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  • Combining soft lithography and functionalmonolayers with electrodeposition to form

    nickel and zinc oxide nanostructuresMasters thesis

    Enne T. FaberEnschede, October 15th 2009Chemical EngineeringUniversity of TwenteFaculty of Science and TechnologyInorganic Materials Science group

    Graduation committee Prof. dr. ing. Dave H. A. Blank Dr. ir. Andr ten Elshof Dr. Regina Luttge Antony George M.Sc.

  • Abstract

    Fabrication techniques for the production of nanostructures were investigated, specifi-cally a combination of microcontact printing, chemical etching, and the electrodepositionof nickel and zinc oxide. Research on electrodeposition at (in some cases exclusively)the sides of structures was performed.

    Chemically etching a surface while using a monolayer to protect certain regions ofthe gold substrate from the etchant is a sensitive process. The quality of gold is ofsignificant influence, and the nature of the etchant is very important. Conducting linepatterns have been realized using chemical etching with octadecanethiol as an etch resist,although the monolayer is not intact after the etching step.

    The electrodeposition of nickel combines well with microcontact printing based pat-terning, resulting in a smooth nickel layer in the unpatterned regions and cleared areain the patterned regions. The deposition of zinc oxide is less regioselective; most of thedeposit is found in the unpatterned regions while some deposit is found in the patternedregions. The conditions used in this research resulted in a rough deposit.

    Deposition on the sides of structures was partially successful. Nickel was deposited ina continuous line along the side of a structure, while zinc oxide deposit could be found ontop of the structure as well. In one test, lines of silver were realized along nickel/gold lineswhich were produced by microcontact printing, etching and electrodeposition. Furtherresearch could include functionalizing surfaces with different monolayers, using etchedfunctionalized structures to deposit other metals, or using a template to deposit zincfeatures in.

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  • Contents

    1 Goals 11.1 Monolayer as an etch resist . . . . . . . . . . . . . . . . . . . . . . . . . . 21.2 Monolayer as an electrodeposition mask . . . . . . . . . . . . . . . . . . . 21.3 Deposition on the side of structures . . . . . . . . . . . . . . . . . . . . . . 2

    2 Theoretical background 32.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32.2 Patterning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

    2.2.1 Photolithography . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32.2.2 Microcontact printing and monolayer formation . . . . . . . . . . . 52.2.3 Etching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

    2.3 Electrodeposition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62.3.1 Nucleation and growth . . . . . . . . . . . . . . . . . . . . . . . . . 72.3.2 Watts bath . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82.3.3 Zinc oxide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

    3 Procedures and materials 113.1 Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113.2 Silicium wafer cleaning procedure . . . . . . . . . . . . . . . . . . . . . . . 123.3 Gold sputtering procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

    3.3.1 Procedure without titanium . . . . . . . . . . . . . . . . . . . . . . 123.3.2 Thin gold layer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133.3.3 Heated during sputtering . . . . . . . . . . . . . . . . . . . . . . . 13

    3.4 Octadecane thiol monolayer procedure . . . . . . . . . . . . . . . . . . . . 133.5 Etching procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143.6 Nickel electrodeposition procedure . . . . . . . . . . . . . . . . . . . . . . 14

    3.6.1 Deposition with higher applied potential . . . . . . . . . . . . . . . 143.6.2 Deposition with more concentrated nickel solution . . . . . . . . . 14

    3.7 Zinc oxide electrodeposition procedure . . . . . . . . . . . . . . . . . . . . 153.8 Pre-fabricated photolithography lift-off structures . . . . . . . . . . . . . . 15

    3.8.1 Insulation of titanium by fluoride monolayer . . . . . . . . . . . . . 153.9 Combination of techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

    4 Results and discussion 184.1 Etching experiments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

    4.1.1 Sputtered gold on titanium . . . . . . . . . . . . . . . . . . . . . . 184.1.2 Functionalized monolayer instead of titanium . . . . . . . . . . . . 194.1.3 Heated sputtered gold . . . . . . . . . . . . . . . . . . . . . . . . . 194.1.4 Sputtered thin gold . . . . . . . . . . . . . . . . . . . . . . . . . . 20

