Low temperature growth of single crystalline germanium nanowires

Article abstract of DOI:10.1016/j.materresbull.2009.09.027

Ge nanowires have been prepared at a low temperature by a simple hydrothermal deposition process using Ge and GeO₂ powders as the starting materials. These as-prepared Ge nanowires are single crystalline with the diameter ranging from 150 nm to 600 nm and length of several dozens of micrometers. The photoluminescence spectrum under excitation at 330 nm shows a strong blue light emission at 441 nm. The results of the pressure and GeO₂ content dependences on the formation and growth of Ge nanowires show that the hydrothermal pressure and GeO₂ content play an essential role on the formation and growth of Ge nanowires under hydrothermal deposition conditions. The growth of Ge nanowires is proposed as a solid state growth mechanism.

Full text of DOI:10.1016/j.materresbull.2009.09.027

Materials Research Bulletin 45 (2010) 153–158
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Materials Research Bulletin
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Low temperature growth of single crystalline germanium nanowires
a
b
a
c
a
a
a
a,
L.Z. Pei a, , H.S. Zhao , W. Tan , H.Y. Yu , Y.W. Chen , J.F. Wang , C.G. Fan , J. Chen , Qian-Feng Zhang
*
*
a School of Materials Science and Engineering, Institute of Molecular Engineering and Applied Chemistry, Key Lab of Materials Science and Processing of Anhui Province, Anhui
University of Technology, Ma’anshan, Anhui 243002, PR China
b Henkel Huawei Electronics Co. Ltd., Lian’yungang, Jiangsu 222006, PR China
c Department of Materials Science, Fudan University, Shanghai 200433, PR China
A R T I C L E I N F O
A B S T R A C T
Article history:
Ge nanowires have been prepared at a low temperature by a simple hydrothermal deposition process
using Ge and GeO2 powders as the starting materials. These as-prepared Ge nanowires are single
crystalline with the diameter ranging from 150 nm to 600 nm and length of several dozens of
micrometers. The photoluminescence spectrum under excitation at 330 nm shows a strong blue light
emission at 441 nm. The results of the pressure and GeO2 content dependences on the formation and
growth of Ge nanowires show that the hydrothermal pressure and GeO2 content play an essential role on
the formation and growth of Ge nanowires under hydrothermal deposition conditions. The growth of Ge
nanowires is proposed as a solid state growth mechanism.
Received 27 April 2009
Received in revised form 8 September 2009
Accepted 24 September 2009
Available online 2 October 2009
Keywords:
A. Nanostructures
B. Crystal growth
C. Electron microscopy
D. Optical properties
ß 2009 Elsevier Ltd. All rights reserved.
1. Introduction
Recently, considerable effort has been devoted to preparing Ge
nanowires by employing different techniques and explaining by
One-dimensional (1D) nanowires have attracted increasing
interest due to their remarkable electrical, optical and mechanical
properties [1,2]. Germanium (Ge) is an important semiconductor
with a direct bandgap of 0.8 eV and an indirect bandgap of 0.66 eV.
Recently, interest in germanium has intensified as the migration
from silicon to other materials is contemplated for enhanced
functionality of future transistors for logic and other functions [3].
Therefore, it is natural that there is intense interest in preparing
wire-like nanostructures of Ge. Germanium nanowires are
recognized as the promising material for the fabrication of
optoelectronic nanodevices and nanowire field effect transistors
(FETs) [4,5]. Fermi pinning in the band gap has important effects on
the effective doping. However, germanium is not used nowadays in
our computers owing to the bad quality of germanium oxide which
is still the challenge to solve. Some efforts have been devoted to the
removing Ge oxide from Ge nanowires and forming passivation
layers in the surface of Ge nanowires. Korgel and Hanrath [6]
investigated the role of the oxide and possible passivations in the
electronic properties. Dai and coworkers [7] showed the core–shell
Ge nanowires formed with a single crystalline Ge core and
concentric shell of nitride and silicon passivation layer by CVD
method.
different growth mechanism, such as CVD method [8–12], laser
ablation method [13], thermal evaporation [14], solution–liquid–
solid synthesis (SLS) [15–17] and template method [18,19].
