This document summarizes a method for growing single crystal silicon wires within the pores of microstructured optical fibers (MOFs) via a high-pressure fluid-liquid-solid (FLS) approach. Key points: 1) Gold catalyst particles are deposited within MOF pores using a photochemical method, then silicon wires are grown by exposing the catalyst to a mixture of silane and helium at high pressure (30 MPa) and temperature (370°C). 2) The wires completely fill the MOF pores and are single crystals with a h112i growth direction. 3) Raman spectroscopy is used to optimize growth conditions and characterize the wires, revealing differences between single crystal and amorphous or

1. DOI: 10.1002/adma.200701569
Single-Crystal Semiconductor Wires Integrated into
Microstructured Optical Fibers**
By Bryan R. Jackson, Pier J. A. Sazio, and John V. Badding*
Assembly and integration of photonic and electronic
building blocks such as semiconductor micro/nanowires
into more complex structures is critical to the realization of
advanced materials and devices useful for a diverse range of
applications.[1]
Strategies employed to date to pattern wires
include fluidic and electric field directed assembly[2,3]
,
patterned vapor-liquid-solid (VLS) growth,[4]
compression of
Langmuir-Blodgett layers,[5]
and many others. Lithographic
and imprinting techniques are being developed to pattern
porous alumina that serves as a template for directed VLS
growth of single crystal nanowires.[6]
We have shown that
silica microstructured optical fibers (MOFs)[7]
can be used as
another class of template that can be drawn with dense arrays
of extreme aspect ratio pores with diameters down to less than
50 nm.[8]
An advantage of these templates over others is that
the extreme aspect ratio hole lattices can be designed with
great flexibility and precision to be periodic or aperiodic and
have engineered ‘‘defects’’ that arise from the absence of
specific holes.[7]
Furthermore, their unparalleled optical
transparency makes them ideally suited for fabrication of
photonic materials and devices. The high geometric perfection
and flexibility of the hole patterning in MOFs, as well as the
perfection of the holes themselves that can have ca. 1 A˚ RMS
surface roughness[9]
makes it straightforward to design them to
exhibit photonic bandgap effects, anti-resonant reflecting
optical waveguiding[10,11]
, and/or conventional index guiding.
Light constrained by such effects can interact with materials
embedded in MOF templates over distances of centimeters or
more.[8]
This long interaction length allows for the exploitation
of phenomena that are otherwise too weak to utilize on shorter
length scales. Here we report the growth of single crystal silicon
wires within the pores of microstructured optical fibers via a
high pressure fluid-liquid-solid approach. High pressures
are critical to overcoming mass transport constraints that
would ordinarily preclude catalytic wire growth in such
extreme aspect ratio templates. This capability will enable
new composite materials that exploit the superior properties of
single crystal wires arrayed to allow for cooperative photonic
and electronic phenomena. High performance devices such as
nanowire lasers within high Q photonic bandgap cavities
and semiconductor based non-linear frequency converters
could result. These fiberized single crystal semiconductor
devices would naturally integrate into existing optical fiber
infrastructure.
The challenge to filling MOF templates with functional
materials is their extreme aspect ratio. Directed VLS growth of
single crystal wires from catalyst particles such as gold at
deposition pressures of less than 1 Torr has been performed in
anodic alumina templates that are ca. 60 mm thick and
have nanoscale to microscale holes.[12]
Even with such thin
templates the reaction conditions, such as precursor partial
pressure and temperature, must be carefully chosen to
facilitate sufficiently rapid mass transport of reactants to the
catalyst particles in the pores while allowing for transport of
reaction byproducts away from them.[13]
The reaction
temperature must be low enough to preclude deposition of
amorphous material on the pore walls before the precursor
reaches the metal catalyst particles yet high enough to allow for
single crystal wire growth. In general deposition within micro
to nanoscale diameter pores that are much longer (e.g., cm) has
been difficult or impossible because of the larger aspect ratio.
Diffusion of reactants into such pores and exit of reaction
byproducts/carrier gas is too slow at sub-atmospheric to
atmospheric pressures. However, we found that by using
high pressures in the range of 30 MPa this difficulty could be
overcome. Our fluid-liquid-solid (FLS) approach inside an
MOF employs a high pressure helium carrier fluid (Fig. 1a).
