Novel BN hollow microspheres with open mouths - Facile synthesis, growth mechanism, resonant Raman scattering effect, and cathodoluminescence performance

Article abstract of DOI:10.1002/ejic.201000703

Novel BN hollow microspheres have been successfully fabricated by a facile chemical vapour reaction approach using ammonia-borane as a precursor. The morphology and structure of the as-synthesized products are characterized by scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), selected-area electron diffraction (SAED), as well as electron energy loss spectroscopy (EELS). The hollow microspheres have open mouths and are 0.5-6 μm in diameter. The walls of the hollow spheres with thicknesses ranging from 200 to 800 nm are composed of poorly crystallized BN. The growth mechanism of the hollow microspheres is investigated and a growth model is proposed. The BN hollow spheres show pronounced resonant Raman scattering character under illumination of a 457.9 nm laser line, which implies a potential photothermal effect. The hollow microspheres also exhibit intense cathodoluminescence emissions in the region of 200-400 nm, indicating that they could be potentially used as compact ultraviolet laser emitters. Moreover, the unique open-mouth feature, in combination with the superior thermal and chemical stability of BN, makes the BN hollow microspheres potential candidates as microreactors for investigations of high-temperature space-confined chemical reactions. Novel BN hollow microspheres with open mouths have been fabricated. The unique open-mouth feature makes them potential candidates as microreactors. They show excellent cathodoluminescence performance in the region of 200-400 nm and could be used as compact ultraviolet laser emitters. Moreover, they exhibit an unexpectedRaman scattering effect. Copyright

Full text of DOI:10.1002/ejic.201000703

FULL PAPER
DOI: 10.1002/ejic.201000703
Novel BN Hollow Microspheres with Open Mouths – Facile Synthesis, Growth
Mechanism, Resonant Raman Scattering Effect, and Cathodoluminescence
Performance
Guangwu Wen,*[a,b] Bo Zhong,[a] Xiaoxiao Huang,[a] Hongming Yu,[a] Xiaodong Zhang,[a]
Tao Zhang,[a] and Hongwei Bai[a]
Keywords: Hollow microspheres / Boron nitride / Raman spectroscopy / Microreactors / Luminescence
Novel BN hollow microspheres have been successfully fabri-
cated by a facile chemical vapour reaction approach using
ammonia–borane as a precursor. The morphology and struc-
ture of the as-synthesized products are characterized by
scanning electron microscopy (SEM), high-resolution trans-
model is proposed. The BN hollow spheres show pronounced
resonant Raman scattering character under illumination of a
457.9 nm laser line, which implies a potential photothermal
effect. The hollow microspheres also exhibit intense cathodo-
luminescence emissions in the region of 200–400 nm, indicat-
mission electron microscopy (HRTEM), selected-area elec- ing that they could be potentially used as compact ultraviolet
tron diffraction (SAED), as well as electron energy loss spec-
troscopy (EELS). The hollow microspheres have open mouths
and are 0.5–6 μm in diameter. The walls of the hollow
spheres with thicknesses ranging from 200 to 800 nm are
composed of poorly crystallized BN. The growth mechanism
of the hollow microspheres is investigated and a growth
laser emitters. Moreover, the unique open-mouth feature, in
combination with the superior thermal and chemical stability
of BN, makes the BN hollow microspheres potential candi-
dates as microreactors for investigations of high-temperature
space-confined chemical reactions.
Introduction
thermal stability are highly desired and urgently needed. To
date, a number of strategies have been reported on the fabri-
cation of micro/nanospheres with hollow interiors, which
include traditional template-assisted methods,[7] self-tem-
plating approaches such as surface-protected etching,[8] and
chemical routes based on Ostwald ripening,[9] the Kirkend-
all effect,[10] and galvanic replacement.[11] These methods
have led to a rich variety of hollow microspheres, such as
CuS,[12] ZnO,[13] CeO2,[14] and FeMoO4.[15] However, these
successes are primarily limited to metals or metal com-
pounds. The strategies listed above are mainly based on wet
chemistry and thus are not applicable to fabricate hollow
spheres of nonmetal covalent compounds which exhibit
good thermal and chemical stability.
Hexagonal boron nitride (h-BN) is an analogue of graph-
ite and has extensive applications in fields ranging from op-
tical storage to medical treatment, photocatalysis, and elec-
trical insulation due to its wide direct band gap (5.79 eV).
