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

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

1. Erhalten LAO / STO Heterostrukturen <ol><li> Erhalten Oxid-Heterostruktur, bestehend aus 3,4 Einheitszellen LAO mittels gepulster Laserabscheidung auf TiO 2-terminierte STO Substraten gewachsen. Einzelheiten sind in Probe Wachstum Ref. 22 beschrieben. </li></ol> 2. Photolithographische Verarbeitung von Proben Neues elektrischen Kontakte an der LAO / STO-Schnittstelle, mit der Bond-Pads für die Verdrahtung Leinwände auf einem Chipträger. Die einzelnen Bearbeitungsschritte werden im Folgenden näher beschrieben. <ol><li> Spin Photolack <ol><li> Spin Photoresist auf die Proben bei 600 rpm für 5 Sekunden und dann bei 4.000 Upm für 30 Sekunden. Die Fotolackschicht wird etwa 2 um dick. Backen die Proben bei 95 ° C für 1 min. </li></ol></li><li> Aussetzen Photoresist unter Verwendung eines Maskenausrichter mit 320 nm-Licht für 100 Sekunden mit einer Dosis von 5 mW / cm 2. </li><li> Entwickeln der Photoresist in Photoresist-Entwickler for 1 min. </li><li> Ionenfräsen <ol><li> Verwenden Sie ein Ar +-Ionen-Mühle bis 15 nm von Material (LAO und STO) in den nicht von Photolack bedeckt entfernen. Die Proben werden in einem 22,5 °-Winkel zu der Richtung senkrecht zu der eingehenden Ar +-Ionenstrahl. Wenn der Ar + Ätzrate nicht kalibriert ist, führen Sie einen Kalibrierungslauf, um sicherzustellen, dass die richtige Menge an Material entfernt wird. Bestimmen Sie die Ätztiefe mit AFM oder gleichwertig profilmetry. </li></ol></li><li> DC-Sputtern von Ti und Au <ol><li> Hinterlegung 4 nm Ti, dann 25 nm Au auf die Proben, so daß die Au elektrischen Kontakt mit dem freiliegenden STO-Schicht. Der Sputterdruck im Bereich 2-6 × 10 -7 Torr, und das Sputtern mit der Probe bei Raumtemperatur stattfindet. Pre-Sputter-Ti für 10 min mit geschlossenem Verschluss bei 100 W, dann offener Blende und Sputter für 20 Sekunden bei 100 W. Nach der Fertigstellung sofort Pre-Sputter-Au 1 min bei 50 W dann Sputter Au für 30 Sekunden zu den Proben, die bei 50 W. CaliBråte die Zeit, um die gewünschten Ti und Au Stärken zu produzieren. </li></ol></li><li> Lift-off <ol><li> Verwenden Sie Aceton / IPA Ultraschall zu waschen, um Fotolack von der Oberfläche der Proben zu entfernen. </li></ol></li><li> Zweite Schicht <ol><li> Eine zweite lithographischen Verfahrens, ohne Schritt 4 (dh., Ohne Ionenätzen) wird verwendet, um Golddrahtverbindungen mit einzelnen Bondkontaktstellen zu schaffen. Die beiden Muster müssen gut ausgerichtet, um sicherzustellen, dass sie nicht zu elektrischen Kurzschlüssen zu erzeugen. </li></ol></li><li> Plasmareinigung. <ol><li> IPC Barrel Etcher wird die Photoresistrückstand im Grabenmuster zu entfernen. Die bei der 100 W und 1 Torr Argon für 1 min verwendete Instrument </li></ol></li></ol> 3. Draht Bond eine Probe für das Schreiben vorbereiten <ol><li> Montieren Sie die LAO / STO Probe in einem Chipträger (2A) mit 28 Pins verfügbar. </li><li> Draht-Bond-Struktur </li></ol> HINWEIS: Verwenden Sie eine Drahtverbinder für elektrische c machennschlüsse zwischen den Bondanschlußflächen auf der Probe und dem Chipträger. Befestigen 1 mil (25 Mikrometer) Golddrähte zwischen den elektrischen Kontakten und dem Chipträger. Schreiben Nanostrukturen 4. Schreiben Nanostrukturen <ol><li> Erstellen Sie eine informelle Skizze des leitfähigen Nanostruktur (Abbildung 3A). </li><li> Öffnen Sie die skalierbare Vektorgrafiken (SVG)-Editor (Abbildung 3B). <ol><li> Verwenden Sie eine Vorlage oder definieren Sie die Fenstergröße auf, dass der AFM-Bild passen. </li><li> Laden der AFM-Bild der Probe in der SVG-Editor. </li><li> Neues Nanostrukturelemente auf der AFM-Bild überlagert. </li></ol></li><li> Laden Sie die SVG-Datei in die Nanolithographie-Programm. </li><li> Führen Sie die Lithographie-Software, um eine leitende Nanostruktur erstellen. <ol><li> Verwenden V Spitze = +10 V Nanostrukturen erstellen und V Spitze = -10 V bis Nanostrukturen zu löschen. </li><li> Bewegen Sie den c-AFM-Spitze mit einer Geschwindigkeit von 200 nm / s bis 2 &amp;mgr; m / Sek. </li></ol></li></ol> 5. Cooles Gerät und Messungen <ol><li> Schalten Sie alle weißen Lichtern und roten Filter verwenden / Lichtquellen. </li><li> Extrahieren der Probe von der AFM-System. </li><li> Legen Sie die Probe in die Verdünnungs Kühlschrank (A). </li><li> Messen von Widerstand gegen Temperatur (B), während die Probe gekühlt wird. </li><li> Messen Sie Transporteigenschaften bei niedrigen Temperaturen (C). </li></ol>

