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Bragg coherent diffraction imaging of iron diffusion into gold nanocrystals
摘要： Understanding how diffusion takes place within nanocrystals is of great importance for their stability and for controlling their synthesis. In this study, we used the strain sensitivity of Bragg coherent diffraction imaging (BCDI) to study the diffusion of iron into individual gold nanocrystals in situ at elevated temperatures. The BCDI experiments were performed at the I-07 beamline at Diamond Light Source, UK. The diffraction pattern of individual gold nanocrystals was measured around the (11-1) Bragg peak of gold before and after iron deposition as a function of temperature and time. Phase retrieval algorithms were used to obtain real space reconstructions of the nanocrystals from their measured diffraction patterns. Alloying of iron with gold at sample temperatures of 300 °C–500 °C and dealloying of iron from gold at 600 °C were observed. The volume of the alloyed region in the nanocrystals was found to increase with the dose of iron. However, no significant time dependence was observed for the structure following each iron deposition, suggesting that the samples reached equilibrium relatively quickly. The resulting phase distribution within the gold nanocrystals after the iron depositions suggests a contraction due to diffusion of iron. Our results show that BCDI is a useful technique for studying diffusion in three dimensions and alloying behaviour in individual crystalline grains.
关键词： gold iron,nanocrystals,diffusion,Bragg coherent diffraction imaging
更新于2025-09-09 09:28:46
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The Study of Features of Formation and Properties of A3B5 Semiconductors Highly Doped with Iron
摘要： Layers of InAs, InSb, and GaSb semiconductors highly doped with iron during their growth by the method of pulsed laser deposition are studied experimentally. The best temperatures for layer formation on GaAs (100) substrates are: 250°C (InSb : Fe), 300°C (InAs : Fe), and 350°C (GaSb : Fe). At high Fe concentration (over 10 at %) the layers display ferromagnetic properties expressed in emergence of a hysteresis curve within the magnetic field dependences of the Hall resistance, negative magnetoresistance, and in some cases, ferromagnetic-type magnetization at measurements at room temperature. The atoms of iron do not change the type of layer conductivity; InAs : Fe and InSb : Fe layers possess n-type conductivity, and GaSb : Fe layers display p-type conductivity due to their intrinsic point defects.
关键词： Hall effect,A3B5 semiconductors,ferromagnetic properties,magnetoresistance,iron doping,pulsed laser deposition
更新于2025-09-09 09:28:46
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Local, electronic and surface structure of multi–component Fe–doped CdTe(S) systems
摘要： Local structural and electronic properties around Fe in multi–component Cd0.99Fe0.01Te0.97S0.03 system were studied by means of X–ray absorption fine structure (XAFS). Composition of non–polar (110) surfaces of Cd0.97Fe0.03Te and Cd0.99Fe0.01Te0.97S0.03 systems and mechanism of their oxidation in ambient conditions were studied by Atomic Force Microscopy (AFM) and X–ray Photoelectron Spectroscopy (XPS). It has been found that Fe preferentially substitutes Cd, but due to much smaller covalent radius and preferences for paring with S, it causes local distortion of the host CdTe lattice. The distortion is confined to the Fe–immediate surrounding and the second and third coordination shell atoms are (inside experimental uncertainties) placed at distances expected in CdTe. Although local structure around Fe is well defined in the bulk of both samples, their near–surface region is completely depleted from Fe, and in case of Cd0.99Fe0.01Te0.97S0.03 somewhat enriched in S. Special attention is, therefore, paid to characterization of the near–surface region and evaluation of its composition and structure. To that end we have introduced a general standard–free algorithm for XPS data analysis of the two–layer surface structure (bulk, oxide layer, and the impurity layer). Results of the in–depth composition analysis revealed that despite different bulk composition and impurity layer thickness, underneath the topmost impurity layer lays approximately one monolayer of CdTeO3 which passivates the surface.
