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arxiv: 1907.08919 · v1 · pith:GBWG52XJnew · submitted 2019-07-21 · ❄️ cond-mat.mtrl-sci

Magnification effects in scanning tunneling microscopy: the role of surface radicals

Ruslan Zhachuk , Jose Coutinho This is my paper

Pith reviewed 2026-05-24 18:57 UTC · model grok-4.3

classification ❄️ cond-mat.mtrl-sci
keywords scanning tunneling microscopysurface radicalssilicongermaniumimage magnificationpentamer structureshigh-index surfaces
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0 comments X

The pith

Polarized surface radicals angled to the normal produce magnified spurious images in STM.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper shows that STM images can indicate atomic locations different from the actual ones when polarized surface radicals tilt away from the surface normal. This creates spurious magnified images, illustrated by pentamer-like structures on (110), (113), and (331) surfaces of silicon and germanium. A reader would care because STM is the main tool for mapping surface atomic structure, and this distortion has been overlooked in surfaces with directional bonds. The effect arises from the geometry and polarization of the radicals altering the tunneling signal.

Core claim

Spurious images are formed in the presence of polarized surface radicals showing a pronounced angle with respect to the surface normal; this magnification effect on pentamer-like structures has been overlooked and must be accounted for when interpreting high-resolution STM images on surfaces with directional bonds.

What carries the argument

Polarized surface radicals tilted away from the surface normal, which distort the STM tunneling current to suggest incorrect atomic positions.

If this is right

  • High-resolution STM data on surfaces with directional bonds require correction for radical-induced magnification.
  • Pentamer-like features on high-index Si and Ge surfaces reflect apparent rather than true atomic positions.
  • Surface structure models derived solely from STM without accounting for radical angle can misidentify atomic arrangements.
  • The effect applies generally to any surface where radicals form at an angle to the normal.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • This mechanism could explain similar image distortions reported on other semiconductor or oxide surfaces with tilted bonds.
  • Combining STM with non-contact AFM might separate the polarization contribution from true topography.
  • Density functional theory simulations of radical tilt could quantify the magnification factor for different angles.

Load-bearing premise

The observed magnification arises primarily from the geometric angle and polarization of surface radicals rather than from other unmodeled aspects of tip-sample electronic coupling or tip geometry.

What would settle it

STM images of the same pentamer structures on Si or Ge surfaces taken with a tip or bias that eliminates interaction with radical polarization, showing no magnification.

Figures

Figures reproduced from arXiv: 1907.08919 by Jose Coutinho, Ruslan Zhachuk.

Figure 1
Figure 1. Figure 1: (a) Experimental high resolution STM image of the S [PITH_FULL_IMAGE:figures/full_fig_p004_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: Vertical cut of the LDOS along the ‘A’ dashed line of [PITH_FULL_IMAGE:figures/full_fig_p005_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: Height profiles along dashed lines ‘A’ and ‘B’ in Fig [PITH_FULL_IMAGE:figures/full_fig_p006_3.png] view at source ↗
read the original abstract

Scanning tunneling microscopy (STM) is a fundamental tool for determination of the surface atomic structure. However, the interpretation of high resolution microscopy images is not straightforward. In this paper we provide a physical insight on how STM images can suggest atomic locations which are distinctively different from the real ones. This effect should be taken into account when interpreting high-resolution STM images obtained on surfaces with directional bonds. It is shown that spurious images are formed in the presence of polarized surface radicals showing a pronounced angle with respect to the surface normal. This issue has been overlooked within the surface science community and often disregarded by experimentalists working with STM. Without loss of generality, we illustrate this effect by the magnification observed for pentamer-like structures on (110), (113) and (331) surfaces of silicon and germanium.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

2 major / 1 minor

Summary. The manuscript argues that STM images on surfaces with directional bonds can produce spurious, magnified atomic positions due to polarized surface radicals oriented at a pronounced angle to the surface normal. This effect is illustrated qualitatively using pentamer-like structures observed on the (110), (113), and (331) surfaces of Si and Ge, with the claim that the geometric/polarization contribution from the radicals has been overlooked in the community.

