Transfer-free Growth Research Articles

Transfer-Free Growth of Atomically Thin Transition Metal Disulfides Using a Solution Precursor by a Laser Irradiation Process and Their Application in Low-Power Photodetectors.

Although chemical vapor deposition is the most common method to synthesize transition metal dichalcogenides (TMDs), several obstacles, such as the high annealing temperature restricting the substrates used in the process and the required transfer causing the formation of wrinkles and defects, must be resolved. Here, we present a novel method to grow patternable two-dimensional (2D) transition metal disulfides (MS2) directly underneath a protective coating layer by spin-coating a liquid chalcogen precursor onto the transition metal oxide layer, followed by a laser irradiation annealing process. Two metal sulfides, molybdenum disulfide (MoS2) and tungsten disulfide (WS2), are investigated in this work. Material characterization reveals the diffusion of sulfur into the oxide layer prior to the formation of the MS2. By controlling the sulfur diffusion, we are able to synthesize continuous MS2 layers beneath the top oxide layer, creating a protective coating layer for the newly formed TMD. Air-stable and low-power photosensing devices fabricated on the synthesized 2D WS2 without the need for a further transfer process demonstrate the potential applicability of TMDs generated via a laser irradiation process.

Transfer-free growth of graphene on SiO2 insulator substrate from sputtered carbon and nickel films

Here we demonstrate the growth of transfer-free graphene on SiO2 insulator substrates from sputtered carbon and metal layers with rapid thermal processing in the same evacuation. It was found that graphene always grows atop the stack and in close contact with the Ni. Raman spectra typical of high quality exfoliated monolayer graphene were obtained for samples under optimised conditions with monolayer surface coverage of up to 40% and overall graphene surface coverage of over 90%. Transfer-free graphene is produced on SiO2 substrates with the removal of Ni in acid when Ni thickness is below 100nm, which effectively eliminates the need to transfer graphene from metal to insulator substrates and paves the way to mass production of graphene directly on insulator substrates. The characteristics of Raman spectrum depend on the size of Ni grains, which in turn depend on the thickness of Ni, layer deposition sequence of the stack and RTP temperature. The mechanism of the transfer-free growth process was studied by AFM in combination with Raman. A model is proposed to depict the graphene growth process. Results also suggest a monolayer self-limiting growth for graphene on individual Ni grains.

Direct Growth of Graphene Nanoribbons for Large-Scale Device Fabrication

Graphene being a zero band gap material hinders the use of its intrinsic form for many applications requiring a moderate band gap, such as field effect transistors and optoelectronic devices. Here we demonstrate a scalable method based on chemical vapor deposition for the direct growth of well-registered graphene nanoribbons on SiO(2) substrates with precise control over their width, length, and position. The width of the graphene nanoribbons (∼20 nm) is defined by the thickness of catalyst film, therefore avoiding the diffraction limit of conventional optical lithographic methods. The carrier mobility (over 1000 cm(2)/V·s) is higher than those previously reported graphene nanoribbons fabricated on SiO(2) substrates, thanks to the present transfer-free and contaminant-free direct growth process. This method overcomes many practical limitations of the previously demonstrated methods for the patterning of graphene nanoribbons and is compatible with large-scale fabrication of graphene nanoelectronics.

Progress of graphene growth on copper by chemical vapor deposition: Growth behavior and controlled synthesis

Recently, chemical vapor deposition (CVD) on copper has been becoming a main method for preparing large-area and high- quality monolayer graphene. In this paper, we first briefly introduce the preliminary understanding of the microstructure and growth behavior of graphene on copper, and then focus on the recent progress on the quality improvement, number of layers control and transfer-free growth of graphene. In the end, we attempt to analyze the possible development of CVD growth of graphene in future, including the controlled growth of large-size single-crystal graphene and bilayer graphene with different stacking orders.

Substrate considerations for graphene synthesis on thin copper films

Chemical vapor deposition on copper substrates is a primary technique for synthesis of high quality graphene films over large areas. While well-developed processes are in place for catalytic growth of graphene on bulk copper substrates, chemical vapor deposition of graphene on thin films could provide a means for simplified device processing through the elimination of the layer transfer process. Recently, it was demonstrated that transfer-free growth and processing is possible on SiO2. However, the Cu/SiO2/Si material system must be stable at high temperatures for high quality transfer-free graphene. This study identifies the presence of interdiffusion at the Cu/SiO2 interface and investigates the influence of metal (Ni, Cr, W) and insulating (Si3N4, Al2O3, HfO2) diffusion barrier layers on Cu–SiO2 interdiffusion, as well as graphene structural quality. Regardless of barrier choice, we find the presence of Cu diffusion into the silicon substrate as well as the presence of Cu–Si–O domains on the surface of the copper film. As a result, we investigate the choice of a sapphire substrate and present evidence that it is a robust substrate for synthesis and processing of high quality, transfer-free graphene.