Atomic-Scale Imaging of the Surface Dipole Distribution of Stepped Surfaces

Abstract

ABSTRACT:Stepped well-ordered semiconductor surfaces are important as nanotemplates for the fabrication of one-dimensional nanostructures. Therefore a detailed understanding of the underlying stepped substrates is crucial for advances in this field. Although measurements of step edges are challenging for scanning force microscopy (SFM), here we present simultaneous atomically resolved SFM and Kelvin probe force microscopy (KPFM) images of a silicon vicinal surface. We find that the local contact potential difference is large at the bottom of the steps and at the restatoms on the terraces, whereas it drops at the upper part of the steps and at the adatoms on the terraces. For the interpretation of the data we performed density functional theory (DFT) calculations of the surface dipole distribution. The DFT images accurately reproduce the experiments even without including the tip in the calculations. This underlines that the high-resolution KPFM images are closely related to intrinsic properties of the surface and not only to tip-surface interactions.Stepped well-ordered surfaces and, in particular vicinal semiconductor surfaces, are well suited for applications as nanotemplates for the fabrication of one-dimensional nanostructures. [1][2][3][4][5][6][7] Among such structures, monoatomic wires are candidates of interesting electronic properties such as Luttinger-liquid behavior. 8 The vicinal Si(111) surface with 10 • miscut towards the [1 1 1 1 2] direction is a popular stepped surface that can be used as a model system. This surface contains (7×7) reconstructed terraces oriented along the Si(111) direction, a well characterized and understood surface, separated by a stepped region. The presence of the (7 × 7) reconstructed areas makes this vicinal system an ideal testbed for surface characterization techniques and investigating its rich morphology and electronic features. Teys et al. proposed that this surface is oriented along the (7 7 10) direction. 2Within Teys model, the stepped part consists of a periodically ordered triple step with a height of 3 atomic layers and a width of 16 atomic rows, corresponding to a lateral periodicity of 5.2 nm.Scanning force microscopy (SFM), particularly in ultra-high vacuum (UHV) and its non-contact mode, has become one of the standard techniques for analyzing the topographic properties of flat surfaces at the atomic scale. 9On conducting surfaces, SFM provides complementary information to that obtained with scanning tunneling microscopy (STM), 10,11 in some cases with even higher spatial resolution. 12,13The atomic resolution capability of SFM arises from the short-range forces acting between an atomically sharp tip and a clean surface. 14 The differences between the work functions of the probing tip and the surface of the sample give rise to contact potential differences (CPD) that can be measured using Kelvin probe force microscopy (KPFM). 15-19The origin of atomic-scale KPFM contrast is still under discussion, since the work function is considered as a macroscopic concep...

Determination of Specific Electrocatalytic Sites in the Oxidation of Small Molecules on Crystalline Metal Surfaces

“…Also, the uncontrolled crystallographic features such as holes, ad-atoms or ad-islands are not considered. In practice, the unevenly distributed sites or atom arrangement at surfaces, reflect in the variation of the local physical properties intrinsic to the surfaces as is the work function [19,20], and imperfections, as the steps, create electronic perturbation on the terraces [21]. These modifications at the catalyst surface originate deep consequences in the catalytic properties and open the possibility of tuning the properties of the catalyst, in a controlled way.…”

Atomically resolved scanning force studies of vicinal Si(111)

“…4(a). They look very similar to silicon atoms, therefore we tentatively ascribe them to additional silicon clusters produced during the preparation of the sample, while further work is needed to fully identify them [15]. Besides the Si clusters, we observe parts of the surface that are not properly reconstructed.…”

“…The D ⊥ -D 1 buckling in turn induces a corresponding tilt in the directly adjacent D 1 row. Interestingly, due to the [15]). Charge transfer between the D ⊥ and D 1 dimers causing buckling is indicated in similarity to the Si(100)-(2 × 1) surface.…”

“…SFM has been mainly applied to flat surfaces, because of the technical difficulties of scanning over a corrugated surface. Recently, we reported that it is possible to apply SFM and Kelvin probe force microscopy on stepped surfaces even with atomic resolution [15].…”

Film Thickness of Pb Islands on the Si(111) Surface

“…The sign of the measured Kelvin voltage was known because we have applied a voltage to the tip. The polarity of the final result has been checked previously 19 . By introducing a negative sign to the data, we represent negative charge by bright contrast, i.e.…”