Pith. sign in

REVIEW 4 major objections 4 minor 9 references

Toward two dimensional MoS2 electrets

T0 review · 4 major / 4 minor · reviewed 2026-08-05 · deepseek-v4-flash

Challenge this review Re-run · record.json Download PDF Read on arXiv ↗ Review JSON

Pith's one-line read Defect-engineered monolayer MoS2 is claimed as the first two-dimensional electret, storing patterned charge at sub-micrometer scale.

desk verdict A real, patternable, long-lived electrostatic contrast on monolayer MoS2, but the charge/vacancy densities are partly circular and the KPFM work-function control is missing. read the letter →

arxiv 2608.03602 v1 pith:O55FX2ED submitted 2026-08-04 cond-mat.mtrl-sci

Eugenio Lunedei , Andrea Liscio , Francesco Borgatti , Edoardo Chini , Pasquale DAngelo , Fiorenza Esposito , Niccolo Borghi , Matteo Mannini
show 3 more authors
Denis Gentili Luca Seravalli Massimiliano Cavallini
This is my paper · ORCID
classification cond-mat.mtrl-sci
keywords MoS2monolayerelectretsulfurvacancieschargetrappingelectrochemicalnanolithographyKelvinprobeforcemicroscopyexcitonquenching2Dmaterials
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 reports that a single atomic layer of molybdenum disulfide can be turned into an electret—a material that stores quasi-permanent electrostatic charge. The key move is to create sulfur vacancies by stamp-assisted electrode-free anodic oxidation nanolithography, with densities programmable from 10^10 to 10^13 cm^-2 and sub-micrometer spatial control. The vacancies act as deep electron traps, yielding a negative surface potential and stored charge densities up to about 1 μC/cm² that persist for hundreds of days in air; the same vacancies quench excitons, cutting the observed photoluminescence lifetime from roughly 15 ns to 180 ps. Because the optical quenching survives for more than a year while the electrostatic contrast decays on a timescale of about 134 days, the paper assigns the persistent functionality to the vacancies themselves, not to transient charge states. If correct, this establishes defect-engineered monolayer MoS2 as the first two-dimensional electret and makes atomic vacancies functional design elements.

What carries the argument

The load-bearing object is the sulfur vacancy (Vs) in the MoS2 lattice, created by stamp-assisted electrode-free anodic oxidation nanolithography (EFLAO), a capacitively coupled electrochemical patterning technique that removes sulfur from selected sub-micrometer regions. The vacancy is claimed to be a deep electron trap: it captures an electron, giving a negative surface potential measured by KPFM and a linear EFM phase-bias response, and it also acts as a non-radiative recombination center that quenches excitons. The quantification runs through a parallel-plate capacitor model (thickness 0.85 nm, εr≈5) that converts surface-potential contrast into charge density, and through the contrast b

What would settle it

Perform KPFM and EFM on a patterned flake after neutralizing the trapped charge (for example by controlled thermal annealing, corona discharge, or prolonged decay) without changing the vacancy population. If the negative surface potential and the linear EFM phase-bias signature persist, the contrast is not caused by trapped electrons and the electret mechanism proposed here is wrong; if they vanish while the Raman or XPS signatures of sulfur vacancies remain, the electron-trapping model is supported.

Watch

Extended reading notes

Core claim

Sulfur vacancies in monolayer MoS2 act as deep electron traps and exciton quenchers. Stamp-assisted electrode-free anodic oxidation nanolithography writes vacancy patterns with densities 10^10–10^13 cm^-2. KPFM shows negative surface-potential stripes matching the stamp (ΔSP to −180 mV); a parallel-plate model gives stored charge up to ~1 μC/cm², decaying with τ≈134 days in air. EFM shows a linear phase-bias response, the signature of static charge. Fluorescence lifetime falls from ~15 ns to ~180 ps, and the optical pattern persists for a year, evidence that vacancies, not transient charge states, are responsible. Thus defect-engineered monolayer MoS2 is the first two-dimensional electret.

Load-bearing premise

The measured negative surface-potential contrast is assumed to come entirely from electrons trapped at sulfur vacancies, not from a vacancy-induced shift of the work function or a surface dipole.

