Through phase transition-induced band edge engineering by dual doping with In and Mo, a new greenish BiVO₄ (Bi1-XInXV1-XMoXO₄) is developed that has a larger band gap energy than the usual yellow ...scheelite monoclinic BiVO₄ as well as a higher (more negative) conduction band than H⁺/H₂ potential 0 VRHE(reversible hydrogen electrode) at pH 7. Hence, it can extract H₂ from pure water by visible light-driven overall water splitting without using any sacrificial reagents. The density functional theory calculation indicates that In³⁺/Mo⁶⁺ dual doping triggers partial phase transformation from pure monoclinic BiVO₄ to a mixture of monoclinic BiVO₄ and tetragonal BiVO₄, which sequentially leads to unit cell volume growth, compressive lattice strain increase, conduction band edge uplift, and band gap widening.
Ordered herringbone patterns with deterministic long and short wavelengths are created using a sequential wrinkling strategy (SWS). Patterns with a prescribed zig‐zag turning angle less than 90° are ...obtained upon sequential wrinkling of non‐equi‐biaxial prestrain for the first time. SWS provides a new method for measuring thin‐film mechanical properties simply through the wrinkling metrology without measurement of film thickness.
Directed self-assembly (DSA) of the domain structure in block copolymer (BCP) thin films is a promising approach for sub-10-nm surface patterning. DSA requires the control of interfacial properties ...on both interfaces of a BCP film to induce the formation of domains that traverse the entire film with a perpendicular orientation. Here we show a methodology to control the interfacial properties of BCP films that uses a polymer topcoat deposited by initiated chemical vapour deposition (iCVD). The iCVD topcoat forms a crosslinked network that grafts to and immobilizes BCP chains to create an interface that is equally attractive to both blocks of the underlying copolymer. The topcoat, in conjunction with a chemically patterned substrate, directs the assembly of the grating structures in BCP films with a half-pitch dimension of 9.3 nm. As the iCVD topcoat can be as thin as 7 nm, it is amenable to pattern transfer without removal. The ease of vapour-phase deposition, applicability to high-resolution BCP systems and integration with pattern-transfer schemes are attractive properties of iCVD topcoats for industrial applications.
This report describes the preparation of superhydrophobic and oleophobic surfaces by grafting of poly(perfluorodecylacrylate) chains with initiated chemical vapor deposition on silicon substrates. ...The grafting enhances the formation of a semicrystalline phase. The crystalline structures reduce the polymer chain mobility, resulting in nonwetting surfaces with both water and mineral oil. On the contrary, the same contacting liquid easily wets the amorphous ungrafted polymer.
Chemical vapor deposition (CVD) polymerization directly synthesizes organic thin films on a substrate from vapor phase reactants. Dielectric, semiconducting, electrically conducting, and ionically ...conducting CVD polymers have all been readily integrated into devices. The absence of solvent in the CVD process enables the growth of high‐purity layers and avoids the potential of dewetting phenomena, which lead to pinhole defects. By limiting contaminants and defects, ultrathin (<10 nm) CVD polymeric device layers have been fabricated in multiple laboratories. The CVD method is particularly suitable for synthesizing insoluble conductive polymers, layers with high densities of organic functional groups, and robust crosslinked networks. Additionally, CVD polymers are prized for the ability to conformally cover rough surfaces, like those of paper and textile substrates, as well as the complex geometries of micro‐ and nanostructured devices. By employing low processing temperatures, CVD polymerization avoids damaging substrates and underlying device layers. This report discusses the mechanisms of the major CVD polymerization techniques and the recent progress of their applications in devices and device fabrication, with emphasis on initiated CVD (iCVD) and oxidative CVD (oCVD) polymerization.
Chemical vapor deposition (CVD) polymerization synthesizes conformal and pinhole‐free organic thin films directly on substrates. Compared with solution‐based techniques, the solvent‐free nature of the CVD process avoids the undesirable monomer–solvent or polymer–solvent and solvent–substrate interactions. Thus, CVD is particularly suitable for synthesizing insoluble conductive polymers and robust crosslinked networks for organic devices.
Poly(4-aminostyrene) (PAS) thin films were synthesized via initiated chemical vapor deposition (iCVD) with tert-butyl peroxide as the initiator, representing the first time that a library of iCVD ...functional groups has been extended to amine moieties. The retention of the pendent amine chemical functionality was confirmed by Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). Scanning electron microscope (SEM) reveals that the iCVD PAS coatings are conformal over nonplanar structures. Fluorescence microscopy and photoluminescence of quantum dot functionalized surfaces confirm that the reactive amine functional group density at the surface of iCVD PAS is ∼1 order of magnitude greater than for films grown by plasma-enhanced chemical vapor deposition (PECVD). The higher amine density of the iCVD films enables the formation of a robust nanoadhesive with complementary epoxy functional groups. Prototype microfluidic structures were fabricated using the low-temperature (50 °C) and zero-outgassing reaction between the amine groups in iCVD PAS and the epoxy groups in iCVD poly(glycidyl methacrylate) (PGMA). Bonded devices able to withstand >150 psi were achieved by combining polydimethylsiloxane (PDMS) and a variety of other materials including Si wafers, polycarbonate (PC), glass, polyethylene terephthalate (PET), polyethylene (PE), polyacrylate (PA), and cyclic olefin copolymer (COC). Additionally, the all-iCVD nanoadhesive bonding process displays high resistance against hydrolytic degradation (>2 weeks). Within the channels of the bonded devices, the epoxy and amine groups remain available for subsequent functionalization.
