Name: seedless growth of bismuth nanowire array via vacuum thermal evaporation
Uploaded: 2015-12-21T13:00:00.000+00:00
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Description: Watch this Scientific Journal Video about Seedless Growth of Bismuth Nanowire Array via Vacuum Thermal Evaporation at JoVE.com

Research is carried out at the Center for Functional Nanomaterials, Brookhaven National Laboratory, which is supported by the U.S. Department of Energy, Office of Basic Energy Sciences, under Contract No. DE-SC0012704.

Precaución: Por favor consulte todas las fichas de datos de seguridad de materiales pertinentes (MSDS) antes de usar. Los nanomateriales pueden tener riesgos adicionales en comparación con su contraparte mayor. Por favor, use todas las prácticas apropiadas de seguridad al manipular sustratos nanomateriales cubiertas, incluyendo el uso de controles de ingeniería (campana extractora de gases) y el equipo de protección personal (gafas de seguridad, guantes, bata de laboratorio, pantalones largos, cerrado-toe zapatos). 1. Trabajo Preparatorio <ol><li> Preparación del sistema de deposición de vapor <ol><li> Purgar la cámara de depósito a la presión ambiente y abrir la cámara. La ventilación se realiza pulsando el botón &quot;Start PC ventilación&quot; en la interfaz de software de control, que se inicia automáticamente una secuencia que ventilar la cámara a la presión ambiente. Al llegar a la presión de la cámara de atmósfera abierta tirando de la puerta frontal que accede. </li><li> Montar un barco evaporación de tungsteno (revestido de alúmina) entre un par de electrodos de evaporación térmica. Coloca 1Bolitas g de bismuto en el barco de la evaporación. </li><li> Montar un blanco de pulverización catódica de vanadio a la fuente de pulverización catódica. Consulte el paso 1.1.4) para el sistema de deposición que no está equipado con una fuente de bombardeo iónico. </li><li> (Opcional, para el sistema de deposición que no está equipado con una fuente de pulverización catódica) Montar un barco evaporación de tungsteno entre un par de electrodos de evaporación térmica. Colocar 0,5 g babosas de vanadio en la barca evaporación. </li><li> Conecte los conectores mini-plátano (dos para la calefacción de alimentación / refrigeración y dos para la sonda de temperatura) del controlador de temperatura de circuito cerrado para el paso de cables eléctricos del sistema de deposición. </li></ol></li><li> Preparación de sustratos de crecimiento Nota: La formación de nanocables de bismuto es insensible al sustrato de crecimiento de elección. Resultados similares se han obtenido a partir de portaobjetos de vidrio, oblea de silicio, o una hoja de metal. Es recomendado por los autores que el sustrato se limpia inmediatamente antes de que el vaporproceso de deposición, con el fin de lograr una adhesión consistente de la capa inferior de vanadio. Diversas técnicas de limpieza del sustrato, incluyendo la limpieza de plasma y la limpieza química húmeda, se pueden aplicar y dar lugar a resultados similares. <ol><li> Limpieza de los sustratos de crecimiento por plasma de oxígeno <ol><li> Coloque los sustratos de crecimiento en un limpiador de plasma y la bomba de la cámara, pulsando la tecla &quot;VAC ON&quot; botón, a su presión base de 10 mTorr. </li><li> Abra la válvula de gas de oxígeno e introducir gas oxígeno a la cámara pulsando el botón &quot;GAS EN&quot; botón en el panel frontal y ajustar el caudal pulsando los botones &quot;Decr&quot; para el control del caudal de gas &quot;INCR&quot; y para mantener una presión de cámara de aproximadamente 100 mTorr. </li><li> Ajuste la potencia del plasma a 20 W pulsando los botones &quot;Decr&quot; &quot;INCR&quot; y para el control de potencia y encender el plasma presionando el botón &quot;RF ON&quot; botón. </li><li> Espere 5 minutos antes de apagar el plasma presionando &quot;; EN RF &quot;. Botón Vent la cámara pulsando el botón&quot; Bleed &quot;y recuperar los sustratos. </li></ol></li><li> Limpieza de los sustratos de crecimiento por método químico húmedo <ol><li> Sumergir los sustratos de crecimiento en acetona contenidas en un vaso de precipitados. Colocar el vaso en un ultrasonicador y sonicar durante 2 min a la máxima potencia. </li><li> Retire los sustratos del vaso de precipitados y enjuagar con un chorro de alcohol absoluto de una botella de lavado durante 30 segundos. </li><li> Secar los sustratos en una corriente de gas nitrógeno. </li></ol></li></ol></li><li> Carga sustrato y sistema de deposición de bombeo <ol><li> Monte el conjunto de control de temperatura del sustrato al titular sustrato. </li><li> Utilice pinzas de resorte para montar los sustratos de crecimiento en la parte superior del conjunto del enfriador / calentador de Peltier. </li><li> Montar el soporte de sustrato totalmente montado en la cámara de deposición de vapor, con los sustratos que enfrentan las fuentes de deposición. Conecte los alimentadores eléctricos alPeltier refrigerador / conjunto del calentador. </li><li> Cierre el