Creador de A. fue apoyado por una Fundación Annenberg de Postgrado de Becas de Investigación, y este trabajo fue apoyado por la National Science Foundation [085281 y 1028440].

1. Fabricación de microesferas <ol><li> Seleccionar una pequeña cantidad (aproximadamente 5 pulgadas) de fibra óptica, tira ~ 1,5 &quot;revestimiento de un extremo y limpiar con metanol o etanol (Figura 1a, b). </li><li> Si está disponible, se unirá al final con una cuchilla de fibra óptica. Si no está disponible, se cortó con tijeras o cortador de alambre tales que ~ 0,5 &quot;que queda. La ventaja de utilizar una cuchilla de fibra óptica es que produce una muy lisa, uniforme corte como en la Figura 1b. Rugosidad excesiva o defectos de un corte puede causar reflujo desigual, reduciendo el factor de calidad de las esferas resultantes. </li><li> Exponer el extremo de la fibra limpia de 3W de potencia láser de CO 2 se centró en un tamaño de spot ~ 500μm de diámetro para ~ 1 segundo (Figura 1c, d, e). Esto produce esferas del ~ 200μm de diámetro, sin embargo, el tamaño puede ser sintonizado aumentando o disminuyendo el diámetro de la fibra óptica. Ligeramente ajustar la intensidad del láser también puede be necesario esferas reflujo mayores o menores. </li></ol> 2. Fabricación Microtoroid <ol><li> Diseñar y realizar una fotomáscara con los círculos oscuros y sólidos, en el espacio y el diámetro de su elección. Es importante señalar que los toroides producidos serán 25-30% menor que los círculos en la máscara. Por ejemplo, un círculo sólido con un diámetro de 100 micras producirá un toroide con un diámetro de aproximadamente 75 micras. Además, se recomienda dejar al menos 1-2mm de espacio entre cada círculo y por lo menos 5 mm de espacio entre las matrices de círculos y alrededor de los bordes de la máscara. Dado que las obleas de la muestra debe ser cuidadosamente manejado con pinzas, es importante dejar espacio para las pinzas de agarre, sin dañar los toroides. El espacio adicional también proporciona espacio para una fibra óptica cónica a la luz par en los dispositivos acabados, y permite que las muestras a ser cortado en pequeños matrices más fácilmente. Para este procedimiento, se utilizó una máscara con filas de 160 micras dicírculos ámetro ~ 1 mm de distancia, con ~ 5 mm de espacio entre cada fila de círculos. Los toroides acabados son de aproximadamente 110 micras de diámetro. </li><li> Comience con las obleas de silicio con una capa de micras de espesor 2 de sílice crecido térmicamente. Cleave las obleas que se ajustan al patrón microsismos deseado en la máscara de la fotolitografía, dejando espacio para la fotoprotección borde de cuentas. Nótese que al comienzo de la fabricación, por lo general es más conveniente para grabar varias matrices de círculos en grandes trozos de obleas de silicio (~ cm x cm varios varios). Obleas de mayor tamaño permiten la fotolitografía y grabado BOE de más muestras a la vez, y se manejan más fácilmente con unas pinzas. Más tarde, antes de la etapa de mordentado XeF 2, se recomienda para escindir las obleas más grandes en pequeñas matrices para permitir más rápido, más uniforme XeF 2 aguafuerte. </li><li> En una campana de humos, limpiar a fondo las obleas enjuagando con acetona, metanol, isopropanol y agua desionizada. Blow secar las muestras utilizando un nitrógeno o un borrador se filtrópistola de aire ressed, y colóquelos en un plato caliente ajustado a 120 ° C durante al menos 2 minutos para que se sequen. </li><li> Después de dejar las obleas fresco y colocarlos en una campana de humos inflamables / solvente y exponga a HMDS durante 2 minutos utilizando el método de deposición de vapor. Un simple método de deposición de vapor: poner unas gotas de HMDS en un vaso de 10 ml pequeña, y luego cubrir las obleas y vaso pequeño con un recipiente de vidrio más grande para sostener el vapor. </li><li> Colocar la muestra en un cono con un montaje de tamaño apropiado. Usando un frasco cuentagotas o una jeringa y el filtro, se aplican CIs a la muestra. Gira capa fotosensible S1813 en cada muestra durante 5 segundos a 500 rpm, seguidos por 45 segundos a 3.000 rpm. Perimetral eliminación talón no es necesario si la oblea es suficientemente grande para que el talón borde no interfiere con el patrón. </li><li> Suave hornear el fotoresist sobre una placa caliente a 95 ° C durante 2 minutos. </li><li> El uso de un alineador de máscara de UV y la fotomáscara se desea, exponer las muestras fotorresistente cubiertas a untotal de 80mJ/cm 2 de la radiación UV. </li><li> Sumergir las muestras en MF-321 