I think besides my presentation, my favorite experience from this year’s APS March Meeting was my interaction with the wonderful scientists from TeachSpin. They had a booth in the Exhibit Hall that was open the whole week. I remember walking up to it on Monday simply because of our school’s use of some of their advanced laboratory apparatuses. The gentleman at the booth Monday evening invited us to breakfast the following morning and gave me the flier for the breakfast. In the morning, I was the only one awake and raring to go at 6:30 AM on Tuesday morning, so I went by myself. I showed up early as I do and got to speak with the gentleman from the night before and another scientist from TeachSpin over some beignets and coffee. Others slowly leaked in and after a small amount of time, I realized that everyone else was either a scientist for TeachSpin or an instructor at a college or university.
I soon discovered that the breakfast was a meeting for the Advanced Laboratory Physics Association (ALPhA). I was asked five or six times how long I’d been teaching at The College of Wooster because I looked like a younger instructor. Each time, this was followed by me saying that I am a student and then being asked what year of my PhD program I am in. To everyone’s surprise I am an undergraduate student who was invited to the breakfast. Everyone there was very kind though, and I even met a friend of College of Wooster President Sarah Bolton from Williams College. At the meeting, TeachSpin unveiled their newest apparatus that can be used for a slew of condensed matter experiments. I was awestruck by the thought and creativity put into the new apparatus. After seeing it used for only a few experiments, I think it should be in every advanced undergraduate laboratory lineup of apparatuses.
Apart from the meeting, my conversations with the scientists from TeachSpin throughout the week were among the most pleasant and thought-provoking. They encouraged me to think about my future in different ways than I have been recently, which has lifted my spirits quite a bit. I also got to have conversations about some very intriguing physics around the new condensed matter apparatus as well as conversations about my own research interests. They also inquired if I was presenting this week and I told them I was to give an oral presentation. They were very encouraging and helped to lift a lot of my fear surrounding my talk. I felt bad that so much of the conversation seemed to be around what I think–I did listen to a lot of their thoughts as well, but I would have liked to hear more about them and what it is like to work at TeachSpin and what the rest of their careers have been like. They have just started a “Food Truck for the Physics Mind”, and I hope they get to bring this truck of experiments to Wooster in the coming year. I would very much like to speak with them again and hear more about their lives as physicists in laboratory education.
Being an undergraduate presenter in a room full of research faculty
Guest Blog by Zane Thornburg ’18
For this year’s APS March Meeting, I decided that it would be a great idea to give an oral presentation on my summer REU research with Dr. Paul Bonvallet on Osorb from this past summer. I didn’t give any thought at the time about what sort of crowd would be present in the room and would be presenting around me. On the first day of the conference, I sat down in another session and realized all the presenters were research professors mixed with an occasional graduate student or post-doc. I became very nervous for my presentation immediately and worked every night to make it better between Monday and Thursday afternoon. I thought it was done upon arrival, but I will always find ways I want to change my work.
Zane presents his work in New Orleans
There I was, Thursday afternoon. I showed up to the start of the session to get a feel for how all the other talks before me went, of which there were nine. I had gone through my presentation multiple times that morning in preparation so I was feeling pretty good. I was nervous the whole week about the presenter before me, because I had looked him up and it turned out he is a distinguished professor working on polymers and I have 10 weeks of experience. I became nervous for a different reason at the end of his presentation, though. He ended up going several minutes over his allotted 12 minutes, which seemed to me to increase the tension in the room, so I had to start my talk with that feeling in my head. I ended up finishing right before the 10 minute mark out of my 12 minutes, which was the fastest I had ever given the presentation. The others in the room seemed pleased with a concise talk. I received a single question at the end, which I was able to answer quickly since I had just reviewed Dr. Bonvallet’s specific aims for the project moving forward that morning.
Overall, I feel like it went really well and I encourage anyone who does any interesting research to present at this conference. Even if you don’t have years of work to report, presenting is still an exhilarating experience.
