| Abstract | Substrate expansion/shrinkage makes it difficult to measure accurately the thermal expansion coefficient (TEC) of thin films. Furthermore, even very thin contamination layers can affect TEC measurements. We excluded the effects of contamination, quantified the effect of substrate, and succeeded in measuring the TEC of suspended single-layer graphene (SLG) at temperatures ranging from room temperature to 900 °C. The SLG was supported by Quantifoil, an amorphous-carbon film with prefabricated holes. The TEC was measured at both the suspended and supported areas of the SLG using electron diffraction in a transmission electron microscope. It was found that the TEC of suspended SLG is positive, and the values are related to a lattice spacing of SLG, which may indicate a tensile/compressive stress of the suspended SLG. The TEC values of suspended SLG ranged from 1.2×10⁻⁶ to 2.4×10⁻⁵ K⁻¹, and were inversely proportional to the measured values of SLG lattice spacing, which ranged from 0.2088 to 0.2110 nm at 400 °C. The TEC values of the supported area were smaller than those of the suspended area, indicating that the support film suppressed SLG expansion. This report also shows how the support film and contamination affect graphene TEC using three different samples, including double-layer graphene. |
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