Synthesis, characterization and application of WS₂ nanowire-nanoflake hybrid nanostructures

56 Pages·2017·2.81 MB·English

by  Asres, Georgies Alene

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UNIVERSITY OF OULU P.O. Box 8000 FI-90014 UNIVERSITY OF OULU FINLAND
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A UUNNIIVVEERRSSIITTAATTIISS OOUULLUUEENNSSIISS
A C T A U N I V E R S I T A T I S O U L U E N S I S C
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Georgies Alene Asres
University Lecturer Tuomo Glumoff G SYNTHESIS,
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g CHARACTERIZATION AND
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University Lecturer Santeri Palviainen s

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l APPLICATION OF WS
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Postdoctoral research fellow Sanna Taskila A NANOWIRE-NANOFLAKE
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HYBRID NANOSTRUCTURES
Professor Olli Vuolteenaho
University Lecturer Veli-Matti Ulvinen
Planning Director Pertti Tikkanen
Professor Jari Juga
University Lecturer Anu Soikkeli
Professor Olli Vuolteenaho
UNIVERSITY OF OULU GRADUATE SCHOOL;
UNIVERSITY OF OULU,
FACULTY OF INFORMATION TECHNOLOGY AND ELECTRICAL ENGINEERING
Publications Editor Kirsti Nurkkala
ISBN 978-952-62-1888-5 (Paperback)
ISBN 978-952-62-1889-2 (PDF)
ISSN 0355-3213 (Print)
ISSN 1796-2226 (Online)

ACTA UNIVERSITATIS OULUENSIS
C Technica 652
GEORGIES ALENE ASRES
SYNTHESIS, CHARACTERIZATION
AND APPLICATION OF WS
2
NANOWIRE-NANOFLAKE HYBRID
NANOSTRUCTURES
Academic dissertation to be presented with the assent of
the Doctoral Training Committee of Information
Technology and Electrical Engineering of the University of
Oulu for public defence in Martti Ahtisaari -sali (L2),
Linnanmaa, on 27 April 2018, at 12 noon
UNIVERSITY OF OULU, OULU 2018
Copyright © 2018
Acta Univ. Oul. C 652, 2018
Supervised by
Professor Krisztian Kordas
Professor Anita Lloyd Spetz
Doctor Gabriela Lorite
Reviewed by
Doctor Ana Laura Elias Arriaga
Professor Harri Lipsanen

