Micro‐Raman investigation of transition‐metal‐doped ZnO nanoparticles

We measured the Raman spectra of ZnO nanoparticles (ZnO‐NPs), as well as transition‐metal‐doped (5% Mn(II), Fe(II) or Co(II)) ZnO nanoparticles, with an average size of 9 nm. A typical Raman peak at 436 cm⁻¹ is observed in the ZnO‐NPs, whereas Zn_1−xMn_xO, Zn_1−xFe_xO and Zn_1−xCo_xO presented characteristic peaks at 661, 665 and 675 cm⁻¹, respectively. These peaks can be related to the formation of Mn₃O₄, Fe₃O₄ and Co₃O₄ species in the doped ZnO‐NPs. Moreover, these samples were analyzed at various laser powers. Here, we observed new vibrational modes (512, 571 and 528 cm⁻¹), which are specific to Mn, Fe and Co dopants, respectively, and ZnO‐NPs did not reveal any additional modes. The new peaks were interpreted either as disorder activated phonon modes or as local vibrations of Mn‐, Fe‐ and Co‐related complexes in ZnO. Copyright © 2007 John Wiley & Sons, Ltd.     

Micro‐photoluminescence spectroscopy on heavily‐doped layers of silicon solar cells

We report and explain the photoluminescence spectra emitted from silicon solar cells with heavily‐doped layers at the surface. A micro‐photoluminescence spectroscopy system is employed to investigate the total spectrum emitted from both the heavily‐doped layer and the silicon substrate with micron‐scale spatial resolution. The two regions of the device give rise to separate photoluminescence peaks, due to band‐gap narrowing effects in the highly‐doped layer. Two key parameters, the absorption depth of the excitation wavelength, and the sample temperature, are shown to be critical to reveal the separate signatures from the two regions. Finally, this technique is applied to locally diffused and laser‐doped regions on silicon solar cell pre‐cursors, demonstrating the potential value of this micron‐scale technique in studying and optimizing locally doped regions. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Micro‐Raman and photoluminescence analysis of composite vanadium oxide/poly‐vinyl acetate fibres synthesised by electro‐spinning

Composite vanadium oxide (VO_x)‐based fibres were synthesised by the electro‐spinning method combined with conventional sol–gel processing using polyvinyl acetate (PVAc) as a polymeric binder and vanadium oxytriisopropoxide as a vanadium oxide precursor. The microstructure and composition of as‐spun and calcined (300–500 °C) VO_x–PVAc fibres were systematically investigated by scanning electron microscopy, thermogravimetry, reflectance infrared Fourier transform, micro‐Raman spectroscopy and photoluminescence in view of their possible use in gas sensor fabrication. The comparative discussion of the characterization results indicates that V₂O₅–PVAc fibres are obtained. Calcination gradually removes PVAc and promotes structural rearrangement with consequent fibre‐morphology changes. With increasing calcination temperature, the crystallinity degree of V₂O₅ improves and a more oxygen‐deficient substoichiometric surface layer forms. Calcination at 400 °C preserves the fibre integrity. Indeed, fibres calcined at this temperature appear as the most suitable ones for use as the active layer in gas‐sensing devices. Copyright © 2011 John Wiley & Sons, Ltd.     

Micro‐PIXE studies of low‐level gold solubility in natural magmas: Experiments on two felsic magmas