revelador para eliminar el fotoresist que fue expuesta a la luz UV. Durante el desarrollo, estrechamente ver como el fotoresist se elimina de la oblea y se disolvió. Es importante agitar / silbido del recipiente constantemente durante este proceso para asegurar la fotoprotección se elimina de manera uniforme. Para los parámetros dados, la capa de protección dura aproximadamente 30 segundos para el desarrollo. </li><li> Cuando la mayoría de la fotoprotección no deseado se ha disuelto en el revelador, enjuague a fondo las muestras con agua corriente, sople suavemente para secar las muestras usando una pistola de nitrógeno o aire, e inspeccionar las muestras con un microscopio para asegurar que todo el fotoprotector no deseado se ha eliminado. Si es necesario, las muestras se pueden sumergir de nuevo en el revelador, sin embargo, se debe tener cuidado de no sobredesarrollar las muestras como los patrones fotorresistentes deseados también podría estar dañado. (Si los patrones deseados son dañado o defectuoso, la fotoprotección puede serquitar con acetona y los pasos 2.1 a 2.9 se pueden repetir de nuevo). </li><li> Después del revelado, enjuague a fondo las muestras de agua corriente, sople suavemente para secar las muestras, y difícil de cocer al horno en una placa caliente a 110 ° C durante 2 minutos. Este paso se calienta el fotoresist encima de su temperatura de transición vítrea, el reflujo fotorresistente y rugosidad parcialmente reparación que se produjo durante el proceso de revelado. </li><li> Uso de contenedores de teflón y el equipo de protección necesario, sumergir las muestras en el mejor grabador de óxido tamponado (BOE). BOE contiene HF, que graba la sílice no cubierta por fotorresistente para formar almohadillas circulares de sílice sobre la oblea de silicio (Figura 2a-c). Mejora de buffer HF produce un suave etch, minimizar la rugosidad en los círculos de sílice resultante. Mientras que es posible mezclar tamponada HF comenzando con 49% de HF, esto puede conducir a resultados muy variables como típicamente sólo pequeñas cantidades se toman. </li><li> Después de aproximadamente 15-20 minutos degún los tamaños de las muestras, los patrones y el número de muestras), retirar las muestras del BOE con teflón pinzas. Enjuagar cuidadosamente las muestras de agua corriente. La sílice se ha eliminado cuando las muestras se hidrófobo. </li><li> Después de ataque químico, enjuague y secado de las muestras, ellos inspeccionar utilizando un microscopio óptico. Asegúrese de que los patrones deseados han sido grabadas por completo y todo el sílice no deseados ha sido eliminado. Si es necesario, devolver las muestras al BOE para el grabado más. Uno debe tener cuidado de no overetch las muestras, o los patrones circulares por debajo de la capa de protección puede estar dañado. </li><li> Una vez grabado BOE es completa, enjuague a fondo las muestras en agua desionizada y secar con aire. Si las muestras están en grandes trozos de oblea de silicio, también se recomienda para cortar (usando una sierra de corte en anillos de diamantes o escriba) en trozos más pequeños con distintas filas de los círculos de sílice. Filas individuales de los círculos están grabados más rápida y uniformemente en la XeF2 aguafuerte paso (2,16). El polvo de silicio producido por el corte se elimina durante la limpieza en la siguiente etapa. </li><li> Quitar la fotoprotección de un enjuague con acetona, metanol, isopropanol y agua desionizada, y secar las muestras utilizando una pistola de nitrógeno y calentamiento en una placa de 120 ° C caliente durante al menos 2 minutos. </li><li> Usando un grabador XeF 2, inferiores a la de silicio por debajo de las almohadillas de sílice circulares para formar microdiscos de sílice (Figura 2d-f). La cantidad grabado debe ser aproximadamente 1/3 del tamaño del círculo de sílice, de manera que el pilar microdisco resultante es de aproximadamente 1.3 a 1.2 del diámetro total del disco, como se determina mediante inspección con un microscopio óptico. El número de XEF 2 impulsos y la duración de cada impulso depende de la cantidad de silicio en la cámara y el tipo de XeF 2 grabador utilizado. </li><li> Después de XeF 2 aguafuerte, exponer las muestras a un rayo láser de CO 2 se centró en aproximadamente 1La intensidad de 2W de 3 segundos o hasta que un toroide se forma suave (Figura 2g-i). Dependiendo del tamaño exacto del disco y la cantidad de XeF 2 subcotizaron, una intensidad ligeramente superior o inferior y el tiempo de exposición puede ser necesaria para formar una microtoroid. Es importante