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Chemical vapor deposition of one dimensional tin oxide nanostructures [Elektronische Ressource] : structural studies, surface modifications and device applications / vorgelegt von Jun Pan

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Chemical Vapor Deposition of One Dimensional Tin Oxide Nanostructures: Structural Studies, Surface Modifications and Device Applications FIB-Tomographic Image of Ordered SnO Nanowires 2DISSERTATION zur Erlangung des Doktorgrades der Mathematisch-Naturwissenschaftlichen Fakultät der Universität zu Köln vorgelegt von Jun Pan Köln, 2010 Chemical Vapor Deposition of One Dimensional Tin Oxide Nanostructures: Structural Studies, Surface Modifications and Device Applications FIB-Tomographic Image of Ordered SnO Nanowires 2DISSERTATION zur Erlangung des Doktorgrades der Mathematisch-Naturwissenschaftlichen Fakultät der Universität zu Köln vorgelegt von Jun Pan Köln, 2010 Tag des Kolloquiums: 22.10.2010 Dekan: Prof. Dr. Hans-Günther Schmalz Vorsitzender: Prof. Dr. Annette Schmidt Berichterstatter: Prof. Dr. Sanjay Mathur Prof. Dr. Gerd Meyer Beisitzer: Dr. Hao Shen This dissertation was carried out at the Leibniz Institute for New Materials (INM), Saarbrücken and Chair of Inorganic and Materials Chemistry, Department of Chemistry, University of Cologne, Cologne, during February 2007 and October 2010 under the supervision of Prof. Dr. Sanjay Mathur and Dr. Hao Shen.
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Chemical Vapor Deposition of
One Dimensional Tin Oxide Nanostructures:
Structural Studies, Surface Modifications
and Device Applications




FIB-Tomographic Image of Ordered SnO Nanowires 2
DISSERTATION
zur Erlangung des Doktorgrades
der Mathematisch-Naturwissenschaftlichen Fakultät
der Universität zu Köln
vorgelegt von

Jun Pan



Köln, 2010
Chemical Vapor Deposition of
One Dimensional Tin Oxide Nanostructures:
Structural Studies, Surface Modifications
and Device Applications




FIB-Tomographic Image of Ordered SnO Nanowires 2
DISSERTATION
zur Erlangung des Doktorgrades
der Mathematisch-Naturwissenschaftlichen Fakultät
der Universität zu Köln
vorgelegt von

Jun Pan



Köln, 2010





















Tag des Kolloquiums: 22.10.2010
Dekan: Prof. Dr. Hans-Günther Schmalz
Vorsitzender: Prof. Dr. Annette Schmidt
Berichterstatter: Prof. Dr. Sanjay Mathur
Prof. Dr. Gerd Meyer
Beisitzer: Dr. Hao Shen
This dissertation was carried out at the Leibniz Institute for New Materials (INM),
Saarbrücken and Chair of Inorganic and Materials Chemistry, Department of
Chemistry, University of Cologne, Cologne, during February 2007 and October
2010 under the supervision of Prof. Dr. Sanjay Mathur and Dr. Hao Shen.
Acknowledgements
The work in the following pages could not have been possible completed
without the assistance, guidance, and support emotionally and critically from
faculty, peers, friends, and family.
First, my committee members and other mentors have made this project a
possibility with their guidance and wisdom. I am grateful for the opportunity to
have been influenced by your experience and advice.
I am indebted to my director and advisor Prof. Dr. Sanjay Mathur for
introducing me to this exciting field and giving me the opportunity, responsibility,
guidance, and freedom work in this area, also his thorough readings and
insightful commentary on multiple drafts, for always challenging me to think
more critically, and for his mentorship and support in the past three years.
Successful completion of this research would not have been possible
without the support and cooperation of the members of staff at the Institute of
Inorganic and Material Chemistry, especially thanks to Dr. N. Donia, Dr. J.
Altmayer and Mr. J. Schläfer in the “MONOGAS” project, who assisted in the
precursor synthesis and sample measurements. The contribution of Dr. Hao
Shen, the leader of “MONOGAS” project, in the material science was
invaluable and deserves special mention. I would like to express my gratitude to
him for helping me always to truly understand my own project in ways I hadn’t
before. I have benefited from his brilliant, generous mind at every stage of this
project.
Thanks to Dr. J. D. Wei, Dr. J. T. Li, Dr. X. F. Song, Mr. L. S. Xiao, Dr. K. Y.
Shi, Mr. T. Fisher and Ms. R. Fiz for your invaluable input regarding AFM, XRD,
SEM, simulation and surface modification and reminding me of how to maintain
a balance in this potentially overwhelming process. Special recognitions are
I extended to: Ms. A. Roth, Dr. W. Tyrra, Mr. T. Rügamer, Ms. N. Tosun, Mr. R.
von Hagen, Ms. R. Werwig, Mr. D. Zopes, Mr. M. Hoffmann, Mr. F. Heinrich, Mr.
O. Arslan, Mr. J. Pfrommer, Ms. C. Hegemann, Ms. I. Obolonskaya, Ms. I.
Trinker and Ms. S. Kremer.
Completion of this project would not have been possible without
cooperation from Dr. F. Hernandez in the University of Barcelona for electrical
property measurement, Dr. U. Werner in the Leibniz Institute for New Material
and Mr. S. M. Hühne in the University of Bonn for TEM measurement, Dr. F.
Soldera in the University of Saarland for FIB-tomography measurement, Dr. N.
Mathews and Mr. G. Karthik in Nanyang Technological University for FET
measurement, and Dr. M. Nicoul in the University of Cologne for PL
measurement.
For their ongoing support and advice, many thanks to Dr. W. D. Shi, Dr. Y.
H. Sehlleier and Dr. X. M. Li.
To my parents, I cannot express enough how grateful I am for your
unconditional and unwavering love, for all you have given. I must express equal
gratitude to my wife’s parents. They have graciously welcomed me into their
lives and have enthusiastically cheered me on as I took each step toward
completing my degree.
And finally my dear wife Ting Ouyang listened and responded to the
excitement and fear that I expressed about this undertaking with patience,
thoughtfulness, and wisdom, for which I am deeply grateful. I am thankful for
her meticulous proofreading skills, her assumption of day-to-day household
tasks, her faith that I would indeed someday finish, and above all her
partnership, love and support.


