Enhancement of nucleation of diamond films deposited on copper substrate by nickel modification layer

A Ni layer with a thickness of about 100 nm was sputtered on Cu substrates,followed by an ultrasonic seeding with nanodiamond suspension.High-quality diamond film with its crystalline grains close to thermal equilibrium shape was deposited on Cu substrates by hot-filament chemical vapor deposition（HF-CVD）,and the sp2 carbon content was less than 5.56%.The nucleation and growth of diamond film were investigated by micro-Raman spectroscopy,scanning electron microscopy,and X-ray diffraction.The results show that the nucleation density of diamond on the Ni-modified Cu substrates is 10 times higher than that on blank Cu substrates.The enhancement mechanism of the nucleation kinetics by Ni modification layer results from two effects：namely,the nanometer rough Ni-modified surface shows an improved absorption of nanodiamond particles that act as starting points for the diamond nucleation during HF-CVD process;the strong catalytic effect of the Ni-modified surface causes the formation of graphite layer that acts as an intermediate to facilitate diamond nucleation quickly.

Growth behavior of CVD diamond in microchannels of Cu template

Deposition of diamond inside the trenches or microchannels by chemical vapor deposition （CVD） is limited by the diffusion efficiency of important radical species for diamond growth （H, CH3） and the pore depth of the substrate template. By ultrasonic seeding with nanodiamond suspension, three-dimensional （3D） penetration structure diamond was successfully deposited in cylindrical microchannels of Cu template by hot-filament chemical vapor deposition. Micro-Raman spectroscopy and scanning electron microscopy （SEM） were used to characterize diamond film and the effects of microchannel depth on the morphology, grain size and growth rate of diamond film were comprehensively investigated. The results show that diamond quality and growth rate sharply decrease with the increase of the depth of cylindrical microchannel. Individual diamond grain develops gradually from faceted crystals into micrometer cluster, and finally to ballas-type nanocrystalline one. In order to modify the rapid decrease of diamond quality and growth rate, a new hot filament apparatus with a forced gas flow through Cu microchannels was designed. Furthermore, the growth of diamond film by new apparatus was compared with that without a forced gas flow, and the enhancement mechanism was discussed.

Preparation of diamond/Cu microchannel heat sink by chemical vapor deposition

A Ti interlayer with thickness about 300 nm was sputtered on Cu microchannels, followed by an ultrasonic seeding with nanodiamond powders. Adherent diamond film with crystalline grains close to thermal equilibrium shape was tightly deposited by hot-filament chemical vapor deposition(HF-CVD). The nucleation and growth of diamond were investigated with micro-Raman spectroscope and field emission scanning electron microscope(FE-SEM) with energy dispersive X-ray detector(EDX). Results show that the nucleation density is found to be up to 1010 cm-2. The enhancement of the nucleation kinetics can be attributed to the nanometer rough Ti interlayer surface. An improved absorption of nanodiamond particles is found, which act as starting points for the diamond nucleation during HF-CVD process. Furthermore, finite element simulation was conducted to understand the thermal management properties of prepared diamond/Cu microchannel heat sink.

Low-temperature epitaxy of transferable high-quality Pd(111)films on hybrid graphene/Cu(111)substrate

The continuous pursuit of miniaturization in the electronics and optoelectronics industry demands all device components with smaller size and higher performance,in which thin metal film is one heart material as conductive electrodes.However,conventional metal filmns are typically polycrystalline with random domain orientations and various grain boundaries,which greatly degrade their mechanical,thermal and electrical properties.Hence,it is highly demanded to produce single-crystal metal films with epitaxy in an appealing route.Traditional epitaxy on non-metal single-crystal substrates has difficulty in exfoliating away due to the formation of chemical bonds.Newly developed epitaxy on single-crystal graphene enables the easy exfoliation of epilayers but the annealing temperature must be high(typical 500-1,000℃ and out of the tolerant range of integrated circuit technology)due to the relative weak intertacial interactions.Here we demonstrate the facile production of 6-inch transferable high-quality Pd(111)filims on single-crystal hybrid graphene/Cu(111)substrate with CMOS-compatible annealing temperature of 150℃ only.The interfacial interaction between Pd and hybrid graphene/Cu(111)substrate is strong enough to enable the low-temperature epitaxy of Pd(111)films and weak enough to facilitate the easy film release from substrate.The obtained Pd(111)films possess superior properties to polyrystalline ones with-0.25 eV higher work function and almost half sheet resistance.This technique is proved to be applicable to other metals,such as Au and Ag.As the single-crystal graphene/Cu(111)substrates are obtained from industrial Cu foils and accessible in meter scale,our work will promote the massive applications of large-area high-quality metal fims in the development of next-generation electronic and optoelectronic devices.

Theoretical investigations on the growth of graphene by oxygenassisted chemical vapor deposition

Recently,graphene has drawn considerable attention in the field of electronics,owing to its favorable conductivity and high carrier mobility.Crucial to the industrialization of graphene is its high-quality microfabrication via chemical vapor deposition.However,many problems remain in its preparation,such as the not fully understood cracking mechanism of the carbon source,the mechanism of its substrate oxidation,and insufficient defect repair theory.To help close this capability gap,this study leverages density functional theory to explore the role of O in graphene growth.The effects of Cu substrate oxidation on carbon source cracking,nucleation barriers,crystal nucleus growth,and defect repairs are discussed.OCu was found to reduce energy change during dehydrogenation,rendering the process easier.Moreover,the adsorbed O in graphene or its Cu substrate can promote defect repair and edge growth.