Skip to content


  • Nano Express
  • Open Access

Fabrication of ZnCoO nanowires and characterization of their magnetic properties

  • 1,
  • 2,
  • 1,
  • 1,
  • 3,
  • 4,
  • 5 and
  • 1Email author
Nanoscale Research Letters20149:221

  • Received: 6 January 2014
  • Accepted: 2 April 2014
  • Published:


Hydrogen-treated ZnCoO shows magnetic behavior, which is related to the formation of Co-H-Co complexes. However, it is not well known how the complexes are connected to each other and with what directional behavior they are ordered. In this point of view, ZnCoO nanowire is an ideal system for the study of the magnetic anisotropy. ZnCoO nanowire was fabricated by trioctylamine solution method under different ambient gases. We found that the oxidation of trioctylamine plays an essential role on the synthesis of high-quality ZnCoO nanowires. The hydrogen injection to ZnCoO nanowires induced ferromagnetism with larger magnetization than ZnCoO powders, while becoming paramagnetic after vacuum heat treatment. Strong ferromagnetism of nanowires can be explained by the percolation of Co-H-Co complexes along the c-axis.


  • ZnCoO
  • Nanowire
  • Solution aqueous method
  • Ferromagnetism


Co-doped ZnO (ZnCoO) has been intensively studied because of its widespread applicability as a magnetic semiconductor[13]. Many studies have shown that its ferromagnetism depends on the fabrication method and the post-treatment conditions. A variety of theoretical models have been suggested to explain experimental results[2, 47]. However, the origin of ZnCoO ferromagnetism remains unclear.

Chemical fabrication of ZnCoO is greatly affected by experimental factors, compared with other deposition methods such as pulsed laser deposition and radio frequency (RF) sputtering[811]. Post heat treatment, used to eliminate organic residuals, can induce secondary phases and crystalline defects, which can interfere with the investigation of intrinsic properties[1215]. Unwanted hydrogen contamination during fabrication, in particular, is known to create defects that degrade the physical properties of ZnO-based materials. However, many experimental results have consistently supported the model of magnetic semiconductors in which Co-H-Co complexes are created by hydrogen doping of ZnCoO[5, 13, 1621].

ZnCoO nanowires have received extensive attention because of advantages such as high aspect ratio and widespread applicability[2225]. However, determining the intrinsic properties has been difficult, and the performance and reliability of ZnCoO nanowire devices have been controversial because they are typically fabricated using chemical methods with non-polar solvents[23, 26].

ZnCoO nanowire fabrication with non-polar solvents is based on thermal decomposition via a well-known chemical mechanism[2730]. The reported fabrication conditions, including temperature, additives, and reaction environment, vary[26, 31]. These factors affect not only the growth of the nanowires but also the physical properties of the final nanowires. Although ambient synthesis has been regarded as a significant condition in such chemical reactions[32], no one has yet reported on the properties of nanowires with respect to their synthesis environment. In this study, we examined the change in the nanowire morphology as a function of the fabrication conditions. This is the first report suggesting that the ambient gas should be carefully considered as one of the more important factors in the chemical synthesis of high-quality nanowires. The high-quality ZnCoO nanowires initially exhibited intrinsic paramagnetic behavior; however, following hydrogen injection, the nanowires became ferromagnetic. This finding is consistent with the hydrogen-mediation model. Additionally, this was the first observation of the superb ferromagnetism of the nanowire, compared with powders, reflecting the favored direction of the ferromagnetism along the c-axis of the nanowires.


For the fabrication of Zn0.9Co0.1O nanowires in this study, we chose the aqueous solution method, which is one of the representative chemical fabrication routes. Zinc acetate (Zn(CH3CO2)2) (2.43 mmol) and cobalt acetate (Co(CH3CO2)2) (0.27 mmol) were used as precursors, and non-polar trioctylamine (N(CH3(CH2)7)3) (25 ml) was used as the solvent; Co doping of ZnO was accomplished using 10 mol.% cobalt acetate. The precursors were rapidly heated to 310°C in an electric furnace with an inert gas atmosphere for fast thermal decomposition (Figure1). The syntheses were carried out using different ambient gases, including flowing inert Ar (99.999%), flowing air (99.999%) with a continuous oxygen supply, and closed air (99.999%) with oxygen inclusion only for the initial reaction (Table1). The gas flow rate was maintained at 25 sccm. The nanowire length was manipulated from 500 nm to 3 μm by controlling the synthesis time between 30 min and 2 h. The synthesized nanowires were cleaned in ethanol and distilled water repeatedly, followed by annealing in stages at 300°C for 10 h and 800°C for 10 h under a vacuum (10-2 Torr) to remove organic residues. For comparison, ZnCoO nanopowder[13] and ZnCoO micropowder[20] were also prepared (see the references for detailed information). Hydrogen injection was performed by plasma treatment using an Ar/H (8:2) mixed gas (99.999%), and all samples were exposed twice for 15 min to hydrogen plasma using an RF power of 80 W.
Figure 1
Figure 1

