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arxiv: 2601.17161 · v4 · submitted 2026-01-23 · ⚛️ physics.ins-det

Industrial Deposition of Wavelength-Shifting Films for Liquid Argon Photon Detection Systems

Babak Azmoun , Aleksey Bolotnikov , Francesca Capocasa , Milind Diwan , Yimin Hu , Jay Hyun Jo , William Lenz , Yichen Li
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Abdul Rumaiz Vyara Tsvetkova Matteo Vicenzi
This is my paper

Pith reviewed 2026-05-16 11:22 UTC · model grok-4.3

classification ⚛️ physics.ins-det
keywords wavelength-shifting filmsp-terphenylphysical vapor depositionliquid argonneutrino detectorsindustrial coatingphoton detectionDUNE
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The pith

An industrial physical vapor deposition process produces uniform p-terphenyl wavelength-shifting films on large substrates.

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

The paper demonstrates that physical vapor deposition techniques originally developed for OLED manufacturing can apply p-terphenyl coatings uniformly on large inorganic substrates to convert 127 nm liquid-argon scintillation light into visible photons. This capability matters because experiments such as DUNE require roughly 2000 square meters of such films to reach target light yields, a scale where conventional laboratory deposition methods face limits on speed, uniformity, and cost. Profilometry and spectroscopy on the resulting films show edge thickness variation below 10 percent and emission spectra that match established reference samples. The process therefore offers reproducibility and substantially shorter production times while preserving the optical behavior needed for photon detection. These outcomes identify a concrete manufacturing route for the wavelength-shifting layers required by next-generation neutrino detectors.

Core claim

The paper reports the successful realization of an industrial physical vapor deposition process for p-terphenyl coatings on large-area inorganic substrates, achieving edge-region thickness variation below 10 percent and emission spectra consistent with high-quality pTP reference samples, thereby establishing reproducibility, scalability, and reduced production time compared with laboratory methods.

What carries the argument

Physical vapor deposition adapted from OLED display manufacturing, which deposits uniform p-terphenyl layers on inorganic substrates despite organic-inorganic adhesion challenges.

If this is right

  • Mass production of wavelength-shifting films becomes feasible for DUNE's approximately 2000 m² photon detection system.
  • Coating production time is reduced significantly relative to laboratory-based deposition.
  • Optical performance remains comparable to established pTP reference samples across large areas.
  • A viable manufacturing pathway exists for high-performance coatings in future large-scale liquid argon experiments.

Where Pith is reading between the lines

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

  • The same industrial deposition approach could be evaluated for alternative wavelength-shifting materials on similar substrates.
  • Successful detector-level validation would lower the cost and timeline barriers for scaling neutrino observatories beyond DUNE.
  • Process adaptations for non-flat or flexible substrates might support novel detector geometries in particle physics.

Load-bearing premise

Surface profilometry and visible emission spectra measurements are sufficient to confirm the films will efficiently convert 127 nm light in liquid argon.

What would settle it

Direct measurement of the wavelength conversion efficiency at 127 nm for the industrial films in a liquid argon environment, showing deviation from reference samples.

Figures

Figures reproduced from arXiv: 2601.17161 by Abdul Rumaiz, Aleksey Bolotnikov, Babak Azmoun, Francesca Capocasa, Jay Hyun Jo, Matteo Vicenzi, Milind Diwan, Vyara Tsvetkova, William Lenz, Yichen Li, Yimin Hu.

