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300 results on '"Bahr, David F."'

12. Enhanced Corrosion Protection of Printed Circuit Board Electronics using Cold Atmospheric Plasma-Assisted SiOxCoatings

Author

Kasi, Venkat, Tien, Jia-Huei, Rahman, Md Mahabubur, Rana, Muhammad Masud, Heredia Rivera, Ulisses Alberto, Shang, Zhongxia, Vidhyadhiraja, Advika, Zhang, Jingxuan, Youngblood, Jeffrey P., Bahr, David F., and Rahimi, Rahim

Abstract

The miniaturization and widespread deployment of electronic devices across diverse environments have heightened their vulnerability to corrosion, particularly affecting copper traces within printed circuit boards (PCBs). Conventional protective methods, such as conformal coatings, face challenges including the necessity for a critical thickness to ensure effective barrier properties and the requirement for multiple steps of drying and curing to eliminate solvent entrapment within polymer coatings. This study investigates cold atmospheric plasma (CAP) as an innovative technique for directly depositing ultrathin silicon oxide (SiOx) coatings onto copper surfaces to enhance corrosion protection in PCBs. A systematic investigation was undertaken to examine how the scanning speed of the CAP deposition head impacts the film quality and corrosion resistance. The research aims to determine the optimal scanning speed of the CAP deposition head that achieves complete surface coverage while promoting effective cross-linking and minimizing unreacted precursor entrapment, resulting in superior electrical barrier and mechanical properties. The CAP coating process demonstrated the capability of depositing SiOxonto copper surfaces at various thicknesses ranging from 70 to 1110 nm through a single deposition process by simply adjusting the scanning speed of the plasma head (5–75 mm/s). Evaluation of material corrosion barrier characteristics revealed that scanning speeds of 45 mm/s of the plasma deposition head provided an effective coating thickness of 140 nm, exhibiting superior corrosion resistance (30-fold) compared to that of uncoated copper. As a proof of concept, the efficacy of CAP-deposited SiOxcoatings was demonstrated by protecting an LED circuit in saltwater and by coating printed circuits for potential agricultural sensor applications. These CAP-deposited coatings offer performance comparable to or superior to traditional conformal polymeric coatings. This research presents CAP-deposited SiOxcoatings as a promising approach for effective and scalable corrosion protection in miniaturized electronics.

Published
2024
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24. Role of ripples in altering the electronic and chemical properties of graphene.

Author

Kim, Chang-Eun, Lee, Jiwoo, Walsh, Aron, Lordi, Vincenzo, and Bahr, David F.

Subjects
CHEMICAL properties, GRAPHENE, HYDROGEN as fuel, SURFACE recombination, SURFACE diffusion, TRANSITION state theory (Chemistry)
Abstract

Ripples of graphene are known to manipulate electronic and hydrogenation properties of graphitic materials. More detailed work is needed to elucidate the structure–property relationship of these systems. In this work, the density functional theory is used to compute the energy and electronic structure of the graphene models with respect to variable curvatures and hydrogen adsorption sites. The magnitude of finite bandgap opening depends on the orientation of ripples, and the hydrogen adsorption energy depends on the local curvature of graphene. An adsorbed hydrogen alters the local curvature, resulting in relatively weakened adsorption on the neighboring three sites, which gives a rationale to experimentally observed dynamic equilibrium stoichiometry (H:C = 1:4) of hydrogenated graphene. The surface diffusion transition state energy of adsorbed hydrogen is computed, which suggests that the Eley–Rideal surface recombination mechanism may be important to establish the dynamic equilibrium, instead of the commonly assumed Langmuir–Hinshelwood mechanism. [ABSTRACT FROM AUTHOR]

Published
2022
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25. Investigating correlations between explosive impact sensitivity and mechanical properties using nanoindentation.

Author

Burch, Alexandra C., Grennan, Hugh P., Bahr, David F., Yeager, John D., Tappan, Bryce C., Marrs, Frank W., Cawkwell, Marc J., and Manner, Virginia W.

Subjects
IMPACT (Mechanics), SINGLE crystals, EXPLOSIVES
Abstract

Handling sensitivity is the first property that must be evaluated in order to work safely with explosive samples, most commonly evaluated using drop-weight impact sensitivity. In addition to safety, there is a longstanding scientific interest in the explosives community to connect, if possible, chemical, physical, and mechanical properties to impact sensitivity. Most mechanical characterization of explosives has historically been done on plastic-bonded composites containing conventional explosives, but recently nanoindentation has been used to probe the mechanical response of pure explosive single crystals. In this study, we employ nanoindentation techniques to measure hardness and elastic modulus of a variety of explosives in order to search for correlations to drop-weight impact sensitivity. Both primary and secondary explosives are studied, along with mechanical behavior and sensitivity trends. [ABSTRACT FROM AUTHOR]

Published
2023
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