Gregory Mulholland

I guess since I am here to do research, all my family and friends should know a little about what I do here in terms of research. Plainly, I work with semiconducting oxides.

I know most of you know that I work with things that are trying to improve the efficiency of solar cells, that is, increase the amount of electrical energy output per unit light input of a solar cell. To do this, I am working with conductive and semiconductive oxides. These are typically metals mixed with oxygen. In my case, I am working with Titanium dioxide (TiO2) and Tin Oxide (SnO2).

Now, for some background: several years ago, a type of solar cell was devised that is called a hybrid organic-inorganic solar cell. These cells have a metallic or oxide part (inorganic) and a part made from a polymer (organic). These cells typically have a better efficiency than purely organic ones but do not do as well as purely inorganic ones. What is nice about them, though, is that they let us carefully examine how organic and inorganic layers connect.

Because these have been around for a bunch of years, a lot has been done with these cells. Different polymers have been tried, different oxides have been tried, lot of combinations have been made. Mine is a pretty new combination, but it is not exclusively the material that is the focus of my work.

Nanowires
Like I said before, I work with what happens at the interface between the two materials. What happens in the main part (officially the bulk) is well known. I am growing what are known as nanowires at the interface. If you want to be able to picture this (I will post real pictures at some point when I know what the rules are on publishing images), think flat hairbrush. There is a single flat surface with really fine, long tines sticking up from it. The reason we want nanowires is twofold. First, these wires are just that, wires. Charges (and thus, energy) can flow down them very efficiently in the long direction. Second, they greatly increase the surface area of the oxide. A flat surface has only one plane of contact. A comb-like surface has all those edges that can make contact with the surrounding material. Because the interface is so much larger now, its effect is maximized and I can compare the materials.

There are other challenges with nanowires: it is hard to get stuff between them because they are so small, they break easily, they are really hard to see (even with an electron microscope). All of these are in various stages of being overcome by me or one of the others working on my project.

Excitons are exciting!
Now into the nitty gritty. If you are not interested in reading about the hardcore science behind what I do, feel free to skip.

My ultimate goal is to hold on to, or keep alive, as many excitons as possible. What is an exciton? Well that is easy! It is a bound, electron-hole pair. If you are Saket, Ben, or Win, you probably understand this, otherwise, here is my quick sentence explanation:

Electrons sit on tracks. These tracks are at different energy levels. An electron can only travel on these tracks (officially known as bands, but tracks are a better common-sense descriptor for this example). So, if I have an electron on a track at 1 Volt, and I want to make it travel on a track at 2 Volts, I have to apply more energy to it to get it there. If if give 1/2 Volt to a 1 Volt electron, it can’t just jump to the 2 Volt track. Tracks are very well defined for all materials, the space between them is known as the band gap and varies by material.

I’m sure most people remember from high school chemistry that electrons (an just about everything else, including me) like to sit in the lowest energy state possible. If an electron can move to a lower track, it will. Thus, the low tracks get filled up fast. In fact, one can define a top level to the electrons. This (a simplification of Fermi level) means that the electrons are like sand grains on a beach. They all pack nicely into their layers with only slight variations on top. But, because they pack so tightly, there is little room for them to move. There is essentially an electron traffic jam on the lower tracks. The only way to allow and electron to move with any haste is to move it up to one of the unoccupied tracks.

Solar cells work by letting the sun provide the extra energy to move an electron from one track to the next one up. This allows the electron to zoom down the nearly empty track toward whatever you are trying to power with the solar cell. The electron leaves a space behind it where it formerly took residence on the lower track. Because the electrons are packed so tightly, they begin to, one by one, move to fill the void left by the zooming electron. This creates a propagating gap (known as a hole) down the lower track, just like when one car is able to get through in a traffic jam.

This electron-hole creation is called an exciton. My goal, like I said, is to make this last as long as possible. The longer I can make them last, the more electrons are able to escape into the next material and be used for energy. How do they die? This is simple, if the electron and hole do not get away from each other fast enough, they will be attracted to one another and the electron will fall back into the hole, and no energy will be extracted.

