We have investigated the effect of film thickness on the nanoindentation measurements of hard diamondlike carbon (DLC) films. The DLC films were deposited on Si (100) substrates by pulsed excimer laser deposition (KrF, λ=248nm, duration=25 ns, energy density about 3.0 J/cm2, repetition rate 10 Hz) in high vacuum (∼5×10−7torr) at room temperature for various periods of time (from 5 minutes to 20 minutes). The thickness of the films was measured by optical profilometry, and ranges from 200 to 50 nm. The nanohardness and elastic modulus of these films were measured by a depth-sensing nanoindentation technique with NanoindenterXP. Preliminary experimental observations show that the nanoindentation results are a function of film thickness. Both the hardness and Young's modulus versus displacement curves of the 200nm thick film exhibit a peak at around tenth of the film thickness. The rest of the samples with smaller film thickness show plateaus, which are higher than the hardness and Young's modulus values of the substrate.

In this study, film interfacial fracture is induced by nanoindentation to quantify the practical work of adhesion of a post-CMP copper film to an amorphous silicon nitride passivation film. Poor adhesion of electrodeposited copper to SiN passivation is observed following CMP due to copper oxide growth prior to plasma enhanced silicon nitride deposition. Four point bend testing has shown that failure by brittle fracture of test structures occurs at the Cu/CuO interface. Hydrogen, ammonia, and nitrogen plasma treatments of the post-CMP copper surface can be used to remove the oxide, shown by auger electron spectroscopy, and to increase the surface roughness of copper, shown by atomic force microscopy. Both effects can be used to improve the Cu/SiN adhesion. Nanoindentation with a conical indenter (1.59 μm tip radius) was used to induce SiN film delaminations from Cu, the sizes of which were measured and correlated with the practical work of adhesion.[1,2] In order to more reliably and repeatably produce these delaminations a TiW (10wt% Ti) superlayer was sputter deposited on to the test structures.[2,3] Mechanical properties, including elastic modulus and hardness of SiN, electrodeposited copper, and TiW measured by nanoindentation are also reported here.

Total energy pseudopotential methods are used to study two different processes involving the mechanical interaction of diamond nanoasperities and diamond surfaces: the wear processes reponsible for diamond polishing, an the mechanical deformation of tip and surface during the operation of the Atomic Force Microscope in contact Mode (CM-AFM). The strong asymmetry in the rate of polishing between different dirctions onthe diamond (110) surface is explained in terms of on atomistic mechanism for nano-groove formation. The pst–polishing surface morphology and the nature of the polishing residue epredicted by this mechanism are consistent with experimental evidence. In the case of CM-FAM, our calculations show that a tip terminated in a single atom is able to sustain forces in excess of 30 nN. The magnitude of the normal force was unexpectedlyfound to be verye similar for th approach on top of an atom or on a hollow position on the surface. This behaviour is due to tip relaxations induced by the interaction with the surface. These forces are also rather insensitive to the chemical nature of the tip apex.

Self-assembled monolayers (SAMs) consisting of hydrocarbon chains attached to silica walls were evaluated computationally for their high temperature stability, life cycle and performance in microelectromechanical systems (MEMS). Ab initio calculations at sufficiently high level of theory were conducted on model compounds to predict the bond strengths holding the monolayer tethered to the MEMS device and relate them to its thermal stability. Non-equilibrium molecular dynamics (NEMD) simulations under sliding periodic boundary conditions were employed to compute the frictional force as a function of applied load. The NEMD trajectories were analyzed for the structure and chain dynamics of the SAMs and compared with NEMD and equilibrium MD results for the fluid. The significance of monolayer penetration depth, monolayer gauche fraction, wall thermostat characteristics and the size of the simulation box on the computed results were investigated.

