First mu+SR studies on thin films with a new beam of low energy positive muons at energies below 20 keV

At the Paul Scherrer Institute slow positive muons (mu(+)) with nearly 100% polarization and an energy of about 10 eV are generated by moderation of a n intense secondary beam of surface muons in an appropriate condensed gas l ayer. These epithermal muons are used as a source of a tertiary beam of tun able energy between 10 eV and 20 keV. The range of these muons in solids is up to 100 nm which allows the extension of the mu(+) SR techniques (muon s pin rotation, relaxation, resonance) to the study of thin films. A basic re quirement for the proper interpretation of mu(+) SR results on thin films a nd multi- layers is the knowledge of the depth distribution of muons in mat ter. To date, no data are available concerning this topic. Therefore, we in vestigated the penetration depth of mu(+) with energies between 8 keV and 1 6 keV in Cu/SiO2 samples. The experimental data are in agreement with simul ated predictions. Additionally, we present two examples of first applicatio ns of low energy mu(+) in mu(+) SR investigations. We measured the magnetic field distribution inside a 500-nm thin High-T-c superconductor (YBa2Cu3O7 -delta), as well as the depth dependence of the field distribution near the surface. In another experiment a 500-nm thin sample of Fe-nanoclusters (di ameter 2.4(4) nm), embedded in an Ag matrix with a volume concentration of 0.1%, was investigated with transverse field mu(+) SR.