ARTICLE IN PRESS

Journal of Crystal Growth 263 (2004) 372–376

*Corresp

571-8795-2

E-mail

0022-0248/

doi:10.101

Synthesis of CdS nanotubes by chemical bath deposition

Hui Zhang, Xiangyang Ma, Jin Xu, Deren Yang*

Department of Material Science & Engineering, State Key Lab. of Silicon Materials, Zhejiang University, Zheda Lu 38,

Hangzhou 310027, PR China

Received 15 January 2003; accepted 17 November 2003

Communicated by R. James

Abstract

CdS nanotubes have been prepared by means of chemical bath deposition (CBD) and nanochannel alumina (NCA)

template. X-ray diffraction (XRD) and selected area electron diffraction (SAED) indicate that the nanotubes are of

cubic structure. Transmission electron microscopy (TEM) shows the diameters of nanotubes are around 50 nm.

Furthermore, high-resolution TEM (HRTEM) reveals a clear lattice image of {1 1 1} planes in the wall of a CdS

nanotube. The directional growth of nanotubes is verified by scanning electron microscopy (SEM). It can be expected

that the method presented in this letter is also appropriate for the preparation of nanotubes of other semiconductors.

r 2003 Elsevier B.V. All rights reserved.

PACS: 81.05.Dz; 73.63.Fg; 81.16.Be

Keywords: A1. Nanotubes; A3. Chemical bath deposition; B1. CdS

1. Introduction

In recent years, one-dimensional semiconduc-tors have been widely studied because of theirnovel properties and wide-range potential applica-tions [1–7]. Undoubtedly, one-dimensional nanos-tructural materials are subjects of paramountimportance in materials science today. There area number of methods to fabricate one-dimensionalsemiconductors, such as electrodeposition [8],chemical vapor deposition (CVD) [9], chemicalbath deposition (CBD) and laser induced chemicalvapor deposition (LICVD) [10–12]. Among them,CBD has been traditionally used to prepare thin

onding author. Tel.: +86-571-8795-1667; fax: +86-

322.

address: mseyang@dial.zju.edu.cn (D. Yang).

$ - see front matter r 2003 Elsevier B.V. All rights reserve

6/j.jcrysgro.2003.11.090

films such as CdS films. However, CBD canpossibly be utilized to derive one-dimensionalnanostructures if the growth direction is limitedto one dimension using appropriate templates. Asfor CdS material, the nanowires have beenfabricated, respectively, by electrodeposition, che-mical solution transport (CST) and CBD [13–19];however, the structure of the nanotube, to ourknowledge, has not been reported up to now. Inthis paper, we have synthesized cubic polycrystal-line CdS nanotubes by means of CBD andnanochannels aluminum (NCA) templates.

2. Experiment

A pure Al plate (99.99%) was annealed at500�C for 2 h in vacuum, degreased in acetone and

d.

ARTICLE IN PRESS

20 30 40 50 60 70

(311)(111)

Al

Al2O3

CdS

CP

S

2θ

Fig. 1. XRD pattern of the CdS nanotubes incorporated into

the NCA template prepared in 10min.

H. Zhang et al. / Journal of Crystal Growth 263 (2004) 372–376 373

anodized at 0–16�C in oxalic acid solution at aconstant potential of 42V for 3 h. Then the anodicoxide layer, part of which was disordered, wasremoved in a mixture of phosphoric acid andchromic acid. Next the plate was anodized againfor 10 h under the conditions identical to those forthe first anodizing step. The Al layer of thespecimen on the backside was then removed inacetone and in a saturated CuCl2 solution,respectively. Subsequently, the membrane on thebackside was removed by exposure to phosphoricacid at 30�C for 90min. Finally the NCA templatewas dried at 30�C.CdS nanotubes were deposited on the NCA

template by reacting 0.02M cadmium chloride,0.05M thiourea and 0.02M sodium citrate in anaqueous solution using sodium citrate as acomplexing agent. The pH of the solution wasadjusted to 11.5 using NH3 �H2O, and the bathtemperature was 80�C. The chemical depositionlasted for 10 and 30min respectively, and then thetwo samples were obtained and washed withdeionized water. After drying in a 60�C oven, thetwo samples were annealed in N2 atmosphere at350�C for 1 h.The phase of CdS nanotubes incorporated into

the NCA templates was characterized by powderX-ray diffraction (XRD) with CuKa radiation.Transmission electron microscopy (TEM) withenergy dispersive X-ray (EDAX) was applied todetermine the microstructure and composition. Toobtain the specimen for TEM observation, theNCA template was completely removed by dis-solution in 1M NaOH at 60�C for 1 h withultrasonic vibration, and then the CdS nanotubeswere dispersed uniformly in the solution. Next, asmall drop of the solution was dipped onto a Cugrid covered with carbon film. The directionalgrowth of CdS nanotubes was characterized usinga scanning electron microscope (SEM).

