Research Article Issue
Theoretical investigations on the growth of graphene by oxygen-assisted chemical vapor deposition
Nano Research 2024, 17 (6): 4645-4650
Published: 07 February 2024

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.

Research Article Issue
Invisible vapor catalysis in graphene growth by chemical vapor deposition
Nano Research 2024, 17 (5): 4259-4269
Published: 01 December 2023

Vapor catalysis was recently found to play a crucial role in superclean graphene growth via chemical vapor decomposition (CVD). However, knowledge of vapor-phase catalysis is scarce, and several fundamental issues, including vapor compositions and their impact on graphene growth, are ambiguous. Here, by combining density functional theory (DFT) calculations, an ideal gas model, and a designed experiment, we found that the vapor was mainly composed of Cui clusters with tens of atoms. The vapor pressure was estimated to be ~ 10−12–10−11 bar under normal low-pressure CVD system (LPCVD) conditions for graphene growth, and the exposed surface area of Cui clusters in the vapor was 22–269 times that of the Cu substrate surface, highlighting the importance of vapor catalysis. DFT calculations show Cu clusters, represented by Cu17, have strong capabilities for adsorption, dehydrogenation, and decomposition of hydrocarbons. They exhibit an adsorption lifetime and reaction flux six orders of magnitude higher than those on the Cu surface, thus providing a sufficient supply of active C atoms for rapid graphene growth and improving the surface cleanliness of the synthesized graphene. Further experimental validation showed that increasing the amount of Cu vapor improved the as-synthesized graphene growth rate and surface cleanliness. This study provides a comprehensive understanding of vapor catalysis and the fundamental basis of vapor control for superclean graphene rapid growth.

Research Article Issue
Substrate screening for superclean graphene growth using first-principles calculations
Nano Research 2024, 17 (4): 2216-2222
Published: 09 November 2023

Suppressing the formation of amorphous surface carbon and contaminants during the preparation of graphene by chemical vapor deposition remains an ongoing issue. Herein, we analyzed how substrate characteristics affect graphene quality by simulating margin extension, the nucleation process, and defect pegging configurations on mono-crystalline oriented metal substrates with the aim of enhancing graphene cleanliness. Defect formation energy and nucleation potential, which are indirect substrate–graphene interaction features, were found to appropriately evaluate graphene quality. The crystallographic orientation of the metal substrate was discovered to be critical for producing superclean graphene. A low graphene defect density and high nucleation rate on the Cu (100) facet guarantee growth of high-quality graphene, especially in terms of suppressing the formation of amorphous carbon. In addition, rapid kink growth and self-healing on the Cu (100) facet facilitate rapid graphene synthesis, which is also promoted by rapid kink splicing and margin self-repair on this facet. This study provides theoretical insight useful for the synthesis of superclean graphene.

Research Article Issue
Fast scanning growth of high-quality graphene films on Cu foils fueled by dimeric carbon precursor
Nano Research 2023, 16 (10): 12246-12252
Published: 22 June 2023

Carbon source precursor is a critical factor governing chemical vapor deposition growth of graphene films. Methane (CH4), has been the most commonly used precursor in the last decade, but it presents challenges in terms of decomposition efficiency and growth rate. Here we thoroughly evaluated acetylene (C2H2), a precursor that is probably for providing carbon dimer (C2) species, for fast growth of large-scale graphene films. We find that the graphene growth behaviors fueled by C2H2 exhibit unconventional localized growth behavior with significant advantages in terms of high growth rate, which mainly ascribe to the as-decomposed C2 species. Therefore, a C2-fueled scanning growth strategy is proposed, and the fast scanning growth rate of 40 cm/min was experimentally demonstrated. This growth strategy is compatible with the approach of unidirectional growth of single-crystal graphene films, and the as-grown graphene films are of high-quality. This work demonstrates a reliable and promising strategy for the rapid synthesis of high-quality graphene film and may pave the avenue to cost-effective mass production of graphene materials in the roll-to-roll system.

Research Article Issue
CO2-promoted transfer-free growth of conformal graphene
Nano Research 2023, 16 (5): 6334-6342
Published: 21 December 2022

Gaseous promotors have readily been adopted during the direct synthesis of graphene over insulators to enhance the growth quality and/or boost the growth rate. The understanding of the real functions of carbon-containing promotors has still remained elusive. In this study, we identify the critical roles of a representative CO2 promotor played in the direct growth of graphene. The comparative experimental trials validate CO2 as an effective modulator to decrease graphene nucleation density, improve growth kinetics, and mitigate adlayer formation. The first-principles calculations illustrate that the generation of gas-phase OH species in CO2-assisted system helps decrease the energy barriers of CH4 decomposition and carbon attachment to the growth front, which might be the key factor to allow high-quality direct growth. Such a CO2-promoted strategy enables the conformal coating of graphene film over curved insulators, where the sheet resistance of grown graphene on quartz reaches as low as 1.26 kΩ·sq−1 at an optical transmittance of ~ 95.8%. The fabricated endoscope lens based on our conformal graphene harvests an apoptosis of 82.8% for noninvasive thermal therapy. The work presented here is expected to motivate further investigations in the controllable growth of high-quality graphene on insulating substrates.

Research Article Issue
Single Cr atom catalytic growth of graphene
Nano Research 2018, 11 (5): 2405-2411
Published: 12 May 2018

Single atoms are the ultimate minimum size limit for catalysts. Graphene, as an exciting, ultimately thin (one atom thick) material can be imaged in a transmission electron microscope with relatively few imaging artefacts. Here, we directly observe the behavior of single Cr atoms in graphene mono- and di-vacancies and, more importantly, at graphene edges. Similar studies at graphene edges with other elemental atoms, with the exception of Fe, show catalytic etching of graphene. Fe atoms have been shown to both etch and grow graphene. In contrast, Cr atoms are only observed to induce graphene growth. Complementary theoretical calculations illuminate the differences between Fe and Cr, and confirm single Cr atoms as superior catalysts for sp2 carbon growth.

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