The long-standing collaboration with Chang-Beom Eom at the University of Wisconsin-Madison, who provided the LAO/STO samples, is gratefully acknowledged. Video editing assistance from Christopher Solis is greatly appreciated. This work is supported by NSF (DMR-1104191, DMR-1124131), ARO (W911NF-08-1-0317), and AFOSR (FA9550-10-1-0524, FA9550-12-1-0268, FA9550-12-1-0057).

1. Obtener LAO / heteroestructuras STO <ol><li> Obtener una heteroestructura de óxido que consiste en 3,4 células por unidad de LAO cultivadas por deposición por láser pulsado en TiO sustratos STO 2 terminados en. Detalles de crecimiento de la muestra se describen en la ref. 22. </li></ol> 2. Fotolitográfico Procesamiento de Muestras Crear contactos eléctricos en la interfaz de LAO / STO, con zonas de unión de los lienzos de cableado a un portador de chip. Los pasos de procesamiento individuales se describen en detalle a continuación. <ol><li> Girar fotoprotector <ol><li> Girar fotorresistente sobre las muestras a 600 rpm durante 5 segundos, luego a 4000 rpm durante 30 seg. La capa fotorresistente será de aproximadamente 2 m de espesor. Hornee las muestras a 95 ° C durante 1 min. </li></ol></li><li> La exposicion fotoprotector utilizando un alineador de máscara con 320 nm de luz de 100 seg con una dosis de 5 mW / cm 2. </li><li> Desarrollar la fotoprotección en desarrollador fotoprotector foR 1 min. </li><li> Fresado Ion <ol><li> Utilice un molino de iones Ar + para eliminar 15 nm de material (LAO y STO) en las zonas no cubiertas por fotoprotector. Colocar las muestras en un ángulo de 22,5 ° respecto a la dirección perpendicular al haz de iones de Ar + entrante. Si la tasa de ataque químico de Ar + no está calibrado, realizar una ejecución de la calibración para garantizar que se elimina la cantidad correcta de material. Determinar la profundidad de grabado usando AFM o profilmetry equivalente. </li></ol></li><li> Sputtering DC de Ti y de Au <ol><li> Depósito 4 nm de Ti, a continuación, 25 nm de Au en las muestras de modo que el Au hace contacto eléctrico con la capa de STO expuesta. La presión de pulverización catódica es en el rango de 2-6 x 10 -7 Torr, y la pulverización catódica se lleva a cabo con la muestra a temperatura ambiente. Pre-pulverización catódica de Ti durante 10 min con el obturador cerrado a 100 W, entonces obturador abierto y pulverización catódica por 20 segundos a 100 W. Una vez terminado, inmediatamente antes de la pulverización catódica de Au durante 1 min a 50 W a continuación, por pulverización catódica de Au durante 30 segundos para las muestras a 50 W. Calibrar el tiempo para producir los espesores de Ti y Au deseados. </li></ol></li><li> El despegue <ol><li> Utilice de lavado por ultrasonidos en acetona / IPA para eliminar el material fotorresistente de la superficie de las muestras. </li></ol></li><li> Segunda capa <ol><li> Un segundo proceso litográfico, con exclusión de la etapa 4 (es decir., Con exclusión de fresado de iones), se utiliza para crear las conexiones de cables de oro a zonas de unión individuales. Los dos patrones deben ser bien alineados para asegurar que no se producen cortocircuitos eléctricos. </li></ol></li><li> La limpieza con plasma. <ol><li> Un IPC Barril Etcher se utiliza para eliminar los residuos de resina fotosensible en la zanja patrón. El instrumento utilizado en el 100 W y 1 Torr argón durante 1 min </li></ol></li></ol> 3. Bonos alambre una muestra de los Preparativos de la escritura <ol><li> Montar la muestra LAO / STO en un portador de chip (Figura 2A) con 28 pines disponibles. </li><li> Estructura de unión de cables </li></ol> NOTA: Utilice un dispositivo de unión de alambre para hacer c eléctricaonexiones entre zonas de unión en la muestra y el soporte de chip. Adjuntar 1 milésima de pulgada (25 micrómetros) alambres de oro entre los contactos eléctricos y el soporte de chip. Escribe nanoestructuras 4. Escribir Nanoestructuras <ol><li> Crear un esbozo informal de la nanoestructura conductor (Figura 3A). </li><li> Abra los gráficos vectoriales escalables editor (SVG) (Figura 3B). <ol><li> Utilice una plantilla o definir el tamaño de la ventana para que coincida con la de la imagen de AFM. </li><li> Cargar la imagen AFM de la muestra en el editor de SVG. </li><li> Crear elementos nanoestructura superpuestos en la imagen AFM. </li></ol></li><li> Cargue el archivo SVG en el programa de nanolitografía. </li><li> Ejecute el software de la litografía para crear una nanoestructura conductora. <ol><li> Sugerencia Utilice V = 10 V para crear nanoestructuras, y la punta de V = -10 V para borrar nanoestructuras. </li><li> Mueva la punta c-AFM, a una velocidad que oscila entre 200 nm / seg a 2 m / seg. </li></ol></li></ol> 5. Dispositivo Enfriar y tomar mediciones <ol><li> Apague todas las luces blancas y utilizar filtros de color rojo / fuentes de luz. </li><li> Extraer la muestra del sistema de AFM. </li><li> Cargar la muestra en el refrigerador de dilución (A). </li><li> Medir la resistencia frente a la temperatura (B) como se enfría la muestra. </li><li> Medir las propiedades de transporte a bajas temperaturas (C). </li></ol>

<ol>
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The authors have nothing to disclose.