关键词： XAS,XPS,II–VI semiconductors,iron impurity,oxidation
更新于2025-09-09 09:28:46
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Photo Protection against Visible Light Induced Pigmentation
摘要： This paper presents in vivo an in vitro studies demonstrating the induction of pigmentation in human skin by visible light which can be blocked by using formulation containing the correct amount of yellow iron oxide (YIO). An in vitro absorption method was developed to determine the protection provided by a test formulation containing 4.5% YIO using an IPD UVA-VIS action spectrum. Following the development of the in vitro method and in vivo study with 10 normal healthy volunteers with Fitzpatrick skin phototypes IV to VI was conducted to verify if the predictive model. The in vitro model for visible light protection provided a protection factor of 2.5 using the in vitro absorption spectrum of 4.5% of YIO with a very similar result from the in vivo study with a protection factor of 3.0. Multiple daily exposures of visible light have shown increase in skin pigmentation and the application of YIO provide less development of pigmentation when compared to unprotected skin. In vitro testing of the absorbance of the pigmented formulation using a proposed action spectrum for immediate pigment darkening (IPD) response in the visible light range supports the in vivo protection observations for persistent pigment darkening (PPD) and can be used as predictor for skin pigmentation induced by visible light.
关键词： visible light,in vitro,in vivo,yellow iron oxide,pigmentation
更新于2025-09-09 09:28:46
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Structural, morphological and optical properties of Cu2ZnxFe1-xSnS4 thin films grown by thermal evaporation
摘要： In this study, Cu2ZnxFe1-xSnS4 (CZFTS) (0≤x≤1) thin films were grown under vacuum evaporation on unheated glass substrates followed by sulfurization at 400 °C. The effects of sulfurization on the structural, morphological and optical properties were investigated for CZFTS material by varying Fe content. Crystal structure and phase of CZFTS thin films were analyzed by X-ray diffraction technique and Raman spectroscopy. In addition, the elemental composition and the stoichiometry of films were studied using energy dispersive spectroscopy. Surface morphology of samples was examined by scanning electron microscopy. Optical properties such as absorption coefficient, and gap energies were determined by the measurement of transmittance and reflectance in the spectral range 300-1800 nm. X-ray analysis indicates that all sulfurized CZFTS films present a polycrystalline nature and exhibit a preferential orientation along (112) plane. Cu2FeSnS4 (x=0) and Cu2ZnSnS4 (x=1) crystallize in stannite structure with I-42m and kesterite structure with I-4 space group, respectively. Raman analysis and elemental composition confirm that only the Cu2ZnSnS4 (x=1) and CZ0.75F0.25TS (x=0.75) phases are present with good crystallinity. Transmittance and reflectance spectra revealed that the films are homogenous mostly for x=0.75 and 1. Structural and optical parameters like crystallite size, absorption coefficient and band gaps were estimated for all the x values.
关键词： Sulfurization,Scanning electron microscopy,X-ray diffraction,Copper zinc iron tin sulfide,Evaporation,Thin films
更新于2025-09-09 09:28:46
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Ultrafast Multilevel Switching in Au/YIG/n-Si RRAM
摘要： Resistive random access memory (RRAM) with ultrafast and multilevel switching is extremely promising for next-generation nonvolatile memory. Here, ultrafast unipolar resistive switchings (≈540 ps) with high off/on resistance ratio (≈104) are obtained in yttrium iron garnet Y3Fe5O12 (YIG)-based resistive memory on n-Si substrate. The sub-nanosecond operation is also successfully performed up to 85 °C with an off/on resistance ratio of ≈103. In addition, by using different compliance currents for the set process, five discrete resistance levels with ultrafast switchings among them are achieved and the multilevel states show reliable retention (>104 s). The large, stable, reproducible, and reliable switching behaviors of the Au/YIG/n-Si RRAM cell shows its great potential for ultrafast multilevel memory applications.
