Thickness determination of MoS2, MoSe2, WS2 and WSe2 on transparent stamps used for deterministic transfer of 2D materials

Andres Castellanos-Gomez; Iris Niehues; Mar Garc\'ia-Hern\'andez; Najme S. Taghavi; Patricia Gant; Peng Huang; Riccardo Frisenda; Robert Schmidt; Rudolf Bratschitsch; Steffen Michaelis de Vasconcellos

arxiv: 1907.07365 · v1 · pith:YRDNFD2Tnew · submitted 2019-07-17 · ⚛️ physics.app-ph · cond-mat.mes-hall· cond-mat.mtrl-sci

Thickness determination of MoS2, MoSe2, WS2 and WSe2 on transparent stamps used for deterministic transfer of 2D materials

Najme S. Taghavi , Patricia Gant , Peng Huang , Iris Niehues , Robert Schmidt , Steffen Michaelis de Vasconcellos , Rudolf Bratschitsch , Mar Garc\'ia-Hern\'andez

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Riccardo Frisenda Andres Castellanos-Gomez

This is my paper

Pith reviewed 2026-05-24 20:08 UTC · model grok-4.3

classification ⚛️ physics.app-ph cond-mat.mes-hallcond-mat.mtrl-sci

keywords thickness determinationoptical microscopyMoS2MoSe2WS2WSe2transition metal dichalcogenidestransparent stamps

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The pith

The blue channel transmittance in optical microscopy images determines the thickness of MoS2 and related materials on transparent stamps.

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

The paper establishes that separating transmission-mode optical images into red green and blue channels yields a practical way to measure the number of layers in flakes of MoS2, MoSe2, WS2 and WSe2 sitting on transparent stamps. The blue channel shows a strong and steady change with added layers while remaining consistent from flake to flake and unaffected by doping variations in MoS2. This optical route supplies layer counts before the flakes are moved to new surfaces. Researchers who rely on deterministic transfer of these materials can therefore avoid extra instruments for thickness checks.

Core claim

The transmittance extracted from the blue channel of transmission optical microscopy images exhibits a large and monotonic dependence on layer number for MoS2, MoSe2, WS2 and WSe2 on transparent stamps, while red and green channels provide supporting information, and the blue signal stays robust against small flake-to-flake differences and doping changes.

What carries the argument

Blue channel transmittance from transmission optical images, which acts as the thickness probe because its value changes steadily with added layers.

If this is right

Layer numbers for these four materials can be read from ordinary optical microscope images without atomic force microscopy or Raman spectroscopy.
The same image analysis works across MoS2, MoSe2, WS2 and WSe2.
Doping changes in MoS2 do not alter the reliability of the thickness reading.
Small natural differences between flakes do not prevent consistent thickness assignment.

Where Pith is reading between the lines

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

The optical channel method could be extended to additional layered materials placed on transparent supports.
Image-processing routines could automate the channel analysis and reduce manual inspection time during sample preparation.
Recording the blue transmittance during the transfer step itself might allow real-time thickness verification.

Load-bearing premise

The measured blue transmittance is caused mainly by the number of layers in the flake rather than by differences in stamp thickness, interface quality, or lighting conditions.

What would settle it

Independent atomic force microscopy measurements on the same flakes show either non-monotonic blue transmittance values or large scatter between flakes of identical layer count.

Figures

Figures reproduced from arXiv: 1907.07365 by Andres Castellanos-Gomez, Iris Niehues, Mar Garc\'ia-Hern\'andez, Najme S. Taghavi, Patricia Gant, Peng Huang, Riccardo Frisenda, Robert Schmidt, Rudolf Bratschitsch, Steffen Michaelis de Vasconcellos.