Electric furnace for the synthesis of ZnCoO nanowires.

Table 1

Controlling ambient gas by gas distinction

Sample name



Argon gas (99.999%, continuous flow)


Air gas (99.999%, continuous flow)


Air gas (99.999%, non-continuous)

The change in nanowire morphology and the secondary phase were investigated by field-emission scanning electron microscopy (FE-SEM, S-4700, Hitachi, Tokyo, Japan) and X-ray diffraction (XRD, Empyrean series2, PANalytical, Almelo, The Netherlands). Magnetic properties such as magnetization were measured using a vibrating sample magnetometer (VSM, model 6000, Quantum Design, San Diego, CA, USA) attached to a physical property measurement system.

Results and discussion

Figure2 shows the FE-SEM images of the ZnCoO nanowires synthesized using different ambient gases. Figure2a shows the FE-SEM images of the samples labeled S1, which were fabricated using ambient Ar gas. Figure2b shows the same image magnified by a factor of three. ZnCoO nanowires were produced sporadically, and the average length was 700 nm. Figure2c shows the FE-SEM images of the samples labeled S2, which were fabricated using air continuously supplied with oxygen. Figure2d shows the same image magnified by a factor of three. ZnCoO nanowires were produced sporadically, and the maximum length was approximately 2.5 μm. Figure2e shows the FE-SEM images of the samples labeled S3, which were generated using a fixed air supply with restricted oxygen content. Figure2f shows the same image magnified by 1.5. The ZnCoO nanowires were produced uniformly, and the average length was 2 μm. These results indicate that the morphology of the ZnCoO nanowires depends on the ambient gas and, in particular, on the oxygen content.
Figure 2
Figure 2

FE-SEM images of ZnCoO nanowires fabricated using different ambient gases. (a) FE-SEM image of sample S1 obtained under continuous argon gas flow and (b) a magnified image. (c) FE-SEM image of sample S2 obtained under continuous air gas flow including oxygen and (d) a magnified image. (e) FE-SEM image of sample S3 obtained under initial air gas conditions without continuous air gas flow and (f) a magnified image.

XRD confirmed that the fabricated samples (S1, S2, and S3) contained no Co-related species and that all peaks corresponded to a single ZnO phase. Figure3 shows magnetization-applied magnetic field (M-H) curves measured by the VSM at room temperature. Different ferromagnetic hysteresis shapes were observed for the three samples, even though they contained equal amounts of Co. This means that the ferromagnetism of ZnCoO nanowires is closely related to the synthesis environment. Therefore, we investigated the dependence of the ferromagnetism on the ambient gas during ZnCoO nanowire fabrication.
Figure 3
Figure 3

M-H curves of the as-grown ZnCoO nanowires. M-H characteristics of ZnCoO nanowires fabricated using different ambient gases. The M-H curves were acquired at 300 K.

Oxidation of trioctylamine solution was considered as a possible explanation for the different morphologies and properties of ZnCoO nanowires depending on ambient gases. It was expected that trioctylamine would react with oxygen at 310°C, near the boiling point, and then trioctylamine oxide would be formed via the following reaction:
2 ( C 2 H 5 ) 3 N ( g ) + O 2 ( g ) 2 ( C 2 H 5 ) 3 N + - O -
The amine oxides generated by the oxidation reaction are polar, allowing them to act as surfactants[33]. The (0001) planes of ZnCoO have relatively low surface energy because of the dangling bonds that induce surface polarity, as shown in Figure4a. The trioctylamine non-polar solution provides a favorable environment for the growth of nanowires along the c-axis, because the plane parallel to the c-axis of ZnCoO has lower surface energy and a different polarity compared with the perpendicular plane[34, 35]. In the case of S2, the oxidation reaction occurred continuously, and the amine oxides were generated in excess, as shown in Figure4b. The excessive formation of amine oxides could change the polarity of the solution from non-polar to polar and hinder the growth of the c-axis-oriented ZnCoO nanowires. However, the correct amount of amine oxides generated in sample S3, in which oxygen gas was supplied only initially, positively affected the synthesis of ZnCoO nanowires. In many studies, oleic acid, a well-known surfactant, was intentionally added during the fabrication of ZnCoO nanowires[36]. In our study, the growth of nanowires was enhanced simply by controlling the ambient gas instead of supplying additional surfactant.
Figure 4
Figure 4

