Atomic and Electronic-Band Structures of Anomalous Carbon Dimers on3C−SiC(001)−c(2×2)

Abstract

The atomic structure of the c͑2 3 2͒ reconstruction of the C-terminated 3C-SiC͑001͒ surface was unambiguously determined by scanning tunneling microscopy and surface-core-level-resolved photoelectron diffraction studies. This surface is found to uniquely and uniformly consist of anomalous bridge-bonded C dimers with a C-C bond length of 1.22 Å. Furthermore, an extensive angleresolved photoemission study clearly identifies two occupied p state bands due to the surface-normal and -parallel p orbitals of the triple-bonded C dimers. This provides an electronic explanation of the stability of this unique surface reconstruction. 68.35.Bs, 79.60.Dp SiC has attracted much recent interest due to its potential for novel device applications [1] as well as due to its unique surface properties, most popularly cubic 3C-SiC͑001͒ [2] and hexagonal 6H͑4H͒-SiC͑111͒ [3] surfaces. The partially ionic character of SiC provides an interesting variety of complex reconstructions and local bond configurations on its surfaces. It has been known that the 3C-SiC͑001͒ surface exhibits three major surface phases [2]: the C-terminated c͑2 3 2͒ surface, the Si-terminated 2 3 1 [or c͑4 3 2͒] surface, and the Si-rich 3 3 2 surface. Peculiar surface properties have been reported such as a metal-insulator transition for the Si-terminated surfaces [4] and a zero-dimensional fluctuation [5] and quantum wires for the Si-rich surface [6]. However, further detailed discussion on such surface properties is mainly prohibited by the lack of consensus on the structures of these surfaces [2,7,8].As for the C-terminated c͑2 3 2͒ surface, the possibility of a very unusual bridge-bonded dimer (BD) structure has been discussed [ Fig. 1(a)] [9-19], which is unprecedented among the known reconstructions of semiconductor surfaces. This was first introduced by a low-energy electron diffraction (LEED) study for the c͑2 3 2͒ surface prepared by Si sublimation [9] against the earlier model of conventional dimers [the staggered dimer (SD) model, Fig. 1(b)] [10]. In contrast to this LEED study suggesting a "double-bonded" BD, a recent x-ray absorption study favored a triple-bonded BD [9] structure for a c͑2 3 2͒ surface prepared by C 2 H 4 flux [11]. Some of the theoretical calculations, contradictorily, suggested a 2 3 1 conventional dimer structure as the energetically favored ground state [12][13][14][15], and others, the SD c͑2 3 2͒ structure [16,17]. Furthermore, in the major ab initio calculations [12,13,18] the total energy differences between the SD and BD c͑2 3 2͒ structures were trivially small, which leads to the prediction of the coexistence of different surface structures or the subtle dependence of surface structures on the preparation methods [12].In this Letter, we provide unambiguous answers to the questions of (i) the uniqueness, (ii) the quantitative details of the surface structure, and (iii) the bond configuration of the 3C-SiC͑001͒-c͑2 3 2͒ surface. Scanning tunneling microscopy (STM) studies for the c͑2 3 2͒ surface FIG. 1. The two structure mo...

Optical Anisotropy of theSiC(001)-(3×2)Surface: Evidence for the Two-Adlayer Asymmetric-Dimer Model

“…The b-SiC(001) surface, exhibiting three major surface phases, c(2 3 2), (2 3 1), and (3 3 2), serves as a prototype in that respect. It has been intensively investigated by both experiment [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] and theory [17][18][19][20][21][22]. Of particular importance are Si-rich conditions, because of the high Si vapor pressure in most methods of growth.…”

Hydrogen-induced3×1phase of the Si-rich3C−SiC(001)surface

“…1,2 Such interests are not only due to the technological importance of SiC thin films for advanced device applications, 3 but also due to the unique surface properties of this partly ionic IV-IV compound semiconductor. Indeed, a variety of intriguing surface properties have been reported, such as a Mott-insulating ground state, 4 an exotic carbon bonding, 5,6 a metal-insulator transition, 7 a cellular fluctuation of unit cells, 8 and Si or C onedimensional chains. 9,10 In spite of vigorous investigations performed so far, the atomic structures of the reconstructions of SiC surfaces are still not clear, especially for the Si-rich and Si-terminated 3C-SiC(001) surfaces.…”

Investigations of SiC semiconductor nanoinclusions formed by sequential ion implantation and annealing in thermally oxidized Si

“…The determined lengths of Si-C and C-C bonds correspond to the staggered-dimer model of SiC nanocrystals surface. [6] A simplified model c(2 × 2) of this structure is shown in Fig. 4(b).…”