Incorporation of Pt Nanoparticles on the Surface of TeO2-Branched Porous Si Nanowire Structures for Enhanced Room-Temperature Gas Sensing.

A new gas sensor working in room temperature, which is compatible with silicon fabrication technology is presented. Porous silicon nanowires (NWs) were synthesized by metal-assisted chemical etching method and then TeO2 NWs branches were attached to their stem by thermal evaporation of Te powders in the presence of air. Afterwards TeO2 branched porous Si NWs were functionalized by Pt via sputtering followed by low temperature thermal annealing. Scanning electron microscopy, transmission electron microscopy and energy-dispersive X-ray spectroscopy collectively confirmed successful formation of TeO2 branched porous Si NWs functionalized by Pt nanoparticles. Their gas sensing properties in the presence of CO, C6H6 and C7H8 were tested at room temperature, for Si wafer, pristine porous Si NWs, pristine TeO2 branched porous Si NWs, and Pt functionalized TeO2 branched porous Si NWs sensors. Pt functionalized TeO2 branched porous Si NWs have higher responses to all tested gases than the other sensors. The origin of high response is discussed in detail. This new room temperature gas sensor can open a new aperture for development of gas sensors with minimum energy consumption which are compatible with silicon fabrication technology.

Pore Characteristics of Lotus-Type Porous Cu-Fe and Cu-Cr Alloys Fabricated by Unidirectional Solidification.

Lotus-type porous Cu-Fe and Cu-Cr with long cylindrical pores was fabricated by centrifugal casting under hydrogen atmosphere and the effect of alloying elements on pore characteristics of lotus-type porous Cu was investigated. For the lotus type porous Cu-Fe alloy, the porosity slightly decreased and the average pore diameter slightly increased with increasing Fe content. For the lotus-type porous Cu-Cr alloy, the porosity sharply decreased and the average pore diameter drastically increased with an increase in the Cr content. From these results, it was found that the pore evolution and growth are affected by alloying element and this leads to the change in the pore characteristics of lotus-type porous Cu-Fe and Cu-Cr alloys.

Effect of Zn on Pore Characteristics in Lotus-Type Porous Cu.

The effect of Zn on pore characteristics in lotus-type porous Cu alloy was investigated. The lotustype porous Cu-Zn alloys were fabricated with Zn content from 0.01 to 0.1 at% by the centrifugal casting method. The results demonstrated that the porosity was rarely affected by Zn content. However, the average pore diameter and pore number density of the lotus type porous Cu-Zn alloys were significantly affected by the Zn content. The average pore diameter decreased as the Zn content increased up to 0.01 at%, and then increased as the Zn content increased up to 0.1 at%. In contrast, the variations in the pore number density of the lotus-type porous Cu-Zn alloys showed the reversed tendency with respect to that of the average pore diameter. The increase in heterogeneous nucleation sites for pores attributed to the decreased average pore diameter and the increased pore number density.

Design and synthesis of amorphous SiOx structures generated by Sn quantum dots: growth mechanism and luminescent origin.

SiOx structures with different diameters of a few hundreds of nanometers and/or a few micrometers are prepared using applied thermal evaporation. Subsequently, Sn quantum dot-based SiOx architectures are synthesized via the continuous steps of the carbothermal reduction of SnO2, substitution of Sn(4+) for In(3+), thermal oxidation of Si, Sn sublimation, interfacial reaction, and diffusion reaction consistent with corresponding phase equilibriums. Several crystalline and spherical-shaped Sn quantum dots with diameters between 2 and 7 nm are observed in the amorphous SiOx structures. The morphological evolution, including hollow Sn (or SnOx) sphere and wire-like, worm-like, tube-like, and flower-like SiOx, occurs stepwise on the Si substrate upon increasing the given process energies. The optical characteristics based on confocal measurements reveal the as-synthesized SiOx structures, irrespective of whether crystallinity is formed, which all have visible-range emissions originating from the numerous different-sized and -shaped Sn quantum dots permeating into the SiOx matrix. In addition, photoluminescence emissions ranging between ultraviolet and red regions are in agreement with confocal measurements. The origins of the morphology- and luminescence-controlled amorphous SiOx with Sn quantum dots are also discussed.

