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Porous silicon (PS) is a material with a great interest due to its optical (photoluminescent) and chemical (reactive surface) properties, for this reason, it is important to find new ways to be applied in the development of new devices. In this work the optic, chemical and morphologic properties of PS compressed into a tablet were characterized. The porous silicon was physically removed from the crystalline silicon and then was compressed to obtain a tablet. The optical characterization was performed through photoluminescence (PL) spectra. The PL spectrum from the PS tablet showed a small shift to higher wavelengths in comparison with the PS layers used to obtain the tablet. The x-ray diffraction pattern showed a loss in PS tablet crystallinity after being subjected to the compression process. The morphological characterization was carried out with a scanning electron microscope and the images showed a compact surface with high rugosity. This result was supported by the profilometry analysis, which also showed an irregular surface. The chemical properties of the surface were characterized with Fourier transform infrared spectroscopy (FTIR). The FTIR characterization showed an oxidized and highly hydrogenated surface.

The content of biogenic amines has been studied due to the toxicity of these compounds in humans when are consumed exogenously, and is used as an indicator of quality in the food industry. The manly method for its determination is high performance liquid chromatography. However, it requires a long time for analysis. An alternative method is the use of biosensors, porous silicon with gold nanoparticles were obtained by electrochemical attack assisted with metal salt. These substrates were used for the construction of a biosensor capable of detecting BA using diamine oxidase enzyme as an element of biological recognition and is binding using the self-assembled monolayers method. The correlation between scanning electron microscopy, X-ray dispersive energy spectroscopy, and Fourier Transform infrared spectroscopy analysis, demonstrated the correct construction of the biosensor and the detection of biogenic amines by interaction with the enzyme. Finally, with the built biosensor it was possible to detect three important biogenic amines found in food.

In this article, physical characteristics of porous silicon (PS) obtained by electro chemical etching using HAuCl4 in the electrolyte are described. The morphological and optical features of PS decorated with gold-nanoparticles (AuNPs) were analyzed in function of the chemical etching time. The insertion of AuNPs inside the PS were performed simultaneously with the formation of the porous silicon layer. Scanning electron microscopy (SEM) analysis showed the formation and incorporation of AuNPs with an average size of 20 nm in the PS structure, which has a pore size of 1.5 μm. Also, it was possible to observe the loss of Si in function of the etching time. Photoluminescence spectroscopy analysis shows a decreasing of the PL intensity, which can be related to the presence of oxygen in the samples. Raman spectroscopy was used to estimate the size of the Si nanocrystals in the PS structure, which suffers a reduction in size due to the presence of HAuCl4 in the electrolyte.

Aluminum is one of the most utilized metals in food, aeronautical, automotive, and architectural industries, due to its intrinsic properties. For this reason, it is important to explore new methods to reuse it. This study was performed to analyze the mechanical and structural properties of aluminum obtained with a homemade oven composed with easily accessible materials. Due to the lack of data about the characteristics of these kinds of materials, its possible applications are unknown. The structural characterization was carried out through optic and electronic microscopy and mechanical testing. The chemical composition was analyzed with energy dispersive spectroscopy. Microscopy images show the presence of cavities in the samples besides the evidence of problems in the solidification phase. The composition analysis shows the presence of Carbon and Magnesium. The mechanical testing showed that the Al obtained had elastic modules and less elongation when compared to commercial Al, which limited the possible uses of this kind of aluminum.

The use of gallium arsenide (GaAs) films to obtain gallium nitride (GaN) on a quartz substrate is reported herein. The GaAs films were deposited on quartz substrates via the close-spaced vapor transport technique (CSVT) with good crystalline quality. GaN was obtained via nitridation wherein the GaAs samples were subjected to ammonia and hydrogen flow at atmospheric pressure. Several experiments were conducted at 800 °C, 900 °C, and 1000 °C, suggesting that nitridation at 900 °C is suitable for GaN obtention. Another group of experiments was conducted to observe the effect of nitridation time on the morphology of GaN. The nitridation temperature was kept at 900 °C while the nitridation times were 10, 20, and 30 min. XRD and EDS characterizations revealed that the nitridation time determines the production of samples with both GaAs and GaN structures (10 min) or only the GaN structure (20 and 30 min). A GaN film exhibiting a wurtzite preferential structure was obtained subsequent to 30 min of nitridation.

