PRODUCTION AND APPLICATIONS OF GRAPHENE AND ITS COMPOSITES

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PRODUCTION AND APPLICATIONS OF GRAPHENE AND ITS COMPOSITES ( production-and-applications-graphene-and-its-composites )

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Chapter 7 – Application of Graphene composites: Raman Strain Sensors lower than exfoliated and in-house produced graphene, respectively. This corresponds to the intrinsic defects (D band) of CVD graphene, reduced stress transfer due to grain boundaries142, 277 and/or incomplete transfer of applied stress to the CVD graphene due to poor interface formed during transfer process. Moreover, the presence of smaller wrinkles281 or boundaries in the transferred film could be a plausible reason for the observed reduced stress transfer. These above reasons indicate that the quality of CVD graphene plays a crucial role in optical based wide-area senor applications where the uniformity of graphene over a large area is required. Presence of few-layer regions and intrinsic defects in the region of interest would result in estimating different strain rather than the actual strain. 7.3.3. Sensing ability of the coatings The resolution and accuracy are the main two parameters that define the sensitivity of any strain sensor. The resolution is the smallest difference in relative strain that can be measured and is typically quoted in microstrain (ΞΌπœ€). The accuracy is the repeatability in measure of an absolute strain from sample to sample and is typically quoted in percentage strain (1 % ο‚Ί 104 ΞΌπœ€). Commercially-available single-point strain sensors have very high resolutions up to 0.1 ΞΌπœ€, whereas large area photo-elasticity based strain sensors have relative resolutions ranging from 10 – 20 ΞΌπœ€ and an absolute accuracy about 0.1 % strain.328, 330 The accuracy of measuring the strain in the graphene coatings could be determined from the cyclic deformational sequences. Absolute accuracy is given by the standard deviation of the difference of the 2D band position at one particular strain level divided by the ideal graphene shift rate of ~ -62 cm-1/% strain as determined by using the Gruneisen parameter. The maximum achievable resolution (absolute resolution) of these graphene-based Raman strain sensors could be calculated from the Equation 7.2. π΄π‘π‘ π‘œπ‘™π‘’π‘‘π‘’ π‘Ÿπ‘’π‘ π‘œπ‘™π‘’π‘‘π‘–π‘œπ‘› (ΞΌπœ€) = π΄π‘π‘ π‘œπ‘™π‘’π‘‘π‘’ π‘Ÿπ‘’π‘ π‘œπ‘™π‘’π‘‘π‘–π‘œπ‘› π‘œπ‘“ π‘…π‘Žπ‘šπ‘Žπ‘› π‘ π‘π‘’π‘π‘‘π‘Ÿπ‘œπ‘šπ‘’π‘‘π‘’π‘Ÿ (π‘π‘šβˆ’1) Γ— 10000 π‘€π‘Žπ‘₯π‘–π‘šπ‘’π‘š π‘π‘Žπ‘›π‘‘ 𝑠h𝑖𝑓𝑑 π‘œπ‘π‘‘π‘Žπ‘–π‘›π‘’π‘‘(π‘π‘šβˆ’1/% π‘ π‘‘π‘Ÿπ‘Žπ‘–π‘› ) Equation 7.2 Example calculations for both absolute accuracy and resolution are given in the following sections. The strain sensing ability of these graphene-based Raman strain 228

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