Publications by authors named "Jung-Hyuk Koh"

Zinc oxide (ZnO) is a wide bandgap semiconductor that holds significant potential for various applications. However, most of the native point defects in ZnO like Zn interstitials typically cause an n-type conductivity. Consequently, achieving p-type doping in ZnO is challenging but crucial for comprehensive applications in the field of optoelectronics.

View Article and Find Full Text PDF

Solid Oxide Fuel Cells (SOFCs) have proven to be highly efficient and one of the cleanest electrochemical energy conversion devices. However, the commercialization of this technology is hampered by issues related to electrode performance degradation. This article provides a comprehensive review of the various degradation mechanisms that affect the performance and long-term stability of the SOFC anode caused by the interplay of physical, chemical, and electrochemical processes.

View Article and Find Full Text PDF

In this study, the characteristics in the lead-free piezoelectric ceramic 0.5Ba(ZrTi)O-0.5(BaCa)TiO (0.

View Article and Find Full Text PDF

In this study, the composition of lead-free piezoelectric ceramics (1 - x)(BiNa)TiO-x(BaSr)TiO with excellent piezoelectric properties was investigated. Crystal analysis and electrical and piezoelectric properties were analyzed according to the content of the BST composition. A phase change from rhombohedral to tetragonal structure was observed in 0.

View Article and Find Full Text PDF

In this study, modeling of optimized lattice mismatch by carbon-dioxide annealing on (In, Ga) co-doped ZnO multi-deposition thin films was investigated with crystallography and optical analysis. (In, Ga) co-doped ZnO multi-deposition thin films with various types of bottom layers were fabricated on sapphire substrates by solution synthesis, the spin coating process, and carbon-dioxide laser irradiation with post annealing. (In, Ga) co-doped ZnO multi-deposition thin films with Ga-doped ZnO as the bottom layer showed the lowest mismatch ratio between the substrate and the bottom layer of the film.

View Article and Find Full Text PDF

In this study, piezoelectric composite nanofiber films were fabricated by introducing nitrogen-doped-reduced-graphene-oxide as a conductive material to a P(VDF-TrFE) polymer and a BiScO-PbTiO ceramic composite employing an electrospinning process. Nitrogen was doped/substituted into rGO to remove or compensate defects formed during the reduction process. Electro-spinning process was employed to extract piezoelectric composite nanofiber films under self-poling condition.

View Article and Find Full Text PDF

Figure of merit the product of piezoelectric charge constant and the piezoelectric voltage constant-d × g in piezoelectric energy harvesting systems are critical measures in energy harvester applications. It is difficult to achieve high figure of merit because of the interdependence of d and the relative dielectric constant, ε. Until now, the prohibitive amount of effort required to solve this problem has led to it being considered an unsolvable issue.

View Article and Find Full Text PDF

In this research, alternative deposition process of ZnO-based thin films have been studied for transparent conducting oxide (TCO) application. To improve the electrical and optical properties of transparent oxide thin films, alternatively stacked Al-doped ZnO and In-doped ZnO thin films were investigated. Multilayer structure of alternative 6 layers of thin films were prepared in this research.

View Article and Find Full Text PDF

In this work, a light grid system with a high-power LED chip was manufactured and employed to analyze the energy efficiency of output optical energy. The high-power LED system based on thermoelectric modules, a heat dissipation structure and optical transmission system with an optical fiber were optimally combined and designed, which increased the efficiency of light grid system. Additionally, by introducing an effective design for the heat dissipation structure, the output optical energy and recycled electrical energy were increased.

View Article and Find Full Text PDF

As a piezoelectric material, (Bi,Sc)O-(Pb,Ti)O ceramics have been tested and analyzed for sensors and energy harvester applications owing to their relatively high Curie temperature and high piezoelectric coefficient. In this work, we prepared optimized (Bi,Sc)O-(Pb,Ti)O piezoelectric materials through the conventional ceramic process. To increase the output energy, a multilayered structure was proposed and designed, and to obtain the maximum output energy, impedance matching techniques were considered and tested.

View Article and Find Full Text PDF

We analyze and compare the differences in the dewetting phenomena and crystal structure between Ag(5.0 nm) and Au(5.0 nm) layers deposited on a Ti(1.

View Article and Find Full Text PDF

Recently, many researches on Al-doped ZnO (AZO) thin film based transparent conducting oxide (TCO) have been intensively investigated for the electronic and display device applications. In this study, AZO thin films with different thicknesses were deposited on polyethylene terephthalate (PET) substrates by sol-gel spin coating at a relatively low temperature. By optimizing the AZO thickness, maximum figure of merit (FOM) values were investigated and discussed.

