Unlike a two-dimensional (2D) electron system at the interface in a heterostructure, the 2D electrons in graphene are open to environment. As a result, many studies have been carried out in examining how adsorption of metal adatoms on graphene sheet can modify its electronic properties. For example, a tunable superconducting phase transition was recently observed in a tin decorated graphene sheet. There, the non-percolating tin clusters dope the graphene sheet and induce long-range superconducting correlations. More excitingly, it was predicted that lithium decorated graphene can display a much higher superconducting transition temperature than in the superconductivity in bulk graphite intercalated by lithium atoms. Three-dimensional (3D) graphene structures, a flexible and conductive interconnected graphene network, have generated a great deal of interests in recent years. Compared to a 2D graphene sheet, surface area in a 3D graphene structure is greatly enhanced. Furthermore, 3D graphene maintains the outstanding electrical, thermal, and mechanical properties as in 2D graphene. Therefore, 3D graphene structures are expected to play an important role in flexible electronics, sensors and energy storage applications (e.g., supercapacitors, battery electrodes, and hydrogen storage).

In this talk, I will present our recent electronic transport results on superconducting properties in tantalum decorated 3D graphene and carbon structures, following pioneering work of decorating 2D graphene sheets with superconducting materials. A superconducting transition is observed in both composite thin films. The magnetoresistance at various temperatures and differential resistance dV/dI at different magnetic fields were also carried out. Moreover, an anomalously large cooling effect was observed in the differential resistance measurements in our 3D graphene - tantalum composite when the device turned superconducting.  This surprisingly large cooling effect plus the nature of flexible 3DG thin film may find promising applications in solid-state cooling.