Fig. 2. A TEM images of the CdS nanotubes prepared in

different time: (a) 30min; (b) 10min. The lower left inset in Fig.

2b is the corresponding SAED pattern; the upper right inset is

an magnified image of Fig. 2b.

3. Results and discussion

An XRD pattern of the sample is shown inFig. 1. As it can be seen, the spectrum consists ofthree sets of peaks. According to the standardJCPDS cards, one set corresponds to the cubic

structure of CdS, while the other two sets tocorrespond g-Al2O3 and Al.Fig. 2 shows two typical TEM images of CdS

nanotubes prepared by CBD for 30 and 10min inthe templates with the pore diameter of about50 nm. From comparison of the two images, wecan see that the channel of CdS nanotube preparedduring the shorter time is wider than that of theCdS nanotube prepared during the longer time.The upper right inset in Fig. 2b is the magnifiedimage of the CdS nanotube shown in Fig. 2b.From the magnified image, the difference is muchmore obvious. The lower left inset in Fig. 2b givesa selected area electron diffraction (SAED) pat-tern. In this pattern, from inside to outside, the

ARTICLE IN PRESS

Fig. 4. HRTEM image of a typical CdS nanotube. (Only one

side-wall of the nanotube is indicated due to the limitation of

the figure size.)

H. Zhang et al. / Journal of Crystal Growth 263 (2004) 372–376374

diffraction cycles, respectively, correspond to the{1 1 1}, {2 0 0}, {2 2 0} and {5 1 1} lattice planeswith an interplanar spacing of about 0.336, 0.291,0.205 and 0.111 (A. This experimental resultindicates that the structure of the CdS nanotubesprepared by CBD is cubic polycrystalline innature.EDX analysis was carried out on the individual

CdS nanotube shown in Fig. 2b, and the resultsare illustrated in Fig. 3. In the EDX spectrum, thepeaks of Cd and S are pronounced. Quantitativeanalysis shows that the CdS nanotubes aredeficient in S in terms of composition, probablydue to the volatility of S. The O peak may be dueto the oxidation of CdS nanotubes exposed to theair. The C peak and Cu peak come from thecopper grid used to support the CdS nanotubes.Fig. 4 shows the high-resolution transmission

electron microscopy (HRTEM) image of theindividual CdS nanotube. In the tube channel,there is no HRTEM crystal lattice fringe except forthose of a few CdS particles formed in the tubechannel by CBD. In general, it is very difficult toavoid the formation of CdS particles during CBD.While, the crystal lattice fringe of the tube wall ismainly revealed as the lattice plane of {1 1 1} withthe lattice spacing about 0.336 nm. Therefore, theCdS nanotubes prepared have been again provedto be of cubic structure with the major planes of

Fig. 3. EDX spectrum of the individual CdS nanotube shown

in Fig. 2b.

Fig. 5. Top-view SEM image of arrayed CdS nanotubes

incorporated into the NCA template.

ARTICLE IN PRESS

H. Zhang et al. / Journal of Crystal Growth 263 (2004) 372–376 375

{1 1 1}, which is in accordance with the XRDpattern shown in Fig. 1.A top-view SEM image of CdS nanotube arrays

embedded into the NCA template is shown in Fig.5. Prior to the SEM observation, the sample wasfirstly put into hydrochloric acid to partly get ridof the CdS particles on the surface, and subse-quently, it was further etched by sodium hydroxideto remove some of the aluminum oxide. From theimage, it can be seen that the uniform CdSnanotubes were embedded into the NCA template.Obviously, the formation of the CdS nanotubearray is due to the confined growth of thenanotubes in the orderly pores of an NCAtemplate.In the CdS thin film growth, two mechanisms

have been put forward [21,22]. One is cluster-by-cluster mechanism described as follows: in theammonia-thiourea system, S2� ions are released bythe alkaline hydrolysis of thiourea and Cd2+ ionsare released by the dissociation of the correspond-ing ammonia complexes. As soon as the product ofthe free S2� and Cd2+ ion concentrations exceedsthe solubility product of CdS, the particles of CdSare produced. The particles of CdS are adsorbedon the substrate, and CdS films are formed. Theother mechanism is an ion-by-ion process compris-ing three steps: (1) the reversible adsorption on thesubstrate surface of dihydroxo-diamino cadmium,(2) the adsorption of thiourea by the formation ofa metastable complex, (3) the formation of CdSand the site regeneration by the metastablecomplex decomposition. In our work, it is believedthat the growth of CdS nanotubes, following theion-by-ion mechanism, occurs in the pore wall ofNCA template just like the growth of CdS thinfilms on flat substrates. The cadmium source andsulfide source enter into the NCA pore where thecadmium source is preferentially adsorbed by theNCA pore wall, then the sulfide source isadsorbed, resulting in the metastable complexwhich is then decomposited into CdS and the siteregeneration by the metastable complex decom-position. As a matter of fact, during the CBD theformation of CdS particles dictated by the cluster-by-cluster mechanism is inevitable, which isundesirable for the formation of the CdS nano-tubes because the formation of large CdS particles

suppresses the process dictated by the ion-by-ionmechanism. For the growth of the CdS nanotubes,it is very important that the ion-by-ion depositionof CdS predominately occurs on the pore wall ofNCA templates, while substantially suppressingthe cluster-by-cluster deposition of CdS. Ourexperiment indicates that the appropriate deposi-tion time and the use of sodium citrate as acomplexing agent are critical for the formation ofCdS nanotubes.

