Silver particulate films have been prepared by exposing aqueous silver nitrate solutions, coated by monolayers and contained in a Lauda film balance, to formaldehyde (HCHO). Monolayers, prepared from dihexadecyl phosphate (1), dioctadecyldimethylammonium bromide (2), n-C16H33C(H)[CON(H)(CH2)2NH 2]2 (3), and (C18H37)2N+(CH2CH 2SH)2Br- (4), have been characterized by surface pressure vs surface area and surface potential vs surface area isotherms. Silver particulate film formation was found to be influenced by the concentration of AgNO3, the time of exposure to formaldehyde, the type of monolayer used, the pH of the subphase, and the presence of ammonia or CuCl2 in the subphase. Under similar conditions, the rate of silver particle growth under monolayers increased in the order 2 < 4 < 1 < 3. Silver particulate films, formed under monolayers, were quantitatively transferred to solid substrates (by horizontal lifting) and characterized thereon by absorption spectroscopy, optical microscopy, X-ray diffraction, and electrical measurements prior and subsequent to annealing them at 300°C. Silver particulate films remained stable for weeks under the monolayers and for months subsequent to their transfer onto substrates. Analyzing the optical microscopic images of silver clusters, grown under monolayers prepared from 1 and 3 (and subsequently transferred to quartz slides), led to fractal dimensions of 1.51 ± 0.13 and 1.68 ± 0.25, respectively, in the relatively short-range scale, indicating a crossover to nonfractal structures during growth. Increasing the time of HCHO exposure shifted the absorption band of silver particles, grown under monolayers prepared from 1, from 270 to 440 nm, signifying the transition of the initially formed small nonmetallic clusters to larger metallic aggregates. Particles grown under monolayers prepared from 3 developed a narrow apparent absorption minimum at 321 nm (interband transition) upon prolonged exposure to HCHO, signaling the presence of rough silver surfaces with large surface-to-volume ratios. The resistivity of relatively thick silver particulate films, generated by the HCHO exposure of an aqueous 5 × 10-2 M AgNO3 solution (coated by a monolayer prepared from 3), was determined to be 1.59 × 10-6 Ω cm on solid substrates.
|Number of pages||10|
|Journal||Journal of physical chemistry|
|Publication status||Published - Dec 1 1994|
ASJC Scopus subject areas
- Physical and Theoretical Chemistry