Positronium lifetimes in porous Vycor glass

Positronium as a probe of small free volumes in crystals, polymers and porous media

“…Thus, the question arises, if a universal value for all these parameters can be found, giving sufficiently good approximation. For the first time such an attempt was presented for porous Vycor glass of relatively narrow pores [204]; the value of ∆ = η = (0,191 ± 0.008) nm was obtained. Gidley et al [199] have found for silica films the value 0.18 nm.…”

PALS investigations of matrix Vycor glass doped with molecules of luminescent dye and silver nanoparticles. Discrepancies from the ETE model

“…In this technique, the probe used for pore size characterization is positronium (bound, quasi-stable state of a positron and an electron). The mean ortho--positronium (o-Ps) lifetime is connected to free volume size, and this relation is given for big pores (R > 1 nm) by extended Tao-Eldrup (ETE) model [9]. In this model, a pore is approximated by the potential well of respective shape, where ortho-positronium can occupy either ground or excited energy levels.…”

Variable-Energy Positron Annihilation as Highly Sensitive Nanoporosimetry for Porous Thin Films

“…Positron annihilation (PA) has been applied to measuring critical pore sizes in polymers, porous oxides, and other systems [1][2][3]. There are several advantages of PA over other methods; it is nondestructive, sensitive to holes of 0.3-50 nm in size and can detect buried, isolated pores that are not accessible to conventional probes.…”

“…If o-Ps is localized in a closed pore, it annihilates with a lifetime shorter than 142 ns by a 2γ pick-off process. The o-Ps lifetime is well correlated with the pore dimension [1][2][3][4], and the pore size can be evaluated by the PAL technique. In the presence of open pores, o-Ps can escape from the film surface into vacuum.…”