Pulsed current-voltage electrodeposition of stoichiometric Bi2Te3 nanowires and their crystallographic characterization by transmission electron backscatter diffraction

Bi2Te3 nanowires with diameters ranging from 25 to 270 nm, ultra-high aspect ratio, and uniform growth front were fabricated by electrodeposition, pulsing between zero current density during the off time and constant potential during the on time (pulsed-current-voltage method, p-IV). The use of zero current density during the off time is to ensure no electrodeposition is carried out and the system is totally relaxed. By this procedure, stoichiometric nanowires oriented perpendicular to the c-axis is obtained for the different diameters of porous alumina templates. In addition, the samples show a uniform growth front with ultra-high aspect ratio single crystal nanowires. The high degree of crystallinity was verified by transmission electron backscatter diffraction. This characterization revealed that the nanowires present both large single crystalline areas and areas with alternating twin configurations

El efecto fotoacústico como técnica de medida de conductividad térmica

Ponencia presentada en las IV Jornadas de Jóvenes Investigadores, celebradas en Madrid el 9 de julio de 2015.La conductividad térmica es una propiedad de los materiales de gran importancia en muchos campos de investigación como por ejemplo, la termoelectricidad. Sin embargo, es una magnitud muy compleja de determinar, especialmente a escala nanométrica. En este trabajo se ha desarrollado un sistema experimental basado en el efecto fotoacústico capaz de medir conductividad térmica de materiales de muy diferentes estructuras, dimensiones y propiedades térmicas. La técnica fotoacústica es una técnica óptica de no contacto que permite obtener la conductividad térmica de diferentes tipos de estructuras desde materiales en volumen, películas delgadas, estructuras multicapa o incluso matrices de nanohilos. En esta técnica, una radiación periódica modulada calienta la muestra de tal forma que el aire en contacto con la superficie de la muestra se caliente y enfría y por tanto se expande y se contrae periódicamente de forma similar a un pistón térmico. Este efecto provoca ondas acústicas que son detectadas por un micrófono. Comparando la onda incidente proveniente del láser con la onda acústica registrada, se pueden extraer las propiedades térmicas de la muestra. El análisis de la señal depende del tipo de muestra que se esté analizando. En este trabajo, se usan dos tipos diferentes de normalización. En el caso de estructuras multicapa, la muestra es iluminada en configuración frontal (o de reflexión) y la señal es normalizada con una muestra de referencia que permite eliminar la contribución de la celda fotoacústica. Para el cálculo de la conductividad térmica se emplea un modelo multicapa desarrollado por Hu et al. En el caso de muestras en volumen, la normalización se lleva a cabo midiendo la muestra tanto en configuración de reflexión como transmisión. El sistema experimental, que se muestra en la figura, fue desarrollado en el laboratorio y consiste en una celda fotoacústica hecha de metacrilato diseñada de tal forma que se evitan posibles resonancias acústicas. En este trabajo, se muestran las capacidades y límites de la técnica junto con algunos resultados experimentales que se han obtenido.Peer Reviewe

