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1.
Adv Mater ; 29(10)2017 Mar.
Artículo en Inglés | MEDLINE | ID: mdl-28092134

RESUMEN

A conducting 2D electron gas (2DEG) is formed at the interface between epitaxial LaFeO3 layers >3 unit cells thick and the surface of SrTiO3 single crystals. The 2DEG is exquisitely sensitive to cation intermixing and oxygen nonstoichiometry. It is shown that the latter thus allows the controllable formation of the 2DEG via ionic liquid gating, thereby forming a nonvolatile switch.

2.
Opt Express ; 20(27): 28009-16, 2012 Dec 17.
Artículo en Inglés | MEDLINE | ID: mdl-23263035

RESUMEN

We demonstrate electrooptic modulation at a wavelength of 2165nm, using a free-carrier injection-based silicon Mach-Zehnder modulator. The modulator has a V(π)∙L figure of merit of 0.12V∙mm, and an extinction ratio of -23dB. Optical modulation experiments are performed at bitrates up to 3Gbps. Our results illustrate that optical modulator design methodologies previously developed for telecom-band devices can be successfully applied to produce high-performance devices for a silicon nanophotonic mid-infrared integrated circuit platform.


Asunto(s)
Interferometría/instrumentación , Semiconductores , Telecomunicaciones/instrumentación , Diseño de Equipo , Análisis de Falla de Equipo
3.
Adv Mater ; 24(17): 2315-9, 2012 May 02.
Artículo en Inglés | MEDLINE | ID: mdl-22467240

RESUMEN

A bulk heterojunction of ordered titania nanopillars and PbS colloidal quantum dots is developed. By using a pre-patterned template, an ordered titania nanopillar matrix with nearest neighbours 275 nm apart and height of 300 nm is fabricated and subsequently filled in with PbS colloidal quantum dots to form an ordered depleted bulk heterojunction exhibiting power conversion efficiency of 5.6%.


Asunto(s)
Coloides/química , Puntos Cuánticos , Energía Solar , Electrodos , Plomo/química , Nanotecnología , Sulfuros/química
5.
ACS Nano ; 5(5): 3536-41, 2011 May 24.
Artículo en Inglés | MEDLINE | ID: mdl-21534536

RESUMEN

We investigate a hybrid nanocomposite combining fluorescent dyes and ultrasmall (<3 nm) silver nanocrystals in a block copolymer micelle. Although the metal nanoparticles are significantly smaller than the electromagnetic skin depth, we observe a modification of the exciton lifetime and the nonradiative energy transfer among the dyes. This behavior is absent in a control experiment with dyes whose energetic levels are far from the plasmonic resonance, establishing the plasmonic nature of the interaction.


Asunto(s)
Cristalización/métodos , Colorantes Fluorescentes/química , Oro/química , Nanoestructuras/química , Nanoestructuras/ultraestructura , Resonancia por Plasmón de Superficie/métodos , Sustancias Macromoleculares/química , Ensayo de Materiales , Conformación Molecular , Tamaño de la Partícula , Propiedades de Superficie
6.
Phys Chem Chem Phys ; 13(9): 3634-7, 2011 Mar 07.
Artículo en Inglés | MEDLINE | ID: mdl-21264396

RESUMEN

Plasma processing at cryogenic temperatures tremendously suppresses the depth penetration of plasma radical species within nanoporous materials. We demonstrate that this confining effect is surprisingly unrelated to changes in the phase diffusivity of radical species gas, but is determined by the increase of the sticking coefficient and the radical recombination and reaction factors, favoring an early irreversible surface adsorption of the plasma radical species.


Asunto(s)
Nanoestructuras/química , Adsorción , Radicales Libres/química , Porosidad , Temperatura
7.
Chem Commun (Camb) ; 46(27): 4971-3, 2010 Jul 21.
Artículo en Inglés | MEDLINE | ID: mdl-20508893

RESUMEN

High quality and monodispersed CdTe nanocrystals with tunable emission spectra ranging from 516 nm to 650 nm were synthesized by a highly reproducible microwave method.