So, with all of that said, I am trying to grown Tin Oxide and Titanium Oxide nanowires and make them ideally suited for solar cells. As time goes on and I have more results (which are finally beginning to look rosy), I will post some pictures and descriptions for those of you who are interested.

If this all is totally unclear, let me know and I can try to explain it using a whole different set of metaphors

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At long last, here is the post about the weekend (+1 day) trip to Seville and Granada.

From London to Seville
On Thursday, we were to fly out of Stansted, an airport about 45 mins from Cambridge by bus, at about 6:00 on RyanAir. Thus, at about 3:00, we boarded the bus at Cambridge City Center with our bags and began our journey. We both felt silly because we both took our bags to work with us, rolling them from the Wychfield site all the way to the Materials Department. This is not a short walk and it seems even longer with the never ending clack-clack of a rolling suitcase behind you. Nevertheless, we made it, and by 3:00, we were off.

We arrived at Stansted. It exists solely for use by RyanAir and EasyJet, the two major low-cost British airlines. We were flying RyanAir. Luckily, when we arrived to check in, the line for our flight wasn’t long. We queued up and checked in. There, we were told that our hand baggage limit was 1 10kg bag per person, and one of ours weighed 12.5kg. Thus, the RyainAir fiasco began. We had to check one of our bags for 10 quid. That quickly explained how RyanAir makes its money. After waiting in a different line, paying that fee, and finally getting checked in, we dashed through security, grabbed some cold sandwiches from a pharmacy, and got in line to board our flight.

RyanAir is a free-for-all boarding system. They let the priority queue on first (people who checked in online, which we can’t do because we are foreign, or paid an extra three pounds). Then they let on the regular people. Then, it is get a seat as quick as you can. The jets they fly are regular Boeing 737s. I think I have seen prison planes more adequately spaced (on movies of course). I could not slouch at all because my knees wouldn’t fit between the seats. It was a tight fit. I think we are going to try EasyJet next time; I hear they are slightly more comfortable.

Sevilla
Our arrival in Sevilla was nothing short of shocking. We disembarked the plane onto the tarmac and it was at least 65 degrees (F) out. After the cold British winter, it was such a nice surprise. We then realized that everyone spoke Spanish. This might sound silly, but there is a big difference between knowing that they speak Spanish and actually hearing it. We made our way through immigration and customs. Since everything seemed to be closed at the airport (bus companies, tourist info, EVERYTHING), we grabbed a taxi to the hotel. Luckily, the driver knew where we were going, so no trouble. At check-in, Kelly and I muddled through with some broken, mumbled Spanish and got in okay. That night, exhausted, we ate at the hotel and crashed early.

The next day was Seville exploration time. We got up early, ate an amazing breakfast at the hotel, and found the bus to the city center. This last part took a little work. The lady at the desk didn’t speak any real English, so we had to ave a conversation about the bus in Spanish. This was getting to be less and less of a challenge. Then, we found the stop, but there were two stops across from one another. We initially went to the right one, thought we were wrong, went to the wrong one, talked to the driver (in Spanish), then went back to the right one. Finally we were on our way to the real Seville.

On the bus, we noticed a few things. First, Spaniards are exceedingly polite. There is never an old lady without a seat on the bus, and people generally try to look our for each other. On more than one occasion, Kelly and I were asked where we were going by a random person, then told that our stop was coming up. We must have looked really lost, but it was still nice of them.