However, high temperature (generally higher than 400 8C, even
800 8C) is required in these preparation methods. Although the
preparation temperature of Ge nanowires prepared by the SLS
growth process is lower than 500 8C [15–17], the pressure for
forming Ge nanowires is very high (generally high than 20 MPa). In
addition, it is also very important that the solvent is poisonous
which will pollute the environments. Therefore, it is very essential
to prepare high quality Ge nanowires at lower temperature using
simple preparation process. Very recently, some efforts have been
done to obtain high quality Ge nanowires using other catalysts,
such as bismuth and indium than gold by CVD method and
reducing the synthesis temperature to about 300 8C for the
fabrication of high quality Ge nanowires [20–22]. Hydrothermal
route is also a kind of simple and effective way to prepare
sufficiently crystallized materials due to its mildness and
simplicity, which need no expensive equipments [23–27]. So
hydrothermal method has been recently reported to grow 1D
nanostructures because of its easy preparation procedure, low
growth temperature, great control over experimental parameters
and convenience for synthesis in high quality [28–31]. In the
present study, we will report on the preparation of Ge nanowires
by a hydrothermal deposition process at much lower temperature
of 250 8C. The experiment results show that the growth of the Ge
nanowires is dominated by a solid state growth process.
* Corresponding authors. Tel.: +86 555 2311570; fax: +86 555 2311570.
E-mail addresses: lzpei@ahut.edu.cn, lzpei1977@163.com (L.Z. Pei),
zhangqf@ahut.edu.cn (Q.-F. Zhang).
0025-5408/$ – see front matter ß 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.materresbull.2009.09.027

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L.Z. Pei et al. / Materials Research Bulletin 45 (2010) 153–158
2. Experimental
3. Results and discussion
The preparation of Ge nanowires was performed in an
autoclave which is described elsewhere [28,29]. All starting
materials are analytic grade reagents without further purification.
1.0 g Ge (purity: ꢀ99.99%) and GeO2 (purity: ꢀ99.99%) powders
were mixed with 48 ml distilled water. The mole ratio of Ge and
GeO2 is 1:1. Then the mixture was put into the autoclave. The
copper substrate with the size of 6 cm  2 cm was put into
distilled water to clean for 10 min using ultrasonic wave
apparatus in order to insure the cleanliness in the surface of
the copper substrate. Then, the latter was fixed in the stainless
steel bracket in the center of the autoclave. After the autoclave
was sealed safely, it was heated to 250 8C of temperature, 3.5–
3.7 MPa of pressure and 100 rpm of the rotating speed for the
stirrer, which was maintained at this stage for 24 h. Subsequently
the autoclave was cooled in air. Finally, the copper substrate with
bulk light blue deposit was obtained.
Fig. 1 shows the representative XRD pattern of the as-grown
products at room temperature. The diffraction peaks at 2 = 27.68,
u
45.28, 53.58, 66.18 and 72.68 can be well indexed to the cubic
diamond phase Ge with the crystalline plane of (1 1 1), (2 2 0),
(3 1 1), (4 0 0) and (3 3 1) (JCPDS File No. 04-0545). Weak CuGeO3
peaks with orthorhombic structure are also observed from the XRD
pattern (JCPDS File No. 54-0089). From the results of the XRD
pattern, it can be concluded that Ge cubic diamond phase is the
main phase of the products besides a small amount of CuGeO3
The prepared samples were characterized by X-ray diffrac-
tion (XRD), scanning electron microscopy (SEM), energy X-ray
spectrum (EDS), transmission electron microscopy (TEM), high-
resolution TEM (HRTEM), Raman and photoluminescence (PL)
spectra. XRD patterns were carried out on a Siemens D5000 X-
ray diffractometer equipped with a graphite monochromatized
˚
a radiation (l = 1.5406 A). The samples were scanned at a
Cu K
scanning rate of 0.058/s in the
2u range of 10–808. SEM
observation was performed using JEOL JSM5410 SEM with a
15-kV accelerating voltage. Chemical analysis was performed
with an EDS attached to the SEM. The product was mechanically
scrapped from the copper substrate. TEM and HRTEM samples
were prepared by putting several drops of solution with Ge
nanowires onto a standard copper grid with a porous carbon
film after the nanowire samples were dispersed into distilled
water and treated for about 10 min using ultrasonic wave
apparatus. TEM and HRTEM observations were performed using
JEOL JEM-2100 transmission electron microscope operating
˚
with 1.9 A point-to-point resolution operating and a 200-kV
accelerating voltage by a GATAN digital photography system.
