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REVIEW 3 major objections 6 minor 3 references

Selective synthesis of large-area monolayer tin sulfide from simple substances

T0 review · 3 major / 6 minor · reviewed 2026-08-12 · deepseek-v4-flash

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Pith's one-line read Monolayer tin sulfide can be grown from plain tin and sulfur, then thinned by nitrogen etching.

desk verdict Solid phase-selective growth of SnS from elemental Sn/S, but the monolayer etching claim rests on too little evidence as written. read the letter →

arxiv 2411.18034 v1 pith:E5AR4JNK submitted 2024-11-27 cond-mat.mtrl-sci

Kazuki Koyama , Jun Ishihara , Takeshi Odagawa , Makito Aoyama , Chaoliang Zhang , Shiro Entani , Ye Fan , Atsuhiko Mori
show 6 more authors
Ibuki Kitakami Sota Yamamoto Toshihiro Omori Yasuo Cho Stephan Hofmann Makoto Kohda
This is my paper · ORCID
classification cond-mat.mtrl-sci
keywords tinmonosulfidemonolayerSnSchemicalvapordepositionselectivegrowthnitrogenetchingphasediagramtwo-dimensionalmaterialsp-typesemiconductor
verification ladder T0 review T1 audit T2 compute T3 formal

The pith

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

The reading

The paper claims that phase-pure tin monosulfide (SnS) can be grown from plain elemental tin and sulfur powders by simply moving the sulfur boat closer to or farther from the tin boat, and that the resulting bulk crystals can then be thinned to monolayers by heating them in pure nitrogen. This matters because monolayer SnS is hard to make: lone-pair electrons strengthen interlayer bonding, so crystals grow thick, and prior routes relied on toxic gases such as H2S or on expensive, less pure precursors. If the claims hold, large-area monolayer SnS on SiO2/Si becomes available with common lab equipment and cheap, safe starting materials, opening a practical path to devices that exploit SnS's room-temperature ferroelectricity, shift-current response, and predicted persistent spin helix state.

What carries the argument

The central control is the S–Sn binary phase diagram, used with thermodynamic parameters from a published assessment to predict which tin sulfide is stable at a given sulfur concentration; the experimental knob is the heater-to-heater distance d, which sets sulfur vapor delivery and therefore the sulfur-to-tin ratio at the growing crystal. The thinning step rests on a different mechanism: high-temperature nitrogen etches SnS layer by layer, and the authors assume, following prior work on SnSe, that strong bonding between the SiO2/Si substrate and the bottom SnS sheet protects that last monolayer from etching. Cooling from the growth temperature converts the high-temperature β phase into the polar α phase, giving the low-symmetry room-temperature structure that is desired for ferroelectric and spin-texture applications.

What would settle it

Repeating the 700°C nitrogen etch on bulk SnS grown on a substrate with known weak interaction, such as hydrogen-terminated silicon or graphite, and finding that no monolayer remains would contradict the substrate-protection mechanism; alternatively, mapping many etched crystals by AFM and finding thicknesses clustered at integer multiples of the 0.87 nm step rather than a dominant monolayer would overturn the monolayer-yield claim.

Watch

Extended reading notes

Core claim

Using a calculated S–Sn phase diagram, the authors show that the stable phase depends on sulfur atomic fraction: below 50 at% S only SnS is stable, above 67 at% only SnS2, and in between the two can coexist. They realize this control in a two-zone CVD furnace by varying the distance between sulfur and tin boats, which changes the sulfur vapor concentration reaching the substrate; Raman, STEM, EDS, EBSD, and S K-edge XANES confirm that the resulting crystals are phase-pure, c-axis-oriented, and free of impurities above the 0.1 at% detection limit. Grown SnS is p-type, as shown by scanning nonlinear dielectric microscopy. Finally, heating the bulk SnS on SiO2/Si at 700°C in flowing nitrogen etches away the upper layers while the layer adjacent to the substrate survives, leaving monolayer crystals with a measured thickness of 0.87 nm and lateral sizes of tens of micrometers.

