Light diffraction on acoustophotorefractive holographic gratings

The intermediate regime of light diffraction on acoustophotorefractive holographic gratings written in cubic photorefractive crystals according to the synchronous-detection mechanism is studied. It is shown that the diffraction efficiency in sillenite-type gyrotropic crystals only slightly depends on the incident light polarization and the external electric field. The highest diffraction efficiency in nongyrotropic crystals was achieved for p-polarized writing and reading light and at a considerable external electric field strength.     

Far UVC light for E. coli disinfection generated by carbon nanotube cold cathode and sapphire anode

Ultraviolet germicidal irradiation (UVGI) is an effective technique that can sterilize bacteria and viruses by UV light. Far UVC lamps of short wavelengths can prevent infectious diseases because they sterilize while minimizing cell damage in mammals. Here, E. coli inactivation by far UVC light with peak wavelength of 230 nm made of carbon nanotube (CNT) emitters and sapphire anode was studied. The κ-Al₂O₃ phase of sapphire with a direct band gap of 5.4 eV was excited with CNT-based cold cathode electron beam (C-beam) to generate far UVC light. It was confirmed that the inactivation of E. coli by far UVC light based on the C-beam was reduced by 5 log reduction within 60 s.     

Regular domain structures fabricated by an electron beam in stoichiometric LiNbO3 crystals

Electron beam writing of regular domain structures in Z-cuts 0.75 mm thick of stoichiometric and close to stoichiometric LiNbO₃ crystals has been carried out. Crystals have been grown by the Czochralski method from a melt with excess Li₂O (58.6 mol %) and from a congruent-composition melt in the presence of 6 wt % K₂O alkali solvent (flux). In both crystals, threshold charge doses required to form individual domains have been determined, and the optimal conditions of periodic structure patterning by sequential local irradiations have been found. Domain gratings of similar type (with periods of 6.5, 7, and 10 ??m) are formed in both types of stoichiometric crystals.     

Detection of bacteria aided by immuno‐nanoparticles

Magnetic immuno‐nanorice particles were used for the capture and detection of Escherichia coli (E. coli) bacteria. The selectivity of the method was attained by attaching a specific anti‐E. coli antibody on the surface of the nanorice, binding exclusively to E. coli. The antibody attachment to the nanorice (60% sorption efficiency) took place through protein‐A molecules (82% uptake). Once E. coli was captured, the immuno‐nanorice‐bacteria complex was separated from the solution using the magnetic property of the nanorice. The detection of bacteria sorbed onto the immuno‐nanorice was accomplished using the ultra‐violet resonance Raman (UVRR) method, detecting single bacterial cells. Specific information concerning the aromatic residues tyrosine (Tyr), phenylalanine (Phe) and tryptophan (Trp) was derived. The discriminant function and cluster hierarchical analysis confirmed the specific and reliable bacteria‐detection capabilities. Copyright © 2007 John Wiley & Sons, Ltd.     

SOS response dynamics in Escherichia coli bacterial cells upon ultraviolet irradiation

A mathematical model of induced mutations in Escherichia coli bacterial cells upon ultraviolet irradiation is developed. The concentration dynamics of inducible protein complexes synthesized in the course of the SOS response of E. coli is described. The mutation induction at translesion synthesis is studied. The solutions to the model are based on experimental data concerning the expression of the main genes of the SOS system of E. coli bacteria.     

Position-controlled and catalyst-free growth of ZnO nanocrystals by nanoparticle-assisted pulsed laser deposition

We have synthesized ZnO nanocrystals, such as nanowires, nanorods, and nanosheets, using a nanoparticle-assisted pulsed laser deposition (NAPLD) method. Recently, we achieved position-controlled growth of the ZnO nanocrystals by means of a ZnO buffer layer and laser irradiation without any catalyst. The periodic structure was formed on the ZnO buffer layer by multi-beam interference patterning, and then vertically aligned ZnO nanowalls, corresponding to the patterning, were grown on the buffer layer. It was found that the periodic ZnO nanowalls grew along the c-axis direction by X-ray diffraction measurement. The well-aligned ZnO nanowalls are expected to be utilized as building blocks for field emitters and UV LEDs. The proposed technique can be used as one of the effective methods to control the growth position of the ZnO nanocrystals because various structures can be easily fabricated by a laser writing and a spatial light modulator.     

Time-dependent growth of crystalline Au0-nanoparticles in cyanobacteria as self-reproducing bioreactors: 1. Anabaena sp.

