Fluorine-doped tin oxide (FTO) has been used as a representative transparent conductive oxide (TCO) in various optoelectronic applications, including light emitting diodes, solar cells, photo-detectors, and electrochromic devices. The FTO plays an important role in providing electron transfer between active layers and external circuits while maintaining high transmittance in the devices. Herein, we report the effects of substrate rotation speed on the electrical and optical properties of FTO films during ultrasonic spray pyrolysis deposition (USPD). The substrate rotation speeds were adjusted to 2, 6, 10, and 14 rpm. As the substrate rotation speed increased from 2 to 14 rpm, the FTO films exhibited different film morphologies, including crystallite size, surface roughness, crystal texture, and film thickness. This FTO film engineering can be attributed to the variable nucleation and growth behaviors of FTO crystallites according to substrate rotation speeds during USPD. Among the FTO films with different substrate rotation speeds, the FTO film fabricated at 6 rpm showed the best optimized TCO characteristics when considering both electrical (sheet resistance of 13.73 Ω/□) and optical (average transmittance of 86.76 % at 400~700 nm) properties with a figure of merit (0.018 Ω-1).

β-Ga2O3 has become the focus of considerable attention as an ultra-wide bandgap semiconductor following the successful development of bulk single crystals using the melt growth method. Accordingly, homoepitaxy studies, where the interface between the substrate and the epilayer is not problematic, have become mainstream and many results have been published. However, because the cost of homo-substrates is high, research is still mainly at the laboratory level and has not yet been scaled up to commercialization. To overcome this problem, many researchers are trying to grow high quality Ga2O3 epilayers on hetero-substrates. We used diluted SiH4 gas to control the doping concentration during the heteroepitaxial growth of β-Ga2O3 on c-plane sapphire using metal organic chemical vapor deposition (MOCVD). Despite the high level of defect density inside the grown β-Ga2O3 epilayer due to the aggregation of random rotated domains, the carrier concentration could be controlled from 1 × 1019 to 1 × 1016 cm-3 by diluting the SiH4 gas concentration. This study indicates that β-Ga2O3 hetero-epitaxy has similar potential to homo-epitaxy and is expected to accelerate the commercialization of β-Ga2O3 applications with the advantage of low substrate cost.

Aluminum alloys, known for their high strength-to-weight ratios and impressive electrical and thermal conductivities, are extensively used in numerous engineering sectors, such as aerospace, automotive, and construction. Recently, significant efforts have been made to develop novel aluminum alloys specifically tailored for additive manufacturing. These new alloys aim to provide an optimal balance between mechanical properties and thermal/ electrical conductivities. In this study, nine combinatorial samples with various alloy compositions were fabricated using direct energy deposition (DED) additive manufacturing by adjusting the feeding speeds of Al6061 alloy and Al-12Si alloy powders. The effects of the alloying elements on the microstructure, electrical conductivity, and hardness were investigated. Generally, as the Si and Cu contents decreased, electrical conductivity increased and hardness decreased, exhibiting trade-off characteristics. However, electrical conductivity and hardness showed an optimal combination when the Si content was adjusted to below 4.5 wt%, which can sufficiently suppress the grain boundary segregation of the α- Si precipitates, and the Cu content was controlled to induce the formation of Al2Cu precipitates.

As the demand for p-type semiconductors increases, much effort is being put into developing new p-type materials. This demand has led to the development of novel new p-type semiconductors that go beyond existing p-type semiconductors. Copper iodide (CuI) has recently received much attention due to its wide band gap, excellent optical and electrical properties, and low temperature synthesis. However, there are limits to its use as a semiconductor material for thin film transistor devices due to the uncontrolled generation of copper vacancies and excessive hole doping. In this work, p-type CuI semiconductors were fabricated using the chemical vapor deposition (CVD) process for thin-film transistor (TFT) applications. The vacuum process has advantages over conventional solution processes, including conformal coating, large area uniformity, easy thickness control and so on. CuI thin films were fabricated at various deposition temperatures from 150 to 250 °C The surface roughness root mean square (RMS) value, which is related to carrier transport, decreases with increasing deposition temperature. Hall effect measurements showed that all fabricated CuI films had p-type behavior and that the Hall mobility decreased with increasing deposition temperature. The CuI TFTs showed no clear on/off because of the high concentration of carriers. By adopting a Zn capping layer, carrier concentrations decreased, leading to clear on and off behavior. Finally, stability tests of the PBS and NBS showed a threshold voltage shift within ±1 V.

