pubs.acs.org/Langmuir © 2010 American Chemical Society
An Approach to Fabrication of Metal Nanoring Arrays Maryam Bayati,† Piotr Patoka,† Michael Giersig,‡ and Elena R. Savinova*,† †
Laboratoire des Mat eriaux, Surfaces et Proc edes pour la Catalyse, UMR 7515 CNRS-UdS-ECPM, Universit e de Strasbourg, 67087, Strasbourg, France, and ‡Helmholtz Zentrum Berlin f€ ur Materialien und Energie GmbH, D-14109 Berlin, Germany Received January 7, 2009. Revised Manuscript Received January 10, 2010 Fabrication of tailored nanomaterials with desired structure and properties is the greatest challenge of modern nanotechnology. Herein, we describe a wet chemical method for the preparation of large area metal nanoring arrays. This method is based on self-assembly of polystyrene sphere template on a flat substrate and wicking/reducing metal precursor into the interstices between the template and the substrate. In this article, platinum, gold, and copper nanorings were fabricated by applying 505 nm polystyrene spheres onto highly oriented pyrolytic graphite (HOPG) and Si(100) substrates, followed by reducing the templated metal salt with NaBH4. AFM images reveal formation of arrays of metal nanorings comprising metal nanoparticles with the average ring height of 5.7 ( 0.8 nm and diameter of 167.3 ( 8.9 nm. XPS confirms that these structures are metallic.
Introduction Recently, size- and shape-dependent properties of nanomaterials have been the subject of intensive research. It is now wellestablished that magnetic,1 optical,2,3 electrocatalytic,4,5 optoelectronic,6 and data storage7 are properties influenced by the shape, size, and interfeature spacing. Hence, fabrication of nanodevices for different applications requires development of building blocks with a wide variety of controlled sizes and shapes. Interest in nanomaterials promoted the development of simple, inexpensive, and robust methods for their preparation. A variety of fabrication techniques have been employed including a wide range of lithography methods.8-13 Among these, template-based methods have become increasingly important due to the suitability to produce nanomaterials of different shapes and structures in two and three dimensions (2D and 3D) and their compatibility with the increasing application demands. Nanoring structures offer high potential for applications in microelectronics, optoelectronics, magnetic storage, and sensors *Corresponding author. E-mail:
[email protected]. Tel: þþ33(0)3 68 85 27 39. (1) Zhu, F. Q.; Fan, D.; Zhu, X.; Zhu, J. G.; Cammarata, R. C.; Chien, C. L. Adv. Mater. 2004, 16, 2155–2159. (2) Aizpurua, J.; Hanarp, P.; Sutherland, D. S.; K€all, M.; Bryant, G. W.; Garcia de Abajo, F. J. Phys. Rev. Lett. 2003, 90, 057401. (3) Larsson, E. M.; Alegret, J.; K€all, M.; Sutherland, D. S. Nano Lett. 2007, 7, 1256–1263. (4) Narayanan, R.; El-Sayed, M. A. Nano Lett. 2004, 4, 1343–1348. (5) Bratlie, K. M.; Lee, H.; Komvopoulos, K.; Yang, P.; Somorjai, G. A. Nano Lett. 2007, 7, 3097–3101. (6) Chovin, A; Garrigue, P.; Manek-H€onninger, I.; Sojic, N. Nano Lett. 2004, 4, 1965–1968. (7) Ma, X. Nanotechnology 2008, 19, 275706. (8) Sun, Y.; Xia, Y. Adv. Mater. 2003, 15, 695–699. (9) Sun, Y.; Gates, B.; Mayers, B.; Xia, Y. Nano Lett. 2002, 2, 165–168. (10) Gao, J.; Bender, C. M.; Murphy, C. J. Langmuir 2003, 19, 9065–9070. (11) Busbee, B. D.; Obare, S. O.; Murphy, C. J. Adv. Mater. 2003, 15, 414–416. (12) Rybczynski, J.; Ebels, U.; Giersig, M. Colloids Surf., A 2003, 219, 1–6. (13) Chai, J.; Wang, D.; Fan, X.; Buriak, J. M. Nat. Nanotechnol. 2007, 2, 500–506. (14) Peng, X.; Kamiya, I. Nanotechnology 2008, 19, 315303. (15) Burda, C.; Chen, X.; Narayanan, R.; El-Sayed, M. A. Chem. Rev. 2005, 105, 1025–1102. (16) Rothman, J.; Kl€aui, M.; Lopez-Diaz, L.; Vaz, C. A. F.; Bleloch, A.; Bland, J. A. C.; Cui, Z.; Speaks, R. Phys. Rev. Lett. 2001, 86, 1098. (17) Li, S. P.; Peyrade, D.; Natali, M.; Lebib, A.; Chen, Y.; Ebels, U.; Buda, L. D.; Ounadjela, K. Phys. Rev. Lett. 2001, 86, 1102.
