Analysis Of Desorption Spectra Research Articles

Underpotential deposition and involved alloy formation of cadmium on silver particles modified HOPG substrates

Cadmium underpotential deposition (UPD) on Ag particles modified highly ordered pyrolytic graphite (HOPG) surfaces, and the involved alloy formation were studied by conventional electrochemical techniques. Voltammetric results indicated that the Cd UPD followed an adsorption behavior different from that observed for massive Ag electrodes and Ag particles supported on vitreous carbon. Nanometer-sized bimetallic Cd–Ag particles were characterized by ex situ atomic force microscopy (AFM). Initially, AFM images show Ag deposits of similar size distributed preferably on HOPG step edges. No remarkable morphological changes are observed on the surface after the subsequent Cd deposition, suggesting that the Cd particles are deposited selectively over the Ag crystals. From the analysis of desorption spectra, employing different polarization times, and density functional theory (DFT) calculations, the formation of a Cd–Ag surface alloy could be inferred.

Study of thermal desorption: The effect of a temperature gradient along the sample

In thermal desorption techniques some difficulties may arise of a thermal gradient in the samples; the analysis of desorption spectra under this circumstance cannot be carried out by the usual methods. We give in the case of a parabolic thermal-gradient profile a procedure for analysis of a simple peak spectrum in a first-order desorption. As a first step we have evaluated the distortion of a theoretical desorption peak by the presence of a temperature gradient. This distortion was characterized by the quantities ΔTm/Tm and Δμ/μ, Tm and μ being, respectively, the maximum peak desorption temperature and the half-width of the peak at midheight. Utilizing some mathematical properties of the desorption rate equation we have shown that ΔTm/Tm and Δμ/μ can be plotted in terms of three independent parameters. The curves so obtained allow the experimental spectra to be corrected to determine the true values of the kinetic parameters: activation energy for desorption Ed and frequency factor 1/τ0.