Microwave-induced release and degradation of airborne antibiotic resistance genes (ARGs) from Escherichia coli bioaerosol based on microwave absorbing material.

Antibiotic resistance genes (ARGs) have been detected in the atmosphere. Airborne ARGs transmission threatens human health. In the present study, we investigated the release and degradation of airborne ARGs from Escherichia coli bioaerosol through microwave (MW) irradiation. In this study, a new MW absorbing material (Fe3O4@SiC ceramic foam) that contributed to its stronger MW absorption is presented. When the MW input energy density was 7.4 × 103 kJ/m3, the concentration of airborne Escherichia coli decreased by 4.4 log. Different DNA forms were found in the air because MW irradiation ruptured cell membranes. The bound particles provide more protection for bound DNA in the degradation process than free DNA. After the self-degradation of the released airborne free ARGs, some of them would remain and continue to spread in the atmosphere. The released airborne free ARGs cannot be ignored. Total ARGs concentrations decrease rapidly with increased temperature. The inactivation rate constant of ARGs through MW irradiation is higher than that through the Fenton and UV, however, the energy efficiency per order of MW irradiation is lower. Therefore, MW irradiation with Fe3O4@SiC ceramic foam could efficiently degrade the distribution of ARGs in the atmosphere.

Sustained molecular oxygen activation by solid iron doped silicon carbide under microwave irradiation: Mechanism and application to norfloxacin degradation.

Sustained molecular oxygen activation by iron doped silicon carbide (Fe/SiC) was investigated under microwave (MW) irradiation. The catalytic performance of Fe/SiC for norfloxacin (NOR) degradation was also studied. Rapid mineralization in neutral solution was observed with a pseudo-first-order rate constant of 0.2239 min-1 under 540 W of MW irradiation for 20 min. Increasing Fe/SiC rod and MW power significantly enhanced the degradation and mineralization rate with higher yield of reactive oxygen species (ROS). Fe shell corrosion and subsequent Fe0/II oxidation by molecular oxygen with MW activation was the key factor for NOR degradation through two-electron-transfer by Fe0 under acidic conditions and single-electron-transfer by FeII under neutral-alkaline solution. Removal rate of NOR was significantly affected by solution pH, showing higher degradation rates at both acidic and alkaline conditions. The highest removal efficiencies and rates at alkaline pH values were ascribed to the contribution of bound FeII species on the Fe shell surface due to the hydroxylation of Fe/SiC. ·OH was the main oxidizing specie for NOR degradation, confirmed by density functional theory (DFT) calculations and radical scavenger tests. DFT calculations were conducted on the reaction/activation energies of the transition/final states of NOR/degradation products, combined with intermediate identification with high performance liquid chromatography coupled with a triple-quadruple mass spectrometer (HPLC-MS/MS), the piperazinyl ring was the most reactive site for ·OH attack, followed by further ring-opening and stepwise oxidation. In this study, Fe/SiC were proved to be an excellent catalyst for the treatment of fluoroquinolone antibiotics with MW activation.

Monte Carlo simulations of time-of-flight PET with double-ended readout: calibration, coincidence resolving times and statistical lower bounds.

This paper demonstrates through Monte Carlo simulations that a practical positron emission tomograph with (1) deep scintillators for efficient detection, (2) double-ended readout for depth-of-interaction information, (3) fixed-level analog triggering, and (4) accurate calibration and timing data corrections can achieve a coincidence resolving time (CRT) that is not far above the statistical lower bound. One Monte Carlo algorithm simulates a calibration procedure that uses data from a positron point source. Annihilation events with an interaction near the entrance surface of one scintillator are selected, and data from the two photodetectors on the other scintillator provide depth-dependent timing corrections. Another Monte Carlo algorithm simulates normal operation using these corrections and determines the CRT. A third Monte Carlo algorithm determines the CRT statistical lower bound by generating a series of random interaction depths, and for each interaction a set of random photoelectron times for each of the two photodetectors. The most likely interaction times are determined by shifting the depth-dependent probability density function to maximize the joint likelihood for all the photoelectron times in each set. Example calculations are tabulated for different numbers of photoelectrons and photodetector time jitters for three 3 × 3 × 30 mm3 scintillators: Lu2SiO5:Ce,Ca (LSO), LaBr3:Ce, and a hypothetical ultra-fast scintillator. To isolate the factors that depend on the scintillator length and the ability to estimate the DOI, CRT values are tabulated for perfect scintillator-photodetectors. For LSO with 4000 photoelectrons and single photoelectron time jitter of the photodetector J = 0.2 ns (FWHM), the CRT value using the statistically weighted average of corrected trigger times is 0.098 ns FWHM and the statistical lower bound is 0.091 ns FWHM. For LaBr3:Ce with 8000 photoelectrons and J = 0.2 ns FWHM, the CRT values are 0.070 and 0.063 ns FWHM, respectively. For the ultra-fast scintillator with 1 ns decay time, 4000 photoelectrons, and J = 0.2 ns FWHM, the CRT values are 0.021 and 0.017 ns FWHM, respectively. The examples also show that calibration and correction for depth-dependent variations in pulse height and in annihilation and optical photon transit times are necessary to achieve these CRT values.

