Electronics - Page 36

Back in May 2011, a graphene research program (called FET Graphene Flagship) was shortlisted for one of two €1 billion EU research initiatives. Today we're happy to report that this project was indeed chosen by the European Commission. This is set to be a huge boost to graphene research and will hopefully accelerate commercialization of graphene based products. The EU will officially announce their decision next week (January 28).

The graphene flagship project is led by theoretical physicist Jari Kinaret at Chalmers University of Technology in Gothenburg, Sweden. The project will focus on developing graphene applications in the computing, batteries and sensor markets. It will also develop related materials. Back in 2011 it was reported that the project already includes over 130 research groups, representing 80 academic and industrial partners in 21 European countries.

Researchers from the Beckman Institute have researchers the electronics behavior of graphene with grain boundaries. They explain that when graphene is grown, lattices of the carbon grains are formed randomly, linked together at different angles of orientation in a hexagonal network. But sometimes when the process is not perfect, defects called grain boundaries (GBs) form. These boundaries scatter the flow of electrons in graphene, which harms the material's electronic performance.

The researchers grew polycrystalline graphene on a silicon wafer using CVD, and then examined the atomic-scale grain boundaries using scanning tunneling microscopy and spectroscopy. The electron scattering at the boundaries significantly limits the electronic performance compared to grain boundary free graphene.  In fact they say that when the electrons' itinerary takes them to a grain boundary, it is like hitting a hill - the electrons bounce off, interfere with themselves and create a wave pattern. The hill slows the electrons down - which means that the grain boundary is a resistor in series with a conductor.

Researchers from the University of Texas at Austin have developed flexible graphene field-effect transistors (G-FET) that features record current densities and the highest power and conversion gain ever. The team says that the transistors show near symmetric electron and hole transport and are the most mechanically robust flexible graphene devices fabricated to date. They are also resistant to water.

The G-FETs were made directly atop patterned dielectrics on plastic sheets using conventional microelectronic lithography. In those devices, multi-finger metal gate electrodes are embedded in the plastic sheet. The graphene was grown using CVD.

Researchers from Georgia Tech have developed a new low-temperature method to dope graphene films using self-assembled monolayers (SAM) that modify the interface of graphene and its support substrate. Using this method the researchers developed graphene p-n junctions.

The researchers used CVD to grow graphene on copper film and then transferred it to silicon dioxide substrates that were functionalized with the self-assembled monolayers. Thus they have shown that you can make fairly well doped p-type and n-type graphene controllably by patterning the underlying monolayer instead of modifying the graphene directly. All previous methods (such as substitution of carbon atoms for nitrogen atoms, compounds addition or graphene ribbons edge modification) or had disrupted the graphene lattice which reduced the electron mobility and the devices were not stable.

Researchers from Monash University (Australia) have managed to grow 3D graphene "towers" that make graphene more elastic. The new 3D material supports 50,000 times its own weight, springs back into shape after being compressed by up to 80% and has a very low density. The material still retains graphene's conductivity.

To develop the new material, the researchers used ice crystal as templates to grow the graphene towers from graphene oxide flakes. The technique was adapted from freeze casting which involves growing layers of soluble graphene oxide between forming ice crystals. By partially stripping the oxygen coating before freeze casting, they could enhance the bonding between adjacent flakes in the network, producing much stronger materials then before. The individual graphene sheets are neatly aligned, forming an ordered network of hexagonal pores.

Researchers from Rice University managed to develop a new hybrid material that combines carbon nanotubes (CNTs) with graphene. The CNTs rise like towers from the graphene - up to 120 microns in height. This material has a massive surface (over 2,000 square meters per gram of material), which will be great for energy storage supercapacitors and other applications. Just to compare, a house on an average plot with the same aspect ratio would rise into space.

The nanotubes do not simply "sit" on the graphene - they are part of it as they share the atoms (the bonds between them are covalent). To develop this material, the researchers grew graphene on metal (copper) and then the CNTs were grown on the graphene. The electrical contact between the nanotubes and the metal electrode is ohmic. That means electrons see no difference, because it's all one seamless material.

Researchers from Rice University discovered a way to create Bernal-stacked bi-layer graphene sheets. These kinds of structures (in which every other carbon atom in the six-carbon rings of the top graphene layer sits over the middle of the hexagonal space created by a six-carbon ring of the bottom layer) exhibit a small band gap.

To create these sheets with controlled thickness on copper substrates, the researchers used pressure-tuned CVD chambers, while keeping constant the pressure ratio of hydrogen to methane. The higher the pressure, the thicker the graphene film. They created all sorts of sheets, and the bi-layer ones indeed were Bernal-stacked. They created a transistor and checked the electronic properties to make sure there's a band gap.

Researchers from the Georgia Institute of Technology managed to create an substantial electronic bandgap in graphene nanoribbons - by coating bi-layer graphene on silicon carbide nanometer-scale steps. This could lead the way towards graphene based electronics.

The 1.4-nanometer ribbons created a bandgap of about 0.5 electron-volts. The researchers do not yet understand why the bent graphene creates the bandgap.

Scientists from the University of Manchester, including Nobel prize-winner Professor Andre Geim constructed a multi-layer graphene structure made by placing individual sheets one on top of the other. This 'cake' like structure behaves like a nanoscale electric transformer - which could be used to make new electronic transistors and photonic detector devices.

In the new device, electrons moving in one metallic layer pull electrons in the second metallic layer by using their local electric fields. The layers are only separated by a tiny (few interatomic) distance - much shorter than anything done before. To achieve this structure they used just four atomic layers of boron nitride to serve as an electric insulator.

Nobel Prize-winner (together with Andre Geim) Professor and Kostya Novoselov Professor Volodya Falko from Lancaster University have released a graphene roadmap. The roadmap discusses the different possible applications for graphene and also the different ways to produce the material.

The authors says that the first key application is conductors for touch-screen displays (replacing ITO), where they expect can be commercialized within 3-5 years. They also see rollable e-paper displays soon - prototypes could appear in 2015. Come 2020, we can expect graphene-based devices such as photo-detectors, wireless communications and THz generators. Replacing silicon and delivering anti-cancer drugs are interesting applications too - but these will only be possible at around 2030.