Recently, the electron transport layer (ETL) has become one of the key components for high-performance perovskite solar cell (PSC). This study is motivated by the nonreproducible performance of ETL made of spin coated SnO2 applied to a PSC. We made a comparative study between tin oxide deposited by atomic layer deposition (ALD) or spin coating to be used as an ETL in N-I-P PSC. 15 nm-thick Tin oxide thin films were deposited by ALD using tetrakisdimethylanmiotin (TDMASn) and using reactant ozone at 120 °C. PSC using ALD SnO2 as ETL showed a maximum efficiency of 18.97 %, and PSC using spin coated SnO2 showed a maximum efficiency of 18.46 %. This is because the short circuit current (Jsc) of PSC using the ALD SnO2 layer was 0.75 mA/cm2 higher than that of the spin coated SnO2. This result can be attributed to the fact that the electron transfer distance from the perovskite is constant due to the thickness uniformity of ALD SnO2. Therefore ALD SnO2 is a candidate as a ETL for use in PSC vacuum deposition.

Nuclear power plants in Korea stores approximately 3,800 drums of paraffin solidification products. Due to the lack of homogeneity, these solidification products are not allowed to be disposed of. There is therefore a need for the separation of paraffin from the solidification products. This work developed an equipment for a selective separation of paraffin from the solidification product using the vacuum evaporation and condensational recovery method in a closed system. The equipment mainly consists of a vacuum evaporator and a condensational deposition recovery chamber. Nonisothermal vacuum TGAs, kinetic analyses and kinetic predictions were conducted to set appropriate operation conditions. Its basic operability under the established conditions was first confirmed using pure paraffin solid. Simulated paraffin solidification product fixing dried boric acid waste including nonradioactive Co and Cs were then fabricated and tested for the capability of selective separation of paraffin from the simulated waste. Paraffin was selectively separated without entertainment of Co and Cs. It was confirmed that the developed equipment could separate and recover paraffin in the form of nonradioactive waste.

For the performance and safety assessments of deep geological disposal, developing scenarios, which represent possible long-term changes in the surface environment, is required. These scenarios are formulated using a list of FEPs (Features, Events, and Processes) that describes characteristics of disposal system components. In this study, using international FEP (IFEP) list from OECD/NEA, the individual FEPs related to uplift-subsidence and erosion-deposition were analyzed, and the correlation between each FEP was evaluated. From the IFEP list, the elements related to uplift-subsidence and erosion-deposition processes that cause long-term changes in the surface environment were identified. Uplift-subsidence, erosion - deposition, and the long-term change factors caused by them were analyzed and a correlation diagram was produced according to their interactions. Basis for the integrated analysis of long-term changes in the surface environment and the construction of long-term change scenarios were established considering the evaluation of the factors that cause uplift-subsidence and erosiondeposition, and their correlation with the hydrology-hydrogeology, topography and local climate of the affected surface. The results of this study will be used for systematically formulating scenarios of long-term changes in the surface environment due to uplift-subsidence and erosion-deposition based on natural phenomena. And, it may be necessary to modify and supplement the correlation of domestic FEPs based on the correlation diagram of IFEPs in order to analyze long-term changes in the surface environment in an integrated manner.