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The authors have nothing to disclose.

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

Oxide Hetero 1-5 zeigen eine bemerkenswert große Auswahl an emergent physikalische Phänomene, die sowohl wissenschaftlich interessanten und potentiell nützlich für Anwendungen, 4 sind. Insbesondere kann die Schnittstelle zwischen LaAlO 3 (LAO) und SrTiO3 (STO) 6 Isolations zeigen, Dirigieren, supraleitenden 7, ferroelektrischen artigen 8 und 9 ferromagnetischen Verhalten. Im Jahr 2006, Thiel et al zeigten, dass 10 gibt es eine scharfe Isolator-Metall-Übergang als die Dicke des LAO Schicht erhöht, mit einer kritischen Dicke von 4 Elementarzellen (4uc). Es wurde anschließend gezeigt, dass 3uc-LAO/STO Strukturen weisen eine Hysterese-Übergang, der lokal mit einem leitenden Rasterkraftmikroskop (AFM-c) Fühler 11 gesteuert werden kann. Die Eigenschaften der Oxid-Schnittstellen wie LaAlO 3 / SrTiO 3 abhängig von der Abwesenheit oder Anwesenheit von leitendenElektronen an der Grenzfläche. Diese Elektronen können mit Top-Gate-Elektroden 12,13, Rücken-Tore 10 gesteuert werden, Oberflächenadsorbaten 14, ferroelektrischen Schichten 15,16 und c-AFM-Lithographie 11. Eine einzigartige Funktion von c-AFM-Lithographie ist, dass sehr kleine Nanostrukturen erstellt werden können. Elektrische Top-Gating, kombiniert mit zweidimensionalen Haft wird oft verwendet, um Quantenpunkte in III-V-Halbleitern 17 erstellen. Alternativ können quasi-eindimensionalen Halbleiter-Nanodrähte elektrisch Nähe blendet werden. Die Verfahren zur Herstellung dieser Strukturen sind zeitaufwendig und in der Regel irreversibel. Demgegenüber ist die C-AFM Lithographietechnik reversibel in dem Sinn, dass eine Nanostruktur kann aus einem Experiment erzeugt werden, und dann &quot;gelöscht&quot; (ähnlich einer Tafel). Im Allgemeinen wird c-AFM Schreiben mit an die AFM Spitze angelegt positive Spannungen durchgeführt, während das Löschenwird unter Verwendung von negativen Spannungen. Die erforderlich ist, um eine bestimmte Struktur zu schaffen Zeit hängt von der Komplexität der Vorrichtung ist jedoch in der Regel weniger als 30 min; die meiste Zeit verbracht Löschen der Leinwand. Die typische räumliche Auflösung ist etwa 10 Nanometern, aber mit der richtigen Abstimmung bietet so klein wie 2 Nanometer erzeugt werden 18. Eine detaillierte Beschreibung der Herstellung der nanoskaligen Verfahren folgt. Das Detail hier bereitgestellten sollte ausreichen, damit ähnliche Experimente von interessierten Forschern durchgeführt werden können. Die hier beschriebene Methode hat viele Vorteile gegenüber herkömmlichen lithographischen Methoden verwendet, um elektronische Nanostrukturen in Halbleitern zu schaffen. Die hier beschriebene c-AFM Lithographieverfahren ist Teil eines viel umfassenderen Klasse von Rastersondenlithographie-basierte Bemühungen, einschließlich Scannen anodische Oxidation 19, Dip-Pen-Nanolithographie 20, piezoelektrische Muster21, und so weiter. Die c-AFM-Technik hier beschrieben, verbunden mit der Verwendung von neuen Oxid-Schnittstellen können einige der höchsten präzise elektronische Strukturen mit einer beispiellosen Vielfalt von physikalischen Eigenschaften herzustellen.