Finally, off the bus, we began our trek around Seville. It was sunny and warm, so we were in no hurry, so we decided to explore our way to the tourist area. This proved a little more difficult then planned. Old Spanish cities have no semblance of grid layout. Streets run in all directions, end in random plazas, and change names at random times. It was a blast. After lots of little city streets, we emerged into a plaza. Attached to it was this church:

It was brightly colored and cool looking. Then we moved on to an even larger plaza. This is a photo of one of the Spanish municipal buildings on the plaza:



Finally, after more walking, we made it down to the to the Guadalquivir river:



We walked along the river for a bit and picked up a Seville tour book at a store called Typical Spanish. We felt dirty even reading the sign — it was too touristy. It did have tour books, so we had success. We also go tickets for the tour bus of the town, which was a really convenient was to travel. In hindsight, maybe not worth it, but it was good to have. As we moved down the river, we saw El Torre de Oro:



It was the gate to Seville when the city was the center of trading to the West Indies and the Regular Indies (East Indies? Indies?). Inside was a museum, which had some interesting things in it, including models of the Nina, Pinta, and Santa Maria. From the top of the tower, we could see much of the city, including the Cathedral in the distance:



After walking around the tower, we hopped on the tour bus, which took us to the Plaza de Espana. It was built in 1929 for the Spanish-American Exhibition and is really amazing to see:



Or if you prefer HDR:



There are more photos. If you click on any of my pictures here, they will take you to one of the 4 galleries about the trip.

After the Plaza de Espana, we rode the tour bus around the city, listening to the recorded tour on headphones. We got off again near the Torre de Oro since we knew we could find food there. We went to a place called Minotauro, where we ordered tapas (in this case pork and peppers):

and sangria:



From there, we walked to the cathedral and alcazar (palace), but they were closed for the day. We got some ice cream and walked back toward the bus stop. Along the way, the streets were getting really busy with shoppers. Apparently, everyone goes shopping at 8:00pm. Since we had to go through the shopping district, we joined in. Kelly stopped at like 97 different shoe stores:



Since we had a late lunch, we decided to have a dinner at Telepizza. It is a Domino’s-like pizza place that I learned to love when I was in Spain the first time. This time it wasn’t quite as good because we went with all cheese and I think their toppings make the pizza. Even so, it was a delicious, low-pressure, and cheap way to end a tiring day.

Seville — Day 2
On our second, and last day in Seville, we had a few things left to do. First, we went to breakfast at a small cafe in town. We then walked to the bus station to drop our bags off (we would head to Granada in the afternoon). Finally, we headed to the cathedral and alcazar to see the insides of them before we left.

First, we went to the alcazar. It is the old palace of the city. Not unlike the Alhambra in artistry and style if not in size and grandeur, the alcazar was built and expanded over a few hundred years and was quite a sight to see. The courtyards were ornately decorated:

Inside each of the rooms, the walls were finely carved as well. You could tell that at one time these carvings had been painted vividly:



The palace also had extensive gardens:



And even a really cool crypt:



After the alcazar, we moved across the street to the cathedral. It is one of the largest in the world, and even bigger in the scale of purely gothic cathedrals. From the outside, it is certainly an impressive structure:



From the inside, it is like a bigger version of most other gothic cathedrals. It has many side chapels, altars, and, in the center, an enormous organ. I have heard classical pipe organs before, but never one of this size. While we were there though there was some sort of demonstration of the organ going on. We were really lucky to hear it played in all of its glory. Here is a picture of a small number of its pipes:





The ceiling of the cathedral was amazing as well:



Finally, one of the side altars (the one that looked like it was actually used for some regular Masses and Benedictions) was pretty amazing as well:



After walking around inside for a while, we were able to go into the cathedral tower, the Giralda. It was a part of the mosque that once stood where the cathedral now does. It is the cathedral’s belltower. It offered an amazing view of parts of the city, including the bullfighting ring:



It also had a best views of the top of the cathedral:



After the Giralda, we headed back to the bus station to catch our bus to Granada. I guess Spanish bus companies don’t put your platform number on the ticket, because we had to ask 2 people, in Spanish, which platform was for our bus. Even then, we didn’t believe it until — sure enough — the correct bus pulled up at about the right time. Soon, we were loaded onto it and on our way to Granada.

