Berkó András, Magony Anett, Szökõ János
Department of Solid State and Radiochemistry and Reaction Kinetics Research Group, Hungarian Academy of Sciences, University of Szeged, P.O. Box 168, H-6701 Szeged, Hungary.
Langmuir. 2005 May 10;21(10):4562-70. doi: 10.1021/la046826m.
The properties of Mo ultrathin films deposited on a TiO2(110) surface were investigated by scanning tunneling microscopy (STM) and spectroscopy (STS), as well as by Auger electron spectroscopy (AES). The substrate exhibited mainly large (1 x 1) terraces decorated by additional [001] rows (missing or added 1D structures) of reduced TiO(x) phases. Only a few percent of the surface exhibited a cross-linked (1 x 2) arrangement. The deposition of Mo layers at room temperature with a rate of approximately 0.4 monolayer/ min resulted in nanoclusters of 1-2 nm with a low-profile shape (2D-like). Preferential decoration of the atomic steps was not found; at the same time, the 1D defect sites of missing or added rows on the (110) terraces were characteristically decorated by larger Mo nanocrystallites. This behavior indicates that the mobility of Mo atoms is higher on the more reduced regions of the substrate. The high dispersion of the Mo adlayer changed only slightly on annealing up to 700 K; in the range of 900-1050 K, however, a significant increase of the particle size accompanied by splitting of the TiO2(110) terraces was observed. This behavior may be explained by the partial oxidation of the supported Mo (accompanied by the reduction of the substrate) into tetragonal crystallites oriented and slightly elongated in the [001] or [110] direction of the TiO2(110) support. STS measurements indicated that the crystallites or the support/crystallite interface formed above 900 K possesses a wide band gap. The annealing above 1050 K resulted in the disappearance of Mo from the TiO2(110) surface, which may be explained by the formation and sublimation of MoO3 species at the perimeter of the nanoparticles. The change of AES signal intensities for O(KLL) and Mo(MNN) as a function of the annealing temperature also supports this mechanism.
通过扫描隧道显微镜（STM）和能谱（STS）以及俄歇电子能谱（AES）研究了沉积在TiO2(110)表面的钼超薄膜的性质。衬底主要呈现出大的(1×1)平台，这些平台由TiO(x)还原相的额外[001]行（缺失或添加的一维结构）修饰。只有百分之几的表面呈现交联的(1×2)排列。在室温下以约0.4单层/分钟的速率沉积钼层，形成了1-2纳米的低轮廓形状（类似二维）的纳米团簇。未发现原子台阶的优先修饰；同时，(110)平台上缺失或添加行的一维缺陷位点特征性地被较大的钼纳米晶体修饰。这种行为表明钼原子在衬底还原程度较高的区域具有更高的迁移率。钼吸附层的高分散性在高达700 K的退火过程中仅略有变化；然而，在900-1050 K范围内，观察到粒径显著增加，同时TiO2(110)平台发生分裂。这种行为可以用负载的钼部分氧化（伴随衬底还原）为沿TiO2(110)载体的[00]或[110]方向取向并略微拉长的四方晶体来解释。STS测量表明，在900 K以上形成的微晶或载体/微晶界面具有宽禁带。在1050 K以上退火导致钼从TiO2(110)表面消失，这可以用纳米颗粒周边MoO3物种的形成和升华来解释。O(KLL)和Mo(MNN)的俄歇电子能谱信号强度随退火温度的变化也支持这一机制。
