Sub-10 nm colloidal lithography for integrated spin-photo-electronic devices

Colloidal lithography [1] is how patterns are reproduced in a variety of natural systems and is used more and more as an efficient fabrication tool in bio-, opto-, and nano-technology. Nanoparticles in the colloid are made to form a mask on a given material surface, which can then be transferred via etching into nano-structures of various sizes, shapes, and patterns [2,3]. Such nanostructures can be used in biology for detecting proteins [4] and DNA [5,6], for producing artificial crystals in photonics [7,8] and GHz oscillators in spin-electronics [9-14]. Scaling of colloidal patterning down to 10-nm and below, dimensions comparable or smaller than the main relaxation lengths in the relevant materials, including metals, is expected to enable a variety of new ballistic transport and photonic devices, such as spin-flip THz lasers [15]. In this work we extend the practice of colloidal lithography to producing large-area, near-ballistic-injection, sub-10 nm point-contact arrays and demonstrate their integration in to spin-photo-electronic devices.Comment: 15 pages, 5 figure

Diode Effect in Asymmetric Double Tunnel Barriers with Single Metal Nanoclusters

Asymmetric double tunnel barriers with the center electrode being a metal cluster in the quantum regime are studied. The zero dimensionality of the clusters used and the associated quantized energy spectra are manifest in well-defined steps in the current voltage characteristic (IVC). Record high current rectification ratios of 10000 for tunneling through such clusters are demonstrated at room temperature. We are able to account for all of the experimentally observed features by modeling our double barrier structures using a combination of discrete states and charging effects for tunneling through quantum dots.Comment: 8 pages and 3 figures. Accepted for publication in Applied Physics Letters in 15 march 200

Characterization of Iron-Imido Species Relevant forN-Group Transfer Chemistry

A sterically accessible tert-butyl-substituted dipyrrinato di-iron(II) complex [(tBuL)FeCl]2 possessing two bridging chloride atoms was synthesized from the previously reported solvento adduct. Upon treatment with aryl azides, the formation of high-spin FeIII species was confirmed by 57Fe Mössbauer spectroscopy. Crystallographic characterization revealed two possible oxidation products: (1) a terminal iron iminyl from aryl azides bearing ortho isopropyl substituents, (tBuL)FeCl(•NC6H3-2,6-iPr2); or (2) a bridging di-iron imido arising from reaction with 3,5-bis(trifluoromethyl)aryl azide, [(tBuL)FeCl]2(μ-NC6H3-3,5-(CF3)2). Similar to the previously reported (ArL)FeCl(•NC6H4-4-tBu), the monomeric iron imido is best described as a high-spin FeIII antiferromagnetically coupled to an iminyl radical, affording an S = 2 spin state as confirmed by SQUID magnetometry. The di-iron imido possesses an S = 0 ground state, arising from two high-spin FeIII centers weakly antiferromagnetically coupled through the bridging imido ligand. The terminal iron iminyl complex undergoes facile decomposition via intra- or intermolecular hydrogen-atom abstraction (HAA) from an imido aryl ortho isopropyl group, or from 1,4-cyclohexadiene, respectively. The bridging di-iron imido is a competent N-group transfer reagent to cyclic internal olefins as well as styrene. Although solid-state magnetometry indicates an antiferromagnetic interaction between the two iron centers (J = −108.7 cm−1) in [(tBuL)FeCl]2(μ-NC6H3-3,5-(CF3)2), we demonstrate that in solution the bridging imido can facilitate HAA as well as dissociate into a terminal iminyl species, which then can promote HAA. In situ monitoring reveals the di-iron bridging imido is a catalytically competent intermediate, one of several iron complexes observed in the amination of C–H bond substrates or styrene aziridination.Chemistry and Chemical Biolog

Sensibilidad y resistencia de gérmenes intra y extra hospitalarios en el Hospital Infantil Universitario de la Cruz Roja de Manizales, 2007