In the experiments, multifunctional nanocomposites with fluorescence, superparamagnetism, and bioactivity were synthesized to isolate and detect bacteria. Fluorescent-magnetic nanocomposites (FMNPs) (Fe₃O₄@SiO₂@FITC–SiO₂, core/shell) were first synthesized. Then, FMNPs were conjugated with N-hydroxysuccinimide-activated 4-oxo-4-(prop-2-ynyloxy) butanoic acid (NHS-activated ester) by the linker of 3-aminopropyltriethoxysilane, and alkyne-functionalized fluorescent-magnetic nanocomposites (FMNPs-alkyne) were produced. After 3′-azidopropyl-O-α-d-manno-pyranoside was grafted on the surface of FMNPs-alkyne by click chemistry, the final product—mannose derivatives-grafted fluorescent-magnetic nanocomposites (FMNPs-mannose) were obtained. Common techniques (Nuclear magnetic resonance, ESI mass spectra, etc.) indicated the successful synthesis of the target products. The results of scanning electron microscopy, transmission electron microscopy, and dynamic light scattering showed that FMNPs with one or more magnetic cores have regular structure with a diameter around 100 nm. Fluorescence spectra and fluorescence microscopy indicated that those nanocomposites exhibited strong and stable fluorescence property. FMNPs-mannose have a saturation magnization of 6.88 emu/g at room temperature. FMNPs-mannose were applied to adhere to Escherichia coli ATCC25722 and Staphylococcus aureus ATCC6538. The results showed that FMNPs-mannose were able to specifically adhere to E. coli ATCC25722. However, it had no effect with S. aureus ATCC6538. The obtained FMNPs-mannose will find its application in bacteria detection and separation.     

Development of high durability plasma filter for air circulating disinfection system

Deadly diseases are caused by pathogenic bacteria and viruses that spread, among other means, through air circulating systems; hence, it is important to focus on pathogen removal from the air before circulating air through the system. Our paper introduces a novel plasma-based filter that, when used in an air circulating system with particulate air filter, disinfects the air flow. This device, based on dielectric filter discharge (DFD) structure with low pressure drops, indicates easy installation into existing air circulating system. Its performance was evaluated in accordance with the specifications of duct used in hospitals, with consistent O₃ generation during 200 h showing high durability. Escherichia coli and Micrococcus luteus were used as the target airborne bacteria; the system exhibited a removal efficiency of approximately 99.99% on bacterial aerosols and continuous bactericidal action, demonstrating that the DFD system can be directly applied to existing air circulating systems.     

THz near-field measurements of metal structures

We report on electro-optic measurements of THz electric fields in the near-field of metal structures lying on GaP electro-optic sampling crystals. With (110) oriented crystals, the x or y component of the THz electric field is measured, whereas with a (001) oriented crystal, the z-component is measured. With an estimated spatial resolution of 20 μm, the technique allows us to map the field on a scale, orders of magnitude smaller than the spatial dimensions of these structures. We illustrate the technique by showing results of measurements of the THz electric field in a plane underneath a metal sphere and a single square hole in a metal foil. The technique provides us with a wealth of information on the time-evolution of light fields near metal structures. To cite this article: A.J.L. Adam et al., C. R. Physique 9 (2008).     

Patterning of nanoparticulate transparent conductive ITO films using UV light irradiation and UV laser beam writing

Indium tin oxide (ITO) thin film is one of the most widely used as transparent conductive electrodes in all forms of flat panel display (FPD) and microelectronic devices. Suspension of already crystalline conductive ITO nanoparticles fully dispersed in alcohol was spun, after modifying with coupling agent, on glass substrates. The low cost, simple and versatile traditional photolithography process without complication of the photoresist layer was used for patterning ITO films. Using of UV light irradiation through mask and direct UV laser beam writing resulted in an accurate linear, sharp edge and very smooth patterns. Irradiated ITO film showed a high transparency (∼85%) in the visible region. The electrical sheet resistance decrease with increasing time of exposure to UV light and UV laser. Only 5 min UV light irradiation is enough to decrease the electrical sheet resistance down to 5 kΩ□.     