ISBN 978-952-62-1888-5 (Paperback)
ISBN 978-952-62-1889-2 (PDF)
ISSN 0355-3213 (Printed)
ISSN 1796-2226 (Online)
Cover Design
Raimo Ahonen
JUVENES PRINT
TAMPERE 2018
Asres, Georgies Alene, Synthesis, characterization and application of WS
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nanowire-nanoflake hybrid nanostructures.
University of Oulu Graduate School; University of Oulu, Faculty of Information Technology
and Electrical Engineering
Acta Univ. Oul. C 652, 2018
University of Oulu, P.O. Box 8000, FI-90014 University of Oulu, Finland
Abstract
Transition metal dichalcogenide (TMD) materials crystalize in a layered structure with a
stoichiometry MX where M is a transition metal (Mo, W, Tc, Re, V, Nb, Ta, Ti, Zr, Hf) and X is
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a chalcogen (S, Se, Te). While there is a strong covalent bond between the chalcogen and the metal
atoms in each 2-dimensional (2D) sheet, the bulk 3-dimensional crystals are held together by weak
van der Waals forces acting on the adjacent 2D sheets allowing for micromechanical and liquid
phase exfoliation into nanostructures composed of either a single layer or a few layers. Since the
electronic band structure depends not only on the chemistry but also on the number of layers, a
whole new range of metal, semimetal and semiconductor materials may be achieved. These
properties, among many other advantages (e.g. tunable band structure, high mobility of carriers,
easy intercalation with ions), make TMDs appealing and timely for applications in solar cells and
photodetectors, heterogeneous catalysis, electrocatalytic electrodes, energy storage and in
(electro) chemical sensing. Motivated by the anticipated fascinating properties of TMDs, this
research work focuses on the synthesis, characterization and application of a novel hybrid WS
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nanomaterial. While the original goal of the research work was to develop a simple method to
synthesize WS nanowires, it became clear that instead of nanowires a hybrid nanowire-nanoflake
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(NW-NF) structure could be synthesized by a simple thermal sulfurization of hydrothermally
grown WO nanowires. The structure, morphology and composition of the new materials were
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analyzed by X-ray diffraction, Raman spectroscopy, electron microscopy and X-ray photoelectron
spectroscopy. Temperature dependent electrical measurements carried out on random networks of
the nanostructures showed nonlinear characteristics and a negative temperature coefficient of
resistance indicating that the hybrids were semiconducting. Resistive gas sensors were prepared
and exposed to H S, CO, NH , H and NO and to which the devices displayed ultra-high
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sensitivity (0.043 ppm-1) towards H2S with a detection limit of 20 ppb. The results suggest further
exploration of gas sensing with TMDs as potential competitive alternatives to the classical metal
oxide based devices. Moreover, photodetector devices with excellent visible light response were
also demonstrated using an individual WS NW-NF hybrid as well as its random networks having
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photoresponsivity of up to 400 mAW-1. This was two orders of magnitude higher than that
measured for other 2D materials based devices. Overall, the WS nanowire-nanoflake hybrid is a
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truly multipurpose and multifunctional semiconductor making it a promising material for
advanced micro, nano and optoelectronics devices.
Keywords: gas sensor, nanoflake, nanohybrids, nanowire, photodetector, WO , WS
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Asres, Georgies Alene, WS -nanolanka-nanohiutale -hybridirakenteen synteesi,
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karakterisointi ja sovellukset.
Oulun yliopiston tutkijakoulu; Oulun yliopisto, Tieto- ja sähkötekniikan tiedekunta
Acta Univ. Oul. C 652, 2018
Oulun yliopisto, PL 8000, 90014 Oulun yliopisto
Tiivistelmä
Siirtymämetallidikalkogenidistä (transition metal dichalcogenide, TMD) olevat materiaalit
kiteytyvät kerroksittaisiksi rakenteiksi, joiden stoikiometria on MX , missä M on siirtymämetalli
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(Mo, W, Tc, Re, V, Nb, Ta, Ti, Zr, Hf) ja X on kalkogeeni (S, Se, Te). 2-ulotteisessa (2D) tasossa
kalkogeenin ja metallin välillä on voimakas kovalenttinen sidos, mutta suuremmassa kolmiulot-
teisessa kiteessä viereisiä tasoja sitoo toisiinsa vain heikot van der Waals-voimat, jolloin tasot on
mahdollista erottaa mikromekaanisesti ja nestefaasikuorinnalla yksittäisiksi tai muutamasta ker-