Electrical conductivity measurements of films

Póster presentado en la 12th European Conference on Thermoelectrics (ECT2014), celebrada en Madrid del 24 al 26 de septiembre de 2014.The characterization of the electrical conductivity of thin films is mandatory in all materials but particularly in thermoelectricity, its measurement is crucial in order to be able to determine the power factor and the figure of merit. A technique that could be used to carry out electrical measurements on thin films is the four probe technique. However, the spreading of the current due to the electrical field or the influence of the electrical contact resistances complicate the determination and analysis of the electrical conductivity of the film. In order to overcome these problems, we carried out a mesa attack on Bi2Te3 films grown by electrodeposition technique, which are hold on a Si substrate with a gold layer of 150nm. The goal is fabricating pillars whose later film resistivity analysis could approach to the 1D electrical model, which cannot be taken into account when dealing with a big film area. For that purpose, a lithography process was done on films with different thicknesses, which consist of a pattern of disks with different diameters ranging between 120µm and 60µm diameter. After the lithography, we evaporated 100nm of gold on top of the disks that would act as the top electrode. Then, we removed the photoresist and we performed a mesa attack with diluted nitric acid (1:2.5). As a result, we obtained pillars as the ones showed in Figure 1. On these pillars, I-V curves with the four probe technique were taken and the resistances of the pillars were determined. Representing the resistance of the pillars versus the inverse of the area of the pillar, the total resistivity of the films, which includes the contact resistances between the electrodes and the pillar, is obtained. Finally, to determine the electrical contact resistance and obtain the pure electrical resistivity of the film, these measurements were performed on different pillar thicknesses. The experimental results have been double-checked with COMSOL simulations of the four probe experiments carried out here, observing a good agreement between them.Peer Reviewe

Optimization of bismuth telluride films and nano-wire arrays via electrodeposition for thermoelectric applications

Comunicación presentada en el 3rd Early Stage Researchers Workshop in Nanoscience, celebrado en Madrid el 27 y 28 de junio de 2013.Due to the current world’s demand for energy, there is a great interest in thermoelectricity, which offers the possibility of increasing the sustainability of our electrical system. Thermoelectric materials can convert heat into electricity and vice versa, and thus they offer a way of recovering wasted heat produced in engines, industrial processes and others into usable power. However, one of the main problems for their actual use is their low efficiency in this conversion. This efficiency is directly related with what is called the thermoelectric figure of merit, described by ZT=(S2·σ·T)/κ ,where S, σ, κ, and T stand for the Seebeck coefficient, electrical and thermal conductivities, and the absolute temperature, respectively. Given that in classical physics S, σ, and κ, are correlated, the improvement of the efficiency is not straightforward. Nevertheless, in 1993 a theoretical work suggested that the efficiency could be greatly enhanced by reducing the dimensionality of the structures under studied and working in the nano-scale. Therefore, much experimental effort has been done to achieve these kind of structures and in some cases, an enhancement of the ZT value has been achieved, although this has not been due to the quantum confinement to the charge carriers, as it was theoretically predicted, but to an increase of the κ due to the increased number of interface boundaries in nanostructures. Among the most efficient thermoelectric materials used for applications at room temperature, bismuth telluride (Bi2Te3) and its different alloys stand out, with a ZT for Bi2Te3of around 1 at RT [2]. We present here an optimized method of obtaining films and nanowire arrays via electrochemical deposition in a conventional three-electrode cell. Different ways of improving the quality of the obtained films have been studied (working electrode, constant and pulsed potentials, different chemical baths, etc.) in order to obtain highly oriented (110) films, which are the most favorable for out-of-plane applications. Then, nanostructuration has been achieved by changing the working electrode to porous alumina templates and realizing the electrochemical deposition inside the pores. The samples produced have been characterized using SEM, EDX, AFM, XRD, and Raman spectrometry, and in the case of the films, their transport properties have also been measured.Peer Reviewe

CoSb3-based skutterudite nanocomposites prepared by cold sintering process with enhanced thermoelectric properties

We show here for the first time the use of a cold sintering process (CSP) to sinter CoSb3-based thermoelectric materials. CSP at 150 {\deg}C for 90 min under a uniaxial pressure of 750 MPa yields pieces with a relative density of 86 %, which is increased to around 92 % after a post-annealing at temperatures > 500 {\deg}C in Ar atmosphere. The reported CSP produces Te doped-CoSb3 nanocomposites with similar morphological and structural characteristics to the starting nanopowders obtained by ball milling in air atmosphere. The post-thermal treatment induces grain coalescence and grain growth, crystallite size growth as well as compositional changes in the nanocomposite, decreasing the amount of the main phase, CoSb3, and increasing the weight of secondary phase, CoSb2, up to a 30 wt% at 600 {\deg}C. Remarkably, the average valence for the Co, Sb and Te absorbing atoms is neither transformed by the sintering process nor by the subsequent heat treatment. The functional response of the sintered thermoelectric nanocomposites exhibits a maximum figure of merit of 0.12(3) at room temperature for the nanocomposites sintered by CSP with a subsequent post-annealing at 500 {\deg}C. This is mainly due to its low thermal conductivity in comparison with similar powders sintered by other approaches, and it is explained by the morphological and structural properties. These findings represent an attractive alternative for obtaining efficient thermoelectric skutterudites by a scalable and cost-effective route