The limits of gold solubility in granitic magmas are poorly constrained, yet may be important for understanding the formation of several gold deposit types. This is largely due to the fact that this parameter cannot be readily measured in natural rocks. Experimental approaches are also difficult, as an analytical technique is required that combines a high level of spatial resolution (typically <5 µm) with the capability to measure gold in low concentrations. In an attempt to address this problem, experiments were conducted to investigate gold solubility in sulphur‐ and chlorine‐bearing granitic and syenitic magmas, and the products were analysed by micro‐PIXE (particle‐induced x‐ray emission). Starting glasses were synthesized from aluminosilicate gels fired at 1000°C, and were sealed within gold capsules, with 4.4 wt% H₂O and variable proportions of either chlorine or sulphur as potential gold complexing agents. The initially gold free glasses were equilibrated with the pure gold capsules at conditions of 1.5 MPa, 750°C and at fO₂≈NNO buffer, for a period of at least 150 h. All experiments produced quenched granitic and syenitic glasses containing a disseminated, high‐temperature silicate mineral assemblage, in addition to oxide and/or sulphide and small gold crystals. The gold, sulphur and chlorine concentrations of the glasses were analysed, and under the specific analytical conditions used in this study micro‐PIXE was able to detect gold in the glasses at levels as low as 2 ppm. The PIXE data demonstrate that, under the conditions used in this investigation, sulphur is a more effective complexing ligand than chlorine for incorporating gold into the melt structures, and that surprisingly high gold concentrations of up to 4400 ppm were attained in the syenitic magma with 1 wt% sulphur added. Thus, micro‐PIXE analysis has been shown to be capable of constraining the concentration of gold at the generally low values encountered in solubility studies on felsic natural magma compositions, thereby laying the groundwork for future research in this field using the PIXE technique. Copyright © 2004 John Wiley & Sons, Ltd.     

Micro‐Raman scattering spectroscopy study of Li‐doped and undoped ZnO needle crystals

ZnO nanostructures have attracted great attention for possible applications in optoelectronic and spintronic devices. The electrical resistivity because of carriers can be improved by the introduction of Li ions, as Li is a possible dopant for achieving p‐type ZnO. We have carried out a comprehensive micro‐Raman scattering study of the phonons in 1% Li‐ and undoped ZnO needle crystals grown and annealed at 1073 K for 1 and 2 h under oxygen environment. Phonon mode of doped and undoped ZnO does not show any measurable shift for the doping concentration of 1%. As line width is related to point defect density, we find for both Li‐ and undoped ZnO crystals the crystallinity is improving towards the tip of the needle crystals. Copyright © 2008 John Wiley & Sons, Ltd.     

Micro‐beam Laue alignment of multi‐reflection Bragg coherent diffraction imaging measurements

Multi‐reflection Bragg coherent diffraction imaging has the potential to allow three‐dimensional (3D) resolved measurements of the full lattice strain tensor in specific micro‐crystals. Until now such measurements were hampered by the need for laborious, time‐intensive alignment procedures. Here a different approach is demonstrated, using micro‐beam Laue X‐ray diffraction to first determine the lattice orientation of the micro‐crystal. This information is then used to rapidly align coherent diffraction measurements of three or more reflections from the crystal. Based on these, 3D strain and stress fields in the crystal are successfully determined. This approach is demonstrated on a focused ion beam milled micro‐crystal from which six reflections could be measured. Since information from more than three independent reflections is available, the reliability of the phases retrieved from the coherent diffraction data can be assessed. Our results show that rapid, reliable 3D coherent diffraction measurements of the full lattice strain tensor in specific micro‐crystals are now feasible and can be successfully carried out even in heavily distorted samples.     

Broad‐beam PIXE and µ‐PIXE analysis of normal and in vitro demineralized dental enamel