Figure 1
Figure 1. Figure 1: (a) Working principle of an X-Arapuca cell, adapted from Ref. [7]. (b) Representative absorption and emission spectra of pTP. The blue curve shows the excitation light peaking at 266 nm, and the red curve shows the emission spectrum of pTP, reproduced from Ref. [8]. coatings. The present work focuses on realizing such a coating through industrial-scale deposi￾tion of p-terphenyl (pTP) films on large-area s… view at source ↗
Figure 2
Figure 2. Figure 2: Plasma-treatment system and substrate placement. Mesh shadowing during treatment produced observable thickness modulation in early trials. 2.1 Vacuum thermal deposition PVD encompasses a class of thin-film techniques wherein material is deposited onto a substrate in a low-pressure environment. Reducing the ambient pressure to the millitorr range (or lower) in￾creases the mean free path of vaporized species… view at source ↗
Figure 3
Figure 3. Figure 3: Uniform pTP film on a 143.75 mm × 143.75 mm B33 substrate. and applied for approximately 15 minutes ( [PITH_FULL_IMAGE:figures/full_fig_p006_3.png] view at source ↗
Figure 4
Figure 4. Figure 4: Throughput scaling with a rotating substrate dome. as the primary substrate of interest in this study. Quartz and sapphire substrates were included to evaluate the general applicability and robustness of the coating technique on alternative opti￾cal materials, as well as to explore potential suitability for other detector or photonic applications. The first campaign (Batch 1) used a generic pTP powder on s… view at source ↗
Figure 5
Figure 5. Figure 5: Monochromator setup used for emission-spectrum measurements. In addition to the deposition step itself, the auxiliary process steps were evaluated for scalabil￾ity. Substrate cleaning and handling scale linearly with batch size but are not rate-limiting relative to the PVD cycle. Plasma surface treatment is performed with substrates loaded in multiple layers within the plasma chamber, whose capacity exceed… view at source ↗
Figure 6
Figure 6. Figure 6: Emission spectra measured from pTP-coated samples under UV excitation at 266 nm. (a) Un￾normalized spectra under identical acquisition conditions, enabling relative fluorescence yield comparison. (b) Area-normalized spectra, facilitating spectral shape comparison across samples and substrates. Emission spectra of pTP-coated samples were acquired with long integration times using the monochromator setup des… view at source ↗
Figure 7
Figure 7. Figure 7: Comparison of emission spectra before and after the cryogenic cycle. to minimize thermal shock. The samples remained fully immersed for ≈ 18 hours. After immer￾sion, they were raised in stages above the liquid surface to allow gradual warming, removed once the surface temperature exceeded 0 ◦C, dried with forced air, and subsequently placed in a ∼30 ◦C dryer for 1 hour. For the horizontal configuration, th… view at source ↗
Figure 8
Figure 8. Figure 8: Representative profilometer scans for each substrate type. Left: thickness vs. lateral scan distance, where the gray band indicates the lateral range used for thickness statistics (0.5–2.5 mm from the step edge). Right: thickness distribution over the same interval. (a, b) B33 glass (Sample S46, Batch 3); (c, d) Sapphire (Sample S35, Batch 2); (e, f) Quartz (Sample S21, Batch 2). The apparent slope in the … view at source ↗
read the original abstract

The Deep Underground Neutrino Experiment (DUNE) Phase-II Far Detector is considering an approximately 2000\,m$^2$ photon detection system to achieve a target mean light yield of 180\,PE/MeV. Meeting this requirement demands scalable, cost-effective, and high-quality wavelength-shifter (WLS) coatings capable of converting 127\,nm liquid-argon scintillation light into visible photons with controlled and reproducible optical performance. We report on the successful realization of an industrial physical vapor deposition (PVD) process for \textit{p}-terphenyl (pTP) coatings, adapted from vacuum deposition techniques developed for OLED display manufacturing, to produce uniform WLS layers on large-area inorganic substrates, a task traditionally challenged by adhesion and uniformity issues at organic--inorganic interfaces. Surface characterization by profilometry and spectroscopic measurements demonstrates edge-region thickness variation below 10\% and emission spectra consistent with high-quality pTP reference samples. The industrial process demonstrates reproducibility, scalability, and significantly reduced production time compared to laboratory-based methods, while maintaining optical characteristics consistent with established pTP reference samples. These results establish a viable pathway for mass production of high-performance pTP coatings for DUNE FD3 and future neutrino experiments, from a coating manufacturing and process standpoint. Detector-level performance validation, including quantitative VUV conversion efficiency measurements at 127\,nm, is identified as future work.

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.

