Search

To fabricate high efficiency photoanodes for water oxidation, it is highly required to engineer their nanoporous architecture and interface to improve the charge separation and transport efficiency...

Low-temperature fuel cells have attracted significant attention owing to their low cost and high performance. Herein, uniform Ru nanoparticles (NPs) with various size distributions were synthesized as a non-Pt catalyst on a carbon support by fluidized bed reactor-atomic layer deposition (FBR-ALD) as a function of ALD cycles for the hydrogen oxidation reaction (HOR) in alkaline medium. With an increase in the number of ALD cycles from 5 to 30 cycles, the wt% of the Ru NPs increased from ∼5 to ∼32 wt%. In addition, the structural characterization of the Ru NPs revealed the formation of Ru NPs with a uniform, dense, and controllable size (∼2–4 nm) and crystallinity depending on the growth cycle of ALD. However, the 10 cycled Ru catalyst with a NP size of ∼2 nm possessed a highly electrochemically active roughened surface (amorphous moiety covered the crystallite), which enhanced its HOR and mass activity. Remarkably, the ALD-synthesized Ru catalyst outperformed a commercial Ru/C catalyst with a similar wt%. Hydrogen binding energy (HBE) calculations revealed that the specific activity of the catalyst increased with decreasing HBE. The mechanistic pathway for the HOR indeed illustrates that enhanced activity under alkaline conditions was found owing to the weakening of the metal–H interaction influenced by the Ru NP crystallinity and size. The findings of this study indicate that the FBR-ALD technique is an effective, scalable approach for the synthesis of active non-Pt metal catalysts.

Extended and oriented rutile nanowires (NWs) hold great promise for numerous applications because of their various tunable physicochemical properties in air and/or solution media, but their direct synthesis on a wide range of conducting substrates remains a significant challenge. Their device performance is governed by relevant NW geometries that cannot be fully controlled to date by varying bulk synthetic conditions. Herein, orientation engineering of rutile SnO2 NWs on a variety of conducting substrates by atomic layer deposition (ALD) seeding has been investigated. The seeded growth controls the nucleation event of the NW, and thicknesses and crystallographic properties of seed layers are the key parameters toward tuning the NW characteristics. The seed layers on carbon cloth produce NWs with highly enhanced electrochemically active surface area, which would show efficient electrochemical CO2 reduction. In addition, the hierarchical architecture resulted from the seeded growth of NWs on SnO2 nanosheets allows thin layers of BiVO4, forming a heterojunction photoanode, which shows a record charge separation efficiency of 96.6% and a charge-transfer efficiency of 90.2% at 1.23 V versus the reversible hydrogen electrode among, to date, the reported BiVO4-based photoanodes for water oxidation. Our study illustrates that such a versatile interfacial engineering effort by the ALD technique would be promising for further wide range of practical applications.

Area-selective atomic layer deposition (AS-ALD) is a promising bottom-up patterning approach for fabricating conformal thin films. One of the current challenges with respect to AS-ALD is the defici...

High-Mn (over 24 wt%) austenitic steels recently have been developed with excellent mechanical properties such as high strength and ductility at very low temperatures for cryogenic application. Especially, cold-rolling process is and effective method to increased yield and tensile strength of high-Mn steel when making products. In our previous work, we have investigated the correlation between microstructure and mechanical properties due to recrystallization without considering the characteristics of the cold-rolling direction of high-Mn steels. In this study, we evaluated the effects of anisotropic behaviors on the heat treatment of cold-rolling high-Mn steels. Despite the heat treatment, differences between transverse and longitudinal direction in the cold-rolled conditions generally affected the recrystallized microstructure. Such anisotropic behaviors caused changes in mechanical properties such as tensile and Charpy impact test, as microstructure along cold-rolling direction.

To fabricate low-cost and highly efficient two-dimensional (2D) alloyed catalysts, the effect of architectures and compositions on their water oxidation activity should be investigated. Focusing on...

Zero-dimensional/two-dimensional (0D/2D) TiO2/g-C3N4 heterostructural photocatalysts were fabricated via ALD technique. TiO2 nanoparticles were “site-selectively grown” on g-C3N4 nanosheets and the surface modification induced band engineering of the composite photocatalysts. Thus, the redox properties of the photocatalysts were fine tuned. Under visible light, since only g-C3N4 was excited, TiO2 was acting as the electron transport channel in the optimized interfacial structures. They effectively suppressed the recombination and facilitated the transfer of photogenerated charges, improving the photocatalytic activity. When both the components were excited under UV–vis light, the dynamic equilibrium of the conduction band positions on these n–n type semiconductor heterojunctions led to the increased recombination rate of charges, decreasing the reactivity for H2 evolution. However, the photocatalytic degradation of organic pollutants by these composite photocatalysts exhibited enhanced activities, resulting from the photogenerated holes on VB of TiO2 which could promote oxidation of organic pollutants with strong oxidation potentials. Furthermore, TiO2/g-C3N4 photocatalysts with limited numbers of deposition cycles exhibited optimal photocatalytic activity under visible light. In contrast, excessive deposition cycles on g-C3N4 for TiO2/g-C3N4 led to continuous film and increased thickness of TiO2, resulting in the attenuation of the reactivity. We verified this TiO2/g-C3N4 photocatalysts with less mass-loading, but more enhanced photocatalytic activity.