que el centro del haz de láser y el centro de la microdisco están alineados, de modo que el microdisco sílice se forma una microtoroid suave y circular. </li></ol> 3. Los resultados representativos Los dispositivos de microesferas y microtoroid se pueden visualizar utilizando microscopía óptica y microscopía electrónica de barrido (Figura 1d 2h, y la figura e, i). En todas las imágenes, la uniformidad de la superficie del dispositivo es claramente evidente. Para verificar que el enfoque detallado crea ultra-alta-Q dispositivos, se caracteriza también el factor Q de varios dispositivos mediante la realización de una anchura de línea (Δλ) de medición y el cálculo de la cargaQ de la simple expresión: Q = λ / Δλ = ωτ, donde λ = longitud de onda de resonancia, la frecuencia ω =, y τ = tiempo de vida de fotones. Espectros representante de cada dispositivo fabricado utilizando los procedimientos anteriormente detallados 1,9 y un gráfico de comparación de varios dispositivos se muestra en la Figura 3. Los factores de calidad de todos los dispositivos están por encima de 10 millones, siendo la mayoría por encima de 100 millones de dólares. El espectro de la microesfera era una sola resonancia, lo que indica que la luz acoplada a ya sea el sentido horario o antihorario de modo óptico de propagación. Sin embargo, el espectro del toroide exhibió una resonancia de división, lo que indica que la luz acoplada en tanto en los modos en sentido horario y antihorario simultáneamente. Este fenómeno se produce cuando hay una ligera imperfección en el sitio de acoplamiento. Al ajustar el espectro a una doble Lorentzian, el factor Q de ambos modos puede ser determinada. El fenómeno de resonancia divididana puede ocurrir tanto en la esfera y resonadores de toroide, pero se observan con mayor frecuencia en los toroides, ya que son más susceptibles a las imperfecciones y tener un menor número de modos ópticos en comparación con las esferas. <img src="/files/ftp_upload/4164/4164fig1.jpg" alt="Figura 1"/> Figura 1. Diagrama de flujo del proceso de fabricación de la cavidad de las microesferas. a) tratamiento y b) micrografía óptica de una fibra óptica limpiado y se escindió. c) micrografía de representación, d) óptica y electrónica) micrografía electrónica de barrido de un microspere resonador. <img src="/files/ftp_upload/4164/4164fig2.jpg" alt="Figura 2"/> Figura 2. Diagrama de flujo del proceso de fabricación de la cavidad microtoroid. una representación), b) de arriba vista micrografía óptica y c) vista lateral micrografía electrónica de barrido de la almohadilla de óxido de circular, como se define por fotolitografía y grabado BOE. Nótese la ligera forma de cuña del óxido que se forma por el BOE. d) Prestación, e) vista superiormicrografía óptica y f) vista lateral micrografía electrónica de barrido de la almohadilla de óxido después de la etapa de grabado XeF 2. Observe que el disco óxido mantiene la periferia en forma de cuña. g) la representación, h) tapa-vista micrografía óptica y i) vista lateral micrografía electrónica de barrido de la cavidad microtoroid. <img src="/files/ftp_upload/4164/4164fig3.jpg" alt="Figura 3"/> Figura 3. Calidad de Representante de los espectros de los factores de la a) de microesferas y b) las cavidades resonantes microtoroid según lo determinado mediante el método de medición de ancho de línea. En los dispositivos Q muy altas, se puede observar el modo de división o de un doble pico, en el que la luz se refleja en un pequeño defecto y circula en ambas direcciones hacia la derecha y hacia la izquierda. c) Comparación gráfica que muestra los factores Q de microesfera y microtoroid varias cavidades resonantes. <a href="http://www.jove.com/files/ftp_upload/4164/4164fig3large.jpg" target="_blank">Haga clic aquí para agrandar la figura</a> . Figura 4. Esquema del reflujo láser de CO 2 set-up. El CO 2 rayo láser (línea azul) se refleja y se centró en la muestra. Pasa a través de los 10,6 m / 633 nm combinador de haz, el cual transmite 10,6 micras y refleja 633 nm. Las imágenes ópticas de columna la reflexión de la muestra fuera del combinador de haz, por lo tanto, la imagen es algo rojo. Una lista de las piezas necesarias para esta configuración es en la Tabla 4. <img src="/files/ftp_upload/4164/4164fig5.jpg" alt="Figura 5"/> Figura 5. Incorrectamente reflujo de una microesfera) y b) cavidades resonantes microtoroid. Debido a la colocación incorrecta dentro del haz, el dispositivo es mala formado. c) Como resultado de una fotomáscara pobres o pobres la litografía, el toroide es en forma de luna.

