The Ge(001) (2 × 1) reconstruction: asymmetric dimers and multilayer relaxation observed by grazing incidence X-ray diffraction

Rossmann, Reinhild; Meyerheim, H. L.; Jahns, V.; Wever, J.; Moritz, Wolfgang; Wolf, D.; Dornisch, D.; Schulz, H.

doi:10.1016/0039-6028(92)90756-v

Cited by 93 publications

(32 citation statements)

References 18 publications

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“…The asymmetric dimer on the Ge(001)-(2 Â 1) surface is here characterized by an inclination of 18.78 and a bond length of 2.38 Å [45], which are in good agreement with theoretical [32,58,59] and experimental [41] values. The positions of the surface dangling bond charges (sc 1 and sc 2 representing the two dimer lobes) were determined by the maxima in the valence-electron density, which was calculated in the work [45] by using ab initio pseudopotential calculations.…”

Section: à2supporting

confidence: 74%

“…As it has been established [32,[40][41][42][43][44][45][46][47][48][49], this kind of surfaces has asymmetric dimer reconstruction with a charge transfer greater than in Si(001)-(2 Â 1) surface. The anisotropy in the electronic structure of the Ge(001)-(2 Â 1) surface with an optical probe as the normal-incidence ellipsometry has been studied in the work [50].…”

Section: à2mentioning

confidence: 99%

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Theoretical study on photon–phonon coupling at (001)‐(2 × 1) surfaces of Ge and α‐Sn

Pérez-Sánchez

Pérez-Rodrı́guez

2010

Physica Status Solidi (b)

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Phone: þ52 222 229 56 10, Fax: þ52 222 229 56 11We present a study of the far-infrared reflectance anisotropy spectra for (001) surfaces of Ge and a-Sn in the (2 Â 1) asymmetric dimer geometry, which exhibit a resonance structure associated with the excitation of surface phonon modes. We have employed a theoretical formalism, based on the adiabatic bond-charge model (ABCM), for computing the far-infrared reflectance anisotropy spectra. In comparison with previous theoretical results for silicon and diamond surfaces, the resonance structure in the reflectance anisotropy spectrum for Ge(001)-(2 Â 1) turns out to be similar to that observed in the spectrum for the Si(001)-(2 Â 1) surface, whereas the spectrum for a-Sn(001)-(2 Â 1) surface is noticeably different from the others. We have established a trend of far-infrared reflectance anisotropy spectra for IV(001) surfaces: the weaker dimer strength, the stronger resonances of low-frequency surface phonons.

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Section: à2supporting

confidence: 74%

Section: à2mentioning

confidence: 99%

Theoretical study on photon–phonon coupling at (001)‐(2 × 1) surfaces of Ge and α‐Sn

Pérez-Sánchez

Pérez-Rodrı́guez

2010

Physica Status Solidi (b)

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“…At lower temperatures these regions of the surface increase. Data from He scattering [48], grazing-incidence X-ray diffraction [49] and ultraviolet photoemission [50,51] point to the dimer model for an explanation of the observed reconstructions. Opposite to the findings for Si(001)(2 x 1), STM measurements show that the dimers at Ge(001)(2 x 1) are buckled almost everywhere already at room temperature [47].…”

Section: Ge(o01)(2 X 1)mentioning

confidence: 88%

Theory of adsorption: Ordered monolayers from Na to Cl on Si(001) and Ge(001)

