Photoluminescence and optical transmission of diamond and its imitators

Photoluminescence and optical transmission spectra of several samples of natural and synthetic diamond and its imitators - fianite and corundum - are investigated. The band-A of luminescence at 440 nm, the vibronic N3 system of luminescence and absorption at 415.2 nm, the fundamental absorption edge at 225 nm, and the secondary absorption below 308 nm are the main identifying markers of natural diamonds. For synthetic diamonds, however, such identifying markers are the free-exciton luminescence at 235 nm, the band-A, and the fundamental absorption edge. Fianites can be identified by the structureless wideband at 500 nm and the wide transmission band in the entire visible range. Colored corundum samples with chrome impurities emit the narrow line at 693 nm and show the absorption band in the 500-600 nm spectral range. A new method for diamond express identification is developed on the basis of measurement of photoluminescence and optical transmission spectra of the samples. It is shown that a diamond tester can be designed combining a spectrometer and a KrCl-excilamp radiating at 222 nm.     

Observation of simultaneous reverse saturation absorption and saturation absorption in silver nanoparticles incorporated into europium oxide thin film

In this work, nano silver clusters incorporated into europium oxide thin films at a level of 3.8% and 12.5% have been prepared by a vacuum evaporation method on glass and silicon substrates. Samples were investigated by X-ray fluorescence, X-ray diffraction, and linear and nonlinear optical absorption methods. The X-ray diffraction reveals that the Eu oxide of these samples remains amorphous after pre-annealing at 400 °C. The linear optical absorption of the samples shows surface plasmon resonance (SPR) phenomena, which varies with the Ag content of the samples. The optical nonlinear absorption properties of the prepared films were investigated using an open Z-scan technique with cw laser at wavelengths 476 nm and 514 nm. A changeover from reverse saturation absorption (RSA) to saturation absorption (SA) was observed. RSA is attributed to interband transition via two photon absorption. SA is attributed to plasmon bleach.     

Ultrathin Fe layers on Ag (1 0 0) surface

Iron layers (0.15-10 ML thick) deposited on Ag (1 0 0) substrates were investigated by conversion electron Mössbauer spectrometry over a broad temperature range. The layers were characterized by scanning tunneling microscopy. Different forms of the layers, depending on their thickness, were observed. Minimum roughness of the layers were found at 0.15 and 10 ML thickness values. The Mössbauer spectra showed systematic thickness dependence. At low thickness values, broad doublets were observed, while above 6 ML, magnetic split spectra appeared at room temperature. At low temperatures, magnetically split spectra appeared with parameter values characteristic of Fe-Ag and Fe-Fe atomic interactions. The hyperfine split spectra indicated magnetic anisotropy and an enhanced saturation hyperfine magnetic field of ?40 T. The latter value is the highest ever measured for iron in thin layers.     

A facile and environmentally friendly chemical route for the synthesis of metastable VO2 nanobelts

Metastable VO₂ nanobelts, designated as VO₂ (B), were successfully fabricated by a facile hydrothermal route in the presence of V₂O₅ and glucose. The samples were characterized by X-ray diffraction (XRD), X-ray photoelectron spectra (XPS), transmission electron microscopy (TEM), selected area electronic diffraction (SAED), high-resolution transmission electron microscopy (HRTEM) and scanning electron microscopy (SEM) techniques. The main synthesis parameters such as temperature, reaction time and molar ratio of the starting materials have been also discussed. The results showed that pure B phase VO₂ nanobelts with high crystallinity can be prepared easily at 180 °C in 24 h at the molar ratio of V₂O₅:glucose=1:1. Typically, the belt-like products were 0.6-1.2 μm long, 80-150 nm wide and 20-30 nm thick. It is noted that the whole process is free of any harmful reducing reagents and surfactants, and valuable gluconic acid can be formed as the main by-product. From an economic and environmental point of view, the present approach is particularly fit for the synthesis of VO₂ (B) nanobelts on a large scale.     

Optical band gap of zinc nitride films prepared on quartz substrates from a zinc nitride target by reactive rf magnetron sputtering

Polycrystalline zinc nitride films have been synthesized onto quartz substrates from the zinc nitride target and the nitrogen working gas by reactive rf magnetron sputtering at room temperature. X-ray diffraction study indicates that polycrystalline zinc nitride films are of cubic structure with the lattice constant a = 0.979(1) nm and have preferred orientations with (3 2 1) and (4 4 2). Its absorption coefficients as well as the film thickness are calculated from the transmission spectra, which are measured with a double beam spectrophotometer. The optical band gap has been determined from the photon energy dependence of absorption coefficient, an indirect transition optical band gap of 2.12(3) eV has been obtained.     

