Organic photovoltaic circuits are monolithically fabricated directly on a variety of common paper substrates using oxidative chemical vapor deposition to vapor print conformal conductive polymer ...electrodes. The paper photovoltaic arrays produce >50 V, power common electronic displays in ambient indoor lighting, and can be tortuously flexed and folded without loss of function.
The transparent conductingpoly(3,4‐ethylenedioxythiophene) (PEDOT) is of interest for various optoelectronic device applications. Here, the conductivity stability of PEDOT processed using oxidative ...chemical‐vapor‐deposition (oCVD) with FeCl3 as an oxidant is primarily dominated by the change in carrier density when aged in air. To establish the mechanism for the conductivity decrease, the changes in carrier density and carrier mobility of PEDOT films are separately monitored using an AC Hall Effect measurement system. The measured electrical properties reveal that a decrease in carrier density dominates the conductivity decrease during annealing. X‐ray diffraction analysis made on the HBr‐ and MeOH‐rinsed PEDOT samples identifies the Fe‐related dedoping phase of Fe(OH)2 and provides the dedoping mechanism. The carrier transport study demonstrates heavily doped oCVD PEDOT with the carrier density higher than ~1020 cm–3, and in this regime, an increase in carrier density yields lower carrier mobility which shows that the carrier transport is governed by the ionized impurity scattering mechanism due to increased dopant counter‐anions. These findings of the mechanisms for PEDOT conductivity decrease and carrier transport behavior may be important to organic optoelectronic device applications that show a strong effect of air‐exposure and low‐temperature annealing on the device stability and performance.
Heavily‐doped poly(3,4‐ethylenedioxythiophene)(PEDOT) films with carrier density higher than ~1020 cm‐3 are produced using oxidative chemical‐vapor‐deposition. The mechanisms for the conductivity decrease and carrier transport behavior in heavily‐doped PEDOT, which are important to organic optoelectronic device applications that show a strong effect of air‐exposure and low temperature annealing on the device stability and performance, are suggested.
In a two-part investigation, an experimental study and a kinetic model analysis of the initiated chemical vapor deposition (iCVD) of alkyl acrylate polymers are described. In this first part, an ...experimental study was performed to look at the effect of process parameters on iCVD polymerization. A homologous series of alkyl acrylates, from ethyl up to hexyl acrylate, were iCVD polymerized. The resulting polymers matched well spectroscopically with those from liquid-phase polymerization, demonstrating that stoichiometric polymers with no observable cross-linking can be achieved in a chemical vapor deposition environment. Deposition rate and molecular weight increased by a factor of over 300 and 60, respectively, when monomer saturated vapor pressure, P sat, was reduced from 42.6 to 0.584 Torr at equal gas pressures, P M. Over three times increase in deposition rate was observed for ethyl acrylate when substrate temperature was reduced from 29 to 17 °C. These trends are attributed to an increase in P M/P sat or, equivalently, monomer surface concentration in Henry's law limit at low P M/P sat. Evidence for adsorption-limited iCVD kinetics came from an apparent negative activation energy of −79.4 kJ/mol obtained experimentally that agreed well with a mathematically derived activation energy of −81.8 kJ/mol equal to twice the heat of desorption in the negative sense. Adsorption measurements found Henry's law limit to be valid and, when fitted to a BET equation, allowed the heat of desorption to be calculated. On the basis of this experimental study, process guidelines were made to define the appropriate parameter space for future iCVD polymerization, with P M/P sat in the range of 0.4−0.7 recommended as an optimal iCVD window.
The techniques of initiated chemical vapor deposition (iCVD) and oxidative chemical vapor deposition (oCVD) enable the fabrication of chemically well‐defined thin polymeric films on complex objects ...with micro‐ and nano‐scale features. By depositing polymers from the vapor phase, many wetting and solution effects are avoided, and conformal films can be created. In iCVD, a variant of hot filament CVD, the deposition rate is enhanced and chemical functionalities of the polymers' constituents are maintained by including a thermally labile initiator in the feed stream. Due to the low energy required when using an initiator, delicate substrates can be coated. In oCVD, infusible, electrically conductive films are formed directly on the substrate of interest as the oxidant and monomer are introduced into the reactor simultaneously. This Feature Article provides an overview of the work that has been done to develop iCVD and oCVD into platform technologies. Relevant background, fundamentals, and applications will be discussed.