The specific capacitance and energy density of antimony trisulfide (Sb2S3)@carbon supercapacitors (SCs) have been limited and are in need of significant improvement. In this work, Sb2S3 nanoparticl...

Pt thin films, using the Pt precursor, dimethyl(N,N-dimethyl-3-butene-1-amine-N)platinum (DDAP, C8H19NPt), were deposited by atomic layer deposition (ALD). The growth characteristics of the Pt thin...

Rutile-TiO2 thin films have potential for use in high-k applications, such as dynamic random-access memory capacitors; however, they are difficult to realize without using noble-metal-based oxide substrates. Therefore, we proposed a new approach for the preparation of rutile TiO2 by a small amount of Sn doping and the insertion of ultra-thin SnO2 to achieve enhanced dielectric performance without using noble-metal-based electrodes. It was confirmed that the crystallinity of rutile TiO2 was remarkably enhanced in Sn-doped TiO2 formed on an ultra-thin SnO2 interlayer. Moreover, 10 nm-thick Sn-doped TiO2 thin film on a 1-nm SnO2 interlayer exhibited a high dielectric constant of about 80.

In this study, Al2O3/CrAlSiN multilayer coatings with various periods were prepared using a hybrid process involving overlapping magnetron sputtering of CrAlSiN and atomic layer deposition (ALD) of Al2O3. The influence of the number of Al2O3 layers on the mechanical properties, corrosion behavior and oxidation characteristics of the coatings was studied using nano/micro indentation, electrochemical corrosion, and high temperature static oxidation tests. The results show that the multilayer structure can effectively prevent crack propagation during the coating and subsequently increase the coating toughness. A substantial improvement in the resistance to electrochemical and oxidation corrosion was observed in the Al2O3/CrAlSiN multilayer coatings and increasing the number of Al2O3 layers dramatically increases the corrosion durability. The Al2O3 ALD layers are expected to inhibit the diffusion of corrosive substances such as ions and oxygen and the increase of the Al2O3 layer number decreases the diffusion fluxes of the coating elements to the surface and limit the oxide growth, resulting in the evolution of the oxidation produces from irregular particles to nano-walls/fibers. It is supposed that the PVD/ALD hybrid process may open a new hard coating design concept by providing a superior toughness and corrosion/oxidation resistance.

Silicon anodes in lithium-ion batteries have attracted attention for their exceptionally high theoretical capacity. However, their practical application is hindered as the capacity fades quickly due to huge volume changes of silicon particles during the lithiation/delithiation process. In order to reduce volume changes, polyvinylidene fluoride, gellan gum, and pullulan modified gellan gum were introduced in the electrode as a binder. This work focuses on understanding the role of these binders on the mechanical behavior and cracking resistance of silicon electrodes during electrochemical cycling. A binder with moderate elasticity can be used to extend the capacity lifetime of a silicon anode.

Recently, porous ceramics have received much attention from researchers because of their excellent thermal and chemical stabilities compared to their counterparts (such as porous polymers and metals), despite their inferior mechanical instability. Among the various types of porous ceramics, reticulated porous ceramics have significant industrial potential because of their synergistic high porosity and permeability. However, to the best of our knowledge, there is insufficient data on the processing conditions or preparing optimal reticulated porous alumina. Therefore, we prepared and characterized reticulated porous alumina specimens by controlling various processing conditions, namely average particle size, solid loading, binder, and dispersant. The data obtained were used to assess whether the compressive strength of the reticulated porous alumina could be enhanced and to discuss the potential of these materials for various applications.

Pt-decorated In2O3 nanofibers with tailored size and morphology were synthesized as sensing materials for a highly sensitive toluene gas sensor. The bridge-type micro-platforms, including micro-heaters and micro-electrodes for the integration of In2O3 nanofibers-based sensing materials, were designed to demonstrate the sensing at high temperature with low power consumption. The gas sensing properties of the fabricated toluene gas sensor were systematically investigated by controlling the power of the micro-heater and the concentration of the toluene gas. Additionally, the enhanced sensing properties for various gas concentrations of toluene were investigated for Pt-nanoparticle-decorated In2O3 nanofibers.

Uniform, well-ordered sub-20 nm patterns can be generated by the templated self-assembly of block copolymers (BCPs) with a high Flory-Huggins interaction parameter (χ). However, the self-assembled BCP monolayers remain limited in the possible structural geometries. Here, we introduce a multiple self-assembly method which uses di-BCPs to produce diverse morphologies, such as dot, dot-in-honeycomb, line-on-dot, double-dot, pondering, dot-in-pondering, and line-on-pondering patterns. To improve the diversity of BCP morphological structures, we employed sphere-forming and cylinder-forming poly(styrene-block-dimethylsiloxane) (PS-b-PDMS) BCPs with a high χ. The self-assembled mono-layer and double-layer SiOx dot patterns were modified at a high temperature (∼800 °C), showing hexagonally arranged (dot) and double-hexagonally arranged (pondering) SiOx patterns, respectively. We successfully obtained additional new nanostructures (big-dot, dot-in-honeycomb, line-on-dot, pondering, dot-in-pondering, and line-on-pondering types) through a second self-assembly of cylinder-forming BCPs using the dot and pondering patterns as guiding templates. This simple approach can likely be extended to the multiple self-assembly of many other BCPs with good functionality, significantly contributing to the development of various nanodevices.

