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In this study, we developed a pioneering non-enzymatic electrochemical sensor utilizing a flexible porous graphene electrode modified with ZnO nanoparticles (ZnO/fPGE sensor) to assess hypoxanthine (HXA) content in pork at post-mortem time. The ZnO/fPGE sensor was synthesized via hydrothermal method and direct laser writing with a CO2 laser on a polyimide film at ambient conditions. Its characterization was analyzed by Raman, Fourier-transform infrared spectroscopy, field-emission scanning microscopy, energy-dispersive x-ray spectroscopy, and cyclic voltammetric techniques. Linear response, the limit of detection, and sensitivity to the HXA were enhanced with the values of the range from 1.5 to 150, 0.14 µM, and 6.6 µA μM−1 cm−2, respectively. Effective resistance to common physiological interferences (such as uric acid, ascorbic acid, dopamine, glucose, and xanthine) was indicated, and additionally, the determination of HXA concentration in real samples with good selectivity is attributed to the synergistic effects between ZnO nanoparticles and fPGE. Therefore, the ZnO/fPGE has provided a favorable electrical environment for developing high-performance electrochemical biosensors to determine hypoxanthine in pork meat. [ABSTRACT FROM AUTHOR]

Metal film over nanosphere (MFON) metasurfaces have numerous applications, specifically as nanosensors for bio and chemical detection. Additionally, their interesting optical properties have also attracted the attention of many research groups. In this work, we study the influence of the metallic underlayer on the surface-enhanced Raman scattering (SERS) effect of the MFON structure. Two sets of MFON on silicon and mirror substrates were prepared for SERS measurement with rhodamine 6G. Experimental results show that the mirror layer boosts the SERS signal by two to five times. Finite difference time domain simulation was performed to gain insights into this improvement. Numerical results show that metallic underlayer helps to increase the concentration of the electric field at the hot spots. Moreover, it reflects the Raman signal via the extraordinary optical transmission channel of the MFON structure, improving the back-scattered Raman signal collection efficiency. Both of these effects can contribute to the increase of the SERS signal in agreement with the experimental results. More importantly, it provides an additional tool to tailor the optical properties of MFON metasurfaces. [ABSTRACT FROM AUTHOR]

A hydrothermal method was used to prepare three nano-crystalline samples of TiO2 (S1), N-doped TiO2 (S2), and (N, Ta)-codoped TiO2 (S3) with average crystallite sizes (D) of 13-25 nm. X-ray diffraction studies confirmed a single phase of the samples with a tetragonal/anatase structure. A slight increase in the lattice parameters was observed when N and/or Ta dopants were doped into the TiO2 host lattice. Detailed analyses of extended X-ray absorption spectra indicated that N- and/ or Ta-doping into TiO2 nanoparticles influenced the co-ordination number and radial distance (R) of Ti ions in the anatase structure. Concerning their absorption spectra, (N, Ta)-doping narrowed the band gap (Eg) of TiO2 from 3.03 eV for S1 through 2.94 eV for S2 to 2.85 eV for S3. Such results revealed the applicability of these nanoparticles in the photocatalytic field working in the ultraviolet (UV)-visible region. Among these, photocatalytic activity of S3 was the strongest. By using S3 as a catalyst powder, the degradation efficiency of methylene blue solution was about 99% and 93% after irradiation of UV-visible light for 75 min and visible-light for 180 min, respectively. [ABSTRACT FROM AUTHOR]

