Surface atomic and domain structures of biomedical carbons observed by scanning tunneling microscopy (STM)

STM has been used to study the surface domain and atomic structures of three biomedical carbons: glassy carbon (GC), low-temperature isotropic carbon (LTI), and ultra-low-temperature isotropic carbon (ULTI). The images show atomic lattices on both GC and LTI, but not on ULTI. The lattices contain many defects; lattices in GC are more ordered than those in LTI. The images also show patchlike carbon crystallites with sizes of 3-15 nm for GC, 2-8 nm for LTI, and 1-3 nm for ULTI. The crystallites from surface domains that may differ in surface properties due to different orientations of the crystallites. Mechanical polishing makes the LTI surface more amorphous and more homogeneous. Based on the STM observations, we evaluate several hypotheses on the blood compatibility of biomedical carbons.