Journal of Crystal Growth 252 (2003) 570–574

Polymer-controlled growth of Sb2Se3 nanoribbons via ahydrothermal process

Qin Xie, Zhaoping Liu, Mingwang Shao, Lingfen Kong, Weichao Yu, Yitai Qian*

Structure Research Laboratory and Department of Chemistry, University of Science and Technology of China, Hefei 230026, Anhui,

People’s Republic of China

Received 24 January 2003; accepted 6 February 2003

Communicated by M. Schieber

Abstract

Sb2Se3 nanoribbons have been prepared by a hydrothermal process at 180�C for 20 h. X-ray diffraction pattern

indicates that the product was orthorhombic Sb2Se3 phase with lattice constants a=11.747, b=11.799 and c=3.987 (A.

Field emission scanning electron microscope images show that nanoribbons have diameters in the range of 25–100 nm

and lengths up toB30 mm. High-resolution transmission electron microscopy image reveals that the nanoribbon was ofsingle crystal and grew along the [0 0 1] direction. The peak of absorption appeared at 727 nm in the UV-vis spectrum. A

possible mechanism on the formation of the nanostructures was also discussed.

r 2003 Elsevier Science B.V. All rights reserved.

PACS: 81.05.Hd; 81.05.Ys

Keywords: A1. Crystal morphology; A2. Hydrothermal crystal growth; A2. Single crystal growth; B1. Nanomaterials; B1. Poly-

mers; B2. Semiconducting materials

1. Introduction

One-dimensional nanostructure materials (suchas nanotubes, nanowires, nanoribbons and nanor-ods) have attracted extensive attention due to theirfundamental properties and potential applicationsin opto-electronic nanodevices [1–3]. Variousmethods have been developed to synthesize 1Dsemiconductor, such as single-source precursormethod [4], electrodeposition method [5], high

temperature evaporation [6–7] and solvothermalmethod [8]. The strategy of using organic mole-cules as templates to control the nucleation andgrowth has been applied to the chemical synthesesof inorganic nanomaterials with unusual or com-plex forms. For example, Cu2O nanowires havebeen prepared with the assistance of PEG [9]. CdSnanowires have been fabricated via a simplepolyacrylamide-controlled growth method [10].As a direct band gap (1.3 eV) semiconductor,

Sb2Se3 exhibits photovoltaic and thermoelectricproperties, which make it potential applications insolar selective and decorative coating, optical andthermoelectric cooling devices [11]. The synthesis

*Corresponding author. Tel.: +86-551-3603204; fax: +86-

551-3607402.

E-mail address: ytqian@ustc.edu.cn (Y. Qian).

0022-0248/03/$ - see front matter r 2003 Elsevier Science B.V. All rights reserved.

doi:10.1016/S0022-0248(03)00962-X

of one-dimensional semiconductor Sb2Se3 hasbeen the subject of considerable interest in recentyears. Sb2Se3 nanorods have been prepared via ahydrothermal treatment in hydrazine hydratemedia [12]. And solvothermal technique has beensuccessfully employed to synthesize Sb2Se3 nano-wires in diethylene glycol solution [13].Herein, we synthesized single-crystal Sb2Se3

nanoribbons by hydrothermal processing of anti-mony complex and Na2SeSO3 solution in thepresence of poly (vinyl alcohol) (PVA) at 180�C.The nanoribbons have widths from 25 to 100 nmwith width-to-thickness ratios of 1.5–4 and lengthsof B30 mm.

2. Experimental section

Sodium selenosulfate (Na2SeSO3) was preparedaccording to the literature [14]. 9.1wt% PVA solwas prepared as followed: 10 g PVA (averagepolymerization degrees: 2400–2500) was dissolvedin 100ml distilled water, then heated to 90�C andmaintained for 2 h.In a typical process, 2mmol of SbCl3 was

dissolved in 6ml of 1M tartaric acid undermagnetic stirring to form a homogeneous solution.Then a certain amount of ammonia, 20ml of 0.1Msodium selenosulfate solution and 20ml of9.1wt% PVA sol were introduced into the formersolution to form the final solution (pH 9–10) withconstantly vigorous stirring. The resulting solutionwas transferred into a Teflon-lined stainless-steelautoclave. The autoclave was sealed and main-tained at 180�C for 20 h, then cooled to roomtemperature naturally. The dark gray productswere filtered, and washed several times with hotdistilled water and absolute ethanol to removePVA and impurities, and then dried in vacuum at70�C for 4–5 h.The X-ray diffraction (XRD) pattern was

