Sodium-doped dimer rows on Si(001)

Abstract

The stability and electronic structure of a nanowire are studied by first-principles calculations. The wire consists of a single depassivated silicon dimer row on the hydrogen passivated Si͑001͒ 2ϫ1 surface. We predict that sodium atoms evaporated onto this surface stick preferentially at the depassivated row and partially fill the empty one-dimensional states of this row. This leads to a thin metallic wire of atomic size dimensions. At room temperature the sodium atoms are mobile along the depassivated row; they become immobile at temperatures below ϳ120 K. ͓S0163-1829͑97͒50328-6͔Nanowires have attracted considerable attention as such small one-dimensional ͑1D͒ structures are expected to exhibit intriguing physical properties such as a quantized conductance or a transition to a Tomonaga-Luttinger liquid at low temperatures.1 In recent years rapid progress has been made in manipulating atoms with the scanning tunneling microscope ͑STM͒, which makes it possible to build 1D structures atom by atom.2 On metallic substrates the 1D electronic states of such structures are usually strongly mixed with the bulk metal states. In order to study unperturbed 1D effects, one would therefore prefer to use semiconducting ͑or insulating͒ substrates. Recent examples of stable 1D structures on semiconductor surfaces constructed using STM techniques, are atomic scale grooves on the Si͑111͒ surface 3 and depassivated single dimer rows on the 2ϫ1 monohydride Si͑001͒ surface.4 Both these structures are semiconducting, however, and a necessary condition for the occurrence of the low-temperature effects mentioned above is that the structures have 1D metallic character at higher ͑e.g., room͒ temperature. The challenge therefore is to construct an atomic scale metallic wire on a semiconducting substrate. There are a number of possible approaches. One could, for instance, modify a specific surface in order to create a wire which is intrinsically metallic. An example of this was explored in recent theoretical work where the possibility of a stable ''dangling bond wire'' on hydrogen passivated Si͑111͒ was discussed.5 Another possibility is to use semiconducting 1D structures as templates for metal atoms evaporated onto the surface, the experimental feasibility of which has recently been demonstrated quite convincingly by Shen et al. 6 The microscopic limit of a single row of metal atoms ͑which interact strongly with the substrate͒ will not necessarily result in a conducting wire. For example, first-principles calculations by Brocks et al. show that lines of aluminum atoms on Si͑001͒ are semiconducting.7 A third approach is to dope semiconducting 1D structures. Some of these structures have states inside the bulk band gap, which have a pure 1D character. Transferring electrons ͑holes͒ from dopant atoms to empty ͑filled͒ 1D states would result in conducting wires.In this paper we propose a specific realization of this last approach and study it by means of first-principles calculations. We start from a single depassivated dimer ͑DD͒ row on th...

Scalable Patterning of One-Dimensional Dangling Bond Rows on Hydrogenated Si(001)

“…4,35 Gallium 12,13 and silver 4 atoms diffuse fast on the hydrogenated surface but stick to DBs. Arsenic, 36 gold, 11 and sodium 37 atoms might follow the same path.…”

“…In addition to templating molecules, silicon DB rows also hold promise to form self-assembled wires of selected atoms. , Gallium , and silver atoms diffuse fast on the hydrogenated surface but stick to DBs. Arsenic, gold, and sodium atoms might follow the same path.…”

Role of Scanning Probes in Nanoelectronics: A Critical Review

“…Second, the conductivity of the metal wire depends critically on the deposition sites of the metal atoms as well as the species of the metal atoms. [33][34][35] It is, therefore, not clear whether the "atom wires" actually conduct, even with the atomically precise fabrication.…”

First-principles calculation of As atomic wires on a H-terminated Si(100) surface

“…Haye et al 5 investigated Na-doped dangling bond wires fabricated on the H-terminated Si͑100͒ surface. They found that for low coverages, Na atoms act simply as electron donors, and that the shapes of the surface energy bands resemble those of a clean Si͑100͒ surface, except for the position of the Fermi level.…”

“…Therefore, we tried to dope an electron into this band by adding one K atom to the unit cell of geometry ͑a͒. 14 Here, we chose an alkali atom as a dopant because Haye et al 5 showed that an alkali atom acts as an ideal electron donor for an atomic wire on the H-terminated Si͑100͒ surface. We tried three starting geometries of K adsorbates, all considered stable.…”