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. Obter LAO / Heteroestruturas STO <ol><li> Obter um heterostructure óxido consistindo de 3,4 células unitárias de LAO crescidos por deposição por laser pulsado em substratos STO TiO 2-terminados. Detalhes de crescimento amostra são descritos na referência. 22. </li></ol> 2. Fotolitográfica Processamento das Amostras Criar contatos elétricos na interface LAO / STO, com almofadas de ligação para telas de fiação para uma transportadora chip. As etapas individuais de processamento são descritos em detalhe abaixo. <ol><li> Giro photoresist <ol><li> Rotação fotorresistência sobre as amostras a 600 rpm durante 5 segundos, em seguida, a 4000 rpm durante 30 segundos. A camada foto-resistente será de cerca de 2 mm de espessura. Asse as amostras a 95 ° C durante 1 min. </li></ol></li><li> Expor fotorresistente usando uma máscara alinhador com luz 320 nm durante 100 segundos com uma dose de 5 mW / cm 2. </li><li> Desenvolver o fotorresiste em desenvolvedor fotorresiste for 1 min. </li><li> Ion moagem <ol><li> Use um moinho de íons Ar + para remover 15 nm de material (LAO e STO) nas áreas não abrangidas por fotorresiste. Colocar as amostras a um ângulo de 22,5 ° para a direcção perpendicular ao feixe de iões de Ar + de entrada. Se a velocidade de gravação de Ar + não está calibrado, executar uma tiragem de calibração para garantir que a quantidade correcta do material é removido. Determinar a profundidade da gravura utilizando AFM ou profilmetry equivalente. </li></ol></li><li> DC pulverização de Ti e Au <ol><li> Depósito 4 nm Ti, em seguida, de 25 nm Au para as amostras, de modo que o Au faz contacto eléctrico com a camada exposta STO. A pressão de pulverização é na gama de 2-6 x 10 -7 Torr, e a pulverização realiza-se com a amostra à temperatura ambiente. Pré-sputter Ti durante 10 min com o obturador fechado, a 100 W, e obturador aberto e por pulverização catódica durante 20 segundos a 100 W. Após a conclusão, imediatamente pré-pulverização catódica Au durante 1 min a 50 W, em seguida, por pulverização catódica Au durante 30 segundos para as amostras em 50 W. Calibrar o tempo para produzir as Ti e Au espessuras desejadas. </li></ol></li><li> Descolagem <ol><li> Use Acetona / IPA lavagem de ultra-sons para remover fotorresistente a partir da superfície das amostras. </li></ol></li><li> Segunda camada <ol><li> Um segundo processo litográfico, excluindo a etapa 4 (ie., Excluindo moagem ion), é usado para criar conexões de fios de ouro para almofadas de ligação individuais. Os dois padrões tem de ser bem alinhados para assegurar que eles não produzirem curto-circuitos eléctricos. </li></ol></li><li> Limpeza Plasma. <ol><li> Um IPC tambor Etcher é usada para remover o resíduo fotorresistente no padrão trincheira. O instrumento utilizado na 100 W e 1 Torr árgon durante 1 min </li></ol></li></ol> 3. Fio de Bond uma amostra para se preparar para Redação <ol><li> Montar a amostra LAO / STO em um suporte de micropastilha (Figura 2A) com 28 pinos disponíveis. </li><li> Estrutura vínculo fio </li></ol> NOTA: Use um fio Bonder para fazer c elétricaonnections entre almofadas de ligação sobre a amostra e o suporte de micropastilha. Anexar 1 mil (25 micrômetros) fios de ouro entre os contatos elétricos ea transportadora chip. Escrever nanoestruturas 4. Escrever Nanoestruturas <ol><li> Criar um esboço informal da nanoestrutura condutora (Figura 3A). </li><li> Abra as Scalable Vector Graphics (SVG) editor (Figura 3B). <ol><li> Use um modelo ou definir o tamanho da janela para coincidir com a imagem AFM. </li><li> Carregar a imagem AFM da amostra para o editor SVG. </li><li> Criar elementos de nanoestrutura sobrepostos à imagem AFM diante. </li></ol></li><li> Carregue o arquivo SVG para o programa nanolithography. </li><li> Executar o software litografia para criar uma nanoestrutura condutora. <ol><li> Dica Use V = +10 V para criar nanoestruturas, e ponta V = -10 V para apagar nanoestruturas. </li><li> Mova a ponta c-AFM, a uma velocidade que varia de 200 nm / s a ​​2 mm / seg. </li></ol></li></ol> 5. Dispositivo fresco e fazer medições <ol><li> Desligar todas as luzes brancas e usar filtros vermelho / fontes de luz. </li><li> Extrai-se a amostra a partir do sistema de AFM. </li><li> Coloque a amostra no refrigerador de diluição (A). </li><li> Resistência contra a temperatura (B) medir quanto a amostra é arrefecida. </li><li> Medir as propriedades de transporte a baixas temperaturas (de 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.

