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1.
Nat Commun ; 5: 3340, 2014.
Artículo en Inglés | MEDLINE | ID: mdl-24535069

RESUMEN

Higher harmonics in current-phase relations of Josephson Junctions are predicted to be observed when the first harmonic is suppressed. Conventional theoretical models predict higher harmonics to be extremely sensitive to changes in barrier thickness, temperature, and so on. Here we report experiments with Josephson junctions incorporating a spin-dependent tunnelling barrier, revealing a current-phase relation for highly spin polarized barriers that is purely second harmonic in nature and is insensitive to changes in barrier thickness. This observation implies that the standard theory of Cooper pair transport through tunnelling barriers is not applicable for spin-dependent tunnelling barriers.

2.
Adv Mater ; 25(39): 5581-5, 2013 Oct 18.
Artículo en Inglés | MEDLINE | ID: mdl-23893892

RESUMEN

Tunnel junctions incorporating GdN ferromagnetic semiconductor barriers show a spin polarization exceeding 90% and a high conductance. These devices show an unusual low-bias conductance peak arising from a strong bias-dependence of the spin polarization. This originates from a strong magneto-electric coupling within a double Schottky barrier formed with the NbN electrodes.

3.
Nanotechnology ; 23(50): 505201, 2012 Dec 21.
Artículo en Inglés | MEDLINE | ID: mdl-23182967

RESUMEN

Superconducting nanowire single photon detectors (SNSPDs) are a key enabling technology for optical quantum information science. In this paper we demonstrate a SNSPD fabricated on lithium niobate, an important material for high speed integrated photonic circuits. We report a system detection efficiency of 0.15% at a 1 kHz dark count rate with a maximum of ~1% close to the critical current at 1550 nm wavelength for a parallel wire SNSPD with front side illumination. There is clear scope for improving on this performance with further materials optimization. Detector integration with a lithium niobate optical waveguide is simulated, demonstrating the potential for high single photon detection efficiency in an integrated quantum optic circuit.

4.
J Phys Condens Matter ; 22(30): 302003, 2010 Aug 04.
Artículo en Inglés | MEDLINE | ID: mdl-21399332

RESUMEN

We report the observation of intrinsic exchange hardening in polycrystalline GdN thin films grown at room temperature by magnetron sputtering. We find, in addition to the ferromagnetic phase, that a fraction of GdN crystallizes in a structural polymorphic form which orders antiferromagnetically. The relative fraction of these two phases was controlled by varying the relative abundance of reactive species in the sputtering plasma by means of the sputtering power and N(2) partial pressure. An exchange bias of ∼ 30 Oe was observed at 10 K. The exchange coupling between the ferromagnetic and the antiferromagnetic phases resulted in an order of magnitude enhancement in the coercive field in these films.

5.
J Nanosci Nanotechnol ; 8(5): 2588-96, 2008 May.
Artículo en Inglés | MEDLINE | ID: mdl-18572689

RESUMEN

Significant surface morphology evolution between relief and wrinkling was observed on a 3.5 microm thick TiNiCu film sputter-deposited on a silicon substrate. At room temperature, variation in surface relief morphology (from separated martensite crystals embedded in amorphous matrix to fully interweaved martensite plates) was observed with slight change in film composition. The phenomenon was attributed to variations in crystallization temperatures of as-deposited amorphous films during annealing because of the compositional difference. During thermal cycling between room temperature and 100 degrees C, reversible surface morphology changes can be observed between surface relief and wrinkling patterns. The formation of the surface wrinkling is attributed to the large compressive stress in the film during high temperature post-annealing and crystallization, whereas surface relief is caused by the martensitic transformation to relieve the large tensile stress in the film. Compositional effect on this surface morphology evolution is discussed. Results also indicate that there is a critical dimension for the wrinkling to occur, and a small circular island can only relax by in-plane expansion.

6.
J Biomed Mater Res A ; 78(1): 121-8, 2006 Jul.
Artículo en Inglés | MEDLINE | ID: mdl-16604532

RESUMEN

The effect of annealing temperature on the physicochemical and biological characteristics of magnetron cosputtered silicon-substituted hydroxyapatite (SiHA) thin coatings was studied. Annealing is required to transform as-sputtered amorphous films into crystalline coatings. A nanocrystalline, single-phase apatite structure was achieved for coatings heated to 600 or 700 degrees C and, with increasing annealing temperature, the crystallite size increased. Small crystallites were found to be more soluble in the physiological environment but, at the same time, were able to induce early formation of a new apatite layer. A human osteoblast-like (HOB) cell model was used to evaluate the performance of these annealed SiHA coatings. HOB cells attached and grew well on coatings and, after 42 days in culture, a mineralization process was observed to be taking place, with evidence of calcium phosphate minerals throughout the extracellular matrix. Our findings indicated that an annealing temperature of 600 degrees C is sufficient to achieve crystalline SiHA coatings and exhibiting good chemical stability and bioactivity.


