Production of Centimeter-Scale Gradient Patterns by Graded Elastomeric Tip Array

Large-area patterned surfaces with chemical and/or morphological gradients have significant applications in biology, chemistry, and materials science. In this work, we developed a unique lithographic strategy to fabricate 2D and 3D gradient patterns with gradually varying feature size or height over centimeter-scale areas by utilizing a large-area polydimethylsiloxane (PDMS) tip array with programmable tip apex as a conformal photomask in near-field photolithography. Meanwhile, a new strategy was developed to create the PDMS tip array with graded apex size, which was employed to fabricate gradient patterns with the lateral feature sizes changing from sub-100 nm to several microns on one single substrate over macroscopic (square centimeter) areas. Furthermore, 3D gradient patterns with spatially varying feature height were enabled by employing gradient exposure dose. The formation of gradient feature size was ascribed either to gradient contact areas between tips and substrates or to exposure dose gradient. This lithography strategy combines the advantages of a wide range of feature sizes, simplicity, high-throughput, low-cost and diversified feature shapes, making it a facile and flexible approach to manufacture various functional gradient structures

Improved Selectivity and Sensitivity of Gas Sensing Using a 3D Reduced Graphene Oxide Hydrogel with an Integrated Microheater

Low-cost, one-step, and hydrothermal synthesized 3D reduced graphene oxide hydrogel (RGOH) is exploited to fabricate a high performance NO₂ and NH₃ sensor with an integrated microheater. The sensor can experimentally detect NO₂ and NH₃ at low concentrations of 200 ppb and 20 ppm, respectively, at room temperature. In addition to accelerating the signal recovery rate by elevating the local silicon substrate temperature, the microheater is exploited for the first time to improve the selectivity of NO₂ sensing. Specifically, the sensor response from NH₃ can be effectively suppressed by a locally increased temperature, while the sensitivity of detecting NO₂ is not significantly affected. This leads to good discrimination between NO₂ and NH₃. This strategy paves a new avenue to improve the selectivity of gas sensing by using the microheater to raise substrate temperature

Large-Area Sub-Wavelength Optical Patterning via Long-Range Ordered Polymer Lens Array

Fabrication of large-area, highly orderly, and high-resolution nanostructures in a cost-effective fashion prompts advances in nanotechnology. Herein, for the first time, we demonstrate a unique strategy to prepare a long-range highly regular polymer lens from photoresist nanotrenches based templates, which are obtained from underexposure. The relationship between exposure dose and the cross-sectional morphology of produced photoresist nanostructures is revealed for the first time. The polymer lens arrays are repeatedly used for rapid generation of sub-100 nm nanopatterns across centimeter-scale areas. The light focusing properties of the nanoscale polymer lens are investigated by both simulation and experiment. It is found that the geometry, size of the lens, and the exposure dose can be deployed to adjust the produced feature size, spacing, and shapes. Because the polymer lenses are derived from top-down photolithography, the nearly perfect long-range periodicity of produced nanopatterns is ensured, and the feature shapes can be flexibly designed. Because this nanolithographic strategy enables subwavelength periodical nanopatterns with controllable feature size, geometry, and composition in a cost-effective manner, it can be optimized as a viable and potent nanofabrication tool for various technological applications

Highly Stretchable and Transparent Thermistor Based on Self-Healing Double Network Hydrogel

An ultrastretchable thermistor that combines intrinsic stretchability, thermal sensitivity, transparency, and self-healing capability is fabricated. It is found the polyacrylamide/carrageenan double network (DN) hydrogel is highly sensitive to temperature and therefore can be exploited as a novel channel material for a thermistor. This thermistor can be stretched from 0 to 330% strain with the sensitivity as high as 2.6%/°C at extreme 200% strain. Noticeably, the mechanical, electrical, and thermal sensing properties of the DN hydrogel can be self-healed, analogous to the self-healing capability of human skin. The large mechanical deformations, such as flexion and twist with large angles, do not affect the thermal sensitivity. Good flexibility enables the thermistor to be attached on nonplanar curvilinear surfaces for practical temperature detection. Remarkably, the thermal sensitivity can be improved by introducing mechanical strain, making the sensitivity programmable. This thermistor with tunable sensitivity is advantageous over traditional rigid thermistors that lack flexibility in adjusting their sensitivity. In addition to superior sensitivity and stretchability compared with traditional thermistors, this DN hydrogel-based thermistor provides additional advantages of good transparency and self-healing ability, enabling it to be potentially integrated in soft robots to grasp real world information for guiding their actions