Suppression of Photoanodic Surface Oxidation of n-Type 6H-SiC Electrodes in Aqueous Electrolytes.

The photoelectrochemical characterization of silicon carbide (SiC) electrodes is important for enabling a wide range of potential applications for this semiconductor. However, photocorrosion of the SiC surface remains a key challenge, because this process considerably hinders the deployment of this material into functional devices. In this report, we use cyclic voltammetry to investigate the stability of n-type 6H-SiC photoelectrodes in buffered aqueous electrolytes. For measurements in pure Tris buffer, photogenerated holes accumulate at the interface under anodic polarization, resulting in the formation of a porous surface oxide layer. Two possibilities are presented to significantly enhance the stability of the SiC photoelectrodes. In the first approach, redox molecules are added to the buffer solution to kinetically facilitate hole transfer to these molecules, and in the second approach, water oxidation in the electrolyte is induced by depositing a cobalt phosphate catalyst onto the semiconductor surface. Both methods are found to effectively suppress photocorrosion of the SiC electrodes, as confirmed by atomic force microscopy and X-ray photoelectron spectroscopy measurements. The presented study provides straightforward routes to stabilize n-type SiC photoelectrodes in aqueous electrolytes, which is essential for a possible utilization of this material in the fields of photocatalysis and multimodal biosensing.

Membrane thickness dependence of nanopore formation with a focused helium ion beam.

Solid-state nanopores are emerging as a valuable tool for the detection and characterization of individual biomolecules. Central to their success is the realization of fabrication strategies that are both rapid and flexible in their ability to achieve diverse device dimensions. In this paper, we demonstrate the membrane thickness dependence of solid-state nanopore formation with a focused helium ion beam. We vary membrane thickness in situ and show that the rate of pore expansion follows a reproducible trend under all investigated membrane conditions. We show that this trend shifts to lower ion dose for thin membranes in a manner that can be described quantitatively, allowing devices of arbitrary dimension to be realized. Finally, we demonstrate that thin, small-diameter nanopores formed with our approach can be utilized for high signal-to-noise ratio resistive pulse sensing of DNA.

Noise sources and improved performance of a mid-wave infrared uncooled silicon carbide optical photodetector.

An uncooled photon detector is fabricated for the mid-wave infrared (MWIR) wavelength of 4.21 µm by doping an n-type 4H-SiC substrate with gallium using a laser doping technique. The dopant creates a p-type energy level of 0.3 eV, which is the energy of a photon corresponding to the MWIR wavelength 4.21 µm. This energy level was confirmed by optical absorption spectroscopy. The detection mechanism involves photoexcitation of carriers by the photons of this wavelength absorbed in the semiconductor. The resulting changes in the carrier densities at different energy levels modify the refractive index and, therefore, the reflectance of the semiconductor. This change in the reflectance constitutes the optical response of the detector, which can be probed remotely with a laser beam such as a He-Ne laser and the power of the reflected probe beam can be measured with a conventional laser power meter. The noise mechanisms in the probe laser, silicon carbide MWIR detector, and laser power meter affect the performance of the detector in regards to aspects such as the responsivity, noise equivalent temperature difference (NETD), and detectivity. For the MWIR wavelengths of 4.21 and 4.63 µm, the experimental detectivity of the optical photodetector of this study was found to be 1.07×10(10) cm·Hz(1/2)/W, while the theoretical value was 1.11×10(10) cm·Hz(1/2)/W. The values of NETD are 404 and 15.5 mK based on experimental data for an MWIR radiation source with a temperature of 25°C and theoretical calculations, respectively.