Recently, research has been conducted on nanocomposite thin films containing new additive elements in ZrN. In this paper, a method for depositing ZrCuSiN nanocomposite coatings using a ZrCuSi single target is presented. The ZrCuSi target that was used to easily deposit a ZrCuSiN coating in a mixed gas atmosphere (Ar + N2) was produced by a simple arc melting method (casting process). The effect of the nitrogen content was investigated by depositing a ZrCuSiN coating using alloy targets at various nitrogen gas flow rates (2, 4, 6, and 8 sccm). X-ray diffraction analysis of the ZrCuSiN coatings revealed a ZrN structure with a preferable orientation (200). As the nitrogen flow rate increased, the formation of o-Zr3N4 was dominant in the ZrN formation. A nitrogen gas flow rate of 4 sccm produced a coating with optimal ZrN and a-Si3N4 coordination and maximum hardness (41 GPa). Reciprocal friction tests of all coatings and uncoated carburized SCM415 steel in a 5W30 lubrication atmosphere demonstrated that the 4 sccm coating had the lowest friction coefficient (0.002). Therefore, our method has the potential to be an alternative surface coating technique for materials used in automotive engine parts and various other wear protection applications.

Fabrication of semiconductor thin films with uniform and vertically aligned one-dimensional nanostructures is an active area of research. We report the synthesis of vertically aligned nanograss (NG...

A method for significantly increasing the growth rates (GRs) of high- k oxide thin films grown via plasma-enhanced atomic layer deposition (PE-ALD) by enhancing the plasma density through the addition of Ar gas to the O2 plasma oxidant was developed. This approach led to improvements of ∼60% in the saturation GRs of PE-ALD ZrO2, HfO2, and SiO2. Furthermore, despite the significantly higher GR enabled by PE-ALD, the mechanical and dielectric properties of the PE-ALD oxide films were similar or even superior to those of films grown via the conventional O2 plasma process. Optical emission spectroscopy analyses in conjunction with theoretical calculation of the electron energy distribution function revealed that adding Ar gas to the O2 plasma increased the density of high-energy electrons, thereby generating more O2 plasma species, such as ions and radicals, which played a key role in improving the GRs and the properties of the films. This promising approach is expected to facilitate the high-volume manufacturing of films via PE-ALD, especially for use as gate insulators in thin-film transistor-based devices in the display industry.

Amorphous carbon films containing a wide-range content of Mo and a small amount of Cu (MoCu:a-C films) were prepared by a hybrid sputtering system. The influences of the doping contents of MoCu on the microstructure and properties of the films were studied. The results show that the doped Cu atoms tend to dissolve in the a-C matrix while the doped Mo atoms exist as solid solution and carbide nanoparticles embedding in the a-C matrix. It is found that the size of the carbide nanoparticles shows an influence on the formation of the sp2-C. Increasing the nanoparticle size will decrease the sp2-C fraction and thus increase the sp3/sp2 in the films. The high sp3/sp2 and hard carbide nanoparticles contribute to the high hardness of the films. However, the hard carbide nanoparticles cause serious abrasive wear performances.

The wear resistance of Ti1−xMexN (Me = Zr, Al, Cr) coatings by the laser carburization process was investigated in terms of local atomic structural changes. The repeated pulsed laser ablation was performed to the Ti1−xMexN coating surfaces after Graphite paste was covered. The friction coefficients of the coating specimens were decreased from ∼0.7 to 0.2, and the formation of cracks and debris was suppressed by implementing the laser ablation process. ToF-SIMS depth profiles showed that the laser carburization helps Carbon penetrate into the coating layer as deep as ∼20 nm below its surface. XPS and XAFS analyses revealed that the improvement of the wear resistance of the coatings was achieved not by formation of TiC or ZrC lattices on the coatings surfaces but by Carbon interstitials to the Ti1−xMexN lattices.

The mechanism of hardness improvement of a TiZrN coating by carbon doping was investigated in terms of the residual stress and the lattice deformation. Carbon was doped using laser carburization to improve the hardness of TiZrN, which was increased from 3025 HV to 3388 HV. The lattice parameter was calculated through Rietveld refinement in order to analyze the behavior inside the lattice due to carbon doping, which showed that the parameter increased from 4.21 A to 4.44 A after the carbon doping process. The diffraction pattern was analyzed using an electron beam to identify the lattice state of the coating layer, and lattice distortion was revealed through a diffused ring pattern. The compressive residual stress was increased by 48%, which was identified through the sin2Ψ method using the lattice constant change due to carburization. After the carbon doping, the hardness of the TiZrN was increased by 10%, which was attributed to the expansion distortion generated in the TiZrN lattice and the increase of the compressive residual stress.

