APPLIED PHYSICS LETTERS 86, 243103 ͑2005͒
Synthesis and field emission properties of TiSi2 nanowires
B. Xiang, Q. X. Wang, Z. Wang, X. Z. Zhang, L. Q. Liu, J. Xu, and D. P. Yua͒
State Key Laboratory for Mesoscopic Physics, and Electron Microscopy Laboratory, School of Physics,
Peking University, Beijing 100871, China
͑Received 15 February 2005; accepted 10 May 2005; published online 7 June 2005͒
TiSi2 is a high-melting compound with excellent conductivity ϳseveral ⍀ cm. TiSi2 nanowires
were fabricated in large scale by a simple vapor phase deposition method. The as-synthesized TiSi2
nanowires were investigated using x-ray diffraction, scanning electron microscopy, transmission
electron microscopy, and Raman scattering. Field emission property of TiSi2 nanowires was studied
and an emission current density of 5 mA/cm2 was obtained and no obvious degradation was
observed in a life stability experiment period for over ϳ40 h. The cathodoluminescence images
were very bright and homogenous. The remarkable performance reveals that the TiSi2 nanowires
can serve as a good candidate for commercial application in vacuum microelectronic devices,
particularly flat panel displays. © 2005 American Institute of Physics. ͓DOI: 10.1063/1.1948515͔
One dimensional ͑1D͒ nanostructures have distinguish-
ing properties compared with their bulk partners and are now
widely studied in view point of fundamental physics and
technological applications.1–5 Recently, 1D nanostructure-
based field emitters have attracted great interest owing to
their potential applications in flat panel displays and vaccum
microelectronics.6–10 It has been reported that the Si
nanowires display manifested field emission properties.11
Zhu et al.12 reported that high emission current from ZnO
nanostructures is relatively uniform and stable. Titanium sil-
icide is known high-melting silicide with very low resistivity
͑ϳseveral ⍀ cm͒, which offers the possibility of electrical
interconnections in a scale that cannot be obtained with con-
ventional lithographic methods. TiSi2 may also be used as
active circuit elements because of its excellent electronic
properties.13 In addition, TiSi2 is one of promising cold cath-
ode materials for field emission due to their high thermal and
chemical stability.14 Stevens et al.15 reported that TiSi2 nano-
wires were prepared by epitaxial method. However, the syn-
thesis process is too expensive for its applications. In this
letter, we report that TiSi2 nanowires were synthesized in
high yield and high purity via a simple low-cost vapor phase
deposition method, and their field emission properties were
studied.
The TiSi2 nanowires were synthesized through a simple
physical vapor deposition method in a conventional alumina
tube furnace. A Si wafer was put in an alumina boat loaded
with pure Ti metal powder, which served as the titanium
source. The boat was transferred into the tube furnace, which
was pumped down to about 150 Torr. The temperature inside
the furnace was increased to 800 °C under flowing Ar
ϳ100 sccm, and held for 3 h. When the furnace was cooled
down to room temperature, a black layer was found depos-
ited on the surface of the Si wafer.
are 192, 207, 245, and 276 cm−1, corresponding to the B3g,
B1g, Ag, and B2g vibration modes, respectively.16 Thus, it
further confirms that the as-synthesized TiSi2 nanowires
have the orthorhombic structure. Scanning electron micros-
copy ͑SEM͒ image provides the representative morphology
of the as-grown TiSi2 nanowires. It can be seen from Fig.
1͑c͒ that there is a large amount of the nanowires randomly
oriented on the substrate, and the length of the nanowires
ranges from a few tenths to hundred micrometers. The aver-
age diameter of the as-grown nanowires is around 40 nm, as
shown in the magnified SEM image in the inset of the
Fig. 1͑c͒. High-resolution transmission electron microscopy
͑HRTEM͒ was conducted to look insight into the atomic
structure of the as-grown TiSi2 nanowires. As shown in the
Fig. 1͑d͒, the HRTEM image shows that the as-synthesized
TiSi2 nanowires are single crystalline with the growth direc-
¯
tion along the ͗022͘ zone axis direction, which is confirmed
by the corresponding fast Fourier transformation ͑FFT͒
shown in the inset.
Because no additional metallic catalysts were used in the
source material, the growth mechanism of the TiSi2 nano-
wires cannot be explained by a conventional vapor-liquid-
solid model,17 in which a metal particle is located at the
growth frontier of the nanowires and acts as the catalytic
active site. It is likely that a vapor-solid growth process
dominates the growth of the TiSi2 nanowires.1 At the begin-
ning, the Si substrate is surrounded by Ti species in the re-
action chamber. Subsequently, the Ti species dissolve into
the Si and form nanosized Si–Ti alloy islands on the Si sub-
strate. Continuous feeding of Ti into the quasi-liquid Si–Ti
nanoislands leads to 1D growth of the TiSi2 crystal. This
growth process can be in fact defined as self-catalytic
growth.
Field emission measurements were carried out in a
All the peaks in the corresponding x-ray diffraction
͑XRD͒ spectrum can be indexed to the structure of an ortho-
rhombic TiSi2 phase, as shown in Fig. 1͑a͒. Room-
temperature Raman spectrum of the as-synthesized TiSi2
nanowires is shown in the Fig. 1͑b͒. The Raman shift peaks
homemade system with
a
high-vacuum chamber
͑ϳ10−7 Pa͒. The emission current is recorded while applying
the voltage at a step of 100 V. Figure 2͑a͒ shows the current–
voltage ͑I-V͒ curves with different electrode spacing between
the anode and tips of TiSi2 nanowires, which varied from
150 to 250 µm. With an electrode spacing of 250 µm, the
turn-on voltage is about 8 V/µm, corresponding to a current
density ϳ0.1 A/cm2, and much lower than that reported
a͒
Author to whom correspondence should be addressed; electronic mail:
0003-6951/2005/86͑24͒/243103/3/$22.50 86, 243103-1 © 2005 American Institute of Physics
128.59.222.12 On: Mon, 01 Dec 2014 01:54:44
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