Flow-Through Atmospheric Pressure-Atomic Layer Deposition Reactor for Thin-Film Deposition in Capillary Columns

We demonstrate the development of a new atmospheric pressure-atomic layer deposition­(AP-ALD) system to coat the inner walls of capillary columns for gas chromatography (GC). Unlike traditional ALD, this reactor operates at near-atmospheric pressure and addresses the challenges of depositing thin fi...

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Bibliographic Details
Published in:Analytical chemistry (Washington) 2022-05, Vol.94 (21), p.7483-7491
Main Authors: Patel, Dhananjay I., Major, George H., Jacobsen, Collin, Shah, Dhruv, Strohmeier, Brian R., Shollenberger, Daniel, Bell, David S., Argyle, Morris D., Linford, Matthew R.
Format: Article
Language:English
Subjects:
Alumina
Aluminum oxide
Atmospheric pressure
Atomic layer epitaxy
Blood vessels
Capillaries
Capillary flow
Capillary pressure
Chemistry
Coatings
Film growth
Film thickness
Fused silica
Gas chromatography
Gases
High aspect ratio
Inorganic coatings
Nuclear reactors
Photoelectron spectroscopy
Photoelectrons
Pinholes
Reactors
Silica
Silicon
Spectroellipsometry
Spectrum analysis
Temperature control
Thickness measurement
Thin films
Transmission electron microscopy
X-ray spectroscopy
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Summary:We demonstrate the development of a new atmospheric pressure-atomic layer deposition­(AP-ALD) system to coat the inner walls of capillary columns for gas chromatography (GC). Unlike traditional ALD, this reactor operates at near-atmospheric pressure and addresses the challenges of depositing thin films inside capillaries, which include long pump down times, deposition in high-aspect-ratio materials, and temperature control. We show ALD of alumina in 5 and 12 m capillaries (0.53 mm ID) via sequential half reactions of trimethylaluminum and water. Our system yields pinhole-free, uniform thin films. It includes small witness chambers for witness silicon shards before and after the capillary. An engineering flow/transport analysis of the device is provided. Our ALD alumina thin films are characterized by spectroscopic ellipsometry (SE), X-ray photoelectron spectroscopy, transmission electron microscopy (TEM), and energy-dispersive X-ray spectroscopy. Alumina film growth achieved is 1.4–1.5 Å/cycle, which is consistent with previously reported results. Film thickness measurements by SE on witness shards of silicon and by TEM at both ends of the capillary are in good agreement. A capillary column coated with alumina is used to separate different gases by GC, although the retention times of gases are essentially the same as with an untreated fused silica capillary. This successful deposition of ALD alumina in long capillaries opens the door for other possible ALD coatings, including hybrid organic–inorganic coatings, using the 450+ ALD precursors available today.
ISSN:0003-2700
1520-6882
DOI:10.1021/acs.analchem.1c05029