An Instrument for Physical Vapor Deposition onto Cryo-EM Samples for Microsecond Time-Resolved Cryo-EM

Axel P. Tracol Gavard; Constantin R. Kr\"uger; Jakub Wenz; Marcel Drabbels; Ulrich J. Lorenz; Wyatt A. Curtis

arxiv: 2512.20522 · v2 · pith:3H5PJQ5Rnew · submitted 2025-12-23 · ⚛️ physics.ins-det

An Instrument for Physical Vapor Deposition onto Cryo-EM Samples for Microsecond Time-Resolved Cryo-EM

Wyatt A. Curtis , Constantin R. Kr\"uger , Axel P. Tracol Gavard , Jakub Wenz , Marcel Drabbels , Ulrich J. Lorenz This is my paper

Pith reviewed 2026-05-21 15:40 UTC · model grok-4.3

classification ⚛️ physics.ins-det

keywords physical vapor depositioncryo-EMtime-resolved cryo-EMsilicon dioxidelaser flash meltingsample preparationmicrosecond resolution

0 comments

The pith

A new apparatus deposits compounds onto frozen cryo-EM samples to enable microsecond time-resolved experiments.

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

The paper presents an apparatus that uses physical vapor deposition to place thin layers of compounds onto cryo-EM samples while they remain frozen. This allows the environment around embedded particles to change so that a laser can briefly melt the sample and initiate reactions or other effects before refreezing. A demonstration shows that silicon dioxide sealing membranes work with a minimum thickness of just over two monolayers. Sympathetic readers would care because the approach could let cryo-EM capture fast protein motions on the microsecond scale that were previously out of reach. The design is positioned as a starting point for more complete time-resolved setups.

Core claim

We describe an apparatus for physical vapor deposition of compounds onto cryo-EM samples, detailing its design and operation. As a demonstration, we determine that the minimum thickness of silicon dioxide sealing membranes in a laser flash melting experiment is just over two monolayers. We propose that our design can form the basis for an integrated platform for microsecond time-resolved cryo-EM experiments.

What carries the argument

The physical vapor deposition apparatus that operates with cryo-EM grids in a vacuum setup compatible with laser flash melting, allowing controlled addition of thin films such as silicon dioxide onto frozen samples.

If this is right

Reagents deposited on frozen samples can mix with particles upon flash melting to trigger protein dynamics.
Ultrathin silicon dioxide layers can detach particles from interfaces and reduce preferred orientations.
The apparatus supports deposition of varied compounds to alter sample conditions in time-resolved work.
It can combine with laser flash melting for higher time resolution in cryo-EM.

Where Pith is reading between the lines

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

The minimal thickness result suggests the seal layer may add little interference to particle imaging.
Similar deposition could be tested with other materials to create new chemical triggers for conformational changes.
The technique might extend to other types of frozen samples for controlled environment changes.

Load-bearing premise

The deposited silicon dioxide layer forms a uniform continuous seal without contaminants or damage to the particles, and thickness can be accurately inferred from deposition parameters alone.

What would settle it

Direct observation of leaks, non-uniform coverage, or particle reattachment with silicon dioxide layers at or below two monolayers thickness during laser flash melting would disprove the minimum thickness result.

read the original abstract

Laser flash melting and revitrification experiments have recently improved the time resolution of cryo-electron microscopy (cryo-EM) to the microsecond timescale, making it fast enough to observe many of the protein motions that are associated with function. The technique has also opened up a new dimension for cryo-EM sample preparation, making it possible to deposit compounds onto a cryo-EM sample while it is frozen, so that upon flash melting, the embedded particles experience an altered environment. For example, we have recently shown that depositing ultrathin silicon dioxide membranes onto a cryo-EM sample causes particles to detach from the interface upon flash melting, removing preferred particle orientation. These experiments also point towards a new strategy for initiating protein dynamics in time resolved experiments by depositing reagents, which will then mix with the sample upon flash melting. Here, we describe an apparatus for physical vapor deposition of compounds onto cryo-EM samples, detailing its design and operation. As a demonstration, we determine that the minimum thickness of silicon dioxide sealing membranes in a laser flash melting experiment is just over two monolayers. We propose that our design can form the basis for an integrated platform for microsecond time-resolved cryo-EM experiments.