It also has excellent chemical stability and resists oxi-
dation.[16] BN crucibles have been traditionally used as
high-temperature reactors for many years owing to their ex-
cellent chemical inertness and thermal stability. Various BN
micro/nanostructures have been successfully fabricated
since the first discovery of BN nanotubes in 1995[17] includ-
ing nanowires,[18] nanoplates,[19] nanomeshes,[20] conical
nanorods,[21] hollow nanoribbons,[22] hollow nanocages,[23]
micro-/nanospheres,[24] core-shell nanostructures,[25] and
Hollow micro/nanospheres are a new class of materials
and have attracted immense interest in recent years owing
to their unique properties and applications.[1] For example,
hollow spheres are conventionally used as fillers, pigments,
coatings, and catalyst carriers due to their relatively low
densities and high specific surface area.[2] They also widely
serve as vehicles for sheltering nanoparticles, proteins, en-
zymes, or DNA for drug delivery, diagnosis, and other bio-
medical applications.[3] In addition, hollow spheres are also
harnessed as ultra-small chemical reactors for the investi-
gations of ultra-small-scale (10–9–10–18 L) chemical reac-
tions.[4] More recently, inspired by the fact that ultra-small-
scale chemical reactions can be dramatically different from
those at macro-scale due to space-confining effects,[4b,5]
there has been an increasing fascination with space-con-
fined reactions, especially those occurring at high tempera-
tures.[6] In this regard, hollow spheres with open mouths,
reliable chemical inertness, and, more importantly, excellent
[a] School of Materials Science and Engineering, Harbin Institute
of Technology,
Harbin 150001, People’s Republic of China
Fax: +86-451-8641-3922
E-mail: g.wen@hit.edu.cn
[b] School of Materials Science and Engineering, Harbin Institute
of Technology (Weihai),
Weihai 264209, People’s Republic of China
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201000703.
5538
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2010, 5538–5544

Novel BN Hollow Microspheres with Open Mouths
few-atomic-layer sheets.[26] However, to the best of our
knowledge, investigations on the fabrication of BN hollow
microspheres with open mouths have not been reported.
Herein, we report the synthesis of unique BN hollow
microspheres with open mouths by a facile chemical vapor
reaction approach employing ammonia–borane as a precur-
sor. The morphology and structure of the BN hollow
microspheres are characterized by means of complementary
techniques. A possible growth mechanism of the hollow
microspheres is proposed based on our experimental obser-
vations. The resonant Raman scattering character and ca-
thodoluminescence (CL) performance of the hollow spheres
have been investigated.
Figure 2. (a)–(c) Low- and (d) high-magnification SEM images of
the BN hollow spheres. Inset: Statistical analysis of the diameters
of the hollow spheres based on SEM images.
Results and Discussion
Morphology and Structure of the Products
Figure 1 presents the XRD pattern of the as-synthesized
BN hollow spheres. All the diffraction peaks can be indexed
to the hexagonal phase of BN with lattice parameters of a
= b = 2.504 Å and c = 6.656 Å (JCPDS card No. 34-0421).
No impurity phase was detected. It is worth noting that the
diffraction peaks are markedly broadened, implying that
the BN crystals in the hollow spheres have very small grain
sizes. The morphology of the BN hollow spheres was exam-
ined by SEM. The low-magnification SEM images shown
in Figure 2a–c demonstrate that the products are composed
of a large number of microspheres. Figure 2d presents a
high-magnification SEM image of the as-synthesized prod-
ucts, from which well-defined BN hollow microspheres with
open mouths are clearly observed. Both the diameters and
thicknesses of the BN hollow spheres have been statistically
analyzed from the SEM images. The diameters of the
microspheres exhibit a relatively wide distribution ranging
from 0.5 to 6 μm with an average diameter of 3.4Ϯ1.3 μm
(see statistical image inset in Figure 2b). The wall thick-
nesses of the microspheres are in the range of 200–800 nm
(see statistical image in Figure S1). It is interesting to note
that nearly all of the spheres are partially broken, which
allows direct observation of the interior of the spheres and
is also clear evidence of their hollow nature.
