Wooster Physicists

Wooster Physics in Vienna, Austria!

Susan Lehman

November 17, 2016

After several years of being department chair, I am very much enjoying being on research leave this year. A research leave is an opportunity for Wooster faculty to take a semester or a year just to focus on our research, without any teaching, committee work, or other kinds of administrative work. It’s a time to meet new people, get new ideas, and learn new things. I have two major research trips planned this year to expand my perspectives, and to develop some collaborations.

I recently returned from the first trip — which was to visit my colleague Dr. Jürgen Smoliner at the Institut für Festkörperelektronik of the Technische Universität Wien, or in other words, the Institute for Solid State Electronics at the Vienna University of Technology. I first visited Dr. Smoliner on my last leave in 2012, when I wanted to get better at the technique of ballistic electron emission microscopy, and it has become a great collaboration for both of us.

Entrance to the main building of TU-Wien, on Karlsplatz in Vienna.

As an American, one of the things that I most love about visiting Vienna is the history. (I’ll get more into this in a later post, about not doing physics in Vienna!) For example, Christian Doppler of the famous Doppler effect was a graduate of TU-Wien!

On this visit, though, there was no Doppler effect involved. We were doing ballistic electron emission microscopy (BEEM), which is a variation of scanning tunneling microscopy (STM) where there is a very thin additional contact on top of the sample of interest. Ultimately, the plan was to investigate nickel on gallium arsenide, but there were some technical challenges, so we spent most of the time with the standard test sample of gold on gallium arsenide.

To make the samples, we need to create a layer of gold that is around 8 nm thick — that is, extremely thin! The gallium arsenide must be absolutely clean first, so it is dipped in hydrochloric acid, and then placed into the vacuum chamber where the gold will be deposited. We used a thermal evaporation system for the gold, which (funnily enough) is the very first thing I ever learned to do in graduate school! (Thank you, Dr. Briscoe!) Unlike my work in grad school, though, we did all of this sample processing in a clean room.

Clean room selfie! That’s Dr. Smoliner with the beard, and also Fabian and Gernot, students who were learning about sample prep and BEEM.

Once the gold layer has been evaporated onto the gallium arsenide, we could make the electrical connections and actually begin making measurements. In BEEM, we need two electrical connections to the sample — one connection to that thin gold layer, and one connection to the gallium arsenide itself. In the top view image, you can see the thicker wire (with a little indium gooped on the end to make it sticky) connecting to the top of the sample. It’s actually touching one of the gold lines on the sample, but that wasn’t visible in the picture. The thinner gold wire was tucked underneath the round mounting disk in this picture, but for our actual measurements it was moved to the top of the sample. I took this picture through the eyepiece of an ordinary optical microscope — the coppery-colored disk that the sample is sitting on is actually about 1 cm in diameter.

Top view of the sample and electrical connections through an optical microscope.

In the side view picture below, you can see the sample once it was mounted in the STM. If you look closely, you can see that same thick gold wire, the thin gold wire, and also the STM tip coming down to image the sample. I was surprised to get this good a picture from an iPhone! (Thank you, optical physicists who work for Apple!)

Side view of the sample and connections, mounted in the STM.

So, like all experimental physics, it takes a good bit of time to get to this point — sample prepared, system working– and then you can actually hope that it will all keep working long enough to get some good data! We were able to get good data for the gold on gallium arsenide sample, so that was a success! Also, I needed to test whether my home-built BEEM amplifier was still working, and fortunately, found out that it was. (There’s a long back story there — short version is that the BEEM current we measure is only on the order of picoamps, so we need a very sensitive, low noise amplifier in order to make this signal measurable. This exact configuration is not something that is available commercially, so we built it ourselves a few years ago, but had been having trouble and were not sure whether something had happened to the amplifier. So, I took it along to check out.)

While at TU-Wien, I also taught a brief graduate seminar on BEEM of nanostructures (aka, Ballistische Elektronenmikroskopie auf Nanostrukturen). It was fun teaching at a very different level than I am used to. And, one of the students taking the course suggested that BEEM might be a good tool to look at some of the samples that his group studies, so it could very well end up in a new collaboration!

Billboard showing the new ZMNS building

The people that I was working with are all in the ZMNS at TU-Wien, which is the Center for Micro and Nano Structures. The university is currently building a new building (actually, starting with the base of an extremely *old* building) for ZMNS which will have a new and larger clean room. So, I am looking forward to checking that out on my next visit to Vienna!

