University of Groningen
Spin transport in graphene - hexagonal boron nitride van der Waals heterostructures
Gurram, Mallikarjuna
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Publication date: 2018
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Gurram, M. (2018). Spin transport in graphene - hexagonal boron nitride van der Waals heterostructures. University of Groningen.
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After nearly four and half years of PhD research including three years worth of looking into optical microscope, hundreds of graphene and hBN flakes, 43 hBN-graphene-hBN stacks, countless optical pictures, cleanroom suits, 19 work-shops/conclaves/conferences, multiple manuscript drafts, four publications, and some more writing, here I get a chance to thank you. I have to admit that I am more of a secret admirer. Now that I get to express my regards in words, it feels a bit awkward ;) This also made me realize that I have been at the receiving end of great helping hands, both for the work presented in this thesis and for the things that led to this thesis. This cannot be expressed much better than Carl Sagan, who once said, “If you wish to make an apple pie from scratch, you must first invent the universe.” My apple pie, this PhD thesis, came to existence, thanks to the continuous support I received from family, friends and colleagues. Therefore, I would like to thank you all.
First and foremost, it’s a great pleasure to express my gratitude to my supervisor Bart van Wees for guidance through my PhD research. Bart, it is humbling to see such a great progress in my PhD research within a short period of time, thanks to your profound insight in understanding and approaching the experiments, and quick reviewing of the manuscripts that I used to spend weeks on. Your critical approach and foresight in undertaking the problems helped me at times to get a reality check about the amount of time I was spending on projects. I also like that you have fun with breaking the formality at workshops, meetings, and talks by creating those light-hearted moments with your sharp sense of humor. I’m glad to have witnessed your Spinoza milestone and received many free beers at borrels and conferences. I’m thankful also for the opportunity to stay back and take my time to finish this thesis. Next, my co-supervisor, Ivan, though we shared little time together at FND, it was inspiring to see how a close-to-ideal postdoc would work, collaborating and sharing ideas with and multiple PhDs, giving feedback on everyone’s science talks and group talks and willing to teach and learn from others. I am thankful to you for finding time to give feedback on the project with magnetic molecules and magnetoresistance measurements. I will always remember your words of wisdom, “Gentleman, hustle!”
The projects carried out during this thesis (Chapters 5 and 7) would not have been successful without the collaboration with Basel team: Simon Zihlmann, Peter Mak, and Christian Sch ¨onenberger. We started out with CVD-hBN from Graphene Supermarket Inc., but when the company stopped producing the materials, all of a sudden, we had to halt the project until we found a new source of CVD-hBN.
170 Acknowledgements It was disappointing but this gave me enough time to explore the possibility of using exfoliated-hBN for tunnel barrier which led to Chapters 5 and 6 and the rest is the glory of hBN! ;) Christian, thank you for sending occasional personal emails acknowledging the efforts in our collaboration which were always encouraging. Peter and Simon, even though you guys were not actively working on spin transport, you always seemed to know what is happening in this field. I am thankful for your quick and critical feedback on numerous failed devices and manuscript drafts, and many skype discussions. I also thank you guys for initiating Basel graphene workshop for young researchers. This was actually where I realized that I am fabricating the most difficult devices with highly sought after single/bi-layer crystalline hBN flakes.
I would like to thank the members of my thesis assessment committee, Christoph Stampfer, Roland Kawakami, and Anton Koster for accepting and then taking their invaluable time to review my thesis.
I would also like to thank the often-taken-for-granted people in the academic world: the editors and anonymous reviewers of my published manuscripts of this thesis whose critical assessment of my research results for the journal publications was highly useful for improving the scientific standard of the manuscripts.
Casper, it’s great to have a professor right across your office for the last four years who has been with/around you right from the beginning: first as a part of my interview panel for TopMaster admissions, then as a coordinator of the TopMaster Nanoscience, gave a chance to be a teaching assistant for the Quantum Mechanics-I course, and who also happens to share the same enthusiasm for running. Someday, I hope to challenge my running routine to level up to your 30 km/week. Thank you also for occasionally managing to drop by my office for a casual chat about how I was doing and cheering me up.
