Force touch sensors have received a great deal of attention for various applications owing to their versatile ability to detect touch and pressure. To demonstrate high‐performance force touch sensors, numerous studies have been performed, focusing on high sensitivity, transparency, and mechanical durability against bending. However, it is still challenging to apply force touch sensors in flexible applications, because their sensing performance is subject to change and degraded by induced mechanical stress and deformation when the device is bent. Here, a high‐performance and transparent nanoforce touch sensor with bending‐insensitivity is reported. This is achieved by developing a thin, flexible, and transparent hierarchical nanocomposite film, which is composed of a nanostructured plastic base, coplanar electrodes, and a dielectric polymer layer with silver nanoparticles. The fabrication process is simple that high manufacturing repeatability, uniformity, and reliability are achieved on a large‐area (8 in.) scale. The fabricated device shows a pressure sensitivity of 0.036 kPa−1 with high transparency (83%) in a pressure range up to 3 kPa. In particular, its thin thickness (45 µm) and the coplanar electrode enable to achieve excellent insensitivity to the bending with a radius of curvature of 4 mm more than 10 000 times.

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Recently, geometrically structured nanomaterials have received great attention due to their unique physical and chemical properties, which originate from the geometric variation in such materials. Indeed, the use of various geometrically structured nanomaterials has been actively reported in enhanced‐performance devices in a wide range of applications. Recent significant progress in the development of geometrically structured nanomaterials and associated devices is summarized. First, a brief introduction of advanced nanofabrication methods that enable the fabrication of various geometrically structured nanomaterials is given, and then the performance enhancements achieved in devices utilizing these nanomaterials, namely, i) physical and gas nanosensors, ii) nanoelectromechanical devices, and iii) nanosieves are described. For the device applications, a systematic summary of their structures, working mechanisms, fabrication methods, and output performance is provided. Particular focus is given to how device performance can be enhanced through the geometric structures of the nanomaterials. Finally, perspectives on the development of novel nanomaterial structures and associated devices are presented.

A partially anchored nanowire structure, which is a highly engineered structure mitigating mechanical stress, exhibits excellent structural stability under significant volume expansion of Pd.

Nanowire-transfer technology has received much attention thanks to its capability to fabricate high-performance flexible nanodevices with high simplicity and throughput. However, it is still challenging to extend the conventional nanowire-transfer method to the fabrication of a wide range of devices since a chemical-adhesion-based nanowire-transfer mechanism is complex and time-consuming, hindering successful transfer of diverse nanowires made of various materials. Here, we introduce a material-independent mechanical-interlocking-based nanowire-transfer (MINT) method, fabricating ultralong and fully aligned nanowires on a large flexible substrate (2.5 × 2 cm) in a highly robust manner. For the material-independent nanotransfer, we developed a mechanics-based nanotransfer method, which employs a dry-removable amorphous carbon (a-C) sacrificial layer between a vacuum-deposited nanowire and the underlying master mold. The controlled etching of the sacrificial layer enables the formation of a mechanical-interlocking structure under the nanowire, facilitating peeling off of the nanowire from the master mold robustly and reliably. Using the developed MINT method, we successfully fabricated various metallic and semiconductor nanowire arrays on flexible substrates. We further demonstrated that the developed method is well suited to the reliable fabrication of highly flexible and high-performance nanoelectronic devices. As examples, a fully aligned gold (Au) microheater array exhibited high bending stability (10 cycling) and ultrafast (∼220 ms) heating operation up to ∼100 °C. An ultralong Au heater-embedded cuprous-oxide (CuO) nanowire chemical gas sensor showed significantly improved reversible reaction kinetics toward NO with 10-fold enhancement in sensitivity at 100 °C.

Recently, copper oxide (CuO)-based visible-light photodetectors have attracted great interest due to their narrow bandgap (1.2 eV), low cost, and ease of fabrication. However, there has been insufficient theoretical analysis and study of CuO-based photodetectors, resulting in inferior performance in terms of responsivity, detectivity, and response speed. This work develops a method to enhance the performance of CuO photodetectors by engineering a grain structure based on a newly-developed theoretical model. In the developed theoretical grain-structure model, the grain size and the connections between grains are considered because they can strongly affect the optoelectronic characteristics of CuO photodetectors. Based upon the proposed model, the engineered CuO device achieves enhanced optoelectronic performance. The engineered device shows high responsivity of 15.3 A/W and detectivity of 1.08 × 10 11 Jones, which are 18 and 50 times better than those of the unoptimized device, and also shows fast rising and decaying response speeds of 0.682 s and 1.77 s, respectively. In addition, the proposed method is suitable for the mass-production of performance-enhanced, reliable photodetectors. By using a conventional semiconductor fabrication process, a photodetector-array is demonstrated on a 4-inch wafer. The fabricated devices show uniform, high, and stable optoelectronic performance for a month.

In spite of the excellent thermal properties of nanowires, the typical form factor of unrefined nanowires has restricted their potential use in developing ultralow power electrothermal heater and application device. In this paper, a nanowire array with a perfectly aligned geometric structure on an air-suspended beam is proposed as a novel heating element. By locally confining the generated heat and suppressing beam conduction loss to the substrate, the proposed nanowire array heater overcomes the fundamental power consumption limits of conventional film-type microheaters. As a result, only 2.51 mW of power is required to reach an average temperature of 300 °C, surpassing the performance of state-of-the-art microheaters. The developed nanowire array heater is monolithically integrated with gas sensing nanowires to demonstrate its full capability as an ultralow power gas sensor. The fabricated device successfully detects low concentration carbon monoxide gas of 1 ppm, using less than 5 mW of power. The presented technique offers a promising pathway toward realizing always-on gas sensors driven by battery-powered mobile devices, which will ensure a hazardous gas-free safe environment. In addition, the proposed strategy of employing geometrically structured nanomaterials in the electrothermal heater design enables to lead out their potential thermal capability in many other applications.

Palladium (Pd) has been drawing increasing attention as a hydrogen (H 2 ) detecting material due to its highly selective sensitivity to H 2 . However, at H 2 concentrations above 2%, Pd undergoes an inevitable phase transition, causing undesirable electrical and mechanical alterations. In particular, nonlinear gas response (ΔR/R 0 ) that accompanies phase transition has been a great bottleneck for detecting H 2 in high concentrations, which is especially important as there is a risk of explosion over 4% H 2 . Here, we propose a phasetransition-inhibited Pd nanowire H 2 sensor that can detect up to 4% H 2 with high linearity and high sensitivity. Based on the calculation of the change in free energy, we designed Pd nanowires that are highly adhered to the substrate to withstand the stress that leads to phase transition. We theoretically optimized the Pd nanowire dimensions using a finite element method simulation and then experimentally fabricated the proposed sensor by exploiting a developed nanofabrication method. The proposed sensor exhibits a high sensing linearity (98.9%) with high and stable sensitivity (ΔR/R 0 /[H 2 ] = 875%•bar −1 ) over a full range of H 2 concentrations (0.1−4%). Using the fabricated Pd sensors, we have successfully demonstrated a wireless sensor module that can detect H 2 with high linearity, notifying real-time H 2 leakage through remote communication. Overall, our work suggests a nanostructuring strategy for detecting H 2 with a phase-transition-inhibited pure Pd H 2 sensor with rigorous scientific exploration.