WANG Zixi^1，2，WU Limei¹ ，LI Shuo² ，ZHANG Dingyun²

1. School of Materials Science and Engineering， Shenyang Jianzhu University， Shenyang110168， China；

2. Technology Innovation Center of Graphene Metrology and Standardization， State Administration for Market Regulation，Center for Advanced Measurement Science， National Institute of Metrology， Beijing 100029， China

Abstract

Objective The laser flash method （LFA） is a non-contact， transient technique for measuring the thermal diffusivity of materials. It offers several advantages such as fast measurement， a wide applicable range， and the ability to test small samples. In recent years， with the rapid development of laser technology， temperature detection， and data processing， LFA has been increasingly applied to measure the in-plane thermal diffusivity of two-dimensional （2D） materials. However， for flexible graphene films with micrometer-scale thickness， challenges such as poor measurement repeatability and difficulties in comparing results still exist. To establish a reliable LFA for measuring the in-plane thermal diffusivity of graphene films， this study analyzes the main factors affecting the measurement results and achieves a stable and repeatable approach for obtaining accurate thermal diffusivity.

Methods Raman spectroscopy， X-ray diffraction （XRD）， transmission electron microscopy （TEM）， and atomic force microscopy （AFM） were used to characterize the graphene oxide powder， which was used as the raw material for preparing graphene films. The graphene films were further characterized using Raman spectroscopy， scanning electron microscopy （SEM）， AFM， and X-ray photoelectron spectroscopy （XPS）. The effects of drying state， graphite coating， surface flatness， and laser pulse conditions on thermal diffusivity of graphene films were investigated. In LFA，the sample surface was heated by a pulse laser，and an infrared detector was used to monitor the temperature response signals on the back or side of the sample over time. As a non-contact technique， it effectively eliminated thermal contact resistance and improved measurement accuracy. There were three commonly used measurement models for LFA：the vertical model， the in-plane model， and the laminate model. In this study， the in-plane model was used for measurements. Due to the high thermal diffusivity of graphene films and their highly reflective surfaces，accurate measurements remain challenging. Therefore， suitable experimental conditions and optimized pretreatment methods were developed to enhance the accuracy of the measurement results.

Results and discussion The results showed that the graphene oxide powder exhibited typical D and G peaks in its Raman spectrum. TEM images revealed that the graphene had minimal wrinkles but significant overlapping layers， with an average thickness of approximately 1.2 nm. The resulting graphene film exhibited a multi-layer structure with an intact carbon lattice， virtually no defects， and minimal impurities. The average thickness of the film was approximately 87 μm， and its surface roughness ranged from approximately 27 nm to 117 nm， indicating a relatively smooth surface. The carbon content of the film was approximately 97.45%， the main impurity was Si， and the degree of graphitization of the sample was high. The moisture content of the graphene film significantly affected its thermal conductivity. The optimized pulse parameters for the 80 μm-thick graphene film used in LFA were as follows： a pulse voltage of 240~260 V， a pulse width of 30~100 μs，and a signal intensity of 3~7 V.Meanwhile，the data fitting model required corrections for finite pulse time and heat loss. Compared with the traditional spraying method，the test curve fitting was significantly improved by spraying the graphite layer only in the laser irradiation and infrared detection areas.After loading onto a metal ring，the average standard deviation of repeated thermal diffusivity measurements was reduced by approximately 50%.

Conclusions This paper summarizes the measurement principle of LFA and its application to determining the thermal diffusivity of 2D materials. A stable and reliable method for measuring in-plane thermal diffusivity of 80 μm graphene films is established with the following key steps： 1） The film should be fully dried before testing； 2） Applying the graphite layer only in the laser irradiation and infrared detection areas ensures sufficient infrared emissivity and reduces the contact resistance between the graphite coating and the graphene film surface； 3） To ensure film surface flatness， the graphene films should be stably loaded onto a metal ring gasket； and 4） The optimized pulse parameters for LFA are a pulse voltage of 240~260 V， a pulse width of 30~100 μs， and a signal intensity of 3~7 V. In addition， the data fitting model requires finite pulse time and heat loss corrections. By applying the optimized in-plane thermal diffusivity measurement method， the 80 μm graphene films successfully passed the uniformity and stability tests， laying a foundation for the development of reference materials.

Keywords： laser flash method； thermal diffusivity； grapheme film； graphite coating； flatness； reference material

Get Citation:WANG Zixi， WU Limei， LI Shuo， et al. Influencing factors of thermal diffusivity of graphene films measured by laser flash method［J］. China Powder Science and Technology， 2026， 32（3）： 1-15.