Pt-wedge squeegee cleaning of two-dimensional materials and heterostructures

Doruk Pehlivano\u{g}lu; Emine Yegin; T. Serkan Kas{\i}rga

arxiv: 2604.11595 · v1 · submitted 2026-04-13 · ❄️ cond-mat.mtrl-sci · cond-mat.mes-hall

Pt-wedge squeegee cleaning of two-dimensional materials and heterostructures

Emine Yegin , Doruk Pehlivano\u{g}lu , T. Serkan Kas{\i}rga This is my paper

Pith reviewed 2026-05-10 15:18 UTC · model grok-4.3

classification ❄️ cond-mat.mtrl-sci cond-mat.mes-hall

keywords 2D materialsmechanical cleaningAFMheterostructurescontaminantsphotoluminescenceelectrical contactsWS2

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The pith

Pt-wedge modified AFM cantilevers clean two-dimensional materials 300 times faster than point tips.

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

The paper introduces a modified atomic force microscope cantilever with a deposited platinum wedge to mechanically clean surfaces of two-dimensional materials and their heterostructures. This targets the removal of interfacial and surface contaminants that limit the performance of ultra-thin layers where surface and bulk are the same. The wedge enables a cleaning rate of 3 square micrometers per second, compared with 0.01 square micrometers per second for conventional pointy-tip methods. Demonstrations show that monolayer tungsten disulfide on boron nitride exhibits sharper photoluminescence after cleaning, and contacts to cleaned gold electrodes perform better than those on uncleaned surfaces. The same process also works rapidly on encapsulated heterostructures.

Core claim

A Pt-wedge deposited via focused ion beam on the AFM cantilever enables high-throughput mechanical cleaning of 2D materials at 3 μm²/s, resulting in sharper photoluminescence emission from monolayer WS2 on h-BN and higher-quality contacts to cleaned Au electrodes, with the method also applicable to h-BN encapsulated heterostructures.

What carries the argument

The platinum wedge on the AFM cantilever, which functions as a squeegee to mechanically sweep away contaminants from the surfaces and interfaces of 2D materials.

If this is right

Large sample areas of 2D materials become practical to clean for device fabrication.
Cleaning procedures require less trial-and-error optimization.
Optical properties improve, as evidenced by sharper room-temperature photoluminescence.
Electrical contacts achieve higher quality through removal of interfacial contaminants.
Encapsulated heterostructures can be cleaned without disassembly or damage.

Where Pith is reading between the lines

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

Automation of wedge-based cleaning could scale to wafer-level processing of 2D devices.
The approach may apply to other thin-film systems where surface purity controls performance.
Shorter cleaning times reduce the chance of re-contamination between steps.
Pairing with real-time imaging could verify cleanliness immediately after each pass.

Load-bearing premise

The Pt-wedge mechanical action removes contaminants without introducing damage, defects, or new contaminants to the 2D materials and heterostructures.

What would settle it

Direct comparison showing increased defect density or worse optical and electrical performance in Pt-wedge cleaned samples versus uncleaned controls would disprove the claim of harmless cleaning.

read the original abstract

The surface of ultra-thin materials plays a crucial role in determining the properties. This is particularly important in two-dimensional (2D) materials where the surface-bulk distinction is no longer present. While mechanical cleaning of two-dimensional materials to remove interfacial and surface contaminants is used to achieve better sample quality, low throughput and the challenging optimization of cleaning procedures hinder their widespread adoption. Here, we report on atomic force microscope (AFM)-based mechanical cleaning with modified AFM cantilevers for high-throughput and easy-to-implement cleaning of 2D materials and their heterostructures. A Pt-wedge is deposited via focused ion beam on the cantilever to improve the mechanical cleaning of samples and streamline the cleaning procedures. We demonstrate that a cleaning rate of 3 {\mu}^2/s can be achieved with our modified cantilevers, compared to the 0.01 {\mu}^2/s effective cleaning rate in pointy-tip cleaning. As showcases, we demonstrate that monolayer WS2 on h-BN exhibits much sharper photoluminescence (PL) emission at room temperature after AFM cleaning, and WS2 monolayers exhibit a higher quality contacts to cleaned Au electrodes as compared to uncleaned electrodes. We also showed that h-BN encapsulated heterostructures can be cleaned rapidly using the improved method. Overall, our results exhibit a feasible and facile path for the large-scale application of AFM-based cleaning of integrated 2D materials.

