Postdoc Spotlight: Thomas Shiell takes silicon synthesis to the next level

Thomas Shiell stands on campus
Wednesday, October 13, 2021 

Thomas Shiell is a materials scientist who works with the synthesis and characterization of new forms of silicon—specifically the newly discovered silicon allotrope Si24. Recently, Shiell used this new form of silicon as a starting point of a multi-stage synthesis pathway to develop a highly ordered form of silicon called 4H-Si for its four repeating hexagonal layers (pictured below).

Hexagonal silicon has long been sought after because of its potential to be highly tunable, which means scientists in the future may be able to use the 4H-Si crystal as the starting point to create materials with enhanced optical and electronic properties—think highly reflective surfaces and room-temperature superconductors.

Shiell’s fellowship is coming to an end later this year, so we caught up with him for a quick postdoc spotlight. 

Who are you and how long have you been at Carnegie?

I’m an Australian with a background in Engineering (welding and small-scale steel fabrication) and a PhD in physics from the Australian National University. During my Ph.D., I visited the Carnegie BBR campus several times and built some strong connections.

I returned to Carnegie after my Ph.D. conferral in mid-2019.

What is your area of research, and why would you say it’s important?

Broadly speaking I’m in the field of high-pressure physics, and my expertise can be broken down into two major areas: 1) New materials synthesis and discovery and 2) Physical properties measurements and characterization.

What would you say are the larger implications of your work?

To make an impact in my field I have managed to publish new materials characterization procedures that can be used by others to measure physical properties and phase transitions in other material systems. 

These days I work to discover or improve the quality of new materials for applications, such as more efficient solar absorbers, and in a past research life, I worked to improve the efficiency of artificial diamond synthesis and thin film diamond coatings for heavy industry applications.

You recently developed a way to make a new and highly useful form of silicon, can you describe that project?

Visualization of the structure of 4H-Si viewed perpendicular to the hexagonal axis. A transmission electron micrograph showing the stacking sequence is displayed in the background.

Recently, I developed a new method for synthesizing a novel crystalline form of silicon, called 4H-Si (pictured above), which has a hexagonal structure and could potentially be used to create next-generation electronic and energy devices with enhanced properties like increased light absorption for PV solar cells that exceed those of the “normal” diamond-cubic form of silicon.

This work involved a multi-step high-pressure synthesis pathway, and we characterized the product using a multitude of diffraction, spectroscopy, and computational techniques. 

It has been received quite well in the first few months since its publication. This is an ongoing project where the next steps include improving crystal size and quality, before tuning the optical and electronic properties through strain engineering and elemental substitution.

What inspired you to choose this field of study?

A combination of factors. I was always naturally good at math and science, and I enjoy getting my hands on physical projects and products, which led me down a path toward mechanical engineering, semiconductor physics, and materials science.

Do you remember the first time you thought you'd be a scientist?

Since I was a little kid I always wanted to be an astronaut. So from the age of ~15 I started to pursue a career in the physical sciences, I learned to fly, and I tried to design a pathway towards a life in the US. Even though I achieved these three goals, reality has set in a little now, and my astronaut aspirations have dissipated somewhat.

When you're not actively researching, do you have any hobbies?

Thomas Shiell poses after the 2019 Mud Cup with former postdoc Tim Jones (left) and the referee. The Mud Cup is an annual soccer match held on the Broad Branch Road campus.

I love physical sports and competition (cricket, golf, etc.), and practically anything outdoorsy like hiking, camping, and hunting.

Why did you choose the Earth and Planets Laboratory? 

I built some great connections during my time as a visitor at Carnegie, and I was attracted to the high-risk projects and autonomy available to those postdocs who seek it.

What's next for you? Any new projects coming up?

I am still directly involved in multiple projects, including silicon-based solar absorbers, high-pressure superconductors, and the synthesis and melting of diamonds. However, my main focus is shifting toward my green card EAD and securing my next position.

Do you have any advice for current graduate students? 

If you’re an international like me, and you want to stay in the US after your time at Carnegie, do not underestimate the complexity, expense, and sluggishness of the US green card and visa application process.

This is especially relevant if you aim to pursue a non-academic career path. Talk to people with experience, and start the process early (i.e. sometime in your first year).

Do you have a favorite rock or mineral?  

I’m definitely not a geologist, so my knowledge of rocks and minerals is quite limited. But I do love gold as a solid long-term investment vehicle!

Shiell is currently looking for a job outside of academia and hopes to stay in the U.S. Learn more about his work here.