Selective deposition of silver and copper films by condensation coefficient modulation

Whilst copper and silver are the conductors of choice for myriad current and emerging applications, patterning these metals is a slow and costly process. We report the remarkable finding that an extremely thin (∼10 nm) printed layer of specific organofluorine compounds enables selective deposition of copper and silver vapour, with metal condensing only where the organofluorine layer is not. This unconventional approach is fast, inexpensive, avoids metal waste and the use of harmful chemical etchants, and leaves the metal surface uncontaminated. We have used this approach to fabricate thin films of these metals with 6 million apertures cm−2 and grids of ∼1 μm lines, through to 10 cm diameter apertures. We have also fabricated semi-transparent organic solar cells in which the top silver electrode is patterned with a dense array of 2 μm diameter apertures, which cannot be achieved by any other scalable means directly on an organic electronic device

Condensation Coefficient Modulation: An Unconventional Approach to the Fabrication of Transparent and Patterned Silver Electrodes for Photovoltaics and Beyond

Silver is the metal of choice for the fabrication of highly transparent grid electrodes for photovoltaics because it has the highest electrical conductivity among metals together with high stability toward oxidation in air. Conventional methods for fabricating silver grid electrodes involve printing the metal grid from costly colloidal solutions of nanoparticles, selective removal of metal by etching using harmful chemicals, or electrochemical deposition of the silver, an inherently chemical intensive and slow process. This Spotlight highlights an emerging approach to the fabrication of transparent and patterned silver electrodes that can be applied to glass and flexible plastic substrates or directly on top of a device, based on spatial modulation of silver vapor condensation. This counterintuitive approach has been possible since the discovery in 2019 that thin films of perfluorinated organic compounds are highly resistant to the condensation of silver vapor, so silver condenses only where the perfluorinated layer is not. The beauty of this approach lies in its simplicity and versatility because vacuum evaporation is a well-established and widely available deposition method for silver and the shape and dimensions of metallized regions depend only on the method used to pattern the perfluorinated layer. The aim of this Spotlight is to describe this approach and summarize its electronic applications to date with particular emphasis on organic photovoltaics, a rapidly emerging class of thin-film photovoltaics that requires a flexible alternative to the conventional conducting oxide electrodes currently used to allow light into the device. AB - Silver is the metal of choice for the fabrication of highly transparent grid electrodes for photovoltaics because it has the highest electrical conductivity among metals together with high stability toward oxidation in air. Conventional methods for fabricating silver grid electrodes involve printing the metal grid from costly colloidal solutions of nanoparticles, selective removal of metal by etching using harmful chemicals, or electrochemical deposition of the silver, an inherently chemical intensive and slow process. This Spotlight highlights an emerging approach to the fabrication of transparent and patterned silver electrodes that can be applied to glass and flexible plastic substrates or directly on top of a device, based on spatial modulation of silver vapor condensation. This counterintuitive approach has been possible since the discovery in 2019 that thin films of perfluorinated organic compounds are highly resistant to the condensation of silver vapor, so silver condenses only where the perfluorinated layer is not. The beauty of this approach lies in its simplicity and versatility because vacuum evaporation is a well-established and widely available deposition method for silver and the shape and dimensions of metallized regions depend only on the method used to pattern the perfluorinated layer. The aim of this Spotlight is to describe this approach and summarize its electronic applications to date with particular emphasis on organic photovoltaics, a rapidly emerging class of thin-film photovoltaics that requires a flexible alternative to the conventional conducting oxide electrodes currently used to allow light into the device

Elucidating the Exceptional Passivation Effect of 0.8 nm Evaporated Aluminium on Transparent Copper Films

Slab-like copper films with a thickness of 9 nm (∼70 atoms) and sheet resistance of ≤9 Ω sq−1 are shown to exhibit remarkable long-term stability toward air-oxidation when passivated with an 0. 8 nm aluminium layer deposited by simple thermal evaporation. The sheet resistance of 9 nm Cu films passivated in this way, and lithographically patterned with a dense array of ∼6 million apertures per cm2, increases by <3.5% after 7,000 h exposure to ambient air. Using a combination of annular-dark field scanning transmission electron microscopy, nanoscale spatially resolved elemental analysis and atomic force microscopy, we show that this surprising effectiveness of this layer results from spontaneous segregation of the aluminium to grain boundaries in the copper film where it forms a ternary oxide plug at those sites in the metal film most vulnerable to oxidation. Crucially, the heterogeneous distribution of this passivating oxide layer combined with its very low thickness ensures that the underlying metal is not electrically isolated, and so this simple passivation step renders Cu films stable enough to compete with Ag as the base metal for transparent electrode applications in emerging optoelectronic devices

Stick-Slip Sliding of Water Drops on Chemically Heterogeneous Surfaces

We present a comprehensive study of water drops sliding down chemically heterogeneous surfaces formed by a periodic pattern of alternating hydrophobic and hydrophilic stripes. Drops are found to undergo a stick-slip motion whose average speed is an order of magnitude smaller than that measured on a homogeneous surface having the same static contact angle. This motion is the result of the periodic deformations of the drop interface when crossing the stripes. Numerical simulations confirm this view and are used to elucidate the principles underlying the experimental observations