obturador sustrato para evitar la deposición no intencional al sustrato. </li><li> Iniciar el bombeo por la cámara de deposición. El bombeo se realiza pulsando el botón &quot;Inicio Bombeo PC&quot; en la interfaz de software de control, que se inicia automáticamente una secuencia que bombee la cámara a su presión de base. </li></ol></li></ol> 2. Crecimiento de bismuto Nanocables Nota: El experimento no se mueve al siguiente paso hasta que la presión base de la cámara de deposición ha llegado a 2 × 10 -6 Torr o inferior. <ol><li> La deposición de capa inferior de vanadio Nota: La mejor reproducibilidad experimental se logra cuando la capa inferior de vanadio es depositado por el método de pulverización catódica con magnetrón. En ausencia de una fuente de pulverización catódica, alta reproducibilidad también se puede lograr aún mediante el depósito de la capa inferior de vanadio utilizando el método de evaporación térmica, siempre que el sistema de deposición hasa presión base bajo (≤ 5 × 10 -7 Torr). Consulte el paso 3.1.2 para los detalles. <ol><li> Deposición de vanadio con una fuente de pulverización catódica con magnetrón. <ol><li> Iniciar flujo de argón en la fuente de bombardeo iónico. Ajuste del caudal de 40 sccm. </li><li> Ajuste tasa de la revolución de la bomba turbomolecular para una presión de la cámara de 2,5 mTorr. </li><li> Mientras la cámara está alcanzando poco a poco su presión en estado estacionario, establecer los factores de calibración de espesor a la QCM. Para vanadio, la densidad es 5,96 g / cm 3 y la Z-factor es 0.530. </li><li> Encienda la fuente de sputtering DC y estableció el poder a 200-250 W. Para el sistema de deposición operado por los autores, la tasa de deposición es de aproximadamente 0.4 A / seg a este poder. Sin abrir el obturador sustrato, mantenga la fuente de corriente durante 2 min. NOTA: A través de este paso se retira el óxido nativo de la fuente de vanadio, exponiendo la superficie de vanadio fresco. </li><li> Abra el obturador sustrato para comenzar depositio vanadionorte. Mientras tanto, restablecer el espesor acumulado de la QCM a cero. </li><li> Continuar la deposición hasta que se acumuló un espesor aparente de 20 nm, por la lectura QCM. Cierre el obturador sustrato. </li><li> Disminuir gradualmente la potencia de bombardeo iónico a cero. Encienda la fuente. </li><li> Cierre el flujo de argón. Devuelva la bomba turbomolecular a su máxima potencia. </li></ol></li><li> (Opcional, para el sistema de deposición que no está equipado con una fuente de pulverización catódica) deposición de vanadio con una fuente de evaporación térmica. <ol><li> Debido al punto de fusión alto de vanadio (1910 ° C) y su disposición a la oxidación, se recomienda que su evaporación térmica que se realiza a una presión base de 5 × 10 -7 Torr o inferior. </li><li> Establecer los factores de calibración de espesor a la QCM. Para vanadio, la densidad es 5,96 g / cm 3 y la Z-factor es 0.530. </li><li> Encienda la evaporación de suministro térmico a la fuente de vanadio.Aumente poco a poco el poder de calentamiento para el barco de tungsteno hasta que las babosas de vanadio se derriten. </li><li> Con el obturador sustrato mantiene cerrada, poco a poco aumentar el poder de calentamiento hasta una velocidad de depósito 2 Å / s se logra, por la lectura QCM. Abra el obturador sustrato para iniciar la deposición de vanadio. Mientras tanto, restablecer el espesor acumulado de la QCM a cero. </li><li> Continuar la deposición hasta que se acumuló un espesor aparente de 50 nm. Cierre el obturador sustrato. </li><li> Disminuir gradualmente la potencia de evaporación térmica a cero. Encienda la fuente. </li></ol></li></ol></li><li> La deposición de nanocables de bismuto <ol><li> Para la deposición de bismuto a temperatura por encima o por debajo de la temperatura ambiente, establecer el valor deseado para el controlador de temperatura. Esperar hasta que se alcanza la temperatura deseada. </li><li> Establecer los factores de calibración de espesor a la QCM. Para bismuto, la densidad es 9,78 g / cm 3 y la Z-factor es 0.790. </li><li> Encienda la evaporación térmica Doplicar a la fuente de bismuto. Aumente poco a poco el poder de calentamiento para el barco de tungsteno hasta que la velocidad de depósito de 2 Å / s se logra, por la lectura QCM. </li><li> Abra el obturador sustrato para iniciar la deposición de bismuto. Mientras tanto, restablecer el espesor acumulado de la QCM a cero. </li><li> Continuar la deposición hasta que se acumuló un espesor aparente de 50 nm. Cierre el obturador sustrato. </li><li> Disminuir gradualmente la potencia de evaporación térmica a cero. Encienda la fuente. </li><li> Apague la fuente de alimentación al enfriador / calentador eléctrico térmico. </li><li> Purgar la cámara de depósito a la presión ambiente y abrir la cámara. Recuperar el soporte de sustrato y recoger los nanocables de bismuto sustratos cubiertos. </li></ol></li></ol>

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Authors have nothing to disclose.