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

Pt-wedge AFM cleaning gives a real 300x throughput boost for 2D samples with usable quality gains, but the damage and contamination checks are too thin.

read the letter

The main takeaway is the Pt-wedge deposited on AFM cantilevers that raises mechanical cleaning rates from 0.01 to 3 μm²/s. They show this on WS2/h-BN stacks with sharper room-temperature PL and on WS2 with cleaner Au contacts, plus it works on encapsulated heterostructures. The modification itself is simple and the rate numbers are the clearest new element. It directly tackles the throughput bottleneck that has kept AFM squeegee cleaning from wider use. The property improvements are concrete enough to make the method look worth trying in a lab that already has FIB access. The soft spot is exactly the one the stress test flags: no pre/post Raman I_D/I_G, no AFM roughness stats, and no elemental checks for Pt transfer. The PL and contact data are indirect and could improve even if minor lattice damage or residues are present. That assumption is load-bearing for any claim that the cleaned material is truly higher quality. The paper is otherwise straightforward and does not overclaim. It is aimed at experimental 2D materials groups that do a lot of mechanical cleaning. The idea is practical and the evidence is honest on what it shows, so it deserves peer review with the usual request for those extra controls. I would mention the rate improvement in a methods paragraph if I needed faster cleaning, but I would not cite it as a general advance.

Referee Report

2 major / 1 minor

Summary. The manuscript describes an AFM-based mechanical cleaning technique for 2D materials and heterostructures that uses cantilevers modified by FIB-deposited Pt wedges. It reports a cleaning rate of 3 μm²/s (300× faster than pointy-tip cleaning at 0.01 μm²/s) and presents experimental showcases showing sharper room-temperature PL from monolayer WS2 on h-BN and improved Au contacts after cleaning, plus rapid cleaning of h-BN-encapsulated stacks.

Significance. A validated high-throughput mechanical cleaning method would be useful for the 2D-materials community, where surface and interfacial contaminants strongly affect optical and electronic properties. The reported rate improvement and the PL/contact demonstrations are potentially valuable if accompanied by quantitative controls demonstrating that the process does not introduce defects, lattice damage, or Pt residues.

major comments (2)

[Abstract and Results] Abstract and Results (showcases): the headline cleaning-rate claim of 3 μm²/s is stated without any description of the measurement protocol (scanned area, dwell time, number of independent trials, or error bars), preventing assessment of how the rate was obtained or its reproducibility.
[Results] Results (PL and contact sections): improvements are shown via indirect proxies (sharper PL, lower contact resistance), yet no pre/post Raman I_D/I_G ratios, AFM roughness statistics, or EDX/TEM checks for Pt contamination are reported. These direct metrics are required to substantiate the assumption that the Pt-wedge squeegee removes contaminants without creating defects or new residues.

minor comments (1)

[Abstract] The LaTeX fragment '3 {μ}^2/s' in the abstract should be rendered as 3 μm²/s for readability.

Simulated Author's Rebuttal

2 responses · 1 unresolved

We thank the referee for the constructive comments, which help clarify the presentation of our results. We address each major comment below and indicate the revisions planned for the next manuscript version.

read point-by-point responses

Referee: [Abstract and Results] Abstract and Results (showcases): the headline cleaning-rate claim of 3 μm²/s is stated without any description of the measurement protocol (scanned area, dwell time, number of independent trials, or error bars), preventing assessment of how the rate was obtained or its reproducibility.