A versatile method to produce superhydrophobic fabrics by combining electrospinning and initiated chemical vapor deposition (iCVD) is reported. In this study, poly(caprolactone) (PCL) was first ...electrospun and then coated with a thin layer of hydrophobic polymerized perfluoroalkyl ethyl methacrylate (PPFEMA) by iCVD. The hierarchical surface roughness inherent in the PCL electrospun mats and the extremely low surface free energy of the coating layer obtained by iCVD yields stable superhydrophobicity with a contact angle of 175° and a threshold sliding angle less than 2.5° for a 20 mg droplet. This PPFEMA-coated PCL mat was also shown to exhibit at least “grade 8” oleophobicity. Hydrophobicity was demonstrated to increase monotonically with a reduction in diameter among bead-free fibers and with the introduction of a high density of relatively small diameter beads. The systematic effect of fiber morphology on superhydrophobicity was also investigated theoretically and experimentally using both beaded and bead-free fibers with diameters ranging from 600 to 2200 nm.
Air-stable, lightweight, and electrically conductive polymers are highly desired as the electrodes for next-generation electronic devices. However, the low electrical conductivity and low carrier ...mobility of polymers are the key bottlenecks that limit their adoption. We demonstrate that the key to addressing these limitations is to molecularly engineer the crystallization and morphology of polymers. We use oxidative chemical vapor deposition (oCVD) and hydrobromic acid treatment as an effective tool to achieve such engineering for conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT). We demonstrate PEDOT thin films with a record-high electrical conductivity of 6259 S/cm and a remarkably high carrier mobility of 18.45 cm
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by inducing a crystallite-configuration transition using oCVD. Subsequent theoretical modeling reveals a metallic nature and an effective reduction of the carrier transport energy barrier between crystallized domains in these thin films. To validate this metallic nature, we successfully fabricate PEDOT-Si Schottky diode arrays operating at 13.56 MHz for radio frequency identification (RFID) readers, demonstrating wafer-scale fabrication compatible with conventional complementary metal-oxide semiconductor (CMOS) technology. The oCVD PEDOT thin films with ultrahigh electrical conductivity and high carrier mobility show great promise for novel high-speed organic electronics with low energy consumption and better charge carrier transport.
A novel approach to fabricate supercapacitors (SCs) via vapor printing, specifically oxidative chemical vapor deposition (oCVD), is demonstrated. Compared to stacking multiple layers into a SC, this ...method enables the monolithic integration of all components into a single‐sheet substrate, minimizing the inactive materials and eliminating the possibility of multilayer delamination. Electrodes comprised of pseudocapacitive material, poly(3,4‐ethylenedioxythiophene) (PEDOT), are deposited into both sides of a sheet of flexible porous substrate. The film deposition and patterning are achieved in a single step. The oCVD PEDOT penetrates partially into the porous substrate from both surfaces, while leaving the interior of the substrate serving as a separator. Near the surface, the PEDOT coating conforms to the substrate's structure without blocking the pores, resembling the substrate's intrinsic morphology with high surface area. The porously structured PEDOT coating, paired with in situ ion gel electrolyte synthesis, gives enhanced electrode–electrolyte interfaces. The monolithic device demonstrates high volumetric capacitance (11.3 F cm−3), energy density (2.98 mWh cm−3), and power density (0.42 W cm−3). These outstanding performance metrics are attributed to the large loading of active materials, minimization of inactive materials, and good electrode–electrolyte interfaces. SC arrays can be printed on a single substrate without the use of wire interconnects.
A monolithically integrated supercapacitor is demonstrated to give high energy and power densities while avoiding delamination when being flexed. It relies on vapor‐deposited poly(3,4‐ethylenedioxythiophene) electrodes that penetrate partially into both sides of a paper/membrane substrate, leaving the substrate's interior as separator. The electrodes conform to the substrate's outer texture, resulting in their large surface area for fast ion transport.
Fouling has been a persistent issue within applications ranging from membrane separation to biomedical implantation. Research to date focuses on fouling-resistant coatings, where electrical ...conductivity is unnecessary. In this study, we report the synthesis of multifunctional thin films with both fouling resistance and electrical conductivity for their potential applications in the electrolysis-based self-cleaning of separation membranes and in the field of bioelectronics. This unique combination of properties results in multifunctional coatings that are a zwitterionic derivative of intrinsically conductive polymer poly(3,4-ethylenedioxythiophene) (PEDOT) synthesized via oxidative chemical vapor deposition (oCVD). Their fouling resistance is shown to be comparable to that of known dielectric fouling-resistant surfaces, such as a poly(4-vinylpyridine)-co-divinylbenzene (p4VP-DVB)-derived zwitterionic coating, an amphiphilic poly(1H,1H,2H,2H-perfluorodecyl acrylate-co-2-hydroxyethyl methacrylate) (pPFDA-HEMA) coating, and a glass surface, and are far superior to the fouling resistance of gold or polydimethylsiloxane (PDMS) surfaces. The fouling resistances of seven surfaces are quantitatively characterized by molecular force probe (MFP) analysis. In addition, four-point probe electrical measurements, Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), variable-angle spectroscopic ellipsometry (VASE), profilometry, water contact angle (WCA) measurements, surface ζ-potential measurements, and atomic force microscopy (AFM) were employed to characterize the physiochemical properties and morphology of the different surfaces.
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