MEASUREMENT OF NANOMECHANICAL PROPERTIES OF METALS USING THE ATOMIC-FORCE MICROSCOPE

The capability of the atomic force microscope (AFM) to quantitatively measure the nanoscale mechanical properties of metals via nanoindentat ion is illustrated with three single-crystal metals-chromium, molybden um, and tungsten. Three distinct regions with differing elastic moduli are found: (1) a low modulus for the outermost surface layer whose th ickness scales with the degree of hydrocarbon surface contamination, ( 2) a much higher modulus at a depth and thickness corresponding to the native oxide layer; and (3) an intermediate modulus at larger depths corresponding to the bulk modulus of the metal. In all cases, the modu lus of the oxide is significantly larger than the bulk metal. Furtherm ore, the AFM can be used to ''depth profile'' the oxide layer giving n ew information about the sharpness of the oxide/metal interface.