Granada
When we arrived in Granada, we had little idea where we were or where we were going. Fortunately, I had printed the reservation for our hotel, so all we had to do was find a map. We picked up a map in a convenience store in the bus station, and hopped on a city bus toward the center of town. The first thing we noticed upon leaving the bus station is that Granada is much cooler than Seville. It is at a higher altitude and is actually a ski town during the winter. At the hotel, there were some traveling students and a bunch of skiers. You can see from this:

that the hotel was not too far from the mountains at all. Our trek to the hotel was a long one. We rode the correct bus until a Spaniard told us that we probably wanted to get off. He had asked us where we were going, and when we said “Alhambra” he told us that this was our stop. Spanish people are so nice. We then set off on foot, suitcases rolling behind us, in the direction of our hotel. Remember how I said our hotel was near the mountains? By the walk, I would have sworn it was on top of a mountain. We walked up and up and up. Finally reaching the Alhambra, realized we were on the wrong side of it, and continued walking up until finally running into our hotel. Conveniently, it was a stone’s throw from the ticket booth of the Alhambra, so our main attraction to the city was right there.

At the hotel, we found a nice surprise: most people in Granada speak English. Speaking Spanish is hard work, and it was nice to occasionally cop out and use good ‘ol English to get a point across. After we checked in and got settled, we found a restaurant, had a long dinner, and headed off to bed early, tired from a long day of walking and traveling.

Granada — Day 2
Our main goal for the day was to see the Alhambra. We headed down pretty early, but the line to buy tickets was really long and very confusing. There were signs for buying tickets with cash, buying tickets with credit card, and buying reserved tickets. Kelly got in what looked like the main line, while I walked around and tried to figure out which line was which and tried to figure out if there was some wy to circumvent all the waiting. While I did that, Kelly eavesdropped on a Spanish guy asking a security guard if there was a faster way than the line. She heard him say that if you wanted to buy it with a card, you could just go to the (ridiculously short) line for pre-reserved tickets (as they were like movie theater kiosks). I took her place in line so we didn’t lose our progress, and she went and tried. Sure enough! we were able to skip the several hundred person line and head right to the site. I think this experience, more than any other of the weekend, convinced her that she could adequately speak and more importantly understand Spanish.

After we got the tickets, we headed into the palace. Alcazar is actually a fortress with 2 palaces inside, and a third on the opposing cliff. The Nasrid Palace is the main event, and each group of tourists is only allowed in during a 30 minute window. Our window was a few hours away, so we headed into the other areas of the Alhambra to look around. First, we went through the outer fortress. We could see the city from the top of the walls:

There were other ramparts and courtyards and such, but they were all outside, so they were mainly weathered:



After walking outside for a bit, we were able to enter the Nasrid Palace. This, to me, is the real Alhambra. Inside, the detail work was amazing:



The courtyards were absolutely beautiful. They make you realize why the Alhambra is such a treasured place. There were cool arches:



Waiting rooms:



and, of course, more courtyards:



After moving through the Nasrid Palace, we moved on to the other main palace on the opposing cliff, El Generalife. As far as we could tell, the Generalife was a palace for the general as Alhambra was a palace for the king. As such, it was a total letdown. We figured that the point of it was to give the general a nice place to live while reminding him constantly that the king was his boss. Every time he would look over the cliff, he would see this:



On the way out of Generalife, there was this cool walkway though:



With that ended our tour of the Alhambra. There was some other brief walking about, but nothing major to see. We went and got our bags and decided to find our way to the airport. We caught a bus back to Avenida Colon and grabbed lunch at a touristy place, then we set off down where we thought the bus for the airport picked up. We walked and walked, but couldn’t find the correct stop. Finally, just as we were about to give up an get our last cup of cafe con leche, the airport bus goes rolling by. We noted where it stopped for later, and went and enjoyed our last Spanish delicacies.

After food, we hopped on the bus and headed for the airport. It was a quick bus ride and we got there with plenty of time to spare. We realized we hadn’t yet registered for Boat Club Dinner, and I was in a panic to find an internet terminal. Apparently the mega-airport at Granada (said sarcastically because the airport only has 4 terminals) doesn’t have internet publicly available. We checked in for our flight and got in line for our plane.

