The element phosphorus can exist in various allotropes and changes its properties with each new form. So far, red, violet, white and black phosphorus have been known. While some phosphorus compounds are essential for life, white phosphorus is poisonous and inflammable and black phosphorus - on the contrary - particularly robust. Now, another allotrope has been identified: In 2014, a team from Michigan State University, USA, performed model calculations to predict that "blue phosphorus" should be also stable.
In this form, the phosphorus atoms arrange in a honeycomb structure similar to graphene, however, not completely flat but regularly "buckled".
Model calculations showed that blue phosphorus is not a narrow gap semiconductor like black phosphorus in the bulk but possesses the properties of a semiconductor with a rather large band gap of 2 electron volts. This large gap, which is seven times larger than in bulk black phosphorus, is important for optoelectronic applications.
Blue P examined at BESSY II
In 2016, blue phosphorus was successfully stabilized on a gold substrate by evaporation. Nevertheless, only now we know for certain that the resulting material is indeed blue phosphorus. To this end, a team from HZB around Evangelos Golias has probed the electronic band structure of the material at BESSY II.
They were able to measure by angle-resolved photoelectron spectroscopy the distribution of electrons in its valence band, setting the lower limit for the band gap of blue phosphorus.
Band structure influenced by the substrate
They found that the P atoms do not arrange independently of the gold substrate but try to adjust to the spacings of the Au atoms. This distorts the corrugated honeycomb lattice in a regular manner which in turn affects the behavior of electrons in blue phosphorus.
As a result, the top of the valence band that defines the one end of the semiconducting band gap agrees with the theoretical predictions about its energy position but is somewhat shifted.
Outlook: optoelectronic applications
"So far, researchers have mainly used bulk black phosphorus to exfoliate atomically thin layers", Prof. Oliver Rader, head of HZB-Department Materials for green spintronics explains. "These also show a large semiconducting band gap but do not possess the honeycomb structure of blue phosphorus and, above all, cannot be grown directly on a substrate.
Our work not only reveals all the material properties of this novel two-dimensional phosphorus allotrope but highlights the impact of the supporting substrate on the behavior of electrons in blue phosphorus, an essential parameter for any optoelectronic application."
Antonia Rötger | EurekAlert!
Tel Aviv University-led team discovers new way supermassive black holes are 'fed'
15.01.2019 | American Friends of Tel Aviv University
Arbitrary quantum channel simulation for a superconducting qubit
14.01.2019 | Science China Press
Cellulose obtained from wood has amazing material properties. Empa researchers are now equipping the biodegradable material with additional functionalities to produce implants for cartilage diseases using 3D printing.
It all starts with an ear. Empa researcher Michael Hausmann removes the object shaped like a human ear from the 3D printer and explains:
The phenomenon of so-called superlubricity is known, but so far the explanation at the atomic level has been missing: for example, how does extremely low friction occur in bearings? Researchers from the Fraunhofer Institutes IWM and IWS jointly deciphered a universal mechanism of superlubricity for certain diamond-like carbon layers in combination with organic lubricants. Based on this knowledge, it is now possible to formulate design rules for supra lubricating layer-lubricant combinations. The results are presented in an article in Nature Communications, volume 10.
One of the most important prerequisites for sustainable and environmentally friendly mobility is minimizing friction. Research and industry have been dedicated...
Just in time for Christmas, a Mars-analogue mission in Morocco, coordinated by the Robotics Innovation Center of the German Research Center for Artificial Intelligence (DFKI) as part of the SRC project FACILITATORS, has been successfully completed. SRC, the Strategic Research Cluster on Space Robotics Technologies, is a program of the European Union to support research and development in space technologies. From mid-November to mid-December 2018, a team of more than 30 scientists from 11 countries tested technologies for future exploration of Mars and Moon in the desert of the Maghreb state.
Close to the border with Algeria, the Erfoud region in Morocco – known to tourists for its impressive sand dunes – offered ideal conditions for the four-week...
Research opens doors in photonic quantum information processing, optical signal processing and microwave photonics
Researchers from the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) have developed a new integrated photonics platform that can...
A team of experimentalists at the U.S. Department of Energy's Ames Laboratory and theoreticians at University of Alabama Birmingham discovered a remarkably long-lived new state of matter in an iron pnictide superconductor, which reveals a laser-induced formation of collective behaviors that compete with superconductivity.
"Superconductivity is a strange state of matter, in which the pairing of electrons makes them move faster," said Jigang Wang, Ames Laboratory physicist and...
14.01.2019 | Event News
12.12.2018 | Event News
10.12.2018 | Event News
15.01.2019 | Life Sciences
15.01.2019 | Information Technology
15.01.2019 | Materials Sciences