Interview: Daniel Gunlycke
2013 Peter Mark Award Recipient
Paul Holloway and Dr. Jack Rowe, October 29, 2013
HOLLOWAY: Good afternoon. My name is Paul Holloway. I’m a member of the AVS History Committee. Today is Tuesday, October 29, 2013. We’re at the 60th annual international meeting of the AVS in Long Beach, California. Today I have the privilege and pleasure of interviewing Daniel Gunlycke. Is that pronounced right?
GUNLYCKE: That’s correct.
HOLLOWAY: Okay. Daniel is from the Naval Research Laboratory, and he is the 2013 Peter Mark Award winner. His citation reads: “For significant contributions to the understanding of electronic properties of low-dimensional graphene nanostructures.” So Daniel, Congratulations on the Mark Award. It is very well-deserved.
GUNLYCKE: Thank you very much, Professor Holloway.
HOLLOWAY: Could we start with you giving me your place and date of birth?
GUNLYCKE: Yes. I was born in Gothenburg in Sweden on May 6, 1977.
HOLLOWAY: Okay. Could you tell us a little bit about your educational background?
GUNLYCKE: Yes. I started at a university in Gothenburg, the University of Gothenburg. Gothenburg has two universities: University of Gothenburg and the Chalmers University of Technology. I started in the former, but then I continued with a master’s in the latter, Chalmers University of Technology. I worked with Professor Goran Wendin. I also got the opportunity at that point to go to Imperial College London and work with Professor Vlatko Vedral. Professor Vedral was one of the early forces in quantum information theory, and I spent a good six months there. After the completion of my thesis, I continued to do a DPhil, which is equivalent to a Ph.D., at the University of Oxford under the supervision of Professor Andrew Briggs and Professor David Pettifor. I also worked with Professor John Jefferson at Qinetiq.
HOLLOWAY: Let me take you back to your second degree, your master’s degree. What did you do your research in for that degree?
GUNLYCKE: I investigated quantum entanglement in an Ising chain. Entanglement is a fascinating subject because it allows you to transfer information between distant objects. Now entanglement is also affected by things like temperature and magnetic fields. That was the subject of my thesis.
HOLLOWAY: Was it theoretical or did you do…
GUNLYCKE: It was theoretical, yes.
HOLLOWAY: Theoretical. Okay. Then when you went on to Oxford, what did you work in there?
GUNLYCKE: I continued to work in quantum information there. The group led by Professor Briggs focused on endohedral fullerenes inside carbon nanotubes. They looked at nitrogen inside a fullerene inside a carbon nanotube, which could potentially be used to do quantum information processing. Now my interest was of course in the quantum information background, but because of the structure, I became aware of the properties of carbon nanotubes. So gradually at that point, my interest shifted from quantum information, and I started to increase my focus on carbon nanotubes and later carbon nanostructures.
HOLLOWAY: So carbon nanostructures entangled you at that point. [Laughs]
GUNLYCKE: Yes.
HOLLOWAY: You did your second degree in what year?
GUNLYCKE: So I finished that degree in 2002. The project I did at Imperial College was actually a part of that master’s degree.
HOLLOWAY: Then you went to Oxford. What year did you finish the Ph.D. at Oxford?
GUNLYCKE: I finished in June 2006.
HOLLOWAY: So you got entangled more and more in nanotubes. Did that come after you went from Oxford to NRL?
GUNLYCKE: My dissertation work was on quantum information processing in gated carbon nanotubes. Now at that point, for family reasons actually, I came across to the U.S. I met my wife over in England. She is American, and she was in Oxford on a FitzGerald scholarship from the US Naval Academy.
HOLLOWAY: Is that right?
GUNLYCKE: She had orders to come back to the U.S. So I actually followed her here. It turned out to be very good because we ended up in the Washington, D.C. area, and I had the chance to work with Dr. Carter White at NRL. Carter White is known to have the very first published paper on single-walled carbon nanotubes. Dr. White has done a lot of interesting work in carbon nanotubes.
HOLLOWAY: So what rank does your wife hold in the Navy? Or did she hold?
GUNLYCKE: She was a lieutenant, but she has since transferred to a civilian.
HOLLOWAY: I see. Was she on the submarine, in the submarine program, when she was in the Navy?
GUNLYCKE: No. She wasn’t. She served on a destroyer out of San Diego, and then later we joined up on the East Coast.
HOLLOWAY: I see. Well, that’s an interesting story. I’m glad you shared it with us. Tell me a little bit more about what you do at the Naval Research Lab now.