Significance. If the proposed mechanism can be shown to dominate other contributions, the result would supply a useful interpretive caution for high-resolution STM work on reconstructed surfaces. The manuscript does not, however, supply machine-checked proofs, reproducible code, or falsifiable quantitative predictions that would strengthen its standing.

major comments (2)
  1. [Abstract and mechanism description] The central attribution—that the observed magnification is driven primarily by the radicals' angle and polarization rather than tip geometry or orbital-overlap details—is presented without systematic variation of tip parameters or full DFT+STM simulations. This leaves the claim under-constrained, as alternative convolution mechanisms could reproduce the same apparent magnification (see skeptic note on the core assertion).
  2. [Illustration on Si/Ge surfaces] No quantitative metric (e.g., apparent vs. true interatomic distances, bias-dependent LDOS maps, or comparison of simulated images with and without the radical tilt) is supplied to demonstrate that the radical-angle effect is load-bearing; the illustrations remain qualitative.
minor comments (1)
  1. Notation for the radical polarization vector and its angle with respect to the surface normal should be defined explicitly in the first figure or equation.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the constructive comments on our manuscript. The work is intended to highlight a qualitative geometric and polarization-based mechanism for spurious magnification in STM images that has been overlooked. We address the major comments point by point below, indicating planned revisions where appropriate.

read point-by-point responses

  1. Referee: [Abstract and mechanism description] The central attribution—that the observed magnification is driven primarily by the radicals' angle and polarization rather than tip geometry or orbital-overlap details—is presented without systematic variation of tip parameters or full DFT+STM simulations. This leaves the claim under-constrained, as alternative convolution mechanisms could reproduce the same apparent magnification (see skeptic note on the core assertion).

    Authors: We agree that the manuscript does not include systematic tip-parameter sweeps or full DFT+STM image simulations, which would provide stronger constraints on the relative importance of the radical-angle effect versus other convolution mechanisms. The paper's scope is limited to a conceptual geometric argument based on the known tilt and polarization of surface radicals on these reconstructed surfaces. We will revise the text to explicitly state the assumptions, discuss possible competing contributions (such as tip geometry), and note that quantitative dominance would require additional simulations beyond the present qualitative illustration. revision: partial

  2. Referee: [Illustration on Si/Ge surfaces] No quantitative metric (e.g., apparent vs. true interatomic distances, bias-dependent LDOS maps, or comparison of simulated images with and without the radical tilt) is supplied to demonstrate that the radical-angle effect is load-bearing; the illustrations remain qualitative.

    Authors: The illustrations are qualitative, as the manuscript aims to draw attention to the effect rather than to deliver quantitative predictions or simulated images. We will add a short supplementary note providing simple geometric projections of apparent versus true interatomic distances based on the reported radical tilt angles for the pentamer structures. Bias-dependent LDOS maps and full image simulations with/without tilt are not available in the current study and would require new computational work; we will acknowledge this limitation explicitly in the revised manuscript. revision: partial

Circularity Check

0 steps flagged

No circularity: mechanism presented as physical insight without self-referential reduction

full rationale

The paper's central claim is that polarized surface radicals at an angle to the normal produce magnified spurious STM images, illustrated on Si/Ge high-index surfaces. The provided abstract and description contain no equations, fitted parameters, self-citations used as load-bearing premises, or derivations that reduce to their own inputs by construction. The argument is framed as overlooked physical insight rather than a prediction derived from prior results of the same authors or a renaming of known patterns. No load-bearing step matches any of the enumerated circularity patterns.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

Only the abstract is available; no free parameters, axioms, or invented entities can be identified from the provided text.

pith-pipeline@v0.9.0 · 5663 in / 973 out tokens · 43732 ms · 2026-05-24T18:57:13.709339+00:00 · methodology

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Reference graph

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