Figure 3a shows a TEM image of a typical BN hollow
sphere, which additionally confirms the hollow nature of
the microspheres. The selected-area electron diffraction
(SAED) pattern of the hollow microsphere is displayed in
the inset of Figure 3a. Two bright diffraction rings arising
from the h-BN (100) and (110) planes are clearly observed,
which indicates that the microspheres are composed of
polycrystalline BN. However, the diffraction ring of the h-
BN (002) planes is dramatically broadened, which indicates
that the BN hollow spheres are poorly crystallized. To fur-
ther characterize the structure of the hollow microspheres,
HRTEM analysis was carried out. The magnified TEM im-
age (Figure 3b) taken from the edge of the hollow micro-
sphere, marked in Figure 3a, clearly shows that the wall
thickness of the microsphere is about 50 nm. HRTEM
images of the sphere wall displayed in Figure 3c,d addition-
ally reveal that the crystallinity of the BN hollow sphere is
poor.
Figure 3. (a) TEM image of a typical BN hollow sphere. Inset:
SAED pattern of the BN hollow sphere. (b)–(d) HRTEM images
taken from the regions framed in (a) and (b).
Figure 1. XRD pattern of the as-synthesized BN hollow spheres.
Eur. J. Inorg. Chem. 2010, 5538–5544
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
5539

G. Wen, B. Zhong, X. Huang, H. Yu, X. Zhang, T. Zhang, H. Bai
FULL PAPER
Figure 4. (a) FTIR and (b) EELS spectra of the BN hollow microspheres.
The BN hollow microspheres were analyzed by FTIR
spectroscopy in transmittance mode to investigate the
bonding nature, as shown in Figure 4a. Strong peaks cen-
tered at 1384.5 and 780.3 cm–1 are characteristic primary
and secondary absorption bands of h-BN, indicating that
the hollow microspheres are composed of h-BN. The broad-
ening of the former peak is attributed to the B–O bond
vibrations since these vibrations have many phonon modes
in the 1500–1200 cm–1 range.[27] The phonon mode at
3346.5 cm–1 is assigned to the O–H stretching mode. The
presence of B–O and O–H bonds is ascribed to the moisture
capture of the poorly crystallized h-BN from its surround-
Figure 5. EFTEM analysis of the BN microspheres reflecting com-
ings.
EELS analysis was performed on the hollow micro-
positional distribution. (a) TEM image showing general mor-
phology; (b) zero-loss image; (c)–(e) elemental maps (B, N, O). All
scale bars represent 100 nm.
spheres to determine their chemical composition (Fig-
ure 4b). The pronounced peaks centred at around 188 and
401 eV in the EELS spectrum correspond to the character-
istic K-shell ionization edges of B and N atoms, respec-
tively.[28] The sharp π* and σ* peaks identified from the
spectrum are typical for the sp2 bonding configuration,
which is commonly observed in EELS spectra of h-BN.[19]
The 284 eV carbon K edge is notably absent, revealing that
the microsphere is free of carbon. A small portion of oxy-
gen was detected, and quasiquantitative analysis gives a
B/N/O atomic ratio of 1:0.87:0.09.
Electron energy filtered TEM (EFTEM) analysis was
conducted to track the compositional distribution within
the BN hollow microspheres (Figure 5). Figure 5a shows
the position where the mapping signals were collected. Fig-
ure 5b is a zero-energy-loss image showing the general mor-
phology of a microsphere. Figure 5c–e shows B, N, and O
elemental maps of the hollow microspheres, which were ob-
tained with the energy loss windows centered at the boron
K edge of 188 eV, the nitrogen K edge of 401 eV, and the
oxygen K edge of 532 eV. These images intuitively suggest
the presence of B, N, and O and that the elemental distribu-
tions are almost uniform throughout the sphere.
(inset upper left in Figure 6). The more intense component
at 190.83 eV is assigned to boron atoms surrounded only
by nitrogen atoms, similar to that in pure h-BN, whereas
the component at 192.62 eV is attributed to boron atoms in
a mixed oxygen/nitrogen environment, because the oxygen
atoms are more electronegative than the nitrogen atoms and
tend to cause the binding energy to shift upwards.[29] The
O1s spectrum, inset upper center in Figure 6, is of Gaussian
type and is not decomposed further. The O1s peak centred
at 532.87 eV is close to, but a little smaller than, the binding
energy of O atoms in B2O3 (533.2 eV).[30] This indicates that
In agreement with the EELS results, XPS analysis ad-
ditionally indicates that the as-obtained products contain
B, N, and O, as evidenced by the wide-survey XPS spectrum
shown in Figure 6. The carbon signal in the XPS profile is
due to surface contamination during the exposure of the
sample in the air before the examination. The broad B1s
Figure 6. Wide scan, B1s (inset: upper left), O1s (inset: upper cen-
ter) and N1s (inset: upper right) XPS spectra recorded from the
band can be decomposed into two Gaussian components BN hollow microspheres.
