Phys. Rev. B 73, 205329 (2006) - Real topography, atomic relaxations, and short-range chemical interactions in atomic force microscopy: The case of the $\ensuremath{\alpha}\text{\ensuremath{-}}\mathrm{Sn}∕\mathrm{Si}(111)\text{\ensuremath{-}}(\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3})R30\ifmmode^\circ\else\textdegree\fi{}$ surface

Real topography, atomic relaxations, and short-range chemical interactions in atomic force microscopy: The case of the $α − Sn ∕ Si (111) − (\sqrt{3} \times \sqrt{3}) R 30 °$ surface

Yoshiaki Sugimoto, Pablo Pou, Óscar Custance, Pavel Jelinek, Seizo Morita, Rubén Pérez, and Masayuki Abe

Phys. Rev. B 73, 205329 – Published 16 May 2006

Abstract

We have investigated the phases of the $Sn ∕ Si (111) − (\sqrt{3} \times \sqrt{3}) R 30 °$ surface below $\frac{1}{3}$ ML coverage at room temperature by means of atomic force microscopy (AFM) and density functional theory based first-principles calculations. By tuning the Sn concentration at the surface we have been able to discriminate between Sn and Si adatoms, and to assure that the AFM topography for the different phases resembles the one reported using scanning tunneling microscopy. In the mosaic and the intermediate phases, a dependence of the topographic height of the Si adatoms on the number of surrounding Sn adatoms has been identified. In the pure phase, however, variations in the measured height difference between the Sn adatoms and the substitutional Si defects, which are intrinsic to the AFM observation, are reported. Reliable room-temperature force spectroscopic measurements using the atom-tracking technique and first-principles calculations provide an explanation for these striking induced height variations on the pure phase in terms of both the different strength of the short-range chemical interaction and tip-induced atomic relaxations. Our results suggest that the corrugation measured with true atomic resolution AFM operated at low interaction forces and close to the onset of significant short-range chemical interactions provides direct access to the real structure of heterogeneous semiconductor surfaces.

Received 25 October 2005

DOI:https://doi.org/10.1103/PhysRevB.73.205329

Authors & Affiliations

Yoshiaki Sugimoto^1,*, Pablo Pou², Óscar Custance¹, Pavel Jelinek³, Seizo Morita¹, Rubén Pérez², and Masayuki Abe^1,4

¹Graduate School of Engineering, Osaka University, 2-1 Yamada-Oka, 565-0871 Suita, Osaka, Japan
²Departamento de Física Teórica de la Materia Condensada, Universidad Autónoma de Madrid, 28049 Madrid, Spain
³Institute of Physics, Academy of Sciences of the Czech Republic, Cukrovarnicka 10, 1862 53, Prague, Czech Republic
⁴PRESTO, Japan Science and Technology Agency, Saitama 332-0012, Japan

^*Corresponding author. Email address: ysugimoto@ele.eng.osaka-u.ac.jp

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Vol. 73, Iss. 20 — 15 May 2006

