Cold-wall Chemical Vapor Deposition System Research Articles

Maximizing the thermal hotspot reduction by optimizing the thickness of multilayer hBN heat spreader

This article investigates the thickness-dependent heat spreading performance of multilayer hexagonal boron nitride (hBN). The growth by a cold-wall chemical vapor deposition system results in large-area and high crystal quality of multilayer hBN. The full width at half maximum of Raman E2g peak is approximately 25 cm−1 and the bandgap is larger than 5.8 eV. Varying the growth duration from 5 to 15 min on Ni foil results in hBN thicknesses of 5–12 nm with comparable crystal quality. The electrothermal analysis using a sensitive Pt/Cu/Ti micro-coil introduces the figure of merit (FoM) of hBN as an insulator heat spreader. Fittings on FoM plots suggest that multilayer hBN with a thickness of ∼2 nm is optimum for a 25% reduction in the thermal hotspot. The initial drop in lateral thermal resistance is significant for a few nanometers-thick hBN, where a 22.5% reduction is measured from the 5.6 nm-thick hBN heat spreader. Further thickening of hBN reduces the lateral thermal resistance by approximately 0.37% nm−1. Findings from this work provide a significant contribution to the implementation of hBN as a direct contact heat spreader on the actual power devices.

Solar-thermal cold-wall chemical vapor deposition reactor design and characterization for graphene synthesis

Manufacturing processes are often highly energy-intensive, even when the energy is primarily used for direct heating processes. The required energy tends to derive from local utilities, which currently employ a blend of sources ranging from fossil fuels to renewable wind and solar photovoltaics, among others, when the end manufacturing need is thermal energy. Direct solar-thermal capture provides a compelling alternative that utilizes renewable energy to reduce greenhouse gas emissions from industrial processes, but one that has rarely been employed to date. In this study, a 10 kWe custom-built high flux solar simulator (HFSS) that closely approximates the solar spectrum produces a heat flux distribution with an adjustable peak between 1.5 and 4.5 MW/m2. The HFSS system is coupled to a cold-wall chemical vapor deposition (CVD) system that is equipped to automate graphene synthesis while providing safe operation, precise control, and real-time monitoring of process parameters. A numerical heat transfer model of a thin copper substrate is derived and validated to compute the substrate’s temperature profile prior to the synthesis process. The peak substrate temperature is correlated to the HFSS supply current and vacuum pressure, as it serves as a critical design parameter during graphene synthesis. We report the synthesis of high-quality graphene films on copper substrates with an average Raman peak intensity ratio ID/IG of 0.17. Backscattered electron microscopy reveals a characteristic grain size of 120 μm, with an area ratio of 16 when compared to that of low-quality graphene on copper. The reported solar-thermal CVD system demonstrates the ability to produce a high-value product, namely, graphene on copper, directly from a renewable energy resource with process control and automation that enables synthesis under a variety of conditions.

Anti-dewetting of Cu thin film on nanostructured black Si template for continuous CVD growth of monolayer graphene

The growth of high-quality continuous film of graphene on less than [Formula: see text]m-thick Cu film is proven to be a challenging task due to the solid-state dewetting of Cu during the high-temperature chemical vapor deposition (CVD) process. In this paper, we introduce the use of nanostructured black Si (b-Si) as a template for Cu evaporation to mitigate the dewetting of Cu thin film. Using a cold-wall CVD system at a process temperature of 825[Formula: see text]C, even Cu thickness, [Formula: see text] nm on polished SiO2/Si substrate is poor for maintaining Cu as a continuous film. If the polished SiO2/Si is replaced with SiO2/b-Si, the minimum [Formula: see text] nm is sufficient. According to the Cu trapping mechanism, moving Cu particle is trapped in the nanostructured trenches of SiO2/b-Si during annealing and CVD growth processes. Continuous monolayer graphene with a grain size of [Formula: see text]m without defect is obtained on Cu/SiO2/b-Si substrate. The improved adhesion of Cu to the SiO2/b-Si enables dry-transfer of graphene by mechanical peeling using a polyvinyl alcohol (PVA) film. Our solution is promising for obtaining flat graphene and a recyclable Cu/SiO2/b-Si substrate.

Superclean Growth of Graphene Using a Cold-Wall Chemical Vapor Deposition Approach.

Chemical vapor deposition (CVD) has become a promising approach for the industrial production of graphene films with appealing controllability and uniformity. However, in the conventional hot-wall CVD system, CVD-derived graphene films suffer from surface contamination originating from the gas-phase reaction during the high-temperature growth. Shown here is that the cold-wall CVD system is capable of suppressing the gas-phase reaction, and achieves the superclean growth of graphene films in a controllable manner. The as-received superclean graphene film, exhibiting improved optical and electrical properties, was proven to be an ideal candidate material used as transparent electrodes and substrate for epitaxial growth. This study provides a new promising choice for industrial production of high-quality graphene films, and the finding about the engineering of the gas-phase reaction, which is usually overlooked, will be instructive for future research on CVD growth of graphene.

Vertically aligned growth of small-diameter single-walled carbon nanotubes by alcohol catalytic chemical vapor deposition with Ir catalyst

We showed that vertically aligned single-walled carbon nanotubes (VA-SWCNTs) can be grown by alcohol chemical vapor deposition (CVD) with an Ir catalyst in a cold-wall CVD system. VA-SWCNTs were grown on SiO2/Si substrates without any buffer layers under an ethanol pressure of 1 × 10−1 Pa at 800 °C. The SWCNT length increased with increasing growth time. The VA-SWCNT thickness reached almost 5 μm for a growth time of 180 min. Raman and photoluminescence spectroscopies showed that the diameters of the grown SWCNTs were mainly between 0.8 and 1.1 nm; this is much smaller than those of VA-SWCNTs grown with Fe and Co catalysts in previous studies. X-ray photoelectron spectroscopy and X-ray absorption near-edge structure spectroscopy showed that the Ir catalyst retained the metallic state during SWCNT growth. We suggest that highly efficient suppression of aggregation, an appropriate carbon–Ir bond strength and dissociation of ethanol molecules led to the growth of vertically aligned small-diameter SWCNTs with an Ir catalyst.

Thin Single-Walled Carbon Nanotubes with Narrow Diameter Distribution Grown by Cold-Wall Chemical Vapor Deposition Combined with Co Nanoparticle Deposition

We have grown thin single-walled carbon nanotubes (SWNTs) with a narrow diameter distribution using the arc-discharge plasma (ADP) technique for Co catalyst metal deposition and a cold-wall chemical vapor deposition (CVD) system for SWNT growth. The diameters of the SWNTs ranged from 0.79 to 1.07 nm. In addition to depositing small and uniform-sized metal catalyst nanoparticles by the ADP technique, decreasing the growth temperature using the cold-wall CVD system seemed to suppress the aggregation of the metal catalyst nanoparitcles leading to SWNTs with small diameters of narrow distribution.

Gas-Phase Synthesis of Nanostructured Anatase TiO2

Nanostructured anatase titanium dioxide (TiO2) has been obtained using chemical vapor deposition (CVD). In order to arrive at a fractal-type morphology, two different titanium precursors were injected simultaneously into a cold-wall CVD system. With this method, a wide variety of morphologies can be obtained. For solar light harvesting, the structures of trees, bushes, and grasses appear to be good choices. Small variations in deposition parameters have a dramatic effect on the structure of the deposits, which allows adequate optimization of nanostructures by gas-phase synthesis techniques.