Photoreflectance study on the photovoltaic effect in InAs/GaAs quantum dot solar cell

To investigate the effect of quantum dot (QD) layers on the photovoltaic process of InAs/GaAs QD solar cell (QDSC), QD layers were embedded in conventional GaAs p-n junction SC (GaAs SC) structures. The photoreflectance (PR) was examined at different temperatures (T) and excitation light intensities (I_ex) to investigate the photovoltaic effects through observation of the Franz-Keldysh oscillations (FKOs) in the PR spectra. The evaluated the p-n junction electric fields (F_pn) of the InAs QDSC was different from that of the GaAs SC. Moreover, InAs QDSC show that the different photovoltaic behaviors compared with GaAs SC by varying I_ex and T. From these considerations, we suggest that the different photovoltaic behaviors are caused by the effect of the additional photo-carrier generation in InAs QD layers resulting in enhancement of the field screening effect in F_pn.     

Self-modulation of infrared waves in rutile

Electromagnetic waves carry angular and linear momentums and exert torques on anisotropic dielectrics, arising from the fact of the tensor property of the dielectric constant, that is, the direction of electric displacement is not parallel to the electric field vector of the incident light. The torque per unit volume exerted on a wave plate is given by P×E$\mathit{P}\times \mathit{E}$, where P is the polarization and E is the electric field, which induces the rotations of eigenvibration direction in the crystals. The rotation angles increase with the intensity of the incident light and the dielectric constant of the crystals. Because of the large dielectric constants, self-modulation of the incident light in the infrared frequency region was clearly demonstrated in the infrared transmission spectra of ferroelectric and piezoelectric crystals. Rutile (TiO₂) is a non-ferroelectric and non-piezoelectric crystal, but it also has the large dielectric constants. Rotations of the vibration direction of the ordinary (o-ray) and the extraordinary (e-ray) waves were shown in the infrared transmission spectra recorded by incidence of the plane-polarized light and transmission through a rutile plate. Interference of the o-ray and the e-ray waves transmitted through the crystals confirms the rotations of eigenvibration direction, a self-modulation effect of light in the crystal of large dielectric constants and large birefringence in the infrared range.     

Direct writing of micro/nano-scale patterns by means of particle lens arrays scanned by a focused diode pumped Nd:YVO4 laser

A practical approach to a well-known technique of laser micro/nano-patterning by optical near fields is presented. It is based on surface patterning by scanning a Gaussian laser beam through a self-assembled monolayer of silica micro-spheres on a single-crystalline silicon (Si) substrate. So far, the outcome of this kind of near-field patterning has been related to the simultaneous, parallel surface-structuring of large areas either by top hat or Gaussian laser intensity distributions. We attempt to explore the possibility of using the same technique in order to produce single, direct writing of features. This could be of advantage for applications in which only some areas need to be patterned (i.e. local area selective patterning) or single lines are required (e.g. a particular micro/nano-fluidic channel). A diode pumped Nd:YVO₄ laser system (wavelength of 532 nm, pulse duration of 8 ns, repetition rate of 30 kHz) with a computer-controlled 3 axis galvanometer beam scanner was employed to write user-defined patterns through the particle lens array on the Si substrate. After laser irradiation, the obtained patterns which are in the micro-scale were composed of sub-micro/micro-holes or bumps. The micro-pattern resolution depends on the dimension of both the micro-sphere’s diameter and the beam’s spot size. The developed technique could potentially be employed to fabricate photonic crystal structures mimicking nature’s butterfly wings and anti-reflective “moth eye” arrays for photovoltaic cells.     

The use of photoinduced light scattering for the evaluation of photoelectric fields in Lithium Niobate Crystals

The photovoltaic and diffusion fields in nominally pure single crystals of stoichiometric composition (R = Li/Nb = 1) grown from the melt with 58.6 mol % of Li₂O (LiNbO₃ stoich), in the nominally pure single crystals of congruent composition (LiNbO₃), and in congruent single crystals doped with Cu²⁺, Zn²⁺, and Gd³⁺ are found from the parameters of the photoinduced light scattering indicatrix obtained with the use of a 60-mW He-Ne laser.     