The sample size employed in high pressure diamond anvil cells is limited to a diameter of typically 25 to 150 microns. While this size is often sufficient for diagnostics using synchrotron x-ray diffraction and Raman scattering, ex-situ measurements of mechanical properties using conventional microhardness indentation techniques is not feasible. For some materials, the high pressure phase(s) can be quenched to ambient pressure allowing further characterization by other techniques. We make use of the very small probe volume allowed by nanoindentation to investigate the pressure-quenched structures of both C70 fullerene and zirconium. For the case of C70, we show that the amorphous phase established above 35 GPa can be quenched to ambient, and that it shows a largely elastic indentation loading behavior with a hardness of 30 GPa. We establish that this hard carbon phase contains a mixture of sp2- and sp3-bonded carbon and that it can be produced from C70 fullerene by application of pressure at room temperature. With regard to zirconium metal, we confirm the irreversible transformation from the ambient hexagonal-close-packed phase to the simple hexagonal Ω-phase (AlB2 structure) and document an 80% increase in hardness that may be attributed to the presence of covalent bonding based on sd2-hybridized orbitals forming graphite-like nets in the (0001) plane of the AlB2 structure.

By analysing the relevant results in the literature, we have found that, when indentation is made on a subgranular level, the hardness varies roughly inversely with the square root of the distance between the indent and the grain boundary. This effect is analogous to the Hall-Petch effect for macroscopic deformation.

This paper reports the results of a study of the dynamic 3-dimensional response between a diamond point probe and a commercial hard-disk overcoat/lubricant system. The specific overcoat was CNx with a thickness of 50 Å. The lubricant layer was ZDOL with nominal thicknesses of 11 Å and 24 Å in unbonded and bonded conditions. The experiments were conducted with a constant lateral displacement oscillation in the z, x & y direction of 1 nm at a frequency of 125 Hz. Results of this study show that the bonded lubricant layer increases the lateral force required to maintain a constant lateral displacement oscillation compared to both the unlubricated CNx coating and the CNx coating with the unbonded lubricant.

A new type of AFM is presented which allows for direct measurements of nanomechanical properties in ultra-high vacuum and liquid environments. The AFM is also capable of atomic-scale imaging of force gradients. This is achieved by vibrating a stiff lever at very small amplitudes of less than 1 Å (peak-to-peak) at a sub-resonance amplitude. This linearizes the measurement and makes the interpretation of the data straight-forward. At the atomic scale, interaction force gradients are measured which are consistent with the observation of single atomic bonds. Also, atomic scale damping is observed which rapidly rises with the tip-sample separation. A mechanism is proposed to explain this damping in terms of atomic relaxation in the tip. We also present recent results in water where we were able to measure the mechanical response due to the molecular ordering of water close to an atomically flat surface.

The elastic modulus and work of adhesion of thin polystyrene (PS) films have been evaluated from nanoindentation load-displacement curves. The modulus was calculated using two methods: an unloading stiffness analysis and an elastoplastic unloading analysis. Results indicate that the latter analysis gives better modulus evaluation for the polymers. Two methods were also utilized in determining the work of adhesion, one using the pull-off forces and one using the displacement difference at zero force and pull-off force. The values given by the two methods are close. The effects of surface roughness and maximum load on the adhesion measurements are discussed. Different molecular weights were also chosen to compare the characteristics of the polymers during use under the same conditions. No significant difference in either modulus or adhesion energy was shown between the PSs of very low, moderate, and high molecular weights at room temperature.

Unexpected friction and wear transitions occur in transition metals associated with dislocation emission, dislocation storage, and oxide break-through phenomena. Both normal nanoindentation and nanoscratch evaluations of conical diamond tips driven into tungsten {100} single crystal surfaces have been conducted. In terms of initiating plasticity undert the contact, this represents a high Peierl's barrier for dislocation motion in transition metals. Both quasi-equilibrium and kinetic aspects are reported along with current but speculative ideas on multiple friction and wear transitions. Preliminary results show that yielding under contacts can produce a 250 nm displacement excursion. Ramifications are seen in terms of friction coefficients which can double during the near-instantaneous yield excursion but then continue to triple from about 0.05 to 0.15 in the pile-up phase in front of the sliding contact. Implications of how nanotribological issues such as adhesion connect through this mesoscale activity to macroscopic friction and wear are discussed.

