Thermodynamic study of NO thin films adsorbed on MgO(100)
Adsorption isotherms of NO on uniform MgO(100) surface have been measured in a wide range of temperature 92K T 138K and a coverage corresponding to two first layering transitions. Thermodynamic properties of the first and the second nitrogen monoxide layers have been reported. Particularly, adsorption heat measured for the first layer adsorbed on MgO Qst(1) = 5.47 kcal.mol-1, is 18% greater than that measured on the hexagonal graphite basal plane surface, indicating the large stability of the NO first layer adsorbed on MgO. This suggestion is supported by the bi-dimensional critical temperature which is displaced to the height temperatures range T2C/T3C = 0.67. By comparison to NO adsorbed on other substrates, the original result in the present study is the absence of bi-dimensional polymorphism in the explored range of temperature. We suggest a configuration where molecules are laying on the MgO(100) surface.
Adsorption isotherms; Bi-dimensional polymorphism; Surface thermodynamics; Magnesium oxide
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