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ABSTRACT: It is usually well accepted that for swift protons, the induced backward and forward electron emission yield is proportional
to the projectile electronic stopping power. This was observed in particular for thin amorphous carbon foils. However, this
law was established from a non extensive set of experimental data and somewhat confirmed by rough macroscopic theories. We
then developed a standard Monte Carlo simulation to predict the yield dependence on proton energy [0.5–10 MeV] and for a wide
range of foil thickness. After evaluating the reliability of this simulation, we showed and explained why the law of proportionality
cannot generally hold for forward electron emission. In particular, the ratio between forward yield and stopping power generally
depends on foil thickness and proton energy. We performed a new experiment that confirmed our theoretical predictions.
The European Physical Journal D 08/2001; 15(3):293-300. · 1.48 Impact Factor
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ABSTRACT: The influence of solid surfaces on the emission of low-energy convoy electrons (8 eV<or=Ee<or=13 eV) from different target materials (C, Al, Cu, Ag, Sm, Gd and Au) after Kr+ impact (1.4 MeV<or=Ep<or=2.2 MeV) has been studied for the first time under ultrahigh-vacuum conditions. It is found that the convoy electron yield increases with decreasing residual surface coverage if the surface is cleaned by dynamic sputtering. The convoy electron yield reaches a saturation value which depends on the work function of the target; the convoy electron yield increases with decreasing work function. This indicates that the transmission of convoy electrons is influenced by both surface contamination and the surface potential barrier.
Journal of Physics C Solid State Physics 11/2000; 21(28):5033.
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ABSTRACT: The characterise the surface condition of thin solid foils (x approximately=1000 AA) by ion impact, a novel combination of different independent methods of control has been used: (1) Auger electron spectroscopy (AES); (2) secondary electron spectroscopy (SES); (3) measurement of the total electron coefficient gamma ; and (4) detection of elastically scattered projectiles. Surfaces of various elemental foils (6<or=ZT<or=83) have been carefully prepared by heavy-ion- (Kr+-) induced sputtering. Coverage could be removed from the target surfaces (better than 0.3 remaining monolayers) and the roughness could be reduced considerably.
Journal of Physics D Applied Physics 11/2000; 21(3):472. · 2.54 Impact Factor
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Radiation Effects and Defects in Solids 10/1989; 110(1-2):149-151. · 0.40 Impact Factor
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H. Rothard,
K. Kroneberger,
M. Burhard,
J. Kemmler,
P. Koschar,
O. Heil,
C. Biedermann,
S. Lencinas,
N. Keller,
P. Lorenzen,
D. Hofmann,
A. Clouvas,
K. O. Groeneveld,
E. Veje
Radiation Effects and Defects in Solids 07/1989; 109(1-4):281-286. · 0.40 Impact Factor
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ABSTRACT: We have measured the target thickness dependent convoy electron yieldsY
c
from hydrogenic Ni27+, Ni28+ (15.6 MeV/u) which is discussed in the framework of an extended model for ELC and ECC in solids considering also contributions
from excited states. To understand the target thickness dependent evolution in the case of incident Ni27+ it must be assumed that convoy electrons produced by ELC arise mainly from excited states. The mean transport length λ
e
for convoy electrons for light projectile ions is equal to the attenuation length of isotachic free electrons λ
e
, whereas for the heavy ions an enhanced transport length λ
e
≫ λ
e
must be introduced.
05/1989; 65(2):135-139.
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ABSTRACT: Based on the results from measurements of equilibrium convoy electron yieldsY
e
(q) in coincidence with projectiles of different outgoing chargesq from Pb31+ (1.4 MeV/u) and C6+ (1 MeV/u) on carbon foils we present a simple rate equation for convoy electron production which gives a consistent interpretation of yields, for light and heavy projectile ions in nonequilibrium and equilibrium of charge exchange. It will be pointed out that from convoy electron yields in the equilibrium regime of charge exchange the relative importance of ELC and ECC processes to the total yield cannot be determined. However, absolute normalized equilibrium convoy electron yieldsY
f
(q) allows us to estimate the overall contribution of convoy electrons to charge exchange in dependence on the ionization stateq.