Load-bearing premise

The etching step relies on the assumption that the SiO2/Si substrate binds the bottom SnS layer strongly enough to protect it from nitrogen etching while every layer above it is removed; this protection has been observed for SnSe but is not independently demonstrated for SnS here, and the monolayer thickness is inferred from a single AFM line profile.

Editorial extensions

If this is right

  • Phase-pure SnS and SnS2 can be grown from single-element precursors, avoiding contamination from transport agents or reactive gases.
  • Large-area bulk SnS grown first, then thinned, bypasses the strong out-of-plane growth tendency that has made direct monolayer SnS synthesis difficult.
  • Monolayer SnS crystals tens of micrometers across on SiO2/Si are available for devices probing in-plane ferroelectricity, shift-current photovoltaics, and the persistent spin helix state.
  • By tuning etching time and nitrogen flow, the same method yields bilayer SnS, in which a gate voltage can break inversion symmetry.
  • The phase-diagram-guided boat-distance control provides a simple knob for selecting SnS, SnS2, or mixed phases in one furnace.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

  • If substrate adhesion is what stops etching, the same nitrogen-etch step should work on other strongly interacting substrates, and should fail on weakly interacting ones; this is directly testable and the paper does not test it.
  • The distance-control strategy should transfer to other chalcogenide systems with competing stoichiometric phases, provided their phase diagrams are known; SnSe, GeS, and GeSe are natural candidates.
  • The monolayer assignment rests on a single 0.87 nm AFM profile; a systematic thickness survey or cross-sectional STEM would strengthen or revise the monolayer yield claim.
  • The paper establishes p-type doping but does not measure spin coherence; a future spin-transport experiment on the etched monolayers would test whether the persistent spin helix actually survives in the CVD-grown material.
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Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, and a circularity audit.

Referee Report

3 major / 6 minor

Summary. The manuscript reports a CVD route to selectively grow SnS and SnS2 from elemental Sn and S powders by varying the separation between the precursor boats, and a subsequent high-temperature nitrogen annealing step intended to etch bulk SnS down to monolayer or few-layer flakes. The as-grown crystals are characterized extensively (angle-resolved Raman, STEM with EDS, SEM-EDS, EBSD, S K-edge XANES with FDMNES simulations) and the data support phase-pure, c-plane-oriented, p-type SnS and SnS2. The monolayer-etching claim, in contrast, is supported only by a single AFM line profile (0.87 nm) and an assumed substrate-bonding etch-stop mechanism taken from prior SnSe work, with no direct evidence of layer-by-layer top-down etching or monolayer-specific characterization of the etched flakes. The layer-thickness calibration is internally inconsistent (0.87 nm monolayer, 1.5 nm bilayer, 1.8 nm '2 or 3 layers').

Significance. The growth part is a solid empirical contribution: selective synthesis of SnS from the simplest precursors, corroborated by redundant phase-identification techniques, with no free parameters and a thermodynamic phase diagram used only as a qualitative guide; this is a useful simplification over prior methods involving toxic gases or expensive powders. The monolayer etching step, if validated, would be a significant practical advance for monolayer SnS devices. However, the monolayer claim is the headline result and currently rests on insufficient evidence, so the paper in its present form cannot support its abstract-level assertions.

