FRACTAL CHARACTERISTICS OF SCANNING TUNNELING MICROSCOPIC IMAGES OF BRITTLE-FRACTURE SURFACES ON MOLYBDENUM

Brittle fracture surfaces at room temperature (approximately 25-degrees-C) and liquid nitrogen temperature (-196-degrees-C) for molybdenum single crystal were observed with a scanning tunneling microscope (STM) and a scanning electron microscope (SEM). STM images obtained showed that fine cleavage steps were formed on the fracture surfaces. The images were analyzed by fractal geometry. The brittle fracture surface of molybdenum single crystal had self-similarity (i.e., fractal characteristics) up to the very high magnification where the scanning range of 40 nm in X and Y directions corresponded to about 150 atoms of molybdenum. However, this characteristics was expected to break down when the scanning range in the X and Y directions was below 20 nm. This was confirmed by STM images with the scanning range of 16 nm, where the cleavage step was not observed.