Successful creation of nanostructures depends on several critical steps. It is important that the LAO/STO samples are grown with a thickness that is known to be at the boundary between the insulating and conductive phase. (Details of sample growth fall outside the scope of this paper, but are crucial for overall success.) Second, it is important to have relative humidity within the range 25-45% for successful c-AFM writing. Values below 25% are unlikely to produce conductive nanostructures, while too high humidity will generally produce uncontrollably large features. Also, temperature control of the AFM is important if the c-AFM tip needs to achieve precise registry over long periods of time. Once the nanostructures are created, they must be placed in a vacuum environment if experiments lasting longer than a few hours are to be performed. For the experiments described here, the structure is created and within minutes transferred to a vacuum environment.
It is recommend before writing that a &#8220;writing test&#8221; be performed on all relevant electrodes. In such a test, two virtual electrodes are first created, and a single nanowire is written while simultaneously monitoring the conductance. A similar test of erasure can be performed by &#8220;cutting&#8221; the nanowire shortly afterwards. If the nanostructure is decaying rapidly, the issue is most likely due either to the interfacial contacts or the canvas itself. To distinguish between these two effects, a four-terminal measurement of the conductance should be performed, and the two-terminal conductance should be compared with the four-terminal conductance as a function of time. If the two-terminal conductance is decaying more rapidly than the four-terminal conductance, then the issue is related to the electrical contacts to the interface. If the four-terminal conductance is decaying at a comparable rate, then most likely the canvas is not suitable and should be replaced.
There are natural limitations of the current method for creating nanostructures. Specifically, the writing speed for the smallest devices is limited to a few hundred nanometers per second. Speeds far above that value lead to unpredictable results. Use of parallel writing techniques are possible27,28, but are not highly developed and have their own drawbacks. The size of nanostructures that can be created is naturally limited by the scan range of the AFM being used. A high-quality AFM with closed-loop feedback in the two scan directions is highly recommended. Tracking of point-like objects on the sample surface should be performed to monitor temporal drift of the sample.
Once creation of conductive nanostructures at oxide interfaces has been mastered, there are a wide range of experimental directions that can be explored. Using this technique, a wide variety of nanostructures and devices have already been demonstrated, including nanowires18, tunnel barriers29, rectifying junctions30, field-effect transistors18, single-electron transistors31, superconducting nanowires32, nanoscale optical detectors33, and nanoscale THz emitters and detectors34.

Heteroestructuras Óxido 1-5 muestran una notable variedad de fenómenos físicos emergentes que son tanto científicamente interesante y potencialmente útil para aplicaciones 4. En particular, la interfaz entre LaAlO3 (LAO) y SrTiO3 (STO) 6 puede exhibir aislante, la realización, superconductores 7, ferroeléctrico-como 8, 9 y ferromagnético comportamiento. En 2006, Thiel et al mostraron que 10 hay una transición brusca-aislante-metal como el espesor de la capa de LAO se incrementa, con un espesor crítico de 4 celdas unitarias (4UC). Posteriormente se demostró que las estructuras 3uc-LAO/STO exhiben una transición de histéresis que puede ser controlado localmente con un microscopio de fuerza atómica conductora (C-AFM) de la sonda 11. Las propiedades de las interfaces de óxido tales como LaAlO3 / SrTiO3 dependen de la ausencia o presencia de llevar a caboelectrones en la interfase. Estos electrones se pueden controlar con los mejores electrodos de puerta 12,13, compuertas traseras 10, superficie adsorbatos 14, capas ferroeléctricos 15,16 y c-AFM litografía 11. Una característica única de c-AFM litografía es que muy pequeñas características a nanoescala se pueden crear. Gating top eléctrico, combinado con reclusión de dos dimensiones, se utiliza a menudo para crear puntos cuánticos en semiconductores III-V 17. Alternativamente, los nanocables semiconductores cuasi-unidimensionales pueden gated eléctricamente por proximidad. Los métodos para producir estas estructuras son mucho tiempo y generalmente irreversible. Por el contrario, la técnica de la litografía C-AFM es reversible en el sentido de que una nanoestructura se puede crear para un experimento, y luego &quot;borrado&quot; (similar a una pizarra). En general, la escritura c-AFM se realiza con tensiones positivas aplicadas a la punta del AFM, mientras que, borrandose realiza utilizando voltajes negativos. El tiempo requerido para crear una estructura particular depende de la complejidad del dispositivo, pero es por lo general menos de 30 min; mayor parte de ese tiempo se dedica a borrar el lienzo. La resolución espacial típica es de unos 10 nanómetros, pero con ajuste adecuado características tan pequeñas como 2 nanómetros se pueden crear 18. Una descripción detallada del procedimiento de fabricación de nanoescala sigue. El detalle que figura aquí debería ser suficiente para que experimentos similares a realizar por los investigadores interesados. El método descrito aquí tiene muchas ventajas sobre los enfoques litográficas tradicionales utilizados para crear nanoestructuras electrónicos en los semiconductores. El método de litografía c-AFM aquí descrito forma parte de una clase mucho más amplia de los esfuerzos de la litografía basada en sonda de barrido, incluyendo la oxidación anódica de exploración 19, nanolitografía dip-pen 20, patrones piezoeléctrico21, y así sucesivamente. La técnica de c-AFM se describe aquí, junto con el uso de interfaces de óxido de nuevos, puede producir algunas de las estructuras electrónicas de más alto de precisión con una variedad sin precedentes de propiedades físicas.

