Optoelectronic studies in nanocrystalline silicon Schottky diodes obtained by Hot-Wire Chemical Vapour Deposition

The very usual columnar growth of nanocrystalline silicon leads to electronic transport anisotropies. Whereas electrical measurements with coplanar electrodes only provide information about the electronic transport parallel to the substrate, it is the transverse transport which determines the collection efficiency in thin film solar cells. Hence, Schottky diodes on transparent electrodes were obtained by hot-wire CVD in order to perform external quantum efficiency and surface photovoltage studies in sandwich configuration. These measurements allowed to calculate a transverse collection length, which must correlate with the photovoltaic performance of thin film solar cells. Furthermore, the density of charge trapped at localized states in the bandgap was estimated from the voltage dependence of the depletion capacitance of these rectifying contacts.

Amorphous silicon thin film solar cells deposited entirely by Hot-Wire Chemical Vapour Deposition at low temperature (<150 ºC)

Amorphous silicon n-i-p solar cells have been fabricated entirely by Hot-Wire Chemical Vapour Deposition (HW-CVD) at low process temperature < 150 °C. A textured-Ag/ZnO back reflector deposited on Corning 1737F by rf magnetron sputtering was used as the substrate. Doped layers with very good conductivity and a very less defective intrinsic a-Si:H layer were used for the cell fabrication. A double n-layer (μc-Si:H/a-Si:H) and μc-Si:H p-layer were used for the cell. In this paper, we report the characterization of these layers and the integration of these layers in a solar cell fabricated at low temperature. An initial efficiency of 4.62% has been achieved for the n-i-p cell deposited at temperatures below 150 °C over glass/Ag/ZnO textured back reflector.

Electronic transport in low temperature nanocrystalline silicon thin-film transistors obtained by Hot-Wire CVD

Hydrogenated nanocrystalline silicon (nc-Si:H) obtained by hot-wire chemical vapour deposition (HWCVD) at low substrate temperature (150 °C) has been incorporated as the active layer in bottom-gate thin-film transistors (TFTs). These devices were electrically characterised by measuring in vacuum the output and transfer characteristics for different temperatures. The field-effect mobility showed a thermally activated behaviour which could be attributed to carrier trapping at the band tails, as in hydrogenated amorphous silicon (a-Si:H), and potential barriers for the electronic transport. Trapped charge at the interfaces of the columns, which are typical in nc-Si:H, would account for these barriers. By using the Levinson technique, the quality of the material at the column boundaries could be studied. Finally, these results were interpreted according to the particular microstructure of nc-Si:H.

Microcrystalline silicon thin film transistors obtained by Hot-Wire CVD

Polysilicon thin film transistors (TFT) are of great interest in the field of large area microelectronics, especially because of their application as active elements in flat panel displays. Different deposition techniques are in tough competition with the objective to obtain device-quality polysilicon thin films at low temperature. In this paper we present the preliminary results obtained with the fabrication of TFT deposited by hot-wire chemical vapor deposition (HWCVD). Some results concerned with the structural characterization of the material and electrical performance of the device are presented.

Thin Film Transistors obtained by Hot-Wire CVD

Hydrogenated microcrystalline silicon films obtained at low temperature (150-280°C) by hot wire chemical vapour deposition at two different process pressures were measured by Raman spectroscopy, X-ray diffraction (XRD) spectroscopy and photothermal deflection spectroscopy (PDS). A crystalline fraction >90% with a subgap optical absortion 10 cm -1 at 0.8 eV were obtained in films deposited at growth rates >0.8 nm/s. These films were incorporated in n-channel thin film transistors and their electrical properties were measured. The saturation mobility was 0.72 ± 0.05 cm 2/ V s and the threshold voltage around 0.2 eV. The dependence of their conductance activation energies on gate voltages were related to the properties of the material.

Microdoping compensation of microcrystalline silicon obtained by Hot-Wire Chemical Vapour Deposition

Undoped hydrogenated microcrystalline silicon was obtained by hot-wire chemical vapour deposition at different silane-to-hydrogen ratios and low temperature (<300 °C). As well as technological aspects of the deposition process, we report structural, optical and electrical characterizations of the samples that were used as the active layer for preliminary p-i-n solar cells. Raman spectroscopy indicates that changing the hydrogen dilution can vary the crystalline fraction. From electrical measurements an unwanted n-type character is deduced for this undoped material. This effect could be due to a contaminant, probably oxygen, which is also observed in capacitance-voltage measurements on Schottky structures. The negative effect of contaminants on the device was dramatic and a compensated p-i-n structure was also deposited to enhance the cell performance.