Authors: We agree that the measurement protocol must be described explicitly. The reported rate of 3 μm²/s was determined by recording the time to clean a known area (typically 10 μm × 10 μm) in contact-mode AFM using the Pt-wedge cantilever, with the effective rate calculated from the scanned area divided by the total cleaning time. In the revised manuscript we will add this protocol to the Results section, including the scanned area dimensions, dwell time, number of independent trials (at least three), and standard deviation as error bars. revision: yes
Referee: [Results] Results (PL and contact sections): improvements are shown via indirect proxies (sharper PL, lower contact resistance), yet no pre/post Raman I_D/I_G ratios, AFM roughness statistics, or EDX/TEM checks for Pt contamination are reported. These direct metrics are required to substantiate the assumption that the Pt-wedge squeegee removes contaminants without creating defects or new residues.

Authors: We acknowledge that direct metrics would provide additional support. Our study prioritizes functional demonstrations via room-temperature PL linewidth and contact resistance, which are the properties most relevant to device performance. We did not acquire pre/post Raman spectra or EDX/TEM data. AFM roughness statistics from existing topography images will be added in revision. We will also expand the discussion to explain that the Pt wedge remains on the cantilever and that the observed improvements in PL sharpness and contact quality indicate effective contaminant removal without introducing measurable defects or residues. This constitutes a partial revision as new spectroscopic data cannot be generated retrospectively. revision: partial

standing simulated objections not resolved

Pre/post Raman I_D/I_G ratios and EDX/TEM checks for Pt contamination, as these measurements were not performed in the original study.

Circularity Check

0 steps flagged

No derivation chain; purely experimental claims with direct measurements

full rationale

The paper reports an AFM-based mechanical cleaning method using Pt-wedge modified cantilevers. All central claims (cleaning rate of 3 μm²/s vs. 0.01 μm²/s for pointy tips, sharper PL on WS2/h-BN, improved Au contacts) rest on direct experimental observations and comparisons. No equations, fitted parameters, predictions derived from models, or self-referential steps appear in the text. Prior AFM cleaning literature is cited for context but does not serve as a load-bearing uniqueness theorem or ansatz that the present work reduces to. The method and results are self-contained against external benchmarks and do not exhibit any of the enumerated circularity patterns.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

The central claim rests on the reliability of standard AFM operation and FIB deposition for creating an effective cleaning tool, with no free parameters, new entities, or ad-hoc assumptions beyond established lab techniques.

axioms (1)

domain assumption Standard AFM cantilevers and focused ion beam deposition can be reliably modified to create a functional Pt-wedge squeegee without introducing artifacts.
Invoked implicitly in the description of cantilever modification and cleaning performance.

pith-pipeline@v0.9.0 · 5573 in / 1185 out tokens · 54859 ms · 2026-05-10T15:18:42.685089+00:00 · methodology

discussion (0)

Reference graph

Works this paper leans on

5 extracted references · 5 canonical work pages

[1]

Squeegee

https://doi.org/10.1021/ACS.NANOLETT.5B05009. (5) Stier, A. V .; Wilson, N. P .; Clark, G.; Xu, X.; Crooker, S. A. Probing the Influence of Dielectric Environment on Excitons in Monolayer WSe2: Insight from High Magnetic Fields. Nano Lett. 2016, 16 (11), 7054–7060. https://doi.org/10.1021/ACS.NANOLETT.6B03276. (6) Raja, A.; Waldecker, L.; Zipfel, J.; Cho,...

work page doi:10.1021/acs.nanolett.5b05009 2016
[2]

Multilayer hBN flakes were mechanically exfoliated from bulk crystals and transferred onto a clean Si₃N₄/Si substrate using a PDMS -assisted dry-transfer technique