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No hay conflictos de interés declarado.

Como con cualquier estructura óptica, mantener la limpieza en cada paso del proceso de fabricación es de importancia crítica. Como hay numerosos libros de texto escritos sobre el tema de la litografía y fabricación, las sugerencias a continuación no se pretende ser exhaustivo, sino destacar algunos de los problemas más comunes los investigadores se han enfrentado. 19-20 Debido a la uniformidad de la periferia de la microtoroid está determinada por la uniformidad del disco ...

<table border="1"><tbody><tr><td> Nombre de la parte </td><td> Empresa </td><td> Número de catálogo </td><td> Comentarios </td></tr><tr><td> Fibra escribano </td><td> Newport </td><td> F-RFS </td><td> Opcional </td></tr><tr><td> Fibra óptica </td><td> Newport </td><td> F-SMF-28 </td><td> Cualquier tipo de fibra óptica puede ser utilizado. </td></tr><tr><td> Fibra separador recubrimiento </td><td> Newport </td><td> F-STR-175 </td><td> Pelacables también se puede utilizar </td></tr><tr><td> Etanol </td><td> Cualquier proveedor </td><td> Disolventes nivel de pureza </td><td> Metanol o isopropanol son sustitutos </td></tr></tbody></table> Tabla 1. Materiales microesferas de fabricación. <table border="1"><tbody><tr><td> Nombre del reactivo </td><td> Empresa </td><td> &lt;strong&gt; Número de catálogo </td><td> Comentarios </td></tr><tr><td> Obleas de silicio con sílice 2μm crecido térmicamente </td><td> WRS Materiales </td><td> n / a </td><td> Usamos intrínseca 8, &lt;100&gt;, 4 &quot;de diámetro </td></tr><tr><td> HMDS (hexametildisilazano) </td><td> Aldrich </td><td> 440191 </td><td></td></tr><tr><td> CIs </td><td> Shipley </td><td> S1813 </td><td></td></tr><tr><td> Promotor </td><td> Shipley </td><td> MF-321 </td><td></td></tr><tr><td> Buffered HF - Mejora de la </td><td> Transene </td><td> n / a </td><td> La mejora de HF tampón da un suave y de mejor calidad de grabado que no sean papel BOE o HF </td></tr><tr><td> La acetona, metanol, isopropanol </td><td> Cualquier proveedor </td><td> 99,8% de pureza </td><td></td></tr></tbody></table> Tabla 2. MicrMateriales otoroid de fabricación. <table border="1"><tbody><tr><td> Nombre del equipo </td><td> Fabricante </td><td> Número de catálogo </td><td> Comentarios </td></tr><tr><td> Hilandero </td><td> Solitec </td><td> 5110-ND </td><td> Cualquier ruleta se puede utilizar. </td></tr><tr><td> Alineador </td><td> Suss Microtec </td><td> MJB 3 </td><td> Cualquier alineador se puede utilizar. </td></tr><tr><td> XeF 2 grabador </td><td> Advanced Communication Devices, Inc. </td><td> # ADCETCH2007 </td><td></td></tr></tbody></table> Tabla 3. Equipo Microtoroid fabricación. <table border="1"><tbody><tr><td> Nombre de la parte </td><td> Empresa </td><td> Número de catálogo </td><td> Comentarios </td></tr><tr><td> De CO 2 </sub&gt; láser </td><td> SYNRAD </td><td> Serie 48 </td><td></td></tr><tr><td> 3-Eje fase </td><td> OptoSigma </td><td> 120-0770 </td><td> Disponible a partir de otros fabricantes también. </td></tr><tr><td> Si el reflector 1 &quot;de diámetro) </td><td> II-VI </td><td> 308325 </td><td> Disponible a partir de otros fabricantes también. </td></tr><tr><td> Montaje cinemático cardán (para el Si reflector) </td><td> Thor Labs </td><td> KX1G </td><td> Disponible a partir de otros fabricantes también. </td></tr><tr><td> Combinador de haz (1 &quot;de diámetro) </td><td> Meller Óptica </td><td> L19100008-B0 </td><td> Disponible a partir de otros fabricantes también. </td></tr><tr><td> 4 &quot;Lente Longitud focal (1&quot; de diámetro) </td><td> Meller óptica o II-VI </td><td></td><td> Disponible a partir de otros proveedores, así </td></tr><tr><td> Surtido de mensajes, soportes de lentes </td><td> Thor Labs, Newport, Edmund Optics o OptoSigma </td><td></td><td></td></tr><tr><td> 6000 zoom de la máquina de sistema de visión </td><td> Navitar </td><td> n / a </td><td> Requiere genérica USB de la cámara y el ordenador de imágenes en tiempo real. Este se compra como un kit. </td></tr><tr><td> Focalizador para el sistema de zoom 6000 </td><td> Edmund Optics </td><td> 54-792 </td><td> Disponible a partir de otros fabricantes también. </td></tr><tr><td> XZ Posicionadores del Eje para 6000 Ampliar </td><td> Parker Daedal </td><td> CR4457, CR4452, 4499 </td><td> CR4457 es el eje X, CR4452 es el eje Z, 4499 es el soporte de montaje. </td></tr></tbody></table> Tabla 4. Láser de CO 2 de reflujo Set-up.

