Low-Temperature Fabrication of Alkali Metal-Organic Charge Transfer Complexes on Cotton Textile for Optoelectronics and Gas Sensing Rajesh Ramanathan, † Sumeet Walia, ‡ Ahmad Esmaielzadeh Kandjani, † Sivacarendran Balendran, ‡ Mahsa Mohammadtaheri, † Suresh Kumar Bhargava, † Kourosh Kalantar-zadeh, ‡ and Vipul Bansal* ,† † NanoBiotechnology Research Laboratory, Centre for Advanced Materials and Industrial Chemistry, School of Applied Sciences, and ‡ School of Electrical and Computer Engineering, RMIT University, GPO Box 2476 V, Melbourne, VIC 3000, Australia * S Supporting Information ABSTRACT: A generalized low-temperature approach for fabricat- ing high aspect ratio nanorod arrays of alkali metal-TCNQ (7,7,8,8- tetracyanoquinodimethane) charge transfer complexes at 140 °C is demonstrated. This facile approach overcomes the current limitation associated with fabrication of alkali metal-TCNQ complexes that are based on physical vapor deposition processes and typically require an excess of 800 °C. The compatibility of soft substrates with the proposed low-temperature route allows direct fabrication of NaTCNQ and LiTCNQ nanoarrays on individual cotton threads interwoven within the 3D matrix of textiles. The applicability of these textile-supported TCNQ-based organic charge transfer complexes toward optoelectronics and gas sensing applications is established. ■ INTRODUCTION Flexible electronics has been a subject of keen interest due to their potential to transform the next generation of electronic devices. 1 This is due to the unique properties exhibited by such devices including being lightweight, bendable, portable, and energy-efficient with huge impact on a wide range of applications including transistors, memristors, and sensors. 1-8 Since most of the flexible substrates are unable to retain their structural properties at high temperatures, a critical aspect that is of paramount importance to produce flexible devices is the efficient low-temperature fabrication of nanostructures on appropriate substrates and templates. 9-11 The interest in the field has led to the use of a wide range of flexible substrates including polymers, thin films, hybrid materials, and foils. 10,12-17 Over the past few years, the potential of employing interwoven threads of cotton textiles as 3-dimensional (3D) substrates for growing nanostructured materials has been explored. 9,16,17 The use of textiles for flexible electronics is gaining increased interest as high throughput processes for manufacturing a range of textile-based materials are already in place; that is likely to allow facile integration of new functionalities in these unique substrates in an economically viable manner. 9,10 Additionally, the interwoven 3D matrix of threads in a textile provides extremely high surface area along with high porosity and required flexibility to create a robust templating platform that can be loaded with fascinating functionalities by growing a range of nanostructured materi- als. 16,17 This has led many research groups including ours to employ textiles as unique substrates to grow a range of functional materials including inorganic semiconducting oxide such as SnO 2 18 and organic semiconducting charge transfer complexes, which has seen renewed applications in electronics, sensing, and antimicrobial textiles. 16,17 Metal-organic semiconducting charge transfer complexes based on 7,7,8,8-tetracyanoquinodimethane (TCNQ) have gained signi ficant importance due to their interesting optoelectronic properties that have generated widespread interest in the area of molecular electronics. 15,16,19-22 This has led to new opportunities for fabricating organic nano- structured optical and electronic devices. Over the past decade, most of the research on metal-TCNQ (MTCNQ) based materials has focused on investigating the synthesis, properties, and applications of CuTCNQ and AgTCNQ, especially by Dunbar, Bond, and Miller et al. 19,20,22-24 In contrast, alkali MTCNQ materials such as LiTCNQ, NaTCNQ, and KTCNQ which exhibit unique electronic properties have not been investigated in detail, predominantly due to the challenges associated with their fabrication. 16,25-27 Such challenges arise due to the extremely high environmental reactivity of alkali metals, 28 which has predominantly restricted the fabrication strategies of alkali MTCNQs to high-temperatures routes that employ physical vapor deposition (PVD) of the alkali metal (e.g., Na 0 ,K 0 , and Li 0 ) on a substrate at temperatures exceeding 800 °C, followed by the growth of alkali MTCNQ in an inert atmosphere using a chemical vapor deposition (CVD) process. 25,29,30 It is obvious that such high temperature routes are not compatible with the fabrication of flexible electronic devices. 16 We recently demonstrated a low-temperature route Received: April 14, 2014 Revised: June 30, 2014 Article pubs.acs.org/Langmuir © XXXX American Chemical Society A dx.doi.org/10.1021/la501446b | Langmuir XXXX, XXX, XXX-XXX