Logo of nanoreslettspringer open web sitethis articlemanuscript submissionregistrationjournal front pagespringer open web site
Nanoscale Res Lett. 2012; 7(1): 220.
Published online 2012 Apr 13. doi:  10.1186/1556-276X-7-220
PMCID: PMC3352247

Growth of catalyst-free high-quality ZnO nanowires by thermal evaporation under air ambient


ZnO nanowires have been successfully fabricated on Si substrate by simple thermal evaporation of Zn powder under air ambient without any catalyst. Morphology and structure analyses indicated that ZnO nanowires had high purity and perfect crystallinity. The diameter of ZnO nanowires was 40 to 100 nm, and the length was about several tens of micrometers. The prepared ZnO nanowires exhibited a hexagonal wurtzite crystal structure. The growth of the ZnO nanostructure was explained by the vapor-solid mechanism. The simplicity, low cost and fewer necessary apparatuses of the process would suit the high-throughput fabrication of ZnO nanowires. The ZnO nanowires fabricated on Si substrate are compatible with state-of-the-art semiconductor industry. They are expected to have potential applications in functional nanodevices.

Keywords: zinc oxide, nanowire, thermal evaporation


In the past decade, significant interest has emerged in the synthesis of one-dimensional semiconductor materials, such as Si [1-3], SiC [4,5], GaN [6-8], SnO2 [9] and ZnO [10-13]. Among these nanoscale semiconductors, ZnO has attracted a great deal of attention because of its potential as a large direct band gap semiconductor (Eg is about 3.35 eV at room temperature) with high exciton binding energy (60 meV). It can act as building blocks for nano-FET, nanolasers, photodetectors and gas sensors [8,14]. In addition, ZnO nanowires have excellent field emission for its good hardness, thermal stability and resistance to oxidation [15,16].

Recently, many methods have been developed to synthesize ZnO nanowires, for example, carbon thermal reduction [13,17], chemical vapor deposition [12,18], physical vapor deposition [19], electrodeposition [20], aqueous synthesis [21] and solvothermal technique [22]. In this paper, we synthesized ZnO nanowires by thermal evaporation without a catalyst under air ambient. The reactions were carried out in a traditional horizontal furnace with one end open at 750°C. The gray-white product was successfully deposited on the Si substrate. The process does not need any metal catalyst, so it avoids catalyst contamination. Furthermore, the simplicity, low cost and fewer necessary apparatuses of the process would suit the high-throughput fabrication of ZnO nanowires.


The experiments were conducted in a horizontal furnace as schematically outlined in Figure Figure1.1. The raw Zn material (99.99%) was loaded into a quartz boat. The Si substrate was cleaned by the standard cleaning process, and then, it was laid above the Zn powders. The furnace was heated to 750°C under a constant flow of pure O2 gas, with the flow rate of 2 ml/min. Afterwards, the quartz boat was put in the central region of the horizontal quartz tube. After 2 h, the furnace was turned off and naturally cooled to room temperature. A gray-white layer was coated on the Si Substrate.

Figure 1
Schematic diagram of the experimental setup for synthesizing ZnO nanowires.

The as-synthesized products were characterized by X-ray diffraction (XRD) with CuKα radiation (wavelength, λ = 1.5406 Å), field emission scanning electron microscopy (SEM) (Hitachi S-4800, Hitachi Ltd., Tokyo, Japan), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM) (JEOL JEM2010F, JEOL Co., Ltd., Beijing, China).

Results and discussion

Phase analysis of as-synthesized products is shown in Figure Figure2.2. All the diffraction peaks can be indexed as wurtzite ZnO with lattice constants of a = 0.325 nm and c = 0.521 nm, agreeing well with the calculated diffraction pattern (JCPDs card no.03-1005). No other diffraction peaks are detected in the spectrum within the instrumental resolution, which indicates that the products are ZnO with high purity.

Figure 2
XRD pattern of the as-synthesized products.

Figure Figure3a3a shows the typical low-magnification SEM images of the products on the Si substrate. It reveals that the products consist of high-density ZnO nanowires with typical lengths in the range of several tens of micrometers. Some aligned ZnO nanowires were also detected, as shown in Figure Figure3b.3b. Figure Figure3c3c shows the larger magnification of the aligned ZnO nanowires. They reveal that the ZnOs with a diameter of 40 to 100 nm were nearly parallel and have a smooth surface. In order to investigate the further structure of the fabricated ZnO nanowires, TEM and HRTEM analyses were also performed.

