Thin silica films on Ru(0001): monolayer, bilayer and three-dimensional networks of [SiO4] tetrahedra

Abstract

The atomic structure of thin silica films grown over a Ru(0001) substrate was studied by X-ray photoelectron spectroscopy, infrared reflection absorption spectroscopy, low energy electron diffraction, helium ion scattering spectroscopy, CO temperature programmed desorption, and scanning tunneling microscopy in combination with density functional theory calculations. The films were prepared by Si vapor deposition and subsequent oxidation at high temperatures. The silica film first grows as a monolayer of corner-sharing [SiO(4)] tetrahedra strongly bonded to the Ru(0001) surface through the Si-O-Ru linkages. At increasing amounts of Si, the film forms a bilayer of corner-sharing [SiO(4)] tetrahedra which is weakly bonded to Ru(0001). The bilayer film can be grown in either the crystalline or vitreous state, or both coexisting. Further increasing the film thickness leads to the formation of vitreous silica exhibiting a three-dimensional network of [SiO(4)]. The principal structure of the films can be monitored by infrared spectroscopy, as each structure shows a characteristic vibrational band, i.e., ∼1135 cm(-1) for a monolayer film, ∼1300 cm(-1) for the bilayer structures, and ∼1250 cm(-1) for the bulk-like vitreous silica.

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

“…In addition, this film was prepared using isotopically labelled molecular oxygen, 18 O 2 . As expected, a new broad band centered at 1190 cm -1 is observed in IRA-spectrum which is characteristic for three-dimensional, bulk-like ( 18 O-labeled) silica [1,7,9] (see Fig. S2), suggesting that this sample contains also some silica nanoparticles.…”

“…It is well established that the thinnest silica film forms a hexagonal layer of corner-sharing [SiO 4 ] tetrahedra (referred to as "silicatene" in analogy to graphene [5]) which is strongly bound to a metal support through Si-O-Metal linkages [6]. On noble metals such as Ru(0001), Pd(100) and Pt(111), double-layer (or bilayer) silicate films may be grown, which are weakly bound to the support via dispersive forces [7][8][9][10]. In this case, a relatively large space between the silicate sheet and the metal support allows, in principle, small molecules to intercalate the interface, diffuse and ultimately react on the metal surface.…”

“…The temperature was measured by a type K thermocouple spot-welded to the backside of the crystal. Silicate films were grown on the Ru(0001) surface as described in detail elsewhere [9]. Briefly, silicon was vapor deposited from a Si rod (99.999%, Goodfellow) onto oxygen precovered 3O(2×2)-Ru(0001) surface at ~100 K, followed by oxidation at ~1250 K in 10 -6 mbar O 2 for 10 min.…”

Atomic Structure Control of Silica Thin Films on Pt(111)

“…Ru(0001) also exhibited this exact trend where a bilayer was first observed 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 with a peak at 1300 cm −1 and upon further film growth the bilayer peak disappeared and a peak centered at 1257 cm −1 with a broad shoulder down to 1100 cm −1 appeared. 15 The clear formation of the bilayer after 4 minutes indicates that the film deposition rate is on the order of 0.5 monolayer/min. The presence of the thick film after 10 minutes would mean a film thickness of 5 atomic layers, which is similar to the thickness of 3-dimensional films grown on Ru(0001).…”

“…Mo(110), Mo(112) and Ru(0001) have all been shown to be ideal candidates for the growth of these films and their structural properties have been well documented. [6][7][8][9][10][11][12][13][14][15][16][17] From these studies it has been shown that the type of silica film can be solely determined by its infrared vibration band: ∼1300 cm −1 for a bilayer, ∼1250 cm −1 for a thick, vitreous film, and ∼1065 or ∼1135 cm −1 for a monolayer film on Mo(112) or Ru(0001), respectively. 16 SiO 2 films have also been successfully grown on Ni(111) 18 , Pd(100) 19 , and Pd(111) 20 , but have not been characterized to the extent of the aforementioned surfaces.…”