HAADF-STEM block-scanning strategy for local measurement of strain at the nanoscale

Lattice strain measurement of nanoscale semiconductor devices is crucial for the semiconductor industry as strain substantially improves the electrical performance of transistors. High resolution scanning transmission electron microscopy (HR-STEM) imaging is an excellent tool that provides spatial resolution at the atomic scale and strain information by applying Geometric Phase Analysis or image fitting procedures. However, HR-STEM images regularly suffer from scanning distortions and sample drift during image acquisition. In this paper, we propose a new scanning strategy that drastically reduces artefacts due to drift and scanning distortion, along with extending the field of view. The method allows flexible tuning of the spatial resolution and decouples the choice of field of view from the need for local atomic resolution. It consists of the acquisition of a series of independent small subimages containing an atomic resolution image of the local lattice. All subimages are then analysed individually for strain by fitting a nonlinear model to the lattice images. The obtained experimental strain maps are quantitatively benchmarked against the Bessel diffraction technique. We demonstrate that the proposed scanning strategy approaches the performance of the diffraction technique while having the advantage that it does not require specialized diffraction cameras

In situ UHVEM study of {113}-defect formation in Si nanowires

Results are presented of a study of {113}-defect formation in vertical Si nanowire n-type tunnel field effect transistors with nanowire diameters ranging from 40 to 500 nm. The nanowires are etched into an epitaxial moderately As doped n-type layer grown on a heavily As doped n(+) Si substrate. p(+) contacts on the nanowire are created by epitaxial growth of a heavily B doped layer. Using focused ion beam cutting, samples for irradiation are prepared with different thicknesses so that the nanowires are fully or partially embedded in the sample thickness. {113}-defects are created in situ by 2 MeV e-irradiation in an ultra-high voltage electron microscope between room temperature and 375 degrees C. The observations are discussed in the frame of intrinsic point defect properties, taking into account the role of dopants and capping layers. The important impact of the specimen thickness is elucidated

Agentes virtuales en atención a clientes – 2013

Los agentes virtuales son programas informáticos que permiten el diálogo entre los seres humanos y las computadoras en lenguaje natural: Chino, Inglés, Español, Ruso, Italiano, etc.En esta investigación se ha revisado el estado del arte de los agentes virtuales especializados en servicios al cliente en idioma Español. Estos, aún no han alcanzado un alto nivel de penetración, a pesar de que el idioma Español es uno de los dos lenguajes nativos mas hablados del mundo, está dentro de los cuatro más hablados como segundo lenguaje, y es uno de los seis idiomas oficiales de las Naciones Unidas.El relevamiento, que incluyó las características de la interfaz, la síntesis de voz y la técnica de reconocimiento de texto aparentemente utilizada, permitió distinguir tres tipos dominantes: “Buscador de palabras claves”; “Buscador tipo IVR”; y “Basado en PLN, Procesamiento de LenguajeNatural”.Mediante una encuesta se relevaron las experiencias de interacción, usuario - agente virtual, considerando tres dimensiones: resolución de problemas, si el agente virtual ha logrado la satisfacciónde las necesidades mediante el uso de conocimiento especializado; interacción, si ha tenido éxito en la comunicación con los usuarios al comprender las frases escritas; y reconocimiento de emociones, si el agente virtual ha reconocido el estado emocional del usuario y ha respondido en consecuencia. Esta actividad fue complementada con un focus group que permitió un mejor entendimiento de aspectos motivacionales, complementando el análisis estadístico.Los resultados sugieren que existen relaciones claras entre la valoración positiva de algunas de las dimensiones estudiadas y la capacidad percibida que tiene un agente virtual de ofrecer un servicio de atención a clientes, similar o superior al que un agente humano típico ofrecería en similares circunstancias

Growth of high quality InP layers in STI trenches on miscut Si (001) substrates

In this work, we report the selective area epitaxial growth of high quality InP in shallow trench isolation (STI) structures on Si (0 0 1) substrates 6° miscut toward (1 1 1) using a thin Ge buffer layer. We studied the impact of growth rates and steric hindrance effects on the nano-twin formation at the STI side walls. It was found that a too high growth rate induces more nano-twins in the layer and results in InP crystal distortion. The STI side wall tapering angle and the substrate miscut angle induced streric hindrance between the InP facets and the STI side walls also contribute to defect formation. In the [-1 1 0] orientated trenches, when the STI side wall tapering angle is larger than 10°, crystal distortion was observed while the substrate miscut angle has no significant impact on the InP defect formation. In the [-1 1 0] trenches, both the increased STI tapering angle and the substrate miscut angle induce high density of defects. With a small STI tapering angle and a thin Ge layer, we obtained extended defect free InP in the top region of the [1 1 0] trenches with aspect ratio larger than 2

Evaluación del rendimiento de CMSNMS en espacios métricos anidados

La mayoría de los métodos de búsqueda en espacios métricos asumen que la topología de la colección de objetos es razonablemente regular. Sin embargo, se sabe de la existencia de Espacios Métricos Anidados, que son espacios en donde los objetos de la colección pueden agruparse en clusters o subespacios. Aquí diferentes dimensiones explican las diferencias entre los objetos dentro de cada subespacio anidado dentro de un espacio métrico más general. En este trabajo se evalúa el rendimiento del CMSNMS que es una estructura de índice de dos niveles para resolver problemas de búsquedas en espacios de esta topología. En un primer nivel esta técnica utiliza una Lista de Clusters (LC), donde se identifican y ordenan estas agrupaciones utilizando el Sparse Spatial Selection (SSS) y técnicas de LC. En un segundo nivel se genera un índice por cada cluster denso, basado en selección de pivotes, empleando también SSS. Las experimentaciones muestran que el desempeño de CMSNMS es mejor que el de las demás en los espacios métricos anidados.Eje: Workshop Bases de datos y minería de datos (WBDDM)Red de Universidades con Carreras en Informática (RedUNCI