Editorial extensions

If this is right

  • A single atomic layer can now function as a charge-storage medium, with patterns written by a stamp in one step and read out by Kelvin probe or electric force microscopy.
  • The same defect pattern can be read optically, since exciton lifetimes and photoluminescence intensity are locally and permanently modified.
  • Charge densities up to about 1 μC/cm² and retention of hundreds of days put monolayer MoS2 in the range of conventional electrets, but with sub-micrometer lateral definition.
  • Vacancies shift from parasitic defects to programmable functional elements, suggesting a general route for adding electret functionality to 2D semiconductors.

Reading between the lines

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

  • If the vacancy-trapping mechanism transfers to other semiconducting transition-metal dichalcogenides, the same stamp-assisted writing could yield a family of 2D electrets; this extension is not tested in the paper.
  • The one-electron-per-vacancy conversion used to estimate vacancy density is an assumption; direct trap counting would tell whether the reported charge density is an upper bound.
  • The co-localized electrostatic and optical contrast suggests a two-channel memory or sensor in one monolayer, but the paper does not demonstrate a device; building one would test the practical reach.
Share X Bluesky LinkedIn Reddit HN

Editorial analysis

A structured set of objections, weighed in public.

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

Referee Report

4 major / 4 minor

Summary. The manuscript reports that monolayer MoS2, patterned by stamp-assisted electrode-free anodic oxidation nanolithography (EFLAO), behaves as a two-dimensional electret. The authors present KPFM maps showing negative surface-potential stripes that replicate the stamp, EFM phase-bias curves attributed to static surface charge, and long-term retention data described by a Hill-type decay with τ ≈ 134 days. They estimate surface charge densities up to about 1 μC/cm2 and, assuming one trapped electron per sulfur vacancy, derive vacancy densities up to about 6 × 10^12 cm−2. Time-resolved fluorescence shows a strongly reduced exciton lifetime (~180 ps) in treated regions, with the optical contrast persisting after one year. The paper concludes that sulfur vacancies created by EFLAO act as deep electron traps, establishing defect-engineered MoS2 as the first two-dimensional electret.

Significance. If the central claim is correct, this would be a notable advance: a single atomic layer storing quasi-permanent electrostatic charge with programmable, submicrometer spatial control, simultaneously defining optical contrast. The work combines a potentially scalable stamp-based patterning method with direct SPM evidence of persistent surface charge and demonstrates co-localized electrostatic and excitonic functionality. The retention data and the time-invariant optical response are valuable experimental observations. However, the manuscript's quantitative conclusions—charge densities, vacancy densities, and the attribution of the charge to sulfur vacancies—depend on assumptions that are not independently verified. The gap between the direct electrostatic measurements and the microscopic vacancy mechanism is the main weakness. If the suggested control experiments and independent vacancy quantification are provided, the paper could justify its conclusions.

major comments (4)
  1. [§2 (p.8) and SI 'Estimation of trapped charge density'] The vacancy density is derived by assuming 'each formed defect traps one electron' and then used to argue that sulfur vacancies are responsible for the trapped charge. This is circular: NVs is computed from the same KPFM-derived σ that the authors want to explain. XPS shows no statistically significant increase in Vs (Table S1), and Raman gives only an average spacing >10 nm, too coarse to validate densities of 10^11–10^13 cm−2. The abstract's 'programmable defect densities' are therefore not measured quantities. An independent measure of Vs (e.g., higher-statistics XPS or a calibrated Raman/PL ratio) is needed to support the vacancy-origin claim.
  2. [§2 (Fig. 2e) and KPFM interpretation] The negative ΔSP is interpreted entirely as trapped electron charge. However, KPFM measures contact potential difference; a defect-induced work-function shift or surface dipole from sulfur vacancies would produce a negative offset of the same polarity. No control experiment distinguishes these contributions. The aging data (Fig. 2e) show ΔSP decaying to ~20% after 300 days; this residual value may be a permanent work-function/dipole component rather than trapped charge. If so, the initial charge densities are overestimated by at least that fraction, and the electret interpretation is weakened. A discharge experiment (e.g., thermal/optical or solvent exposure) with KPFM after discharge would clarify the reversible versus permanent components.
  3. [§2 (Fig. 2f)] The EFM phase-bias curves are presented as confirming static surface charge ('almost linear dependence'). In EFM, a work-function offset shifts the parabolic C′V2 curve so that over a limited bias range the response can appear quasi-linear. The claimed distinction between 'purely capacitive' and 'static charge' is therefore not decisive without a full bias-range fit or frequency-dependent measurement. This issue further weakens the quantitative charge-density extraction and should be addressed by modeling the complete EFM response, including the contact potential offset.
  4. [Conclusion and Scheme S1] The desulfurization mechanism (water oxidation, H2S release) is presented as the dominant pathway, but the manuscript's own XPS data show no significant compositional change, and the authors state that 'other mechanisms' are not excluded. As the electret claim depends on vacancy formation, the lack of direct chemical evidence for S loss (e.g., evolved H2S detection, ex situ S quantification, or atomic-resolution imaging) is a load-bearing gap. The authors should either provide such evidence or temper the claim that sulfur vacancies, specifically, are the charge-trapping species.
minor comments (4)
  1. [Abstract and p.3] The phrase 'first two-dimensional electret' is a strong claim. Given that charge trapping has been reported in other 2D systems (refs. 10–13), the novelty should be framed as the combination of high density, retention, and patterning, or the claim should be qualified.
  2. [p.7 and Figure 2d] The statement 'ΔSP increases linearly with treatment duration' is based on a small number of points with error bars that partially overlap. Please provide the fit residuals or confidence bounds; the linearity is used to infer 'non-interacting isolated Vs.'
  3. [p.10, Figure 4] The decay times in Figure 4c are described as '10–15 ns' for pristine and '~180 ps' for treated. The fitted components in Figures S5–S6 should be presented more clearly in the main text, including the intensity-averaged lifetimes, to make the comparison quantitative.
  4. [General] There are several typographical issues: 'electrect' (p.4), 'n»2' (p.8), and inconsistent use of subscripts (e.g., E1₂g vs E12g). The references include entries with future dates (e.g., refs. 6, 18, 37); these should be updated or marked as in press.