This is the area for my rant. I have come to love England. It is a little rainy, yes, but in general I have really enjoyed it here. One thing that I really do question is their legendary ability to avoid queues and maintain politeness at all times (except maybe during football matches). While waiting in line to check in for our flight, a group of 11 Brits joined 1 person holding their place in line. RyanAir checks in everyone seperately. This really put off the people behind them. Whatever, I thought, its check-in, it isn’t a big deal. Then, while in line at the terminal to board the plane, it happened again. Now I would like to point out that at no point was I cut, so this is not a personal thing. Instead, this family or large, family-type group, cut 2 ladies traveling with children under the age of 3. When one said something, she was verbally assaulted by the group. Even a British guy in another line was telling them to get at the end because they “[were] making us all look bad”. They were totally without class the whole time, used foul language, and were generally offensive to everyone around. I guess there is always one group, but this one left a particularly bad impression. Say what you will about America, I have never seen anything like that level of selfishness and rudeness take place there.

Once on the plane, we braced ourselves for a 3 hour flight. It was over the Sierra Nevada mountains, so it got really bumpy at times. When we finally landed at Stansted, we were really glad to be back. We just had to go through customs. Once through, we found an internet kiosk (just in time), and got to our bus with minutes to spare. In just a few hours, we went from the cool 55 degrees to 25 degrees. It was painfully cold and we were both just a little sunburned from a great trip.

Welcome back to England!

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This Saturday, Will, Jackie, Kelly, and I made our way to Oxford. According to Will: 90% of the civil service is from Oxbridge (the combined Universities of Oxford and Cambridge), 70% of those are from Cambridge, so they decided to make it really easy to get from Cambridge to London, but not from London to Oxford. Also to avoid a corridor of education between Oxford and Cambridge, there are no direct routes between the two Universities. Thus, wanting to have a whole day in the City, we set off at about 6:00 for the train station.

The Train Ride
The ride to London was nothing special. The 40 minute direct train was nice enough and we all just chatted for a while. When we got to London, we had to take the tube to Paddington station. Because of some crazy construction, it took us longer than usual, and we missed the quick(er) train to Oxford. When we finally got to Paddington, we had about 45 minuntes until our train for Oxford. Luckily, there was a Krispy Kreme in the station so we were able to get breakfast and indluge a sweet tooth at the same time. Finally, it was time to get our train.

We went to one of the middle cars on the train that was essentially empty, sat down in a group of 6 seats that faced each other, and started talking. A few minutes later, a guy walked onto the train and sat across the aisle from us. This guy had scarred and tatooed arms, was on the skinniner side, balding, and looked like he had lived a somewhat rough life. We didn’t really think anything of it. As the doors of the train closed, he asked us where we were going. We told him Oxford, and he made some comment about it that I didn’t completely understand. He had a heavy accent. Over the next 45 minutes or so, he lectured us on lots of things. We could hardly get a word in edgewise, which is probably a good thing considering most of what he said took a while to translate. His topics included, but were not limited to:
- his luck at gambling and knowledge of when to get out of the game and collect his winnings
- how he is a good dancer
- his divorces and children and step-children
- how America is ruining the world (despite our accents, he somehow did not pick up on the fact that we were Americans, or didnt acknowledge it)
- how Oxford and Cambridge and educated people are ruining the world (despite his knowing that we come from Cambridge and are going to Oxford)
- how he occasionally liked to enjoy a ‘joint’ but had a safety valve and would never touch crack or heroin
- how it is impolite to call someone who uses crack a crackhead
- the state and current cost of social housing
- his experience with psychiatric help
- his medical history
- something about a fox
Obviously, this guy made quite an impression. Fortunately, he disembarked about halfway to Oxford. It was an experience, but especially with Kelly there, he made me really uncomfortable.

