Photo-oxidation of polymer-like amorphous hydrogenated carbon under visible light illumination

Abstract

Amorphous hydrogenated carbon (a-C:H), a polymer-like network typically synthesized by plasma chemical vapor deposition, has long been known to exhibit optical absorption of visible light (λ > 400 nm). Here, we report that this absorption is accompanied by rapid photooxidation (within minutes) that behaves in most respects like classic polymer photo-oxidation with the exception that it occurs under visible light illumination rather than ultraviolet illumination. Lower plasma power during deposition produces a-C:H that is less crosslinked, is less absorptive, has longer photoluminescence lifetimes, and has a slower photo-oxidative degradation than a-C:H deposited at higher plasma power. The optical gap of the material deposited here is ~2.5 eV, and we correspondingly observe photo-oxidation at photon energies of 2.7 and 3.1 eV. A reduced photo-oxidative response is observed at sub-gap energies, suggesting that defect states or absorption tails enable absorption at lower energies. The photo-oxidation depends on both the total accumulated dose as well as the intensity of the illumination,

Ultralow Stress, Thermally Stable Cross-Linked Polymer Films of Polydivinylbenzene (PDVB)

“…Unlike highly energetic plasma-enhanced CVD (PECVD), iCVD is able to easily translate established chemical polymerization mechanisms known for the liquid phase into the vapor phase, since the temperature is warm enough to promote thermolysis of the initiator but not of the monomer molecules. This avoids the well-known − undesirable optical and chemical instabilities exhibited in plasma polymers due to the existence of residual radicals, dangling bonds, and photoactive defects in their structure . Additionally, the iCVD working pressure range of 0.01–0.3 Torr is compatible with many monomers, enabling the vapor-phase synthesis of free-radical polymers, including highly cross-linked materials otherwise unattainable through standard techniques.…”

“…This avoids the well-known 5−7 undesirable optical and chemical instabilities exhibited in plasma polymers due to the existence of residual radicals, dangling bonds, and photoactive defects in their structure. 8 Additionally, the iCVD working pressure range of 0.01−0.3 Torr is compatible with many monomers, enabling the vaporphase synthesis of free-radical polymers, including highly crosslinked materials otherwise unattainable through standard techniques. As an adsorption-controlled process, 9 substrate temperatures in iCVD are typically kept close or slightly below room temperature (i.e., 5−40 °C) during polymer deposition, which is advantageous to extend coating capabilities to a variety of materials such as paper, fabric, and other synthetic and natural polymers.…”

Hydrodynamic instability seeding by oxygen nonuniformities in glow discharge polymer inertial fusion ablators

“…While most polymer materials require UV light to photoexcite the electrons and induce reaction, GDP photo-oxidizes at wavelengths as long as 530 nm [23]. It has been confirmed by Baxamusa et al [24] and Huang et al [25] that the light exposure experienced by the target during normal fabrication processes can introduce measurable variations in the surface oxygen concentration [24]. The additional oxygen is primarily in the form of carbonyl and hydroxyl groups that replace existing CH bonds and form carboxylic acid groups, although there is evidence for the formation of additional byproducts that could not be identified [24].…”