Projected surface energy bands, Shockley surface states, and bonding in transition‐metal monocompounds with rock‐salt structure: Example of NbC

Abstract

AbstractsThe qualitative theory of Shockley surface states is used to discuss the existence of surface states on three faces of niobium carbide: (OOl), (01 l), and (1 11). The results obtained for NbC are generalized to include other simple transition metal compounds MX, X = C, N, 0. Surface states of these and related materials are of interest in chemisorption and catalysis. The qualitative theory of Shockley states appears to be useful tool in detecting strong covalency effects in solids.La thdorie qualitative des Ctats de surface de Shockley est utilisCe pour discuter l'existence d'ktats desurfacesur troisfacesducarburede niobium: (OOl), (Oll), et (111). LesrCsultatsobtenuspour NbC sont gCnCralisCs pour inclure d'autres composes de mCtauxde transition MX, X = C, N, 0. Les Ctats de surface dans les matiriaux de ce type48 sont importants pour la chemisorption et la catalyse. La thCorie qualitative des Ctats de Shockley parait &tre utile pour voir des effets de covalence forte dans les solides.Die qualitative Theorie der Schockley'schen Oberflachenzustande wird angewandt um die Existenz von Oberflachenzustanden auf drei Flachen von NbC: (OOl), (011) und (11 1) zu diskutieren. Die fur NbC erhaltenen Resultate werden zu anderen einfachen Ubergangsmetallverbindungen, MX,, X = C, N, 0, verallgemeinert. Oberflachenzustande in solchen Verbindungen sind fur Chemisorption und Katalyse wichtig. Die qualitative Theorie der Shockleyzustande scheint fur die Analyse von starken kovalenten Effekten in Festkorpern nutzlich zu sein.

On surface states of transition metal carbides, nitrides, and oxides: (001), (011), and (111) surfaces

“…Nevertheless, for carbides (and in some cases also for nitrides), the p and d contributions in limited parts of SBZ are comparable in size, or it happens that the p-d ordering is reversed near the band edge, giving rise to a hybridizational (inverted) gap (HG) [25-271. In the point r, such a HG is present in r5 (A5) states for *Note that the choice of p, is strongly restricted by these properties and prevents one from constructing physically meaningless wave functions. carbides [25,26], and the presence of Shockley surface states is expected. For VC, Tic, and NbC, a doubly degenerate hydridized ss of mainly p(C)-character is situated slightly (0.2-0.3 eV) below the upper gap edge, in agreement with Ref.…”