Stay tuned for posts on what else there is to do in Vienna besides physics!
Raptor Interplanetary Transport Engine

John F. Lindner

October 13, 2016

Why has SpaceX chosen methane to fuel its Raptor rocket engine? Robert Goddard’s first rockets used liquid oxygen O₂or LOX and gasoline. The Saturn V moon rocket first stage used LOX and refined kerosene. The Saturn V second stage used LOX and hydrogen that burn to water in my favorite chemical reaction, 2H₂ + O₂ → 2H₂O. Methane CH₄, gasoline (a C₇H₁₆ to C₁₁H₂₄blend), and kerosene (a C₁₂H₂₆ to C₁₅H₃₂ blend) are all linear hydrocarbons C_nH_2n+2 that burn to carbon dioxide and water (and residual carbon if the burning is incomplete).

Hydrolox is most efficient but requires huge tanks (due to hydrogen’s low density), which must be cooled to just a few degrees above absolute zero. Kerolox is less efficient but needs smaller tanks (due to kerosene’s high density), which can be at normal temperature and pressure. Methalox is a compromise. But unlike kerolox, methalox does not coke the engines with residual carbon that makes reuse more difficult. Also, to improve efficiency, SpaceX will densify the oxygen and methane by cooling them to just above their freezing points (rather than just below their boiling points).

However, the real advantage of methalox is that it can be manufactured from carbon dioxide and water by CO₂ + 2H₂O → CH₄ + 2O₂ on Mars.

Raptor rocket engine powered by supercooled liquid methane and oxygen or methalox.
Maggie Lankford `16: National Finalist for Top Award in Undergraduate Physics Research!

Cody Leary

September 29, 2016

I’m excited to report that Maggie Lankford, who graduated summa cum laude this year as a Wooster physics major, has been selected as a finalist for the American Physical Society’s LeRoy Apker Award– known as the preeminent honor for undergraduate physics research in the United States! Maggie received this recognition for work reported in her Senior Independent Study thesis, entitled “The Production and Manipulation of Nonseparable Spin-Orbit Modes of Light Under Hong-Ou-Mandel Interference Conditions.”

Maggie with the apparatus she helped to design and build.

In short, Maggie built a device which produced novel structures of light (photons), in which two of the light’s degrees of freedom–polarization and spatial intensity distribution–could not be characterized or described without direct reference to one another. Her thesis also demonstrated that this setup is capable of imparting such structures onto pairs of photons that are simultaneously exhibiting quantum interference, which is a key component in a number of quantum computing protocols. If you’d like to know more, just click this link to our open-access publication, which recently appeared in the research journal Optics Express.

Maggie presented her work last June at a poster session at the Quantum Electronics and Laser Science conference in San Jose, CA (see photo above). Then in August, she gave an oral presentation on her research before the Apker Award selection committee in Washington, D.C., along with the six other finalists from other institutions including MIT, Kenyon and Dartmouth. Two winners – one from a Ph.D. granting institution and one from a non-Ph.D. granting institution – will be announced in October. She is the third Wooster physics graduate to be named as an Apker finalist.

Maggie’s Apker recognition has been reported by the American Physical Society Newsletter and Wooster News. A quote from Maggie from one of these articles sums up her research nicely: “We developed this new apparatus … made a mathematical model of it, then built it, then used it to generate this new type of pattern of light that can be used for information processing or for communicating between two parties.”

This is what I love about being a tabletop experimental physicist– a field in which it is still possible for a small group of scientists to hatch an original idea, work out the relevant predictions from first principles, design and build the associated experiment, and carry it on to completion!
Summer Research Program 2016

Susan Lehman

September 9, 2016

We had a fun and productive summer research program again this summer! We were fortunate last fall to be awarded an REU site grant from the National Science Foundation, so that enabled us to enlarge the program from the size that it has been for the last few years. We have a very long history of summer research, but this was one of our biggest programs ever, with five faculty and 14 students!

Figuring out the size of the solar system at BWISER

The outreach program for BWISER is always a hit with both the BWISER campers and the summer research students. The group doing the “Lightyears in the Movies” demo had the students put on caps with various solar system objects (the sun, the moon, Pluto, etc) and try to stand at scale distances apart. We have a complicated program where the BWISER campers rotate through seven different demonstrations, learning about light and sound waves, and are completely wowed by the end of two hours.