The formation of thin amorphous cobalt titanium nitride (CoTiN) layers was investigated using a supercycle method of atomic layer deposition (ALD). The stoichiometry of the resultant ALD CoTiN films was controlled by changing the ratio of Co and TiN thicknesses. X-ray diffraction analysis and transmission electron microscopy observations showed that the microstructure of the ALD Co and TiN was transformed from polycrystalline to amorphous CoTiN. The stoichiometry of the CoTiN layer was affected by the growth characteristics of ALD Co and TiN on each surface. The results revealed that ALD TiN undergoes nucleation incubation on the ALD Co surface, whereas ALD Co does not undergo nucleation incubation on the ALD TiN surface. The properties of the amorphous CoTiN layers were evaluated by diffusion experiments and mechanical tests. Because of the lack of grain boundaries, the CoTiN efficiently blocks the diffusion of Cu at elevated temperatures and exhibits higher hardness compared with ALD Co.

Direct electron transfer between a redox label and an electrode requires a short working distance (

In this paper, diamond-like carbon (DLC) coatings with AlCrSi co-doping were deposited by a reactive high power impulse magnetron sputtering (HiPIMS) with utilizing a gas mixture of Ar and C2H2 as the precursor. The doping contents of Al, Cr and Si in the coatings were controlled by adjusting the C2H2 flow fraction in the gas mixture. The influences of the HiPIMS frequency and C2H2 flow on the microstructure, composition, mechanical properties and tribological behaviors of the AlCrSi-DLC coatings were researched carefully by using scanning electron microscope, X-ray photoelectron spectroscopy, nano-indentation and ball-on-plate tribometer, respectively. The results show that the doping AlCrSi contents increased as the C2H2 flow fraction decreased, along with the obvious structural transformation of the coatings from amorphous feature to carbide composites. The high C2H2 flow fraction tends to cause the target poisoning, resulting in the instability of the coating composition and the appearance of macro-droplets on the coating surface. The high pulse repeating frequency can effectively prevent the poisoning of the metal target and avoid the form of the arcing even at high C2H2 fraction, which is conducive to control the doping contents of the metal atoms and improve the surface quality of the AlCrSi-DLC coatings. In addition, the high frequency can facilitate the formation of the carbide, which has been expected to improve the hardness of the coatings. However, the existence of a mass of carbide phase causes serious abrasive wear of the coatings at low C2H2 fraction.

Diamond-like carbon (DLC) coatings with AlTiSi multi-doping were prepared by a reactive high power impulse magnetron sputtering with using a gas mixture of Ar and C2H2 as precursor. The composition, microstructure, compressive stress, and mechanical property of the as-deposited DLC coatings were studied systemically by using SEM, XPS, TEM, Raman spectrum, stress-tester, and nanoindentation as a function of the Ar fraction. The results show that the doping concentrations of the Al, Ti and Si atoms increased as the Ar fraction increased. The doped Ti and Si preferred to bond with C while the doped Al mainly existed in oxidation state without bonding with C. As the doping concentrations increased, TiC carbide nanocrystals were formed in the DLC matrix. The microstructure of coatings changed from an amorphous feature dominant AlTiSi-DLC to a carbide nanocomposite AlTiSi-DLC with TiC nanoparticles embedding. In addition, the coatings exhibited the compositionally modulated multilayer consisting of alternate Al-rich layer and Al-poor layer due to the rotation of the substrate holder and the diffusion behavior of the doped Al which tended to separate from C and diffuse towards the DLC matrix surface owing to its weak interactions with C. The periodic Al-rich layer can effectively release the compressive stress of the coatings. On the other hand, the hard TiC nanoparticles were conducive to the hardness of the coatings. Consequently, the DLC coatings with relatively low residual stress and high hardness could be acquired successfully through AlTiSi multi-doping. It is believed that the AlCrSi multi-doping may be a good way for improving the comprehensive properties of the DLC coatings. In addition, we believe that the DLC coatings with Al-rich multilayered structure have a high oxidation resistance, which allows the DLC coatings application in high temperature environment.

High-Mn austenitic steels have been recently developed for a storage or transportation application of liquefied natural gas (LNG) in cryogenic fields. Since the structural materials are subjected to extremely low temperature, it requires excellent mechanical properties such as high toughness strength. In case of high-Mn steels, twinning deformation during the cold-working process is known to increase strength yet may cause embrittlement of heavy deformed twin and anisotropic properties. In this study, a recrystallization process through appropriate annealing heat treatments after cold-working was applied to improve the impact toughness for high-Mn austenitic steels. Microstructure and mechanical properties were performed to evaluate the influence of cold-worked and annealed high-Mn austenitic steels. Mechanical properties, such as strength and impact toughness, were investigated by tensile and Charpy impact tests. The relationship between strength and impact toughness was determined by microstructure analysis such as the degree of recrystallization and grain refinement. Consequently, both elongation and toughness were significantly increased after cold-working and subsequent annealing at 1000 &deg, C as compared to the as-received (hot-rolled) specimen. The cold-worked high-Mn steel was completely recrystallized at 1000 &deg, C and showed a homogeneous micro-structure with high-angle grain boundaries.

