Superconductivity in doped semiconductors

International audienceA historical survey of the main normal and superconducting state properties of several semiconductors doped into superconductivity is proposed. This class of materials includes selenides, tellurides, oxides and column-IV semiconductors. Most of the experimental data point to a weak coupling pairing mechanism, probably phonon-mediated in the case of diamond, but probably not in the case of strontium titanate, these being the most intensively studied materials over the last decade. Despite promising theoretical predictions based on a conventional mechanism, the occurrence of critical temperatures significantly higher than 10 K has not been yet verified. However, the class provides an enticing playground for testing theories and devices alike

Spatially-Correlated Microstructure and Superconductivity in Polycrystalline Boron-Doped Diamond

Scanning tunneling spectroscopies are performed below 100~mK on nano-crystalline boron-doped diamond films characterized by Transmission Electron Microscopy and transport measurements. We demonstrate a strong correlation between the local superconductivity strength and the granular structure of the films. The study of the spectral shape, amplitude and temperature dependence of the superconductivity gap enables us to differentiate intrinsically superconducting grains that follow the BCS model, from grains showing a different behavior involving the superconducting proximity effect

Tunneling Spectroscopy and Vortex Imaging in Boron-Doped Diamond

We present the first scanning tunneling spectroscopy study of single-crystalline boron doped diamond. The measurements were performed below 100 mK with a low temperature scanning tunneling microscope. The tunneling density of states displays a clear superconducting gap. The temperature evolution of the order parameter follows the weak coupling BCS law with $\Delta(0)/k_B T_c \simeq 1.74$. Vortex imaging at low magnetic field also reveals localized states inside the vortex core that are unexpected for such a dirty superconductor.Comment: 4 pages, 4 figures, replaced with revised versio

Non-adiabatic Kohn Anomaly in Heavily Boron-doped Diamond

We report evidence of a non-adiabatic Kohn anomaly in boron-doped diamond, using a joint theoretical and experimental analysis of the phonon dispersion relations. We demonstrate that standard calculations of phonons using density functional perturbation theory are unable to reproduce the dispersion relations of the high-energy phonons measured by high-resolution inelastic x-ray scattering. On the contrary, by taking into account non-adiabatic effects within a many-body field-theoretic framework, we obtain excellent agreement with our experimental data. This result indicates a breakdown of the Born-Oppenheimer approximation in the phonon dispersion relations of boron-doped diamond.Comment: 6 pages, 2 figure

TEM study of homoepitaxial diamond layers scheduled for high power devices: FIB method of sample preparation

Homoepitaxial diamond structure observation by transmission electron microscopy (TEM) is still a very hard job due to the difficulty in preparing electron transparent samples for the further observation. The present contribution details the experimental operations with their respective conditions step by step. Finally high resolution TEM (HREM) observations of a CVD grown epilayer on a unnintentionally doped HPHT (001) oriented substrate are present to show the high quality of the sample preparation method.4 page

Spectroscopic ellipsometry of homoepitaxial diamond multilayers and delta-doped structures

5 pagesInternational audienceThe optimization of diamond-based unipolar electronic devices such as pseudo-vertical Schottky diodes or delta-doped field effect transistors relies in part on the sequential growth of nominally undoped (p-) and heavily boron doped (p þþ ) layers with well-controlled thicknesses and steep interfaces. Optical ellipsometry offers a swift and contactless method to characterize the thickness, roughness, and electronic properties of semiconducting and metallic diamond layers. We report ellipsometric studies carried out on delta-doped structures and other epitaxial multilayers with various boron concentrations and thicknesses (down to the nanometer range). The results are compared with Secondary Ion Mass Spectroscopy and transport measurements. Copyright 2014 AIP Publishing LLC

Boron concentration profiling by high angle annular dark field-scanning transmission electron microscopy in homoepitaxial delta-doped diamond layers

To develop further diamond related devices, the concentration and spatial location of dopants should be controlled down to the nanometer scale. Scanning transmission electron microscopy using the high angle annular dark field mode is shown to be sensitive to boron doping in diamond epilayers. An analytical procedure is described, whereby local boron concentrations above 1020 cm-3 were quantitatively derived down to nanometer resolution from the signal dependence on thickness and boron content. Experimental boron local doping profiles measured on diamond p-/p++/p- multilayers are compared to macroscopic profiles obtained by secondary ion mass spectrometry, avoiding reported artefacts.4 page

