Boron Nitride - Page 8

A team of researchers from China and Japan has designed a new method to make minuscule ribbons of graphene that are highly sought-after building blocks for semiconductor devices thanks to their predicted electronic properties. These structures, however, have proven challenging to make.

Previous attempts at making graphene nanoribbons relied on placing sheets of graphene over a layer of silica and using atomic hydrogen to etch strips with zigzag edges, a process known as anisotropic etching. This method, however, only worked well to make ribbons that had two or more graphene layers. Irregularities in silica created by electronic peaks and valleys roughen its surface, so creating precise zigzag edges on graphene monolayers was a challenge.

Researchers from the University of California, Riverside (UCR) and the University of Georgia have made use of three 2D materials graphene, tantalum sulphide and boron nitrate to create a simple, compact and fast voltage controlled oscillator (VCO). According to the team, this is the first useful device that exploits the potential of charge density waves to modulate an electrical current through a 2D material.

Apart from having the potential of being an ultralow power alternative to silicon based devices, the device is thin and flexible, making it suitable for use in wearable technologies. But graphene’s potential has been limited by its inability to function as a semiconductor, and the researchers attempted to overcome this by adding tantalum sulphide (TaS2), which has been shown to act as an electrical switch at room temperature. The researchers then coated TaS2 with hexagonal boron nitrate to prevent oxidation. In the design, graphene functions as an integrated tunable load resistor, which enables precise voltage control of the current and VCO frequency.

Scientists from the Moscow Institute of Physics and Technology (MIPT), the Institute of Physics and Technology RAS, and Tohoku University (Japan) have developed a new type of graphene-based transistor and using modelling they have demonstrated that it has ultralow power consumption compared with other similar transistor devices. Reducing power consumption enables the clock speed of processors to be increased, according to calculations, to as high as two orders of magnitude, since the electronic components heat up less.

Building transistors that are capable of switching at low voltages (less than 0.5 volts) is one of the major challenges of modern electronics. Tunnel transistors seem to be the most promising candidates to solve this problem. Unlike in conventional transistors, where electrons jump through the energy barrier, in tunnel transistors the electrons filter through the barrier due to the quantum tunneling effect. However, in most semiconductors the tunneling current is very small and this prevents transistors that are based on these materials from being used in real circuits.

University of Washington scientists have designed a way to use graphene to encourage photons into stimulating multiple electrons, thus maximizing the transfer of energy and making efficient light-captured energetics possible.

The method exploits graphene's efficient interaction with light; The researchers took a single layer of graphene and sandwiched it between two thin layers of boron-nitride. Boron-nitride has a lattice structure very similar to graphene's, but has very different chemical properties as electrons do not flow easily within boron-nitride so it basically acts as an insulator. The team discovered that when the graphene layer's lattice is aligned with the layers of boron-nitride, a type of "superlattice" is created with desirable properties that enable efficient optoelectronics. These properties rely on quantum mechanics, and the researchers detected unique quantum regions within the superlattice known as Van Hove singularities.

CVD Equipment, a provider of chemical vapor deposition systems, announced the next phase in its industrial partnership with Penn State University to advance 2D crystal device development.

The National Science Foundation’s Materials Innovation Platform (MIP) recently announced that it has awarded Penn State University (PSU) $17.8 million payable over five years. This award will fund a national user facility, based at PSU’s Materials Research Institute, for developing new materials for next generation electronics. CVD will contribute through supply and development of equipment required for synthesizing the 2D materials at wafer scale. The promise of emerging 2D materials, including graphene, boron nitride, and transition metal dichalcogenides, for revolutionizing the semiconductor and electronic device industries is reinforced by this platform award from the National Science Foundation. The user facility at PSU will aim to synthesize 2D crystals for use in faster, more energy efficient, and flexible electronics.

Researchers from the University of Tokyo demonstrated an electrically controllable valleytronics device. The device converts regular electrical current to valley current and then passes it through a 3.5 micron channel. The valley current is then converted back to electrical current that can be detected (via its voltage).

To create this new device, the researchers used a bi-layer graphene that is placed between two insulator layers made from hexagonal boron nitride (hBN). This structure is then placed between two conductive layers (or gates) which control the valley. This device operates at -203 degrees Celsius - much higher than expected, and the researchers hope that in the future devices such as this could operate at room temperatures.

An international team of researchers from six countries have designed a highly sensitive gas sensor made from boron-doped graphene, able to detect noxious gas molecules at extremely low concentrations, parts per billion in the case of nitrogen oxides and parts per million for ammonia. These sensors can be used for labs and industries that use ammonia, a highly corrosive health hazard, or to detect nitrogen oxides, a dangerous atmospheric pollutant emitted from automobile tailpipes. In addition to detecting toxic or flammable gases, theoretical work indicates that boron-doped graphene could lead to improved lithium-ion batteries and field-effect transistors. 

The sensor reaches a 27 times greater sensitivity to nitrogen oxides and 10,000 times greater sensitivity to ammonia compared to pristine graphene. The researchers believe these results will open a path to high-performance sensors that can detect trace amounts of many other molecules.

Researchers from the National University of Singapore (NUS) have developed a hybrid magnetic sensor that is reportedly more sensitive than most commercially available sensors. This could encourage the development of smaller and cheaper sensors for areas like consumer electronics, information and communication technology and automotive, as well as applications like thermal switches, hard drives and magnetic field sensors.

The sensor is made of graphene and boron nitride, and includes layers of carrier-moving channels, each of which can be controlled by the magnetic field. The researchers characterized the sensor by testing it at various temperatures, angles of magnetic field, and with a different pairing material. Graphene-based magnetoresistance sensors hold immense promise over existing sensors due to their stable performance over temperature variation and eliminating the necessity for expensive wafers or temperature correction circuitry. Production cost for graphene is also much lower than silicon and indium antimonide.

Scientists at the University of Basel have managed to synthesize boron-doped graphene nanoribbons and characterize their structural, electronic and chemical properties. The modified material could potentially be used as a sensor for ecologically damaging nitrogen oxides.

Altering graphene sheets to nanoribbon shape is known as a way of inducing a bandgap, whose value is dependent on the width of the shape. To tune the band gap in order for the graphene nanoribbons to act like a silicon semiconductor, the ribbons usually undergo doping. That means the researchers intentionally introduce impurities into pure material for the purpose of modulating its electrical properties. While nitrogen doping has been realized, boron-doping has remained unexplored. Subsequently, the electronic and chemical properties have stayed unclear thus far.

A collaboration between Flagship-affiliated physicists from RWTH Aachen University and Forschungszentrum Jülich, together with colleagues in Japan, devised a method for peeling graphene flakes from a CVD substrate with the help of intermolecular forces. It is an innovative variant on the traditional CVD process, which yields high quality material in a scalable manner, that might significantly narrow the performance gap between synthetic and natural graphene.

The process is heavily based on the strong van der Waals interaction that exists between graphene and hexagonal boron nitride, another 2D material within which it is encapsulated. Thanks to strong van der Waals interactions between graphene and boron nitride, CVD graphene can be separated from the copper and transferred to an arbitrary substrate. The process allows for re-use of the catalyst copper foil in further growth cycles, and minimizes contamination of the graphene due to processing.