Thomas Metcalf

Shear Modulus of Monolayer Graphene Prepared by Chemical Vapor Deposition

We report shear modulus (G) and internal friction (Q(-1)) measurements of large-area monolayer graphene films grown by chemical vapor deposition on copper foil and transferred onto high-Q silicon mechanical oscillators. The shear modulus, extracted from a resonance frequency shift at 0.4 K where the apparatus is most sensitive, averages 280 GPa. This is five times larger than those of the multilayered graphene-based films measured previously. The internal friction is unmeasurable within the sensitivity of our experiment and thus bounded above by Q(-1) ≤ 3 × 10(-5), which is orders-of-magnitude smaller than that of multilayered graphene-based films. Neither annealing nor interface modification has a measurable effect on G or Q(-1). Our results on G are consistent with recent theoretical evaluations and simulations carried out in this work, showing that the shear restoring force transitions from interlayer to intralayer interactions as the film thickness approaches one monolayer.

Thermoelastic damping in micromechanical resonators

We show that the dominant energy loss mechanism in plate modes of a 1.5 μm thick silicon micromechanical resonator is thermoelastic damping. In situ ultra-high vacuum annealing lowers the dissipation of two neighboring resonance modes (460 and 510 kHz) at 120 K to Q−1≤5×10−7. From 120 to 400 K, the Q−1 of these modes increase at different rates, in quantitative agreement with a modification (that accounts for mode shape) of Zener’s theory of thermoelastic damping.

Low temperature internal friction in nanocrystalline diamond films

Measurements of the temperature dependence of the internal friction and frequency of three nanocrystalline diamond films grown on silicon oscillator substrates indicate that the mechanical properties of the films are dominated by their interface layers. The films, with thicknesses of 0.3, 0.6, and 1.14μm, were measured between 0.4K and room temperature and have low temperature (below 10K) internal frictions between 2×10−6 and 5×10−6, which is an order of magnitude lower than has been reported previously. Additionally, all films display an internal friction peak at approximately 1.7K. The shear modulus of the films, 545–551GPa, is comparable to that for single-crystal diamond.

Two-level systems in evaporated amorphous silicon

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An Ultra-High Q Silicon Cantilever Resonator for Thin Film Internal Friction and Young's Modulus Measurements

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From amorphous to nanocrystalline: the effect of nanograins in amorphous matrix on the thermal conductivity of hot-wire chemical-vapor deposited silicon films

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Analysis of thickness and quality factor of a double paddle oscillator at room temperature

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Light-induced metastability in pure and hydrogenated amorphous silicon

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Improving the mechanical quality factor of ultra-low-loss silicon resonators

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Low temperature mechanical properties of nanocrystalline diamond films

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