Investigation of the structural distortion in FeSex crystals by X-ray absorption near edge structures (XANES) spectroscopy

Crystals of the new superconductor FeSe were investigated by X-ray absorption near edge structures spectroscopy (XANES) in the temperature range 300-77 K. Crystals with Se content varying from x=1-0.8 were used. The Fe K-edge spectra show a structure distortion and increase in hole content as x decreases. The Fe K-edge spectra also show changes when the crystals are cooled to 100 K which may be related to the orthorhombic distortion reported in these crystals. The data is examined in conjunction with XRD measurements on the crystals to seek a correlation.     

Effects of the sputtering time of ZnO buffer layer on the quality of GaN thin films

ZnO thin films with different thickness (the sputtering time of ZnO buffer layers was 10 min, 15 min, 20 min, and 25 min, respectively) were first prepared on Si substrates using radio frequency magnetron sputtering system and then the samples were annealed at 900 °C in oxygen ambient. Subsequently, a GaN epilayer about 500 nm thick was deposited on ZnO buffer layer. The GaN/ZnO films were annealed in NH₃ ambient at 950 °C. X-ray diffraction (XRD), atom force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and photoluminescence (PL) were used to analyze the structure, morphology, composition and optical properties of GaN films. The results show that their properties are investigated particularly as a function of the sputtering time of ZnO layers. For the better growth of GaN films, the optimal sputtering time is 15 min.     

Optical properties of cadmium sulfide nanocrystal film prepared by electrochemical synthesis at liquid-liquid interface

Dendritic nanocrystalline CdS film was deposited at liquid-liquid interface of surfactants and an electrolyte containing 4 mmol L⁻¹ cadmium chloride (CdCl₂) and 16 mmol L⁻¹ thioacetamide (CH₃CSNH₂) with an initial pH value of 5 at 15 °C by electrochemical synthesis. The nanofilm was characterized by transmission electron microscopy (TEM), field emission scanning electron microscope (FE-SEM), atomic force microscopy (AFM), ultraviolet visible (UV-vis) absorption spectroscopy and fluorescence spectroscopy. The surface morphology and particle size of the nanofilm were investigated by AFM, SEM and TEM, and the crystalline size was 30-50 nm. The thickness of the nanofilm calculated by optical absorption spectrum was 80 nm. The microstructure and composition of the nanofilm was investigated by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), showing its polycrystalline structure consisting of CdS and Cd. Optical properties of the nanofilm were investigated systematically by UV-vis absorption and fluorescence spectroscopy. A λ_onset blue shift compared with bulk CdS was observed in the absorption spectra. Fluorescence spectra of the nanofilm indicated that the CdS nanofilm emitted blue and green light. The nanocomposites film electrode will bring about anodic photocurrent during illumination, showing that the transfer of cavities produces photocurrent.     

Surface enhanced infrared absorption on Au nanoparticle films deposited on SiO2/Si for optical biosensing: Detection of the antibody-antigen reaction

The specific antibody-antigen reaction was detected by taking advantage of the effect of surface enhanced infrared absorption (SEIRA). For the SEIRA active film, single Au nanoparticles (AuNP) deposited on the SiO₂/Si wafer surface were used. After immobilizing specific antibodies onto the AuNP, these samples were then exposed to specific antigens (unspecific antigens, respectively); then the samples were investigated with infrared spectroscopy. In addition, the same kind of sample preparation was done using a 40 nm thick non-enhancing Au film, in order to compare the SEIRA transmission spectra to the infrared reflection absorption spectra (IRRAS) and therefore to determine the factor of the SEIRA enhancement. In both geometries, SEIRA transmission and IRRAS, the antibody-antigen coupling could clearly be detected; a comparison of the spectra showed, that the enhancement factor due to the Au nanoparticles is roughly 25.     

Transmission performance of 20 × 10 Gb/s WDM signals using cascaded optimized SOAs with OOK and DPSK modulation formats

We investigated 20 channels at 10 Gb/s wavelength division multiplexing (WDM) transmission over 1190 km single mode fiber and dispersion compensating fiber using cascaded inline semiconductor optical amplifier at a span of 70 km for RZ-DPSK (return zero differential phase-shift keying) modulation format by using same channel spacing, i.e. 100 GHz. We show for RZ-OOK (return zero on-off keying) format a transmission distance of up to 1050 km with Q factor more than 15 dB, without any power drops. We developed the SOA model for inline amplifier having minimum cross-talks and ASE (amplified spontaneous emission) noise power with sufficient gain. At optimal bias current of 400 mA, a high constant gain of 36.5 dB is obtained up to a saturation power of 21.36 mW. So reduction of cross-talk and distortion is possible by decreasing the bias current at appropriate amplification factor.The DPSK modulation format has less cross-talk as compared to OOK format for nonlinearities and saturation case. The impact of optical power received and Q factor at different distance for both RZ-OOK and RZ-DPSK modulation format has been illustrated. We have shown the optical spectrum and clear Eye diagram at the transmission distance of 1190 km in RZ-DPSK system and 1050 km in RZ-OOK systems.The bit error rate (BER) for all channels observed is less than 10⁻¹⁰ up to gain saturation for both DPSK and OOK systems. Finally, we investigated that the transmission distance decreases with a decrease in channel spacing of up to 20 GHz.     

