Highly transparent light emitting diodes on graphene encapsulated Cu nanowires network.

The internal quantum efficiency of blue LEDs is almost close to the limit, therefore, advanced transparent electrode has been long explored for gaining high external quantum efficiency. However, work function mismatch at electrode-semiconductor interface remains the fundamental difficulty in obtaining low resistance ohmic contact. Here, we demonstrate the gas phase encapsulation of graphene layer on superfine Cu nanowires network by chemical vapor deposition for highly transparent LEDs. The fast encapsulation of graphene shell layer on Cu nanowires achieves high optoelectronic performance (33 Ω/sq @ 95% T), broad transparency range (200~3000 nm) and strong antioxidant stability. A novel phenomenon of scattered-point contact is revealed at the Cu nanowires/GaN interface. Point discharge effect is found to produce locally high injection current through contact points, which can effectively overcome Schottky barrier and form ohmic contact. The transparent LED on Cu@graphene nanowire network is successfully lighted with bright blue emission.

Large-roll growth of 25-inch hexagonal BN monolayer film for self-release buffer layer of free-standing GaN wafer.

Hexagonal boron nitride (h-BN) is known as promising 2D material with a wide band-gap (~6 eV). However, the growth size of h-BN film is strongly limited by the size of reaction chamber. Here, we demonstrate the large-roll synthesis of monolayer and controllable sub-monolayer h-BN film on wound Cu foil by low pressure chemical vapor deposition (LPCVD) method. By winding the Cu foil substrate into mainspring shape supported by a multi-prong quartz fork, the reactor size limit could be overcome by extending the substrate area to a continuous 2D curl of plane inward. An extremely large-size monolayer h-BN film has been achieved over 25 inches in a 1.2" tube. The optical band gap of h-BN monolayer was determined to be 6.0 eV. The h-BN film was uniformly transferred onto 2" GaN or 4" Si wafer surfaces as a release buffer layer. By HVPE method, overgrowth of thick GaN wafer over 200 µm has been achieved free of residual strain, which could provide high quality homo-epitaxial substrate.

One-Pot Synthesis of Superfine Core-Shell Cu@metal Nanowires for Highly Tenacious Transparent LED Dimmer.

We demonstrate a one-pot, low-cost, and scalable method for fast synthesis of superfine and uniform core-shell Cu nanowires (NWs) coated with optional metals and/or alloy. Cu NWs in high aspect ratio (>3000) were synthesized through an oleylamine-mediated solution method, and tunable shell coating was performed by injecting metal-organic precursors at the last stage of reaction. Superfine Cu@metal NWs (Ti, Zn, V, Ni, Ag, NiZn, etc) were achieved in diameter of ∼30 nm and length of ∼50 µm. Transparent conductive films were obtained by imprinting method, showing high optoelectronic performance (51 Ω/sq at 93% transmittance), high mechanical tenacity over bending, twisting, stretching, and compressing, and robust antioxidant ability (high temperature and high humidity). A transparent film dimmer for light-emitting diode (LED) lighting was fabricated with the stretchable Cu@Ti NWs network. The LED luminance could be accurately tuned by the deformation strain of Cu@Ti NWs film.