Enhanced near-band edge emission from ZnO nanorods by V2Os coating and subsequent thermal annealing.

V2O5-coated ZnO 1D nanostructures were prepared by using a two step process: thermal evaporation of a mixture of ZnO and graphite powders (ZnO:C = 1:1) in an oxidative atmosphere and sputter-deposition of V2O5. Scanning electron microscopy revealed that the nanostructures had a rod-like morphology with the thickness diminishing gradually from an end to the other. The thicknesses and lengths of the nanorods range from a few tens to a few hundreds of nanometers and from a few to a few tens of micrometers, respectively. Transmission electron microscopy and X-ray diffraction analyses revealed that the ZnO cores and V2O5 shells of the core-shell nanorods were wurtzite-type hexagonal close-packed structured single crystal and amorphous, respectively. The intensity ratio of the near-band edge (NBE) emission to the deep-level emission was increased about three times by coating the ZnO nanorods with a V2o5 thin film about 10 nm thick. The NBE emission enhancement may be mainly attributed to two sources: the effects of suppression of capturing of carriers by surface states and suppression of visible emission and nonradiative recombination by depletion regions formed in the ZnO cores. In addition, it was found that postannealing of V2O5-coated ZnO nanorods is not desirable, whereas post annealing makes a positive effect on the NBE emission enhancement in uncoated ZnO nanorods.

Physical interpretation of entropy, Boltzmann constant, and temperature.

Through the previously reported the quantum-identity, the light-model, and the T(temperature) · S(entropy) energy, the implied meaning of temperature and entropy, respectively, which it was difficult to intuitively recognize, was clearly defined. In order to minimize possible errors at this time, the interrelationship of the SI base unit, which is the smallest unit, and the T(temperature) · S(entropy) unit integration was used. In the process of converting to Planck units, each unit (criterion) for entropy and temperature was calculated, and their physical and chemical meanings were compared and reinterpreted. Thus, the unit of entropy is related to the Boltzmann constant, and the temperature is the oscillation of pure mass units. Therefore, the intuitive recognition of physical and chemical factors based on the unit of meter(m)-time(s) is considered sufficient as an initiator to move closer to new science beyond the current limited application.

Enhanced gas sensing properties of multiple networked In2O3-core/ZnO-shell nanorod sensors.

The influence of the encapsulation of In2O3 nanorods with ZnO on the H2S gas sensing properties was studied. In2O3-core/ZnO-shell nanorods were fabricated by a two step process comprising the thermal evaporation of an 1:1 mixture of In2O3 and graphite powders and the atomic layer deposition of ZnO. The core-shell nanorods ranged from 100 to 200 nm in diameter and were up to a few hundreds of micrometers in length. The thickness of the ZnO shell layer in the core-shell nanorod ranged from 5 to 10 nm. Multiple networked In2O3-core/ZnO-shell nanorod sensors showed the response of more or less 4 times higher than bare In2O3 nanorod sensors to H2S in a concentration range of 10-100 ppm at 300 degrees C. The substantial improvement in the response of In2O3 nanorods to H2S gas by the encapsulation with ZnO can be accounted for based on the space-charge model. Besides the enhanced sensor response, both the response and recovery times of the core-shell nanorods were shorter than those of the bare-In2O3 nanorods for any H2S concentration, respectively.

Synthesis, structure and gas-sensing properties of Pd-functionalized ZnSnO3 rods.

ZnSnO3 one-dimensional (1D) strutures were synthesized by using an evaporation technique. The morphology, crystal structure, and enhanced sensing properties of the ZnSnO3 structures functionalized with Pd to CO gas at 300 degrees C were investigated. The diameters of the 1D structures ranged from a few hundreds to a few thousands of nanometers and that the lengths were up to a few hundreds of micrometers. The gas sensors fabricated from multiple networked ZnSnO3 rods functionalized with Pd showed the enhanced electrical responses to CO gas. The responses of the rods were improved 10.7, 13.7, 13.4, and 12.5 fold at the CO concentrations of 10, 25, 50, and 100 ppm, respectively. In addition, the mechanism for the enhancement in the gas sensing properties of ZnSnO3 rods by Pd functionalization is discussed.