El crecimiento de nanocables de bismuto se lleve a cabo en un sistema de deposición física de vapor con al menos dos fuentes de deposición, uno para el bismuto y el otro para el vanadio. Se recomienda que una de las fuentes es una fuente de pulverización catódica magnetrón, para la deposición de vanadio. Alto vacío se consigue mediante una bomba turbomoleculares respaldados por una bomba de desplazamiento seco. El sistema de deposición de vapor está equipado con una microbalanza de cristal de cuarzo calibrado ...

Nanocables limitan el transporte de portadores de carga y otros cuasi-partículas, tales como los fotones y los plasmones en una dimensión. En consecuencia, los nanocables generalmente exhiben novedosas propiedades eléctricas, magnéticas, ópticas y químicas, que les otorgan potencial casi infinito para aplicaciones en electrónica, fotónica, tecnologías biomédicas, ambientales y relacionados con la energía de micro / nano 1,2. Durante las dos últimas décadas, numerosos de arriba hacia abajo y los enfoques de abajo hacia arriba se han desarrollado para la síntesis de una amplia gama de metales o semiconductores nanocables de alta calidad a escala de laboratorio. 3.6 A pesar de estos avances, cada enfoque se basa en ciertas propiedades únicas del producto final para su éxito. Por ejemplo, el método de vapor-líquido-sólido populares (VLS) es mejor ajuste para los materiales semiconductores que tienen puntos de fusión más altos y forman aleación eutéctica con el correspondiente &quot;semillas&quot; catalíticos. 7 Como resultado, la síntesis de un nanocablemateriales de especial interés no puede ser cubierto por las técnicas existentes. Como semimetal con pequeño solapamiento indirecta banda (-38 meV en 0 K) y portadores de carga inusualmente luz, bismuto es un ejemplo de ello. El material se comporta radicalmente diferente en dimensión reducida en comparación con su volumen, como confinamiento cuántico podría convertir nanocables de bismuto o películas delgadas en un estrecho intervalo de banda semiconductor 8-12. En el ínterin, la superficie de las formas de bismuto un metal cuasi bidimensional que es significativamente más metálico que su granel. 13,14 Se demostró que la superficie de bismuto logra una movilidad de los electrones de 2 × 10 4 cm 2 V -1 s -1 y contribuye fuertemente a su energía termoeléctrica en forma de nanocables. 15 Como tal, hay intereses importantes en el estudio de nanocables de bismuto para electrónica y, en particular, aplicaciones termoeléctricas. 12-16 Sin embargo, debido al bismuto de muy bajopunto de fusión (544 K) y la preparación para la oxidación, sigue siendo un desafío para la síntesis de alta calidad y nanocables individuales de bismuto cristalino utilizando técnicas de fase en fase de vapor o soluciones tradicionales. Anteriormente, se ha informado por algunos grupos que solo cristalinas nanocables bismuto crecen a bajo rendimiento durante la deposición al vacío de película fina de bismuto, que se atribuye a la liberación de la tensión integrado en la película. 17-20 Recientemente, descubrimos una novela técnica que se basa en la evaporación térmica de bismuto a alto vacío y conduce a la formación escalable de nanocables individuales de bismuto cristalino con un alto rendimiento. 21 En comparación con informes anteriores métodos, la característica más singular de esta técnica es que el sustrato de crecimiento es recién recubierto con una capa delgada de nanoporoso vanadio antes de la deposición de bismuto. Durante la evaporación térmica de este último, el vapor de bismuto se infiltra en la estructura nanoporosa de la furgonetapelícula Adium y se condensa allí como nanodominios. Desde vanadio no se moja por bismuto condensada, los dominios infiltrados son posteriormente expulsados ​​de la matriz de vanadio para liberar su energía superficial. Es la expulsión continua de los nanodominios de bismuto que forma los nanocables de bismuto verticales. Dado que los dominios de bismuto son sólo el 1-2 nm de diámetro, están sujetos a la supresión punto de fusión significativa, lo que los hace casi fundido a RT. Como resultado, el crecimiento de nanocables procede con el sustrato celebrada en RT. Por otra parte, como la migración de los dominios de bismuto se activa térmicamente, la longitud y anchura de los nanocables pueden ajustarse en un amplio intervalo simplemente controlando la temperatura del sustrato de crecimiento. Este protocolo vídeo detallado está destinado a ayudar a los nuevos profesionales en el campo de evitar diversos problemas comunes asociados con la deposición física de vapor de películas delgadas en un ambiente libre de oxígeno de alto vacío.

