Low energy ion scattering (LEIS) spectra of thin film structures are analyzed by Monte-Carlo simulations using the TRBS code. Although originally developed for the analysis of Rutherford backscattering (RBS) spectra, the TRBS code can be used to obtain valid simulations of LEIS data, which take place at energies several orders of magnitude lower than in RBS, when the appropriate adjustments are made. Experimental results from a set of Al2O3/HfO2 thin film stacks are shown, and their analysis by means of TRBS simulations is demonstrated. The authors show that the simulations yield valuable insights, especially in the case of ultrathin films <1 nm, where traditional evaluation methods using empirical models can be misleading.

The determination of the electronic stopping power for low-energy ions is an experimentally demanding task. In this paper we elaborate on the different effects of nuclear stopping and multiple scattering on the energy spectra for different experimental geometries, i.e., transmission through thin foils and backscattering from thin films. By calculating distributions of path lengths and scattering angles we demonstrate how electronic stopping, nuclear stopping, and multiple scattering add up to the total energy loss. We show that at low energies it is important to properly disentangle these effects to extract electronic stopping from the measured energy loss spectra.

Scattering cross sections for He+ ions in the energy range of 100eV to 100keV and for Al, Cu and Au target atoms were calculated. Employing the Thomas–Fermi–Molière model the potential strength was tuned by variation of the screening length. The resulting change in scattering cross section was analyzed and the absolute value is compared to cross sections obtained from potentials commonly employed in the medium-energy ion scattering (MEIS) regime. A large influence on the scattering cross section is observed for targets with large atomic number in the very low energy range. For instance, the scattering cross section for 100eV He+-ions scattered from Au by 129° changes by a factor of 2.5 between different potential strengths claimed in the literature to be suitable for low-energy ion scattering (LEIS) energies. An experiment to determine electronic energy loss of very slow ions in metals is presented. It shows how uncertainties in the scattering potential strength can lead to systematically wrong results, although perfect agreement between experimental data and simulations is found. The impact of these results on quantitative surface structure and composition analysis is discussed.

Chemokine receptors mediate migration and activation of lymphocytes through binding of their ligands. Recent studies have revealed important contributions of chemokine receptors to the development, progression, and dissemination of haematopoietic neoplasms. Because the chemokine receptor expression profile in extragastric MALT lymphoma is unknown, we performed a comprehensive study on tissue samples of parotid glands, parotid glands affected by Sjögren syndrome, extragastric MALT lymphoma, and extranodal diffuse large B‐cell lymphoma (eDLBCL) originating from MALT lymphoma (transformed MALT lymphoma). By investigating the expression of 19 chemokine receptors by real‐time PCR using a semi‐quantitative approach and of four chemokine receptors (CCR1, CCR5, CXCR6, and XCR1) by immunohistochemistry, we show that the chemokine receptor expression profiles of extragastric MALT lymphomas differ substantially from those of extranodal DBLCL, with lower expression of CCR1, CCR8, and CXCR3, and the absence of expression of CX3CR1 and XCR1 in eDLBCL. Expression of CCR6, CCR7, CXCR3, CXCR4, and CXCR5, responsible for B‐cell homing to secondary lymphoid tissue, was detected in both B‐cell malignancies. Expression of CCR4 was just detected in trisomy 3‐positive MALT lymphoma cases. Comparing gastric with extragastric MALT lymphomas, up‐regulation of CXCR1 and CXCR2 accompanied by down‐regulation of CCR8 and CX3CR1 and loss of XCR1 expression in extragastric MALT lymphomas appear to be key determinants for the site of origin of MALT lymphomagenesis. Our results support a model of stepwise progression of extragastric MALT lymphoma from a non‐neoplastic event to Sjögren syndrome, to MALT lymphoma, and finally to overt eDLBCL, guided by differentially expressed B‐cell homeostatic and activation‐dependent chemokine receptors and their ligands. Copyright © 2008 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Protons and deuterons with energies 0.33–10 keV were used to obtain time-of-flight low energy ion scattering (TOF-LEIS) spectra for thin layers of Au evaporated onto a B/Si substrate. The thickness (2.4 nm) and the root-mean-square roughness (0.5 nm) of the Au layer were determined by Rutherford Backscattering Spectrometry (RBS) and Atomic Force Microscopy (AFM), respectively. To deduce the electronic stopping power, TRBS simulations were performed with dE/dx as an input parameter that was optimized to fit the experimental spectra. At energies above 3 keV, the low energy edge in the experimental spectra was widened due to the film roughness. Therefore, the simulations were carried out for the Au layer composed by two different thicknesses in order to yield optimum agreement. The resulting stopping values compare favourably to literature data. No proton/deuteron isotope effect in stopping of hydrogen ions was observed.