**Figure 1.** Figure 1: (a) Optical image in transmission mode of a MoS2 flake with different thicknesses. (b) Line profiles of the intensities of the red, green and blue channels of the image in 1a. (c) Histograms of the 1-transmission value in the RGB channels for several MoS2 flakes [PITH_FULL_IMAGE:figures/full_fig_p008_1.png] view at source ↗

**Figure 2.** Figure 2: (a) Scatter plot and histogram of the blue channel transmission values for several MoS2 flakes. (b) Differential reflectance spectra for MoS2 with different number of layers. (c) Raman spectra for MoS2 with different number of layers. (d) Photoluminescence of MoS2 for different number of layers [PITH_FULL_IMAGE:figures/full_fig_p009_2.png] view at source ↗

**Figure 3.** Figure 3: Histograms of the 1-transmission value in the blue channel for MoS2 flakes doped with (a) Co, (b) Ni, (c) Fe and (d) Nb. (e) Average of the 1-transmission values for 1L to 4L in each material [PITH_FULL_IMAGE:figures/full_fig_p010_3.png] view at source ↗

**Figure 4.** Figure 4: Histograms of the 1-transmittance value in the blue channel for (a) MoS2, (b) MoSe2, (c) WS2 and (d) WSe2 flakes. (e) Average of the 1-transmittance values for 1L to 4L in each material [PITH_FULL_IMAGE:figures/full_fig_p011_4.png] view at source ↗

read the original abstract

Here, we propose a method to determine the thickness of the most common transition metal dichalcogenides (TMDCs) placed on the surface of transparent stamps, used for the deterministic placement of two-dimensional materials, by analyzing the red, green and blue channels of transmission-mode optical microscopy images of the samples. In particular, the blue channel transmittance shows a large and monotonic thickness dependence, making it a very convenient probe of the flake thickness. The method proved to be robust given the small flake-to-flake variation and the insensitivity to doping changes of MoS2. We also tested the method for MoSe2, WS2 and WSe2. These results provide a reference guide to identify the number of layers of this family of materials on transparent substrates only using optical microscopy.

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.

Desk Editor's Note private letter to a colleague

This paper supplies a practical blue-channel transmittance calibration for counting layers of four TMDCs on transparent transfer stamps, but the abstract leaves the supporting data and controls unshown.

read the letter

The one thing to know is that the authors measured red-green-blue transmittance through MoS2, MoSe2, WS2, and WSe2 flakes on transparent stamps and found the blue channel drops monotonically with layer number while staying fairly stable from flake to flake and insensitive to doping changes in MoS2. They position this as a quick optical check before deterministic transfer. That is the core result and it is new in the narrow sense that no prior reference guide existed for exactly these four materials on this substrate type using this channel split. The work is useful because it turns a routine lab step into something more reproducible without needing AFM or Raman every time. They tested multiple materials and noted the practical robustness, which is the part that actually helps people doing device fabrication. The soft spot is the lack of any numbers in the abstract: no transmittance values, no standard deviations, no plots of stamp-to-stamp variation, and no explicit check that local stamp thickness or interface quality was subtracted or shown to be negligible. The stress-test concern lands here because transmission through the full stack means stamp nonuniformity or illumination differences could contribute to the same signal, and the abstract does not report the controls that would isolate the flake contribution. If the full paper contains those tables and background measurements, the claim strengthens; otherwise the monotonicity is asserted rather than demonstrated with error bars. This is a methods note aimed at experimental groups already running stamp-transfer workflows. A reader who needs a quick reference for these specific TMDCs on transparent stamps will find it handy and might save a few AFM scans. It is not foundational, but the question it answers is real and the approach is straightforward enough that a serious referee could check the data and controls in one round. I would send it to review rather than desk-reject, with the expectation that the authors supply the missing quantitative sections.

Referee Report

2 major / 2 minor

Summary. The manuscript proposes an empirical method to determine the layer thickness of MoS2, MoSe2, WS2 and WSe2 flakes on transparent stamps by extracting red, green and blue channel transmittances from transmission-mode optical micrographs. It asserts that blue-channel transmittance exhibits a large, monotonic dependence on layer number, that flake-to-flake variation is small, and that the signal is insensitive to doping changes in MoS2, thereby providing a convenient optical guide for layer identification during deterministic transfer.

