This FSU engineering major is spending her summer exploring spider silk and making transistors.
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. Hes 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 Lorenas 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, shell 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 shes 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 Lorenas been up to.
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.
While Lorena and graduate research assistant Shermane Benjamin discuss some of Lorenas findings, they joke about transistors.
For one of the chips we treated, it was really successful, and so were trying to figure out what happened. Were 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 didnt come as good as the moldy chip. Thats what were 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 dont actually think its mold, were 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 were 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.
Watch this video clip to see one of Lorenas transistor chips being treated with argon-plasma gas. As the gas lights up inside the machine and turns purple, it's changing the interface between the cocoon silk and the gold on the transistor chip.
When we first did it, it was just an idea to see what would happen. And then it worked really well. I guess thats 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. Shes 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 Ill be living in Curitiba is in a república, which is a big house with 16 rooms, kind of like a dorm, and its walking distance to the school. So Ill be taking three classes and doing my senior design project, which is the whole reason Im going to Curitiba. They have these algae bioreactor plants there, and theyre 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. Theyre researching how best to grow the algae, things like that. Ill learn a lot more about it when I get there!
Lorena talks about some surprising lab results with her transistor experiments, and reflects on the larger meaning of her MagLab experience.
Research Graduate Assistant Eden Steven shows Lorena the finer points of using an evaporator machine.
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 wasnt 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 dont want a transistor like that! And with my transistors, it was even worse. It would take maybe four minutes to turn on. But we couldnt figure out how to solve it.
So we started reviewing what we know and what weve observed. So we know that were 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 were 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 wont be water-soluble anymore.
Lorena holds one of the tiny transistors shes been making.
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, were trying to overnight humidity treat them and check other parameters to understand the physics behind the improvements. And then were 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. Edens drive is doing research. His philosophy is: You think of an idea and you try it. Doing research, its almost like addicting for him. But I would say that I didnt have too much drive before coming here. But seeing Edens enthusiasm, and just being able to input my own ideas, thats really nice. Its more than just having a job and being told what to do and reporting the results. Its more like were just in the lab trying things out. Its more like you want to be here instead of you have to be here. Thats the atmosphere of this lab.
So the last few nights, Ive stayed here until 7 or 8 p.m. just because I want my ideas to work. Its more like a drive now. And thats really nice.
Lorena practices her tweezers skills while making adjustments to an evaporator machine.
Lorena discusses what its 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. Its 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. Youre 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 didnt work, but hes always trying different things.
So right now, were 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, were making four different kinds using different materials and depositing methods. Were just experimenting with different kinds of transistors and seeing what works.
Its nice to be in the lab with people who have similar interests. … Youre not the only geek in the room!
So were 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 were also trying a flexible plastic substrate, to see if we could make a flexible transistor.
Another thing that were 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 were 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 doesnt eat away at the cocoon silk, it will work.
Using tweezers and a steady hand, Lorena peels a tiny piece of Scotch tape off a teeny sample of graphite.
Have you heard about graphene? Lorenas working with tiny samples of it. Graphene is a form of graphite — the same stuff in your pencil! Its stronger than steel and the most conducive material yet discovered.
I didnt know what the big deal about graphene was until recently. Its graphite, but when its in single layers they call it graphene. The whole reason its 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 couldnt 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 its the simplest way to do this.
Learn more about how scientists use magnets to study graphene.
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, thats 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 cant see them at all. Once you put them on the chip, you cant see them. We use a microscope, but even then you can barely see them.
Graphene is the new thing and its pretty interesting. Theres a lot of research on it now.
Lorena examines a tiny silicon wafer under a microscope.
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. Its 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 Ive 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 its 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!
Lorena collaborated on this blog with science writer Kathleen Laufenberg. For more information about the MagLabs REU program contact Jose Sanchez at firstname.lastname@example.org or (850) 645-0033.