Prof. Tamalika, as my student advisor during the first year of TopMaster, you played a big role in familiarizing me with the dutch academics. I deeply appreciate the support received from you and Casper when I failed the first round of exams in my Master. I also had the pleasure of working with you as a part of Indian student association, GISA, and sharing the stories of art and craft of weaving. Thank you for being there for a friendly conversation, a word of advice or encouragement, discussions on the tunneling spin polarizations and the useful references you shared. I would like to thank our technical and administrative task force: Anna, Johan, Martijn, Tom and Hermann for making sure things run smoothly in this group so that we get to focus on doing research. Johan, I appreciate your ability to deal with things with energy and no-nonsense approach. Thank you also for sharing stories about your weekend project. I think, everyone should be working on one, not necessarily related to academics. Martijn, you were always the first one I approached for technical help, especially wire bonding most of my samples and fixing the dilfridge setup. Thanks also for patiently listening to and correcting my broken spoken dutch, especially translating the summary of this thesis into Dutch, and for sharing stories about
fitness, traveling and parties. Tom, thank you for keeping track of technical issued raised during the meetings and making sure they get fixed asap. Hermann, you are super good at building things and always seemed to have an answer for the related problems. Anna, thank you for helping me with many administrative issues without any hiccups and alwayss on time. Bernard, even though we shared a few common months at FND, I find you are quite welcoming. I’d say that I hope to be as strong and active as you when I reach your age! I would also thank Johan Kuiper at liquid N2/He facility for helping me many times with the huge liquid nitrogen cylinders and for a friendly discussions and stories about the facility.
Working on a challenging project in a narrow field means you need support from colleagues. I had privilege of working with fine people, some of whom have became my friends along the way. Sid, we met in 2011 and started together with TopMaster and then PhD. Looking back, I’d say, surely time flies! I can’t stress enough how grateful I am for your constant support over these years. Especially, when I was late to prepare my first spin valve device, with your help, I was able to get on easily with spin transport measurements within a short time. Thanks to your down to earth nature and willingness to help others, you patiently answered plenty of my questions and discussed concepts which made sure that you have a large contribution to this thesis. Moreover, with your intellect and work ethics, I hope you continue to lead a great career and further retire to the downhills of Dehradun! Madhu, it is great to have someone to share lunch times, who cheer you up through ups and downs of PhD. The fact that we seem to have many things in common but agree on very little makes our conversations interesting to me. I hope you remember to keep your spirits up and move on, till you get there. Thanks to both of you for listening to my complaints and the fun times sharing countless discussions, drinks and dinners over these years. These mean a lot and also important to me that you guys are my paranymphs.
Pep, your ability to learn quickly, explaining to others and cite papers with journal names and years at your fingertips has been a great help. Thanks also for teaching me the transfer technique which has been instrumental for this thesis. Christian, always good to hear from you that hBN is working great for your devices. I hope, you don’t have to prepare many more devices. Alexey, thanks for the helpful discussions with the porphyrin-graphene project and bonding my samples at times on a short notice. Julian, I believe you are making the most complicated devices in our group combining the multiple 2D layers. I appreciate your efforts in getting the new setup to the group. Jorge and Lei, it’s great to see the progress you are making within a short time at FND. Keep it up. To the young graphene team Tian, Talieh, Xu, Lei and Jorge, I wish you success in all your efforts. I hope you guys work together and achieve great success. Jing, Crystal, and Ping, you guys always come across as kind with big smile on face. I wish you success with the rest of your PhD. Juan, we joined FND at the same time but somehow you managed to churn papers right from your masters. It’s always
172 Acknowledgements pleasure talking to you. Wish you best for your defense and the following career step.
Kumar, you always seemed to have had fun enticing the lab members with your dressing style and the deliciously smelling lunch boxes. You and Talieh scared me enough times in the measurement room at night for which a favour shall be returned! Arijit, you always seem to be occupied with handful of Bachelor and Master students working with you but don’t forget to take care of yourself whom you need the most for your PhD. Eric (DJ deVries!), thanks to your welcoming nature and enthusiasm in creating fun activities since our Master time together, I had fun joining concerts in Amsterdam with you and Jorge, and also had pleasure watching you spinning the mixers in the dungeon of USVA. Man, parties will never be the same after you leaving the group! I wish you good luck with your next career move.
To Jasper, Sander O, Olger, Joost and Jakko, I admire how you guys used to switch to english whenever you notice the non-dutch students come around in the coffee room. It’s always pleasant to strike up a conversation with you guys. To Niko, Thomas, Marcos, Paul, Magda, Ivan, and Jasper, thank you for leaving a legacy in graphene spintronics in our group. Special thanks to Niko and Paul for being around the lab and sharing their wisdom when things didn’t seem to move.
Many thanks to the present and past friends of nanodevices (FND): Fasil, Gaurav, Subir, Sander K, Saurabh, Nynke, Roald, Ludo, Gertjan, Aisha, Nilesh, Carmen, Xu, Geert, Timo, Tom, Arjan, Jeroen, Jantje, Rick, Micheal, Javaid, Alok, and many other visitors of FND for the feedback on my science talks and group talks, and for the fun times at group outings, borrels, dinners and the pleasant working environment. I would also like to extend my thanks to fellow PhDs from neighbor groups: Ankur, RP Singh, Tarun, Edwin, Ling, Neeraj, Selvaraj, Jamo, Shreyans, Soheil and Daniel.
