MIT - Page 9

Graphenea demonstrated how gallium nitride (GaN) can be grown on silicon using graphene as an intermediary layer. GaN (and other semiconductors) are very appealing for applications such as LEDs, lasers and high-frequency and high-power transistors, and silicon is a great substrate for this, but it is very difficult to grown high-quality epitaxial GaN films on Si(100).

Graphene (in collaboration with MIT,Ritsumeikan University, Seoul National University and Dongguk University) found out that graphene can be used as an intermediary layer in such a structure. The hexagonal lattice of graphene has the same symmetry as that of GaN, and it can also be easily transferred to a silicon wafer. The company's method results in the best GaN(0001) layers on Si(100) demonstrated to date.

Researchers from MIT developed a carbon-based sponge that can be used to make a steam-based energy generation device. They say that such a device can reach an energy efficiency of 85%, better than current solar-powered commercial devices.

The newly developed sponge is made from a combination of graphite flakes and carbon foam. It floats on water, and when sunlight hits it, it creates a hotspot which draws up water through the pores in the material, which evaporates as steam. The process generates very little heat and can produce steam at low solar intensity (the lowest optical concentration reported thus far).

Researchers from MIT and the University of Michigan developed a new way to deposit graphene on nonmetal substrates. Current methods usually involved growing graphene on metal substrates, but this creates problems when you try to transfer the material to a different substrates.

The new method still grows the graphene on a metal substrate - but they do it in a way that grows the graphene on both sides of the metal substrate. The process starts with the nonmetal substrate of choice, which is coated with nickel. Using CVD, graphene is grown on the nickel - but the graphene forms two layers, one of them between the nickel and the nonmetal substrate. The nickel is then easily peeled off which leaves a single graphene layer on the nonmetal substrate.

Researchers from MIT, Oak Ridge National Laboratory (ORNL) and Saudi Arabia developed a new two-step process that creates subnanoscale pores in graphene. This could enable a cheaper way to create graphene membranes for water purification, desalination and other applications.

The new process starts with a graphene sheet placed on a substrate. The graphene is bombarded with gallium ions, and then etched with an oxidizing solution that reacts strongly with the disrupted carbon bonds and produces a hole (at each spot where the gallium ions hit the graphene). The average size of the hold is determined by how long the graphene sheet is in contact with the oxidizing solution.

Researchers from MIT discovered that under a powerful magnetic field and at very low temperatures, graphene can filter electrons according to the direction of their spin. This is something that cannot be done by any conventional electronic system - and may make graphene very useful for quantum computing.

It is known that when a magnetic field is turned on perpendicular to a graphene flake, current flows only along the edge, and in one direction (clockwise or counterclockwise, depending on the magnetic field orientation), while the bulk graphene sheet remains insulating. This is called the Quantum Hall effect.

Researchers from MIT and the University of California at Berkeley developed a new way to evenly functionalize graphene with oxygen at low (50-80 C) temperatures. The method is environmentally friendly (no harsh chemical treatment) and can be applied on a large scale.

The researchers use low-temperature annealing and this cause the oxygen atoms to form clusters. This leaves areas of pure-graphene between the oxygen clusters. This decreases the graphene's electrical resistance by four to five orders of magnitude (the oxygen clusters are insulating) which is good for applications such as sensing, electronics and catalysis.

Researchers from MIT developed a new process that can transfer graphene directly onto a variety of flexible substrates using a lamination process that does not require an intermediate "glue" step. The new process does not leave any residues that can affect the graphene like in other transfer processes. The new method can also be used for other materials, such as boron nitride.

The process starts by synthesizing graphene flakes on both sides of a copper foil sheet. Then the flakes are sandwiched between the target flexible surface and a protective paper layer. This structure is placed between two plastic (PET) sheets. This goes into a lamination machine in which the temperature can be controlled, and the components bond together. The plastic film and paper where removed and this leaves a copper foil with graphene and the target substrate. The copper was dissolved (or etched away) using a copper etchant.

The National Science Foundation (NSF) awarded $20 million towards a new Science and Technology Center, the Center for Integrated Quantum Materials. In the next five years, this new center will support science and education programs that explores unique electronic behavior of quantum materials. One of those new quantum materials is graphene.

Harvard university will lead the center, and they believe that quantum materials are an emerging technology with enormous promise for science and engineering. The new center will also collaborate with MIT, the Museum of Science in Boston and Howard University in Washington, D.C.

Today two different teams of researchers released articles describing new advances in graphene-on-silicon based photodetectors. These devices hold promise because it could lead to more simple device fabrication - and those devices will be very fast compared to current photo detectors and be responsive to a wider range of light frequencies.

But basic graphene photodetectors suffer from low responsivity as graphene will only convert about 2% of the light passing through it to electrical current. This is a high value for an atom-thick material, but it's not enough for a real photodetector.

Researchers from MIT developed a new way to p-dope graphene (and open up a bandgap) without harming the material's electronic properties a lot. The process basically dopes with chlorine using a plasma-based surface functionalization technique. The researcher say that their chlorine-doped graphene keeps a high charge mobility (around 1500 cm²/V) after the hole doping.

Using this process, you can get the chlorine to cover over 45% of the graphene surface, the highest surface coverage area reported for any graphene doping material. In theory, covering 50% of the graphene with chlroine in both sides can open up a 1.2 eV band gap. This means that the 45% currently achieved is very close to this target. The researchers plan to start using suspended graphene sheets so that they can cover both sides.