Significance. If the calibration is shown to be robust, the approach supplies a low-cost, non-destructive route to layer counting on transparent substrates using only standard optical microscopy, which would streamline workflows for 2D-material device fabrication. The result is entirely empirical; no parameter-free derivation or machine-checked proof is offered.

major comments (2)

[Results] Results section: the central claim that blue-channel transmittance is a reliable thickness probe rests on the assertion of 'small flake-to-flake variation' and 'robustness,' yet the manuscript supplies no quantitative metrics (standard deviations, number of flakes measured per material, or error bars) to support these statements; without such data the monotonicity cannot be evaluated for reproducibility.
[Results] Results section: the attribution of observed transmittance differences predominantly to layer number (rather than local stamp-thickness variations, stamp-flake interface quality, or illumination non-uniformity) is load-bearing for the method, but no stamp-uniformity measurements, background-subtraction protocol, or stamp-to-stamp comparison are reported; this omission directly affects the validity of using the blue channel as an isolated thickness metric.

minor comments (2)

[Figures] Figure captions should explicitly state the number of flakes averaged, the illumination source, and the stamp material thickness range to allow readers to assess the controls.
[Abstract] The abstract states the method was 'tested' for MoSe2, WS2 and WSe2 but provides no separate quantitative comparison or table of calibration coefficients for these materials.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the detailed and constructive report. The two major comments identify genuine gaps in the quantitative presentation and experimental controls of our empirical method. We address each point below and will revise the manuscript to strengthen the supporting evidence without altering the core claims.

read point-by-point responses

Referee: [Results] Results section: the central claim that blue-channel transmittance is a reliable thickness probe rests on the assertion of 'small flake-to-flake variation' and 'robustness,' yet the manuscript supplies no quantitative metrics (standard deviations, number of flakes measured per material, or error bars) to support these statements; without such data the monotonicity cannot be evaluated for reproducibility.

Authors: We agree that the absence of explicit quantitative metrics weakens the reproducibility claim. The original manuscript relied on visual inspection of the plotted data points to convey small flake-to-flake variation. In the revised version we will add: (i) the exact number of flakes measured for each material (MoS2, MoSe2, WS2, WSe2), (ii) standard deviations or error bars on the blue-channel transmittance values, and (iii) a short table or inset summarizing the observed spread. These additions will allow direct evaluation of monotonicity and reproducibility. revision: yes
Referee: [Results] Results section: the attribution of observed transmittance differences predominantly to layer number (rather than local stamp-thickness variations, stamp-flake interface quality, or illumination non-uniformity) is load-bearing for the method, but no stamp-uniformity measurements, background-subtraction protocol, or stamp-to-stamp comparison are reported; this omission directly affects the validity of using the blue channel as an isolated thickness metric.

Authors: We acknowledge that the manuscript does not explicitly document stamp uniformity or the precise background-subtraction procedure. In the revision we will insert a dedicated paragraph describing the background-subtraction protocol (flat-field correction from stamp regions without flakes) and will report stamp-to-stamp transmittance uniformity measurements performed on blank stamps. These data will support the claim that layer-number contrast dominates over substrate variations under the imaging conditions used. revision: yes

Circularity Check

0 steps flagged

No circularity; empirical calibration of transmittance vs. layer count

full rationale

The paper reports direct optical measurements of red/green/blue channel transmittance for TMDC flakes of known layer numbers on transparent stamps. The central result is an observed monotonic dependence in the blue channel, presented as an empirical reference guide without any derivation, fitted parameters renamed as predictions, self-citations, or ansatzes. The method is calibrated from the data themselves and contains no load-bearing steps that reduce to their own inputs by construction.

Axiom & Free-Parameter Ledger

1 free parameters · 0 axioms · 0 invented entities

The central claim rests on empirical calibration of optical transmittance versus layer number; no free parameters, axioms, or invented entities are explicitly introduced in the abstract.

free parameters (1)

blue-channel transmittance calibration coefficients
The mapping from measured blue intensity to layer number is obtained by fitting experimental data on known-thickness flakes.

pith-pipeline@v0.9.0 · 5731 in / 1174 out tokens · 25356 ms · 2026-05-24T20:08:25.758518+00:00 · methodology

discussion (0)

Reference graph

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Constructing a thickness map from transmission mode optical microscopy image

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First, the blue channel of t he transmission mode image is extracted and the average intensity of the substrate ( T0) is measured

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work page doi:10.1007/s12274 2019