Figure 3
SEM images of as-synthesized ZnO nanowires. (a) Low-magnification, (b) aligned ZnO nanowires and (c) its larger-magnification Figure 4a shows the typical low-magnification TEM image of the prepared ZnO nanowire, which indicates that the ZnO nanowire has ...

The vapor-liquid-solid (V-L-S) and vapor-solid (V-S) formation mechanisms are usually responsible for the one-dimensional (1-D) semiconductor nanowires. For the V-L-S mechanism, the metal nanoclusters act as catalyst and guide the nanowire to grow towards the 1-D direction. It is evident that the nanowire tip will have an alloy droplet. In our experiment, no impurity metal particles were detected in the ZnO nanowires (from the SEM and TEM images). Hence, the V-S growth process could be well accepted in our work. Firstly, a reaction occurs between Zn and O2 to form ZnOx (x < 1); the ZnOx vapor is transferred by the O2 to the nuclei at the Si substrate. The continuously introduced O2 oxidizes ZnOx to ZnO. Due to the high supersaturation of Zn, ZnOx vapor and oxygen, the ZnO nanostructures can easily nucleate and grow along the [0001] direction, which was substantiated by the HRTEM image (Figure (Figure4b).4b). The already-formed ZnO nucleation continues to grow along the direction of the O2 gas flow, so some aligned ZnO nanowires on the Si substrate are formed.

Figure 4
TEM (a) and HRTEM (b) images of as-synthesized ZnO nanowire.


ZnO nanowires with high purity and perfect crystallinity were fabricated by simple thermal evaporation of pure Zn powders under air ambient without any catalyst. The diameter of the ZnO nanowires was 40 to 100 nm, and the length was about several tens of micrometers. Some aligned ZnO nanowires with smooth surface were also detected. The growth of ZnO nanostructure was explained by the V-S mechanism. The prepared ZnO nanowires exhibited a hexagonal wurtzite crystal structure. The as-fabricated ZnO nanowires are expected to find applications in nanosensors and nanodetectors.

Competing interests

The authors declare that they have no competing interests.

Authors' contributions

PL prepared the manuscript and supervised all of the study. YBL performed the experiment. YQG helped in the technical support for the experiments. ZHZ participated in the measurements. All the authors discussed the results and approved the final manuscript.

Authors' information

Dr. Ping Liu got her PhD degree in 2010. She has devoted her effort in the research of one-dimensional semiconductor materials for 7 years. Her research interest lies in the fabrication and application of zinc oxide nanowires. She has published her work in several important international journals.


The authors thank the Foundation of He'nan Educational Committee (no. 2011A470015) and the Henan province science and technology tackling key project (no. 102102210444).


