David Waterhouse

Highly efficient time-of-flight spectrometer for studying low-energy secondary emission from dielectrics: Secondary-electron emission from LiF film

A highly efficient time-of-flight electron spectrometer is described. An incident electron current of the order of 10−14u2009A makes it suitable for studying secondary emission from dielectric surfaces. A microchannel plate position-sensitive detector allows flight distance correction while keeping a large acceptance angle. Measured energy distribution curves of secondary electrons generated from a LiF film by 19–31 eV incident electrons demonstrate good energy resolution and reveal reproducible and stable emission features at 2.6±0.3u2009eV, 7.2±0.3u2009eV, and 10.3±0.3u2009eV.

The performance of a microchannel-plate-based position sensitive detection system

The characteristics and calibration of a microchannel-plate-based resistive-anode position-sensitive detector (PSD) are reported. Factors affecting the spatial uniformity of the fast rise-time timing signals and the position-dependent performance are discussed. When two such detectors are used for (e,2e) coincidence measurements, the detection efficiency of the PSDs must be uniform to within 5% for reliable quantitative comparisons of data acquired on different sections of the PSD. The relative efficiency in coincidence mode reflects the single detector efficiency uniformity. Such an apparatus was used to measure argon triple differential cross sections (TDCS) to determine the validity of the distorted wave Born approximation (DWBA) quantum scattering model. Relative to the argon 3s TDCS, the simultaneously acquired 3p TDCS is smaller than the DWBA prediction by a factor of 1.15±0.05.

Interference and PCI in argon Auger (e,2e) spectra

Angle-dependent interference is observed in electron-impact ionization (e, 2e) coincidence experiments on the argon and Auger transitions. Recapture of the slow ejected electron from the Auger process leads to interference with the satellite-state ionization processes. The post-collision interaction (PCI) and interference effects are quantified for a large range of excess energies.

Double-cantilever mount for angle-resolving particle detectors

A double cantilever detector mount, constructed from aluminum, was designed to support an angle-resolving particle detector mounted on a rotary table. The mount allows precise and accurate alignment of the detector’s field of view in the Cartesian x, y, and z plane, and allows precise control of the azimuthal angle of the detector. The mount is simple to adjust, provides high precision and stability, and can be used in any situation where precise and accurate detector alignment is required.

Momentum resolution in (e,2e) experiments

Abstract The influence of electron spectrometer alignment on the momentum resolution of electron-impact ionisation (e,2e) experiments is quantified. We show that for coplanar measurements with circular detector apertures, the azimuthal spectrometer alignment should be determined with an accuracy of ±0.001 rad to optimise the momentum resolution of an (e,2e) apparatus. Using this criterion, we predict an improvement in the (e,2e) momentum resolution of ∼30% near q =0 a.u., where quantum-mechanical scattering models predict a minimum in the triple differential cross-section (TDCS) of atomic p states. This result will assist in determining an upper limit on the effects of second order scattering processes that contribute to small momentum transfers.

Electron recapture near thresholds

Electron recapture following photon or electron-impact ionisation near thresholds attracts considerable interest. A comparison is made of the information gained from studies utilising different methods of observation including ion yields, (e, 2e) coincidence, and photo-electron spectroscopy, to increase understanding of the electron recapture process.