The Interfacial Phenomena Between Graphene on Cu Substrate Covered by Ni, Cu, or W Layer, with Liquid Ga-Sn-Zn Alloy

To obtain better parameters of wetting and interfacial properties, the Cu substrate was covered by graphene. The first experiment showed that the liquid metal mechanically destroys the graphene layer. Therefore, the Ni, Cu, or W layer was sputtered to secure the graphene. The obtained graphene was examined by micro-Raman spectrometry. The thickness of the Cu, Ni, or W layer was ~ 25 nm, compared to previous work, where the thickness of the Ni-W electrochemically deposited layer varied from 8-10 μm. To observe changes at the interface, the experiments were performed with Ga-Sn-Zn eutectic alloy using the sessile drop method at temperatures of 100, 150, and 250 °C long-time contact of 1, 10, or 30 days. Atomic force microscopy was used to show the topology of obtained samples. The microstructure observation of the cross-sectioned samples was made by scanning electron microscopy combined with energy dispersive x-ray spectroscopy. The x-ray diffraction was conducted to identify occurring phases at the interface from the Cu-Ga system. The investigation showed that such a very thin Ni, Cu, or W layer is not sufficient to protect the Cu substrate from a reaction with liquid metals such as eutectic Ga-Sn-Zn, which can be used in cooling systems. The performed XRD analysis and microstructure observations show the occurring CuGa phase at the interface and dissolution of the Cu substrate in molten alloy with increasing temperature and time. The interfacial CuGa phase grows very slowly at annealing temperatures below 150 °C for the graphene/Ni and graphene/W coatings. Therefore, these coatings can be used to protect a copper substrate in cooling electronic devices.