New method uses hydrogen plasma to smooth out wrinkles in graphene

Researchers from Nanjing University in China have developed a method to make large graphene films free of any wrinkles. The ultra-smooth films could enable large-scale production of electronic devices that harness the unique physical and chemical properties of graphene and other 2D materials.

Wrinkles  disappear when graphene is treated with a hydrogen plasma imageWrinkles in graphene films grown via chemical vapor deposition appear as jagged white lines at the top of this atomic force microscope image (left), but they disappear when the material is treated with a hydrogen plasma (right). Credit: Nature

Chemical vapor deposition (CVD) is the best-known method for making high-quality graphene sheets. It typically involves growing graphene by pumping methane gas onto copper substrates heated to temperatures around 1,000 °C, and then transferring the graphene to another surface such as silicon. But some of the graphene sticks to the copper surface, and as the graphene and copper expand and contract at different rates, wrinkles form in the graphene sheets. Such wrinkles often present hurdles for charge carriers and lower the film’s conductivity. Other researchers have tried to reduce wrinkles using low growth temperatures or special copper substrates, but the wrinkles have proven difficult to eliminate entirely, according to Libo Gao, a physicist at Nanjing University.

An activated carbon-coated lint roller can yield super-clean graphene

In order for CVD graphene to be used in its intended application, it needs to be transferred from the growth substrate to a target substrate – a challenging but extremely important process step. Typically the transfer is done by spin-coating a supporting polymer layer and then chemically dissolving away the copper to release the graphene film from the substrate. The transferred graphene produced in this way is prone to contamination from the chemical agents used to remove the growth substrate as well as defective amorphous carbon generated during the high-temperature CVD growth. It also frequently leads to a substantial amount of polymer particle residue on the graphene generated during the transfer process. A third source of contamination could be airborne particles that are adsorbed onto the graphene surface.

Graphene treated by the activated carbon-coated lint roller imageTop: Schematic of the activated carbon-coated lint roller for cleaning the graphene surface. Bottom left: AFM image of unclean graphene on Cu foil. Bottom right: AFM image of superclean graphene on Cu foil. Image taken from Nanowerk

Researchers from Peking University and Tsinghua University in China and University of Manchester in the UK have recently demonstrated that the amorphous carbon contaminants on CVD-produced graphene, which could greatly degrade its properties, can be removed by an activated carbon-coated lint roller, relying on the strong interactions between the amorphous carbon and activated carbon.

LG Electronics to start offering CVD graphene materials

According to our information, LG Electronics is aiming to start supplying CVD graphene materials worldwide soon, with an aim to accelerate the adoption of CVD graphene in various applications. LG is collaborating with research groups to identify new applications for graphene sheets.

Large LG Electronics logo
LG Electronics developed its own roll-to-roll production process in addition to a specific quality control system for its graphene. LG says that its inspection system can manage uniformity deviations in crystal size, defects and electrical properties in its graphene to within 10%.

University of Illinois team finds that defects in graphene membranes may improve biomolecule transport

Researchers at the University of Illinois examined how tiny defects in graphene membranes, formed during fabrication, could be used to improve molecule transport. They found that the defects make a big difference in how molecules move along a membrane surface. Instead of trying to fix these flaws, the team set out to use them to help direct molecules into the membrane pores.

Nanopore membranes have generated interest in biomedical research because they help researchers investigate individual molecules - atom by atom - by pulling them through pores for physical and chemical characterization. This technology could ultimately lead to devices that can quickly sequence DNA, RNA or proteins.

MIT team uses wax to smooth out wrinkles in graphene

Researchers at MIT have utilized an everyday material - wax- to protect graphene from performance-impairing wrinkles and contaminants. Removing graphene from the substrate it’s grown on and transferring it to a new substrate is known t be challenging. Traditional methods encase the graphene in a polymer that protects against breakage but also introduces defects and particles onto graphene’s surface. These interrupt electrical flow and stifle performance.

MIT process for smoothing out graphene wrinkles with wax imagea Schematics showing the process of paraffin-assisted graphene transfer. b Schematics showing the effect of paraffin’s thermal expansion on graphene wrinkle. c A typical paraffin-supported graphene film floated on water at different temperatures

The MIT team describes a fabrication technique that applies a wax coating to a graphene sheet and heats it up. Heat causes the wax to expand, which smooths out the graphene to reduce wrinkles. Moreover, the coating can be washed away without leaving behind much residue.

Versarien - Think you know graphene? Think again! Versarien - Think you know graphene? Think again!