E. Weigold - Academia.edu (original) (raw)

Papers by E. Weigold

Nuclear Instruments and Methods, 1961

The design of a counter telescope to measure angular distributions in the range 0°-150 ° for neut... more The design of a counter telescope to measure angular distributions in the range 0°-150 ° for neutron induced reactions is outlined. The operation and performance of the equipment which includes, in addition to the usual circuitry, fast coincidence equipment based on the detection of the associated ~-particle from the d(t,n)ct reaction and equipment to identify charged particles of different mass is described.

Coincidence Studies of Electron and Photon Impact Ionization, 1997

Australian Journal of Physics, 1996

Electron momentum spectroscopy (EMS), based on kinematically complete observations of high energy... more Electron momentum spectroscopy (EMS), based on kinematically complete observations of high energy electron impact ionisation events, directly observes energymomentum dispersion laws and densities of electrons in solids. The valence electronic structure in the near surface region, up to a depth of about 20 Å is probed for thin free-standing films (about 100 Å) by the multiparameter EMS spectrometer at Flinders University. The principles of the measurement are described and its application to the determination of energymomentum densities in a range of amorphous, polycrystalline and crystalline materials is discussed.

AIP Conference Proceedings, 2003

Electron momentum spectroscopy measurements of graphite single-crystals are presented. Data were ... more Electron momentum spectroscopy measurements of graphite single-crystals are presented. Data were taken for incoming electrons with an energy of 50 keV, and both outgoing electrons with an energy near 25 keV. Spectra are presented for the major symmetry directions of graphite. To remove the effect of inelastic multiple scattering we use in all cases an identical deconvolution procedure, which consistently

Nuclear Physics A, 2004

Correlated many-particle dynamics in Coulomb systems, which is one of the unsolved fundamental pr... more Correlated many-particle dynamics in Coulomb systems, which is one of the unsolved fundamental problems in AMO-physics, can now be experimentally studied with so far unprecedented completeness and precision of the momenta of all particles involved in the reaction. The recent development of the COLTRIMS technique (COLd Target Recoil Ion Momentum Spectroscopy) provides a coincident multi-fragment imaging technique for eV and sub eV particle detection (1,2). In its completeness, e.g. measuring the fully differential cross section of a reaction by detecting the particles in 47r for all energies up to a couple of 100 eV so far, it is as powerful as the bubble chamber in high energy physics. Based on state-of-the-art cooling techniques (super sonic jets, MOT etc.) and nuclear physics imaging methods, fragmentation processes of atoms, molecules, clusters, as well as the dynamics of electron emission from solid state surfaces which are induced by single photon or multi photon laser absorption, electron or ion impact can be explored completely in momentum space and, for ions, with micro eV resolution. In recent benchmark experiments quasi snapshots (duration as short as an attosec) of the correlated dynamics between electrons and nuclei are taken for atomic and molecular systems. This new imaging technique has opened a powerful observation window into the hidden world of many-particle dynamics. So far, it was generally assumed that the observation of correlated dynamics of electrons and the nuclei in atoms or molecules is beyond any technical realization, since it requires detection techniques, which can detect the electronic motion in the low attosecond domain. Purthermore it requires the observation of several particles at the same time with high momentum resolution. With the recent development of the COLTRIMS imaging technique this observation window is now opened. Instead of measuring two transition energies in atoms or molecules at two a few femtosec separated moments (e.g. with pump and probe laser technique) here the atom or molecule is very suddenly (a few attosec time duration) fragmented into several free particles. Thus the

Nuclear Physics, 1961

... Soc. 75 (1960) 526 13) RN Glover and E. Weigold, Nuclear Physics, to be published 14) N. Aust... more ... Soc. 75 (1960) 526 13) RN Glover and E. Weigold, Nuclear Physics, to be published 14) N. Austern, ST Butler and H. McManus, Phys. Rev. 92 (1953) 350 15) J. Benveniste, AC Mitchell, CD Schrader and JH Zenger, UCRL 5619 (1959); Nuclear Instruments 7 (1960) 306 16) SJ ...