Dental enamel has been widely studied by particle‐induced x‐ray emission (PIXE), but less attention was paid to its demineralization, which leads to caries formation. Using broad‐beam PIXE and µ‐PIXE, we investigated normal enamel and the in vitro formation of pre‐carious lesion in lactic acid solution, aiming also to evaluate intercusp differences within the same tooth. Broad‐beam PIXE was performed using 3.0 MeV protons, and µ‐PIXE maps of Ca, Fe and Zn were collected with 3.1 MeV protons at ～4 µm resolution. In normal enamel a differentiated Ca‐rich surface layer was observed, where Fe and Zn reached their highest levels. In deeper layers, Fe and Zn evidenced quasiperiodic patterns of maxima, possibly due to coupled diffusion‐reaction catalytic processes involved in the enamel growth. Both Fe and Zn appeared to be located in a few distinct types of pools. Near the surface, demineralization induced an increase of Fe, Cu, Zn, Sr and Pb with respect to Ca, attributed to partial hydroxyapatite dissolution and/or to chelate extraction and concentration of trace metals. Ca maps revealed limited changes in the surface layer and a massive loss in the inner enamel; here, Fe was almost depleted and Zn partially removed. The maps of Ca, Fe and Zn demonstrated major intercusp variations in both normal and altered enamel. Thus, broad‐beam PIXE and µ‐PIXE, which do not require (semi)thin sectioning of the tooth as the conventional methods, provide compositional and structural insight of normal dental enamel, of its intercusp variability and of the alterations produced by in vitro demineralization, largely not accessible to the current techniques, and highly relevant for understanding the incipient caries formation. Copyright © 2008 John Wiley & Sons, Ltd.     

Temperature dependence of a Ce3+ doped SiO2 radioluminescent dosimeter for in vivo dose measurements in HDR brachytherapy

Fiber-optic-coupled scintillation dosimeters are characterized by their small active volume if compared to other existing systems, and are therefore particularly suited for internal in vivo dosimetry. Due to possible differences between calibration conditions (i.e., room temperature) and conditions of clinical application (i.e., body temperature), their temperature dependence should be accurately studied. In this work, the temperature dependence of a Ce³⁺ doped SiO₂ scintillation detector coupled to a SiO₂ optical fibre was investigated for high dose rate brachytherapy applications. To this aim, two sets of irradiations with two different Ir-192 sources were performed in a water bath phantom at water temperatures ranging between 17 °C and 40.4 °C (Experiment 1). The relative response of the dosimeter was collected and analyzed. The same experiment was repeated with a second optical fibre which was designed without the active Ce³⁺ doped part at its end (Experiment 2) as well as by changing the length of the passive fibre inserted in water (Experiment 3). The two sets of measurements of experiment 1 were in accordance, indicating a linear increase with temperature of the scintillator sensitivity, with an average increase of 0.27 ± 0.2%/°C. In experiment 2, a 0.5%/°C increase of the collected signal resulted for the passive fibre. No significant difference of the temperature coefficient was found by changing the length of the fibre inserted in water (experiment 3). The obtained results show that a temperature-specific correction factor should be adopted at temperatures different than room temperature (e.g. for in vivo internal dosimetry). Further studies are required to understand the observations.     

Characterization of a Ce3+ doped SiO2 optical dosimeter for dose measurements in HDR brachytherapy

Aim of this work was to study the application of a new miniaturized Ce³⁺ doped SiO₂ scintillation detector to in vivo dosimetry in high dose rate brachytherapy. Energy, dose-rate, temperature and angular dependences of the detector response to ¹⁹²Ir HDR brachytherapy fields were investigated, as well as sensitivity reproducibility and linearity. To this aim, two ad hoc phantoms were designed and developed to perform measurements in water. Intra-session reproducibility resulted to be very high, however inter-session reproducibility showed too high statistical variation. Detector response resulted to increase linearly with dose (R² = 0.997), with no evidence of energy and dose-rate dependence. Sensitivity resulted to increase linearly with temperature (R² = 0.995), with a 0.2% increase each °C. Finally, no significant angular dependence for the source moving around a circle in the azimuthal plane centered at the scintillator was observed. The obtained results show that the proposed detector is suitable for in vivo real-time dosimetry in high dose rate brachytherapy.     