Transparent Fused Nanowire Electrodes by Condensation Coefficient Modulation

Silver nanowire networks can offer exceptionally high performance as transparent electrodes for stretchable sensors, flexible optoelectronics, and energy harvesting devices. However, this type of electrode suffers from the triple drawbacks of complexity of fabrication, instability of the nanowire junctions, and high surface roughness, which limit electrode performance and utility. Here, a new concept in the fabrication of silver nanowire electrodes is reported that simultaneously addresses all three of these drawbacks, based on an electrospun nanofiber network and supporting substrate having silver vapor condensation coefficients of one and near‐zero, respectively. Consequently, when the whole substrate is exposed to silver vapor by simple thermal evaporation, metal selectively deposits onto the nanofiber network. The advantage of this approach is the simplicity, since there is no mask, chemical or dry metal etching step, or mesh transfer step. Additionally, the contact resistance between nanowires is zero and the surface roughness is sufficiently low for integration into organic photovoltaic devices. This new concept opens the door to continuous roll‐to‐roll fabrication of high‐performance fused silver nanowire electrodes for myriad potential applications

Drop motion induced by vertical vibrations

We have studied the motion of liquid drops on an inclined plate subject to vertical vibrations. The liquids comprised distilled water and different aqueous solutions of glycerol, ethanol and isopropanol spanning the range 1–39 mm2 s−1 in kinematic viscosities and 40–72 mN m−1 in surface tension. At sufficiently low oscillating amplitudes, the drops are always pinned to the surface. Vibrating the plate above a certain amplitude yields sliding of the drop. Further increasing the oscillating amplitude drives the drop upward against gravity. In the case of the most hydrophilic aqueous solutions, this motion is not observed and the drop only slides downward. Images taken with a fast camera show that the drop profile evolves in a different way during sliding and climbing. In particular, the climbing drop experiences a much bigger variation in its profile during an oscillating period. Complementary numerical simulations of 2D drops based on a diffuse interface approach confirm the experimental findings. The overall qualitative behavior is reproduced suggesting that the contact line pinning due to contact angle hysteresis is not necessary to explain the drop climbing

Doped MXenes—A new paradigm in 2D systems: Synthesis, properties and applications

Since 2011, 2D transition metal carbides, carbonitrides and nitrides known as MXenes have gained huge attention due to their attractive chemical and electronic properties. The diverse functionalities of MXenes make them a promising candidate for multitude of applications. Recently, doping MXene with metallic and non-metallic elements has emerged as an exciting new approach to endow new properties to this 2D systems, opening a new paradigm of theoretical and experimental studies. In this review, we present a comprehensive overview on the recent progress in this emerging field of doped MXenes. We compare the different doping strategies; techniques used for their characterization and discuss the enhanced properties. The distinct advantages of doping in applications such as electrocatalysis, energy storage, photovoltaics, electronics, photonics, environmental remediation, sensors, and biomedical applications is elaborated. Additionally, theoretical developments in the field of electrocatalysis, energy storage, photovoltaics, and electronics are explored to provide key specific advantages of doping along with the underlying mechanisms. Lastly, we present the advantages and challenges of doped MXenes to take this thriving field forward

Doped MXenes—A new paradigm in 2D systems: Synthesis, properties and applications

Since 2011, 2D transition metal carbides, carbonitrides and nitrides known as MXenes have gained huge attention due to their attractive chemical and electronic properties. The diverse functionalities of MXenes make them a promising candidate for multitude of applications. Recently, doping MXene with metallic and non-metallic elements has emerged as an exciting new approach to endow new properties to this 2D systems, opening a new paradigm of theoretical and experimental studies. In this review, we present a comprehensive overview on the recent progress in this emerging field of doped MXenes. We compare the different doping strategies; techniques used for their characterization and discuss the enhanced properties. The distinct advantages of doping in applications such as electrocatalysis, energy storage, photovoltaics, electronics, photonics, environmental remediation, sensors, and biomedical applications is elaborated. Additionally, theoretical developments in the field of electrocatalysis, energy storage, photovoltaics, and electronics are explored to provide key specific advantages of doping along with the underlying mechanisms. Lastly, we present the advantages and challenges of doped MXenes to take this thriving field forward

Surface Functionalized MXenes for Wastewater Treatment-A Comprehensive Review.

Funder: European Regional Development Fund; Id: http://dx.doi.org/10.13039/501100008530Over 80% of wastewater worldwide is released into the environment without proper treatment. Whilst environmental pollution continues to intensify due to the increase in the number of polluting industries, conventional techniques employed to clean the environment are poorly effective and are expensive. MXenes are a new class of 2D materials that have received a lot of attention for an extensive range of applications due to their tuneable interlayer spacing and tailorable surface chemistry. Several MXene-based nanomaterials with remarkable properties have been proposed, synthesized, and used in environmental remediation applications. In this work, a comprehensive review of the state-of-the-art research progress on the promising potential of surface functionalized MXenes as photocatalysts, adsorbents, and membranes for wastewater treatment is presented. The sources, composition, and effects of wastewater on human health and the environment are displayed. Furthermore, the synthesis, surface functionalization, and characterization techniques of merit used in the study of MXenes are discussed, detailing the effects of a range of factors (e.g., PH, temperature, precursor, etc.) on the synthesis, surface functionalization, and performance of the resulting MXenes. Finally, the limits of MXenes and MXene-based materials as well as their potential future research directions, especially for wastewater treatment applications are highlighted