# Special Issue on Nano-Electronic Devices and Functional Applications
###### Abstract  
Nano-electronic devices and materials hold considerable promise due to their inherent structural and material benefits, such as device miniaturization, increased integration density, and reduced power consumption. Streamlined techniques for nano-scale fabrication of these devices and materials, which are compatible with large-scale production and solution processes, help us to further understand their operational mechanisms or their respective formation processes. These advancements have resulted in significant breakthroughs in functional electronic devices, including light-emitting diodes, photodetectors, photovoltaics, transistors, and sensors. In addition, devices that feature flexibility and stretchability offer unprecedented performance for user-friendly electronic applications. This Special Issue is dedicated to discussing the most recent advancements and trends in nano-electronic devices and materials research. It includes a total of seven papers--five original research articles and two review articles as follows. First, this Special Issue examines methods aimed at enhancing the performance of nano-electric devices by improving their electrical properties. [PERSON] and colleagues [1] proposed a simple and economical thermal passivation method on crystalline silicon wafers under H\({}_{2}\)S gas to improve the minority carrier lifetime (up to 2030%). Through surface analysis of the silicon wafers post-annealing, they demonstrated that the quantity of sulfur present is pivotal in dictating the effectiveness of the passivation process. In a separate study, [PERSON] and co-authors [2] propose a two-photon lithography technique for the creation of extensive photonic crystal structures. This method allows the production and control of defects within these repeated photonic crystal structures, thereby enhancing the simple array of patterns traditionally obtained via interference lithography. Second, this Special Issue features two research papers focused on nano-electronic switching electronics. [PERSON] and colleagues [3] reported a new design and the feasibility of a vertical quaternary inverter (QNOT) for four data levels (\"1\", \"2\", \"3\", \"4\"). Remarkably, this design involves the use of only two field-effect transistors, as verified by a finite-element drift-diffusion simulation. [PERSON] et al. [4] demonstrated ZnO/ZnS core/shell NW arrays with a significant incensement of output current (from 42.7% to 91.1%). They attributed this increase to the strain-induced piezo-polarization charges present at the ZnO/ZnS core/shell layer, which modulate the energy band structure, and thus enable more efficient charge carrier transport. Lastly, this Special Issue explores the use of nano-electronic devices as sensors. [PERSON] and colleagues [5] present an overview of the current state of fiber-based electronics, examining their potential for future applications in wearable devices. This review encompasses the architecture, electrical properties, fabrication methods, and applications of these fiber-based electronics. It also addresses the critical challenges facing this technology, along with the practical enhancements required for its widespread adoption. In a separate study, [PERSON] et al. [6] report the successful implementation of amorphous indium-gallium-zinc oxide thin-film transistors on a reverse-trapezoid polydimethylsiloxane substrate, designed to distribute stress for skin-compatible electronic applications effectively. Finally, [PERSON] andco-authors [7] provide a comprehensive review of the current state and future perspectives of wearable photoplethysmography (PPG) sensors. This is achieved through a systematic literature review, analyzing various semiconducting materials from a skin-compatibility viewpoint. The ongoing research into nano-electronic devices necessitates an interdisciplinary approach, requiring the convergence of multiple fields. These include, but are not limited to, biology, physics, engineering, optics, material science, computer science, and biomedicine.