关键词： yttrium iron garnet (YIG),unipolar resistance switching,multistates,fast switching
更新于2025-09-09 09:28:46
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Synthesis, crystal structure, M?ssbauer spectroscopy, optical and magnetic properties of Cs2M2Fe(PO4)3 (M = Mn, Co, Ni, Cu) ordered pollucite structure
摘要： Four isomorphous iron phosphates Cs2M2Fe(PO4)3 (M = Mn, Co, Ni, Cu) have been synthesized as powder by conventional solid state technic and characterized by X-ray diffraction, magnetic susceptibility, diffuse reflectance and M?ssbauer spectroscopies. All these compounds crystallize in the space group I4132 of the cubic system with similar cell parameters: a = 13.8268(1) ?, 13.7624(1) ?, 13.5917(1) ? or 13.5834(1) ? for M = Mn, Co, Ni or Cu, respectively and eight formula units per cell. Their structure closely related to that of pollucite, is built up from [M2/3,Fe1/3]O4 tetrahedra connected to each other through the common corners with PO4 tetrahedra. The resulting anionic three-dimensional framework leads to the formation along [1 1 1] direction, of channels where the large cesium ions occupy two independent crystallographic sites. A M?ssbauer study at room temperature, confirmed the +3 oxidation state of iron and its tetrahedral coordination. Diffuse reflectance spectroscopy also confirmed the occurrence of isolated Fe3+ ions: low energy gap due to oxygen to iron (III) inter-electronic transition and absence of d-d transition linked to iron; the colorimetric properties of the compounds were shown to be mainly governed by the visible d-d transitions linked to the M2+ cation in tetrahedral coordination. Magnetic susceptibility measurements reveal that the title compounds are weakly magnetically ordered at very low temperature due to super-superexchange magnetic interaction. The thermal evolution of χm follows in a wide temperature range, a Curie-Weiss law χ = C/(T-θ) with θ = -59, -36, -50 and -39 K for Mn, Co, Ni and Cu phases, respectively.
关键词： iron phosphates,M?ssbauer spectroscopy,optical properties,magnetic properties,pollucite structure
更新于2025-09-09 09:28:46
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Quantification of Different Forms of Iron from Intact Soil Cores of Paddy Fields with Vis-NIR Spectroscopy
摘要： Iron (Fe) occurs in almost all soils and the analysis of various forms of Fe in the soil is of great pedological interest. Very little is known, however, about how visible and near-infrared (Vis-NIR) spectroscopy performs in intact soil cores of paddy fields for quantifying Fe concentrations. Our objective was to evaluate the feasibility of Vis-NIR spectroscopy of intact soil cores for rapid determination of the four Fe forms: total Fe (Fet), pyrophosphate-extractable Fe (Fep), dithionite-citrate-bicarbonate extractable Fe (Fed), and oxalate-extractable Fe (Feo). A total of 148 intact soil cores in Yujiang County, China, were sampled, and Vis-NIR spectra (350–2500 nm) were sectioned and scanned on four horizontal surfaces (5-cm depth intervals) of each soil core in the laboratory. Partial least squares regression (PLSR) and support vector machine regression (SVMR) models were compared using 70% of the section samples for calibration and 30% for independent validation. Results showed that the nonlinear SVMR models performed better than the PLSR models for the predictions of all Fe forms. The SVMR models produced the best predictions in the independent validation set for Fed (RMSEP = 2.223; R2 P = 0.85; RPDP = 2.59), Fet (RMSEP = 3.693; R2 P = 0.82; RPDP = 2.32), and Fep (RMSEP = 0.086; R2 P = 0.79; RPDP = 2.17). It was concluded that Vis-NIR spectroscopy coupled with SVMR is suitable for quantitatively determining different Fe forms in intact soil cores of paddy fields.