roksesta koostuvaksi nanorakenteeksi. Koska elektronivyörakenne ei riipu ainoastaan kemialli-
sesta koostumuksesta vaan myös kerrosten lukumäärästä, voidaan muodostaa täysin uusia metal-
lisia, puolimetallisia tai puolijohdemateriaaleja. Nämä ominaisuudet monien muiden lisäksi
(esim. räätälöity vyörakenne, korkeanliikkuvuuden varauksen kuljettajat, helppo ionien interke-
laatio) tekevät TMD-materiaaleista kiinnostavia ja ajankohtaisia aurinkokennoihin, valokennoi-
hin, heterogeeniseen katalyysiin, sähkökatalyyttisiin elektrodeihin, energiavarastoihin ja sähkö-
kemiallisiin antureihin. TDM-materiaalien oletettavasti kiehtovien ominaisuuksien motivoima-
na tämä tutkimus keskittyy uusien hybridi-WS –nanomateriaalien synteesiin, karakterisoimi-
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seen ja sovellutuksiin. Tutkimuksen alkuperäinen tavoite oli kehittää yksinkertainen menetelmä
WS -nanolankojen syntetisoimiseksi, mutta kävi ilmi että nanolankojen sijaan syntyi nanolanka-
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nanohiutale –hybridirakenne (nanowire-nanoflake, NW-NF), kun hydrotermisesti kasvatettuja
WO -nanolankoja rikitettiin termisesti. Näiden uusien materiaalien rakenne, morfologia ja koos-
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tumus on analysoitu röntgendiffraktiolla, Raman-spekstrokopialla, elektronimikroskoopilla ja
röntgenfotoelektronispektroskopialla. Valikoimattomista nanorakenteista koostuvien verkosto-
jen lämpötilasta riippuvien sähköisten ominaisuuksien mittaukset osoittavat epälineaarisia piir-
teitä ja negatiivinen resistanssin lämpötilakerroin viittaa hybridien puolijohtavuuteen. Materiaa-
lista valmistettiin resistiivisiä kaasuantureita, jotka altistettiin H S:lle, CO:lle, NH :lle, H :lle ja
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NO:lle, näistä anturi osoitti erittäin suurta herkkyyttä H S:lle (0.043 ppm) havaintorajan ollessa
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20 ppb. Tulokset kannustavat TMD-materiaalien kaasuanturisovellutusten jatkotutkimukseen
tarjoten potentiaalisesti kilpailukykyisen vaihtoehdon perinteisille metallioksidi-pohjaisille lait-
teille. Lisäksi, yksittäisillä WS –nanolanka-nanohiutalepartikkeleilla sekä valikoimattomilla
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nanolanka-nanohiutalehybridiverkostoilla demonstroitiin valokenno, jonka vaste näkyvään
valoon oli jopa 400 mAW-1 ollen kaksi kertaluokkaa korkeampi kuin muilla 2D-materiaaleihin
perustuvilla kennoilla. Kaiken kaikkiaan, WS nanolanka-nanohiutalehybridi on todella moni-
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käyttöinen ja monipuolinen puolijohde ollen lupaava materiaali kehittyneille mikro- nano- ja
optoelektronisille laitteille.
Asiasanat: kaasuanturi, nanohiutale, nanohybridit, nanolanka, valokenno, WO , WS
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Acknowledgements
This work has been conducted in the Microelectronics Research Unit of the
University of Oulu under a grant provided by the Graduate School Infotech Oulu.
First, I would like to thank my advisor Prof. Krisztian Kordas for his
continuous support of my PhD study and related research work, for his patience,
motivation, encouragement and knowledge. Without his kind guidance it would not
have been possible to accomplish it. My sincere thanks also goes to my co-
supervisors Prof. Anita Lloyd Spetz and Dr. Gabriela Lorite for their guidance and
help.
Besides my advisors, I would like to thank my follow-up group members:
Docent Juha Hagberg, Dr. Jani Perantie and Dr. Merja Teirikangas for their
constructive comments and for checking that the research was proceeding as planned.
I am grateful to my current and former research group members: Dr. Melinda
Mohl, Dr. Geza Toth, Dr. Jhih-Fong Lin, Topias Järvinen, Olli Pitkänen, Aron
Dombovari, Teemu Sipola and Rashad Hajimammadov for their unfailing support
and assistance during my research work. Also to everyone in the Microelectronics
Research Unit and Microscopy and Nanotechnology Centre of the University of
Oulu; it was great sharing the laboratory with all of you during last four years. I
also very much appreciate the extensive support of collaborators from the Umeå
University, University of Szeged, Max Planck Institute, Universidad del País
Vasco, Rice University, Southern Illinois University, Linköping University and
VTT Technical Research Centre of Finland.
Last but not least, I would like to thank my family: my parents and my brothers
and sisters for supporting me spiritually throughout this research work and my life
in general.
Oulu, February 2018 Georgies Alene

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