Eutectic gallium indium (EGaIn) is actively investigated toward wearable and stretchable electronic devices due to the high fluidity, high electrical conductivity, and low toxicity. However, high ...surface tension along with spontaneous oxidation makes fine patterning below ≈10 µm challenging. In this paper, a novel manufacturing technique that enables EGaIn patterns of single‐digit micrometer widths on planar elastomeric substrates is presented. First, a custom direct printing setup is constructed for continuous and uniform printing of EGaIn by feedback control of the distance between the dispensing needle and the substrate. With this setup, a 120 µm wide linear pattern is printed on the Ecoflex, a stretchable elastomer. Then, the initial printed line is stretched, frozen with deionized water, and transferred to an unstretched Ecoflex substrate. Upon gentle heating after the pick‐n‐place of the EGaIn line frozen with deionized water, only the stretched EGaIn line is left on the new Ecoflex substrate. The aforementioned pick‐n‐place transfer of the stretched EGaIn frozen with water is cascaded multiple times until a target width is obtained. Finally, a 2 µm wide linear pattern, 60‐fold reduction with respect to the initial dimension, is acquired. For practical applications, strain and tactile sensors are demonstrated by width‐reduced EGaIn patterns.
Phase change mediated pick‐n‐place transfer combines direct printing of liquid metal patterns and transfer of liquid metal patterns stretched on elastomer and then frozen with water. Cascading this new approach enables eutectic gallium‐indium patterns of single‐digit micrometer width without using soft lithographically prepared elastomeric molds for the first time.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Liquid metals are one of the most interesting and promising materials due to their electrical, fluidic, and thermophysical properties. With the aid of their exceptional deformable natures, liquid ...metals are now considered to be electrically conductive materials for sensors and actuators, major constituent transducers in soft robotics, that can experience and withstand significant levels of mechanical deformation. For the upcoming era of wearable electronics and soft robotics, we would like to offer an up-to-date overview of liquid metal-based soft (thus significantly deformable) sensors mainly but not limited to researchers in relevant fields. This paper will thoroughly highlight and critically review recent literature on design, fabrication, characterization, and application of liquid metal devices and suggest scientific and engineering routes towards liquid metal sensing devices of tomorrow.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Due to their ability to confine light in a sub-wavelength scale and achieve coherent absorption, plasmonic nanostructures have been intensively studied for solar energy harvesting. Although ...nanoparticles generating localized surface plasmon resonance (LSPR) have been thoroughly studied for application in a direct absorption solar collector (DASC), nanoparticles exciting magnetic polaritons (MP) for use in a DASC have not drawn much attention. In this work, we report a metal-insulator-metal (MIM) nanodisk that can excite MP peaks apart from the LSPR in the solar spectrum. It was found that the MIM nanodisk generates a broader and relatively more uniform absorption band compared to a pure metallic nanodisk. The MP peaks were also found to cause less significant scattering compared to those associated with the LSPR. We finally showed that the peaks induced by the MIM nanodisk are highly tunable by varying the particle dimensions, making the proposed MIM nanodisk a potential candidate for solar thermal applications.
This paper reports design, fabrication, and characterization of liquid metal-based microheaters. Liquid metal microheaters designed via finite element simulation were fabricated by simply injecting ...eutectic gallium indium into polydimethylsiloxane (PDMS) microfluidic chips bonded to either silicon or PDMS substrates. Considering the net positive volume change of the microheater upon heating, both nonpressurized and pressurized contacts between the power supply and the liquid metal wires were investigated. The pressurized contact was found to provide more reliable electrical connection, thus more stable long-term operation than the nonpressurized contact. Due to higher thermal conductivity, liquid metal microheaters with silicon substrate exhibit better temperature uniformity than ones with PDMS substrate. However, liquid metal microheaters with PDMS substrate are flexible and deformable, thus more suitable than ones with silicon substrate when microheaters should be applied to nonflat objects.
During deep reactive ion etching (DRIE), microscale etch masks with small opening such as trenches or holes suffer from limited aspect ratio because diffusion of reactive ions and free radicals ...become progressively difficult as the number of DRIE cycle increases. For this reason, high aspect ratio structures of microscale trenches or holes are not readily available with standard DRIE recipes and microscale holes are more problematic than trenches due to omnidirectional confinement. In this letter, we propose an optimization for fabrication of high aspect ratio microscale hole arrays with an improved cross-sectional etch profile. Bias voltage and inductively coupled plasma power are considered as optimization parameters to promote the bottom etching of the high aspect ratio hole array. In addition, flow rates of octafluorocyclobutane (C
4
F
8
) and sulfur hexafluoride (SF
6
) for passivation and depassivation steps, respectively, are considered as optimization parameters to reduce the etch undercut. As a result of optimization, the aspect ratio of 20 is achieved for 1.3 μm-diameter hole array and etch area reduction at the bottom relative to the top is improved to 21%.