Needless to say, there were plenty of things that did not work during my PhD. This also mean that next to myself, few others spent their precious time without seeing its fruits. Magda, thanks for patiently teaching me the CVD transfer technique and sharing your knowledge on graphene/YIG experiments. Somehow it wasn’t for me but I’m glad to see your work led by a great successor, Christian. Juliana, many thanks for teaching me about the dilution refrigerator and transferring the setup responsibilities even while you were in Brazil. It was also the time that the setup had technical problems and then I had to move on to different project. I wish you good times in Brazil. Petra Rudolf and Tashfeen Zehra, thank you for our short collaborative work on characterizing the magnetic molecules on graphene. Even though we were successful in finding the signatures of the cobalt on graphene via XPS, unfortunately, I couldn’t get enough supporting transport measurements done. Tashfeen, many thanks for your help characterizing my samples, at times even during the weekends. I hope that your hard work in PhD pays off with a successful career in future. Ivan and Alexey, you also helped me with the discussions and thank you for that.
instructors’ engaging teaching style and the importance of the content. Thanks to Lilian Eggens for giving the course on Teaching for PhDs. I learned the nuances of teaching in a classroom and enjoyed the discussions. Thanks to Danie Black for teaching the course on Publishing in English. This topic has been of great help in improving my writing standard. There is still a lot to learn for me though.
Before starting my PhD journey, I have been fortunate to meet great people who nurtured my interest in pursuing research towards PhD. Thanks to Perumal Alagarsamy at IITG for guiding my bachelor thesis and introducing me to the world of nanotechnology. I thank Debabrata for daily supervision, sharing the stories of his PhD life and word of advice about higher studies right after my bachelor. During my Bachelor, I also had an opportunity to do a short internship at UGC-DAE CSR Indore, with Rajeev Rawat and his team Pallavi, Pallab and Sachin. I still remember the chai breaks and lunches we used to have on hot summer days and broad range of topics that we discussed with equal importance. Thanks to the interdisciplinary curriculum of the TopMaster program, I was introduced to the wet chemistry lab in a short project with Andreas Hermann and his PhD, Pavlo at RuG. Pavlo, many thanks for teaching me the AFM techniques. I still remember how enthusiastically you work in the lab, it was contagious! I hope everything is working out well in your postdoc position in USA. Another short internship during my Master, with Gustau Catalan in Barcelona and his team, Jackeline, Neus and fellow researchers showed me the joy of doing research and having fun at the same time. Especially, the Friday evening group talks with beers (wish, many groups introduce this idea!) and Wednesday rock climbing evenings stand out in my memory.
Eek, special thanks for your supervision during master thesis which is still an invaluable learning experience as I further stepped in to PhD. I learned a great deal about personal and time management in regard to research by watching you closely how you worked at FND. Thanks also for sharing your thoughts on research and on life in general.
Xiaoyan, thank you for teaching me about the molecular self-assembly technique during my master project. This also helped me to start my first project in my PhD to study the influence of magnetic molecules on graphene via magneto transport. We had good results with spin transport experiments by Siddhartha. With your kindness and hardworking nature, I hope you get deserving success in near future.
Finishing my PhD also means that my stay in Groningen city is nearly coming to end. It has been nearly 6.5 years since arrived here. Through these years, I am fortunate to have met some great people and become friends with few along the way. Big thanks to the most welcoming Jason, Christy, Pia, Carmen, Elias and Guilherme for being awesome flatmates, for making sure I get to know this city and feel comfortable living here in the early days of my stay in Groningen. Soon after my arrival, I discovered a great but small Indian community in this seemingly remote place who made sure I don’t lose touch with my roots. As time passed by, Pranov,
174 Acknowledgements Praneeth and Goutham became good friends of mine since my Masters. Now we live in different places yet these guys make time for get-togethers and fun. Thank you guys also making room for sharing stories of our PhD lives and encourage each other through these years. Suresh Vijay, thanks for introducing and encouraging me to visit Springs. It has now become a important part of my schedule and helped me many ways in the last two years. I wish you great future for you and Christel together. Gaurav K, its great to have a super active party fly along. Thanks also for hosting me at your place. Shilpa-Rjender, Saritha-Gopi, Saisree-Raj, Spoorthi-Akshay and Monica-Eswar, I enjoyed being a little brother around and our gatherings filled with nonstop satires and laughter. To Vikram, Kiran-Shruthi, Ashoka-Rama, and Aditya, thanks for sharing your humbling advice from your seniority. Eswar, Suresh, Sandeep and Sai, I can’t thank enough for the fun times we had in the last two years especially your kullu jokes at Hema breakfasts and weekend dinners, made my days in the difficult times. Dhwani, often I fail to notice how you easily get me engaged in discussions despite my aloofness. I enjoyed (cautiously!) your adventures with cooking new stuff. Now that you are finding the joy of traveling alone by yourself, I wish you all the best. Hemanth, thanks for introducing me to the circuit training. I would also like to extend my thanks to Gurudas, Avishek, Arunesh, Ankur, Arun, Ashish, Anil, Afzal, Balaji, Hemanth, Kiran K, Milon, Muthu, Pulkesh, R.P. Singh, Silva, Saurabh Soni, Sumit, Tarun, Vasudev, and many other fellow Indians.