<table border="0" cellpadding="0" cellspacing="0" width="889">
	<tbody>
		<tr height="20">
			<td height="20" style="height:20px;width:165px;">Name</td>
			<td style="width:169px;">Company</td>
			<td style="width:108px;">Catalog Number</td>
			<td style="width:447px;">Comments</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Equipment</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Contact Aligner</td>
			<td>Karl-Suss</td>
			<td>MA6</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Spinner</td>
			<td>Solitec</td>
			<td>5110C</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Ion Mill</td>
			<td>Commonwealth Scientific</td>
			<td>8C</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Sputtering System</td>
			<td>Leybold-Heraeus</td>
			<td>Z-650</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Barrel Etcher</td>
			<td>Branson/IPC</td>
			<td>3000C</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Wire Bonder</td>
			<td>Westbond</td>
			<td>7700E</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">AFM</td>
			<td>Asylum Research</td>
			<td>MFP-3D</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Dilution Refrigerator</td>
			<td>Quantum Design</td>
			<td>P850</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Ultrasonic Wash Machine</td>
			<td>Fisher Scientific</td>
			<td>15-335-6</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Current Amplifier</td>
			<td>Femto</td>
			<td>DLPCA-200</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;"></td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Materials</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">LaAlO3/SrTiO3</td>
			<td>Prof. Chang-Beom Eom</td>
			<td>N/A</td>
			<td>5mm x 1mm with ~3.4 unit cells of LAO (See Reference 18)</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Photoresist</td>
			<td>AZ Electronic Materials</td>
			<td>P4210</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Developer</td>
			<td>AZ Electronic Materials</td>
			<td>400K</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Acetone</td>
			<td>Fisher Scientific</td>
			<td>A929SK-4</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Isopropyl Alcohol</td>
			<td>Fisher Scientific</td>
			<td>A459-1</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Deionized Water</td>
			<td>Fisher Scientific</td>
			<td>23-290-065</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Gold Wire</td>
			<td>DuPont</td>
			<td>5771</td>
			<td>1 mil diameter</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Chip Carrier</td>
			<td>NTK Technologies</td>
			<td>IRK28F1-5451D</td>
			<td></td>
		</tr>
	</tbody>
</table>

writing and low-temperature characterization of oxide nanostructures

Oxide nanoelectronics is a rapidly growing field which seeks to develop novel materials with multifunctional behavior at nanoscale dimensions. Oxide interfaces exhibit a wide range of properties that can be controlled include conduction, piezoelectric behavior, ferromagnetism, superconductivity and nonlinear optical properties. Recently, methods for controlling these properties at extreme nanoscale dimensions have been discovered and developed. Here are described explicit step-by-step procedures for creating LaAlO3/SrTiO3 nanostructures using a reversible conductive atomic force microscopy technique. The processing steps for creating electrical contacts to the LaAlO3/SrTiO3 interface are first described. Conductive nanostructures are created by applying voltages to a conductive atomic force microscope tip and locally switching the LaAlO3/SrTiO3 interface to a conductive state. A versatile nanolithography toolkit has been developed expressly for the purpose of controlling the atomic force microscope (AFM) tip path and voltage. Then, these nanostructures are placed in a cryostat and transport measurements are performed. The procedures described here should be useful to others wishing to conduct research in oxide nanoelectronics.

