Like graphene, only from phosphorus

Scientists are actively exploring the possibility of obtaining new materials similar to graphene - consisting of a layer of matter one atom thick. Significant progress has recently been demonstrated in the production of phosphorus, a material consisting of a single layer of phosphorus atoms.
Phosphoren crystal structure
Phosphoren Crystal Structure (Credit: Han Liu et al. )

In January of this year, two independent groups, American and Chinese , were publishedwho have been able to significantly advance in the production of phosphorus. Phosphorene is obtained from the so-called black phosphorus - a layered material similar to graphite, from which graphene is obtained. Black phosphorus has been known since the 1960s, but only in 2013 began attempts to separate a separate layer from it. In the works in question, black phosphorus was purified to a thickness of two to three atomic layers. Interestingly, as with the first graphene production in 2004, a commonplace adhesive tape was used to remove extra layers.
Black phosphorus
Appearance of Black Phosphorus (Credit: Theodore W. Gray) The

production of new materials consisting of a single layer of atoms of various substances has become one of the notable trends in materials science in recent years. Scientists even dubbed this trend the "post-graphenian era."

Graphene, which is a single layer of carbon atoms, has unique properties that make it almost ideal for use in electronic devices. In particular, graphene has an extremely high electron mobility, that is, it conducts electricity well, as well as heat. The problem is that in graphene there is no so-called forbidden band - an interval of energies that the electron is forbidden to have. The presence of such a zone is highly desirable, since it is the basis of all modern semiconductor electronics, allowing you to create such critical elements as diodes and transistors.

That is why actively searching for substances with high electron mobility, and at the same time with the presence of the forbidden zone. Since the high electrical conductivity of graphene is largely associated with its two-dimensional, flat structure, new materials are also sought among those substances that are capable of forming a two-dimensional network. In July 2013, 92 candidates for such materials were found by numerical modeling , but their experimental preparation turned out to be associated with a large number of difficulties.

Like graphene, phosphorus consists of hexagons, but is not completely flat - some atoms are slightly above the plane, others are slightly lower. However, this slightly slows down the electrons compared to graphene. At the same time, phosphorus has a forbidden zone, which allows it to conduct current in different conditions, or not.
image
Another illustration of the crystal structure of phosphorus (Credit:  Likai Li et al. )

Despite the fact that it has not been possible to reach a thickness of one layer, that is, to obtain pure phosphorus, scientists are full of optimism. For example, it was shown that even in the obtained samples, the electron velocity is comparable with another candidate for “postgrafen” - molybdenum disulfide, consisting of sulfur and molybdenum atoms. Moreover, the presence in the phosphorus structure of atoms of only one substance - phosphorus - and not two, makes the new material more attractive from the point of view of ease of manufacture.

Phosphoren is not the only analog of graphene, consisting of one type of atom. Previously, it was possible to obtain monatomic silicon layers - silicene - and germanium - germanene. Both of these materials have a higher electrical conductivity than phosphorus, but, like graphene, do not have a forbidden zone. Theoretically, stan is a more interesting candidate - a monoatomic tin layer having both high electron mobility and a forbidden band, but predicted only in 2013 and so far not received by anyone.

A common problem with all the materials discussed is their instability. In air, they begin to actively oxidize and are rapidly destroyed. Special tricks, which managed to stabilize silicene in 2012, still do not yet allow the use of this material in real devices. Phosphoren should be more stable than its competitors, but its production is more complicated: to obtain a black modification of high purity phosphorus, it is necessary to place it under tremendous pressure. The process of further removing layers is also not yet optimized.

In any case, the very possibility of obtaining a two-dimensional material with a forbidden zone is attractive enough to continue research in this area, and potential commercial success promises to cover any time costs.

In preparing the text usedNature News content .

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