5540
www.eurjic.org
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2010, 5538–5544

Novel BN Hollow Microspheres with Open Mouths
the O atoms not only bond with the B atoms, but also inter-
act with the N atoms, as N atoms are less electronegative
than O atoms and may cause the downward shift of the
binding energy of O atoms. The N1s spectrum is presented
in the inset upper right in Figure 6. One component at
398.10 eV can be associated with the presence of N–B
bonds and the other component at 398.78 eV can be as-
cribed to oxynitrides.[29]
It is worth noting that the presence of a small amount of
oxygen appears to be inexplicable as we did not intention-
ally introduce any oxygen precursors during the sample fab-
rication, although the occurrence of trace oxygen is inevi-
table in high purity nitrogen. The trace oxygen is involved
in the reaction, which results in oxygen in the BN micro-
spheres. Moreover, it is well documented that h-BN (espe-
cially samples that are not well crystallized) tends to absorb
moisture from its surroundings.[31] Since these BN micro-
spheres are poorly crystallized, the intrinsic moisture-ab-
sorption nature may also contribute to the oxygen in the
BN microspheres.
Figure 7. Schematic illustrations and representative SEM images
showing the formation process of the BN microspheres: (a) initial
bare graphite substrate; (b) formation of a thin film on the sub-
strate; (c), (d) buckling of the thin film from the substrate due to
hydrogen accumulation; (e), (f) cracking of the thin film to form
BN hollow microspheres.
Another issue that should be clarified is that why the BN
microspheres are not uniform. In our opinion, the size of
the BN microspheres may be determined by the thickness
of the B–N containing film. The thicker film possesses a
higher strength and thus can trap more hydrogen before
buckling and cracking than the thinner one. Therefore, the
thicker film results in larger BN microspheres, whereas the
thinner film results in smaller ones. This is supported by
our SEM observations. Careful SEM examinations reveal
that there is a positive relationship between the diameters
and the wall thicknesses of the BN microspheres, i.e. larger
microspheres always have thicker wall thicknesses and vice
versa. The growth model proposed here is merely a phe-
nomenological model. A detailed thermodynamic and ki-
netic model involving film formation, microsphere buck-
ling, and cracking is required to give a complete and accu-
rate description of the growth process of the BN micro-
spheres and is currently underway.
Growth Mechanism
Based on our experimental observations, a growth model
has been proposed to comprehend the formation process of
the BN hollow microspheres. Figure 7a–f presents sche-
matic illustrations and typical SEM images showing the dif-
ferent stages of the formation process. The growth process
begins with the decomposition of the precursor ammonia–
borane (AB). At elevated temperatures, AB decomposes ac-
cording to the reaction H3BNH3 Ǟ H2 + BNxHy, where
BNxHy indicates gaseous residues containing B and N
atoms, including monomeric aminoborane (BH2NH2), bor-
azine (B3N3H6), and traces of diborane (B2H6).[32] These
gases could deposit on the bare graphite substrate and react
with each other at appropriate temperatures resulting in a
film (Figure 7a,b). Figure S2 presents a typical SEM image
of the substrate obtained after pyrolysis, which clearly
shows a thin film on the bare graphite substrate. The film
is believed to be formed by the polymerization of gases de-
composed from AB and is probably in a liquid state at high
Resonant Raman Scattering Effect
The Raman spectrum of the BN hollow microspheres,
temperatures. During the polymerization of the B–N-con- excited by using a 457.9 nm laser line, shows unanticipated
taining film, hydrogen is released, and the film becomes features (Figure 8a, see also Figure S4 in the Supporting
more viscous. In this process, some hydrogen may be Information). The dominant peak at ca. 1367 cm–1, which
trapped in the viscous film, and when the hydrogen ac- is normally observed for in-plane B–N vibrations (E2g
cumulation reaches the saturation point, the thin film may mode)[33] in the Raman spectrum of h-BN is notably absent.