<table><tbody><tr><td>Equipment</td><td></td><td></td><td></td></tr><tr><td>Contact Aligner</td><td>Karl-Suss</td><td>MA6</td><td></td></tr><tr><td>Spinner</td><td>Solitec</td><td>5110C</td><td></td></tr><tr><td>Ion Mill</td><td>Commonwealth Scientific</td><td>8C</td><td></td></tr><tr><td>Sputtering System</td><td>Leybold-Heraeus</td><td>Z-650</td><td></td></tr><tr><td>Barrel Etcher</td><td>Branson/IPC</td><td>3000C</td><td></td></tr><tr><td>Wire Bonder</td><td>Westbond</td><td>7700E</td><td></td></tr><tr><td>AFM</td><td>Asylum Research</td><td>MFP-3D</td><td></td></tr><tr><td>Dilution Refrigerator</td><td>Quantum Design</td><td>P850</td><td></td></tr><tr><td>Ultrasonic Wash Machine</td><td>Fisher Scientific</td><td>15-335-6</td><td></td></tr><tr><td>Current Amplifier</td><td>Femto</td><td>DLPCA-200</td><td></td></tr><tr><td>Materials</td><td></td><td></td><td></td></tr><tr><td>LaAlO&lt;sub&gt;3&lt;/sub&gt;/SrTiO&lt;sub&gt;3&lt;/sub&gt;</td><td>Prof. Chang-Beom Eom</td><td></td><td>5 mm x 1 mm with ~3.4 unit cells of LAO (See Reference 18)</td></tr><tr><td>Photoresist</td><td>AZ Electronic Materials</td><td>P4210</td><td></td></tr><tr><td>Developer</td><td>AZ Electronic Materials</td><td>400K</td><td></td></tr><tr><td>Acetone</td><td>Fisher Scientific</td><td>A929SK-4</td><td></td></tr><tr><td>Isopropyl Alcohol</td><td>Fisher Scientific</td><td>A459-1</td><td></td></tr><tr><td>Deionized Water</td><td>Fisher Scientific</td><td>23-290-065</td><td></td></tr><tr><td>Gold Wire</td><td>DuPont</td><td>5771</td><td>1 mm diameter</td></tr><tr><td>Chip Carrier</td><td>NTK Technologies</td><td>IRK28F1-5451D</td><td></td></tr></tbody></table>

