APPLIED PHYSICS LETTERS 94, 253110 ͑2009͒
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L. Z. Liu, X. L. Wu,
Z. Y. Zhang, T. H. Li, and Paul K. Chu
1
Department of Physics and Nanjing National Laboratory of Microstructures, Nanjing University,
Nanjing 210093, People’s Republic of China
Department of Physics and Materials Science, City University of Hong Kong, Tat Chee Avenue,
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Kowloon, Hong Kong
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Received 23 May 2009; accepted 9 June 2009; published online 24 June 2009͒
Amorphous foliaceous SiO helical nanobelts with equidistant alternating bright and dark stripes are
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synthesized using thermal evaporation. A very thin polar crystalline layer spontaneously formed on
the nanobelt surface stabilizes the twist and the internal shear stress imbalance induces the periodic
reconstruction. The periodic bright and dark stripes disappear slowly with growth time because the
polar crystalline SiO layers are covered slowly by an amorphous layer. The polar surface-driven
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The growth and properties of nanostructures have at-
tracted much attention in recent years because of their
interesting optical and electrical properties, as well as poten-
copy ͑SEM͒. Nanostructures several tens of micrometers
long with helical pitches L ͑a whole repeat unit of helical
belt͒ of about 3.2–3.8 m are found on the substrate. The
respectively. Figures 1͑a͒ and 1͑c͒ show helical nanobelts
with W=500, 524 nm; L=1.90, 1.93 m; and h=75, 70 nm
for a synthesis time of 180 min, whereas Figs. 1͑b͒ and 1͑d͒
display helical nanobelts with W=1.25, 1.39 m; L=3.23,
4.45 m; and h=46, 130 nm for a growth time of 160 min.
samples produced with the shorter time ͓Figs. 1͑b͒ and 1͑d͔͒
exhibit alternating dark and bright stripes on the nanobelt
surfaces. The central axis parts ͓the white broken line in Fig.
1͑b͔͒ of the nanobelts are pale while the edge parts of nano-
belts are bright. These stripes have a very orderly periodic
structure and are distributed equally on two sides of the cen-
tral axis. The spacing intervals l are equidistant but different
optoelectronics.
As a quasi-one-dimensional nanostruc-
ture, the helical nanobelts exhibit a unique growth direction
and typical rectangular cross section.
Helical Si oxide
materials,
and some helical Si oxide nanostructures have
cal properties.
In this letter, we report the fabrication of
helical amorphous SiO nanobelts using a thermal evapora-
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tion technique. Different from other nanobelts,
the peri-
odic bright and dark stripes on the amorphous twisted SiO2
nanobelts surface disappear if the fabrication time is long. To
better understand the phenomenon and the formation mecha-
nism of the helical amorphous SiO nanobelts stripes, the
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formation process is simulated. The formation mechanism
can explain some experimental phenomena about stripes for-
mation pertaining to amorphous nanobelts, which are obvi-
by transmission electron microscopy.
The helical amorphous SiO nanobelt samples were pro-
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duced by thermal evaporation. Si monoxide powders
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99.99% purity͒ placed in an alumina crucible on one side of
an alumina boat were evaporated onto a series of cleaned Si
100͒ substrates located 9–15 cm away on the other side of
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the alumina boat. The alumina boat was inserted into an
alumina tube with the alumina crucible located at the center
of an electric heater. The alumina tube was evacuated to a
−
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pressure of 1ϫ10 Pa, and 99.99% Ar was introduced as
the carrier gas at 150 SCCM ͑SCCM denotes cubic centime-
ter per minute at STP͒ throughout the experiment, during
which the alumina tube was heated to 1300 °C for 3 h. Fi-
nally, the alumina tube was cooled slowly to room tempera-
ture and the products were synthesized on the Si substrate.
Figures 1͑a͒–1͑d͒ depict the general morphology of the
products on Si ͑100͒ observed by scanning electron micros-
FIG. 1. SEM images of the helical amorphous twisted SiO nanobelts. Im-
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ages ͑a͒ and ͑c͒ are from the products with a longer synthesis time ͑180
min͒. Images ͑b͒ and ͑d͒ are from the products with a shorter growth time
͑160 min͒.
a͒Authors to whom correspondence should be addressed. Electronic ad-
dresses: hkxlwu@nju.edu.cn and paul.chu@cityu.edu.hk.
0003-6951/2009/94͑25͒/253110/3/$25.00
94, 253110-1
© 2009 American Institute of Physics
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