Micro‐Raman analysis of GaAs Schottky barrier solar cell

Gallium arsenide (GaAs) cells have been in the race with silicon single‐crystal cells for the highest efficiency photovoltaic devices. The annealed, irradiated Schottky barrier (SB) solar cells were characterised using micro‐Raman spectroscopy at three different regions: namely, at the (1) ohmic contact region, (2) unirradiated region and (3) irradiated region. We also present a micro‐Raman study of the damage process in annealed GaAs SB solar cells bombarded by high‐energy ions. A Gaussian line shape was fitted to the Raman spectra of the longitudinal optical phonon A₁(LO), and parameters such as intensity, full width at half maximum (FWHM) and the area under the peak were obtained for the different annealing temperatures. Biaxial stress (σ), carrier concentration (n), depletion length (L_d), dislocation velocity (ν) and life time of the first‐order optical phonon (τ) of the A₁(LO) mode of the irradiated region of the samples annealed at different temperatures were calculated. Copyright © 2010 John Wiley & Sons, Ltd.     

Micro‐beam x‐ray fluorescence analysis of individual particles with correction for absorption effects

A method of correction for absorption effects in micro‐beam x‐ray fluorescence analysis is described. A fast, energy‐dispersive, silicon drift detector (SDD) was used to measure the primary x‐ray beam transmitted through the sample. The absorption factors were calculated using the data acquired with the SDD. The possibility of using the coherently, incoherently and multiple scattered primary radiation for determining the mass of individual particles was examined. The proposed methods were validated with the use of NIST K3089 glass micro‐spheres of known composition. Copyright © 2006 John Wiley & Sons, Ltd.     

Development of new CdZnTe detectors for room‐temperature high‐flux radiation measurements

Recently, CdZnTe (CZT) detectors have been widely proposed and developed for room‐temperature X‐ray spectroscopy even at high fluxes, and great efforts have been made on both the device and the crystal growth technologies. In this work, the performance of new travelling‐heater‐method (THM)‐grown CZT detectors, recently developed at IMEM‐CNR Parma, Italy, is presented. Thick planar detectors (3 mm thick) with gold electroless contacts were realised, with a planar cathode covering the detector surface (4.1 mm × 4.1 mm) and a central anode (2 mm × 2 mm) surrounded by a guard‐ring electrode. The detectors, characterized by low leakage currents at room temperature (4.7 nA cm^?2 at 1000 V cm^?1), allow good room‐temperature operation even at high bias voltages (>7000 V cm^?1). At low rates (200 counts s^?1), the detectors exhibit an energy resolution around 4% FWHM at 59.5 keV (²⁴¹Am source) up to 2200 V, by using commercial front‐end electronics (A250F/NF charge‐sensitive preamplifier, Amptek, USA; nominal equivalent noise charge of 100 electrons RMS). At high rates (1 Mcounts s^?1), the detectors, coupled to a custom‐designed digital pulse processing electronics developed at DiFC of University of Palermo (Italy), show low spectroscopic degradations: energy resolution values of 8% and 9.7% FWHM at 59.5 keV (²⁴¹Am source) were measured, with throughputs of 0.4% and 60% at 1 Mcounts s^?1, respectively. An energy resolution of 7.7% FWHM at 122.1 keV (⁵⁷Co source) with a throughput of 50% was obtained at 550 kcounts s^?1 (energy resolution of 3.2% at low rate). These activities are in the framework of an Italian research project on the development of energy‐resolved photon‐counting systems for high‐flux energy‐resolved X‐ray imaging.     

