First principles calculations of charge and spin density waves of -adsorbates on semiconductors

Scandolo, Sandro; Ancilotto, Francesco; Chiarotti, G.; Santoro, Giuseppe E.; Serra, Stefano; Tosatti, Erio

doi:10.1016/s0039-6028(97)01098-4

Cited by 24 publications

(27 citation statements)

References 13 publications

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“…The suggestion that a commensurate charge density wave can form in Pb [1] and Sn [2,3] overlayers on Ge(111) demonstrated the importance of such simple model systems as testing grounds for modern theories [4]. Upon cooling both of these adsorbate systems undergo a structural phase transition from a surface reconstruction with a ( √ 3 × √ 3)R30…”

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Phase Transitions in Two Dimensions: The Case of Sn Adsorbed on Ge(111) Surfaces

et al. 1999

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Accurate atomic coordinates of the room-temperature ( √ 3× √ 3)R30 • and low-temperature (3×3) phases of 1/3 ML Sn on Ge(111) have been established by grazing-incidence x-ray diffraction with synchrotron radiation. The Sn atoms are located solely at T4-sites in the ( √ 3 × √ 3)R30 • structure. In the low temperature phase one of the three Sn atoms per (3×3) unit cell is displaced outwards by 0.26±0.04 Å relative to the other two. This displacement is accompanied by an increase in the first to second double-layer spacing in the Ge substrate.

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Phase Transitions in Two Dimensions: The Case of Sn Adsorbed on Ge(111) Surfaces

et al. 1999

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“…2 Both theory 2,5 and experiment 6 indicate that Fermi surface nesting is not an appropriate model for this transition, and there is no metal-to-nonmetal transition for Sn/Ge. 2,6 Scandolo et al 5 proposed, based on theoretical calculations, that the ͱ3 phase is paramagnetic and is unstable towards a commensurate spin-density wave with periodicity (3ϫ3) and magnetization 1 3 . Le Lay et al 7 proposed, based on core-level data, that dynamic fluctuations between the sp 3 /sp 2 hybridization states at room temperature would condense into a (3ϫ3) low-temperature phase.…”

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Periodic lattice distortion accompanying the charge-density-wave transition for Sn/Ge(111)

et al. 1999

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The periodic lattice distortion ͑PLD͒ accompanying the charge-density-wave ͑CDW͒ transition ͑at Ϫ60°C͒ in the ␣ phase of Sn on Ge͑111͒ has been determined by combining the distinct sensitivities of low-energy electron diffraction ͑LEED͒ and surface x-ray diffraction ͑SXRD͒. New LEED I-V data combined with a SXRD analysis yield a significant lattice distortion. The PLD accompanying the CDW transition is a 0.37-Å vertical rippling of the Sn atoms accompanied by a perpendicular ͑0.17 Å͒ and parallel ͑0.12 Å͒ distortion of the first-layer Ge atoms, consistent with a band Jahn-Teller-like distortion. ͓S0163-1829͑99͒01128-5͔A charge-density-wave ͑CDW͒ transition has been observed for thin films ͑␣ phase with 1 3 monolayer density͒ of Pb and Sn on the ͑111͒ surface of Ge, using a variable temperature scanning tunneling microscope ͑STM͒. 1,2 STM images reveal a (3ϫ3) symmetry in the low-temperature CDW phase with the filled and empty state images being complimentary. 1,2 Electron-diffraction studies of both of these systems show that there is a commensurate lattice distortion that accompanies the CDW transition, from a roomtemperature (ͱ3ϫͱ3)R30°structure ͑labeled ͱ3͒ to a (3 ϫ3) low-temperature structure. 1,2 For the Pb film, firstprinciples density-functional calculations confirmed that the CDW (3ϫ3) phase was in fact the ground state of the system, and that the Fermi contour of the high-temperature ͱ3 phase, confirmed by angle-resolved photoemission measurements, 3 had a shape that would suggest Fermi surface nesting. 1 It was proposed, based on these calculations, that the transition was driven by Fermi surface nesting, 1 but stabilized by electron correlation effects, since experiments showed that this CDW transition was accompanied by a metal-to-nonmetal transition, 1,4 unexplainable with band theory.At first glance, the behavior of the Sn film is very similar to that of the Pb film. The CDW transition is at Ϫ60°C compared to Ϫ20°C for Pb, the STM images are nearly identical, and the commensurate lattice distortion, as seen with low-energy electron diffraction ͑LEED͒, is qualitatively similar. Upon close inspection, the details are significantly different. First-principles density-functional calculations show that the CDW configuration is not the ground state for Sn/Ge. 2 Both theory 2,5 and experiment 6 indicate that Fermi surface nesting is not an appropriate model for this transition, and there is no metal-to-nonmetal transition for Sn/Ge. 2,6 Scandolo et al. 5 proposed, based on theoretical calculations, that the ͱ3 phase is paramagnetic and is unstable towards a commensurate spin-density wave with periodicity (3ϫ3) and magnetization 1 3 . Le Lay et al. 7 proposed, based on core-level data, that dynamic fluctuations between the sp 3 /sp 2 hybridization states at room temperature would condense into a (3ϫ3) low-temperature phase. A key to determining the origin of the CDW transition in the Sn/Ge͑111͒ system is the structure of the periodic lattice distortion accompanying the electronic transition.A recent surfac...

