Search results for "SED"
showing 10 items of 21612 documents
Real space observation of two-dimensional Bloch wave interferences in a negative index photonic crystal cavity
2008
We report here the direct observation of two-dimensional (2D) Bloch wave interferences in a negative index photonic crystal by using optical near-field microscopy techniques. The photonic crystal is formed by a defectless honeycomb lattice of air holes etched in III-V semiconductor slab. A scanning near-field optical microscope is used to visualize spatially, as well as spectrally, the light distribution inside the photonic crystal. The recorded near-field spectra and maps presented here unambiguously demonstrate the Bloch wave interferences within the photonic crystal. Then, the spectral and spatial evolution of these interferences allows us to recover experimentally the 2D band diagram of…
Hydrogen plasma induced photoelectron emission from low work function cesium covered metal surfaces
2017
Experimental results of hydrogen plasma induced photoelectron emission from cesium covered metal surfaces under ion source relevant conditions are reported. The transient photoelectron current during the Cs deposition process is measured from Mo, Al, Cu, Ta, Y, Ni, and stainless steel (SAE 304) surfaces. The photoelectron emission is 2–3.5 times higher at optimal Cs layer thickness in comparison to the clean substrate material. Emission from the thick layer of Cs is found to be 60%–80% lower than the emission from clean substrates. peerReviewed
Structure and dielectric properties at phase transition of Na1/2Bi1/2TiO3-BaTiO3 solid solutions
2016
ABSTRACTPhase coexistence region is studied by x-ray diffraction for Na1/2Bi1/2TiO3-BaTiO3 solid solutions in the tetragonal phase side from the morphotropic phase boundary. The first order ferroelectric phase transition, determined from a jump in the temperature dependence of dielectric permittivity, is located inside the coexistence region of cubic and tetragonal phases and is below the temperature, where tetragonality disappears. At low BaTiO3 concentrations phase transition into ferroelectric state at cooling is slowly approached in time and is smeared over large temperature range. Rietveld method, applied for more precise evaluation of phase content, reveals large local deformations in…
Magnetic field control of gas-liquid mass transfer in ferrofluids
2020
Abstract Gas-liquid mass transfer plays a key role in a broad range of industrial processes. The magnetic field control over the morphology of the gas-liquid interface and solute transport is an attractive feature if it can be realized efficiently. However, the magnetic properties of typical liquids and gases are rather weak. The experimental investigation is carried out to evaluate the effect of the magnetic field, which is mediated by magnetic nanoparticles, on the gas-liquid mass exchange during the sparging run through a hydrocarbon ferrofluid. The results indicate that the gradient field is especially effective at controlling the gas-liquid contact volume: the foaming of the liquid dur…
Spontaneous order in ensembles of rotating magnetic droplets
2019
Ensembles of elongated magnetic droplets in a rotating field are studied experimentally. In a given range of field strength and frequency the droplets form rotating structures with a triangular order - rotating crystals. A model is developed to describe ensembles of several droplets, taking into account the hydrodynamic interactions between the rotating droplets in the presence of a solid wall below the rotating ensemble. A good agreement with the experimentally observed periodic dynamics for an ensemble of four droplets is obtained. During the rotation, the tips of the elongated magnetic droplets approach close to one another. An expression is derived that gives the magnetic interaction be…
Negative differential resistance and threshold-switching in conical nanopores with KF solutions
2021
Negative differential resistance (NDR) phenomena are under-explored in nanostructures operating in the liquid state. We characterize experimentally the NDR and threshold switching phenomena observed when conical nanopores are immersed in two identical KF solutions at low concentration. Sharp current drops in the nA range are obtained for applied voltages exceeding thresholds close to 1 V and a wide frequency window, which suggests that the threshold switching can be used to amplify small electrical perturbations because a small change in voltage typically results in a large change in current. While we have not given a detailed physical mechanism here, a phenomenological model is also includ…
The role of disorder on Er3+ luminescence in Na1/2Bi1/2TiO3
2018
Abstract Photoluminescence in Er-doped NBT is studied at different temperatures. Remarkable reduction of the luminescence intensity in the green spectral range is found in the poled state comparing with the depoled state. Luminescence spectra at low temperatures reveal continuous wavelength shift of some maxima belonging to the 4 S 3/2 → 4 I 15/2 transition depending on the excitation wavelength, which is explained by large variety of different environments around Er 3+ related to the random distribution of Na + and Bi 3+ in A-sublattice of the ABO 3 perovskite structure. Poling extends the wavelength range where shift of luminescence maxima is observed in the direction of longer excitati…
Nanoscale Etching of GaAs and InP in Acidic H<sub>2</sub>O<sub>2</sub> Solution: A Striking Contrast in Kinetics and Surface …
2018
In this study of nanoscale etching for state-of-the-art device technology the importance of the nature of the surface oxide, is demonstrated for two III-V materials. Etching kinetics for GaAs and InP in acidic solutions of hydrogen peroxide are strikingly different. GaAs etches much faster, while the dependence of the etch rate on the H+ concentration differs markedly for the two semiconductors. Surface analysis techniques provided information on the surface composition after etching: strongly non-stoichiometric porous (hydr)oxides on GaAs and a thin stoichiometric oxide that forms a blocking layer on InP. Reaction schemes are provided that allow one to understand the results, in particular…
Microfabricated high temperature sensing platform dedicated to scanning thermal microscopy (SThM)
2018
Abstract The monitoring of heat flux is becoming more and more critical for many materials and structures approaching nanometric dimensions. Scanning Thermal Microscopy (SThM) is one of the tools available for thermal measurement at the nanoscale and requires calibration. Here we report on a micro-hotplate device made of a platinum heater suspended on thin silicon nitride (SiN) membranes integrating specific features for SThM calibration. These heated reference samples can include a localized resistive temperature sensors (RTD) or standalone platinum membranes (typically 10 × 10 μm2) on which the temperature can be measured precisely. This functional area is dedicated to (1) estimate the th…
Localized domain wall nucleation dynamics in asymmetric ferromagnetic rings revealed by direct time-resolved magnetic imaging
2016
We report time-resolved observations of field-induced domain wall nucleation in asymmetric ferromagnetic rings using single direction field pulses and rotating fields. We show that the asymmetric geometry of a ring allows for controlling the position of nucleation events, when a domain wall is nucleated by a rotating magnetic field. Direct observation by scanning transmission x-ray microscopy (STXM) reveals that the nucleation of domain walls occurs through the creation of transient ripplelike structures. This magnetization state is found to exhibit a surprisingly high reproducibility even at room temperature and we determine the combinations of field strengths and field directions that all…