Soft X-ray spectromicroscopy of phase-change microcapsules

A synchrotron-based scanning transmission X-ray microscope (STXM) is used to investigate Micronal^® phase-change microcapsules. Prolonged X-ray illumination of the specimen leads to the breaking of the microcapsules’ protective polymer shell and a partial separation of the core–shell species occurs. The paraffin wax and acrylic polymer components are characterized by carbon K-edge near X-ray edge absorption fine structure (NEXAFS) spectroscopy and components distribution mapping of the beam-damaged specimen is performed.     

A knife-edge measurement of the beam profile of STXM 5.3.2.2 using a focussed ion beam milled metallic glass

We present a simple knife-edge measurement of the STXM 5.3.2.2 synchrotron X-ray beam width. The knife edge was constructed by ion beam milling a metallic glass alloy consisting of 60% gold, 20% nickel and 20% hafnium and was determined to be well-defined to within 2 nm by TEM. An asymmetric beam profile of 120 nm FWHM in the vertical direction and 150 nm FWHM in the horizontal direction was determined and was observed to depart from the expected Airy function profile.     

Structural characterization and optical properties of ZnSe thin films

Zinc selenide (ZnSe) thin films (d = 0.11-0.93 μm) were deposited onto glass substrates by the quasi-closed volume technique under vacuum. Their structural characteristics were studied by X-ray diffraction (XRD) and atomic force microscopy (AFM). The experiments showed that the films are polycrystalline and have a zinc blende (cubic) structure. The film crystallites are preferentially oriented with the (1 1 1) planes parallel to the substrate surface. AFM images showed that the films have a grain like surface morphology. The average roughness, R_a = 3.3-6.4 nm, and the root mean square roughness, R_rms = 5.4-11.9 nm, were calculated and found to depend on the film thickness and post-deposition heat treatment.The spectral dependence of the absorption coefficient was determined from transmission spectra, in the range 300-1400 nm.The values of optical bandgap were calculated from the absorption spectra, E_g = 2.6-2.7 eV.The effect of the deposition conditions and post-deposition heat treatment on the structural and optical characteristics was investigated.     

The influence of temperature on magnetic and microwave absorption properties of Fe/graphite oxide nanocomposites

Fe/graphite oxide nanocomposites were prepared by inserting Fe³⁺ into layers of graphite oxide and then reducing Fe³⁺/graphite oxide compound at different reduced reaction temperatures in H₂. The composition, crystal structure, magnetic and microwave absorption properties of Fe/graphite oxide nanocomposites were investigated using elemental analysis, transmission electron microscope (TEM), X-ray diffraction (XRD), magnetic hysteresis curve and electromagnetic parameter analysis. The results show that the densities of samples are 2.43–2.47 g/cm³ and the nanocomposites are soft magnetic materials. The optimum reduced reaction temperature for preparing Fe/graphite oxide nanocomposites is 600 °C. With the increase of the thickness of the sample, the matching frequency tends to shift to the lower frequency region, and theoretical reflection loss becomes less at the matching frequency. Microwave absorption property of Fe/graphite oxide nanocomposites prepared at 600  °C (FeGO600) is the best. When the thickness is 1 mm, the maximum theoretical reflection loss of FeGO600 is −9 dB and the frequency region in which the maximum reflection loss is more than −6.0 dB is 11–18 GHz. In conclusion, FeGO600 is a good candidate for microwave absorbent due to its low density, wide frequency region for microwave absorption and large reflection loss.     

