Graphene Tech Digest - January 2017

Method to unlock graphene’s superconductivity

Scientists at Cambridge University UK have discovered a technique to exploit graphene’s superconductive properties. Graphene’s superconductive properties have been exploited before, but the graphene required doping or placing on a superconducting material. In this new work the scientists made it a superconductor in its own right. To achieve this they coupled the graphene with praseodymium cerium copper oxide (PCCO) – a superconducting material with well understood electronic properties – that unlocks the dormant superconductivity within the graphene.  Using scanning and tunnelling microscopy the scientists were able to ascertain whether the superconductivity apparent in the graphene was truly occurring in the graphene itself. It was. 
The scientists believe that the superconductivity in the graphene was indicative of the theoretical p-wave conductivity (a type of electron coupling which results in reduced collisions with other electrons, hence smoothing electron flow, enabling superconductivity) – which is poorly understood but scientists believe holds promise for quantum computing. 

Graphene tattoo

A graphene sensor that can be worn on the skin like a tattoo was revealed at the International Electron Devices Meeting 2016. The proof of concept device is able to read skin temperature, hydration and electrical activity in the heart, muscles and brain, say the researchers behind the product, who are from the University of Texas. The device is made by growing a sheet of graphene on a copper substrate. The graphene is then coated in a polymer and the copper is etched off. Then the graphene sheet is placed on temporary tattoo paper and a circuit is etched out of it. It can be transferred to the skin just like a temporary tattoo. The scientists say that due to graphene’s 2D structure it conforms to the skin’s ridges and wrinkles allowing for more accurate biological measurements. 

Nano calligraphy

Scientists at The University of Manchester and Karlsruhe Institute of Technology have developed a method to chemically modify small regions of graphene. The system is described as being similar to writing with a quill. Above a sheet of graphene a device deposits a small drop of chemical onto the graphene, a process termed microchannel cantilever spotting. Another device acts like a quill’s nib which can dip into the chemical droplet, and write in another area using the residue on its tip, a process called dip-pen nanolithography. The scientists see this having applications for sensors that could be used in blood tests to reduce the amount of blood needed to carry out the test.

Graphene puts a stop to electron migration

Stanford University scientists have suggested a way to overcome the increasing problem of electron migration in copper wiring. Electron migration is the result of an atom being moved out of place by the force of electrons – this is a consequence of copper wires, such as on circuit boards, becoming thinner and thinner, but the current they need to carry increasing. The scientists found that adding graphene to the copper alleviates this problem, improving electro-migration by a factor of ten. It also halved the wire’s resistance. 

Chimneys help heat dissipation in forest

Rice University scientists have discovered that adding cone-like chimneys between graphene and nanotubes assists with heat dissipation in a graphene-nanotube junction. Forests of nanotubes grown on graphene are good at storing hydrogen, but when it comes to electronics the heptagonal molecular ring structure scatters phonons (elastic energy) and reduces the ability of heat to escape through the pillars. Through computer simulations the Rice team discovered that removing atoms from the graphene base would cause a cone to form between the nanotube and the graphene. This causes the spacing of heptagonal rings to become wider allowing heat to escape up the chimney. The scientists also discovered that the nano-chimneys acted like thermal diodes, meaning that heat travels faster in one direction than the other. 

Fractals increase graphene’s photovoltaic properties

Purdue University researchers have discovered that using a snowflake-like fractal design can increase graphene’s photovoltaic properties. They designed a graphene photodetector with gold contacts in a fractal shape. With this they demonstrated that the fractal pattern is a more efficient collector of photons than a plain gold-graphene edge. This fractal method could generate ten times more photovoltage. The researchers claim that this method is also sensitive to light of any polarization angle, is able to detect a broad band of light, and can detect light very quickly.

Graphene in fuel cells

Scientists from the University of Manchester have demonstrated that 2D materials such as graphene can be used in an operating methanol fuel cell. One of the problems with methanol fuel cells is loss of charge as methanol moves through the cell from anode to cathode, creating a short circuit. This can be stopped by using a barrier layer in addition to the membrane. They found that adding a single layer of graphene onto the membrane reduces methanol cross over while offering minimal resistance to protons, enhancing the performance of the cell by 50%. 

Antioxidant graphene

Five years ago, Rice University and Baylor University scientists created PEG-HCCs (hydrophilic carbon clusters functionalised with polyethylene glycol – or treated graphene derived from carbon nanotubes), which can help neutralise toxic molecules (oxidants) released by cells in response to an injury before they cause damage or mutations. PEG-HCCs have shown promise in the treatment of cancer. Now Rice University scientists have discovered another molecule called PEG-PDI which is functionally similar to a PEG-HCC; moreover, it shows up in X-ray crystallography. This property allows the scientists to observe the mechanics of how the molecules eliminate the oxidants in cells. PEG-PDI molecules mimic a natural enzyme that breaks down oxidants into harmless oxygen and hydrogen peroxide by pulling electrons from the oxidant.

Graphene making explosion

Kansas State University researchers have found that graphene can be made by subjecting graphite to an explosion. They took a 17-litre container containing graphite, filled it with a combination of oxygen and either acetylene or ethylene gas, and introduced a spark to create a controlled explosion. Then, the resulting soot-like graphene clumps needs to be collected.  The whole process takes a couple of minutes, and, the researchers claim is cheaper than other methods because of its low energy requirements. 

Graphene dress

A black graphene dress has been made in a collaboration between intu Trafford Centre (a shopping centre in Manchester, UK), Cute Circuit, a wearable tech company, and the University of Manchester. The dress is made of 3D printed graphene filaments printed into the hexagonal structure of graphene. The dress has a graphene sensor which captures the wearer’s breathing rate via a graphene band round the waist. A micro LED across the chest flashes in rhythm with the breathing of the wearer. 

Graphene and porphyrin working together

Porphyrin is a molecule constituent of haemoglobin and chlorophyll; now it could be useful in combination with graphene. Scientists at the Technical University of Munich have bonded porphyrin to graphene without altering the properties of either. They see the carrying function of porphyrin being useful in the fields of molecular electronics, in catalytic processes and in the development of sensors.

Graphene watch

A graphite composite mechanical watch was recently unveiled in Geneva. The result of cooperation between the University of Manchester, Richard Mille and McLaren F1, the graphite composite casing containing the delicate watch mechanism takes advantage of graphene’s light but strong properties. The total weight of the watch is 40 grams. The makers also modified the watchstrap, incorporating graphene with the intention of making it more resistant to wear and improve its mechanical properties. 

 

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