Methane as an effective hydrogen source for single-layer graphene synthesis on Cu foil by plasma enhanced chemical vapor deposition

A single-layer graphene is synthesized on Cu foil in the absence of H2 flow by plasma enhanced chemical vapor deposition (PECVD). In lieu of an explicit H2 flow, hydrogen species are produced during methane decomposition process into their active species (CHx<4), assisted by the plasma. Notably, the early stage of growth depends strongly on the plasma power. The resulting grain size (the nucleation density) has a maximum (minimum) at 50 W and saturates when the plasma power is higher than 120 W because hydrogen partial pressures are effectively tuned by a simple control of the plasma power. Raman spectroscopy and transport measurements show that decomposed methane alone can provide sufficient amount of hydrogen species for high-quality graphene synthesis by PECVD.Comment: 22 pages, 6 figure

Enhanced Thermal Conductivity of the Underfill Materials Using Insulated Core/shell Filler Particles for High Performance Flip Chip Applications

In this study, we investigated the correlation between thermal conductivity and insulative shell thickness of SiO2 coated Ag (SCA) particles for the thermal filler material in the high performance underfill with focus on improved thermal conductivity. We synthesized the coating of various SiO2 insulation layer on the surface of spherical Ag powder and used them for underfill material formulation to achieve &gt;2 W/mK grade high thermal conductivity capillary underfill. In order to achieve powder distribution with gaussian curve additional spherical alumina was mixed with SCA powder. This mixture blended with epoxy based multifunctional resin matrix. Trend profiling of thermal conductivity and electrical resistivity as a function of SiO2 shell thickness were performed. In addition, correlation of thermal conductivity and viscosity were investigated. Resulting capillary underfill with SCA powders showed 2.14 W/mK thermal conductivity and passed thermal cycling test corresponding to JEDEC LEVEL 3. © 2017 IEEE.N

Enhancements on Underfill Materials&apos; Thermal Conductivity by Insulation Coating Layer Control of Conductive Particles

In this study, an alumina coated silver core/shell structure particles were prepared through a sol-gel approach. Various techniques were used to characterize the as-prepared products, including field emission scanning electron microscopy (FE-SEM), field emission transition electron microscopy(FE-TEM), energy-dispersive X-ray spectroscopy (EDS) and thermal transient method. FE-SEM images showed a morphology of alumina coated Ag(ACA) particle and FE-TEM images showed a cross- section of synthesized alumina shell. EDS mapping confirmed that the synthesized shell was composed of Al and O. The thickness of the alumina shell satisfying high insulation resistivity and thermal conductivity was 23.5 nm. The electrical resistance and thermal conductivity of underfill using this alumina coated Ag (ACA) particle was 1.6E12 Omega-cm and 1.9 Wm(-1)K(-1). When alumina coated Ag (ACA) particle and alumina were mixed to increase the thermal conductivity, it could be possible to achieve 2.34 Wm(-1)K(-1).N

Direct Integration of Polycrystalline Graphene into Light Emitting Diodes by Plasma-Assisted Metal-Catalyst-Free Synthesis

The integration of graphene into devices is a challenging task because the preparation of a graphene-based device usually includes graphene growth on a metal surface at elevated temperatures (∼1000 °C) and a complicated postgrowth transfer process of graphene from the metal catalyst. Here we report a direct integration approach for incorporating polycrystalline graphene into light emitting diodes (LEDs) at low temperature by plasma-assisted metal-catalyst-free synthesis. Thermal degradation of the active layer in LEDs is negligible at our growth temperature, and LEDs could be fabricated without a transfer process. Moreover, <i>in situ</i> ohmic contact formation is observed between DG and p-GaN resulting from carbon diffusion into the p-GaN surface during the growth process. As a result, the contact resistance is reduced and the electrical properties of directly integrated LEDs outperform those of LEDs with transferred graphene electrodes. This relatively simple method of graphene integration will be easily adoptable in the industrialization of graphene-based devices

One-step graphene coating of heteroepitaxial GaN films

Today, state-of-the-art III-Ns technology has been focused on the growth of c-plane nitrides by metal-organic chemical vapor deposition (MOCVD) using a conventional two-step growth process. Here we show that the use of graphene as a coating layer allows the one-step growth of heteroepitaxial GaN films on sapphire in a MOCVD reactor, simplifying the GaN growth process. It is found that the graphene coating improves the wetting between GaN and sapphire, and, with as little as similar to 0.6 nm of graphene coating, the overgrown GaN layer on sapphire becomes continuous and flat. With increasing thickness of the graphene coating, the structural and optical properties of one-step grown GaN films gradually transition towards those of GaN films grown by a conventional two-step growth method. The InGaN/GaN multiple quantum well structure grown on a GaN/graphene/sapphire heterosystem shows a high internal quantum efficiency, allowing the use of one-step grown GaN films as &apos;pseudo-substrates&apos; in optoelectronic devices. The introduction of graphene as a coating layer provides an atomic playground for metal adatoms and simplifies the III-Ns growth process, making it potentially very useful as a means to grow other heteroepitaxial films on arbitrary substrates with lattice and thermal mismatch.close55