Raman measurements were conducted using a Laboram-010
Raman laser spectrometer with a resolution of 2 cmÀ1. The light
source is He–Ne laser with the wavelength of 632.8 nm. PL
measurement was carried out at room temperature using
330 nm as the excitation wavelength with a luminescence
spectrometer (Edinburgh Instruments, FLS920) in the range of
350–600 nm.
Fig. 2. (a) and (b) General SEM images of the products with different magnifications.
(c) The corresponding EDS spectrum.
Fig. 1. XRD pattern of the products.

L.Z. Pei et al. / Materials Research Bulletin 45 (2010) 153–158
155
orthorhombic phase. CuGeO3 may form from the reaction of GeO2
and CuO.
The general morphology, size and composition of the products
were examined with a SEM and EDS equipped to the SEM. Fig. 2(a)
shows the general morphology of the products. It can be seen that
abundant of free-standing nanowires grown on the substrate. The
Ge nanowires. The nanowires can be isolated from one another by
dispersing them into the distilled water and treating for about
10 min using ultrasonic wave apparatus. EDS was used to analyze
the composition of the nanowires (Fig. 2(c)). Strong Ge, Cu and O
peaks confirm that the products are composed of Cu, Ge and O. Cu
peak mainly originates from the copper substrate besides the Cu in
the CuGeO3 phase of the products. Therefore, the nanowires are
composed of Ge and O with a small quantity of Cu.
TEM and HRTEM analyses were used to explore the morphology
and crystalline structure of the as-grown nanowires. Fig. 3(a)
shows a typical TEM image of the products, which clearly displays
that the products are composed of smooth nanowires with a
diameter distribution of about 140–500 nm. The morphology of
the nanowires observed by TEM is similar to that by SEM. A HRTEM
image of single nanowire at the growth tip is shown in Fig. 3(b). As
can be seen from the image, the nanowire is a structurally uniform
single crystalline. The observed interplanar spacing is about
0.346 nm, which corresponds to the separation between (1 1 1)
lattice planes of cubic Ge. The corresponding fast Fourier
transformation (FFT) diffraction pattern of the nanowire (inserted
in the right-upper part of Fig. 3(b)) also indicates the single
crystalline nature. The irregular surface at the tip of the nanowire
can be obviously observed which may originate from the fracture
surface of the nanowire. Numerous twins are also observed by the
high-resolution TEM image. Nanowires grow along the direction
with minimum surface energy, such as different defects [32,33].
length is several dozens of micrometers, even up to 100
mm. The
SEM image of the nanowires with higher magnification (Fig. 2(b))
further displays the smooth and straight structure. Almost no other
structures can be observed from the SEM image showing the
products with the same nanowire structure. The obtained
nanowires have a diameter distribution ranging from 150 nm to
600 nm. And the nanowires are forming entangled chunks. The
entangled chunks may originate from the continuous deposition of
nanoclusters with Ge and GeO2 onto the substrates and growth of
Fig. 3. (a) General TEM image of the products. (b) HRTEM image of single nanowire.
The inset in the right-upper part is the corresponding diffraction pattern obtained
by fast Fourier transformation (FFT).
Fig. 4. (a) Raman spectrum of the products. (b) PL spectrum of the products.

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L.Z. Pei et al. / Materials Research Bulletin 45 (2010) 153–158
Twin is a kind of defect which has minimum surface energy.
Therefore, the twins are considered to induce the growth of the
nanowires along the nanowire axis.
Hydrothermal pressure and GeO2 content dependences of the
Ge nanowires were researched in detail in order to understand the
roles of these factors on the formation, growth process of the Ge
nanowire. The SEM images on the hydrothermal pressure
dependence of the Ge nanowires are shown in Fig. 5 with the
hydrothermal temperature of 250 8C and the pressure of 2.1–
2.5 MPa and 4.3–4.7 MPa, respectively. The hydrothermal pressure
can be controlled by changing the water content. Compared to the
nanowires obtained from the hydrothermal pressure of 3.5–
3.7 MPa, the length of the Ge nanowires increases obviously
Fig. 4(a) shows the Raman spectrum of the products. The strong
peak located at 297.1 cmÀ1 originates from the optical phonons of
the Ge–Ge stretching mode showing the Raman characteristics of
cubic Ge. The shape of the peak at 297.1 cmÀ1 is similar to that of
the Ge nanowires prepared by other methods [30,34]. The peak of
the Ge–Ge mode of the nanowires at 297.1 cmÀ1 is red shifted by
4.9 cmÀ1 as compared with that from bulk Ge at 302.0 cmÀ1 [30].