Heteroestruturas Óxido 1-5 exibem uma notável variedade de fenômenos físicos emergentes que são cientificamente interessante e potencialmente útil para aplicações 4. Em particular, a interface entre LaAlO 3 (LAO) e SrTiO3 (STO) 6 podem apresentar isolante, conduzindo, supercondutores 7, ferroeléctrico semelhante 8, e 9 comportamento ferromagnético. Em 2006, Thiel et al mostraram que 10 existe uma transição brusca isolador-metal como a espessura da camada é aumentada de LAO, com uma espessura crítica de 4 células unitárias (4uc). Posteriormente, foi demonstrado que estruturas 3uc-LAO/STO exibem uma transição de histerese, que pode ser controlado localmente com uma força condutora atómica-microscópio (c-AFM), sonda 11. As propriedades das interfaces, tais como óxido de LaAlO 3 / SrTiO3 depender da presença ou ausência de realizaçãoelectrões na interface. Estes elétrons pode ser controlado usando top eletrodos de porta 12,13, costas portões 10, superfície adsorbatos 14, as camadas ferroelétricos 15,16 e c-AFM litografia 11. Uma característica única do c-AFM litografia é que pequenas características em nanoescala pode ser criado. Gating topo Elétrica, combinada com confinamento bidimensional, é freqüentemente usado para criar pontos quânticos em semicondutores III-V 17. Alternativamente, nanofios semicondutores quase unidimensionais podem ser electricamente fechado por proximidade. Os métodos para a produção destas estruturas são demoradas e geralmente irreversível. Em contraste, a técnica de litografia c-AFM é reversível no sentido em que uma nanoestrutura pode ser criado para uma experiência, e em seguida &quot;apagado&quot; (semelhante a um quadro). Geralmente, c-AFM a escrita é realizada com tensões positivas aplicadas à ponta de AFM, enquanto, apagandoé realizada usando as tensões negativas. O tempo necessário para criar uma estrutura em particular, depende da complexidade do dispositivo, mas é geralmente inferior a 30 minutos; a maior parte desse tempo é gasto apagar a tela. A resolução espacial típica é cerca de 10 nanômetros, mas com ajuste adequado apresenta tão pequena quanto 2 nanômetros podem ser criados 18. Uma descrição detalhada do processo de fabricação em nanoescala segue. O detalhe aqui fornecida deve ser suficiente para permitir que experiências semelhantes para ser realizada por investigadores interessados. O método aqui descrito tem muitas vantagens sobre as abordagens tradicionais litográficas utilizados para criar nanoestruturas electrónicos em semicondutores. O método de litografia c-AFM aqui descrito é parte de uma classe muito maior de esforços baseados em litografia de varredura-sonda, incluindo varredura anódica de oxidação 19, dip-pen nanolithography 20, padronização piezoelétrico21, e assim por diante. A técnica c-AFM descrito aqui, juntamente com a utilização de interfaces de óxido de novos, podem produzir algumas das estruturas electrónicas mais alta precisão com uma variedade sem precedentes de propriedades 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.

