1322 wileyonlinelibrary.com applications in fi elds of healthcare monitoring, human-computer interaction, and electronic skin. [ 12 ] The relative resistance Δ R normalized by the initial resistance R 0 depends on Poisson's ratio ( ν ) and resistivity variation (Δ ρ ) normalized by its initial resistivity ρ 0 through the expression ΔR / R 0 = (1 + 2ν) ε + Δ ρ / ρ 0.[ 13 ] The sensitivity revealed by gauge factor (GF, defi ned as ( ΔR / R 0 )/ ε ) depends on both intrinsic property and structural feature. According to this formula, graphene-based strain sensors have shown low sensitivities due to the rigid and stable structure of intrinsic graphene. [ 14 ] With hardly opened band gap, the GF of a suspended graphene is only about 1.9 under moderate uniaxial strains. [ 15 ] Therefore, structural engineering of graphene is needed to boost the sensitivity of graphene-based strain sensors.Adjustment of the connection channels in graphene is an effective way to alter its resistivity for improved sensitivity in strain sensors. Two common methods for the structural construction of graphene include high temperature processing based chemical vapor deposition (CVD) and solution processing based sheets/fl akes assembly. As for CVD, the resistivity of graphene would be affected by its grain boundary, grain size, and the defect density. [16][17][18] Continuous graphene fi lms grown by CVD could sustain 1% strain with a GF of only 6.1, [ 19 ] and the GF increases to 151 for a 5% strain due to the morphological Large-Area Ultrathin Graphene Films by Single-Step Marangoni Self-Assembly for Highly Sensitive Strain Sensing ApplicationXinming Li , Tingting Yang , Yao Yang , Jia Zhu , Li Li , Fakhr E. Alam , Xiao Li , Kunlin Wang , Huanyu Cheng , Cheng-Te Lin , * Ying Fang , * and Hongwei Zhu * Promoted by the demand for wearable devices, graphene has been proved to be a promising material for potential applications in fl exible and highly sensitive strain sensors. However, low sensitivity and complex processing of graphene retard the development toward the practical applications. Here, an environment-friendly and cost-effective method to fabricate large-area ultrathin graphene fi lms is proposed for highly sensitive fl exible strain sensor. The assembled graphene fi lms are derived rapidly at the liquid/air interface by Marangoni effect and the area can be scaled up. These graphene-based strain sensors exhibit extremely high sensitivity with gauge factor of 1037 at 2% strain, which represents the highest value for graphene platelets at this small deformation so far. This simple fabrication for strain sensors with highly sensitive performance of strain sensor makes it a novel approach to applications in electronic skin, wearable sensors, and health monitoring platforms.

With the increasing integration of devices in electronics fabrication, there are growing demands for thermal interface materials (TIMs) with high through-plane thermal conductivity for efficiently solving thermal management issues. Graphene-based papers consisting of a layer-by-layer stacked architecture have been commercially used as lateral heat spreaders; however, they lack in-depth studies on their TIM applications due to the low through-plane thermal conductivity (<6 W m–1 K–1). In this study, a graphene hybrid paper (GHP) was fabricated by the intercalation of silicon source and the in situ growth of SiC nanorods between graphene sheets based on the carbothermal reduction reaction. Due to the formation of covalent C–Si bonding at the graphene–SiC interface, the GHP possesses a superior through-plane thermal conductivity of 10.9 W m–1 K–1 and can be up to 17.6 W m–1 K–1 under packaging conditions at 75 psi. Compared with the current graphene-based papers, our GHP has the highest through-plane thermal conductivity value. In the TIM performance test, the cooling efficiency of the GHP achieves significant improvement compared to that of state-of-the-art thermal pads. Our GHP with characteristic structure is of great promise as an inorganic TIM for the highly efficient removal of heat from electronic devices.

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