The minimum size of the nanowires observed is 150 nm. With this
size no quantum confinement can be observed. The phonon
confinement effect can cause an insignificant shift of the peak to
lower energy [31,35]. Therefore, the red shift by 4.9 cmÀ1 of the
Ge–Ge Raman stretching peak may be caused owing to the phonon
confinement effect. In addition, lattice strain also causes frequency
shift of the Raman mode. A simple comparison between the XRD
result, e.g., Ge (1 1 1) = 27.68, and the power diffraction data (JCPDS
File No. 04-0545, Ge (1 1 1) = 27.3068) reveals that lattice strains
are built in the grown germanium structures. Therefore, the lattice
strains also play an important effect on the on Raman shift of Ge–
(generally 100
mm) with the hydrothermal pressure decreasing to
2.1–2.5 MPa (Fig. 5(a)). However, definite quantities of clusters
with nanoscale and microscale size are observed (designated by
black arrow in Fig. 5(b)) showing the impurities of the products.
Only nanowire with the length of about 30
mm is obtained with the
hydrothermal pressure increasing to 4.3–4.7 MPa (Fig. 5(c) and
(d)). However, different from the SEM images obtained from other
hydrothermal pressures, some microscale rod structures with the
length of about 10
mm is found (shown by the white arrow in
Fig. 5(d)) which may be caused by the aggregation of nanoclusters
during the deposition process of the nanowires. The hydrothermal
pressure dependence results show that the hydrothermal pressure
plays a very important role on the purity in morphology, formation
and growth of the Ge nanowires. Therefore, an appropriate
hydrothermal pressure is required for the formation of the high
pure nanowires under hydrothermal deposition conditions.
Supercritical hydrothermal temperature is not the key factor for
the formation and growth of the Ge nanowires under hydro-
thermal deposition conditions because the Ge nanowires can be
obtained easily at the hydrothermal temperature which is far
lower than the supercritical hydrothermal temperature 374 8C
[40]. The experiment using only Ge as the starting material was
conducted in order to demonstrate the effect of GeO2 on the
formation of Ge nanowires. Only irregular particles form showing
that GeO2 plays essential role on the formation and growth of the
Ge mode. Some relatively weak Raman peaks at 185.8 cmÀ1
,
221.0 cmÀ1, 325.8 cmÀ1, 436.2 cmÀ1, 592.5 cmÀ1, 711.2 cmÀ1 and
854.6 cmÀ1 are also observed. These Raman peaks are attributed to
the typical CuGeO3 orthorhombic characteristic peaks according to
the Raman result of the CuGeO3 powders [36,37]. The result is in
accordance with that of the XRD analysis of the products. A strong
blue light emission is revealed at 441 nm with a band width from
400 nm to 500 nm at room temperature under excitation at
330 nm (Fig. 4(b)). Blue light emission has also been reported from
germanium oxide nanowires and the peaks at 448 nm and 442 nm
which were proposed to be attributed to oxygen vacancies and
oxygen–germanium vacancies [38–40]. Therefore, the intense blue
light emission of the nanowires is considered to be caused by
oxygen vacancies and oxygen–germanium vacancies.
Fig. 5. SEM images of the products with different magnifications obtained from the hydrothermal conditions of 250 8C and different pressures for 24 h. (a) and (b) 2.1–2.5 MPa
and (c) and (d) 4.3–4.7 MPa.

L.Z. Pei et al. / Materials Research Bulletin 45 (2010) 153–158
157
Fig. 6. SEM images of the products obtained using Ge and GeO2 with different mole ratios as the starting materials from the hydrothermal conditions of 250 8C, 3.5–3.7 MPa.
(a) 20:1, (b) 10:1, (c) 10:3, (d) 5:3 and (e) 5:4.
