August 12 2006 - As part of a collaboration with the Hahn Meitner Institut (HMI) in Germany, undergraduate and graduate students have been able to travel and do research at the German institute. Senior Materials Science undergrad Jennifer Gaddis spent the summer at HMI working on photoluminescence of CuGaSe2 solar cells. Graduate student Damon Hebert spent a month working on polarization dependent PL on CGS. The collaboration is part of the "Materials World Network: Correlation of the Structural and Optoelectronic Properties of Grain Boundaries in Polar Covalent Semiconductors" NSF award granted to professor Rockett.
Damon Hebert worked under the supervision of Susanne Siebentritt of the Heterogeneous Material Systems group. His project was titled "Polarization dependent photoluminescence on epitaxial CGS layers grown by metalorganic vapor phase epitaxy (MOVPE) on (111) and (100) GaAs substrates". The goal of this project was to identify from which planes of atoms the major PL peaks are emitted. Damon also worked with Hall effect on CIS-on-GaAs bicrystals, MOVPE of CGS epilayer on p-type GaAs, and other projects.
Check out some of Damon's and Jennifer's journal entries below:
Arrival in Berlin (October 11,2006)
I just wanted to let you all know that I've arrived safely here in Berlin. I'm working at the Hahn Meitner Institute (http://www.hmi.de/index_en.html) in Berlin for a month. It's a special place that's pretty much devoted to solar cell research. There are 800 employees, most of whom are willing to speak English with me. My German is aweful to non-existent, but I'm trying to learn. I am doing pretty good so far at least at pronouncing things. I can read words and make the correct sounds, but I have no idea what they mean. I checked in last night at ~6pm, and was exhausted. Needless to say, I woke up at 5am this morning, ready to go. But I couldn't get here too early because my boss (Susanne Siebentritt) doesn't arrive before 10am. She gave me a little tour and took care of some administrative tasks, and now I'm sort of on my own to meet the group's members and perform the research. She has allowed me time to do some of my own (Hall effect) research on the side as I help her with an unfinished thesis (polarization dependent PL on CGS-on-(111) GaAs). I'm looking forward to getting research started and seeing some of Germany. I'll keep you all updated, please send emails!
The Berlin Laundry Club (October 23, 2006)
Once again I am writing you with an update from Berlin. I have been getting more comfortable with my accomodation, the local public transportation, and the institute. I'm not learning much German except for how to read basic signs and the names of the bus stops. Last week on the institute's monthly Free Friday, I traveled a short distance southwest of Berlin to Potsdam, where I had been invited for dinner by my friend and collegue Niklas. He visited our research group in Illinois three years ago, and now he's got his phd and is doing post-doctoral work here at HMI. He's also recently married to a former collegue of his and has changed his surname to hers (weird!). Once in Potsdam, I wandered around looking at the bustling shops and a large outdoor market. Most food vendors sell typical German items like pretzels, sausages (wurst) and cheese. There are many bakeries. Potsdam is a medium-sized city just outside the Berlin border, so it was part of East Germany. You c! an! 't tell by looking, though, as the city is taken up largely by the vast Park Sancoussi, and its various palaces and monuments from the 18th century. I toured several sites, including King Frederick's rococo palace San Soucci. It included a string of rooms ornately decorated in floral and animal patterns, a very summery feel. One room was said to house the poet and philosopher Voltaire for some period. I also toured a reconstruction of an old 7-story windmill, the palace's art gallery, and a Chinese Tea House. All were spread out in the park, which was full of sculpted fauna and colorful flowers. At the end of the park was Niklas's neigborhood, so I bought some random German wine and brought it over. We had pumpkin soup with toasted pumpkin seeds and buttery coutons and a potato, zuchini, rosemary and cheese hotdish. It was delicious and very fitting for the season.
