Name: writing and low-temperature characterization of oxide nanostructures
Uploaded: 2014-07-18T15:00:00.000+00:00
Duration: 6 min 43 s
Description: Watch this Scientific Journal Video about Writing and Low-Temperature Characterization of Oxide Nanostructures at JoVE.com

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>

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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><tbody><tr><td>Equipment</td><td></td><td></td><td></td></tr><tr><td>Contact Aligner</td><td>Karl-Suss</td><td>MA6</td><td></td></tr><tr><td>Spinner</td><td>Solitec</td><td>5110C</td><td></td></tr><tr><td>Ion Mill</td><td>Commonwealth Scientific</td><td>8C</td><td></td></tr><tr><td>Sputtering System</td><td>Leybold-Heraeus</td><td>Z-650</td><td></td></tr><tr><td>Barrel Etcher</td><td>Branson/IPC</td><td>3000C</td><td></td></tr><tr><td>Wire Bonder</td><td>Westbond</td><td>7700E</td><td></td></tr><tr><td>AFM</td><td>Asylum Research</td><td>MFP-3D</td><td></td></tr><tr><td>Dilution Refrigerator</td><td>Quantum Design</td><td>P850</td><td></td></tr><tr><td>Ultrasonic Wash Machine</td><td>Fisher Scientific</td><td>15-335-6</td><td></td></tr><tr><td>Current Amplifier</td><td>Femto</td><td>DLPCA-200</td><td></td></tr><tr><td>Materials</td><td></td><td></td><td></td></tr><tr><td>LaAlO&lt;sub&gt;3&lt;/sub&gt;/SrTiO&lt;sub&gt;3&lt;/sub&gt;</td><td>Prof. Chang-Beom Eom</td><td></td><td>5 mm x 1 mm with ~3.4 unit cells of LAO (See Reference 18)</td></tr><tr><td>Photoresist</td><td>AZ Electronic Materials</td><td>P4210</td><td></td></tr><tr><td>Developer</td><td>AZ Electronic Materials</td><td>400K</td><td></td></tr><tr><td>Acetone</td><td>Fisher Scientific</td><td>A929SK-4</td><td></td></tr><tr><td>Isopropyl Alcohol</td><td>Fisher Scientific</td><td>A459-1</td><td></td></tr><tr><td>Deionized Water</td><td>Fisher Scientific</td><td>23-290-065</td><td></td></tr><tr><td>Gold Wire</td><td>DuPont</td><td>5771</td><td>1 mm diameter</td></tr><tr><td>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

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

Fabrication of Nano-engineered Transparent Conducting Oxides by Pulsed Laser Deposition

Nanosecond Pulsed Laser Deposition (PLD) in the presence of a background gas allows the deposition of metal oxides with tunable morphology, structure, density and stoichiometry by a proper control of the plasma plume expansion dynamics. Such versatility can be exploited to produce nanostructured films from compact and dense to nanoporous characterized by a hierarchical assembly of nano-sized clusters. In particular we describe the detailed methodology to fabricate two types of Al-doped ZnO (AZO) films as transparent electrodes in photovoltaic devices: 1) at low O2 pressure, compact films with electrical conductivity and optical transparency close to the state of the art transparent conducting oxides (TCO) can be deposited at room temperature, to be compatible with thermally sensitive materials such as polymers used in organic photovoltaics (OPVs); 2) highly light scattering hierarchical structures resembling a forest of nano-trees are produced at higher pressures. Such structures show high Haze factor (&gt;80%) and may be exploited to enhance the light trapping capability. The method here described for AZO films can be applied to other metal oxides relevant for technological applications such as TiO2, Al2O3, WO3 and Ag4O4.

We describe the experimental method to deposit nanostructured oxide thin films by nanosecond Pulsed Laser Deposition (PLD) in the presence of a background gas. By using this method Al-doped ZnO (AZO) films, from compact to hierarchically structured as nano-tree forests, can be deposited.

La fabricación de nano-ingeniería óxidos conductores transparentes por deposición por láser pulsado

Nanosecond Pulsed  Laser Deposition (PLD) in the presence of a background gas allows the deposition  of metal oxides with tunable morphology, structure, ...

Fabrication of Spatially Confined Complex Oxides

Complex materials such as high Tc superconductors, multiferroics, and colossal magnetoresistors have electronic and magnetic properties that arise from the inherent strong electron correlations that reside within them. These materials can also possess electronic phase separation in which regions of vastly different resistive and magnetic behavior can coexist within a single crystal alloy material. By reducing the scale of these materials to length scales at and below the inherent size of the electronic domains, novel behaviors can be exposed. Because of this and the fact that spin-charge-lattice-orbital order parameters each involve correlation lengths, spatially reducing these materials for transport measurements is a critical step in understanding the fundamental physics that drives complex behaviors. These materials also offer great potential to become the next generation of electronic devices 1-3. Thus, the fabrication of low dimensional nano- or micro-structures is extremely important to achieve new functionality. This involves multiple controllable processes from high quality thin film growth to accurate electronic property characterization. Here, we present fabrication protocols of high quality microstructures for complex oxide manganite devices. Detailed descriptions and required equipment of thin film growth, photo-lithography, and wire-bonding are presented.