Ge nanowires. In order to further verify the role of GeO2 on the
formation and growth of the Ge nanowires, the GeO2 content
dependence of the Ge nanowires is analyzed in detail. Therefore,
the experiments using Ge and GeO2 with different mole rates as the
starting materials were conducted under the hydrothermal
conditions of 250 8C and 3.5–3.7 MPa. The mole ratio of Ge and
GeO2 is 20:1, 10:1, 10:3, 5:3 and 5:4, respectively. The
corresponding SEM images are shown in Fig. 6(a)–(e). A small
100 mm and 100–500 nm, respectively. So GeO2 is believed to play
an essential effect on the formation and growth of the nanowires
besides the hydrothermal pressure. In addition, the nanowires can
also be obtained effectively with the decreasing of the content of
GeO2 in the starting materials. Therefore, the phase purity of the Ge
nanowires obtained from the mixture of Ge and GeO2 with a small
amount of GeO2 may be improved.
Generally, nanowires grow via liquid droplets at the tips
according to the oxide-assisted growth process proposed by Lee
and coworkers [41,42]. But no semi-circular tips with the liquid
state characteristic are observed according to the electron
microscopy images of the products. Therefore, possibly no liquid
phases form during the growth process of the Ge nanowires at
250 8C, a relatively low hydrothermal deposition temperature. In
fact, liquid phase is not the essential factor for the formation and
growth of Ge nanowires according to the recent research results
[43–45]. The formation and growth of the nanowires also occurred
via the solid state which is below the liquid temperature. The
radian and size at the growth tip of the nanowires decrease with
quantity of nanowires with the length of about 10
mm form when
the mole ratio of Ge/GeO2 is 20:1, where the GeO2 content is less
than 5 mol%. The result shows that the small amount of GeO2 also
induces the formation of a small amount of nanowires. However,
the products are mainly composed of microscale clusters which
cannot form nanowires owing to the small quantities of GeO2. Pure
nanowire structures form with the increase in the Ge/GeO2 mole
ratio (shown in Fig. 6(b)–(e)) which is similar to that of the
nanowires formed from the Ge and GeO2 with the mole ratio of 1:1.
The length and diameter of the nanowires are similar with the
increase in the mole ratio of the Ge and GeO2 which are about 50–

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L.Z. Pei et al. / Materials Research Bulletin 45 (2010) 153–158
References
the decrease in the preparation temperature. Metal copper
metagermanate nanowires can also be prepared in a copper
substrate by a similar hydrothermal deposition process using only
GeO2 as the starting material at 250 8C [46]. Similarly, no semi-
circular tips with the liquid state characteristic are found, which
shows that the nanowires are formed by a solid state growth
process. Therefore, the metal compound CuGeO3 generated from
CuO and GeO2 is believed to play an essential role on the formation
and growth of the Ge nanowires. The metal compound assisted
growth mechanism via solid state is proposed to understand the
growth process of the Ge nanowires. To further verify the proposed
mechanism, an experiment was done using a silicon substrate
instead of copper substrate. No nanowires were obtained in the
product except some particles with different sizes. The result
reveals that the Cu substrate is also necessary for the formation of
the Ge nanowires by the metal compound assisted growth process.
Normally, CuO originates from the surface of the copper
substrate owing to the oxidation effect. The starting materials Ge
and GeO2 particles undergo a conformation change from the solid
phase to the vapor phase in the nanocluster state under the
hydrothermal conditions. The surface of the copper substrate is
further oxidized owing to the existence of oxygen in the
hydrothermal environment. The nanoclusters in the vapor state
are driven continuously by flowing vapor water and the stirring of
the stirrer equipped in the autoclave. Therefore, Ge and GeO2
nanoclusters deposit onto the copper substrate continuously and
react with CuO in the surface of the copper substrate forming metal
compound CuGeO3 nanoclusters. CuGeO3 nanoclusters absorb Ge
and GeO2 nanoclusters in the gas state continuously from the
atmosphere forming CuGeO3, Ge and GeO2 cores resulting in the
supersaturation state of germanium and internal recrystallization
process. Growth at the fast growing tip continues with the
crystalline germanium expelled. Nanowire growth in the lateral or
diameter direction is terminated at the smooth surface of the
amorphous sheath. In addition, numerous twins with minimum
surface energy are also considered to induce the growth of the
nanowires along the nanowire axis.
[1] Y. Cui, Q.Q. Wei, H.K. Park, C.M. Lieber, Science 293 (2001) 1289.
[2] C.J. Lee, T.J. Lee, C.S. Lyu, Y. Zhang, H. Ruh, H.J. Lee, Appl. Phys. Lett. 81 (2002) 3648.