recorded using a Rigaku (Japan) D/max-rA X-ray diffractometer equipped with graphite mono-chromatized Cu Ka radiation (l ¼ 0:154178 nm)at a scanning rate of 0.02�/s in 2y ranging from10� to 70�. The field emission scanning electronmicroscope (FESEM) images were taken with aFESEM (JEOL-6300F15 kV). SEM images were

obtained with a Hitachi X-650 SEM. Transmiss-sion electron microscopy (TEM) images weretaken with a Hitachi H-800 TEM operating at200 kV. The high-resolution transmission electronmicroscopy (HRTEM) images and the corre-sponding selected area electron diffraction(SAED) pattern were taken on a JEOL 2010HRTEM with energy-dispersive X-ray spectro-scopy (EDS) performed at 200 kV. Absorptionspectrum was collected on a UV-vis spectro-photometer (Shimadzu UV-240) in the wavelengthrange of 190-900 nm.

3. Results and discussion

Fig. 1 shows the XRD pattern of the sampleobtained. All peaks can be indexed to orthorhom-bic Sb2Se3 phase (space group: Pbnm) withcalculated lattice constants a=11.747, b=11.799and c=3.987 (A, which are close to the literaturevalues (JCPDS 15-861). And no impurities can bedetected in this pattern.FESEM images (as shown in Figs. 2a and b) of

the sample display the general morphology of thewire-like nanostructure. We can find that most ofthe wire-like products are smooth and straightthroughout their lengths, while some of them havecurved sections. Further investigation of the FESEMimages, we find the wire-like nanostructures are

10 20 30 40 50 60 70

621

061

351

160

501 060250

141

321

240

221

211

231

130

120

020

Inte

ns

ity

(a

. u

.)

2θ (deg.)

Fig. 1. XRD pattern of Sb2Se3 nanoribbons prepared at 180�C

for 20 h.

Q. Xie et al. / Journal of Crystal Growth 252 (2003) 570–574 571

nanoribbons with low width-to-thickness ratio.Fig. 2c shows a typical Sb2Se3 nanoribbon withrectangular cross-section. These nanoribbons havetypical widths of 25–100 nm with width-to-thick-ness ratios of 1.5–4 and lengths of B30 mm. EDSindicates that these nanoribbons are composed ofthe element Sb and Se with the ratio of 1:1.4(Fig. 2d).Fig. 3a shows the HRTEM image of an

individual nanoribbon with a diameter of about45 nm. The corresponding HRTEM image andSAED pattern are shown in Fig. 3b. The HRTEMimage reveals that the ribbon is a single crystal andfree from dislocation. The fringe spacing of ca.0.39, 0.52 and 0.31 nm correspond to (0 0 1), (1 2 0)and (1 2 1) planes of orthorhombic phase Sb2Se3,respectively. It can be seen that the (0 0 1) planesare perpendicular to the surface of the individualnanoribbon, from which it can be deduced that thenanoribbon grew along the [0 0 1] direction. The

inset shows the electron diffraction pattern re-corded with the incident electron beam. It in-dicates that the nanoribbons are single crystals andhave a preferential growth direction, which areconsistent with the result of the HRTEM image.The growth direction of Sb2Se3 nanoribbons iscoincident with that of Sb2Se3 nanorods reportedpreviously [12].The possible chemical reactions and explana-

tions for hydrothermal processing are described asfollowing: First, Se2� can be released from sodiumselenosulfate in the alkaline medium. Then activeSe2� combines with Sb(III) complex to produceamorphous Sb2Se3 particles. In the presence ofPVA, Sb2Se3 particles grew into wire-like struc-tures. The chemical reaction can be formulated as

SeSO2�3 þ2OH�-Se2� þ SO2�

4 þH2O; ð1Þ

3Se2� þ 2SbðIIIÞðtartÞ-Sb2Se3kþ 2 tart: ð2Þ

0 2 4 6 8 10 12 140

1000

2000

3000

(d)

Sb

Sb

Se

Se

Cu

Cu

Se

Cu

C

CP

S

Energy (keV)

(a) (b)

(c)

Fig. 2. (a) Low-magnification and (b) high-magnification FESEM images of as-synthesized Sb2Se3 nanoribbons. (c) The rectangular

cross-section of a typical Sb2Se3 nanoribbon with width of about 85 nm and thickness of about 20 nm. (d) EDS pattern of the final

product (C and Cu signals can be attributed to the copper microgrid and carbon film supporting the Se2Se3 nanoribbons).