Circularity Check

1 steps flagged · score 6.0 of 10

Vacancy density is computed from the KPFM charge density and then used as the cause of that charge; central 'defect density' numbers reduce to σ/e.

  1. self definitional [Main text, Figure 2d–e paragraph; Methods 'Estimation of trapped charge density'; Abstract/Conclusion ('programmable defect densities')]
    "Using an infinite plane electrostatic approximation19, the trapped charge density was estimated to range from ~130 ± 10 nC/cm2 after 10 min of treatment to −1000 ± 50 nC/cm2 after 150 min. ... Assuming each formed defect traps one electron, the number of sulfur vacancies (NVs) per surface unit increases from 8.1 x 10^11 NVs/cm2 after 10 minutes of treatment to 6.3 x 10^12 NVs/cm2 after 150 minutes."

    NVs is not an independent measurement: it is obtained by dividing the surface charge density σ (derived from KPFM ΔSP via a parallel-plate model) by the elementary charge, under the assumption that every vacancy traps exactly one electron. The paper then presents these NVs values as the 'defect densities' that 'act as deep electron traps and produce surface charge densities' (abstract, conclusion). Thus the vacancy density is constructed from the very charge signal it is invoked to explain; the apparent consistency between ΔSP, σ, and NVs is enforced by the conversion factor e and by the model assumptions (h_eff=0.85 nm, εr≈5), not by an independent vacancy count. XPS shows no significant Vs increase and Raman only a coarse spacing estimate, so the quantitative 'programmable defect densiti

full rationale

The paper has a genuine measured core: KPFM surface-potential contrast, EFM phase–bias response, and time-resolved fluorescence are external observations, and the electret-type retention (hundreds of days) is not itself a tautology. However, the quantitative defect-density claim is circular. The sulfur-vacancy density NVs is not measured; it is defined as σ/e, where σ is estimated from the KPFM ΔSP through the parallel-plate capacitor formula. The paper then uses the resulting NVs to assert that sulfur vacancies are the origin of the stored charge ('The resulting vacancy domains act as deep electron traps and produce surface charge densities...'). This is a self-definitional reduction: the explanatory variable is the measured effect divided by e. The absence of a control for a vacancy-induced work-function/dipole contribution to ΔSP is an additional interpretation risk, but it is a correctness concern rather than a circularity. Self-citations (refs. 4, 18, 24, 37, 38) are present but not the main load-bearing circular step; the cited EFLAO method and Vs trapping are from prior work, and the circularity is internal to the paper's own equation chain. Score 6 reflects that the central charge-storage observation is independent, while the headline 'programmable defect densities' and vacancy-origin quantification reduce by construction.