GUNLYCKE: I came to the Naval Research Laboratory soon after groups had started to study graphene. It was known that graphene has fantastic electronic transport properties but that it did not have a bandgap. If you come from the carbon nanotube background, you know that if you use some kind of boundary condition on graphene, you can use quantum confinement to create a gap. There was very much excitement in the beginning about creating confinements directly in graphene. Straight confinements are known as graphene nanoribbons. It’s the one-dimensional analog of graphene. So the expectation was that these graphene nanoribbons would have a bandgap and have fantastic electronic properties.
HOLLOWAY: What dimension did you need to get the width of the ribbon to in order to get the confinement?
GUNLYCKE: There is no direct sharp transition.
HOLLOWAY: I see.
GUNLYCKE: It’s a gradual transition. The bandgap is inversely proportional to the width. Now if you want to get band gaps similar to what you see in many other semiconducting materials of order a few hundred millielectron volts, then we are really talking about ribbon widths of order 10 nanometers.
HOLLOWAY: 10 nanometers.
GUNLYCKE Yes.
HOLLOWAY: That’s pretty narrow. So how were you trying to define these? By electron beam lithography, for example?
GUNLYCKE: Well actually, that’s one of the things that I have left to experimental colleagues at NRL and throughout the U.S to figure out.
HOLLOWAY: So it’s easy. You can strike 10 nanometers in theory, right? [Laughs]
GUNLYCKE: That’s absolutely correct. [Laughs] In fact, in theory, the smaller the structure, the easier it is to model, and in that sense we actually come from the opposite point where anything small is easy and anything large is hard—just the opposite of what experimentalists face.
HOLLOWAY: Good. We’re joined by Jack Rowe. So we’ll continue unless you have something to add right now, Jack.
ROWE: No, I don't. Sorry I’m a little late getting here.
HOLLOWAY: No. That’s all right.
ROWE: I ran into a couple of people.
HOLLOWAY: We unlocked the door for you.
ROWE: Yeah, thank you. I appreciate that.
HOLLOWAY: We were talking about graphene ribbons. So you were talking about the edge defects, edge effects on the ribbons.
GUNLYCKE: Initially it was thought that the ribbons would share the fantastic properties of carbon nanotubes, but with the advantage of being flat. Now the presence of edges is of course a big difference. Carbon nanotubes are seamless. Graphene nanoribbons are not. The edges are typically rough when you create nanoribbons in experiment, and it turns out that edge roughness has a very strong effect on the electronic transport properties. The reason is that the boundary condition you have at the edges of the ribbons is extremely sensitive to the width at the atomic level; if you change the width by just one atom, you have significantly changed your boundary condition. So, if you’re a carrier and you want to move through this material, these width variations look like obstacles. It’s an obstacle course that is almost impossible for a carrier to get through, and that’s the reason why the transport properties degrade.
HOLLOWAY: Now this is based upon theory or experiment or both?
GUNLYCKE: Yes. In experiment, you see an effect known as variable range hopping. That could be seen as a manifestation of Anderson localization, and the Anderson localization is a concept that we predicted in these nanoribbons.
HOLLOWAY: Now if you talk about—You say the width was like 10 nanometers or less.
GUNLYCKE: Yes.
HOLLOWAY: How long could you make these ribbons experimentally and theoretically?
ROWE: Theoretically I think you can make them as long as you want.
GUNLYCKE: Yes. Yes.
ROWE: Infinite.
HOLLOWAY: Well, you run out of computer power sooner or later.
ROWE: Well, you just…
GUNLYCKE: There is a paper by Philip Kim’s group at Columbia where they looked at the transport through nanoribbons. One of the things that they noticed was how the bandgap in the material becomes larger as you reduce the width just as theory predicted. Now when they came down to widths at about 20 nanometers and a bit less, the transport really degraded so much that they couldn’t really see clear transport features. That brings one question to my mind: Was it that these ribbons broke and you essentially had a circuit that was shortcut or was it because your localization effect is now so strong that even if your material is intact, you cannot have any appreciable transport through it?
ROWE: It’s likely that is what happens when you make them narrow enough is that fluctuations in the width become significant as you mentioned just a short while ago. I don't think there’s a problem with them breaking because they’re supported on the substrate.
GUNLYCKE: Yes.
ROWE: In fact, I’m somewhat familiar with these experiments. So they’re supported on a very hard semi-insulating substrate, so they’re not going to break very readily. It’s not like the ones that are transferred to silicon oxide. It’s a much more robust substrate.
GUNLYCKE: Yes, and that certainly is my view as well.
ROWE: Yeah. That’s probably right, yeah.
HOLLOWAY: Now you talk about trying to clean up the surface roughness by reactivity, I believe—reaction at the edges. Is that accurate or not accurate?
