Accessing Thin Film Wetting Regimes during Polymer Growth by Initiated Chemical Vapor Deposition

Surface Nanostructure Fabrication by Initiated Chemical Vapor Deposition and Its Combined Technologies

Initiated chemical vapor deposition (iCVD) is a versatile technique that enables the direct growth of nanostructures and surface modification of such structures. Unlike traditional CVD methods, iCVD operates under mild conditions, allowing for damage-free processing of delicate substrates. It can produce highly uniform polymer layers, with thicknesses ranging from over 15 μm to sub-10 nm, conformally coating intricate geometries. The broad range of polymer compositions achievable with iCVD offers precise control of surface chemistry. In this Viewpoint, we present iCVD's mechanisms and the principles for controlling the composition and morphology of deposited layers. We summarize various surface nanostructures including nanodomes, nanocones, nanowrinkles, nanoparticles, and nanoporous structures that are directly fabricated using iCVD. We also demonstrate the integration of iCVD with other advanced methods, such as photo, soft, and nanoimprint lithography; template-assisted growth; and thermal CVD, to leverage the advantages of multiple methods and overcome individual limitations in nanofabrication. Through these combined strategies, we show the iCVD's potential for creating multifunctional nanostructures with broad applications across engineering and biomedical fields.

Single-step synthesis of shaped polymeric particles using initiated chemical vapor deposition in liquid crystals

We elucidate a previously unknown synthesis pathway that leads to polymeric nanospheres, orientation-controlled microgels, or microspheroids via single-step polymerization of divinylbenzene (DVB) using initiated chemical vapor deposition (iCVD) in liquid crystals (LC). iCVD supplies vapor-phase reactants continuously, avoiding the critical limitation of reactant-induced disruption of LC structure that has plagued past LC-templated polymerization processes. LC is leveraged as a real-time display of the polymerization conditions and particle emergence, captured using an in situ long-focal range microscope. Detailed image analysis unravels key LC-guided mechanisms during polymerization. pDVB forms nanospheres due to poor solubilization by nematic LC. The nanospheres partition to the LC-solid interface and further assemble into microgel clusters whose orientation is guided by the LC molecular alignment. On further polymerization, microgel clusters transition to microspheroids that resemble liquid drops. We identify key energetic factors that guide trajectories along the synthesis pathway, providing the fundamental basis of a framework for engineering particle synthesis with shape control.

Designing Organic and Hybrid Surfaces and Devices with Initiated Chemical Vapor Deposition (iCVD)

The initiated chemical vapor deposition (iCVD) technique is an all-dry method for designing organic and hybrid polymers. Unlike methods utilizing liquids or line-of-sight arrival, iCVD provides conformal surface modification over intricate geometries. Uniform, high-purity, and pinhole-free iCVD films can be grown with thicknesses ranging from >15 µm to <5 nm. The mild conditions permit damage-free growth directly onto flexible substrates, 2D materials, and liquids. Novel iCVD polymer morphologies include nanostructured surfaces, nanoporosity, and shaped particles. The well-established fundamentals of iCVD facilitate the systematic design and optimization of polymers and copolymers. The functional groups provide fine-tuning of surface energy, surface charge, and responsive behavior. Further reactions of the functional groups in the polymers can yield either surface modification, compositional gradients through the layer thickness, or complete chemical conversion of the bulk film. The iCVD polymers are integrated into multilayer device structures as desired for applications in sensing, electronics, optics, electrochemical energy storage, and biotechnology. For these devices, hybrids offer higher values of refractive index and dielectric constant. Multivinyl monomers typically produce ultrasmooth and pinhole-free and mechanically deformable layers and robust interfaces which are especially promising for electronic skins and wearable optoelectronics.