The Effect Of Thickness And Temperature On The Surface Properties Of The Film Of Bi

Bismuth(Bi)is a semimetal with unusual electronic properties resulting from its very light effective masses,large mean free path,highly anisotropic Fermi surface,and very small band overlap energy between the L-point conduction band and T-point valence band,which provides a very attractive model system for studying many physical phenomena.In this paper,a comprehensive study of the surface properties of bismuth thin films was carried out from thickness and temperature.The results of this paper are as follows:In the present work,the effects of the thickness on the surface and electronic properties of(00L)and(012)oriented films of Bi using the first-principles method were studied.It was found that,i)With the increase of the thickness,the(00L)oriented Bi films become more stable,and the film with the even-number layers is more stable than that of the films with the odd-number layers.ii)The(012)oriented Bi films present totally different behavior comparing with that of the(00L)oriented Bi film.The stabilities of(012)oriented film become less stable as the thickness increased,and possessed the approximated surface energy of 4-layers(00L)oriented Bi films when their layer numbers were closed to four.iii)Further analysis of the cohesive energy,the geometry structure and the electronic band structures showed that,all the thin films present the transition from semi-conductors to semi-metal or metal as the thickness increases.The bonding behavior in the surface plays the different roles for different orientations.We further studied the effect of the temperature on the surface properties of(00L)and(012)oriented films of Bi using the first-principles method.It was found that,i)With the increase of the temperature,(00L)and(012)oriented Bi films become more unstable.The comparison of the corresponding stabilities shows that,the(00L)oriented Bi film with the even-numbered layers possess the highest stabilities,follows the(00L)oriented Bi film with the odd-numbered layers and(012)oriented Bi film.ii)The surface energy of(012)oriented film are approximate with that the(00L)film with the odd-numbered layers when the temperature is closed to 400K,which may indicate that the Bi film is tend to undergo phase transition between these two orientations at 400K.iii)Further analysis of the geometry structure reveals the relations between the surface energy,atomic average energy and the atomic thermodynamic behavior with the increase of the temperature.