Journal of Physics B: Atomic and Molecular Physics, 1979

The authors have measured absolute (e,2e) cross sections for electron impact ionisation of helium... more The authors have measured absolute (e,2e) cross sections for electron impact ionisation of helium with a much higher accuracy than obtained before. In a coplanar symmetric geometry ( theta =45 degrees ) both outgoing electrons-with equal velocities-were detected in coincidence. The resulting experimental triple differential cross sections for incoming electrons of 200-2800 eV contain an experimental error smaller than 20%.

Accurate measurements of the 1000-eV noncoplanar symmetric (e, 2e) reaction on xenon are reported... more Accurate measurements of the 1000-eV noncoplanar symmetric (e, 2e) reaction on xenon are reported. Cross-section calculations are carried out with the use of both the plane-wave and distorted-wave impulse approximations. The distorted-wave impulse approximation accurately describes both the 5p ' and Ss ' angular correlations and their relative cross sections. It also describes accurately the Sp3/2..5p&q2 branching ratios if Dirac-Fock target wave functions are used. The branching ratios show the inadequacy of Hartree-Fock wave functions for xenon. The planewave impulse approximation overestimates the 5s ' cross section relative to the Sp ' and underestimates the cross section at large angles. The Ss ' spectroscopic factors are assigned up to a separation energy of 45 eV, and the distorted-wave impulse-approximation calculation verifies that all the Ss ' strength has been found. The spectroscopic factors for the Ss ' manifold are obtained at 1000 and 1200 eV at a number of angles and are found to be independent of incident energy and ion recoil momentum. The spectroscopic factor for the lowest Ss ' transition at 23.4 eV is 0.37+0.01, whereas that for the ground-state Sp ' transition is greater than or equal to 0.98.

Journal of Electron Spectroscopy and Related Phenomena, 1998

The first experimental observation of 'orientational dichroism' in electron impact-induced ioniza... more The first experimental observation of 'orientational dichroism' in electron impact-induced ionization is discussed. (e,2e) experiments on pure angular momentum states of sodium, excited by right-and left-handed circularly polarized laser light, show that the angular distributions of the final state electron pair are strongly dependent on initial state orientation of the target. Comparison with calculation demonstrates the dependence of the dichroism on details of the scattering dynamics.

Journal of Physics D: Applied Physics, 1995

We have measured the spectral momentum densities of thin foils of diamond-like carbon using (e,2e... more We have measured the spectral momentum densities of thin foils of diamond-like carbon using (e,2e) spectroscopy. Transmission electron energy loss spectra and (e,2e) spectra were measured before and after annealing a thin foil at around 900% and before and after thinning the foil using reactive ion etching in an argor@xygen plasma. The valence band spectral momentum densities are compared with spherically averaged graphite and diamond band theory calculations. After annealing the surface sensitive (e,Ze) data are closer to the graphite theory for the foil. Before annealing and also after plasma etching the (e,2e) data compare more favourably with the diamond theory. Bulk-sensitive transmission energy loss spectra for the annealed sample show a weak graphitic plasmon at around 6 eV energy loss which disappears after subsequent plasma etching. These measurements show that the diamond-like carbon films become graphitic only at the surface after annealing and that the graphitic surface layer can be easily removed by reactive ion etching.

Chemical Physics, 1982

Abstract Electron detachment in collision of halogen anions and noble gas atoms was investigated ... more Abstract Electron detachment in collision of halogen anions and noble gas atoms was investigated in the collision energy range of 500-3000 eV. Differential cross sections were determined both for elastic scattering and for the electron detachment process in the angular range of 0-3°. It was found that direct electron detachment, due to the interaction of the discrete ion-atom state with a continuum of states increases with increasing collisional energy. Furthermore, the experimental evidence indicates that direct detachment primarily occurs in a limited range of impact parameters. A model, based on angular coupling, is described which qualitatively explains these two experimentally observed features.

