Prospects for Photo Electron Spectroscopy in a Scanning Transmission Electron Microscope

High spatial resolution microanalysis in scanning transmission electron microscopes is most easily performed when the specimen is inside a magnetic immersion objective lens. Recently a technique has been developed to perform spectroscopy of electrons that originate in this magnetic field. A very special form of photo electron spectroscopy is then possible for thin specimens in the microscope. An energy loss ΔE of a primary electron has the same physical effect as the absorption of a photon of energy ΔE. A coincidence measurement between energy loss electrons and the emitted electrons is expected to give a so called coincidence electron spectrum, or (e,2e) spectrum, of a very small area, which gives the same physical information as photo electron spectroscopy. Normal photo electron spectroscopy of limited spatial resolution, but with high collection efficiency, should also be possible in a scanning transmission electron microscope if the specimen is illuminated with a photon beam. Experiments to test the expectations are in progress

Charge transport and trapping in Cs-doped poly(dialkoxy-p-phenylene vinylene) light-emitting diodes

Al/Cs/MDMO-PPV/ITO (where MDMO-PPV stands for poly[2-methoxy-5-(3'-7'-dimethyloctyloxy)-1,4phenylene vinylene] and ITO is indium tin oxide) light-emitting diode (LED) structures, made by physical vapor deposition of Cs on the emissive polymer layer, have been characterized by electroluminescence, current-voltage, and admittance spectroscopy. Deposition of Cs is found to improve the balance between electron and hole currents, enhancing the external electroluminescence efficiency from 0.01 cd A-1 for the bare Al cathode to a maximum of 1.3 cd A-1 for a Cs coverage of only 1.5×1014 atoms/cm2. By combining I-V and admittance spectra with model calculations, in which Cs diffusion profiles are explicitly taken into account, this effect could be attributed to a potential drop at the cathode interface due to a Cs-induced electron donor level 0.61 eV below the lowest unoccupied molecular orbital. In addition, the admittance spectra in the hole-dominated regime are shown to result from space-charge-limited conduction combined with charge relaxation in trap levels. This description allows us to directly determine the carrier mobility, even in the presence of traps. In contrast to recent literature, we demonstrate that there is no need to include dispersive transport in the description of the carrier mobility to explain the excess capacitance that is typically observed in admittance spectra of p-conjugated materials

Setting benchmarks for modelling gas–surface interactions using coherent control of rotational orientation states

A fundamental and predictive understanding of molecule-surface interactions is challenging to obtain. Here the authors report an experimental technique allowing direct measurement of the scattering matrix, which reports on the coherent evolution of quantum states of a molecule scattering from a surface

Sub-nanometre resolution imaging of polymer-fullerene photovoltaic blends using energy-filtered scanning electron microscopy

The resolution capability of the scanning electron microscope has increased immensely in recent years, and is now within the sub-nanometre range, at least for inorganic materials. An equivalent advance has not yet been achieved for imaging the morphologies of nanostructured organic materials, such as organic photovoltaic blends. Here we show that energy-selective secondary electron detection can be used to obtain high-contrast, material-specific images of an organic photovoltaic blend. We also find that we can differentiate mixed phases from pure material phases in our data. The lateral resolution demonstrated is twice that previously reported from secondary electron imaging. Our results suggest that our energy-filtered scanning electron microscopy approach will be able to make major inroads into the understanding of complex, nano-structured organic materials

Plasma Filamentation in the Rijnhuizen-Tokamak Rtp

Evidence for small scale magnetic structures in the Rijnhuizen tokamak RTP is presented. These are manifest through steps and peaks in the electron temperature and pressure, measured with multiposition Thomson scattering. During central electron cyclotron heating, several filaments of high pressure are found in the power deposition region. They live hundreds of microseconds. Near the sawtooth inversion radius a \u27\u27step\u27\u27 in the temperature profile occurs. Further out, quasiperiodic structures are observed, in both Ohmic and heated discharges

Enhanced Transport During Pellet Injection in the Rijnhuizen-Tokamak-Rtp

The evolution of the radial profiles of electron temperature and density in a tokamak plasma during ablation of an injected hydrogen pellet is studied by Thomson scattering with a resolution of 1% of the mirror plasma radius. The energy content is hardly affected until the pellet reaches the sawtooth inversion radius when strongly enhanced transport sets in throughout the plasma. Asymmetric profiles are observed. Peaks of high density are formed, one of which often develops into a density \u27\u27snake.\u27\u2