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Xie, Z. Y.

Publications and source records attributed to Xie, Z. Y..

4 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Epitaxial Growth and Band Alignment of p-NiO/n-Fe2O3 Heterojunction on Al2O3(0001)

Fe2O3 is one of the promising oxide semiconductors as photoanodes for photoelectrochemical water splitting, but its efficiency is still limited by the short diffusion length of photo-excited carriers. Using the internal electric field formed at a p-n heterojunction (HJ) is an efficient strategy to mitigate such limitation. Accordingly, the interfacial atomic structure and band alignment are the most crucial parameters for efficiency optimization. In this work, we report on the epitaxial growth and determination of the band energy alignment of NiO/Fe2O3 p-n heterojunction grown on Al2O3(0001) substrate by pulsed laser deposition. We show that high crystalline quality NiO(111) thin films can be grown on Fe2O3(0001) with epitaxial relationships of [1 ¯11]NiO||[0001 ¯ ]Fe2O3(out-of-plane), [1 ¯1 ¯0]NiO||[011 ¯0]Fe2O3 and [1 ¯12 ¯ ]NiO||[21 ¯1 ¯0]Fe2O3(in-plane). The rotation of NiO hexagons by 30° can effectively reduce the lattice mismatch from ~17.4% to ~1.58%. High resolution X-ray photoelectron spectroscopy reveals that valence and conduction band offset of NiO/Fe2O3 heterojunction are 0.7 eV and 2.3 eV with an upward band bending potential of 0.23 eV for Fe2O3 and a downward band bending potential of 0.32 eV for NiO, respectively. This kind of interfacial band alignment not only facilitates the charge separation, but lowers the overpotentials for oxygen evolution reaction.

Photoelectrochemical Water Splitting, Oxide Semico↗
DOE OSTI2014

Progress towards quantum simulating the classical O ( 2 ) mode

We connect explicitly the classical $O(2)$ model in 1+1 dimensions, a model sharing important features with $U(1)$ lattice gauge theory, to physical models potentially implementable on optical lattices and evolving at physical time. Using the tensor renormalization group formulation, we take the time continuum limit and check that finite dimensional projections used in recent proposals for quantum simulators provide controllable approximations of the original model. We propose two-species Bose-Hubbard models corresponding to these finite dimensional projections at strong coupling and discuss their possible implementations on optical lattices using a $^{87}$Rb and $^{41}$K Bose-Bose mixture.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2014

Controlling sign problems in spin models using tensor renormalization

We consider the sign problem for classical spin models at complex $\beta =1/g_0^2$ on $L\times L$ lattices. We show that the tensor renormalization group method allows reliable calculations for larger Im$\beta$ than the reweighting Monte Carlo method. For the Ising model with complex $\beta$ we compare our results with the exact Onsager-Kaufman solution at finite volume. The Fisher zeros can be determined precisely with the TRG method. We check the convergence of the TRG method for the O(2) model on $L\times L$ lattices when the number of states $D_s$ increases. We show that the finite size scaling of the calculated Fisher zeros agrees very well with the Kosterlitz-Thouless transition assumption and predict the locations for larger volume. The location of these zeros agree with Monte Carlo reweighting calculation for small volume. The application of the method for the O(2) model with a chemical potential is briefly discussed.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