REU 2012 Blog: Lorena Sanchez

This FSU engineering major is spending her summer exploring spider silk and making transistors.

Meet Lorena

Lorena Sanchez faces a summer full of spider silk and materials so tiny you really need a microscope to see them. The 22-year-old Florida State University engineering major is one of 14 college undergraduates spending eight weeks this summer doing a Research Experiences for Undergraduates (REU) internship at the Magnet Lab.

Each REU is matched with one or more MagLab scientists. Physicist Theo Siegrist is Sanchez's mentor; she's working in physicist James Brooks' lab with graduate research assistant Eden Steven. Her internship work will contribute to a National Science Foundation-funded project being done by Brooks and Steven.

Her younger brother, 20-year-old Juan Sanchez of Dartmouth College in New Hampshire, is also doing an REU at the lab. He’s in the Ion Cyclotron Resonance program where oil and biofuel research is underway.

Their family is originally from Venezuela; they moved to Pembroke Pines near Miami when Lorena was 8 years old.

Her MagLab summer internship is Lorena’s fourth REU experience. During her three other REUs (at the University of Idaho, University of Chicago and Carnegie Mellon University) she studied nanoparticles. Here at the MagLab, she’ll continue to work with nanomaterials, exploring how spider silk can be used to make electrical wires with exciting potentials. Spider silk is stronger than steel and very stretchy.

But first she’s refining her skills in photolithography, a complex process used to make integrated circuits, transistors and chips by photographing the circuit pattern onto a photosensitive material, and then chemically etching away the background.

Check back each week to see what Lorena’s been up to.

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Final Post: July 6

Lorena talks about the outcome of humidity-treating her transistor chips and realizes that successful science is sometimes in the details.

For one of the chips we treated, it was really successful, and so we’re trying to figure out what happened. We’re trying to recreate what we did with that one chip that turned out so good.

So we thought it was maybe because we left that one chip in the humidity treatment overnight. But when we did that to the other chips, they didn’t come as good as the moldy chip. That’s what we’re calling the really good chip now, because if you look at it under a microscope, it looks like it has mold growing on it. We don’t actually think it’s mold, we’re just calling it the moldy chip for fun. But we know that something changed in it physically or chemically for it to look like that, so we’re trying to recreate it.

So we know we treated the moldy chip at 95 percent humidity and then we left it at 80 percent humidity. And we know that Eden passed the voltage through it when it was at high humidity, so maybe it was that.

But it also might have been the kind of chip it is, because it was spin-cast as opposed to the other depositing methods on some of the other chips. So Eden was reading up on a bunch of different literature trying to see what influences the cocoon silk.

When we first did it, it was just an idea to see what would happen. And then it worked really well. I guess that’s why you should always have great notes … like, “Was drinking water by sample then coughed!” But we do have some data to show.

Lorena may not be at the MagLab, however, when the puzzle is completely solved. She’s headed to Curitiba, Brazil, later in July to work on her senior-year engineering project — which has nothing to do with transistors!

The place where I’ll be living in Curitiba is in a “república,” which is a big house with 16 rooms, kind of like a dorm, and it’s walking distance to the school. So I’ll be taking three classes and doing my senior design project, which is the whole reason I’m going to Curitiba. They have these algae bioreactor plants there, and they’re harvesting algae. They bring the algae into the lab, and they make algae oil out of it. They want to use that oil to power up their building. They’re researching how best to grow the algae, things like that. I’ll learn a lot more about it when I get there!

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June 29

Lorena talks about some surprising lab results with her transistor experiments, and reflects on the larger meaning of her MagLab experience.

We had a breakthrough this week!

The thing with transistors is, after you apply a gate voltage, you should see an effect in a few seconds. Like, if you went into your bathroom and switched on the light, it should come on in a second or two.

But that wasn’t happening with the transistors we were making. With the transistors Eden was making, he would apply the gate voltage and then it would take, like, 30 seconds or a minute to see an effect. Which would mean, sort of like if you went into the bathroom and switched on the light, it would take like a minute to turn on. And you don’t want a transistor like that! And with my transistors, it was even worse. It would take maybe four minutes to turn on. But we couldn’t figure out how to solve it.

So we started reviewing what we know and what we’ve observed. So we know that we’re using a layer of cocoon silk to make the transistor. And we noticed that the amount of humidity in the air would change the turn-on time and the voltage. Eden reasoned that it was happening because the cocoon silk is soluble in water.

So that means the cocoon silk is humidity dependent. The humidity in the air is influencing the cocoon silk, which is the layer in the transistor that we’re testing. So his idea was that if you vapor treat the cocoon silk — if you expose it to humidity for a few hours — then after that it won’t be water-soluble anymore.

So we did that, and we retested it — and it basically turned on almost instantly! So that was the breakthrough: If you humidity treat it beforehand and make the cocoon silk no longer water soluble, you get a faster turn-on time. So now all the samples we have, we’re trying to overnight humidity treat them and check other parameters to understand the physics behind the improvements. And then we’re going to gather data and see the differences between each one.

One of the great things about being in this lab is working with Eden. Eden’s drive is doing research. His philosophy is: You think of an idea and you try it. Doing research, it’s almost like addicting for him. But I would say that I didn’t have too much drive before coming here. But seeing Eden’s enthusiasm, and just being able to input my own ideas, that’s really nice. It’s more than just having a job and being told what to do and reporting the results. It’s more like we’re just in the lab trying things out. It’s more like you want to be here instead of you have to be here. That’s the atmosphere of this lab.