Minimizing Area-Specific Resistance of Electrochemical Hydrogen Compressor under Various Operating Conditions Using Unsteady 3D Single-Channel Model.

Extensive research has been conducted over the past few decades on carbon-free hydrogen energy. Hydrogen, being an abundant energy source, requires high-pressure compression for storage and transportation due to its low volumetric density. Mechanical and electrochemical compression are two common methods used to compress hydrogen under high pressure. Mechanical compressors can potentially cause contamination due to the lubricating oil when compressing hydrogen, whereas electrochemical hydrogen compressors (EHCs) can produce high-purity, high-pressure hydrogen without any moving parts. A study was conducted using a 3D single-channel EHC model focusing on the water content and area-specific resistance of the membrane under various temperature, relative humidity, and gas diffusion layer (GDL) porosity conditions. Numerical analysis demonstrated that the higher the operating temperature, the higher the water content in the membrane. This is because the saturation vapor pressure increases with higher temperatures. When dry hydrogen is supplied to a sufficiently humidified membrane, the actual water vapor pressure decreases, leading to an increase in the membrane's area-specific resistance. Furthermore, with a low GDL porosity, the viscous resistance increases, hindering the smooth supply of humidified hydrogen to the membrane. Through a transient analysis of an EHC, favorable operating conditions for rapidly hydrating membranes were identified.

Room-temperature ammonia gas sensing via Au nanoparticle-decorated TiO2 nanosheets.

A high-performance gas sensor operating at room temperature is always favourable since it simplifies the device fabrication and lowers the operating power by eliminating a heater. Herein, we fabricated the ammonia (NH3) gas sensor by using Au nanoparticle-decorated TiO2 nanosheets, which were synthesized via two distinct processes: (1) preparation of monolayer TiO2 nanosheets through flux growth and a subsequent chemical exfoliation and (2) decoration of Au nanoparticles on the TiO2 nanosheets via hydrothermal method. Based on the morphological, compositional, crystallographic, and surface characteristics of this low-dimensional nano-heterostructured material, its temperature- and concentration-dependent NH3 gas-sensing properties were investigated. A high response of ~ 2.8 was obtained at room temperature under 20 ppm NH3 gas concentration by decorating Au nanoparticles onto the surface of TiO2 nanosheets, which generated oxygen defects and induced spillover effect as well.

Fabrication and optical emission of TiO2-sheathed ZnO nanowires.

The ZnO nanowires were synthesized by using vapor-liquid-solid mechanism and then the ZnO nanowires were sheathed with TiO2 by metal organic chemical vapor deposition. The coaxial nanowires were 30-200 nm in diameter and up to 0.2 microm in length. Transmission electron microscopy and X-ray diffraction analysis results showed that the ZnO cores and TiO2 shells of the core-shell nanowires had wurtzite and amorphous structures, respectively. Photoluminescence measurement showed that TiO2 coating increased and decreased the near-band edge (NBE) and deep-level emissions of the ZnO nanowires in intensity, respectively. However, it appeared that subsequent annealing was undesirable since it decreased the NBE emission in intensity.

Preparation and characterization of MgO nanorods coated with SnO2.

MgO nanorods have been grown by thermal evaporation of Mg3N2 powders on Si (100) substrates coated with gold (Au) thin films. The MgO nanorods grown on Al2O3 (0001) were 0.1-0.2 microm in diameter and up to a few tens of micrometers in length. MgO/SnO2 coaxial nanorods have also been prepared by atomic layer deposition (ALD) of SnO2 onto the nanorods. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) analysis results indicate that the MgO-cores and the SnO2 shells of the annealed coaxial nanorods are of a single crystalline nature with cubic and orthorhombic structures, respectively. The photoluminescence (PL) spectroscopy analysis results show that SnO2 coating slightly increases the PL emission intensity of MgO nanorods. The PL emission of the SnO2-coated MgO nanorods is found to be considerably enhanced by thermal annealing and to strongly depend on the annealing atmosphere. The PL emission intensity of the MgO/SnO2 coaxial nanorods has been significantly increased by annealing in a reducing atmosphere. The origin of the PL enhancement by annealing in a reducing atmosphere is discussed on the basis of energy-dispersive X-ray spectroscopy analyses.