major comments (3)
  1. [Bulk SnS is etched... (p. 11) and Fig. 5] The monolayer claim rests on a single AFM line profile (0.87 nm, Fig. 5c) and the assertion that 'the strong bonding between the substrate and the bottom of the crystals prevents the etching of the lowest layered structure of SnS' (p. 11), which is imported from the SnSe study of ref 40 without independent verification. No before/after thickness measurement on the same crystal demonstrates that etching proceeds top-down and stops at one layer, and no monolayer-specific Raman, EDS, XPS, or cross-sectional STEM data are presented for the etched flakes. Because the abstract's central promise is 'monolayer SnS crystals, up to several tens of micrometers,' this is load-bearing. The authors should provide statistical AFM height data across many flakes, a time-series or same-crystal before/after thickness comparison, and an independent calibration of the monolayer thickness (e.g., Raman or cross-sectional STEM).
  2. [Fig. 5c–e and the etching paragraph] The layer-count calibration is internally inconsistent: 0.87 nm is labelled monolayer (Fig. 5c), 1.5 nm is labelled bilayer (Fig. 5e), and 1.8 nm is labelled '2 or 3 layers' (Fig. 5d). If the monolayer step is 0.87 nm, a bilayer should be ~1.74 nm and 1.8 nm should be ~2 layers, while 1.5 nm is below the expected bilayer value. This ambiguity undermines the claim that etch time and flow rate control the layer number. A histogram of measured step heights and a self-consistent height-to-layer-number conversion are required.
  3. [Abstract and Fig. 5a–b] The claim of 'monolayer SnS crystals, up to several tens of micrometers in lateral scale' is not quantified. The lateral dimensions of the monolayer flakes are not reported, and no distribution or yield statistics are given. Please provide the lateral sizes of all remaining monolayer flakes observed and the fraction of crystals that reached monolayer thickness.
minor comments (6)
  1. [Page 10] 'fee from the influence' should be 'free from the influence.'
  2. [Page 11] 'tunning' should be 'tuning.'
  3. [Etching paragraph (p. 11)] The sentence 'This nitrogen etching method facilitates the synthesis not only of monolayer40 but also bilayer SnS' cites ref 40, which is a study of SnSe, not of monolayer SnS; this citation is misleading and should be corrected.
  4. [Abstract and Fig. 1f] The lateral-size claims ('exceeding 14,000 μm2' for bulk; 'several tens of micrometers' for monolayers) are stated without specifying how these dimensions were measured; please provide measurement details and statistics.
  5. [Page 6] 'adjusting d allows accurate control of the sulfur concentration' overstates the evidence, since the sulfur vapor concentration is not directly measured; please moderate the wording or include a concentration measurement.
  6. [Etching section (p. 11)] The role of nitrogen in the etching step is not addressed; a comparison with argon or vacuum annealing would clarify whether the effect is specific to N2.

Circularity Check

0 steps flagged · score 0.0 of 10

No significant circularity: the growth and phase-selection claims are independently verified by multiple structural probes, and the monolayer etching claim, though thinly supported, rests on external prior work rather than on fitted or self-cited inputs.

full rationale

The paper's derivation chain is not circular. The thermodynamic guide for selective SnS/SnS2 growth is an external S–Sn phase diagram (Guan et al., Thermo-Calc), used only as a guide; the resulting phases are independently identified by angle-resolved Raman, cross-sectional and top-view STEM, EDS, EBSD, and S K-edge XANES with ab initio FDMNES simulations, all compared against reported external spectra and structures. The p-type carrier assignment is made by SNDM and attributed to external prior results on Sn vacancies, not to a parameter fit in this paper. The monolayer claim from nitrogen etching is supported by one AFM line profile (0.87 nm) compared to the previously reported monolayer SnS thickness (ref 4), and the etching-stop mechanism is imported from an external SnSe study (ref 40); while this is an unverified assumption and a correctness risk, it is not circular because it is not an input of the derivation and no fitted quantity is renamed as a prediction. No self-citation is load-bearing: the authors' own persistent-spin-helix references motivate applications but do not determine the experimental results. The paper therefore exhibits no step in which a prediction is equivalent to an input by construction, no fitted parameter called a prediction, and no uniqueness theorem imported from the authors' prior work.

Assumptions & free parameters 0 free parameters · 5 assumptions · 0 invented entities

The paper introduces no new particles or fitted constants. Its load-bearing imports are the thermodynamic database of the S-Sn system, the unverified monotonic distance-to-concentration mapping, the monolayer thickness calibration from prior literature, and the etching-stop mechanism borrowed from SnSe. These are plausible but not independently established here.