buckle (Figure 7c,d) and subsequently crack from the sub- Instead, we observed a series of periodic peaks with nearly
strate, forming hollow microspheres and leaving holes on uniform intervals. A Raman spectrum recorded from a dif-
the substrate (Figure 7e,f). These assumptions are sup- ferent sample by using the same laser line shows a similar
ported by our experimental observations. First, the dia- feature (see Figure 8b). The Raman spectra of the BN hol-
meters of the holes are around 3 μm and are comparable low microspheres exhibit multipeaks at nearly equal inter-
to that of the microspheres. This indicates that the hollow vals, but the intervals of the peaks are microsphere-depend-
microspheres and the holes on the film are closely related ent and are not necessarily the same for different spheres.
and the hollow microspheres may be originally parts of the These exceptional Raman scatting phenomena are tenta-
thin film on the substrate. Moreover, EDX analysis shows tively explained within the framework of the resonant Ra-
that the chemical compositions of the hollow BN spheres man scattering (RRS) theory.[34] RRS occurs where the fre-
and that of the film are nearly identical (see Figure S3 in quency of the incident radiation matches that of an elec-
Supporting Information).
tronic transition so that the selection rule for normal Ra-
Eur. J. Inorg. Chem. 2010, 5538–5544
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
5541

G. Wen, B. Zhong, X. Huang, H. Yu, X. Zhang, T. Zhang, H. Bai
FULL PAPER
Figure 8. Representative Raman spectra of BN hollow microspheres recorded under different conditions: (a), (b) 457.9 nm laser line,
20 mW laser power, 5 s acquisition time, (c) 633 nm laser line, 10 mW laser power, 10 s acquisition time, and (d) 488 nm laser line, 20 mW
laser power, 10 s acquisition time. Spectra (a), (c), and (d) are recorded from the same sample, whereas spectrum (b) is recorded from
another sample to show the universality of the phenomenon. Insets: SEM images of corresponding samples.
man scattering is broken. Since there is no selection rule could facilitate the application of the BN hollow micro-
to forbid the overtones occurring, periodic multipeaks are spheres for the investigations of ultra-small-scale reactions
expected in resonant Raman spectra. Therefore, the nearly since heating by laser could be well controlled in both time
equally spaced peaks observed in our Raman spectra are and space.
believed to be the overtones of one vibration. It is worth
noting that not all vibrations observed in conventional Ra-
man spectra of h-BN are intensified by resonance,[35] which
accounts for the absence of the normal vibration mode at
1367 cm–1. Another two laser lines (488 and 688 nm) were
also used to irradiate the samples of the hollow micro-
spheres, and the Raman spectra obtained are shown in Fig-
ure 8c,d. Overtones could also be identified in these spectra,
but they are not as definite as in that irradiated by the
457.9 nm laser line. This means that lasers operating at 488
and 688 nm are not as effective as that at 457.9 nm in in-
ducing RRS, probably because the condition for observing
effective RRS is not satisfied by using 488 and 688 nm laser
lines. It is generally accepted that the closer the excitation
frequency of a laser beam is to that of an electron transi-
tion, the more effective the RRS.[36] Therefore, the 457.9 nm
laser line is closer to the frequency of an electron transition
than the other two laser lines.
Cathodoluminescence Performance
Figure 9 displays a CL spectrum recorded from a typical
hollow microsphere. Intense UV emission peaks in the re-
gion of 300–400 nm are clearly observed, indicating that the
novel BN hollow microspheres could be potentially used as
compact UV laser emitters. The broad luminescence bands
at around 338.7 nm as well as the emission peaks located at
A crucial implication, which arises from the RRS effect
of the BN hollow spheres, is that they possess a potential
photothermal effect. In conventional Raman scattering
analysis, spectroscopists prefer to avoid RRS, because when
resonance conditions occur, the power of the laser is liable
to adsorb into the sample. This may cause sample decom-
position through photothermal effects or strong fluores-
cence.[36,37] In our case, the photothermal effect of the RRS
Figure 9. CL spectrum of the BN hollow microspheres. Inset: Sche-
was utilized to heat the hollow microspheres. This heating matic energy level diagram.
5542
www.eurjic.org
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2010, 5538–5544

Novel BN Hollow Microspheres with Open Mouths
FEG equipped with electron energy loss spectroscopy (EELS),
respectively], X-ray photoelectron spectroscopy [XPS, PHI 5700
ESCA System with a PC-ACCESS data analysis system (Physical
Electronics Inc.)], and Fourier transformation infrared spec-
troscopy (FTIR, Perkin–Elmer spectrum one system by using
pressed KBr disks). CL measurements were performed by using a
Gatan MONOCL3+ system installed on a JSM-7000F FESEM.