Los resultados mostrados aquí son representativos del comportamiento de transporte que puede ser exhibida por esta clase de nanoestructuras, y ha sido descrito en detalle en otra parte 23-26. En este ejemplo, una cavidad de nanocables se ha construido (Figura 4) a partir de una heteroestructura de LAO celular 3,3 unidad / STO. Vías de conducción (que se muestran en verde) son típicamente de 10 nm de ancho, según lo determinado por el nanocable &quot;corte&quot; experimentos 11. La velocidad punta y la tensión de cada segmento es independientemente configurable desde el panel frontal de litografía (Figura 4 B), al igual que la velocidad de escritura de punta. &quot;Electrodos virtuales&quot; que se interconectan con los contactos interfaciales aseguran que hay una conexión eléctrica altamente conductor de las nanoestructuras. Después de la nanoestructura está escrito, se transfiere al refrigerador de dilución. La exposición a la luz en o por debajo de 550 nm producirá fotoconducción no deseado, por lo que es importante para transferir el dispositivo en la oscuridad o con la ayuda de un rojo &quot;cuarto oscuro&quot; de luz (Figura 5 A). Las conexiones eléctricas deben hacerse a temperatura ambiente, y como con la mayoría de las nanoestructuras de semiconductores, el gran cuidado debe ser tomado al cambiar las conexiones eléctricas a temperaturas criogénicas. Si los dispositivos se somete a las descargas electrostáticas, lo más probable es llegar a ser aislante. Sorprendentemente, la funcionalidad del dispositivo puede ser recuperado por &quot;ciclo&quot; la temperatura a 300 K y enfriamiento de nuevo. Durante el tiempo de reutilización, es rutina para controlar la resistencia de dos terminales, e incluso la resistencia de cuatro terminales, como una función de la temperatura. Para estas mediciones se aplica una tensión de corriente alterna (normalmente ~ 1 mV) a una baja frecuencia (&lt;10 Hz) a uno de los electrodos, mientras que la corriente de CA se mide usando un amplificador de transimpedancia. Lock-in demodulación y filtrado se realiza mediante un amplificador lock-in casa-desarrollado. La cu acrrent se controla como una función de la temperatura (Figura 5B). Una vez que el dispositivo se enfría a la temperatura de base del refrigerador de dilución (50 mK), mediciones de transporte de cuatro terminales se llevan a cabo (Figura 5C). Para estas mediciones, la corriente se transmite a través del canal principal del dispositivo, mientras el voltaje a través del dispositivo se mide simultáneamente. En lugar de medir con un amplificador lock-in, un voltaje de corriente completo (IV) traza se mide. Este método contiene más información y la conducción diferencial se puede calcular a través de la diferenciación numérica. Para el dispositivo en particular, la conducción diferencial se mide como una función de la puerta de lado-tensión V sg. Esta puerta permite que el potencial químico del dispositivo para ser cambiado. El transporte a través del dispositivo muestra una fuerte dependencia no monotónica, lo que indica las regiones en las que tiene lugar el bloqueo de Coulomb para los valores más pequeños, y strong superconductividad para valores grandes de V sg. Los detalles sobre la interpretación física para esta clase de dispositivo se describen en otra parte. <img alt="Figura 1" src="/files/ftp_upload/51886/51886fig1highres.jpg" /> .. Figura 1 pasos de procesamiento fotolitográficas Paso 1: fotoprotector giro. Paso 2: exponer fotoprotector utilizando alineador de la máscara. Paso 3: desarrollar fotoprotector. Paso 4: fresado de iones. Paso 5: DC sputtering depositar Ti y Au. Paso 6: despegue. Paso 7: depositar la segunda capa. Paso 8: limpieza por plasma. <img alt="Figura 2" src="/files/ftp_upload/51886/51886fig2highres.jpg" /> Figura 2. Imágenes de litográficamente estampadas heteroestructuras LAO / STO. (A) Imagen que muestra a 5 mm x 5 mm de alambre muestra unido a un portador de chip. (B)<html> Optical imagen que muestra zonas de unión y uno de los lienzos. (C) Primer plano de un solo lienzo. <a href="https://www.jove.com/files/ftp_upload/51886/51886fig2highres.jpg" target="_blank">Haga clic aquí para ver una versión más grande de esta figura.</a> <img alt="Figura 3" src="/files/ftp_upload/51886/51886fig3highres.jpg" /> Figura 3. (A) el diseño informal de nanoestructura LAO / STO. (B) la disposición precisa de nanoestructuras usando un código abierto escalable de gráficos vectoriales editor (SVG). <img alt="Figura 4" src="/files/ftp_upload/51886/51886fig4highres.jpg" /> Figura 4. (A) Litografía panel frontal para c-AFM patrones. (B) posición y tensión de c-AFM punta Captura de pantalla del simulador 3D que muestra.w.jove.com/files/ftp_upload/52058/52058fig4large.jpg &quot;target =&quot; _blank &quot;&gt; Haga clic aquí para ver una versión más grande de esta figura. <img alt="La figura 5" src="/files/ftp_upload/51886/51886fig5highres.jpg" /> Figura 5. (A) nanoestructura LAO / STO que se inserta en el refrigerador de dilución. (B) Vigilancia de la resistencia de la muestra ya que se enfría desde 300 K a 50 mK. (C) Monitoreo de la conductancia diferencial de cuatro terminales de dispositivo como una función de Vsg voltaje de la puerta lateral y el voltaje a través del dispositivo (V4T). Gráfico de intensidad mostrada en unidades de siemens (S), y las tensiones se visualiza en unidades de voltios (V).

Watch this Scientific Journal Video about Writing and Low-Temperature Characterization of Oxide Nanostructures at JoVE.com

Writing and Low-Temperature Characterization of Oxide Nanostructures

Oxide nanostructures provide new opportunities for science and technology. The interfacial conductivity between LaAlO3 and SrTiO3 can be controlled with near-atomic precision using a conductive atomic force microscopy technique. The protocol for creating and measuring conductive nanostructures at LaAlO3/SrTiO3 interfaces is demonstrated.

