Researchers measured the thermal expansion coefficient (TEC) of single-layer graphene (SLG) using Raman spectroscopy between 200 and 400 K. The TEC was found to be negative throughout the temperature range, with a room temperature value of (-8.0 ± 0.7) × 10⁻⁶ K⁻¹. This negative TEC is crucial for understanding the physical properties of graphene, as strain caused by TEC mismatch between graphene and the substrate significantly affects its behavior. Previous studies showed conflicting results, with some indicating a negative-to-positive transition in TEC at around 350 K. However, this study found that the TEC remains negative across the entire temperature range, suggesting that the previous discrepancies may be due to experimental or theoretical limitations. The results highlight the importance of accounting for strain effects when interpreting experimental data, especially at cryogenic or elevated temperatures. The study used Raman spectroscopy to analyze the temperature-dependent shift of the Raman G band, subtracting the strain effect to determine the TEC. The findings provide a more accurate estimation of the TEC of graphene, which is essential for designing graphene-based devices and heat management systems. The results also emphasize the need for careful consideration of TEC matching between graphene and the substrate to accurately determine intrinsic physical properties of graphene over a wide temperature range.Researchers measured the thermal expansion coefficient (TEC) of single-layer graphene (SLG) using Raman spectroscopy between 200 and 400 K. The TEC was found to be negative throughout the temperature range, with a room temperature value of (-8.0 ± 0.7) × 10⁻⁶ K⁻¹. This negative TEC is crucial for understanding the physical properties of graphene, as strain caused by TEC mismatch between graphene and the substrate significantly affects its behavior. Previous studies showed conflicting results, with some indicating a negative-to-positive transition in TEC at around 350 K. However, this study found that the TEC remains negative across the entire temperature range, suggesting that the previous discrepancies may be due to experimental or theoretical limitations. The results highlight the importance of accounting for strain effects when interpreting experimental data, especially at cryogenic or elevated temperatures. The study used Raman spectroscopy to analyze the temperature-dependent shift of the Raman G band, subtracting the strain effect to determine the TEC. The findings provide a more accurate estimation of the TEC of graphene, which is essential for designing graphene-based devices and heat management systems. The results also emphasize the need for careful consideration of TEC matching between graphene and the substrate to accurately determine intrinsic physical properties of graphene over a wide temperature range.