Graphene Tech Digest - December 2016

New method to manufacture graphene devices

Engineers at the University of Exeter’s Centre for Graphene Science have developed a new way to manufacture nanoscale graphene devices directly onto a copper substrate during graphene manufacture. This is achieved through a plasma activation (a processing technology to modify the properties of a surface) and lithographic patterning (used to etch a circuit or structure onto the graphene). After this the device can be applied to another substrate. 
The team claim that this simplifies the manufacturing process significantly. They demonstrated their method by making a humidity sensor that outperforms a conventional commercial sensor. 

G-Putty

Researchers at Trinity College Dublin have created a material called ‘G-putty’ – the result of adding graphene to silly putty. The researchers observed that, ‘the electrical resistance of G-putty is very sensitive to deformation and impact.’ When the researchers used the putty to measure breathing, pulse and blood pressure, they discovered that it is far more sensitive to strain and pressure than normal sensors. It is reportedly also able to work as an impact sensor – being able to detect the footsteps of a spider. 

Made from 99.9% cotton, 0.1% graphene ink

Researchers at the Cambridge Graphene Institute at the University of Cambridge, in collaboration with Jiangnan University, China, have realised a method to apply graphene based inks onto cotton, and demonstrated a wearable motion sensor using the method. An ink made of graphene oxide flakes was applied to the cotton and then heat treated to improve conductivity (graphene oxide flakes are more adhesive to cotton than untreated graphene). This graphene ink is flexible. Showing little functional damage after 400 bends, it was able to still act as a strain sensor. It is washable, showing little resistance increase after ten wash cycles. The team also claim it is cost effective and environmentally friendly, with potential for easy scalability. 

Gas detecting graphene 

Fujitsu Laboratories, a subsidiary of Fujitsu focusing on R&D (research and development), has announced its new gas sensor, which takes advantage of graphene. In its sensor the gate part of a silicon transistor is replaced by graphene to which gas molecules can adhere, allowing gas detection. According to Fujitsu, this has resulted in a tenfold increase in detection ability of nitrogen dioxide. Fujitsu see this being used to provide real-time air quality measurements substantially quicker than existing sensor technology. They claim graphene-based sensors have the potential to be far more sensitive and adept at detecting certain types of gas than other commercially available sensors. Currently the sensor can only detect nitrogen dioxide and ammonia. 
Fujitsu plans to develop a portable sensor which would enable detection of lifestyle diseases through analysis of ammonia in a person’s breath. It also plans to increase the detector’s gas sensing abilities by testing graphene in combination with other molecules.

Colourful graphene for low-power colour screens

Researchers from TU Delft and Graphenea in Spain can create colour changing mechanical pixels from balloon-like structures. The pixels are circular indents cut into silicon and covered by a double layer of graphene. The graphene acts as a lid to enclose the air in the indents. The researchers noticed that the structure created colours which would change over time. This colour change is the result of graphene warping caused by the air pressure difference between the cavity and the outside air. If the graphene was pulled into the cavity, the light appeared as blue, if it was pushed up and out of the cavity, the light appeared red. By manually mimicking this process the colour can be continuously and reliably changed. The team see applications for this technology in low power graphic displays like e-reader screens. They hope to have a screen prototype built by Mobile World Conference 2017. 

Huawei’s graphene-assisted li-ion battery

Huawei has announced results of research on a graphene-assisted lithium-ion battery. Huawei’s research shows that the battery is able to withstand temperatures of up to 60°C, with a lifespan twice as long as conventional li-ion batteries – up to four years. Huawei said this was achieved through adding an electrolyte that can remove trace water and prevent electrolyte decomposition; using a modified large-crystal lithium nickel manganese cobalt oxide cathode; and then exploiting graphene’s ability to more efficiently cool the battery than other common li-ion battery cooling materials. They see the battery technology being used in electric vehicles (especially in hot countries) and drones (which often produce large amounts of heat).

Graphene can handle unexpectedly high current density

An international research team led by Professor Fritz Aumayr from the Institute of Applied Physics at TU Wien has discovered that graphene has extremely high electron mobility. As a highly-charged xenon ion shoots towards a sheet of single layer graphene, due to its highly charged electrical field it begins taking electrons from the graphene. After the ion passes through the sheet the sheet has a positive charge of less than ten electrons compared to a starting charge of 30. Consequent to the loss of electrons the atoms surrounding the hole become positively charged and should repel each other causing the hole to widen. However, this doesn’t happen. The graphene can replace the missing electrons within several femtoseconds (quadrillionths of a second). The rush of electrons from other areas of the sheet to the puncture spot creates currents 1000 times higher than the graphene would usually be able to withstand. The scientists believe that this property could be exploited for use in optics ultra-fast electronics in the future.

Graphene OLED demonstrated

Fraunhofer FEP, a partner in the EU (European union) funded GLADIATOR (Graphene Layers: Production, Characterization and Integration) project, has produced OLED (organic light emitting diode) electrodes from graphene. (The electrodes sandwich an organic semiconductor that emits light in response to a current). The team believes that the first products could be launched within two to three years. They argue that OLEDs would be a suitable for touch screens as they do not break when dropped.

Medical uses for graphene

Below are three recent stories about graphene in medical use.
Researchers at Lawrence Berkeley National Laboratory and UC Berkeley, have discovered that graphene’s sensitivity to microvolt (millionth of a volt) level electrical activity can be recorded. The level of voltage that heart and nerve cell networks work on is in the microvolt level. The team’s CAGE (critically coupled waveguide-amplified graphene electric field imaging device) platform’s integration of graphene enables them to read an electrical signal as a visual image that shows the strength and location on the graphene of the signal. They plan to test the platform on living heart cells.

A team of scientists from Harvard University have successfully used nanoscale graphene field-effect transistor (FET) sensors to detect molecules in high-ionic-strength solutions (conditions which would be faced in the human body). FETs are transistors that, among other functions, can amplify weak signals e.g. a wireless signal.  Nanomaterial-based FET sensors can provide high sensitivity and spatial resolution for chemical and biological detection, however they suffer from the Debye screening effect (lack of clarity in electrical signal, resulting from interference) when in high-ionic-strength conditions. The team discovered that this effect can be reduced by applying a layer of bio-molecule permeable polymers to the surface of the graphene FET sensors. They see these coated FETs having applications in healthcare and physiological research.

Scientists at the University of Illinois at Chicago have discovered that graphene is able to detect cancer cells. In an experiment, they took mice astrocytes (glial braincells) and placed them onto a graphene sheet which detected the cancerous cell. This works because the cancerous cells have higher levels of activity than normal cells. The electric field surrounding the hyperactive cell displaces electrons in graphene’s electron cloud. This causes distinctive changes in the graphene’s carbon atoms’ vibration energy. The vibration intensity can be mapped and cell differences highlighted. 

 

 

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