La escritura y la caracterización de baja temperatura de óxido de Nanoestructuras

Oxide nanoelectronics is a rapidly growing field which seeks to develop novel materials with multifunctional behavior at nanoscale dimensions.  Oxide ...

writing-and-low-temperature-characterization-of-oxide-nanostructures

Research

JoVE Journal

Engineering

9.9K vistas.  University of Pittsburgh. Oxide nanostructures provide new opportunities for science and technology. The interfacial conductivity between LaAlO3 and SrTiO3 can be controlled with near-atomic precision using a conductive atomic force microscopy technique. The protocol for creating and measuring conductive nanostructures at LaAlO3/SrTiO3 interfaces is demonstrated.

Video: Writing and Low-Temperature Characterization of Oxide Nanostructures

A Method to Fabricate Disconnected Silver Nanostructures in 3D

The standard nanofabrication toolkit includes techniques primarily aimed at creating 2D patterns in dielectric media. Creating metal patterns on a submicron scale requires a combination of nanofabrication tools and several material processing steps. For example, steps to create planar metal structures using ultraviolet photolithography and electron-beam lithography can include sample exposure, sample development, metal deposition, and metal liftoff. To create 3D metal structures, the sequence is repeated multiple times. The complexity and difficulty of stacking and aligning multiple layers limits practical implementations of 3D metal structuring using standard nanofabrication tools. Femtosecond-laser direct-writing has emerged as a pre-eminent technique for 3D nanofabrication.1,2 Femtosecond lasers are frequently used to create 3D patterns in polymers and glasses.3-7 However, 3D metal direct-writing remains a challenge. Here, we describe a method to fabricate silver nanostructures embedded inside a polymer matrix using a femtosecond laser centered at 800 nm. The method enables the fabrication of patterns not feasible using other techniques, such as 3D arrays of disconnected silver voxels.8 Disconnected 3D metal patterns are useful for metamaterials where unit cells are not in contact with each other,9 such as coupled metal dot10,11or coupled metal rod12,13 resonators. Potential applications include negative index metamaterials, invisibility cloaks, and perfect lenses.
In femtosecond-laser direct-writing, the laser wavelength is chosen such that photons are not linearly absorbed in the target medium. When the laser pulse duration is compressed to the femtosecond time scale and the radiation is tightly focused inside the target, the extremely high intensity induces nonlinear absorption. Multiple photons are absorbed simultaneously to cause electronic transitions that lead to material modification within the focused region. Using this approach, one can form structures in the bulk of a material rather than on its surface.
Most work on 3D direct metal writing has focused on creating self-supported metal structures.14-16 The method described here yields sub-micrometer silver structures that do not need to be self-supported because they are embedded inside a matrix. A doped polymer matrix is prepared using a mixture of silver nitrate (AgNO3), polyvinylpyrrolidone (PVP) and water (H2O). Samples are then patterned by irradiation with an 11-MHz femtosecond laser producing 50-fs pulses. During irradiation, photoreduction of silver ions is induced through nonlinear absorption, creating an aggregate of silver nanoparticles in the focal region. Using this approach we create silver patterns embedded in a doped PVP matrix. Adding 3D translation of the sample extends the patterning to three dimensions.

Femtosecond-laser direct-writing is frequently used to create three-dimensional (3D) patterns in polymers and glasses. However, patterning metals in 3D remains a challenge. We describe a method for fabricating silver nanostructures embedded inside a polymer matrix using a femtosecond laser centered at 800 nm.

Un método para fabricar nanoestructuras desconectados de plata en 3D

The standard nanofabrication toolkit includes  techniques primarily aimed at creating 2D patterns in dielectric media. Creating  metal patterns on a ...

Investigación

Ingeniería

Probing and Mapping Electrode Surfaces in Solid Oxide Fuel Cells

Solid oxide fuel cells (SOFCs) are potentially the most efficient and cost-effective solution to utilization of a wide variety of fuels beyond hydrogen 1-7. The performance of SOFCs and the rates of many chemical and energy transformation processes in energy storage and conversion devices in general are limited primarily by charge and mass transfer along electrode surfaces and across interfaces. Unfortunately, the mechanistic understanding of these processes is still lacking, due largely to the difficulty of characterizing these processes under in situ conditions. This knowledge gap is a chief obstacle to SOFC commercialization. The development of tools for probing and mapping surface chemistries relevant to electrode reactions is vital to unraveling the mechanisms of surface processes and to achieving rational design of new electrode materials for more efficient energy storage and conversion2. Among the relatively few in situ surface analysis methods, Raman spectroscopy can be performed even with high temperatures and harsh atmospheres, making it ideal for characterizing chemical processes relevant to SOFC anode performance and degradation8-12. It can also be used alongside electrochemical measurements, potentially allowing direct correlation of electrochemistry to surface chemistry in an operating cell. Proper in situ Raman mapping measurements would be useful for pin-pointing important anode reaction mechanisms because of its sensitivity to the relevant species, including anode performance degradation through carbon deposition8, 10, 13, 14 ("coking") and sulfur poisoning11, 15 and the manner in which surface modifications stave off this degradation16. The current work demonstrates significant progress towards this capability. In addition, the family of scanning probe microscopy (SPM) techniques provides a special approach to interrogate the electrode surface with nanoscale resolution. Besides the surface topography that is routinely collected by AFM and STM, other properties such as local electronic states, ion diffusion coefficient and surface potential can also be investigated17-22. In this work, electrochemical measurements, Raman spectroscopy, and SPM were used in conjunction with a novel test electrode platform that consists of a Ni mesh electrode embedded in an yttria-stabilized zirconia (YSZ) electrolyte. Cell performance testing and impedance spectroscopy under fuel containing H2S was characterized, and Raman mapping was used to further elucidate the nature of sulfur poisoning. In situ Raman monitoring was used to investigate coking behavior. Finally, atomic force microscopy (AFM) and electrostatic force microscopy (EFM) were used to further visualize carbon deposition on the nanoscale. From this research, we desire to produce a more complete picture of the SOFC anode.