Vertical integration of high-Q silicon nitride microresonators into silicon-on-insulator platform.

We demonstrate a vertical integration of high-Q silicon nitride microresonators into the silicon-on-insulator platform for applications at the telecommunication wavelengths. Low-loss silicon nitride films with a thickness of 400 nm are successfully grown, enabling compact silicon nitride microresonators with ultra-high intrinsic Qs (~ 6 × 10(6) for 60 µm radius and ~ 2 × 10(7) for 240 µm radius). The coupling between the silicon nitride microresonator and the underneath silicon waveguide is based on evanescent coupling with silicon dioxide as buffer. Selective coupling to a desired radial mode of the silicon nitride microresonator is also achievable using a pulley coupling scheme. In this work, a 60-µm-radius silicon nitride microresonator has been successfully integrated into the silicon-on-insulator platform, showing a single-mode operation with an intrinsic Q of 2 × 10(6).

Integrated TE and TM optical circulators on ultra-low-loss silicon nitride platform.

In this paper, we present two four-port optical circulators for TE and TM modes, respectively. Exploiting the recent technological development concerning Ce:YIG pulse laser deposition on silicon nitride platform, we design two integrated circulators, which can be used to implement several functions in integrated optics, such as de-interleavers, input/output amplifier isolators and output laser isolators. The proposed devices combine the benefit of low loss silicon nitride waveguides with the non-reciprocal properties of magneto-optical materials. The ring cross-section has been optimized in order to maximize the non-reciprocal phase shift and finally the scattering coefficients have been computed using the transfer matrix method. The material stability and refractive index regularity of silicon nitride, the small micro-ring footprint, and the high wavelength selectivity make these devices particularly attractive.

Third-harmonic UV generation in silicon nitride nanostructures.

We report on strong UV third-harmonic generation from silicon nitride films and resonant waveguide gratings. We determine the absolute value of third-order susceptibility of silicon nitride at wavelength of 1064 nm to be χ(³) (-3ω,ω,ω,ω) = (2.8 ± 0.6) × 10⁻²°m²/V², which is two orders of magnitude larger than that of fused silica. The third-harmonic generation is further enhanced by a factor of 2000 by fabricating a resonant waveguide grating onto a silicon nitride film. Our results extend the operating range of CMOS-compatible nonlinear materials to the UV spectral regime.

Epitaxial graphene nanoribbon array fabrication using BCP-assisted nanolithography.

A process for fabricating dense graphene nanoribbon arrays using self-assembled patterns of block copolymers on graphene grown epitaxially on SiC on the wafer scale has been developed. Etching masks comprising long and straight nanoribbon array structures with linewidths as narrow as 10 nm were fabricated, and the patterns were transferred to graphene. Our process combines both top-down and self-assembly steps to fabricate long graphene nanoribbon arrays with low defect counts. These are the narrowest nanoribbon arrays of epitaxial graphene on SiC fabricated to date.

High-efficiency electrochemical hydrogen evolution based on surface autocatalytic effect of ultrathin 3C-SiC nanocrystals.

Good understanding of the reaction mechanism in the electrochemical reduction of water to hydrogen is crucial to renewable energy technologies. Although previous studies have revealed that the surface properties of materials affect the catalytic reactivity, the effects of a catalytic surface on the hydrogen evolution reaction (HER) on the molecular level are still not well understood. Contrary to general belief, water molecules do not adsorb onto the surfaces of 3C-SiC nanocrystals (NCs), but rather spontaneously dissociate via a surface autocatalytic process forming a complex consisting of -H and -OH fragments. In this study, we show that ultrathin 3C-SiC NCs possess superior electrocatalytic activity in the HER. This arises from the large reduction in the activation barrier on the NC surface enabling efficient dissociation of H(2)O molecules. Furthermore, the ultrathin 3C-SiC NCs show enhanced HER activity in photoelectrochemical cells and are very promising to the water splitting based on the synergistic electrocatalytic and photoelectrochemical actions. This study provides a molecular-level understanding of the HER mechanism and reveals that NCs with surface autocatalytic effects can be used to split water with high efficiency thereby enabling renewable and economical production of hydrogen.

Si/InGaN core/shell hierarchical nanowire arrays and their photoelectrochemical properties.

