ONE STEP ELECTRODEPOSITION OF CuInSe2 THIN FILMS

Formation of CuInSe2 (CIS) thin films from aqueous solution containing citrate as complexing agent is reported. The surface morphology and the composition of the deposited films are characterized by scanning electron microscopy (SEM). The texture of the deposits and their compositions are analyzed by X-ray diffraction and transmission electron microscopy (TEM). Annealing of the films at 350°C in flowing argon electrodeposited at potentials in the range [-0.24, -0.4 (V vs Ag/AgCl)] resulted in the formation of alpha-Cu 2 Se (JCPDS 24-1131) and CuSe (JCPDS 6-0427). On the contrary, annealing in the same conditions of the films electrodeposited between -0.4 and -0.6 V vs Ag/AgCl led to the formation of chalcopyrite CuInSe 2 (JCPDS 23-209) with alpha-Cu 2 Se (JCPDS 24-1131) as secondary phase. The formation of CuInSe 2 films with a chalcopyrite structure and good stoichiometry is observed.Formation of CuInSe2 (CIS) thin films from aqueous solution containing citrate as complexing agent is reported. The surface morphology and the composition of the deposited films are characterized by scanning electron microscopy (SEM). The texture of the deposits and their compositions are analyzed by X-ray diffraction and transmission electron microscopy (TEM). Annealing of the films at 350°C in flowing argon electrodeposited at potentials in the range [-0.24, -0.4 (V vs Ag/AgCl)] resulted in the formation of alpha-Cu 2 Se (JCPDS 24-1131) and CuSe (JCPDS 6-0427). On the contrary, annealing in the same conditions of the films electrodeposited between -0.4 and -0.6 V vs Ag/AgCl led to the formation of chalcopyrite CuInSe 2 (JCPDS 23-209) with alpha-Cu 2 Se (JCPDS 24-1131) as secondary phase. The formation of CuInSe 2 films with a chalcopyrite structure and good stoichiometry is observed

Astrometry with the Keck-Interferometer: the ASTRA project and its science

The sensitivity and astrometry upgrade ASTRA of the Keck Interferometer is introduced. After a brief overview of the underlying interferometric principles, the technology and concepts of the upgrade are presented. The interferometric dual-field technology of ASTRA will provide the KI with the means to observe two objects simultaneously, and measure the distance between them with a precision eventually better than 100 uas. This astrometric functionality of ASTRA will add a unique observing tool to fields of astrophysical research as diverse as exo-planetary kinematics, binary astrometry, and the investigation of stars accelerated by the massive black hole in the center of the Milky Way as discussed in this contribution.Comment: 22 pages, 10 figures (low resolution), contribution to the summerschool "Astrometry and Imaging with the Very Large Telescope Interferometer", 2 - 13 June, 2008, Keszthely, Hungary, corrected authorlis

The ESPRI project: astrometric exoplanet search with PRIMA I. Instrument description and performance of first light observations

The ESPRI project relies on the astrometric capabilities offered by the PRIMA facility of the Very Large Telescope Interferometer for the discovery and study of planetary systems. Our survey consists of obtaining high-precision astrometry for a large sample of stars over several years and to detect their barycentric motions due to orbiting planets. We present the operation principle, the instrument's implementation, and the results of a first series of test observations. A comprehensive overview of the instrument infrastructure is given and the observation strategy for dual-field relative astrometry is presented. The differential delay lines, a key component of the PRIMA facility which was delivered by the ESPRI consortium, are described and their performance within the facility is discussed. Observations of bright visual binaries are used to test the observation procedures and to establish the instrument's astrometric precision and accuracy. The data reduction strategy for astrometry and the necessary corrections to the raw data are presented. Adaptive optics observations with NACO are used as an independent verification of PRIMA astrometric observations. The PRIMA facility was used to carry out tests of astrometric observations. The astrometric performance in terms of precision is limited by the atmospheric turbulence at a level close to the theoretical expectations and a precision of 30 micro-arcseconds was achieved. In contrast, the astrometric accuracy is insufficient for the goals of the ESPRI project and is currently limited by systematic errors that originate in the part of the interferometer beamtrain which is not monitored by the internal metrology system. Our observations led to the definition of corrective actions required to make the facility ready for carrying out the ESPRI search for extrasolar planets.Comment: 32 pages, 39 figures, Accepted for publication in Astronomy and Astrophysic