View Article and Find Full Text PDF

Light Emitting Diodes (LED) are highly energy efficient and offer long-life times for display applications. Long life and minimal energy consumption are often the most attractive advantages for electronic devices. Because LEDs are based on compound semiconductors, which explore the direct transition between the conduction and valance band edges, thermal energy loss can be minimized during operation.

View Article and Find Full Text PDF

In this study, Ga-doped ZnO thin films were prepared, and their potential for transparent conducting oxide applications was assessed. To increase the electrical mobility and reduce the resistance of Ga-doped ZnO thin films, CO₂ laser annealing was employed. Recently, the use of transparent conducting oxides (TCOs) have increased, particularly ZnO-based TCOs have been intensively investigated for display applications.

View Article and Find Full Text PDF

Piezoelectric and dielectric materials have attracted much attention for their functional device applications. Despite its excellent piezoelectric properties, the content of lead in piezoelectric materials should be restricted to prevent future environmental problems. Therefore, reduced lead content in piezoelectric materials with similar piezoelectric properties is favorable.

View Article and Find Full Text PDF
Article Synopsis
  • * High power LEDs are efficient in producing light but also generate waste thermal energy, which can be converted back into electrical energy using the thermoelement and heat sink in the system.
  • * The research examines how the light grid system can optimize the management of both optical and thermal energy, aiming to improve energy conversion efficiency and enhance energy harvesting from thermal energy.
View Article and Find Full Text PDF

In this research, energy harvesters with different types of spring-based shock absorbers were invested for the active shock absorber applications. Two different types of spring-based shock absorbers were prepared for the comparison, coil type spring-based shock absorbers and specially designed slice type spring-based shock absorbers. Shock absorbers have been widely employed to protect the complicated main system by cancelling the applied mechanical forces from outsides.

View Article and Find Full Text PDF

Piezoelectric ceramics such as Pb(Zr,Ti)O₃ (PZT) are currently used by electronic devices because of their superb properties. Lead-based ceramics has caused a lot of environmental problems due to their toxicity. So, lead-free ceramics have been studied as an alternative method due to the toxicity of lead-based ceramics.

View Article and Find Full Text PDF

In these days, we are facing emerging energy crisis due to depletion of fossil fuels. Therefore, renewable energy which is based on wind energy, mechanical force energy, microwave energy and vibrations energy have attracted a lot of attentions. Piezoelectric energy harvesting is one of the promising renewable energy sources.

View Article and Find Full Text PDF

The pyrochlore phase in ferroelectric and piezoelectric materials is the main obstacle device application due to its poor electrical properties. Especially, the pyrochlore phase is frequently observed in the perovskite-based metal-oxide materials including piezoelectric and ferroelectric ceramics, which are based on solid-state reaction methods for fabrication. To overcome these problems, advanced innovative methods such as partial oxalate process will be investigated.

View Article and Find Full Text PDF

In this study, inertial mass-based piezoelectric energy generators with and without a spring were designed and tested. This energy harvesting system is based on the shock absorber, which is widely used to protect humans or products from mechanical shock. Mechanical shock energies, which were applied to the energy absorber, were converted into electrical energies.

View Article and Find Full Text PDF

Laser direct patterning (LDP) technology has attracted great attention due to its process simplification and environmental friendliness. It is replacing the existing photo-lithography technology. Infrared (IR) laser equipment also has advantages such as low cost and long duration, although it is difficult to implement fine line width compared to ultraviolet (UV) or excimer laser.

View Article and Find Full Text PDF

In this research, the recycled electrical energy from wasted thermal energy in high power Light Emitting Diode (LED) system will be investigated. The luminous efficiency of lights has been improved in recent years by employing the high power LED system, therefore energy efficiency was improved compared with that of typical lighting sources. To increase energy efficiency of high power LED system further, wasted thermal energy should be re-considered.

View Article and Find Full Text PDF

In this research, the pyroelectric and piezoelectric properties of (1 - x)Na0.5K0.5NbO3-xBiScO3 ceramics were investigated and analyzed.

View Article and Find Full Text PDF

The silver migration effect into the metastable phase forms a micro-electric path, to enhance the relative dielectric permittivity of CaCuTiO ceramics for electronic devices. Controlling the sintering time uniquely develops the metastable phase of as-sintered CaCuTiO ceramics. A post-heating process that applies the migration of silver into the metastable phase increases the relative dielectric permittivity.

View Article and Find Full Text PDF