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The use of heat dissipation materials in various field such as power semiconductor device, LED and microelectronic system. Therefore, there is a need for heat dissipation materials using copper (Cu) and graphite (Gr). These materials have high thermal conductivity. In particular, graphite has high thermal stability with a low coefficient of thermal expansion. This study was conducted to enhance the thermal properties of Cu for use in heat dissipation materials, using a spark plasma sintering method. Cu-Gr powders were mixed by a shaking mixer and fabricated with volume fractions of 7:3, 6:4, 5:5, 4:6 and 3:7. The spark plasma sintering method is a uniaxial pressurization process, which can control the direction of Gr. The Cu- Gr powders were sintered at a temperature of 850℃ at a heating rate of 30℃/min and a sintering pressure of 40MPa. Consequently, as the Gr contents were increased, the relative densities of the Cu-Gr composites decreased from 99.25 to 94.85%. Gr has high resistance to high-temperature deformation, which contributed to a decrease in shrinkage and relative density. The highest thermal conductivity was measured at 539.7 W/ m·K for a Cu-Gr volume ratio of 5:5. The thermal conductivity of the directionally controlled Gr was measured to be about 20-30 W/m·K higher than the uncontrolled sample. Furthermore, the TDP (Thermal distortion parameter), for which a lower value indicates better thermal stability, was systematically investigated. (Received 10 January, 2024; Accepted 18 March, 2024)

keyword : Cu-Gr, composite, spark plasma sintering method, sintering behavior, thermal properties

Focused ion beam (FIB) technology is one of the most widely used methods for fabricating crosssectional analysis specimens because of its high precision and characteristics that minimize the occurrence of defects. Demand for large cross-sectional area analysis is increasing to improve product reliability in various industries, but is limited by the low milling speed of FIB. Other potential techniques such as Ar ion milling and plasma FIB have been adopted, but low milling speed for large areas still remains a problem. A promising solution to this issue involves laser machining prior to FIB milling. In laser machining a laser beam is irradiated to remove materials from the target. This technique can provide several orders of magnitude higher material removal rate than FIB, however, tapering of the machined surface and laser induced damage can occur. Removing these defects leads to increased FIB milling time. In this study, the laser parameters including angle of incident (AOI) were optimized to achieve a vertical like sidewall and minimize laser induced defects. Before applying AOI, laser machining parameters were optimized to reduce the angle of the machined sidewall. The taper angle of 2.5° was fabricated using the optimized parameters and application of AOI. Raman spectroscopy, SEM, and EDS analysis were used to measure not only the geometry of the laser machined sidewalls, but laser induced residual stress and defects. These results were then used to calculate the volume of FIB milling required to remove the laser induced damages and achieve vertical sidewalls. The application of AOI can significantly reduce the processing time in the FIB milling compared to the processing time when AOI is not applied. (Received 26 December, 2023; Accepted 15 February, 2024)

keyword : Angle of incident, Femtosecond laser, Laser machining, Silicon wafer

In this study, we investigated the influence of cold rolling reduction on microstructural evolution and slip behavior in Ta-10W alloy fabricated by vacuum arc melting (VAM). As the reduction increased, both single and multiple slips were observed within some grain interiors. At reductions of 20% and 40%, deformation bands, primarily consisting of γ-fiber components, formed within the grain interiors. The fraction of deformation bands (DBs) increased with higher reduction. Conversely, at 60% reduction, in addition to DBs, experimentally observed shear bands (SBs) with a herringbone pattern were formed. Both DBs and SBs predominantly formed in regions of concentrated strain (areas with high kernel average misorientation (KAM) and geometrically necessary dislocations (GND)). As the reduction increased, the misorientation angle between the matrix and the DBs or SBs gradually increased, while the width of the DBs decreased. To investigate the violation of Schmid’s law in Ta-10W alloy, slip trace and resolved shear stress (RSS) analyses were performed on observed slip lines within deformed grains. Contrary to conventional slips, where slip typically occurs on the plane with the highest RSS, slips in the Ta-10W alloy were confirmed to occur even on planes with lower RSS in certain grains. Hence, this study provides experimental evidence of Schmid’s law violation in Ta-10W alloy. (Received 15 January, 2024; Accepted 21 February, 2024)

keyword : Ta-10W alloy, Cold rolling, Deformation bands, Shear bands, Non-Schmid effect

