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 nanoindentation is illustrated with three single-crystal metals--chromium, molybdenum, and tungsten. Three distinct regions with differing elastic moduli are found: (1) a low modulus for the outermost surface layer whose thickness 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 modulus of the oxide is significantly larger than the bulk metal. Furthermore, the AFM can be used to ''depth profile'' the oxide layer giving new information about the sharpness of the oxide/metal interface