Finite element simulations of ball indentation tests were performed and analyzed using the automated ball indentation method. The accuracy and reliability of this methods were assessed.

The atomic force microscope in the shear force modulation microscopy (SMFM) mode has been used to characterize the surface modulus and cross-link density of elastomer thin films, where standard rheological methods cannot be applied. Brominated poly(isobutylene-co-4-methylstyrene) (BIMS) is a synthetic terpolymer which can be stoichiometrically cross-linked by N, N'-dicinnamylidene-1,6-hexanediamine. The results on several types of BIMS elastomers with different bromide content are reported. The cross-linking reaction at the surface is found to be significantly faster than that of bulk. The estimated shear moduli of the thin films were found to be proportional to the cross-link density, as expected from the rubber elasticity theory for bulk materials.

We have reported results of nanoindentation using spherical indenters to observe the full indentation stress-strain curve. We observe the onset of plasticity in semiconductor strained-layer superlattices. These structures have alternating layers with strains of opposite sign. The yield pressure is reduced by the presence of the coherency strain. By varying the thicknesses and strains, we have been able to show that both sets of layers, compressive and tensile, reduce the yield pressure. This requires that a yield criterion must be satisfied over a volume, large enough to include layers of both sign. In these studies, we observe a large and reproducible size effect in the yield pressure. That is, with smaller radius indenters the mean pressure acting over the contact area at the deviation from purely elastic behaviour increases, by up to a factor of two for a 2μm radius indenter tip. Here we show how the requirement for meeting a yield criterion over a finite volume naturally leads to the size effect. Essentially, with smaller radius indenters, the peak stresses must be greater in order to satisfy the yield criterion over a finite volume. By integrating the strain energy over a suitable volume we show that there is a critical volume of ≍ 0.5μm radius over which yield is initiated for all indenter radii in the range 1-35μm. This is an important result for the understanding of nanoindentation and other systems in which stresses are highly inhomogeneous on a small scale.

Using dimensional analysis and finite element calculations, the relationships between hardness, elastic modulus, final contact depth, and the work of indentation are extended to conical indentation in elastic-plastic solids with various cone angles. These relationships provide new insights into indentation measurements. They may also be useful to the interpretation of results obtained from instrumented indentation experiments.

A series of model ferritic alloys and two commercial steels were used to develop a correlation between tensile yield strength and nano-indentation hardness measurements. The NanoIndenterII® was used with loads as low as 0.05 gf (0.490 mN) and the results were compared with conventional Vickers microhardness measurements using 200 and 500 gf (1.96 and 4.90 N) loads. Two methods were used to obtain the nanohardness data: (1) constant displacement depth and (2) constant load. When the nanohardness data were corrected to account for the difference between projected and actual indenter contact area, good correlation between the Vickers and nanohardness measurements was obtained for hardness values between 0.7 and 3 GPa. The correlation based on constant nanoindentation load was slightly better than that based on constant nanoindentation displacement. Tensile property measurements were made on these same alloys, and the expected linear relationship between Vickers hardness and yield strength was found, leading to a correlation between measured changes in nanohardness and yield strength changes.

The variations of hardness, composition, and microstructure within a carbon implanted region – about 350 nm thick – of a Ti-6Al-4V alloy were measured using nanoindentation, Auger electron spectroscopy and transmission electron microscopy, respectively. Correlations among hardness, composition, and microstructure were made with a spatial resolution of about ±20 nm. The variation in hardness within the implanted regions was quantitatively explained as due to the formation of an almost continuous TiC layer and precipitate hardening. The problems that may arise in measuring and correlating spatial variations in such a complex material on this scale are outlined and a successful method to solve them is proposed. The need for highly spatially resolved measurement techniques is emphasized.