Raman spectra were recorded with a Jobin–Yvon HR800 spectrom-
eter by using three laser lines (457.9, 488, and 633 nm) as excitation
sources. The laser beams were focused to ca. 1 μm in diameter. The
403.1 and 458.2 nm are assigned either to impurity (poss-
ibly oxygen) and defect centers or to radiative excitonic
dark states. These bands are commonly observed in the lu-
minescence spectra of multiwalled BN nanotubes, BN
nanorods, and BN whiskers.[38] An electron energy level dia-
gram based on the CL spectrum was obtained, shown in
the inset of Figure 9. It is worth noting that one of the
energy levels (around 458.2 nm) is very close to the wave-
length of the laser line (457.9 nm), which induces the maxi-
mum RRS. This means that the 457.9 nm laser used in the spectra were collected at ambient conditions.
Raman analysis matches the true resonance frequency of an
electron energy level so that the maximum RRS occurs.
This further confirms that the peculiar Raman spectra exhi-
biting overtones are essentially caused by the RRS effect.
Supporting Information (see footnote on the first page of this arti-
cle): Statistical analysis of the wall thickness of the BN hollow
spheres; SEM image showing a thin layer was formed on the sub-
strate; EDX spectra of the hollow microspheres and the layer de-
posited on the substrate; additional Raman spectra of the BN hol-
low microspheres obtained using a 457.9 nm laser line.
Conclusions
Acknowledgments
Novel BN hollow microspheres were successfully fabri-
cated by a facile one-step approach employing ammonia–
borane as a precursor. The hollow microspheres exhibit
open mouths and have diameters ranging from 0.5 to 6 μm.
The growth mechanism of the BN microspheres has been
revealed based on our experimental findings, and the for-
mation of a thin film containing B and N on the substrate
is shown to be a crucial step in the growth process. The BN
hollow microspheres exhibit an unexpected resonant Ra-
man scattering effect under the illumination of a 457.9 nm
laser line and show intense UV CL emissions in 200–
400 nm wave bands. Such BN hollow microspheres may
find application in the field of UV lasing and as small
chemical reactors for the investigations of high-temperature
space-confined reactions.
This work was supported by the National High-tech R&D Program
(863 Program) (No. 2007AA03Z340), the National Science Foun-
dation of China (No. 50672018), and the Program of Excellent
Team in Harbin Institute of Technology.
[1] a) Q. Zhang, W. Wang, J. Goebl, Y. Yin, Nano Today 2009, 4,
494–507; b) H. P. Cong, S. H. Yu, Adv. Funct. Mater. 2007, 17,
1814–1820.
[2] a) M. Ohmori, E. Matijevic, J. Colloid Interface Sci. 1992, 150,
594–598; b) W. W. Wang, Y. J. Zhu, L. X. Yang, Adv. Funct.
Mater. 2007, 17, 59–64; c) J. K. Yuan, K. Laubernds, Q. H.
Zhang, S. L. Suib, J. Am. Chem. Soc. 2003, 125, 4966–4967.
[3] a) W. M. Zhang, J. S. Hu, Y. G. Guo, S. F. Zheng, L. S. Zhong,
W. G. Song, L. J. Wan, Adv. Mater. 2008, 20, 1160–1165; b)
Y. F. Zhu, J. L. Shi, W. H. Shen, X. P. Dong, J. W. Feng, M. L.
Ruan, Y. S. Li, Angew. Chem. Int. Ed. 2005, 44, 5083–5087;
c) P. R. Leduc, M. S. Wong, P. M. Ferreira, R. E. Groff, K.
Haslinger, M. P. Koonce, W. Y. Lee, J. C. Love, J. A. McCam-
mon, N. A. Monteiro-Riviere, V. M. Rotello, G. W. Rubloff, R.
Westervelt, M. Yoda, Nat. Nanotechnol. 2007, 2, 3–7.
[4] a) A. Dudia, A. Kocer, V. Subramaniam, J. S. Kanger, Nano
Lett. 2008, 8, 1105–1110; b) T. Shimizu, J. Polym. Sci. Pol.
Chem. 2008, 46, 2601–2611.
[5] a) Q. H. Yang, D. F. Han, H. Q. Yang, C. Li, Chem. Asian J.
