Publications by authors named "Hoe Joon Kim"

Parkinson's disease (PD) prevalence is projected to reach 12 million by 2040. Wearable sensors offer a promising approach for comfortable, continuous tremor monitoring to optimize treatment strategies. Here, we present a wristwatch-like triboelectric sensor (WW-TES) inspired by automatic watches for unobtrusive PD tremor assessment.

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Energy harvesting, the process of capturing ambient energy from various sources and converting it into usable electrical power, has attracted a lot of attention due to its potential to provide long-term and self-sufficient energy solutions. This comprehensive review thoroughly explores the use of metal-organic frameworks (MOFs) and covalent organic frameworks (COFs) for energy harvesting by piezoelectric and triboelectric nanogenerators (PENGs and TENGs). It begins by classifying and outlining the structural diversity of MOFs and COFs, which is key to understanding their importance in energy applications.

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Structures such as 3D buckling have been widely used to impart stretchability to devices. However, these structures have limitations when applied to piezoelectric devices due to the uneven distribution of internal strain during deformation. When strains with opposite directions simultaneously affect piezoelectric materials, the electric output can decrease due to cancellation.

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In recent years, the automotive industry has made significant progress in integrating multifunctional sensors to improve vehicle performance, safety, and efficiency. As the number of integrated sensors keeps increasing, there is a growing interest in alternative energy sources. Specifically, self-powered sensor systems based on energy harvesting are drawing much attention, with a main focus on sustainability and reducing reliance on typical batteries.

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In the face of mounting environmental concerns, we must seek out innovative solutions for remediation. Using nanomaterials to degrade organic pollutants in water under ambient visible light holds great promise as a safe, cost-efficient, and effective approach to addressing pollution in our water bodies. The development of novel materials capable of such pollution degradation is desired to preserve the environment.

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Battery-free and biodegradable sensors can detect biological elements in remote areas. The triboelectric nanogenerator (TENG) can potentially eliminate the need for a battery by simply converting the abundant vibrations from nature or human motion into electricity. A biodegradable sensor system integrated with TENG to detect commonly found disease-causing bacteria () in the environment is showcased herein.

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Oral healthcare monitoring is a vital aspect of identifying and addressing oral dental problems including tooth decay, gum pain, and oral cancer. Day by day, healthcare facilities and regular checkups are becoming more costly and time-consuming. In this context, consumers are moving toward advanced technology, such as bite sensors, to obtain regular data about their occlusal chewing patterns and strength.

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The nanorods of bismuth sulfoiodide (BiSI) were synthesized at relatively low temperature (393 K) through a wet chemical method. The crystalline one-dimensional (1D) structure of the BiSI nanorods was confirmed using high resolution transmission microscopy (HRTEM). The morphology and chemical composition of the material were examined by applying scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS), respectively.

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The underwater ultrasound power measurement has become necessary due to the rapid development of sonochemistry and sonocatalysis. This article presents construction of novel triboelectric nanogenerator (TENG) and its application for a detection of ultrasonic waves in water. The device was 3D printed using widely available and cost-effective materials.

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This work presents the single-chip integration of a multi-frequency surface acoustic wave resonator (SAWR) based humidity sensor. Graphene oxide (GO), a humidity-sensing material, is integrated onto a confined sensing area of SAWR via electrospray deposition (ESD). The ESD method allows ng-resolution deposition of GO, optimizing the amount of sensing material.

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Article Synopsis
  • The ocean is a significant potential source for renewable energy, but its low-frequency stimulation poses challenges in harnessing this power.
  • Hybrid nanogenerators (HNGs), which combine triboelectric, piezoelectric, and electromagnetic technologies, can efficiently convert ocean energy, making them ideal for remote and low-frequency environments.
  • The study reviews advancements in HNGs, explores their applications in self-powered systems like wireless communication and climate monitoring, and discusses both their advantages and the challenges that lie ahead.
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The use of cellular structures has led to unprecedented outcomes in various fields involving optical and mechanical cloaking, negative thermal expansion, and a negative Poisson's ratio. The unique characteristics of periodic cellular structures primarily originate from the interconnectivity, periodicity, and unique design of the unit cells. However, the periodicity often induces unfavorable mechanical behaviors such as a "post-yielding collapse", and the mechanical performance is often limited by the design of the unit cells.

