PEAKFORCE QUANTITATIVE NANOMECHANICAL MAPPING FOR SURFACE ENERGY CHARACTERIZATION ON THE NANOSCALE: A MINI-REVIEW

Surface energy characterization is important to design the fabrication process of reliable electronic devices. Surface energy is influenced by various factors such as surface functionality and morphology. Owing to the high surface-to-volume ratio, surface energy at the nanoscale can be different from that of the bulk. However, the conventional methods for characterization of surface energy such as a sessile drop or Washburn methods cannot be used for nanoscale samples, owing to the limited volume for characterization. Recently, surface energy characterization on the nanoscale using atomic force microscopy (AFM) with Peak Force-Quantitative Nanomechanical Mapping (PF-QNM) imaging mode has been proposed. The nanoscale AFM tips measure the adhesion forces at the nanoscale, which are converted into surface energy through pre-calibrated curves. Successful surface energy characterization of nanoscale metal samples using AFM with the PF-QNM method has been reported previously. This mini-review discusses the recent progress on surface energy characterization at the nanoscale using AFM with the PF-QNM method. The fundamentals of the PF-QNM mode are introduced, and the results of surface energy characterization are summarized. Consequently, the future research direction for surface energy characterization at the nanoscale is discussed

SENSING MECHANISM AND APPLICATION OF MECHANICAL STRAIN SENSOR: A MINI-REVIEW

This study reviews the potential of flexible strain sensors based on nanomaterials such as carbon nanotubes (CNTs), graphene, and metal nanowires (NWs). These nanomaterials have excellent flexibility, conductivity, and mechanical properties, which enable them to be integrated into clothing or attached to the skin for the real-time monitoring of various activities. However, the main challenge is balancing high stretchability and sensitivity. This paper explains the basic concept of strain sensors that can convert mechanical deformation into electrical signals. Moreover, this paper focuses on simple, flexible, and stretchable resistive and capacitive sensors. It also discusses the important factors in choosing materials and fabrication methods, emphasizing the crucial role of suitable polymers in high-performance strain sensing. This study reviews the fabrication processes, mechanisms, performance, and applications of stretchable strain sensors in detail. It analyzes key aspects, such as sensitivity, stretchability, linearity, response time, and durability. This review provides useful insights into the current status and prospects of stretchable strain sensors in wearable technology and human–machine interfaces

A Review on the Deformation Behavior of Silver Nanowire Networks under Many Bending Cycles

Silver nanowire networks are attractive for flexible transparent electrodes due to their excellent optical transparency and electrical conductivity. Their mechanical reliability under bending is an important feature for the adoption of silver nanowire transparent electrodes for flexible electronics. Therefore, various studies have been conducted to understand the deformation behavior of silver nanowire networks, which are different from those of bulk silver or silver thin films. The focus of this review is to elucidate the deformation mechanism of silver nanowire networks under high cycles of bending and to present ways to improve the mechanical reliability of silver nanowire transparent electrodes

PeakForce Quantitative Nanomechanical Imaging for Characterization of the Surface Energy of Nano-Patterned Au Strip

Precise measurement of the surface energy of nanoscale metal thin films is crucial for the fabrication of reliable miniaturized electronic devices consisting of multi-stacked thin film strips. However, the conventional method utilizing sessile drops to measure the surface energy is not suitable for nanoscale samples owing to the much larger size of the liquid droplets than those of the samples being measured. Herein, nCA-AFM (nano contact angle-atomic force microscopy) based on PF-QNM (PeakForce quantitative nanomechanical mapping) imaging mode is explored as a novel tool to measure the surface energy of nanoscale Au strips. Au strips with thicknesses of 50 and 100 nm were patterned to have widths in a range from 200 to 500 nm. The surface energy of the nano-patterned Au strips measured with PF-QNM methods revealed that grain size is the most important factor determining the surface energy. The sample having different widths with the same grain size showed similar surface energy values, regardless of the sample dimensions. Our results highlight that grain size control is required to achieve the target surface energy of metal strips for applications in nanoscale electronic devices

Printability of the Screen-Printed Strain Sensor with Carbon Black/Silver Paste for Sensitive Wearable Electronics

Printing technology enables not only high-volume, multipurpose, low-impact, low-cost manufacturing, but also the introduction of flexible electronic devices, such as displays, actuators, and sensors, to a wide range of consumer markets. Consequently, in the past few decades, printed electronic products have attracted considerable interest. Although flexible printed electronic products are attracting increasing attention from the scientific and industrial communities, a systematic study on their sensing performance based on printability has not been reported so far. In this study, carbon black/Ag nanocomposites were utilized as pastes for a flexible wearable strain sensor. The effects of the rheological property of the pastes and the pattern dimensions of the printed electrodes on the sensor’s performance were investigated. Consequently, the printed sensor demonstrated a high gauge factor of 444.5 for an applied strain of 0.6% to 1.4% with a durability of 1000 cycles and a linearity of R2 = 0.9974. The sensor was also stable under tough environmental conditions