The strength of Ni-base superalloys mainly depends on theγ' precipitates that improve the strength of the materials at high temperatures. The presence ofγ' particles within the matrix restricts dislocation movement, and optimized heat treatments can tailor the size, shape, and volume fraction ofγ'. In this study the effects of solidification rate and solution temperature on the tensile properties of IN738LC superalloy were investigated. The secondary dendritic arm spacing of casting materials with different diameters was measured and the solidification rate of the casting materials was derived by comparing the results of the solidification microstructure obtained from a directional solidification experiment. The D17 material, which had a faster solidification rate, showed higher values of tensile strength and yield strength than the D60 material, which had a slower solidification rate. The study also concluded that the monomodalγ' precipitates in the S80 material have higher tensile strength and yield strength at room temperature and 760℃ than the bimodalγ' precipitates in the S20 material. As for the deformation behavior at 760℃, an isolated stacking fault was observed in the S20 material only within the largeγ’ precipitates. In the S80 material, the high dislocation density increased the yield strength due to the strong interaction between dislocations and fineγ’ precipitates. (Received 2 January, 2024; Accepted 8 March, 2024)

keyword : IN738LC, Solidification rate, Tensile property, Stacking fault

This research explores how aggregation influences the electrical behavior at both the planar - heterojunction poly(3-hexylthiophene) (P₃HT)/SiO₂ and P3HT/ZnO nanocrystal (NC) interfaces. The formation of H- and J-type aggregates leads to distinct molecular ordering and packing structures, manifesting as changes in threshold voltage shifts (electrical gating) as well as absorption and luminescence properties. Ultrasound irradiation (sonication) significantly alters the molecular arrangement in P3HT, favoring the formation of H-aggregates over the typically formed J-aggregates. In pristine P3HT, J-aggregates facilitate efficient exciton movement and electrical generation, resulting in higher photocurrents compared to sonicated-P3HT, which predominantly forms H-aggregates. Field-effect transistors (FETs) based on sonicated P3HT exhibit a more positive threshold voltage and increased mobility, indicating the presence of more mobile charge carriers, even in the absence of an applied voltage. In interfaces with ZnO NC, pristine P3HT demonstrates a considerable shift in threshold voltage under illumination, attributed to electron trapping. Conversely, sonicated P3HT interfaced with ZnO NC shows less electron trapping and minimal change in threshold voltage. This study underscores how the type of aggregate (H or J) in P3HT significantly dictates light-induced electrical gating. Ultrasound irradiation (sonication), while enhancing mobility by improving crystallinity, leads to a decrease in photocurrent efficiency in H-aggregates compared to the J-aggregates present in pristine-P3HT. (Received 12 December, 2023; Accepted 26 February, 2024)

keyword : P3HT, sonication, aggregate, electrical gating, FET

It is well-known that optical transparence and electric resistance have a trade-off relationship in transparent electrodes. For this reason, developing methods to predict this relation have been important in various fields of academic research as well as for industrial applications. Herein, we suggest a simple method which reveals the relationship between optical transparence and electric resistance using MATLAB, based on the geometric characteristics of a random metal network. Ag metal-mesh transparent electrodes were fabricated with various conditions using colloidal silica cracked-templates and a Radio Frequency (RF) sputtering system. MATLAB software was used to analyze structural images of the Ag mesh network, automatically quantifying the density and width of the Ag meshes. From these data, the transparency and sheet resistance values of the Ag mesh electrodes were predicted and compared with measured values. Regarding transparency, the introduction of fitting parameters revealed minimal differences between the experimental and predicted values obtained from the structure images. Although the predicted sheet resistance was slightly different than the real measured values due to atomic defects or imperfections in the crystals of the Ag-mesh network, it was possible to observe a similar trend between the measured and predicted sheet resistances with changes in the fractional coverage area of the Ag-mesh network. (Received 23 January, 2024; Accepted 5 March, 2024)

keyword : transparent electrodes, Ag, mesh-network, MATLAB, transmittance, resistance

