Schottky barrier heights of tantalum oxide, barium strontium titanate, lead zirconate titanate and strontium bismuth tantalate

Schottky barrier heights of various metals on tantalum pentoxide, barium strontium titanate, lead zirconate-titanate and strontium bismuth tantalate have been calculated as a function of metal work function. These oxides have a dimensionless Schottky barrier pinning factor, S, of 0.28 - 0.4 and not close to 1, because S is controlled by the Ti-O type bonds not Sr-O type bonds, as assumed previously. Band offsets on silicon are asymmetric with much smaller offset at the conduction band, so that Ta2O5 and barium strontium titanate (BST) are relatively poor barriers to electrons on Si.

A New Modified Expanding Cavity Model for Characterizing the Spherical Indentation Behaviour of Bulk Metallic Glass with Pile-up

Spherical nanoindentation tests were performed on Zr41.2Ti13.8Cu12.5Ni10Be22.5 bulk metallic glass and pile-ups were observed around the indenter. A new modified expanding cavity model was developed to characterize the indentation deformation behavior of strain-hardening and pressure-dependent materials. By using this model, the representative stress-strain response of this bulk metallic glass to hardness and indentation in the elastic-plastic regime were obtained taking into consideration the effect of pile-up.

Observation of the ordered growth of coronene on Ag(111): a scanning tunnelling microscopy study of vacuum deposited molecules

The molecular ordering of coronene (C24H12) obtained by vacuum-deposition onto predominantly Ag(111) on mica has been investigated using the scanning tunnelling microscope. Real-space topographic images reveal that in certain regions we obtain layer-by-layer ordered growth of the molecules on this substrate which agrees with previous indirect measurements (the growth did not display this ordering in other regions). In our experiments on the ordered regions, we observe the best imaging contrast at a voltage bias of -0.28 V which may correspond to a resonant tunnelling process through the molecules. © 1995.

GaN-based LEDs grown on 6-inch diameter Si (111) substrates by MOVPE

The issues and challenges of growing GaN-based structures on large area Si substrates have been studied. These include Si slip resulting from large temperature non-uniformities and cracking due to differential thermal expansion. Using an A1N nucleation layer in conjunction with an AlGaN buffer layer for stress management, and together with the interactive use of real time in-situ optical monitoring it was possible to realise flat, crack-free and uniform GaN and LED structures on 6-inch Si (111) substrates. The EL performance of processed LED devices was also studied on-wafer, giving good EL characteristics including a forward bias voltage of ∼3.5 V at 20 mA from a 500 μm × 500 μm device. © 2009 SPIE.

InGaN/GaN LEDs grown on Si(111): Dependence of device performance on threading dislocation density and emission wavelength

We demonstrate the growth of crack-free blue and greenemitting LED structures grown on 2-inch and 6-inch Si(111) substrates by metalorganic vapour phase epitaxy (MOVPE), using AlN nucleation layers and AlGaN buffer layers for stress management. LED device performance and its dependence on threading dislocation (TD) density and emission wavelength were studied. Despite the inherently low light extraction efficiency, an output power of 1.2 mW at 50 mA was measured from a 500 μm square planar device, emitting at 455 nm. The light output decreases dramatically as the emission wavelength increases from 455 nm to 510 nm. For LED devices emitting at similar wavelength, the light output was more than doubled when the TD density was reduced from 5×1 09 cm-2 to 2×109 cm-2. Our results clearly show that high TD density is detrimental to the overall light output, highlighting the need for further TD reduction for structures grown on Si. © 2010 Wiley-VCH Verlag GmbH & Co. KGaA.

Scanning transmission electron microscopy investigation of the Si(111)/AlN interface grown by metalorganic vapor phase epitaxy

The structure and chemistry of the interface between a Si(111) substrate and an AlN(0001) thin film grown by metalorganic vapor phase epitaxy have been investigated at a subnanometer scale using high-angle annular dark field imaging and electron energy-loss spectroscopy. 〈1120̄〉AlN ∥ 〈110〉Si and 〈0001〉AlN ∥ 〈111〉 Si epitaxial relations were observed and an Al-face polarity of the AlN thin film was determined. Despite the use of Al deposition on the Si surface prior to the growth, an amorphous interlayer of composition SiNx was identified at the interface. Mechanisms leading to its formation are discussed. © 2010 American Institute of Physics.