Such high pressure fluids (for which the reaction conditions are
above the critical pressure and temperature of helium) are
exceedingly useful in nanoscience because they have high
diffusivities that facilitate transport into extreme aspect ratio
structures with diameters down to less than 10 nm.[8]
In the
approach described below, the silica template itself is used as a
nano or microscale reaction chamber, in contrast to the usual
COMMUNICATION
[*] Prof. J. V. Badding, Dr. B. R. Jackson[+]
Department of Chemistry and Materials Research Institute
Pennsylvania State University
University Park, PA 16802 (USA)
E-mail: jbadding@pearl.chem.psu.edu
Dr. P. J. A. Sazio
Optoelectronics Research Centre
Southampton University
Highfield, Southampton, SO17 1BJ (UK)
[+] Present address: Department of Materials Science and Engineering,
Rutgers University, Piscataway, NJ 08854, USA.
[**] J.V.B. acknowledges support from NSF (DMR-0502906), the Penn
State Materials Research Science and Engineering Center (NSF
DMR-0213623), and the Penn State-Lehigh Center for Optical
Technologies. TEM work was performed at the Materials Research
Institute at Penn State. P.J.A.S. thanks EPSRC for support. Support-
ing Information is available online from Wiley InterScience or from
the author.
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2. COMMUNICATION
approach of immersing the entire template inside a separate
low pressure reaction chamber[12]
or high pressure auto-
clave.[14]
The MOF reaction chamber and associated reservoir
require only milligram or smaller quantities of precursor,
opening the possibility of employing precursors to a wide
range of elemental and compound semiconductors at high
pressure that would otherwise present too large a safety hazard
because of their toxicity and flammability. High pressure FLS
with silane, which is pyrophoric, potentially explosive, and
toxic, has not been previously reported. Fluid organosilicon
precursors dissolved in supercritical hexane and contained
within an autoclave have been employed previously for
non-catalytic growth of silica nanowires inside mesoporous
silica templates that have pore lengths considerably shorter
than MOFs.[14]
However, in general hydride precursors are
preferred for semiconductor deposition to eliminate the
possibility of incorporating carbon impurities into the reaction
product. We found that the organosilicon precursor/super-
critical hexane approach did not work well for deposition
within MOF capillaries due to contamination with carbon.
High pressure alone allows for transport of sufficiently high
concentrations of SiH4 precursor for the initial stages of wire
growth. However, diffusion of the hydrogen reaction by
product and carrier gas away from the catalyst may still be too
slow to allow for continued reaction without some additional
transport mechanism. The permeability of silica to hydrogen
and helium (but not silane) is high; thus the heated zone
is flushed with a new helium volume every few hundred
milliseconds (Fig. 1a) (see Supporting Information). There-
fore, the semipermeable silica fiber templates allow for
pressure driven transport of new precursor mixture into
extreme aspect ratio pores, facilitating continuous wire growth.
The first step in FLS growth within MOF templates is
deposition of a gold catalyst particle at a suitable location
within the template. Electrochemical methods are usually
used for the deposition of gold catalyst within alumina and
other templates that are relatively short.[12]
Such methods
present many difficulties for use with extreme aspect ratio
MOF templates because of the much higher viscosity and
surface tension of liquids relative to high-pressure fluids.
Instead we use a photochemical method[8]
that exploits the
optical transparency of the silica fiber template (Fig. 1b).
An organometallic gold precursor, Me2Au(tfac), dissolved in
supercritical carbon dioxide is configured to flow down the
MOF template pores. Gold plugs can then be deposited in a
particular pore at a precise location along its length by
decomposing the precursor with 514 nm laser light focused with
a high numerical aperture oil immersion objective mounted on
a confocal Raman microscope. Following deposition of the
gold plugs, we found it is necessary to remove all traces of the
precursor; otherwise, many 30 to 40 nm diameter branched
silicon nanowires nucleate and grow from gold nanoparticles
formed on the silica pore walls (Fig. 2a) by decomposition of
these traces. Nanowire based chemical sensors are currently
being intensively investigated[15]
and these structures may find
application in integrating nanowire sensing methodologies
into microfluidic and nanofluidic capillaries and channels.