fabrication of silica ultra high quality factor microresonators

Whispering gallery resonant cavities confine light in circular orbits at their periphery.1-2 The photon storage lifetime in the cavity, quantified by the quality factor (Q) of the cavity, can be in excess of 500ns for cavities with Q factors above 100 million. As a result of their low material losses, silica microcavities have demonstrated some of the longest photon lifetimes to date1-2. Since a portion of the circulating light extends outside the resonator, these devices can also be used to probe the surroundings. This interaction has enabled numerous experiments in biology, such as single molecule biodetection and antibody-antigen kinetics, as well as discoveries in other fields, such as development of ultra-low-threshold microlasers, characterization of thin films, and cavity quantum electrodynamics studies.3-7
The two primary silica resonant cavity geometries are the microsphere and the microtoroid. Both devices rely on a carbon dioxide laser reflow step to achieve their ultra-high-Q factors (Q&gt;100 million).1-2,8-9 However, there are several notable differences between the two structures. Silica microspheres are free-standing, supported by a single optical fiber, whereas silica microtoroids can be fabricated on a silicon wafer in large arrays using a combination of lithography and etching steps. These differences influence which device is optimal for a given experiment.
Here, we present detailed fabrication protocols for both types of resonant cavities. While the fabrication of microsphere resonant cavities is fairly straightforward, the fabrication of microtoroid resonant cavities requires additional specialized equipment and facilities (cleanroom). Therefore, this additional requirement may also influence which device is selected for a given experiment.
Introduction
An optical resonator efficiently confines light at specific wavelengths, known as the resonant wavelengths of the device. 1-2 The common figure of merit for these optical resonators is the quality factor or Q. This term describes the photon lifetime (&tau;o) within the resonator, which is directly related to the resonator's optical losses. Therefore, an optical resonator with a high Q factor has low optical losses, long photon lifetimes, and very low photon decay rates (1/&tau;o). As a result of the long photon lifetimes, it is possible to build-up extremely large circulating optical field intensities in these devices. This very unique property has allowed these devices to be used as laser sources and integrated biosensors.10
A unique sub-class of resonators is the whispering gallery mode optical microcavity. In these devices, the light is confined in circular orbits at the periphery. Therefore, the field is not completely confined within the device, but evanesces into the environment. Whispering gallery mode optical cavities have demonstrated some of the highest quality factors of any optical resonant cavity to date.9,11 Therefore, these devices are used throughout science and engineering, including in fundamental physics studies and in telecommunications as well as in biodetection experiments. 3-7,12
Optical microcavities can be fabricated from a wide range of materials and in a wide variety of geometries. A few examples include silica and silicon microtoroids, silicon, silicon nitride, and silica microdisks, micropillars, and silica and polymer microrings.13-17 The range in quality factor (Q) varies as dramatically as the geometry. Although both geometry and high Q are important considerations in any field, in many applications, there is far greater leverage in boosting device performance through Q enhancement. Among the numerous options detailed previously, the silica microsphere and the silica microtoroid resonator have achieved some of the highest Q factors to date.1,9 Additionally, as a result of the extremely low optical loss of silica from the visible through the near-IR, both microspheres and microtoroids are able to maintain their Q factors over a wide range of testing wavelengths.18 Finally, because silica is inherently biocompatible, it is routinely used in biodetection experiments.
In addition to high material absorption, there are several other potential loss mechanisms, including surface roughness, radiation loss, and contamination loss.2 Through an optimization of the device size, it is possible to eliminate radiation losses, which arise from poor optical field confinement within the device. Similarly, by storing a device in an appropriately clean environment, contamination of the surface can be minimized. Therefore, in addition to material loss, surface scattering is the primary loss mechanism of concern.2,8
In silica devices, surface scattering is minimized by using a laser reflow technique, which melts the silica through surface tension induced reflow. While spherical optical resonators have been studied for many years, it is only with recent advances in fabrication technologies that researchers been able to fabricate high quality silica optical toroidal microresonators (Q&gt;100 million) on a silicon substrate, thus paving the way for integration with microfluidics.1
The present series of protocols details how to fabricate both silica microsphere and microtoroid resonant cavities. While silica microsphere resonant cavities are well-established, microtoroid resonant cavities were only recently invented.1 As many of the fundamental methods used to fabricate the microsphere are also used in the more complex microtoroid fabrication procedure, by including both in a single protocol it will enable researchers to more easily trouble-shoot their experiments.

Watch this Scientific Journal Video about Fabrication of Silica Ultra High Quality Factor Microresonators at JoVE.com

Fabrication of Silica Ultra High Quality Factor Microresonators

Se describe la utilización de una técnica de dióxido de carbono reflujo láser para fabricar cavidades resonantes de sílice, incluyendo independiente microesferas y microtoroids en el chip. El método de reflujo elimina imperfecciones de la superficie, permitiendo largos tiempos de vida de fotones dentro de ambos dispositivos. Los dispositivos resultantes tienen factores de ultra alta calidad, permitiendo a las aplicaciones que van desde las telecomunicaciones a biodetección.

La fabricación de sílice de alta calidad Ultra microresonators Factor

Whispering gallery resonant cavities confine light in circular orbits at their periphery.1-2 The photon storage lifetime in the cavity, quantified by the ...

fabrication-of-silica-ultra-high-quality-factor-microresonators

Research

JoVE Journal

Engineering

16.0K vistas.  University of Southern California. Se describe la utilización de una técnica de dióxido de carbono reflujo láser para fabricar cavidades resonantes de sílice, incluyendo independiente microesferas y microtoroids en el chip. El método de reflujo elimina imperfecciones de la superficie, permitiendo largos tiempos de vida de fotones dentro de ambos dispositivos. Los dispositivos resultantes tienen factores de ultra alta calidad, permitiendo a las aplicaciones que van desde las telecomunicaciones a biode...

Video: Fabrication of Silica Ultra High Quality Factor Microresonators

Angle-resolved Photoemission Spectroscopy At Ultra-low Temperatures

The physical properties of a material are defined by its electronic structure. Electrons in solids are characterized by energy (&omega;) and momentum (k) and the probability to find them in a particular state with given &omega; and k is described by the spectral function A(k, &omega;). This function can be directly measured in an experiment based on the well-known photoelectric effect, for the explanation of which Albert Einstein received the Nobel Prize back in 1921. In the photoelectric effect the light shone on a surface ejects electrons from the material. According to Einstein, energy conservation allows one to determine the energy of an electron inside the sample, provided the energy of the light photon and kinetic energy of the outgoing photoelectron are known. Momentum conservation makes it also possible to estimate k relating it to the momentum of the photoelectron by measuring the angle at which the photoelectron left the surface. The modern version of this technique is called Angle-Resolved Photoemission Spectroscopy (ARPES) and exploits both conservation laws in order to determine the electronic structure, i.e. energy and momentum of electrons inside the solid. In order to resolve the details crucial for understanding the topical problems of condensed matter physics, three quantities need to be minimized: uncertainty* in photon energy, uncertainty in kinetic energy of photoelectrons and temperature of the sample.
In our approach we combine three recent achievements in the field of synchrotron radiation, surface science and cryogenics. We use synchrotron radiation with tunable photon energy contributing an uncertainty of the order of 1 meV, an electron energy analyzer which detects the kinetic energies with a precision of the order of 1 meV and a He3 cryostat which allows us to keep the temperature of the sample below 1 K. We discuss the exemplary results obtained on single crystals of Sr2RuO4 and some other materials. The electronic structure of this material can be determined with an unprecedented clarity.