A conscious rethink : Why is brain tissue commonly preserved in the archaeological record? Commentary on: Petrone P, Pucci P, Niola M, et al. Heat-induced brain vitrification from the Vesuvius eruption in C.E. 79. N Engl J Med 2020;382:383-4. DOI: 10.1056/NEJMc1909867

Brain tissue is ubiquitous in the archaeological record. Multiple, independent studies report the finding of black, resinous or shiny brain tissue, and Petrone et al. [2020 “Heat-induced Brain Vitrification from the Vesuvius Eruption in C.E. 79.” N Engl J Med. 382: 383–384; doi:10.1056/NEJMc1909867] raise the intriguing prospect of a role for vitrification in the preservation of ancient biomolecules. However, Petrone et al. (2020) have not made their raw data available, and no detailed laboratory or analytical methodology is offered. Issues of contamination and misinterpretation hampered a decade of research in biomolecular archaeology, such that addressing these sources of bias and facilitating validation of specious findings has become both routine and of paramount importance in the discipline. We argue that the evidence they present does not support their conclusion of heat-induced vitrification of human brain tissue, and that future studies should share palaeoproteomic data in an open access repository to facilitate comparative analysis of the recovery of ancient proteins and patterns of their degradation

First principles study of point defects in titanium oxycarbide

We have performed first principles density functional theory calculations to study the formation energy of point defects in TiC, TiO and TiCO compounds. The formation energy of isolated vacancies were obtained for different equilibrium conditions. For binary compounds, we have also calculated the formation energy of antisite defects. It was found that the defect formation energies strongly depend on the chemical environment. Our results show that C vacancies are easily formed in TiC and TiCO. For the TiO compound, Ti vacancies are highly probable to occur and O vacancies are also easily formed under titanium rich atmosphere.Fundação para a Ciência e a Tecnologia (FCT) – Programa Operacional “Ciência , Tecnologia, Inovação” – CONC-REEQ/443/EEI/2005, POCTI/CTM/69362/200

Improving the astrometric performance of VLTI-PRIMA

In the summer of 2011, the first on-sky astrometric commissioning of PRIMA-Astrometry delivered a performance of 3 m'' for a 10 '' separation on bright objects, orders of magnitude away from its exoplanet requirement of 50 {\mu}'' ~ 20 {\mu}'' on objects as faint as 11 mag ~ 13 mag in K band. This contribution focuses on upgrades and characterizations carried out since then. The astrometric metrology was extended from the Coud\'e focus of the Auxillary Telescopes to their secondary mirror, in order to reduce the baseline instabilities and improve the astrometric performance. While carrying out this extension, it was realized that the polarization retardance of the star separator derotator had a major impact on both the astrometric metrology and the fringe sensors. A local compensation of this retardance and the operation on a symmetric baseline allowed a new astrometric commissioning. In October 2013, an improved astrometric performance of 160 {\mu}'' was demonstrated, still short of the requirements. Instabilities in the astrometric baseline still appear to be the dominating factor. In preparation to a review held in January 2014, a plan was developed to further improve the astrometric and faint target performance of PRIMA Astrometry. On the astrometric aspect, it involved the extension of the internal longitudinal metrology to primary space, the design and implementation of an external baseline metrology, and the development of an astrometric internal fringes mode. On the faint target aspect, investigations of the performance of the fringe sensor units and the development of an AO system (NAOMI) were in the plan. Following this review, ESO decided to take a proposal to the April 2014 STC that PRIMA be cancelled, and that ESO resources be concentrated on ensuring that Gravity and Matisse are a success. This proposal was recommended by the STC in May 2014, and endorsed by ESO.Comment: 12 pages, 9 figures, 2 tables, Proceeding of SPIE conference in Montrea

