Na Lin

Copper Nanowires as Fully Transparent Conductive Electrodes

In pondering of new promising transparent conductors to replace the cost rising tin-doped indium oxide (ITO), metal nanowires have been widely concerned. Herein, we demonstrate an approach for successful synthesis of long and fine Cu nanowires (NWs) through a novel catalytic scheme involving nickel ions. Such Cu NWs in high aspect ratio (diameter of 16.2 ± 2u2005nm and length up to 40u2005μm) provide long distance for electron transport and, meanwhile, large space for light transmission. Transparent electrodes fabricated using the Cu NW ink achieve a low sheet resistance of 1.4u2005Ohm/sq at 14% transmittance and a high transparency of 93.1% at 51.5u2005Ohm/sq. The flexibility and stability were tested with 100-timebending by 180°and no resistance change occurred. Ohmic contact was achieved to the p- and n-GaN on blue light emitting diode chip and bright electroluminescence from the front face confirmed the excellent transparency.

In situ self-release of thick GaN wafer from sapphire substrate via graded strain field engineering

We present a scheme for in situ self-release of thick GaN 2-in. wafer from sapphire substrate by engineering the gradient of misfit strains. Release energies of a-, m-, and c-planes of wurtzite GaN are systematically calculated under different biaxial strains by using first-principles method. The results reveal that the c-plane separation will take place under graded strains around −2.8%, where a drastic transition interface of release energy may strongly reduce the strength of c-plane bonding. Based on this mechanism, uniform thick GaN epilayer (>450u2009μm) is grown on (0001) sapphire substrate by hydride vapor phase epitaxy and subjected to a graded compressive strain field by bowing, fulfilling the c-plane separation condition. As a result, high quality free-standing GaN wafer (350u2009μm) can be achieved by self-release simply during the cooling process.

Modified pulse growth and misfit strain release of an AlN heteroepilayer with a Mg–Si codoping pair by MOCVD

We report the modified pulse growth method together with an alternating introduction of larger-radius impurity (Mg) for the quality improvement and misfit strain release of an AlN epitaxial layer by the metal–organic chemical vapour deposition (MOCVD) method. Various pulse growth methods were employed to control the migration of Al atoms on the substrate surface. The results showed that the pulse time and overlapping of V/III flux is closely related with the enhancement of the 2D and 3D growth mode. In order to reduce the misfit strain between AlN and sapphire, an impurity of larger atomic radius (e.g. Mg) was doped into the AlN lattice to minimize the rigidity of the AlN epilayer. It was found that the codoping of Mg–Si ultrathin layers could significantly minimize the residual strain as well as the density of threading dislocations.

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.

Extraordinary N atom tunneling in formation of InN shell layer on GaN nanorod m-plane sidewall.

We report the extraordinary tunneling process that finds the lower cohesive energy route for stablizing InN shell layer on m-plane sidewall of GaN nanorod. The [0001] orientated GaN nanorod array is grown on sapphire substrate patterned with Ga nanoparticle by metal-organic vapor deposition method, based on which the simulation structures of c-plane top surface and m-plane sidewall surface is constructed for the first-principles calculations. The results show that the introduction of In wetting monolayer could effectively lower the cohesive energy of adalayers on non-polar GaN surfaces. Most importantly, it is revealed that there exists an extraordinary tunneling process in which the N atoms will drag out the In wetting atoms and tunnel through to form stable InN shell layer on the nanorod sidewall.

Ideal square quantum wells achieved in AlGaN/GaN superlattices using ultrathin blocking-compensation pair

A technique for achieving square-shape quantum wells (QWs) against the intrinsic polar discontinuity and interfacial diffusion through self-compensated pair interlayers is reported. Ultrathin low-and-high % pair interlayers that have diffusion-blocking and self-compensation capacities is proposed to resist the elemental diffusion at nanointerfaces and to grow the theoretically described abrupt rectangular AlGaN/GaN superlattices by metal-organic chemical vapor deposition. Light emission efficiency in such nanostructures is effectively enhanced and the quantum-confined Stark effect could be partially suppressed. This concept could effectively improve the quality of ultrathin QWs in functional nanostructures with other semiconductors or through other growth methods.