8.
Opt Express ; 18(5): 4986-99, 2010 Mar 01.
Artículo en Inglés | MEDLINE | ID: mdl-20389510

RESUMEN

A compact waveguide-integrated Germanium-on-insulator (GOI) photodetector with 10 +/- 2fF capacitance and operating at 40Gbps is demonstrated. Monolithic integration of thin single-crystalline Ge into front-end CMOS stack was achieved by rapid melt growth during source-drain implant activation anneal.

9.
Phys Rev Lett ; 102(24): 247205, 2009 Jun 19.
Artículo en Inglés | MEDLINE | ID: mdl-19659044

RESUMEN

Using cross-section transmission electron microscopy we show that films of CoFe alloys, sandwiched between two conventional amorphous materials, are amorphous when less than approximately 25-30 A thick. When these amorphous layers are integrated into magnetic tunnel junctions with amorphous alumina tunnel barriers, significantly higher tunneling magnetoresistance is found compared to when these layers are made crystalline (e.g., by heating or by thickening them). We postulate that this is likely due to changes in interfacial bonding at the alumina-CoFe interface. Indeed, x-ray emission spectroscopy shows a significant increase in the Fe, but not the Co, 3d density of states at the Fermi energy for thin amorphous CoFe layers.

10.
Microsc Microanal ; 12(2): 156-9, 2006 Apr.
Artículo en Inglés | MEDLINE | ID: mdl-17481352

RESUMEN

Ultramicrotomy, the technique of cutting nanometers-thin slices of material using a diamond knife, was applied to prepare transmission electron microscope (TEM) specimens of nanoporous poly(methylsilsesquioxane) (PMSSQ) thin films. This technique was compared to focused ion beam (FIB) cross-section preparation to address possible artifacts resulting from deformation of nanoporous microstructure during the sample preparation. It was found that ultramicrotomy is a successful TEM specimen preparation method for nanoporous PMSSQ thin films when combined with low-energy ion milling as a final step. A thick, sacrificial carbon coating was identified as a method of reducing defects from the FIB process which included film shrinkage and pore deformation.


Asunto(s)
Crioultramicrotomía/métodos , Microscopía Electrónica/métodos , Microscopía/métodos , Nanopartículas , Procesamiento de Imagen Asistido por Computador , Iones
11.
Nano Lett ; 5(10): 2014-8, 2005 Oct.
Artículo en Inglés | MEDLINE | ID: mdl-16218729

RESUMEN

Coassemblies of block copolymers and inorganic precursors offer a path to ordered inorganic nanostructures. In thin films, these materials combined with domain alignment provide highly robust nanoscopic templates. We report a simple path to control the morphology, scaling, and orientation of ordered mesopores in organosilicate thin films through the coassembly of a diblock copolymer, poly(styrene-b-ethylene oxide) (PS-b-PEO), and an oligomeric organosilicate precursor that is selectively miscible with PEO. Continuous films containing cylindrical or spherical pores are generated by varying the mixing composition of symmetric PS-b-PEO and an organosilicate precursor. Tuning interfacial energy at both air/film and film/substrate interfaces allows the control of cylindrical pore orientation normal to the supported film surfaces. Our method provides well-ordered mesoporous structures within organosilicate thin films that find broad applications as highly stable nanotemplates.

12.
Nano Lett ; 5(2): 379-82, 2005 Feb.
Artículo en Inglés | MEDLINE | ID: mdl-15794629

RESUMEN

Dumbbell-like Au-Fe(3)O(4) nanoparticles are synthesized using decomposition of Fe(CO)(5) on the surface of the Au nanoparticles followed by oxidation in 1-octadecene solvent. The size of the particles is tuned from 2 to 8 nm for Au and 4 nm to 20 nm for Fe(3)O(4). The particles show the characteristic surface plasmon absorption of Au and the magnetic properties of Fe(3)O(4) that are affected by the interactions between Au and Fe(3)O(4). The dumbbell is formed through epitaxial growth of iron oxide on the Au seeds, and the growth can be affected by the polarity of the solvent, as the use of diphenyl ether results in flower-like Au-Fe(3)O(4) nanoparticles.