본 연구에서는 공정 간소화, 균일한 나노 입자 형성, 백금 저감 및 활용도를 높이기 위하여 원자층 증착법 (Atomic Layer Deposition, ALD)을 통하여 양이온 교환막 연료전지용 촉매를 제조하고 증착 온도에 따른 백금 입자 형성 거동 을 확인하였다. 증착 온도는 250 °C, 300 °C, 350 °C로 조절하여 백금 촉매를 형성하였으며 각 각의 촉매의 증착 양 상을 확인하기 위하여 Thermogravimetric analysis, X-ray diffraction 및 Transmission electron microscopy를 도입하여 담지량, 백금 입자 분포, 크기 및 결정구조 등을 확인하였다. 합성된 백금 촉매를 연료전지에 적용하기 위해서 Cyclic Voltammetry 기법을 통해서 전기화학적 활성 표면적를 구하고, Membrane Electrode Assembly 셀을 제작하여 전지 특성을 확보하였다. 최종적으로, 백금 촉매 제조 시 ALD 증착 온도는 300 °C 이하에서 합성해야 됨을 밝혀냈으며, ALD으로 제작된 백금 촉매가 기존 습식 촉매보다 더 우수한 특성을 보임을 확인하였다. 해당 연구는 ALD을 통하여 다양한 접근법으로 촉매를 제조할 시, 기본적인 ALD 공정 정보 및 ALD 촉매 합성 방향성을 제공할 수 있다.

Bentonite is a widely used buffer material in high-level radioactive waste repositories due to its favorable properties, including its ability to swell and low permeability. Bentonite buffers play an important role in safe disposal by providing a low permeability barrier and preventing radionuclides migration into the surrounding rock. However, the long-term performance of the bentonite buffer is still an area of research, and one of the main concerns is the erosion of the buffer due to swelling and groundwater flow. Erosion of the bentonite buffer can have a significant impact on repository safety by reducing the integrity of the buffer and forming colloids that can transport radionuclides through groundwater, potentially increasing the risk of radionuclide migration. Therefore, understanding the mechanisms and factors that influence the erosion of the bentonite buffer is critical to the safety assessment of high-level radioactive waste repositories. In this study, we attempted to develop the bentonite buffer erosion model using Adaptive Processbased total system performance assessment framework for a geological disposal system (APro) proposed by the Korea Atomic Energy Research Institute (KAERI). First, the erosion phenomenon was divided into two stages: bentonite buffer penetration into rock fractures and colloid formation. As an initial step in the development of the buffer erosion model, a bentonite buffer intrusion into the fracture and consequent degradation of buffer property were considered. For this purpose, a tworegion model based on the dynamic bentonite diffusion model was adopted which is one of the methods for simulating bentonite buffer intrusion. And, it was assumed that the buffer properties, such as density, porosity and permeability, thermal conductivity, modulus of elasticity, and mechanical strength, are degraded as the buffer erodes. The bentonite buffer degradation model developed in this study will serve as a foundation for the comprehensive buffer erosion model, in conjunction with the colloidal formation model in the future.

Performance and safety assessments for deep geological disposal are often conducted over a longterm time scale, such as from hundreds of thousands to a million years. During this period, it is expected that the surface environment will be changed significantly. Uplift-subsidence and erosion-deposition are thought to be included as the main causes of the changes, and it is necessary to evaluate their expected effects. In this study, the conceptual processes of the changes in the surface environment components were to be presented by identifying the uplift-subsidence and erosion-deposition processes and analyzing their effect on the surface environment components. For inferring the long-term change process of the surface environment due to the internal activities of the Earth, the process of uplift and subsidence caused by crustal movements that change the subsurface environment through the deep and sallow underground was briefly presented in the form of a chain flowchart. Uplift-subsidence is mainly caused by diastrophism due to tectonic movement, such as subduction at the boundary of plates. They can change the geomorphology by affecting sealevel change and erosion-deposition. The changed geographical features have an influence on the distribution of surface water and the flow path of groundwater. They also have an impact on the scale and processes of local uplift and erosion, which can be the main factors of pedogenesis and vegetation in the local site. The results of this study can be helpful for formulating scenarios related to long-term evolution in the surface environment required for performance and safety assessments of deep geological disposal.