However, our goal in the present work is to grow wires along
the length of MOF pores that completely fill them. Thus we
flush the pores with pure CO2 at 133 MPa after deposition
of the gold plugs to dissolve and expel any residual
Me2Au(tfac)precursor that may remain and avoid nucleation
and growth of these ‘‘nosehair’’ nanowires.
To initiate FLS growth of silicon wires, a helium carrier gas
at a (typical) high pressure of 33 MPa is mixed with 3.3 to
5 MPa (ca. 10 to 15%) of silane and configured to flow into the
MOF pores toward a gold plug. After heating the template to
370 8C, the gold catalyzes the decomposition of silane and
silicon diffuses into the gold. At the saturation point, silicon is
precipitated from the gold-silicon alloy, growing single crystal
wires ca. 200 mm long (Fig. 1a). A single gold particle divides
into two as growth proceeds; only the particle on the side (left
in Fig. 1a) from which the precursor is entering the pore moves
while the other one (right in Fig. 1a) remains stationary. We
find a growth rate of ca. 0.7 mm minÀ1
at 370 8C, higher than the
0.01 mmÀ1
min rate predicted from an Arrhenius expression for
Figure 1. In-fiber FLS growth. (a) Schematic of the high-pressure FLS
process within a capillary MOF, showing high pressure silane/helium
precursor entering a pore from the left side (large arrow pointing right)
and single crystal silicon deposited behind a gold catalyst particle moving
towards the left side (small arrow pointing left). (b) Schematic of super-
critical fluid deposition of gold catalyst particles via a focused laser beam
(vertical triangles) inside a single MOF capillary. The arrow represents high
pressure gold precursor entering the pore. Inset: optical micrographs of a
gold plug deposited inside a 1.6 mm capillary.
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3. COMMUNICATION
wires grown in alumina templates at 0.65 Torr because of the
much higher precursor pressure.[13]
Wires grown in 1.6 mm
diameter pores can be etched out of the silica matrix to reveal
that they have smooth surfaces and assume the diameter of the
pores (Fig. 2b). After longitudinally cross sectioning and
thinning the wires with a focused ion beam (FIB), bright field
transmission electron microscopy (TEM) images (Fig. 3a)
reveal no grain boundaries and/or dislocations, indicating that
they are single crystals. The FIB thinning damaged the edges of
wires (Fig. 3a), but not the center. Multiple electron diffraction
patterns (Fig. 3a inset) collected along the [110] zone axis on a
15 micron length of a sectioned wire indicate that it is a single
crystal with uniform orientation. High contrast {111} lattice
planes (Fig. 3b) with interplanar spacings of 0.3098 nm, were
observed at close to 20 8 to the growth axis in high resolution
images, indicating a h112i wire growth direction sometimes
observed for VLS grown silicon wires.[16]
Electron diffraction
patterns collected on wires sectioned via FIB perpendicular to
the growth axis confirmed that the h112i zone is parallel to this
axis. We find no evidence for twinning, which often observed in
wires with this growth direction.[16]
Non-templated VLS wires
of a similar diameter typically grow in a h111i direction,
indicating that either the very high pressure growth process
or the presence of the template are affecting the growth
direction.[17]
Although a very large body of work regarding growth of
wires by means of VLS has been reported, the kinetics and
mechanism of growth have been much less thoroughly
investigated. These details are important as they can strongly
influence parameters such as how much catalyst remains in the
wires and how it is distributed[18]
as well as the surface
structure, surface chemistry, and bulk composition of the wires.
Therefore, techniques that allow for in-situ, real time probing
of growth are valuable. Direct observation of VLS growth in
Figure 2. SEM Images of FLS grown wires. (a) SEM micrograph of the
silicon ‘‘nosehair’’ branched nanowires grown within a capillary of an MOF.
(b) SEM micrograph of a typical FLS grown wire etched from a 1.6 mm
capillary MOF. The length and diameter of the protruding wire are ca.
80 mm and 1.6 mm respectively.