Tumor expression of cyclin-dependent kinase 5 (Cdk5) is a prognostic biomarker and predicts outcome of oxaliplatin-treated metastatic colorectal cancer patients

In recent years, an increasing number of studies have shown that elevated expression of cyclin dependent kinase (Cdk5) contributes to the oncogenic initiation and progression of many types of cancers. In this study, we investigated the expression pattern of Cdk5 in colorectal cancer (CRC) cell lines and in a large number of tumor samples in order to evaluate its relevance in this pathogenesis and possible use as a prognostic marker. We found that Cdk5 is highly expressed and activated in CRC cell lines and that silencing of the kinase decreases their migration ability. In tumor tissues, Cdk5 is overexpressed compared to normal tissues due to a copy number gain. In patients with localized disease, we found that high Cdk5 levels correlate with poor prognosis, while in the metastatic setting, this was only the case for patients receiving an oxaliplatin-based treatment. When exploring the Cdk5 levels in the consensus molecular subtypes (CMS), we found the lowest levels in subtype 1, where high Cdk5 again was associated with a poorer prognosis. In conclusion, we confirm that Cdk5 is involved in CRC and disease progression and that it could serve as a prognostic and predictive biomarker in this disease

Constraints on the χ_(c1) versus χ_(c2) polarizations in proton-proton collisions at √s = 8 TeV

The polarizations of promptly produced χ_(c1) and χ_(c2) mesons are studied using data collected by the CMS experiment at the LHC, in proton-proton collisions at √s=8  TeV. The χ_c states are reconstructed via their radiative decays χ_c → J/ψγ, with the photons being measured through conversions to e⁺e⁻, which allows the two states to be well resolved. The polarizations are measured in the helicity frame, through the analysis of the χ_(c2) to χ_(c1) yield ratio as a function of the polar or azimuthal angle of the positive muon emitted in the J/ψ → μ⁺μ⁻ decay, in three bins of J/ψ transverse momentum. While no differences are seen between the two states in terms of azimuthal decay angle distributions, they are observed to have significantly different polar anisotropies. The measurement favors a scenario where at least one of the two states is strongly polarized along the helicity quantization axis, in agreement with nonrelativistic quantum chromodynamics predictions. This is the first measurement of significantly polarized quarkonia produced at high transverse momentum

Evaluation of Interferon-Gamma Release Assays in the Diagnosis of Recent Tuberculosis Infection in Health Care Workers