The overall goal of this method is to determine the low-energy electronic structure of solids at ultra-low temperatures using Angle-Resolved Photoemission Spectroscopy with synchrotron radiation.

De ángulo resuelto espectroscopia de fotoemisión a bajas temperaturas

The physical properties of a material are defined by its  electronic structure. Electrons in solids are characterized by energy (&omega;)  and momentum ...

Investigación

Ingeniería

Synthesis and Microdiffraction at Extreme Pressures and Temperatures

High pressure compounds and polymorphs are investigated for a broad range of purposes such as determine structures and processes of deep planetary interiors, design materials with novel properties, understand the mechanical behavior of materials exposed to very high stresses as in explosions or impacts. Synthesis and structural analysis of materials at extreme conditions of pressure and temperature entails remarkable technical challenges. In the laser heated diamond anvil cell (LH-DAC), very high pressure is generated between the tips of two opposing diamond anvils forced against each other; focused infrared laser beams, shined through the diamonds, allow to reach very high temperatures on samples absorbing the laser radiation. When the LH-DAC is installed in a synchrotron beamline that provides extremely brilliant x-ray radiation, the structure of materials under extreme conditions can be probed in situ. LH-DAC samples, although very small, can show highly variable grain size, phase and chemical composition. In order to obtain the high resolution structural analysis and the most comprehensive characterization of a sample, we collect diffraction data in 2D grids and combine powder, single crystal and multigrain diffraction techniques. Representative results obtained in the synthesis of a new iron oxide, Fe4O5 1 will be shown.

The laser heated diamond anvil cell combined with synchrotron micro-diffraction techniques allows researchers to explore the nature and properties of new phases of matter at extreme pressure and temperature (PT) conditions. Heterogeneous samples can be characterized in situ under high pressure by 2D mapping and combined powder, single-crystal and multigrain diffraction approaches.

Síntesis y microdifracción a presiones y temperaturas extremas

High pressure compounds and polymorphs are investigated for a broad range of purposes such as determine structures and processes of deep planetary ...

Convergent Polishing: A Simple, Rapid, Full Aperture Polishing Process of High Quality Optical Flats &amp; Spheres

Convergent Polishing is a novel polishing system and method for finishing flat and spherical glass optics in which a workpiece, independent of its initial shape (i.e., surface figure), will converge to final surface figure with excellent surface quality under a fixed, unchanging set of polishing parameters in a single polishing iteration. In contrast, conventional full aperture polishing methods require multiple, often long, iterative cycles involving polishing, metrology and process changes to achieve the desired surface figure. The Convergent Polishing process is based on the concept of workpiece-lap height mismatch resulting in pressure differential that decreases with removal and results in the workpiece converging to the shape of the lap. The successful implementation of the Convergent Polishing process is a result of the combination of a number of technologies to remove all sources of non-uniform spatial material removal (except for workpiece-lap mismatch) for surface figure convergence and to reduce the number of rogue particles in the system for low scratch densities and low roughness. The Convergent Polishing process has been demonstrated for the fabrication of both flats and spheres of various shapes, sizes, and aspect ratios on various glass materials. The practical impact is that high quality optical components can be fabricated more rapidly, more repeatedly, with less metrology, and with less labor, resulting in lower unit costs. In this study, the Convergent Polishing protocol is specifically described for fabricating 26.5 cm square fused silica flats from a fine ground surface to a polished ~&#955;/2 surface figure after polishing 4 hr per surface on a 81 cm diameter polisher.

A novel optical polishing process, called &#8220;Convergent Polishing&#8221;, which enables faster, lower cost polishing, is described. Unlike conventional polishing processes, Convergent Polishing allows a glass workpiece to be polished in a single iteration and with high surface quality to its final surface figure without requiring changes to polishing parameters.

Convergentes Pulido: Una simple, rápida, completa Apertura Pulido Proceso de alta calidad óptica Pisos y Esferas

Convergent Polishing is a novel polishing system and method for finishing flat and spherical glass optics in which a workpiece, independent of its initial ...

Fabrication of High Contrast Gratings for the Spectrum Splitting Dispersive Element in a Concentrated Photovoltaic System

High contrast gratings are designed and fabricated and its application is proposed in a parallel spectrum splitting dispersive element that can improve the solar conversion efficiency of a concentrated photovoltaic system. The proposed system will also lower the solar cell cost in the concentrated photovoltaic system by replacing the expensive tandem solar cells with the cost-effective single junction solar cells. The structures and the parameters of high contrast gratings for the dispersive elements were numerically optimized. The large-area fabrication of high contrast gratings was experimentally demonstrated using nanoimprint lithography and dry etching. The quality of grating material and the performance of the fabricated device were both experimentally characterized. By analyzing the measurement results, the possible side effects from the fabrication processes are discussed and several methods that have the potential to improve the fabrication processes are proposed, which can help to increase the optical efficiency of the fabricated devices.

The fabrication of high contrast gratings as the parallel spectrum splitting dispersive element in a concentrated photovoltaic system is demonstrated. Fabrication processes including nanoimprint lithography, TiO2 sputtering and reactive ion etching are described. Reflectance measurement results are used to characterize the optical performance.