Figure 3. TEM images of FLS grown wires. (a) Bright-field TEM image of a
typical FIB sectioned and thinned wire. Inset: Electron diffraction pattern
along the h110i zone axis. (b) High resolution bright-field image of a wire
showing {111} lattice planes (oriented vertically) at ca. 208 to the growth
axis (arrow), indicating a h112i growth direction.
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4. COMMUNICATION
a transmission electron microscope has recently been
reported[19]
and approaches such as in-situ reflectometry[20]
are also being pursued. Because of the constraint of the
template, however, it is likely that the mechanism and kinetics
of templated growth will differ from the non-templated growth
investigated in theses studies. It has not been possible to
directly observe growth in-situ in templates such as anodic
alumina because of their opacity at wavelengths from the UV
to the infrared. In contrast, MOFs are transparent, making it
possible to directly observe the semiconductor wires while they
are growing and characterize them after termination of growth
via optical spectroscopy inside the template.
This ability to probe the FLS growth of silicon inside the
template by means of both direct optical observation and
Raman spectroscopy is invaluable to the time consuming
and critical task of optimizing the growth conditions. The
‘‘nosehair’’ growth mode that occurs if the precursor is not
completely removed can be observed with an oil immersion
objective and exhibits Raman modes that can be downshifted
and asymmetrically broadened to varying degrees by the
heating of the low thermal mass wires with different laser
excitation powers (Fig. 4a). Similar behavior due to Fano
resonance effects upon heating from laser excitation powers as
low as 40 mW has been observed for silicon nanowires laying on
a substrate.[21]
At reaction temperatures between 400 and
450 8C (in the range of the lowest temperatures reported for
VLS growth in alumina templates),[13]
amorphous silicon tubes
are formed that appear different from nosehair growth and
have very broad Raman modes (Fig. 4b).[22]
Raman spectra
collected on the FLS grown silicon single crystals while they are
still encased in the silica template are not nearly as sensitive to
heating with the laser excitation as the ‘‘nosehair’’ wires
because of their larger thermal mass. The centroid of the T2g
mode in these spectra is 520.85 cmÀ1
and the full width at half
maximum (FWHM) of the Lorentzian component, which is
intrinsic to the Raman mode, is 2.7 cmÀ1
all along the length of
the wire (Fig. 4c). Identical values for the Lorentzian FWHM
of silicon reference wafers are observed under the same
experimental conditions and also reported in the literature,[23]
consistent with the observation via TEM that the wires are high
quality single crystals. At temperatures below 350 8C, no silicon
is deposited.
The T2g Raman mode FWHM and position are very
sensitive to the presence of defects and/or strain, which can
have a large effect on electronic and photonic properties. Little
strain is present in the FLS grown wires, even when contained
in the template, as there is little difference in these parameters
between the wires and the silicon reference. In contrast, when
Figure 4. In-situ optical micrographs and Raman spectra of FLS grown wires. Optical micrographs and Raman spectra of (a) ‘‘Nosehair’’ nanowire
growth. (b) Amorphous silicon wires (c) FLS grown single crystal wires.
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5. COMMUNICATION
polycrystalline silicon tubes are deposited within silica MOF
templates, considerable strain is induced upon cooling due to
the strong bonding and large difference in thermal expansion
between silicon and its native oxide.[8,22]
The absence of strain
in the FLS grown wires in MOF templates is likely due to
weaker bonding of the wire to the pore walls because of the
exceptionally low reaction temperature.
A femtosecond laser can be used to micromachine[24]
sections of MOFs containing single crystal silicon at any
desired positions along their length with micron scale accuracy
(see methods). It is thus straightforward to laser machine and
then cleave the end of the silicon wire containing the
gold catalyst particle, which would otherwise block wave-
guided light. These cleaved sections can either be butt coupled
or even spliced to other fibers, potentially allowing for the
facile integration of fiberized semiconductor devices into
existing fiber infrastructure.