Os resultados aqui mostrados são representativos do comportamento de transporte que pode ser exibida por esta classe de nanoestruturas, e tem sido descrita em detalhe noutro local 23-26. Neste exemplo, uma cavidade nanofio foi calculado (Figura 4) a partir de uma heterostrutura LAO célula 3,3 unidade / STO. Caminhos condutores (mostrado em verde) são tipicamente de 10 nm de largura, conforme determinado pelo nanofio &quot;corte&quot; experiências 11. A velocidade de ponta e de tensão para cada segmento é configurável independentemente a partir do painel dianteiro da litografia (Figura 4B), como é a velocidade de ponta de escrita. &quot;Eléctrodos virtuais&quot; que interagem com os contactos interfaciais assegurar que há uma ligação eléctrica altamente condutora para as nanoestruturas. Após a nanoestrutura é escrita, ela é transferida para o refrigerador de diluição. A exposição à luz a ou abaixo de 550 nm vai produzir fotocondução indesejada, de modo que é important para transferir o dispositivo no escuro ou com o auxílio de um vermelho &quot;câmara escura&quot; luz (Figura 5A). As ligações eléctricas devem ser feitas à temperatura ambiente, e como a maioria das nanoestruturas semicondutoras, muito cuidado deve ser tomado quando se muda as conexões elétricas em temperaturas criogênicas. Se os dispositivos é submetido a descargas eletrostáticas, ele provavelmente irá se tornar isolante. Notavelmente, a funcionalidade do dispositivo pode ser recuperado por &quot;bicicleta&quot; a temperatura de 300 K e arrefecimento novamente. Durante a recarga, é de rotina para monitorizar a resistência de dois terminais, e ainda a resistência de quatro terminais, como uma função da temperatura. Para as medições de tensão de corrente alternada (tipicamente ~ 1 mV) é aplicado a uma baixa frequência (&lt;10 Hz) a um dos eléctrodos, enquanto que a corrente alternada é medido usando um amplificador de transimpedância. Lock-in desmodulação e filtragem é realizada usando um amplificador lock-in home-desenvolvidos. O cu acrrent é monitorizada como uma função de temperatura (Figura 5B). Uma vez que o dispositivo é arrefecida para a temperatura de base do refrigerador de diluição (50 mK), as medições de transporte de quatro terminais são realizadas (Figura 5C). Para estas medições, a corrente é obtida através do canal principal do dispositivo, enquanto a tensão sobre o dispositivo é medido simultaneamente. Em vez de medir com um amplificador lock-in, uma corrente de tensão máxima (IV) traço é medido. Este método contém mais informações e condução diferencial pode ser calculado através de diferenciação numérica. Para que o dispositivo particular, a condução diferencial é medido como uma função do sg lado portão tensão V. Esta porta permite que o potencial químico do dispositivo a ser mudado. O transporte através do dispositivo mostra uma forte dependência não-monotônica, indicando as regiões em que Coulomb bloqueio ocorre para valores menores, e strong supercondutividade para valores maiores de V sg. Os detalhes sobre a interpretação física para esta classe de dispositivo será descrito em outro lugar. <img alt="Figura 1" src="/files/ftp_upload/51886/51886fig1highres.jpg" /> .. Figura 1 as etapas de processamento de fotolitografia Passo 1: rotação photoresist. Passo 2: expor photoresist usando alinhador de máscara. Passo 3: desenvolver photoresist. Passo 4: moagem de íons. Passo 5: DC sputtering para depositar Ti e Au. Passo 6: a decolagem. Passo 7: depositar a segunda camada. Passo 8: limpeza de plasma. <img alt="Figura 2" src="/files/ftp_upload/51886/51886fig2highres.jpg" /> Figura 2. Imagens de lithographically estampados heteroestruturas LAO / STO. (A) Imagem mostrando 5 milímetros x 5 milímetros fio amostra ligado a uma transportadora chip. (B)<html> Óptico de imagem mostrando almofadas de ligação e uma das telas. (C) Close-up de uma única tela. <a href="https://www.jove.com/files/ftp_upload/51886/51886fig2highres.jpg" target="_blank">Clique aqui para ver uma versão maior desta figura.</a> <img alt="Figura 3" src="/files/ftp_upload/51886/51886fig3highres.jpg" /> Figura 3. (A) Projeto Informal de LAO / STO nanoestrutura. (B) layout preciso de nanoestruturas usando um open-source gráficos vetoriais escaláveis ​​(SVG) do editor. <img alt="Figura 4" src="/files/ftp_upload/51886/51886fig4highres.jpg" /> Figura 4. (A) Litografia painel frontal para c-AFM padronização. (B) Screenshot do simulador 3D que mostra a posição ea tensão do c-AFM ponta.w.jove.com/files/ftp_upload/52058/52058fig4large.jpg &quot;target =&quot; _blank &quot;&gt; Clique aqui para ver uma versão maior desta figura. <img alt="Figura 5" src="/files/ftp_upload/51886/51886fig5highres.jpg" /> Figura 5. (A) LAO / STO nanoestrutura sendo inserido na diluição refrigerador. (B) Acompanhamento da resistência da amostra, uma vez que é arrefecido a partir de 300 K para 50 mK. (C) Avaliação da condutância diferencial de quatro terminais do dispositivo como uma função de Vsg tensão portão lateral e tensão sobre o dispositivo (V4T). Gráfico de intensidade apresentado em unidades de siemens (S), e as tensões são apresentados em unidades de volts (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.

Escrita e Caracterização baixa temperatura de óxido de Nanoestruturas

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

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9.9K visualizações.  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.

Vídeo: 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.

Um método para fabricar nanoestruturas de prata desconectados em 3D

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

Engenharia

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.

Sondagem e Mapeamento superfície do eletrodo em células a combustível 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.

De luz visível redução induzida de óxido de grafeno Usando nanopartículas plasmonic

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.

Ohmic Contato Fabrication usando uma técnica Focused-ion Beam e caracterização elétrica para camada semicondutora Nanoestruturas

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.

Fabricação de Baixa Temperatura de Nanotubos de Carbono Vertical Interconexões Compatível com Semiconductor Tecnologia

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.

Integração da luz Interceptação de prata Nanoestruturas em células solares de silício hidrogenado microcristalina por Transferência de impressão

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.

Escrevendo redes de Bragg em 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.

Grafeno Oxide Nanohybrid Thin Film eléctrodos modificados serigrafado reduzida de óxido de irídio como papel Electrochemical descartável microfluídicos 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.

Métodos experimentais avançados para baixa temperatura Magnetotransporte Medição de novos materiais

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.

Desenvolvimento de método para estudos espectroscópicos dielétricos de cavidade ressonante sem contato de papel Celulóico

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