Ice cream social for all summer research students

In addition to our weekly picnics, and infamous pie festival, we also had a delicious ice cream social for not just the REU students but all the summer research students on campus. I’m pretty sure the professors had as much fun dishing up the ice cream as possible.

The finale for the program was the poster session where all the REU students presented their work to family, friends, and colleagues. Due to the size of the program, we held the poster session upstairs in the Taylor atrium for the first time, and it was a lovely sunlit space for the event.

We had a great turn-out with lots of interested people asking questions about the research each of the students did. It never fails to amaze me how much the students learn and accomplish during the 10 week program!
First Deep Space Walk

John F. Lindner

August 20, 2016

In 1971 during Apollo 15’s return from Earth’s moon, astronaut Al Worden performed the first deep space walk nearly 200 000 miles from Earth to recover external service module film canisters that had mapped the lunar surface. Worden was able to pause and orient himself to simultaneously see both Earth and moon as disks against the blackness of space, the first human to do so. Looking back toward the command module, he saw astronaut Jim Irwin waiting in the open hatch against a colossal moon — but did not have a camera to record the breathtaking view, the iconic photograph that never was. Fortunately, back on Earth Worden was able to collaborate with artist Pierre Mion for National Geographic magazine to reconstruct the vista. Deep space walks may occur again next decade from NASA’s Orion spacecraft.

The first deep space walk, by Al Worden reflected in Jim Irwin’s visor, during 1971’s Apollo 15 mission to the moon, as painted by Pierre Mion for National Geographic magazine.
Found in a Box

John F. Lindner

July 30, 2016

I recently ascended to Czar of Physics. (Oops — I mistyped Chair and it autocompleted to Czar!) It’s not my first year as Czar, but this time, during the handover from the previous Czar, I inherited a small cardboard box. Inside I found a stack of old Wooster ΣΠΣ membership cards. (ΣΠΣ is Greek for SPS and signifies the SPS honor society; SPS is an initialism for the Society of Physics Students.) The two cards in the accompanying photograph are especially interesting. Karl modestly lists his position as president of the Massachusetts Institute of Technology. His brother Arthur reports being a professor at the University of Chicago but doesn’t mention the Nobel Prize he won four years earlier for scattering light from electrons. The Compton effect helped convince physicists of the wave-particle duality of matter and subsume classical mechanics in quantum mechanics.

Some Wooster Sigma Pi Sigma membership cards; click for a larger view.
If Apple Designed Buildings…

John F. Lindner

June 26, 2016

When Steve Jobs phoned Pritzker Prize architect Norman Foster in 2009 for help designing Apple’s new Cupertino California campus, he said “Don’t think of me as your client; think of me as one of your team”. The design that evolved from that collaboration features an unprecedented annular building over a mile in circumference enclosing an orchard and park. The roof is covered with solar panels and the basement is underground parking for thousands of cars. The inner and outer walls are giant uninterrupted curved panes of glass. From inside, one can always see outside to the park-like surroundings. A thousand bikes help people get around the campus.

The combined ceiling-and-floor “void slabs” are factory-made hollow polished concrete forms. The awnings block the direct rays of the high summer sun for cooling but transmit the direct rays of the low winter sun for heating. Mirrored undersides (added after the cross sectional illustration below was created) provide indirect illumination. The new campus is powered by 100% renewable energy, and the HVAC system is only for backup. Apple Campus 2 opens in early 2017.

Apple Campus 2 main building partial cross section illustrates over a mile of uninterrupted curved glass with awnings and empty spaces to passively control natural light and temperature.
Commencement Weekend

Susan Lehman

June 7, 2016

It was a beautiful weekend for Commencement this year. With the record number of majors (20 physics majors!!) graduating, we tried hard to get some group photos, but of course we knew it was hopeless to get absolutely everyone looking into a camera all at the same time.

Sunday of commencement weekend, we were able to gather almost half the class for a nice photo in front of Kauke Arch. It was a little chilly at that point!

Faculty marshals begin leading the graduates through the lines of faculty and through Kauke Arch

Monday was also slightly chilly at the start of commencement, but (speaking from experience), slightly chilly is definitely better than too warm!