By varying the precursor chemistry and catalyst, VLS
growth is possible for many direct and indirect gap semi-
conductor materials; proof of concept demonstrations of
photonic and optoelectronic function of the resulting micro-
wires and nanowires, including lasing, has been reported.[25,26]
In the majority of these demonstrations the wires have been
much larger in diameter than those that exhibit quantum
confinement, as their superior properties for such applications
do not necessarily require quantization. A broad range of
materials should also be realizable with catalyzed FLS
growth[27,28]
and hydride precursors are available for some
of them (although the present approach may also work with
suitable non-hydride precursors),[29–31]
indicating the possibi-
lities for incorporating materials other than silicon into MOFs
via the methods reported here. Although it does not have a
direct gap, silicon can be used for optically pumped Raman
lasers and amplifiers.[32]
Organizing catalytically grown high
quality single crystal micro and nanowires with great precision
into designed arrays for device applications represents a
significant engineering challenge that we have begun to address
by incorporating them into MOFs. Coherent beam combining
in optics, for example, has its foundations in microwave and
radio implementations of phased array antennas. The optical
analogue of this technique seeks to combine several laser
beams into a single output with well preserved spectral
bandwidth that not only scales linearly with the number of
elements, but also with well preserved beam quality (M2
)[33]
and thus increased brightness. However, such optical imple-
mentations are significantly harder to practically realize than in
the RF domain due to the much smaller wavelength of
light, which necessitates a very high degree of mechanical
tolerance in alignment and optical path length accuracy to
ensure adequate performance. In particular, evanescent or
leaky wave coupling of for example, VCSEL arrays, requires
the array elements to be in sufficiently close proximity such
that their field distributions overlap, thus creating a phase
locked coupled oscillator system. Phase locked VCSEL array
operation has been experimentally observed,[34]
but stable,
high power, diffraction limited beam operation from a 2D
VCSEL array remains a technologically demanding goal. In
contrast, the stable phase locking of Yb3þ
doped multicore
microstructured optical fiber (single mode) lasers[35]
through
evanescent coupling have recently been demonstrated, with a
pure in-phase supermode that is quasi-diffraction limited with
a high output power of 44 W.
Thus far it has not been possible to organize high quality
VLS grown single crystal semiconductor wires suitable for
photonic and optoelectronic applications with sufficient
precision and hierarchical rational organization to enable
coherent beam combining and in fact they have only just begun
to be patterned as structures that exhibit photonic bandgap
effects.[36]
By replacing the rare earth doped cores of the MOFs
with single crystal semiconductor micro/nanowire lasers based
on silicon or direct gap semiconductors, it may be possible to
similarly exploit both the inherent mechanical stability and the
precisely engineered periodic or aperiodic spatial geometry of
MOFs to realize high performance laser action. The high
precision afforded by the MOF approach could also be
exploited for the formation of nanowire based photonic
crystals, where the high dielectric contrast and extremely high
aspect ratio available inside a MOF (indeed, the highest aspect
ratio of any artificially engineered micro or nanostructured
template) are ideal for fabrication of, for example, high Q
microcavities[37,38]
with a very small mode volume for the
defect state. The very strong energy confinement in these
cavities will enhance non-linear photonic effects,[39]
enabling
all-optical signal processing,[40]
quantum optical applications,
and biological and chemical sensors, for example. These high
quality, small volume cavities will furthermore allow for a
strongly modified Purcell effect,[41]
resulting in low threshold
electrically[42]
or optically pumped semiconductor lasers inside
an optical fiber operating at wavelengths from the UV to the
mid-infrared that are not possible with current rare-earth
doped glass media.
Experimental
Gold Deposition: Dimethyl(trifluoroacetylacetonate)gold(III), 98%
(%20 mg), purified by vacuum sublimation, was placed into a
high-pressure stainless-steel gas reservoir with a volume of approxi-
mately 0.5 cm3
. The reservoir was then charged with carbon dioxide,
99.999% (6–7 MPa) and a long MOF (30 cm) was attached to it. 514 nm
laser light was focused through a Olympus 100Â (NA ¼ 1.25) oil
immersion microscope objective for ca. 20 s with a laser power of 5 mW
to deposit gold plugs within the capillaries. Next the MOF was flushed
with carbon dioxide at a pressure of 133 MPa to expel any residual
precursor.
