Langmuir 2000, 16, 9963-9967
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Surface-Induced Photoreaction of Benzyl Phenyl Sulfide Monolayers on Silver and Its Application to Preparing Patterned Binary Monolayers Inhyung Lee, Sang Woo Han, Chang Hwan Kim, Taeg Gyum Kim, Sang Woo Joo, Du-Jeon Jang, and Kwan Kim* School of Chemistry and Molecular Engineering and Center for Molecular Catalysis, Seoul National University, Seoul 151-742, Korea Received September 8, 2000. In Final Form: November 1, 2000 Benzyl phenyl sulfide (BPS, C6H5CH2-S-C6H5) is readily converted on silver to benzenethiolate by irradiation with visible light. By using this knowledge and invoking the fact that BPS is easily replaced by carboxylic acids, we have demonstrated by surface-enhanced Raman scattering that patterned binary monolayers can be prepared on silver using the self-assembled monolayers of BPS as a lithographic template. Although the example shown in this work, that is, binary monolayers composed of benzenethiolate and 4-cyanobenzoate, is rather preliminary and quite limited in scope, its application prospects are thought to be very good. Because surface-induced photoreaction of aromatic sulfides including BPS can occur even on gold induced by UV radiation, the present method is expected to be applicable to forming patterns and structures with a wide variety of materials on silver and gold with features that range from nanometers to micrometers in size.
1. Introduction In our earlier surface-enhanced Raman scattering (SERS) study, aromatic sulfides adsorbed on the surfaces of colloidal silver sol were found to undergo surface reactions involving facile cleavage of C-S bonds by 514.5nm radiation;1,2 such a reaction was found to hardly occur for alkyl sulfides such as dimethyl sulfide and diethyl sulfide adsorbed on a colloidal silver surface.3 Benzyl phenyl sulfide (BPS) was exclusively decomposed into benzenethiolate on the silver surface, whereas dibenzyl sulfide (DBS) was converted into benzyl mercaptide by 514.5-nm radiation. These molecules were recently found not to undergo such reactions on a gold surface with visible light. The reaction does occur on gold with UV light, however.4 Microfabrication is essential for much of modern science and technology.5 The patterning required in microfabrication is usually carried out with photolithography. In the past decade, a number of nonphotolithographic techniques have also been demonstrated for fabricating high-quality microstructures and nanostructures.6-8 In particular, self-assembled monolayers (SAMs) have been developed as ultrathin resisting or passivating layers for fabrication of patterns and structures with lateral dimensions in the nanometer-to-micrometer range.6,9 Patterning of SAMs has been accomplished using X-rays,10 high * To whom all correspondence should be addressed. Tel: +822-8806651. Fax: +82-2-8743704. E-mail:
[email protected]. (1) Joo, T. H.; Yim, Y. H.; Kim, K.; Kim, M. S. J. Phys. Chem. 1989, 93, 1422. (2) Yim, Y. H.; Kim, K.; Kim, M. S. J. Phys. Chem. 1990, 94, 2552. (3) Joo, T. H.; Kim, K.; Kim, M. S. J. Mol. Struct. 1987, 162, 191. (4) Joo, S. W.; Han, S. W.; Kim, K. Appl. Spectrosc. 2000, 54, 378. (5) Xia, Y.; Whitesides, G. M. Angew. Chem., Int. Ed. Engl. 1998, 37, 550. (6) Kumar, A.; Biebuyck, H. A.; Whitesides, G. M. Langmuir 1994, 10, 1498. (7) James, C. D.; Davis, R. C.; Kam, L.; Craighead, H. C.; Isaacson, M.; Turner, J. N.; Shain, W. Langmuir 1998, 14, 741. (8) Piner, R. D.; Zhu, J.; Xu, F.; Hong, S.; Mirkin, C. A. Science 1999, 283, 661. (9) Kumar, A.; Whitesides, G. M. Appl. Phys. Lett. 1993, 63, 2002. (10) Brandow, S. L.; Chen, M. S.; Dulcey, C. S.; Calvert, J. M.; Dressick, W. J. Langmuir 1999, 15, 5429.