Electronic properties of a quantum wire with arbitrary bending angle

The electron transmission and bound state properties of a quantum wire with a sharp bend at arbitrary angle are studied, extending results on the right angle sharp bend (the L¿shaped wire). These new results are compared to those of a similar structure, the circular bend wire. The possibility of using a bent wire to perform transistor action is also discussed.

Disseny, modelat i fabricació d'una antena "trap" per aplicacions WLAN

En aquest treball s’ha dissenyat i fabricat una antena monopol en estructura planar capaç de treballar correctament a les freqüències WLAN de 2,45-2,5 GHz (802.11b/g) i 4,9-5,875 GHz (802.11a/h/j). Per arribar a aquest objectiu primer s’ha presentat el model de línia de transmissió acabada en circuit obert per simular el comportament d’una antena. S’han comparat i verificat els resultats amb el model d’antena de fil. Seguidament, s’ha estudiat el comportament que introdueix el fet de carregar l’antena amb un ressonador LC. Finalment, s’ha passat del model d’antena de fil a una estructura planar. Aquesta geometria ha permès la realització del trap LC de forma distribuïda a través d’un ressonador CLL. El principi de disseny de l’antena està basat en la introducció d’aquest ressonador CLL amb freqüència de ressonància situada entre les dos bandes de treball i que junt amb l’ajust dels diversos paràmetres que defineixen l’antena han permès obtenir més 1 GHz d’ample de banda a la freqüència de 5 GHz.

La construcción del espacio dramático en la ficción televisiva norteamericana. Análisis del espacio vivencial en las series dramáticas de la HBO

El presente trabajo analiza la construcción del espacio vivencial en cinco series televisivas producidas por la cadena norteamericana HBO: Carnivàle, Deadwood, The Sopranos, The Wire y Treme. La investigación parte de la convicción de una posible reelaboración de la historia del espacio doméstico norteamericano a través de la puesta en escena y de la potencialidad simbólica del espacio serial. De este modo, el trabajo propone un recorrido hermenéutico en el que se analiza la evolución del espacio narrativo, su evolución morfológica en dependencia de las necesidades diegéticas de cada una de las obras analizadas.

Effective one-dimensional square well for two-dimensional quantum wires

The symmetrical two-dimensional quantum wire with two straight leads joined to an arbitrarily shaped interior cavity is studied with emphasis on the single-mode approximation. It is found that for both transmission and bound-state problems the solution is equivalent to that for an energy-dependent one-dimensional square well. Quantum wires with a circular bend, and with single and double right-angle bends, are examined as examples. We also indicate a possible way to detect bound states in a double bend based on the experimental setup of Wu et al.

Exchange-correlation effects on quantum wires with spin-orbit interactions under the influence of in-plane magnetic fields.

Within the noncollinear local spin-density approximation, we have studied the ground state structure of a parabolically confined quantum wire submitted to an in-plane magnetic field, including both Rashba and Dresselhaus spin-orbit interactions. We have explored a wide range of linear electronic densities in the weak (strong) coupling regimes that appear when the ratio of spin-orbit to confining energy is small (large). These results are used to obtain the conductance of the wire. In the strong coupling limit, the interplay between the applied magnetic field¿irrespective of the in-plane direction, the exchange-correlation energy, and the spin-orbit energy-produces anomalous plateaus in the conductance vs linear density plots that are otherwise absent, or washes out plateaus that appear when the exchange-correlation energy is not taken into account.

Understanding quantum wires with circular bends

It is shown that propagation around a circular bend in a quantum wire is well approximated by a one¿dimensional problem with a square¿well potential replacing the bend. Simple analytic expressions are obtained for the transmission and bound states.

