K. Kroneberger

Secondary electron yields from the entrance and exit surfaces of thin carbon foils induced by penetration of H+, H0 and H+2 projectiles (1.2 MeV/u)☆

We report experimental work on secondary electron emission from both entrance (γb) and exit (γf) surfaces of thin carbon foils traversed by H+, H0 and H+2 projectiles (1.2 MeV/u). Secondary electron coefficients γb and γf, were measured simultaneously. The results are discussed in the framework of a semiempirical model for kinetic emission of target electrons from solid surfaces.

Secondary-electron velocity spectra and angular distributions from ions penetrating thin solids☆

Abstract We present velocity spectra and angular distributions of secondary electrons emitted from cleaned surfaces of thin carbon and gold foils penetrated by H+ (Ep = 0.8 and 1.2 MeV), H2+ (Ep/Mp = 0.8 MeV/u) and C+ (Vp = 2.30− and 2.85 VB). Prominent structures in doubly differential velocity spectra d 2 n/ d E d Ω of secondary electrons (SE) are (1) the “true SE” peak at low electron energies Ee

A heavy-ion beam current monitor with a wide dynamic range☆

We present a new current monitor concept for relativistic heavy-ion beams based on secondary electron emission. The detector is capable of measuring beam intensities from single particles up to several 109 Hz.

Search for solitons in solids

Abstract It has been suggested that solitons might be created during radiation damage processes. Circumstantial evidence for such solitons has been found in the layered crystal muscovite. An attempt was made to detect such solitons by their inelastic scattering at a crystal surface in a single crystal of silicon.

Surface characterisation of thin solid foil targets by ion impact

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.

Secondary electron emission from entrance and exit surfaces of thin clean foils bombarded with H+, C+, and O+

Abstract We have measured secondary electron emission from thin, clean foils of C, Al, Ti, Ni, and Cu bombarded with H+, C+, and O+, at energies between 0.3 and 1.2 MeV/amu for protons and 20 to 80 keV/amu for the heavy projectiles. We observe in some but not all cases a proportionality between the secondary electron yield and the stopping power, but such a proportionality seems to break down at the lower projectile energies used by us. The yields emitted in forward direction are generally somewhat larger than those emitted backwards. The results are discussed in the frame of an extended Sternglass model.

Study of convoy electrons from collisions of hydrogenic projectiles (Z = 1 and Z = 28) with solids

Abstract The target thickness dependent convoy electron yields Y e from hydrogenic projectile ions H 0 , H + (3 MeV) and Ni 27+ , Ni 28+ (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 Ni 27+ it must be assumed that convoy electrons produced by ELC arise mainly from excited states. The mean transport length λ c 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.

Target characterization by fast ion impact

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.

Production and transport of electrons in thin carbon foils

Abstract We present measurements for elastic (angular straggling) and inelastic scattering (energy loss) of low energy electrons (1633 eV) after penetration through thin carbon foils. The resulting double differential electron spectra are compared to calculations of the electronic energy loss in a linear response approximation. The multiple elastic scattering of the electrons is treated in the first Born approximation for scattering on a screened Coulomb potential. With the derived cross sections for inelastic and elastic scattering the transport of convoy electrons through thin foils is simulated. The calculations show that with the assumption of continuous production of convoy electrons during the passage of the ion through the solid the remaining convoy electron peak can be understood. It will be shown that under these conditions the effect of multiple elastic scattering can be neglected, whereas the inelastic contributions cause a change in the peak shape.

Electron emission and desorption from frozen gases under fast (MeV) ion bombardment

Abstract First results of the adsorbate-thickness dependence of electron yields obtained with thin copper foils covered with solid CO 2 are presented. Absolute values of the CO 2 coverage were determined by Rutherford forward scattering. The erosion of frozen CO 2 by transmission of protons (1 MeV) was observed for the first time. The obtained CO 2 thickness was related to the yield of convoy electrons ( E e ≈ 540 eV) being emitted along the beam direction ( Θ = 0°) with a velocity ν c equal to the projectile velocity ν p and to the intensity of low energy “true” secondary electrons ( E e λ ( E e ). Our alternative interpretation is based on nonuniform erosion, which generates a modificaton of the bombarded and the contaminated target area with increasing irradiation time.