Don Mark Lipkin

SAMPLE-PROBE INTERACTIONS IN SPECTROSCOPY : SAMPLING MICROSCOPIC PROPERTY GRADIENTS

An analytical model is presented to describe the influence of sample‐probe interactions on the shape of spectroscopic lines. By considering the discrete sampling of spatial property variations using a focused probe, the model predicts gradient‐induced line broadening, as well as probe channeling near free surfaces. The magnitude of sample‐probe interactions is governed by two system parameters: the probe size and the spatial property gradient. Furthermore, certain spatial heterogeneities are found to contribute appreciably to the signal and its associated line shape over distances several times the probe size. Experimental observations in fluorescence spectroscopy are used to evaluate the line‐shape model. Spectra measured along an embedded ruby fiber under a residual stress gradient are in good agreement with those calculated using the model.

Effect of interfacial carbon on adhesion and toughness of gold-sapphire interfaces

Abstract The effect of carbon on the interfacial fracture of gold–sapphire bonds is quantified by partitioning the measured fracture energy into the works of adhesion and plastic dissipation. The variation in each quantity with interfacial carbon is independently measured. The strong correlation between interfacial adhesion and plastic dissipation suggests synergistic coupling between crack-tip bond rupture and the surrounding plastic deformation in the metal. Possible origins of the observed sensitivity of adhesion to carbon heat treatment are discussed.

Estimating the metal-ceramic van der Waals adhesion energy

Abstract We invoke the Lifshitz theory of van der Waals forces to derive a simple, analytical expression for the adhesion across a planar metal-ceramic interface. The van der Waals energy is conveniently expressed as a function of readily accessible bulk properties of the respective materials. Application to several non-reactive metal-sapphire systems shows the predicted van der Waals energy to provide a good lower-bound estimate of the measured adhesion energy. Apart from platinum and palladium, where strong metal-aluminium interactions have been predicted, adhesion energies in noble-metal systems are well accounted for by van der Waals interactions alone. Not surprisingly, adhesion in the more chemically active metals exceeds the van der Waals energy.

Mechanical strengthening, stiffening, and oxidation behavior of pentatwinned Cu nanowires at near ambient temperatures

The complex effects of near ambient temperature exposure, i.e. 20?150 ?C, on the oxidation and the mechanical properties of thermal solution grown faceted Cu nanowires were investigated. The mechanical behavior was quantified with experiments on individual Cu nanowires using a MEMS-based method for nanoscale mechanical property studies. The elastic modulus of pristine Cu nanowires with diameters 300?550 nm was 117???1.2 GPa which agreed very well with polycrystalline bulk Cu, while the ultimate tensile strength was more than three times higher than bulk Cu, averaging 683???55 MPa. Annealing at just 50 ?C resulted in marked strengthening by almost 100% while the elastic modulus remained unchanged. Heat treatment in ambient air distinguished three different regimes of oxidation, namely the (a) formation of a thin passivation oxide at temperatures up to 50 ?C, (b) formation of thermal oxide obeying an Arrhenius type process for Cu+ migration at temperatures higher than 70 ?C, which was accelerated by grain boundary diffusion resulting in activation energies of 0.17?0.23 eV, and (c) complete oxidation following the Kirkendall effect at temperatures higher than 150 ?C and for prolonged exposure times, which did not obey an Arrhenius law. Notably, the formation of a weaker and more compliant thermal Cu2O did not compromise the effective strength and elastic modulus of oxidized Cu nanowires: experiments in Ar at temperatures higher than 70 ?C showed mechanical strengthening by ?50% and ultimate stiffening to ?190 GPa, which is near the upper limit for the elastic modulus of single crystal Cu in the direction.