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“…Several workers have studied the atomic structure of the surface using the scanning tunneling microscope (STM) [25,26]. A set of reconstructions of the Si terminated (0001) surface has been discovered, one of which, the √3×√3, has evoked much experimental [15,16,27] and theoretical [17,[28][29][30] interest. Theoretically, the lowest energy model for this reconstruction consists of Si adatoms at T 4 positions on a Si terminated bulk crystal.…”

Section: Mott-hubbard Gap Of Sic(0001)√3×√3 Surfacementioning

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Recent developments in scanning tunneling spectroscopy of semiconductor surfaces

2001

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Several recent developments in scanning tunneling spectroscopy (STS) of semiconductor surfaces are reviewed. First, the normalization of spectra is discussed, which for the Si(111)2×1 surface is found to produce a small shift in the apparent position of band edges. With this correction, the surface band gap measured by STS is found to be in good agreement with that obtained by other experimental and theoretical techniques. Second, it is shown for the SiC(0001)√3×√3 surface that the tunneling spectra show a remarkable evolution with decreasing current, and at pA levels they reveal a Mott-Hubbard gap for the surface states, in agreement with that seen by other methods. Finally, a detailed discussion is presented on the absence of electronic effects for the tunnel current into empty states of III-V (110) cleaved surfaces. From this result it is demonstrated that one can use observed strain induced displacements of such surfaces to yield information on the chemical composition of the underlying material. I IntroductionSince the early days of the scanning tunneling microscopy (STM), spectroscopy of semiconductor surfaces has played an important role both in furthering our understanding of the the STM technique as well as in yielding new information about the surfaces themselves. For example, early voltage-dependent results on Si(111)2×1 and Si(111)7×7 surfaces enabled a determination of their structures and also illustrated the exquisite sensitivity of the STM to the surface states [1][2][3][4]. Complete conductance spectra as a function of tip-sample bias voltage clearly revealed the surface state bands. This early development of the scanning tunneling spectroscopy (STS) field has been reviewed [5].Slightly after the development of STS for semiconductor surface states, further studies were performed on cleaved GaAs(110) surface for which surface states do not play a large role in the results [6]. The difference in these two situations, with or without surface states, is quite dramatic. For Si(111)7×7 the surface state band is essentially metallic (i.e. no band gap), and the conductance dI/dV varies by less than three orders of magnitude over the voltage range −3 to +3 V. In contrast, for GaAs(110) a large band gap opens up in the spectrum and one requires 5-6 orders of magnitude in dynamic range to accurately measure the spectrum. Special techniques have been developed to achieve this high dynamic range [7]. For all of the direct gap III-V semiconductors, STS of the (110) surface can be used to reveal the bulk band gap as well as some other bulk critical point of the band structure [7]. Surface states make a small (but still noticeable) contribution of the spectra.Published in Appl. Phys. A 72 [Suppl.], S193 (2001).

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First principles calculations of charge and spin density waves of -adsorbates on semiconductors

Cited by 24 publications

References 13 publications

Phase Transitions in Two Dimensions: The Case of Sn Adsorbed on Ge(111) Surfaces

Phase Transitions in Two Dimensions: The Case of Sn Adsorbed on Ge(111) Surfaces

Periodic lattice distortion accompanying the charge-density-wave transition for Sn/Ge(111)

Recent developments in scanning tunneling spectroscopy of semiconductor surfaces

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