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. Obtenir AJO / hétérostructures de la STO <ol><li> Obtenir une hétérostructure d&#39;oxyde constitué de 3,4 cellules unitaires d&#39;AJO cultivées par ablation laser sur des substrats de TiO 2 de la STO à terminaison. Détails de la croissance de l&#39;échantillon sont décrits dans la référence. 22. </li></ol> 2. Traitement photolithographie des échantillons Créer des contacts électriques à l&#39;interface LAO / STO, avec des plots de connexion pour câblage toiles à un support de puce. Les différentes étapes de transformation sont décrites en détail ci-dessous. <ol><li> Spin résine photosensible <ol><li> Spin résine photosensible sur les échantillons à 600 tpm pendant 5 secondes, puis à 4000 rpm pendant 30 s. La couche de résine photosensible sera d&#39;environ 2 um d&#39;épaisseur. Cuire les échantillons à 95 ° C pendant 1 min. </li></ol></li><li> Exposer photoresist en utilisant un aligneur de masque avec la lumière à 320 nm pendant 100 secondes avec une dose de 5 mW / cm 2. </li><li> Développer la résine photosensible dans un révélateur de résine photosensible for 1 min. </li><li> Ion fraisage <ol><li> Utilisez une usine d&#39;ions Ar + à retirer 15 nm de matériau (LAO et STO) dans les zones non couvertes par résine photosensible. Placer les échantillons à un angle de 22,5 ° par rapport à la direction perpendiculaire au faisceau d&#39;ions Ar + entrante. Si la vitesse de gravure Ar + n&#39;est pas calibré, effectuer un essai d&#39;étalonnage afin de s&#39;assurer que la quantité correcte de la matière est enlevée. Déterminer la profondeur de gravure par AFM ou profilmetry équivalent. </li></ol></li><li> DC pulvérisation de Ti et Au <ol><li> Caution 4 nm Ti, puis 25 nm Au sur les échantillons de sorte que l&#39;Au contact électrique avec la couche de STO exposée. La pression de pulvérisation est dans la gamme de 2 à 6 x 10 -7 Torr, et la pulvérisation a lieu avec l&#39;échantillon à température ambiante. Pré-pulvérisation cathodique Ti pendant 10 min avec obturateur fermé à 100 W, alors obturateur ouvert et par pulvérisation pendant 20 secondes à 100 W. À la fin, immédiatement avant pulvérisation Au 1 min à 50 W, puis pulvériser Au 30 sec pour les échantillons à 50 W. Calibrer le temps de produire les épaisseurs de Ti et Au souhaités. </li></ol></li><li> Décollage <ol><li> Utilisez acétone / IPA lavage à ultrasons pour éliminer résine photosensible de la surface des échantillons. </li></ol></li><li> Deuxième couche <ol><li> Un deuxième procédé de lithographie, à l&#39;exclusion de l&#39;étape 4 (c.-à-., À l&#39;exclusion usinage ionique), est utilisé pour créer des connexions de fils d&#39;or à des plots de connexion individuels. Les deux modèles doivent être bien alignées pour s&#39;assurer qu&#39;elles ne produisent pas de courts-circuits électriques. </li></ol></li><li> nettoyage de plasma. <ol><li> Un IPC Barrel Etcher est utilisé pour enlever les résidus de résine photosensible dans la tranchée de modèle. L&#39;instrument utilisé à 100 W et 1 Torr argon pendant 1 min </li></ol></li></ol> 3. Fil Bond un échantillon se préparer à l&#39;écriture <ol><li> Monter l&#39;échantillon LAO / STO dans un support de puce (figure 2A) avec 28 broches disponibles. </li><li> structure de liaison de fil </li></ol> REMARQUE: Utilisez une colle de fil pour faire c électriqueonnexions entre les plots de connexion sur l&#39;échantillon et le support de puce. Attacher 1 mil (25 micromètres) des fils d&#39;or entre les contacts électriques et le support de puce. Ecrire nanostructures 4. Donnez Nanostructures <ol><li> Créer un croquis informel de la nanostructure conducteur (figure 3A). </li><li> Ouvrez les scalable vector graphics (SVG) éditeur (figure 3B). <ol><li> Utiliser un modèle ou définir la taille de la fenêtre pour correspondre à celle de l&#39;image de l&#39;AFM. </li><li> Chargez l&#39;image AFM de l&#39;échantillon dans l&#39;éditeur de SVG. </li><li> Créer des éléments de nanostructure superposées sur l&#39;image AFM. </li></ol></li><li> Chargez le fichier SVG dans le programme de nanolithographie. </li><li> Exécutez le logiciel de lithographie pour créer une nanostructure conducteur. <ol><li> Pointe l&#39;utilisation de V = +10 V pour créer des nanostructures, et la pointe de V = -10 V pour effacer nanostructures. </li><li> Placez l&#39;extrémité C-AFM à une vitesse allant de 200 nm / sec à 2 pm / sec. </li></ol></li></ol> 5. Refroidir l&#39;appareil et prendre les mesures <ol><li> Éteindre toutes les lumières blanches et utiliser des filtres rouge / sources de lumière. </li><li> Extraire l&#39;échantillon à partir du système de l&#39;AFM. </li><li> Chargez l&#39;échantillon dans le réfrigérateur à dilution (A). </li><li> Mesurer la résistance fonction de la température (B) que l&#39;échantillon est refroidi. </li><li> Mesurer les propriétés de transport à basse température (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.

