Band gap - Page 5

Researchers from the University of California and Rice University developed a new rapid method to synthesize high quality large-area Bernal (AB) stacked bilayer graphene sheets.

During the same research, the first bi-layer graphene double-gate field-effect transistor (G-FET) was also demonstrated. This G-FET features the best on/off switching ratio and carrier mobility.

Researchers from the University of Arizona discovered how to change the crystal structure of graphene with an electric field. This unique technique may enable graphene transistors - and electronics and microprocessors applications.

The researchers used trilayer graphene, in which the top layer can be placed in two different ways - either the atoms are placed on the atoms of the bottom layer or with a slight offset (so the atoms are placed on the space between the bottom layer atoms). In a tri-layer graphene sheet, this happens naturally and actually the two stacking configurations exist together with a sharp boundary between them.

Researchers from the University of Utah developed a new way to develop large arrays of graphene nanoribbons (GNRs), aiming for applications in photodetectors. Their method can directly write a large array of 15nm GNRs on a multilayer epitaxial graphene sheet using Focused Ion Beam (FIB).

The researchers accelerated ga+ ions to 30 keV in vacuum using a FEI Helios NanoLab 650 dual-beam FIB machine. This removed carbon atoms from the graphene sheet with a 1.3 sputtering yield (carbon/Ga+ ratio). This technology can be easily transferred to pattern other graphene nanostructures such as spheres, rings and blocks.

Resaerchers from Japan's National Institute for Materials Science (NIMS) developed a method to tune the band-gap of graphene oxide. The new method changes the bonding state of carbon atoms that compose graphene through reversible absorption and desorption of oxygen atoms on the graphene, and tuning the band-gap in situ.

The researchers say that this method enables band-gap tuning in a non-volatile manner - the tuned band-gap continues to exist even when voltage supply is stopped. To control the absorption and desorption of oxygen atoms on the graphene, the group used solid electrolytes in which hydrogen ions can move, thereby causing electrochemical reactions between oxygen atoms, which are chemically bonded to the graphene, and hydrogen ions.

Researchers from the US, Singapore, Brazil and Ireland have theoretically shown that if you fold a graphene sheet in a fin-like structure and expose it to a magnetic field you open up a bandgap. This will also produce spin-polarized current, which should make it useful in Spintronics applications.

The researchers say that this folding can be easily achieved by depositing graphene on a substrate with periodic trenches.

Researchers from Korea's Ulsan National Institute of Science and Technology (UNITS) developed new graphene-based FETs (G-FETs), based on boron/nitrogen co-doped graphene nanoplatelets.

The researchers major breakthrough is the development of a new efficient method to produce those BCN-graphene platelets via a simple solvothermal reaction using potassium. Doping the GNPs opens up a bandgap.

Researchers from the University of Twente have looked into graphene's behavior when it is placed on boron nitride. It turns out that if the graphene is placed in a certain angle over the BN, it opens a bandgap. If it is placed in a random angle, the band gap will not open.

The researchers also discovered that if the graphene/BN structure is placed on copper, that can be contacted with other devices, a charge distribution (dipole layer) is also formed on the interface between copper and boron nitride.

Researchers from the Max Planck Institute in Hamburg demonstrated that graphene can be used to emit terahertz laser pulses with long wavelengths. This has been theorized before, but now the researchers actually proved that it can be done. A terahertz direct emission is useful in science but this is the first time that such a laser was developed.

The researcher explain that while graphene band-gap is usually referred to as a zero bandgap, it does have an infinitesimally small bandgap. But the electrons still behave like those of a classic semiconductor, and the population inversion in graphene only lasts for around 100 femtoseconds, less than a trillionth of a second. This means you cannot use graphene for continuous lasers, but it can be used for ultrashort laser pulses.

A few month ago we reported on Carbyne, a chain of carbon atoms linked either by alternate triple and single bonds or by consecutive double bonds, which was found to be twice as strong as graphene. Carbyne is difficult to synthesize (it does not exist in nature, but it may exist in interstellar space) but a few years ago researchers managed to make carbyne chains up to 44 atoms long in solution.

Now researchers from Rice University have performed more theoretical calculations on this new material. They say that a Carbyne nano-rod (also called nano-ropes) is pretty much like a very thin (one-atom wide) graphene ribbon. When you twist this nano-rod, you change the band gap of the material.

Researchers from Stanford developed a new way to produce graphene ribbons using DNA strands. GNRs have a bandgap and so can be used as building blocks for transistors, and indeed the researchers produced transistors based on GNRs produced using this new process.

The process goes like this: it starts with a silicon substrate, dipped in a DNA solution (derived from bacteria). They then combed the DNA strands into relatively straight lines (using a common technique). They exposed the DNA to a copper salt solution which allowed the copper ions to be absorbed into the DNA.