In situ scanning tunneling microscopy of individual supported metal clusters at reactive gas pressures from 10-8 to 104 Pa

An experimental apparatus has been designed and an approach developed for imaging individual oxide supported nanoparticles with scanning tunneling microscopy (STM) during their nucleation, growth, alloying, and "real world" chemical, thermal, and other in situ treatments. By careful selection of the tunneling conditions and using the STM tip to index the surface, it is demonstrated that preselected individual particles can be imaged at elevated temperatures while changing the reactive gas pressure over 12 orders of magnitude. The experimental challenges due mainly to tunnel junction instabilities, a relatively weak cluster-support interaction, and sample drift are considered and strategies to overcome these obstacles proposed. Using Au and Ag clusters deposited on TiO2(110) as a model system, the potential of the method is demonstrated for exploring on a particle-by-particle basis cluster growth, alloying, thermal coarsening, and the evolution of particle morphology in a reactive gas environment. An additional advantage of the approach is that a wide cluster size distribution can be synthesized and surveyed on the same substrate. The size effects on cluster morphology therefore can be probed in situ for a wide variety of treatments on preselected clusters. (C) 2003 American Institute of Physics.