4. Conclusion

In conclusion, we have synthesized cubic poly-crystalline CdS nanotubes incorporated into theNCA templates by CBD under appropriate con-ditions. The diameter of the CdS nanotubes isabout 50 nm as measured using TEM. The growthof CdS nanotubes on the pore wall of NCAtemplate is considered to be the ion-by-ionmechanism. The CBD method is believed to bealso appropriate for the growth of other semi-conductor nanotubes.

5. Uncited references

[20].

Acknowledgements

The authors would like to appreciate thefinancial supports of 863 project(No.2001AA513023) and the Zhejiang ProvincialNatural Science Foundation of China (No.601092).

References

[1] H. Dai, E.W. Wang, Y.Z. Lu, S. Fan, C.M. Lieber, Nature

375 (1995) 769.

[2] Weiqiang Han, Shoushan Fan, Qunqing Li, Yongdan Hu,

Science 277 (1997) 1287.

[3] J.R. Heath, F.K. Le Goues, Chem. Phys. Lett. 208 (1993)

263.

ARTICLE IN PRESS

H. Zhang et al. / Journal of Crystal Growth 263 (2004) 372–376376

[4] Z.F. Ren, Z.P. Huang, J.W. Xu, J.H. Wang, P. Bush, M.P.

Siegal, P.N. Provencio, Science 282 (1998) 1105.

[5] M.S. Fuhrer, J. Nygard, L. Shih, M. Forero, Young-Gui

Yoon, M.S.C. Mazzoni, Hyoung Joon Choi, Science 288

(2000) 494.

[6] Jing Kong, Nathan R. Franklin, Chongwu Zhou, Michael

G. Chapline, Shu Peng, Kyeongjae Cho, Hongjie Dai,

Science 287 (2000) 622.

[7] J. Hone, B. Batlogg, Z. Benes, A.T. Johnson, J.E. Fischer,

Science 289 (2000) 1730.

[8] Dongsheng Xu, Yajie Xu, Dapeng Chen, Guolin Guo,

Linlin Gui, Youqi Tang, Chem. Phys. Lett. 325 (2000) 340.

[9] Xinyi Zhang, Lide Zhang, Guowen Meng, GuangHai Li,

Neng Yun, Jin Phillipp, Fritz Phillipp, Adv. Mater. 13(16)

(2001) 1238.

[10] Wensheng Shi, Yufeng Zhang, Ning Wang, Chunsing Lee,

Shuittong Lee, Adv. Mater. 13(8) (2001) 591.

[11] Wenshong Shi, Hongying Peng, Yufeng Zhang, Ning

Wang, Naigui Shang, Zhenwei Pan, Chunsing Lee,

Shuittong Lee, Adv. Mater. 12(18) (2000) 1343.

[12] W.S. Shi, Y.F. Zhang, N. Wang, C.S. Lee, S.T. Lee, Appl.

Phys. Lett. 78 (21) (2001) 3304.

[13] Hui Zhang, Xiangyang Ma, Jin Xu, Junjie Niu, Jian Sha,

Deren Yang, J. Crystal Growth 246 (2002) 108.

[14] D. Routkevitch, T. Bigioni, M. Moskovits, Jing Ming Xu,

J. Phys. Chem. 100 (1996) 14037.

[15] Jinhua Zhang, Xiaogang Yang, Dunwei Wang, Shengdong

Li, Yi Xie, Younan Xia, Yitai Qian, Adv. Mater. 12 (2000)

1348.

[16] Dongsheng Xu, Yajie Xu, Dapeng Chen, Guolin Guo,

Linlin Gui, Youqi Tang, Adv. Mater. 12 (2000) 520.

[17] D. Routkevitch, T.L. Haslett, L. Ryan, T. Bigioni, C.

Douketis, M. Moskovits, Chem. Phys. 210 (1996)

343.

[18] Yan Li, Jinghua Wan, Zhennan Gu, Mater. Sci. Eng. A

286 (2000) 106.

[19] Jung Sang Suh, Jin Seung Lee, Chem. Phys. Lett. 281

(1997) 384.

[20] J.H. Zhan, X.G. Yang, S.D. Li, D.W. Wang, Y. Xie, Y.T.

Qian, J. Crystal Growth 220 (2000) 231.

[21] J.M. Dona, J. Herrero, J. Electrochem. Soc. 144 (1997)

4081.

[22] R. Ortega-Borges, D. Lincolm, J. Electrochem. Soc. 140

(1993) 3464.