Electrical properties of extended defects in strain relaxed GeSn

We report the electrical properties of 60 degrees dislocations originating from the +1.2% lattice mismatch between an unintentionally doped, 315 nm thick Ge0.922Sn0.078 layer (58% relaxed) and the underlying Ge substrate, using deep level transient spectroscopy. The 60 degrees dislocations are found to be split into Shockley partials, binding a stacking fault. The dislocations exhibit a band-like distribution of electronic states in the bandgap, with the highest occupied defect state at similar to E-V + 0.15 eV, indicating no interaction with point defects in the dislocation's strain field. A small capture cross-section of 1.5 x 10(-19) cm(2) with a capture barrier of 60 meV is observed, indicating a donor-like nature of the defect-states. Thus, these dislocation-states are not the source of unintentional p-type doping in the Ge0.922Sn0.078 layer. Importantly, we show that the resolved 60 degrees dislocation-states act as a source of leakage current by thermally generating minority electrons via the Shockley-ReadHall mechanism

Combining methods for searches in nested metric spaces

Most search methods in metric spaces assume that the topology of the object collection is reasonably regular. However, there exist nested metric spaces, where objects in the collection can be grouped into clusters or subspaces, in such a way that different dimensions or variables explain the differences between objects inside each subspace. This paper proposes a two levels index to solve search problems in spaces with this topology. The idea is to have a first level with a list of clusters, which are identified and sorted using Sparse Spatial Selection (SSS) and Lists of Clusters techniques, and a second level having an index for each dense cluster, based on pivot selection, using SSS. It is also proposed for future work to adjust the second level indexes through dynamic pivots selection to adapt the pivots according to the searches performed in the database.Presentado en el VIII Workshop Bases de Datos y Minería de Datos (WBDDM)Red de Universidades con Carreras en Informática (RedUNCI

Diffraction studies for stoichiometry effects in BaTiO3 grown by molecular beam epitaxy on Ge(001)

In this work, we present a systematic study of the effect of the stoichiometry of BaTiO3 (BTO) films grown on the Ge(001) substrate by molecular-beam-epitaxy using different characterization methods relying on beam diffraction, including reflection high-energy electron diffraction (RHEED), X-ray diffraction (XRD), and selected-area electron diffraction in transmission electron microscopy. Surprisingly, over a wide range of [Ba]/[Ti] ratios, as measured by the Rutherford backscattering spectrometry, all the BTO layers exhibit the same epitaxial relationship BTO(001)// Ge(001) with the substrate, describing a 45 degrees lattice rotation of the BTO lattice with respect to the Ge lattice. However, varying the [Ba]/[Ti] ratio does change the diffraction behavior. From RHEED patterns, we can derive that excessive [Ba] and [Ti] generate twinning planes and a rougher surface in the non-stoichiometric BTO layers. XRD allows us to follow the evolution of the lattice constants as a function of the [Ba]/[Ti] ratio, providing an option for tuning the tetragonality of the BTO layer. In addition, we found that the intensity ratio of the 3 lowest-order Bragg peaks I-(001)/I-(002), I-(101)/I-(002), and I-(111)/I-(002) derived from omega - 2 theta scans characteristically depend on the BTO stoichiometry. To explain the relation between observed diffraction patterns and the stoichiometry of the BTO films, we propose a model based on diffraction theory explaining how excess [Ba] or [Ti] in the layer influences the diffraction response. Published by AIP Publishing

Nucleation Mechanism during WS2 Plasma Enhanced Atomic Layer Deposition on Amorphous Al2O3 and Sapphire Substrates

The structure, crystallinity and properties of as-deposited two-dimensional (2D) transition metal dichalcogenides are determined by nucleation mechanisms in the deposition process. 2D materials grown by atomic layer deposition (ALD) in absence of a template, are polycrystalline or amorphous. Little is known about their nucleation mechanisms. Therefore, we investigate the nucleation behavior of WS2 during plasma enhanced ALD from WF6, H2 plasma and H2S at 300 °C on amorphous ALD Al2O3 starting surface and on monocrystalline, bulk sapphire. Preferential interaction of the precursors with the Al2O3 starting surface promotes fast closure of the WS2 layer. The WS2 layers are fully continuous at WS2 content corresponding to only 1.2 WS2 monolayers. On amorphous Al2O3, (0002) textured and polycrystalline WS2 layers form with grain size of 5 nm to 20 nm due to high nucleation density (~1014 nuclei/cm2). The WS2 growth mode changes from 2D (layer-by-layer) growth on the initial Al2O3 surface to three-dimensional (Volmer-Weber) growth after WS2 layer closure. Further growth proceeds from both WS2 basal planes in register with the underlying WS2 grain, and from or over grain boundaries of the underlying WS2 layer with different in-plane orientation. In contrast, on monocrystalline sapphire, WS2 crystal grains can locally align along a preferred in-plane orientation. Epitaxial seeding occurs locally albeit a large portion of crystals remain randomly oriented, presumably due to the low deposition temperature. The WS2 sheet resistance is 168 MΩµm suggesting that charge transport in the WS2 layers is limited by grain boundaries.status: publishe