ABSTRACT
Atomic force microscopy (AFM), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), and near-field scanning optical microscopy (NSOM) have been used to characterize the nanostructure of Au colloid-based surfaces. Because these substrates are composed of particles whose dimensions are known prior to assembly, they are well-suited for a critical comparison of the capabilities and limitations of each nanoscale imaging technique. The three criteria for this comparison, which are relevant to the field of nanoparticle assemblies in general, are (i) accuracy in establishing particle size, particle coverage, and interparticle spacing; (ii) accuracy in delineating surface topography; and (iii) ease of sample preparation, data acquisition, and image analysis. For colloidal Au arrays, TEM gives the most reliable size and spacing information but exhibits the greatest constraints with regard to sample preparation; in contrast, AFM is widely applicable but yields data that are the least straightforward to interpret. For accurate information regarding nanometer-scale architecture of particle-based surfaces, a combination of at least one scanning probe method (AFM, NSOM) and one accelerated-electron method (TEM, FE-SEM) is required.
ABSTRACT
The interface between a two-dimensional (2D) molecular gas and a 2D molecular solid has been imaged with a low-temperature, ultrahigh-vacuum scanning tunneling microscope. The solid consists of benzene molecules strongly bound to step edges on a Cu{111} surface. Benzene molecules on the Cu{111} terraces move freely as a 2D gas at 77 kelvin. Benzene molecules transiently occupy well-defined adsorption sites at the 1D edge of the 2D solid. Diffusion of molecules between these sites and exchange between the two phases at the interface are observed. On raised terraces of the copper surface, the 2D gas is held in a cage of the solid as in a 2D nanometer-scale gas bulb.