assumptions (5)
  • domain assumption The S-Sn phase diagram computed at 10^5 Pa with the Guan et al. thermodynamic database predicts the stable solid phases under the open-flow CVD conditions.
    Used to map sulfur at% to stable phases and to design growth conditions (Section 'To explore selective growth...', Fig. 1c); the actual reactor is a non-equilibrium open tube with Ar flow.
  • domain assumption Varying the heater distance d monotonically and repeatably controls the sulfur vapor concentration reaching the substrate.
    No partial-pressure measurement is reported; selectivity is inferred from the resulting crystal phases (Section 'SnS and SnS2 crystals are grown...', Fig. 1d,e).
  • domain assumption An AFM step height of 0.87 nm corresponds to monolayer SnS.
    Calibrated against the reported thickness of approximately 0.8 nm for monolayer SnS in ref 4; the paper uses this to identify the etched product as a monolayer (Fig. 5c).
  • domain assumption The substrate-SnS interfacial bonding prevents etching of the bottommost SnS layer.
    Borrowed from SnSe (ref 40) and invoked to explain why etching leaves a monolayer rather than removing everything (Section 'Bulk SnS is etched...').
  • domain assumption The sign of the SNDM dC/dV signal can be read as carrier type for atomically thin SnS.
    Based on prior SNDM studies on MoS2 (refs 36,37); the paper uses it to conclude grown SnS is p-type (Fig. 4).

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Cite this review

Pith. "Pith review of Selective synthesis of large-area monolayer tin sulfide from simple substances." pith.science (2026). https://pith.science/paper/E5AR4JNK

@misc{pith2026241118034,
  author       = {Pith},
  title        = {Pith review of: Selective synthesis of large-area monolayer tin sulfide from simple substances},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/E5AR4JNK}},
  note         = {Machine review of arXiv:2411.18034}
}
read the original abstract

Both tin monosulfide (SnS) and tin disulfide (SnS2) are thermodynamically stable layered materials with potential for spin-valleytronic devices and photodetectors. Notably, monolayer SnS, owing to its low symmetry, exhibits interesting properties such as ferroelectricity, shift-current, and a persistent spin helix state in the monolayer limit. However, creating atomic-thickness crystals of SnS is challenging owing to the enhanced interlayer interactions caused by lone pair electrons, unlike to SnS2. Here, we demonstrate that p-type SnS can be selectively grown by simply varying the sulfur vapor concentration relative to tin using single-element precursors. We show that monolayer SnS crystals, up to several tens of micrometers in lateral scale, can be easily and safely obtained by high-temperature etching of bulk SnS in a pure nitrogen gas atmosphere. These findings pave the way for device applications based on high-quality tin sulfide.

Discussion (0). Continue with ORCID to comment.

Reference graph

Works this paper leans on

3 extracted references · 2 canonical work pages

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    https://doi.org/10.1016/j.solener.2017.07.017

    work page doi:10.1016/j.solener.2017.07.017 2017

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    Fingerprint

    https://doi.org/10.1021/acsnano.6b08704. (26) Yu, D.; Li, Q.; Wei, A.; Zhao, Y .; Liu, J.; Xiao, Z. Synthesis and Characterization of the Ultra -thin SnS Flakes and the Micron -Thick SnS Crystals by Chemical Vapor Deposition. J. Mater. Sci.: Mater. Electron. 2019, 30 (11), 10879 –10885. https://doi.org/10.1007/s10854-019-01431-9. (27) Yorulmaz, B.; Özden,...

    work page arXiv

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    (5) Chang, Y .-R.; Nanae, R.; Kitamura, S.; Nishimura, T.; Wang, H.; Xiang, Y .; Shinokita, K.; Matsuda, K.; Taniguchi, T.; Watanabe, K.; Nagashio, K

    https://doi.org/10.1038/s41467-020-16291-9. (5) Chang, Y .-R.; Nanae, R.; Kitamura, S.; Nishimura, T.; Wang, H.; Xiang, Y .; Shinokita, K.; Matsuda, K.; Taniguchi, T.; Watanabe, K.; Nagashio, K. Shift -Current Photovoltaics Based on a Non -centrosymmetric Phase in in -Plane Ferroelectric SnS. Adv. Mater. 2023, 35 (29), e2301172. https://doi.org/10.1002/ad...

    doi:10.1038/s41467-020-16291-9

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Reviewed August 12, 2026 · model on record in the stance chip above.