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.

Nanoindentation measurements performed using the atomic force microscope (AFM) are significantly affected, both with regard to indentation curve shape and quantitative values of the measurements (70% variation in measured modulus), by the well-known effects of hysteresis and creep in the lead zirconate titanate (PZT) piezoceramic actuators used to control the positioning and motion of the mechanical components of the AFM. A capacitance-based displacement calibrator has been built and it was discovered that the response of PZT ceramics may vary (up to 66%) depending upon the conditions under which the piezoceramic is calibrated. By replacing the PZT actuators with lead magnesium niobate (PMN) electrostrictive actuators, nanoindentation measurements have been obtained using the AFM that are both reproducible and quantitative.

Atomic force microscopy (AFM) was invented in 1986 by Binnig, Quate, and Gerber as “a new type of microscope capable of investigating surfaces of insulators on an atomic scale.” Stemming from developments in scanning tunneling microscopy (STM), it became possible to image insulators, organic and biological molecules, salts, glasses, and metal oxides — some under a variety of conditions, e.g., ambient pressure, in aqueous or cryogenic liquids, etc. In 1987, Mate and co-workers introduced a new application for AFM where atomic-scale frictional forces could be measured. Likewise, in 1989, Burnham and Colton used the AFM to measure the surface forces and nano-mechanical properties of materials. Today, there are many examples of using AFM as a high-resolution profilometer, surface force probe, and nanoindentor. Several new imaging techniques have been introduced; each depending on the type of force measured, e.g., magnetic, electrostatic, and capacitative. Because of the diverse nature of the field and instrumentation, the names “scanned probe microscopy” and “XFM” (where X stands for the force being measured, e.g., MFM is magnetic force microscopy) have been adopted.

Thin multilayer samples of Si/Ge, with individual layer thicknesses of 4-33 om, have been analyzed by secondary ion mass spectrometry (SIMS) using AT' , 0,' and Cs' primary ion beams. Bombardment with both Ar' and 0,' produced positive secondary ion depth profiles in which pronounced distortions were observed. Similar effects were found in negative secondary ion depth profiles with Cs* bombardment. In each case, the SIMS depth profiles were characterized by abrupt interfacial secondary ion signal variations and a shift in the secondary ion signal maxima indicating that the layers were superposed, a condition that was not consistent with sample preparation, as verified by Auger electron spectroscopy. Auger electron spectroscopy depth profiling was also used to quantify the level of oxygen in the films. From these data it was concluded that the distortions in the positive secondary ion depth profiles under Ar' bombardment were the result of secondary ion yield variations induced by enhanced incorporation of ambient oxygen, during sample preparation, into the stronger oxide-forming silicon layers. Under 0,' and Cs' bombardment, the profile distortions were introduced by differential incorporation of the implanted primary species into the lower-sputter-yield silicon layers.

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