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due to their novel physical and chemical properties2,14-17 and have thus attracted great interest from a broad range of scientific and industrial communities. To this end, various methods for nanoring fabrication have been employed, which include electron-beam lithography,16 molecular-beam epitaxy,18 chemical modification,19 shadow nanosphere lithography,20 porous polymer membrane templating,21 structured template techniques,22-25 and colloidal (or nanosphere)2 and capillary lithography.13,26-29 Among these methods, colloidal lithography in combination with capillary lithography offers a low-cost and relatively simple means for fabrication of large area nanofeature arrays.26,28 It has been shown that this combinational method can be used to prepare polymer and semiconductor nanorings.26,28 Herein, we report a new large-scale wet chemical method of preparing metal nanoring arrays on flat substrates and apply it for preparing gold, platinum, and copper nanostructures on HOPG and Si(100) surfaces. Pt and gold nanorings are of interest due to their catalytic and optical properties, respectively.31,2 It has been reported that gold nanorings possess unique optical properties because of the local surface plasmon resonance. (18) Warburton, R. J.; Schaeflein, C.; Haft, D.; Bickel, F.; Lorke, A.; Karrai, K.; Garcia, J. M.; Schoenfeld, W.; Petroff, P. M. Nature 2000, 405, 926–929. (19) Li, F.; Dong, Y.; Gao, P.; Xin, X.; Wang, Z. Angew. Chem., Int. Ed. 2004, 43, 5238–5242. (20) Kosiorek, A.; Kandulski, W.; Glaczynska, H.; Giersig, M. Small 2005, 1, 439–444. (21) Yan, F.; Goedel, W. A. Nano Lett. 2004, 4, 1193–1196. (22) Hobbs, K. L.; Larson, P. R.; Lian, G. D.; Keay, J. C.; Johnson, M. B. Nano Lett. 2004, 4, 167–171. (23) Pearson, D. H.; Tonucci, R. J.; Bussmann, K. M.; Bolden, E. A. Adv. Mater. 1999, 11, 769–773. (24) Voigtl€ander, B.; Kawamura, M.; Paul, N.; Cherepanov, V. Thin Solid Films 2004, 464-465, 185–189. (25) Wang, Y.; Han, S.; Briseno, A. L.; Sanedrin, R. J. G.; Zhou, F. J. Mater. Chem. 2004, 14, 3488–3494. (26) Chen, X.; Chen, Z.; Fu, N.; Lu, G.; Yang, B. Adv. Mater. 2003, 15, 1413– 1417. (27) Lee, S. Y.; Jeong, J. R.; Kim, S. H.; Kim, S.; Yang, S. M. Langmuir 2009, 25, 12535–12540. (28) Chen, J.; Liao, W. S.; Chen, X.; Yang, T.; Wark, S. E.; Son, D. H.; Batteas, J. D.; Cremer, P. S. ACS Nano 2009, 3, 173–180. (29) Suh, K. Y.; Park, M. C.; Kim, P. Adv. Funct. Mater. 2009, 19, 2699–2712. (30) Trau, M.; Yao, N.; Kim, E.; Xia, Y. N.; Whiteside, G. M.; Aksay, I. A. Nature 1997, 390, 674–676. (31) Abdelsalam, M. E.; Mahajan, M.; Bartlett, P. N.; Baumberg, J. J.; Russell, A. E. J. Am. Chem. Soc. 2007, 129, 7399–7406.
Published on Web 01/28/2010
DOI: 10.1021/la904287t
3549
Article
Bayati et al.