To achieve net zero emissions, green hydrogen should be produced via water electrolysis with renewable energy. To develop efficient anion exchange membrane water electrolyzers (AEMWE), the development of efficient and stable non-precious metal electrocatalysts for the oxygen evolution reaction (OER) is essential. In this study, a high-performance ternary NiFeCo-layer double hydroxide (LDH) electrocatalyst for AEMWE was easily developed by the co-precipitation method. The introduction of Co has been shown to have an effect on the electronic structure of Ni and Fe, improving their intrinsic OER properties. In addition, the three-dimensional flower-like nanosheet morphology improved mass transfer and achieved excellent current density at high voltages. The ternary NiFeCo-LDH electrocatalyst requires low overpotentials (253 mV at 10 mA cm^-2) and Tafel slope (45 mV dec^-1) in 1 M KOH. AEMWE using the ternary NiFeCo-LDH electrocatalyst showed excellent electrolysis performance with a high current density of 2.27 A cm^-2 at 1.8 V cell. Moreover, an energy conversion efficiency of 86.73 % was achieved during the durability test for 100 hours at a current density of 0.5 A cm-2. The performance of the AEMWE electrolyzer utilizing the ternary NiFeCo-LDH electrocatalyst surpassed that of previously reported AEMWE electrolyzers. This work reports a highly active OER electrocatalyst that could open numerous opportunities for the development of ternary LDH electrocatalysts in AEMWE. (Received 4 December, 2023; Accepted 20 December, 2023)

keyword : Anion Exchange Membrane Water Electrolysis (AEMWE), Oxygen Evolution Reaction (OER), Layered Double Hydroxide, Ternary, co-precipitation

In this study, thermoelectric chalcostibite (CuSbS₂) compounds were fabricated using mechanical alloying (MA) and hot pressing (HP), and phase identification, microstructural observation, and thermal analysis were conducted. The thermal properties were then measured and compared with those of other Cu- Sb-S ternary compounds synthesized by the same solid-state process, namely, skinnerite (Cu₃SbS₃), famatinite (Cu₃SbS₄), and tetrahedrite (Cu₁₂Sb₄S₁₃). Both the MA powder and HP-sintered samples contained a single-phase chalcostibite with an orthorhombic structure, and relative densities of 94.6-99.7% were obtained based on HP temperature. The full width at half maximum of the X-ray diffraction peak was significantly reduced for the HP specimens compared to that of the MA powder due to stress relaxation and grain growth during HP at elevated temperatures. However, practically no changes were observed in the lattice constants based on HP temperature. Differential scanning calorimetric analysis revealed that one endothermic reaction occurred at 814-815 K for the MA powder and at 818-821 K for the HP specimen, which were interpreted as the melting points of chalcostibite. Densely sintered compacts with densities close to the theoretical density were obtained using HP at temperatures of 623 K or higher. The constituent elements of the chalcostibites were uniformly distributed. As the HP temperature increased, thermal diffusivity and conductivity increased, but they decreased significantly as the measurement temperature increased. For the chalcostibite specimen hot-pressed at 623 K, the thermal diffusivity and conductivity were (0.75-0.36) × 10^-2 cm² s^-1 and 1.47-0.72 W m^-1 K^-1 at 323-623 K, respectively. Compared with other Cu-Sb-S ternary compounds, the thermal diffusivity was higher at low temperatures but similar at high temperatures, and the thermal conductivity above 500 K was lower than 1 W m^-1 K^-1. (Received 7 February, 2024; Accepted 19 March, 2024)

keyword : thermoelectric, chalcostibite, thermal diffusivity, thermal conductivity, thermal analysis

Cu₃SbSe₄ is considered a promising thermoelectric material because of its large effective mass and low thermal conductivity, originating from its unique lattice structure. However, Cu₃SbSe₄ has intrinsically low carrier concentration and relatively high electric resistance which limit performance. Recently, a zT improvement in Cu₃SbSe₄ was reported where doping/precipitation is controlled by changing the content of the starting materials. However, the effect of these changes in starting content on electronic band structures has not been studied. Here, we investigate how the change in starting materials content (x varying from 6 to 20) affects band parameters like density-of-states effective mass (m_d *), non-degenerate mobility (μ0), weighted mobility (μW), and B-factor using the Single Parabolic Band (SPB) model. For x greater than 8, precipitation of the secondary phase (CuSe) was observed, and the band parameters changed differently for x greater than 8. The m_d * increases up to x = 8 and then rapidly decreases for x > 8. For μ0, an overall decrease is observed for increasing x, but the rate of decrease is suppressed for x > 8. The μW reaches the maximum at x = 8. As x increases, the experimental lattice thermal conductivity also increases, especially for x > 8. Therefore, the B-factor, which is directly related to the theoretical maximum zT, becomes maximum at = 8. Hence the SPB model predicts a maximum zT of 0.0484 for x = 8 at 300 K, which is 15.5% higher than the experimental zT of 0.0419, which can be achieved by tuning the Hall carrier concentration to 4.44 × 10¹⁹ cm^-3. (Received 8 February, 2024; Accepted 7 March, 2024)

keyword : Cu₃SbSe₄, Single Parabolic Band model, density-of-states effective mass, non-degenerate mobility, weighted mobility