Stopping of protons Improved accuracy of the UCA model

Recent theoretical developments in the unitary convolution approximation UCA for electronic energy losses of bare and screened ions are presented. Examples are given for proton beams and rare gas targets. For gas targets there exists a sufficient amount of experimental data on charge exchange, for pinpointing the largely unknown stopping power contribution of electron capture processes at low and intermediate energie

Impact parameter dependence of the electronic energy loss of fast cluster projectiles

Electronic energy loss of molecular clusters as a function of impact parameter is less understood than atomic energy loss. Vicinage effects due to mutual interference between cluster fragments play a key role in the determination of the cluster electronic energy loss. In this work, we describe a molecular extension of the perturbative convolution approximation PCA energy loss model, namely MPCA molecular PCA , which yields remarkable agreement with first order Born semiclassical approximation SCA results. The physical inputs of the model are the oscillators strengths of the target atoms and the projectile electron density. A very good agreement is obtained with time consuming full first order calculations for bare incident molecular clusters for several angles between cluster axis and velocity directio

Femtosecond dynamics snapshots of the early ion track evolution

The energy dissipation and femtosecond dynamics due to fast heavy ions in matter is critically reviewed with emphasis on possible mechanisms that lead to materials modi cations. Starting from a discussion of the initial electronic energy deposition processes, three basic mechanisms for the conversion of electronic into atomic energy are investigated by means of Auger electron spectroscopy. Results for amorphous Si, amorphous C and polypropylene are presented and discussed. Experimental evidence for a highly charged track region as well as for hot electrons inside tracks is shown. As follows mainly from Auger electron spectroscopy, there are strong indications for di erent track production mechanisms in di erent material

An analytical energy loss line shape for high depth resolution in ion beam analysis

The knowledge of the energy loss distribution in a single ion atom collision is a prerequisite for subnanometric resolution in depthprofiling techniques such as nuclear reaction profiling NRP and medium energy ion scattering MEIS . The usual Gaussian approximation specified by the stopping power and energy straggling is not valid for near surface regions of solids, where subnanometric or monolayer resolution can be achieved. In this work we propose an analytical formula for the line shape to replace the usual Gaussian distribution widely used in low resolution ion beam analysis. Furthermore, we provide a simple physical method to derive the corresponding shape parameters. We also present a comparison with full coupled channel calculations as well as with experimental data at nearly single collision condition

Search for short time phase effects in the electronic damage evolution A case study with silicon

This work focusses on the production and decay properties of inner shell vacancies and valence band excitations induced by swift highly charged ions interacting with amorphous and crystalline Si. High resolution electron spectra have been taken for fast heavy ions at 1.78 5 MeV u as well as for electrons of similar velocity incident on atomically clean Si targets of well defined phase. Various Augerelectron structures are analyzed concerning their width, their intensity and exact peak position. All measured peaks show a small shift towards lower energy when the charge of the projectile is increased. This finding is an indication for a nuclear track potential inside the ion track. A detailed analysis of the Auger electron spectra for amorphous Si and crystalline Si 111 7 x 7 points to a small but significant phase effect in the short time dynamics of ion track

Asymmetric line shapes for medium energy H and He ions undergoing a large angle collision

Asymmetric line shapes for medium energy H and He ions backscattered from topmost adatoms such as Si 111 3x 3 Sb and Ni 111 2x2 O are measured by a toroidal electrostatic analyzer with an excellent energy resolution. The spectra exhibit a pronounced asymmetric nature and are well fitted by an exponentially modified Gaussian profile. It is found that the nonperturbative coupled channel calculations reproduce well the observed asymmetric line shapes for He impact on different materials, although slightly overestimate the asymmetry for H impact on Au. On the other hand, the CASP 3.2 program involving additional approximations gives large underestimates for He ions and overestimates for H ions. This problem has been partially solved by modifying the order of the implementation of the shell corrections and higher order effects in the CASP mode

High energy ion beam irradiation of Co NiFe Co Cu multilayers Effects on the structural, transport and magnetic properties

The aim of this work is to investigate the effects of 593 MeVAu irradiation using two different projectile charges, namely Au30 and Au46.3 on the structural, transport and magnetization properties of Co NiFe Co Cu multilayers. X Ray diffraction and extended X ray absorption fine structures measurements show no significant structural change for as deposited and irradiated multilayers. On the other hand, the magnetoresistance amplitude decreases with the ion fluence but it is insensitive to the projectile charge state. The correlation between changes in the magnetoresistance and remanent magnetization suggests that the main effect responsible for the decrease of the magnetoresistance is the creation of ferromagnetic pinholes. These results are discussed on basis of the electronic thermal spike model and nuclear cascades theory and show similarities to the effects observed at low energy ion beam irradiatio

Influence of tunneling on electron screening in low energy nuclear reactions in laboratories

Using a semiclassical mean field theory, we show that the screening potential exhibits a characteristic radial variation in the tunneling region in sharp contrast to the assumption of the constant shift in all previous works. Also, we show that the explicit treatment of the tunneling region gives a larger screening energy than that in the conventional approach, which studies the time evolution only in the classical region and estimates the screening energy from the screening potential at the external classical turning point. This modification becomes important if the electronic state is not a single adiabatic state at the external turning point either by pre-tunneling transitions of the electronic state or by the symmetry of the system even if there is no essential change with the electronic state in the tunneling region.Comment: 3 figure

Ultrafast electronic processes in an insulator The Be and O sites in BeO

The short time dynamics of amorphous beryllium oxide a BeO has been investigated for electronic excitation ionization by fast incident electrons, as well as by Ar7 , Ar15 , Xe15 , and Xe31 ions at velocities of 6 10 the speed of light. Site specific Auger electron spectra induced by fast heavy ions are the central point of this investigation. Electron induced Auger spectra serve as a reference and electron energy loss EELS spectroscopy as well as resonant inelastic X ray scattering RIXS are invoked for quantitative understanding. For the heavy ion case, we observe strong variations in the corresponding spectral distributions of Be K and O K Auger lines. These are related to local changes of the electron density, of the electron temperature and even of the electronic band structure of BeO on a femtosecond time scale after the passage of highly charged heavy ions