II Abstract
One-dimensional (1D) metal oxide nanostructures such as wires, rods,
belts and tubes have become the focus of intensive research for investigating
structure-property relationship under diminishing dimensions and probing their
possible scientific and technological applications. Chemical vapor deposition
(CVD), based on catalyzed vapor-liquid-solid (VLS) growth mechanism, is an
efficient way to synthesize 1D metal oxide nanostructures, which can be
implored by combining molecular precursors with CVD-VLS growth. This
thesis contains results obtained on a molecule-based CVD approach to grow
metal oxide nanowires, elaboration of experimental parameters enabling
control over random and orientated growth.
(1) Controlled synthesis, growth mechanism and plasma-treatment of SnO 2
nanowires.
Uniform and high-density single crystalline SnO NWs were fabricated by 2
optimization of deposition temperature, precursor temperature, size of catalyst
and angle of graphite holder, and the electrical, photoluminescence, gas
sensing and field emission properties were also systematically investigated, it
enabled us to have a better understanding of SnO nanowires. 2
The technical highlights of this work include the successful demonstration
of oriented growth of SnO nanowires arrays on TiO (001) substrates by 2 2
MB-CVD method for the first time. A growth model for the nanowire
morphology based upon crystallographic relation between the substrate and
NW material is proposed. Electrical and gas sensing properties of SnO [101] 2
single nanowire showed that oriented nanowire arrays can be potentially used
towards diameter- and orientation-dependent sensing unit for detection of gas
molecules.
Surface modification of SnO nanowires in an argon-oxygen (Ar/O ) 2 2
plasma treatment caused preferential etching of the oxygen atoms from
III surface and the inner volume (lattice) producing a non-stoichiometric overlayer,
resulting in the higher sensitivity for ethanol gas at lower operating temperature
and exhibited improved transducing response towards changing gas
atmospheres.
(2) New architectures of SnO nanowire based 1D heterostructure: Synthesis 2
and properties.
New morphological SnO nanowire based heterostructures (such as 2
SnO @TiO , SnO @SnO , SnO @VO and SnO @CdS) were fabricated by 2 2 2 2 2 x 2
chemical surface modification via a two-step process.
Structural characterization of SnO /TiO core-shell structures revealed the 2 2
formation of mixed-cation phases of composition Sn Ti O (x = 0.857 ~ 1.0) x 1-x 2
depended on the annealing temperatures, the excellent electrical property and
gas sensing performance of SnO /TiO core-shell structures are attributed to 2 2
nanowire based sensor applications.
The SnO @SnO heterostrucutres with contact angle (CA) of 133° 2 2
exhibited a superhydrophobic property in comparison with the superhydrophilic
SnO nanowires (CA = 3° ). Switchable surface wettability of SiO coated 2 x
SnO @SnO heterostructure (CA = 155.8° ) was observed by alternation of UV 2 2
irradiation, dark storage and O annealing. Geometric microstructure was the 2
major determinant in the switchable wettability from superhydrophilic to
superhydrophobic.
The SnO @CdS QDs heterostructures were fabricated by a chemical bath 2
deposition (CBD) method via hydroxide cluster growth mechanism, and had a
remarkably enhancement in photoconductivity than non-coated SnO 2
nanowires when the wavelength was below 450 nm.
The work carried out in this thesis is supported by Federal Ministry of
Education and Research (BMBF) in the frame of the priority program
“BMBF-NanoFutur” (FKZ 03X5512).