BACKGROUND:Health care workers (HCWs) are a group at risk of latent tuberculosis infection (LTBI). The aims of this study were to determine IFN-gamma response by QuantiFERON-TB GOLD In Tube (QFN-G-IT) and T-SPOT.TB in HCWs, comparing the results with tuberculin skin test (TST); and to analyze the capacity of IFN-gamma tests to detect recent versus remote LTBI with a prolonged stimulation test (PST). METHODOLOGY/PRINCIPAL FINDINGS:A total of 147 HCWs were enrolled; 23 of whom were BCG vaccinated. 95 HCWs (64.6%) had a previous positive TST and were not retested; and 52 HCWs had a previous negative TST or were tested for the first time. When we analysed individuals without previous positive TST, the number of positive results for T-SPOT.TB was 12/52 (23.1%); and for QFN-G-IT, 9/52 (17.3%). The global concordance (kappa) between T-SPOT.TB and QFN-G-IT with TST was 0.754 and 0.929 respectively. Of individuals with previous positive TST, T-SPOT.TB and QFN-G-IT were negative in 51.6% (49/95) and 62.1% (59/95) respectively, decreasing the concordance to 0.321 and 0.288, respectively. In non-BCG vaccinated HCWs with previous positive TST a positive IFN-gamma test was associated with degree of exposure and diameter of TST. PST was performed in 24 HCW with previous positive TST and negative IFN-gamma tests. PST was developed in 3 cell cultures stimulated with medium alone, ESAT-6 and CFP-10, respectively. In the third and sixth day of incubation period, part of the supernatants were replaced with complete medium supplemented with (rIL)-2. On day 9, ELISPOT assay was performed. In 14 samples PST was not valid due to not having enough cells. In 8 cases, the response was negative, and in 2 cases positive, suggesting that these patients were infected with Mycobacterium tuberculosis in some point in the past. CONCLUSIONS:Both IFN-gamma tests showed a similar number of positive results, and concordance between the tests was excellent. None of the tests was affected by prior BCG vaccination. IFN-gamma tests are a useful tool for detecting recent infection in HCW population

Transcriptome characterization and high throughput SSRs and SNPs discovery in Cucurbita pepo (Cucurbitaceae)

Background: Cucurbita pepo belongs to the Cucurbitaceae family. The "Zucchini" types rank among the highest-valued vegetables worldwide, and other C. pepo and related Cucurbita spp., are food staples and rich sources of fat and vitamins. A broad range of genomic tools are today available for other cucurbits that have become models for the study of different metabolic processes. However, these tools are still lacking in the Cucurbita genus, thus limiting gene discovery and the process of breeding.Results: We report the generation of a total of 512,751 C. pepo EST sequences, using 454 GS FLX Titanium technology. ESTs were obtained from normalized cDNA libraries (root, leaves, and flower tissue) prepared using two varieties with contrasting phenotypes for plant, flowering and fruit traits, representing the two C. pepo subspecies: subsp. pepo cv. Zucchini and subsp. ovifera cv Scallop. De novo assembling was performed to generate a collection of 49,610 Cucurbita unigenes (average length of 626 bp) that represent the first transcriptome of the species. Over 60% of the unigenes were functionally annotated and assigned to one or more Gene Ontology terms. The distributions of Cucurbita unigenes followed similar tendencies than that reported for Arabidopsis or melon, suggesting that the dataset may represent the whole Cucurbita transcriptome. About 34% unigenes were detected to have known orthologs of Arabidopsis or melon, including genes potentially involved in disease resistance, flowering and fruit quality. Furthermore, a set of 1,882 unigenes with SSR motifs and 9,043 high confidence SNPs between Zucchini and Scallop were identified, of which 3,538 SNPs met criteria for use with high throughput genotyping platforms, and 144 could be detected as CAPS. A set of markers were validated, being 80% of them polymorphic in a set of variable C. pepo and C. moschata accessions.Conclusion: We present the first broad survey of gene sequences and allelic variation in C. pepo, where limited prior genomic information existed. The transcriptome provides an invaluable new tool for biological research. The developed molecular markers are the basis for future genetic linkage and quantitative trait loci analysis, and will be essential to speed up the process of breeding new and better adapted squash varieties. © 2011 Blanca et al; licensee BioMed Central Ltd.Blanca Postigo, JM.; Cañizares Sales, J.; Roig Montaner, MC.; Ziarsolo Areitioaurtena, P.; Nuez Viñals, F.; Picó Sirvent, MB. (2011). Transcriptome characterization and high throughput SSRs and SNPs discovery in Cucurbita pepo (Cucurbitaceae). BMC Genomics. 12:104-117. doi:10.1186/1471-2164-12-104S1041171