Chemical Vapor Deposition Growth and Characterization of Two-Dimensional Hexagonal Boron Nitride

152 Pages·2018·6.674 MB·English

by  Roland Yingjie Tay

Springer Theses
Recognizing Outstanding Ph.D. Research
Roland Yingjie Tay

Chemical Vapor
Deposition Growth
and Characterization
of Two-Dimensional
Hexagonal Boron
Nitride
Springer Theses
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Roland Yingjie Tay
Chemical Vapor Deposition
Growth and Characterization
of Two-Dimensional
Hexagonal Boron Nitride
Doctoral Thesis accepted by
the Nanyang Technological University, Singapore
123
Author Supervisor
Dr. RolandYingjie Tay Asst. Prof.Edwin Hang TongTeo
Schoolof Electrical andElectronic Schoolof Electrical andElectronic
Engineering Engineering
NanyangTechnological University NanyangTechnological University
Singapore Singapore
Singapore Singapore
ISSN 2190-5053 ISSN 2190-5061 (electronic)
SpringerTheses
ISBN978-981-10-8808-7 ISBN978-981-10-8809-4 (eBook)
https://doi.org/10.1007/978-981-10-8809-4
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’
Supervisor s Foreword
2D materials as a relatively new class of nanomaterials have been gaining traction
rapidlyinthepastdecadeduetotheirmanyuniquecharacteristicsnotfoundintheir
bulkcounterparts.2Dhexagonalboronnitride(h-BN)isonesuchmaterialthathas
a honeycomb atomic configuration similar to graphene (except h-BN is composed
of B and N instead of C). With this shared configuration also comes many similar
properties such as high mechanical strength and thermal conductivity, etc.
However,contrastingwithgraphene,h-BNisawidebandgapsemiconductorthatis
electrically insulating. And it is this insulating nature together with its intrinsic
atomicsmoothnessandtheabilitytobechemicallyinertthatmakeh-BNoneofthe
bestknownsubstratematerialforhigh-performancegrapheneandother2Dmaterial
based devices. This interest thus drives the need to look into the practical fabri-
cation of large 2D h-BN for various applications.
Inthisthesis,Rolandhadmadeseveralkeycontributionstothedevelopmentof
scalable growth of 2D h-BN films. He developed a process using atmospheric
pressure chemical vapor deposition (CVD) to synthesize monolayer
single-crystalline h-BN domains on Cu (and other dielectric substrates) and
investigated the effects on the h-BN crystals with changing parameters. He later
discovered that the shape and size of the crystals can be tailored from the usual
small equilateral triangles (*1 µm) into large hexagons (*10 µm).
Moreover, the unique hexagonal shaped crystal has important implication
toward the theoretical aspect and energy dynamics on its formation mechanism.
Beyond fundamental analysis, this thesis also reports on synthesis techniques that
aregearedtowardindustrialadaptation.Large-areaalignedgrowthwhichimproves
theoverallqualityoftheh-BNfilmandtechniquestoreducethecostofproduction
are demonstrated. At present, almost all other 2D materials generally use h-BN as
theirdielectriclayerandalsoforencapsulation.Thisthesison2Dh-BNthuspaves
the way forward in the use of CVD 2D h-BN for this purpose.
Singapore Asst. Prof. Edwin Hang Tong Teo
March 2018
v
Abstract
Atomicallythinhexagonalboronnitride(h-BN)filmisahighlyattractivedielectric
and a crucial material for next-generation high-performance two-dimensional (2D)
heterostructure devices. In this thesis, controllable growth of 2D h-BN films on
various substrates using chemical vapor deposition (CVD) is demonstrated. An
atmospheric pressure CVD system is developed for h-BN growth using ammonia
borane (AB) as precursor and the effects of various critical parameters are sys-
tematicallyinvestigated.Theh-BNfilmgrownonCusubstrateissubstrate-position
dependent due to gas flow dynamics, which result in an increase in nucleation
density as well as domain size downstream along the quartz tube. The effects of
other CVD parameters such as growth temperature, growth time, and various
precursor conditions are further examined. Importantly, a slight increase in the
growth temperature of 50 °C (from 1000 to 1050 °C) resulted in a significant
increaseinaveragedomainsizeof*17-fold.Thisparametricstudythushighlights
theimpactofthecrucialparameterstocontrolthegrowthofh-BNfilmsintermsof
domain sizes, film coverage, and thickness of the films.
