Seong J. Cho

Preparation of stable superhydrophobic mesh with a biomimetic hierarchical structure

Stable superhydrophobic meshes with a biomimetic hierarchical structure were fabricated via simple electropolymerization and chemical polymerization processes. Because the multi-scale hierarchical structure provides a stable superhydrophobic state by maintaining a Cassie state, these meshes have high static and dynamic waterproof capabilities.

Replicable Multilayered Nanofibrous Patterns on a Flexible Film

This report describes a simple method for the direct patterning of nanofibers on a flexible, insulating film. The method allows the replication of nanofibrous patterns from a single patterned electrode and the fabrication of multilayered patterns from various electrode shapes. The architecture of the fibrous patterns can be controlled by tailoring the ambient humidity, thickness of the insulating film, polarity of the electrode, and size of the patterned electrode. Using this novel technique, it is possible to fabricate various complex patterns of nanofibers as well as inexpensive patterned structures.

A stretchable humidity sensor based on a wrinkled polyaniline nanostructure

A humidity sensor has received great interest in sensor fields because of their various applications. Especially, a stretchable humidity sensor which has mechanical stability has remained challenging issue in stretchable electronics. Here, we report a novel stretchable nanostructured polyaniline humidity sensor. The sensor was fabricated by simple fabrication methods such as pre-stretching process and self-assembly texturing process. The periodically wrinkled structure supported by microstructured elastomeric substrates provides an excellent stretchability. The micro-textured substrate was introduced for solving crack problem by Poisson effect as a stretchable sensor. The sensor maintains its humidity sensitivity well at the differed elongations. To the best our knowledge, this is the first report for a stretchable humidity sensor.

Omni-purpose stretchable strain sensor based on a highly dense nanocracking structure for whole-body motion monitoring

Here, we report an omni-purpose stretchable strain sensor (OPSS sensor) based on a nanocracking structure for monitoring whole-body motions including both joint-level and skin-level motions. By controlling and optimizing the nanocracking structure, inspired by the spider sensory system, the OPSS sensor is endowed with both high sensitivity (gauge factor ≈ 30) and a wide working range (strain up to 150%) under great linearity (R2 = 0.9814) and fast response time (<30 ms). Furthermore, the fabrication process of the OPSS sensor has advantages of being extremely simple, patternable, integrated circuit-compatible, and reliable in terms of reproducibility. Using the OPSS sensor, we detected various human body motions including both moving of joints and subtle deforming of skin such as pulsation. As specific medical applications of the sensor, we also successfully developed a glove-type hand motion detector and a real-time Morse code communication system for patients with general paralysis. Therefore, considering the outstanding sensing performances, great advantages of the fabrication process, and successful results from a variety of practical applications, we believe that the OPSS sensor is a highly suitable strain sensor for whole-body motion monitoring and has potential for a wide range of applications, such as medical robotics and wearable healthcare devices.

Development of a Waterproof Crack-Based Stretchable Strain Sensor Based on PDMS Shielding

This paper details the design of a poly(dimethylsiloxane) (PDMS)-shielded waterproof crack-based stretchable strain sensor, in which the electrical characteristics and sensing performance are not influenced by changes in humidity. This results in a higher number of potential applications for the sensor. A previously developed omni-purpose stretchable strain (OPSS) sensor was used as the basis for this work, which utilizes a metal cracking structure and provides a wide sensing range and high sensitivity. Changes in the conductivity of the OPSS sensor, based on humidity conditions, were investigated along with the potential possibility of using the design as a humidity sensor. However, to prevent conductivity variation, which can decrease the reliability and sensing ability of the OPSS sensor, PDMS was utilized as a shielding layer over the OPSS sensor. The PDMS-shielded OPSS sensor showed approximately the same electrical characteristics as previous designs, including in a high humidity environment, while maintaining its strain sensing capabilities. The developed sensor shows promise for use under high humidity conditions and in underwater applications. Therefore, considering its unique features and reliable sensing performance, the developed PDMS-shielded waterproof OPSS sensor has potential utility in a wide range of applications, such as motion monitoring, medical robotics and wearable healthcare devices.

