One-dimensional structures of Bi2O3 synthesized via metalorganic chemical vapor deposition process

Article abstract of DOI:10.1016/j.ssc.2005.11.012

We have demonstrated the synthesis of one-dimensional (1D) structures of bismuth oxide (Bi₂O₃) by a reaction of a trimethylbismuth (TMBi) and oxygen (O₂) mixture at 450 °C. Scanning electron microscopy showed that the product consisted of 1D materials with width or diameters less than 1 μm and lengths up to several tens of micrometers. The X-ray energy dispersive spectroscopy revealed that the materials contained elements of Bi and O. The results of X-ray diffraction and selected area electron diffraction pattern indicated that the obtained Bi₂O ₃ were crystalline with monoclinic structure.

Full text of DOI:10.1016/j.ssc.2005.11.012

Solid State Communications 137 (2006) 196–198
www.elsevier.com/locate/ssc
One-dimensional structures of Bi2O3 synthesized via metalorganic
chemical vapor deposition process
*
Hyoun Woo Kim , Ju Hyun Myung, Seung Hyun Shim
School of Materials Science and Engineering, Inha University, Incheon 402-751, South Korea
Received 23 August 2005; received in revised form 14 October 2005; accepted 8 November 2005 by P. Sheng
Available online 21 November 2005
Abstract
We have demonstrated the synthesis of one-dimensional (1D) structures of bismuth oxide (Bi2O3) by a reaction of a trimethylbismuth (TMBi)
and oxygen (O2) mixture at 450 8C. Scanning electron microscopy showed that the product consisted of 1D materials with width or diameters less
than 1 mm and lengths up to several tens of micrometers. The X-ray energy dispersive spectroscopy revealed that the materials contained elements
of Bi and O. The results of X-ray diffraction and selected area electron diffraction pattern indicated that the obtained Bi2O3 were crystalline with
monoclinic structure.
q 2005 Elsevier Ltd. All rights reserved.
PACS: 81.07.Kb; 81.15.Gh
Keywords: A. Nanostructures; B. Chemical synthesis; C. Transmission electron microscopy
1. Introduction
In this letter, we report the fabrication of crystalline 1D
materials of Bi2O3 using a reaction of a trimethylbismuth
(TMBi) and O2 mixture.
The discovery of carbon nanotubes has initiated an exciting,
challenging, and rapidly expanding research field for one-
dimensional (1D) nanostructures [1]. Since 1D nanostructures
are of great interest for their novel physical properties [2–6],
considerable efforts have been placed on the synthesis and
characterization of those materials over the past several years.
The bismuth oxide (Bi2O3) has attracted great attention due
to their applications in several technological fields, such as
oxide-ion conductors, piezo-optic materials, solar cells, gas
sensors, and ceramic glass manufacturing [7–11]. Additionally,
Bi2O3 is a component of various important electroceramic
oxides including Bi–Sr–Ca–Cu–O superconductors [12,13],
and Sr–Bi,Ta–O/Sr–Bi–Nb–Ta–O ferroelectric oxides, which
have applications in non-volatile computer memories [14].
In contrast to their scientific and technological importance,
the synthesis of 1D structures of Bi2O3 has not received great
attention; Yang et al. synthesized Bi2O3 nanotubes (NTs) by
oxidizing the bismuth NTs in air [15] and Takeyama et al.
reported the growth of Bi2O3 rods using BiI3 and O2 [16].
2. Experimental
A schematic illustration of the metalorganic CVD
(MOCVD) reactor used in our experiments was previously
reported [17]. We used p-type Si(100), precleaned with acetone
and methanol, as starting materials onto which a layer of Au
(about 50 nm) was deposited by the radio frequency magnetron
sputtering. In the growth process of Bi2O3, TMBi and O2 were
used as the Bi and O sources, respectively, with Ar as the
carrier gas. The temperature of TMBi bubbler was fixed at
K5 8C. The Ar and O2 gas flow rates, respectively, were set to
20 standard cubic centimeters per minute (sccm) and 30 sccm.
The reactor pressure of approximately 1 Torr was maintained
during the growth for 1 h. The substrate temperature was
measured to be approximately 450 8C. After cooling down to
room temperature, a thin layer of wool-like material was found
on the surface of the substrate.
The resulting material was characterized by X-ray diffrac-
tion (XRD, X’pert MRD-Philips) using Cu Ka radiation
(lZ0.154056 nm), scanning electron microscopy (SEM,
Hitachi S-4200), and transmission electron microscopy
(TEM, Philips CM-200) with energy-dispersive X-ray (EDX)
spectroscopy installed. TEM specimens were prepared by
*
Corresponding author. Tel.: C82 32 860 7544; fax: C82 32 862 5546.
E-mail address: hwkim@inha.ac.kr (H.W. Kim).
0038-1098/$ - see front matter q 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.ssc.2005.11.012

