[ad_1]
Until recently, the existence of "blue phosphor" was a pure theory.
Now, a team from the Helmholtz-Zentrum Berlin has been able to examine blue phosphorus samples for the first time at BESSY II and confirm by mapping the structure of their electronic band that this is the modification of the exotic phosphorus. .
Blue phosphorus is an interesting candidate for new optoelectronic devices.
The results were published in Nano Letters.
The phosphorus element can exist in various allotropes and modifies its properties with each new form. Until now, red, purple, white and black phosphors were known.
Some phosphorus compounds are essential for life, but white phosphorus is a flammable poison and black phosphorus, on the other hand, is particularly robust.
Another allotrope has now been identified: in 2014, a team from Michigan State University performed calculations on a model to predict that "blue phosphorus" should also be stable.
In this form, the phosphorus atoms form a honeycomb structure similar to graphene, but not completely flat but regularly "deformed".
Model calculations showed that blue phosphorus was not a narrow-band semiconductor like black phosphorus but possessed the properties of a semiconductor with a fairly large band gap of two electron-volts .
This large difference, seven times greater than that of black phosphorus in bulk, is important for optoelectronic applications.
In 2016, blue phosphorus was successfully stabilized on a gold substrate by evaporation. Nevertheless, we only know with certainty that the resulting material is blue phosphorus.
To this end, a team from the Helmholtz-Zentrum Berlin around Evangelos Golias probed the electronic tape structure of the BESSY II material. They were able to measure by angular resolution photoelectron spectroscopy the distribution of electrons in its valence band, by fixing the lower limit of the forbidden band of blue phosphorus.
They discovered that the phosphorus atoms did not organize independently of the gold substrate but tried to adjust to the spacings of the Au atoms. This deforms the honeycomb network regularly, which affects the behavior of electrons in blue phosphorus.
As a result, the top of the valence band that defines one of the ends of the semiconductor band gap is in agreement with the theoretical predictions of its energetic position, but it is somewhat shifted.
"Until now, researchers have mostly used loose black phosphorus to exfoliate atomically thin layers," says Professor Oliver Rader, head of the HZB department of the Materials Department for Green Spintronics.
"These also have a large semiconductor band gap, but do not have the honeycomb structure of blue phosphorus and can not be grown directly on a substrate." Our work not only reveals all the properties highlights the impact of the support substrate on the behavior of electrons in blue phosphorus, an essential parameter for any optoelectronic application. "
Source: Helmholtz-Zentrum Berlin
[ad_2]
Source link