Zeitschrift für Physik D 02/1989; 13(1):45-49.
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O. Heil,
J. Kemmler,
K. Kroneberger,
A. Kövér,
Gy. Szabó,
L. Gulyás,
R. DeSerio,
S. Lencinas,
N. Keller,
D. Hofmann, H. Rothard,
D. Berényi,
K. O. Groeneveld
[show abstract]
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ABSTRACT: We have measured the cusp electron yield in coincidence with the transmitted charge state (He0, He+ and He++) when3He+ collides with He and Ne under single collision conditions. For the first time this enables the electron capture to the continuum (ECC) yield to be directly compared with that from electron loss to continuum (ELC). While the ECC contribution is smaller than that from ELC at high projectile velocities (V
p
>3 au) the data suggest that ECC will dominate belowV
p
=2.8 au. The relevance of the results to the projectile velocity dependence of existing capture theories is discussed.
Zeitschrift für Physik D 08/1988; 9(3):229-234.
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ABSTRACT: We have studied the target thickness (rho x) dependence of the convoy electron yield Y/sub e/(q/sub f/) for the incident projectiles of nickel ions (charge q/sub i//sup +/) (15.6 MeV/u) with q/sub i/ = 28 and 27 on carbon foils in coincidence with outgoing projectiles with charge q/sub f/ = 28 and 27. Simultaneously the charge state evolution F(q/sub f/, rho x) dependence on the incident charge q/sub i/ has been measured. For this collision system the charge state distribution equilibrates for target thicknesses > 650 ..mu..g/cm/sup 2/. In the framework of a model for convoy electron production the rho x dependence of the yield Y/sub e/ (q/sub i/,q/sub f/) can be explained if one introduces and electron transport length lambda/sub c/ which is much larger than the attenuation length lambda/sub e/ of free electrons.
12/1986
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J. Kemmler,
O. Heil,
C. Biedermann,
P. Koschar, H. Rothard,
K. Kroneberger,
K. O. Groeneveld,
A. Kövér,
G. Szabò,
L. Gulyàs,
D. Berényi,
P. Focke,
W. Meckbach
[show abstract]
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ABSTRACT: The target thickness dependence of the convoy electron yield in carbon foils (3.1 < x < 22 g/cm2) from incident projectiles Cqi qi=2, 4, 6 at 1 MeV/u has been measured in coincidence with the outgoing projectile charge states qf. The observed charge state distributions of the carbon ions are in non-equilibrium for the thinnest targets. We find that the coincident convoy electron yield Ye(qf) in the non-equilbrium regime is dependent on x, qi and qf. In contradiction to earlier findings, these results cannot be explained only by assuming electron loss to continuum processes (ELC). For the first time, the cusp-electron yield in the single collision system 3He+(0.2 < Ep/m < 0.33 MeV/u) on a He gas target in coincidence with the emergent projectiles 3He+ and 3He++ has been measured. Surprisingly, a significant contribution of cusp electrons in coincidence with He+ has been found which is attributed to electron capture to continuum (ECC).
01/1970: pages 362-373;
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ABSTRACT: The yields of backward and forward electrons resulting from Hn+ cluster (n=1–13) interactions with carbon foils in the 40–120 keV/proton energy range have been measured as a function of the cluster size and of the foil thickness. A strong reduction of both backward and forward yields per proton is observed in comparison to free proton yields, with a saturation for n ⋍ 9. Surprisingly the forward cluster effect persists for foils as thick as 3000 Å.
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms.