<table><tbody><tr><td>Bismuth</td><td>Sigma-Aldrich</td><td>556130</td><td>Granular, 99.999%</td></tr><tr><td>Vanadium Slug</td><td>Alfa Aesar</td><td>42829</td><td>3.175&amp;nbsp;mm (0.125&amp;nbsp;in) dia x 6.35&amp;nbsp;mm (0.25&amp;nbsp;in) length, 99.8%</td></tr><tr><td>Vanadium Sputtering Target</td><td>Kurt J. Lesker</td><td>EJTVXXX253A2</td><td>3.00&quot; Dia. x 0.125&quot; Thick, 99.5%</td></tr><tr><td>Acetone</td><td>Sigma-Aldrich</td><td>179124</td><td>&gt;99.5%</td></tr><tr><td>Ethanol</td><td>Alfa Aesar</td><td>33361</td><td>Anhydrous</td></tr><tr><td>Silicon Wafer</td><td>University Wafers</td><td></td><td>300 microns in thickness, (100) orientation</td></tr><tr><td>Silver Filled Epoxy</td><td>Circuit Works</td><td>CW2400</td><td>Two part conductive epoxy resin</td></tr><tr><td>Tungsten Boat, Alumina Coated</td><td>R. D. Mathis</td><td>S9B-AO-W</td><td>For bismuth thermal evaporation</td></tr><tr><td>Tungsten Boat</td><td>R. D. Mathis</td><td>S4-.015W</td><td>For vanadium thermal evaporation</td></tr><tr><td>RIE Plasma</td><td>Nordson March</td><td>CS-1701</td><td></td></tr><tr><td>PVD 75 Vapor Deposition Platform</td><td>Kurt J. Lesker</td><td>PEDP75FTCLT001</td><td>Equipped with three thermal evaporation source and one DC magnetron sputtering source</td></tr><tr><td>Thermoelectric Temperature Controller</td><td>LairdTech</td><td>MTTC-1410</td><td></td></tr><tr><td>PT1000 RGD</td><td>LairdTech</td><td>340912-01</td><td>Temperature sensor for MTTC-1410</td></tr><tr><td>Thermoelectric Module</td><td>LairdTech</td><td>56910-502</td><td></td></tr><tr><td>Ultrasonicator</td><td>Crest Ultrasonics</td><td>Tru-Sweep 175</td><td></td></tr></tbody></table>

seedless growth of bismuth nanowire array via vacuum thermal evaporation

Aquí una técnica sin semilla y libre de la plantilla se demuestra a escalable crecer nanocables de bismuto, a través de la evaporación térmica en alto vacío a temperatura ambiente. Convencionalmente reservado para la fabricación de películas delgadas de metal, depósitos de evaporación térmica de bismuto en una matriz de nanocables sola cristalinas verticales sobre una película delgada plana de vanadio celebrada en RT, que está recién depositado por pulverización catódica con magnetrón o evaporación térmica. Mediante el control de la temperatura del sustrato de crecimiento de la longitud y anchura de los nanocables pueden ajustarse en un amplio intervalo. El responsable de esta nueva técnica es un mecanismo de crecimiento de nanocables previamente desconocido que las raíces de la porosidad leve de la película delgada de vanadio. Infiltrado en los poros de vanadio, los dominios de bismuto (~ 1 nm) llevan energía superficial excesiva que suprime su punto de fusión y los expulsa continuamente fuera de la matriz de vanadio para formar nanocables. Este descubrimiento demuestra la viabilidad de la fase vapor synth escalableESIS de alta pureza nanomateriales sin usar catalizadores.

Las imágenes de SEM de la sección transversal de capas inferiores de vanadio formados por pulverización catódica con magnetrón y los métodos de evaporación térmica se presentan en la Figura 2. Microscopía electrónica de barrido imágenes (SEM) se presentan para nanocables de bismuto formadas a diferentes temperaturas de sustrato (Figura 3). La estructura cristalina de los nanocables de bismuto se determina mediante microscopía electrónica de transmisión (TE...

Watch this Scientific Journal Video about Seedless Growth of Bismuth Nanowire Array via Vacuum Thermal Evaporation at JoVE.com

Seedless Growth of Bismuth Nanowire Array via Vacuum Thermal Evaporation

A protocol for seedless and high yield growth of bismuth nanowire arrays through vacuum thermal evaporation technique is presented.

Crecimiento Seedless de bismuto nanocables matriz a través del vacío de evaporación térmica

Here a seedless and template-free technique is demonstrated to scalably grow bismuth nanowires, through thermal evaporation in high vacuum at RT. ...

seedless-growth-bismuth-nanowire-array-via-vacuum-thermal

Research

JoVE Journal

Engineering

8.3K vistas.  Brookhaven National Laboratory. A protocol for seedless and high yield growth of bismuth nanowire arrays through vacuum thermal evaporation technique is presented. 