We have prepared polycrystalline samples BaTi1-xCoxO3 (x=0-0.1) by solid-state reaction. X-ray diffraction and Raman-scattering studies reveal the phase separation in crystal structure as changing Co-doping content (x). The samples with x=0-0.01 are single phase in a tetragonal structure. At higher doping contents (x>0.01), there is the formation and development of a secondary hexagonal phase. Magnetization measurements at room temperature indicate a coexistence of paramagnetic and weak-ferromagnetic behaviors in BaTi1-xCoxO3 samples with x>0, while pure BaTiO3 is diamagnetic. Both these properties increase with increasing x. Analyses of X-ray absorption spectra recorded from BaTi1-xCoxO3 for the Co and Ti K-edges indicate the presence of Co2+ and Co3+ ions. They locate in the TiCo4+ site of the tetragonal and hexagonal BaTiOCo2 structures. Particularly, there is a shift of oxidation state from Co2+ to Co3+ when Co-doping content increases. We believe that the paramagnetic nature in BaTi1-xCoxO3 samples is due to isolated Co2+ and Co3+ centers. The addition of Co3+ ions enhances the paramagnetic behavior. Meanwhile, the origin of ferromagnetism is due to lattice defects, which is less influenced by the changes caused by the variation in concentration of Co2+ and Co3+ ions. [ABSTRACT FROM AUTHOR]

Polycrystalline BaTi1-xFexO3 ceramics have been prepared by conventional solid-state reaction. Their structural, optical and magnetic properties are then studied by means of x-ray diffraction (XRD), Raman scattering (RS) and absorption spectrometers, and a physical properties measurement system. Detailed analyses of XRD patterns and RS spectra reveal the phase separation of the tetragonal-hexagonal structure at a threshold concentration of x = 0.005. The increase in the Fe-doping content (x) leads to development of the hexagonal phase. Magnetic measurements prove that many BaTi1-xFexO3 samples exhibit the room-temperature ferromagnetic order, excepting the samples with x = 0.02-0.06. The ferromagnetism depends strongly on concentration of Fe impurities. The nature of this ferromagnetism is discussed by means of the results of structural analyses and optical absorption spectra. [ABSTRACT FROM AUTHOR]

We prepared Zn1-xMnxO nanorods by thermal diffusion. These samples were then studied the structural, optical, and magnetic properties. The structural analyses basing on x-ray diffraction and transmission electron microscope revealed the absence of Mn-related secondary phases. The study of photoluminescence spectra revealed the blueshift in the UV emission when the Mn doping concentration was increased, as a consequence of the extension of the band gap energy. Besides this situation, the increase in emission intensity associated with extrinsic defects at about 680 nm also took place. Concerning the Raman scattering spectra, apart from conventional phonon modes related to the ZnO wurtize-type structure, there were some additional modes introduced by the doping. Their origin was assessed carefully. Particularly, the shift in peak position of E2(high) toward low frequencies due to the increase in the Mn doping concentration could be explained well by means of the spatial correlation model. Magnetic measurements proved the samples with Mn concentrations above 1.15 at. % exhibiting the weak-ferromagnetic order at low temperatures. The nature of the ferromagnetism was discussed by means of the results of the structural and optical investigations. [ABSTRACT FROM AUTHOR]

We experimentally and numerically studied the transmission spectra of a combined metamaterial structure whose negative refractive index was supposed to be achievable only with simultaneously negative permittivity and permeability. However, it was found that the negativity of the refractive index of such a structure could be obtained not only when both parameters were negative but also when only one parameter, more specifically the permittivity was negative. These characteristics of combined structure were analyzed in detail by using the standard retrieval effective-medium method. According to the analyses, it can be concluded that the negativity originates from the complex permittivity and permeability. The interplay among the real and the imaginary parts of those parameters is the key to the negative behavior of refractive index. [ABSTRACT FROM AUTHOR]

We studied both theoretically and experimentally the influence of the lattice constant on the resonance frequencies of cut-wire-pair structures, which are essential components in assembling left-handed materials. These structures were designed and fabricated, and the transmission spectra were measured in the microwave-frequency regime. Numerical simulation was performed using the transfer-matrix method. All the numerical results were in good agreement with the experimental data. It was found that the lattice parameters of the cut-wire-pair structure provide sensitive effects on the electric resonance, especially, in the propagation k and the electric field E directions, while the magnetic resonance frequency is nearly unchanged, except for its bandwidth and depth. In addition, we also studied the effect of dielectric layer thickness on the resonance frequencies of the cut-wire-pair structure. These sensitive changes in the electric resonance might have remarkable effects on the effective plasma frequency and therefore on the left-handed behavior of combined structures consisting of cut-wire pairs and continuous wires. [ABSTRACT FROM AUTHOR]