Micropropagacion de dos clones de caña de azucar (Saccharum sp.) ISA 96-110 e ISA 96-111

El presente estudio se realizó con el objetivo de desarrollar metodología para la micropropagación a partir de ápices caulinares, utilizando la técnica Spinder, y posteriormente aclimatación de las vitroplantas de dos clones de caña de azúcar (Saccharum sp.) (ISA 96-110 e ISA 96- 111). Se estudió el efecto que sobre el establecimiento tendrian 4 variantes del medio de cultivo MS (1962), suplidas con 0.0, 0.2 y 0.6 mg/1 de 6-BAP. Se utilizaron 15 réplicas por tratamiento. Se evaluó el efecto que sobre la brotación tuvieron 4 variantes del medio MS (1962), a las que se les adicionó 0.0, 0.1 y 0.5 mg/1 de 6 BAP durante tres subcultivos sucesivos. Se utilizaron 5 réplicas por variante en estudio. Para inducir el mayor enraizamiento se probaron 4 variantes líquidas del medio MS ( 1962), suplidas con 0.0, 1.0 y 1.6 mg/1 de AlA. Para el estudio de aclimatación se emplearon 30 plantas por cultivar y se establecieron en un sustrato de lombrices Californiana (Eisenia foetida). El clon ISA 96-110 presentó mayor porcentaje de fenolización y menor curvatura que el clon ISA 96-111. El medio de cultivo MS + 0.60 m g/1 de 6-BAP indujo al menor porcentaje de fenolización (33.0) y mayor de curvatura (60.0) en el clon ISA 96-110, el medio MS + 0.20 mg/1 de 6- BAP en el clon ISA 96-111. La sobrevivencia de las plantas del clon ISA- 111 fue de 100 % en todos los medios de cultivo, para el ISA 96-11O sólo los medios MS + 0.20 y MS + 0.00 mg/1 de 6-BAP. No hubo aumento de los valores de las variables altura de la planta, número de brotes y de hojas con el aumento del número de subcultivos. El medio de cultivo que indujo mayor brotación para el clon ISA 96-11 O fue el MS + 0.30 mg/1, mientras que para el clon ISA 96-111 fue el MS + 0.1 mg/1 de 6- BAP. El clon ISA 96-111 reportó resultados superiores en longitud (5.75 cm) y número de raices (7.4) por planta. El medio de cultivo MS + 1.3 mg/1 de AlA indujo los mejores resultados en ambos clones. El comportamiento de las plantas del clon ISA 96-1 11 fueron superiores a las del clon ISA 96-11O al momento de la aclimatación

Bismuth-doped fiber integrated ring laser mode-locked with a nanotube-based saturable absorber

We demonstrate passive mode-locking of a bismuth-doped fiber laser using a singlewall nanotube-based saturable absorber. Stable operation in the all-normal dispersion and average soliton regime is obtained, with an all-fiber integrated format. © 2010 Optical Society of America.

Modified Generalized Beam Lattice Model Associated With Fracture Of Reinforced Fiber/Particle Composites

Lattice-type model can simulate in a straightforward manner heterogeneous brittle media. Mohr-Coulomb failure criterion has recently been involved into the generalized beam (GB) lattice model, and as a result, numerical experiments on concrete under various loading conditions can be conducted. The GB lattice model is further used to investigate the reinforced fiber/particle composites instead of only particle composites as the model did before. Numerical examples are given to show the effectiveness of the modeling procedure, and influences of inclusions (particle, fiber and rebar) on the fracture processes are also discussed. (c) 2008 Elsevier Ltd. All rights reserved.

A Modified Free Volume Model For Characterizing Of Rate Effect In Bulk Metallic Glasses

We investigate the plastic deformation and constitutive behaviour of bulk metallic glasses (BMGs). A dimensionless Deborah number De(ID) = t(r)/t(i) is proposed to characterize the rate effect in BMGs, where t(r) is the structural relaxing characteristic time of BMGs under shear load, t(i) is the macroscopic imposed characteristic time of applied stress or the characteristic time of macroscopic deformation. The results demonstrate that the modified free volume model can characterize the strain rate effect in BMGs effectively.

Synchronization of modified Chua's circuit with x vertical bar x vertical bar function

This paper considers the chaos synchronization of the modified Chua's circuit with x vertical bar x vertical bar function. We firstly show that a couple of the modified Chua systems with different parameters and initial conditions can be synchronized using active control when the values of parameters both in drive system and response system are known aforehand. Furthermore, based on Lyapunov stability theory we propose an adaptive active control approach to make the states of two identical Chua systems with unknown constant parameters asymptotically synchronized. Moreover the designed controller is independent of those unknown parameters. Numerical simulations are given to validate the proposed synchronization approach.

Sapientia, 1974, Vol. XXIX, nº 111 (número completo)

Contenido: Actualidad perenne del tomismo / Octavio N. Derisi – The commentary of St. Thomas on the Decaelo of Aristotle / James A. Weisheipl – Desocultamiento y creación / Raúl Echauri – le cercle de la connaissance et du vouloir á propos d’un texte de Saint Thomas / Joseph de Finance -- Notas y comentarios -- Bibliografía