We present a unique platform for characterizing electrode surfaces in solid oxide fuel cells (SOFCs) that allows simultaneous performance of multiple characterization techniques (e.g. in situ Raman spectroscopy and scanning probe microscopy alongside electrochemical measurements). Complementary information from these analyses may help to advance toward a more profound understanding of electrode reaction and degradation mechanisms, providing insights into rational design of better materials for SOFCs.

Sondeo y Cartografía superficies de los electrodos en pilas de óxido sólido

Solid oxide fuel cells (SOFCs) are potentially the most efficient and cost-effective solution to utilization of a wide variety of fuels beyond hydrogen ...

Visible-light Induced Reduction of Graphene Oxide Using Plasmonic Nanoparticle

Present work demonstrates the simple, chemical free, fast, and energy efficient method to produce reduced graphene oxide (r-GO) solution at RT using visible light irradiation with plasmonic nanoparticles. The plasmonic nanoparticle is used to improve the reduction efficiency of GO. It only takes 30 min&#160;at RT by illuminating the solutions with Xe-lamp, the r-GO solutions can be obtained by completely removing gold nanoparticles through simple centrifugation step. The spherical gold nanoparticles (AuNPs) as compared to the other nanostructures is the most suitable plasmonic nanostructure for r-GO preparation. The reduced graphene oxide prepared using visible light and AuNPs was equally qualitative as chemically reduced graphene oxide, which was supported by various analytical techniques such as UV-Vis spectroscopy, Raman spectroscopy, powder XRD and XPS. The reduced graphene oxide prepared with visible light shows excellent quenching properties over the fluorescent molecules modified on ssDNA and excellent fluorescence recovery for target DNA detection. The r-GO prepared by recycled AuNPs is found to be of same quality with that of chemically reduced r-GO. The use of visible light with plasmonic nanoparticle demonstrates the good alternative method for r-GO synthesis.

A simple protocol for the preparation of reduced graphene oxide using visible light and plasmonic nanoparticle is described.

Luz visible reducción inducida de grafeno Óxido Usando plasmónica de nanopartículas

Present work demonstrates the simple, chemical free, fast, and energy efficient method to produce reduced graphene oxide (r-GO) solution at RT using ...

Ohmic Contact Fabrication Using a Focused-ion Beam Technique and Electrical Characterization for Layer Semiconductor Nanostructures

Layer semiconductors with easily processed two-dimensional (2D) structures exhibit indirect-to-direct bandgap transitions and superior transistor performance, which suggest a new direction for the development of next-generation ultrathin and flexible photonic and electronic devices. Enhanced luminescence quantum efficiency has been widely observed in these atomically thin 2D crystals. However, dimension effects beyond quantum confinement thicknesses or even at the micrometer scale are not expected and have rarely been observed. In this study, molybdenum diselenide (MoSe2) layer crystals with a thickness range of 6-2,700 nm were fabricated as two- or four-terminal devices. Ohmic contact formation was successfully achieved by the focused-ion beam (FIB) deposition method using platinum (Pt) as a contact metal. Layer crystals with various thicknesses were prepared through simple mechanical exfoliation by using dicing tape. Current-voltage curve measurements were performed to determine the conductivity value of the layer nanocrystals. In addition, high-resolution transmission electron microscopy, selected-area electron diffractometry, and energy-dispersive X-ray spectroscopy were used to characterize the interface of the metal&#8211;semiconductor contact of the FIB-fabricated MoSe2 devices. After applying the approaches, the substantial thickness-dependent electrical conductivity in a wide thickness range for the MoSe2-layer semiconductor was observed. The conductivity increased by over two orders of magnitude from 4.6 to 1,500 &#937;&#8722;1 cm&#8722;1, with a decrease in the thickness from 2,700 to 6 nm. In addition, the temperature-dependent conductivity indicated that the thin MoSe2 multilayers exhibited considerably weak semiconducting behavior with activation energies of 3.5-8.5 meV, which are considerably smaller than those (36-38 meV) of the bulk. Probable surface-dominant transport properties and the presence of a high surface electron concentration in MoSe2 are proposed. Similar results can be obtained for other layer semiconductor materials such as MoS2 and WS2.

