Ultrahigh Electrical Conductivity of Graphene Embedded in Metals

Abstract

Highly efficient conductors are strongly desired because they can lead to higher working performance and less energy consumption in their wide range applications. However, the improvements on the electrical conductivities of conventional conductors are limited, such as purification and growing single crystal of metals. Here, by embedding graphene in metals (Cu, Al, and Ag), the trade-off between carrier mobility and carrier density is surmount in graphene, and realize high electron mobility and high electron density simultaneously through elaborate interface design and morphology control. As a result, a maximum electrical conductivity three orders of magnitude higher than the highest on record (more than 3,000 times higher than that of Cu) is obtained in such embedded graphene. As a result, using the graphene as reinforcement, an electrical conductivity as high as ≈117% of the International Annealed Copper Standard and significantly higher than that of Ag is achieved in bulk graphene/Cu composites with an extremely low graphene volume fraction of only 0.008%. The results are of significance when enhancing efficiency and saving energy in electrical and electronic applications of metals, and also of interest for fundamental researches on electron behaviors in graphene.

The Influence of Interface Structure on the Electrical Conductivity of Graphene Embedded in Aluminum Matrix

“…As previously confirmed, graphene/metal interface bonding would be promoted by hot pressing, and ultrahigh conductivity in graphene would be promoted by doping electrons from the surrounding metal atoms . Compared to the maximum peak current of 265.4 pA in the Cu/Gr/Cu interface and 329.2 pA in the Ag/Gr/Ag interface ( Table 1 ), the conductivity of graphene in Al/Gr/Al (maximum peak current 29.3 pA) is almost one order of magnitude weaker, and the average peak (5.58 pA) in the Al/Gr/Al interface is ≈15 times lower than that of graphene embedded in the Cu matrix (85.8 pA) . The number of electrons (per unit cell) transferred from metal to graphene is given by N = D 0 (Δ E F ) 2 /2 (The density of states of graphene is described as D ( E ) = D 0 | E |, D 0 = 0.09 per (eV 2 unit cell) for E within 1 eV of the conical points, Δ E F = W M − W G is the Fermi level shift in graphene), and the above results basically agree with the degree of the doping effect.…”

“…The W M of Al, Cu, and Ag is higher than that of graphene, resulting in n‐type doping of graphene . As previously confirmed, graphene/metal interface bonding would be promoted by hot pressing, and ultrahigh conductivity in graphene would be promoted by doping electrons from the surrounding metal atoms . Compared to the maximum peak current of 265.4 pA in the Cu/Gr/Cu interface and 329.2 pA in the Ag/Gr/Ag interface ( Table 1 ), the conductivity of graphene in Al/Gr/Al (maximum peak current 29.3 pA) is almost one order of magnitude weaker, and the average peak (5.58 pA) in the Al/Gr/Al interface is ≈15 times lower than that of graphene embedded in the Cu matrix (85.8 pA) .…”

“…As shown in the CP‐AFM result of Cu/Gr/Cu, periodic and altitudinal fluctuations of the current signal exist along the interface and can be explained by two facts: 1) the laminated composite contained two face‐to‐face stacked graphene/metal heterogeneous films and the graphene is one or two layers thick, as verified by Raman mapping; thus, the layer number of graphene embedded in the composite varies from 1 to 4, which contributes to the intensity fluctuation in the current signal; 2) the coverage of graphene on the target substrate is not absolutely 100%, and the partial interface without graphene in the composite results in the periodic nature of the current peak. Comparing the distribution of the current peaks in Al/Gr/Al and Cu/Gr/Cu, the average distance of the two neighboring current peaks in Al/Gr/Al is significantly larger than that for Cu/Gr/Cu and does not match the microstructure of the graphene alignment along the interface. Due to the shielding interference of the doping effect from the amorphous alumina impurity at the graphene/aluminum interface, the periodic interval distance caused by the in‐plane spacing of graphene crystals is much less than the distance of neighboring current peaks in Al/Gr/Al.…”

“…In the Cu(111)/Gr bilayer/Cu(111) model, the primitive cell obtains ≈0.24 doped electrons, several times higher than that in the graphene/Al system, but its electrical conductivity measured by CP‐AFM is ≈40 times higher that of graphene embedded in Al/Gr/Al. This incompatible phenomenon may be explained by the existence of amorphous alumina on the surface of pristine Al, which inhibits the transfer of doped electrons, intensifies the scattering of charge carriers on phonons, and reduces the mobility of graphene.…”

“…As a result, an enhancement of 8% in the relative conductivity was measured in the 1.0 wt% high‐quality graphene/copper matrix composites, but no absolute value of the electrical conductivity of this composite was reported. Recently, we have demonstrated that three orders of magnitude enhancement of the electrical conductivity of graphene was realized by stacking and hot‐pressing chemical vapor deposition (CVD) graphene/copper foils . As a result, the electrical conductivity of the composite is as high as ≈117% IACS (international annealed copper standard) with an extremely low graphene content of only 0.008 vol%.…”