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Two globular proteins, lysozyme and chymotrypsinogen A, were imaged on graphite using a scanning tunneling microscope. In contrast to the isolated molecules typically seen, long-range order was observed in both of these systems when the protein concentration of the solution deposited on the graphite was sufficient for multilayer coverage. For lysozyme, regular two-dimensional arrays of protein molecules were seen, with periodicities ranging from about 40 (the approximate size of a lysozyme molecule) to about 150 Å. These length scales depend on the lysozyme concentration in the initial solution. For chymotrypsinogen A, two-dimensional structures that covered a much smaller area of the graphite were observed. The structural features observed suggest such possibilities as protein structure determination using surface structural techniques and epitaxial growth of protein crystals on these two-dimensional structures.

Scanning tunneling microscopy (STM) was used to image Ratawi (neutral zone) asphaltenes deposited on highly oriented pyrolytic graphite (HOPG). STM images revealed the formation of ordered arrays covering hundreds of angstroms of the surface. Samples deposited from pyridine solutions above and below the critical micelle concentration were quite similar. The individual features imaged in these arrays were attributed to the termini of the pendant aliphatic chains known to be a part of the asphaltene molecular structure. The ordered arrays imaged were extremely flat and uniform, in contrast to the assumed molecular complexity and the absence of unique structure of asphaltenes. The formation of these ordered surface arrays is further evidence of the tendency of asphaltenes to self-associate.

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