Video: Seedless Growth of Bismuth Nanowire Array via Vacuum Thermal Evaporation

Fabrication, Densification, and Replica Molding of 3D Carbon Nanotube Microstructures

The introduction of new materials and processes to microfabrication has, in large part, enabled many important advances in microsystems, lab-on-a-chip devices, and their applications. In particular, capabilities for cost-effective fabrication of polymer microstructures were transformed by the advent of soft lithography and other micromolding techniques 1, 2, and this led a revolution in applications of microfabrication to biomedical engineering and biology. Nevertheless, it remains challenging to fabricate microstructures with well-defined nanoscale surface textures, and to fabricate arbitrary 3D shapes at the micro-scale. Robustness of master molds and maintenance of shape integrity is especially important to achieve high fidelity replication of complex structures and preserving their nanoscale surface texture. The combination of hierarchical textures, and heterogeneous shapes, is a profound challenge to existing microfabrication methods that largely rely upon top-down etching using fixed mask templates. On the other hand, the bottom-up synthesis of nanostructures such as nanotubes and nanowires can offer new capabilities to microfabrication, in particular by taking advantage of the collective self-organization of nanostructures, and local control of their growth behavior with respect to microfabricated patterns. 
Our goal is to introduce vertically aligned carbon nanotubes (CNTs), which we refer to as CNT "forests", as a new microfabrication material. We present details of a suite of related methods recently developed by our group: fabrication of CNT forest microstructures by thermal CVD from lithographically patterned catalyst thin films; self-directed elastocapillary densification of CNT microstructures; and replica molding of polymer microstructures using CNT composite master molds. In particular, our work shows that self-directed capillary densification ("capillary forming"), which is performed by condensation of a solvent onto the substrate with CNT microstructures, significantly increases the packing density of CNTs. This process enables directed transformation of vertical CNT microstructures into straight, inclined, and twisted shapes, which have robust mechanical properties exceeding those of typical microfabrication polymers. This in turn enables formation of nanocomposite CNT master molds by capillary-driven infiltration of polymers. The replica structures exhibit the anisotropic nanoscale texture of the aligned CNTs, and can have walls with sub-micron thickness and aspect ratios exceeding 50:1. Integration of CNT microstructures in fabrication offers further opportunity to exploit the electrical and thermal properties of CNTs, and diverse capabilities for chemical and biochemical functionalization 3.

We present methods for fabrication of patterned microstructures of vertically aligned carbon nanotubes (CNTs), and their use as master molds for production of polymer microstructures with organized nanoscale surface texture. The CNT forests are densified by condensation of solvent onto the substrate, which significantly increases their packing density and enables self-directed formation of 3D shapes.

Fabricación, densificación, y la réplica de Moldeo por inyección de microestructuras 3D nanotubos de carbono

The introduction of new materials and processes to microfabrication has, in large part, enabled many important advances in microsystems, lab-on-a-chip ...

Investigación

Ingeniería

Dry Oxidation and Vacuum Annealing Treatments for Tuning the Wetting Properties of Carbon Nanotube Arrays

In this article, we describe a simple method to reversibly tune the wetting properties of vertically aligned carbon nanotube (CNT) arrays. Here, CNT arrays are defined as densely packed multi-walled carbon nanotubes oriented perpendicular to the growth substrate as a result of a growth process by the standard thermal chemical vapor deposition (CVD) technique.1,2 These CNT arrays are then exposed to vacuum annealing treatment to make them more hydrophobic or to dry oxidation treatment to render them more hydrophilic. The hydrophobic CNT arrays can be turned hydrophilic by exposing them to dry oxidation treatment, while the hydrophilic CNT arrays can be turned hydrophobic by exposing them to vacuum annealing treatment. Using a combination of both treatments, CNT arrays can be repeatedly switched between hydrophilic and hydrophobic.2 Therefore, such combination show a very high potential in many industrial and consumer applications, including drug delivery system and high power density supercapacitors.3-5
The key to vary the wettability of CNT arrays is to control the surface concentration of oxygen adsorbates. Basically oxygen adsorbates can be introduced by exposing the CNT arrays to any oxidation treatment. Here we use dry oxidation treatments, such as oxygen plasma and UV/ozone, to functionalize the surface of CNT with oxygenated functional groups. These oxygenated functional groups allow hydrogen bond between the surface of CNT and water molecules to form, rendering the CNT hydrophilic. To turn them hydrophobic, adsorbed oxygen must be removed from the surface of CNT. Here we employ vacuum annealing treatment to induce oxygen desorption process. CNT arrays with extremely low surface concentration of oxygen adsorbates exhibit a superhydrophobic behavior.

This article describes a simple method to fabricate vertically aligned carbon nanotube arrays by CVD and to subsequently tune their wetting properties by exposing them to vacuum annealing or dry oxidation treatment.

La oxidación en seco y vacío Recocido Tratamientos para Ajuste las propiedades humectantes de conjuntos de nanotubos de carbono

In this article, we describe a simple method to reversibly  tune the wetting properties of vertically aligned carbon nanotube (CNT) arrays.  Here, CNT ...