Momentum conservation (or Newton’s third law) ensures two-way or bidirectional coupling for typical media like guitar strings and spring mattresses. One-way or unidirectional coupling enables the propagation of solitary waves or solitons with diverse behaviors in otherwise dissipative media, but at the expense of both momentum and energy conservation. Nevertheless, one-way media are possible, provided the coupling is powered to conserve overall momentum and energy.
We recently published an article in Chaos describing the design, construction, and dynamics of low-cost mechanical arrays of 3D-printed bistable elements whose shapes interact with wind to couple them one-way. Periodic boundaries enable solitons to annihilate in pairs in arrays with an even number of elements. Solitons propagate indefinitely in odd arrays that frustrate pairing.
Topological frustration and the power of invisible wind ensure perpetual motion, as in the video below. The mechanical analogue of an electronic ring oscillator of inverting NOT gates, the one-way array is a mechanical clock whose ticks are the reversals of its bistable elements. The design, development, and construction of the array involved five undergraduate co-authors and incorporated two Wooster yearlong senior thesis projects and one NSF REU summer project.
Wind blows down, soliton move right. Each bistable element and the gears were 3D printed in nylon plastic. The parity (odd) of the array guarantees perpetual motion.
Last week I had a wonderful trip to the University of Oregon in Eugene to give a colloquium for the Department of Physics. This was my first visit to the university, and actually my first visit to Oregon at all!
Wooster Physics and Oregon Physics are connected in a number of ways — Dr. Leary did his Ph.D. there, and he recommended the department to several Wooster physics graduates. So there are now four Wooster alums doing their graduate work there! Saul Propp and Amanda Steinhebel are both second year grad students and they recommended me to the colloquium organizers and set up my schedule.
The Wooster physics crew: Nicu, Saul, me, Amanda, and Andrew.
I spent the morning talking about active matter, flocking, and granular flow with a number of different faculty. This might have been my favorite part of the day — as a curious person, I find it so wonderful to just sit down with a really smart person and have them explain their current research to you. For me, these kinds of discussions are where I really see how various areas of physics, which may seem totally different at first, really fit together and complement each other. I love seeing these connections between different fields. Over my physics career, I’ve changed areas several times (always as a condensed matter experimentalist), so I know a little about a lot of subjects, and I think that gives me a good starting point for these conversations. I saw some amazing cell behavior, learned a new video analysis tool that I can use right away in my own work, met a post-doc who I knew previously as a grad student at Illinois, talked about gender issues in physics, ate pizza and got totally quizzed by the grad students, talked about art and physics, saw an awesome new AFM and other enviable equipment, and saw some photon anti-bunching results that were only a few hours old. Sweet!
Atrium at Willamette Hall, the main physics building at the University of Oregon
The physical space at Oregon was really attractive. I know Oregon has more than its share of cloudy days, and it was raining while I was there, but the physics building is designed with large windows and a central atrium, so that despite the grayness outside, it still felt light inside.
There is a lot of art incorporated into the building as well, although it might be helpful to have some obvious signs explaining the meaning of the art. The Feynman diagrams in the floor are pretty straight-forward to recognize (if not understand!), but I didn’t find out the meaning behind the cool starry metal-work at the top of the atrium. Maybe they are just stars… Or hyperbolic surfaces? Somehow related to DNA? It’s a mystery, but great art.
Metalwork art installation at the top of the atrium
I am totally a physicist and not a biologist, but I am a gardener and I enjoy seeing how plants are different across our country and in different landscapes. For example, this tree just outside Willamette Hall was just covered in moss, so you can see this silvery green outlining the trunk and limbs. And the crocuses were in full bloom elsewhere on campus, while here in Ohio, the snowdrops (which are an earlier bulb than the crocus) have just started blooming in my yard.
Crocuses!Moss-covered tree on campus
I will say it was a lot of travel from Ohio to Oregon for a one-day visit. I was lucky to get a good flight though, so that I only had to change planes once in each direction. And, the change of planes was in Denver. I used to live in Denver, so it always feels like home when I fly through the airport. On the way out, we landed just as the sun was setting behind the Front Range, and it was beautiful. As my plane left Denver for the trip farther west to Eugene, I made full use of my window seat and played a little game of “what can I recognize”. It was fully dark by then but I recognized the patterns of the lights, and followed the trail of Interstate 70 from downtown, past our old neighborhood on Sheridan Boulevard, out to Denver West and Golden and up into the mountains.