Long-term safe storage of spent nuclear fuel (SNF) determines sustainability of the current light water reactor (LWR) fleet. In the U.S., SNF is stored in stainless steel canister in dry cask storage system (DCSS) after spending several years in wet pool storage system while there is no DSCC in Republic of Korea. The SNF storage time in DSCC is expected to be multiple decades since no permanent geological repositories are identified in both countries. One limiting factor for extended storage of SNF in DSCC is chloride-induced stress corrosion cracking (CISCC) in the welded regions of the stainless steel canisters. The propensity for the occurrence of CISCC has warranted the development of the mitigation and repair technologies to ensure the safe and long-term storage for both present and new canister although no CISCC failure was reported yet. This study investigates cold spray deposition coatings of 304 L and 316 L stainless steels on prototypical stainless steel canisters such as sensitized flat and C-ring samples. The cold spray technology has been identified as the most promising approach by Extended Storage Collaboration Program (ESCP) driven by Electric Power Research Institute (EPRI). The talk includes microstructural characterization, adhesion strength measurement, residual stress evaluation, and corrosion behavior of the coated materials in boiling MgCl2 solution and electrochemical corrosion tests in NaCl solution. In addition, the capability of repair of cracks on the canister surface using the coating technology will be presented.

The semiconductor industry faces physical limitations due to its top-down manufacturing processes. High cost of EUV equipment, time loss during tens or hundreds of photolithography steps, overlay, etch process errors, and contamination issues owing to photolithography still exist and may become more serious with the miniaturization of semiconductor devices. Therefore, a bottom-up approach is required to overcome these issues. The key technology that enables bottom-up semiconductor manufacturing is area-selective atomic layer deposition (ASALD). Here, various ASALD processes for elemental metals, such as Co, Cu, Ir, Ni, Pt, and Ru, are reviewed. Surface treatments using chemical species, such as self-assembled monolayers and small-molecule inhibitors, to control the hydrophilicity of the surface have been introduced. Finally, we discuss the future applications of metal ASALD processes.

AZO/Cu/AZO thin films were deposited on glass by RF magnetron sputtering. The specimens showed the preferred orientation of (0002) AZO and (111) Cu. The Cu crystal sizes increased from about 3.7 nm to about 8.5 nm with increasing Cu thickness, and from about 6.3 nm to about 9.5 nm with increasing heat treatment temperatures. The sizes of AZO crystals were almost independent of the Cu thickness, and increased slightly with heat treatment temperature. The residual stress of AZO after heat treatment also increased compressively from -4.6 GPa to -5.6 GPa with increasing heat treatment temperature. The increase in crystal size resulted from grain growth, and the increase in stress resulted from the decrease in defects that accompanied grain growth, and the thermal stress during cooling from heat treatment temperature to room temperature. From the PL spectra, the decrease in defects during heat treatment resulted in the increased intensity. The electrical resistivities of the 4 nm Cu film were 5.9 × 10-4 Ω ‧ cm and about 1.0 × 10-4 Ω ‧ cm for thicker Cu films. The resistivity decreased as the temperature of heat treatment increased. As the Cu thickness increased, an increase in carrier concentration resulted, as the fraction of AZO/Cu/AZO metal film increased. And the increase in carrier concentration with increasing heat treatment temperature might result from the diffusion of Cu ions into AZO. Transmittance decreased with increasing Cu thicknesses, and reached a maximum near the 500 nm wavelength after being heat treated at 200 °C.