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

New PVD instrument for frozen cryo-EM grids with thin SiO2 membrane demo, but thickness claim rests on uncalibrated deposition parameters.

read the letter

Hi, The main thing here is a custom physical vapor deposition rig that works on already-frozen cryo-EM grids. They describe the design and operation, then show as a demonstration that silicon dioxide sealing membranes only need to be just over two monolayers thick to function in laser flash melting experiments. The instrument itself is the clearest new element. It gives a practical route for depositing compounds onto cold samples so that flash melting can alter the local environment around the particles on microsecond timescales. That lines up with earlier work on reducing preferred orientation or starting dynamics, and the setup details are concrete enough that someone trying to build similar hardware could use them. The thin-membrane result is presented directly and supports the idea that the added layer can stay minimal. The soft spot is how the thickness number was obtained. It appears to come from deposition time and an assumed rate, with no reported in-situ calibration, quartz monitor data under cryogenic conditions, or post-deposition checks like ellipsometry or TEM on the actual grids. Uniformity across holey carbon regions and possible shadowing also go unaddressed. A 30 percent rate error would move the result into a different regime, so the minimum-thickness claim is only partially supported. This is aimed at cryo-EM groups already doing or planning microsecond time-resolved work with flash melting. Readers focused on sample-preparation hardware would get the most value from the design notes. The paper shows clear technical thinking and engages the right literature for its subfield, so it deserves a serious referee. I would send it out and ask for more on the thickness verification in revision.

Referee Report

1 major / 2 minor

Summary. The manuscript describes the design and operation of an instrument for physical vapor deposition (PVD) of compounds onto cryo-EM samples to support microsecond time-resolved experiments via laser flash melting and revitrification. As a demonstration, the authors report that the minimum thickness of silicon dioxide sealing membranes is just over two monolayers, enabling particle detachment from the interface upon flash melting.

Significance. If the central demonstration holds with proper verification, the instrument could serve as a foundation for integrated platforms in time-resolved cryo-EM, allowing deposition of reagents or sealing layers onto frozen samples to study protein dynamics and mitigate preferred orientations. The work extends recent advances in laser flash melting techniques and provides practical details on apparatus design that may aid reproducibility in the field.

major comments (1)

[Demonstration of minimum membrane thickness] Demonstration section (minimum SiO2 membrane thickness): The claim that the minimum sealing thickness is 'just over two monolayers' is presented as a direct result but appears to rest on conversion of deposition time/rate parameters without reported in-situ calibration (e.g., quartz-crystal microbalance under cryogenic conditions), post-deposition verification (TEM, ellipsometry, or XPS on witness samples or grids), or corrections for source geometry, grid shadowing, or sticking coefficient. If the actual rate differs by 30-50% (common without tooling-factor calibration), the threshold shifts and cannot be reliably compared to prior work or used to establish the sealing regime.

minor comments (2)

[Abstract] The abstract references prior work on ultrathin silicon dioxide membranes causing particle detachment, but the manuscript should include the full citation in the main text for context.
[Methods/Results] Figure captions and methods should explicitly state any controls for uniformity of deposition across holey carbon regions and potential introduction of contaminants.

Simulated Author's Rebuttal

1 responses · 0 unresolved

We thank the referee for their careful and constructive review of our manuscript. We address the major comment regarding the demonstration of the minimum membrane thickness below.

read point-by-point responses

Referee: Demonstration section (minimum SiO2 membrane thickness): The claim that the minimum sealing thickness is 'just over two monolayers' is presented as a direct result but appears to rest on conversion of deposition time/rate parameters without reported in-situ calibration (e.g., quartz-crystal microbalance under cryogenic conditions), post-deposition verification (TEM, ellipsometry, or XPS on witness samples or grids), or corrections for source geometry, grid shadowing, or sticking coefficient. If the actual rate differs by 30-50% (common without tooling-factor calibration), the threshold shifts and cannot be reliably compared to prior work or used to establish the sealing regime.