关键词： intact soil cores,iron forms,SVMR,Vis-NIR spectroscopy,paddy fields,PLSR
更新于2025-09-09 09:28:46
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Sensing coated iron-oxide nanoparticles with spectral induced polarization (SIP): Experiments in natural sand packed flow-through columns
摘要： The development of nanoparticle-based soil remediation techniques is hindered by the lack of accurate in situ nanoparticle (NP) monitoring and characterization methods. Spectral induced polarization (SIP), a non-invasive geophysical technique, offers a promising approach to detect and quantify NPs in porous media. However, its successful implementation as a monitoring tool requires an understanding of the polarization mechanisms, the governing NP-associated SIP responses and their dependence on the stabilizing coatings that are typically used for NPs deployed in environmental applications. Herein, we present SIP responses (0.1-10,000 Hz) measured during injection of a poloxamer-coated super-paramagnetic iron-oxide nanoparticle (SPION) suspension in flow-through columns packed with natural sand from the Borden Aquifer. An advective-dispersive transport model is fitted to outflow SPION concentration measurements to compute average concentrations over the SIP spatial response domain (within the columns). The average SPION concentrations are compared with the real and imaginary components of the complex conductivity. Excellent correspondence is found between the average SPION concentrations the columns and the imaginary conductivity values, suggesting that NP-mediated polarization (that is, charge storage) increases proportionally with increasing SPION concentration. Our results support the possibility of SIP monitoring of spatial and temporal NP distributions, which can be immediately deployed in bench-scale studies with the prospect of future real-world field applications.
关键词： Maxwell-Wagner polarization,relaxation time,super paramagnetic iron-oxide nanoparticles (SPIONs),Spectral induced polarization (SIP),chargeability
更新于2025-09-09 09:28:46
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Photocatalytic Activity and Humidity Sensor Studies of Magnetically Reusable FeWO <sub/>4</sub> –WO <sub/>3</sub> Composite Nanoparticles
摘要： Different mole ratios of (8:2, 6:4, 4:6 and 2:8) iron tungstate–tungsten trioxide (FeWO4–WO3) composite nanoparticles were synthesized by solid state method. The synthesized composite nanoparticles were characterized by powder X-ray diffraction analysis (XRD), field-emission scanning electron microscopy (FE-SEM) with energy dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM) and vibrating sample magnetometer (VSM) studies. The crystalline nature and particle size of the samples were characterized by powder X-ray diffraction analysis (XRD). The morphology was confirmed by field-emission scanning electron microscopy (FE-SEM) analysis and transmission electron microscope (TEM). The energy dispersive X-ray spectroscopy (EDX) proved the purity of nanocomposites. Vibrating sample magnetometer reveals that the sample shows paramagnetic property based on the metal present in the prepared nanocomposites at room temperature. The magnetic property is due to the structural defects rather than the impurity phase. Magnetization saturation value (Ms = 398.7 emu/g) of FWWO-46 composite nanoparticles is high enough to be magnetically removed by applying a magnetic field. The composites were subjected to DC conductance measurement as a function of relative humidity in the range of 5–98%, achieved by different water vapour buffers thermostated at room temperature. The sensitivity factor, Sf = R5%/R98%, where R5% and R98% the values of the resistances measured at different RH respectively, are evaluated in Table I. If the composite has the greater value of Sf, then those materials possess the greater sensitivity towards moisture. The sensitivity factor (Sf) of the prepared composite nanoparticles was FWWO-10 (473), FWWO-82 (209), FWWO-64 (323), FWWO-46 (3956), FWWO-28 (361) and FWWO-01 (373). From this experimental value FWWO-46 exhibit the maximum Sf value of 3956 among the composites. This was due to the presence of more pores and cavities in the morphology of FWWO-46 then the other composite nanoparticles. Meanwhile the composite FWWO-46 can interact with water molecules easily then the others. The absorption and desorption of water molecules vary from the other composites. In the presence of water molecules on the morphology of FWWO-46 shows higher conductivity and higher sensitivity factor (Sf). At low relative humidity, water adsorption on the surface of the sample was likely the dominant factor for electronic conduction. The adsorbed water increases the surface electrical conductivity of the ceramic due to the increased charge carrier, protons in the ceramic/water system. The conductivity was further increased by the presence of pores on the sample surface. In the initial stage of water adsorption, a few water vapour molecules chemisorbed on the grain surface by a dissociative mechanism to form two surface hydroxyls per water molecule. In this chemisorbed layer charge transport occurs by the hopping mechanism. Conduction probably occurs by the Grotthus transport mechanism.
关键词： Composite,Photocatalytic Activity,Iron Tungstate,VSM,Humidity Sensors,Tungsten Trioxide
更新于2025-09-09 09:28:46