Ultrahigh Density Array of Vertically Aligned Small-molecular Organic Nanowires on Arbitrary Substrates

In recent years &pi;-conjugated organic semiconductors have emerged as the active material in a number of diverse applications including large-area, low-cost displays, photovoltaics, printable and flexible electronics and organic spin valves. Organics allow (a) low-cost, low-temperature processing and (b) molecular-level design of electronic, optical and spin transport characteristics. Such features are not readily available for mainstream inorganic semiconductors, which have enabled organics to carve a niche in the silicon-dominated electronics market. The first generation of organic-based devices has focused on thin film geometries, grown by physical vapor deposition or solution processing. However, it has been realized that organic nanostructures can be used to enhance performance of above-mentioned applications and significant effort has been invested in exploring methods for organic nanostructure fabrication.	
A particularly interesting class of organic nanostructures is the one in which vertically oriented organic nanowires, nanorods or nanotubes are organized in a well-regimented, high-density array. Such structures are highly versatile and are ideal morphological architectures for various applications such as chemical sensors, split-dipole nanoantennas, photovoltaic devices with radially heterostructured "core-shell" nanowires, and memory devices with a cross-point geometry. Such architecture is generally realized by a template-directed approach. In the past this method has been used to grow metal and inorganic semiconductor nanowire arrays. More recently &pi;-conjugated polymer nanowires have been grown within nanoporous templates. However, these approaches have had limited success in growing nanowires of technologically important &pi;-conjugated small molecular weight organics, such as tris-8-hydroxyquinoline aluminum (Alq3), rubrene and methanofullerenes, which are commonly used in diverse areas including organic displays, photovoltaics, thin film transistors and spintronics.	
Recently we have been able to address the above-mentioned issue by employing a novel "centrifugation-assisted" approach. This method therefore broadens the spectrum of organic materials that can be patterned in a vertically ordered nanowire array. Due to the technological importance of Alq3, rubrene and methanofullerenes, our method can be used to explore how the nanostructuring of these materials affects the performance of aforementioned organic devices. The purpose of this article is to describe the technical details of the above-mentioned protocol, demonstrate how this process can be extended to grow small-molecular organic nanowires on arbitrary substrates and finally, to discuss the critical steps, limitations, possible modifications, trouble-shooting and future applications.

We report a simple method for fabricating an ultrahigh density array of vertically ordered small-molecular organic nanowires. This method allows for synthesis of complex heterostructured hybrid nanowire geometries, which can be inexpensively grown on arbitrary substrates. These structures have potential applications in organic electronics, optoelectronics, chemical sensing, photovoltaics and spintronics.

Ultra Alta Densidad conjunto de nanocables orgánicos pequeña moleculares verticalmente alineados sobre sustratos arbitrarias

In  recent years &pi;-conjugated  organic semiconductors have emerged as the active material in a number of  diverse applications including large-area, ...

Analysis of Contact Interfaces for Single GaN Nanowire Devices

Single GaN nanowire (NW) devices fabricated on SiO2 can exhibit a strong degradation after annealing due to the occurrence of void formation at the contact/SiO2 interface. This void formation can cause cracking and delamination of the metal film, which can increase the resistance or lead to a complete failure of the NW device. In order to address issues associated with void formation, a technique was developed that removes Ni/Au contact metal films from the substrates to allow for the examination and characterization of the contact/substrate and contact/NW interfaces of single GaN NW devices. This procedure determines the degree of adhesion of the contact films to the substrate and NWs and allows for the characterization of the morphology and composition of the contact interface with the substrate and nanowires. This technique is also useful for assessing the amount of residual contamination that remains from the NW suspension and from photolithographic processes on the NW-SiO2 surface prior to metal deposition. The detailed steps of this procedure are presented for the removal of annealed Ni/Au contacts to Mg-doped GaN NWs on a SiO2 substrate.

A technique was developed that removes Ni/Au contact metal films from their substrate to allow for the examination and characterization of the contact/substrate and contact/NW interfaces of single GaN nanowire devices.

Análisis de Contacto Interfaces para individuales GaN nanocables Dispositivos

Single GaN nanowire (NW) devices fabricated on SiO2 can exhibit  a strong degradation after annealing due to the  occurrence of void formation at the ...