High-strength steel is widely used in hot forging products for application to the oil and gas industry because it has good mechanical properties under severe environment. In order to apply to the extreme environment industry requiring high temperature and high pressure, heat treatments such as austenitizing, quenching and tempering are required. The microstructure of high-strength steel after heat treatment has various microstructures such as Granular Bainite (GB), Acicular Ferrite (AF), Bainitic Ferrite (BF), and Martensite (M) depending on the heat treatment conditions and cooling rate. Especially in large forged products, the difference in microstructure occurs due to the difference in the forging ratio depending on the location and the temperature gradient according to the thickness during post-heat treatment. Therefore, this study attempted to quantitatively analyze various phases of F70 high-strength steel according to the austenitizing temperature and hot forging ratio using the existing EBSD analysis method. In addition, the correlation between microstructure and mechanical properties was investigated through various phase analysis and fracture behavior of high-strength steel. We found that various microstructures of strength steel depend on the austenitizing temperature and hot forging ratio, and influence the mechanical properties and fracture behavior.

Although MXenes with outstanding electrical conductivity possess great potential as energy-storage materials for flexible supercapacitors (SCs), the electrochemical performance of the pure MXene-based SCs are often restricted by inherent limitations such as inferior energy densities and serious aggregation. Alternatively, it will be an effective strategy to develop rationally designed composite electrodes that can simultaneously provide both high electrical conductivity and large surface area via complementary functions of each constituent. Here, hierarchically layered MXene nanosheets on nickel cobalt sulfide/carbon cloth (Ti3C2Tx/NiCo2S4@CC, herein TNSC) was prepared through spray injection of MXene on nickel cobalt sulfide, which not only achieved an excellent specific capacitance at high current densities but also possess improved cycling stability. The optimized TNSC electrode shows maximum specific capacities of 2326F g−1 at a current density of 1 A g−1, and excellent cycling stability of 93.8% at 10 A g−1. We show that these outstanding electrochemical performances can be achieved by a proper loading amount of surface-coated Ti3C2Tx, which can simultaneously enhance electrical conductivity and permeate ions to nickel cobalt sulfide. Furthermore, a quasi-solid‐state flexible SC (QFSC) based on TNSC presents a high energy density of 57.5 W h kg−1 at a power density of 800 W kg−1 in a wide potential window of 1.6 V. Therefore, the excellent electrochemical performances of the TNSC electrode makes it as a prominent candidate for high-performance and flexible energy storage devices.

Here, we report that Nb doping of two-dimensional (2D) MoSe2 layered nanomaterials is a promising approach to improve their gas sensing performance. In this study, Nb atoms were incorporated into a 2D MoSe2 host matrix, and the Nb doping concentration could be precisely controlled by varying the number of Nb2O5 deposition cycles in the plasma enhanced atomic layer deposition process. At relatively low Nb dopant concentrations, MoSe2 showed enhanced device durability as well as NO2 gas response, attributed to its small grains and stabilized grain boundaries. Meanwhile, an increase in the Nb doping concentration deteriorated the NO2 gas response. This might be attributed to a considerable increase in the number of metallic NbSe2 regions, which do not respond to gas molecules. This novel method of doping 2D transition metal dichalcogenide-based nanomaterials with metal atoms is a promising approach to improve the performance such as stability and gas response of 2D gas sensors.

In this study, 3-dimensional ripple structured anion (chlorine) doped ZnO thin film are developed, and used as electron transporting layer (ETL) in inverted organic photovoltaics (I-OPVs). Optical and electrical characteristics of ZnO:Cl ETL are investigated depending on the chlorine doping ratio and optimized for high efficient I-OPV. It is found that optimized chlorine doping on ZnO ETL enhances the ability of charge transport by modifying the band edge position and carrier mobility without decreasing the optical transmittance in the visible region, results in improvement of power conversion efficiency of I-OPV. The highest performance of 8.79 % is achieved for I-OPV with ZnO:Cl-x (x=0.5wt%), enhanced ~10% compared to that of ZnO:Cl-x (x=0wt%).

Manufacturing high-quality, two-dimensional (2D), layered materials with crystal-growth techniques is an important challenge for the advancement of 2D communication technologies. In this study, a simple method was developed for synthesizing 2D nanocrystals based on the model system of SnS2. The method involves the sulfurization of a metal oxide to a metal chalcogenide, which subsequently acts as a source of vapors for the growth of 2D crystals. The effect of the annealing conditions on the thermal sulfurization of SnO2 powder was investigated. The results showed that pure SnS2 powder could be obtained in a N2 atmosphere at 700 °C. SnS2 nanocrystals were successfully synthesized from the as-prepared SnS2 powder by the vapor transport method. The synthesized SnS2 nanocrystals had a 2D layered structure with hexagonal symmetry and exhibited typical n-type semiconducting characteristics, with an optical band gap of 2.05 eV. This novel method, which uses a preferentially prepared source for vapor transport, co...

