Positron annihilation gamma energy distribution, lifetime spectroscopy and time-of-flight method were used to study surfactant-templated mesoporous silica films deposited on glass. The lifetime depth profiling was correlated to Doppler broadening and 3γ annihilation fraction measurements to determine the annihilation characteristics inside the films. A set of consistent fingerprints for positronium annihilation, o-Ps reemission into vacuum, and pore size was directly determined. The lifetime measurements were performed in reflection mode with a specially designed lifetime spectrometer mounted on a slow positron beam system. The intensity of the 142 ns vacuum lifetime component was recorded as a function of the energy of the positron beam. In a film with high porosity a reemission efficiency of as high as 40％ was found at low positron energy. Positron lifetime in samples capped by a thin silica layer was used to determine the pore size. The energy of the reemitted o-Ps fraction was measured by a time-of-flight detector, mounted on the same system, allowing determination of both o-Ps re-emission efficiency and energy in the same sample. We demonstrate the potential of the simultaneous use of different positron annihilation techniques in the study of thin porous films.
CEA Saclay,IRFU,F-91191 Gif-sur-Yvette Cedex,France Institut für Teilchenphysik,ETHZ,CH-8093 Zürich,Switzerland LCPME,CNRS-Nancy-Université,405 rue de Vandoeuvre,F-54600 Villers-lès-Nancy,France CEA Saclay,IRAMIS,F-91191 Gif-sur-Yvette Cedex,France CNRS-CEMHTI,3A rue de la Férollerie,F-45071 Orléans Cedex 2,France National Institute of Advanced Industrial Science and Technology (AIST),Tsukuba,Ibaraki 305-8568,Jap