Authors: We appreciate the referee highlighting the need for greater rigor in reporting the thickness calibration. The thickness value in the manuscript was derived from the deposition time multiplied by the nominal rate of the physical vapor deposition source, as calibrated by the manufacturer for silicon dioxide. We acknowledge that this does not include in-situ measurements under the specific cryogenic and geometric conditions of the experiment, nor post-deposition verification on the grids themselves. In the revised manuscript, we will expand the methods section to provide more details on the deposition setup, including source-to-sample distance, any estimated corrections for geometry, and the basis for the rate used. We will also qualify the 'just over two monolayers' statement as an approximate value based on the nominal rate, noting the potential for 30-50% uncertainty as suggested. Importantly, the experimental observation—that the particle detachment effect is achieved with the thinnest depositions we tested—remains valid and supports the conclusion that ultrathin sealing layers are effective. This revision will allow better comparison to prior work while preserving the manuscript's central demonstration. revision: yes

Circularity Check

0 steps flagged

No circularity: experimental instrumentation report with direct measurement

full rationale

The paper describes the design and operation of a physical vapor deposition apparatus for cryo-EM samples and presents a demonstration that the minimum thickness of silicon dioxide sealing membranes is just over two monolayers. This thickness result is stated as a direct outcome of deposition parameters in an experimental context, with no mathematical derivations, equations, fitted parameters renamed as predictions, or self-referential chains. No uniqueness theorems, ansatzes, or load-bearing self-citations are invoked. The work is self-contained as an apparatus description against external experimental benchmarks and does not reduce any claim to its own inputs by construction.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

This is an experimental instrumentation paper. It introduces no free parameters, new physical entities, or ad-hoc mathematical axioms. It rests on standard assumptions from vacuum technology and prior laser-flash cryo-EM work.

axioms (1)

domain assumption Physical vapor deposition under the described vacuum conditions produces uniform, pinhole-free layers on frozen grids without sample damage.
The demonstration of minimum membrane thickness implicitly relies on this standard assumption of the deposition process.

pith-pipeline@v0.9.0 · 5761 in / 1393 out tokens · 66410 ms · 2026-05-21T15:40:35.712041+00:00 · methodology

discussion (0)

Lean theorems connected to this paper

Citations machine-checked in the Pith Canon. Every link opens the source theorem in the public Lean library.

IndisputableMonolith/Cost/FunctionalEquation.lean washburn_uniqueness_aczel unclear

?

unclear
Relation between the paper passage and the cited Recognition theorem.

We determine that the minimum thickness of silicon dioxide sealing membranes in a laser flash melting experiment is just over two monolayers.
IndisputableMonolith/Foundation/AbsoluteFloorClosure.lean absolute_floor_iff_bare_distinguishability unclear

?

unclear
Relation between the paper passage and the cited Recognition theorem.

The physical vapor deposition rate (typically 10–30 Å/min) is actively stabilized during the deposition process and is calibrated with a quartz crystal microbalance (QCM).

What do these tags mean?

matches: The paper's claim is directly supported by a theorem in the formal canon.
supports: The theorem supports part of the paper's argument, but the paper may add assumptions or extra steps.
extends: The paper goes beyond the formal theorem; the theorem is a base layer rather than the whole result.
uses: The paper appears to rely on the theorem as machinery.
contradicts: The paper's claim conflicts with a theorem or certificate in the canon.
unclear: Pith found a possible connection, but the passage is too broad, indirect, or ambiguous to say the theorem truly supports the claim.