Development of an Integrated Evaluation System for a Stretchable Strain Sensor

Recently, much research has been focused on stretchable or flexible electronic sensors for the measurement of strain or deformation on movable and variably shaped objects. In this research, to evaluate the performance of stretchable strain sensors, we have designed an integrated evaluation system capable of simultaneously measuring the change in stress and conductance of a strain sensor. Using the designed system, we have successfully evaluated the deformation characteristics, sensing range and sensing sensitivity of a stretchable strain sensor. We believe that the developed integrated evaluation system could be a useful tool for performance evaluation of stretchable strain sensors.

One-step fabrication of hierarchically structured silicon surfaces and modification of their morphologies using sacrificial layers

Fabrication of one-dimensional nanostructures is a key issue for optical devices, fluidic devices, and solar cells because of their unique functionalities such as antireflection and superhydrophobicity. Here, we report a novel one-step process to fabricate patternable hierarchical structures consisting of microstructures and one-dimensional nanostructures using a sacrificial layer. The layer plays a role as not only a micromask for producing microstructures but also as a nanomask for nanostructures according to the etching time. Using thismethod, we fabricated patterned hierarchical structures, with the ability to control the shape and density of the nanostructure. The various architectures provided unique functionalities. For example, our sacrificial-layer etching method allowed nanostructures denser than what would be attainable with conventional processes to form. The dense nanostructure resulted in a very low reflectance of the silicon surface (less than 1%). The nanostructured surface and hierarchically structured surface also exhibited excellent antiwetting properties, with a high contact angle (>165°) and low sliding angle (<1°). We believe that our fabrication approach will provide new insight into functional surfaces, such as those used for antiwetting and antireflection surface applications.

Bio-molecules detection sensor using silicon nanowire

To detect a signal change in nano scale, Schottky barrier - silicon nanowire field effect transistor (SB-SiNWFET) for detecting a bio-molecule was fabricated by combining E-beam lithography and conventional MEMS technique. Detection of few bio-molecules is enabled by realizing the gold nanodots on silicon nanowire (SiNW). By performing pH test and carbohydrate binding measurement, we conclude that our sensor can detect very small quantity of biomolecules.

One-Step Laser Encapsulation of Nano-Cracking Strain Sensors

Development of flexible strain sensors that can be attached directly onto the skin, such as skin-mountable or wearable electronic devices, has recently attracted attention. However, such flexible sensors are generally exposed to various harsh environments, such as sweat, humidity, or dust, which cause noise and shorten the sensor lifetimes. This study reports the development of a nano-crack-based flexible sensor with mechanically, thermally, and chemically stable electrical characteristics in external environments using a novel one-step laser encapsulation (OLE) method optimized for thin films. The OLE process allows simultaneous patterning, cutting, and encapsulating of a device using laser cutting and thermoplastic polymers. The processes are simplified for economical and rapid production (one sensor in 8 s). Unlike other encapsulation methods, OLE does not degrade the performance of the sensor because the sensing layers remain unaffected. Sensors protected with OLE exhibit mechanical, thermal, and chemical stability under water-, heat-, dust-, and detergent-exposed conditions. Finally, a waterproof, flexible strain sensor is developed to detect motions around the eye, where oil and sweat are generated. OLE-based sensors can be used in several applications that are exposed to a large amount of foreign matter, such as humid or sweaty environments.

Development of stretchable strain sensor using elastic fibrous membrane coated with conducting polymer

Recently, much attention has been drawn to stretchable or flexible electronic sensors for measuring input pressure or deformation on movable and arbitrarily shaped objects. In this research, as a preliminary study for developing a new stretchable stain sensor, we designed an experimental system for applying strain and measuring conductance change. The results show that the developed membrane has a great potential to measure strain and stress applied to the membrane with high sensitivity.