The deformation behavior of as-grown and ion-beam-modified wurtzite GaN films is studied by a nanoindentation with a spherical indenter. Atomic force microscopy (AFM) and cathodoluminescence are used to characterize the deformation mode. No systematic dependence of the mechanical properties on the film thickness ( at least for thicknesses from 1.8 to 4 μm) as well as on doping type is observed. Results strongly suggest that (i) slip is the major contributor to the plastic deformatio of crystalline GaN and (ii) slip nucleation (rater than a phae transformation) is responsible for “pop-in” events observed during loading. Indentation with an ∼ 4.2 μm radius spherical indenter at maximum loads up to 900 mN does not produce any cracking visible by AFM in crystalline GaN. Instead, under such loads, indentation results in a pronounced elevation of the material around the impression. Implantation disorder dramatically changes the deformation behaviour of GaN. In particular, implanation-produced defects in crystalline GaN syppress (i) “pop-in” events during loading, (ii) slip bands observed by AFM, and (iii) the plastic component of deformation. GaN amorphized by in bombardment exhibits plastic flow even for very low loads. The values of hardness and elastic modulus of amorphous GaN are dramatically reduced compared to those of as-grown GaN.

A constitutive equation is developed for geometrically-similar sharp indentation of a material capable of elastic, viscous, and plastic deformation. The equation is based on a series of elements consisting of a quadratic (reversible) spring, a quadratic (time-dependent, reversible) dashpot, and a quadratic (time-independent, irreversible) slider—essentially modifying a model for an elastic-perfectly plastic material by incorporating a creeping component. Load-displacement solutions to the constitutive equation are obtained for load-controlled indentation during constant loading-rate testing. A characteristic of the responses is the appearance of a forward-displacing “nose” during unloading of load-controlled systems (e.g., magnetic-coil-driven “nanoindentation” systems). Even in the absence of this nose, and the associated initial negative unloading tangent, load-displacement traces (and hence inferred modulus and hardness values) are significantly perturbed on the addition of the viscous component. The viscous-elastic-plastic (VEP) model shows promise for obtaining material properties (elastic modulus, hardness, time-dependence) of time-dependent materials during indentation experiments.

Nanoindentation is a technique commonly used for measuring thin film mechanical properties such as hardness and stiffness. Typically, shallow indentations with contact depths less than 10-20% of the film thickness are used to ensure that measurements are not affected by the presence of the substrate. In this study, we have used the finite element method to investigate the effect of substrate and pile-up on hardness and stiffness measurements of thin film systems. We find that: i) for soft films on hard substrates, the hardness is independent of the substrate as long as the indentation depth is less than 50% of the film thickness; ii) as soon as the hardness exceeds that of the substrate, the substrate effect becomes significant, even for indentations as shallow as 5% of the film thickness; iii) if the film is at least 40 times harder than the substrate, the plastic zone is mostly confined to the substrate while the film conforms to the deformed substrate by bending. We define a substrate effect factor and construct a map that may be useful in the interpretation of indentation measurements on thin films. It is found that the yield stress mismatch is a key factor characterizing the hardness of thin film system, and the elastic mismatch is important when making stiffness measurements. The results obtained in this study are very useful when it is difficult to avoid the influence of the substrate on the measurements.

Johnson's cavity model relating indenter geometry and deformation resulting from elastic-plastic indentations is appropriate for a wide variety of materials. In the case of nanoindentations in single crystal BCC metals, limitations are reached when creep is not fully accounted for. Both the standard Berkovich and cube corner geometries show that the ratio of plastic zone radius to contact radius increases with the duration of time at the peak load. Indenter tip geometry is shown to play an important role in this phenomenon. Length scale phenomena, such as the indentation size effect, are also subject to various interpretations. The traditional definition of hardness does not produce similar trends with indentation length scale between the blunt Berkovich geometry and the sharper cube corner tip. However, the ratio of plastic zone radius to contact radius proves to be a tip geometry independent method of assessing the plasticity of these metals.