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Featured researches published by E. Jung.


Journal of Electron Spectroscopy and Related Phenomena | 1995

Auger line shape measurements using positron annihilation induced Auger electron spectroscopy

A.H. Weiss; S. Yang; H.Q. Zhou; E. Jung; S. Wheeler

Abstract Conventional methods of Auger electron spectroscopy (AES) make use of energetic electron or photon beams to create the core-hole excitations that lead to the Auger transition. The energetic beams result in a large secondary electron background in the Auger peak region. In positron annihilation induced Auger electron spectroscopy (PAES), the core holes are created by matter-antimatter annihilation and not through collisional ionization. Measurements are reviewed which indicate that PAES can eliminate the secondary electron background by the use of very low (∼10 eV) positron beam energies and that PAES has greatly increased surface selectivity due to the trapping of positrons in surface state prior to annihilation. A new PAES spectrometer has been developed in our laboratory with an energy resolution which is an order of magnitude better than previous PAES spectrometers. The high-resolution PAES system has been used to measure the Auger M 2,3 VV line shape from a clean polycrystalline Cu surface. The atomic-like Auger M 2 VV and M 3 VV features are clearly resolved. Differences observed between the PAES spectra and spectra obtained using electron induced Auger spectroscopy are discussed.


Applied Surface Science | 1997

Energy spectra of electrons and positrons emitted from surfaces as a result of low energy positron bombardment

A.H. Weiss; E. Jung; J.H. Kim; A. Nangia; Ranjani Venkataraman; Shannon G. Starnes; G. Brauer

Abstract Recent measurements of the energy spectra of electrons and positrons emitted from metal and semiconductor surfaces as a result of bombardment with low energy electrons and positrons are reviewed. The high resolution positron re-emission spectra show a close correspondence with that part of the electron induced electron spectrum termed ‘redistributed primaries’ while positron impact-induced secondary electrons show a close correspondence with that part of the electron induced electron spectrum termed ‘true secondaries’. Positron re-emission data from a SiC(0001) surface indicate that this surface has a negative positron workfunction. Peaks in the positron induced electron spectra for Ge(100) and SiC(0001) corresponding to Auger electrons resulting from the annihilation of positrons trapped in a surface state with core electrons in the surface layer are identified and discussed. Additional evidence for the existence of a positron surface state on SiC is provided by data indicating thermal desorption of positronium (Ps).


Applied Surface Science | 1997

Background-free Auger line shape of Ag N2,3VV measured with positron annihilation induced Auger electron spectroscopy

E. Jung; H.Q. Zhou; J.H. Kim; S. Starnes; R. Venkataraman; A.H. Weiss

Abstract Auger spectra for the Ag(100) N 2,3 VV transition obtained utilizing positron annihilation induced Auger electron spectroscopy (PAES) are presented. This low energy transition of Ag is difficult to separate from the large secondary background which is present using electron induced Auger electron spectroscopy (EAES) and has not been studied extensively. In our measurements, the secondary electron background is eliminated by utilizing a positron beam whose energy is below the energy range of the of the Auger electrons. Measurements of the temperature dependence of PAES intensity, I PAES , and positronium fraction, f Ps , indicate that I PAES is proportional to the quantity (1 − f Ps . Electron energy spectra taken at high temperature ( f Ps ≈ 1) clearly demonstrate that the prominent low energy tail (LET) present in the PAES spectra is associated with Auger transitions and is not due to secondary electrons induced by collisions with the primary positron beam. The Auger line shape of the N 2,3 VV transition of Ag(100) is accounted for in terms of the convolution of the density of states of the N 2,3 core levels and the density of states of the correlated two-hole final states estimated from the N 2,3 XPS core level spectra and the Auger line shape of the M 4 VV transition. In addition, possible mechanisms leading to the production of the LET including a N 2 N 3 V transition followed by a N 3 V-VVV transition and/or electron energy loss during the escape from the topmost layer are discussed.


