Results are presented from a series of atomic force microscope (AFM) experiments, wherein a sharp diamond indentor with a sub-micron tip radius. was directed to plow along specific crystallographic directions on selected alloy aluminum surfaces. A set of four. two-dimensionally polycrystalline aluminum alloys was chosen for this work. viz.. Al-99.99wt%. Al-0.2wt%Mg. Al-l.Owt%Mn. and Al-0.5wt%Cu. Crystallographic orientations of the surface grains upon which plowing was conducted were determined a priori through orientation imaging microscopy (OIM). Two sets of plow tracks were generated in four crystallographic directions. each set containing four plow tracks generated at four different normal indentor forces. The plow tracks were subsequently imaged to provide measurements of the plow track depths. ridge heights, and ridge angles relative to the nominal (undisturbed) surface plane. This data was then input to a model of single asperity plowing based on the upper bound theorem of plasticity for isotropic. non-strain hardening materials. The model provided estimates of surface flow strength as a function of depth of cut for each of the crystallographic directions. Experimental measurements of the friction (or plowing) force and depth of cut variations with normal indentor force are also presented.

The characterization of near surface mechanical properties and the study of wear and friction behavior of materials is performed using the three-axial surface force apparatus developed in our laboratory.

Depth-sensing nanoindentation is coupled with surface imaging procedures performed with the same tip, which allows a precise choice of the indentation point before the test and then to measure the residual indent without moving the sample. Accurate stiffness measurements and precise contact area determination associated with an appropriate mechanical model give access to the elastoplastic properties of the material and to its structure (surface layers, film thickness).

With the same diamond tip, a new nano-machining procedure is used in order to remove the material from the surface to a pre-described depth. A succession of parallel scratches are made using both normal and tangential motion of the tip in the controlled displacement mode.

First this allows the creation of a new and flat area necessary for reliable nanoscale indentation and to access the mechanical properties at a given depth.

Second, as the friction and loading forces are recorded continuously during the process, the dissipated energy required to create the worn surface is measured. Information about wear and friction behavior of the surface can be obtained through this new development.

The characterization of coated systems by scratch tests usually consists in the empirical determination of wear and friction. In this paper, a theoretical model is presented, which makes it possible to explain the tribological behavior of materials in various scratch modes. Examples of measurements on coated systems as well as on their uncoated substrates confirm the assumptions of the model

Microploughing experiments were used as a method for better understanding the ploughing mechanism in gold and iridium single crystals. The plough depths ranged from 20 nm in iridium to 1600 nm in gold. Yield stress profiles and TEM analyses indicate that both materials strain harden even when very small volumes of material are involved. Strain hardening theory, as applied to bulk material, is useful in analyzing the results.

The role of organic additives in dry pressing of metallic powders can be studied with the atomic force microscope (AFM) in terms of interaction forces, friction forces and shearing behavior. Material dependent properties in contact can be determined with the appropriate calibration of instrument sensitivities and spring constants. Force-distance curves give information about particle-particle interactions; measurement of static and dynamic friction provide additional information directly related to surface deformation. We present a fast and simple method for calibration of lateral cantilever deflection, independent of experimental setup. Experimental results on iron surfaces in contact show how adsorption of 12-hydroxy stearic acid yields different contact behaviour than commercial lubricants. This information also explains the hysteresis in friction-load experiments which can not be obtained from normal force curves or standard friction measurements alone.

The scratch test is often used for assessing the properties of coated systems since it readily allows the differing dominance of various deformation mechanisms - and the friction response - to be measured as a function of contact severity. Further, the scratch test can be used to determine a critical load at which failure of the coating-substrate interface occurs and thus give a semiquantitative measure of the adhesion of the coating. Usually, micro- and macro-scratch tests arc performed in the load range between 0.05N to 100N but here, to explore the response of a much thinner coating (300nm of CNX on silicon), we report on scratches made with loads between I and 20rnN. We have found a load dependent transition in the scratch and friction responses. Below 4mN, the scratches exhibited a completely elastic response with no evidence of failure. At 5mN, the scratches showed some completely elastic areas and some areas that were typical of a buckle failure of the coating and at the same tirne, the coefficient of friction rose from ˜0.1 to ˜0.5. Above 5mN, the scratches showed a continuous plastic groove and buckle-type failure. We discuss these results in relation to the scratch response and tribology of ultra-thin films.

Friction and wear properties of aluminum oxide, aluminum oxynitride and aluminum nitride ceramic thin films were examined by contacting the film surfaces with sapphire spheres and conical diamond tips and using applied forces in the microNewton to milliNewton range. With our contact geometry, forces in this range create sub-micron to micron-sized contacts, which are comparable in size to the microstructural features present on the film surfaces. Samples studied include bulk sapphire crystals, and Al2O3, AIOxNy, and AIN thin films grown to thicknesses ranging from 50 nm to 200 nm on sapphire substrates by a variety of deposition techniques. Film growth (microstructure) was controlled to contain either amorphous, random polycrystalline, or highly-oriented crystalline architecture as characterized during film growth by RHEED analysis. Film composition was measured with XPS. Friction and wear data were obtained during low-cycle and high-cycle reciprocal sliding experiments performed on the University of Maine nanotribometer, which is designed for the meso-scale regime. Variations in friction coefficient and wear resistance are correlated to differences in composition and microstructure.