Oxyde hétérostructures 1-5 présentent une remarquable variété de phénomènes physiques émergentes qui sont à la fois scientifiquement intéressantes et potentiellement utiles pour les applications 4. En particulier, l&#39;interface entre LaAlO 3 (AJO) et SrTiO3 (STO) 6 peut présenter isolant, conducteur, supraconducteur 7, ferroélectrique comme 8, 9 et ferromagnétique comportement. En 2006, Thiel et al ont montré que 10 il ya une transition isolant-métal pointu que l&#39;épaisseur de la couche AJO est augmentée, avec une épaisseur critique de 4 cellules élémentaires (4uc). Il a ensuite été montré que les structures présentent une transition 3uc-LAO/STO hystérétique qui peut être contrôlé localement avec un microscope à force atomique conductrice (c-AFM) sonde 11. Les propriétés des interfaces d&#39;oxydes tels que LaAlO 3 / SrTiO 3 dépendent de la présence ou de l&#39;absence de conducteurdes électrons à l&#39;interface. Ces électrons peuvent être contrôlés à l&#39;aide meilleurs électrodes de grille 12,13, dos portes 10, surface adsorbats 14, couches ferroélectriques 15,16 et c-AFM lithographie 11. Une caractéristique unique de c-AFM lithographie est que de très petites caractéristiques nanométriques peuvent être créés. Déclenchement top électrique, combiné avec confinement à deux dimensions, est souvent utilisé pour créer des points quantiques dans les semi-conducteurs III-V 17. Alternativement, les nanofils semi-conducteurs quasi-unidimensionnels peuvent être déclenchés électriquement par la proximité. Les procédés de production de ces structures sont longs et généralement irréversible. En revanche, la technique de lithographie c-AFM est réversible dans le sens d&#39;une nanostructure peut être créé pour une expérience, puis &quot;effacée&quot; (équivalent d&#39;un tableau blanc). En général, l&#39;écriture c-AFM est réalisée avec des tensions positives appliquées à la pointe de l&#39;AFM, tandis que, effaçantest réalisée en utilisant des tensions négatives. Le temps nécessaire pour créer une structure particulière dépend de la complexité du dispositif, mais est habituellement inférieure à 30 min; la plupart du temps est consacré à l&#39;effacement de la toile. La résolution spatiale typique est d&#39;environ 10 nanomètres, mais avec un bon réglage comporte aussi petit que 2 nanomètres peuvent être créées 18. Une description détaillée de la procédure de fabrication à l&#39;échelle nanométrique suit. Le niveau de détail ici devrait être suffisante pour permettre des expériences similaires à réaliser par les chercheurs intéressés. La méthode décrite ici présente de nombreux avantages par rapport aux approches traditionnelles lithographiques utilisés pour créer des nanostructures électroniques dans les semi-conducteurs. Le procédé de lithographie c-AFM décrite ici fait partie d&#39;une classe beaucoup plus large des efforts de lithographie à base de sonde à balayage, y compris l&#39;oxydation balayage anodique 19, dip-pen nanolithographie 20, motif piézoélectrique21, et ainsi de suite. La technique c-AFM décrit ici, couplé avec l&#39;utilisation de nouvelles interfaces d&#39;oxyde, peut produire certaines des structures électroniques la plus grande précision avec une variété sans précédent de propriétés physiques.