2008, 3, 1214–1229; b) P. Anzenbacher, M. A. Palacios, Nat.
Chem. 2009, 1, 80–86.
[6] G. Dmitri, B. Yoshio, M. Masanori, F. Keita, T. Chengchun,
Acta Mater. 2004, 52, 3295–3303.
[7] J. G. Wang, Q. Xiao, H. J. Zhou, P. C. Sun, Z. Y. Yuan, B. H.
Li, D. T. Ding, A. C. Shi, T. H. Chen, Adv. Mater. 2006, 18,
3284–3288.
Experimental Section
Material Preparation: All the chemical reagents used in this study
were of analytical grade (Shanghai Chemical Reagent Corp.). We
prepared the BN hollow microspheres by a facile chemical vapor
reaction route in a gas pressure furnace. Ammonia–borane (AB,
H3B·NH3) was used as a starting material. AB was synthesized
according to the method proposed by Ramachandran et al.[39] In a
typical run, AB powder (3.0 g) was charged into an alumina cruci-
ble with a piece of graphite paper suspended in the center acting
as a substrate. The crucible was subsequently mounted into the
furnace chamber. The chamber was sealed and pumped to a base
pressure of 0.1 Pa. High-purity nitrogen was introduced into the
furnace chamber until a pressure of 0.5 MPa was reached. The fur-
nace was heated to 900 °C at a rate of about 10 °Cmin–1 and kept
at this temperature for 60 min before it was cooled to room tem-
perature. White products resembling white coatings were obtained
on the surface of the graphite paper and were directly used for
characterization.
[8] Q. Zhang, T. R. Zhang, J. P. Ge, Y. D. Yin, Nano Lett. 2008, 8,
2867–2871.
[9] W. S. Wang, L. Zhen, C. Y. Xu, W. Z. Shao, J. Phys. Chem. C
2008, 112, 14360–14366.
[10] H. C. Zeng, J. Mater. Chem. 2006, 16, 649–662.
[11] Y. G. Sun, B. T. Mayers, Y. N. Xia, Nano Lett. 2002, 2, 481–
485.
[12] L. Ge, X. Y. Jing, J. Wang, S. Jamil, Q. Liu, D. L. Song, J.
Wang, Y. Xie, P. P. Yang, M. L. Zhang, Cryst. Growth Des.
2010, 10, 1688–1692.
[13] Y. C. Qiu, W. Chen, S. H. Yang, B. Zhang, X. X. Zhang, Y. C.
Zhong, K. S. Wong, Cryst. Growth Des. 2010, 10, 177–183.
[14] Z. J. Yang, D. Q. Han, D. L. Ma, H. Liang, L. Liu, Y. Z. Yang,
Cryst. Growth Des. 2010, 10, 291–295.
Characterization Techniques: The as-prepared samples were charac-
terized by a variety of techniques including X-ray powder diffrac-
tion [XRD, Rigaku D/max-γB X-ray diffractometer with Cu-K ra-
diation (λ = 0.154178 nm)], scanning electron microscopy [SEM,
MX2600EF equipped with energy-dispersive X-ray spectroscopy
(EDX)], conventional and high-resolution transmission electron
microscopy [TEM and HRTEM, Philips Tecnai 20 and Tecnai F30
[15] L. Zhang, X. F. Cao, Y. L. Ma, X. T. Chen, Z. L. Xue, Crys-
tengcomm 2010, 12, 207–210.
Eur. J. Inorg. Chem. 2010, 5538–5544
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
5543

G. Wen, B. Zhong, X. Huang, H. Yu, X. Zhang, T. Zhang, H. Bai
FULL PAPER
[16] a) K. Watanabe, T. Taniguchi, H. Kanda, Nat. Mater. 2004, 3,
404–409; b) Y. Kubota, K. Watanabe, O. Tsuda, T. Taniguchi,
Science 2007, 317, 932–934.
[17] N. G. Chopra, R. J. Luyken, K. Cherrey, V. H. Crespi, M. L.
Cohen, S. G. Louie, A. Zettl, Science 1995, 269, 966–967.
[18] K. F. Huo, Z. Hu, F. Chen, J. J. Fu, Y. Chen, B. H. Liu, J. Ding,
Z. L. Dong, T. White, Appl. Phys. Lett. 2002, 80, 3611–3613.
[19] L. Q. Xu, J. H. Zhan, J. Q. Hu, Y. Bando, X. L. Yuan, T. Sekig-
uchi, M. Mitome, D. Golberg, Adv. Mater. 2007, 19, 2141–
2144.