The electron emission yield was measured for impact of 3 keV electrons, 2 MeV H+, 4 MeV He2+ and 6 MeV O3+ ions on polycrystalline Al, Cu and Ag samples as a function of sample temperature in the temperature range of 25–450 °C. A significant influence of the surface morphology was found. For annealed samples, a linear decrease of the yield was observed for increasing temperature, which is quantitatively described by a temperature coefficient t. It is found that the values for t depend both on the sample material and on the type of projectile. The largest value was found for proton impact on Ag, when the yield decreased by 2% for 100 K temperature increase. In addition, the change of work function for sample temperatures of 25 and 450 °C were also measured. The temperature dependence of the yield on the type of projectile is qualitatively discussed. The influence of the temperature dependence of the work function on the yield is quantitatively estimated. It is found that this contributes significantly, but cannot completely explain the observed temperature dependence of the yield.

The kinetic electron yield was measured for the impact of 3 MeV He2+ ions and 3 keV electrons on thin layers of Al on Cu, of Al2O3 on Al, and of CeO2 and CaF2 on Si backings. The dependence of the yield on the layer thickness was determined. For Al on Cu a decreasing yield was observed for increasing Al layer thickness, since the yield of Cu is higher than that of Al. For insulating layers increasing yields were measured for increasing layer thickness. The observed yield dependencies were fitted by sums of exponential functions. The characteristic lengths of the exponential terms were interpreted as emission lengths. For Al and the metal oxides a small emission length in the range of 2–3 nm was found, for CeO2 and electron impact on Al a second exponential term with a large emission length, 20–100 nm, was necessary to describe the measured yield dependence, which is probably due to backscattered projectile electrons and δ-electrons. The Al results are compared with computer simulations. The increasing yield of CaF2 layers could be fitted by a function with only one exponential term and an emission length of 10.8 nm for He impact and 20.6 nm for electron impact.

The electron emission yield was measured for the impact of 3 keV electrons and 2 MeV H+ ions on Al as a function of target temperature. A strong influence of the surface morphology was found. For annealed samples a linear decrease of the yield was observed for increasing temperature. In the temperature range 50–440°C the yield for electron impact decreased by 4%, for proton impact by 6%. In addition, the work function of Al was measured for 25°C and for 440°C. The dependence of the yield on the work function was investigated by Monte Carlo simulation of the electron emission process for electron and proton impact. The temperature dependence of the yield is discussed in terms of work function changes.

In this paper, elastic recoil detection (ERD) measurements at recoil angle of 60° using ion-induced electron emission (IEE) for particle identification are presented. In our IEE system for particle identification, recoiled target atoms and scattered projectiles penetrate a set of thin carbon foils before their energy is analyzed in a solid state detector. Particle identification is based on the fact that the total number of electrons emitted from the foils depends on the particle nuclear charge. This method is characterized by its low minimum detectable energy, which stimulated us to study ERDA at 60°. Due to collision kinematics and due to the angular dependence of the scattering cross-sections, it is expected that the sensitivity can be significantly improved. In this work, the detection efficiency of the IEE particle identification system for H recoils at energies below 1 MeV was determined. LA-ERDA measurements were performed with 4He and 12C projectiles using two different types of samples with a well-known amount and depth distribution of H atoms near the surface. Sample 1 consisted of a 50 μg/cm2 melamine layer evaporated on a flat Si substrate, sample 2 was a Si wafer with implanted H. Sensitivity and depth resolution were measured using LA-ERDA with a recoil angle of 60° and ERDA with recoil angles of 30° and 45°. The results for different recoil geometries and projectiles are discussed and compared with theoretical predictions.

For 3 MeV He++ and 3 keV electron projectiles the kinetic electron emission yield for copper layers of different thickness on an aluminum backing was measured. Since the electron emission yield of Cu is almost a factor of 2 higher than that of Al an increasing electron yield was measured for increasing thickness of the Cu layer until the yield of pure Cu was reached. For impinging He++ ions the measured yields can be fitted by a function of the layer thickness which contains an exponential term with a characteristic length of 2.6 nm. For 3 keV electron projectiles a much longer characteristic length of 4.8 nm was observed.To explain this dependence our Monte-Carlo simulation program for electron excitation and transport in metals was extended to handle layered structures. In this program the incoming projectiles generate primary electrons due to excitation or ionization of the target (electron gas and core electrons). The primary electrons propagate through the amorphous target and interact with the atomic cores and with the target electrons, thereby generating electron cascades. The propagating electrons are traced until they possibly leave the target or until their energy drops below the energy of the surface barrier. At the layer interfaces the energy levels of the metals are adjusted to have equal Fermi energy. Possible reflection of moving electrons at the interface is taken into account.Using this model the electron emission yield from the surface has been calculated as a function of layer thickness. The measured thickness dependence of the electron yield is well reproduced by the simulation which permits an interpretation on the basis of the underlying interaction processes. (C) 2000 Elsevier Science B.V. All rights reserved.