Christ Church
When we finally arrived at Oxford, we really didn’t have a plan. Win had emailed me a list of fun things to do while we were there, but in my haste to leave, I had forgotten to print it. We will cover the ones we didn’t hit on this trip next time we go to Oxford, which will probably be in the spring. We started down toward city center and walked along High Street, a pedesrian only promenade with a list of shops almost identical to that of Cambridge. We turned down another street and found our first college of the day: Christ Church. It worked out perfectly, because it let us take an up-close look at some of the architecture and enjoy a little time away from the city. We walked across Christ Church Meadow:

to the river and followed the river down to the boathouses. We were able to see some of the teams practicing, mostly novice by the look of it. We then followed the river up to Magdalen bridge, where we rejoined one of the main roads. Apparently, Magdalen bridge is famous. By looking at it, you wouldn’t think so. It isn’t very impressive. The tradition, however, is that after exams, people run to Magdalen bridge and vault into the river. I am not sure about the river in Oxford, but if you did that in Cambridge, you wouldn’t have to worry about passing your exams, you would be in the hospital with all sorts of infections first. From, the bridge, you could see Magdalen tower:

One small note. I recently bought a tripod because I was sick of my pictures turning out blurry. I also tried out this program that lets you take bracketed photos (3 photos of the same scene: properly exposed, underexposed, and overexposed) and merge them into what is called a High Dynamic Range photo. It basically lets you take pictures of things that have really high contrast within the frame and show all of the areas of the picture. This is really good for shooting old buildings, or places with lots of shadows. It creates pictures that mimic more what the human eye sees naturally (though it can be argued that from a photography point of view this is somewhat cheating, but it makes neat pictures so I don’t really care). This also made me slightly annoying, I think, to my travel companions because I was always stopping to take multiple long-exposure photos of cool things. Some of them turned out really well and are posted here, the rest can be seen on my photo website.

Magdalen Bridge
From the bridge, we walked to the Radcliffe:

the famed reading room of the famed Bodelian Library (everything is famed in Oxford):



We also returned here after sunset to get some night photos.

The Eagle and Child

After all the walking, we were cold and hungry. We had all heard of the Eagle and Child, a famous pub where C.S. Lewis and J.R.R. Tolkein would hang out and talk about whatever insanely famous authors discuss. Apparently they would call it the Bird and Baby. It was the perfect English pub. It was dark and sort of cavernous. The bartenders were funny and I had to duck to get though every doorway. Most importantly the food was amazing. Like I mentioned, we were chilled to the bone, so the steak and ale pie that I ordered was just the right thing. It is essentially a steak pot pie minus the vegetables. Pure comfort food.

The Museums
After lunch, we decided to head for the Museum of History of Science. It turns out that this was rightly not on Win’s list of things to do. It was essentially the museum of astrolabes, quadrangles, and sextants. There was one cool exhibit, though. Apparently Einstein has visited Oxford to give a lecture in the 1930s. When he did, they cut about 5 lines of the chalkboard away from the wall and saved it. It has his original handwriting where he describes the density of the universe, or something. Its especially neat because you can see where he made a small error and used his hand to smudge it out.

We then went to the Museum of Oxford. It was pretty informative, but not exciting (also not on Win’s list). I fell asleep for about 13 minutes of the 15 minute short film they had on the town. It wasn’t very exciting. The museum did drive home the point that the Oxford colleges are essentially a set of former monasteries that were disbanded over a course of several hundred years.

Food
After a bit more walking, it was tea time. We found a restaurant to have tea in. Then, walked around a little more. We went and took some more pictures and went to a pub that Will and Jackie suggested. It is called the Turf Tavern. Never have I seen a pub hidden in the middle of a city block. After going down 2 tiny allies, we found our way to the pub. It was a really cool place. Unfortunately, despite its difficult location, all the tables were taken. so instead, we went to Nando’s. It is a Portugese restaurant. It is the closest thing to am American dining experience

I have had since I have been here. They had real lemonade, not Sprite relabeled as lemonade. The food was quick, plentiful, and delicious. Even better: we have one in Cambridge. I’ll definitely be going there again.

Finally, we got back on the train and headed home. I can honestly say that from that I saw, I like Cambridge much better than Oxford. I am sure once you get into the colleges and everything, it is a great place, but they aren’t very inviting to visitors.

This weekend we have our first race: the Bedford Head.

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