Tag Archives: graphene

New Graphene Sensors

While more advanced technology sectors have been late in adopting graphene, it finds plenty of interest in both lower- and high-tech applications. One of these applications is sensors based on graphene. Different industry sectors have steadily been using these sensors.

This is because graphene can be the basis of an effective sensing platform. Several interesting applications manifest this in many ways. Of these, the biosensor subsector is especially notable in attracting heavy investment. This trend is likely to continue even beyond 2022.

With graphene properties being exhaustively documented, many are now aware that they can do a lot with graphene and that many applications can benefit from its properties. Although many of these aspects are often subject to some hype, the fundamental properties of graphene make it a superior material of choice. This is primarily of account of graphene being suitable as an active sensing surface in many sensing applications.

The major advantage of graphene is its inherent thinness. This allows sensing devices made from graphene to be far more flexible and smaller in comparison to many other materials. In addition, graphene forms a very high-end active surface area.

In applications involving sensing, a high surface area is beneficial as it allows interaction with a larger range of molecules like different gases, water, biomolecules, and many other molecular stimuli. With graphene being an active surface, it is possible to attach a number of different molecular receptors and molecules to a sheet of graphene. This helps to create sensors that can detect specific molecules.

However, graphene has more advantages. Because of the high electrical conductivity of graphene, its high charge transfer properties, and high charge carrier mobility, sensors made from graphene exhibit very high sensitivity. That means, graphene sensors will generate a detectable response even from a small interaction with the environment. This happens because the excellent properties of graphene help in changing the resistivity across the graphene sheet with each small interaction. Therefore, graphene sensor help to detect even the smallest amounts of stimuli from the environment.

Because of their innate thinness, it is possible to make graphene-based sensors in small form factors, while retaining their highly sensitive sensing characteristics. It is also possible to tailor the sensors chemically for detecting a range of stimuli from the environment. This characteristic has led to the generation of much commercial interest in developing various graphene-based sensors for a variety of commercial markets involving many applications.

For instance, Paragraf has a graphene-based Hall-effect sensor that can measure changes in a magnetic field using the Hall effect. Therefore, this has increased the possibility of adding many new and interesting application areas to those that graphene sensors had not ventured into so far.

In the past year, Paragraf has demonstrated that Hall-effect sensors based on graphene are highly sensitive. They can measure currents flowing in batteries within electric vehicles for monitoring their status. Paragraf makes these sensors by depositing single layers of contamination-free graphene directly on a wafer. They repeat this following standard semiconductor manufacturing processes. This has allowed them to make several volume applications possible now, including those for fast and sensitive biosensors for detecting biomarkers within liquid samples.

The Latest Ultra-sensitive Gas Sensors

By using Graphene doped with Boron, scientists have developed ultra-sensitive gas sensors that could one day be able to detect the presence of one molecule of gas in a thousand trillion molecules of air.

Various gases, such as those produced by explosives, are specifically difficult to detect – you need extra-sensitive sensors. However, scientists are considering Graphene as being the new material for creating a stream of electronic devices, including sensitive gas detectors. Graphene has high conductivity and is useful as a gas detector as a one-atom thick, two-dimensional material.

In the Pennsylvania State University, a team of international researchers has created an amalgam from Graphene and Boron. This amalgam has the property to detect particular gases down to the level of mere parts per billion. The team is confident of ultimately making detectors sensitive enough to detect exceedingly tiny amounts of gas in the order of parts per quadrillion.

Scientists have paired Boron atoms with Graphene and created a heteroatom structure. Here, non-carbon atoms bond with carbon atoms to form part of a molecular ring. The structure acts as a sensitive sensor to detect exceptionally low concentrations of gas molecules. It can detect parts per million of Ammonia and parts per billion of Nitrogen Oxide. According to the scientists, this is equal to an ammonia detection rate of 105 times and Nitrogen Oxide sensitivity of 27 times more than what the untreated Graphene can detect.

Mauricio Terrones, a professor of physics, chemistry and materials science at the Pennsylvania State University, says they have been pursuing the project for the past four years. Although they had doped Graphene with atoms of Nitrogen earlier, doping with Boron proved much more challenging. However, once they sorted out that difficulty, they were able to synthesize the boron graphene, collaborations with experts in the US and other countries in the world confirmed their research and the properties of the material.

Graphene is essentially Carbon, while Boron is an element sitting right next to Carbon on the periodic table. That means they have similar atomic structures and therefore, should combine relatively well. However, compounds of Boron are not stable with exposed to air – they break down rapidly – making it difficult to combine the two elements when using normal Graphene production methods.

Researchers overcame this by using a special technique called chemical vapor deposition assisted with a bubbler. This method isolates the atmospheric boron when incorporating the element with the Graphene. The process produces sheets of Boron-doped Graphene of size equal to one-square centimeter.

They then transferred the sheets to the Honda Research Institute USA in Columbia, OH. Here, they compared the performance of the sheets with the performance of known highly sensitive gas sensors. Scientists at the Novoselov lab at the University of Manchester, UK examined the electron transport function of the sensors. Simultaneously, contributing researchers in Belgium and the US established the meld of Boron atoms within the Graphite lattice and studied the influence of their interaction and influence with Nitrogen Oxide or Ammonia.

According to Dr. Avetik Harutyunyan, the Chief Scientist and project leader at the Honda Research Institute USA Inc., this multidisciplinary research offers new avenues for further exploring ultrasensitive gas sensors.

