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

UE112_PGM-1: An open-port low-energy beamline at the BESSY II undulator UE112

The X-ray optical and mechanical designs of a low-energy high-flux VUV- to soft-X-ray beamline for photon energies between 17 and 200 eV (with lower flux up to 690 eV) are presented

Thermoelastic Damping in MEMS Gyroscopes at High Frequencies

Microelectromechanical systems (MEMS) gyroscopes are widely used, e.g. in modern automotive and consumer applications, and require signal stability and accuracy in rather harsh environmental conditions. In many use cases, device reliability must be guaranteed under large external loads at high frequencies. The sensitivity of the sensor to such external loads depends strongly on the damping, or rather quality factor, of the high frequency mechanical modes of the structure. In this paper, we investigate the influence of thermoelastic damping on several high frequency modes by comparing finite element simulations with measurements of the quality factor in an application-relevant temperature range. We measure the quality factors over different temperatures in vacuum, to extract the relevant thermoelastic material parameters of the polycrystalline MEMS device. Our simulation results show a good agreement with the measured quantities, therefore proving the applicability of our method for predictive purposes in the MEMS design process. Overall, we are able to uniquely identify the thermoelastic effects and show their significance for the damping of the high frequency modes of an industrial MEMS gyroscope. Our approach is generic and therefore easily applicable to any mechanical structure with many possible applications in nano- and micromechanical systems

Internationale Konferenz 'Nysa / Neisse - Kulturalität und Regionalität'

Bericht über die Internationale Konferenz 'Nysa / Neisse - Kulturalität und Regionalität

The retarding Bessel Box an electron spectrometer designed for pump probe experiments

A new type of electrostatic electron spectrometer is developed, capable of particular sensitive measurements of energy spectra and time of flight distributions. This instrument is specifically designed and optimized for laser pump X ray probe measurements, where photo electrons or Auger electrons from surfaces, clusters, molecular or atomic targets are being measured with high time resolution at an extremely low detection noise level. The compact and robust cylinder symmetrical system is a strongly improved Bessel Box design, featuring electron retardation, a large detection solid angle, about 100 electron transmission gridless design and excellent time resolution. In this paper we describe the principle of operation of this type of spectrometer and various tests. We present quantitative results for electron measurements with different solid state targets and two different electron detection systems in comparison to electron trajectory simulations inside the electrostatic spectrometer fields. Picosecond pump probe operation has been tested with high laser power and even the ability to work under femtosecond pump probe conditions with electron detection at the BESSY II slicing facility has been prove

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

Laser pump X ray probe experiments with electrons ejected from a Cu 111 target space charge acceleration

A comprehensive investigation of the emission characteristics for electrons induced by X rays of a few hundred eV at grazing incidence angles on an atomically clean Cu 111 sample during laser excitation is presented. Electron energy spectra due to intense infrared laser irradiation are investigated at the BESSY II slicing facility. Furthermore, the influence of the corresponding high degree of target excitation high peak current of photoemission on the properties of Auger and photoelectrons liberated by a probe X ray beam is investigated in time resolved pump and probe measurements. Strong electron energy shifts have been found and assigned to space charge acceleration. The variation of the shift with laser power and electron energy is investigated and discussed on the basis of experimental as well as new theoretical result