Monolayer Contact Doping of Silicon Surfaces and Nanowires Using Organophosphorus Compounds

Monolayer Contact Doping (MLCD) is a simple method for doping of surfaces and nanostructures1. MLCD results in the formation of highly controlled, ultra shallow and sharp doping profiles at the nanometer scale. In MLCD process the dopant source is a monolayer containing dopant atoms.
In this article a detailed procedure for surface doping of silicon substrate as well as silicon nanowires is demonstrated. Phosphorus dopant source was formed using tetraethyl methylenediphosphonate monolayer on a silicon substrate. This monolayer containing substrate was brought to contact with a pristine intrinsic silicon target substrate and annealed while in contact. Sheet resistance of the target substrate was measured using 4 point probe. Intrinsic silicon nanowires were synthesized by chemical vapor deposition (CVD) process using a vapor-liquid-solid (VLS) mechanism; gold nanoparticles were used as catalyst for nanowire growth. The nanowires were suspended in ethanol by mild sonication. This suspension was used to dropcast the nanowires on silicon substrate with a silicon nitride dielectric top layer. These nanowires were doped with phosphorus in similar manner as used for the intrinsic silicon wafer. Standard photolithography process was used to fabricate metal electrodes for the formation of nanowire based field effect transistor (NW-FET). The electrical properties of a representative nanowire device were measured by a semiconductor device analyzer and a probe station.

A detailed procedure for surface doping of Silicon interfaces is provided. The ultra-shallow surface doping is demonstrated by using phosphorus containing monolayers and rapid annealing process. The method can be used for doping of macroscopic area surfaces as well as nanostructures.

Monolayer Contact Doping (MLCD) is a simple method for doping of surfaces and nanostructures1. MLCD results in the formation of highly controlled, ultra ...

Atomically Defined Templates for Epitaxial Growth of Complex Oxide Thin Films

Atomically defined substrate surfaces are prerequisite for the epitaxial growth of complex oxide thin films. In this protocol, two approaches to obtain such surfaces are described. The first approach is the preparation of single terminated perovskite SrTiO3 (001) and DyScO3 (110) substrates. Wet etching was used to selectively remove one of the two possible surface terminations, while an annealing step was used to increase the smoothness of the surface. The resulting single terminated surfaces allow for the heteroepitaxial growth of perovskite oxide thin films with high crystalline quality and well-defined interfaces between substrate and film. In the second approach, seed layers for epitaxial film growth on arbitrary substrates were created by Langmuir-Blodgett (LB) deposition of nanosheets. As model system Ca2Nb3O10- nanosheets were used, prepared by delamination of their layered parent compound HCa2Nb3O10. A key advantage of creating seed layers with nanosheets is that relatively expensive and size-limited single crystalline substrates can be replaced by virtually any substrate material.

Various procedures are outlined to prepare atomically defined templates for epitaxial growth of complex oxide thin films. Chemical treatments of single crystalline SrTiO3 (001) and DyScO3 (110) substrates were performed to obtain atomically smooth, single terminated surfaces. Ca2 Nb3 O10- nanosheets were used to create atomically defined templates on arbitrary substrates.

Plantillas Atómicamente definidos para crecimiento epitaxial de óxido complejo Películas Delgadas

Atomically defined substrate surfaces are prerequisite for the epitaxial growth of complex oxide thin films. In this protocol, two approaches to obtain ...

Química

Fabrication of Carbon Nanotube High-Frequency Nanoelectronic Biosensor for Sensing in High Ionic Strength Solutions

The unique electronic properties and high surface-to-volume ratios of single-walled carbon nanotubes (SWNT) and semiconductor nanowires (NW) 1-4 make them good candidates for high sensitivity biosensors. When a charged molecule binds to such a sensor surface, it alters the carrier density5 in the sensor, resulting in changes in its DC conductance. However, in an ionic solution a charged surface also attracts counter-ions from the solution, forming an electrical double layer (EDL). This EDL effectively screens off the charge, and in physiologically relevant conditions ~100 millimolar (mM), the characteristic charge screening length (Debye length) is less than a nanometer (nm). Thus, in high ionic strength solutions, charge based (DC) detection is fundamentally impeded6-8.
We overcome charge screening effects by detecting molecular dipoles rather than charges at high frequency, by operating carbon nanotube field effect transistors as high frequency mixers9-11. At high frequencies, the AC drive force can no longer overcome the solution drag and the ions in solution do not have sufficient time to form the EDL. Further, frequency mixing technique allows us to operate at frequencies high enough to overcome ionic screening, and yet detect the sensing signals at lower frequencies11-12. Also, the high transconductance of SWNT transistors provides an internal gain for the sensing signal, which obviates the need for external signal amplifier.
Here, we describe the protocol to (a) fabricate SWNT transistors, (b) functionalize biomolecules to the nanotube13, (c) design and stamp a poly-dimethylsiloxane (PDMS) micro-fluidic chamber14 onto the device, and (d) carry out high frequency sensing in different ionic strength solutions11.

We describe the device fabrication and measurement protocol for carbon nanotube based high frequency biosensors. The high frequency sensing technique mitigates the fundamental ionic (Debye) screening effect and allows nanotube biosensor to be operated in high ionic strength solutions where conventional electronic biosensors fail. Our technology provides a unique platform for point-of-care (POC) electronic biosensors operating in physiologically relevant conditions.

La fabricación de nanotubos de carbono de alta frecuencia Nanoelectrónica biosensor para la detección in High Solutions fuerza iónica

The unique electronic properties and high surface-to-volume ratios of single-walled carbon nanotubes (SWNT) and semiconductor nanowires (NW) 1-4 make them ...