[3] L. Wang, X.S. Wang, J.C. Tang, N. Cue, Mater. Charact. 48 (2002) 189.
[4] D.W. Wang, Q. Wang, A. Javey, R. Tu, H.J. Dai, H. Kim, P.C. McIntyre, T. Krishna-
mohan, K.C. Saraswat, Appl. Phys. Lett. 83 (2003) 2432.
[5] A.B. Greytak, L.J. Lauhon, M.S. Gudiksen, C.M. Lieber, Appl. Phys. Lett. 84 (2004)
4176.
[6] T. Hanrath, A.B. Korgel, J. Am. Chem. Soc. 124 (2002) 1424.
[7] L. Zhang, R. Tu, H.J. Dai, Nano Lett. 6 (2006) 2785.
[8] P. Nguyen, H.T. Ng, M. Meyyappan, Adv. Mater. 17 (2005) 549.
[9] G. Gu, M. Burghard, G.T. Kim, G.S. Du¨ sberg, P.W. Chiu, V. Krstic, S. Roth, W.Q. Han, J.
Appl. Phys. 90 (2001) 5747.
[10] N. Zaitseva, J. Harper, D. Gerion, C. Saw, Appl. Phys. Lett. 86 (2005) 053105.
[11] T.I. Kamins, X. Li, R.S. Williams, X. Liu, Nano Lett. 4 (2004) 503.
[12] B.S. Kim, T.W. Koo, J.H. Lee, D.S. Kim, Y.C. Jung, S.W. Hwang, B.L. Choi, E.K. Lee, J.M.
Kim, D. Whang, Nano Lett. 9 (2009) 864.
[13] A.M. Morales, C.M. Lieber, Science 279 (1998) 208.
[14] Y.F. Zhang, Y.H. Tang, N. Wang, C.S. Lee, I. Bello, S.T. Lee, Phys. Rev. B 61 (2000)
4518.
[15] T. Hanrath, B.A. Korgel, Small 1 (2005) 717.
[16] X.M. Lu, F.D.D. Fanfair, K.P. Johnston, B.A. Korgel, J. Am. Chem. Soc. 127 (2005)
15718.
[17] N.R.B. Coleman, K.M. Ryan, T.R. Spalding, J.D. Holmes, M.A. Morris, Chem. Phys.
Lett. 343 (2001) 1.
[18] Y.F. Mei, Z.M. Li, R.M. Chu, Z.K. Tang, G.G. Siu, R.K.Y. Fu, P.K. Chu, W.W. Wu, K.W.
Cheak, Appl. Phys. Lett. 86 (2005) 021111.
[19] Y.Z. Lv, L. Guo, H.B. Xu, L. Ding, C.L. Yang, J.N. Wang, W.K. Ge, S.H. Yang, Z.Y. Wu,
Appl. Phys. Lett. 99 (2006) 114302.
[20] Y. Xiang, L.Y. Cao, J. Arbiol, M.L. Brongersma, A.F.I. Morral, Appl. Phys. Lett. 94
(2009) 163101.
[21] Y. Xiang, L.Y. Cao, S. Conesa-Boi, S. Estrade, J. Arbiol, F. Peiro, M. Heiß, I. Zardo, J.R.
Morante, M.L. Brongersma, A.F.I. Morral, Nanotechnology 20 (2009) 245608.
[22] J.L. Lensch-Falk, E.R. Hemesath, D.E. Perea, L.J. Lauhon, J. Mater. Chem. 19 (2009)
849.
[23] C. Pacholski, A. Kornowski, H. Weller, Angew. Chem. Int. Ed. 41 (2002) 1188.
[24] K.H. Tam, C.K. Cheung, Y.H. Leung, A.B. Djurisic, C.C. Ling, C.D. Beling, S. Fung,
ˇ
W.M. Kwok, W.K. Chan, D.L. Phillips, L. Ding, W.K. Ge, J. Phys. Chem. B 110 (2006)
20865.
[25] L.E. Greene, M. Law, D.H. Tan, M. Montano, J. Goldberger, G. Somorjai, P. Yang,
Nano Lett. 5 (2005) 1231.
[26] M. Law, L.E. Greene, J.C. Johnson, R. Saykally, P. Yang, Nat. Mater. 4 (2005) 455.