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A. L’Hoir,
C. Koumeir,
S. Della Negra,
P. Boduch,
P. Roussel-Chomaz,
A. Cassimi,
M. Chevallier,
C. Cohen,
D. Dauvergne,
M. Fallavier,
D. Jacquet,
B. Manil,
J.-C. Poizat,
C. Ray, H. Rothard,
D. Schmaus,
M. Toulemonde
[show abstract]
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ABSTRACT: A thin germanium crystal has been irradiated at GANIL by Pb beams of 29 MeV/A (charge state Qin = 56 and 72) and of 5.6 MeV/A (Qin = 28). The induced ion emission from the sample entrance surface was studied, impact per impact, as a function of Qin, velocity vin and energy loss ΔE in the crystal. The Pb ions transmitted through the crystal were analyzed in charge (Qout) and energy using the SPEG spectrometer. The emitted ionized species were detected and analyzed in mass by a time-Of-flight multianode detector (LAG). Channeling was used to select peculiar ΔE values in Ge and hence peculiar Pb ion trajectories close to the emitting entrance surface. The experiment was performed in standard vacuum. No Ge emission was found. The dominating emitted species are H+ and hydrocarbon ions originating from the contamination layer on top of the crystal. The mean value 〈M〉 of the number of detected species per incoming Pb ion (multiplicity) varies as (Qin/vin)p, with p values in agreement with previous results. We have clearly observed an influence of the energy deposition ΔE in Ge on the emission from the top contamination layer. When selecting increasing values of ΔE, we observed a rather slow increase of 〈M〉. On the contrary, the probabilities of high multiplicity values, which are essentially connected to fragmentation after emission, strongly increase with ΔE.
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms.
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[show abstract]
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ABSTRACT: We measured energy spectra of electrons from sputter cleaned amorphous carbon targets induced by swift ions of constant velocity (Ep/Mp=9 MeV/u) with a new mobile ultra high vacuum set-up designed for large scale accelerators. We varied the projectile charge qp from 6 to 27. The shape of the spectra was found to depend strongly on qp: a qp2 scaling law at large electron energies and a strong saturation with increasing qp for low energy electrons (below the 1 s ionization threshold) are observed. We also observed an additional feature on the high energy side of the KLL Auger peak, for large projectile charges only. This additional peak may be interpreted as a hypersatellite line due to the double ionization of the K shell.
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms.
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ABSTRACT: Desorption of nitrogen adsorbates from amorphous carbon (a-C) surfaces due to swift ion (Z=6–73, q=6–54, energy 6–13 MeV/u) and electron impact (5 keV) was studied by secondary electron emission (SEE) measurements. The fluence dependence of ion induced electron emission obeys an exponential decay law as the coverage rate is in the sub-mono-layer range. The desorption yield σ varies approximately as σ∼(dE/dx)3/2 or σ∼q3 as a function of the electronic energy loss dE/dx and the projectile charge q, respectively. We discuss the possible desorption mechanisms connected to electronic excitation. Furthermore, we present an ESCA investigation on the mechanism for the influence of nitrogen adsorbates on SEE yields. The mechanism for the SEE enhancement effect is connected to the surface termination: nitrogen adsorbates are believed to provide surface states which generate a downwards energy band bending, which on relative scale pushes up the Fermi level towards the conduction band minimum, reducing the work function.
Surface Science.
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ABSTRACT: Doubly differential cross sections for electron emission induced by the passage of swift heavy ions such as Fq+ (1.5-2.0 MeV/u) through thin solid foil targets were measured at the Tandem accelerator of the JR Macdonald Laboratory at Kansas State University. The complete angular distribution of electron emission up to 4000 eV (beyond the maximum of the "binary encounter" electron peak) was determined as a function of the projectile charge state (q = 5 and 9) and the target material in a wide Z range: C (Z = 6), At (Z = 13) and Au (Z = 79). Electrons emitted from the foils between 0 and +/-180degrees with respect to the beam axis were energy and angle analysed by means of a toroidal electrostatic electron spectrometer equipped with a 2D position sensitive channelplate detector. In addition to low energy cascade electrons, electrons from collective excitation (plasmons), target Auger electrons, convoy electrons and binary encounter electrons, we also observe a new feature never before seen in electron angular distributions: narrow electron jets ("spikes") emitted along the ion beam axis in forward and backward directions. This observation is made possible by the good angular resolution of our spectrometer and the possibility to record the entire angular distribution in a single run. (C) 2002 Elsevier Science B.V. All rights reserved.