Bioingeniería

Synthesis of Substrate-Bound Au Nanowires Via an Active Surface Growth Mechanism

Advancing synthetic capabilities is important for the development of nanoscience and nanotechnology. The synthesis of nanowires has always been a challenge, as it requires asymmetric growth of symmetric crystals. Here, we report a distinctive synthesis of substrate-bound Au nanowires. This template-free synthesis employs thiolated ligands and substrate adsorption to achieve the continuous asymmetric deposition of Au in solution at ambient conditions. The thiolated ligand prevented the Au deposition on the exposed surface of the seeds, so the Au deposition only occurs at the interface between the Au seeds and the substrate. The side of the newly deposited Au nanowires is immediately covered with the thiolated ligand, while the bottom facing the substrate remains ligand-free and active for the next round of Au deposition. We further demonstrate that this Au nanowire growth can be induced on various substrates, and different thiolated ligands can be used to regulate the surface chemistry of the nanowires. The diameter of the nanowires can also be controlled with mixed ligands, in which another &#34;bad&#34; ligand could turn on the lateral growth. With the understanding of the mechanism, Au nanowire-based nanostructures can be designed and synthesized.

We report a solution-based method to synthesize substrate-bound Au nanowires. By tuning the molecular ligands used during the synthesis, the Au nanowires can be grown from various substrates with different surface properties. Au nanowire-based nanostructures can also be synthesized by adjusting the reaction parameters.

Síntesis de nanocables de Au sustrato enlazado mediante un mecanismo activo crecimiento superficial

Advancing synthetic capabilities is important for the development of nanoscience and nanotechnology. The synthesis of nanowires has always been a ...

A Standard and Reliable Method to Fabricate Two-Dimensional Nanoelectronics

Two-dimensional (2D) materials have attracted huge attention due to their unique properties and potential applications. Since wafer scale synthesis of 2D materials is still in nascent stages, scientists cannot fully rely on traditional semiconductor techniques for related research. Delicate processes from locating the materials to electrode definition need to be well controlled. In this article, a universal fabrication protocol required in manufacturing nanoscale electronics, such as 2D quasi-heterojunction bipolar transistors (Q-HBT), and 2D back-gated transistors are demonstrated. This protocol includes the determination of material position, electron beam lithography (EBL), metal electrode definition, et al. A step by step narrative of the fabrication procedures for these devices are also presented. Furthermore, results show that each of the fabricated devices has achieved high performance with high repeatability. This work reveals a comprehensive description of process flow for preparing 2D nano-electronics, enables the research groups to access this information, and pave the way toward future electronics.

The article aims to introduce a standard and reliable fabrication procedure for the development of future low dimensional nanoelectronics.

Un método estándar y fiable para la fabricación nanoelectrónica bidimensional

Two-dimensional (2D) materials have attracted huge attention due to their unique properties and potential applications. Since wafer scale synthesis of 2D ...

Fabrication of Schottky Diodes on Zn-polar BeMgZnO/ZnO Heterostructure Grown by Plasma-assisted Molecular Beam Epitaxy

Heterostructure field effect transistors (HFETs) utilizing a two dimensional electron gas (2DEG) channel have a great potential for high speed device applications. Zinc oxide (ZnO), a semiconductor with a wide bandgap (3.4 eV) and high electron saturation velocity has gained a great deal of attention as an attractive material for high speed devices. Efficient gate modulation, however, requires high-quality Schottky contacts on the barrier layer. In this article, we present our Schottky diode fabrication procedure on Zn-polar BeMgZnO/ZnO heterostructure with high density 2DEG which is achieved through strain modulation and incorporation of a few percent Be into the MgZnO-based barrier during growth by molecular beam epitaxy (MBE). To achieve high crystalline quality, nearly lattice-matched high-resistivity GaN templates grown by metal-organic chemical vapor deposition (MOCVD) are used as the substrate for the subsequent MBE growth of the oxide layers. To obtain the requisite Zn-polarity, careful surface treatment of GaN templates and control over the VI/II ratio during the growth of low temperature ZnO nucleation layer are utilized. Ti/Au electrodes serve as Ohmic contacts, and Ag electrodes deposited on the O2 plasma pretreated BeMgZnO surface are used for Schottky contacts.

Attainment of high-quality Schottky contacts is imperative for achieving efficient gate modulation in heterostructure field effect transistors (HFETs). We present the fabrication methodology and characteristics of Schottky diodes on Zn-polar BeMgZnO/ZnO heterostructures with high-density two dimensional electron gas (2DEG), grown by plasma-assisted molecular beam epitaxy on GaN templates.

Fabricación de diodos de Schottky en Zn-polar heteroestructura de BeMgZnO/ZnO por Epitaxy de viga Molecular asistida por Plasma

Heterostructure field effect transistors (HFETs) utilizing a two dimensional electron gas (2DEG) channel have a great potential for high speed device ...