Schematics illustrating the growth processes of ZnCoO nanowires and photographs of trioctylamine solution. Under (a) Ar and (b) air ambient gas. Oxidation of trioctylamine in (b) produces polar amine oxides. (c) Photographs of trioctylamine solution and the ZnCoO nanowire solutions, showing the different colors during the reaction, depending on O2 content.

Figure4c shows color changes during the reaction, as the solution turned brown after the synthesis of nanowires under each ambient gas. Generally, such browning reaction results from the oxidation of the chemical specimen. Because the color brightness is dependent on the oxygen content during the synthesis reaction, we assumed that the browning originated from the creation of the oxidized specimen in the presence of trioctylamine. The formation of an amine oxide specimen can be a contributing factor in the determination of the ZnCoO nanowire morphology. Therefore, we suppose that the variation in the synthesized ZnCoO nanowires shown in Figure2 is the result of different amine oxide contents generated under different ambient gases.

It has been reported that ZnCoO doves not exhibit intrinsic ferromagnetism, whereas our as-grown nanowires showed clear ferromagnetic hysteresis, as shown in Figure3. For more detailed analysis of the intrinsic properties of ZnCoO nanowires, vacuum annealing was performed at 800°C on S3 ZnCoO nanowires. Figure5a,b shows the FE-SEM images of the ZnCoO nanowires as grown and after the annealing treatment. The nanowires retained their shape after heat treatment at 800°C, with no noticeable change in morphology. Figure5c shows the XRD patterns of ZnCoO nanowires as grown and after annealing. All patterns correspond to those of a single ZnO phase, and no secondary phases were observed within the detection limit. The full-width at half maximum values of the peaks did not change after annealing, indicating that the size of the nanowires did not change significantly after the heat treatment.
Figure 5
Figure 5

FE-SEM image and XRD patterns of ZnCoO nanowire. FE-SEM image of ZnCoO nanowire (a) before annealing (As-grown Nanowire) and (b) after vacuum annealing process at 800°C (Nanowire at @800). (c) XRD patterns of ZnCoO nanowire before and after the thermal treatment.

Figure6a shows the M-H curves of the ZnCoO nanowires before and after heat treatment and subsequent hydrogen plasma treatment. Before heat treatment, the nanowires showed a clear ferromagnetic hysteresis, but the curves became completely paramagnetic after heat treatment at 800°C. We assumed that the ferromagnetic behavior observed in the nanowires before thermal heat treatment was attributed to (Co related-) organic residue on the surface of the nanowires synthesized via the aqueous solution method[15, 20, 37]. However, a more detailed analysis of the surface composition would require an additional investigation utilizing a surface characterization technique, such as XPS or Raman spectroscopy. It was evident that the vacuum heat treatment effectively eliminated the (Co related-) organic residue, and the pure ZnCoO nanowires without (Co related-) organic residue exhibited paramagnetic properties[20, 38, 39]. The paramagnetic behavior became ferromagnetic after hydrogen plasma treatment. The ferromagnetic hysteresis curve itself was similar to those of the as-grown nanowires, but the origin of the ferromagnetism was different. This result is also consistent with previous studies suggesting that hydrogen mediates ferromagnetism in ZnCoO by the formation of a C-H-Co complex. Figure6b shows an XRD pattern of nanowires after hydrogen treatment, where all the diffraction peaks correspond to those of a single ZnO phase with no Co secondary phases. Considering the above results, the ferromagnetism of ZnCoO nanowires grown by Yuhas et al.[26] using the same aqueous solution method was attributed to surface contamination by hydrogen compounds, such as organic residue. Therefore, it should be noted that the magnetic characteristics of the as-grown ZnCoO nanowires fabricated using the aqueous solution method are not intrinsic but are due to surface contamination.
Figure 6
Figure 6

M-H curves and XRD patterns of ZnCoO nanowire. (a) M-H curves of the as-grown nanowire without annealing (Nanowire raw), nanowire after vacuum annealing at 800°C (Nanowire @800), and nanowire after hydrogen treatment of the vacuum-annealed nanowire at 800°C (Nanowire:H), respectively. (b) XRD patterns of hydrogenated ZnCoO nanowire (Nanowire:H).