Sunset behind the Front Range in Denver
All in all an excellent trip! I have a few more trips planned during this research leave — a research trip coming up soon and another trip to give a colloquium. Sadly, I’m going to miss the March Meeting in New Orleans, so I am relying on my colleagues (hint, hint!) and the students to blog about that always-amazing meeting!
View of mountains from our plane window on the way to San Francisco
When I began studying physics, I had no idea that scientists travel so much. In the fall of 2016, I attended the Quadrennial Physics Congress, PhysCon. Before I get to talking about the conference itself, I think it is worth mentioning that this was the farthest I have ever traveled, so I had a lot of excitement knowing it was the first time I had ever been in a different time zone.
The flight there had very tight timing, and we were to have a tour of Google X very soon after our flight was to land. When we arrived and found that we had made it in time for the tour, I was absolutely ecstatic. We stood in a lobby containing over 100 physics students and got to socialize while we waited, and although I had not slept in over 24 hours, I was having a blast meeting physics students from across the country.
The tour of Google X was not at all what I expected. It was more of two and a half hours of talks about their public projects followed by a twenty minute walk-through of the first floor of one of their buildings. At first I was mildly upset, but then I couldn’t help but laugh at myself. I am not sure why I ever expected them to show us anything truly confidential, as we were only a bunch of undergraduate students. I must say, though, I highly encourage anyone to look up the public projects of Google X and read about them. The work being done on those projects is astounding.
Justine, Nathaniel, Emma, and Zane in front of Google X
After we got back from Google X, we had a snack and were directed into the ballroom for the opening session and the first plenary speaker. There were over 1000 physics undergraduates in that room, and it was a beautiful sight. The first plenary speaker was Dame Jocelyn Bell-Burnell, who discussed many exciting recent discoveries as well as unsolved mysteries in astrophysics. Although I have never had much interest in astronomy beyond being an amateur astronomer, she made me feel like I am missing out by not studying astrophysics. At the end of her talk, the floor was opened to questions. This was promptly ended when a student rudely inquired about her feeling of “being cheated out of a Nobel Prize.”
The next morning we had breakfast with volunteering professional scientists. I sat down apart from the rest of the group with a younger woman who works at Lawrence-Berkeley National Laboratory. Some of the other students at this table seemed very self-centered with the conversation and kept interrupting as I tried to listen to her stories, one of which may be the most hilarious lab safety story I have ever heard. I have tried telling it, but she told it much better. We then had the pleasure to hear Dr. Neil Turok speak. I don’t think I got much out of the science in his talk other than laughter from hearing him tease the ideas of theories such as multiverse theory and string theory. What I really picked up from his talk was something he said at the beginning that was something along the lines of saying, “In science, there is still room for individual brilliance, but the day of the independent scientist is over. The big problems of today are too difficult for any one person.”
View of the bay from our hotel in San Francisco
The afternoon consisted of a workshop in which groups had to make something that solved a problem out of construction paper. The required materials and functions were given by drawing three random cards from a deck. Brainstorming and working with individuals from across the country was compelling since we had many different thoughts and ideas from having different backgrounds. The group Nathaniel Moore and I worked with designed mobile greenhouses to traverse the surface of Mars to stay with the sunlit side of the planet. This was followed by a talk from Dr. Persis Drell, which I found to be inspirational in the area of diversity in STEM. During the questions after the talk, a white male asked her what actions white males should take to want to make STEM environments more comfortable for women and minorities. I found this question to be important and have decided to ask that question myself whenever I can because I cannot understand what needs to be done since I do not experience the discomfort of not being a white male. Her response to the question was for white males to not be afraid to stand up to people who are discriminating against others and to not show strange behavior that might make someone feel they are out of place. After the plenary session, there were three workshops from which we had to choose one. Nate and I went to “What is Grad School Really Like?” It turned out to be a panel session from which I feel I did not learn much. I’m not sure what all I hoped to get from that session, but I don’t feel like I learned much that will be useful to me.