The left-handed (LH) behavior of a combined structure of cut wire pair and continuous wire was experimentally studied. It was found that the LH behavior of a combined structure can still be observed as the width of cut wire pair increases until the cut wire joins the continuous wire, the so-called fishnet structure. These structures were designed, fabricated, and measured in the microwave frequency regime. In addition, we report the experimental results of the parametric study on the fishnet structure, which are also compared with the previous theoretical studies. [ABSTRACT FROM AUTHOR]

We numerically and experimentally investigated the negative refractive index effect in a single subwavelength magnetic “meta-atom,” a flower-shaped metamaterial (MM) structure. In our effort to understand the electromagnetic properties of flower-shaped structure, the third resonance has been considered for a rather high frequency in the gigahertz range of electromagnetic wave. It is found that the negative refractive index is a result of the tail of electric gap and the magnetic resonance at the third-order resonance. The effect is switched OFF by adjusting the density of flowers. In addition, the negative refractive index behavior is accompanied by polarization insensitivity resulting from its geometry. Finally, the electromagnetic and the loss properties of the MM were clarified at the third-order gap. [ABSTRACT FROM PUBLISHER]

We have studied magnetic and magnetotransport properties of a polycrystalline ceramics of La0.7Sr0.2Ca0.1MnO3 (LSCM) prepared from nanoparticles. The Curie temperature (TC) of the sample is about 340 K. Basing on the magnetic-field dependences of magnetization measured around TC, maximum magnetic-entropy changes under the applied fields of 10, 20 and 30 kOe are about 1.73, 2.74, 3.52 J/kg.K, respectively, which are higher than those reported on a parent compound of La0.7Sr0.3MnO3. To understand magnetic-interaction mechanisms taking place in the system, the critical behavior has been taken into account. By using the modified Arrott plot method, \beta and \gamma values associated with the spontaneous magnetization (Ms) and inverse initial susceptibility (\chi0^{-1}) have been obtained to be 0.472 \pm 0.016 and 1.061 \pm 0.024, respectively. These critical parameters are close to those expected for the mean-field theory (with \beta=0.5, and \gamma=1.0). A small deviation in value between our results and those expected for the mean-field theory could be due to an inhomogeneity in magnetism and/or interaction competitions between antiferromagnetic pairs (Mn^3+-Mn^3+ and Mn^4+-Mn^4+) and a ferromagnetic pair of Mn^3+-Mn^4+ in LSCM. Interestingly, in the temperature range of 180–300 K, magnetoresistance values keep quite stable at about 16 and 27% for the magnetic fields of 1 and 7 kOe, respectively. This makes LSCM more suitable to applications of magnetic sensitive sensors and reading heads working in a large temperature range. [ABSTRACT FROM PUBLISHER]

The search for a simple meta-system with negative refractive index has attracted a lot of attention recently. In this paper, we study a negative refractive transmission operating at 300 GHz by using "single-atom" metamaterials which were initially designed for achieving negative permeability. The nature of the negativity is discussed extensively by the effective medium analysis and confirmed by the dispersion diagram. [ABSTRACT FROM AUTHOR]

In this report, we experimentally and numerically studied the transmission spectra of combined metamaterial structure which consists of cut-wire pairs and continuous wires. The effective permittivity and permeability were extracted from the complex scattering parameters utilizing the standard retrieval procedure. By examining the influence of the width of continuous wires, we were able to investigate the important role of electric response for the left-handed transmission. It is found that the changed electric component either enhances or even destroys the left-handed behavior of combined structure. Our experimental and numerical results expand the understanding on the electromagnetic behavior of combined metamaterial structure. [ABSTRACT FROM AUTHOR]

We investigate the transmission properties of a metamagnetic structure, the so-called cut-wire pair (CWP), using the transfer-matrix method and the finite integration technique. The electric and magnetic resonances of the CWP structure are demonstrated by the effective medium analyses. The corresponding effective permittivity and permeability are calculated from the complex scattering parameters using the standard retrieval procedure. Importantly, the dependence of transmission properties and resonance frequencies on the periodicities as well as the shape of CWP are systematically examined. [ABSTRACT FROM AUTHOR]

