Watch out Graphene MOS is here

In the public eye Graphene seems to be the mascot for a whole world of 2 Dimensional materials, this ‘wonder’ material gained notoriety in the scientific community in 2004 when a research group at Manchester decided to pull apart what is basically pencil graphite with cellotape. This sparked an upsurge in research on graphene, but it wasn't until 2010 where Geim and Nosolev were awarded the Nobel Prize in Physics for its discovery, thus attracting more media attention. So that was just a little back story of why people have heard of this magical material, which could pave the way for a future of touch screen phones (that are supposed to bend). I won’t go too much into the details of what graphene is, and what it can do, save for saying it is a sheet of carbon atoms arranged in hexagonal pattern, but most amazingly it is merely one atom thick.

However, it’s not just graphene that’s one atom thick, there are a whole host of other materials that can be made into monolayer sheets, such as Silicene, Germanene, Boron Nitride and what this article is about; Molybdenum Di-Sulphide (MoS2).

In their publication in Nanoscale, Dr K. Huang and his team from the ORC have synthesised large scale flakes of MoS2. This is a huge advance in materials science, as previously, production was random and led to unpredictable small flakes, not really useful when this material wants to contend with graphene. To find out more I went to find Dr Huang, and asked him some questions about this material.

1) Can you describe what MoS2 is, and how it differs from other layered materials, like graphene?

Transition metal dichalcogenides (TMDCs), two-dimensional layered materials, such as MoS2, have become a noteworthy complimentary material to graphene sharing many of its properties. They offer properties that are unattainable in graphene, in particular providing a tuneable bandgap of ~1.8 eV transition from indirect to direct within the single layer.

3) Can you detail your work specifically on MoS2, you produce larger surface areas of this material, compared to flakes previously produced. This obviously makes it more desirable in production now, so what's the future of this, could it lead to a mono-layer revolution against graphene?

The major challenge is producing single atomic layers of MoS2.  Most researchers start with bulk MoS2 and then exfoliate and remove layers until they end with one.  This technique results in material in the form of flakes, typically only a few hundred square microns in area. The current challenge in the fabrication of MoS2 thin films is to form an industrially scalable and controllable deposition methodology which makes uniform thin films suitable for integration into optoelectronic devices. Unlike others who make MoS2 flakes, we are able to fabricate large sheets of MoS2 by chemical vapour deposition which grows the films from the bottom up.  Our technique also has the advantage of deposition at room temperature which is compatible with the conventional photolithography process.

MoS2 is a n-type semiconductor and it works perfectly with other p-type 2D materials such as WS2, WSe2. It addition, they could work alongside with graphene for 2D heterostructures.

2) Can you detail potential applications?

MoS2 is emerging for electronic applications in the transistor channel and graphene as contact electrodes and circuit interconnects. These high-performance large-scale devices and circuits based on this 2D heterostructure pave the way for practical flexible transparent electronics. In addition, MoS2 is being used as photodetectors, electroluminescent and biosensing devices too. 

In summary, Dr. Huang and his group have produced large sheets Molybdenum Di-Sulphide, through CVD (chemical vapour deposition) allowing them to grow sheets of this material of any size, and be able to tune its electronic properties. This has massive potential in industry (and research) for applications in nano-electronics. I'm fairly confident we’ll be reaping the benefits of research by Dr Huang and others in similar fields of research within the next couple of years.

Three Minute Thesis

So I found this on you tube, it's my 3MT presentation at the University of Southampton.

I talk about nano-scale devices and give some indication as to how small things are.

The Sound of Physics - Raman Spectroscopy

So funnily enough my PhD is in Raman spectroscopy and currently I'm in Jena at a conference on Raman Spectroscopy, so not too many brain cells were stretched when my first blog post is on Raman Spectorscopy.
If you ask anyone here at the conference explain Raman, they'll probably say something similar to me along the lines of
"Measurement of low energy excitations of molecular or crystalline systems, most commonly vibrational modes, by use of ineleastic scattering of light."
But that doesn't really help when explaining to someone who has no idea what any of that means, namely people with out a degree in physics. So how do I go about demystifying this and explaining the concept.

Well first off I'm going to say what Raman Spectroscopy does for us. As I'm sitting here I gather a real appreciation for the scale of the field, the technique is used widely in physics for looking at the structure of crystals, but also spans to biomedical research to characterise drugs and understand how the skin absorbs things.
So what is it?
Well Raman is a tool, a tool to look at the structure of things, everything essentially has a unique Raman fingerprint and using this technique we can identify the compositions and structure of a sample by understanding this finger print.

Let me elaborate on this thought, as I sit here tapping my finger on the wooden table I hear a sound, this is the result of my imparting energy to the table, energy transfers through the whole structure of the table and a sound is generated due to the vibrations, try it yourself, and you know the sounds, a solid 'thunk' if you heard it experience will tell you it's wood. Now the glass next to me, I tap that and the sound produced is much lighter, a ringing sound that lasts as the vibrations are dissipated through the glass. I'm sure you know this sound as well. In fact you can identify most things by the sound they make, and that is akin to Raman. Instead of hitting an object, we transfer energy using a laser, this produces vibrations and by looking at the 'spectra' we can identify the structure.

Uh-oh! Spectra....I've said something new, so now let's get physical.
After exciting our material with a laser and energy is transferred to the vibrations, the system then re emits the light, except it doesn't have the same energy, it can't, as some of it has been turned to vibrations. So it emits this light at a different energy to the incident energy.
If we count the photons of light emitted and compare them to the incident light energy then that difference must be the energy of the vibration.
There we go, Raman Spectroscopy in a nutshell.

So to review in a bit more physical way
When I get back to a computer I'll repost this with pictures and equations, but hope this helps.