Strontium niobate thin films have potential for next-generation high-k dielectric applications. In this work, we investigated the fabrication of SrxNb1-xOy thin films by atomic layer deposition for the first time and examined their physical and electrical characteristics. The composition of the SrxNb1-xOy thin film could be effectively controlled by introducing a super-cycle, and it was confirmed that the crystallinity after annealing varied depending on the composition. The Sr-rich film was crystalline after annealing and showed a high dielectric constant of approximately 75. In addition, it was observed that the Nb-rich film had a relatively large dielectric constant of approximately 65 even though it was amorphous, confirming that it could be applied as a next-generation high-k material. This research is the first step toward a new high-k dielectric candidate, which we believe can be applied to next-generation semiconductor devices through further research to improve the characteristics.

Plasma-enhanced atomic layer deposition (PEALD) of TiN thin films were investigated as an effective Se diffusion barrier layer for Cu (In, Ga) Se2 (CIGS) solar cells. Before the deposition of TiN thin film on CIGS solar cells, a saturated growth rate of 0.67 Å/cycle was confirmed using tetrakis(dimethylamido)titanium (TDMAT) and N2 plasma at 200 °C. Then, a Mo (≈30 nm)/PEALD-TiN (≈5 nm)/Mo (≈600 nm) back contact stack was fabricated to investigate the effects of PEALD-TiN thin films on the Se diffusion. After the selenization process, it was revealed that ≈5 nm-thick TiN thin films can effectively block Se diffusion and that only the top Mo layer prepared on the TiN thin films reacted with Se to form a MoSe2 layer. Without the TiN diffusion barrier layer, however, Se continuously diffused along the grain boundaries of the entire Mo back contact electrode. Finally, the adoption of a TiN diffusion barrier layer improved the photovoltaic efficiency of the CIGS solar cell by approximately 10%.

Owing to the scaling down of dynamic random-access-memory, the development of new high-k dielectrics as well as the reduction in the equivalent-oxide-thickness value using ZrO2 and TiN electrode-based capacitors have become crucial. Because the unwanted interfacial layer between ZrO2 and TiN electrodes can induce the degradation of electrical properties, we propose a new approach for improving capacitor properties by introducing ultrathin metal oxides as the buffers. Each ultrathin TiO2, Ta2O5, and ZnO is inserted between ZrO2 thin films and the top or bottom electrodes, and the variations in their electrical properties are investigated. We discovered that the electrical properties of ZrO2-based capacitors, such as the dielectric constant and leakage current density, can be improved by introducing certain types of buffers without requiring a noble metal electrode and higher-k dielectrics. Furthermore, we discovered that the EOT scaling of approximately 0.15 nm is achievable only through the introduction of the appropriate buffer.

Spectroscopic and microscopic techniques are not suitable for the rapid monitoring of time-dependent dissolution behavior (particularly, pinhole changes) of a layer deposited by atomic layer deposition (ALD). Here, we present a simple electrochemical method that provides information on the dissolution mechanism including pinhole generation and thickness change. Because indium tin oxide (ITO) electrodes exhibit flat capacitive currents and good (electro)chemical stability, they are selected as ideal underlying substrates for the electrochemical monitoring of the ALD layers even under harsh conditions. Two ALD layers (Al2O3 and TiO2 layers) that exhibit opposite dissolution behaviors are chosen as model layers because the as-deposited Al2O3 layers are pinhole-free but unstable in aqueous solutions, whereas the as-deposited TiO2 layers are not pinhole-free but stable in aqueous solutions. The combination of capacitive current level (in an electrolyte solution containing no redox-active species) and electrochemical blocking behavior (in an electrolyte solution containing a redox-active species such as Ru(NH3)63+ and ferrocenemethanol) obtained from cyclic voltammograms enables us to verify whether the dissolution of an ALD layer occurs, to evaluate the dissolution rate, and to identify the plausible dissolution mechanism. The electrochemical results reveal that the Al2O3 layers are dissolved in biological buffers, along with pinhole generation, and that the TiO2 layers are stable with no pinhole generation. The difference in electrochemical blocking behavior between Ru(NH3)63+ and ferrocenemethanol provides information on the approximate size of the pinholes. The present method is appealing for practical use because even an ALD layer with a thickness of only a few nanometers can be tested to monitor the dissolution behavior and because any ALD layer that can be readily deposited on ITO electrodes can be easily examined using this method.

The stainless steel (SS)-based bipolar plate with high conductivity and corrosion resistance is one of the key components in recent polymer electrolyte membrane fuel cells. Therefore, an excellent corrosion protection and good electrical conductivity in SS316L-based bipolar plates can be achieved through plasma-enhanced atomic layer deposition (PEALD) of ultrathin (25–67 nm) TiN thin films. To this end, two types of TiN protective coatings deposited by PEALD using tetrakis(dimethylamino)titanium (TDMAT) and titanium tetrachloride (TiCl4) precursors were evaluated; the evaluations were conducted under conditions simulating the operating conditions of PEMFCs. Regardless of the precursor type, PEALD-TiN onto SS316L resulted in great improvements in electrical conductivity and corrosion resistance. Notably, the TiN thin films prepared using TDMAT exhibited excellent corrosion resistance (

For cryogenic applications, materials must be cautiously selected because of a drastic degradation in the mechanical properties of materials when they are exposed to very low temperatures. We have developed a new technique using a cold-working and surface-cracking process to overcome such degradation of mechanical properties at low temperatures. This technique intentionally induced surface-cracks in cold-worked austenitic stainless steels and resulted in a significant increase in both strength and fracture at low temperatures. According to the microstructure observations, dissipation of the crack propagation energy with surface-cracks enhanced the impact toughness, showing a ductile fracture mode in even the cryogenic temperature region. In particular, we obtained the high strength and toughness materials by a surface-cracking technique at 5% cold-worked specimen with surface-cracks.