Q. Xie et al. / Journal of Crystal Growth 252 (2003) 570–574572

To understand the possible formation mechan-ism of Sb2Se3 nanoribbons, a series of experimentsunder different conditions have been carried out.We studied the influence of reaction time on thenanostructure growth by TEM images. Fig. 4shows TEM images of products at differentreaction times. When reaction time continued for2 h, the whole solution turned red. But noprecipitate was found. After another hour, someproducts began to turn up and suspended on theautoclave. Further elongating the reaction time,

the whole autoclave was full of dark grayprecipitates. It can be deduced that the process isa homogeneous nucleation process. Consideringthe structure of infinite links, Sb2Se3 nucleationeasily grew into 1D nanostructure under thehydrothermal condition.The use of tartaric acid as a coordination

reagent is necessary in our experiment. If SbCl3was directly dissolved in distilled water, it wouldhydrolyze and produce a precipitate of Sb(OH)Cl,which would bring the impurities of antimonyoxides and decrease aspect ratios. Tartaric acid asa coordination reagent is believed to kineticallycontrol the reaction rates.Despite of a strong 1D growth tendency, we still

believe that PVA sol played an important role inthe formation and growth of Sb2Se3 nanoribbons.Fig. 5 shows the SEM images of different samplesprepared according to the typical synthesis routeexcept for the molar ratio of PVA to Sb(III)increasing from 6:1 to 23:1. The exact mechanismis not clear up to date. PVA may act as a cappingreagent to kinetically control the growth rate ofdifferent crystal faces through selective absorptionand desorption. At the molar ratio of 6:1, thesamples were rod-like structures with averagediameters of about 300 nm and some aggregatedparticles. In this case, the low ratio of PVA/Sb(III)may cause a low coverage on surfaces of theincipient Sb2Se3 particles. The incomplete cover-age on surfaces could not effectively hold back thelateral growth and Sb2Se3 nanoribbons with widerdiameters were formed. When the ratio was

Fig. 4. TEM images of the products obtained after hydro-

thermal processing at 180�C for different time. (a) 3 h and (b)

20 h.

Fig. 5. SEM images of the products obtained at different molar

ratio of PVA/Sb(III) showing the effect of PVA on the

morphology of products. (a) nPVA=nSbðIIIÞ ¼6:1 and (b)

nPVA=nSbðIIIÞ ¼ 23 : 1:

Fig. 3. (a) and (b) HRTEM images of an individual nanor-

ibbon with a diameter of about 45 nm. The inset in (b) is the

corresponding ED pattern recorded with the incident beam

perpendicular to the surface.

Q. Xie et al. / Journal of Crystal Growth 252 (2003) 570–574 573

increased to 23:1, nanoribbons were formed afterhydrothermal treatment for 3 h. The relatively highmolar ratio of PVA/Sb(III) caused the high cover-age on the surfaces of the initial Sb2Se3 particles.The effect of PVA on the shape and size of Sb2Se3nanostructures is similar to the results obtained byZhou et al. [15] and Xia’group [16], which were theratio of the capping polymer to cation influencingthe morphology and size of the products.We also investigated the influence of tempera-

ture on the growth of Sb2Se3 nanoribbons. We didthe experiments using the typical synthesis route atdifferent temperatures. We found that only a fewrod-like Sb2Se3 crystals were produced when thetemperature was below 160�C even if the reactionlasted for 2d. In the range of 160–180�C, Sb2Se3nanoribbons were easily obtained as the majorproducts. The size of nanostructures wouldincrease when the temperature increased.The UV-vis absorption spectrum of the Sb2Se3

nanostructures was shown in Fig. 6. The peak ofabsorption appears at 727 nm and the correspond-ing absorption energy is 1.7 eV, which shows anobvious blue-shift relative to that of the bulkSb2Se3 (1.3 eV). This may be attributed to quan-tum-confined effect of nanostructure.

4. Conclusion

In summary, Sb2Se3 nanoribbons with dia-meters in the range of 25–100 nm and lengths of

tens of micrometers have been synthesized via asimple hydrothermal process in the presence ofPVA as a capping polymer reagent. It was foundthat reaction temperature, time, tartaric acid andthe ratio of PVA to Sb(III) performed importantroles in the growth of antimony nanostructures.Sb2Se3 nanoribbons can be synthesized using ahigh molar ratio of PVA/Sb(III) at 160–180�C for20 h. The synthesis route may be applied tosynthesize other one-dimensional metals chalco-genides semiconductors such as A2B3 (A=Sb, Bi;B=S, Te ) group complexes.

Acknowledgements

This work was supported by National NaturalScience Foundation of China and the 973 Projectof China.

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400 500 600 700 8000.0

0.1

0.2

AB

S (

a.u

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Wavelength (nm)

Fig. 6. UV-visible spectrum of the final product (180�C, 20 h).

Q. Xie et al. / Journal of Crystal Growth 252 (2003) 570–574574