Publications
Tunable nanophotonic array traps with enhanced force and stability
A nanophotonic trapping platform based on on-chip tunable optical interference allows parallel processing of biomolecules and holds promise to make single molecule manipulation and precision measurements more easily and broadly available. The nanophotonic standing wave array trap (nSWAT) device [Nat. Nanotechnol. 9, 448 (2014); Nano Lett. 16, 6661 (2016)] represents such a platform and can trap a large array of beads by the evanescent field of the standing wave of a nanophotonic waveguide and reposition them using an integrated microheater.
High Dynamic Range X-Ray Detector Pixel Architectures Utilizing Charge Removal
Several charge integrating CMOS pixel front ends utilizing charge removal techniques have been fabricated to extend dynamic range for X-ray diffraction applications at synchrotron sources and X-ray free electron lasers (XFELs). The pixels described herein build on the mixed mode pixel array detector (MM-PAD) framework, developed previously by our group to perform high dynamic range imaging.
Nematic fluctuations balancing the zoo of phases in half-filled quantum Hall systems
Half-filled Landau levels form a zoo of strongly correlated phases. These include non-Fermi-liquids (NFLs), fractional quantum Hall (FQH) states, nematic phases, and FQH nematic phases. This diversity begs the following question: what keeps the balance between the seemingly unrelated phases? The answer is elusive because the Halperin-Lee-Read description that offers a natural departure point is inherently strongly coupled. However, the observed nematic phases suggest that nematic fluctuations play an important role.
Thermodynamic constraints on the amplitude of quantum oscillations
Magneto-quantum oscillation experiments in high-temperature superconductors show a strong thermally induced suppression of the oscillation amplitude approaching the critical dopings [B. J. Ramshaw, Science 348, 317 (2014)SCIEAS0036-807510.1126/science.aaa4990; H. Shishido, Phys. Rev. Lett. 104, 057008 (2010)PRLTAO0031-900710.1103/PhysRevLett.104.057008; P. Walmsley, Phys. Rev. Lett. 110, 257002 (2013)PRLTAO0031-900710.1103/PhysRevLett.110.257002] - in support of a quantum-critical origin of their phase diagrams.
Grand canonical electronic density-functional theory: Algorithms and applications to electrochemistry
First-principles calculations combining density-functional theory and continuum solvation models enable realistic theoretical modeling and design of electrochemical systems. When a reaction proceeds in such systems, the number of electrons in the portion of the system treated quantum mechanically changes continuously, with a balancing charge appearing in the continuum electrolyte. A grand-canonical ensemble of electrons at a chemical potential set by the electrode potential is therefore the ideal description of such systems that directly mimics the experimental condition.
Nanosecond magnetization dynamics during spin Hall switching of in-plane magnetic tunnel junctions
We present a study of the magnetic dynamics associated with nanosecond scale magnetic switching driven by the spin Hall effect in 3-terminal nanoscale magnetic tunnel junctions (MTJs) with in-plane magnetization.
Surface atomic structure of epitaxial LaNiO3 thin films studied by in situ LEED- I(V)
We report in situ low-energy electron diffraction intensity versus voltage [LEED-I(V)] studies of the surface atomic structure of epitaxially grown (001)pc-oriented (pc=pseudocubic) thin films of the correlated 3d transition-metal oxide LaNiO3. Our analysis indicates the presence of large out-of-plane bucklings of the topmost LaO layers but only minor bucklings of the topmost NiO2 layers, in close agreement with earlier surface x-ray diffraction data.
Influence of Surface Adsorption on the Oxygen Evolution Reaction on IrO2(110)
A catalyst functions by stabilizing reaction intermediates, usually through surface adsorption. In the oxygen evolution reaction (OER), surface oxygen adsorption plays an indispensable role in the electrocatalysis. The relationship between the adsorption energetics and OER kinetics, however, has not yet been experimentally measured. Herein we report an experimental relationship between the adsorption of surface oxygen and the kinetics of the OER on IrO2(110) epitaxially grown on a TiO2(110) single crystal.
Characterization and control of ZnGeN2 cation lattice ordering
ZnGeN2 and other heterovalent ternary semiconductors have important potential applications in optoelectronics, but ordering of the cation sublattice, which can affect the band gap, lattice parameters, and phonons, is not yet well understood. Here the effects of growth and processing conditions on the ordering of the ZnGeN2 cation sublattice were investigated using x-ray diffraction and Raman spectroscopy. Polycrystalline ZnGeN2 was grown by exposing solid Ge to Zn and NH3 vapors at temperatures between 758 °C and 914 °C.
Control of spin–orbit torques through crystal symmetry in WTe2/ferromagnet bilayers
Recent discoveries regarding current-induced spin-orbit torques produced by heavy-metal/ferromagnet and topological-insulator/ferromagnet bilayers provide the potential for dramatically improved efficiency in the manipulation of magnetic devices. However, in experiments performed to date, spin-orbit torques have an important limitation - the component of torque that can compensate magnetic damping is required by symmetry to lie within the device plane.