Nuclear resonant scattering of synchrotron radiation by physisorbed Kr on TiO$_{2}$(110) surfaces in multilayer and monolayer regimes

TL;DR

This study investigates nuclear resonant scattering of synchrotron radiation by physisorbed krypton layers on TiO₂(110) surfaces, revealing phase transition behavior and quantifying monolayer coverage effects.

Contribution

It provides the first detailed analysis of NRS signals for Kr layers on TiO₂, highlighting phase transition effects and recoiless fraction variations with temperature.

Findings

NRS intensity for monolayer Kr is estimated at 0.23 cps.

Recoiless fraction decreases significantly from 19 K to 25 K.

Evidence suggests an order-disorder phase transition in the monolayer.

Abstract

Physisorbed Kr layers on TiO$_{2}$(110) surfaces were investigated by means of nuclear resonant scattering (NRS) of synchrotron radiation at Kr thicknesses ranging from multilayer to monolayer. The NRS intensity was measured as a function of the Kr exposure, from which the NRS signal corresponding to monolayer was estimated as 0.23 cps. The time spectra measured at various thicknesses showed a monotonous decay without any quantum beat features. The recoiless fraction $f$ evaluated from the analysis of the time spectrum revealed a substantial reduction upon temperature rise from 19 to 25 K. As its origin, an order-disorder phase transition of the monolayer Kr is proposed.