IV Zusammenfassung
Eindimensionale (1D) Metalloxid Nanostrukturen wie z. B. Drähte (wires),
Stäbe (rods), Bänder (belts) und Röhren (tubes) sind Inhalt intensiver
Forschung, um deren diverse Struktur-Eigenschafts Beziehungen,
insbesondere in Bezug auf deren reduzierte Dimensionalität, aufzuklären, und
die Möglichkeiten einer potentiellen wissenschaftlichen bzw. technologischen
Anwendung auszuloten. Hierbei bietet die Methode der chemischen
Gasphasenabscheidung (engl. Chemical Vapor Deposition, CVD) durch den
so genannten VLS-Mechanismus (engl. Vapor-Liquid-Solid) einen guten
Zugang zu 1D Metalloxid-Nanostrukturen durch die Zersetzung von
molekularen Vorstufen in einem CVD-VLS Prozess. Die vorliegende Arbeit
behandelt die Synthese von Metalloxid-Nanodrähten im CVD-Prozess, sowie
die Optimierung der Reaktionsparameter, um ein gerichtetes Wachstum der
Nanostrukturen auf Substraten zu ermöglichen, und studien von
physikalischen Eigenschaften für die Anwendung im Bauteilen.
(1) Gezielte Synthese, Wachstumsmechanismus und Plasmabehandlung von
SnO Nanodrähten. 2
Einheitliche einkristalline SnO Nanodrähte konnten nach einer 2
Optimierung der Substrattemperatur, Precursortemperatur, Größe der
Katalysatorpartikel, sowie Winkel des Substrathalters erhalten werden.
Darüber hinaus lieferten elektrische Messungen, Photolumineszenz
Spektroskopie, Gas-Sensor Untersuchungen Studien ein tieferes Verständnis
der physikalischen Eigenschaften von SnO Nanodrähten. 2
Diese Arbeit beschreibt zum ersten Mal das gerichtete Wachstum von
SnO Nanodrähten auf TiO (001) Substraten mit der molekülbasierten 2 2
CVD-Methode. Darauf aufbauend konnte ein Wachstumsmodell der
Nanodrähte vorgeschlagen werden, welche auf der Interaktion der
verschiedenen kristallographischen Ebenen (Substrat/Nanodraht) beruht.
V Sowohl elektrische, als auch Gas-Sensor-Messungen an einzelnen SnO [101] 2
Nanodrähten zeigten, dass ausgerichtete Nanodrähte abhängig vom
jeweiligen Durchmesser und ihrer Ausrichtung unterschiedlich auf
Gasmoleküle reagieren, was für zukünftige Gassensoren genutzt werden
könnte.
Die Oberflächenmodifikation von SnO Nanodrähten in einem 2
Argon-Sauerstoff (Ar/O ) Plasma führte zu einer Verringerung der 2
Sauerstoffkonzentration in der Oberfläche der Nanodrähte, worauf sich eine
nicht-stöchiometrisch zusammengesetzte Schicht ausbildete, welche
wiederum zu einer höheren Empfindlichkeit und besseren Dynamik, bei
gleichzeitig geringeren Temperaturen, gegenüber Ethanol in
Gas-Sensor-Messungen führte.
(2) Neuartige SnO Heterostrukturen: Synthese und Eigenschaften Neue 2
Heterostrukturen (wie z. B. SnO @TiO , SnO @SnO , SnO @VO und 2 2 2 2 2 x
SnO @CdS) wurden durch chemische Oberflächenmodifikation von SnO2 2
SnO Nanodrähten in einem zweistufigen CVD-Prozess hergestellt. 2
Eine strukturelle Charakterisierung von SnO /TiO Kern-Schale 2 2
Strukturen zeigte, dass sich Mischphasen abhängig von der Sintertemperatur
mit der Zusammensetzung Sn Ti O (x = 0.857 ~ 1.0) ausbilden. Die x 1-x 2
hervorragenden elektrischen Eigenschaften von SnO /TiO2 2
Kern-Schale-Strukturen ermöglichen den Einsatz solcher Strukturen in
Nanodraht Gassensoren.
SnO @SnO Heterostrukturen weisen mit einem Kontaktwinkel (KW) von 2 2
133° superhydrophobe Eigenschaften auf, während einfache SnO 2
Nanodrähte mit einem Kontaktwinkel von 3° superhydrophile Oberflächen
ausbilden. Eine schaltbare Oberflächenbenetzbarkeit von SiO beschichteten x
SnO @SnO Heterostrukturen (KW = 155.8° ) wurde bei einem Wechsel von 2 2
UV-Bestrahlung zu Dunkelheit und O Behandlung beobachtet. 2
Die geometrische Mikrostruktur der Nanodrähte war hierbei der
Hauptgrund in der schaltbaren Benetzbarkeit von superhydrophil zu
VI