Atomically Flat, 2D Edge-Directed Self-Assembly of Block Copolymers.

Nanoscale shape engineering is an essential requirement for the practical use of 2D materials, aiming at precisely customizing optimal structures and properties. In this work, sub-10-nm-scale block copolymer (BCP) self-assembled nanopatterns finely aligned along the atomic edge of 2D flakes, including graphene, MoS2 , and h-BN, are exploited for reliable nanopatterning of 2D materials. The underlying mechanism for the alignment of the self-assembled nanodomains is elucidated based on the wetting layer alternation of the BCP film in the presence of intermediate 2D flakes. The resultant highly aligned nanocylinder templates with remarkably low levels of line edge roughness (LER) and line-width roughness (LWR) yield a sub-10-nm-wide graphene nanoribbon (GNR) array with noticeable switching characteristics (on-to-off ratio up to ≈6 × 104 ).

Effects of Al Precursors on the Characteristics of Indium-Aluminum Oxide Semiconductor Grown by Plasma-Enhanced Atomic Layer Deposition.

Atomic layer deposition (ALD) has attracted much attention, particularly for applications in nanoelectronics because of its atomic-level controllability and high-quality products. In this study, we developed a plasma-enhanced atomic layer deposition (PEALD) process to fabricate a homogeneous indium aluminum oxide (IAO) semiconductor film. Trimethylaluminum (TMA) and dimethylaluminum isopropoxide (DMAI) were used as Al precursors, which yielded different compositions. Density functional theory (DFT) calculations on the surface reactions between indium and aluminum precursors showed that while highly reactive TMA would etch In, DMAI with lower reactivity would allow indium to persist in the films, resulting in a more controlled doping of Al. The In/Al composition ratio could be further precisely controlled by adjusting the indium precursor dose time to sub-saturation. IAO based on DMAI was applied to fabricate thin-film transistors (TFTs), showing that Al can be a carrier suppressor of indium oxide. TFTs with PEALD IAO containing 3.8 atomic % Al showed a turn-on voltage of -0.4 ± 0.3 V, a subthreshold slope of 0.09 V/decade, and a field effect mobility of 18.9 cm2/(V s).

Ultrathin Nanofibrous Membranes Containing Insulating Microbeads for Highly Sensitive Flexible Pressure Sensors.

Highly sensitive and flexible pressure sensors were developed based on dielectric membranes composed of insulating microbeads contained within polyvinylidene fluoride (PVDF) nanofibers. The membrane is fabricated using a simple electrospinning process. The presence of the microbeads enhances porosity, which in turn enhances the sensitivity (1.12 kPa-1 for the range of 0-1 kPa) of the membrane when used as a pressure sensor. The microbeads are fixed in position and uniformly distributed throughout the nanofibers, resulting in a wide dynamic range (up to 40 kPa) without any sensitivity loss. The fluffy and nonsticky PVDF nanofiber features low hysteresis and ultrafast response times (∼10 ms). The sensor has also demonstrated reliable pressure detection over 10 000 loading cycles and 250 bending cycles at a 13 mm bending radius. These pressure sensors were successfully applied to detect heart rate and respiratory signals, and an array of sensors was fabricated and used to recognize spatial pressure distribution. The sensors described herein are ultrathin and ultralight, with a total thickness of less than 100 µm, including the electrodes. All of the materials comprising the sensors are flexible, making them suitable for on-body applications such as tactile sensors, electronic skins, and wearable healthcare devices.

Highly Sensitive Active-Matrix Driven Self-Capacitive Fingerprint Sensor based on Oxide Thin Film Transistor.

The fingerprint recognition has been widely used for biometrics in mobile devices. Existing fingerprint sensors have already been commercialized in the field of mobile devices using primarily Si-based technologies. Recently, mutual-capacitive fingerprint sensors have been developed to lower production costs and expand the range of application using thin-film technologies. However, since the mutual-capacitive method detects the change of mutual capacitance, it has high ratio of parasitic capacitance to ridge-to-valley capacitance, resulting in low sensitivity, compared to the self-capacitive method. In order to demonstrate the self-capacitive fingerprint sensor, a switching device such as a transistor should be integrated in each pixel, which reduces a complexity of electrode configuration and sensing circuits. The oxide thin-film transistor (TFT) can be a good candidate as a switching device for the self-capacitive fingerprint sensor. In this work, we report a systematic approach for self-capacitive fingerprint sensor integrating Al-InSnZnO TFTs with field-effect mobility higher than 30 cm2/Vs, which enable isolation between pixels, by employing industry-friendly process methods. The fingerprint sensors are designed to reduce parasitic resistance and capacitance in terms of the entire system. The excellent uniformity and low leakage current (<10-12) of the oxide TFTs allow successful capture of a fingerprint image.

Inorganic Polymer Micropillar-Based Solution Shearing of Large-Area Organic Semiconductor Thin Films with Pillar-Size-Dependent Crystal Size.

It is demonstrated that the crystal size of small-molecule organic semiconductors can be controlled during solution shearing by tuning the shape and dimensions of the micropillars on the blade. Increasing the size and spacing of the rectangular pillars increases the crystal size, resulting in higher thin-film mobility. This phenomenon is attributed as the microstructure changing the degree and density of the meniscus line curvature, thereby controlling the nucleation process. The use of allylhybridpolycarbosilane (AHPCS), an inorganic polymer, is also demonstrated as the microstructured blade for solution shearing, which has high resistance to organic solvents, can easily be microstructured via molding, and is flexible and durable. Finally, it is shown that solution shearing can be performed on a curved surface using a curved blade. These demonstrations bring solution shearing closer to industrial applications and expand its applicability to various printed flexible electronics.

Superfast Room-Temperature Activation of SnO2 Thin Films via Atmospheric Plasma Oxidation and their Application in Planar Perovskite Photovoltaics.

The power conversion efficiency (PCE) of perovskite solar cells (PSCs) has now exceeded 20%; thus, research focus has shifted to establishing the foundations for commercialization. One of the pivotal themes is to curtail the overall fabrication time, to reduce unit cost, and mass-produce PSCs. Additionally, energy dissipation during the thermal annealing (TA) stage must be minimized by realizing a genuine low-temperature (LT) process. Here, tin oxide (SnO2 ) thin films (TFs) are formulated at extremely high speed, within 5 min, under an almost room-temperature environment (<50 °C), using atmospheric Ar/O2 plasma energy (P-SnO2 ) and are applied as an electron transport layer of a "n-i-p"-type planar PSC. Compared with a thermally annealed SnO2 TF (T-SnO2 ), the P-SnO2 TF yields a more even surface but also outstanding electrical conductivity with higher electron mobility and a lower number of charge trap sites, consequently achieving a superior PCE of 19.56% in P-SnO2 -based PSCs. These findings motivate the use of a plasma strategy to fabricate various metal oxide TFs using the sol-gel route.