So the last few nights, I’ve stayed here until 7 or 8 p.m. just because I want my ideas to work. It’s more like a drive now. And that’s really nice.

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June 22

Lorena discusses what it’s like to work in a lab with others, and a bit about her work with transistors and testing an idea she had.

Lab has gotten fun. It’s nice to be in the lab with people who have similar interests. You can laugh and talk about transistors, or get real excited about something. You’re not the only geek in the room! Shermane (Benjamin, a graduate research assistant) is really funny and Eden (Steven, a graduate research assistant) is always trying different things. He stayed up here until 2 in the morning trying some crazy paper idea. It didn’t work, but he’s always trying different things.

So right now, we’re working with transistors, which are semiconductor devices that change the resistance between two terminals by varying the voltage of a third terminal. So now with the transistors, we’re making four different kinds using different materials and depositing methods. We’re just experimenting with different kinds of transistors and seeing what works.

So we’re using rubrene, which is a man-made organic semiconductor (and also the organic crystal used in glow sticks) and a type of pentacene called TIPS pentacene, which is also a man-made organic semiconductor and looks really cool. It looks like little, purple, metallic shards.

Most of the transistors we make are on a glass slide. On top of the slide we put the gold, the cocoon silk, the pentacene and the gold again. But now we’re also trying a flexible plastic substrate, to see if we could make a flexible transistor.

Another thing that we’re doing is experimenting with two different ways to apply the pentacene to the slide. The first way is to put it in an evaporator and heat it up until it evaporates. The second way, a new way that we’re going to try, is drop casting. Basically, you mix the pentacene, which is a solid, with toluene (a solvent found in paint thinner), dissolve it and then you drop a little drop of that on the slide and wait until it dries. The drop casting was kind of my idea! Hopefully, if the toluene doesn’t eat away at the cocoon silk, it will work.

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June 13

Have you heard about graphene? Lorena’s working with tiny samples of it. Graphene is a form of graphite — the same stuff in your pencil! It’s stronger than steel and the most conducive material yet discovered.

I didn’t know what the big deal about graphene was until recently. It’s graphite, but when it’s in single layers they call it graphene. The whole reason it’s so cool is because all the computers nowadays are made with silicon, but people are now thinking about using graphene. So graphene is pretty big.

For years, they couldn’t make single layers of graphene, but in 2010, two scientists (Andre Geim and Konstantin Novoselov) won the Nobel Prize in Physics for making single-layer graphene. The way they did this was really simple. They just put the graphite on one piece of Scotch tape and peeled it off, and then they stuck another piece of tape on top of that graphite tape and peeled it and then another and another.

The chunks of graphite that we work with here are like little silver dots, less than a millimeter, maybe like grains of sand, but smaller. We want single, or just a few, layers. So we have to use the Scotch-tape method. They have some fancy name for it — mechanical exfoliation — but we just call it the scotch-tape method. And we use it because it’s the simplest way to do this.

We start out with a big layer of graphite. We put it on a piece of tape and transfer it around 10 times. Once you can just barely see the graphene on the Scotch tape, that’s when you can transfer it over on top of a precut silicon chip.

You transfer it over onto the chip: You stick the tape on top of the chip, you remove the tape, and little pieces of graphene will stay deposited on the silicon wafer.

After we have the graphene, then we have to do the whole photolithography process. You just have to make sure you get at least two of the electrodes touching the graphene. That way you can measure the current going through the graphene. The little pieces of graphene that get deposited are, at largest, 20 micrometers, so you can’t see them at all. Once you put them on the chip, you can’t see them. We use a microscope, but even then you can barely see them.

Graphene is the new thing and it’s pretty interesting. There’s a lot of research on it now.

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June 8

Lorena talks about making teeny transistor chips.

I start out with a silicon wafer (which is about half the size of your pinkie nail) and I cut it into little squares (with) a diamond-tip cutter that looks sort of like a pen. It’s kind of a talent to build them.

The first time I broke one I was in Chicago and I got a piece of silicon wafer in my eye (during her sophomore year doing an REU at the University of Chicago). It was OK; I got it out. But I’ve worn safety eye protection after that, for everyone out there breaking silicon wafers.

So first you cut it and then you have to clean it. We clean it with hot acetone and water. To cut and clean it, it probably takes about an hour for one wafer. And out of that one wafer we get 30 to 40 tiny wafers.

We glue the tiny wafers onto slide glasses (each about the size of your thumbnail), and then we use this purplish liquid, a photoresist (a light-sensitive liquid used in photolithography and photoengraving).

We put the wafer we just cut and cleaned on top of a little drop of photoresist, and then we put it on top of a hot plate at 95 degrees so it can harden … and then you let it dry. Once it’s dry, we want to put photoresist on top of it. In order to get a smooth surface on top, we put it on a spinner … so we get a nice smooth photoresist cover.

We do everything under the microscope. I would say I am developing great tweezer skills!

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Lorena collaborated on this blog with science writer Kathleen Laufenberg. For more information about the MagLab’s REU program contact Jose Sanchez at sanchez@magnet.fsu.edu or (850) 645-0033.