AIP President Robert Brown and Zane at the PhysCon dance
The events of the evening are still one of the best highlights in my mind. After dinner, we had the opportunity to go to a PhysCon dance party. Not half an hour after it started, I noticed that the president of the American Institute of Physics, Dr. Robert Brown, had showed up. I thought it was amazing that he showed up to see all of the students dance, but then he handed his jacket to someone and joined us on the dance floor. I thought I had to be dreaming. There I was, doing the Cupid Shuffle with the president of the AIP. He was done dancing after just a few songs, so I went over to him after he was finished and introduced myself and told him that I admired him for joining us on the dance floor. He gave me some advice in response, “Never stop being around young people.” The rest of the dance was great too, even though my dancing skills are quite poor and mostly involve flailing around. Also, I have never heard so much music from the early- to mid- 2000s in one night.
The last morning and early afternoon were composed of a plenary talk by the string theorist Dr. S. James Gates and two other workshops. Later in the afternoon, there was a plenary talk given by Dr. Eric Cornell. I found his plenary talk to be very inspirational in several regards. To begin, he told us that he would not be discussing the Bose-Einstein condensate, but would be discussing his more recent research in trying to measure the dipole moment of an electron. I found it difficult not to laugh at one of his comments. He was giving us the introduction to the research and he said that he had some difficulties with some of the background regarding ions when he started. This is where he inserted the comment, “My chemistry level is that of a high school freshman at best.” I just found that comment to be amusing. Near the end of the talk, he spoke briefly about his feelings toward taking on a completely new area of research. He told us he felt that he was in way over his head with the new area of research at times and told us to always challenge ourselves. Hearing a Nobel laureate say that he is in over his head is something I never thought I would hear.
At the end of the talk, the floor was opened to questions and Dr. Cornell told us that we could ask him about anything including his asymmetry (he is missing his left arm if you aren’t aware). Someone did ask about his arm, which turned out to be a tear-jerking story. One of the other questions asked was for a brief description of the timeline of his career since he had mentioned his regular life events accompanying his work leading to the Nobel Prize. We ended up getting a five to ten minute overview of his life, which I think was one of the most influential things I have heard in a research talk. I felt awestruck and happy to hear about the life of a Nobel laureate that sounded very commonplace. He also made some comments regarding his recognition he was given and his gift that were hilarious. His comment after being given his gift was, “Swag!”
After the talk, the second poster session began (we had missed the first). There were literally hundreds of posters being presented by undergraduates. I could write another entire blog post purely on everything I learned during that poster session. The quality of the work being presented as well as the presentations was incredibly high, and even included work in physics education and outreach. As the poster session was ending and I was walking out of the poster area, but I noticed someone was walking the opposite direction into the poster session. After closer observation, I noticed that the person was Eric Cornell. All of the other plenary speakers had been hounded by students after their talks, so I did not get to meet any of them. I knew he wanted to get to see some of the posters, so I did not want to take up a lot of his time. I walked over to him, though, since there was no one else gathering around him, and meeting him one on one was truly delightful and humbling.
The last events of PhysCon were a banquet followed by the last plenary talk given by Patrick Brady. Sadly, the banquet was not very enjoyable. The food was very good, but I felt uncomfortable at the table we had seated ourselves at. After the talk began, I realized it was going to be another LIGO talk. I understand that it is one of the most astounding experiments in recent physics, and I find it to be amazing and exciting, but I had already heard talks about it multiple times. This combined with my discomfort at the table and my desire to sleep before our early morning flight led me to leave and go to sleep.
Overall, PhysCon is a true highlight of my undergraduate career in physics. I would recommend the event to anyone and everyone who can find their way to the next one. I am so glad I have chosen to go into physics, not only because of the incredible ways we find to explain and predict physical phenomena, because the people I have met and the places I’ve gone and will go are astounding.
Wind is free and ubiquitous and can be harnessed in multiple ways. We recently published an article in the Physical Review demonstrating mechanical stochastic resonance in a tabletop experiment that harvests wind energy to amplify weak periodic signals detected via the movement of an inverted pendulum. Unlike earlier mechanical stochastic resonance experiments, where noise was added via electrically driven vibrations, our broad-spectrum noise source is a single flapping flag.