energy e-beams,11 atomic force microscopy (AFM),12 conductive tip AFM,13 scanning tunneling microscopy (STM),14 and microcontact printing (µCP).6,9 It has been reported that coplanar arrays can be fabricated with organosilanes15,16 and alkanethiol SAMs17 via UV photoreactions. Herein, we hope to report that the SAMs of BPS on silver can also be used as a template for fabrication of patterned surfaces. The strategy is the combined use of a photoinduced surface reaction and the exchange of adsorbates by self-assembly. That is, as drawn in Scheme 1, irradiation of an argon ion laser (514.5 nm) onto a selected region of BPS SAMs on silver should lead to the formation of benzenethiolate monolayers. The unilluminated sulfides are thereafter replaced with thiols or carboxylic acids. Because a surface-induced photoreaction of BPS can occur even on gold by UV irradiation, the present method is expected to be applicable to forming patterns and structures with a wide variety of materials on gold and silver with features that range from nanometers to micrometers in size. 2. Experimental Section BPS and 4-cyanobenzoic acid (4-CBA) were purchased from Aldrich and used as received. AgNO3 and KAuCl4 used for preparing silver and gold nanoparticles were also purchased from Aldrich. High-purity silver plate was obtained from Aldrich (0.05 mm thick, 99.9%). Unless specified, organic solvents used were all reagent grade, and triply distilled water (resistivity greater than 18.0 MΩ cm) was used when preparing aqueous solutions. (11) Lercel, M. S.; Craighead, H. G.; Parikh, A. N.; Seshadri, K.; Allara, D. L. Appl. Phys. Lett. 1996, 68, 1504. (12) Kumar, A.; Biebuyck, W.; Abbott, N. L.; Whitesides, G. M. J. Am. Chem. Soc. 1992, 114, 9188. (13) Brandow, S. L.; Calvert, J. M. J. Vac. Sci. Technol., A 1997, 15, 1455. (14) Perkins, F. K.; Dobisz, E. A.; Brandow, S. L.; Calvert, J. M.; Kosakowsk, J. E.; Marrian, C. R. K. Appl. Phys. Lett. 1996, 68, 550. (15) Dulcey, C. S.; Georger, J. H.; Krauthamer, V.; Stenger, D. A.; Fare, T. L.; Calvert, F. J. Science 1991, 252, 551. (16) Stenger, D. A.; Georger, J. H.; Dulcey, C. S.; Hickman, J. J.; Rudolph, A. S.; Nielsen, T. B.; McCort, S. M.; Calvert, J. M. J. Am. Chem. Soc. 1992, 114, 8435. (17) Tarlov, M. J.; Burgess, D. R. F.; Gillen, G. J. Am. Chem. Soc. 1993, 115, 5305.
10.1021/la001293c CCC: $19.00 © 2000 American Chemical Society Published on Web 11/30/2000
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Langmuir, Vol. 16, No. 26, 2000
Letters
Scheme 1 . Flowchart Showing the Strategy for Preparing Patterned Binary Monolayers on a Silver Substrate
The method of preparation of gold and silver nanoparticles suspended in water was reported previously.4 To 0.1-1 mL of Ag or Au sol solution, a 10-3 M aqueous solution of BPS was added dropwise to a final concentration of 10-5 M with a micropipet. The SERS active Ag plate was prepared by immersion in diluted (1:1) HNO3. The experimental procedure for the preparation of the patterned binary monolayers is presented in Scheme 1. SER spectra were obtained using a Renishaw Raman system model 2000 spectrometer equipped with an integral microscope (Olympus BH2-UMA). The 514.5-nm radiation from a 20-mW air-cooled Ar ion laser (Spectra Physics model 163-C4210) was used as the excitation source. Raman scattering was detected with 180° geometry using a Peltier cooled (-70 °C) charge-coupled device (CCD) camera (400 × 600 pixels). The Raman spectrometer was interfaced with an IBM-compatible PC, and the spectral data were analyzed using Renishaw WiRE software, version 1.2, based on the GRAMS/32C suite program (Galactic). Raman images were recorded with a narrow-band multiplier dielectric filter with a 20-cm-1 band-pass. When the Raman images were taken, the laser beam was defocused to illuminate the area from which the image was required.18 Raman mapping was performed with