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  • 4.1.5 Vapor-deposited gold . . . . . . . . . . . . . . . . . . . . . . . . . . 214.2 Electrodeposition of nickel . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

    4.2.1 Nickel deposition with a thiol pattern as a mask . . . . . . . . . . 224.3 Pre-fabricated photolithography lift-off structures . . . . . . . . . . . . . . 23

    4.3.1 Insulation by passive oxidation of titanium . . . . . . . . . . . . . 244.3.2 Insulation by fluoride monolayer . . . . . . . . . . . . . . . . . . . 244.3.3 Influence of voltage on nickel nucleation . . . . . . . . . . . . . . . 264.3.4 Influence of nickel ion concentration on nucleation . . . . . . . . . 27

    4.4 Electrodeposition of zinc oxide . . . . . . . . . . . . . . . . . . . . . . . . 274.4.1 Zinc oxide deposition using a thiol pattern as a mask . . . . . . . . 274.4.2 Zinc oxide deposition using a prefabricated structure . . . . . . . . 27

    4.5 Combination of techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

    5 Conclusion and recommendations 305.1 Monolayer as an etch resist . . . . . . . . . . . . . . . . . . . . . . . . . . 305.2 Monolayer as an electrodeposition mask . . . . . . . . . . . . . . . . . . . 305.3 Deposition on the side of structures . . . . . . . . . . . . . . . . . . . . . . 31

    Bibliography 31

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  • Foreword

    A master project is not something that should be undertaken easily, and a masters thesisdoesnt write itself. It is not a five-days experiment or a case study, and it definitelyneeds to be organized to a degree if it is to be successful. While I knew these thingsbefore I started last year, I relearned them so well I feel I have to restate them.

    It is hard to oversee all the research one can do in a year beforehand. On the otherhand, after all the research is done it can be difficult to see what is accomplished. Forsomeone with a brain as chaotic as mine, it is very important to add a certain amountof order to the system - this in the form of hypotheses, tests and outcomes, or of coursesimply deadlines. When trying to get something done, I found it very important to havegoals, and to monitor my progress. And when I did get something done, it was usuallyafter asking myself Wait a minute - what do I actually know about this?. In the end,I feel satisfied - but only partially. There is so much more that can be discovered, somany more tests can be done! However, my time for this has run out, and while Id loveto see where this subject goes its probably not going to be me who does the next part.It is time for me to let go.

    Research has left a mixed impression on me. I have always had a dream of becomingan inventor, especially a crazy, somewhat distracted inventor like professor Farnsworthfrom futurama. By now I completely understand why the archetype is like that. Notonly should the inventor bring a degree of order to the chaos that is his mind; he shouldalso be flexible and creative, relaxed and open to new ideas. This is not for everyone,and I hope Ive got what it takes to carve out some knowledge for the world, or to realizethings that havent been done before.

    However, I found that I did not much like the practical part of the lab work. Ilike making and disproving theories, thinking up new experiments and analyzing theresults. Perhaps Id also be one for building models and testing them. I dont much likemeasuring things in jars or cleaning or trying to get the next test to work the way I wantit to. Still, I think this has taught me the value of the time invested in experiments.While experiments in my mind were always instantly finished and analyzed, in realityeven simple experiments can last days, weeks even. Especially the analytical part. Forthose reasons, it pays to think very well about experiments before even starting them.

    In any case, Im going to do what I always do, be it in sports, studies, socializings orlove - Im going to throw myself at it and see what happens. To further prepare myselffor the world, I plan to learn in practice. I look for work where I can help with therealization of new things and discover new ideas.

    For helping me stay on track with my research, for helping me out practical issues aswell as theoretical problems, Id like to thank my committee. Anthony, Andre, Regina,Dave - thank you very much. Your guidance gave me some room to breathe in the sheeramount of data and knowledge there is to consider while planning your next experiment.Id like to thank my girlfriend Anne, my parents and my sister for supporting me in a

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  • time of need and for keeping me going. And finally Id like to thank everyone whoshelped or motivated me while I was doing my research; the members of the IMS group,my fellow students and friends, as well as Frank Roesthuis and Svetlana Bystrova.

    Thank you, everyone. I hope to meet you again in the future - wherever it takes me.Enne Faber

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