Reference graph

Works this paper leans on

24 extracted references · 24 canonical work pages

[1]

Williams, R. C. & Wyckoff, R. W. G. Applications of Metallic Shadow‑Casting to Microscopy. J. Appl. Phys. 17, 23–33 (1946)

work page 1946
[2]

& Müller, M

Hermann, R., Pawley, J., Nagatani, T. & Müller, M. Double-Axis Rotary Shadowing for High-Resolution Scanning Electron Microscopy. Scanning Microscopy 2, (1988)

work page 1988
[3]

Goldstein, J. I. et al. Coating Techniques for SEM and Microanalysis. in Scanning Electron Microscopy and X-Ray Microanalysis: A Text for Biologist, Materials Scientist, and Geologists (eds Goldstein, J. I. et al.) 461–494 (Springer US, Boston, MA, 1981). doi:10.1007/978-1-4613-3273-2_10

work page doi:10.1007/978-1-4613-3273-2_10 1981
[4]

Wagner, F. R. et al. Preparing samples from whole cells using focused-ion-beam milling for cryo-electron tomography. Nat Protoc 15, 2041–2070 (2020)

work page 2041
[5]

Lorenz, U. J. Microsecond time-resolved cryo-electron microscopy. Current Opinion in Structural Biology 87, 102840 (2024)

work page 2024
[6]

M., Harder, O

Voss, J. M., Harder, O. F., Olshin, P. K., Drabbels, M. & Lorenz, U. J. Rapid melting and revitrification as an approach to microsecond time-resolved cryo-electron microscopy. Chemical Physics Letters 778, 138812 (2021)

work page 2021
[7]

F., Drabbels, M

Bongiovanni, G., Harder, O. F., Drabbels, M. & Lorenz, U. J. Microsecond melting and revitrification of cryo samples with a correlative light-electron microscopy approach. Front. Mol. Biosci. 9, (2022)

work page 2022
[8]

Straub, M. S. et al. Laser flash melting cryo-EM samples to overcome preferred orientation. Nat Methods 1–7 (2025) doi:10.1038/s41592-025-02796-y

work page doi:10.1038/s41592-025-02796-y 2025
[9]

Glaeser, R. M. & Han, B.-G. Opinion: hazards faced by macromolecules when confined to thin aqueous films. Biophys Rep 3, 1–7 (2017)

work page 2017
[10]

Drulyte, I. et al. Approaches to altering particle distributions in cryo-electron microscopy sample preparation. Acta Cryst D 74, 560–571 (2018)

work page 2018
[11]

Challenges and opportunities in cryo-EM single-particle analysis

Lyumkis, D. Challenges and opportunities in cryo-EM single-particle analysis. Journal of Biological Chemistry 294, 5181–5197 (2019). 13

work page 2019
[12]

J., Thomas, W

Hirst, I. J., Thomas, W. J. R., Davies, R. A. & Muench, S. P. CryoEM grid preparation: a closer look at advancements and impact of preparation mode and new approaches. Biochem Soc Trans 52, 1529–1537 (2024)

work page 2024
[13]

Barrass, S. V. et al. Cryo-EM Sample Preparation with Soft-Landing and Laser Flash Melting. 2025.06.05.657968 Preprint at https://doi.org/10.1101/2025.06.05.657968 (2025)

work page doi:10.1101/2025.06.05.657968 2025
[14]

Mertz, K. L. et al. Laser-Induced Rehydration of Cryo-Landed Proteins Restores Native Structure. Molecular & Cellular Proteomics 24, (2025)

work page 2025
[15]

Curtis, W. A. et al. Ultrathin Liquid Cells for Microsecond Time-Resolved Cryo-EM. 2025.05.05.652279 Preprint at https://doi.org/10.1101/2025.05.05.652279 (2025)

work page doi:10.1101/2025.05.05.652279 2025
[16]

F., Barrass, S

Harder, O. F., Barrass, S. V., Drabbels, M. & Lorenz, U. J. Fast viral dynamics revealed by microsecond time-resolved cryo-EM. Nature Communications 14, 5649 (2023)

work page 2023
[17]