This research results from a novel collaboration between The College of Wooster and Grinnell College over several years and includes six undergraduate coauthors. The first version of the apparatus was created in the Taylor Hall’s shop at Wooster and used wooden wheels and grocery-store syrup for damping! The design evolved over several years, with the final version at Grinnell sporting shiny aluminum U-channels and 3D-printed plastic wheels. Schematic of the mechanical stochastic resonance apparatus. At lower right, a wind-blown flapping flag delivers noise to the main axle via a slipless pulley. At lower left, a rotary motor delivers a subthreshold sinusoidal signal to the main axle indirectly via a tensioned slipping belt. At upper left, a bistable inverted pendulum rotates back and forth between two stops.
As promised, I have one more post from my recent research trip to Vienna, Austria. First, a confession which will act as a bit of a spoiler, I had never heard of supernumerary rainbows until Dr. Leary joined the College and used a picture of one he had seen in Poland on his web page. Ever since then, I have been jealous and longing to see one myself.
One Sunday when I was in Austria, my host Dr. Smoliner and his wife and I went on an excursion east of Vienna to Schloss Hof, a palace built by Prince Eugene of Savoy in the 1720s and later renovated by Empress Maria Theresa. I love visiting these types of palaces — not just for the buildings themselves but especially for the gardens.
Late fall flowers at Schloss Hof
It was raining on and off, so we went to see the gardens first, and got caught in the rain. After drying off a bit, we went through the rooms, which mainly had their window shutters closed to protect the furniture and wall-coverings from sunlight. As we reached the room in the front corner of the building, the shutters were open to allow views of the Baroque gardens. I looked out the window to the side of the Schloss and gasped in surprise — out the window was a supernumerary rainbow!
Supernumerary rainbow over Schloss Hof, Austria, 9 October 2016
The supernumerary part of a supernumerary rainbow is the extra fringes that you can see on the inside part of the bow. Most of the colors are washed out in the fainter bow, but you can generally see the extra greenish/purple lines. In my picture, you can mostly just see one extra light green line, especially toward the top of the bow. You get supernumerary rainbows when the rain droplets are particularly uniform in size.
The sky cleared quickly while we were looking at the rainbow, so our timing was so very lucky! Here’s the view directly to the front of the Schloss just a moment later. By the way, the large hill you can see is actually in Slovakia! The border is a river which you can kind of see in the picture as the line of trees that follow the river.
View toward Slovakia, from Schloss Hof
So, we left Schloss Hof and headed toward a national park on the Danube, because I wanted to see the wetlands (the Auen) around the river. As we drove, another rainbow appeared and became so bright and vivid that we had to pull off the road to get a picture.
Supernumerary rainbow and double rainbow outside Engelhartstetten, Austria, 9 October 2016
Everybody on the road was stopping, it was so amazing. A nice Austrian man tried to tell me something that my German was not quite up to at first, but then I realized he was saying the rainbow was so close that you could see that it was in front of the trees at the back of the field. That is, if you enlarge this picture (just click on it), and look at where the rainbow appears to meet the ground, you can see that the trees are behind the rainbow. Totally awesome. And, it’s another supernumerary! Look towards the top of the bow to see the extra fringes. Apparently, Thomas Young used the existence of supernumerary rainbows as part of his argument that light was a wave. The extra fringes cannot be explained by ray optics — you need interference effects.
Finally, we wrapped up the sight-seeing at the Donau-auen park, and the light of the late evening sun was just beautiful. Sunshine on the water looks so lovely….
Panorama of the Danube River between Vienna and Bratislava
That’s the beautiful blue Danube! Again, you should click on this image to make it full size. You should even be able to spot the moon, in the middle of that amazing sky.
Me, capturing the moment in the national park Donau-auen
We wrapped off the day with a good meal and conversation at a very traditional Wiener heurige at the edge of the Wiener Wald. It was definitely one of those tremendous days to keep in your memory to cheer you up when things are darker. When I’m scraping the ice off my windshield this winter, I can just go back in my mind to Schloss Hof and my two supernumerary rainbows!