The structural and electronic properties of Znm@C60 and Znm@C70 endohedral metallofullerenes (m = 1-5) were obtained by means of DFT calculations. The whole set of endohedral metallofullerenes (EMFs) are energetically stable despite of they are higher in binding energy than the pristine ones (C60 and C70). There is a structural transformation for Zn4 and Zn5 clusters, when these are encapsulated inside of C60 and C70 fullerenes; the first one changes from trigonal by-pyramid to square pyramid and the second one goes from tetrahedron to planar rhombus, respectively. This effect generates transitions on their electronic behavior, the Znm@C60 systems exhibit two of them: from semiconductor →conductor →semiconductor and the Znm@C70 systems present just one: from semiconductor →conductor. These electronic changes are explained by means of PDOS, HOMO and LUMO iso-surfaces and charge transference. From absorption specters, these EMFs improve the collection of visible and ultraviolet light for both cases, respect to their pristine cases. These physic-chemical properties generate potential applications such as: encapsulation of heavy metals, design of electronic devices, gases sensors and solar cells.

DFT calculations were carried out to determine the electronic and structural properties of titanium dioxide clusters either pristine or doped. In this work, a maximum size of approximately 1.5 nm for the three cases was considered. There are no drastic changes concerning the geometry for larger clusters; however there is an important reduction of electronic gap for doped clusters compared to pristine ones in all range considered. The pristine clusters enhance the visible-light photocatalytic activity, whereas those of systems doped with one nitrogen and carbon atom exhibit a spectral shift in the near-infra-red region due to the introduction of additional electronic states originating from the N and C 2p orbitals in the band gap.

We present zinc oxide (ZnO) particles obtained inside a porous silicon matrix in the same electrolytic process using a p-type silicon wafer in a hydrofluoric acid (HF) solution containing formaldehyde (CH2O) and hydrated zinc sulfate as additives. The X-ray diffraction pattern of the sample confirmed the presence of ZnO with a hexagonal-type wurtzite structure. Photoluminescence (PL) spectra of the samples, before and after the functionalization process, were measured to observe the effect of ZnO inside the porous silicon. The PL measurements of porous silicon functionalized with ZnO (ZnO/PS) revealed infrared, red, blue, and ultraviolet emission bands. The ultraviolet region corresponds to the band-band emission of ZnO, and the visible emission is attributed to defects. The results of the nitrogen adsorption/desorption isotherms of the PS and ZnO/PS samples revealed larger BET surface areas and pore diameters for the ZnO/PS sample. We conclude that ZnO/PS can be obtained in a one-step electrolytic process. These types of samples can be used in gas sensors and photocatalysis.

The effect of using different electrolytes in the physical and optical properties of porous silicon was studied. To do this porous silicon (PS) samples photoluminescent in the visible range from (100) oriented n-type crystalline silicon prepared by anodic etching were obtained. The first electrolyte was composed of a mixture of hydrofluoric acid (HF) and ethanol (CH3-CH2-OH) in a ratio of 1 : 2, respectively. The second was composed of hydrofluoric acid (HF), ethanol (CH3-CH2-OH), and hydrogen peroxide (H2O2) in a ratio of 1 : 1 : 2, respectively. Raman scattering, photoluminescence (PL), gravimetry, scanning electron microscopy (SEM), and energy dispersive spectrometer (EDS) measurements on the PSL were carried out. Raman scattering showed that the disorder in the samples obtained with H2O2is greater than in the samples obtained without this. The PL from PS increased in intensity with the incremental change in the anodization time and showed a blueshift. The blueshift of PL is consistent with the reduction in size of the silicon nanocrystallites. The sizes of nanocrystals were estimated to be 3.08, 2.6, and 2.28 nm. The gravimetric analysis showed that the porosity increased with the incorporation of H2O2. SEM images (morphological analysis) showed an incremental change in the quantity and in the porous size.