Assumptions & free parameters 5 free parameters · 6 assumptions · 0 invented entities

The central claim rests on several unverified assumptions. The most important is that KPFM contrast is caused solely by trapped electrons, which is used to derive both charge density and vacancy density. The vacancy density is not independently measured, and the mechanism is explicitly hypothesized. There are no new physical entities, but the parameters h_eff, εr, and the one-electron-per-vacancy conversion factor are free choices that directly set the reported numbers.

free parameters (5)
  • effective electrostatic thickness (h_eff) = 0.85 nm (monolayer thickness)
    Used in parallel-plate model to convert ΔSP to surface charge density; chosen as one monolayer thickness, not independently measured for charge distribution.
  • relative permittivity (εr) = ~5 (assumed)
    Used in charge density estimation; value for MoS2 is not well established at monolayer scale; introduces systematic error.
  • charge-to-vacancy conversion factor = 1 electron per vacancy (assumed)
    Used to convert trapped charge density to sulfur vacancy density NVs; not independently verified.
  • Hill relaxation time τ = 134 ± 4 days
    Fitted to ΔSP decay data to characterize retention.
  • Hill exponent n = ≈2
    Fitted to decay data; interpreted as spatially correlated relaxation.
assumptions (6)
  • domain assumption The EFLAO treatment selectively creates sulfur vacancies in MoS2 without other significant compositional changes
    Based on prior electrochemical desulfurization reports (refs 23,24) and Raman shift; XPS shows no significant change in Vs within error, so this is inferred, not directly measured.
  • domain assumption The negative ΔSP in KPFM arises exclusively from trapped negative charge, not from work function changes induced by defects
    EFM linear phase-bias supports static charge, but no control for work function contribution; charge density values depend on this assumption.
  • domain assumption Parallel-plate capacitor model with h_eff=0.85 nm and εr≈5 applies to a monolayer on SiO2
    Used to estimate charge density; the delocalized charge distribution and tip geometry are not accounted for.
  • ad hoc to paper Each sulfur vacancy traps exactly one electron
    Needed to convert charge density to vacancy density; no evidence for a specific charge state.
  • domain assumption The long-term quenching of photoluminescence is due to sulfur vacancies rather than transient charge states
    Based on persistence over one year and literature on Vs quenching; but the defect identity is not directly imaged.
  • ad hoc to paper The desulfurization mechanism (water oxidation, H2S release) is the dominant reaction pathway
    Proposed as hypothesis; authors explicitly state other mechanisms are possible.

how reviews work

0 comments
Cite this review

Pith. "Pith review of Toward two dimensional MoS2 electrets." pith.science (2026). https://pith.science/paper/O55FX2ED

@misc{pith2026260803602,
  author       = {Pith},
  title        = {Pith review of: Toward two dimensional MoS2 electrets},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/O55FX2ED}},
  note         = {Machine review of arXiv:2608.03602}
}
read the original abstract

Here, we show that controlled sulfur vacancy engineering converts monolayer MoS2 into an electret, imparting the ability to store quasi-permanent electrostatic charge within a single atomic layer. Sulfur vacancies are generated with submicrometer spatial control by stamp-assisted electrode-free electrochemical nanolithography, yielding programmable defect densities from 10 10 to 10 13 1 cm-2. The resulting vacancy domains act as deep electron traps and produce surface charge densities up to 1 uCcm-2, with charge retention in the order of hundreds days under ambient conditions. Kelvin probe and electric force microscopies directly reveal stable electrostatic patterns that replicate the lithographic motif. The same vacancy landscape simultaneously defines exciton-quenching regions, generating co-localized optical and electrostatic contrast and reducing the apparent exciton lifetime from 15 ns to 180 ps through enhanced nonradiative recombination. The persistence of the optical response over one year identifies sulfur vacancies, rather than transient charge states, as the origin of the patterned functionality. These results establish defect-engineered MoS2 as the first two-dimensional electret and demonstrate that atomic vacancies can be exploited as functional elements for encoding electrostatic and excitonic behavior in a single atomic layer.

Discussion (0). Continue with ORCID to comment.