Applied Surface Science | 1995

Method for the measurement of positron affinities and positron work functions suitable for both positive and negative work function materials

A.H. Weiss; S. Yang; H.Q. Zhou; E. Jung; Ali R. Koymen; S. Naidu; G. Brauer; Martti J. Puska

Abstract The positron affinity A + , defined by A + + Φ − + Φ + = 0, where Φ − ( Φ + ) refer to the electron (positron) work functions, is a fundamental property of solids which is useful for the determination of the behavior of positrons in multicomponent systems. For systems with a negative positron work function it is often possible to estimate the positron work function and affinity by measuring the energy of positrons re-emitted from the surface. However, this method will not work in those cases for which the positron work function is positive. While the positron affinity may, in principle, be determined in these cases from positronium time-of-flight measurements, such measurements are technically difficult. In this paper, a new method for the determination of positron affinities and positron work functions will be outlined. This method, which is based upon measurements of the cut-off energy in positron-induced secondary electron spectra, is of particular interest in that it may be used in cases where the positron work function is positive.


Applied Surface Science | 1997

Positron annihilation induced Auger electron spectroscopy (PAES) study of the structure of Si/H/Ge(100) interfaces

J.H. Kim; S. Wheeler; A. Nangia; E. Jung; A.H. Weiss

Abstract Positron annihilation induced Auger electron spectroscopy (PAES), which makes use of low energy positrons to excite Auger transitions by annihilation of core electrons, was applied to the study of the effect of adsorbed atomic hydrogen on the stability of Si films grown on a Ge(100) substrate. Previous work has shown that PAES has a high degree of selectivity for the topmost atomic layer due to the trapping of positrons in an image potential well just outside the surface before annihilation. The concentration of Si and Ge atoms on the surface layer were monitored by measuring PAES intensities of the Si LVV and Ge MVV peaks after deposition of Si on Ge(100) with and without the prior adsorption of H on the substrate. The PAES results indicated that when 8 ML of Si was deposited on Ge(100) after introducing 5000 L H 2 , the surface consisted almost exclusively of Si atoms. In the absence of H, segregation of Ge atoms to the surface was observed even after deposition of 8 ML of Si at room temperature.


APPLICATION OF ACCELERATORS IN RESEARCH AND INDUSTRY: Twentieth International#N#Conference | 2009

The Effects of Surface Reconstruction and Electron‐Positron Correlation on the Annihilation Characteristics of Positrons Trapped at Semiconductor Surfaces

Nail G. Fazleev; E. Jung; A.H. Weiss

Experimental positron annihilation induced Auger electron spectroscopy (PAES) data from Ge(100) and Ge(111) surfaces display several strong Auger peaks corresponding to M4,5N1N2,3, M2,3M4,5M4,5, M2,3M4,5V, and M1M4,5M4,5 Auger transitions. The integrated peak intensities of Auger transitions have been used to obtain experimental annihilation probabilities for the Ge 3d and 3p core electrons. The experimental data were analyzed by performing theoretical studies of the effects of surface reconstructions and electron‐positron correlations on image potential induced surface states and annihilation characteristics of positrons trapped at the reconstructed Ge(100) and Ge(111) surfaces. Calculations of positron surface states and annihilation characteristics have been performed for Ge(100) surface with (2×1), (2×2), and (4×2) reconstructions, and for Ge(111) surface with c(2×8) reconstruction. Estimates of the positron binding energy and annihilation characteristics reveal their sensitivity to the specific atomi...


Materials Science Forum | 1997

The Study of Secondary Electrons and Redistributed Primaries (Electrons and Positrons) from Ge(100) Surface Utilizing the Electron and the Positron Beams

E. Jung; Ranjani Venkataraman; Shannon G. Starnes; A.H. Weiss


Materials Science Forum | 1997

Measurement of Positron Work Function, Positronium Fraction and PAES Intensities from GaAs(100)

Jeong-han Kim; A. Nangia; E. Jung; A.H. Weiss


Materials Science Forum | 1994

Auger Line Shape of M2,3VV Measured with Positron Annihilation Induced Auger Electron Spectroscopy

S. Yang; H.Q. Zhou; E. Jung; A.H. Weiss


Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms | 2007

Positron probes of the Ge(100) surface : The effects of surface reconstructions and electron-positron correlations on positron trapping and annihilation characteristics

Nail G. Fazleev; E. Jung; A.H. Weiss

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A.H. Weiss

University of Texas at Arlington

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H.Q. Zhou

University of Texas at Arlington

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A. Nangia

University of Texas at Arlington

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J.H. Kim

University of Texas at Arlington

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Shannon G. Starnes

University of Texas at Arlington

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Nail G. Fazleev

University of Texas at Arlington

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Ranjani Venkataraman

University of Texas at Arlington

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S. Wheeler

University of Texas at Arlington

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G. Brauer

Helmholtz-Zentrum Dresden-Rossendorf

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