Usages des supports d’écriture au xviiie siècle : une esquisse codicologique

L’analyse matérielle des manuscrits du xviiie siècle procure une moisson d’indices non négligeables. Un inventaire méthodique détaillé (ne se limitant pas au relevé de filigranes) permet d’identifier les différents types de papier employés par Diderot, Buffon ou Condorcet. Toutefois, ces données codicologiques ne deviennent exploitables que si l’on se réfère à l’histoire de la fabrication du papier à l’ère préindustrielle : une approche critique des formats, des provenances et des éléments de datation s’avère nécessaire. La codicologie donne aussi accès aux usages du papier : plier, découper, assembler et réemployer sont des gestes courants au xviiie siècle, tant du fait des secrétaires que des auteurs eux-mêmes. Ces pratiques favorisent la plasticité et la mobilité des unités textuelles : « papillons » épinglés de Montesquieu, fiches sur cartes à jouer de Rousseau, cahiers in-4° de l’Esprit des Lois ou de l’Histoire naturelle. Ainsi l’approche de l’objet écrit dans sa dimension la plus strictement matérielle permet d’articuler l’étude des pratiques intellectuelles et des processus créatifs avec l’histoire de la consommation et des usages du papier.The material analysis of 18th century manuscripts yields a significant amount of clues. A detailed and methodological inventory, not limited to a list of watermarks, allows us to identify the different types of paper used by Diderot, Buffon or Condorcet. However, this codicological data can only be exploited if referred to the history of paper making in the pre-industrial era: a critical approach to format, provenance and elements allowing dating is essential. Codicology also enlightens us on the various paper uses: folding, cutting, assembling and re-using were common gestures in the 18th century, as much of the secretaries as of the authors themselves. This practice favors the plasticity and mobility of textual units: Montesquieu’s pinned-on “butterflies”, Rousseau’s notes on playing cards, quarto notebooks for l’Esprit des Lois or l’Histoire naturelle. Thus, by approaching the written object in its strictly material dimension we can associate the study of intellectual practices and the creative processes with the history of paper’s consumption and usage.El análisis material de los manuscritos del siglo XVIII brinda una cosecha de indicios nada desdeñable. Un inventario metódico detallado (que no se limite al registro de filigranas) permite identificar los diferentes tipos de papel utilizados por Diderot, Buffon o Condorcet. No obstante, estos datos codicológicos son explotables solamente si se los enmarca en la historia de la fabricación del papel en la era preindustrial: un enfoque crítico de los formatos, las proveniencias y los elementos de datación se torna necesario. La codicología abre también el acceso a las utilizaciones del papel: plegar, recortar, ensamblar y reutilizar son gestos corrientes en el siglo XVIII, tanto por parte de los secretarios como de los autores mismos. Estas prácticas favorecen la plasticidad y la movilidad de las unidades textuales: los papelitos abrochados de Montesquieu, las fichas en naipes de Rousseau, los cuadernos in-4° de El espíritu de las leyes o de La historia natural. De este modo, el enfoque del objeto escrito en su dimensión más estrictamente material permite articular el estudio de las prácticas intelectuales y los procesos creativos con la historia del consumo y los usos del papel.Die materielle Analyse von Manuskripten des 18. Jahrhunderts liefert eine Fülle äußerst wichtiger Indizien. Ein detailliertes methodisches Inventar (das sich nicht nur auf Wasserzeichen beschränkt) erlaubt es, die verschiedenen Papiersorten zu identifizieren, die von Diderot, Buffon oder Condorcet verwendet wurden. Jedoch werden diese kodikologischen Daten erst nutzbar, wenn man sie auf die Geschichte der Papierherstellung im vorindustriellen Zeitalters bezieht, d.h. kritisches Erfassen von Formaten, Herkunft und Datierungselementen. Die Kodikologie verschafft auch Zugang zu den Nutzweisen des Papiers: falten, zuschneiden, zusammenfügen und wiederverwenden sind die gängigen Nutzweisen im 18. Jahrhundert, und zwar ebenso bei Sekretären wie bei den Autoren selbst. Diese Praktiken favorisierten die Plastizität und Mobilität der Texteinheiten: Montesquieus aufgesteckte „Schmetterlinge“, Rousseaus Zettel auf Spielkarten, Quarthefte vom Esprit des Lois oder der Histoire naturelle. So ermöglicht es die Definition geschriebener Objekte auf streng materieller Ebene, die Erforschung intellektueller Praktiken und kreativer Prozesse mit der Geschichte des Verbrauchs und der Nutzung von Papier zu verbinden.L’analisi materiale dei manoscritti del XVIII secolo offre una messe di indizi non trascurabile. Un inventario metodico dettagliato (che non si limiti al rilevamento delle filigrane) permette di identificare i diversi tipi di carta utilizzati da Diderot, Buffon e Condorcet. Tuttavia questi dati codicologici non possono essere impiegati a meno di riferirli alla storia della fabbricazione della carta in epoca preindustriale: si rivela dunque necessario un approccio critico ai formati, alle provenienze e agli elementi di datazione. La codicologia offre anche accesso agli usi della carta: piegare, tagliare, incollare e reimpiegare sono gesti correnti nel XVIII secolo, sia da parte dei segretari sia da parte degli stessi autori. Queste pratiche favoriscono la plasticità e la mobilità delle unità di testo: le “farfalle” spillate di Montesquieu, le schede su carte da gioco di Rousseau, quaderni in-4° dell’Esprit des Lois o dell’Histoire naturelle. Di conseguenza l’approccio all’oggetto scritto nella sua dimensione più strettamente materiale permette lo studio di pratiche intellettuali e di processi creativi con la storia del consumo e degli usi della carta.A análise material dos manuscritos do século XVIII proporciona uma boa colheita de índices relevantes. Um inventário sistemático (que não se limite ao levantamento das filigranas) permite identificar os diferentes tipos de papel empregados por Diderot, Buffon ou Condorcet. No entanto, tais dados codicológicos só são aproveitáveis com referência à história do fabrico do papel na era pré-industrial: revela-se necessária uma abordagem crítica dos formatos, das proveniências e dos elementos de datação. A codicologia interessa-se também pelos usos dados ao papel: dobrar, recortar, montar e reutilizar são gestos correntes no século XVIII, e próprios tanto de secretários como dos próprios autores. Estas práticas favorecem a plasticidade e a mobilidade das unidades textuais: “papillons” fixados com alfinetes por Montesquieu, fichas sobre cartas de jogar de Rousseau, cadernos in-4° de Esprit des Lois ou de Histoire naturelle. Em suma, tomar o objecto escrito na sua dimensão mais estritamente material permite articular o estudo de práticas intelectuais e de processos criativos com a história do consumo e dos usos do papel