The growth of h-BN films is further investigated using a metal-catalyst-free
approachdirectlyonamorphousSiO /Siandquartzsubstrates.Theas-grownfilms
2
are continuous and smooth with no observable pinholes or wrinkles across the
entire deposited surface. Varying thickness of *2 to 25 nm can be obtained
through process control. The crystallite sizes are small of *25 nm, as determined
by Raman spectroscopy, due to the random and uncontrolled nucleation. The
absence of transfer process eliminates additional degradation of the film which is
detrimental to device performance.
In order to increase the size of the single-crystal h-BN domains, highly
smoothened electropolished Cu foils are utilized to suppress the amount of
nucleation and enhance the lateral growth of the 2D crystals. Large domains with
sizeofupto*35µm2whicharehexagonalinshapeareobservedforthefirsttime.
Thisdiscoveryisincontradictiontomanytheoreticalworkswhichrevealedthat2D
h-BN domains are mostly stable in the form of triangles because of their asym-
metric N- and B-edge energies. Therefore, these hexagonal shaped h-BN domains
are extensively characterized to prove its validity. This work verifies that h-BN
vii
viii Abstract
domains are stable in the form of hexagons and open up new avenues for further
theoretical exploration.
A“multi-nucleation”approachtoobtainmosaicsingle-crystallineh-BNfilmsis
furtherexplored.Alignedh-BNdomainsforovercentimeterdistancesareachieved
using resolidfied Cu substrate with (110) surface orientation and the edge interac-
tions between coalesced domains are investigated. Due to the strict epitaxial rela-
tionshipbetweenh-BNandCulattices,well-definedsymmetricmultifacetedshapes
such as “butterfly” and “6-apex star” are formed by the convergence between
adjacent triangular or hexagonal shaped domains. Defect lines are generated along
thegrain boundaries ofmirroringh-BN domains duetothetwodifferent polarities
(BN and NB) and edges with the same termination. The triangular domains with
truncated edges and alternatively hexagonal domains are rationalized with Wulff
shapesthathaveminimumedgeenergy.Thisworkestablishesacompletestudyand
reveals essential insights into the various issues on the in-plane coalescence of 2D
materials with binary configuration.
Lastly, a new single-source precursor, trimethylamine borane (TMAB), is suc-
cessfully used for the first time to grow monolayer h-BN single crystals as well as
few-layer C-doped h-BN (h-BCN) films. As compared to AB, TMAB is a much
cheaper alternative making it highly attractive in a manufacturing perspective.
Importantly, pristine 2D h-BN films with a wide bandgap of *6.1 eV can be
achieved by limiting the sublimation temperature of TMAB at 40 °C, while C
dopants are introduced to the h-BN films when the sublimation temperature is
furtherincreased.Theh-BCNthinfilmsdisplayedbandgapnarrowingeffectsdueto
substitutional C doping. The chemical structure of the h-BCN films can be per-
ceivedastheBatomsarepartiallysubstitutedbyCatomsinanh-BNmatrix.This
study thus provides new insights into the design and fabrication of large-area
atomically thin h-BN/h-BCN films toward practical applications and suggests that
other anime borane complexes can be potentially used to synthesize such films as
well.
