Tighe Timothy B, Daniel Thomas A, Zhu Zihua, Uppili Sundarajan, Winograd Nicholas, Allara David L
Department of Chemistry and The Materials Research Institute, Pennsylvania State University, University Park, PA 16802, USA.
J Phys Chem B. 2005 Nov 10;109(44):21006-14. doi: 10.1021/jp054174k.
The combination of in situ X-ray photoelectron spectroscopy, infrared reflection spectroscopy, atomic force microscopy, and time-of-flight secondary ion mass spectrometry are used to probe the nature of the evolving interface chemistry and metal morphology arising from Ti vapor deposition onto the surface of a CH(3)(CH(2))(15)S/Au{111} self-assembled monolayer (SAM) at ambient temperature. The results show that for a deposition rate of approximately 0.15 Ti atom.nm(-2).s(-1) a highly nonuniform Ti overlayer is produced via a process in which a large fraction of impinging Ti atoms do not stick to the bare SAM surface. The adsorbed atoms form isolated Ti clusters and react with CH(3) groups to form carbide products at the cluster-SAM interfaces. Further growth of Ti clusters appears to be concentrated at these scattered reaction centers. The SAM molecules in the local vicinity are subsequently degraded to inorganic products, progressing deeper into the monolayer as the deposition proceeds to give an inorganic/organic nanocomposite. A continuous overlayer does not form until metal coverage approaches approximately 50 Ti atoms per SAM molecule. These data indicate that for applications such as molecular device contacts the use of Ti may be highly problematic, suffering from both a highly nonuniform contact area and the presence of extensive inorganic products such as nonstoichiometric carbides and hydrides.
利用原位X射线光电子能谱、红外反射光谱、原子力显微镜和飞行时间二次离子质谱相结合的方法，来探究在室温下将钛蒸气沉积到CH(3)(CH(2))(15)S/Au{111}自组装单分子层（SAM）表面时，不断演变的界面化学性质和金属形态。结果表明，对于大约0.15个钛原子·纳米(-2)·秒(-1)的沉积速率，通过一种过程会产生高度不均匀的钛覆盖层，在该过程中，大部分撞击的钛原子不会附着在裸露的SAM表面。吸附的原子形成孤立的钛簇，并与CH(3)基团反应，在簇-SAM界面处形成碳化物产物。钛簇的进一步生长似乎集中在这些分散的反应中心。局部附近的SAM分子随后会降解为无机产物，随着沉积的进行，会深入到单分子层中，形成无机/有机纳米复合材料。直到金属覆盖率接近每个SAM分子约50个钛原子时，才会形成连续的覆盖层。这些数据表明，对于诸如分子器件接触等应用，使用钛可能会存在很大问题，会出现接触面积高度不均匀以及存在大量无机产物（如非化学计量碳化物和氢化物）的情况。
