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. Ottenere LAO / STO Eterostrutture <ol><li> Ottenere un eterostruttura ossido costituito da 3.4 celle elementari di LAO coltivati ​​da deposizione laser pulsata su TiO substrati STO 2-terminati. Dettagli di crescita campione sono descritti in rif. 22. </li></ol> 2. Fotolitografica Trattamento dei campioni Creare contatti elettrici per l&#39;interfaccia LAO / STO, con cuscinetti di legame per tele di cablaggio ad un chip carrier. Le singole fasi di lavorazione sono descritte in dettaglio di seguito. <ol><li> Spin fotosensibile <ol><li> Spin photoresist sui campioni a 600 rpm per 5 secondi, poi a 4000 rpm per 30 sec. Lo strato fotosensibile sarà spessore di circa 2 micron. Cuocere i campioni a 95 ° C per 1 min. </li></ol></li><li> Esporre photoresist utilizzando un allineatore maschera con luce 320 nm per 100 sec con una dose di 5 mW / cm 2. </li><li> Sviluppare il photoresist in sviluppatore fotosensibile for 1 min. </li><li> Ion fresatura <ol><li> Utilizzare un mulino ioni Ar + per rimuovere i 15 nm di materiale (LAO e STO) nelle zone non coperte da photoresist. Porre i campioni con un angolo di 22,5 ° rispetto alla direzione perpendicolare al fascio di ioni Ar + in entrata. Se la velocità di attacco Ar + non è tarato, eseguire una corsa di taratura per garantire la corretta quantità di materiale viene rimosso. Determinare la profondità di incisione con AFM o profilmetry equivalente. </li></ol></li><li> DC sputtering di Ti e Au <ol><li> Cassetta 4 nm Ti, poi 25 nm Au sui campioni in modo che l&#39;Au fa contatto elettrico con lo strato STO esposto. La pressione sputtering è nell&#39;intervallo 2-6 x 10 -7 Torr, e lo sputtering avviene con il campione a temperatura ambiente. Pre-polverizzazione catodica Ti per 10 min con otturatore chiuso a 100 W, poi otturatore aperto e polverizzazione catodica per 20 secondi a 100 W. Al termine, immediatamente pre-sputter Au per 1 min a 50 W poi polverizzare Au per 30 sec per i campioni a 50 W. CaliBrate il tempo per produrre gli spessori Ti e Au desiderati. </li></ol></li><li> Lift-off <ol><li> Utilizzare lavaggio ultrasonico Acetone / IPA per rimuovere photoresist dalla superficie dei campioni. </li></ol></li><li> Secondo strato <ol><li> Un secondo processo litografico, escluso il punto 4 (ie., Escludendo la fresatura di ioni), viene utilizzato per creare i collegamenti dei cavi d&#39;oro ai singoli pad legame. I due modelli devono essere ben allineate per garantire che essi non producono cortocircuiti. </li></ol></li><li> Pulizia al plasma. <ol><li> Un IPC Barrel Etcher viene utilizzato per rimuovere il photoresist residuo nella trincea pattern. Lo strumento utilizzato al 100 W e 1 Torr argon per 1 min </li></ol></li></ol> 3. Wire James Bond un campione prepararsi per la scrittura <ol><li> Montare il campione LAO / STO in un chip carrier (Figura 2A) con 28 pin disponibili. </li><li> Struttura legame Wire </li></ol> NOTA: Utilizzare un bonder filo per fare c elettricaollegamenti tra i rilievi di legame sul campione e il chip carrier. Attaccare 1 mil (25 micron) fili d&#39;oro tra i contatti elettrici e il chip carrier. Scrivi nanostrutture 4. Scrivere Nanostrutture <ol><li> Creare uno schizzo informale della nanostruttura conduttrice (Figura 3A). </li><li> Aprire le Scalable Vector Graphics (SVG), montaggio (Figura 3B). <ol><li> Utilizzare un modello o definire le dimensioni della finestra in base a quella dell&#39;immagine AFM. </li><li> Caricare l&#39;immagine AFM del campione nell&#39;editor SVG. </li><li> Creare elementi di nanostrutture sovrapposte l&#39;immagine AFM su. </li></ol></li><li> Caricare il file SVG nel programma nanolitografia. </li><li> Eseguire il software di litografia per creare una nanostruttura conduttrice. <ol><li> Suggerimento Utilizzare V = +10 V per creare nanostrutture, e mancia V = -10 V per cancellare nanostrutture. </li><li> Spostare la punta c-AFM ad una velocità compresa tra 200 nm / sec a 2 micron / sec. </li></ol></li></ol> 5. Raffreddare dispositivo e prendere le misure <ol><li> Spegnere tutte le luci bianche e utilizzare filtri rosso / sorgenti luminose. </li><li> Estrarre il campione dal sistema AFM. </li><li> Caricare il campione in frigorifero diluizione (A). </li><li> Misurare la resistenza in funzione della temperatura (B) come il campione viene raffreddato. </li><li> Misurare le proprietà di trasporto a basse temperature (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.