Parts of this thesis have been published in the following journal articles:
1. Tay, R. Y., Wang, X., Loh, G. C., Singh, R. S., Li, H., Mallick, G. & Teo, E.
H. T. A Systematic Study of the Atmospheric Pressure Growth of Large-Area
Hexagonal Crystalline Boron Nitride Film. J. Mater. Chem. C 2, 1650–1657
(2014).
2. Tay, R. Y., Griep, M. H., Mallick, G., Tsang, S. H., Singh, R. S., Tumlin, T.,
Teo, E. H. T. & Karna, S. P. Growth of Large Single-Crystalline
Two-Dimensional Boron Nitride Hexagons on Electropolished Copper. Nano
Lett. 14, 839–846 (2014).
3. Tay, R. Y., Tsang, S. H., Loeblein, M., Chow, W. L., Loh, G. C., Toh, J. W.,
Ang,S.L.&Teo,E.H.T.DirectGrowthofNanocrystallineHexagonalBoron
Nitride Films on Dielectric Substrates. Appl. Phys. Lett. 106, 101901 (2015).
4. Tay,R.Y.,Park,H.J.,Ryu,G.H.,Tan,D.,Tsang,S.H.,Li,H.,Liu,W.,Teo,
E. H. T., Lee, Z., Yeshayahu, L. & Ruoff, R. S. Synthesis of Aligned
Symmetrical Multifaceted Monolayer Hexagonal Boron Nitride Single Crystals
on Resolidified Copper. Nanoscale 8, 2434–2444 (2015).
5. Tay,R.Y.,Li,H.,Tsang,S.H.,Zhu,M.,Loeblein,M.,Jing,L.,Leong,F.N.&
Teo, E. H. T. Trimethylamine Borane: A New Single-Source Precursor for
Monolayer h-BN Single Crystals and h-BCN Thin Films. Chem. Mater. 28,
2180–2190 (2016).
ix
List of Publications
Awards
1. TL@NTU Best Publication Award (2014) for “Growth of Large
Single-Crystalline Two-Dimensional Boron Nitride Hexagons on
Electropolished Copper” featured in Nano Letters.
Journals
Published/in press/accepted
1. Tay, R.Y., Wang,X., Loh,G.C., Singh, R. S., Li,H., Mallick, G.&Teo, E.
H.T.*ASystematicStudyoftheAtmosphericPressureGrowthofLarge-Area
Hexagonal Crystalline Boron Nitride Film. J. Mater. Chem. C 2, 1650–1657
(2014).
2. Tay, R. Y., Griep, M. H., Mallick, G., Tsang, S. H., Singh, R. S., Tumlin, T.,
Teo, E. H. T.* & Karna, S. P. Growth of Large Single-Crystalline
Two-Dimensional Boron Nitride Hexagons on Electropolished Copper. Nano
Lett. 14, 839–846 (2014).
3. Tay, R.Y., Tsang, S. H., Loeblein, M.,Chow,W. L., Loh, G.C., Toh,J. W.,
Ang, S. L. & Teo, E. H. T.* Direct Growth of Nanocrystalline Hexagonal
Boron Nitride Films on Dielectric Substrates. Appl. Phys. Lett. 106, 101901
(2015).
¶ ¶
4. Tay,R.Y., Li,H., Tsang,S.H.,Jing,L.,Tan,D.,Wei,M.&Teo,E.H.T.*
¶
( equal contribution) Facile Synthesis of Millimeter-Scale Vertically Aligned
Boron Nitride Nanotube Forests by Template-Assisted Chemical Vapor
Deposition. Chem. Mater. 27, 7156–7163 (2015).
5. Tay,R.Y.,Park,H.J.,Ryu,G.H.,Tan,D.,Tsang,S.H.,Li,H.,Liu,W.,Teo,
E. H. T.,* Lee, Z., Yeshayahu, L. & Ruoff, R. S. Synthesis of Aligned
SymmetricalMultifacetedMonolayerHexagonalBoronNitrideSingleCrystals
on Resolidified Copper. Nanoscale 8, 2434–2444 (2015).
xi