writing and low-temperature characterization of oxide nanostructures

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

Die hier gezeigten Ergebnisse sind repräsentativ für das Transportverhalten, das von dieser Klasse von Nanostrukturen ausgestellt werden können, und an anderer Stelle im Detail 23-26 beschrieben. In diesem Beispiel wurde ein Nanodraht-Hohlraum ist von einem 3.3 Einheitszelle LAO / STO-Heterostruktur ausgebildet (Fig. 4). Leitfähige Wegen (grün dargestellt) sind in der Regel 10 nm breit, wie von Nanodraht bestimmt &quot;cutting&quot;-Experimente 11. Die Spitzengeschwindigkeit und die Spannung für jedes Segment unabhängig einstellbar von Lithographie Vorderseite (4B), so ist die Spitze Schreibgeschwindigkeit. &quot;Virtuelle Elektroden&quot;, die Schnittstelle mit den Grenzflächen der Kontakte zu gewährleisten, dass es eine gut leitende elektrische Verbindung zu den Nanostrukturen. Nachdem die Nanostruktur geschrieben wird, wird es dem Verdünnungskühler überführt. Lichtexposition bei oder unter 550 nm unerwünschte Photoleitung erzeugen, so ist es important, um das Gerät bei Dunkelheit oder mit Hilfe von einem roten &quot;Dunkelkammer&quot; Licht (5A) zu übertragen. Elektrische Verbindungen sollten bei RT hergestellt werden, und wie bei den meisten Halbleiternanostrukturen, sollte darauf geachtet werden, beim Wechsel elektrischen Verbindungen bei kryogenen Temperaturen. Wenn die Geräte elektrostatischer Entladung ausgesetzt ist, wird es wahrscheinlich geworden isolierend. Bemerkenswert ist, kann das Gerät die Funktionalität von &quot;Radfahren&quot; der Temperatur auf 300 K und Abkühlen wieder zurückgewonnen werden. Während des Abkühlens ist es Routine, um die Zweianschlusswiderstand zu überwachen, und auch die Vier-Anschluß-Widerstand als Funktion der Temperatur. Aus diesen Messungen wird eine Wechselspannung (typischerweise ~ 1 mV) bei einer niedrigen Frequenz (&lt;10 Hz) an eine der Elektroden angelegt wird, während der Netzstrom wird unter Verwendung eines Transimpedanzverstärkers gemessen. Lock-In-Demodulation und Filterung mit einem Heim-entwickelten Lock-In-Verstärker durchgeführt. Die Wechsel current wird als eine Funktion der Temperatur (5B) beobachtet. Sobald das Gerät an die Basistemperatur des Mischungskühlers (50 mK) abgekühlt ist, werden vier-terminale Transportmessungen durchgeführt (5C). Für diese Messungen wird der Strom durch den Hauptkanal der Vorrichtung bezogen, während die Spannung über der Vorrichtung wird gleichzeitig gemessen. Anstelle der Messung mit einem Lock-in-Verstärker, einem vollen Strom-Spannungs-(IV)-Kurve wird gemessen. Diese Methode enthält mehr Informationen und die Differentialleitung kann über numerische Differentiation berechnet werden. Für die besondere Vorrichtung wird der Differenzleitungs als Funktion der Seitengatespannung V SG gemessen. Dieses Gatter kann das chemische Potential des Gerätes geändert werden. Der Transport durch das Gerät zeigt eine starke nicht-monotonen Abhängigkeit, was auf Regionen, in denen Coulomb-Blockade für kleinere Werte stattfindet, und strong Supraleitung für größere Werte von V sg. Einzelheiten über das physikalische Interpretation für diese Geräteklasse wird an anderer Stelle beschrieben werden. <img alt="Figur 1" src="/files/ftp_upload/51886/51886fig1highres.jpg" /> .. Abbildung 1 Photolithographische Verarbeitungsschritte Schritt 1: Spin Photolack. Schritt 2: aussetzen Photolack mit Mask Aligner. Schritt 3: Photolack zu entwickeln. Schritt 4: Ionenfräsen. Schritt 5: DC-Sputtern Ti und Au zu hinterlegen. Schritt 6: Lift-Off. Schritt 7: die Hinterlegung der zweiten Schicht. Schritt 8: Plasmareinigung. <img alt="Figur 2" src="/files/ftp_upload/51886/51886fig2highres.jpg" /> Abbildung 2. Bilder von lithographisch LAO / STO-Heterostrukturen. (A) Bild zeigt 5mm x 5mm Probe Draht zu einem Chipträger verbunden. (B)<html> Optische Bild zeigt Bond-Pads und einer der Leinwände. (C) Close-up von einer einzigen Leinwand. <a href="https://www-jove-com.bdigitaluss.remotexs.co/files/ftp_upload/51886/51886fig2highres.jpg" target="_blank">Bitte klicken Sie hier, um eine größere Version dieser Figur zu sehen.</a> <img alt="Fig. 3" src="/files/ftp_upload/51886/51886fig3highres.jpg" /> Abbildung 3. (A) Informelle Design der LAO / STO Nanostruktur. (B) Präzise Layout der Nanostruktur unter Verwendung eines Open-Source-skalierbare Vektorgrafiken (SVG)-Editor. <img alt="Fig. 4" src="/files/ftp_upload/51886/51886fig4highres.jpg" /> Abbildung 4. (A) Lithographie Frontplatte für c-AFM-Strukturierung. (B) Screenshot von 3D-Simulator, die Position und die Spannung der c-AFM-Spitze.w.jove.com/files/ftp_upload/52058/52058fig4large.jpg &quot;target =&quot; _blank &quot;&gt; Bitte klicken Sie hier, um eine größere Version dieser Figur zu sehen. <img alt="Figur 5" src="/files/ftp_upload/51886/51886fig5highres.jpg" /> 5. (A) LAO / STO Nanostruktur ist in Verdünnungskühlers in Abhängigkeit von der einge. (B) Überwachung des Messwiderstand, wenn es von 300 K auf 50 mK gekühlt. (C) Überwachen von vier Anschlüssen der differentiellen Leitfähigkeit der Vorrichtung Seiten-Gate-Spannung Vsg und Spannung an der Vorrichtung (V4t). Intensity Graph in Einheiten von Siemens (S), und Spannungen angezeigt werden in Einheiten von Volt (V) angezeigt.

