Santos F. Alvarado

Nanometer resolution in luminescence microscopy of III‐V heterostructures

In a scanning tunneling microscope experiment, the luminescence induced by the recombination of holes with electrons tunneling into cleaved (110) GaAs/AlGaAs heterostructures is used to image the interface region with nanometer resolution.

Unidirectional spin Hall magnetoresistance in ferromagnet/normal metal bilayers

A unidirectional magnetoresistance observed in bilayer metal films could be used to add directional sensitivity to conventional magnetic sensors based on anisotropic magnetoresistance.

Transition-metal-oxide-based resistance-change memories

We provide a status report on the development of perovskite-based transition-metal-oxide resistance-change memories. We focus on bipolar resistance switching observed in Cr-doped SrTiO3 memory cells with dimensions ranging from bulk single crystals to CMOS integrated nanoscale devices. We also discuss electronic and ionic processes during electroforming and resistance switching, as evidenced from electron-parametric resonance (EPR), x-ray absorption spectroscopy, electroluminescence spectroscopy, thermal imaging, and transport experiments. EPR in combination with electroluminescence reveals electron trapping and detrapping processes at the Cr site. Results of x-ray absorption experiments prove that the microscopic origin of the electroforming, that is, the insulator-to-metal transition, is the creation of oxygen vacancies. Cr-doped SrTiO3 memory cells exhibit short programming times (≤100 ns) and low programming currents (<100 µA) with up to 105 write and erase cycles.

4.1: A 20‐inch OLED Display Driven by Super‐Amorphous‐Silicon Technology

A 20-inch, largest OLED display in the world is demonstrated which is driven by “Super Amorphous Silicon” technology. It has been widely believed that the characteristics of amorphous silicon TFT is not sufficient to drive OLED display. This paper turns over the hypothesis to prove that amorphous silicon can be applied to the large active-matrix driven displays. Novel approaches to enable amorphous silicon to drive bright and long life OLED display are shown to open a bright future to realize larger OLED televisions.

Interplay of spin-orbit torque and thermoelectric effects in ferromagnet/normal-metal bilayers

We present harmonic transverse voltage measurements of current-induced thermoelectric and spin-orbit torque (SOT) effects in ferromagnet/normal-metal bilayers, in which thermal gradients produced by Joule heating and SOT coexist and give rise to ac transverse signals with comparable symmetry and magnitude. Based on the symmetry and field dependence of the transverse resistance, we develop a consistent method to separate thermoelectric and SOT measurements. By addressing first ferromagnet/light-metal bilayers with negligible spin-orbit coupling, we show that in-plane current injection induces a vertical thermal gradient whose sign and magnitude are determined by the resistivity difference and stacking order of the magnetic and nonmagnetic layers. We then study ferromagnet/heavy-metal bilayers with strong spin-orbit coupling, showing that second harmonic thermoelectric contributions to the transverse voltage may lead to a significant overestimation of the antidamping SOT. We find that thermoelectric effects are very strong in Ta(6 nm)/Co(2.5 nm) and negligible in Pt(6 nm)/Co(2.5 nm) bilayers. After including these effects in the analysis of the transverse voltage, we find that the antidamping SOTs in these bilayers, after normalization to the magnetization volume, are comparable to those found in thinner Co layers with perpendicular magnetization, whereas the fieldlike SOTs are about an order of magnitude smaller.

Temperature dependence of the nonlocal voltage in an Fe/GaAs electrical spin-injection device

The nonlocal spin resistance is measured as a function of temperature in a Fe/GaAs spin-injection device. For nonannealed samples that show minority-spin injection, the spin resistance is observed up to room temperature and decays exponentially with temperature at a rate of 0.018\,K

Indium Distribution in Ingaas Quantum Wires Observed with the Scanning Tunneling Microscope

^{-1}

STM-excited electroluminescence and spectroscopy on organic materials for display applications

. Post-growth annealing at 440\,K increases the spin signal at low temperatures, but the decay rate also increases to 0.030\,K

ELECTROLUMINESCENCE FROM A SOLUBLE POLY(P-PHENYLENEVINYLENE) DERIVATIVE GENERATED USING A SCANNING TUNNELING MICROSCOPE

^{-1}

Atomic structure and luminescence excitation of GaAs/(AlAs)n(GaAs)m quantum wires with the scanning tunneling microscope

. From measurements of the diffusion constant and the spin lifetime in the GaAs channel, we conclude that sample annealing modifies the temperature dependence of the spin transfer efficiency at injection and detection contacts. Surprisingly, the spin transfer efficiency increases in samples that exhibit minority-spin injection.