Anal. Chem. 1989, 61, 1983-1984
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Flgure 4. I C I S S intensity scattered from Cd atoms measured in the [ l o l o ] azimuth of (0OOj)S face (0)and (0001)Cd face (X). The measurements were carried out under the conditions shown schematically in the inset. The intensity of the I C I S S spectrum for the (0001)s face was multiplied by 3 so that the comparison between the intensity at the (0001)Cd face and that at the (0OOq)S face becomes more accurate for smaller values of a (a 40). The shadowing critical angles calculated (26) for the surface without disorder are indicated by crosses. The difference between calculated (---) and experimental (-) values at a a. (shaded portion) is due to Cd atoms exposed as a result of steps and/or sulfur a t o m defects at the surface.
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and the (0OOT)S face to Cd2+rather than SH-(S2-). These results were explained by a reversible adsorption/desorption model together with the data for flat-band potentials. ICISS measurements demonstrated the existence of Cd atoms at the (0OOT)S face and S atoms a t the (0001)Cd face, which led to a poor but measurable response of the (0oOI)S face to SH-(S2-) and the (W1)Cd face to Cd2+. The smaller slope is considered to be due to the failure of co-ion exclusion in the classical ion-exchange mechanism without quantitative treatment (2). The employment of a single-crystal CdS ISE with the adsorption/desorption model makes it possible to treat the response of the ISE to specific ions quantitatively.
(30) (31) (32) (33) (34) (35) (36) (37) (38)
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