Three-dimensional hierarchical nanostructures were synthesized by the halide chemical vapor deposition of InGaN nanowires on Si wire arrays. Single phase InGaN nanowires grew vertically on the sidewalls of Si wires and acted as a high surface area photoanode for solar water splitting. Electrochemical measurements showed that the photocurrent density with hierarchical Si/InGaN nanowire arrays increased by 5 times compared to the photocurrent density with InGaN nanowire arrays grown on planar Si (1.23 V vs RHE). High-resolution transmission electron microscopy showed that InGaN nanowires are stable after 15 h of illumination. These measurements show that Si/InGaN hierarchical nanostructures are a viable high surface area electrode geometry for solar water splitting.

Low divergence photonic nanojets from Si3N4 microdisks.

High intensity sub-wavelength spots and low divergence nanojets are observed in a system of Si3N4 microdisks illuminated from the side with laser light of wavelengths 488 nm, 532 nm and 633 nm. The disks are of height 400 nm with diameters ranging from 1µm to 10µm. Light scattered from the disk and substrate is observed by imaging from above. In free space light is focused inside the disks and a sub wavelength spot is observed, whereas in water the refractive index contrast is such that photonic nanojets are formed. The angular distribution of the intensity compares well to the analytical solution for the case of an infinite cylinder. Two distinct cases of scattering pattern are observed with even and odd numbers of lobes. Finally when the disks are illuminated with a focused Gaussian beam perpendicular to the substrate an extremely low divergence beam is observed. This beam has a divergence angle over 10 times smaller than a focused Gaussian in free space with the same waist.

Protein-repellent silicon nitride surfaces: UV-induced formation of oligoethylene oxide monolayers.

The grafting of polymers and oligomers of ethylene oxide onto surfaces is widely used to prevent nonspecific adsorption of biological material on sensors and membrane surfaces. In this report, we show for the first time the robust covalent attachment of short oligoethylene oxide-terminated alkenes (CH(3)O(CH(2)CH(2)O)(3)(CH(2))(11)-(CH═CH(2)) [EO(3)] and CH(3)O(CH(2)CH(2)O)(6)(CH(2))(11)-(CH═CH(2)) [EO(6)]) from the reaction of alkenes onto silicon-rich silicon nitride surfaces at room temperature using UV light. Reflectometry is used to monitor in situ the nonspecific adsorption of bovine serum albumin (BSA) and fibrinogen (FIB) onto oligoethylene oxide coated silicon-rich silicon nitride surfaces (EO(n)-Si(x)N(4), x > 3) in comparison with plasma-oxidized silicon-rich silicon nitride surfaces (SiO(y)-Si(x)N(4)) and hexadecane-coated Si(x)N(4) surfaces (C(16)-Si(x)N(4)). A significant reduction in protein adsorption on EO(n)-Si(x)N(4) surfaces was achieved, adsorption onto EO(3)-Si(x)N(4) and EO(6)-Si(x)N(4) were 0.22 mg m(-2) and 0.08 mg m(-2), respectively. The performance of the obtained EO(3) and EO(6) layers is comparable to those of similar, highly protein-repellent monolayers formed on gold and silver surfaces. EO(6)-Si(x)N(4) surfaces prevented significantly the adsorption of BSA (0.08 mg m(-2)). Atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), X-ray reflectivity and static water contact angle measurements were employed to characterize the modified surfaces. In addition, the stability of EO(6)-Si(x)N(4) surfaces in phosphate-buffered saline solution (PBS) and alkaline condition (pH 10) was studied. Prolonged exposure of the surfaces to PBS solution for 1 week or alkaline condition for 2 h resulted in only minor degradation of the ethylene oxide moieties and no oxidation of the Si(x)N(4) substrates was observed. Highly stable antifouling coatings on Si(x)N(4) surfaces significantly broaden the application potential of silicon nitride-coated microdevices, and in particular of microfabricated filtration membranes.

Enhanced electroluminescence from SiN-based multilayer structure by laser crystallization of ultrathin amorphous Si-rich SiN layers.

