Atomic Layer Deposition of Conductive Coatings on Cotton, Paper, and Synthetic Fibers: Conductivity Analysis and Functional Chemical Sensing Using “All‐Fiber” Capacitors

Abstract

Conductive coatings on complex fibrous systems are attracting interest for new electronic and other functional systems. Obtaining a quantitative conductivity value for complex surface coatings is often difficult. This work describes a procedure to quantify the effective electrical conductivity of conductive coatings on non‐conductive fibrous networks. By applying a normal force orthogonal to the current and field direction, fiber/fiber contact is improved and consistent conductance values can be measured. Nylon fibers coated with an electroless silver plating shows effective conductivity up to 1950 S cm−1, and quartz fibers coated with tungsten by atomic layer deposition (ALD) show values up to ∼1150 S cm−1. Cotton fibers and paper coated with a range of ZnO film thicknesses by ALD show effective conductivity of up to 24 S cm−1 under applied normal force, and conductivity scaled as expected with film coating thickness. Furthermore, we use the conductive coatings to produce an “all‐fiber” metal–insulator–metal capacitor that functions as a liquid chemical sensor. The ability to reliably analyze the effective conductivity of coatings on complex fiber systems will be important to design and improve performance of similar devices and other electronic textiles structures.

Polymer–Inorganic Core–Shell Nanofibers by Electrospinning and Atomic Layer Deposition: Flexible Nylon–ZnO Core–Shell Nanofiber Mats and Their Photocatalytic Activity

“…Recently, atomic layer deposition (ALD) technique has been explored to produce conformal and very thin inorganic coatings on fibrous systems such as cotton, 26,27 cellulose-based filter paper, 27−30 nonwovens, 26 synthetic 27,29 and natural fibers 31 and nanofibrillated cellulose 32 as well. ALD, which is a special type of low-temperature chemical vapor deposition, proceeds though the sequential pulses of two or more precursors separated by purging/evacuation periods.…”

“…33−35 ALD process provides flexibility so that very thin conformal layers of metals, metal oxides or metal nitrides can be coated onto different types of three-dimensional substrates. 33−35 ALD was mostly studied on inorganic substrates, yet, recent studies showed that polymeric films 36 and complex surfaces such as fibers and nonwovens [26][27][28][29][30][31][32]36 can also be coated by ALD. It has also been shown that electrospun nanofibers can be used as a template for producing hollow nanofibers.…”

“…33 As the substrate is exposed to a certain precursor, gaseous precursor molecules saturate the surface by reacting with available surface sites, creating new sites for the following precursor. Film growth mechanism of ALD is inherently self-limiting, which gives rise to unique properties such as high uniformity and conformality, as well as subnanometer precise thickness control.33−35 ALD process provides flexibility so that very thin conformal layers of metals, metal oxides or metal nitrides can be coated onto different types of three-dimensional substrates.33−35 ALD was mostly studied on inorganic substrates, yet, recent studies showed that polymeric films 36 and complex surfaces such as fibers and nonwovens [26][27][28][29][30][31][32]36 can also be coated by ALD. It has also been shown that electrospun nanofibers can be used as a template for producing hollow nanofibers.…”

Transformation of polymer-ZnO core–shell nanofibers into ZnO hollow nanofibers: Intrinsic defect reorganization in ZnO and its influence on the photocatalysis

“…The catalysts examined here were fabricated via a renounced and industrially applicable combination [10,11,18,28,29,[39][40][41], viz. electrospinning [42][43][44] and atomic layer deposition (ALD) [45][46][47][48][49].…”

Flexible Thermoelectric ZnO–Organic Superlattices on Cotton Textile Substrates by ALD/MLD

“…[20] The ALD of ZnO and Al-doped ZnO on cotton and nylon nonwoven fiber mats has already been investigated in the context of fabricating conductive coatings for sensor applications. [21,22] While ZnO is known to be a promising TE material for remarkably high operating temperatures (about 1000 °C), [23] the relatively high thermal conductivity of bulk ZnO results in rather poor TE efficiency at low temperatures. However, the thermal conductivity of ZnO can be decreased by nanostructuring, which results in high scattering of the heat-carrying phonons while the electronic conductivity still remains at a reasonable level.…”