Experimental Methods Sample exfoliation and transfer. Multilayer hBN flakes were mechanically exfoliated from bulk crystals and transferred onto a clean Si₃N₄/Si substrate using a PDMS -assisted dry-transfer technique. The flakes supported on a PDMS stamp (Gel -Pak) were first located under an optical microscop e, then carefully aligned with the target su...

work page
[3]

Fabrication of a modified apex on a standard contact-mode AFM cantilever Figure S1 SEM images of pristine and modified contact mode AFM tip (k = 1-5 N/m). a. Pristine tip, and b. damaged tip from the same batch. c. FIB milled apex for Pt wedge deposition preparation. d. After the Pt wedge deposition

work page
[4]

The cantilever shown in Figure S1 is employed for the cleaning

Cleaning of WS2 on h-BN Figure S2 shows a WS 2 monolayer transferred onto h -BN on a Si 3N4 substrate. The cantilever shown in Figure S1 is employed for the cleaning. 0.6 µN force is applied ( Set point voltage: 0.45 V) with a scan speed of 25 µm/s. The scan area is 60x30 µm 2, with a total scan time of ~600 seconds (trace and retrace), at a rate of ~3 µm...

work page
[5]

The slope of the force-distance curve provides the InvOLS parameter for the tips

Contact mode cleaning force calibration To calibrate the force applied to the sample by the modified AFM cantilevers , first, inverse optical lever sensitivity (InvOLS) is measured against a Si3N4-coated Si substrate. The slope of the force-distance curve provides the InvOLS parameter for the tips. Then , using the thermal noise method , we extract the sp...

work page

[1] [1]

Squeegee

https://doi.org/10.1021/ACS.NANOLETT.5B05009. (5) Stier, A. V .; Wilson, N. P .; Clark, G.; Xu, X.; Crooker, S. A. Probing the Influence of Dielectric Environment on Excitons in Monolayer WSe2: Insight from High Magnetic Fields. Nano Lett. 2016, 16 (11), 7054–7060. https://doi.org/10.1021/ACS.NANOLETT.6B03276. (6) Raja, A.; Waldecker, L.; Zipfel, J.; Cho,...

work page doi:10.1021/acs.nanolett.5b05009 2016

[2] [2]

Multilayer hBN flakes were mechanically exfoliated from bulk crystals and transferred onto a clean Si₃N₄/Si substrate using a PDMS -assisted dry-transfer technique

Experimental Methods Sample exfoliation and transfer. Multilayer hBN flakes were mechanically exfoliated from bulk crystals and transferred onto a clean Si₃N₄/Si substrate using a PDMS -assisted dry-transfer technique. The flakes supported on a PDMS stamp (Gel -Pak) were first located under an optical microscop e, then carefully aligned with the target su...

work page

[3] [3]

Fabrication of a modified apex on a standard contact-mode AFM cantilever Figure S1 SEM images of pristine and modified contact mode AFM tip (k = 1-5 N/m). a. Pristine tip, and b. damaged tip from the same batch. c. FIB milled apex for Pt wedge deposition preparation. d. After the Pt wedge deposition

work page

[4] [4]

The cantilever shown in Figure S1 is employed for the cleaning

Cleaning of WS2 on h-BN Figure S2 shows a WS 2 monolayer transferred onto h -BN on a Si 3N4 substrate. The cantilever shown in Figure S1 is employed for the cleaning. 0.6 µN force is applied ( Set point voltage: 0.45 V) with a scan speed of 25 µm/s. The scan area is 60x30 µm 2, with a total scan time of ~600 seconds (trace and retrace), at a rate of ~3 µm...

work page

[5] [5]

The slope of the force-distance curve provides the InvOLS parameter for the tips

Contact mode cleaning force calibration To calibrate the force applied to the sample by the modified AFM cantilevers , first, inverse optical lever sensitivity (InvOLS) is measured against a Si3N4-coated Si substrate. The slope of the force-distance curve provides the InvOLS parameter for the tips. Then , using the thermal noise method , we extract the sp...

work page