Nuclear Instruments & Methods in Physics Research Section B- Beam Interactions with Materials and Atoms, v.193, 651-655 (2002).
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ABSTRACT: Electron spectra were measured at GANIL with different heavy ions (C–Mo) and various charge states q (q = 6–39) at fixed projectile velocity v (v = 19 atomic units, 9.2 MeV/u). A projectile dependent broadening of ion induced KVV Auger electron peaks from carbon targets was observed. From this broadening, one can deduce a mean “electronic temperature” of the heavy ion induced track at the corresponding Auger decay time (10 fs). We compare the measured temperature values to the predictions of an inelastic-thermal spike model, which takes into account the electron–phonon coupling. The model underestimates the experimental values, but reproduces the increase with ion charge.
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms.
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S. Andriamonje,
B. Blank,
R. Del Moral,
J.P. Dufour,
L. Faux,
A. Fleury,
M.S. Pravikoff,
C. Röhl,
M. Chevallier,
D. Dauvergne, [......],
Y. Girard,
A. L'Hoir,
J.P. Rozet,
D. Schmaus,
D. Vernhet,
J. Dural, H. Rothard,
M. Toulemonde,
Y. Quéré,
N. Cue
[show abstract]
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ABSTRACT: Two aspects of heavy ion channeling are presented. The first aspect is related to the fact that channeled ions interact only with the most loosely bound target electrons. One can take benefit of this feature to study processes such as radiative electron capture (REC) and resonant transfer and excitation (RTE) in a dense quasi-free electron gas. The experimental work, performed at GANIL, devoted to these two processes is described. A possible extension to Nuclear RTE or NEEC (nuclear excitation by electron capture) studies is also described. The second aspect discussed is related to the periodicity of the potential experienced by channeled ions. We show that in a well chosen case this could lead to a significant and detectable coherent excitation of the projectile nucleus.
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms.
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[show abstract]
[hide abstract]
ABSTRACT: The target thickness dependent convoy electron yields Ye from hydrogenic projectile ions H0, H+ (3 MeV) and Ni27+, Ni28+ (15.6 MeV/u) are compared and discussed in the framework of an extended model for ELC and ECC in solids considering also contributions from excited states. It is shown that convoy electrons from light and heavy projectile ions in principle can be described with the same Ansatz, but discrepancies remain. To understand the target thickness dependent evolution in the case of incident Ni27+ it must be assumed that convoy electrons produced by ELC arise mainly from excited states. The mean transport length λc for convoy electrons for light projectile ions is equal to the attenuation length of isotachic free electrons λe, whereas for the heavy ions an enhanced transport length λe ⪢ λe must be introduced.
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms.
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[show abstract]
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ABSTRACT: Accelerator based, easily accessible methods are discussed to control and characterize targets and their surfaces by (MeV) ion impact. Independent, but simultaneously applicable techniques such as Rutherford backscattering (RBS), elastic recoil detection (ERD), secondary electron emission (SEE), ion induced Auger electron spectroscopy (IIAES), and particle induced X-ray emission (PIXE) will be shown as tools for bulk and surface analyses. We also present studies of the transformation of the surface conditions, e.g. surface cleaning and smoothing under UHV conditions by heavy-ion sputtering. Possibilities, limitations, and sensitivities of the techniques are discussed.
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment.
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S Hagmann,
Th. Stöhlker,
Ch. Kozhuharov,
V Shabaev,
I Tupitsyn,
Y Kozhedub, H Rothard,
U Spillmann,
R Reuschl,
S Trotsenko, [......],
R Dörner,
R Moshammer,
P -M Hillenbrand,
D Jakubassa-Amundsen,
A Voitkiv,
A Surzhykov,
D Fischer,
E Filippo,
X Wang,
B Weij
AIP Conf. Proc. 1336:115.