Reference graph

Works this paper leans on

9 extracted references · 9 canonical work pages

  1. [2]

    surface. Surf. Sci. 2003, 532, 249-254. 18 Toward two-dimensional MoS2 electrets Eugenio Lunedei, Andrea Liscio, Francesco Borgatti, Edoardo Chini, Pasquale D’Angelo, Fiorenza Esposito, Niccolò Borghi, Matteo Mannini, Denis Gentili*, Luca Seravalli, Massimiliano Cavallini* SUPPLEMENTARY MATERIAL Experimental Section Growth MoS₂ Monolayer Crystals: MoS2 sa...

    work page 2003

  2. [4]

    dark zones

    Time-resolved fluorescence spectroscopy. a) Sub-ns time evolution of fluorescence spectrum of pristine 2D-MoS2 under microscope (objective 100x, lexc=402 nm, f=5 MHz, time separation between spectra: Dt = 444 ps). False color normalized intensity map, traced up to 37 ns (Dt = 74 ps) b) Same visualization for treated sample. c) Normalized micro-fluorescenc...

    work page 2017

  3. [8]

    Liquid-precursor-intermediated synthesis of atomically thin transition metal dichalcogenides

    (16) Guan, H.; Zhao, B.; Zhao, W.; Ni, Z. Liquid-precursor-intermediated synthesis of atomically thin transition metal dichalcogenides. Mater Horiz 2023, 10, 1105-1120. (17) Seravalli, L.; Esposito, F.; Bosi, M.; Aversa, L.; Trevisi, G.; Verucchi, R.; Lazzarini, L.; Rossi, F.; Fabbri, F. Built-in tensile strain dependence on the lateral size of monolayer ...

    work page 2023

  4. [9]

    Built-in tensile strain dependence on the lateral size of monolayer MoS2 synthesized by liquid precursor chemical vapor deposition

    (2) Seravalli, L.; Esposito, F.; Bosi, M.; Aversa, L.; Trevisi, G.; Verucchi, R.; Lazzarini, L.; Rossi, F.; Fabbri, F. Built-in tensile strain dependence on the lateral size of monolayer MoS2 synthesized by liquid precursor chemical vapor deposition. Nanoscale 2023, 15, 14669-14678. (3) Wang, T.; Zhang, Y.; Liu, Y.; Li, J.; Liu, D.; Luo, J.; Ge, K. Layer-...

    work page 2023

  5. [10]

    surface. Surf. Sci. 2003, 532, 249-254. (9) Garcı́a, R.; Pérez, R. Dynamic atomic force microscopy methods. Surf Sci Rep 2002, 47, 197-301

    work page 2003

  6. [18]

    !# !"# # !$!%!&!'!#!!#$!#%!#&!#'!$!! ($!$ F F *+,-

    Relative humidity was continuously monitored using a commercial hygrometer (Thermopro). Patterning was achieved by bringing the conductive stamp into conformal contact with the sample surface and applying an alternating bias of 15 V at 50 kHz for a defined duration under high-humidity conditions (95% relative humidity). A schematic representation of the p...

    work page

  7. [21]

    Dynamic atomic force microscopy methods

    (19) Garcı́a, R.; Pérez, R. Dynamic atomic force microscopy methods. Surf Sci Rep 2002, 47, 197-301. (20) Grünleitner, T.; Henning, A.; Bissolo, M.; Zengerle, M.; Gregoratti, L.; Amati, M.; Zeller, P.; Eichhorn, J.; Stier, A. V.; Holleitner, A. W.; Finley, J. J.; Sharp, I. D. Real-Time Investigation of Sulfur Vacancy Generation and Passivation in Monolaye...

    work page 2002

  8. [639]

    Layer-Number-Dependent Exciton Recombination Behaviors of MoS2 Determined by Fluorescence-Lifetime Imaging Microscopy

    (36) Wang, T.; Zhang, Y.; Liu, Y.; Li, J.; Liu, D.; Luo, J.; Ge, K. Layer-Number-Dependent Exciton Recombination Behaviors of MoS2 Determined by Fluorescence-Lifetime Imaging Microscopy. The Journal of Physical Chemistry C 2018, 122, 18651-18658. (37) Gentili, D.; Chini, E.; Cavallini, M. Generation and Tuning of Semiconductor Electronic and Functional Pr...

    work page 2018

Show all 9 references
  1. [1546]

    J.; Liao, W.; Chai, Y

    (3) Jiang, J.; Yang, P.; Liou, J. J.; Liao, W.; Chai, Y. Defect engineering of two-dimensional materials towards next-generation electronics and optoelectronics. Nano Res 2023, 16, 3104-3124. (4) Cavallini, M.; Gentili, D. Atomic Vacancies in Transition Metal Dichalcogenides: ...

    2023

Pith tools

Reviewed August 5, 2026 · model on record in the stance chip above.