Graphene-induced unusual microstructural evolution in Ag plated Cu foils.

Graphene-induced abnormal grain growth of Cu with a grain size of more than 1 mm(2) was observed on Cu-Ag alloy foil, and this phenomenon occurred only with graphene synthesis and only on the Cu-Ag alloy among various types of Cu foils.

Highly reliable ag nanowire flexible transparent electrode with mechanically welded junctions.

Deformation behavior of the Ag nanowire flexible transparent electrode under bending strain is studied and results in a novel approach for highly reliable Ag nanowire network with mechanically welded junctions. Bending fatigue tests up to 500,000 cycles are used to evaluate the in situ resistance change while imposing fixed, uniform bending strain. In the initial stages of bending cycles, the thermally annealed Ag nanowire networks show a reduction in fractional resistance followed by a transient and steady-state increase at later stages of cycling. SEM analysis reveals that the initial reduction in resistance is caused by mechanical welding as a result of applied bending strain, and the increase in resistance at later stages of cycling is determined to be due to the failure at the thermally locked-in junctions. Based on the observations from this study, a new methodology for highly reliable Ag nanowire network is proposed: formation of Ag nanowire networks with no prior thermal annealing but localized junction formation through simple application of mechanical bending strain. The non-annealed, mechanically welded Ag nanowire network shows significantly enhanced cyclic reliability with essentially 0% increase in resistance due to effective formation of localized wire-to-wire contact.

Highly uniform growth of monolayer graphene by chemical vapor deposition on Cu-Ag alloy catalysts.

One of the major challenges for the practical application of graphene is the large scale synthesis of uniform films with high quality at lower temperature. Here, we demonstrate the use of Ag-plated Cu substrates in the synthesis of high-quality graphene films via chemical vapor deposition (CVD) of methane gas at temperatures as low as 900 °C. Various experimental analyses show that the plated Ag diffuses into Cu to form a uniform Cu-Ag alloy that suppresses the formation of multilayer nucleation and decreases the activation energy of precursor formation, leading to a lower synthesis temperature with enhanced monolayer coverage. In addition, we also observed an unusual Ag-assisted abnormal grain growth of Cu into the cube texture with larger grain sizes and reduced grain boundaries, which is believed to provide the homogeneous environment needed for uniform graphene growth.

Fast synthesis of high-performance graphene films by hydrogen-free rapid thermal chemical vapor deposition.

The practical use of graphene in consumer electronics has not been demonstrated since the size, uniformity, and reliability problems are yet to be solved to satisfy industrial standards. Here we report mass-produced graphene films synthesized by hydrogen-free rapid thermal chemical vapor deposition (RT-CVD), roll-to-roll etching, and transfer methods, which enabled faster and larger production of homogeneous graphene films over 400 × 300 mm(2) area with a sheet resistance of 249 ± 17 Ω/sq without additional doping. The properties of RT-CVD graphene have been carefully characterized by high-resolution transmission electron microscopy, Raman spectroscopy, chemical grain boundary analysis, and various electrical device measurements, showing excellent uniformity and stability. In particular, we found no significant correlation between graphene domain sizes and electrical conductivity, unlike previous theoretical expectations for nanoscale graphene domains. Finally, the actual application of the RT-CVD films to capacitive multitouch devices installed in the most sophisticated mobile phone was demonstrated.

Fatigue-free, electrically reliable copper electrode with nanohole array.

Design and fabrication of reliable electrodes is one of the most important challenges in flexible devices, which undergo repeated deformation. In conventional approaches, mechanical and electrical properties of continuous metal films degrade gradually because of the fatigue damage. The designed incorporation of nanoholes into Cu electrodes can enhance the reliability. In this study, the electrode shows extremely low electrical resistance change during bending fatigue because the nanoholes suppress crack initiation by preventing protrusion formation and damage propagation by crack tip blunting. This concept provides a key guideline for developing fatigue-free flexible electrodes.