[20] M. Corso, W. Auwarter, M. Muntwiler, A. Tamai, T. Greber,
J. Osterwalder, Science 2004, 303, 217–220.
[21] H. Z. Zhang, M. R. Phillips, J. D. Fitzgerald, J. Yu, Y. Chen,
Appl. Phys. Lett. 2006, 88, 0931171–0931173.
[27]
[28]
T. Matsuda, J. Mater. Sci. 1988, 24, 2353–2357.
Z. G. Chen, J. Zou, F. Li, G. Liu, D. M. Tang, D. Li, C. Liu,
X. L. Ma, H. M. Cheng, G. Q. Lu, Z. D. Zhang, Adv. Funct.
Mater. 2007, 17, 3371–3376.
C. Guimon, D. Gonbeau, G. Pfister-Guillouzo, O. Dugne, A.
Guette, R. Naslain, M. Lahaye, Surf. Interface Anal. 1990, 16,
440–445.
D. J. Joyner, D. M. Hercules, J. Chem. Phys. 1980, 72, 1095–
1108.
C. G. Cofer, J. Economy, Carbon 1995, 33, 389–395.
F. Baitalow, J. Baumann, G. Wolf, K. Jaenicke-Rossler, G. Le-
[29]
[30]
[31]
[32]
itner, Thermochim. Acta 2002, 391, 159–168.
C. H. Lee, J. S. Wang, V. K. Kayatsha, J. Y. Huang, Y. K. Yap,
Nanotechnology 2008, 19, 455605.
[33]
[22] Z. G. Chen, J. Zou, G. Liu, F. Li, Y. Wang, L. Z. Wang, X. L.
Yuan, T. Sekiguchi, H. M. Cheng, G. Q. Lu, Acs Nano 2008,
2, 2183–2191.
[34] R. J. H. Clark, T. J. Dines, Angew. Chem. Int. Ed. Engl. 1986,
25, 131–158.
[23] a) W. S. Zhang, J. G. Zheng, W. F. Li, D. Y. Geng, Z. D. Zhang,
J. Nanomater. 2009, 264026; b) Y. Pan, K. F. Huo, Y. M. Hu,
J. J. Fu, Y. N. Lu, Z. D. Dai, Z. Hu, Y. Chen, Small 2005, 1,
1199–1203.
[24] a) Y. T. Wang, Y. Yamamoto, H. Kiyono, S. Shimada, J. Am.
Ceram. Soc. 2009, 92, 787–792; b) L. Y. Chen, Y. L. Gu, L. Shi,
[35] E. V. Efremov, F. Ariese, A. J. G. Mank, C. Gooijert, Anal.
Chem. 2006, 78, 3152–3157.
[36] E. Smith, G. Dent, Modern Raman Spectroscopy: A Practical
Approach, John Wiley & Sons, Chichester, 2005.
[37] K. A. Alim, V. A. Fonoberov, A. A. Balandin, Appl. Phys. Lett.
2005, 86, 053103.
Z. H. Yang, J. H. Ma, Y. T. Qian, Solid State Commun. 2004, [38] a) C. C. Tang, Y. Bando, C. Y. Zhi, D. Golberg, Chem. Com-
130, 537–540; c) T. Zhang, G. Wen, L. Xia, X. X. Huang, B.
Zhong, X. D. Zhang, H. W. Bai, H. M. Yu, Scripta Mater.
2010, 63, 415–417.
mun. 2007, 4599–4601; b) C. Y. Su, W. Y. Chu, Z. Y. Juang,
K. F. Chen, B. M. Cheng, F. R. Chen, K. C. Leou, C. H. Tsai,
J. Phys. Chem. C 2009, 113, 14732–14738.
[39] P. V. Ramachandran, P. D. Gagare, Inorg. Chem. 2007, 46,
7810–7817.
[25] Y. Zhang, K. Suenaga, C. Colliex, S. Iijima, Science 1998, 281,
973–975.
[26] D. Pacile, J. C. Meyer, C. O. Girit, A. Zettl, Appl. Phys. Lett.
2008, 92, 1331071–1331073.
Received: June 28, 2010
Published Online: October 29, 2010
5544
www.eurjic.org
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2010, 5538–5544