Luminescent SiN-based multilayers were prepared in a plasma enhanced chemical vapor deposition system followed by subsequently laser crystallization of ultrathin amorphous Si-rich SiN sublayers. The cross-sectional TEM analysis reveals that grain size of Si nanocrystals embedded in the Si-rich SiN sublayers is independent of the laser fluence, while the grain density can be well controlled by the laser fluence. The devices containing the laser crystallized multilayers show a low turn-on voltage of 5 V and exhibit strong green light emission under both optical and electrical excitations. Moreover, the device after laser-irradiated at 554 mJ/cm(2) shows a significantly enhanced EL intensity as well as external quantum efficiency compared with the device without laser irradiation. The EL mechanism is suggested from the bipolar recombination of electron-hole pairs at Si nanocrystals. The improved performance of the devices was discussed.

Studies on destruction of silicon tetrachloride using microwave plasma jet.

A new method for destroying silicon tetrachloride has been proposed, which is based on a microwave plasma jet that operates at atmospheric pressure using hydrogen as work gas. The influence of input power (P) and silicon tetrachloride concentration (phi) on the percent destruction and removal of SiCl(4) was investigated. And the reclaimed solid byproducts were characterized by SEM, EDX and XRD. Species in the plasma, which were identified by atomic emission spectroscopy were found to include no halogen. Results indicate that the destruction efficiency of silicon tetrachloride can reach 96% when P=800 W and phi=1.0%, and the main solid byproduct was Si. The silicon deposited on the molybdenum substrate of the plasma reactor was yellow and typical nano-sized particles with grain size of 54 nm.

The controlled fabrication of nanopores by focused electron-beam-induced etching.

The fabrication of nanometric holes within thin silicon-based membranes is of great importance for various nanotechnology applications. The preparation of such holes with accurate control over their size and shape is, thus, gaining a lot of interest. In this work we demonstrate the use of a focused electron-beam-induced etching (FEBIE) process as a promising tool for the fabrication of such nanopores in silicon nitride membranes and study the process parameters. The reduction of silicon nitride by the electron beam followed by chemical etching of the residual elemental silicon results in a linear dependence of pore diameter on electron beam exposure time, enabling accurate control of nanopore size in the range of 17-200 nm in diameter. An optimal pressure of 5.3 x 10(-6) Torr for the production of smaller pores with faster process rates, as a result of mass transport effects, was found. The pore formation process is also shown to be dependent on the details of the pulsed process cycle, which control the rate of the pore extension, and its minimal and maximal size. Our results suggest that the FEBIE process may play a key role in the fabrication of nanopores for future devices both in sensing and nano-electronics applications.

Polymeric synthesis of silicon carbide with microwaves.

The aim of this work is conducting polymeric synthesis with microwaves for producing beta-SiC. A polymeric precursor was prepared by means of hydrolysis and condensation reactions from pheniltrimethoxysilane, water, methanol, ammonium hydroxide and chloride acid. The precursor was placed into a quartz tube in vacuum; pyrolysis was carried out conventionally in a tube furnace, and by microwaves at 2.45 GHz in a multimode cavity. Conventional tests took place in a scheme where temperature was up to 1500 degrees C for 120 minutes. Microwave heating rate was not controlled and tests lasted 60 and 90 minutes, temperature was around 900 degrees C. Products of the pyrolysis were analyzed by means of x-ray diffraction; in the microwave case the diffraction patterns showed a strong background of either very fine particles or amorphous material, then infrared spectroscopy was also employed for confirming carbon bonds. In both processes beta-SiC was found as the only produced carbide.

Electron beam induced structural transformations of SWNTs and DWNTs grown on Si3N4/Si substrates.

Electron beam induced structural transformations are investigated in single-wall carbon nanotubes (SWNTs), double-wall carbon nanotubes (DWNTs) and crossed nanotube junctions. The nanotubes studied here are synthesized by the chemical vapor deposition method. The response of the nanotubes to an electron beam is found to be influenced by the presence of coatings of amorphous carbon, graphene fragments and structural defects on the tube surface. The dependence of structural modifications on electron beam irradiation dose is measured. While nanotubes with amorphous carbon, graphene fragment coverage and/or defects undergo rapid transformation leading to structure disintegration, those without such coverage or defects are more resistant to beam damage. In addition, it is shown that the amorphous carbon coverage on the double-wall nanotubes can be transformed into graphene layers during electron beam irradiation of coated nanotubes. Finally, the relative stability of nanotube side-wall and end-walls are investigated through sub-threshold energy and above threshold energy irradiation of a model system, C60-filled nanotubes (Peapods). The data indicates that electron beams could be used to join nanotubes end-to-end without damaging the side-walls.