Controllable Growth of the Graphene from Millimeter-Sized Monolayer to Multilayer on Cu by Chemical Vapor Deposition

A Steep-Slope MoS2/Graphene Dirac-Source Field-Effect Transistor with a Large Drive Current

In the continuous transistor feature size scaling down, the scaling of the supply voltage is stagnant because of the subthreshold swing (SS) limit. A transistor with a new mechanism is needed to break through the thermionic limit of SS and hold the large drive current at the same time. Here, by adopting the recently proposed Dirac-source field-effect transistor (DSFET) technology, we experimentally demonstrate a MoS₂/graphene (1.8 nm/0.3 nm) DSFET for the first time, and a steep SS of 37.9 mV/dec at room temperature with nearly free hysteresis is observed. Besides, by bringing in the structure of gate-all-around (GAA), the MoS₂/graphene DSFET exhibits a steeper SS of 33.5 mV/dec and a 40% increased normalized drive current up to 52.7 μA·μm/μm (V_DS = 1 V) with a current on/off ratio of 10⁸, which shows potential for low-power and high-performance electronics applications.

Growth and in situ characterization of 2D materials by chemical vapour deposition on liquid metal catalysts: a review

2D materials (2DMs) have now been established as unique and attractive alternatives to replace current technological materials in a number of applications. Chemical vapour deposition (CVD), is undoubtedly the most renowned technique for thin film synthesis and meets all requirements for automated large-scale production of 2DMs. Currently most CVD methods employ solid metal catalysts (SMCat) for the growth of 2DMs however their use has been found to induce structural defects such as wrinkles, fissures, and grain boundaries among others. On the other hand, liquid metal catalysts (LMCat), constitute a possible alternative for the production of defect-free 2DMs albeit with a small temperature penalty. This review is a comprehensive report of past attempts to employ LMCat for the production of 2DMs with emphasis on graphene growth. Special attention is paid to the underlying mechanisms that govern crystal growth and/or grain consolidation and film coverage. Finally, the advent of online metrology which is particularly effective for monitoring the chemical processes under LMCat conditions is also reviewed and certain directions for future development are drawn.

Graphene growth with no intended carbon precursor feeding into the LPCVD process: causes, solutions, and effects

In this research, we have investigated the unintended graphene nucleation problem and its damaging effects on monolayer graphene synthesis in low-pressure chemical vapor deposition (LPCVD) process. This problem is the growth of graphene on the copper surface with no carbon feedstock. A new source of undesired carbon species was identified which has not been addressed so far. The hydrogen-rich heating stage was diagnosed as the onset of the unintended nucleation for the first time owing to the determinant catalytic role of hydrogen in this stage. It was found out that this problem leads to uncontrollable growth of multilayer graphene, growth of defective graphene film and also inhibition of the reliable synthesis of monolayer graphene. We managed to grow enhanced-quality monolayer graphene by developing some innovative solutions to the problem containing a general solution based on the hydrogen effects in the heating stage. The results reveal a significant decrease in the unintended nucleation density from ∼2000 to almost zero domains per 100 × 100 μm² copper area. Furthermore, Raman, HRTEM and SAED analysis confirm the defect-free growth of monolayer graphene after employing the solutions. These findings could pave the way for the reliable synthesis of high-quality monolayer graphene as well as large-sized graphene domains.

Different graphene layers to enhance or prevent corrosion of polycrystalline copper

Graphene was used as an anticorrosive coating for metals as it can effectively isolate the corrosion factors such as oxygen. However, we found that the anticorrosive and corrosive effects on metal surface were related to graphene layers and metal crystal faces. In this paper, we found that different layers of graphene had significantly different effects on the corrosion of polycrystalline copper during long-term storage under atmospheric conditions. Optical images and Raman spectra showed that single layer graphene (SLG)-coated copper had a higher degree of corrosion than bare copper. However, when covered with CVD in situ-grown bilayer graphene (BLG), the copper foil was effectively prevented from being etched as it exhibited a bright yellow color despite the differences in crystal faces. The surface potential differences measured by an electric force microscope (EFM) showed that a contact potential difference (V_CPD) between 30 and 40 mV existed between Cu/SLG and bare copper. The SLG-coated areas had a higher surface potential (SP), which meant that the (SLG)-coated copper was more prone to lose electrons to exhibit galvanic corrosion. The BLG coating made SP of underlying copper lower making it harder to lose electrons; thus, BLG successfully protected the copper from being corroded. These findings have a foreseeable significance for graphene as a metal anti-corrosion coating.

The degree of corrosion depends on the crystal faces and number of graphene layers, whereas BLG can be used as an anticorrosion coating.

High White Light Photosensitivity of SnSe Nanoplate-Graphene Nanocomposites

The multi-functional nanomaterial constructed with more than one type of materials has gained a great attention due to its promising application. Here, a high white light photodetector prototype established with two-dimensional material (2D) and 2D nanocomposites has been fabricated. The 2D-2D nanocomposites were synthesized with SnSe nanoplate and graphene. The device shows a linear I-V characterization behavior in the dark and the resistance dramatically decreases under the white light. Furthermore, the photosensitivity of the device is as large as 1110% with a rapid response time, which is much higher than pristine SnSe nanostructure reported. The results shown here may provide a valuable guidance to design and fabricate the photodetector based on the 2D-2D nanocomposites even beyond the SnSe nanoplate-graphene nanocomposites.

Review of the synthesis, transfer, characterization and growth mechanisms of single and multilayer graphene

Graphene has emerged as the most popular topic in the active research field since graphene's discovery in 2004 by Andrei Geim and Kostya Novoselov.

Double hexagonal graphene ring synthesized using a growth-etching method

Precisely controlling the layer number, stacking order, edge configuration, shape and structure of graphene is extremely challenging but highly desirable in scientific research. In this report, a new concept named the growth-etching method has been explored to synthesize a graphene ring using the chemical vapor deposition process. The graphene ring is a hexagonal structure, which contains a hexagonal exterior edge and a hexagonal hole in the centre region. The most important concept introduced here is that the oxide nanoparticle derived from annealing is found to play a dual role. Firstly, it acts as a nucleation site to grow the hexagonal graphene domain and then it works as a defect for etching to form a hole. The evolution process of the graphene ring with the etching time was carefully studied. In addition, a double hexagonal graphene ring was successfully synthesized for the first time by repeating the growth-etching process, which not only confirms the validity and repeatability of the method developed here but may also be further extended to grow unique graphene nanostructures with three, four, or even tens of graphene rings. Finally, a schematic model was drawn to illustrate how the double hexagonal graphene ring is generated and propagated. The results shown here may provide valuable guidance for the design and growth of unique nanostructures of graphene and other two-dimensional materials.