Self-assembly of dandelion-like Fe3O4@C@BiOCl magnetic nanocomposites with excellent solar-driven photocatalytic properties

In comparison with conventional organic dyes, quantum dots (QDs) have unique optical and electronic properties, which provide QDs with a wide scope of prospective application in biology and biomedicine. However, the toxicity of QDs and the fluorescence intensity of labeled bacteria must precede their application in bacterial imaging and tracing in vivo. Here, we show that treatment with CaCl₂ significantly improved bacterial labeling efficiency of CdSe/ZnS QDs with the CdSe core size of ~3.1 nm (relative fluorescence unit (RFU) value and ratio of fluorescent E. coli) with rising CdSe/ZnS QDs concentration in a concentration-dependent manner. At 12.5 nmol/L CdSe/ZnS QDs concentration, labeled Escherichia coli (E. coli) DH5α appeared as short rod-shaped and luminescent with normal size, and the survival rate and ultrastructure did not change in comparison to the control. But the ratio of fluorescent bacteria and RFU were very low. However, the survival rate of transformed E. coli was significantly inhibited by high CdSe/ZnS QDs concentrations (≥25 nmol/L). Moreover, internalization of CdSe/ZnS QDs resulted in ultrastructure damage of transformed E. coli in a concentration-dependent manner (≥25 nmol/L). Therefore, CdSe/ZnS QDs may not suitable for tracing of bacteria in vivo. Moreover, our study also revealed that colony-forming capability assay and transmission electron microscopy could be used to comprehensively evaluate the toxicity of QDs on labeled bacteria. Our findings do provide a new direction toward the improvement and modification of QDs for use in imaging and tracing studies in vivo.     

Neutron optics of noncentrosymmetric crystals: New possibility of searches for the neutron electric dipole moment and CP-violating forces

New neutron-optics effects, which were predicted and discovered quite recently in noncentrosymmetric crystals and which can be used to study the fundamental properties of the neutron, are discussed. In particular, strong electric fields of strength up to 10⁸ or 10⁹ V/cm may act in such crystals on the neutron, and this provides new possibilities for measuring the neutron electric dipole moment (EDM) by the crystal-diffraction method. It also becomes possible to perform searches for pseudomagnetic forces acting on neutrons and violating CP invariance. For the range of such forces that satisfies the condition λ _A < 10^?5 cm, the best constraints on the product of the scalar and pseudoscalar coupling constants have already been obtained for the interaction induced by the exchange of a light pseudoscalar (axion-like) particle. The present-day status and prospects of neutron-optics crystal-diffraction experiments aimed at searches for the neutron EDM and pseudomagnetic forces are considered.     

Tuning the band gap of self-assembled superparamagnetic photonic crystals in colloidal magnetic fluids using external magnetic fields

The model of tunable superparamagnetic photonic crystals self-assembled in colloidal magnetic fluids under externally applied magnetic fields is established. The mechanisms, which are in charge of the tunability of the band gaps with magnetic fields are clarified. The band structures of the triangularly-arrayed two-dimensional photonic crystals with limited heights of magnetic columns are calculated with the experimental data of structures and refractive indices in the literatures. The field-dependent properties of the first band gaps are gained for the z-odd and z-even modes, respectively. Simulation results indicate that the mid frequencies of the first band gaps of the z-odd modes can be easily tuned by the external magnetic fields, while those of the z-even modes bear relatively weak dependence on the external magnetic fields. Simultaneously, the first band gaps of both kinds of modes become wide along with the increase of the magnetic fields. The results presented in this work give a guideline for realizing the tunable photonic crystals with magnetically colloidal materials and magnetic stimuli.     

Stilbene composite scintillators as detectors of fast neutrons emitted by a 252Cf source

The results of the measurements are presented of the relative efficiency ε for ²⁵²Cf fast neutron detection by composite detectors based on stilbene crystalline grains. The effects of the grain size and height of the composite detector on its scintillation properties were studied. It is shown that the efficiency of fast neutron detection of stilbene composite scintillators ranges up to 60% of that of bulk single crystals. The results are also presented for relative light output measurements of stilbene composite detectors irradiated by gamma photons of ¹³⁷Cs, as well as transmittance data of samples in the range of their transparency absorption.     

Space‒time inhomogeneity of the electron flow in pyroelectric X-ray sources

The operating conditions of X-Ray sources based on LiNbO₃ crystals are investigated during heating-cooling cycles. It is demonstrated that the radiation intensity is unstable. The radiation is accompanied by electrical breakdowns in the Z plane of the crystals and emission of photon packets not described by the Poisson distribution. Visualization of the electron beam through the grid electrode by a luminescent screen showed that the electron beam is not uniform in the Z-plane of the crystal and greatly changes with temperature. It is found that, under definite conditions, the numerous redistributions of the intense emission zones occurred between different areas at Z-surface of the crystal. Possible reasons for the observed effects are examined. The obtained data are important for creating pyroelectric X-ray and neutron sources presuming the usage of strong electric fields whose strength reaches 10⁵ V/cm.