Siempre que se plantea la resistencia antibiótica como un problema ambiental,no se debe centrar solamente en el ámbito hospitalario, pues también se debe tener en cuenta que el uso que se dé a los antibióticos se puede extender al medio ambiente donde se vive o, simplemente, originarse desde el medioambiente externo y migrar al ámbito hospitalario. Por esta razón, se deben tener en cuenta las relaciones interespecíficas que caracterizan nuestro planeta, así como las relaciones humanas con los microorganismos, reconociendo el papel esencial de estos en el mantenimiento de la actividad médica y farmacéutica, que ha dado lugar a la sensibilidad y a la resistencia de diferentes patógenos a través del uso de antibióticos. La resistencia de los microorganismos es muy desesperanzadora. Desde el punto de vista de la clínica y experiencia práctica, cada vez se observa un mayor aumento de la resistencia antibiótica, que ocasiona dificultad en la implementación de un tratamiento adecuado. Pocas estrategias encaminadas en el control de este problema realmente están funcionando en la actualidad.ABSTRACTWhenever antibiotic resistance is posed as an environmental problem, it shouldn’t be centered only in the hospital setting. The use given to antibiotics must also be considered because it might be extended to the surrounding environment or, simply it might be originated in external surroundings and migrate to the hospital setting. For this reason, the inter-specific relationships which characterize our planet must be taken into consideration, as well as the human relationships with microorganisms, recognizing their essential role in the maintenance of the medical and pharmaceutical activity, which has generated the sensibility and resistance of different pathogens through the use of antibiotics. The resistance of microorganisms is hopeless. From the clinic and practical experience, more and more a greater increase in the antibiotic resistance is observed which causes difficulty in the implementation of an adequate treatment. Few strategies aimed to the control of this problem are really working presently.Siempre que se plantea la resistencia antibiótica como un problema ambiental,no se debe centrar solamente en el ámbito hospitalario, pues también se debe tener en cuenta que el uso que se dé a los antibióticos se puede extender al medio ambiente donde se vive o, simplemente, originarse desde el medioambiente externo y migrar al ámbito hospitalario. Por esta razón, se deben tener en cuenta las relaciones interespecíficas que caracterizan nuestro planeta, así como las relaciones humanas con los microorganismos, reconociendo el papel esencial de estos en el mantenimiento de la actividad médica y farmacéutica, que ha dado lugar a la sensibilidad y a la resistencia de diferentes patógenos a través del uso de antibióticos. La resistencia de los microorganismos es muy desesperanzadora. Desde el punto de vista de la clínica y experiencia práctica, cada vez se observa un mayor aumento de la resistencia antibiótica, que ocasiona dificultad en la implementación de un tratamiento adecuado. Pocas estrategias encaminadas en el control de este problema realmente están funcionando en la actualidad.ABSTRACTWhenever antibiotic resistance is posed as an environmental problem, it shouldn’t be centered only in the hospital setting. The use given to antibiotics must also be considered because it might be extended to the surrounding environment or, simply it might be originated in external surroundings and migrate to the hospital setting. For this reason, the inter-specific relationships which characterize our planet must be taken into consideration, as well as the human relationships with microorganisms, recognizing their essential role in the maintenance of the medical and pharmaceutical activity, which has generated the sensibility and resistance of different pathogens through the use of antibiotics. The resistance of microorganisms is hopeless. From the clinic and practical experience, more and more a greater increase in the antibiotic resistance is observed which causes difficulty in the implementation of an adequate treatment. Few strategies aimed to the control of this problem are really working presently

Spin Diode Based on Fe/MgO Double Tunnel Junction

We demonstrate a spin diode consisting of a semiconductor free nano-scale Fe/MgO-based double tunnel junction. The device exhibits a near perfect spin-valve effect combined with a strong diode effect. The mechanism consistent with our data is resonant tunneling through discrete states in the middle ferromagnetic layer sandwiched by tunnel barriers of different spin-dependent transparency. The observed magneto-resistance is record high, ~4000%, essentially making the structure an on/off spin-switch. This, combined with the strong diode effect, ~100, offers a new device that should be promising for such technologies as magnetic random access memory and re-programmable logic.Comment: 14 page

Stimulated emission of radiation using spin-population inversion in metals: a spin-laser

Arrays of 10 nm-diameter point contacts of exchange-coupled spin-majority/spin-minority ferromagnetic metals, integrated into infrared-terahertz range photon resonators, are fabricated and measured electrically and optically. Giant, threshold-type electronic excitations under high-current pumping of the devices are observed as abrupt but reversible steps in device resistance, in many cases in access of 100%, which correlate with optical emission from the devices. The results are interpreted as due to stimulated spin-flip electron-photon relaxation in the system.Comment: 5 page

Statistical analysis of the magnetization processes in arrays of electrodeposited ferromagnetic nanowires

We present a statistical analysis of the magnetization processes in arrays of 22-mum-long, 40-nm-wide Co and Ni nanowires, with parallel-to-wire magnetic anisotropy, electrodeposited into porous polycarbonate membranes. This analysis is based on usual magnetization measurements taken with a magnetic field applied parallel to the average wire direction. It is shown that the magnetization curves may contain, in proportions which depend on the magnetic history of the arrays prior to the measurement, two contributions corresponding, respectively, to single-domain wires reversing their magnetization and to wires initially in a multidomain state which are remagnetized to saturation. Despite the extremely large number of wires involved, these two contributions exhibit clearly discernible substructures. These are related to the different and rather weakly distributed characteristic fields that describe the reversal and remagnetization processes: the nucleation and propagation fields. Numerical simulations of the magnetization curves are carried out which allow one to deduce the statistical distributions of these fields. From this modeling of the experimental data, it is shown that two distinct kinds of defects with very different pinning strength are certainly present in the nanowires. Finally, the analysis of the magnetization curves also provides accurate information concerning the distribution of wire orientation in the polycarbonate templates