As mentioned in my previous post, I’ve just recently returned from a research trip to Vienna, Austria. I was there for two and a half weeks, and fortunately, I had plenty of time to see some sights! I first visited Vienna when I was in college and on a whirlwind tour of Europe (Marburg, Berlin, Prague, Vienna, and Paris, all in two weeks!) with my aunt. It was my favorite city during that tour, and so I’ve created opportunities to return!
I remember visiting Schönbrunn Palace with tired feet on a hot August day back on that first time in Vienna. Although we didn’t have the energy to explore the gardens that time, Schönbrunn did become one of my favorite places, and I have since explored those gardens thoroughly! I’m not really a runner, but during my last visit to Vienna in 2013, I ran on the garden paths of Schönbrunn several times, and I finally feel that I’ve seen the full grounds. This visit was colder, but I did manage it one morning, and the view of the Schloss from the Gloriette in the (relatively) early morning was wonderful. This is the view that Empress Maria Theresa had most mornings for breakfast.
Schloss Schönbrunn, from the Gloriette
I took a few excursions out of Vienna on the weekends, including a 2 hour river cruise on the Danube through the Wachau Valley from Melk to Krems (and connecting to Vienna by train). The entire valley of the Wachau is a world heritage site and has been inhabited by humans for around 30,000 years, since the Paleolithic! The village of Willendorf, where the famous female figure known as the Venus of Willendorf was found, is here in this valley. One of my favorite sights on this trip is the ruins of the castle at Dürnstein. This castle is where Richard the Lionheart was held captive on his way home to England from the Crusades. That was in 1192! Without this captivity, we wouldn’t have the stories of Robin Hood or Ivanhoe. Frankly, I’m not sure King Richard was as great as he was made out to be in either of those stories, though.
The ruins at Dürnstein, on the Danube River
Another excursion took me east of Vienna, to Carnuntum, an excavation and reconstruction of a Roman military installation and city.
Heidentor (Heathen’s Gate) outside CarnuntumColiseum ruins at CarnuntumA well-preserved Roman mosaic floor at Carnuntum, with a reconstructed typical Roman room around it
So you can see my little mascot Leo in some of these pictures. I keep him in my bag and put him in a lot of my pictures — I like the personal character he brings to my otherwise standard tourist shots!
On the Graben
Leo also enjoyed visiting with another lion at a fountain on the Graben, right in the heart of Vienna.
The last weekend that I was in Austria, we made an excursion to Styria, in southern Austria, and saw some amazing things. It is so different to be shown around a country by a native, rather than just being a tourist. We were able to see things I would have never found on my own. Namely, we stayed at a hotel in this amazing castle, south of Graz.
Burg Deutschlandberg
And we went to see the Weltmaschine (World Machine) of Franz Gsellmann. The Weltmaschine really defies easy characterization, but I would describe it as a type of outsider art. Gsellmann wanted to be an electrical engineer but was unable to afford school. At his family farm, he gradually built this electrical machine with bells, lights, and many moving parts out of bits and pieces that he collected from flea markets. There are some videos online, but it is amazing in person. Imagine all these bits whirring around, quite loudly, with ringing bells and flashing lights.
WeltmaschineDetail of some of the construction of the WeltmaschineAnother Detail of the Weltmaschine
It was an amazing trip, and I haven’t even told you about the cheese cave, the pumpkin seed oil, the Lainzer Tiergarten, or the art at the Albertina! I do have one more awesome thing to share, but it deserves its own post, so you’ll have to wait and see! I promise, I’ll get back into physics for that one!
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!
Why has SpaceX chosen methane to fuel its Raptor rocket engine? Robert Goddard’s first rockets used liquid oxygen O2 or 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 C11H24 blend), and kerosene (a C12H26 to C15H32 blend) are all linear hydrocarbons CnH2n+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 + 2O2on Mars.
Raptor rocket engine powered by supercooled liquid methane and oxygen or methalox
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Thanks, Mark! I enjoy reading your posts as well.
Nice post, John! Thanks for writing these. I always enjoy them.
Thanks, Mark! I enjoy reading your posts as well.