Ellis-Davies, G. C. R. Caged compounds: photorelease technology for control of cellular chemistry and physiology. Nat Methods 4, 619–628 (2007)

work page 2007
[18]

Kolasinski, K. W. Surface and Adsorbate Structure. in Surface Science: foundations of catalysis and nanoscience 9–49 (John Wiley & Sons, Ltd, 2012). doi:https://doi.org/10.1002/9781119941798.ch1

work page doi:10.1002/9781119941798.ch1 2012
[19]

R., Mowry, N

Krüger, C. R., Mowry, N. J., Bongiovanni, G., Drabbels, M. & Lorenz, U. J. Electron diffraction of deeply supercooled water in no man’s land. Nat Commun 14, 2812 (2023)

work page 2023
[20]

Malis, R. F., T. ;. Cheng, S. C. ;. Egerton. EELS Log-Ratio Technique for Specimen- Thickness Measurement in the TEM. J. Electron Microsc. Tech. 8, 193–200 (1988)

work page 1988
[21]

Yesibolati, M. N. et al. Electron inelastic mean free path in water. Nanoscale 12, 20649– 20657 (2020)

work page 2020
[22]

Ross, F. M. Opportunities and challenges in liquid cell electron microscopy. Science 350, aaa9886 (2015)

work page 2015
[23]

& Robertson, A

Pu, S., Gong, C. & Robertson, A. W. Liquid cell transmission electron microscopy and its applications. Royal Society Open Science 7, 191204 (2020). 14

work page 2020
[24]

& Parlińska-Wojtan, M

Tarnawski, T. & Parlińska-Wojtan, M. Opportunities and Obstacles in LCTEM Nanoimaging – A Review. Chemistry–Methods 4, e202300041 (2024)

work page 2024

[1] [1]

Williams, R. C. & Wyckoff, R. W. G. Applications of Metallic Shadow‑Casting to Microscopy. J. Appl. Phys. 17, 23–33 (1946)

work page 1946

[2] [2]

& Müller, M

Hermann, R., Pawley, J., Nagatani, T. & Müller, M. Double-Axis Rotary Shadowing for High-Resolution Scanning Electron Microscopy. Scanning Microscopy 2, (1988)

work page 1988

[3] [3]

Goldstein, J. I. et al. Coating Techniques for SEM and Microanalysis. in Scanning Electron Microscopy and X-Ray Microanalysis: A Text for Biologist, Materials Scientist, and Geologists (eds Goldstein, J. I. et al.) 461–494 (Springer US, Boston, MA, 1981). doi:10.1007/978-1-4613-3273-2_10

work page doi:10.1007/978-1-4613-3273-2_10 1981

[4] [4]

Wagner, F. R. et al. Preparing samples from whole cells using focused-ion-beam milling for cryo-electron tomography. Nat Protoc 15, 2041–2070 (2020)

work page 2041

[5] [5]

Lorenz, U. J. Microsecond time-resolved cryo-electron microscopy. Current Opinion in Structural Biology 87, 102840 (2024)

work page 2024

[6] [6]

M., Harder, O

Voss, J. M., Harder, O. F., Olshin, P. K., Drabbels, M. & Lorenz, U. J. Rapid melting and revitrification as an approach to microsecond time-resolved cryo-electron microscopy. Chemical Physics Letters 778, 138812 (2021)

work page 2021

[7] [7]

F., Drabbels, M

Bongiovanni, G., Harder, O. F., Drabbels, M. & Lorenz, U. J. Microsecond melting and revitrification of cryo samples with a correlative light-electron microscopy approach. Front. Mol. Biosci. 9, (2022)

work page 2022

[8] [8]

Straub, M. S. et al. Laser flash melting cryo-EM samples to overcome preferred orientation. Nat Methods 1–7 (2025) doi:10.1038/s41592-025-02796-y

work page doi:10.1038/s41592-025-02796-y 2025

[9] [9]