We describe the use of pulsed laser deposition (PLD), photolithography and wire-bonding techniques to create micrometer scale complex oxides devices. The PLD is utilized to grow epitaxial thin films. Photolithography and wire-bonding techniques are introduced to create practical devices for measurement purposes.

La fabricación de óxidos complejos espacialmente confinados

Complex materials such as high Tc superconductors, multiferroics, and colossal magnetoresistors have electronic and magnetic properties that arise from ...

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

Preparation and Reactivity of Gasless Nanostructured Energetic Materials

High-Energy Ball Milling (HEBM) is a ball milling process where a powder mixture placed in the ball mill is subjected to high-energy collisions from the balls. Among other applications, it is a versatile technique that allows for effective preparation of gasless reactive nanostructured materials with high energy density per volume (Ni+Al, Ta+C, Ti+C). The structural transformations of reactive media, which take place during HEBM, define the reaction mechanism in the produced energetic&#160;composites. Varying the processing conditions permits fine tuning of the milling-induced microstructures of the fabricated composite particles. In turn, the reactivity, i.e., self-ignition temperature, ignition delay time, as well as reaction kinetics, of high energy density materials depends on its microstructure. Analysis of the milling-induced microstructures suggests that the formation of fresh oxygen-free intimate high surface area contacts between the reagents is responsible for the enhancement of their reactivity. This manifests itself in a reduction of ignition temperature and delay time, an increased rate of chemical reaction, and an overall decrease of the effective activation energy of the reaction. The protocol provides a detailed description for the preparation of reactive nanocomposites with tailored microstructure using short-term HEBM method. It also describes a high-speed thermal imaging technique to determine the ignition/combustion characteristics of the energetic materials. The protocol can be adapted to preparation and characterization of a variety of nanostructured energetic composites.

This protocol describes the preparation of gasless nanostructured energetic materials (Ni+Al, Ta+C, Ti+C) using the short-term high-energy ball milling (HEBM) technique. It also describes a high-speed thermal imaging method to study the reactivity of mechanically fabricated nanocomposites. These protocols can be extended to other reactive nanostructured energetic materials.

Preparación y reactividad de sin gas Nanoestructurados materiales energéticos

High-Energy Ball Milling (HEBM) is a ball milling process where a powder mixture placed in the ball mill is subjected to high-energy collisions from the ...

Atomically Traceable Nanostructure Fabrication

Reducing the scale of etched nanostructures below the 10 nm range eventually will require an atomic scale understanding of the entire fabrication process being used in order to maintain exquisite control over both feature size and feature density. Here, we demonstrate a method for tracking atomically resolved and controlled structures from initial template definition through final nanostructure metrology, opening up a pathway for top-down atomic control over nanofabrication. Hydrogen depassivation lithography is the first step of the nanoscale fabrication process followed by selective atomic layer deposition of up to 2.8 nm of titania to make a nanoscale etch mask. Contrast with the background is shown, indicating different mechanisms for growth on the desired patterns and on the H passivated background. The patterns are then transferred into the bulk using reactive ion etching to form 20 nm tall nanostructures with linewidths down to ~6 nm. To illustrate the limitations of this process, arrays of holes and lines are fabricated. The various nanofabrication process steps are performed at disparate locations, so process integration is discussed. Related issues are discussed including using fiducial marks for finding nanostructures on a macroscopic sample and protecting the chemically reactive patterned Si(100)-H surface against degradation due to atmospheric exposure.

We report a protocol for combining the atomic metrology of the Scanning Tunneling Microscope for surface patterning with selective Atomic Layer Deposition and Reactive Ion Etching. Using a robust process involving numerous atmospheric exposures and transport, 3D nanostructures with atomic metrology are fabricated.

La fabricación de nanoestructuras Atómicamente trazable

Reducing the scale of etched nanostructures below the 10 nm range eventually will require an atomic scale understanding of the entire fabrication process ...

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 ...

Growth and Electrostatic/chemical Properties of Metal/LaAlO3/SrTiO3 Heterostructures

The quasi 2D electron system (q2DES) that forms at the interface between LaAlO3 (LAO) and SrTiO3 (STO) has attracted much attention from the oxide electronics community. One of its hallmark features is the existence of a critical LAO thickness of 4 unit-cells (uc) for interfacial conductivity to emerge. Although electrostatic mechanisms have been proposed in the past to describe the existence of this critical thickness, the importance of chemical defects has been recently accentuated. Here, we describe the growth of metal/LAO/STO heterostructures in an ultra-high vacuum (UHV) cluster system combining pulsed laser deposition (to grow the LAO), magnetron sputtering (to grow the metal) and X-ray photoelectron spectroscopy (XPS). We study step by step the formation and evolution of the q2DES and the chemical interactions that occur between the metal and the LAO/STO. Additionally, magnetotransport experiments elucidate on the transport and electronic properties of the q2DES. This systematic work not only demonstrates a way to study the electrostatic and chemical interplay between the q2DES and its environment, but also unlocks the possibility to couple multifunctional capping layers with the rich physics observed in two-dimensional electron systems, allowing the fabrication of new types of devices.