A Neanderthal Lower Incisor from Cova del Gegant (Sitges, Barcelona, Spain)

Cova del Gegant is located near the city of Sitges (Barcelona, Spain). The cave is a small karst system which contains Upper Pleistocene archaeological and paleontological material (DauRa et al., 2005). The site was first excavated in 1954 and then in 1972 and 1974- (Viñas, 1972; Viñas & Villalta, 1975) and in 1985 and 1989 (maRtínez et al., 1985; moRa, 1988; maRtínez et al., 1990). Finally, in 2007, Grup de Recerca del Quaternari has restarted the archaeological research at Cova del Gegant (DauRa, 2008; DauRa et al., 2010). A human mandible was recovered during the first field season in 1954 and was recently published by DauRa et al. (2005). In the present study, we describe a new human tooth (left I2) that appeared, like the mandible, in a revision of the faunal material recovered from the site in 1974-1975. The specimen preserves the entire crown and the cervical two thirds of the root (Figure 1). The lack of the root apex makes it difficult to determine if the tooth was fully developed at the time of death. However, CT analysis reveals a pulp cavity that could be still open, suggesting root formation was incomplete. The specimen shows only slight dental wear corresponding to stage 2 of Molnar (1971 en Hillson, 1996). Morphologically, the crown shows slight shovelling and a lingual tubercle and appears similar to Neandertal incisors. Standard crown measurements (buccolingual diameter=7.7 mm; mesiodistal diameter= 7.3 mm) (Figure 2) suggest a fairly large tooth, particularly in the BL dimension, again resembling Neandertals in this regard. Discriminant analysis classified the Gegant incisor as Neandertal with a 99.8% posterior probability (Table 2). Association of this tooth with the previously described mandible is considered unlikely given the different ages at death estimated for each. Thus, there appear to be two individuals preserved in the sediments of the Gegant cave, one adult and one subadult (around 8-10 years old).

Bond strength of orthodontic brackets using different light and self-curing cements

The purpose of the study was to evaluate the shear bond strength of stainless steel orthodontic brackets directly bonded to extracted human premolar teeth. Fifty teeth were randomly divided into ¿ve groups: (1) System One (chemically cured composite resin), (2) Light Bond (light-cured composite resin), (3) Vivaglass Cem (self-curing glass ionomer cement), (4) Fuji Ortho LC (light-cured glass ionomer cement) used after 37% orthophosphoric acid¿etching of enamel (5) Fuji Ortho LC without orthophosphoric acid¿etching. The brackets were placed on the buccal and lingual surfaces of each tooth, and the specimens were stored in distilled water (24 hours) at 378C and thermocycled. Teeth were mounted on acrylic block frames, and brackets were debonded using an Instron machine. Shear bond strength values at fracture (Nw)were recorded. ANOVA and Student-Newman-Keuls multiple comparison tests were performed (P , .05). Bonding failure site was recorded by stereomicroscope and analyzed by Chi-square test, selected specimens of each group were observed by scanning electron microscope. System One attained the highest bond strength. Light Bond and Fuji Ortho LC, when using an acid-etching technique, obtained bond strengths that were within the range of estimated bond strength values for successful clinical bonding. Fuji Ortho LC and Vivaglass Cem left an almost clean enamel surface after debracketing.

Influencia de diferentes sistemas de profilaxis en la adhesión de un sellador de fisuras al esmalte

Introducción: La adhesión de las resinas dentales al esmalte no depende solamente del grabado ácido del esmalte. Otros factores, como el pulido de la superficie del esmalte pueden influir en la fuerza de adhesión de las resinas. El objetivo de este estudio es evaluar la adhesión de un sellador de fisuras fotopolimerizable tras la utilización previa de distintos métodos de profilaxis y dos diferentes tiempos de grabado. Material y método: Ochenta terceros molares extraídos quirúrgicamente se seccionaron en dos mitades (vestibular y lingual). Los dientes se dividieron en ocho grupos de 20 muestras cada uno, de acuerdo con los métodos de profilaxis: polvo de piedra pómez, pasta fluorada, espray de bicarbonato y control (sin profilaxis); y dos tiempos de grabado: 15 y 30 segundos. Se midió la fuerza de adhesión mediante una prueba de tracción en una máquina de ensayos universal INSTRON. Resultados y conclusión: Se utilizó el test estadístico ANOVA, detectándose diferencias significativas en la resistencia a la tracción; el posterior test de Dunnett encontró estas diferencias entre los grupos control y de profilaxis con piedra pómez para 15 y 30 segundos de grabado respecto de los grupos tratados con pasta fluorada y espray de bicarbonato, para los mismos tiempos de grabado (p<0,05), siendo esta diferencia mayor en el grupo de espray con bicarbonato.