BLACK phosphorus:the NEW graphene?

Materials World Magazine,3 OctLink:http://www.iom3.org/materials-world-magazine/news/2015/oct/03/black-phosphorus-new-graphene

Black phosphorus is coming-prominence in the field of 2D materials, as Simon Frost reports.

A team at Pohang University of the Science and Technology (Postech), South Korea, have formed a tuneable band gap in T He 2D material black phosphorus (BP) that could make it suitable for flexible electronic and optoelectronic devices.

BP is made by heating red phosphorus–the material used for the head of a match–at high pressure. In its single layer form it is known as Phosphorene, and is arranged in a honeycomb atomic structure similar to that of GR Aphene.

But there is a key difference between the Materials–while BP have a natural band gap, graphene, in its pristine St Ate, has a band gap of zero. Postech Professor Keun Su Kim, explains, ' Because of this, one can flow current in graphene very efficiently, but it is ex tremely difficult to switch off this conduction. ' This inflexibility makes graphene a difficult candidate for semiconducting materials, which require their conductivity to is switched on or off. ' Researchers has tried to open a band gap in graphene, and so far it turns off to being difficult without degrading the mate Rial ' s quality ', says Kim.

Antonios Oikonomou, Associate at the University of Manchester's national graphene Institute, UK, says of graphene ' s band gap Issue, ' Indeed, pristine graphene faces challenges in it application in digital electronics (logic transistor s) due to its zero band gap. This was responsible for the low on/off Non-zero off state drain current in graphene field-effect transistors, which leads To considerable power dissipation. '

But Graphene's band gap issue, he says, does not make it as unworkable as one might think. ' Over the past years, a number of band gap engineering strategies has been explored successfully, such as quantum confine ment (graphene nanoribbons and graphene quantum dots), substrate-induced band gap, molecular doping/charge transfer method s and selective chemical functionalisation. '

Inspired by graphene

Professor Kim's team had another idea for creating a highly conductive material this could work as a semiconductor. ' The alternative approach to this problem are to start with a 2D semiconductor with a natural band gap and then modify its Properties similar to that of graphene. '

The team opted for black phosphorus. ' The honeycomb structure of black Phosophorus is regularly puckered. This makes it highly susceptible to external perturbations such as strain and electric field. We deposited potassium atoms on the surface of black phosphorus to induce a strong electric field nearby, and this applied Electric field changed the distribution of electrons. ' When the band gap approached zero, the researchers observed Dirac semimetal state–the unique quantum state of matter Res Ponsible for graphene's high conductivity–and therefore achieved a tuneable band gap in black phosphorus. ' This means so one can induce the important properties of graphene into another 2D material that's more flexible, ' says Kim.

Rise in Patents

While researchers is now inducing the properties of graphene in other 2D materials, graphene remains the popular leade R in the field. The number of international patent applications involving graphene published by the World Intellectual Property Organizati On have risen from 2005 to 4,051 in 2014. Nick Braddon, a patent attorney specialising in materials science and metallurgy for Barker Brettell, UK, says, ' the appli Cations for graphene that is attracting the most significant R/R interest appear to being in the fields of semiconductor Devices, electric solid state devices and processes or means–for example, betteries, for the direct conversion of Chemi Cal Energy to electrical energy. Perhaps, therefore, we can expect to see graphene and other 2D materials being used in these technology areas before long. '

But Braddon also notes that graphene's popularity may has somewhat skewed the figures relating to patents. ' The ongoing interest in graphene as a ' wonder material ' could have made it something of a buzzword, which would have been in Cluded in some patent applications as a possible (potentially speculative) variation of a invention, as opposed to Graphe NE being at the core of the invention. '

A surge ahead?

of wide reports that the Postech-signals a ' surge ahead ' of graphene by BP, Oikonomou says, ' I-would like to s Tress that there are no competition but rather and different opportunities. Both graphene and Phosphorene derive from the family of layered materials–some people even speak of different ones. All of these materials, and their 2D allotropes, could enable a new approach to an application's design process by Combini Ng their unique properties through heterostructures. ' This approach was being used to control BP's high reactivity with oxygen by researchers at the Hong Kong University of Scie NCE and Technology by sandwiching Few-layer BP between sheets of hexagonal boron nitride.

Several institutions is now turning to Phosphorene, which is first synthesised in, pursuit of the next genera tion of semiconductors. In Canada, a joint study by McGill University and universitéde Montréal observed that electrons move in only the Dimensio NS in a phosphorus transistor, making them especially efficient. Researchers at the Technical University of Munich and University of Regensburg, Germany, and University of South Californi A and Yale University, USA, with been synthesising black arsenic phosphorus for field effect transistors. Adjusting the concentration of arsenic atoms replacing phosphorus, they were able to tune the material ' s band gap–with A n Arsenic concentration of 83%, for example, their band gap of 0.15 electron volts makes it suitable for application in Sens ORS that can detect long wavelength infrared radiation, such as distance sensors in cars.

' It may take more than five to ten years to commercialise, ' says Kim. ' There is certainly still many obstacles to overcome–for example, we need to realise the tuneable band gap in a real GA Ted device. But it isn't an innovation if one can easily imagine it. '

BLACK phosphorus:the NEW graphene?