Growth and Electrostatic/chemical Properties of Metal/LaAlO3/SrTiO3 Heterostructures

We fabricate metal/LaAlO3/SrTiO3 heterostructures using a combination of pulsed laser deposition and in situ magnetron sputtering. Through magnetotransport and in situ X-ray photoelectron spectroscopy experiments, we investigate the interplay between electrostatic and chemical phenomena of the quasi two-dimensional electron gas formed in this system.

Crecimiento y propiedades electrostáticas químico de Metal/LaAlO3/SrTiO3 heteroestructuras

The quasi 2D electron system (q2DES) that forms at the interface between LaAlO3 (LAO) and SrTiO3 (STO) has attracted much attention from the oxide ...

Bulk and Thin Film Synthesis of Compositionally Variant Entropy-stabilized Oxides

Here, we present a procedure for the synthesis of bulk and thin film multicomponent (Mg0.25(1-x)CoxNi0.25(1-x)Cu0.25(1-x)Zn0.25(1-x))O (Co variant) and (Mg0.25(1-x)Co0.25(1-x)Ni0.25(1-x)CuxZn0.25(1-x))O (Cu variant) entropy-stabilized oxides. Phase pure and chemically homogeneous (Mg0.25(1-x)CoxNi0.25(1-x)Cu0.25(1-x)Zn0.25(1-x))O (x = 0.20, 0.27, 0.33) and (Mg0.25(1-x)Co0.25(1-x)Ni0.25(1-x)CuxZn0.25(1-x))O (x = 0.11, 0.27) ceramic pellets are synthesized and used in the deposition of ultra-high quality, phase pure, single crystalline thin films of the target stoichiometry. A detailed methodology for the deposition of smooth, chemically homogeneous, entropy-stabilized oxide thin films by pulsed laser deposition on (001)-oriented MgO substrates is described. The phase and crystallinity of bulk and thin film materials are confirmed using X-ray diffraction. Composition and chemical homogeneity are confirmed by X-ray photoelectron spectroscopy and energy dispersive X-ray spectroscopy. The surface topography of thin films is measured with scanning probe microscopy. The synthesis of high quality, single crystalline, entropy-stabilized oxide thin films enables the study of interface, size, strain, and disorder effects on the properties in this new class of highly disordered oxide materials.

The synthesis of high quality bulk and thin film (Mg0.25(1-x)CoxNi0.25(1-x)Cu0.25(1-x)Zn0.25(1-x))O and (Mg0.25(1-x)Co0.25(1-x)Ni0.25(1-x)CuxZn0.25(1-x))O entropy-stabilized oxides is presented.

A granel y síntesis de la película fina de composición variantes óxidos entropía estabilizada

Here, we present a procedure for the synthesis of bulk and thin film multicomponent (Mg0.25(1-x)CoxNi0.25(1-x)Cu0.25(1-x)Zn0.25(1-x))O (Co variant) and ...

Tuning Oxide Properties by Oxygen Vacancy Control During Growth and Annealing

Electrical, optical, and magnetic properties of oxide materials can often be controlled by varying the oxygen content. Here we outline two approaches for varying the oxygen content and provide concrete examples for tuning the electrical properties of SrTiO3-based heterostructures. In the first approach, the oxygen content is controlled by varying the deposition parameters during a pulsed laser deposition. In the second approach, the oxygen content is tuned by subjecting the samples to annealing in oxygen at elevated temperatures after the film growth. The approaches can be used for a wide range of oxides and nonoxide materials where the properties are sensitive to a change in the oxidation state.
The approaches differ significantly from electrostatic gating, which is often used to change the electronic properties of confined electronic systems such as those observed in SrTiO3-based heterostructures. By controlling the oxygen vacancy concentration, we are able to control the carrier density over many orders of magnitude, even in nonconfined electronic systems. Moreover, properties can be controlled, which are not sensitive to the density of itinerant electrons.

Oxide materials show many exotic properties that can be controlled by tuning the oxygen content. Here, we demonstrate the tuning of oxygen content in oxides by varying the pulsed laser deposition parameters and by performing postannealing. As an example, electronic properties of SrTiO3-based heterostructures are tuned by growth modifications and annealing.

Ajuste de las propiedades del óxido mediante el control de vacantes de oxígeno durante el crecimiento y el recocido

Electrical, optical, and magnetic properties of oxide materials can often be controlled by varying the oxygen content. Here we outline two approaches for ...