Advanced materials are being designed and tested for high-stress, high-cycle ball bearing applications. Important information about the tribological performance of these materials is gained through rolling contact fatigue (RCF) measurements. No such data have been reported to date for hybrid bearings consisting of titanium carbide (TiC)-coated REX20 steel balls and REX20 steel raceways. Chemical vapor deposition (CVD) was used for depositing the TiC coating. In this paper, we present the first report of the effects of RCF tests on this particular combination of hybrid bearings. Post-test characterizations of these bearings are discussed. Our investigations include plan-view and cross-sectional scanning electron microscopy, chemical compositional analyses, X-ray diffraction, and nano-indentation measurements. Results of these investigations provide a detailed understanding of the TiC coating on REX20 steel balls following extended rolling contact.

Microstructural aspects of wear resistance have been investigated using cross-sectional transmission electron microscopy (TEM) to analyze both as-deposited and worn films. Asdeposited Pb-Mo-S films were virtually amorphous, i.e., show no long range structure. Wear tracks revealed a two-part wear process localized at the sliding surface. First, Pb-Mo-S at the sliding surface was transformed into basal-oriented, crystalline MoS2 from I to 4 monolayers thick. Then, as sliding continued, the MoS2 layers were detached one or two layers at a time. Evidence for the nanometer scale wear process is presented.

CaF2 films with 40 nm depth were grown on Si(111) wafers by thermal evaporation in UHV machine and submitted at a RTA in situ. Three different lateral forces were observed to affect behavior during the scratch. This corresponded to three different compositions at different profiles: the CaF2 film, the interface region and the silicon substrate. The XPS spectrum shows the presence of calcium silicide at the interface region. The X-ray reflectivity measurements show that the interfaces are sharpest in annealed samples. This is in accordance with nanoscratch results, showing that the intermediary value for the friction coefficient is due the calcium silicide interface layer.

We report observations of contrasting surface modification behavior of the Au(111) surface in the presence of an electric field and field-emission currents using interfacial force microscopy (IFM) and scanning tunneling microscopy (STM). Our experiments consist of surface modification procedures which allow for large tip-sample gaps, in contrast to fast voltage pulses (applied at tunneling distances) employed by previous STM investigations. Dramatic surface distortions are observed when a 200 nm-radius tip, biased at -100 V, is brought toward the Au surface at a field emission current level of 400 nA and then retracted. In other experiments, we raise the sample voltage to field-emission levels while maintaining a constant current. STM images, measured in a time-resolved manner after each such procedure, show that the presence of a higher electric field (˜0.07 V/Å) results in step retraction and the disappearance of small islands on the Au(111) surface followed by the formation of vacancy islands in the area directly beneath the apex of the tip where the field is highest. We discuss the implications of these contrasting surface modifications in terms of the various key parameters and in relation to previous studies using voltage pulses in the STM.

The study of a hinge is a new trial in tribology for reducing friction and controlling traction. This paper describes the results that we obtained concerning the tribology of a friction plate in a hinge by AFM, SEM and TEM. These measurements are effective in providing quantitative information for the traction control and failure probabilities of the hinge.

The characterization of metallic electrodes in semiconducting devices with high spacial resolution has become increasingly important. Scanning force microscopy (SFM) enables us to observe surface topographies on a nanometer scale as well as local mechanical properties such as friction force without any spacial surface treatment, while it is difficult to obtain high resolution with the conventional methods such as static time of flight-secondary ion mass spectroscopy and Auger electron spectroscopy because of their beam size. Here we have demonstrated the possibility of two dimensional mapping of the mechanical properties by friction force microscopy (FFM) and force modulation method (FMM) for Gold islands deposited on Nickel flat substrate. The FFM observation revealed that the grain size of the metallic islands ranged from 5 to 7000 nm. The friction force measurement showed that the friction force on Au islands was lower than the Ni substrate. The compositional high resolution mapping of metal films was obtained by FFM. In addition to the local mechanical measurement, FMM also showed the difference in stiffness between two materials.

Nanotribological improvements concerning adhesion and friction can be obtained by chemical modification of the sample surface. Due to adsorption a thin water film is always present. However, the thickness of the fim can be reduced or temporarily suppressed by hydrofluoric (HF) acid etching, leading to hydrophobic surface conditions for the case of silicon. Using a novel micro/nano tribo-tester capable of probing two planar samples in contact, adhesion and friction forces in the range of mN down to nN can be resolved using force-distance mode or tangential force mode, respectively. It can be shown that the reduction of the water layer reduces the adhesion effectively. The tangential force measurements, however, indicate strong stick/slip events. Those stick/slips were not observed with samples having a thicker water film. The thickness of the water film controls the type of sliding. As the thickness decreases stick/slips appear and vanish. This phenomenon is attributed to the formation of ordered layers. Experimental results will be presented for silicon samples (A = 3 mm2). The surface chemistry was monitored using Auger Electron Spectroscopy. Topography was measured by Atomic Force Microscope (AFM).