Para to ortho transition of metallic dimers on Si(001)

Abstract

Extensive electronic structure calculations are performed to obtain the stable geometries of metals like Al, Ga and In on the Si(001) surface at 0.5 ML and 1 ML coverages. Our results coupled with previous theoretical findings explain the recent experimental data in a comprehensive fashion. At low coverages, as shown by previous works, 'Para' dimers give the lowest energy structure. With increasing coverage beyond 0.5 ML, 'Ortho' dimers become part of low energy configurations leading toward a 'Para' to 'Ortho' transition at 1 ML coverage. For In mixed staggered dimers ('Ortho' and 'Para') give the lowest energy configuration. For Ga, mixed dimers are non-staggered, while for Al 'Para' to 'Ortho' transition of dimers is complete. Thus at intermediate coverages between 0.5 and 1 ML, the 'Ortho' and 'Para' dimers may coexist on the surface. Consequently, this may be an explanation of the fact that the experimental observations can be successfully interpreted using either orientation. A supported zigzag structure at 0.5 ML, which resembles (CH)x, does not undergo a dimerization transition, and hence stays semi-metallic. Also, unlike (CH)x the soliton formation is ruled out for this structure.

Metallic atomic wires on patterned dihydrogenated Si(001)

“…Two electrons from two Al atoms become non-itinerant in the unit cell, prefer to be occupied by a single band and hence the Al structure (with P 1 P 2 configuration) extending along the y direction becomes non-metallic. Similar to the zigzag Al chain considered earlier 15,16 on the bare Si(001): 2×1, we also considered a zigzag Al chain configuration by displacing the Al atom at S 1 site by ∆ along the +ve x direction and the Al atom at S 2 site by ∆ along the -ve x direction. This zigzag chain configuration turned out to be unstable and readily reverted to the S 1 S 2 configuration.…”

“…The Si atoms on the top four layer of the slab and hydrogen atoms attached to top layer Si atoms are allowed to relax while Si atoms in the bottom layer of the slab and the passivating Hydrogen atoms are kept fixed to simulate the bulk like termination. The convergence with respect to the energy cutoff and the number of k points for similar structures has been examined earlier 16 .…”

“…In recent studies, it was shown that the zigzag Al chain is hard to fabricate as it is energetically 1.6 eV higher than the most favorable structure. However, this chain does not undergo a Peierls distortion and remains semimetallic in character 16 .…”

“…There continues to be a persistent search for metallic nanowires on clean Si(001): 2× 1 surface as well as on the hydrogen terminated Si(001): 2 × 1 surface 4,15,16,17,18,19,20 . In an early study 15 , Batra proposed the formation of a zigzag atomic chain of Al on Si(001): 2×1 but energetically it was not the most favored structure.…”

Interrupted chain-assisted Al atomic wires on Si(211): Density functional calculations

“…1,2 In particular, metals such as Al, Ga, and In at submonolayer coverages on the Si͑001͒ surface have been examined 3,4 for the formation of stable atomic wires on surfaces. Though, stable atomic wire structures have not been found on the bare Si͑001͒ surface, there has been some progress [5][6][7] towards the formation of stable atomic wires on the patterned hydrogen terminated Si͑001͒ surface.…”