Patterning porous matrices and planar substrates with quantum dots
Silica hydrogels and planar substrates were patterned with CdS nanoparticles using a photolithographic method based on the photo dissociation of thiols and cadmium-thiolate complexes. Silica hydrogels were prepared via a standard base-catalyzed route. The solvent was exchanged with an aqueous solution of CdSO4 and 2-mercaptoethanol, and the samples were then exposed to a focused ultraviolet beam. Planar substrates were patterned by illuminating a precursor solution spin coated on the substrates. CdS nanoparticles formed in the illuminated spots, and had a diameter below about 2 nm. The diameter of the spots illuminated by the UV beam could be varied from a few hundred to a few μm, on both hydrogels and planar substrates. Samples were characterized with transmission electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and optical absorption, photoluminescence and Raman spectroscopies. All these techniques confirmed the chemical identity of the CdS nanoparticles. To investigate the mechanism of nanoparticle formation, we took absorption spectra of the precursor solution as a function of irradiation time. In unirradiated solutions, we noticed a maximum at 250 nm, characteristic of Cd-thiolate complexes. The absorption at 250 nm decreased with increasing irradiation time. A new band appeared at 265 nm for exposures around 5 min, and that band shifted to 290 nm in samples exposed for 10 min. A yellow precipitate formed after about 30 min. XRD showed that the precipitate was cubic CdS, with a mean particle size of 1.4 nm. We attribute formation of CdS to the photodissociation of the thiols and of the Cd-thiolates. UV irradiation of these precursors yields a series of species that can react with Cd2+, such as RS·, S2− and H2S. Small CdS nanoparticles form in the initial stages of illumination, and present absorption bands in the 265–290 nm region. These CdS aggregates grow, coalesce and precipitate for longer irradiation times.
KeywordsQuantum dots Photolithography Nanocomposites Aerogels
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- 1.For example: Evident Technologies, 216 River Street, Suite 200, Troy, New York 12180; Quantum Dot Corp. 26118 Research Road Hayward, CA 94545Google Scholar
- 4.Tohge N, Asuka M, Minami T (1990) SPIE 1328:125Google Scholar
- 10.Knight AR (1974) In: Patai S (ed) The chemistry of the thiol group, Part 1. John Wiley & Sons Ltd., London, Chapter 10Google Scholar
- 11.De Brabander HF, Van Poucke LC (1974) J Coord Chem 3:301; Said FF, Tuck DG (1982) Inorg Chem Acta 59:1Google Scholar
- 18.Hasegawa Y, Afzaal M, O’Brien P, Wada Y, Yanagida S (2005) Chem Commun 242–243Google Scholar
- 34.Kitaev GA, Uritskaya AA, Mokrushin SG (1965) Zhurnal Fizicheskoi Khimii 38:2065Google Scholar
- 35.Bertino MF, Gadipalli RR, Martin LA, Heckman B, Story JG, Leventis N, Fraundorf P, Guha S, to be submitted to J Sol-Gel Sci Technol, in pressGoogle Scholar