Paper of the Month — March

   Atomic Force Microscopy image of black phosphorous. (Image from Su & Zhang, 2015).


Atomic Force Microscopy image of black phosphorous. (Image from Su & Zhang, 2015).

March’s ‘Paper of the Month’ comes from Dr Yong Zhang and Dr Liqin Su at the University of North Carolina Charlotte (UNCC).

They have used the Linkam high temperature TS1500 stage to conduct research on the properties of emerging 2D materials. 2D materials – a category which includes the widely publicised graphene – have been studied extensively in recent years, due to their potential for application in novel electronic and optoelectronic devices.

Graphene, a layered form of carbon atoms, is extremely thin and has many remarkable properties: as well as being incredibly strong and flexible, graphene is an excellent conductor of heat and electricity. Graphene’s downfall however is its inability to shut off conductivity completely.

As a result, scientists have been seeking alternative 2D materials with large band gaps, such as molybdenum disulphide (MoS2), tungsten disulphide (WS2), copper zinc tin selenide (CZT Se), and black phosphorous.

Black phosphorous is a particularly promising material due to its layer-dependant band gap, meaning it can function as a semi-conductor – essentially, it can be switched on and off. Its application in new nanotechnologies could give rise to a range of high performance microprocessors, transistors, lasers, solar cells and more.

In their paper “Temperature coefficients of phonon frequencies and thermal conductivity in black phosphorous layers” (Applied Physics Letters, 2015), Zhang and Su investigate the vibrational properties and electron-phonon interactions of black phosphorous, as well as how epitaxial or supporting substrates can impact the properties of a 2D material which is often presumed to have weak bonding with the substrate.

It is essential to understand these properties if black phosphorous is going to be successfully utilised in electronic and optoelectronic devices.

This work further demonstrates that high temperature Raman spectroscopy is an efficient technique for probing the 2D film/substrate interaction for a broad range of 2D materials, including graphene and transition metal dichalcogenides, as reported in another paper of Zhang’s group “Effects of substrate type and material-substrate bonding on high-temperature behaviour of monolayer WS2” (Nano Research, 2015).

The Linkam TS1500 stage allows them to investigate a thermal activation process that requires high temperatures, as well as the thermal stability under different conditions. 

Su, L. & Zhang, Y. (2015). Temperature Coefficients of Phonon Frequencies & Thermal Conductivity in Thin Black Phosphorous Layers. Applied Physics Letters 107(7)