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Figure 1
(Color online) Topographic images of the $Sn ∕ Si (111) - (\sqrt{3} \times \sqrt{3}) R 30 °$ surface at different Sn coverage: (a) the mosaic phase, (b) the intermediate phase, and (c) the pure phase. Scan size is $(8.5 \times 8.5) {nm}^{2}$ . The arrows in (a) and (b) mark Si adatoms showing an unexpected topographic contrast due to variations in the number of the surrounding Sn adatoms. The acquisition parameters—the free-oscillation first mechanical resonant frequency $(f_{0})$ , the cantilever stiffness $(K)$ , the cantilever oscillation amplitude $(A)$ , and the $Δ f$ set point—for each image were (a) $f_{0} = 162 167.6 Hz$ , $K = 30.5 N ∕ m$ , $A = 19 nm$ , and $Δ f = - 2.9 Hz$ ; (b) $f_{0} = 161 363.9 Hz$ , $K = 30.0 N ∕ m$ , $A = 24 nm$ , and $Δ f = - 5.1 Hz$ ; and (c) $f_{0} = 162 173.1 Hz$ , $K = 30.5 N ∕ m$ , $A = 20 nm$ , and $Δ f = - 4.7 Hz$ , respectively.Reuse & Permissions
Figure 2
(Color online) Topographic height variations of substitutional Si defects on the $\frac{1}{3}$ ML (pure phase) $Sn ∕ Si (111) - (\sqrt{3} \times \sqrt{3}) R 3 °$ surface when decreasing the tip-sample distance. (a)–(c) selected frames from a series of images (Ref. 60) showing the reduction of the topographic height on the Si adatoms when increasing the tip-surface interaction. Image dimensions are $(8.5 \times 8.5) {nm}^{2}$ . (d) Dependence of the Sn-Si topographic height difference with the $Δ f$ set point. The acquisition parameters were $f_{0} = 162 285.8 Hz$ , $K = 30.5 N ∕ m$ , and $A = 20 nm$ .Reuse & Permissions
Figure 3
(Color online) Room-temperature atomic force spectroscopic measurements. In (a) and (c) each of the displayed curves was obtained from the average of a hundred of equivalent $Δ f (Z)$ curves measured over the Si and the Sn adatoms pointed in the inset image using the atom-tracking technique. In (c), the $Δ f (Z)$ curve for the Si adatom has been shifted to take topographic effects during the acquisition into account. The dotted line indicates the crossing point between both curves. (b) Topographic profile highlighted in the image. The acquisition parameters were $f_{0} = 162 285.8 Hz$ , $K = 30.5 N ∕ m$ , and $A = 25.9 nm$ . The set-point value for imaging and atom-tracking operation was $Δ f = - 5.4 Hz$ . Image size is $(8.5 \times 8.5) {nm}^{2}$ .Reuse & Permissions
Figure 4
(Color online) Short-range force associated with the $Δ f (Z)$ curve shown in 3c. Acquisition parameters are listed in the caption of Fig. 3.Reuse & Permissions
Figure 5
(Color online) Results from first-principles calculations on the interaction of a Si tip apex with the Sn and the Si adatoms of the $Sn ∕ Si (111) - \sqrt{3} \times \sqrt{3} R 3 °$ surface. (a) Tip and surface atomic models used in the calculations. (b) Comparison of the calculated covalent interaction forces with the experimental short-range forces displayed in Fig. 4. (c) Induced relaxations on the adatom vertical positions due to the interaction force as the tip approaches the surface. The dotted line marks the corresponding position of the crossing point between the $Δ f (Z)$ curves displayed in Fig. 3c. For a proper comparison with the theoretical curves, both the experimental force curves and the dotted line have been shifted as a unit in $2.25 Å$ towards the origin with respect to Figs. 3, 4.Reuse & Permissions

Physical Review B

covering condensed matter and materials physics

Real topography, atomic relaxations, and short-range chemical interactions in atomic force microscopy: The case of the $α − Sn ∕ Si (111) − (\sqrt{3} \times \sqrt{3}) R 30 °$ surface

Yoshiaki Sugimoto, Pablo Pou, Óscar Custance, Pavel Jelinek, Seizo Morita, Rubén Pérez, and Masayuki Abe

Phys. Rev. B 73, 205329 – Published 16 May 2006

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Physical Review B

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Real topography, atomic relaxations, and short-range chemical interactions in atomic force microscopy: The case of the α−Sn∕Si(111)−(3×3)R30° surface

Yoshiaki Sugimoto, Pablo Pou, Óscar Custance, Pavel Jelinek, Seizo Morita, Rubén Pérez, and Masayuki Abe

Phys. Rev. B 73, 205329 – Published 16 May 2006

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Real topography, atomic relaxations, and short-range chemical interactions in atomic force microscopy: The case of the $α − Sn ∕ Si (111) − (\sqrt{3} \times \sqrt{3}) R 30 °$ surface