Asunto(s)
Sustitutos de Huesos , Calcificación Fisiológica/fisiología , Materiales Biocompatibles Revestidos , Durapatita , Osteoblastos/fisiología , Silicio , Sustitutos de Huesos/síntesis química , Sustitutos de Huesos/química , Línea Celular , Materiales Biocompatibles Revestidos/síntesis química , Materiales Biocompatibles Revestidos/química , Cristalización , Durapatita/química , Matriz Extracelular/metabolismo , Calor , Humanos , Ensayo de Materiales , Membranas Artificiales , Osteoblastos/ultraestructura , Silicio/química , Factores de Tiempo
7.
J Biomed Mater Res B Appl Biomater ; 76(2): 326-33, 2006 Feb.
Artículo en Inglés | MEDLINE | ID: mdl-16080174

RESUMEN

Magnetron co-sputtering was used to produce silicon-doped hydroxyapatite (Si-HA) as coatings intended for potential applications such as orthopedic and dental implants. It was found that the crystallinity of the as-sputtered coatings increased after annealing, resulting in a nanocrystalline apatite structure. Subsequently, the bioactivity of the coatings was evaluated in an acellular simulated body fluid (SBF). Physicochemical evaluation demonstrated that a carbonate-containing apatite layer, which is essential for bonding at the bone/implant interface, was formed on the coating surfaces after immersion in SBF between 4 and 7 days. The annealed coatings exhibited enhanced bioactivity and chemical stability under physiological conditions, as compared with the as-sputtered coatings. It is proposed that the rate at which the carbonate-containing apatite layer forms is dependent on the scale factor of the structure. A nanocrystalline structure can provide a higher number of nucleation sites for the formation of apatite crystallites, leading to a more rapid precipitation of carbonate-containing apatite layer. This work shows that Si-HA coatings offer considerable potential for applications in hard tissue replacement, owing to their ability to form a carbonate-containing apatite layer rapidly.


Asunto(s)
Líquidos Corporales/química , Materiales Biocompatibles Revestidos/química , Durapatita/química , Silicio/química , Líquidos Corporales/metabolismo , Materiales Biocompatibles Revestidos/metabolismo , Durapatita/metabolismo , Humanos , Ensayo de Materiales , Microscopía Electrónica de Rastreo , Espectroscopía Infrarroja por Transformada de Fourier , Propiedades de Superficie , Difracción de Rayos X
8.
J Mater Sci Mater Med ; 16(5): 411-5, 2005 May.
Artículo en Inglés | MEDLINE | ID: mdl-15875250

RESUMEN

Bioactive silicon-containing hydroxyapatite (Si-HA) thin films that can be used as coatings for bone tissue replacement have been developed. A magnetron co-sputtering technique was used to deposit Si-HA films up to 700 nm thick on titanium substrates, with a silicon level up to 1.2 wt%. X-ray diffraction demonstrated that annealing transformed the as-deposited Si-HA films which were amorphous, into a crystalline HA structure. A human osteoblast-like (HOB) cell model was used to determine the biocompatibility of these films. HOB cells were seen to attach and grow well on the Si-HA films, and the metabolic activity of HOB cells on these films was observed to increase with culture time. Furthermore, mineralisation of the cell layers was observed after 8 weeks of culture. Based on the present findings, Si-HA of different film compositions demonstrate bioactive properties in-vitro, and indicate the potential as biocoatings for a wide variety of medical implants including load-bearing applications such as the femoral stem of hip replacement implants.