We describe the approaches for the device fabrication and electrical characterization of molybdenum diselenide (MoSe2) layer semiconductor nanostructures with different thicknesses. In addition, the fabrication of ohmic contacts for MoSe2-layer nanocrystals by the focused-ion beam deposition method using platinum (Pt) as a contact metal is described.

Óhmico Contacto Fabricación Usando una técnica enfocada-ion Beam y Eléctrica Caracterización de Nanoestructuras capa semiconductora

Layer semiconductors with easily processed two-dimensional (2D) structures exhibit indirect-to-direct bandgap transitions and superior transistor ...

Fabrication of Low Temperature Carbon Nanotube Vertical Interconnects Compatible with Semiconductor Technology

We demonstrate a method for the low temperature growth (350 &#176;C) of vertically-aligned carbon nanotubes (CNT) bundles on electrically conductive thin-films. Due to the low growth temperature, the process allows integration with modern low-&#954; dielectrics and some flexible substrates. The process is compatible with standard semiconductor fabrication, and a method for the fabrication of electrical 4-point probe test structures for vertical interconnect test structures is presented. Using scanning electron microscopy the morphology of the CNT bundles is investigated, which demonstrates vertical alignment of the CNT and can be used to tune the CNT growth time. With Raman spectroscopy the crystallinity of the CNT is investigated. It was found that the CNT have many defects, due to the low growth temperature. The electrical current-voltage measurements of the test vertical interconnects displays a linear response, indicating good ohmic contact was achieved between the CNT bundle and the top and bottom metal electrodes. The obtained resistivities of the CNT bundle are among the average values in the literature, while a record-low CNT growth temperature was used.

A method for the growth of low temperature vertically-aligned carbon nanotubes, and the subsequent fabrication of vertical interconnect electrical test structures using semiconductor fabrication is presented.

Fabricación de Baja Temperatura de nanotubos de carbono Interconexiones verticales Compatible con la tecnología de semiconductores

We demonstrate a method for the low temperature growth (350 &#176;C) of vertically-aligned carbon nanotubes (CNT) bundles on electrically conductive ...

Integration of Light Trapping Silver Nanostructures in Hydrogenated Microcrystalline Silicon Solar Cells by Transfer Printing

One of the potential applications of metal nanostructures is light trapping in solar cells, where unique optical properties of nanosized metals, commonly known as plasmonic effects, play an important role. Research in this field has, however, been impeded owing to the difficulty of fabricating devices containing the desired functional metal nanostructures. In order to provide a viable strategy to this issue, we herein show a transfer printing-based approach that allows the quick and low-cost integration of designed metal nanostructures with a variety of device architectures, including solar cells. Nanopillar poly(dimethylsiloxane) (PDMS) stamps were fabricated from a commercially available nanohole plastic film as a master mold. On this nanopatterned PDMS stamps, Ag films were deposited, which were then transfer-printed onto block copolymer (binding layer)-coated hydrogenated microcrystalline Si (&#181;c-Si:H) surface to afford ordered Ag nanodisk structures. It was confirmed that the resulting Ag nanodisk-incorporated &#181;c-Si:H solar cells show higher performances compared to a cell without the transfer-printed Ag nanodisks, thanks to plasmonic light trapping effect derived from the Ag nanodisks. Because of the simplicity and versatility, further device application would also be feasible thorough this approach.

A viable transfer printing-based methodology to introduce plasmonic metal nanostructures in solar cells is described. Using nanopillar poly(dimethylsiloxane) stamps, an Ag-based ordered nanodisk array was integrated with standard hydrogenated microcrystalline Si solar cells, which led to improved device performances due to plasmonic light trapping.

Integración de luz de captura de plata de nanoestructuras en células solares de silicio hidrogenado microcristalina por transferencia Impresión

One of the potential applications of metal nanostructures is light trapping in solar cells, where unique optical properties of nanosized metals, commonly ...

Writing Bragg Gratings in Multicore Fibers

Fiber Bragg gratings in multicore fibers can be used as compact and robust filters in astronomical and other research and commercial applications. Strong suppression at a single wavelength requires that all cores have matching transmission profiles. These gratings cannot be inscribed using the same method as for single-core fibers because the curved surface of the cladding acts as a lens, focusing the incoming UV laser beam and causing variations in exposure between cores. Therefore we use an additional optical element to ensure that the beam shape does not change while passing through the cross-section of the multicore fiber. This consists of a glass capillary tube which has been polished flat on one side, which is then placed over the section of the fiber to be inscribed. The laser beam enters the fiber through the flat surface of the capillary tube and hence maintains its original dimensions. This paper demonstrates the improvements in core-to-core uniformity for a 7-core fiber using this method. The technique can be generalized to larger multicore fibers.

We describe a technique for inscribing identical fiber Bragg gratings into each core of a multicore fiber. This is achieved by introducing an additional surface into the optical path to mitigate lensing by the curved surface of the fiber cladding.

La escritura de Bragg en fibras Multicore

Fiber Bragg gratings in multicore fibers can be used as compact and robust filters in astronomical and other research and commercial applications. Strong ...