That weekend I spent being frustrated about the laundry situation. I found out that I had to pay 14 euro to join a "student club" to use the facilities, and that I could only join it on Tues or Thurs from 8-8:30pm. I thought the system was rediculous for visitors, especially because they didn't explain any of it when I checked in. It seems like this place (and maybe it's a German trait) is always on a need-to-know basis. If you don't ask they won't tell you. I followed some American football on the Internet on Sunday but with the Vikings off it wasn't so interesting.
The work week was enjoyable. I've been waking up really early so I can check emails at work and catch the World Series update. During the week I ran several experiments in the lab that kept me there until past dinner time. It's interesting to compare this place to the U of I research labs. Here, people all check out at 5pm. I am literally the only one here at night and the halls are dark. They make me leave by 9pm, or my passcard won't allow me to leave. Imagine being stuck overnight! Experiments are going alright but I had to redo a day's worth because Susanne didn't like the way the data turned out. Such is the life of an experimentalist.
During the week I also figured out the laundry situation and I avoided joining the club. I just had to ask around.
Downtown Berlin (October 23, 2006)
This past weekend I journeyed to downtown Berlin on Saturday to just get to know the city. I walked all over the "museum island" but decided that the museums were too busy to go into. Plus I had seen them in 2001 with Nate. It was a beautiful 60 degree day and people were out in droves. I made it to Potsdamer Platz where I found a booth selling tickets for Berlin shows. I am going to try to see Ben Harper's concert on Nov2. Sunday I met Maarja and Kristi, Estonian co-workers from HMI, at the Kultucenter near Potsdamer Platz to see the temporary Rembrandt exhibit. They had a wide collection of his paintings. I was impressed at his use of light to give his paintings warmth. The backgrounds and surroundings were always dark and drab, but the highlight was always lit and gave a sense of hope. Last night I followed the Vikings in their upset of the Seahawks (yeah!).
The weather is amazing - my favorite time of year for sure. I am getting my share of German food at the HMI cafeteria. I basically point to something and the lunch lady smiles and dishes it up. I've had pasta, sausages, rumpsteak, boiled potatoes, saurkraut, lasagna, even a rice/mushroom bake. It's all ok, and pretty hearty. They have Coke and Fanta here, but no Mountain Dew. Germans typically eat a lot for lunch and lighter for dinner, so I guess that's what I'm doing too.
Overall I'm getting used to things here and am pretty happy to be here. I forgot my camera-to-computer cable at home so I won't be able to send any pictures, although I am taking plenty.
Until next time,
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My First Week (June 23, 2005)
Hi everyone. I am currently finishing up my first week at HMI. Friday is a free day for the whole institute, so that was a nice surprise. I'm really liking it here, and I get to speak a lot of German, which is fun. A lot of people want to practice English, but others will only speak German, so it's a nice mix. This week I've been observing some PL measurements and getting trained on the instrument.Their system is very similar to the one Allen showed me at MRL. There are two main people who I am working with. One speaks German with me and the other speaks English. I really like the arrangement because I can learn the words in both languages. All of that aside, I thought I would tell you all what little I know about my project.
Basically, I will be doing high-excitation photoluminescence on CGS. The idea is that there might be fluctuating potentials in CGS. In highly compensated samples most shallow impurities are ionized and randomly distributed over a long range, which generates strong electric fields. By varying the excitation densities in the PL measurement you can see the effect on the PL spectra (blue shift, red shift, broadening of peaks), and eventually at highest excitation densities the photogenerated carrier concentration should be high enough to screen the electric fields and restore the flat band situation. I think it just returns to a shape that would be characteristic of a lesser doped sample.
If any parts of my summary appear wrong, please let me know. Also, if you have any comments about the experiment please let me know as well. I will probably not be performing this experiment until late next week at the earliest. We will be using UV light, so we have to order special glasses. Also, if I finish with this project, I will start another project with EL. Finally, I am very excited because the lady here who actually completes the devices is going to show me the process of actually finishing the cells.
As for Berlin, I love the city. The place where I live is unfortunately pretty far from the city, but I can get pretty much anywhere within an hour. Tonight is free museum night, so Museeninsel is where I will be. I hope you all are having great summers! -Jennifer
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