Electronics - Page 18

Researchers at the Technical University of Munich have found that graphene can be combined with porphyrins, the molecules that convey oxygen in haemoglobin and absorb light during photosynthesis, to get a material with exciting new properties. The resulting hybrid structures could be used in the field of molecular electronics, solar cells and in developing new sensors.

The technique involves growing a graphene layer on a surface of silver to use its catalytic properties. Then, under ultra-high vacuum conditions, porphyrin molecules are added. These lose the hydrogen atoms from their periphery when heated on the metal surface, and they end up connecting to the graphene edges.

Researchers at Rice University have found that it may be possible to make graphene-carbon nanotube junctions excel at transferring heat, turning these into an attractive way to channel damaging heat away from next-generation nano-electronics. This could, in theory, be done by putting a cone-like chimney between the graphene and nanotube to eliminate the barrier that blocks heat from escaping.

Graphene and carbon nanotubes both excel at the rapid transfer of electricity and phonons, but when a nanotube grows from graphene, atoms facilitate the turn by forming heptagonal (seven-member) rings instead of the usual six-atom rings. Scientists have determined that forests of nanotubes grown from graphene are excellent for storing hydrogen for energy applications, but in electronics, the heptagons scatter phonons and hinder the escape of heat through the pillars.

Resistive RAM (RRAM) is a promising new next-generation memory technology that is being commercialized by several companies. Researchers at the Chinese Academy of Sciences have been study a device failure caused by two processes in cation-based RRAM, and have discovered that graphene may hold the key.

If a single-layer graphene is added to the device, and used as an ion barrier between two metallic layers in the device, the RRAM cell is more reliable while still maintaining high performance.

A group of scientists from the National Research University of Electronic Technology MIET (Russia), Technological Center AIMEN (Spain) and Forschungszentrum Jülich (Germany) has developed an approach for graphene physical and chemical modification avoiding the step of resist deposition, that can be useful for graphene-based electronics technologies.

This work demonstrates the mask-less and resist-free patterning of graphene by two different routes: thermal ablation or oxidative etching. That means that by varying the parameters of laser pulses, chemical tuning (energy gap control) and isolation line patterning is possible in a single process without any chemicals. The same group published the results of graphene oxide reduction by using thermal and chemical effects from laser irradiation. Moreover the laser pulses provide 3D embossing of graphene that open the way for single processing of NEMS and microfluidic-based sensors in graphene.

Scientists from Russia's National Research Nuclear University MEPhI have succeeded in producing graphene with a very high stability to ozonation using high-temperature sublimation of silicon carbide (SiC). The resulting graphene maintains contact with ozone for more than 10 minutes (while ordinary graphene loses its properties after only three or four minutes under such conditions). These results may hold great potential for the development of nanoelectronics.

To further examine the effects, scientists from Greece, France and Sweden were brought onto the team. Using computer modeling, the experts were able to figure out why SiC-graphene was more stable under the impact of aggressive oxygen free radicals. The new graphene's abnormal stability appeared to be associated with the low roughness of epitaxial graphene on SiC-substrate (epitaxy is a natural buildup of one crystalline material upon the surface of another).

Researchers at Pennsylvania State University have developed a device made of bilayer graphene, which provides experimental proof of the ability to control the momentum of electrons. The study is considered as a step forward in a new field of physics called valleytronics.

The team explains that current silicon-based transistor devices rely on the charge of electrons to turn the device on or off, but valleytronics looks into a new way to manipulate electrons based on other variables, called degrees of freedom. Charge is one degree of freedom. Electron spin is another, and the ability to build transistors based on spin, called spintronics, is still in the development stage. A third electronic degree of freedom is the valley state of electrons, which is based on their energy in relation to their momentum.

Graphene 3D Lab, a leader in the development, manufacturing and marketing of proprietary composites and coatings based on graphene and other advanced materials, recently announced the release of a new product. The Company will now offer a filament for 3D printing that is both highly electrically conductive and flexible.

G3L reports that the enhanced properties of this product make it ideal for applications involving flexible sensors, electromagnetic/radiofrequency shielding, flexible conductive traces and electrodes to be used in wearable electronics. This new material will be available for purchase in 1.75mm diameter 100 gram spools at the Company's on-line store, www.blackmagic3D.com, under the trade name of "Conductive Flexible TPU Filament".

Researchers from the ICFO, in collaboration with CIC nanoGUNE, Columbia University and the National Institute for Materials Science in Japan, have been able to fabricate an all-graphene mid-infrared plasmon detector operating at room temperature, where a single graphene sheet serves simultaneously as the plasmonic generation medium and detector.

The team used an experimental design with two local gates—a split metal sheet located underneath the graphene—to fully tune the thermoelectric and plasmonic behavior of the graphene. In contrast to the conventional back gating through a thick SiO2 layer, the separate local gates not only induce free carriers in the graphene to act as a plasmonic channel, but also create a thermoelectric detector for the plasmons. The resulting device converts the conveniently available natural decay product of the plasmon, electronic heat, directly into a voltage through the thermoelectric effect.

Researchers at the Technical University of Munich (TUM) have succeeded in linking graphene with a chemical group called porphyrins, which are well-known because of their notable functional properties (for instance, playing a central role in chlorophyll during photosynthesis). These new hybrid structures could be used in the field of molecular electronics, catalysis or even as sensors.

Many researchers focus on wet-chemical methods for attaching the molecules to the surface of the material. The TUM team, however, decided to take a different approach: The researchers were able to link porphyrin molecules to graphene in a controlled manner in an ultra-high vacuum using the catalytic properties of a silver surface on which the graphene layer rested. When heated, the porphyrin molecules lose hydrogen atoms at their periphery and can thus form new bonds with the graphene edges.

Researchers at North Carolina State University have developed a technique that enables the integration of graphene, graphene oxide (GO) and reduced graphene oxide (rGO) onto silicon substrates at room temperature by using nanosecond pulsed laser annealing. The advance may open the door to the possibility of creating new electronic devices, such as smart biomedical sensors.

In this new technique, the researchers start with a silicon substrate. They top that with a layer of single-crystal titanium nitride, using domain matching epitaxy to ensure the crystalline structure of the titanium nitride is aligned with the structure of the silicon. They then place a layer of copper-carbon alloy on top of the titanium nitride, again using domain matching epitaxy. Finally, the researchers melt the surface of the alloy with nanosecond laser pulses, which pulls carbon to the surface.