Stanford team finds novel form of magnetism in twisted bi-layer graphene

Stanford physicists recently observed a novel form of magnetism, predicted but never seen before, that is generated when two graphene sheets are carefully stacked and rotated to a special angle. The researchers suggest the magnetism, called orbital ferromagnetism, could prove useful for certain applications, such as quantum computing.

bi-layer graphene between hBN gives off orbital ferromagnetism imageOptical micrograph of the assembled stacked structure, which consists of two graphene sheets sandwiched between two protective layers made of hexagonal boron nitride. (Image: Aaron Sharpe)

“We were not aiming for magnetism. We found what may be the most exciting thing in my career to date through partially targeted and partially accidental exploration,” said study leader David Goldhaber-Gordon, a professor of physics at Stanford’s School of Humanities and Sciences. “Our discovery shows that the most interesting things turn out to be surprises sometimes.”

Graphene coating on copper wires may help prevent electromigration and help minimize future electronics

As electronics keep shrinking in size, several problems arise. One of these is that the copper wires that connect transistors to form complex circuits need to be very thin, but carry so much current that can cause them to break apart due to atoms being knocked out of place. One way of solving this, studied by a group led by Stanford University, is to wrap copper with graphene. The group found that this can alleviate this major problem called electromigration.

This was presented at a recent IEEE meeting that addressed the coming problems for copper interconnects and debated ways of getting around them. Growing graphene around copper wires can help prevent electromigration, and also seems to bring down the resistance of the copper wires. Generally speaking, the narrower the wire, the higher its resistance. “Interconnects have had to shrink while increasing the current densities by 20 times,” said Intel Fellow Ruth Brain at the meeting.

Stanford team demonstrates a graphene-based thermal-to-electricity conversion technology

Researchers at Stanford University have recently demonstrated a graphene-based high efficiency thermal-to-electricity conversion technology, called thermionic energy convertor. By using graphene as the anode, the efficiency of the device is increased by a factor of 6.7 compared with a traditional tungsten anode. This technology can work in a tandem cycle with existing thermal-based power plants and significantly improve their overall efficiencies.

Stanford team creates graphene-based TEC image

Hongyuan Yuan and Roger T. Howe, among the leading researchers in the Stanford team, explain that one of the major challenges for wide adoption of TECs is high anode work function, which directly reduces the output voltage as well as the net efficiency. The theoretical maximum efficiency for a TEC with a 2 eV work function anode is 3% at a cathode temperature of 1500 K, compared to an astonishing 10-fold increment to 32% with a 1 eV work function anode.

Graphene-based system may enable imaging of electrical activity in heart and nerve cells

Researchers at the Berkeley Lab and Stanford University have used graphene as the film of an ultra-sensitive camera system designed for visually mapping tiny electric fields in a liquid. The new platform should permit single-cell measurements of electrical impulses traveling across networks containing 100 or more living cells. The researchers hope it will allow more extensive and precise imaging of the electrical signaling networks in our hearts and brains. Additional potential applications include the development of lab-on-a-chip devices, sensing devices and more.

The team explains that the basic concept was examining how graphene could be used as a general and scalable method for resolving very small changes in the magnitude, position, and timing pattern of a local electric field, such as the electrical impulses produced by a single nerve cell. Other techniques have been developed to measure electrical signals from small arrays of cells, but these can be difficult to scale up to larger arrays and in some cases cannot trace individual electrical impulses to a specific cell. In addition, this new method does not perturb cells in any way, which is fundamentally different from existing methods that use either genetic or chemical modifications of the cell membrane.

Graphene "cages" may open the door to silicon Li-ion battery anodes

A team of scientists at Stanford University and the Department of Energy's SLAC National Accelerator Laboratory has come up with a possible answer to the question of how to make lithium-ion battery anodes out of silicon, as these tend to swell and crack, as well as react with the battery electrolyte to form a coating that harms their performance.

The scientists wrapped each silicon anode particle in a custom-fit "cage" made of graphene, in a simple, three-step method for building microscopic graphene cages of just the right size: roomy enough to let the silicon particle expand as the battery charges, yet tight enough to hold all the pieces together when the particle falls apart, so it can continue to function at high capacity. The strong, flexible cages also block destructive chemical reactions with the electrolyte.