Characterization of luminescence properties of V2O5-capped ZnSe nanowires.

ZnSe-core/V2O5-shell nanowires were synthesized by the thermal evaporation of ZnSe powders on gold-coated Si (100) substrates followed by the sputter depositon of V2O5. Scanning electron microscopic images showed that the core-shell nanowires were a few tens to a few hundreds of nanometers in diameter and a few hundreds of micrometers in length. Transmission electron microscopy and X-ray diffraction analyses revealed that the core and shell of the core-shell nanowires were single crystal wurtzite-structured ZnSe and amorphous V2O5, respectively. Photoluminescence measurement showed that the core-shell nanowires as-synthesized or annealed in an oxidative atmosphere had a green emission band centered at around 520 nm whereas the as-synthesized ZnSe nanowires and the ZnSe-core/V2O5-shell nanowires annealed in a reducing atmosphere had a yellow emission band centered at around 590 nm. Our results also showed that V2O5 capping with an optimal thickness and subsequent annealing in a reducing atmosphere could significantly enhance the emission intensity of the ZnSe nanowires. In addition, the origins of the enhancement in intensity and the blue shift of the major emission by V2O5 capping are discussed.

The structure and photoluminescence properties of Bi2O3-core/SnO2-shell nanowires.

Bi2O3-core/SnO2-shell nanowires have been prepared by using a two-step process: thermal evaporation of Bi2O3 powders and sputtering of SnO2. The crystalline nature of the Bi2O3-core/SnO2-shell nanowires has been revealed by high resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED). TEM analysis and X-ray diffraction (XRD) results indicate that the Bi2O3-core/SnO2-shell nanowires consist of pure tetragonal alpha-Bi2O3-phase momocrystalline cores and tetragonal SnO2-phase polycrystalline shells. The photoluminescence (PL) measurements show that Bi2O3 nanowires have a broad emission band centered at around 560 nm in the yellow-green region. On the other hand, the Bi2O3-core/SnO2-shell coaxial nanowires with the sputtering times of 4 and 8 min have a blue emission band centered at around 450 nm. In contrast, those with a sputtering time of 10 min have a broad emission band centered at approximately 550 nm again. The origin of this yellow-green emission from the core/shell nanowires, however, quite differs from that from Bi2O3 nanowires, i.e., it is not from the Bi2O3 cores but from the SnO2 shells.

Chemical and Biological Profiles of Dendrobium in Two Different Species, Their Hybrid, and Gamma-Irradiated Mutant Lines of the Hybrid Based on LC-QToF MS and Cytotoxicity Analysis.

The Dendrobium species (Orchidaceae) has been cultivated as an ornamental plant as well as used in traditional medicines. In this study, the chemical profiles of Dendrobii Herba, used as herbal medicine, Dendrobium in two different species, their hybrid, and the gamma-irradiated mutant lines of the hybrid, were systematically investigated via ultra-performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry (UPLC-QToF MS). Among the numerous peaks detected, 17 peaks were unambiguously identified. Gigantol (1), (1R,2R)-1,7-hydroxy-2,8-methoxy-2,3-dihydrophenanthrene-4(1H)-one (2), tristin (3), (-)-syringaresinol (4), lusianthridin (5), 2,7-dihydroxy-phenanthrene-1,4-dione (6), densiflorol B (7), denthyrsinin (8), moscatilin (9), lusianthridin dimer (10), batatasin III (11), ephemeranthol A (12), thunalbene (13), dehydroorchinol (14), dendrobine (15), shihunine (16), and 1,5,7-trimethoxy-2-phenanthrenol (17), were detected in Dendrobii Herba, while 1, 2, and 16 were detected in D. candidum, 1, 11, and 16 in D. nobile, and 1, 2, and 16 in the hybrid, D. nobile × candidum. The methanol extract taken of them was also examined for cytotoxicity against FaDu human hypopharynx squamous carcinoma cells, where Dendrobii Herba showed the greatest cytotoxicity. In the untargeted metabolite analysis of 436 mutant lines of the hybrid, using UPLC-QToF MS and cytotoxicity measurements combined with multivariate analysis, two tentative flavonoids (M1 and M2) were evaluated as key markers among the analyzed metabolites, contributing to the distinction between active and inactive mutant lines.