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Three-dimensional (3D) bioprinting technology has attracted a great deal of interest because it can be easily adapted to many industries and research sectors, such as biomedical, manufacturing, education, and engineering. Specifically, 3D bioprinting has provided significant advances in the medical industry, since such technology has led to significant breakthroughs in the synthesis of biomaterials, cells, and accompanying elements to produce composite living tissues. 3D bioprinting technology could lead to the immense capability of replacing damaged or injured tissues or organs with newly dispensed cell biomaterials and functional tissues.

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The mass concentration of fine dust or particles acts as a standard measure to express the severity of air pollution. In connection with this, many related sensor technologies have been suggested for both indoor and outdoor uses. Among several technologies, the direct measurement of the dust mass using resonant platforms is the most preferable as it possesses multiple advantages including high sensitivity, low limit of detection, and a rapid response time.

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Carbon quantum dots (CQDs) have recently emerged as innovative theranostic nanomaterials, enabling fast and effective diagnosis and treatment. In this study, a facile hydrothermal approach for N-doped biomass-derived CQDs preparation from peel and amino acids glycine (Gly) and arginine (Arg) has been presented. The gradual increase in the N-dopant (amino acids) nitrogen content increased the quantum yield of synthesized CQDs.

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This paper presents the novel use of a sonochemical reaction product as a sensing material in self-powered ultrasonic reactor devices for determination of ultrasound parameters. A piezoelectric nanogenerator was fabricated via sonochemical synthesis of SbSeI nanowires compressed into a bulk sample. The prepared device was used to develop two fast and simple evaluation methods for acoustic power in liquid.

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This study presents the effects of bottom electrode designs on the operation of laterally vibrating aluminum nitride (AlN) contour-mode resonators (CMRs). A total of 160 CMRs were analyzed with varying bottom electrode areas at two resonant frequencies () of about 230 MHz and 1.1 GHz.

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This work presents the fabrication of crumpled carbon nanotubes (C-CNTs) thin film heaters and their application towards high sensitivity and low drift hydrogen gas sensing. Utilizing a spray coating of pristine multi-walled carbon nanotubes (MWCNTs) and thermal shrinkage of polystyrene (PS) substrate, we have fabricated C-CNTs with closely packed junctions. Joule heating of C-CNTs gives higher temperature at a given input voltage compared to as-deposited CNTs.

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The transfer of graphene from its growth substrate to a target substrate has been widely investigated for its decisive role in subsequent device integration and performance. Thus far, various reported methods of graphene transfer have been mostly limited to planar or curvilinear surfaces due to the challenges associated with fractures from local stress during transfer onto three-dimensional (3D) microstructured surfaces. Here, we report a robust approach to integrate graphene onto 3D microstructured surfaces while maintaining the structural integrity of graphene, where the out-of-plane dimensions of the 3D features vary from 3.

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One of the most pressing technological challenges in the development of next generation nanoscale devices is the rapid, parallel, precise and robust fabrication of nanostructures. Here, we demonstrate the possibility to parallelize thermochemical nanolithography (TCNL) by employing five nano-tips for the fabrication of conjugated polymer nanostructures and graphene-based nanoribbons.

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We report parallel topographic imaging and nanolithography using heated microcantilever arrays integrated into a commercial atomic force microscope (AFM). The array has five AFM cantilevers, each of which has an internal resistive heater. The temperatures of the cantilever heaters can be monitored and controlled independently and in parallel.

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We report a wear-resistant ultrananocrystalline (UNCD) diamond tip integrated onto a heated atomic force microscope (AFM) cantilever and UNCD tips integrated into arrays of heated AFM cantilevers. The UNCD tips are batch-fabricated and have apex radii of approximately 10 nm and heights up to 7 μm. The solid-state heater can reach temperatures above 600 °C and is also a resistive temperature sensor.

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