Eterostrutture Ossido 1-5 mostrano una notevole varietà di fenomeni fisici emergenti che sono sia scientificamente interessante e potenzialmente utile per le applicazioni 4. In particolare, l&#39;interfaccia tra LaAlO 3 (LAO) e SrTiO 3 (STO) 6 può esibire isolante, conduzione, superconduttori 7, ferroelettrici come 8 e 9 comportamento ferromagnetico. Nel 2006, Thiel et al hanno dimostrato 10 che c&#39;è una transizione netta isolante-metallo come lo spessore dello strato LAO viene aumentata, con uno spessore critico di 4 celle unitarie (4uc). Successivamente è stato dimostrato che le strutture 3uc-LAO/STO presentano una transizione isteresi che può essere controllato localmente con un conduttore microscopio a forza atomica (AFM-c) sonda 11. Le proprietà delle interfacce ossido come LaAlO 3/3 SrTiO dipendono dalla assenza o presenza di condurreelettroni all&#39;interfaccia. Questi elettroni possono essere controllate utilizzando migliori elettrodi di gate 12,13, schiena Portone 10, superficie adsorbati 14 strati ferroelettrici 15,16 e c-AFM litografia 11. Una caratteristica unica di c-AFM litografia è che molto piccole caratteristiche nanoscala possono essere creati. Gating top elettrico, in combinazione con la reclusione bidimensionale, viene spesso utilizzato per creare punti quantici di semiconduttori III-V 17. In alternativa, nanofili semiconduttori quasi-unidimensionali possono essere gated elettricamente dalla vicinanza. I metodi per produrre queste strutture sono in termini di tempo e generalmente irreversibile. Al contrario, la tecnica litografia c-AFM è reversibile, nel senso che una nanostruttura può essere creato per un esperimento, e poi &quot;cancellata&quot; (simile ad una lavagna). Generalmente, scrittura c-AFM viene eseguita con tensioni positive applicate alla punta AFM, mentre, cancellandoviene eseguita utilizzando tensioni negative. Il tempo necessario per creare una particolare struttura dipende dalla complessità del dispositivo, ma è di solito meno di 30 min; maggior parte del tempo viene speso cancellando la tela. La risoluzione spaziale tipica è di circa 10 nanometri, ma con la sintonizzazione corretta caratteristiche piccolo come 2 nanometri possono essere creati 18. Una descrizione dettagliata della procedura di fabbricazione su scala nanometrica segue. Il dettaglio fornito qui dovrebbe essere sufficiente a consentire esperimenti simili da eseguire da ricercatori interessati. Il metodo qui descritto presenta numerosi vantaggi rispetto agli approcci litografiche tradizionali utilizzati per creare nanostrutture elettronici nei semiconduttori. Il metodo di litografia c-AFM qui descritto è parte di una classe molto più ampia di iniziative litografia a base di scansione a sonda, tra cui la scansione di ossidazione anodica 19, dip-pen nanolitografia 20, patterning piezoelettrico21, e così via. La tecnica c-AFM qui descritto, insieme con l&#39;uso di interfacce ossido nuovi, può produrre alcune delle strutture elettroniche massima precisione con una varietà senza precedenti di proprietà fisiche.

<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.

