Welcome to hengwang group

We are a group of experimental material scientists at Illinois Institute of Technology, right next to the heart of the vibrant city of Chicago. We study the transport of charge (aka, electrons or holes) and heat (aka, phonons) in semiconductors.

Understanding, and being able to manipulate how the electrons and phonons move through a solid form the foundation of semiconductor industry and essentially every piece of electronic devices. The same question is of great importance to numerous areas of material research: thermoelectrics, photovoltaics (solar cells), battery, flexible electronics, just to name a few. 

Now that you are here, please spend some time to learn more about our research, our team, or just have fun. 

Oh, We would also like you to know that we are looking for motivated undergraduate and Masters students to join the group. please email us.

Group News

July 01, 2020

The updated test system

We have now completed our photo-thermoelectric measurement system. tunable light source, Seebeck and Hall effect tests in DC and AC modes, variable temperature RT to 200C. Had to change course a few times: box design, magnet driving, optics...The next would be better and more efficient light focusing/collimating from that monochromator. 

January 03, 2020

Update underway

​Happy New Year of 2020! A brighter, tunable light source for our photo-thermoelectric test system is being set up. We hope everything will be done by end of January.

December 16, 2019

High resistance Seebeck measurement now published

Well, it took us really a long time to arrive at this. Fortunately our work is now published in Advanced Electronic Materials. And even though we might be slow working it out, it is well-received and accepted within two weeks without revision (https://doi.org/10.1002/aelm.201901340). Way to go team!  

January 25, 2019

Glovebox number 2

Take a look at our second glovebox. We were able to save it from being scrapped. It needs quite some work but overall is in good condition. Great opportunity to learn how a glovebox works and more importantly, the engineering thoughts behind in order to make it work in a beautiful way. People say new PIs shouldn't waste their time saving money and building things from scratch. We believe the educational opportunities they bring are irreplaceable. Lots of fun to have (now we need a volunteer...) (still do...)   

December 26, 2018

The Solid State Synthesis Fleet

It's nothing to brag about but, we now have a "small fleet" of furnaces to help us with synthesis of bulk materials: the three little guys here and another box furnace, two MoSi2 1600 degree furnaces, and a arc melter (Prof. Philips group). We will make any compound that exists (or should exist), if we need to. That is our ambition.... 

September 15, 2018

'Dragonsalyers' in thermoelectric measurement

If you are familiar with thermoelectric effects, you might recall that the Seebeck coefficient is larger in materials with fewer free carriers. Here is a question: what Seebeck coefficient would an 'insulator' have? We added the quotation mark because we are not really considering typical insulators, but rather, insulating semiconductors (the boundary between semiconductors and insulators has been increasingly blurred). The challenges come with Seebeck coefficient measurement from insulating semiconductors, is a 'dragon' for thermoelectric research. It is formidable: at high sample resistances over 1Gohm, precise open circuit voltage measurements become almost impossible. At the same time, it is somewhat illusional: thermoelectrics are highly conductive semiconductors so why would anyone care about Seebeck coefficients in 'insulators' anyway.

Actually, Seebeck coefficient is a universal transport property. It provides a probe to the natures of conducting electrons and holes in a semiconductor. This is especially true for insulating semiconductors where both electrons and holes contributed to the transport. 

If you accept that such measurements are important for fundamental sciences, then the 'dragon is real'. Fortunately, we have now acquired this 'dragon-slaying' skill in thermoelectric research. Shown below is an example of Seebeck voltage measurement of a methylammonium lead iodide (MAPbI3) film with >100 Gohm (10^11 ohm) measured resistance. Few (if any) could perform such type of measurement.

September 01, 2018

Quartz-sealing station

This setup allows us to seal air-sensitive samples in quartz ampoules under vacuum, so high-temperature reaction or heat treatment can be easily performed afterwards. Sealing station is an essential piece of equipment for doing solid-state chemistry. You find its use in various researches in thermoelectrics, crystal-growth, graphene or 2D materials. We are happy to share a few thoughts if you are considering building one of these:

1. Vacuum fittings are expensive. Buying used/old stock parts could help. We would however have the pipes custom-made to reduce the number of connections.

2. We would use NW16 pipes to reduce total volume to be evacuated.

3. We custom-made the fittings to go with the quick disconnect adapters, so we can handle quartz tubes of different sizes.

4. A diffusion pump is better suited for sealing stations than turbos. It won't be as easily damaged in case the tubes pop during sealing.

5. Choose silicone based diffusion pump oil will give it better resilience against oxidization.

6. The diffusion pump in picture is too small. We should have got a bigger one. 

7. Get compact torches instead of standard welding torches for better maneuverability.

August 17, 2018

First anniversary

We are young. We have not many stuff, but we are definitely growing! Synthesis is underway, testing abilities are being built up. The room no longer looks that open (although it is still tide , clean, and safe). It will take quite some effort to take our lab to full speed, and we (at least some of us) can't wait.

March 26, 2018

This is where it all begins

As experimentalists, We feel impelled to record every "ground state" or "control sample". So, Here it is we mark our dear lab its ground state. The MMAE department has been very accommodating providing us this spacious room. No remodeling was needed, although we did performed basic house cleaning (and hided away stuff from this picture). On this day March 26th. we officially started populating it with our stuff. We might later on feel shy because this is such a big room and we have such limited resource to fill it, But we will make every effort we can to keep it safe, clean, and organized. Most of all, we will enjoy our days spent here, and we will do some great science. Let it all begin!

January 19, 2018

Our Website Is Online

This is quite an accomplishment for us. We hope you, our visitors will enjoy it. Please provide feedback about anything. We will try to update as often as possible.

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