Graphene sensors: introduction and market status - Page 45

Researchers at the University of Wisconsin-Madison have discovered a way of growing graphene nanoribbons with desirable semiconducting properties directly on a conventional germanium semiconductor wafer. This finding may allow manufacturers to easily use graphene nanoribbons in hybrid integrated circuits, which promise to deliver a major boost to the performance of next-gen electronic devices. This technology could also have specific uses in industrial and military applications, such as sensors that detect specific chemical and biological species and photonic devices that manipulate light.

The technique for producing graphene nanoribbons is said to be scalable and compatible with the prevailing infrastructure used in semiconductor processing - nanoribbons that can be grown directly on the surface of a semiconductor like germanium are more compatible with planar processing used in the semiconductor industry, and so would pose less of a barrier to integrating these materials into electronics in the future.

Researchers from the EPFL in Switzerland have created the first perovskite nanowire-graphene hybrid phototransistors. Even at room temperature, the devices are highly sensitive to light, making them outstanding photodetectors. 

Perovskites are known for their efficient capability of turning light into electricity, which is why they are attracting massive interest in the solar field. The scientists microengineered nanowires out of the perovskite methylammonium lead iodide, in an intricate method that was developed in 2014 and called slip-coating method. The advantage of nanowires is their consistency, while their manufacturing can be controlled to modify their architecture and explore different designs. 

Researchers at the University of Aveiro, Portugal, the Institute of Natural Sciences, Russia and the Instituto de Fisica, Brazil observed a strong piezoelectric activity of single-layer graphene (SLG) deposited on Si/SiO2calibration grating substrates. The scientists perceive the piezoelectric effect to be strong enough to enable future applications like graphene-based actuators, sensors and other electronic components based on the direct and converse piezoelectric effects.  

The researchers performed an experimental study of single-layer graphene (SLG) deposited on SiO2 calibration grating substrates by piezoresponse force microscopy (PFM) and confocal Raman spectroscopy. Piezoelectric activity was mainly observed on the supported graphene regions where van der Waals and/or chemical interaction between the SiO2 surface and graphene layer can induce an anisotropic strain and detectable PFM signal. The piezoelectric activity in the graphene layers was attributed to the chemical interaction of graphene atoms with underlying oxygen from SiO2 substrate. Piezoelectric effect was found to be relatively high, more than twice that of the best piezoelectric ceramics such as modified lead zirconate titanate.

Researchers at EPFL's Bionanophotonic Systems Laboratory (BIOS) together with researchers from the Institute of Photonic Sciences (ICFO, Spain) have harnessed graphene's unique optical and electronic properties to develop a reconfigurable and highly sensitive sensor that detects molecules like proteins and drugs.

The researchers used graphene to improve on a well-known molecule-detection method: infrared absorption spectroscopy. In that method, light is used to excite the molecules, which vibrate differently depending on their nature. The specific vibration means the molecules reveal their presence and even their identity. This "signature" can be "read" in the reflected light. This, however, is not an efficient method for the detection of nanomolecules. The wavelength of the infrared photon directed at a molecule is around 6 microns (6,000 nanometres - 0.006 millimeters), while the target measures only a few nanometres (about 0.000001 mm).

A recent IDTechEx research predicts that the graphene market will reach nearly $200 million by 2026, with the estimation that the largest sectors will be composites, energy applications and graphene coatings.

Graphene inks are said to be constantly improving (while their prices seem to be dropping), which might promote, among others, applications like sensor electrodes and smart packaging. In the transparent conductive film industry, however, it is estimated that graphene will not be able to compete with ITO films.

Researchers at VIT University, India demonstrated the application of conjugated polymer/Graphene oxide nanocomposite for thermistor applications. The study resulted in a thermistor that boasted excellent performance, suitable for electronics and sensors. A thermistor is a type of resistor whose resistance is dependent on temperature, more so than in standard resistors.

Interestingly, the study showed that lower amounts of graphene oxide (0.5, 1%) loading exhibited positive temperature coefficient, and higher loading (1.5, 2%) yielded negative temperature coefficient.

A collaboration between Bosch, the Germany-based engineering giant, and scientists at the Max-Planck Institute for Solid State Research yielded fascinating results, shown in a presentation during Graphene Week 2015. The researchers jointly created a graphene-based magnetic sensor 100 times more sensitive than an equivalent device based on silicon.

The research team used hexagonal boron nitride as substrate for the magnetic sensor, which is based on the Hall effect (a magnetic field that induces a Lorentz force on moving electric charge carriers, leading to deflection and a measurable Hall voltage). Graphene's high carrier mobility makes it useful in sensing applications, and the results achieved by the Bosch-led team confirm this. The presentation displaying the team's results showed that the worst case graphene scenarios roughly match a silicon equivalent. In the best case scenario, the result is a huge improvement over silicon, with much lower source current and power requirements for a given Hall sensitivity. In short, graphene provides for a high-performance magnetic sensor with low power and footprint requirements.

Researchers from the University of Exeter have designed a new method to produce graphene significantly cheaper and easier than previously production methods. The researchers claim that this high-quality, low cost graphene could pave the way for the development of the first truly flexible 'electronic skin', that could be used in robots.

The new method grows graphene in an industrial cold wall CVD system, a state-of-the-art piece of equipment recently developed by UK graphene company Moorfield. This nanoCVD system is based on a concept already used for other manufacturing purposes in the semiconductor industry. This new technique is said to grow graphene 100 times faster than conventional methods, reduce costs by 99% and have enhanced electronic quality. The research team used this new technique to create the first transparent and flexible touch-sensor that could enable the development of artificial skin for use in robot manufacturing as well as flexible electronics. 

A team of scientists from the HZB Institute for Silicon Photovoltaics in Germany managed to increase the selectivity of graphene to various molecules in order to make more efficient sensors. The scientists were successful in electrochemically activating graphene and preparing it to host molecules that act as selective binding sites.

For this task, para-maleimidophenyl groups from an organic solution were grafted to the surface of the graphene. These organic molecules act as mounting brackets to which the selective detector molecules can be attached in the next step of the process. The attched graphene can then be employed for detecting various substances with a precise matching mechanism, similar to a "lock and key" paradigm. The "lock" molecules on the surface are highly selective and only absorb the matching "key" molecules.

Researchers from the University of Illinois at Urbana-Champaign have developed a new approach for forming 3D shapes from flat sheets of graphene. This technique may open the door to future integrated systems of graphene-MEMS hybrid devices and flexible electronics.

The study demonstrated graphene integration to a variety of different microstructured geometries, including pyramids, pillars, domes, inverted pyramids, and the 3D integration of gold nanoparticles (AuNPs)/graphene hybrid structures. The flexibility and 3D nature of the structures could enable biosensing devices which can be made in various shapes and carry many biological functions. The scientists also expect that the new 3D integration approach will facilitate advanced classes of hybrid devices between microelectromechanical systems (MEMS) and 2D materials for sensing and actuation.