A growth technique to directly prepare two-dimensional (2D) materials onto conventional semiconductor substrates, enabling low-temperature, high-throughput, and large-area capability, is needed to realize competitive 2D transition-metal dichalcogenide (TMD)/three-dimensional (3D) semiconductor heterojunction devices. Therefore, we herein successfully developed an atmospheric-pressure plasma-enhanced chemical vapor deposition (AP-PECVD) technique, which could grow MoS2 and WS2 multilayers directly onto PET flexible substrate as well as 4-in. Si substrates at temperatures of

SnO 2 thin films were deposited by plasma-enhanced atomic layer deposition (PEALD) using SnCl 4 and O 2 plasma at the temperature between 150 and 350 °C. The self-limiting growth of PEALD-SnO 2 was confirmed by a careful study of the growth kinetics at 350 °C. At optimized growth conditions, PEALD-SnO 2 exhibited a saturated growth per cycle of 0.072 nm/cycle, which is almost two times higher than that deposited by thermal ALD using SnCl 4 reported earlier. Regardless of the growth temperatures, there were no Cl impurities within the films. Furthermore, the film density of rutile SnO 2 was comparable to bulk density. With those favorable properties of PEALD-SnO 2 , the lower electrical resistivity and improved corrosion resistance of the films were obtained at 350 °C.

Vanadium oxide (V 2 O 5-x ) thin films with a thickness of about 4 nm were prepared by atomic layer deposition (ALD) to be used as a hole-transporting layer in an amorphous silicon solar cell. The ALD growth characteristics (growth rate, crystallinity, and surface morphology) of the V 2 O 5-x films were investigated while exposed to different pulse times of ozone (O 3 ), which was used as an oxidant. The effect of the different ozone pulse times, used in the V 2 O 5 layer, on the device performance was also investigated. At the ozone pulse time of 1 s, the maximum value of power conversion efficiency (PCE), i.e., 5.35%, was achieved, whereas at the ozone pulse time of 5 s, the PCE was 4.18%. Ultraviolet photoelectron spectroscopy (UPS) and X-ray photoelectron spectroscopy (XPS) analyses confirmed that increasing the proportion of crystalline phase in the V 2 O 4 films with lower work function of V 2 O 5 resulted in decreased open-circuit voltage and conversion efficiency as the ozone pulse time increased.

Plasma-enhanced atomic layer deposition (PEALD) of tantalum nitride (TaN) thin films was investigated at a growth temperature of 230 °C using an alternating supply of tertiary-amylimido-tris(dimethylamido)tantalum (TAIMATA, Ta[NC(CH3)2C2H5][N(CH3)2]3) and hydrogen (H2) plasma. As the H2 plasma power increased from 75 to 175 W, the electrical resistivity of the films was improved from 1900 to 680 μΩ·cm, mainly due to the improved crystallinity. Moreover, the preferred orientation ratio between TaN (200) and TaN (111) planes also abruptly increased from 0.8 to 2.8 with increasing the H2 plasma power. This preferred orientation change of the films from (111) to (200) improves the adhesion properties between Cu and TaN, while the Cu diffusion barrier performance was not significantly affected.

The particle size effect of MgO as a sintering additive on the thermal conductivity of sintered reaction-bonded silicon nitride (SRBSN) was investigated. It was revealed that the size of MgO is critical for thermal conductivity with regard to the microstructural evolution process. That is, the abnormal grain growth promoted by an inhomogeneous liquid-phase distribution led to higher thermal conductivity when coarser MgO was added, whereas a relatively homogeneous liquid-phase distribution induced moderate grain growth and lower thermal conductivity when finer MgO was added.

Multilayered hard coatings with a CrN matrix and an Al2O3, TiO2, or nanolaminate-Al2O3/TiO2 sealing layer were designed by a hybrid deposition process combined with physical vapor deposition (PVD) and atomic layer deposition (ALD). The strategy was to utilize ALD thin films as pinhole-free barriers to seal the intrinsic defects to protect the CrN matrix. The influences of the different sealing layers added in the coatings on the microstructure, surface roughness, and corrosion behaviors were investigated. The results indicated that the sealing layer added by ALD significantly decreased the average grain size and improved the corrosion resistance of the CrN coatings. The insertion of the nanolaminate-Al2O3/TiO2 sealing layers resulted in a further increase in corrosion resistance, which was attributed to the synergistic effect of Al2O3 and TiO2, both acting as excellent passivation barriers to the diffusion of corrosive substances.