The effect of Fe doping on the crystalline phase transformation and on the local environment around Fe dopant ions is investigated for BaTi1-xFexO3-δ (0.0 ≤ x ≤ 0.5) polycrystalline samples, using x-ray diffraction, x-ray absorption spectroscopy, and Raman scattering spectroscopy. Our experimental results show that the tetragonal-to-hexagonal transformation is gradually taken place when increasing the Fe content in the range 0.02 ≤ x ≤ 0.12. Although both hexagonal and tetragonal polymorphs coexist in this doping range, Fe ions preferably substitute for Ti sites in the hexagonal lattice and exist in both Fe3+ and Fe4+ forms. Our work is of paramount importance to provide a direct evidence to the preferable substitution of transition metal ions for Ti ions. [ABSTRACT FROM AUTHOR]

Polycrystalline samples of BaTiO3 doped with 2.0 at. % Mn were prepared by solid-state reaction at various temperatures (Tan) ranging from 500 to 1350 °C, used high-pure powders of BaCO3, TiO2, and MnCO3 as precursors. Experimental results obtained from x-ray diffraction patterns and Raman scattering spectra reveal that tetragonal Mn-doped BaTiO3 starts constituting as Tan ≈ 500 °C. The Tan increase leads to the development of this phase. Interestingly, there is the tetragonal-hexagonal transformation in the crystal structure of BaTiO3 as Tan ≈ 1100 °C. Such the variations influence directly magnetic properties of the samples. Besides paramagnetic contributions of Mn2+ centers traced to electron spin resonance, the room-temperature ferromagnetism found in the samples is assigned to exchange interactions taking place between Mn3+ and Mn4+ ions located in tetragonal BaTiO3 crystals. [ABSTRACT FROM AUTHOR]

Our work studies the influences of the Mn doping on structural characterization and optical and magnetic properties of BaTi1-xMnxO3 (x = 0.0-0.12) prepared by conventional solid-state reaction. Detailed analyses of XRD patterns and Raman scattering spectra indicate an incorporation of Mn dopants into the Ti sites of BaTiO3 host lattices, and the tetragonal-hexagonal transformation taking place at a threshold concentration of xc ≈ 0.01. An increase of Mn-doping content in BaTi1-xMnxO3 introduces more electronic levels associated with lattice defects and Mn ions to the forbidden gap and thus reduces luminescent intensity in the visible region. Magnetic data recorded at room temperature reveal that all the samples exhibit ferromagnetic order, and there is a phase separation in magnetism as varying x values. Particularly, the samples with x = 0.5-0.7 have a coexistence of two ferromagnetic phases with different coercivities, which are associated with tetragonal and hexagonal Mn-doped BaTiO3 structures. The nature of ferromagnetism is explained by means of the results of structural and optical analyses, where Mn3+ and Mn4+ ions play a crucial role. [ABSTRACT FROM AUTHOR]

The effect of Fe dopant content, x, on the magnetism of polycrystalline BaTi1-xFexO3-δ (BTFO) multiferroic samples was investigated using magnetization measurements in correlation with the crystallographic and local structures. The changes of coercivity and magnetization as functions of x are closely related to the variation of oxygen vacancy content, δ, which can be deduced from the Fe oxidation number estimation using Fe K-edge x-ray absorption spectroscopy. It is shown that although the samples exhibit ferromagnetic (FM) hysteresis at room temperature, a dominant paramagnetic phase coexisting with the FM phase makes it difficult to identify the FM contribution to the total magnetization. Spin-glass and/or superparamagnetic behavior may be ruled out due to the fact that both zero-field-cooled and field-cooled thermomagnetization curves almost totally overlap together over the whole range of measured temperatures. [ABSTRACT FROM AUTHOR]