[27] L.E. Greene, M. Law, J. Goldberger, F. Kim, J.C. Johnson, Y. Zhang, R.J. Saykally, P.
Yang, Angew. Chem. Int. Ed. 42 (2003) 3031.
[28] L.Z. Pei, H.S. Zhao, W. Tan, Q.F. Zhang, J. Appl. Phys. 105 (2009) 054313.
[29] L.Z. Pei, Y.H. Tang, Y.W. Chen, C. Guo, X.X. Li, Y. Yuan, Y. Zhang, J. Appl. Phys. 99
(2006) 114306.
[30] G. Jin, Y.S. Tang, J.L. Liu, K.L. Wang, Appl. Phys. Lett. 74 (1999) 2471.
[31] P. Sutter, C. Schwarz, E. Muller, V. Zelezny, S. Goncalves-Conto, H.V. Kanel, Appl.
Phys. Lett. 65 (1994) 2220.
4. Conclusions
[32] D.H. Wang, D. Xu, Q. Wang, Y.J. Hao, G.Q. Jin, X.Y. Guo, K.N. Tu, Nanotechnology 19
(2008) 215602.
[33] R.E. Algra, M.A. Verheijen, M.T. Borgstro¨m, L.F. Feiner, G. Immink, W.J.P.V. Encke-
vort, E. Vlieg, E.P.A.M. Bakkers, Nature 456 (2008) 369.
[34] Y.H. Tang, Y.F. Zhang, N. Wang, I. Bello, C.S. Lee, S.T. Lee, Appl. Phys. Lett. 74 (1999)
3824.
[35] R. Jalilian, G.U. Sumanasekera, H. Chandrasekharan, M.K. Sunkara, Phys. Rev. B 74
(2006) 155421.
[36] H. Kuroe, T. Sekine, M. Hase, Y. Sasago, K. Uchinokura, H. Kojima, I. Tanaka, Y.
Shibuya, Phys. Rev. B 50 (1994) 16468.
[37] L.C. Ming, S.K. Sharma, A.J. Jayaraman, Y. Kobayashi, E. Suzuki, S. Endo, V.
Prakapenka, D. Yang, Spectrochim. Acta A 61 (2005) 2418.
[38] X.C. Wu, W.H. Song, B. Zhao, Y.P. Sun, J.J. Du, Chem. Phys. Lett. 349 (2001) 210.
[39] Y. Su, X.M. Liang, S. Li, Y.Q. Chen, Q.T. Zhou, S. Yin, X. Meng, M.G. Kong, Mater. Lett.
62 (2008) 1010.
In summary, we have prepared Ge nanowires in bulk quantities
at low temperature of 250 8C by a simple hydrothermal deposition
process, which offers a more convenient route to fabricate Ge
nanowires. Such a low temperature growth of Ge nanowires may
provide a possibility to fabricate nanodevices onto various low
temperature endurance substrates. These Ge nanowires are single
crystalline with diameters ranging from 150 nm to 600 nm and
lengths of several tens of micrometers. The PL spectrum at a room
temperature shows the blue light emission at 441 nm. The growth
process of Ge nanowires may be attributed to a solid state growth
mechanism.
[40] P.T. Cummings, H.D. Cochran, J.M. Simonson, R.E. Mesmer, S. Karaborni, J. Chem.
Phys. 94 (1991) 5606.
[41] J.Y. Zhang, X.M. Bao, Y.H. Ye, X.L. Tan, Appl. Phys. Lett. 73 (1998) 1790.
[42] S.T. Lee, N. Wang, Y.F. Zhang, Y.H. Tang, MRS Bull. 24 (1999) 37.
[43] S. Kodambaka, J. Tersoff, M.C. Reuter, F.M. Ross, Science 316 (2007) 729.
[44] K. Kang, D.A. Kim, H.S. Lee, C.J. Kim, J.E. Yang, M.H. Jo, Adv. Mater. 20 (2008) 4684.
[45] V. Schmidt, U. Go¨sele, Science 316 (2007) 698.
Acknowledgments
This work was supported by the National Basic Research
Program of China (973 Program, 2008CB617605) and the Program
for New Century Excellent Talents in University of China (NCET-06-
0556).
[46] L.Z. Pei, H.S. Zhao, W. Tan, Y.H. Yu, Y.W. Chen, Q.F. Zhang, C.G. Fan, CrystEngComm
11 (2009) 1696.