Epitaxial integration of perovskite-based multifunctional oxides on silicon

We review recent developments in the epitaxial integration of multifunctional oxide thin film heterostructures on silicon (Si). Perovskite oxides have been extensively studied for use in multifunctional devices due to a wide range of functional properties. To realize multifunctional oxide devices, these multifunctional films should be integrated directly on Si, maintaining high crystalline quality. Molecular beam epitaxy growth of epitaxial SrTiO₃ (STO) on Si provides a template for incorporating the epitaxial oxide films on Si. However, the dissimilar physical nature of Si from most oxide materials influences the properties of oxide films on Si, especially with regard to structural defects and thermal strains. Therefore, in this review, we present a comprehensive overview of epitaxial integration of various model oxide systems on Si, addressing how STO/Si can be used to explore the novel phenomenon of oxide heterostructures as well as to realize multifunctional devices.     

Development and application of a needle trap device for time-weighted average diffusive sampling

A simple, cost-effective analysis combining solventless extraction, thermal desorption, and determination of volatile organic compounds (VOCs) was developed and validated. A needle trap device (NTD) packed with the sorbent Carboxen1000 was used as a time-weighted average (TWA) diffusive sampler to collect target compounds by molecular diffusion and adsorption to the packed sorbent. This process can be described with derivations of Fick's first law of diffusion, which expresses the relation between the TWA concentrations to which the passive sampler is exposed and the mass of analytes adsorbed to the packed sorbent in the sampler. The effects of experimental factors such as temperature, pressure, humidity, and face velocity were taken into account in applying diffusive sampling under nonideal conditions. This study demonstrates that NTD is effective for air analysis of benzene, toluene, ethylbenzene, and o-xylene (BTEX), due to the good adsorption/desorption quality of Carboxen 1000 and to the special geometric shape of the needle with a small cross section avoiding the need for calibration. Storage tests showed good storage stability for BTEX. Verification of the theoretical model showed good agreement between theoretical and experimental sampling rates. Method validation done against NIOSH method 1501, SPME, and NTD active sampling revealed good agreement between those methods. Automated NTD sample introduction to a gas chromatograph facilitates the use of this technology for industrial hygiene applications.     

Nanomechanical characterization of chemical interaction between gold nanoparticles and chemical functional groups

Core/shell nanostructured carbon materials with carbon nanofiber (CNF) as the core and a nitrogen (N)-doped graphitic layer as the shell were synthesized by pyrolysis of CNF/polyaniline (CNF/PANI) composites prepared by in situ polymerization of aniline on CNFs. High-resolution transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared and Raman analyses indicated that the PANI shell was carbonized at 900°C. Platinum (Pt) nanoparticles were reduced by formic acid with catalyst supports. Compared to the untreated CNF/PANI composites, the carbonized composites were proven to be better supporting materials for the Pt nanocatalysts and showed superior performance as catalyst supports for methanol electrochemical oxidation. The current density of methanol oxidation on the catalyst with the core/shell nanostructured carbon materials is approximately seven times of that on the catalyst with CNF/PANI support. TEM tomography revealed that some Pt nanoparticles were embedded in the PANI shells of the CNF/PANI composites, which might decrease the electrocatalyst activity. TEM-energy dispersive spectroscopy mapping confirmed that the Pt nanoparticles in the inner tube of N-doped hollow CNFs could be accessed by the Nafion ionomer electrolyte, contributing to the catalytic oxidation of methanol.     

Mobile Robot Navigation Using Wireless Sensor Networks Without Localization Procedure

In this paper, algorithms for navigating a mobile robot through wireless sensor networks are presented. The mobile robot can navigate without the need for a map, compass, or GPS module while interacting with neighboring sensor nodes. Two navigation algorithms are proposed in this paper: the first uses the distance between the mobile robot and each sensor node and the second uses the metric calculated from one-hop neighbors’ hop-counts. Periodically measuring the distance or metric, the mobile robot can move toward a point where these values become smaller and finally come to reach the destination. These algorithms do not attempt to localize the mobile robot for navigation, therefore our approach permits cost-effective robot navigation while overcoming the limitations of traditional navigation algorithms. Through a number of experiments and simulations, the performance of the two proposed algorithms is evaluated.     

Continuous Control of Charge Transport in Bi‐Deficient BiFeO3 Films Through Local Ferroelectric Switching

It is demonstrated that electric transport in Bi‐deficient Bi_1‐δFeO₃ ferroelectric thin films, which act as a p‐type semiconductor, can be continuously and reversibly controlled by manipulating ferroelectric domains. Ferroelectric domain configuration is modified by applying a weak voltage stress to Pt/Bi_1‐δFeO₃/SrRuO₃ thin‐film capacitors. This results in diode behavior in macroscopic charge‐transport properties as well as shrinkage of polarization‐voltage hysteresis loops. The forward current density depends on the voltage stress time controlling the domain configuration in the Bi_1‐δFeO₃ film. Piezoresponse force microscopy shows that the density of head‐to‐head/tail‐to‐tail unpenetrating local domains created by the voltage stress is directly related to the continuous modification of the charge transport and the diode effect. The control of charge transport is discussed in conjunction with polarization‐dependent interfacial barriers and charge trapping at the non‐neutral domain walls of unpenetrating tail‐to‐tail domains. Because domain walls in Bi_1‐δFeO₃ act as local conducting paths for charge transport, the domain‐wall‐mediated charge transport can be extended to ferroelectric resistive nonvolatile memories and nanochannel field‐effect transistors with high performances conceptually.     

