Wang Han-Chun, Sun Shi-Gang, Yan Jia-Wei, Yang Hong-Zhou, Zhou Zhi-You
State Key Lab of Physical Chemistry of Solid Surfaces, Department of Chemistry, Xiamen University, Xiamen 361005, China.
J Phys Chem B. 2005 Mar 17;109(10):4309-16. doi: 10.1021/jp046313o.
We have extended the study of anomalous IR properties, which were initially discovered on nanostructured films of platinum group metals and alloys, to nanostructured films of nickel, a member of the iron group triad, and broadened the fundamental knowledge on this subject. Nanostructured thin films of nickel supported on glassy carbon [nm-Ni/GC(n)] were prepared by electrochemical deposition under cyclic voltammetric conditions, and the thickness of films was altered systematically by varying the number (n) of potential cycling within a defined potential range for electrodeposition. Electrochemical in situ scanning tunneling microscopy (STM) was employed to monitor the electrochemical growth of nanostructured Ni films. These in situ STM images illustrated that, along the increase of the film thickness, Ni films have undergone a transformation from layer structure to island structure and finally to lumpish arris structure. Investigations by in situ FTIR spectroscopy employing adsorbed CO as the probe revealed that these nanostructures of Ni films yield abnormal IR features, Fano-like IR features, and normal IR features, respectively. The IR bands of CO adsorbed on Ni thin films of a layer structure were inverted in their direction and enhanced in their intensity up to 15.5 times on an nm-Ni/GC(4) electrode. The Fano-like IR features, which are defined as a bipolar band with its negative-going peak on the low wavenumber side and its positive-going peak on the high wavenumber side, are observed for the first time on Ni thin films of an island nanostructure, i.e., at the nm-Ni/GC(16) electrode. IR features changed to normal absorption in CO adsorbed on the nm-Ni/GC(25) electrode, i.e., that with lumpish arris nanostructured Ni film of a larger thickness.
我们将最初在铂族金属及其合金的纳米结构薄膜上发现的异常红外特性的研究扩展到了铁族元素三元组成员之一的镍的纳米结构薄膜，并拓宽了该领域的基础知识。在循环伏安条件下通过电化学沉积制备了玻碳负载的镍纳米结构薄膜[nm-Ni/GC(n)]，通过在电沉积的定义电位范围内改变电位循环次数(n)来系统地改变薄膜厚度。采用电化学原位扫描隧道显微镜(STM)监测纳米结构镍薄膜的电化学生长。这些原位STM图像表明，随着薄膜厚度的增加，镍薄膜经历了从层状结构到岛状结构，最终到块状棱边结构的转变。采用吸附的CO作为探针的原位傅里叶变换红外光谱研究表明，这些镍薄膜的纳米结构分别产生异常红外特征、类法诺红外特征和正常红外特征。在nm-Ni/GC(4)电极上，吸附在层状结构镍薄膜上的CO的红外波段方向反转，强度增强至15.5倍。在岛状纳米结构的镍薄膜上，即在nm-Ni/GC(16)电极上，首次观察到类法诺红外特征，其定义为双极带，在低波数侧有负向峰，在高波数侧有正向峰。在nm-Ni/GC(25)电极上吸附的CO中，红外特征变为正常吸收，即具有较大厚度的块状棱边纳米结构镍薄膜。
