Permeation of a Single-Layer SiO₂ Membrane and Chemistry in Confined Space

Abstract

Well-ordered, ultrathin silica films grown on metal substrates are composed of layers of corner-sharing [SiO4] tetrahedra (silicatene). Yet unrealized in practice as unsupported material, the double-layer silicatene could constitute the thinnest silica membrane ever fabricated. We addressed here the permeability of such a membrane by using a metal substrate as a gas detector. Permeation of CO and D2 was examined by infrared reflection absorption spectroscopy and temperature-programmed desorption. The results reveal a complex response of such systems upon gas exposures which involves gas transport through amorphous silica pores as well as chemisorption and diffusion across the metal surface underneath the silicatene. Such a hybrid system, which would combine a robust molecular-sieve membrane and a chemically active metal underneath, could become interesting materials for technological applications, in particular, in catalysis and sensors.

Oxidation of the Ru(0001) surface covered by weakly bound, ultrathin silicate films

“…However, following the TPD results of Böttcher and coworkers of bare Ru(0001) [17], this desorption temperature does not shift much with increasing oxygen content. On the basis of our previous studies of CO and D 2 adsorption showing such shifts at nearly the same coverages [13], the shift observed in Fig. 1a can be explained in a similar way by that oxygen molecules, produced upon decomposition of Ru-oxide, need some time to find the pores in silicate to escape.…”

“…1a, green curve). As silicate itself does not decompose or dewet at these temperatures as judged by IRAS [13], the small desorption signal above ~1100 K could be assigned to the onset of oxygen desorption from the Ru(0001) surface underneath, which fully occurs only at temperatures as high as 1400 K [17].…”

“…Combined TPD and IRAS studies showed that these O ad-atoms suppresses CO and D 2 adsorption even after UHV annealing at 1275 K [13]. In order to get rid of O species from the Ru(0001) surface underneath the film via chemical reaction, the sample was exposed to high pressures of H 2 (1 mbar, 470 K).…”

Confined catalysis under two-dimensional materials

“…1). The planar microenvironment walls can be appropriately modeled in theoretical calculations (20,21) and investigated well by advanced characterization techniques, particularly surface science methods (22)(23)(24)(25)(26). The newly emerging 2D materials such as graphene (Gr) and hexagonal boron nitride (h-BN) have been facilely supported on solid surfaces via surface deposition or transfer methods (27).…”

LEEM and PEEM as Probing Tools to Address Questions in Catalysis

“…In the case of the SiO 2 / Ru(0001) system, it has been reported the possibility of intercalating simple molecules such as CO and D 2 under the amorphous film, that means into the confined space enclosed between the silica sheet and the Ru(0001) surface, under well-defined experimental conditions. By using infrared reflection absorption spectroscopy (IRAS) Emmez et al have shown by means of temperature programmed desorption (TPD) experiments that the silica bilayer acts as a barrier for CO and D 2 to diffuse away from the Ru surface once they desorb [60]. In this sense, the thin silicon oxide film behave as a membrane that could, in principle, act as a size selective barrier ("molecular sieve") for diffusion of molecules being consumed or produced on the transition metal surface underneath during a chemical reaction, as illustrated in the scheme shown in Fig.…”