Glaeser, R. M. & Han, B.-G. Opinion: hazards faced by macromolecules when confined to thin aqueous films. Biophys Rep 3, 1–7 (2017)

work page 2017

[10] [10]

Drulyte, I. et al. Approaches to altering particle distributions in cryo-electron microscopy sample preparation. Acta Cryst D 74, 560–571 (2018)

work page 2018

[11] [11]

Challenges and opportunities in cryo-EM single-particle analysis

Lyumkis, D. Challenges and opportunities in cryo-EM single-particle analysis. Journal of Biological Chemistry 294, 5181–5197 (2019). 13

work page 2019

[12] [12]

J., Thomas, W

Hirst, I. J., Thomas, W. J. R., Davies, R. A. & Muench, S. P. CryoEM grid preparation: a closer look at advancements and impact of preparation mode and new approaches. Biochem Soc Trans 52, 1529–1537 (2024)

work page 2024

[13] [13]

Barrass, S. V. et al. Cryo-EM Sample Preparation with Soft-Landing and Laser Flash Melting. 2025.06.05.657968 Preprint at https://doi.org/10.1101/2025.06.05.657968 (2025)

work page doi:10.1101/2025.06.05.657968 2025

[14] [14]

Mertz, K. L. et al. Laser-Induced Rehydration of Cryo-Landed Proteins Restores Native Structure. Molecular & Cellular Proteomics 24, (2025)

work page 2025

[15] [15]

Curtis, W. A. et al. Ultrathin Liquid Cells for Microsecond Time-Resolved Cryo-EM. 2025.05.05.652279 Preprint at https://doi.org/10.1101/2025.05.05.652279 (2025)

work page doi:10.1101/2025.05.05.652279 2025

[16] [16]

F., Barrass, S

Harder, O. F., Barrass, S. V., Drabbels, M. & Lorenz, U. J. Fast viral dynamics revealed by microsecond time-resolved cryo-EM. Nature Communications 14, 5649 (2023)

work page 2023

[17] [17]

Ellis-Davies, G. C. R. Caged compounds: photorelease technology for control of cellular chemistry and physiology. Nat Methods 4, 619–628 (2007)

work page 2007

[18] [18]

Kolasinski, K. W. Surface and Adsorbate Structure. in Surface Science: foundations of catalysis and nanoscience 9–49 (John Wiley & Sons, Ltd, 2012). doi:https://doi.org/10.1002/9781119941798.ch1

work page doi:10.1002/9781119941798.ch1 2012

[19] [19]

R., Mowry, N

Krüger, C. R., Mowry, N. J., Bongiovanni, G., Drabbels, M. & Lorenz, U. J. Electron diffraction of deeply supercooled water in no man’s land. Nat Commun 14, 2812 (2023)

work page 2023

[20] [20]

Malis, R. F., T. ;. Cheng, S. C. ;. Egerton. EELS Log-Ratio Technique for Specimen- Thickness Measurement in the TEM. J. Electron Microsc. Tech. 8, 193–200 (1988)

work page 1988

[21] [21]

Yesibolati, M. N. et al. Electron inelastic mean free path in water. Nanoscale 12, 20649– 20657 (2020)

work page 2020

[22] [22]

Ross, F. M. Opportunities and challenges in liquid cell electron microscopy. Science 350, aaa9886 (2015)

work page 2015

[23] [23]

& Robertson, A

Pu, S., Gong, C. & Robertson, A. W. Liquid cell transmission electron microscopy and its applications. Royal Society Open Science 7, 191204 (2020). 14

work page 2020

[24] [24]

& Parlińska-Wojtan, M

Tarnawski, T. & Parlińska-Wojtan, M. Opportunities and Obstacles in LCTEM Nanoimaging – A Review. Chemistry–Methods 4, e202300041 (2024)

work page 2024