Thermoelectric materials and devices are energy-harvesting devices that can effectively recycle waste heat into electricity. Thermoelectric power generation is widely used in factories, engines, and even in human bodies as they continuously generate heat. However, thermoelectric elements exhibit poor performance and low energy efficiency; research is being conducted to find new materials or improve the thermoelectric performance of existing materials, that is, by ensuring a high figure-of-merit (zT) value. For increasing zT, higher σ (electrical conductivity) and S (Seebeck coefficient) and a lower к (thermal conductivity) are required. Here, interface engineering by atomic layer deposition (ALD) is used to increase zT of n-type BiTeSe (BTS) thermoelectric powders. ALD of the BTS powders is performed in a rotary-type ALD reactor, and 40 to 100 ALD cycles of ZnO thin films are conducted at 100oC. The physical and chemical properties and thermoelectric performance of the ALD-coated BTS powders and pellets are characterized. It is revealed that electrical conductivity and thermal conductivity are decoupled, and thus, zT of ALD-coated BTS pellets is increased by more than 60% compared to that of the uncoated BTS pellets. This result can be utilized in a novel method for improving the thermoelectric efficiency in materials processing.

The surface of carbon films deposited with inverted plasma fireballs is analysed in this paper. Measurements were conducted with Raman spectroscopy, atomic force microscopy and nanoindentation. The latter was used to obtain Young’s modulus as well as Martens and Vickers hardness. The roughness of the film was measured by atomic force microscopy and its thickness was measured. It was shown with Raman spectroscopy that the films are homogeneous in terms of atomic composition and layer thickness over an area of about 125 × 125 mm. Furthermore, it was demonstrated that inverted plasma fireballs are a viable tool for obtaining homogeneous, large area carbon films with rapid growth and very little energy consumption. The obtained films show very low roughness.

Carbon nanotube fiber is a promising material in electrical and electronic applications, such as, wires, cables, batteries, and supercapacitors. But the problem of joining carbon nanotube fiber is a main obstacle for its practical development. Since the traditional joining methods are unsuitable because of low efficiency or damage to the fiber structure, new methods are urgently required. In this study, the joining between carbon nanotube fiber was realized by deposited nickel–copper doublelayer metal via a meniscus-confined localized electrochemical deposition process. The microstructures of the double-layer metal joints under different deposition voltages were observed and studied. It turned out that a complete and defect-free joint could be fabricated under a suitable voltage of 5.25 V. The images of the joint cross section and interface between deposited metal and fiber indicated that the fiber structure remained unaffected by the deposited metal, and the introduction of nickel improved interface bonding of double-layer metal joint with fiber than copper joint. The electrical and mechanical properties of the joined fibers under different deposition voltages were studied. The results show that the introduction of nickel significantly improved the electrical and mechanical properties of the joined fiber. Under a suitable deposition voltage, the resistance of the joined fiber was 37.7% of the original fiber, and the bearing capacity of the joined fiber was no less than the original fiber. Under optimized condition, the fracture mode of the joined fibers was plastic fiber fracture.

In this paper, the CFRP(Carbon Fiber Reinforced Plastic) parts were printed and cut in a large-scale additive and subtractive hybrid manufacturing system. A method to increase the strength and durability of a product by identifying the interlayer adhesion during the printing process of a large-scale additive manufacturing hybrid system was investigated. According to the printing conditions(CF content, deposition temperature, compaction process), the specimen was printed and cut to determine the tensile strength in the printing direction. As a result of the experiment, the highest tensile strength was shown when ABS-CF 20wt.% Compound was printed at 230℃ extrusion temperature, and the higher the CF content of the material, the lower the tensile strength. As a result of observing the inside of the test piece through an optical microscope, a large number of voids were kept inside the test piece. To remove voids generated inside the test piece, a compaction process was applied to the additive manufacturing hybrid system to prepare a test piece. As a result, void size decreased, and the strength of the part showed a tendency to increase. It is thought that additive manufacturing with high tensile strength can be obtained through studies on the optimization of deposition conditions in additive manufacturing hybrid systems.