayer ZnO, both of which possess out of plane dipole moments. The effects of alignment, biaxial and uniaxial strain, orientation, and electric field on dipole moments and band edge energies of this heterostructure are calculated and examined. We find that the out of plane dipole moment of the ZnO monolayer is highly sensitive to strain, leading to the broad tunability of the heterostructure band edge energies over a range of experimentally-relevant strains. The use of strain-tunable 2D materials to control band offsets and alignment is a general strategy applicable to other vdW heterostructures, one that may be advantageous in the context of clean energy applications, including photocatalytic applications, and beyond.

Using strain engineering to optimize novel heterostructure materials to produce hydrogen from water.

Local electronic structure, work function, and line defect dynamics of ultrathin epitaxial ZnO layers on a Ag(1 1 1) surface

Using combined low-temperature scanning tunneling microscopy and Kelvin probe force microscopy we studied the local electronic structure and work function change of the (0 0 0 1)-oriented epitaxial ZnO layers on a Ag(1 1 1) substrate. Scanning tunneling spectroscopy (STS) revealed that the conduction band minimum monotonically downshifts as the number of the ZnO layers increases up to 4 monolayers (ML). However, it was found by field emission resonance (FER) spectroscopy that the local work function of Ag(1 1 1) slightly decreases for 2 ML thick ZnO but it dramatically changes and drops by about 1.2 eV between 2 and 3 ML, suggesting a structural transformation of the ZnO layer. The spatial variation of the conduction band minimum and the local work function change were visualized at the nanometer scale by mapping the STS and FER intensities. Furthermore, we found that the ZnO layers contained line defects with a few tens of nm long, which can be removed by the injection of a tunneling electron into the conduction band.