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Open spaces in amorphous Al2O3 films fabricated by atomic layer deposition and in AlONx deposited by a reactive sputtering technique were probed by using monoenergetic positron beams. In these films, open spaces with three different sizes were found to coexist. The mean size and the concentration of open spaces were decreased by annealing at 800 °C in N2 atmosphere, which was associated with rearrangements of the amorphous network in the films and their crystallization. Nitrogen incorporation into Al2O3 suppressed the shrinkage of network structures due to the annealing, which was attributed to the formation of a stable network through the introduction of Al-N bonding. For Al2O3 deposited on GaN, the temperature treatment above 800 °C led to the introduction of vacancytype defects in the GaN substrate. This fact suggests that the change in the network structure of Al2O3 enhances chemical instability at the Al2O3/GaN interface and the out-diffusion of atoms from the substrate. [ABSTRACT FROM AUTHOR]

Low-energy positron beams are applied in a number of experiments in solid state physics and materials science as well as in atomic and particle physics. These experiments comprise of surface studies, depth dependent defect spectroscopy, and fundamental research with leptonic systems. The neutron induced positron source in Munich (NEPOMUC) is operated as a user facility providing a positron beam with an intensity of about 109 moderated positrons per second. In this paper, a review of the status of the positron beam facility with its instruments is given and several experiments are exemplarily highlighted. Recent and future developments for further improving the performance of positron beam experiments are discussed. [ABSTRACT FROM AUTHOR]

Relativistic positron beams were generated by laser wakefield electrons bombarding on solid target. Very stable positron beams were generated in our experiments. The total yield of positrons is about 4.4×108/shot. The energy spectra of positrons and electrons obey quasi-Maxwell distribution. Compared with the direct method, the indirect method produces positrons (38.5 MeV) and electrons (50.5 MeV) with much higher slope temperature. [ABSTRACT FROM AUTHOR]

We report here positron annihilation-induced Auger electron spectroscopy measurements of an as received TiO2(110) surface. We observe peaks at ~ 250 eV and ~ 500 eV due to the Auger decay of annihilation-induced 1s holes in carbon (C KVV), and oxygen (O KVV) respectively. In addition to these KVV Auger peaks we observe a broad, low energy peak extending up to 15 eV. Since the incident positron beam energy of 1.5 eV is well below the energy threshold required to directly knock out electrons with kinetic energies up to 15 eV, this peak must be Auger-related. Based on energy conservation requirements and its considerable spectral weight, we argue that this low energy peak is principally due to the Auger decay of both annihilation induced 2s core holes in oxygen and annihilation induced valence holes in carbon. [ABSTRACT FROM AUTHOR]

This paper shows results of conventional positron lifetime and slow positron beam studies of the long range effect. These techniques are not commonly used for this topic. The experimental investigations of pure metals exposed to ion irradiation are reported and discussed on the basis of the literature data. The positron lifetimes measured in the etching experiment give information about kind of defects, their distribution, and existence of the long range effect. The above can be achieved using the positron beam for the case of low energy ion implantation. [ABSTRACT FROM AUTHOR]

The neutron-induced positron source Munich (NEPOMUC) provides a monochromatic low-energy positron beam with an intensity of > 1 × 109e+ s-1 and a full width at half maximum (FWHM) diameter of about 10 mm. To create a small beam focus or sharp positron pulses of 100 ps FWHM the beam brightness needs to be enhanced by remoderation. This is achieved by focusing the primary beam magnetically onto a tungsten single crystal W(100) in reflection geometry. Afterwards the beam exhibits an intensity of > 5 × 107e+s-1 and a diameter of < 2 mm FWHM. To further optimize the beam quality of NEPOMUC we redesigned the remoderation unit. The new setup allows a precise positioning of the remoderator crystal within the focus of the magnetic lens. Additionally, a replacement of the crystal within several minutes and without breaking the beamline vacuum is possible that offers the opportunity for systematic tests of different remoderator materials. [ABSTRACT FROM AUTHOR]