To determine the direction of the spin ordering, we compared the ferromagnetic M-H curves of the nanowires, nanopowder, and micropowder for 10 mol% Co-doped ZnO under the same hydrogen injection conditions. The nano- and micro-powder samples had diameters of 20 nm and 1 μm, respectively. The lengths of the nanowires were manipulated from 0.5 to 2 μm, while the diameter was constant at 40 nm, by varying the synthesis processing time. Figure7 shows the magnetic characteristics of the samples obtained from VSM measurements. The c-axis-oriented nanowires showed increasing magnetization with increasing nanowire length, as well as the largest remnant magnetization (MR) compared to the powder samples. The ZnCoO nanowires showed a higher squareness ratio (MR/MS) (more than 10 times compared with the other samples). It has been reported that squareness ratio is related to the magnetic domain size formed by the ferromagnetic units[13, 15, 40]. In previous studies, ferromagnetic models suggested that hydrogen was introduced by Co-H-Co complexes[5], but these reports did not fully explain how the complexes were ordered and aligned. We found that the ferromagnetism in nanowires depended on the nanowire length and was greatly enhanced compared to that of nano- and micro-powders. Such results imply that magnetic ordering in ZnCoO nanowires occurs preferentially along the c-axis due to the percolation of the Co-H-Co complex unit.
Figure 7
Figure 7

Magnetic properties depending on the different shapes and sizes of ZnCoO:H. Each ZnCoO hydrogenated at 80 W (Nanopowder:H, Micropowder:H, and Nanowire:H). Nanowire:H shows relatively higher MR and squareness ratio (MR/MS) than Nanopowder:H and Micropowder:H.


High-quality ZnCoO nanowires were obtained by the aqueous solution method. The ambient gas affected the magnetic properties of the fabricated samples, and the oxidation of trioctylamine solution played an important role. The generation of an appropriate amount of amine oxide due to a limited oxygen supply enhanced the growth of ZnCoO nanowires because the amine oxide acted as a surfactant. However, excessive oxygen inhibited the growth by changing the polarity of the solution. The as-grown ZnCoO nanowires exhibited magnetic properties, but these properties were extrinsic due to the thermal heat treatment process. Intrinsic ferromagnetism in ZnCoO nanowires was only obtained after hydrogen treatment. The room-temperature ferromagnetism of nanowires grown along the c-axis was larger than those of the nano- and micro-powders.

We suggest that the magnetic units of Co-H-Co formed in ZnCoO percolated efficiently along the c-axis. Furthermore, we expect that the nanowire structure of ZnCoO will enable further studies of magnetic anisotropy.

Authors’ information

BSK, WKK, and JHP are graduate students of the Department of Cogno-Mechatronics Engineering, Pusan National University, Republic of Korea. SL is a research professor at the Institute of Basic Science, Korea University, Republic of Korea. YCC is a research professor at the Crystal Bank Institute, Pusan National University, Republic of Korea. JK is an associate professor at the Department of Physics, University of Ulsan, Republic of Korea. CRC is an associate professor at the Department of Nano Fusion Technology, Pusan National University, Republic of Korea. SYJ, the corresponding author, is a professor at the Department of Cogno-Mechatronics Engineering, Pusan National University, Republic of Korea.



This research was supported by the Converging Research Center Program through the Ministry of Science, ICT, and Future Planning, Korea (MSIP) (2013K000310), by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIP) (No. 2011-0016525).

