Photonics - Page 8

Veeco Instruments announced that the University of Nottingham in the UK purchased two GENxplor R&D Molecular Beam Epitaxy (MBE) Systems for its School of Physics and Astronomy. The University will use the systems to grow high-quality large-area graphene and boron nitride for electronic and optoelectronic applications.

Veeco's MBE systems can deposit epitaxial graphene layers on substrates up to 3" in diameter. The company says that their vertical chamber technology enables them to build smaller MBE systems - up to 40% smaller than the competition. The MBE is an open architecture that provides convenient access to effusion cells and e-beam sources.

Researchers from Manchester University have demonstrated that graphene can be used to investigate how light interacts (via plasmon resonance) with gold nanostructures of different shape, size and geometry. This could lead to more efficient solar cells and photo detectors.

The researchers explain that when light shines on a metal particle smaller than the wavelength of the light, the electrons in the particle start to move back and forth along with the light wave. This causes an increase in the electric field at the surface of the particle. When two such metal particles are close to each other, the oscillating electrons in the two particles interact with each other, forming an even higher electric field which results in a coupling between the two particles. Up until now it was difficult to experimentally observe and measure the magnitude of this coupling and electric field.

Today two different teams of researchers released articles describing new advances in graphene-on-silicon based photodetectors. These devices hold promise because it could lead to more simple device fabrication - and those devices will be very fast compared to current photo detectors and be responsive to a wider range of light frequencies.

But basic graphene photodetectors suffer from low responsivity as graphene will only convert about 2% of the light passing through it to electrical current. This is a high value for an atom-thick material, but it's not enough for a real photodetector.

IBM researchers have developed a graphene-based infrared detector, driven by intrinsic plasmons. This new design proved to be much more photo-responsive compared to non-plasmonic graphene detectors.

The researchers used CVD to grow graphene on copper foil. The copper was etched away and the graphene sheet was transferred to a silicon/silicon-oxide chip. The researchers patterned graphene ribbons (widths of 80 to 200 nm).

Researchers from the Universities of Bath and Exeter have developed and demonstrated an optical switch made from graphene. this switch has an incredibly short optical response - nearly a hundred times quicker than current materials.

This fast response is in the infrared part of the electromagnetic spectrum, which makes it useful for telecommunications, security and also medicine applications. Current optical switches have as response rate of a few picoseconds, and the few-layer-graphene switch's response rate is about one hundred femtoseconds.

MIT researchers developed a new system, based on ferroelectric materials and graphene, that uses plasmons wave control to interconnect between electronic devices and light wave devices (such as fiber optics and photonic chips). Current such interconnectors are relatively slow and are often a bottleneck in those systems.

The new hybrid-material device can control surface plasmons wave (oscillations of electrons confined at interfaces between materials). The waves operate at terahertz frequencies in this new device, which is considered ideal for next-gen computing devices.

Researchers from Rice University and the Oak Ridge National Laboratory (ORNL) found a new method to control the growth of uniform atomic layers of molybdenum disulfide (MDS), a semiconductor together with graphene can be used to make 2D electronic devices. Unlike graphene, MDS has a band gap.

The researchers goal is to create large MDS sheets (using CVD) and then use it together with graphene and the insulator hexagonal boron nitride (hBN) to form field-effect transistors, integrated logic circuits, photodetectors and flexible optoelectronics. MD5 isn't flat - it's actually a stack, with a layer of molybdenum atoms between two layers of sulfur atoms. It's a challenge to actually bind these three materials together.

Researchers from Korea's Ulsan National Institute of Science and Technology (UNIST) managed to embed a LED inside a regular soft contact lens, using transparent and conductive electrodes made from graphene and silver nanowires. This is the first time an electronic device was embedded inside a contact lens using flexible and transparent materials.

The researchers final goal is to develop wearable computer displays inside contact lenses. Basically it will be like a Google Glass HMD, but without any external display components. Obviously that goal is still far in the future: currently they manged to embed just one LED and not a full display.

We already know that laser can be used to produce graphene (see here and here), and in 2010 researchers developed an ultra-fast mode-locked laser using Graphene. A recent research improved their graphene-based laser device to produce a broad spectrum of infrared wavelengths. This may be useful for applications such as fiber optic communications.

The researchers say that their results suggest it will be possible to create graphene-base lasers that emit light over the entire spectrum of visible light.

Korean researchers have developed a new blue nitride LED that uses 3D graphene foam as a transparent conductor for the p-contact. They say that the graphene foam reduced the forward voltage by 26% and increased the light output by 14%.

The researchers used commercial 3D graphene foam, produced on 3D copper foam using chemical vapor deposition. The graphene foam on copper was then spin-coated with PMMA and the copper etched away (using ammonium sulfate). The graphene foam was cut into a square and transferred to the p-type gallium nitride layer of a commercial blue LED.