We describe a novel approach for Au and Ag colloid monolayer formation on different silicon oxide surfaces such as glass, silicon, and ITO. The preparation method is simple and yields monolayers with easily controlled spacing within the monolayer without aggregation of metal particles. The colloid monolayers are prepared in two steps: (1) modification of the substrates with starburst dendrimers and (2) noble metal colloid deposition onto the dendrimer layer. Different Au and Ag colloids, ranging from 15 to 80 nm in particle diameter, have been deposited onto the dendrimer-modified surfaces. The structure and properties of the resulting particle arrays have been studied by atomic force microscopy (AFM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), UV-vis spectroscopy, and surface-enhanced Raman scattering (SERS). XPS data show that the dendrimers spontaneously adsorb to various silicon oxide surfaces. The thickness of the dendrimer overlayer has been calculated and lies in the d ) 14-25 Å range. SEM and AFM data show that the colloids spontaneously form continuous films on the dendrimermodified surfaces. The noble metal particles are well isolated and confined to a single layer, and aggregation does not occur on the surface. The interparticle spacing (74-829 nm) and surface coverage can be controlled over a wide range by colloid size, colloid concentration, and immersion time. UV-vis spectroscopic data show that the microstructure directly controls the optical properties of the layer. Finally, we demonstrate that the prepared substrates provide a useful platform for SERS studies of materials adsorbed on the metal particles.
The vapor deposition of Bi on Pt (111) at 110 and 600 K have been characterized by Auger electron spectroscopy (AES), thermal desorption mass spectroscopy (TDMS), low-energy electron diffraction (LEED ), and changes in the work function ( ). At 110 K Bi growth follows a layer-by-layer mechanism. At 600 K Bi fills the first monolayer (0,, -0.56) relatively uniformly, followed by 3D island growth. Bi desorption is characterized by a large, coverage-dependent desorption energy, Edes = (81 -34.2 0,,) kcal mo1 -1 , in the first monolayer, and zero-order kinetics with constant activation energy (Edes = 53-56 kcal mo1 -1 ) for the multilayer. Many LEED patterns are observed within the first monolayer for both cold and hot substrates. Structural models for these are proposed which are consistent with coverages obtained by AES. Annealed structures show continuous compression of hexagonal Bi overlayers with increasing coverage, subject to mild substrate constraints. At 110 K and 0,, > 0.33, uniaxial compression is instead seen, due to an unsurmounted energy barrier. Weakly repulsive lateral Bi-Bi interactions (due to dipole repulsions) dominate submonolayer growth. These results for the semimetal Bi are intermediate in behavior between alkali and transition metal overlayers on Pt ( 111). This is consistent with the relative strengths of the surface dipole of these adsorbed metals. 6176
We emphasize two points: (l) the properties and mechanisms of very low-fluence ablation of copper surfaces and (2) the sensitivity and selectivity of resonant laser ablation (RLA). We present results for ablation of bulk copper and copper thin films; spot-size effects; the effects of surface-sample preparation and beam polarization; and an accurate measurement of material removal rates, typically ≤ 10(-3) Å at 35 mJ/cm(2). Velocity distributions were Maxwellian, with peak velocities ≈ 1-2 × 10(5) cm/s. In addition, we discuss the production of diffractionlike surface features, and the probable participation of nonthermal desorption mechanisms. RLA is shown to be a sensitive and useful diagnostic for studies of low-fluence laser-material interactions.
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