Experimental study of superheating of tin powders.

An unstable energy-unbalanced state such as superheating or supercooling is often unexpectedly observed because a factor of energy depends not only on the temperature but is a product of temperature (T) and entropy (S). Thus, at the same temperature, if the entropy is different, the total energy of the system can be different. In such cases, the temperature-change-rate cannot match the entropy-change-rate, which results in a hysteresis curve for the temperature/entropy relationship. Due to the difference between the temperature- and entropy-change-rates, properties of a material, such as the boiling and freezing points, can be extended from point to area. This study confirmed that depending on the heating rate, tin powders exhibit different melting points. Given the contemporary reinterpretation of many energy-non-equilibrium phenomena that have only been discussed on the basis of temperature, this study is expected to contribute to the actual expansion of scientific/engineering applications.

Interface treatment using amorphous-carbon and its applications.

Breakthrough process technologies have been introduced that can increase the chemical sensitivity of an interface at which reactions occur without significantly altering the physico-chemical properties of the material. Such an interfacial treatment method is based on amorphous-carbon as a base so that fluids can be deposited, and the desired thickness and quality of the deposition can be ensured irrespective of the interface state of the material. In addition, side effects such as diffusion and decreasing strength at the interface can be avoided. This is simpler than existing vacuum-based deposition technology and it has an unmatched industrial advantage in terms of economics, speed, accuracy, reliability, accessibility, and convenience. In particular, this amorphous-carbon interface treatment technology has been demonstrated to improve gas-sensing characteristics of NO2 at room temperature.

Synthesis of Au/SnO2 nanostructures allowing process variable control.

Theoretical advances in science are inherently time-consuming to realise in engineering, since their practical application is hindered by the inability to follow the theoretical essence. Herein, we propose a new method to freely control the time, cost, and process variables in the fabrication of a hybrid featuring Au nanoparticles on a pre-formed SnO2 nanostructure. The above advantages, which were divided into six categories, are proven to be superior to those achieved elsewhere, and the obtained results are found to be applicable to the synthesis and functionalisation of other nanostructures. Furthermore, the reduction of the time-gap between science and engineering is expected to promote the practical applications of numerous scientific theories.

Fast Semiconductor-Metal Bidirectional Transition by Flame Chemical Vapor Deposition.

A simple yet powerful flame chemical vapor deposition technique is proposed that allows free control of the surface morphology, microstructure, and composition of existing materials with regard to various functionalities within a short process time (in seconds) at room temperature and atmospheric pressure as per the requirement. Since the heat energy is directly transferred to the material surface, the redox periodically converges to the energy dynamic equilibrium depending on the energy injection time; therefore, bidirectional transition between the semiconductor/metal is optionally available. To demonstrate this, a variety of Sn-based particles were created on preformed SnO2 nanowires, and this has been interpreted as a new mechanism for the response and response times of gas-sensing, which are representative indicators of the most surface-sensitive applications and show one-to-one correspondence between theoretical and experimental results. The detailed technologies derived herein are clearly influential in both research and industry.

New type of doping effect via metallization of surface reduction in SnO2.

The use of conventional doping methods requires consideration of not only the energy connection with the base material but also the limits of the type and doping range of the dopant. The scope of the physico-chemical change must be determined from the properties of the base material, and when this limit is exceeded, a large energy barrier must be formed between the base material and the dopant as in a heterojunction. Thus, starting from a different viewpoint, we introduce a so-called metallization of surface reduction method, which easily overcomes the disadvantages of existing methods while having the effect of doping the base material. Such new synthetic techniques enable sequential energy arrangements-gradients from the surface to the centre of the material-so that free energy transfer effects can be obtained as per the energies in the semiconducting band, eliminating the energy discontinuity of the heterojunction.