Authors’ Affiliations

Department of Cogno-Mechatronics Engineering, Pusan National University, 1268-50, Samnangin-ro, Samnangjin-eup, Miryang, 627-706, Republic of Korea
The Institute of Basic Science, Korea University, Seoul, 136-713, Republic of Korea
Crystal Bank Institute, Pusan National University, 1268-50, Samnangin-ro, Samnangjin-eup, Miryang, 627-706, Republic of Korea
Department of Physics, University of Ulsan, 93 Daehak-ro, Nam-gu, Ulsan, 680-749, Republic of Korea
Department of Nano Fusion Technology, Pusan National University, Samnangin-ro 1268-50, Republic of Korea


  1. Dietl T, Ohno H, Matsukura F, Cibert J, Ferrand D: Zener model description of ferromagnetism in zinc-blende magnetic semiconductors. Science 2000, 287: 1019–1022. 10.1126/science.287.5455.1019View ArticleGoogle Scholar
  2. Lee H-J, Jeong S-Y, Cho CH, Park CH: Study of diluted magnetic semiconductor: Co-doped ZnO. Appl Phys Lett 2002, 81: 4020–4022. 10.1063/1.1517405View ArticleGoogle Scholar
  3. Cao P, Bai Y: Structural and optical properties of ZnCoO thin film prepared by electrodeposition. Adv Mater Res 2013, 323: 781–784.Google Scholar
  4. Park JH, Kim MG, Jang HM, Ryu S, Kim YM: Co-metal clustering as the origin of ferromagnetism in Co-doped ZnO thin films. Appl Phys Lett 2004, 84: 1338–1340. 10.1063/1.1650915View ArticleGoogle Scholar
  5. Park CH, Chadi DJ: Hydrogen-mediated spin-spin interaction in ZnCoO. Phys Rev Lett 2005, 94: 127204.View ArticleGoogle Scholar
  6. Ney A, Opel M, Kaspar TC, Ney V, Ye S, Ollefs K, Kammermeier T, Bauer S, Nielsen K-W, Goennenwein STB, Engelhard MH, Zhou S, Potzger K, Simon J, Mader W, Heald SM, Cezar JC, Wilhelm F, Rogalev A, Gross R, Chambers SA: Advanced spectroscopic synchrotron techniques to unravel the intrinsic properties of dilute magnetic oxides: the case of Co:ZnO. New J Phys 2010, 12: 013020. 10.1088/1367-2630/12/1/013020View ArticleGoogle Scholar
  7. Coey JMD, Venkatesan M, Fitzgerald CB: Donor impurity band exchange in dilute ferromagnetic oxides. Nat Mater 2005, 4: 173–179. 10.1038/nmat1310View ArticleGoogle Scholar
  8. Belghazi Y, Schmerber G, Colis S, Rehspringer JL, Dinia A, Berrada A: Extrinsic origin of ferromagnetism in ZnO and Zn0.9Co0.1O magnetic semiconductor films prepared by sol-gel technique. Appl Phys Lett 2006, 89: 122504. 10.1063/1.2355462View ArticleGoogle Scholar
  9. Samanta K, Bhattacharya P, Katiyar RS: Optical properties of Zn 1-x Co x O thin films grown on Al2O3 (0001) substrates. Appl Phys Lett 2005, 87: 101903. 10.1063/1.2039995View ArticleGoogle Scholar
  10. Dinia A, Schmerber G, Mény C, Pierron-Bohnes V, Beaurepaire E: Room-temperature ferromagnetism in Zn 1-x Co x O magnetic semiconductors prepared by sputtering. J Appl Phys 2005, 97: 123908. 10.1063/1.1937478View ArticleGoogle Scholar
  11. Lee H-J, Park CH, Jeong S-Y, Yee K-J, Cho CR, Jung M-H, Chadi DJ: Hydrogen-induced ferromagnetism in ZnCoO. Appl Phys Lett 2006, 88: 062504. 10.1063/1.2171789View ArticleGoogle Scholar
  12. Lee H-J, Choi SH, Cho CR, Kim HK, Jeong S-Y: The formation of precipitates in the ZnCoO system. Europhys Lett 2005, 72: 76–82. 10.1209/epl/i2005-10191-2View ArticleGoogle Scholar
  13. Lee S, Cho YC, Kim S-J, Cho CR, Jeong S-Y, Kim SJ, Kim JP, Choi YN, Sur JM: Reproducible manipulation of spin ordering in ZnCoO nanocrystals by hydrogen mediation. Appl Phys Lett 2009, 94: 212507. 10.1063/1.3136845View ArticleGoogle Scholar
