Graphene phononic crystals fabricated with electron-beam lithography

Koska grafeeni on aito kaksiulotteinen materiaali, sen avulla voidaan tutkia käytännössä teorioiden ennustamaa käyttäytymistä sellaisissa järjestelmissä. Yksi erityisen kiinnostava ilmiö on lämmönjohtavuuden lasku kun materiaaliin luodaan säännöllinen reikien joukko. Tällöin puhutaan fononikiteestä....

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Main Author: Lankinen, Aaro
Other Authors: Matemaattis-luonnontieteellinen tiedekunta, Faculty of Sciences, Fysiikan laitos, Department of Physics, Jyväskylän yliopisto, University of Jyväskylä
Format: Master's thesis
Language:eng
Published: 2021
Subjects:
Online Access: https://jyx.jyu.fi/handle/123456789/79111
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author Lankinen, Aaro
author2 Matemaattis-luonnontieteellinen tiedekunta Faculty of Sciences Fysiikan laitos Department of Physics Jyväskylän yliopisto University of Jyväskylä
author_facet Lankinen, Aaro Matemaattis-luonnontieteellinen tiedekunta Faculty of Sciences Fysiikan laitos Department of Physics Jyväskylän yliopisto University of Jyväskylä Lankinen, Aaro Matemaattis-luonnontieteellinen tiedekunta Faculty of Sciences Fysiikan laitos Department of Physics Jyväskylän yliopisto University of Jyväskylä
author_sort Lankinen, Aaro
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description Koska grafeeni on aito kaksiulotteinen materiaali, sen avulla voidaan tutkia käytännössä teorioiden ennustamaa käyttäytymistä sellaisissa järjestelmissä. Yksi erityisen kiinnostava ilmiö on lämmönjohtavuuden lasku kun materiaaliin luodaan säännöllinen reikien joukko. Tällöin puhutaan fononikiteestä. Tässä pro gradu -tutkielmassa kehitettiin elektronisuihkulitografiaan pohjautuva prosessi, jolla voidaan valmistaa fononikiteitä useilla eri hilan parametreillä. Lisäksi kokeiltiin grafeenipinnan puhdistusta reaktiivisen ionietsauksen (RIE) avulla. Valmiit grafeenifononikidelaitteet kuvannettiin optisen, elektronisuihku-, heliumionija atomivoimamikroskopian keinoin, sekä karakterisoitiin sähköisesti differentiaalikonduktanssin mittauksilla nestetypen lämpötilasta 75 K nesteheliumin läpötilaan 4 K. Työssä näytettiin, että valmistusmenetelmällä voidaan tuottaa vakaita rakenteita, joissa pienimmät kohdat ovat kymmenien nanometrien luokkaa, ja RIE-puhdistus paransi grafeenipinnan laatua kvalitatiivisesti. Grafeenifononikidelaitteiden differentiaalikonduktanssissa nähtiin huomattava aleneminen, kun jännitebias oli nolla alhaisemmilla lämpötiloilla. Tämä mahdollistaa tulevissa mittauksissa grafeenin lämmönmittauksen lokaalisti. Lisää tutkimusta tarvitaan, jotta tällaisten laitteiden lämmönjohtavuus saadaan mitattua alle 4 K:n lämpötiloissa. Graphene, as a true 2D material, presents the possibility of studying in practice many theoretical models for the behaviour of such systems. One area of particular interest is the suppression of thermal conductance resulting from the introduction of a periodic array of holes into a material, then known as a phononic crystal (PnC). In this thesis work, an electron-beam lithography based process for fabricating PnCs of varying lattice parameters in graphene was developed. Additionally, a method for cleaning carbon contamination off graphene surfaces by reactive ion etching (RIE) was tested. The resulting graphene PnC (GPnC) devices were imaged through optical, scanning electron, helium ion and atomic force microscopy, as well as electrically characterized through differential conductance measurements at temperatures ranging from liquid nitrogen 75 K to liquid helium 4 K. The fabrication method was demonstrated to be capable of producing stable structures with feature sizes down to tens of nanometers, and the RIE cleaning method showed qualitative improvement of the graphene surfaces. Differential conductance of GPnC devices displayed a significant decrease at zero voltage bias with decreasing temperature, which provides a way for local thermometry of graphene in future work. Further research is required to measure the thermal conductance of such devices at temperatures below 4 K.
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spellingShingle Lankinen, Aaro Graphene phononic crystals fabricated with electron-beam lithography phononic crystal electron-beam lithography Fysiikka Physics 4021 grafeeni fononit graphene phonons
title Graphene phononic crystals fabricated with electron-beam lithography
title_full Graphene phononic crystals fabricated with electron-beam lithography
title_fullStr Graphene phononic crystals fabricated with electron-beam lithography Graphene phononic crystals fabricated with electron-beam lithography
title_full_unstemmed Graphene phononic crystals fabricated with electron-beam lithography Graphene phononic crystals fabricated with electron-beam lithography
title_short Graphene phononic crystals fabricated with electron-beam lithography
title_sort graphene phononic crystals fabricated with electron beam lithography
title_txtP Graphene phononic crystals fabricated with electron-beam lithography
topic phononic crystal electron-beam lithography Fysiikka Physics 4021 grafeeni fononit graphene phonons
topic_facet 4021 Fysiikka Physics electron-beam lithography fononit grafeeni graphene phononic crystal phonons
url https://jyx.jyu.fi/handle/123456789/79111 http://www.urn.fi/URN:NBN:fi:jyu-202112226093
work_keys_str_mv AT lankinenaaro graphenephononiccrystalsfabricatedwithelectronbeamlithography