Fabricación de rejillas de alto contraste para la División del espectro de dispersión de elementos en un Sistema de Concentración Fotovoltaica

High contrast gratings are designed and fabricated and its application is proposed in a parallel spectrum splitting dispersive element that can improve ...

The Evolution of Silica Nanoparticle-polyester Coatings on Surfaces Exposed to Sunlight

Corrosion of metallic surfaces is prevalent in the environment and is of great concern in many areas, including the military, transport, aviation, building and food industries, amongst others. Polyester and coatings containing both polyester and silica nanoparticles (SiO2NPs) have been widely used to protect steel substrata from corrosion. In this study, we utilized X-ray photoelectron spectroscopy, attenuated total reflection infrared micro-spectroscopy, water contact angle measurements, optical profiling and atomic force microscopy to provide an insight into how exposure to sunlight can cause changes in the micro- and nanoscale integrity of the coatings. No significant change in surface micro-topography was detected using optical profilometry, however, statistically significant nanoscale changes to the surface were detected using atomic force microscopy. Analysis of the X-ray photoelectron spectroscopy and attenuated total reflection infrared micro-spectroscopy data revealed that degradation of the ester groups had occurred through exposure to ultraviolet light to form COO&#903;, -H2C&#903;, -O&#903;, -CO&#903; radicals. During the degradation process, CO and CO2 were also produced.

Two types of surfaces, polyester-coated steel and polyester coated with a layer of silica nanoparticles, were studied. Both surfaces were exposed to sunlight, which was found to cause substantial changes in the chemistry and nanoscale topography of the surface.

La evolución de sílice recubrimientos de nanopartículas-poliéster sobre superficies expuestas al sol

Corrosion of metallic surfaces is prevalent in the environment and is of great concern in many areas, including the military, transport, aviation, ...

High Temperature Fabrication of Nanostructured Yttria-Stabilized-Zirconia (YSZ) Scaffolds by In Situ Carbon Templating Xerogels

We demonstrate a method for the high temperature fabrication of porous, nanostructured yttria-stabilized-zirconia (YSZ, 8 mol% yttria - 92 mol% zirconia) scaffolds with tunable specific surface areas up to 80 m2&#183;g-1. An aqueous solution of a zirconium salt, yttrium salt, and glucose is mixed with propylene oxide (PO) to form a gel. The gel is dried under ambient conditions to form a xerogel. The xerogel is pressed into pellets and then sintered in an argon atmosphere. During sintering, a YSZ ceramic phase forms and the organic components decompose, leaving behind amorphous carbon. The carbon formed in situ serves as a hard template, preserving a high surface area YSZ nanomorphology at sintering temperature. The carbon is subsequently removed by oxidation in air at low temperature, resulting in a porous, nanostructured YSZ scaffold. The concentration of the carbon template and the final scaffold surface area can be systematically tuned by varying the glucose concentration in the gel synthesis. The carbon template concentration was quantified using thermogravimetric analysis (TGA), the surface area and pore size distribution was determined by physical adsorption measurements, and the morphology was characterized using scanning electron microscopy (SEM). Phase purity and crystallite size was determined using X-ray diffraction (XRD). This fabrication approach provides a novel, flexible platform for realizing unprecedented scaffold surface areas and nanomorphologies for ceramic-based electrochemical energy conversion applications, e.g. solid oxide fuel cell (SOFC) electrodes.

High Temperature Fabrication of Nanostructured Yttria-Stabilized-Zirconia YSZ Scaffolds by In Situ Carbon Templating Xerogels

A protocol for fabricating porous, nanostructured yttria-stabilized-zirconia (YSZ) scaffolds at temperatures between 1,000 &#176;C and 1,400 &#176;C is presented.

Alta Fabrication Temperatura de-estabilizada con itria-óxido de circonio andamios nanoestructurados (YSZ) por<em&gt; In Situ</em&gt; carbono Templating xerogeles

We demonstrate a method for the high temperature fabrication of porous, nanostructured yttria-stabilized-zirconia (YSZ, 8 mol% yttria - 92 mol% zirconia) ...

Scalable Solution-processed Fabrication Strategy for High-performance, Flexible, Transparent Electrodes with Embedded Metal Mesh

Here, the authors report the embedded metal-mesh transparent electrode (EMTE), a new transparent electrode (TE) with a metal mesh completely embedded in a polymer film. This paper also presents a low-cost, vacuum-free fabrication method for this novel TE; the approach combines lithography, electroplating, and imprint transfer (LEIT) processing. The embedded nature of the EMTEs offers many advantages, such as high surface smoothness, which is essential for organic electronic device production; superior mechanical stability during bending; favorable resistance to chemicals and moisture; and strong adhesion with plastic film. LEIT fabrication features an electroplating process for vacuum-free metal deposition and is favorable for industrial mass production. Furthermore, LEIT allows for the fabrication of metal mesh with a high aspect ratio (i.e., thickness to linewidth), significantly enhancing its electrical conductance without adversely losing optical transmittance. We demonstrate several prototypes of flexible EMTEs, with sheet resistances lower than 1 &#937;/sq and transmittances greater than 90%, resulting in very high figures of merit (FoM) &#8211; up to 1.5 x 104 &#8211; which are amongst the best values in the published literature.

This protocol describes a solution-based fabrication strategy for high-performance, flexible, transparent electrodes with fully-embedded, thick metal mesh. Flexible transparent electrodes fabricated by this process demonstrate among the highest reported performances, including ultra-low sheet resistance, high optical transmittance, mechanical stability under bending, strong substrate adhesion, surface smoothness, and environmental stability.