Gery, I am happy to have met you as my flatmate at my longest stay in one place. We had great time sharing our cooked meals, running, going out for parties and little adventures. I forever cherish our times together with Melissa and Wijnand. Special thanks to you, Emilio and Rich, I learned the importance of keeping myself active and healthy. I wish you great time in Spain.
I used to wonder if I could find a Dutch friend with whom I can be friendly enough to just drop by their home without any prior appointment and grab a beer from their fridge on a Friday evening and crash on a couch and watch TV. It’s happening, since nearly four years after my stay here, when I met friendly and welcoming locals, Stefan, Huib, Dennis, Wesley, Ileen, and Lars. Stefan, it’s great to have a neighbor who also loves my favorite shows like Prison Break and Planet Earth. Like always, stay dangerous! Huib, it’s interesting to listen to your politically incorrect discussions and jokes. Now that I am leaving, I have left very few days to answer ‘dude, when are we going to smoke a joint together!?’. Ileen, you come across as a very understanding person. I cherish the times how we managed to touch upon the topics like traveling, philosophy and culture that very few people seemed to show interest.
Thanks to the lively community of Groningen, I found many interesting activities and also had pleasure being a part of few of them over the course of my PhD time. It was a great experience being a member of GISA’2013 team along with Anurag, Ekta, Arijit, Saurabh, and Siddhartha and organize several cultural events successfully even with only six members on board. I am grateful to have met Melissa and Kirsten in the
early days of my PhD. I still remember the first email correspondence that turned out to be a longtime companionship with the last four editions of TEDxGroningen. Just for the fun of it, I had great time training for and participating in the Batavierenrace and its accompanying mammoth parties in the last four years, thanks to the cheerful team including Banda, Bjorn and Pugilice for having me. I would like to thank the energetic ToastmastersGroningen community for helping me with finding my stance on the communication part. USVA stands out as one of the great places for keeping me sane with the opportunities to dabble at fun and learning activities including improvisation (thanks to Thomas, Kees, and Naomi), piano (thanks Dana) and spinning the CDJs (thanks Johanz). Marijn and Lucas, you guys are awesome teachers with passion. I am happy to be your student along with Oleg and fellow enthusiasts and I hope to continue learning those challenging moves and freezes even after leaving this place. I would also like to extend my gratitude to my friends and teachers from primary school to graduate studies in India at ZPHS Ghattupal, APRS Nagarjuna Sagar, SR JC Hanamkonda, SriChaitanya Vijayawada, and IIT Guwahati for being part of my education. Special thanks to Kranthi, Anvesh, and Chari for sticking with me all this long and the great times we will still continue to have, and Subbu, Chaitanya B, Ravikiran, Shashank, Vineeth for staying in touch. Kranthi, special thanks for your time and effort for the Telugu translation of this thesis’ summary.
There are of course some free tools on internet that made my learning a rich experi-ence. Thanks to the open source communities like Wikipedia, stackexchange, Matlab-documentation, and LaTeX, and the social media communities Quora, 9gag, Reddit and Google for giving me just the right amount of tools/news/information/trivia needed to keep myself and this thesis sane!
I would like to thank funding agencies supporting my studies at RuG. First of all, TopMasters Nanoscience fellowship for giving me the opportunity for pursing my Masters at RuG and then Graphene Flagship and NanolabNL for supporting my PhD projects.
All of this would not have been realized without endless support from my parents and sisters. No word of thank is enough for the unconditional love I received all this long. I am also grateful for the big support from Bhaskar mama, Kondal babai, and my cousins. Their belief in the importance of education has been instrumental in my journey so far.
Mallikarjuna (Mallik) Gurram Groningen 28 February, 2018.
