Self-Terminating Confinement Approach for Large-Area Uniform Monolayer Graphene Directly over Si/SiO_x by Chemical Vapor Deposition

Abstract

To synthesize graphene by chemical vapor deposition (CVD) both in large area and with uniform layer number directly over Si/SiO has proven challenging. The use of catalytically active metal substrates, in particular Cu, has shown far greater success and therefore is popular. That said, for electronics applications it requires a transfer procedure, which tends to damage and contaminate the graphene. Thus, the direct fabrication of uniform graphene on Si/SiO remains attractive. Here we show a facile confinement CVD approach in which we simply "sandwich" two Si wafers with their oxide faces in contact to form uniform monolayer graphene. A thorough examination of the material reveals it comprises faceted grains despite initially nucleating as round islands. Upon clustering, they facet to minimize their energy. This behavior leads to faceting in polygons, as the system aims to ideally form hexagons, the lowest energy form, much like the hexagonal cells in a beehive, which requires the minimum wax. This process also leads to a near minimal total grain boundary length per unit area. This fact, along with the high graphene quality, is reflected in its electrical performance, which is highly comparable with graphene formed over other substrates, including Cu. In addition, the graphene growth is self-terminating. Our CVD approach is easily scalable and will make graphene formation directly on Si wafers competitive against that from metal substrates, which suffer from transfer. Moreover, this CVD route should be applicable for the direct synthesis of other 2D materials and their van der Waals heterostructures.

Enhanced electrochemical biosensor and supercapacitor with 3D porous architectured graphene via salt impregnated inkjet maskless lithography

“…9,10 Graphene is typically produced by chemical vapor deposition (CVD) which can yield nearly pristine (defect-free) single or few layer 2D sheets. 11 In the context of electrochemistry, these 2D pristine sheets or basal plane geometry exhibit four orders of magnitude lower specific capacitance and seven orders of magnitude lower electron transfer rates than the edges planes or edge defect sites of the graphene. 12 Numerous methods have been used to increase the electrochemical surface area (ECSA) of graphene.…”

Substrate Developments for the Chemical Vapor Deposition Synthesis of Graphene

“…However, large area, homogeneous monolayer graphene is particularly difficult to obtain. To overcome this issue, a confinement technique in which two Si/SiO x wafers with their oxide faces in contact in a sandwich configuration was used to yield homogeneous single‐layer large area graphene 53. The graphene is polycrystalline and the grain boundaries are facetted (see Figure ) indicating further improvements are needed for single‐layer material, but this is still a positive development.…”

“…e) False‐color composite micrograph image highlighting the different domain (grain) orientations and faceted grain boundaries. Reproduced with permission 53. Copyright 2017, American Chemical Society.…”

Edge‐State‐Enhanced Ultrahigh Photoresponsivity of Graphene Nanosheet‐Embedded Carbon Film/Silicon Heterojunction

“…Heterojunction photodetector becomes an indispensable part in the electronic components and optoelectronic products. Plane graphene–silicon junction attracts growing attentions in various applications such as solar cells, tunable Schottky barrier triodes, complementary metal‐oxide‐semiconductor (CMOS)‐compatible optical modulator, gas sensors, and photodetectors . Particularly, plane graphene–silicon photodetectors are suitable for weak light detection (approximately picowatt incidences' detection), which is crucial for wide applications including taking high‐quality photos under insufficient light, infrared monitoring, and optical spectroscopic analysis.…”