Multilayered Solar Energy Converters with Flexible Sequence of p and n Semiconductor Films

Non-traditional design of multi-layered solar energy converters is proposed, with electrically independent p-i-n junctions. This new approach allows utilization of cheap and abundant II-VI, IV and IV-VI materials instead of III-V ones, using also cheap and economic deposition techniques like Chemical Bath Deposition (CBD) or Chemical Vapor Deposition (CVD) instead of expensive Molecular Beam Epitaxy (MBE). The CVD reactor with three atomic sources was built and used. II-VI and IV-VI semiconductor materials were prepared either in CVD reactor, or by CBD techniques. Besides, the original two-stage technology was employed: first the precursor oxide/hydroxide film of corresponding metal (like cadmium oxide/hydroxide) was prepared by some variety of CBD methods, and at the second stage, in CVD reactor the non-metallic component of precursor film was substituted by chalcogen, producing materials like CdS, CdSe, PbTe, etc. The semiconductor materials thus produced were of high quality, with basic parameters corresponding to those for the single crystals. Several experimental multilayered converters were constructed (in particular, with CdS/CdTe, CdS/PbS and Si/PbTe active bilayers). The preliminary results of their studying have shown that these and similar devices can be used in solar cells and photo sensors with satisfactory efficiency, and have great potential for improvement

PbS Thin Films for Photovoltaic Applications Obtained by Non-Traditional Chemical Bath Deposition

To optimize cost-efficiency relation for thin film solar cells, we explore the recently developed versions of chemical deposition of semiconductor films, together with classic CBD (Chemical Bath Deposition): SILAR (Successive Ionic Layer Adsorption and Reaction) and PCBD (Photo Chemical Bath Deposition), all of them ammonia-free and ecologically friendly. The films of CdS and PbS were made, and experimental solar cells with CdS window layer and PbS absorber elaborated. We found that band gap of PbS films can be monitored by deposition process due to porosity-induced quantum confinement which depends on the parameters of the process. We expect that the techniques employed can be successfully used for production of optoelectronic devices

Reactive Extrusion as a Pretreatment in Cassava (Manihot esculenta Crantz) and Pea (Pisum sativum L.) Starches to Improve Spinnability Properties for Obtaining Fibers

Starch is a biocompatible and economical biopolymer in which interest has been shown in obtaining electrospun fibers. This research reports that cassava (CEX) and pea (PEX) starches pretreated by means of reactive extrusion (REX) improved the starches rheological properties and the availability of amylose to obtain fibers. Solutions of CEX and PEX (30–36% w/v) in 38% v/v formic acid were prepared and the rheological properties and electrospinability were studied. The rheological values indicated that to obtain continuous fibers without beads, the entanglement concentration (Ce) must be 1.20 and 1.25 times the concentration of CEX and PEX, respectively. In CEX, a higher amylose content and lower viscosity were obtained than in PEX, which resulted in a greater range of concentrations (32–36% w/v) to obtain continuous fibers without beads with average diameters ranging from 316 ± 65 nm to 394 ± 102 nm. In PEX, continuous fibers without beads were obtained only at 34% w/v with an average diameter of 170 ± 49 nm. This study showed that starches (20–35% amylose) pretreated through REX exhibited electrospinning properties to obtain fibers, opening the opportunity to expand their use in food, environmental, biosensor, and biomedical applications, as vehicles for the administration of bioactive compounds

Aplicación de la técnica de separación granulométrica por vía húmeda para determinar el origen del fe en zeolitas naturales

Las zeolitas son un grupo de minerales considerados industriales ya que por sus características físicas y químicas tienen una aplicación muy amplia. La fórmula general de las zeolitas es la siguiente: Mx Dy (Alx+2y Sin-(x+2y) O2n).mH2 O, donde M y D representan cationes intercambiables que pueden balancear la carga negativa de la molécula AlO2, dichos cationes generalmente son elementos alcalinos y alcalinotérreos como Na, K y Ca. Sin embargo, al revisar la composición química de algunas zeolitas estudiadas en Sonora y en otros lugares del mundo, llama la atención la presencia de fierro en una proporción muy similar a la de los elementos alcalinos y alcalinotérreos, normalmente representados por más del 1% (principalmente el Ca). Particularmente se experimentó con zeolitas del yacimiento de La Palma en Sonora, para probar que el Fierro presente en las zeolitas corresponde a una mezcla de minerales como magnetita y hematita, demostrando que no se encuentra formando parte de la estructura de la zeolita como catión intercambiable

Crystallization of II-VI semiconductor compounds forming long microcrystalline linear assemblies

In this work we report the formation of long microcrystalline linear self-assemblies observed during the thin film growth of several II-VI compounds. Polycrystalline CdTe, CdS, CdCO3, and nanocrystalline CdTe:Al thin films were prepared on glass substrates by different deposition techniques. In order to observe these crystalline formations in the polycrystalline materials, the thin film growth was suspended before the grains reached to form a continuous layer. The chains of semiconductor crystals were observed among many isolated and randomly distributed grains. Since CdTe, CdTe:Al, CdS and CdCO3 are not ferroelectric and/or ferromagnetic materials, the relevant problem would be to explain what is the mechanism through which the grains are held together to form linear chains. It is well known that some nanocrystalline materials form rods and wires by means of electrostatic forces. This occurs in polar semiconductors, where it is assumed that the attraction forces between surface polar faces of the small crystals are the responsible for the chains formation. Since there are not too many mechanisms responsible for the attraction we assume that a dipolar interaction is the force that originates the formation of chain-like grain clusters. The study of this property can be useful for the understanding of nucleation processes in the growth of semiconductor thin films

Propiedades magnéticas y distribución de tamaños de nanopartículas de magnetita recubiertas con ácido oleico

"The particle size and particle size distribution are very important to biomedical applications because the uptake of nanoparticles is strongly dependent on particle size. Oleic acid coated magnetite nanoparticles were synthesized by using chemical co-precipitation. The average particle size and particle size distribution measured by different techniques are compared. The crystallite sizes estimated by X-Ray Diffraction (9.32 nm) and the average particle size calculated by Transmission Electron Microscopy (9.46 nm) are very similar. Atomic Force Microscopy revealed an average diameter of 1030 nm, which is bigger than estimated by other techniques due to the oleic acid layer covering the nanoparticles. The distribution of magnetic sizes of nanoparticles was also estimated through the magnetic response of the system, using the Langevin model (9.11 nm). Anisotropy constant (Ka = 4.74 *105 erg/cm3) and blocking temperature (TB = 118 K) were obtained.

Sujetos de la masa. Visiones del nacionalismo después de la Primera Guerra Mundial

One of the most popular or widespread theories of nationalism postulates the existence of dark, atavistic forces, the outbreak of irrational compulsions and the regression to barbarism, in a collective process that would in any case pass through the control and unconscious manipulation of the masses. What is the origin of such an interpretation? In this article we explore the influence of biology and turn-of-the-century psychiatry in the academic representation of nationalism at the end of the Great War. As we shall see, the representation of nationalism after the war would incorporate the concepts and terms atavism, degenerationism and mass psychology, thus initiating an epistemological turn that would not be complete until mid-century, with the popularization of psychoanalysis and denunciation of the Holocaust