Asunto(s)
Cristalización/métodos , Compuestos Férricos/química , Oro/química , Magnetismo , Nanoestructuras/análisis , Nanoestructuras/química , Nanotecnología/métodos , Adsorción , Ensayo de Materiales , Conformación Molecular , Tamaño de la Partícula
13.
Nat Mater ; 3(12): 862-7, 2004 Dec.
Artículo en Inglés | MEDLINE | ID: mdl-15516928

RESUMEN

Magnetically engineered magnetic tunnel junctions (MTJs) show promise as non-volatile storage cells in high-performance solid-state magnetic random access memories (MRAM). The performance of these devices is currently limited by the modest (< approximately 70%) room-temperature tunnelling magnetoresistance (TMR) of technologically relevant MTJs. Much higher TMR values have been theoretically predicted for perfectly ordered (100) oriented single-crystalline Fe/MgO/Fe MTJs. Here we show that sputter-deposited polycrystalline MTJs grown on an amorphous underlayer, but with highly oriented (100) MgO tunnel barriers and CoFe electrodes, exhibit TMR values of up to approximately 220% at room temperature and approximately 300% at low temperatures. Consistent with these high TMR values, superconducting tunnelling spectroscopy experiments indicate that the tunnelling current has a very high spin polarization of approximately 85%, which rivals that previously observed only using half-metallic ferromagnets. Such high values of spin polarization and TMR in readily manufactureable and highly thermally stable devices (up to 400 degrees C) will accelerate the development of new families of spintronic devices.


Asunto(s)
Cristalización/métodos , Electrónica/instrumentación , Almacenamiento y Recuperación de la Información/métodos , Óxido de Magnesio/química , Magnetismo/instrumentación , Materiales Manufacturados , Procesamiento de Señales Asistido por Computador/instrumentación , Computadores , Conductividad Eléctrica , Electrodos , Diseño de Equipo , Ensayo de Materiales , Temperatura
14.
J Am Chem Soc ; 126(37): 11458-9, 2004 Sep 22.
Artículo en Inglés | MEDLINE | ID: mdl-15366890

RESUMEN

Monodisperse MnFe2O4 nanoparticles with cubelike and polyhedron shapes were synthesized by reaction of Fe(acac)3 and Mn(acac)2 with 1,2-hexadecanediol, oleic acid, and oleylamine. Controlled evaporation of the particle dispersion led to nanoparticle superlattices. The crystal orientation of the particle in the assembly depends on the shape of the particles, with particles in a cubelike shape showing (100) texture and those in the polyhedron shape exhibiting (110) texture.

15.
J Am Chem Soc ; 126(1): 273-9, 2004 Jan 14.
Artículo en Inglés | MEDLINE | ID: mdl-14709092

RESUMEN

High-temperature solution phase reaction of iron(III) acetylacetonate, Fe(acac)(3), with 1,2-hexadecanediol in the presence of oleic acid and oleylamine leads to monodisperse magnetite (Fe(3)O(4)) nanoparticles. Similarly, reaction of Fe(acac)(3) and Co(acac)(2) or Mn(acac)(2) with the same diol results in monodisperse CoFe(2)O(4) or MnFe(2)O(4) nanoparticles. Particle diameter can be tuned from 3 to 20 nm by varying reaction conditions or by seed-mediated growth. The as-synthesized iron oxide nanoparticles have a cubic spinel structure as characterized by HRTEM, SAED, and XRD. Further, Fe(3)O(4) can be oxidized to Fe(2)O(3), as evidenced by XRD, NEXAFS spectroscopy, and SQUID magnetometry. The hydrophobic nanoparticles can be transformed into hydrophilic ones by adding bipolar surfactants, and aqueous nanoparticle dispersion is readily made. These iron oxide nanoparticles and their dispersions in various media have great potential in magnetic nanodevice and biomagnetic applications.

16.
Chem Commun (Camb) ; (8): 1010-1, 2003 Apr 21.
Artículo en Inglés | MEDLINE | ID: mdl-12744344

RESUMEN

Using the controlled precipitation of silicic acid on functionalized polystyrene latexes, nanometer sized silica-coated spheres could be prepared and subsequently modified to allow dispersion in non-aqueous solvents; removal of the interior polymer by calcination resulted in the formation of hollow silica spheres.

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