Commercial LaAlO3 substrates were thermally cycled simulating a procedure similar to those followed during TiO2 and SnO2 dilute magnetic semiconductors’ film pulsed laser deposition. Ferromagneticlike behavior was found in some substrates, in which metallic iron impurities were detected by x-ray photoelectron spectroscopy and total reflection x-ray fluorescence measurements. A thorough experimental investigation, using high resolution techniques, showed that these impurities were introduced by the procedure used to fix the substrates to the oven silicon holders. It is suggested that magnetism observed previously in nominally pure SnO2 films is of extrinsic origin.

The growth of graphene on an irregular threedimensional (3D) Ni structure is demonstrated to be an interesting platform for molecular sensing, graphene-enhanced Raman scattering, and surface-enhanced Raman scattering (SERS) applications after galvanic exchange of Ag + ions. Raman, scanning electron microscopy (SEM), energydispersive spectroscopy (EDX), optical images, and diffuse reflectance demonstrate that graphene grows in a multilayer fashion with different stacking configurations. Statistics performed employing Raman show that the as-grown graphene can be classified into two main stacking configurations: AB (or Bernal stacking) and rotated graphene, which are separated by a full width at half-maximum (fwhm) threshold of ∼30 cm −1 corresponding to the 2D Raman band. The rotated stacking senses low concentrations of methylene blue (MB), whereas the AB stacking seems to be much less sensitive upon molecular adsorption. The galvanic exchange of Ag leads to agglomerates preferentially formed on top of graphene wrinkles, which ultimately became the target spots for performing SERS. Our experiments demonstrate that the as-grown graphene, composed of different stacking configurations, can be used as a molecular sensor to detect 10 −6 M concentration of MB as well as nanomolar concentrations of MB and thiram (by SERS applications), after the galvanic exchange with Ag.

Articles you may be interested inMicrostructure and magnetic properties of MFe2O4 (M = Co, Ni, and Mn) ferrite nanocrystals prepared using colloid mill and hydrothermal method J. Appl. Phys. 117, 17A328 (2015) We report by the first time a high pressure X-ray diffraction and Raman spectroscopy study of cobalt ferrite (CoFe 2 O 4 ) nanoparticles carried out at room temperature up to 17 GPa. In contrast with previous studies of nanoparticles, which proposed the transition pressure to be reduced from 20-27 GPa to 7.5-12.5 GPa (depending on particle size), we found that cobalt ferrite nanoparticles remain in the spinel structure up to the highest pressure covered by our experiments. In addition, we report the pressure dependence of the unit-cell parameter and Raman modes of the studied sample. We found that under quasi-hydrostatic conditions, the bulk modulus of the nanoparticles (B 0 ¼ 204 GPa) is considerably larger than the value previously reported for bulk CoFe 2 O 4 (B 0 ¼ 172 GPa). In addition, when the pressure medium becomes non-hydrostatic and deviatoric stresses affect the experiments, there is a noticeable decrease of the compressibility of the studied sample (B 0 ¼ 284 GPa). After decompression, the cobalt ferrite lattice parameter does not revert to its initial value, evidencing a unit cell contraction after pressure was removed. Finally, Raman spectroscopy provides information on the pressure dependence of all Raman-active modes and evidences that cation inversion is enhanced by pressure under non-hydrostatic conditions, being this effect not fully reversible. V C 2015 AIP Publishing LLC. [http://dx

The way graphene (GDs) and carbon dots (CDs) are synthesized and combined with TiO2 determine their photoelectrochemical efficiency upon UV and visible LED lights. GDs and CDs are obtained by relatively unexplored top-down methods and conventional bottom-up methods, respectively. Top-down methods consist in the seedless growth of ZnO nanoparticles on the surface of graphene and the electrochemical cleavage of graphene grown on Ni foam. These carbon nanoparticles are later combined with TiO2 by different approaches such as solution mixing, adsorption via APTES linkers, and drop-casting on an already formed TiO2 film. Once the films are formed, they are placed into a photoelectrochemical Zahner cell and irradiated with LED lights at 450 and 360 nm. It is determined that CDs and GDs perform as efficient photosensitizers as demonstrated by an increase of ∼19- and 20-fold net photocurrent density when irradiated with UV and visible LED lights, respectively. We encountered that CDs are more sensitive upon visible light, whereas GDs promptly respond to UV light due to their difference in size-dependent band gap. Importantly, GDs obtained from seedless growth of ZnO are sensitive to both: UV and Vis LED irradiation. The combination of both nanocarbons would expand the absorption range and may be potentially used as cosensitizers toward the construction of more effective and advanced photoanodes.

The structural and magnetic properties of Fe (3−x) Zn x O 4 (x : 0, 0.1, 0.2, 0.5, 1) nanoparticles, prepared by wet chemical method, have been studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), Mössbauer spectroscopy, and magnetization measurements. The nanoparticles are polyhedrical-shaped with a narrow distribution in size as it was verified by SEM. By Rietveld analysis of XRD patterns, it was determined that the crystallites' sizes of Fe (3−x) Zn x O 4 in spinel structure is in the range of 30 to 50 nm. Hysteresis cycles, measured at different temperatures (300, 200, 100, 50, and 7 K), showed an increase in saturation, while temperature is diminished, as it is expected. All the samples, exhibited a high blocking temperature of ∼350 K, as it was determined by ZFC-FC measurements. This fact, reveals their strongly interacting superparamagnetic nature. Real ac susceptibility increases with temperature, while the imaginary part has a maximum, which depends on frequency, and it is related to a critical temperature, which depends on composition. A Néel-Arrhenius dependence of frequency on the critical temperature was found for all the samples. We determined a minimum of the effective anisotropy for x = 0.2.