Ofer Neufeld

Novel High-Throughput Screening Approach for Functional Metal/Oxide Interfaces

Metal/oxide interfaces have long been studied for their fundamental importance in material microstructure as well as their broad applicability in electronic devices. However, the challenge involved in characterizing the relation between structure and electron transport of a large number of metal/oxide combinations inhibits the search for interfaces with improved functionality. Therefore, we develop a novel high-throughput screening approach that combines computational and theoretical techniques. We use a Density Functional Theory + U (DFT+U) quantum mechanical formalism to produce effective Schrödinger equations, which are solved by wave packet propagation to simulate charge transport across the metal/oxide interface. We demonstrate this method on α-Fe2O3/Mt interfaces, for Mt = Ag, Al, Au, Ir, Pd, or Pt metals. We use this novel method to screen for binary alloys of these metals at the α-Fe2O3/Mt interface and perform a successful validation test of the methodology. Finally, we correlate the interface potential energy and the charge transport permeability through the interface. Counterintuitively, among the interfaces studied, we find that higher mismatch interfaces have better charge transport permeability. We anticipate that this method will be useful as a computationally tractable strategy to perform high-throughput screening for new metal/oxide interfaces.

Selective suppression of high-order harmonics within phase-matched spectral regions

Phase matching in high-harmonic generation leads to enhancement of multiple harmonics. It is sometimes desired to control the spectral structure within the phase-matched spectral region. We propose a scheme for selective suppression of high-order harmonics within the phase-matched spectral region while weakly influencing the other harmonics. The method is based on addition of phase-mismatched segments within a phase-matched medium. We demonstrate the method numerically in two examples. First, we show that one phase-mismatched segment can significantly suppress harmonic orders 9, 15, and 21. Second, we show that two phase-mismatched segments can efficiently suppress circularly polarized harmonics with one helicity over the other when driven by a bi-circular field. The new method may be useful for various applications, including the generation of highly helical bright attosecond pulses.

Metallic back-contact interface design in photoelectrochemical devices

Metal/metal-oxide interfaces appear in a wide variety of electronic applications. One such example is oxide based photoelectrochemical (PEC) cells in which the oxide constitutes the cells active material, and is in contact with a metal back-contact that assists in charge transport. The proper choice of contact can have a substantial impact on the cells performance. Hence, understanding the correlation between contact composition and performance is of crucial importance. For these reasons, in this paper we perform DFT+U calculations on several metal/oxide interfaces. Specifically, we examine the Mt/Fe2O3 interfaces for: Mt = Ag, Al, Au, Ir, Pd, and Pt, and the Pt/M2O3 interfaces for: M = Al, Cr, and Fe. The above interfaces have recently attracted much attention in PEC water splitting based on α-Fe2O3. We find a trend which describes the adhesion energy as a function of the interface bond distance between the metal and the oxide. This can be used to predict adhesion energies without performing a very expensive interface calculation, or experimental measurements. Furthermore, we find a correlation between the energy of adhesion and the surface charge in the first bonded layer of the FCC metal, such that a larger adhesion is associated with an increase in the bond ionicity. Finally, in each interface we find that the effective mass is reduced in the oxide due to metallic deposition and there are metal induced gap states (MIGS). These can help identify metal/oxide junctions that provide good contacts for charge transport. We predict that Ir metal should provide an ideal contact for Fe2O3 based PEC cells.