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.

Schreiben und Niedertemperatur-Charakterisierung von Nanostrukturen

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

Universidad San Sebastian

Research

JoVE Journal

Engineering

9.9K Aufrufe.  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.

Serie: Writing and Low-Temperature Characterization of Oxide Nanostructures

Angle-resolved Photoemission Spectroscopy At Ultra-low Temperatures

The physical properties of a material are defined by its electronic structure. Electrons in solids are characterized by energy (&omega;) and momentum (k) and the probability to find them in a particular state with given &omega; and k is described by the spectral function A(k, &omega;). This function can be directly measured in an experiment based on the well-known photoelectric effect, for the explanation of which Albert Einstein received the Nobel Prize back in 1921. In the photoelectric effect the light shone on a surface ejects electrons from the material. According to Einstein, energy conservation allows one to determine the energy of an electron inside the sample, provided the energy of the light photon and kinetic energy of the outgoing photoelectron are known. Momentum conservation makes it also possible to estimate k relating it to the momentum of the photoelectron by measuring the angle at which the photoelectron left the surface. The modern version of this technique is called Angle-Resolved Photoemission Spectroscopy (ARPES) and exploits both conservation laws in order to determine the electronic structure, i.e. energy and momentum of electrons inside the solid. In order to resolve the details crucial for understanding the topical problems of condensed matter physics, three quantities need to be minimized: uncertainty* in photon energy, uncertainty in kinetic energy of photoelectrons and temperature of the sample.
In our approach we combine three recent achievements in the field of synchrotron radiation, surface science and cryogenics. We use synchrotron radiation with tunable photon energy contributing an uncertainty of the order of 1 meV, an electron energy analyzer which detects the kinetic energies with a precision of the order of 1 meV and a He3 cryostat which allows us to keep the temperature of the sample below 1 K. We discuss the exemplary results obtained on single crystals of Sr2RuO4 and some other materials. The electronic structure of this material can be determined with an unprecedented clarity.

The overall goal of this method is to determine the low-energy electronic structure of solids at ultra-low temperatures using Angle-Resolved Photoemission Spectroscopy with synchrotron radiation.

Angle-Photoemissionsspektroskopie Bei extrem niedrigen Temperaturen

The physical properties of a material are defined by its  electronic structure. Electrons in solids are characterized by energy (&omega;)  and momentum ...

Forschung

Ingenieurwesen

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

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

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

Herstellung von transparenten leitenden Oxide durch Pulsed Laser Deposition Nano-engineered

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

Fabrication of Spatially Confined Complex Oxides

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

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

Herstellung von räumlich getrennter komplexe Oxide

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

Atomically Defined Templates for Epitaxial Growth of Complex Oxide Thin Films

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

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

Atomar definierte Vorlagen Epitaxieausrüstung komplexer Oxide Thin Films

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

Chemie

Preparation and Reactivity of Gasless Nanostructured Energetic Materials

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

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

Vorbereitung und Reaktivität von Gaslose Nanostrukturierte Energetische Materialien

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

Atomically Traceable Nanostructure Fabrication

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

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

Atomar Traceable Nanostrukturen

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

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

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

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

Erweiterte Experimentelle Methoden für Niedertemperatur-Magneto Messung der 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 ...

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

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

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

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

Wachstum und elektrostatischen/chemischen Eigenschaften von Metall/LaAlO3/SrTiO3 Heterostrukturen

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

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

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

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

Bulk- und Dünnschicht-Synthese von kompositorisch Variante Entropie-stabilisierten Oxide

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

Tuning Oxide Properties by Oxygen Vacancy Control During Growth and Annealing

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

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

Einstellen der Oxideigenschaften durch Sauerstoff-Fehlstellen-Kontrolle während des Wachstums und Glühens

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