Sincrotrone Trieste SCpA, Strada Statale 14, Basovizza (TS), Italy.
J Phys Condens Matter. 2011 Jun 1;23(21):215001. doi: 10.1088/0953-8984/23/21/215001. Epub 2011 May 9.
The interaction of tungsten with CeO(2)(111) layers grown on Cu(111) was studied in the temperature range between 300 and 870 K by photoelectron spectroscopy of the core levels and resonant valence band spectroscopy. The interaction was found to be very strong even at 300 K, leading to the formation of cerium tungstate Ce(6)WO(12) in which the metal atoms were in Ce(3+) and W(6+) chemical states. The growth was limited by the diffusion of W atoms into the ceria layer, so subsequent tungsten deposition led to formation of W suboxides with consecutively lower chemical oxidation states, i.e. W(4+), W(2+) and metallic W(0) with an almost negligible contribution of W(5+). Step-wise annealing of the layer showed that due to stimulated diffusion of tungsten into ceria at higher temperature, Ce(6)WO(12) was formed more easily. Larger W overlayer thicknesses needed higher annealing temperature to promote diffusion. The thickest sample studied, 1.4 nm W/CeO(2), was transformed by annealing to 870 K to the Ce(6)WO(12)/W system with a tungsten monoxide (WO) interface, whereas the rest of the tungsten was converted to the W(6 + ) oxidation state.
在 300 至 870 K 的温度范围内，通过核心能级光电子能谱和共振价带光谱研究了钨与 CeO(2)(111)层在 Cu(111)上生长的相互作用。即使在 300 K 时，相互作用也非常强烈，导致形成钨酸铈 Ce(6)WO(12)，其中金属原子处于 Ce(3+)和 W(6+)化学状态。生长受到 W 原子扩散进入氧化铈层的限制，因此随后的钨沉积导致形成具有连续较低化学氧化态的 W 亚氧化物，即 W(4+)、W(2+)和金属 W(0)，其中 W(5+)的贡献几乎可以忽略不计。对该层的逐步退火表明，由于在较高温度下钨对氧化铈的刺激扩散，更容易形成 Ce(6)WO(12)。较大的钨覆盖层厚度需要更高的退火温度来促进扩散。研究的最厚样品，即 1.4 nm W/CeO(2)，在 870 K 退火后转变为 Ce(6)WO(12)/W 体系，具有钨氧化物 (WO) 界面，而其余的钨则转化为 W(6+)氧化态。