Confocal Raman Spectroscopy: Spectra were collected using a
Renishaw InVia Raman microscope with 514 nm excitation and
a 1800 gr/mm grating at laser powers of less than 1 mW focused through
a 1.25 NA oil immersion objective. Excitation powers were varied to
insure that there was no broadening or shifting of the T2g Raman mode
due to sample heating. Raman modes were fit to Voigt profiles to allow
for separation of the Lorentzian Raman component from the Gaussian
instrumental component.
Femtosecond Laser Machining: A mode-locked Spectra Physics
Tsunami laser (model 3960-X1BB) with an energy per pulse
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6. COMMUNICATION
approximately of 500 mJ at 1-kHz repetition rate operating at 797 nm
was used for femtosecond laser machining. The power of the pulses was
reduced using a 3.0 neutral density filter resulting to 0.5 mJ (average
laser fluence of 30 J cmÀ1
). The focused laser spot was rastered
perpendicular to the fiber axis to machine a groove that facilitated
cleaving at a precise location.
Transmission Electron Microscopy: The silicon wires were removed
from the MOFs by etching with a buffered oxide etch (BOE) solution
(15%) prepared by mixing concentrated 52% HF and 40% ammonium
fluoride (NH4F) in a 1:2 v/v ratio. The tip of the capillary MOF was
inserted into the BOE solution less than 1 mm. The capillary MOF was
checked using optical microscopy every 10–15 min to ensure that the
VLS grown wires were still present either inside the MOF or
protruding from the MOF. A FEI Quanta 200 focused ion beam was
used section and thin the silicon wires for TEM analysis. A Philips 420,
Tungsten-based 120 keV Transmission Electron Microscope was
used for sample imaging and electron diffraction. A JEOL 2010 LaB6,
200 keV high resolution TEM was used to image the crystalline
lattice plane.
Received: July 2, 2007
Revised: September 10, 2007
[1] M. Law, J. Goldberger, P. D. Yang, Ann. Rev. Mater. Res. 2004, 34, 83.
[2] P. A. Smith, C. D. Nordquist, T. N. Jackson, T. S. Mayer, B. R. Martin,
J. Mbindyo, T. E. Mallouk, Appl. Phys. Lett. 2000, 77, 1399.
[3] Y. Huang, X. F. Duan, Q. Q. Wei, C. M. Lieber, Science 2001, 291, 630.
[4] X. D. Wang, C. J. Summers, Z. L. Wang, Nano Lett. 2004, 4, 423.
[5] S. Acharya, A. B. Panda, N. Belman, S. Efrima, Y. Golan, Adv. Mater.
2006, 18, 210.
[6] B. Wolfrum, Y. Mourzina, D. Mayer, D. Schwaab, A. Offenhausser,
Small 2006, 2, 1256.
[7] J. C. Knight, Nature 2003, 424, 847.
[8] P. J. A. Sazio, A. Amezcua-Correa, C. E. Finlayson, J. R. Hayes, T. J.
Scheidemantel, N. F. Baril, B. R. Jackson, D. J. Won, F. Zhang, E. R.
Margine, V. Gopalan, V. H. Crespi, J. V. Badding, Science 2006, 311,
1583.
[9] P. J. Roberts, F. Couny, H. Sabert, B. J. Mangan, D. P. Williams, L.
Farr, M. W. Mason, A. Tomlinson, T. A. Birks, J. C. Knight, P. S. J.
Russell, Opt. Express 2005, 13, 236.
[10] B. T. Kuhlmey, K. Pathmanandavel, R. C. McPhedran, Opt. Express
2006, 14, 10851.
[11] N. M. Litchinitser, A. K. Abeeluck, C. Headley, B. J. Eggleton, Opt.
Lett. 2002, 27, 1592.
[12] T. E. Bogart, S. Dey, K. K. Lew, S. E. Mohney, J. M. Redwing, Adv.
Mater. 2005, 17, 114.
[13] K. K. Lew, J. M. Redwing, J. Cryst. Growth 2003, 254, 14.
[14] N. R. B. Coleman, N. O’Sullivan, K. M. Ryan, T. A. Crowley, M. A.
Morris, T. R. Spalding, D. C. Steytler, J. D. Holmes, J. Am. Chem. Soc.
2001, 123, 7010.
[15] Y. Cui, Q. Q. Wei, H. K. Park, C. M. Lieber, Science 2001, 293, 1289.
