Gabriele Navarra

Cationic distribution and spin canting in CoFe2O4 nanoparticles

CoFe(2)O(4) nanoparticles (D(NPD) ~6 nm), prepared by a thermal decomposition technique, have been investigated through the combined use of dc magnetization measurements, neutron diffraction, and (57)Fe Mössbauer spectrometry under high applied magnetic field. Despite the small particle size, the value of saturation magnetization at 300 K (M(s) ͠= 70 A m(2) kg(-1)) and at 5 K (M(s) ͠= 100 A m(2) kg(-1)) are rather close to the bulk values, making the samples prepared with this method attractive for biomedical applications. Neutron diffraction measurements indicate the typical ferrimagnetic structure of the ferrites, showing an inversion degree (γ(NPD) = 0.74) that is in very good agreement with cationic distribution established from low temperature (10 K) Mössbauer measurements in high magnetic field (γ(moss) = 0.76). In addition, the in-field Mössbauer spectrum shows the presence of a non-collinear spin structure in both A and B sublattices. The results allow us to explain the high value of saturation magnetization and provide a better insight into the complex interplay between cationic distribution and magnetic disorder in ferrimagnetic nanoparticles.

Structural characterization study of FeCo alloy nanoparticles in a highly porous aerogel silica matrix

A series of FeCo-SiO(2) nanocomposite aerogels having different FeCo loadings of 3, 5, and 8 wt % were prepared using a novel urea-assisted sol-gel route. The size of the nanoparticles, which was estimated using Scherrer analysis of the main peak of the x-ray diffraction pattern, varies from 3 to 8 nm. X-ray absorption fine structure (EXAFS) and x-ray absorption near edge structure (XANES) techniques at both Fe and Co K edges were used to investigate the structure of the FeCo nanoparticles. EXAFS and XANES show that FeCo nanoparticles have the typical bcc structure. Evidence of oxidation was observed in low FeCo content aerogels. Spatially resolved electron energy loss spectroscopy analysis suggests the formation of a passivation layer of predominantly iron oxide.

Characterization of FeOOH nanoparticles and amorphous silica matrix in an FeOOH-Sio 2 nanocomposite

A nanocomposite with an FeOOH/SiO2 ratio equal to 17.7 wt% and the pertinent matrix, obtained by etching away the nanoparticles through reaction with hydrochloric acid, were investigated by XRD, TGA-DTA, heliostereopicnometry, BET, and TEM techniques. The study shows the presence in the nanocomposite of ferrihydrite nanoparticles phase with average dimensions around 4 nm. The FeOOH nanoparticles structure was analyzed by synchrotron X-ray diffraction data using the distribution difference curve method. The porous structure of the matrix resulting by etching away the nanoparticles differs significantly from that of a pure SiO2 sample obtained by hydrolysis of TEOS under the same operative conditions followed in the nanocomposite preparation.

1H NMR metabolite fingerprinting as a new tool for body fluid identification in forensic science

In this feasibility study, we propose, for the first time, 1H NMR spectroscopy coupled with mathematical strategies as a valid tool for body fluid (BF) trace identification in forensic science. In order to assess the ability of this approach to identify traces composed either by a single or by two different BFs, samples of blood, urine, saliva, and semen were collected from different donors, and binary mixtures were prepared. 1H NMR analyses were carried out for all samples. Spectral data of the whole set were firstly submitted to unsupervised principal component analysis (PCA); it showed that samples of the same BF cluster well on the basis of their characterizing molecular components and that mixtures exhibit intermediate characteristics among BF typologies. Furthermore, samples were divided into a training set and a test set. An average NMR spectral profile for each typology of BF was obtained from the training set and validated as representative of each BF class. Finally, a fitting procedure, based on a system of linear equations with the four obtained average spectral profiles, was applied to the test set and the mixture samples; it showed that BFs can be unambiguously identified, even as components of a mixture. The successful use of this mathematical procedure has the advantage, in forensics, of overcoming bias due to the analysts personal judgment. We therefore propose this combined approach as a valid, fast, and non‐destructive tool for addressing the challenges in the identification of composite traces in forensics. Copyright

Structural investigation of Fe2O3–SiO2 nanocomposites through radial distribution functions analysis

Two Fe2O3–SiO2 nanocomposites containing 50% by weight of iron oxide were prepared by a sol–gel method. By changing the surface to volume ratio of the gelling mass from 0.04 (sample A) to 0.3 cm−1 (sample B), gelation times changed, resulting in nanoparticles of average size of about 10 and 4 nm, respectively. Accurate X-ray diffraction (XRD) data were collected and used to calculate total structure and correlation functions. The analysis of these functions unequivocally proved that in both samples maghemite is the iron oxide formed. The result demonstrated that decreasing the gelation time gives rise to the formation of smaller and smaller nanoparticles of the same phase. The possibility of interpreting the XRD pattern of sample B in terms of occurrence of 2-line ferrihydrite was discussed.

A reverse Monte Carlo study of SiO2 and B2O3 glasses

Abstract The reverse Monte Carlo simulation method has been applied to study the structure of B 2 O 3 and SiO 2 glasses. The standard procedure starting from a random distribution of atoms has not provided satisfactory results. In both cases, a considerable fraction of the network forming atoms has been found to be incorrectly coordinated. To overcome this fact, some constraints have been added in the refinement process. Advantages and disadvantages of this method are discussed. Different starting distributions of atoms have been used for simulating the structure of vitreous B 2 O 3 . No particular preference for the presence of boroxol rings has been found. The structure of vitreous SiO 2 has been well reproduced starting from the α-quartz crystalline form. A small amount of oxygen atoms has been allowed to be far from the first Si coordination shell.

Partial structure factors of amorphous Ni2Zr by anomalous X-ray scattering

Abstract The anomalous X-ray scattering technique has been employed to extract the partial structure factors for an amorphous Ni2Zr sample prepared by mechanical alloying. Four independent measurements were used to build a suitable system of equatuions where the differential structure factors were also introduced in order to reduce the ill-conditioning. A comparison of the short range atomic distribution with a rapidly quenched sample of similar composition investigated by different techniques is also reported.

The structure of a zinc metaphosphate glass. A reverse Monte Carlo study

A combination of six sets of independent experimental data has been used in a reverse Monte Carlo procedure to obtain information about the structure of a zinc metaphosphate glass. The model structural functions have been fitted simultaneously against structural functions obtained from neutron diffraction data, from four X-ray diffraction experiments carried out at different energies, and from an extended X-ray absorption fine structure (EXAFS) spectroscopy data set. The final model structure is consistent with a description of the vitreous structure made of long phosphate chains, with the zinc ions interposed in between.

Application of a regularization method to anomalous X-ray scattering of amorphous materials

Abstract A regularization algorithm is applied to the extraction of the partial structure factors (PSFs) of amorphous binary alloys from anomalous X-ray scattering data. Simulated scattering intensities, calculated by known PSFs, are used to test the stability and accuracy of the method when increasing noise levels are introduced in the input data. The regularized PSFs are rather good approximations to the original ones.

An EXAFS study on iron-cobalt-silica nanocomposite materials prepared by the sol-gel method

The structural evolution of FeCo-SiO2 xerogel and aerogel nanocomposite samples during their sol-gel preparation have been studied by EXAFS (extended X-ray absorption fine structure) technique. Depending on the precursors of the alloy nanoparticles different intermediate are formed which have a strong influence on the formation of the FeCo alloy of the desired composition. The porous structure also plays an important role.