Iridium Oxide-reduced Graphene Oxide Nanohybrid Thin Film Modified Screen-printed Electrodes as Disposable Electrochemical Paper Microfluidic pH Sensors

A facile, controllable, inexpensive and green electrochemical synthesis of IrO2-graphene nanohybrid thin films is developed to fabricate an easy-to-use integrated paper microfluidic electrochemical pH sensor for resource-limited settings. Taking advantages from both pH meters and strips, the pH sensing platform is composed of hydrophobic barrier-patterned paper micropad (&#181;PAD) using polydimethylsiloxane (PDMS), screen-printed electrode (SPE) modified with IrO2-graphene films and molded acrylonitrile butadiene styrene (ABS) plastic holder. Repetitive cathodic potential cycling was employed for graphene oxide (GO) reduction which can completely remove electrochemically unstable oxygenated groups and generate a 2D defect-free homogeneous graphene thin film with excellent stability and electronic properties. A uniform and smooth IrO2 film in nanoscale grain size is anodically electrodeposited onto the graphene film, without any observable cracks. The resulting IrO2-RGO electrode showed slightly super-Nernstian responses from pH 2-12 in Britton-Robinson (B-R) buffers with good linearity, small hysteresis, low response time and reproducibility in different buffers, as well as low sensitivities to different interfering ionic species and dissolved oxygen. A simple portable digital pH meter is fabricated, whose signal is measured with a multimeter, using high input-impedance operational amplifier and consumer batteries. The pH values measured with the portable electrochemical paper-microfluidic pH sensors were consistent with those measured using a commercial laboratory pH meter with a glass electrode.

The study demonstrates the growth of iridium oxide-reduced graphene oxide (IrO2-RGO) nanohybrid thin films on irregular and rough screen-printed carbon substrate through a green electrochemical synthesis, and their implementation as a pH sensor with a patterned paper-fluidic platform.

Iridium grafeno óxido nanohíbrido Thin Film Modificados electrodos serigrafiados reducida de óxido-como Papel desechable de microfluidos electroquímico de pH Sensores

A facile, controllable, inexpensive and green electrochemical synthesis of IrO2-graphene nanohybrid thin films is developed to fabricate an easy-to-use ...

Advanced Experimental Methods for Low-temperature Magnetotransport Measurement of Novel Materials

Novel electronic materials are often produced for the first time by synthesis processes that yield bulk crystals (in contrast to single crystal thin film synthesis) for the purpose of exploratory materials research. Certain materials pose a challenge wherein the traditional bulk Hall bar device fabrication method is insufficient to produce a measureable device for sample transport measurement, principally because the single crystal size is too small to attach wire leads to the sample in a Hall bar configuration. This can be, for example, because the first batch of a new material synthesized yields very small single crystals or because flakes of samples of one to very few monolayers are desired. In order to enable rapid characterization of materials that may be carried out in parallel with improvements to their growth methodology, a method of device fabrication for very small samples has been devised to permit the characterization of novel materials as soon as a preliminary batch has been produced. A slight variation of this methodology is applicable to producing devices using exfoliated samples of two-dimensional materials such as graphene, hexagonal boron nitride (hBN), and transition metal dichalcogenides (TMDs), as well as multilayer heterostructures of such materials. Here we present detailed protocols for the experimental device fabrication of fragments and flakes of novel materials with micron-sized dimensions onto substrate and subsequent measurement in a commercial superconducting magnet, dry helium close-cycle cryostat magnetotransport system at temperatures down to 0.300 K and magnetic fields up to 12 T.

We describe the methodology of mechanical exfoliation and deposition of flakes of novel materials with micron-sized dimensions onto substrate, fabrication of experimental device structures for transport experimentation, and the magnetotransport measurement in a dry helium close-cycle cryostat at temperatures down to 0.300 K and magnetic fields up to 12 T.

Avanzados métodos experimentales para baja temperatura magnetotransporte Medición de Nuevos Materiales

Novel electronic materials are often produced for the first time by synthesis processes that yield bulk crystals (in contrast to single crystal thin film ...

Method Development for Contactless Resonant Cavity Dielectric Spectroscopic Studies of Cellulosic Paper

The current analytical techniques for characterizing printing and graphic arts substrates are largely ex situ and destructive. This limits the amount of data that can be obtained from an individual sample and renders it difficult to produce statistically relevant data for unique and rare materials. Resonant cavity dielectric spectroscopy is a non-destructive, contactless technique which can simultaneously interrogate both sides of a sheeted material and provide measurements which are suitable for statistical interpretations. This offers analysts the ability to quickly discriminate between sheeted materials based on composition and storage history. In this methodology article, we demonstrate how contactless resonant cavity dielectric spectroscopy may be used to differentiate between paper analytes of varying fiber species compositions, to determine the relative age of the paper, and to detect and quantify the amount of post-consumer waste (PCW) recycled fiber content in manufactured office paper.

A protocol for the non-destructive analysis of the fiber content and relative age of paper.

Desarrollo del método para estudios espectroscópicos dieléctricos de cavidad resonante sin contacto de papel celulósico

The current analytical techniques for characterizing printing and graphic arts substrates are largely ex situ and destructive. This limits the amount of ...