A Monte-Carlo computer code for the simulation of particle transport in metallic solids has been developed. Electrons or bare ion projectiles can be used. The code is able to calculate a wide variety of phenomena such as electronic energy loss, electronic energy loss straggling, particle-induced yield of emitted electrons or the statistical distribution of the number of emitted electrons per incident projectile. The theoretical models used in the simulation partially follow the basic work of Ganachaud and Cailler. However, for the loosely bound outer electrons of copper, the classical model of core ionization as it has been used by previous authors breaks down. Therefore, a fully quantum- mechanical description has been used in this work. For aluminum and copper the simulation results are compared with experimental and theoretical data. Excellent agreement is found.

We propose two new detector concepts that may be particularly well suited for AMS measurements with small accelerators: (i) an all solid state ΔE-E detector for light ions utilizing ion-induced electron emission from thin foils, and (ii) a time-of-flight system that does not use a start foil but derives the start information from the spatial information imposed on the beam by a time dependent deflection field.

The distribution of the number of emitted electrons is measured for the impact of He+ and He2+ ions on Al, Cu and Au targets. The ion energy is between 0.6 MeV (He+) and 4.8 MeV (He2+). The obtained results are very well represented by Polya distributions and the parameters of the fitted distributions are given. The measured distributions for He+ impact are explained by a model which takes into account stripping of the bound electron. It is found that the mean depth, where He+ ions penetrate the solid without losing their bound electron, is about 10 Angstrom and it decreases with increasing projectile energy. These results, obtained from measurements of the emission statistics, are also compared with results obtained from yield measurements.

For ion-atom collisions the mean energy loss per collision and hence the stopping cross section depends on the state of aggregation (phase effect). The stopping cross section of gases is usually measured by transmission experiments where ions penetrate through a gas cell. This contribution deals with the question whether the observed phase effect might be partially due to the inevitable particle selection when the ions leave the gas cell through a small aperture. If this were true it would imply systematic errors in many energy loss measurements in gases. We present Monte Carlo calculations of the statistical distribution of the impact parameters in ion-atom collisions when the ions penetrate a gas cell of 30 cm length and an exit aperture with a diameter of 1 mm and exit with a direction of flight to reach the detector (exit angle below 1°). The calculations are done for hydrogen ions with impact energies from 40 to 1000 keV impinging on zinc vapor with gas densities n of 8.9 × 1014 to 8.9 × 1015 atoms/cm3. We find that at high energies, all impact parameters larger than 0.1 Å contribute, even at the low density. At low energies a noticeable cut-off at small impact parameters appears for the low density, which is quenched by multiple scattering at higher densities. By applying calculations in First Born Approximation, we determine how the cut-off at small impact parameters influences the energy loss of the ions quantitatively for 100 keV protons in zinc. We find a reduction of the stopping cross section by 15% for the low density and by 2% for the high density.

For rare event experiments (environmental, solar neutrino, ββ-decay and dark matter) a careful selection of the construction materials of the detectors with respect to low radioactive contamination is fundamental. Non-destructive low-level γ-ray spectrometry serves this purpose best. To improve the sensitivity of a germanium detector, background reduction is a prerequisite. This paper describes an active background discrimination technique, which in principle is a coincidence method. Instead of an active veto, an event-by-event recording technique is used to improve the signature of each event. Two detectors, one low level HPGe-detector in a lead shield and a large area plastic scintillation detector (above the Ge-detector and outside the lead shield) are operated simultaneously (the system allows up to 12 ADC inputs). For each event the detector identification number, the measured pulse-height and the time of occurrence of the event are stored. The coincidence or anti-coincidence conditions can be chosen by software after the measurement, the conditions can be optimised and altered without losing information. The technique allows to distinguish between fast muon induced events, radioimpurity events and, under special detector conditions, Compton events. These background events can then be subtracted, leading to a smaller statistical uncertainty of the net signal from the sample. From the recorded data the muon flux can be extracted as well. Experiments at ground level and in a depth of 500 m water equivalent are described.

We propose a new method to identify particles in ERD analysis, using their electron emission yield from a thin carbon foil. Before the particles reach a silicon surface barrier detector (SB) they penetrate a set of thin foils (typically 6 foils) with a thickness of 3 μgcm2 each). The emission yield depends on the nuclear charge of the penetrating ion and it is roughly proportional to the energy loss in the foil. The emitted electrons are accelerated to a muchannel plate (MCP) by a voltage of 300 V. The electron signal from the MCP is proportional to the number of emitted electrons and it occurs in coincidence with the energy signal from the energy detector. For data acquisition we developed a dual parameter multichannel analyzer (M2D) as an add on board for an industry standard personal computer. The two-dimensional spectrum of coincidences and the one-dimensional spectra from both detectors are recorded simultaneously. The M2D has 256K channels which can be freely configured as a two-dimensional matrix. For example a resolution of 1024 × 256 channels is possible. For optimum suppression of random coincidences the coincidence time window can be set from 0.125 μs up to 32 μs. For this new setup the ability for particle identification is discussed for different projectiles (He, C, O, Cl) and targets. H recoil ions can be well separated from He projectiles so that for H analysis the H recoil spectrum and the He forward energy spectrum can be measured simultaneously. An example for depth-profiling of 100 keV H implantations in silicon is given.