Electroluminescent Devices Based on Junctions of Silicon-Rich Oxide with Indium Doped Zinc Oxide Thin Solid Films F. Severiano1, G. Garcia2, L. Castaneda3 ∗, J. M. Gracia-Jimenez1, A. Maldonado4, M. Avendano-Alejo5, A. Coyopol2, and T. Diaz2 1Instituto de Fisica, Benemerita Universidad Autonoma de Puebla, Apartado Postal J-48, 72570, Mexico 2CIDS-ICUAP, Benemerita Universidad Autonoma de Puebla, 14 sur y Avenida San Claudio, Edif. 137, 72570 Puebla, PUE, Mexico 3Escuela Superior de Ingenieria Mecanica y Electrica Unidad Ticoman, Instituto Politecnico Nacional, 07340 Mexico, DF, Mexico 4Departamento de Ingenieria Electrica, Centro de Investigacion y de Estudios Avanzados del Instituto Politecnico Nacional CINVESTAV-IPN, SEES, Apartado Postal 14740, Mexico 5Centro de Ciencias Aplicadas y Desarrollo Tecnologico, Universidad Nacional Autonoma de Mexico, Apartado Postal 70-186, 04510, D. F., Mexico

Electroluminescent devices (ELD) based on junctions of indium doped zinc oxide (ZnO:In) and porous silicon layers (PSL) are presented in this work. PSL with different thicknesses and photoluminescent emission, around 680 nm, were obtained by anodic etching. PSL were coated with a ZnO:In film which was obtained by ultrasonic spray pyrolysis technique. Once obtained, this structure was optically and electrically characterized. When the devices were electrically polarized they showed stable electroluminescence (EL) which was presented as dots scattered over the surface. These dots can be seen with the naked eye. The observed EL goes from the 410 to 1100 nm, which is formed by different emission bands. The EL emission in the visible region was around 400 to 750 nm, and the emission corresponding to the infrared part covers the 750 to 1150 nm. The electrical characterization was carried out by current-voltage curves(I-V)which show a rectifying behavior of the devices. Observed electroluminescent dots are associated with the electron-hole injection into quantized states in PS as well as the emission from the ZnO:In film.

We report the obtaining of electroluminescent devices (ELD) from porous silicon (PS) and indium doped zinc oxide (ZnO:In) junctions. PS presented photoluminescence (PL) in the visible region of the electromagnetic spectrum. ZnO:In thin film was obtained by dip coating technique. SEM images and IR measurements showed the incorporation of the ZnO:In in the PS structure. Once obtained, the device was optically and electrically characterized. The ELD showed emission in the visible (450–850 nm) and infrared region (900–1200 nm) where it was electrically polarized. The visible emission was detected as luminescent spots on the surface. Electrical characterization was carried out by current-voltage (I-V) curves. The I-V curves showed rectifying behavior. It was related to the quenching of the EL with the process that takes place in the PS when it was immersed in the precursor solution of the ZnO:In.

The aim of this work was to study the structural modification in the porous silicon layer (PSL), when they are obtained from electrodeposition using a metal salt of Au (HAuCl4) in the electrolyte. The deposition of Au nanoparticles and the formation of the PSL were performed simultaneously. The structural and optical properties of the gold/porous-Si were analyzed by scanning electron microscopy (SEM), X-ray energy dispersive spectroscopy (EDS), photoluminescence (PL) and Raman scattering. Through the methodology implemented, it was obtained gold/porous-Si nanocomposites. The size of the gold nanoparticles was above 15 nm, and the pore size was 18 nm. The PL intensity showed an increase with the incorporation of gold nanoparticles due to the enhancement of a surface plasmon effect. The size of Si nanocrystals in the PSL structure was estimated through PL and Raman measures and it was ~3 nm.

A theory for calculating the effective optic response of photonic crystals with metallic and magnetic inclusions is reported, for the case when the wavelength of the electromagnetic fields is much larger than the lattice constant. The theory is valid for any type of Bravais lattice and arbitrary form of inclusions in the unitary cell. An equations system is obtained for macroscopic magnetic field and magnetic induction components expanding microscopic electromagnetic fields in Bloch waves. Permittivity and permeability effective tensors are obtained comparing the equations system with an anisotropic nonlocal homogenous medium. In comparison with other homogenization theories, this work uses only two tensors: nonlocal permeability and permittivity. The proposal showed here is based on the use of permeability equations, which are exact and very simple. We present the explicit form of these tensors in the case of binary 1D photonic crystals.