Referee Report

1 major / 2 minor

Summary. The manuscript reports the successful adaptation of an industrial physical vapor deposition (PVD) process, drawn from OLED manufacturing, for producing uniform p-terphenyl (pTP) wavelength-shifting coatings on large-area inorganic substrates. Surface profilometry shows edge-region thickness variation below 10%, while spectroscopic measurements indicate emission spectra consistent with laboratory pTP reference samples. The work emphasizes process reproducibility, scalability to the ~2000 m² area needed for DUNE Phase-II, and substantially reduced production time relative to lab methods, while explicitly identifying quantitative VUV conversion efficiency at 127 nm and full detector validation as future work.

Significance. If the industrial process maintains the claimed uniformity and optical consistency at scale, it would provide a practical manufacturing route for the large photon detection system required to reach DUNE's target mean light yield of 180 PE/MeV. The approach leverages existing high-volume deposition infrastructure, which is a concrete strength for reproducibility and cost reduction in future neutrino experiments.

major comments (1)
  1. [Abstract] Abstract and Results: The claim that the coatings maintain 'optical characteristics consistent with established pTP reference samples' rests on visible-range emission spectra and profilometry; because quantitative VUV efficiency at 127 nm is deferred to future work, the direct link to liquid-argon scintillation performance (the load-bearing requirement for DUNE) is not yet demonstrated.
minor comments (2)
  1. [Figures] Figure captions should explicitly state the substrate dimensions and measurement locations used for the <10% edge-variation claim to allow readers to assess scalability.
  2. [Methods] The text would benefit from a brief table comparing key process parameters (deposition rate, temperature, chamber pressure) between the industrial PVD run and the laboratory reference process.

Simulated Author's Rebuttal

1 responses · 0 unresolved

We thank the referee for the positive evaluation and constructive comment. We agree that the manuscript's claims about optical performance should be stated more precisely given the absence of quantitative VUV efficiency data, and we have revised the abstract accordingly.

read point-by-point responses

  1. Referee: [Abstract] Abstract and Results: The claim that the coatings maintain 'optical characteristics consistent with established pTP reference samples' rests on visible-range emission spectra and profilometry; because quantitative VUV efficiency at 127 nm is deferred to future work, the direct link to liquid-argon scintillation performance (the load-bearing requirement for DUNE) is not yet demonstrated.

    Authors: We agree that quantitative VUV conversion efficiency at 127 nm has not been measured and is correctly identified as future work. The present results demonstrate visible-range emission spectra matching laboratory pTP references together with edge thickness variation below 10% via profilometry. We have revised the abstract to replace the general phrase 'optical characteristics consistent with established pTP reference samples' with the more specific wording 'visible-range emission spectra consistent with high-quality pTP reference samples and surface uniformity below 10% thickness variation,' while retaining the explicit statement that detector-level VUV validation remains future work. This change clarifies the scope of the current measurements without implying a direct demonstration of LAr scintillation performance. revision: yes

Circularity Check

0 steps flagged

No significant circularity

full rationale

The manuscript is a purely experimental report on realizing an industrial PVD process for pTP coatings. It presents direct measurements of film thickness by profilometry and visible emission spectra, compared against reference samples, with no equations, fits, predictions, or self-referential definitions. The central claims concern process reproducibility, scalability, and reduced production time; quantitative VUV efficiency at 127 nm is explicitly deferred to future work. No load-bearing steps reduce to inputs by construction, self-citation chains, or ansatz smuggling. The work is self-contained against external benchmarks.

Axiom & Free-Parameter Ledger

1 free parameters · 1 axioms · 0 invented entities

The work relies on standard vacuum deposition physics and known pTP optical properties; no new entities or heavily fitted parameters are introduced beyond process tuning parameters whose values are not specified here.

free parameters (1)
  • PVD process parameters
    Deposition rate, temperature, and pressure chosen to achieve uniformity on inorganic substrates; specific values not reported in abstract.
axioms (1)
  • domain assumption Standard physical vapor deposition behavior applies to p-terphenyl on inorganic substrates
    Assumes film adhesion and growth follow established OLED-derived models without new validation at 127 nm.

pith-pipeline@v0.9.0 · 5590 in / 1380 out tokens · 30770 ms · 2026-05-16T11:22:48.276228+00:00 · methodology

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Reference graph

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