Silicon nanoparticles have emerged as pivotal components in nanoscience and nanoengineering due to their inherent characteristics such as high energy capacity and outstanding optical properties. ...Numerous fabrication and characterization techniques have been researched so far, while a range of applications utilizing them have been developed. In this review, we aim to provide a brief overview of the distinct and representative fabrication methods of silicon nanoparticles, including top-down, bottom-up, and reduction approaches. Then, we look into various characterization techniques essential for assessing and ensuring quality and performance of fabricated silicon nanoparticles. In addition, we provide insights for silicon nanoparticle technology towards further advancements.
Silicon-on-insulator (SOI) wafers offer significant advantages for both Integrated circuits (ICs) and microelectromechanical systems (MEMS) devices with their buried oxide layer improving electrical ...isolation and etch stop function. For past a few decades, various approaches have been investigated to make SOI wafers and they tend to exhibit strength and weakness. In this review, we aim to overview different manufacturing routes for SOI wafers with specific focus on advantages and inherent challenges. Then, we look into how SOI wafers are characterized for quality assessment and control. We also provide insights towards potential future directions of SOI technology to further accelerate ever-growing IC and MEMS industries.
Sensors are vital components in a wide variety of applications throughout our everyday lives. Two critical factors that contribute to their importance are sensitivity and selectivity. To achieve ...high-performance sensors, modification and functionalization of the sensing surface become imperative. The process involves altering the surface properties of the sensor and introducing a recognition element to optimize its response to the target analyte. However, when it comes to internal sensing surfaces, such as those found in microchannel-based sensors, challenges arise. Being narrow and confined makes the modification process particularly arduous. Accessing the internal surfaces for modification becomes difficult due to their small size, and achieving uniformity across the microchannel surface poses a considerable challenge. Overcoming these obstacles demands innovative fabrication techniques, specialized equipment, and precise control during the modification process. This paper will review the potential approaches for the modification and functionalization of the sensor surface, as well as offer a variety of strategies to effectively enhance the internal sensing surface.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
This letter reports ultra-stretchable strain gauges based on a liquid metal (eutectic gallium-indium) and a platinum-catalyzed silicone elastomer (EcoFlex). A custom liquid metal printing setup was ...constructed and operated in the pressure controlled mode to offer high quality printing by eliminating undulation typically encountered in the flow rate control mode via a syringe pump. Printed liquid-metal strain gauges were thoroughly tested under cyclic uniaxial stretching and twisting. We achieved the stretchability of ~700%, which can cover any high strain from human motion. In case of moderate strain of 350%, our liquid-metal strain gauge could be operated more than 4500 cycles without showing any degradation.
Empty space in germanium (ESG) or germanium-on-nothing (GON) are unique self-assembled germanium structures with multiscale cavities of various morphologies. Due to their simple fabrication process ...and high-quality crystallinity after self-assembly, they can be applied in various fields including micro-/nanoelectronics, optoelectronics, and precision sensors, to name a few. In contrast to their simple fabrication, inspection is intrinsically difficult due to buried structures. Today, ultrasonic atomic force microscopy and interferometry are some prevalent non-destructive 3-D imaging methods that are used to inspect the underlying ESG structures. However, these non-destructive characterization methods suffer from low throughput due to slow measurement speed and limited measurable thickness. To overcome these limitations, this work proposes a new methodology to construct a principal-component-analysis based database that correlates surface images with empirically determined sub-surface structures. Then, from this database, the morphology of buried sub-surface structure is determined only using surface topography. Since the acquisition rate of a single nanoscale surface micrograph is up to a few orders faster than a thorough 3-D sub-surface analysis, the proposed methodology benefits from improved throughput compared to current inspection methods. Also, an empirical destructive test essentially resolves the measurable thickness limitation. We also demonstrate the practicality of the proposed methodology by applying it to GON devices to selectively detect and quantitatively analyze surface defects. Compared to state-of-the-art deep learning-based defect detection schemes, our method is much effortlessly finetunable for specific applications. In terms of sub-surface analysis, this work proposes a fast, robust, and high-resolution methodology which could potentially replace the conventional exhaustive sub-surface inspection schemes.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
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