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			<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>
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		<tr height="20">
			<td height="20" style="height:20px;">Contact Aligner</td>
			<td>Karl-Suss</td>
			<td>MA6</td>
			<td></td>
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		<tr height="20">
			<td height="20" style="height:20px;">Spinner</td>
			<td>Solitec</td>
			<td>5110C</td>
			<td></td>
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		<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.

Les résultats présentés ici sont représentatifs du comportement de transport qui peut être exposé par cette classe de nanostructures, et a été décrit ailleurs en détail 23-26. Dans cet exemple, une cavité de nanofil a été construit (figure 4) à partir d&#39;une hétérostructure LAO cellulaire de 3,3 unité / STO. Chemins conducteurs (en vert) sont généralement de 10 nm de large, tel que déterminé par nanofil &quot;coupe&quot; expériences 11. La vitesse de pointe et la tension pour chaque segment est configurable indépendamment à partir du panneau avant de la lithographie (figure 4B), ainsi que la vitesse d&#39;écriture de pointe. &quot;Électrodes virtuelles&quot; que l&#39;interface avec les contacts d&#39;interface assurent qu&#39;il existe une connexion électrique fortement conducteur pour les nanostructures. Après la nanostructure est écrite, elle est transférée au réfrigérateur à dilution. Exposition à la lumière ou au-dessous de 550 nm se produire photoconduction indésirables, il est important de transférer le dispositif dans l&#39;obscurité ou à l&#39;aide d&#39;un rouge &quot;chambre noire&quot; de lumière (figure 5A). Les branchements électriques doivent être effectués à la température ambiante, et comme la plupart des nanostructures de semi-conducteurs, un grand soin doit être pris lors de la modification des connexions électriques à des températures cryogéniques. Si les appareils sont soumis à des décharges électrostatiques, il deviendra très probablement isolante. Remarquablement, la fonctionnalité de l&#39;appareil peut être récupéré par «cycle» de la température à 300 K et en refroidissant à nouveau. Au cours de recharge, il est courant de contrôler la résistance à deux bornes, et la même résistance à quatre bornes, en fonction de la température. Pour ces mesures, une tension alternative (typiquement ~ 1 mV) est appliquée à une fréquence faible (&lt;10 Hz) à l&#39;une des électrodes, tandis que le courant alternatif est mesuré en utilisant un amplificateur à transimpédance. Lock-in démodulation et de filtrage est effectué en utilisant un amplificateur lock-in home-développé. L&#39;ac current est surveillée en fonction de la température (Figure 5B). Une fois que l&#39;appareil est refroidi à la température de base du réfrigérateur à dilution (50 mK), des mesures de transport de quatre terminaux sont effectuées (figure 5C). Pour ces mesures, le courant provient travers le canal principal de l&#39;appareil, tandis que la tension aux bornes du dispositif est mesurée simultanément. Au lieu de mesurer avec un amplificateur lock-in, un courant-tension complète (IV) trace est mesurée. Ce procédé contient plus d&#39;informations et la conduction de différentiel peut être calculée par l&#39;intermédiaire d&#39;une différenciation numérique. Pour le dispositif particulier, la conduction différentielle est mesurée en fonction du côté sg-tension de grille V. Cette grille permet le potentiel chimique de l&#39;appareil devant être modifié. Le transport à travers le dispositif montre une forte dépendance non-monotone, indiquant les régions dans lesquelles le blocage de Coulomb a lieu pour des valeurs plus petites, et strong supraconductivité pour les plus grandes valeurs de V sg. Détails sur l&#39;interprétation physique de cette classe d&#39;appareil seront décrites ailleurs. <img alt="Figure 1" src="/files/ftp_upload/51886/51886fig1highres.jpg" /> .. Figure 1 photolithographiques des étapes de traitement Étape 1: rotation résine photosensible. Étape 2: exposer résine photosensible à l&#39;aide d&#39;alignement de masque. Étape 3: développer résine photosensible. Etape 4: usinage ionique. Étape 5: DC pulvérisation pour déposer Ti et Au. Étape 6: lift-off. Etape 7: déposer la seconde couche. Étape 8: nettoyage au plasma. <img alt="Figure 2" src="/files/ftp_upload/51886/51886fig2highres.jpg" /> Figure 2. Images de lithographier hétérostructures LAO / STO. (A) Image montrant 5mm x 5mm fil de l&#39;échantillon lié à un support de puce. (B)<html> Image optique montrant plots de connexion et l&#39;une des toiles. (C) Close-up d&#39;une seule toile. <a href="https://www.jove.com/files/ftp_upload/51886/51886fig2highres.jpg" target="_blank">S&#39;il vous plaît cliquer ici pour voir une version plus grande de cette figure.</a> <img alt="Figure 3" src="/files/ftp_upload/51886/51886fig3highres.jpg" /> Figure 3. (A) de conception informelle des LAO / STO nanostructure. (B) mise en page précise de nanostructure en utilisant un open-source Scalable Vector Graphics (SVG) éditeur. <img alt="Figure 4" src="/files/ftp_upload/51886/51886fig4highres.jpg" /> Figure 4. (A) Lithographie panneau avant pour c-AFM motifs. (B) la position et la tension de pointe c-AFM Capture d&#39;écran de simulateur 3D montrant.w.jove.com/files/ftp_upload/52058/52058fig4large.jpg &quot;target =&quot; _blank &quot;&gt; S&#39;il vous plaît cliquer ici pour voir une version plus grande de cette figure. <img alt="Figure 5" src="/files/ftp_upload/51886/51886fig5highres.jpg" /> Figure 5. (A) LAO / STO nanostructure étant inséré dans réfrigérateur à dilution. (B) Surveillance de la résistance de l&#39;échantillon comme il est refroidi de 300 K à 50 mK. (C) Surveillance de conductance différentielle à quatre bornes de dispositif en fonction de Vsg de tension de la porte latérale et de la tension aux bornes du dispositif (V4T). graphique de l&#39;intensité affichée dans les unités de siemens (S), et les tensions sont affichés en unités 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.