2D layered materials with sensitive surfaces are promising materials for use in chemical sensing devices, owing to their extremely large surface-to-volume ratios. However, most chemical sensors based on 2D materials are used in the form of laterally defined active channels, in which the active area is limited to the actual device dimensions. Therefore, a novel approach for fabricating self-formed active-channel devices is proposed based on 2D semiconductor materials with very large surface areas, and their potential gas sensing ability is examined. First, the vertical growth phenomenon of SnS2 nanocrystals is investigated with large surface area via metal-assisted growth using prepatterned metal electrodes, and then self-formed active-channel devices are suggested without additional pattering through the selective synthesis of SnS2 nanosheets on prepatterned metal electrodes. The self-formed active-channel device exhibits extremely high response values (>2000% at 10 ppm) for NO2 along with excellent NO2 selectivity. Moreover, the NO2 gas response of the gas sensing device with vertically self-formed SnS2 nanosheets is more than two orders of magnitude higher than that of a similar exfoliated SnS2 -based device. These results indicate that the facile device fabrication method would be applicable to various systems in which surface area plays an important role.

Multilayered hard coatings with a CrN matrix and an Al2O3, TiO2, or nanolaminate-Al2O3/TiO2 sealing layer were designed by a hybrid deposition process combined with physical vapor deposition (PVD) and atomic layer deposition (ALD). The strategy was to utilize ALD thin films as pinhole-free barriers to seal the intrinsic defects to protect the CrN matrix. The influences of the different sealing layers added in the coatings on the microstructure, surface roughness, and corrosion behaviors were investigated. The results indicated that the sealing layer added by ALD significantly decreased the average grain size and improved the corrosion resistance of the CrN coatings. The insertion of the nanolaminate-Al2O3/TiO2 sealing layers resulted in a further increase in corrosion resistance, which was attributed to the synergistic effect of Al2O3 and TiO2, both acting as excellent passivation barriers to the diffusion of corrosive substances.

For achieving improved electrical conductivity through surface passivation of crystalline silicon, we investigated TiON films by combining TiO2 and TiN deposition cycles in plasma-enhanced atomic layer deposition. To control the composition of the TiON films, a super-cycle—composed of one cycle of TiO2 and x-cycles of TiN—was adopted. The thickness of the films could be precisely controlled on the nanometer and sub-nanometer scale, regardless of the TiO2:TiN sub-cycle ratio. The chemical state, crystalline phase, and interface characteristics of the TiON films were examined. For the TiO2:TiN = 1:20 film, the carrier lifetime was increased from 30 to 243 μs, while the resistivity decreased from 3.1 × 108 to 7.1 × 10 − 1 Ω•cm compared to the TiO2 film.

Using the high working pressure plasma-enhanced chemical vapor deposition (HWP-PECVD) technique, the hydrogenated microcrystalline silicon (μc-Si:H) films for photovoltaic layers of thin film solar cells was investigated. The $\pmb{\mu \mathrm{c}-\mathrm{Si}:\mathrm{H}}$ films were deposited on surface textured fluorine-doped tin oxide (FTO) glass substrates at 100 Torr in a 100 MHz very high frequency (VHF) plasma of gas mixtures containing He, H2, and SiH4. It was found that an optimum ratio of the H2/SiH4 flowrate existed for growing a homogenous microcrystalline through the whole film without amorphous incubation layer. When an intrinsic $\pmb{\mu \mathrm{c}-\mathrm{Si}:\mathrm{H}}$ thin film was deposited at n-i-p single junction solar cell, the cell performances were dependent on with or without an amorphous incubation layer. With an amorphous incubation layer, the open circuit voltage $(\mathrm{V}_{\mathrm{oc}})$ of cell was 0.8V, which was typical cell property of hydrogenated amorphous silicon (a-Si:H). On the other hand, at the optimum ratio of the H2/SiH4 flow-rate, μc-Si:H single cell responding an infrared light showed the Voc of 0.49 V. Intrinsic hydrogenated microcrystalline silicon (μc-Si:H) thin film, exhibiting the photovoltaic performance (Eff: 7.2%, $\pmb{\mathrm{V}_{\mathrm{oc}}:0.49\mathrm{V}, \mathrm{J}_{\mathrm{sc}}:23\mathrm{mA}/\mathrm{cm}^{2}}$ , FF:64%) was able to be successfully fabricated.

We demonstrated a novel porous Ni foam (PNF) with small voids/pores penetrating the skeleton wall by a simple etching process using commercial Ni foam, aiming to achieve the maximum use of its hollow structure for various nanostructured materials growing as the electrode for supercapacitor application. The hydrothermal Ni(OH)2 nanosheets, functioning as the battery-type active material, were successfully grown vertically on both inner and outer surface of the PNF skeleton. The Ni(OH)2/PNF electrodes exhibited high capacity of ∼578 C/g at 1 A/g current density with capacitance retention of ∼90% after 3000 cycles, which was much higher than those of the Ni(OH)2/NF electrodes. The strategy suggests that 3D PNF not only provides a universal route for the rational design of biface (inner and outer) growth of various nanostructured electrode materials, but also reducing the total mass of the electrode supporter by take full advantage of the hollow structure of Ni foam for the industrial applications.