Initiated and oxidative chemical vapor deposition are techniques that enable the deposition of conformal polymeric thin films (electrically insulating and conductive) on complex shapes with micro‐ and nano‐scale features. These techniques adapt well‐known solution chemistry into vacuum processes (vacuum chamber shown in figure). This Feature Article discusses the background, fundamentals, and applications of both techniques.
A new volatile organic compounds (VOCs) sensing concept called humidity‐initiated gas (HIG) sensors is described and demonstrated. HIG sensors employ the impedance of water assembled at sensor ...interfaces when exposed to humidity to sense VOCs at low concentrations. Here, two HIG sensor variants are studied—Type I and Type II. Type I sensors benefit from simplicity, but are less attractive in terms of key performance metrics, including response time and detection limits. Type II sensors are more complex, but are more attractive in terms of key performance metrics. Notably, it is observed that the best‐in‐class Type II HIG sensors achieve <2 min response times and <10 ppb detection limit for geranyl acetone, a VOC linked to the asymptomatic form of Huanglongbing (HLB) citrus disease. Both Type I and Type II sensors are assembled from off‐the‐shelf materials and demonstrate remarkable stability at high humidity. HIG sensors are proposed as an attractive alternative to existing VOCs sensors for remote field detection tasks, including VOCs detection to diagnose HLB citrus disease.
A new volatile organic compounds (VOCs) sensing concept called humidity‐initiated gas (HIG) sensors is demonstrated. HIG sensors detect VOCs using the impedance of water vapor assembled at sensor interfaces. Two HIG sensor variants are described—Type I and Type II—that have different sensing characteristics. HIG sensors represent a potential alternative to existing VOCs sensors for remote field detection applications.
Conducting polymers (CPs) combine electronic conductivity, optical transparency, and mechanical flexibility compatible with lightweight substrates. Due to these features CPs exhibit promising ...performance for a wide range of applications including electronic, optoelectronic, electrochemical, optochemical, and energy storage and harvesting devices. Fabrication of high‐quality CPs thin film in a large scale is of high demand in multiple industrial sectors. Chemical vapor deposition (CVD) is a promising approach for scale‐up and commercialization of CPs in large‐scale thin film applications by a roll‐to‐roll process. The CVD technique is a versatile deposition technique for fabricating CPs due to its unique combination of characteristics, including formation of conformal coatings, processing at low temperatures, solvent‐free synthesis, uniformity of growth, mechanical flexible films, industrial scale‐up, and substrate‐independence. This review focuses primarily on the oxidative CVD technique for the fabrication of CPs and related conjugated polymers by emphasizing on their applications in devices.
Conducting polymers (CPs) exhibit promising performance for a wide range of electronic device applications. The oxidative chemical vapor deposition is a versatile deposition technique for fabricating CPs due to its unique characteristics, including formation of conformal coatings, processing at low temperatures, solvent‐free synthesis, uniformity of growth, mechanical flexible films, industrial scale‐up, and substrate‐independence.
Biofouling is a crucial consideration in a variety of applications including biosensors, biomedical implants and devices, food packaging, and industrial and marine equipment. On the other hand, the ...controlled adsorption of proteins is desired in certain fields such as bioassays and tissue engineering. As such, significant progress has been made in fabricating surface chemistries that are able to resist or regulate protein adsorption through the manipulation of the protein-water-surface interactions. However, a conformal, substrate-independent surface modification method is required in order to extend such chemistries to a wider range of applications including delicate substrates, nanostructured surfaces, and polymer nanotubes. Here, we review the chemical vapor deposition (CVD) of coatings to control protein adsorption. These CVD coatings can be classified into four categories: hydrophilic coatings or hydrogels, which resist protein adsorption through surface hydration; fluorinated coatings, which have especially been studied in the context of fouling release in marine environments; amphiphilic coatings involving a unique antifouling mechanism; and switchable or stimuli-responsive coatings. Many of the techniques in each group are compatible with the synthesis of surface or free-standing nanostructures, and can be easily integrated into the existing fabrication infrastructure.
This review highlights the recent advances in the chemical vapor deposition of thin films and nanostructures to control surface protein adsorption.
