A diode for ferroelectric domain-wall motion

For over a decade, controlling domain wall injection, motion and annihilation along nanowires has been the preserve of the nanomagnetics research community. Revolutionary technologies have resulted, like race-track memory and domain wall logic. Until recently, equivalent research in analogous ferroic materials did not seem important. However, with the discovery of sheet conduction, the control of domain walls in ferroelectrics has become vital for the future of what has been termed “domain wall electronics”. Here we report the creation of a ferroelectric domain wall diode, which allows a single direction of motion for all domain walls, irrespective of their polarity, under a series of alternating electric field pulses. The diode’s saw-tooth morphology is central to its function. Domain walls can move readily in the direction in which thickness increases gradually, but are prevented from moving in the other direction by the sudden thickness increase at the saw-tooth edge.

An alternative methodology in Schottky diode physics

The fabrication and electrical characterization of Schottky junction diodes have been extensively researched for three-quarters of a century since the original work of Schottky in 1938. This study breaks from the highly standardized regime of such research and provides an alternative methodology that prompts novel, more efficient applications of the adroit Schottky junction in areas such as chemical and thermal sensing. The core departure from standard Schottky diode configuration is that the metal electrode is of comparable or higher resistance than the underlying semiconductor. Further, complete electrical characterization is accomplished through recording four-probe resistance-temperature (R-D-T) characteristics of the device, where electrical sourcing and sensing is done only via the metal electrode and not directly through the semiconductor. Importantly, this results in probing a nominally unbiased junction while eliminating the need for an Ohmic contact to the semiconductor. The characteristic R-D-T plot shows two distinct regions of high (metal) and low (semiconductor) resistances at low and high temperatures, respectively, connected by a crossover region of width, DT, within which there is a large negative temperature coefficient of resistance. The R-D-T characteristic is highly sensitive to the Schottky barrier height; consequently, at a fixed temperature, R-D responds appreciably to small changes in barrier height such as that induced by absorption of a chemical species (e.g., H-2) at the interface. A theoretical model is developed to simulate the R-D-T data and applied to Pd/p-Si and Pt/p-Si Schottky diodes with a range of metal electrode resistance. The analysis gives near-perfect fits to the experimental R-D-T characteristics, yielding the junction properties as fit parameters. The modelling not only helps elucidate the underlying physics but also helps to comprehend the parameter space essential for the discussed applications. Although the primary regime of application is limited to a relatively narrow range (DT) for a given type of diode, the alternative methodology is of universal applicability to all metal-semiconductor combinations forming Schottky contacts. (C) 2015 AIP Publishing LLC.

Effectiveness of diode laser trans-scleral cyclophotocoagulation in patients following silicone oil-induced ocular hypertension in Chinese eyes.

We evaluated the effectiveness of diode laser trans-scleral cyclophotocoagulation (TSCPC) on intraocular pressure (IOP) in nine patients having raised IOP following use of silicone oil (SO) for retinal detachment (RD) surgery in a retrospective observational case series. Diode laser TSCPC was applied at a power setting of 1.75 to 2.5 watts, for two sec with a maximum of 30 applications. The patients were followed up for 40 to 312 weeks. The mean pre-laser IOP was 32.06 mm Hg (SD 7.32). The mean post-laser IOP at one month, three months and six months was 17.89 mm Hg (SD 8.23), 21.89 mm Hg (SD 8.16) and 21.67 mm Hg (SD 7.55) respectively. The final IOP (at the last follow-up) was 19.56 mm Hg (SD 7.85) (P=0.021). Seven of them had undergone SO removal. In our observation, effectiveness of TSCPC in long-term control of SO-induced ocular hypertension was limited as compared to short-term control of IOP.

XFEL resonant photo-pumping of dense plasmas and dynamic evolution of autoionizing core hole states

Similarly to the case of LIF (Laser-Induced Fluorescence), an equally revolutionary impact to science is expected from resonant X-ray photo-pumping. It will particularly contribute to a progress in high energy density science: pumped core hole states create X-ray transitions that can escape dense matter on a 10 fs-time scale without essential photoabsorption, thus providing a unique possibility to study matter under extreme conditions. In the first proof of principle experiment at the X-ray Free Electron Laser LCLS at SCLAC [Seely, J., Rosmej, F.B., Shepherd, R., Riley, D., Lee, R.W. Proposal to Perform the 1^st High Energy Density Plasma Spectroscopic Pump/Probe Experiment", approved LCLS proposal L332 (2010)] we have successfully pumped inner-shell X-ray transitions in dense plasmas. The plasma was generated with a YAG laser irradiating solid Al and Mg targets attached to a rotating cylinder. In parallel to the optical laser beam, the XFEL was focused into the plasma plume at different delay times and pump energies. Pumped X-ray transitions have been observed with a spherically bent crystal spectrometer coupled to a Princeton CCD. By using this experimental configuration, we have simultaneously achieved extremely high spectral (λ/δλ ≈ 5000) and spatial resolution (δx≈70 μm) while maintaining high luminosity and a large spectral range covered (6.90 - 8.35 Å). By precisely measuring the variations in spectra emitted from plasma under action of XFEL radiation, we have successfully demonstrated transient X- ray pumping in a dense plasma.