Structural and spectroscopic studies of thin film of silver nanoparticles

We report the deposition of thin film of silver (Ag) nanoparticles by wet chemical method. The as-synthesized Ag nanoparticles have been characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), X-ray energy dispersive spectroscopy (EDS), field emission transmission electron microscopy (FETEM) and high-resolution TEM (HRTEM), UV-vis spectroscopy and thermogravimetric-differential thermal analysis (TG-DTA) respectively. FESEM image indicates that the silver film prepared on the quartz substrate is smooth and dense. XRD pattern reveals the face-centered cubic (fcc) structure of silver nanoparticles. EDS spectrum indicates that samples are nearly stoichiometric. From TEM analysis, it is found that the size of high purity Ag nanoparticles is ranging from 10 to 20 nm with slight agglomeration. Absorption in UV-vis region by these nanoparticles is characterized by the features reported in the literature, namely, a possible Plasmon peak at ∼403 nm. Optical absorbance spectra analysis reveals that the Ag film has an indirect band structure with bandgap energy 3.88 eV. TGA/DTA studies revealed that a considerable weight loss occurs between 175 and 275 °C; and the reaction is exothermic.     

Structural investigations of ITO-ZnO films grown by the combinatorial pulsed laser deposition technique

Mixtures of transparent and conductive oxides such as ITO-ZnO have been grown by a combinatorial pulsed laser deposition technique from two targets that were located 15 mm apart. The films were deposited on (1 0 0)Si and quartz substrates that were heated at temperatures from 300 to 500 °C. Measurements of the In to Zn ratios along the transversal axis of the substrates, which passes through the maximum thickness points corresponding to each target position were performed using energy dispersive X-ray spectroscopy and spectroscopic ellipsometry. From simulations of the X-ray reflectivity spectra, collected with a 2 mm mask on different locations along the transversal axis of the samples, the density and thickness of the deposited films were calculated and then the In to Zn ratios. The crystalline structure and electrical properties of the deposited films were also investigated along the same axis. Changes in the ratio of In/Zn along this axis resulted in changes of the film lattice constant and texture.     

High-frequency nanostructured magnetic materials for integrated inductors

Electroplating is compatible with the deposition of relatively thick layers i.e. several μm to 10s- of μm. However eddy current losses mean that thick layers will have an inferior frequency response. We have used a low content phosphorous bath together with pulse reverse plating to generate Co-rich and Co-deficient multi-nanolayers of CoP having improved saturation magnetisation and a better frequency response. The plating parameters have been optimised in order to produce a material with low loss, and a high permeability of around 700 retained up to 103 MHz for a sample with a thickness of 1.7 μm and a resistivity of 136 μΩ cm.     

Preparation and luminescent characteristic of Li3NbO4 nanophosphor

Synthesis and luminescence properties of Li₃NbO₄ oxides by the sol-gel process were investigated. The products were characterized by the X-ray diffraction (XRD), scanning electron microscopy (SEM), photoluminescence (PL) spectroscopy and absorption spectra. The PL spectra excited at 247 nm have a broad and strong blue emission band maximum at 376 nm, corresponding to the self-activated luminescence of the niobate octahedra group [NbO₆]⁷⁻. The optical absorption spectra of the samples sintered at temperatures of 600 and 700 °C exhibited the band-gap energies of 4.0 and 4.08 eV.     

Raman spectroscopic and photoluminescence study of single-crystalline SnO2 nanowires

Single-crystalline SnO₂ nanowires with sizes of 4-14 nm in diameter and 100-500 nm in length were produced in a molten salt approach by using hydrothermal synthesized precursor. Structural characters of the nanowires were examined by X-ray diffraction and high-resolution electron transmission microscopy. Raman, photoluminescence and X-ray photoelectron spectra of the samples were examined under heat treatments. Three new Raman modes at 691, 514 and 358 cm⁻¹ were recorded and assigned. The former two are attributed to activation of original Raman-forbidden A_2uLO mode and the third is attributed to defects in small-sized nanowires. A strong photoluminescence is observed at about 600 nm, the temperature effects is examined and the origin of the PL process is discussed via X-ray photoelectron spectra.     

Structural and magnetic properties of Pt in Co/Pt multilayers

[Co(30 Å)/Pt(x Å)]₂₀ multilayers with the Pt layer thicknesses varying from 5 Å to 20 Å were characterized structurally by high angle X-ray diffraction, X-ray reflectivity, X-ray absorption spectroscopy and magnetically by X-ray magnetic circular dichroism. It is found that the structure and magnetic properties of Pt have a strong correlation with the Pt layer thickness. The 20 Å thickness Pt layer is not almost influenced by the adjacent Co layer and the nearest neighbors are dominated by Pt-Pt shells. With decreasing Pt layer thickness, the nearest neighbors are gradually dominated by Pt-Co shells and the Pt-Co intermixing regions also remarkable increase at the interfaces, especially for the 5 Å thickness Pt layer. The orbital and spin magnetic moments as well as the ratio m_orb/m_spin all decrease systematically with increasing Pt layer thickness, indicating that the interface atoms are polarized by direct Pt-Co hybridization, but that the adjacent layers are polarized by Pt-Pt interactions.