Fouling refers to the undesirable attachment of organic molecules and microorganisms to submerged surfaces. It is an obstacle to the purification of shale gas produced water and is currently without ...an effective solution due to the highly contaminated nature of produced water. Here, we demonstrate the direct vapor application of a robust zwitterionic coating to a variety of substrates. The coating remains unprecedentedly hydrophilic, smooth, and effectively antifouling in extremely high salinity solutions (with salt concentration of 200 000 ppm). The fouling resistance is assessed rapidly and quantitatively with a molecular force spectroscopy-based method and corroborated using quartz crystal microbalance system with dissipation monitoring. Grazing angle attenuated total reflectance Fourier transform infrared is used in combination with X-ray photoelectron spectroscopy, atomic force microscope, and in situ spectroscopic ellipsometry to lend insight into the underlying mechanism for the exceptional stability and effectiveness of the zwitterionic coating under high-salinity conditions. A unique coating architecture, where the surface is concentrated with mobile zwitterionic moieties while the bulk is cross-linked to enhance coating durability, was discovered to be the origin of its stable fouling resistance under high salinity. Combined with previously reported exceptional stability in highly oxidative environments and strong fouling resistance to oil and grease, the zwitterionic surface here has the potential to enable low-cost, membrane-based techniques for the purification of produced water and to eventually balance the favorable economics and the concerning environmental impacts of the hydraulic fracturing industry.
Abstract
For fabricating devices with three-dimensional (3D) architectures, oxidative chemical vapor deposition (oCVD) offers conformal nanocoatings of polymers with designable composition. Pure, ...uniform, and pinhole-free oCVD layers are achievable with sub-10 nm thickness and sub-1 nm roughness. The low substrate temperature used for oCVD allows direct deposition on to the thermally sensitive substrates desired for flexible and wearable devices. The oCVD polymers can graft to the underlying material. The covalent chemical bonds to the substrate create a robust interface that prevents delamination during the subsequent device fabrication steps and exposure to the environmental conditions of device operation. Both electrically conducting and semiconducting polymers have been synthesized by oCVD. Small ions act as dopants. The oCVD process allows for systematic tuning of electrical, optical, thermal, and ionic transport properties. Copolymerization with oCVD can incorporate specific organic functional groups into the resulting conjugated organic materials. This short review highlights recent examples of using oCVD polymer to fabricate organic and hybrid organic–inorganic devices. These optoelectronic, electrochemical, and sensing devices utilize 3D architectures made possible by the conformal nature of the oCVD polymers.
Introduction
oCVD Chemistry and Process
Optoelectronic Devices
Electrochemical Devices
Sensing Devices
Conclusions and Outlook
Poly(fluoroalkyl acrylate)s with long perfluorooctyl pendant groups have been found to lead to the release of biopersistent perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS). ...Those with no more than six perfluorinated carbons in pedant groups do not cause such problems. They, however, give poor dynamic water repellency due to extensive reorganization of surface fluorinated groups when exposed to the water interface. In this work, thin films exhibiting improved dynamic water repellency, as evidenced by water contact angle (WCA) measurements, were synthesized via substrate-independent initiated chemical vapor deposition (iCVD) from 1H,1H,2H,2H-perfluorooctyl acrylate (C6PFA) and divinylbenzene (DVB) using two methods: copolymerization and ultrathin grafted gradation. The copolymerization between C6PFA and the cross-linker, DVB, was confirmed by Fourier transform infrared (FTIR) spectroscopy. The cross-linking is concluded to hinder the reorganization of surface fluorinated groups. The grafted gradation, consisting of an ultrathin pC6PFA top layer and a pDVB base layer, was characterized by angle-resolved X-ray photoelectron spectroscopy (ARXPS) measurements, which indicated that the top layer of pC6PFA is <2.5 nm thick to achieve the best dynamic water repellency. The outmost surface of this structure is fully covered by fluorinated groups, giving hydrophobicity. Concurrently, thanks to the interlayer grafting and the ultrathinness of the top layer, the fluorinated groups’ tendency to migrate away from water interface is sterically blocked by the highly cross-linked pDVB base layer. The proposed approaches effectively reduced WCA hysteresis of C6PFA-based thin film to as low as 26.9° while maintaining sufficient hydrophobicity (advanced WCA of 119.6°). Due to the conformal and substrate-independent nature of iCVD technique, the films could be used to coat textured surfaces to generate superhydrophobicity.
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