One of my favorite parts of commencement is when the students precess through the lines of faculty as they walk through Kauke Arch on their way to the ceremony. We faculty applaud the students as they walk through, and it’s a nice opportunity to congratulate individual students, if you spot them as they walk past.

The commencement ceremony was quite nice this year, with very good student speeches and a nice address from President Nugent. And, it really kept moving, which is always good!

Many graduates and faculty!

Yash, Ziyi, Maggie, Catherine, and Carlos

Woo Women in Physics!

Congratulations, Wooster Physics Graduates of 2016!

(And if you have better pics you want me to add here — please just send them!)
Singing in the Wind

John F. Lindner

May 26, 2016

Wires suspended above our streets are a late 19th century technology stubbornly persisting into the 21st century. They can hum in a breeze. A wire disturbs the air flow by shedding eddies alternately up and down, sometimes fast enough to be heard as a musical note. The wire’s vibration can enhance the sound’s volume and persistence.

The animation above shows a section of a wire shedding vortices and oscillating transversely to the wind. Saturation indicates wind speed (with white least), and hues indicate wind direction (with cyan rightward), like the polar plot legend. The simulation is an example of desktop computational fluid dynamics, a trans-generational collaboration between the senior thesis of Danielle Shepherd’14 and the junior thesis of Dylan Hamilton’17. Until recently, such simulations have required supercomputers.
April Whirlwind – Part 2!

Susan Lehman

May 15, 2016

In addition to the outreach events in April, we also had a lot going on to finish up Senior IS — the senior research project or thesis that all Wooster students complete. You might think that IS Monday is the end of IS, but after handing the thesis in, students also defend their thesis in an oral exam.
In the physics department, we ask the student to prepare a 20 minute presentation summarizing the key points of their IS project, and then after that the advisor, 2nd reader, and any other physics faculty able to attend ask questions. Since we advised a record 17 IS theses this year, it was pretty challenging just to get all of these oral defenses scheduled before the IS symposium!

I know the IS defense is stressful for the students, but as a faculty member, it is one of my favorite parts of the IS process. It isn’t that we are only asking questions that we know the answer to — rather the student is now the expert and we are really asking their opinion or perspective on a problem. Because of the way that the defense requires that we pull together information from a lot of sources, and because we have multiple perspectives on the problem, it is often a time when we figure out something new, which is tremendously satisfying.

Popi smiles with relief at being done with the defense!

After the question period, the student steps out for a few moments, the faculty confer, and then we invite the student back in to tell them whether they have officially passed their Senior IS. Then, we have a nice ceremony of the advisor and second reader officially signing the thesis.

Personally, I am a fan of ceremonies — it is important to take a moment and recognize an accomplishment, to take stock of where we were before and how far we have come!

Dr. Ramsey of the Math Department signs Popi’s thesis.

Every department has slightly different traditions and requirements for their students IS defense. In physics, we have intentionally modeled it after a Ph.D. defense, and I know that it is a bit intense. For double majors, we do compromise between the traditions of the two different departments. Luckily, since we have a good number of physics – math double majors, the traditions of the Math Department are pretty close to the Physics Department, so it is not too challenging to merge our requirements.

Finally, the culminating event of Senior IS is the Senior Research Symposium, held on the next-to-the-last Friday of the spring semester. Classes are canceled for the full day, and the whole campus takes part in an awesome celebration of the research that the students have done all year.

Physics students have always been required to do a poster presentation to complete their I.S., but we used to have our own poster session all on our own. Since the IS Symposium started about 8 years ago, we’ve been able to be part of an all-campus event, which is more fun.

In addition to the posters, students can also elect to do a “Digital IS” presentation and develop alternative ways of presenting their IS research. This year, senior Nathan Johnson built a Lego Mindstorms version of a scanning tunneling microscope (STM) to show attendees the concept of how an STM uses feedback as it scans in order to map out an image of the surface of the sample. It was a bit challenging to get the built-in Mindstorms sensors to work well enough and the Lego pieces were not quite as rigid as we really wanted, but it worked to map out the surface, which was cool!

Nathan shows off his Mindstorms STM to President-elect Sarah Bolton

He had a good crowd interested in it during the digital IS session in CoRE, including President-elect Sarah Bolton. Since she is a physicist and actually knows how an STM works, her questions were rather more perceptive than the average ones!

Overall, the IS Symposium is one of my favorite days of the year!