Enhanced Sedimentation Stability of Carbonyl Iron Powders with Hydrophilic Siloxane Polymer Coatings in Ethanol

Achieving resistance to sedimentation of carbonyl iron powders (CIPs) in ethanol is important to fabricate reliable magnetorheological suspensions. The traditional method to improve the sedimentation stability is to add dispersants, but this approach can suffer from high costs and toxicity of added surfactants. In this study, the surface of CIPs was modified with 3-aminopropyl triethoxysilane (APTES) or tetraethyl orthosilicate (TEOS) to enhance the sedimentation stability of CIP suspensions without using toxic dispersants. After coating APTES or TEOS on the CIP surface, the surface energy of the CIP powders increased, which was attributed to the increased amino or hydroxyl groups on the CIP surface due to APTES or TEOS, respectively. The Gibbs free wetting enthalpy (ΔG) was calculated to evaluate the wettability of the modified CIPs, and APTES@CIPs or TEOS@CIPs had a low ΔG, indicating that both had a high thermodynamic spontaneity of wetting in ethanol. The enhanced wettability due to APTES or TEOS coating resulted in low CIP agglomeration, which resulted in APTES@CIPs or TEOS@CIPs dispersions having smaller average particle sizes than pure CIP dispersions. Therefore, APTES@CIPs or TEOS@CIPs showed more than 2 times slower sedimentation velocity than pure CIPs, resulting in enhanced sedimentation stability.</p

Highly Stretchable CIP–PDMS Composites with Partial Interface Bonding for Electromagnetic Noise Suppression in GHz Frequency Range

With the technological progress of wearable electronics operated in 5 G network communication system, a stretchable noise suppressor at GHz bandwidth that is reliable under severe deformation coming from the user’s motion should be developed. However, current material systems for the noise suppressor showed a limited stretchability. This study introduces a carbonyl iron powder – polydimethylsiloxane (CIP – PDMS) composite with partially bonded interface as a solution to enhance the stretchability. Modulation of CIP surface to have the partial interface bonding (CIP-PID) results in the ultra large strain of ~165% even at the 40 vol% of CIP-PIDs, while only ~71% of strain is observed for CIPs with the full interface bonding (CIP-FID). According to a microstructural analysis and FEM simulation of the strained composite specimens, when partially bonded to CIP at the interface, the PDMS matrix forms a free surface that can be deformed like pure PDMS, resulting in high stretchability. The wettability of CIP offers protection against eddy current loss while retaining strong magnetic properties, suppressing the EM noise. Thus, the approach eliminates the tradeoff between EM suppression and stretchability

Effect of a Urethane Acrylate-Based Photosensitive Coating on the Reliability of Ag Nanowire Transparent Electrodes

Due to the susceptibility of Ag nanowires to external mechanical and chemical damage, maintaining high optical performance and ambient and mechanical stability during the fabrication process is important for the industrial use of Ag nanowire transparent electrodes (TEs). In this study, urethane acrylate-based photosensitive resin (UAPR) is used as the coating material for Ag nanowire TEs to improve their optical transmittance, ambient stability, and resistance to external wiping damage. In the proposed method, UV-curable UAPR is coated onto Ag nanowire TEs using a simple doctor blade, forming a protective coating that increases the optical transmittance of the electrodes due to the refractive index of the UAPR between the air and the substrate. The UAPR coating successfully protects the Ag nanowires from corrosion in ambient air, with no significant change in their optical or electrical properties observed after 180 h of exposure to ambient air. Mechanical wiping tests also confirm that the UAPR coating is effective in protecting the Ag nanowires from external wiping damage, with no degradation of the optical or electrical properties observed after six wiping cycles

Recent research trends in textile-based temperature sensors: a mini review

In this review, the current state of research on textile-based temperature sensors is explored by focusing on their potential use in various applications. The textile-based sensors show various advantages including flexibility, conformability and seamlessness for the wearer. Integration of the textile-based sensors into clothes or fabric-based products enables continuous and sensitive monitoring of change in temperature, which can be used for various medical and fitness applications. However, there are lacks of comprehensive review on the textile-based temperature sensors. This review introduces various types of textile-based temperature sensors, including resistive, thermoelectric and fibre-optical sensors. In addition, the challenges that need to be addressed to fully realise their potential, which include improving sensitivity and accuracy, integrating wireless communication capabilities, and developing low-cost fabrication techniques. The technological advances in textile-based temperature sensors to overcome the limitations will revolutionize wearable devices requiring function of temperature monitoring