Francesca Cozzolino, Peindre pour agir. Muralisme et politique en Sardaigne

C’est un étonnant visage de la Sardaigne qu’offre aux visiteurs le village d’Orgosolo, situé au centre de l’île, à distance des côtes vouées au tourisme de masse. Les façades d’habitations, les murs longeant rues et places sont en effet devenus le support d’une intense activité picturale exprimant diverses revendications politiques. L’accumulation, depuis 1969, de plusieurs centaines de fresques, un phénomène rare en zone rurale, témoigne de l’engagement politique d’une communauté qui, en pei..

Absence of boron aggregates in superconducting silicon confirmed by atom probe tomography

Superconducting boron-doped silicon films prepared by gas immersion laser doping (GILD) technique are analyzed by atom probe tomography. The resulting three-dimensional chemical composition reveals that boron atoms are incorporated into crystalline silicon in the atomic percent concentration range, well above their solubility limit, without creating clusters or precipitates at the atomic scale. The boron spatial distribution is found to be compatible with local density of states measurements performed by scanning tunneling spectroscopy. These results, combined with the observations of very low impurity level and of a sharp two-dimensional interface between doped and undoped regions show, that the Si:B material obtained by GILD is a well-defined random substitutional alloy endowed with promising superconducting properties.Comment: 4 page