Krüger

Pollmann

1994

Appl. Phys. A

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Abstract. First principles calculations of clean and adsorbate-covered surfaces of Si(001) and Ge(001) are reported. Chemical trends in the adsorption of ordered Na, K, Ge, As, Sb, S, Se and CI overlayers are discussed. The calculations are based on the local-density approximation and employ non-local, norm-conserving pseudopotentials together with Gaussian orbital basis sets. The semi-infinite geometry of the substrate is properly taken into account by employing our scattering theoretical method. From total-energy minimization calculations we obtain optimal surface reconstructions which show asymmetric dimers for Si(001), Ge(001) and Ge:Si(001). For As:Si(001), Sb:Si(001) and Sb:Ge(001), we find symmetric adatom dimers in the equilibrium geometries. S or Se adlayers are found to be adsorbed in bridge positions forming a (1 x 1) unit cell with a geometry very close to the configuration of a terminated bulk lattice. C1 atoms adsorb on top of the dangling bonds of symmetric Si dimers residing in the first substrate-surface layer. Our calculations for Na:Si(001) and K:Si(001) confirm valleybridge site adsorption for half monolayer coverage. For full monolayer alkali-metal coverage, adsorption in pedestal and valley-bridge positions is found to be energetically most favourable. The calculated optimal adsorption configurations are in excellent agreement with a whole body of recent experimental data on surface-structure determination. For these structural models, we obtain electronic surface band structures which agree very good with a wealth of data from angle-resolved photoemission spectroscopy investigations. The adsorption of adlayers at semiconductor surfaces has been under intensive study in recent years. These investigations are motivated by fundamental physical reasons and important technological applications. In basic research, semiconductors are interesting substrates for adsorption systems due to the unsaturated directional bonds at their surfaces. This allows the formation of chemical compounds which are neither stable as small, isolated molecules nor as extended solids. The technological interest ranges from homoand heteroepitaxy and growth, via surface passivation and doping to dry etching and photo-surface cleaning. For example, the quality of the heteroepitaxial growth of GaAs on Si is determined by the initial stage of this process which consists in formation of As adlayers. Furthermore, surface passivation may involve As, S or Se atoms. In the fabrication of electronic devices, dry etching and photo-surface cleaning is carried out by the reaction of C1 on Si. The adsorption of alkali metals in the range of monolayer coverage leads to a drastic reduction of the ionization energy. These systems have important applications as high-efficiency emitters. They are also widely discussed in the context of the Schottky-barrier problem [1].

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“…the direct interpretation of the difference Patterson function (Takruchi, 1972), which is briefly described in the next section. Recently, this method has experienced a revival in the determination of reconstructed surfaces (Rossmann et al, 1992;Ferrer, Torrelles, Etgens, van der Vegt & Fajardo, 1995). Unfortunately, its interpretation is very often far from trivial.…”

Section: 'Klassengleiche' Superstructures -Some Basic Concepts and Dementioning

confidence: 99%

A Tangent Formula Derived from Patterson-Function Arguments. IV. The Solution of Difference Structures Directly from Superstructure Reflections

Rius¹,

Miravitlles²,

Allmann³

1996

Acta Cryst Sect A

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The possibility of solving by direct methods the difference structure 6 of a superstructure using only the intensities of the superstructure reflections h is shown. The refinement of the phases • of the strong superstructure E values, which are normalized separately from the E values of the main or substructure reflections, is carried out maximizing the function Z~p, = y]h(Eh-(Eh))Ch(~), where Ch(~b ) is the amplitude of the structure factor of 63 expressed in terms of ~. The maximization is performed with a new tangent formula that only differs from that given previously [Rius (1993). Acta Cryst. A49, 406-409] by an extra summation, i.e. the phase information is now derived from quartets and negative quintets instead of triplets and negative quartets. A preliminary test calculation demonstrates the capability of this tangent formula to solve the difference structure of the mineral wermlandite using only the measured superstructure intensities. Although more tests covering a variety of situations are still required to allow for a generalization, this result seems to confirm the viability of determining the internal structure of reconstructed surfaces by interpreting the corresponding three-dimensional difference Patterson function by direct methods. Access to this function is now possible, since, with the advent of intense synchrotron sources, not only in-plane intensity data but also the corresponding diffraction rods can be measured.is a subgroup of index n of the space group of the average structure. If the subgroup is maximal and if the reduction of symmetry operations affects the number of lattice points, the resulting superstructure is called klassengleich (Hermann, 1929). The reduction of lattice points causes the appearance of superstructure reflections (h), which are systematically weaker than the main reflections (H). The different mean intensity of the two reflection sets is due to the different amounts of electron density that contribute to each set. This can be best illustrated with the one-dimensional superstructure in Fig. l(a) consisting of two heavy atoms with form factors fp placed at the origin of the 'subcells' (at x = 0, 1/2) and of two lighter atoms with form factors fL at x = +x L. The structure-factor expression for the main (m) and superstructure (s) reflections are, respectively,

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The Ge(001) (2 × 1) reconstruction: asymmetric dimers and multilayer relaxation observed by grazing incidence X-ray diffraction

Cited by 93 publications

References 18 publications

Theoretical study on photon–phonon coupling at (001)‐(2 × 1) surfaces of Ge and α‐Sn

Theoretical study on photon–phonon coupling at (001)‐(2 × 1) surfaces of Ge and α‐Sn

Theory of adsorption: Ordered monolayers from Na to Cl on Si(001) and Ge(001)

A Tangent Formula Derived from Patterson-Function Arguments. IV. The Solution of Difference Structures Directly from Superstructure Reflections

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