GUNLYCKE: There are a lot of efforts to create nanoribbons with perfect edges, so there are a few different approaches. Some groups are trying to clean the edges. There are groups that have unfolded carbon nanotubes—that cut carbon nanotubes and have them unfold into nanoribbons. There are groups that have taken graphene and let nanoparticles cut up graphene. These nanoparticles predominantly follow the crystallographic directions in graphene. That way you can get perfect edges. Now recently there’s even been an effort to grow nanoribbons using precursors in a bottom-up approach. So there are many different approaches to creating ribbons with perfect edges.
HOLLOWAY: Do you believe that ultimately you’re going to be able to create perfect edges and use this in a device somewhere?
GUNLYCKE: Given time, yes. I think as a theoretician you realize that a year or a few years is a short time. Keep in mind that the theory of graphene was developed in the 1940s, and graphene nanoribbons was modeled back in the ’80s, I believe, in Japan. So a lot of theories are done in kind of a vacuum, but sooner or later, the experiments are catching up. I think the same could happen in graphene nanoribbons. They really have exceptional intrinsic properties, and I’m very hopeful.
HOLLOWAY: Now if you take a surface of a solid and terminate it, particularly the compound semiconductors, that surface may tend to relax and rearrange to minimize energy. Does the same thing happen on the edges of the graphene sheets?
GUNLYCKE: Yes. It has been suggested that there is edge construction. However, that’s in the absence of having any stable species terminating the graphene.
HOLLOWAY: I see.
GUNLYCKE: So if you have edges terminated by something like hydrogen or fluorine, then I think they are expected to be quite stable.
ROWE: I happen to be very interested in graphene, so I was very interested to try to participate here. The graphene nanoribbons that the Columbia group has measured were actually originally grown at the Naval Research Lab in the group that Kurt Gaskill and Chip Eddy are involved in. One of my former students actually worked in that group as a post-doc several years back. But on the substrates, the substrate is silicon carbide, which of course is a compound semiconductor. There is a reconstruction of that surface with a so-called carbon buffer layer, and so the edges of the nanoribbons after processing are likely to be partly carbon atoms bonded in a non-sp2-type bonding that are part of this reconstructed carbon buffer layer. So that makes for a more difficult theoretical treatment because one has to worry about, well, the actual structure of this buffer layer is not known. The periodicity is known, and it forms a coincidence lattice with graphene so you get epitaxy. It’s quite a very interesting system. So it will be challenging to try to make progress with the experimental realization of some of these nanoribbons that are really very well formed.
HOLLOWAY: Let me ask the question at this point in time. You know, we talked about the nanoribbons. You do the theory and other people contribute to the experimental investigations. Who are some of the people you’ve worked with that have mentored you or collaborated with you in this area?
GUNLYCKE: I have focused solely on the theory. I have worked with of course Dr. Carter White at NRL, but also Professor John Mintmire at Oklahoma State University. I should mention Dr. Denis Areshkin. I have worked with Junwen Li.
ROWE: Excuse me for interrupting again, but one interesting thing to me is that the first two people that you mentioned actually have a strong connection with the institution that Paul Holloway represents, the University of Florida, because both of those people got their Ph.D. degrees in physics at the University of Florida.
HOLLOWAY: Is that right?
ROWE: Yeah.
HOLLOWAY: I didn’t know that. Good! We’re populating the world.
GUNLYCKE: Yeah, yeah.
ROWE: That’s right. Yes. [Laughs]
HOLLOWAY: Are there other names that come to mind?
GUNLYCKE: I think those are the main collaborators on the graphene nanoribbons. Now more recently I have worked with Dr. Paul Sheehan at NRL and I’ve worked with Berry Jonker, also at NRL.
ROWE: I was in a talk earlier this morning that Berry Jonker gave on graphene that was very interesting. I plan to talk to him further at the meeting about that.
HOLLOWAY: Well, in your talk yesterday you also talked about line defects. Could you tell us what line defects constitute?
GUNLYCKE: Yes. So a line defect is a highly symmetric structure in graphene. It’s, as the name suggests, a one-dimensional defect. One thing that’s special is that it’s perfectly straight. To allow it to be straight, the defect has a particular configuration consisting of double pentagons and an octagon, and this pattern just repeats along the line defect. This is something that was observed at the University of South Florida in 2010, and since it has been shown that this line defect could be controllably grown. So any time a theoretician sees a structure that is reproducible and you know the exact structure, then you really want to throw yourself into it and explore the properties.
HOLLOWAY: So what are the properties? How do they modify the properties of graphene by line defects?
GUNLYCKE: Well, one fascinating aspect is that graphene has a few different degrees of freedom. It has a spin degree of freedom, but it has also a valley degree of freedom. The two valleys in graphene are inequivalent, but degenerate. So any time people do measurements and they want to consider valleys, they typically just multiply their result by a factor of two. That’s kind of the level that valleys are considered mostly. But using the line defect, you can actually filter carriers (and by carriers I mean electrons or holes) according to which valley they belong to. You can now start to think of valley polarization, which you can measure. In principle, this could open up a new field similar to spintronics.