Estrategia escalable de fabricación procesada por soluciones para electrodos transparentes de alto rendimiento y flexibles con malla metálica integrada

Here, the authors report the embedded metal-mesh transparent electrode (EMTE), a new transparent electrode (TE) with a metal mesh completely embedded in a ...

Fabrication of Ultra-thin Color Films with Highly Absorbing Media Using Oblique Angle Deposition

Ultra-thin film structures have been studied extensively for use as optical coatings, but performance and fabrication challenges remain.&#160; We present an advanced method for fabricating ultra-thin color films with improved characteristics. The proposed process addresses several fabrication issues, including large area processing. Specifically, the protocol describes a process for fabricating ultra-thin color films using an electron beam evaporator for oblique angle deposition of germanium (Ge) and gold (Au) on silicon (Si) substrates.&#160; Film porosity produced by the oblique angle deposition induces color changes in the ultra-thin film. The degree of color change depends on factors such as deposition angle and film thickness. Fabricated samples of the ultra-thin color films showed improved color tunability and color purity. In addition, the measured reflectance of the fabricated samples was converted into chromatic values and analyzed in terms of color. Our ultra-thin film fabricating method is expected to be used for various ultra-thin film applications such as flexible color electrodes, thin film solar cells, and optical filters. Also, the process developed here for analyzing the color of the fabricated samples is broadly useful for studying various color structures.

We present a detailed method for fabricating ultra-thin color films with improved characteristics for optical coatings. The oblique angle deposition technique using an electron beam evaporator allows improved color tunability and purity. Fabricated films of Ge and Au on Si substrates were analyzed by reflectance measurements and color information conversion.

Fabricación de películas ultra delgadas Color con altamente absorbente de los medios de comunicación mediante deposición oblicua

Ultra-thin film structures have been studied extensively for use as optical coatings, but performance and fabrication challenges remain.&#160; We present ...

Flow-assisted Dielectrophoresis: A Low Cost Method for the Fabrication of High Performance Solution-processable Nanowire Devices

Flow-assisted dielectrophoresis (DEP) is an efficient self-assembly method for the controllable and reproducible positioning, alignment, and selection of nanowires. DEP is used for nanowire analysis, characterization, and for solution-based fabrication of semiconducting devices. The method works by applying an alternating electric field between metallic electrodes. The nanowire formulation is then dropped onto the electrodes which are on an inclined surface to create a flow of the formulation using gravity. The nanowires then align along the gradient of the electric field and in the direction of the liquid flow. The frequency of the field can be adjusted to select nanowires with superior conductivity and lower trap density. 
In this work, flow-assisted DEP is used to create nanowire field effect transistors. Flow-assisted DEP has several advantages: it allows selection of nanowire electrical properties; control of nanowire length; placement of nanowires in specific areas; control of orientation of nanowires; and control of nanowire density in the device. 
The technique can be expanded to many other applications such as gas sensors and microwave switches. The technique is efficient, quick, reproducible, and it uses a minimal amount of dilute solution making it ideal for the testing of novel nanomaterials. Wafer scale assembly of nanowire devices can also be achieved using this technique, allowing large numbers of samples for testing and large-area electronic applications.

In this paper, flow assisted dielectrophoresis is demonstrated for the self-assembly of nanowire devices. The fabrication of a silicon nanowire field effect transistor is shown as an example.

Asistida por flujo dielectroforesis: Un método de bajo costo para la fabricación de dispositivos de nanocable procesables en solución de alto rendimiento

Flow-assisted dielectrophoresis (DEP) is an efficient self-assembly method for the controllable and reproducible positioning, alignment, and selection of ...

Determination of Aggregate Surface Morphology at the Interfacial Transition Zone (ITZ)

Here, we present a comprehensive method to illustrate the uneven distribution of the interfacial transition zone (ITZ) around the aggregate and the effect of aggregate surface morphology on the formation of ITZ. First, a model concrete sample is prepared with a spherical ceramic particle in roughly the central part of the cement matrix, acting as a coarse aggregate used in common concrete/mortar. After curing until the designed age, the sample is scanned by X-ray computed tomography to determine the relative location of the ceramic particle inside the cement matrix. Three locations of the ITZ are chosen: above the aggregate, on the side of the aggregate, and below the aggregate. After a series of treatments, the samples are scanned with a SEM-BSE detector. The resultant images were further processed using a digital image processing method (DIP) to obtain quantitative characteristics of the ITZ. The surface morphology is characterized at the pixel level based on the digital image. Thereafter, K-means clustering method is used to illustrate the effect of surface roughness on ITZ formation.

Determination of Aggregate Surface Morphology at the Interfacial Transition Zone ITZ

Hereby, we proposed a protocol to illustrate the effect of aggregate surface morphology on the ITZ microstructure. The SEM-BSE image were quantitatively analyzed to obtain ITZ's porosity gradient via digital image processing and a K-means clustering algorithm was further employed to establish a relationship between porosity gradient and surface roughness.

Determinación de la Morfología De la Superficie Agregada en la Zona de Transición Interfacial (ITZ)

Here, we present a comprehensive method to illustrate the uneven distribution of the interfacial transition zone (ITZ) around the aggregate and the effect ...