Journal of Physical Chemistry, Vol.100, No.12, 4954-4960, 1996
Structural Characteristics of Ag Colloid-Adsorbate Films Determined from Transmission Electron-Microscopic Images - Fractal Dimensions, Particle-Size and Spacing Distributions, and Their Relationship to Formation and Optical-Responses of the Films
Ag colloid-adsorbate films (similar in appearance to MELLFs) containing 2,2’-bipyridine (bpy), 2,2’,6,6’-bipyrimidine (bpm), 2,3,5,6-tetrakis(2’-pyridyl)pyrazine (tppz), 5,10,15,20-tetrakis(4’-pyridyl)porphine (TPyP), and 5,10,15,20-tetraphenylporphine (TPP) adsorbates, respectively, were prepared at the interface between the aqueous Ag colloid and the solution of adsorbate in dichloromethane, deposited on carbon-coated copper grids and imaged by transmission electron microscopy (TEM). The films are mostly two-dimensional (monolayer) structures providing good quality TEM images suitable for image analysis. Fractal dimensions (D), Ag colloidal particle-size distributions, and relative particle-spacing distributions of the films were analyzed. Both the fractal (D = 1.23 for Ag-TPP) and nonfractal (D = 1.97 for Ag-TPyP and D = 1.93 for Ag-tppz) film structures were observed. Fractality of the Ag colloid-adsorbate films appears to be a function of the hydrophobic/hydrophilic character of the adsorbates. Further on, preparation and TEM imaging of nonfractal, monolayer metal-adsorbate films (such as Ag-TPyP an Ag-tppz) are proposed as new suitable techniques for particle-size distribution analysis of metal colloids. Furthermore, all the films investigated prove themselves to be SERS-active. In particular, a SERS spectrum of the seal TEM microscopic sample of Ag-bpm film deposited on carbon-coated copper grid is reported and analyzed.