The method is a combination of template and capillary nanofabrication means and is based on infiltration of the reactant/patterning materials into the interstices between a mold and a substrate through capillary suction. To our knowledge, this methodology was first applied by Trau et al.30 for preparing nanochannels. Chen et al.26 applied similar methodology and demonstrated preparation of nonmetal nanoring arrays of poly(vinyl alcohol) and titanium oxide nanopatterned films by wicking structural material around microspheres and heat treating the pattern. Recently, Motavas et al.32 utilized a similar approach for fabrication of carbon nanoring arrays of carbon nanotubes on silicon wafers. A similar method has recently been employed for tailoring the cell-material interface.29 The purpose of this work is to explore the potential of templating and capillary nanofabrication methodology for preparing metal nanorings and define major factors influencing the shape and the quality of the nanostructures. The influence of the type of substrate (HOPG or Si(100)), the metal precursor (Pt, Au, or Cu complexes), and the incubation time is examined. In addition, we demonstrate the effect of the metal precursorsubstrate interaction on the resulting structure.
Experimental Section Unless otherwise stated, all experiments were performed under ambient conditions. Sulfuric acid (Aldrich, 99.999%), potassium tetrachloroplatinate (Aldrich, 99.9þ%), sodium borohydride (Sigma-Aldrich, >98.5%), copper sulfate pentahydrate (SigmaAldrich, 99.995%), sodium tetrachloroaurate dihydrate (Alfa Aesar, >99.99%), chloroform (Riedel-de Ha€en, Puriss), and ethanol (Carlo Erba, absolute) were used as received. All aqueous solutions were prepared with ultrapure water (18 MΩ 3 cm, 1-3 ppb TOC, from ELGA LabWater Purelab Ultra). HOPG plates were purchased from Momentive Performance, Ohio, USA. Silicon (100) wafers of 4 in diameter and (0.5° miscut were purchased from SILTRONIX. Polystyrene (PS) spheres with an average diameter of 505 nm (10% aqueous suspension, size uniformity e3%) were received from Duke Scientific Corporation, California, USA. These PS spheres contain surface sulfate groups, which are derived from the initiators used in the synthesis of the particles and thus bear small negative charge. Substrate Cleaning Procedures. Silicon wafer was diced into small pieces by a diamond blade. The pieces were degreased in an ethanol ultrasonic bath for 10 min and dried under nitrogen flow. The samples were rinsed with water thoroughly and dried in nitrogen before the experiments. HOPG pieces were cleaved with an adhesive tape. Both substrates were transferred and kept under water for 5 min before sinking into the PS mask container. PS Mask Preparation. Since floating PS spheres on waterair interface are very sensitive to the surface tension, the preparation container must be properly cleaned and kept away from any chemicals which may affect the surface tension at the water/air interface. The dispersion of PS beads was prepared by adding 0.15 μL sulfuric acid to a solution containing 0.5% styrene, 49.5% PS (as received 10% aqueous dispersion), and 50 vol % ethanol. The mixture was ultrasonicated for 15 min to ensure the homogeneity of dispersion. It was gently applied to the water/air interface in the center of the container using a glass pipet. To enable formation of large self-organized two-dimensionally ordered domains of PS particles at the interface, gentle waves were created by slowly tilting the vessel. Finally, PS spheres were applied to the substrates by placing the latter under the PS monolayer and slowly evaporating water.33 (32) Motavas, S.; Omrane, B.; Papadopoulos, C. Langmuir 2009, 25, 4655–4658. (33) Ctistis, G.; Patoka, P.; Wang, X.; Kempa, K.; Giersig., M. Nano Lett. 2007, 7, 2926–2930.
3550 DOI: 10.1021/la904287t
Figure 1. AFM image of the PS array on HOPG (A) and Si(100) (B).
Metal Deposition on Substrates. After drying the mask in air, 300 μL of 10 mM metal salt was cast on PS patterned substrate of about 1 1 cm2 and allowed to remain for 2 to 4 h. The sample was subsequently rinsed and sunk in ultrapure water for 1 min (if not otherwise stated) and exposed to 300 μL of 1 mM NaBH4. Finally, the sample was rinsed thoroughly with ultrapure water to terminate the reduction and dried under the nitrogen stream. The PS mask removal was achieved by rinsing the samples with chloroform. Surface Characterization. AFM images were obtained at room temperature in a noncontact mode with a Nanoscope IIIa scanning probe microscope from Digital Instruments with silicon tip (spring constant 42 N/m, resonance frequency 320 kHz). The nanoparticle height was calculated by averaging at least 100 particles. The diameter of nanorings was measured between the highest points on the circumference. The mean value was obtained by averaging 50 rings with at least three measurements per ring. X-ray photoelectron spectroscopy (XPS) characterization of the samples was performed with Thermo VG Scientific Multilab 2000 spectrometer (UK, England) using Al KR radiation (1486.6 eV) at a base pressure of