Applied Physics A Materials Science & Processing, 1995

Physical Review B, 1995

The (e, 2e) technique is well known to be able to measure the momentum profiles of the electron o... more The (e, 2e) technique is well known to be able to measure the momentum profiles of the electron orbitals in molecules. In crystalline solids energy levels are replaced by bands, and the momentum profiles simplify to energy-dependent b functions. In this paper the development from a molecular to a crystalline picture of the electronic structure is illustrated using a simple model of a linear chain of atoms of increasing length. From this model we try to get some insight into the (e, 2e) momentum profiles expected for disordered solids. These results are compared to the experimental data for carbon films with difFerent degrees of order, i.e. , amorphous carbon films, annealed amorphous carbon films, and highly oriented pyrolitic graphite (HOPG) films. The intensity of the vr-electron contribution is suppressed in HOPG, due to the orientation chosen. In the annealed evaporated samples, the planes of graphite atoms have random orientation and the vr electrons are clearly seen. With increasing order the momentum profiles show increasingly well defined peaks. The Electronic Structure of Materials Centre is supported by a grant of the Australian Research Council.

Physical Review B, 1997

The energy-resolved electron momentum density of graphite has been measured along a series of wel... more The energy-resolved electron momentum density of graphite has been measured along a series of welldefined directions using (e,2e) spectroscopy. This is the first measurement of this kind, to our knowledge, performed on a single-crystal target with a thoroughly controlled orientation which clearly demonstrates the different nature of the and bands in graphite. Good agreement between the calculated density and the measured one is found, further establishing the fact that (e,2e) spectroscopy yields more direct and complete information on the valence electronic structure than any other method. ͓S0163-1829͑97͒04627-4͔

Surface Science, 1997

Electron momentum spectroscopy has been used to measure the electronic structure of aluminium aft... more Electron momentum spectroscopy has been used to measure the electronic structure of aluminium after exposure to increasing amounts of oxygen. The experimental valence band results showed the structural features of aluminium oxide beginning to dominate the free electron contribution of metallic aluminium as the exposure increased. The interpretation of this is that the aluminium oxide layer increases in thickness as the exposure increases, eventually saturating at a thickness of about 15 A. Alter subtracting the intensity of the underlying AI metal contribution from the oxidised states the valence band features of aluminium oxide were resolved even after exposure to only 600 L of oxygen. It is estimated that only about 5 A, of aluminium oxide is formed at this stage. A quantitative comparison was made to a linear muffin-tin orbital (LMTO) calculation for spherically averaged ~-AI203. Best agreement was obtained for the results of the lowest oxygen exposure (600 L). The chemical shifts of the AI 2p core level were also measured in separate experiments for two intermediate oxygen exposures between the aluminium and aluminium oxide cases for further characterisation. These measurements show that electron momentum spectroscopy is able to obtain the electron bands and the momentum densities of very thin disordered surface layers. ~/ 1997 Elsevier Science B.V.

Journal of Physics B: Atomic and Molecular Physics, 1974

Measurements are reported of angular distributions for electrons elastically scattered from krypt... more Measurements are reported of angular distributions for electrons elastically scattered from krypton in the energy range 30 eV to 200 eV. Distributions are also given for neon at 100 eV and xenon at 60 eV. The results agree reasonably well with those of previous workers, but, as observed for argon by Lewis et al. (1974), at the lower energies an increasing discrepancy is observed. The authors calculate angular distributions using a semi-phenomenological optical model and find good agreement with the experimental data at 100 eV and above. At all but low angles the relativistic calculations of Walker (1971) which ignore excitations of non-elastic channels, are in very good agreement with the data. The relative dependence with energy of the differential cross section at 30 degrees scattering angle has been measured for krypton, neon and xenon in the range 30 eV to 200 eV and the results are compared with available theoretical and experimental data.

Journal of Physics B: Atomic and Molecular Physics, 1976

The cross section ratio for the symmetric (e,2e) reaction on helium leading to the n=2 and ground... more The cross section ratio for the symmetric (e,2e) reaction on helium leading to the n=2 and ground states of the helium ion has been calculated as a function of the ion recoil momentum q, using a correlated helium wavefunction, and compared with the results of a 1200 eV non-coplanar experiment and some previous results at 800 eV. The calculation agrees well with the measured (e,2e) cross section ratios and at high q with ratios measured in photoelectron spectroscopy experiments.