September 2011

The following article was sent to us by Corey McCarren and Dr. Elena Polyakova from Graphene Laboratories (a Graphene-Info sponsor), discussing Graphene Oxide and its applications:

Graphene, a multi or single layer sheet of graphite, is considered a key material in producing the next generation of low-cost carbon-based transparent and flexible electronics. Graphene is the strongest material available, as well as being highly transparent, flexible, and the best conductor of heat and electricity. Great effort is devoted to developing an effective yet inexpensive way to produce graphene materials in industrial quantities.

Graphene Supermarket announced that they have expanded their product line and reduced the prices of many current graphene products. They are now offering highly concentrated graphene oxide at the lowest price per gram. The company also added two high-surface area materials, Reduced Graphene Oxide and ultrafine Graphene Nanoplatelets.

Graphene Supermarket is operated by Graphene Laboratories and is a sponsor of Graphene-Info.

MIT's new Center for Graphene Devices and Systems (MIT-CG) has an ambitious plan - to produce a one-kilometer square sheet of graphene. They are currently starting to develop the basic science and technology - which is based on the printing press. The idea is to grow graphene in a roll to roll process. MIT hopes that if they manage to develop this technology they'll enable a whole new graphene industry.

Currently they've been able to grow small sheets only using this technology (a "few centimeters" in size). The largest graphene sheet made to date was 30" square (produced by Japanese and Korean researches in June 2010) - which was also made in a roll-to-roll printing process. There were reports of a 40" graphene sheet produced by Samsung in January 2011 but these reports weren't confirmed.

Researchers from the Georgia Institute of Technology developed a new method to grow high quality layers of epitaxial graphene on silicon carbide wafers. They call this method confinement controlled sublimation, and it relies on controlling the vapor pressure of gas-phase silicon in the high-temperature furnace used for fabricating the material.

Basically, growing graphene on silicon carbide requires heating the material to about 1,500 degrees Celsius under high vacuum. But uncontrolled evaporation lead to poor quality material. Controlling the temperature is essential for high-quality graphene. The new developed method begins by placing a silicon carbide wafer into an enclosure made of graphite. A small hole in the container controls the escape of silicon atoms as the one-square-centimeter wafer is heated, maintaining the rate of silicon evaporation and condensation near its thermal equilibrium. The growth of epitaxial graphene can be done in a vacuum or in the presence of an inert gas such as argon, and can be used to produce both single layers and multiple layers of the material.

NPL researchers used graphene to make the most precise measurements of the quantum Hall effect ever made. It turns out that the quantum Hall effect in graphene is very robust and easy to measure.

Researchers from the National Institute for Materials Science managed to dramatically increase the energy density of supercapacitors - using a new electrode in which graphene nanosheets are stacked in a layered structure with carbon nanotubes sandwiched between the graphene layers.

The researchers designed and developed a graphene-based composite structure, in which graphene is used as the base material of the capacitor electrodes and carbon nanotubes (CNT) are inserted between the graphene sheets. In this structure graphene offers a far larger specific surface area (2630 m2/g) than the conventional materials and the CNTs function as spacers as well as conducting paths to enable adsorption of a larger quantity of electrolyte ions on the graphene surface. With this graphene-CNT composite as the capacitor electrodes, Professor Tang has obtained a high energy density of 62.8 Wh/kg and output power density of 58.5 kW/kg using organic electrolyte. By using an ionic liquid as the electrolyte, they have achieved an energy density of 155.6 Wh/kg, which is comparable to that of nickel metal hydride batteries.

Finish researchers developed a new hybrid material which combines graphene nanoribbons and Single-Walled Carbon Nanotubes (SWNT). They call this GNR@SWNT - and they say that its synthesis is simple. The graphene nanoribbons should keep their unique properties inside the nanotubes, and they will be protected and aligned.

Nanoribbons can be either metallic or semiconductor (depending on their width and type) and the SWNTs can be either metallic, semiconducting (depending on their chirality) or insulating (when chemically modified). So you can create GNR@SWNT in six combinations which creates all sort sof interesting applications - transistors, solar cells, radio signal transmitters and more.

The National Science Foundation (NSF) awarded a research grant to a Stevents Institute of Technology researcher to study the properties of graphene nanoribbons for use in infrared (IR) detection.

This funded research is to investigate the properties of actively controlled graphene nanoribbon arrays that researchers can "tune" for use in IR detectors covering an ultra-wide spectral range. In their awarded research, Dr. Yang and Dr. Strauf investigate nanoelectromechanical devices employing graphene nanoribbons to significantly improve IR detection schemes. Current IR detectors experience both limitations in their spectral range, for those that rely on the fixed IR absorption properties of detector materials, or their general sensitivities, in the case of tunable thermal detectors. The proposed concept offers the unique possibility of achieving high sensitivity across a wide spectral range with a single detection system.

Graphene is strong - about 200 times greater than steel, but new research has shown that folding graphene nanoribbons can make a material that's ever stronger. The Chinese researchers call the new material Grafold.

The researchers say that while graphene is very high tensile strength (i.e. it is difficult to pull it apart) it is not strong under compression and cannot be squeezed. Grafold, however can withstand much larger amounts of compression (10-25 GPa depending on the structure of grafold compared with less than 2 GPa for graphene). The tensile strength is almost similar to graphene.

According to James Meindl (from the Georgia Institute of Technology) graphene will only become a viable alternative once CMOS semiconductor manufacturing will reach 7 nanometer - which will happen around 2024 (according to Moore's law).

Meindl believes that the most likely usages of graphene is switches - and he's working on 15 nanometer-wide ribbons that could rival silicon.