Écrit et à basse température Caractérisation des nanostructures d&#39;oxyde

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

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9.8K vues.  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.

Vidéo: 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.

Une méthode pour fabriquer des nanostructures d&#39;argent déconnectés en 3D

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

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Ingénierie

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.

Exploration et cartographie des surfaces d&#39;électrodes en piles à oxyde solide

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.

Lumière visible réduction induite de graphène oxyde Utilisation plasmonique nanoparticules

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.

Contact ohmique fabrication utilisant une technique Focused Ion Beam-et caractérisation électrique pour la couche semi-conducteurs Nanostructures

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.

Fabrication de basse température de nanotubes de carbone interconnexions verticales Compatible avec la technologie des semiconducteurs

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.

Intégration de la Lumière de piégeage argent Nanostructures dans hydrogénée microcristalline cellules solaires en silicium par impression par transfert

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.

Rédaction de Bragg dans les fibres multipaires

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.

Electrodes sérigraphiés oxyde d&#39;iridium réduite graphène Oxyde nanohybrides Thin Film modifié comme papier jetable Electrochemical microfluidiques pH Capteurs

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.

Méthodes expérimentales avancées pour basse température magnétotransport mesure de nouveaux matériaux

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

Fabrication and Characterization of Superconducting Resonators

Superconducting microwave resonators are of interest for a wide range of applications, including for their use as microwave kinetic inductance detectors (MKIDs) for the detection of faint astrophysical signatures, as well as for quantum computing applications and materials characterization. In this paper, procedures are presented for the fabrication and characterization of thin-film superconducting microwave resonators. The fabrication methodology allows for the realization of superconducting transmission-line resonators with features on both sides of an atomically smooth single-crystal silicon dielectric. This work describes the procedure for the installation of resonator devices into a cryogenic microwave testbed and for cool-down below the superconducting transition temperature. The set-up of the cryogenic microwave testbed allows one to do careful measurements of the complex microwave transmission of these resonator devices, enabling the extraction of the properties of the superconducting lines and dielectric substrate (e.g., internal quality factors, loss and kinetic inductance fractions), which are important for device design and performance.

Superconducting microwave resonators are of interest for detection of light, quantum computing applications and materials characterization. This work presents a detailed procedure for fabrication and characterization of superconducting microwave resonator scattering parameters.

Fabrication et caractérisation de supraconductrices Resonators

Superconducting microwave resonators are of interest for a wide range of applications, including for their use as microwave kinetic inductance detectors ...