  • Shiu SC, Lin SB, Hung SC, Lin CF. Influence of pre-surface treatment on the morphology of silicon nanowires fabricated by metal-assisted etching. Appl Surf Sci. 2011;257:1829–1834. doi: 10.1016/j.apsusc.2010.08.086. [Cross Ref]
  • Cheng YK, Chie G, Bau TD. Photovoltaic characteristics of silicon nanowire arrays synthesized by vapor-liquid-solid process. Sol Energ Mat Sol C. 2011;95:154–157. doi: 10.1016/j.solmat.2010.04.028. [Cross Ref]
  • Kumar D, Srivastava SK, Singh PK, Husain M, Kumar V. Fabrication of silicon nanowire arrays based solar cell with improved performance. Sol Energ Mat Sol C. 2011;95:215–218. doi: 10.1016/j.solmat.2010.04.024. [Cross Ref]
  • Zhou WM, Yang B, Yang ZX, Zhu F, Yan LJ, Zhang YF. Large-scale synthesis and characterization of SiC nanowires by high-frequency induction heating. Appl Surf Sci. 2006;252:5143–5148. doi: 10.1016/j.apsusc.2005.07.031. [Cross Ref]
  • Li XT, Chen XH, Song HH. Preparation of silicon carbide nanowires via a rapid heating process. Mater Sci Eng B. 2011;176:87–91. doi: 10.1016/j.mseb.2010.09.007. [Cross Ref]
  • Wang X, Sun XY, Fairchild M, Hersee SD. Fabrication of GaN nanowire arrays by confined epitaxy. Appl Phys Lett. 2006;89:233115. doi: 10.1063/1.2402893. [Cross Ref]
  • Navamathavan R, Ra YH, Song KY, Kim DW, Lee CR. Different growth behaviors of GaN nanowires grown with Au catalyst and Au + Ga solid solution nano-droplets on Si(111) substrates by using MOCVD. Curr Appl Phys. 2011;11:77–81. doi: 10.1016/j.cap.2010.06.022. [Cross Ref]
  • Chen J, Xue CS. Catalytic growth of large-scale GaN nanowires. J Mater Eng Perform. 2010;19:1054–1057. doi: 10.1007/s11665-009-9574-8. [Cross Ref]
  • Zhou ZH, Wu J, Li HD, Wang ZM. Field emission from in situ-grown vertically aligned SnO2 nanowire arrays. Nanoscale Res Lett. 2012;7:117. doi: 10.1186/1556-276X-7-117. [PMC free article] [PubMed] [Cross Ref]
  • Ma CY, Zhou ZH, Wei H, Yang Z, Wang ZM, Zhang YF. Rapid large-scale preparation of ZnO nanowires for photocatalytic application. Nanoscale Res Lett. 2011;6:536. doi: 10.1186/1556-276X-6-536. [PMC free article] [PubMed] [Cross Ref]
  • Wang ZL, Song JH. Piezoelectric nanogenerators based on zinc oxide nanowire arrays. Science. 2006;312:242–246. doi: 10.1126/science.1124005. [PubMed] [Cross Ref]
  • Wang XH, Li RB, Fan DH. Control growth of catalyst-free high-quality ZnO nanowire arrays on transparent quartz glass substrate by chemical vapor deposition. Appl Surf Sci. 2011;257:2960–2964. doi: 10.1016/j.apsusc.2010.10.100. [Cross Ref]
  • Zhou ZH, Zhan CH, Wang YY, Su YJ, Yang Z, Zhang YF. Rapid mass production of ZnO nanowires by a modified carbothermal reduction method. Mater Lett. 2011;65:832–835. doi: 10.1016/j.matlet.2010.12.032. [Cross Ref]
  • Khan R, Ra HW, Kim JT, Jang WS, Sharma D, Im YH. Nanojunction effects in multiple ZnO nanowire gas sensor. Sens Actuators B. 2011;150:389–393.
  • Luo L, Sosnowchil BD, Lin LW. Room temperature fast synthesis of zinc oxide nanowires by inductive heating. Appl Phys Lett. 2007;90:093101. doi: 10.1063/1.2709618. [Cross Ref]
  • Ramanathan S, Chen YC, Tzeng Y. Zinc oxide nanowire based field emitters. Physica E. 2010;43:285–288. doi: 10.1016/j.physe.2010.07.072. [Cross Ref]
  • Wang FF, Cao L, Pan AL, Liu RB, Wang X, Zhu X, Wang HQ, Zou BS. Synthesis of tower-like ZnO structures and visible photoluminescence origins of varied-shaped ZnO nanostructures. J Phys Chem C. 2007;111:7655–7660. doi: 10.1021/jp067151u. [Cross Ref]
  • Wu JJ, Liu SC. Low-temperature growth of well-aligned ZnO nanorods by chemical vapor deposition. Adv Mater. 2002;14:215–218. doi: 10.1002/1521-4095(20020205)14:3<215::AID-ADMA215>3.0.CO;2-J. [Cross Ref]
  • Zhu G, Yang R, Wang S, Wang ZL. Flexible high-output nanogenerator based on lateral ZnO nanowire array. Nano Lett. 2010;10:3151–3155. doi: 10.1021/nl101973h. [PubMed] [Cross Ref]
  • Zhang Z, Meng GW, Xu QL, Hu YM, Wu Q, Hu Z. Aligned ZnO nanorods with tunable size and field emission on native Si substrate achieved via simple electrodeposition. J Phys Chem C. 2010;114:189–193. doi: 10.1021/jp9087223. [Cross Ref]
  • Breedon M, Rahmani MB, Keshmirii SH, Wlodarski W, Kalantarzadeh K. Aqueous synthesis of interconnected ZnO nanowires using spray pyrolysis deposited seed layers. Mater Lett. 2010;64:291–294. doi: 10.1016/j.matlet.2009.10.065. [Cross Ref]
  • Sarkar S, Patra S, Bera SK, Paul GK, Ghosh R. Water repellent ZnO nanowire arrays synthesized by simple solvothermal technique. Mater Lett. 2010;64:460–462. doi: 10.1016/j.matlet.2009.11.047. [Cross Ref]

Articles from Nanoscale Research Letters are provided here courtesy of Springer
PubReader format: click here to try


Save items

Related citations in PubMed

See reviews...See all...

Cited by other articles in PMC

See all...


  • MedGen
    Related information in MedGen
  • PubMed
    PubMed citations for these articles

Recent Activity

Your browsing activity is empty.

Activity recording is turned off.

Turn recording back on

See more...