  14. Kim SJ, Cha SY, Kim JY, Shin JM, Cho YC, Lee S, Kim W-K, Jeong S-Y, Yang YS, Cho CR, Choi HW, Jung MH, Jun B-E, Kwon K-Y, Kuroiwa Y, Moriyoshi C: Ferromagnetism in ZnCoO due to hydrogen-mediated Co–H–Co complexes: how to avoid the formation of Co metal clusters? J Phys Chem C 2012, 116: 12196–12202. 10.1021/jp300536wView ArticleGoogle Scholar
  15. Lee S, Kim B-S, Cho YC, Shin J-M, Seo S-W, Cho CR, Takeuchi I, Jeong S-Y: Origin of the ferromagnetism in ZnCoO from chemical reaction of Co3O4. Curr Appl Phys 2013, 13: 2005–2009. 10.1016/j.cap.2013.08.014View ArticleGoogle Scholar
  16. Cho YC, Kim S-J, Lee S, Kim SJ, Cho CR, Nahm H-H, Park CH, Jeong IK, Park S, Hong TE, Kuroda S, Jeong S-Y: Reversible ferromagnetism spin ordering governed by hydrogen in Co-doped ZnO semiconductor. Appl Phys Lett 2009, 95: 172514. 10.1063/1.3257733View ArticleGoogle Scholar
  17. Cho YC, Lee S, Nahm HH, Kim SJ, Park CH, Lee SY, Kim S-K, Cho CR, Koinuma H, Jeong S-Y: Conductive and ferromagnetic contributions of H in ZnCoO using H2 hot isostatic pressure. Appl Phys Lett 2012, 100: 112403. 10.1063/1.3694040View ArticleGoogle Scholar
  18. Li L, Guo Y, Cui XY, Zheng R, Ohtani K, Kong C, Ceguerra AV, Moody MP, Ye JD, Tan HH, Jagadish C, Liu H, Stampfl C, Ohno H, Ringer SP, Matsukura F: Magnetism of Co-doped ZnO epitaxially grown on a ZnO substrate. Phys Rev B 2012, 85: 174430.View ArticleGoogle Scholar
  19. Kim SJ, Lee S, Cho YC, Choi YN, Park S, Jeong IK, Kuroiwa Y, Moriyoshi C, Jeong S-Y: Direct observation of deuterium in ferromagnetic Zn0.9Co0.1O:D. Phys Rev B 2010, 81: 212408.View ArticleGoogle Scholar
  20. Lee S, Kim B-S, Seo S-W, Cho YC, Kim SK, Kim JP, Jeong I-K, Cho CR, Jung CU, Koinuma H, Jeong S-Y: A study of the correlation between hydrogen content and magnetism in ZnCoO. J Appl Phys 2012, 111: 07C304.Google Scholar
  21. Shin JM, Lee HS, Cha SY, Lee S, Kim JY, Park N, Cho YC, Kim SJ, Kim S-K, Bae J-S, Park S, Cho CR, Koinuma H, Jeong S-Y: Strong ferromagnetism in Pt-coated ZnCoO: the role of interstitial hydrogen. Appl Phys Lett 2012, 100: 172409. 10.1063/1.4705304View ArticleGoogle Scholar
  22. Chen I-J, Ou Y-C, Wu Z-Y, Chen F-R, Kai J-J, Lin J-J, Jian W-B: Size effect on thermal treatments and room-temperature ferromagnetism in high-vacuum annealed ZnCoO nanowire. J Phys Chem C 2008, 112: 9168–9171. 10.1021/jp711775rView ArticleGoogle Scholar
  23. Yao T, Yan W, Sun Z, Pan Z, Xie Y, Jiang Y, Ye J, Hu F, Wei S: Magnetic property and spatial occupation of Co dopants in Zn0.98Co0.02O nanowire. J Phys Chem C 2009, 113: 14114–14118. 10.1021/jp902685kView ArticleGoogle Scholar
  24. Liang W, Yuhas BD, Yang P: Magnetotransport in Co-doped ZnO nanowires. Nano Lett 2009, 9: 892–896. 10.1021/nl8038184View ArticleGoogle Scholar
  25. Zhang S, Pelligra CI, Keskar G, Jiang J, Majewski PW, Taylor AD, Ismail-Beigi S, Pfefferle LD, Osuji CO: Directed self-assembly of hybrid oxide/polymer core/shell nanowires with transport optimized morphology for photovoltaics. Adv Mater 2012, 24: 82–87. 10.1002/adma.201103708View ArticleGoogle Scholar
  26. Yuhas BD, Zitoun DO, Pauzauskie PJ, He R, Yang P: Transition-metal doped zinc oxide nanowire. Angew Chem Int Ed 2006, 45: 420–423. 10.1002/anie.200503172View ArticleGoogle Scholar