Manufacture and quality evaluation of purple sweet potato Makgeolli vinegar using a 2-stage fermentation

Purple sweet potato makgeolli vinegar made using a 2-stage fermentation method was evaluated. The highest alcohol concentration was 4% in a growth medium containing Acetobacter aceti ATCC 15973. Purple sweet potato makgeolli vinegar (PMV) had higher pH and lower acidity values than rice makgeolli vinegar (RMV). The total polyphenol content was 327.14 mg of GAE/L and the DPPH radical scavenging activity was 67.63% for PMV. Both values were much higher than for RMV. The total polyphenol and the DPPH radical scavenging activities of PMV decreased slowly during storage for 20 days, showing that stability of the antioxidant effect during storage was maintained.     

Development and validation of an analytical method for quantification of sulfuryl fluoride residues in agricultural products using gas chromatography with electron capture detection

Sulfuryl fluoride (SF) is used as a broad-spectrum fumigant due to toxicity against target pests, good dispersion, and a good penetrating ability. An analytical method for SF quantification in agricultural products was developed and validated to ensure food safety. SF residues were extracted from agricultural product samples using water in an airtight blender jar. Subsequently, an aliquot of the headspace was analyzed using capillary GC with an electron capture detector. Results were confirmed using GC-MS. The linear range of SF was 0.01–1.0 μg/mL with a correlation coefficient (r ²) of 0.999. Average SF recovery values ranged from 74.1 to 108.9% from spiked levels of 0.04–2.0 mg/kg, and the relative standard deviation was 0.5–6.8%. The limit of detection and the limit of quantification were 0.01 and 0.04 mg/L, respectively.     

Bacillus subtilis HJ18‐4 from Traditional Fermented Soybean Food Inhibits Bacillus cereus Growth and Toxin‐Related Genes

Bacillus subtilis HJ18‐4 isolated from buckwheat sokseongjang, a traditional Korean fermented soybean food, exhibits broad‐spectrum antimicrobial activity against foodborne pathogens, including Bacillus cereus. In this study, we investigated the antibacterial efficacy and regulation of toxin gene expression in B. cereus by B. subtilis HJ18‐4. Expression of B. cereus toxin–related genes (groEL, nheA, nheC, and entFM) was downregulated by B. subtilis HJ18‐4, which also exhibited strong antibacterial activity against B. cereus. We also found that water extracts of soy product fermented with B. subtilis HJ18‐4 significantly inhibited the growth of B. cereus and toxin expression. These results indicate that B. subtilis HJ18‐4 could be used as an antimicrobial agent to control B. cereus in the fermented soybean food industry. Our findings also provide an opportunity to develop an efficient biological control agent against B. cereus.     

Sketched oxide single-electron transistor

Devices that confine and process single electrons represent an important scaling limit of electronics. Such devices have been realized in a variety of materials and exhibit remarkable electronic, optical and spintronic properties. Here, we use an atomic force microscope tip to reversibly 'sketch' single-electron transistors by controlling a metal-insulator transition at the interface of two oxides. In these devices, single electrons tunnel resonantly between source and drain electrodes through a conducting oxide island with a diameter of ～1.5 nm. We demonstrate control over the number of electrons on the island using bottom- and side-gate electrodes, and observe hysteresis in electron occupation that is attributed to ferroelectricity within the oxide heterostructure. These single-electron devices may find use as ultradense non-volatile memories, nanoscale hybrid piezoelectric and charge sensors, as well as building blocks in quantum information processing and simulation platforms.     

Immobilization of aptamer-based molecular beacons onto optically-encoded micro-sized beads

This paper presents a method for the novel immobilization of aptamer-based molecular beacons (apta-beacons) onto optically-encoded micro-sized beads (apta-beacon beads). To immobilize apta-beacons onto flourescently-encoded micro-sized beads, core-shell type beads containing a fluorescent dye-encoded core and apta beacon-coupled shell were prepared. The fluorescent dye-encoded beads were prepared from TentaGel resins by coupling RITC to the amino groups of the core region, after partial protection of amino groups with Fmoc-OSu in a diffusion-controlled manner. After deprotection of the Fmoc-amino groups, FITC-coupled molecular beacons (MBs) were immobilized to the beads together with a quencher by covelent bonding. Briefly, aspartic acid (Asp) was coupled to the shell part of the beads. Then, the quencher was coupled to the N-terminal amino group of Asp and the MBs were coupled to the side chain carboxyl group. In a model study, thrombin was directly detected using this apta-beacon bead method. The thrombin-bound apta-beacon beads were easily recognized by the appearance of fluorescence without any further labeling step.