Phosphorene Challenges Graphene as a Semiconductor

Though silicon has been the basis of semi-conductors for decades, it is facing stiff competition from other materials that promise to deliver several extras to consumers who like to enjoy more flexibility with their gadgets.

For some time, graphene, a one atom thick allotrope of carbon has been under consideration for use in electronic devices because its thin structure allows electrons to travel across it much more rapidly than they would do across silicon. However, graphene has severe limitations, as its conductivity is a little too high to be of much use in electronic devices, which need semi-conductors or materials with medium levels of conductivity. Another newly developed material dubbed phosphorene, which can form identical thin layers and is a semiconductor as well, offers a wider scope in electronics.

Phosphorene particulars

Scientists at the Technical University of Munich (TUM) have prepared a semiconducting material with black phosphorus in which a few phosphorus atoms have been swapped by arsenic atoms. Replacement of the phosphorus atoms with arsenic has caused the band gap to reduce to 0.15eV, which makes the material an effective semiconductor.

Phosphorene or black arsenic phosphorus can form very thin layers like graphene. Unlike silicon, which is hard and brittle, phosphorene is easy to manipulate into different kinds of structures and shapes. This makes possible a great range of electronic devices with considerable mechanical flexibility.

Scientists at TUM have built on technology that allows the fabrication of phosphorene with the application of high pressure. This reduces the production costs considerably. The research workers have been able to fine-tune the band gap exactly according to specific requirements by tweaking the arsenic concentration. According to Tom Nilges, who is heading the research team at TUM this has enabled them to produce a wide range of materials with diverse electronic properties that were not possible earlier.

Field Effect Transistors

American scientists from Yale University and the University of Southern California (USC) have collaborated with the researchers at TUM to build devices like field effect transistors with phosphorene. A group headed by Dr. Liu and Professor Zhou of the Electrical Engineering Department at USC has studied the transistor characteristics.

Infrared Detectors

Further exploration of the material by the scientists revealed that the material when heavily doped with arsenic could be used for infrared detection. For instance, when the arsenic concentration is as high as 83%, the band gap in phosphorene is about 0.15eV. This fact makes it an effective sensor for infrared rays of long wavelengths. Researchers expect that the new substance can be effectively used as Light Detection and Ranging (LIDAR) sensors, which find use in applications for tracing dust particles and pollutants in the atmosphere and as distance sensors in vehicles.

Anisotropic behavior

Another noteworthy feature of phosphorene is its anisotropic nature. Electronic and optical properties of the material were studied using ultra-thin films in two mutually perpendicular, x- and y-axes. It was observed that the properties were different in the two directions.

Phophorene has an edge over other newly discovered thin-layered semiconductors because it is very easy to peel off layers from a parent black phosphorus crystal.

Graphene Metal Sandwich Improves Electronics

Heat conducting properties of the metal Copper are well known. However, scientists have been able to improve this property even further. By creating a sandwich of graphene with copper, scientists have found that the heat conducting properties of copper are strongly enhanced. Expectedly, this discovery could lead to further downscaling of electronic products.

This pioneering discovery is the work of two professors – Alexander A. Balandin and Konstantin S. Novoselov. Balandin is a professor of electrical engineering at the Bourns College of Engineering at the University of California, Riverside. Novoselov is a professor of physics at the University of Manchester in the United Kingdom. Both are corresponding authors for the paper they have published in the journal Nano Letters.

In their experiments, the researchers added a one-atom thick graphene layer on both sides of a copper film. The graphene layer had highly desirable mechanical, thermal and electrical properties. The researchers found that the addition of graphene layers on the two sides of the copper film increased the heat conducting properties of the sandwich by up to 24 percent.

According to Balandin, who initially discovered the unusual heat conducting properties of graphene in 2013, the enhancement of the ability of copper to conduct heat was an important discovery. Hybrid copper-graphene interconnects in electronic chips could now be made much smaller.

Copper is the most popular metal used for semiconductor interconnects and it replaced aluminum because of its better electrical conductivity. Layering copper with graphene and increasing the heat conducting properties of copper, therefore, became an important factor for the electronic industry.

Manufacturers tend to downscale the size of interconnects and transistors in computer chips with the intention of increasing the number of transistors therein. This puts an enormous strain on the performance of the copper interconnects they use. Downscaling had reached a point where there is little room for further improvement. Therefore, manufacturers were actively seeking improved interconnect structures with better conduction properties for current and heat.

Initially, even the researchers were surprised at the significant improvement in the thermal conduction properties of copper film despite the thickness of the graphene coating being only one atom thick. However, they soon realized that the improvement was not from the graphene acting as an additional heat-conducting channel. Rather, the improvement came about as changes occurred in the copper’s Nano- and microstructure because of the graphene layer deposition.

Researchers used microscopes to examine the grain sizes within the copper film both before and after adding graphene. They found that the high temperature deposition of graphene, in vapor form, stimulated the growth of grain sizes in the copper film. Ultimately, it was found the larger grain sizes in the copper coated with graphene that caused the improvement in heat conduction.

Another finding of the research was the improvement in heat conduction of copper was limited to thin copper films alone. This is a significant find since the future copper interconnects will be scaling down to the nanometers range. A nanometer is one-thousandth of a micrometer. Balandin and his team will be researching the heat conduction properties in copper films of nanometer thickness coated with graphene.