光刻胶辅助的石墨烯晶圆无损转移

为实现石墨烯在光通讯、光互联、太赫兹探测等电子和光电子领域的应用价值,需要在硅基衬底上得到大面积、均一且性能优异的石墨烯薄膜材料。而高品质石墨烯薄膜的制备衬底多为金属,因此制备的石墨烯薄膜不可避免地需要通过合适的转移方法,转移到目标应用衬底上。而转移过程通常会引入破损、褶皱和污染物,其原因之一是石墨烯转移和器件加工过程中表面反复涂覆和去除转移介质聚合物和光刻胶类聚合物。为避免反复涂覆与去除高分子聚合物,本文直接利用光刻胶作为转移介质,成功实现了石墨烯的洁净转移。同时,转移后石墨烯的电学性质得到明显改善,平均载流子迁移率可达6200 cm^(2)·V^(−1)·s^(−1)。此方法可实现石墨烯等二维材料无损、洁净转移和高性能器件的构筑,将有助于推动二维材料在电子、光电子器件领域的应用。

Ultraclean transfer of graphene by mechanically exfoliating polymer with modified crosslink density

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.

Invisible vapor catalysis in graphene growth by chemical vapor deposition

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^(-1)1 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.

Porous-structure engineered spacer for high-throughput and rapidgrowth of high-quality graphene films

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.

The role of Cu crystallographic orientations towards growing superclean graphene on meter-sized scale

Chemical vapor deposition(CVD)-grown graphene films on Cu foils,exhibiting fine scalability and high quality,are still suffering from the adverse impact of surface contamination,i.e.,amorphous carbon.Despite the recent successful preparation of superclean graphene through Cu-vapor-assisted reactions,the formation mechanism of amorphous carbon remains unclear,especially with regard to the functions of substrates.Herein,we have found that the crystallographic orientations of underlying metal substrates would determine the cleanness of graphene in such a way that slower diffusion of active carbon species on asformed graphene-Cu(100)surface is the key factor that suppresses the formation of contamination.The facile synthesis of clean graphene is achieved on the meter-sized Cu(100)that is transformed from the polycrystalline Cu foils.Furthermore,a clean surface of graphene on Cu(100)ensures the reduction of transfer-related polymer residues,and enhanced optical and electrical performance,which allows for versatile applications of graphene in biosensors,functioning as flexible transparent electrodes.This work would offer a promising material platform for the fundamental investigation and create new opportunities for the advanced applications of high-quality graphene films.

Toward batch synthesis of high-quality graphene by cold-wall chemical vapor deposition approach

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.