Micro‐Raman analysis and finite‐element modeling of 3 C‐SiC microstructures

Micro‐ and nano‐electromechanical systems (MEMS and NEMS) fabricated in 3 C‐SiC are receiving particular attention thanks to the material physical properties: its wide band gap (2.3 eV), its ability to operate at high temperatures, its mechanical strength and its inertness to the exposure in corrosive environments. However, high residual stress (which is normally generated during the hetero‐epitaxial growth process) makes the use of 3 C‐SiC in Si‐based MEMS fabrication techniques very limited leading to a failure of micro‐machined/sensor structures. In this paper, micro‐Raman characterizations and finite‐element modeling (FEM) of microstructures realized on poly and single‐crystal (100) 3 C‐SiC/Si films are performed. Transverse optical (TO) Raman mode analysis reveals the stress relaxation on the free standing structure (796.5 cm⁻¹) respect to the stressed unreleased region (795.7 cm⁻¹). Also, microstructures as cantilever, bridge and planar rotating probe show an intense stress field located around the undercut region. Here, the TO Raman mode undergoes an intense shift, up to 2 cm⁻¹, ascribed to the modification of the Raman stress tensor. Indeed, the generalized axial regime, described by diagonal components of the Raman stress tensor, cannot be applied in this region. Raman maps analysis and FEM simulations show the ‘activation’ of the shear stress, i.e. non‐diagonal components of the stress tensor. The stress‐Raman modes shift correlation, in the case of fully non‐diagonal stress tensors, has been investigated. The aim of future works will be to minimize the stress field generation and the defects density within the epitaxial layer. Copyright © 2012 John Wiley & Sons, Ltd.     

Development of Ag doped crystalline SiO2 for possible applications in real-time in-vivo OSL dosimetry

A new Ag-doped crystalline SiO₂ based OSL phosphor is developed. This phosphor shows good OSL properties and the sensitivity is comparable to that of the commercial Al₂O₃:C. For the luminescence integrated over initial 3s, BSL (blue stimulated luminescence) and GSL (green stimulated luminescence) sensitivities were found to be 0.54 and 3.1 times the respective BSL and GSL sensitivities of the commercial Al₂O₃:C. The PL emission is found to vary from UV to visible range with the change in the Ag concentration. Thus the material can be used as BSL or GSL phosphor. The simple preparation procedure, fast decay, very good sensitivity will make this phosphor suitable for real-time dosimetric applications, using OSL technique.     

Micro‐Raman spectroscopy and VP‐SEM/EDS applied to the identification of mineral particles and fibres in histological sections

Histological sections of a patient affected by an important respiratory disease were analysed firstly by optical microscope(OM)—crossed polarisers—to identify the presence of incorporated inorganic particles, with particular attention to the fibrous ones. Then, the particles/fibres that were found were studied both with micro‐Raman spectroscopy and variable‐pressure scanning electron microscopy with energy‐dispersive spectroscopy (VP‐SEM/EDS). The two techniques allowed the in situ characterisation of the inorganic phases without disintegration of the organic matter. Micro‐Raman spectroscopy was able to identify the vibrating chemical groups of the mineral phase associated with the inorganic grain while the crystalline structure was preserved by the biological system. The VP‐SEM/EDS characterisation, defining the elemental chemical composition of the analysed particle/fibre, allowed confirmation of the mineral phase deducible from spectroscopic data or its identification with certainty when the spectroscopic data were not exhaustive. Copyright © 2009 John Wiley & Sons, Ltd.     

XRF analysis of arsenic‐doped skin phantoms

Chronic arsenic poisoning can lead to serious health problems including vascular disorders and cancer. Therefore, the development of a system to measure arsenic in vivo would be useful in monitoring exposure. In particular, as skin is one of the tissues in which arsenic has health consequences and is stored for a prolonged period of time, an in vivo measure of skin arsenic content would be a clinically useful measure of chronic exposure. The preliminary development of an x‐ray fluorescence system to measure arsenic in vivo is reported. Standard addition arsenic‐ doped polyester resin phantoms were prepared, and the fluorescence induced by silver K x‐rays from a ¹⁰⁹Cd source was measured. Preliminary estimates of detection limits for an 8 mm thick phantom and an effective dose of ～0.3 µSv are 3.5 ± 0.2 and 10.3 ± 0.5 ppm in 90 and 180° measurement geometries, respectively, for a measurement time of 30 min. Copyright © 2004 John Wiley & Sons, Ltd.     