[16] A. H. Carim, K. K. Lew, J. M. Redwing, Adv.Mater. 2001, 13, 1489.
[17] P. C. Nordine, S. C. Delaveaux, F. T. Wallenberger, Appl. Phys. Mater.
Sci. Process. 1993, 57, 97.
[18] D. E. Perea, J. E. Allen, S. J. May, B. W. Wessels, D. N. Seidman, L. J.
Lauhon, Nano Lett. 2006, 6, 181.
[19] S. Kodambaka, J. Tersoff, M. C. Reuter, F. M. Ross, Phys. Rev. Lett.
2006, 96, 096105.
[20] T. Clement, S. Ingole, S. Ketharanathan, J. Drucker, S. T. Picraux,
Appl. Phys. Lett. 2006, 89, 163125/1.
[21] R. Gupta, Q. Xiong, C. K. Adu, U. J. Kim, P. C. Eklund, Nano Lett.
2003, 3, 627.
[22] C. E. Finlayson, A. Amezcua-Correa, P. J. A. Sazio, N. F. Baril, J. V.
Badding, Appl. Phys. Lett. 2007, 90, 132110/1.
[23] M. Grimsditch, M. Cardona, Phys. Status Solidi B 1980, 102, 155.
[24] C. B. Schaffer, A. Brodeur, J. F. Garcia, E. Mazur, Opt. Lett. 2001, 26,
93.
[25] Y. N. Xia, P. D. Yang, Y. G. Sun, Y. Y. Wu, B. Mayers, B. Gates, Y. D.
Yin, F. Kim, Y. Q. Yan, Adv. Mater. 2003, 15, 353.
[26] M. H. Huang, S. Mao, H. Feick, H. Q. Yan, Y. Y. Wu, H. Kind, E.
Weber, R. Russo, P. D. Yang, Science 2001, 292, 1897.
[27] F. M. Davidson, A. D. Schricker, R. J. Wiacek, B. A. Korgel, Adv.
Mater. 2004, 16, 646.
[28] F. M. Davidson, R. Wiacek, B. A. Korgel, Chem. Mater. 2005, 17, 230.
[29] C. W. Hu, J. L. Taraci, J. Tolle, M. R. Bauer, P. A. Crozier, I. S. T.
Tsong, J. Kouvetakis, Chem. Mater. 2003, 15, 3569.
[30] J. McMurran, D. Dai, K. Balasubramanian, C. Steffek, J. Kouvetakis,
J. L. Hubbard, Inorg. Chem. 1998, 37, 6638.
[31] J. McMurran, J. Kouvetakis, D. J. Smith, Appl. Phys. Lett. 1999, 74,
883.
[32] B. Jalali, V. Raghunathan, D. Dimitropoulos, O. Boyraz, IEEE J. Sel.
Top. Quantum Electron. 2006, 12, 412.
[33] T. F. Johnston, Appl. Opt. 1998, 37, 4840.
[34] J. P. Vanderziel, D. G. Deppe, N. Chand, G. J. Zydzik, S. N. G. Chu,
IEEE J.Quantum Electron. 1990, 26, 1873.
[35] L. Michaille, C. R. Bennett, D. M. Taylor, T. J. Shepherd, J. Broeng,
H. R. Simonsen, A. Petersson, Opt. Lett. 2005, 30, 1668.
[36] C. Jingbiao, G. Ursula, Nanotechnology 2007, 18, 155302.
[37] B. S. Song, S. Noda, T. Asano, Y. Akahane, Nat. Mater. 2005, 4,
207.
[38] T. Xu, S. X. Yang, S. V. Nair, H. E. Ruda, Phys. Rev. B 2007, 75.
[39] V. B. Braginsky, M. L. Gorodetsky, V. S. Ilchenko, Phy. Lett. A 1989,
137, 393.
[40] K. J. Huang, S. Y. Yang, L. M. Tong, Appl. Opt. 2007, 46, 1429.
[41] K. J. Vahala, Nature 2003, 424, 839.
[42] X. F. Duan, Y. Huang, R. Agarwal, C. M. Lieber, Nature 2003, 421,
241.
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