Asunto(s)
Sustitutos de Huesos/química , Materiales Biocompatibles Revestidos/química , Cristalización/métodos , Durapatita/química , Membranas Artificiales , Osteoblastos/citología , Silicio/química , Sustitutos de Huesos/análisis , Línea Celular , Proliferación Celular , Tamaño de la Célula , Supervivencia Celular , Materiales Biocompatibles Revestidos/análisis , Durapatita/análisis , Humanos , Ensayo de Materiales , Osteoblastos/fisiología , Silicio/análisis , Propiedades de Superficie
9.
Biomaterials ; 26(16): 2947-56, 2005 Jun.
Artículo en Inglés | MEDLINE | ID: mdl-15603789

RESUMEN

The use of silicon-substituted hydroxyapatite (Si-HA) as a biomaterial has been reported recently. In vivo testing has shown that Si-HA promotes early bonding of the bone/implant interface. In order to extend its usage to major load-bearing applications such as artificial hip replacement implants, it has been proposed that the material could be used in the form of a coating on implant surfaces. This paper reports a preliminary study of the biocompatibility of magnetron co-sputtered silicon-containing hydroxyapatite (Si-HA) coatings on a metallic substrate. Magnetron co-sputtered Si-HA films of thickness 600 nm with a Si content of approximately 0.8 wt% were produced on titanium substrates. X-ray diffraction analysis showed that the as-deposited Si-HA films were either amorphous or made up of very small crystals. The crystallinity of Si-HA films was increased after post-deposition heat treatment at 700 degrees C for 3 h, and the principal peaks were attributable to HA. The formation of nano-scale silicon-calcium phosphate precipitates was noted on the heat-treated films. In vitro cell culture has demonstrated that human osteoblast-like cells attached and grew well on all films, with the highest cell growth and signs of mineralisation observed on the heat-treated Si-HA films. In addition, many focal contacts were produced on the films and the cells had well-defined actin cytoskeletal organisation. This work shows that as-deposited and heat-treated Si-HA films have excellent bioactivity and are good candidates when rapid bone apposition is required. Furthermore, heat-treated Si-HA films have improved biostability compared to as-deposited films under physiological conditions.


Asunto(s)
Fosfatos de Calcio/química , Materiales Biocompatibles Revestidos/química , Hidroxiapatitas/química , Silicio/química , Actinas/química , Proliferación Celular , Células Cultivadas , Citoesqueleto/química , Citoesqueleto/metabolismo , Durapatita/química , Adhesiones Focales , Calor , Humanos , Técnicas In Vitro , Indicadores y Reactivos/farmacología , Ensayo de Materiales , Microscopía Confocal , Microscopía Electrónica , Microscopía Electrónica de Rastreo , Microscopía Fluorescente , Osteoblastos/metabolismo , Oxazinas/farmacología , Espectroscopía Infrarroja por Transformada de Fourier , Propiedades de Superficie , Factores de Tiempo , Vinculina/química , Difracción de Rayos X , Xantenos/farmacología
10.
Phys Rev Lett ; 90(24): 247006, 2003 Jun 20.
Artículo en Inglés | MEDLINE | ID: mdl-12857220

RESUMEN

Transport critical current measurements have been performed on 5 degrees [001]-tilt thin film YBa(2)Cu(3)O(7-delta) single grain boundaries with the magnetic field rotated in the plane of the film, phi. The variation of the critical current has been determined as a function of the angle between the magnetic field and the grain boundary plane. In applied fields above 1 T the critical current j(c) is found to be strongly suppressed only when the magnetic field is within an angle phi(k) of the grain boundary. Outside this angular range the behavior of the artificial grain boundary is dominated by the critical current of the grains. We show that the phi dependence of j(c) in the suppressed region is well described by a flux cutting model.

11.
Ultramicroscopy ; 87(1-2): 19-23, 2001 Mar.
Artículo en Inglés | MEDLINE | ID: mdl-11310538

RESUMEN

A novel application of coated silica tips for use in high-pressure, high-temperature, scanning tunneling microscopy is introduced. Thermal drift is reduced in the Z-direction due to the low thermal expansion of silica. Virtually, any conducting material that can be evaporated or sputtered can be used as a tip material. Experimental results are shown for tips sputter coated with platinum, along with images obtained.

12.
Phys Rev Lett ; 85(19): 4168-71, 2000 Nov 06.
Artículo en Inglés | MEDLINE | ID: mdl-11056651

RESUMEN

We have studied the temperature dependence of the in-plane resistivity of NbN/AlN multilayer samples with varying insulating layer thickness in magnetic fields up to 7 T parallel and perpendicular to the films. The upper critical field shows a crossover from 2D to 3D behavior in parallel fields. The irreversibility lines have the form (1-T/T(c))(alpha), where alpha varies from 4 / 3 to 2 with increasing anisotropy. The results are consistent with simultaneous melting and decoupling transitions for the low anisotropy sample, and with melting of decoupled pancakes in the superconducting layers for higher anisotropy samples.

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