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) containin g 2,2'-bipyridine (bpy), 2,2',6,6'-bipyrimidine (bpm), 2,3,5,6-tetraki s(2'-pyridyl)pyrazine (tppz), 5,10,15,20-tetrakis(4'-pyridyl)porphine (TPyP), and 5,10,15,20-tetraphenylporphine (TPP) adsorbates, respectiv ely, were prepared at the interface between the aqueous Ag colloid and the solution of adsorbate in dichloromethane, deposited on carbon-coa ted 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 dimensio ns (D), Ag colloidal particle-size distributions, and relative particl e-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 coll oid-adsorbate films appears to be a function of the hydrophobic/hydrop hilic character of the adsorbates. Further on, preparation and TEM ima ging of nonfractal, monolayer metal-adsorbate films (such as Ag-TPyP a n Ag-tppz) are proposed as new suitable techniques for particle-size d istribution analysis of metal colloids. Furthermore, all the films inv estigated prove themselves to be SERS-active. In particular, a SERS sp ectrum of the seal TEM microscopic sample of Ag-bpm film deposited on carbon-coated copper grid is reported and analyzed.