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Ultraclean transfer of graphene by mechanically exfoliating polymer with modified crosslink density
Nano Research
Published: 30 May 2024
Downloads:52

The transfer of graphene from metallic substrates onto application-specific substrates is usually inevitable for the applications of high-quality graphene films derived from chemical vapour deposition (CVD) approaches. Commonly used to support the graphene films during the transfer, the coating of the polymer would produce the surface contaminations and hinder the industrially compatible transfer. In this work, through the thermal imidization of polyamide acid (PAA) to polyimide (PI) and tuning of the concentration of dangling chains, we achieved the ultraclean and crack-free transfer of graphene wafers with high electronic quality. The resulting contamination-free and hydrophilic surface also enabled the observed improved cell viability in a biomedical applications. By avoiding aqueous etching or the usage of strong bases, our proposed transfer method is industrially compatible for batch transfer of graphene films towards the real applications.

Research Article Online first
Co-enhancement of thermal conduction and radiation through morphologies controlling of graphene functional layer for chip thermal management
Nano Research
Published: 04 April 2024
Downloads:114

With the continuous advancements in electronics towards downsizing and integration, efficient thermal dissipation from chips has emerged as a critical factor affecting their lifespan and operational efficiency. The fan-less chip cooling system has two critical interfaces for thermal transport, which are the contact interface between the base and the chip dominated by thermal conduction, and the surface of the fins dominated by thermal radiation. The different thermal transfer modes of these two critical interfaces pose different requirements for thermal management materials. In the study, a novel approach was proposed by developing graphene thermal transport functional material whose morphology could be intentionally designed via reformed plasma-enhanced chemical vapor deposition (PECVD) methods to meet the diverse requirements of heat transfer properties. Specifically, graphene with multilevel branching structure of vertical graphene (BVG) was fabricated through the hydrogen-assisted PECVD (H2-PECVD) strategy, which contributed a high emissivity of ~ 0.98. BVG was deposited on the fins’ surface and functioned as the radiation enhanced layer to facilitate the rapid radiation of heat from the heat sinks into the surrounding air. Meanwhile, the well-oriented vertical graphene (OVG) was successfully prepared through the vertical electric field-assisted PECVD process (EF-PECVD), which showed a high directional thermal conductivity of ~ 53.5 W·m−1·K−1. OVG was deposited on the contact interface and functioned as the thermal conduction enhanced layer, allowing for the quick transmission of heat from the chip to the heat sink. Utilizing this design concept, the two critical interfaces in the chip cooling system can be jointly enhanced, resulting in a remarkable cooling efficiency enhancement of ~ 30.7%, demonstrating that this novel material possessed enormous potential for enhancing the performance of cooling systems. Therefore, this research not only provided new design concepts for the cooling system of electronic devices but also opened up new avenues for the application of graphene materials in thermal management.

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
Downloads:149

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
Downloads:102

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
Downloads:62

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
Downloads:81

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
Downloads:61

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
Porous-structure engineered spacer for high-throughput and rapid growth of high-quality graphene films
Nano Research 2022, 15 (11): 9741-9746
Published: 01 July 2022
Downloads:72

Chemical vapor deposition (CVD) in conjunction with batch-to-batch manufacturing process is considered as the most promising technical route for mass-production of high-quality graphene films. To improve the space utilization of the CVD chamber and increase the throughput per batch, stacking of the Cu foil substrates is efficient, but suffers from the problems of adjacent fusion and the poor mass-transfer. Here, we demonstrate an efficient strategy for high-throughput and rapid growth of high-quality graphene by alternate stacking of Cu foils and porous carbon fiber paper (CFP). Relying on the unhindered mass-transfer through the pores of CFPs, full-covered high-quality graphene films on compact-stacked Cu foils were achieved within 2 min. Computational fluid dynamics (CFD) simulation and isotope labeling technique were performed to explore the gas diffusion and graphene growth process in the confined space of the Cu-CFP stacks. This work provides a feasible method for industrial production of graphene films, which may also be used for batch production of other two-dimensional materials.

Research Article Issue
Toward batch synthesis of high-quality graphene by cold-wall chemical vapor deposition approach
Nano Research 2022, 15 (11): 9683-9688
Published: 29 April 2022
Downloads:136

Chemical vapor deposition (CVD) has emerged as a promising approach for the controlled growth of graphene films with appealing scalability, controllability, and uniformity. However, the synthesis of high-quality graphene films still suffers from low production capacity and high energy consumption in the conventional hot-wall CVD system. In contrast, owing to the different heating mode, cold-wall CVD (CW-CVD) system exhibits promising potential for the industrial-scale production, but the quality of as-received graphene remains inferior with limited domain size and high defect density. Herein, we demonstrated an efficient method for the batch synthesis of high-quality graphene films with millimeter-sized domains based on CW-CVD system. With reduced defect density and improved properties, the as-received graphene was proven to be promising candidate material for electronics and anti-corrosion application. This study provides a new insight into the quality improvement of graphene derived from CW-CVD system, and paves a new avenue for the industrial production of high-quality graphene films for potential commercial applications.

Research Article Issue
In situ separator modification via CVD-derived N-doped carbon for highly reversible Zn metal anodes
Nano Research 2022, 15 (11): 9785-9791
Published: 23 November 2021
Downloads:178

Attention toward aqueous zinc-ion battery has soared recently due to its operation safety and environmental benignity. Nonetheless, dendrite formation and side reactions occurred at the anode side greatly hinder its practical application. Herein, we adopt direct plasma-enhanced chemical vapor deposition strategy to in situ grow N-doped carbon (NC) over commercial glass fiber separator targeting a highly stabilized Zn anode. The strong zincophilicity of such a new separator would reduce the nucleation overpotential of Zn and enhance the Zn-ion transference number, thereby alleviating side reactions. Symmetric cells equipped with NC-modified separator harvest a stable cycling for more than 1,100 h under 1 mA·cm−2/1 mAh·cm−2. With the assistance of NC, the depth of discharge of Zn anode reaches as high as 42.7%. When assembled into full cells, the zinc-ion battery based on NC-modified separator could maintain 79% of its initial capacity (251 mAh·g−1) at 5 A·g−1 after 1,000 cycles.

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