  27. Greene LE, Yuhas BD, Law M, Zitoun D, Yang P: Solution-grown zinc oxide nanowires. Inorg Chem 2006, 45: 7535–7543. 10.1021/ic0601900View ArticleGoogle Scholar
  28. Paraguay DF, Estrada LW, Acosta NDR, Andrade E, Miki-Yoshida M: Growth, structure and optical characterization of high-quality ZnO thin films obtained by spray pyrolysis. Thin Solid Films 1999, 350: 192–202. 10.1016/S0040-6090(99)00050-4View ArticleGoogle Scholar
  29. Yin M, Gu Y, Kuskovsky IL, Andelman T, Zhu Y, Neumark GF, O´Brien S: Zinc oxide quantum rods. J Am Chem Soc 2004, 126: 6206–6207. 10.1021/ja031696+View ArticleGoogle Scholar
  30. Lin C-C, Li Y-Y: Synthesis of ZnO nanowires by thermal decomposition of zinc acetate dehydrate. Mater Chem Phys 2009, 113: 334–337. 10.1016/j.matchemphys.2008.07.070View ArticleGoogle Scholar
  31. Inamdar DY, Lad AD, Pathak AK, Dubenko I, Ali N, Mahamuni S: Ferromagnetism in ZnO nanocrystals: doping and surface chemistry. J Phys Chem C 2010, 114: 1451–1459. 10.1021/jp909053fView ArticleGoogle Scholar
  32. Zhang YF, Tang YH, Peng HY, Wang N, Lee CS, Bello I, Lee ST: Diameter modification of silicon nanowires by ambient gas. Appl Phys Lett 1999, 75: 1842–1844. 10.1063/1.124846View ArticleGoogle Scholar
  33. Rosen MJ: Surfactants and interfacial phenomena. In Characteristic Features and Uses of Commercially Available Surfactants. Edited by: Rosen MJ. Hoboken: Wiley; 2004:16–20.Google Scholar
  34. Zhou X, Xie Z-X, Jiang Z-Y, Kuang Q, Zhang S-H, Xu T, Huang R-B, Zheng L-S: Formation or ZnO hexagonal micro-pyramids: a successful control of the exposed polar surfaces with the assistance of an ionic liquid. Chem Commun 2005, 2005(44):5572–5574.View ArticleGoogle Scholar
  35. Sugunan A, Warad HC, Boman M, Dutta J: Zinc oxide nanowires in chemical bath on seeded substrates: role of hexamine. J Sol-Gel Sci Techn 2006, 39: 49–56. 10.1007/s10971-006-6969-yView ArticleGoogle Scholar
  36. Goris L, Noriega R, Donovan M, Jokisaari J, Kusinski G, Salleo A: Intrinsic and doped zinc oxide nanowires for transparent electrode fabrication via low-temperature solution synthesis. J Electro Mater 2009, 38: 586–595. 10.1007/s11664-008-0618-xView ArticleGoogle Scholar
  37. Li S, Bi H, Cui B, Zhang F, Du Y, Jiang X, Yang C, Yu Q, Zhu Y: Anomalous magnetic properties in Co3O4 nanoparticles covered with polymer decomposition residues. J Appl Phys 2004, 95: 7420–7422. 10.1063/1.1688218View ArticleGoogle Scholar
  38. Zhang S, Pelligra CI, Keskar G, Majewski PW, Ren F, Pfefferle LD, Osuji CO: Liquid crystalline order and magnetocrystalline anisotropy in magnetically doped semiconducting ZnO nanowires. ACS Nano 2011, 5: 8357–8364. 10.1021/nn203070dView ArticleGoogle Scholar
  39. Pelligra CI, Majewski PW, Osuji CO: Large area vertical alignment of ZnO nanowires in semiconducting polymer thin films directed by magnetic fields. Nanoscale 2013, 5: 10511–10517. 10.1039/c3nr03119eView ArticleGoogle Scholar
  40. Singhal RK, Dhawan MS, Gaur SK, Dolia SN, Kumar S, Shripathi T, Deshpande UP, Xing YT, Saitovitch E, Garg KB: Room-temperature ferromagnetism in Mn-doped dilute ZnO semiconductor: an electronic structure study using X-ray photoemission. J Alloys Compd 2009, 477: 379–385. 10.1016/j.jallcom.2008.10.005View ArticleGoogle Scholar