World Journal Of Engineering
Growth of Catalyst-free SiC and SiC/SiO2 Nanowires
using the Precursor of Methyltrichlorosilane
Yoo Youl Choi and Doo Jin Choi*
Department of Materials Science and Engineering,
Yonsei University, 50 Yonsei-ro, Seodaemun-gu, Seoul 120-749, Korea
Results and Discussion
Abstract- This study provides the possibility to synthesize
variant shapes and sizes of noncatalytic SiC wires (SiCw) by
controlling the deposition conditions and not using any catalysts.
The deposition temperature difference has showed large
difference in the aspect of SiCw growth. The SiC/SiO2 core-shell
wires have been synthesized by adjusting the oxygen
concentration and controlling the decomposition and deposition
area respectively. All SiCws have been confirmed to be 3C-SiC.
Introduction
Fig. 1. Morphology of SiCws deposited at (a) 1200 ° C, α =30 and
(b) 1300°C, α= 30 conditions.
Silicon carbide (SiC) is a crucial material due to its superior
mechanical, physical properties and chemical resistances [1].
According to these high features, the syntheses of SiC
nanowires (SiCw), rods and whiskers have been studied in
various methods and lots of improved properties have been
reported. The typical synthesis processes are reducing silica by
carbothermal reaction [2], or using metallic catalysts for the
vapor-liquid-solid (VLS) growth [3, 4]. In this paper, we have
chosen the vapor-solid growth mechanism and proved the
possibility for building variant types of SiCws without using
any catalysts. In addition, precursor for SiCw growth,
methyltrichlorosilane (MTS) was used. Previously, several
groups have shown SiCws growth by MTS [5], but no trial for
synthesizing SiC/SiO2 core-shell wires via the single gas state
precursor has been done. The morphology and internal
structure of SiCws were altered by controlling variant
conditions of chemical vapor deposition (CVD).
Fig. 1 proves the temperature effect for growing SiCws in the
same deposition conditions except temperatures were
differently controlled. Each wire of (a) and (b) was deposited
at 1200°C and 1300°C. We observed all SiCws possessing a
sharp or narrow tip which can form only by the growth of no
catalyst used. As the growth rate follows the source
decomposition, the diameter difference has occurred between
(a) and (b).
Experimental
SiCws were grown in horizontal hot-wall furnace using lowpressure chemical vapor deposition (LPCVD). P-type Si wafer
was used as a substrate, and Si wafer was fully cleaned by
acetone and
hydrofluoric acid (HF) solution before
deposition. The precursor for SiCw deposition, MTS was
used. Input gas ratios (α= Total gas/MTS) was fixed at 30 and
deposition temperatures were held at 1200 ° C and 1300 °C
respectively. For SiC/SiO2 deposition, the hot zone was settled
Fig. 2. SEM morphology of SiC/SiO2 core-shell wires deposited at variant
oxygen concentrations. Magnified TEM images are implicated in each figure.
at 1200°C and deposition was treated at 1000°C area. The
morphology and microstructure were characterized using field
emission
scanning
electron
microscopy
(FESEM),
transmission electron microscopy (TEM) and X-ray
diffractometer (XRD).
We tried to synthesize a new core-shell structure via the
chemical reaction between oxygen and MTS. To maximize the
chemical reaction and synthesize SiO2 on the surface of
SiCws, we divided the source reaction and wire producing
zone. Concretely, as silica evaporates upper 1200°C, the hot
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World Journal Of Engineering
zone area was heated up to 1200°C and the Si substrate was
placed on the 1000 °C area. Fig. 2 shows the morphology
appearance how SiC/SiO2 wire differs from altering the
oxygen concentration. The wire deposition of (a) to (d) used
oxygen of 1, 3, 6, 10sccm, respectively. Comparing (a) to (d),
we observed the diameter to be larger as inserted oxygen
increases, and the shape has been more curly. However, the
ratio of core and shell showed that the core shrinking and shell
to be increased as oxygen concentration increased. This
proved that oxidized MTS produces both SiC and SiO, and the
structure of wire starts to synthesize building the core SiC
wire first and SiO2 simultaneously grows together by the
lateral direction as wire grows up.
Fig. 4. XRD spectrum of HF etched SiCws of fig. 2(b)
Conclusion
We synthesized variant shapes and sizes of SiC wires by
altering the deposition conditions and not using any catalysts.
Especially, deposition temperature effected large difference in
SiCw growth. The SiC/SiO2 core-shell wires have been
synthesized by adjusting the oxygen concentration and
controlling the decomposition and deposition area
respectively. By TEM and XRD analysis, SiCws were all
confirmed to be FCC β-SiC.
References
[1] Dai, H. J., Wong, E. W., Lu, T. Z., Fan, S. S., Lieber, C. M., Nature
1995 375, 679
[2] Wei, J., Li, K.Z., Li, H.J., Fu, Q.G., Zhang, L., Mater. Chem. Phys.
2006 95, 140
[3] Leu, I. C., Lu, Y. M., Hon, M. H. Mater. Chem. Phys. 1998 56, 256
[4] Seeger, T., Redich, P., Ruhle, M. Adv. Mater. 2000 12, 279
[5] Deng, J., Su, K., Zeng, Q., Wang, X., Cheng, L., Xu Y., Zhang, L.,
Chem. Vap. Deposition 2009 15, 281
[6] Chen, J., Shi, Q., Tang, Q., Mater. Chem. Phys. 2011 126, 655
Fig. 3. TEM microstructures of SiCws: (a) wire grown at 1300°C, (c)
SiC/SiO2 wire grown at 1000°C, (b) and (d) are the HRTEM image of (a) and
(c). SADP patterns are included in (b) and (d).
Fig. 3 shows the high resolution image of Fig. 1(b) and Fig.
2(b) wire. As (a) was grown in higher growth rate, the defect
lines have been observed. Wire of (c) shows the obvious
section of SiC crystalline core and SiO2 amorphous shell.
Each diffraction pattern indicates that both SiCws are highly
crystalline within FCC structures [6]. The structure was also
explained by the XRD spectrum in fig. 4 which describes the
wire to be cubic β-SiC.
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