Graphene Quantum Dots: Introduction and Market News - Page 8

Researchers from the National Physical Laboratory (the NPL) and the University of Cambridge wants to redefine the ampere, using the world's first graphene single-electron pump (SEP).

The idea is to redefine the ampere in terms of the electron charge. The SEP creates a flow of individual electrons by shutting them in a quantum dot and then emitting them one at a time at a well-defined rate. The researchers managed to produce such a pump for the first time, and this can provide the speed of electron flow - which can be used to redefine the ampere.

Researchers from Kansas State University developed improved electron-tunneling based humidity, pressure or temperature sensing devices using graphene quantum dots. Those devices are more responsive in vacuum compared to most sensors. They will be able to detect trace amounts of water on Mars, for example.

To create the Quantum Dots, the researchers used nanoscale graphite cuttings to produce graphene nanoribbons. Chemically cleaving those ribbons into 100 nanometer sized pieces created the quantum dots.

Researchers from Japan's Advanced Institute of Science and Technology (JAIST) and the University of Southampton in the UK have developed a new way to fabricate ultra-fine graphene nanodevices using helium-ion microscopy. Usually this tool is used for sub-nanometer probing and high-resolution imaging, but this time they have used to it to selectively sputter graphene to create intricate nanoscale designs.

The researchers used their new technique to develop two devices: ultrathin suspended graphene nanoribbons for extremely sensitive gas molecular sensors and densely integrated graphene Quantum Dots for quantum information processing technologies.

Researchers from the National Institute of Standards and Technology (NIST) and the University of Maryland have shown that subjecting graphene to mechanical strain can mimic the effects of magnetic fields and create a quantum dot.

The researchers fabricated graphene "drumheads" by suspending graphene over shallow holes in a substrate of silicon dioxide. When using unique scanning probe microscope designed and built at NIST, they noticed that the graphene rose up to meet the tip of the microscope— a result of the van der Waals force, a weak electrical force that creates attraction between objects that are very close to each other. The strain in the "drumhead" could be tuned by using the conducting plate upon which the graphene and substrate were mounted to create a countervailing attraction and pull the drumhead down. This changed the material's electrical properties.

Researchers from the Institute of Photonic Sciences (ICFO) in Barcelona, Spain have developed a highly sensitive photodetector that uses graphene and quantum dots. They say that the new device is a billion times more sensitive to light than previous graphene-based photodetectors because of the quantum dots. A photo-detector such as this can be used in light sensors, solar cells, infrared cameras and biomedical imaging.

Graphene's external quantum efficiency (EQE) is low as it absorbs less than 3% of the light that falls on it. It is also quite difficult to actually extract the electrical current from the graphene. Adding the quantum dots on the graphene sheet helps both of these issues.

Researchers from Rice University, together with colleagues in China, India, Japan and Texas, discovered a new one-step wet chemical process that turns carbon fiber into graphene quantum dots. The process enables making the GQDs in bulk - which are highly soluble.

The size of the QDs can be controlled via the temperature at which they're created. At 120 degrees they got a blue QD, at 100 a green one and a 80 degrees - a yellow QD.

Scientists from the National Physical Laboratory in New Delhi, India developed graphene based quantum dots (GQDs) blended with organic polymers that can be used in new photovoltaics (solar) cells. This may solve the problem of toxic metals (cadmium and lead) used in today's quantum dots, and the new material is also more stable then current organic materials.

The GQDs are 9-nm in size have similar electronic properties to normal QDs, and actually perform better (less current loss and improved efficiency) because of graphene's high charge carrier mobility. This work could lead to light-weight, flexible and cheap panels - used in large-area roll-to-roll manufacturing. In fact they say that these GQDs may also be used in other applications such as OLED displays, and indeed the team fabricated OLEDs using the new material - with "good performance".

Researchers from the National University of Singapore (NUS) and A*STAR developed a new method to create Quantum Dots from Graphene. The idea is to start with a C60 fullerene (a soccer ball like spherical carbon structure that costs of 60 carbon atoms) and 'open' them up (or decompose them) at high temperature using ruthenium as a catalyst.

The researcher performed the decomposition using a sparser coverage of fullerenes on the catalytic ruthenium surface than previously tried - which gave the fullerenes room to prevent carbon atoms from diffusing from one fullerene to the next.

Researchers from Singapore discovered that graphene quantum dots can be made from carbon-60 molecules (C60, known as buckyballs). This is the first "bottom-up" approach to make graphene quantum dots - which could lead to more efficient and cheaper designs.

The QDs are smaller then 10nm in size and are all in the same size and shape. The idea is to decompose C60 molecules at high temperatures on a ruthenium metal surface. The metal acts as a catalyst and causes the C60 to break down into carbon clusters. The researchers were able to limit cluster aggregation and at around 825K temperature the clusters merged and crystallized into hexagonal-shaped graphene QDs.

Researchers from Rice University say that have plans to create Graphene based quantum dots - which could enable single-molecule sensors and could lead to ultra-small transistors and on-chip communications with semiconductor lasers.

Quantum dots are vacancies (wells) that can confine excitons—bound electron-hole pairs—in a semiconductor to achieve properties that are superior to those of bulk materials. The Rice University researchers have added a new twist—leaving a single layer of carbon in the bottom of the well. The researchers reasoned that by removing islands of hydrogen from both sides of the sheets, tiny wells of conductive graphene, surrounded by the graphene insulator, will be left behind that could be used as quantum dots.