H.W. Kim et al. / Solid State Communications 137 (2006) 196–198
197
Fig. 3. EDX pattern of a Bi2O3 structure.
Fig. 1. (a) Side-view and (b) plan-view SEM image of the products. (c, d)
Enlarged SEM images showing the individual 1D structures.
the monoclinic a-Bi2O3 structure with lattice constants
˚
˚
˚
aZ5.848 A, bZ8.166 A, and cZ7.510 A (JCPDS: 27-0053),
revealing the production of a-Bi2O3 deposits.
sonicating in alcohol by ultrasonic treatment, and subsequently
dropping onto a porous carbon film supported on a copper grid.
The EDX analysis indicates that the 1D materials consist of
only Bi and O elements, regardless of position, from the stems
to the ends (Fig. 3). C peaks and Cu peaks were raised from
TEM Cu grid coated with amorphous carbon film. Although we
do not know the exact chemical composition, we reveal that the
as-synthesized structure comprises Bi and O elements.
Fig. 4(a) shows a representative TEM image of a single 1D
structure. The structure has an almost uniform width along
3. Results and discussion
The whole substrate surface was found to be covered with
the uniform film of dense structures (Fig. 1(a)). Fig. 1(b) shows
the typical plan-view SEM image of the deposits, indicating
that this raw material consists of aggregates of 1D structures.
The SEM images reveals that the growth direction of the
structure is randomized. Fig. 1(c) shows the nanostructures
with a rectangular cross-section, indicating that it has the
thickness less than 1/3 of the widths. Fig. 1(d) shows the 1D
structures with a circular cross-section. Close examination
reveals that both straight and curved morphologies are apparent
and no metal particle can be seen at tips of the 1D structures
(Fig. 1(c) and (d)). Statistical analysis of many SEM images
shows that most structures have average diameters or widths
ranging from 60 to 800 nm and the lengths reach up to several
tens of micrometers.
Fig. 2 displays the typical XRD spectrum of the products.
Apart from the Si- and Au-related peaks which are from the
underlying substrate, all recognizable reflection peaks includ-
ꢀ
ꢀ
ꢀ
ꢀ
ing (002), ð112Þ, ð121Þ, (012), ð202Þ, and ð223Þ correspond to
Fig. 4. (a) TEM image of a single structure (inset: corresponding electron
diffraction pattern). (b) HRTEM image taken at the area marked with the dotted
box in (a).
Fig. 2. X-ray diffraction pattern recorded from the products.

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H.W. Kim et al. / Solid State Communications 137 (2006) 196–198
the length direction. The length direction of the structure,
ꢀ
applied XRD, SEM and TEM techniques to characterize the
structure of the samples. Most materials obtained are
rectangular or circular cross-sectional shape with width or
diameter of 60–800 nm and lengths up to several tens of
micrometers. The 1D materials are composed of Bi2O3 with
monoclinic structure.
indicated by an arrow, is along the ½102ꢀ direction. Selected
area electron diffraction (SAED) patterns, with the incident
electron beam parallel to the [010] direction, were recorded
perpendicular to the long axis of the structure (inset in
Fig. 4(a)). The reflections in the SAED pattern correspond to
the lattice planes of bulk Bi2O3, indicating that the 1D material
is crystalline. Fig. 4(b) shows the visible lattice fringes of the
high resolution TEM (HRTEM) image recorded near the edge
of the 1D material in Fig. 4(a), suggesting that the 1D material
is structurally uniform with a smooth surface.
Acknowledgements
This work was supported by Korea Research Foundation
Grant (KRF-2004-003-D00141).
In the present work, we guess that the Bi-containing vapor
which is in ambient or adsorbed on substrate surface combines
with oxygen gas, resulting in the formation of solid Bi2O3 on
the substrate. Although Au-coated Si was used as a substrate
material, SEM image, TEM image (not shown here) and EDX
measurement coincidently indicated that the structure tips were
free of Au-related particles, ruling out the possibility that the
growth of Bi2O3 in the present route was dominated by a tip-
growth vapor–liquid–solid (VLS) mechanism. To investigate
the role that Au played in the formation of Bi2O3
nanomaterials, the Si substrate without the Au layer was
employed in the experiment under the same condition,
revealing that thicker but less dense 1D structures were formed
on bare Si substrate. At this moment, the specific role of Au
layer in the formation of the Bi2O31D nanomaterials by
MOCVD is not clear. Although we have succeeded in
providing a method to fabricate the 1D materials of Bi2O3 on
a large scale, we believe that further experimental study is
needed to fine-tune the growth process and to clearly
understand the synthesis mechanism.
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