In this study, Er-doped CoAl 2 O 4 nanocrystals (NCs) were synthesized via co-precipitation. All the NCs were crystallized in the form of a single phase with a spinel structure and Er 3+ ions replaced Al 3+ ions in the formation of the CoAl 2- x Er x O 4 alloy structure. The optical characteristics of the Er 3+ ion-doped CoAl 2 O 4 NCs were thoroughly investigated by analyzing both the UV-VIS and photoluminescence spectra, using the Judd-Ofelt theory. The effect of Er doping content on the luminescent properties of the CoAl 2 O 4 pigment (using lasers emitting at wavelengths of 413 and 978 nm) has been studied. The values of Judd-Oflet intensity parameters ( Ω 2 , Ω 4 , and Ω 6 ) were determined from the absorption spectra using the least square fitting method. The J-O parameters were calculated and compared with those of other host materials; the values of the Ω 2 , Ω 4 , and Ω 6 parameters decreased with an increase in Er concentration. This suggests that the rigidity and local symmetry of the host materials become weaker as the concentration of Er 3+ ions increases. The highest value of the Ω 2 parameter, when compared with Ω 4 and Ω 6 , suggests that the vibrational frequencies in the given samples are relatively low. The upconversion fluorescence phenomenon was observed and explained in detail under an excitation wavelength of 978 nm when the excitation power was varied., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Cobalt doped magnetite nanoparticles (Co x Fe 3- x O 4 NPs) are investigated extensively because of their potential hyperthermia application. However, the complex interrelation among chemical compositions and particle size means their correlation with the magnetic and heating properties is not trivial to predict. Here, we prepared Co x Fe 3- x O 4 NPs (0 ≤ x ≤ 1) to investigate the effects of cobalt content and particle size on their magnetic and heating properties. A detailed analysis of the structural features indicated the similarity between the crystallite and particle sizes as well as their non-monotonic change with the increase of Co content. Magnetic measurements for the Co x Fe 3- x O 4 NPs (0 ≤ x ≤ 1) showed that the blocking temperature, the saturation magnetization, the coercivity, and the anisotropy constant followed a similar trend with a maximum at x = 0.7. Moreover, 57 Fe Mössbauer spectroscopy adequately explained the magnetic behaviour, the anisotropy constant, and saturation magnetization of low Co content samples. Finally, our study shows that the relaxation loss is a primary contributor to the SAR in Co x Fe 3- x O 4 NPs with low Co contents as well as their potential application in magnetic hyperthermia., Competing Interests: The authors declare no competing financial interest., (This journal is © The Royal Society of Chemistry.)

We studied both experimentally and theoretically the influence of the distance between adjacent cut-wire-pair layers on the magnetic and the electric resonances in the microwave-frequency regime. Besides the dependence on the separation between cut-wire pairs, along the electric-field direction, the electric resonance strongly depends on the distance between cut-wire-pair layers, while the magnetic resonance is almost unchanged. This contrast can be understood by the difference in the distribution of induced-charge density and in the direction of the induced current between the electric and magnetic resonances. A simple model is proposed to simulate our experimental results and the simulation results are in good agreement with the experiment. This result provides important information in obtaining left-handed behavior when the cut-wire pairs are combined with the continuous wire.

We investigated some magnetic metamaterials based on cut-wire pairs instead of split-ring resonators to quest for the possibility of a negative magnetic permeability. Several periodic structures of cut-wire pairs were designed and fabricated, and their transmission spectra were measured in the microwave-frequency regime. The width dependence of magnetic-resonance frequency was studied both theoretically and experimentally for the periodic structures of cut-wire pairs. It was found that, besides the length dependence, the magnetic-resonance frequency also depends significantly on the width of cut-wire pair. A simple equivalent-circuit model proposed by Zhou et al. [Opt. Lett. 31, 3620-3622 (2006)] was employed to elucidate this interesting phenomenon and to simulate the width dependence. In the simulation the magnetic and the electric energies of the cut-wire pair were directly calculated to obtain the magnetic-resonance frequency. The theoretical results are in good agreement with the experimental ones. It reveals that there is a rather easy way to manipulate the magnetic-resonance frequency of magnetic-magnetic metamaterials.