Opening a new window to other worlds with spectropolarimetry

A high level of diversity has already been observed among the planets of our own Solar System. As such, one expects extrasolar planets to present a wide range of distinctive features, therefore the characterisation of Earth- and super Earth-like planets is becoming of key importance in scientific research. The SEARCH (Spectropolarimetric Exoplanet AtmospheRe CHaracerisation) mission proposal of this paper represents one possible approach to realising these objectives. The mission goals of SEARCH include the detailed characterisation of a wide variety of exoplanets, ranging from terrestrial planets to gas giants. More specifically, SEARCH will determine atmospheric properties such as cloud coverage, surface pressure and atmospheric composition, and may also be capable of identifying basic surface features. To resolve a planet with a semi major axis of down to 1.4AU and 30pc distant SEARCH will have a mirror system consisting of two segments, with elliptical rim, cut out of a parabolic mirror. This will yield an effective diameter of 9 meters along one axis. A phase mask coronagraph along with an integral spectrograph will be used to overcome the contrast ratio of star to planet light. Such a mission would provide invaluable data on the diversity present in extrasolar planetary systems and much more could be learned from the similarities and differences compared to our own Solar System. This would allow our theories of planetary formation, atmospheric accretion and evolution to be tested, and our understanding of regions such as the outer limit of the Habitable Zone to be further improved.Comment: 23 pages, accepted for publication in Experimental Astronom

The Genomic Signature of Crop-Wild Introgression in Maize

The evolutionary significance of hybridization and subsequent introgression has long been appreciated, but evaluation of the genome-wide effects of these phenomena has only recently become possible. Crop-wild study systems represent ideal opportunities to examine evolution through hybridization. For example, maize and the conspecific wild teosinte Zea mays ssp. mexicana, (hereafter, mexicana) are known to hybridize in the fields of highland Mexico. Despite widespread evidence of gene flow, maize and mexicana maintain distinct morphologies and have done so in sympatry for thousands of years. Neither the genomic extent nor the evolutionary importance of introgression between these taxa is understood. In this study we assessed patterns of genome-wide introgression based on 39,029 single nucleotide polymorphisms genotyped in 189 individuals from nine sympatric maize-mexicana populations and reference allopatric populations. While portions of the maize and mexicana genomes were particularly resistant to introgression (notably near known cross-incompatibility and domestication loci), we detected widespread evidence for introgression in both directions of gene flow. Through further characterization of these regions and preliminary growth chamber experiments, we found evidence suggestive of the incorporation of adaptive mexicana alleles into maize during its expansion to the highlands of central Mexico. In contrast, very little evidence was found for adaptive introgression from maize to mexicana. The methods we have applied here can be replicated widely, and such analyses have the potential to greatly informing our understanding of evolution through introgressive hybridization. Crop species, due to their exceptional genomic resources and frequent histories of spread into sympatry with relatives, should be particularly influential in these studies

Circumstellar disks and planets. Science cases for next-generation optical/infrared long-baseline interferometers

We present a review of the interplay between the evolution of circumstellar disks and the formation of planets, both from the perspective of theoretical models and dedicated observations. Based on this, we identify and discuss fundamental questions concerning the formation and evolution of circumstellar disks and planets which can be addressed in the near future with optical and infrared long-baseline interferometers. Furthermore, the importance of complementary observations with long-baseline (sub)millimeter interferometers and high-sensitivity infrared observatories is outlined.Comment: 83 pages; Accepted for publication in "Astronomy and Astrophysics Review"; The final publication is available at http://www.springerlink.co