HOLLOWAY: Spintronics may get off the ground yet.
ROWE: That’s right. Yes.
HOLLOWAY: And maybe valley polarization will, too.
HOLLOWAY: Let me ask you, Daniel, where you want to go in the future. You won the Mark Award. That’s very significant, very prestigious for somebody under 35. Where do you envision yourself five years from now?
GUNLYCKE: I think that depends. At the moment, we are settled in in the Washington area. Now did you mean professionally or research-wise?
HOLLOWAY: Yes. [Laughter]
GUNLYCKE: [Laughter] Either one, yeah.
ROWE: Either one. There are many universities in the Washington area.
GUNLYCKE: Absolutely. That’s right.
ROWE: One extension of that question is do you aspire to be a university professor? Do you enjoy…I mean at the Naval Research Lab there are many other scientists that are well-known. Many of those, as we’ve already talked about, are active here at the AVS, so there are a lot of people to interact with more or less on your same level.
GUNLYCKE: Yes. That’s certainly true.
ROWE: So what about universities? Is that something you would enjoy?
GUNLYCKE: I think I would enjoy being at the university very much. Now there are pros and cons like with everything in life, I imagine. We have a fantastic opportunity at the NRL to focus on research and really dedicate our time to research. But I think there is more to life. I enjoy teaching as well, so that’s an aspect that we don’t have at any of the federal laboratories. So there really are pros and cons, I think.
ROWE: I thought that some federal laboratories did have some students. I mean there is not a well-defined program, but there are special cases. So I don't know.
ROWE: Maybe you can have the best of both worlds and have some very bright students come and work with you at the Naval Research Lab.
GUNLYCKE: Yeah. There are some programs. I mean I know at the Naval Academy, for example, that there they have students and they can do research. We have different programs that allow us to mentor post-docs. I had one post-doc, Smitha Vasudevan—
ROWE: I mean you were a post-doc yourself, so yeah.
GUNLYCKE: Absolutely. I had a post-doc a couple of years ago, Smitha Vasudevan, who worked with me on line defects. She was specifically looking at different adsorbates you can put on the line defects to change the properties.
ROWE: Yeah. In fact, many of the people prominent in the AVS had started their careers just like you did as post-doc at the Naval Research Lab. I think that Alison Baski is one of the examples of that. She’s done extremely well.
GUNLYCKE: Yeah. It’s a fantastic institution, and I’m very, very grateful to NRL for the opportunities I’ve had.
HOLLOWAY: What advice would you give to young people that aspire to win the Mark Award?
GUNLYCKE: One thing that I got from Dr. Carter White is that you shouldn’t necessarily just follow the pack and follow the flow in research. Some of the more interesting problems you encounter by taking a step outside the picture and think of your own problems. I think that’s one philosophy that I hope that other people will also take to heart.
HOLLOWAY: What about interaction in professional societies? Do you find that necessary, an advantage, beneficial?
GUNLYCKE: Oh, absolutely. We have many important tasks as researchers and one of them is to become involved in the professional societies. We do reviewing for journals and for different organizations. So there are many aspects of a researcher’s life, and the professional societies certainly serve one of these important areas.
HOLLOWAY: One of the messages I will give in my Thursday talk is that the professional societies are by and large volunteer societies. But to get back out something that is valuable to you, you must give something, put something in.
GUNLYCKE: Yes.
ROWE: That’s right.
HOLLOWAY: So I think that’s an important lesson for people to contemplate. So I presume you agree with that.
GUNLYCKE: Oh, absolutely. I mean all of the good scientific exchanges that result from the meetings that we have, such as the meeting here at Long Beach, none of that would be possible if it wasn’t for all of the time put in by scientists around the country. It’s a tradition that is very important and should be carried on.
HOLLOWAY: Good. I think that covers the territory that I wanted to explore with the interview. Do you have anything that you want to add, Jack?
ROWE: No. I think we’ve covered quite a lot of ground. I’ve enjoyed being able to participate in this interview, and I’d like to wish Daniel the best of success in his continued research and hope to see him at the Baltimore meeting next year.
HOLLOWAY: Good. Well, congratulations on the Mark Award, Daniel.
GUNLYCKE: Thank you very much. I also look forward to meeting you at Baltimore provided nothing happens with the government. But the good thing is that Baltimore is close to the NRL, so one way or another…
ROWE: You can always drive.
HOLLOWAY: If you’re…whatever they call it. If you’re shut down, then you’re free to go where you want to go. [Laughter] Again, congratulations, Daniel.
GUNLYCKE: Thank you very much.