Choice of X‐ray mass attenuation coefficients for PIXE analysis of silicate minerals and rocks

The accuracy of each of three mass attenuation coefficient databases was assessed using particle‐induced X‐ray emission measurements performed on well‐characterized, homogeneous silicate glass and mineral standards. In a fundamental parameters computation, the absolute efficiency constants of the light elements Mg, Al and Si, found within each standard, were determined. These were compared with the efficiency constants deduced from separate particle‐induced X‐ray emission measurements performed on pure targets of the same three elements. In this comparison, a 7–9% discrepancy was found when using the XCOM database for the computation, but this was reduced to 2–5% when FFAST coefficients were substituted. Further improvement was achieved when a hybrid database was adopted. This ‘Mixed’ database consisted of primarily XCOM coefficients with FFAST values inserted for the light element (Z = 11,…, 14) attenuation of photons having energy less than their K edge and for oxygen in the 1–2 keV range. The average efficiency constant discrepancies were reduced to ?0.5–2%. Copyright © 2015 John Wiley & Sons, Ltd.     

Micro‐Raman study of PET single fibres under high hydrostatic pressure: phase/conformation transition and amorphization

The micro/nano structural evolution of a PET single fibre under hydrostatic pressure has been studied by Raman micro spectroscopy in a diamond anvil cell (DAC). Different bands in the Raman spectra were used as probes: the low wavenumber collective modes (<250 cm⁻¹) representative of the long‐range chain organization, as well as the stretching and bending amide and aromatic ring modes representative of the local chain behaviour. The in situ analysis at different pressures shows an evolution from an axial oriented trans‐conformation to an amorphous, isotropic material, i.e. the reverse transformation observed during the process of drawing the fibre from an isotropic amorphous precursor. Copyright © 2007 John Wiley & Sons, Ltd.     

Micro‐Raman spectroscopy analysis of 16th century Portuguese Ferreirim Masters oil paintings

In the present work a set of eight altarpieces of the 16th century (1532–1534), attributed to the Ferreirim Masters (Gregório Lopes, Garcia Fernandes and Cristóvão de Figueiredo), from the Santo António de Ferreirim Monastery (North of Portugal), were analysed by micro‐Raman spectroscopy. For this purpose some samples were taken from the paintings to characterise its artist's ‘school’. It was found that the preparation was made with chalk and gypsum and the palette composed mainly of lamp black, azurite, lead white (mixed with other pigments), lead–tin yellow type I, goethite (the main constituent of yellow ochre), red lead (as under painting), haematite (the main constituent of red ochre) and vermilion. Indigo was detected in one sample. Some derivatives and degradation products were found mainly in the panels subjected to high temperatures during a fire occurred in 1954: a degradation product from massicot or red lead, lead carbonate (dehydrated derivative of lead white), bassanite and anhydrite (hemi‐ and dehydrated forms of gypsum). These results are compared with those of previous total reflection X‐ray fluorescence spectroscopy (TXRF) analyses. Copyright © 2009 John Wiley & Sons, Ltd.     

Micro‐Raman and IR study of the compressive behaviour of poly(paraphenylene benzobisoxazole) (PBO) fibres in a diamond‐anvil cell

The micro/nano structural evolution of PBO (poly(paraphenylenebenzobisoxazole), commercial name Zylon) fibres has been studied by Raman and IR spectroscopy in a diamond‐anvil cell, up to ∼15 GPa. Different modes were considered in the 900–1700 cm⁻¹ (Raman) and 800–3300 cm⁻¹ (IR) spectral range. The material behaviour appears more similar to that of a densely packed inorganic structure than to the behaviour previously observed for polyamide fibres, and is related to the compact arrangement of the rigid heterocyclic rings. Wavenumber shift starts with increase in pressure and a transition between the two regimes was revealed at ∼2–2.5 GPa, and it was assigned to the loss of order between neighbouring PBO chains. A good correlation is observed between the macroscopic mechanical properties and the nanomechanics at the chemical bond scale. Copyright © 2006 John Wiley & Sons, Ltd.