I risultati mostrati qui sono rappresentative del comportamento dei trasporti che può essere esposto da questa classe di nanostrutture, ed è stato descritto altrove in dettaglio 23-26. In questo esempio, una cavità nanofili è stato costruito (figura 4) da una eterostruttura LAO cella 3,3 unità / STO. Percorsi conduttivi (in verde) sono tipicamente 10 nm di larghezza, come determinato dal nanowire &quot;tagliando&quot; esperimenti 11. La velocità di punta e la tensione per ogni segmento è configurabile in modo indipendente dal pannello di litografia anteriore (Figura 4B), così come la velocità di scrittura di punta. &quot;Elettrodi virtuali&quot; che si interfacciano con i contatti interfacciali assicurano che vi sia una connessione elettrica altamente conduttivo sulle nanostrutture. Dopo la nanostruttura è scritto, è trasferito al frigorifero diluizione. L&#39;esposizione alla luce o al di sotto di 550 nm produrrà photoconduction indesiderato, quindi è important trasferire il dispositivo al buio o con l&#39;ausilio di un rosso &quot;camera oscura&quot; luce (Figura 5A). I collegamenti elettrici devono essere effettuate a temperatura ambiente, e come con la maggior parte delle nanostrutture di semiconduttori, grande attenzione dovrebbero essere prese quando si cambia i collegamenti elettrici a temperature criogeniche. Se i dispositivi vengono sottoposti a scariche elettrostatiche, molto probabilmente diventerà isolante. Sorprendentemente, la funzionalità può essere recuperato da &quot;bicicletta&quot; la temperatura di 300 K e raffreddamento di nuovo. Durante cooldown, è di routine per monitorare la resistenza a due terminali, e anche la resistenza a quattro terminali, in funzione della temperatura. Per queste misure una tensione alternata (tipicamente ~ 1 mV) viene applicato ad una bassa frequenza (&lt;10 Hz) a uno degli elettrodi, mentre la corrente alternata è misurata con un amplificatore di transimpedenza. Lock-in demodulazione e il filtraggio viene eseguita utilizzando un amplificatore lock-in casa-sviluppato. Il cu acrrent viene monitorata in funzione della temperatura (Figura 5B). Una volta che il dispositivo viene raffreddata alla temperatura di base del frigorifero diluizione (50 mK), misure di trasporto a quattro terminali vengono eseguite (Figura 5C). Per le misurazioni di corrente viene prelevato attraverso il canale principale del dispositivo, mentre la tensione ai capi del dispositivo viene misurata simultaneamente. Invece di misurare con un amplificatore lock-in, un pieno corrente-tensione (IV) traccia viene misurata. Questo metodo contiene più informazioni e la conduzione differenziale può essere calcolato tramite differenziazione numerica. Per il particolare dispositivo, la conduzione differenziale è misurata in funzione del lato sg-gate tensione V. Questa porta consente il potenziale chimico del dispositivo da modificare. Il trasporto attraverso il dispositivo mostra una forte dipendenza non monotona, indicando regioni in cui Coulomb blocco avviene per i valori più piccoli, e strong la superconduttività per i più grandi valori di V sg. Dettagli sulla interpretazione fisica per questa classe di dispositivi saranno descritte altrove. <img alt="Figura 1" src="/files/ftp_upload/51886/51886fig1highres.jpg" /> .. Figura 1, fasi di lavorazione fotolitografiche Fase 1: centrifuga fotosensibile. Fase 2: esporre photoresist utilizzando la maschera allineatore. Fase 3: sviluppare fotosensibile. Fase 4: fresatura di ioni. Fase 5: DC sputtering a depositare Ti e Au. Fase 6: lift-off. Fase 7: depositare il secondo strato. Fase 8: pulizia plasma. <img alt="Figura 2" src="/files/ftp_upload/51886/51886fig2highres.jpg" /> Figura 2. Immagini di lithographically fantasia eterostrutture LAO / STO. (A) Immagine che mostra 5mm x 5mm campione filo legato a un chip carrier. (B)<html> Ottico d&#39;immagine che mostra i rilievi di legame e una delle tele. (C) Close-up di un&#39;unica tela. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/51886/51886fig2highres.jpg" target="_blank">cliccate qui per vedere una versione più grande di questa figura.</a> <img alt="Figura 3" src="/files/ftp_upload/51886/51886fig3highres.jpg" /> Figura 3. (A) progettazione informale dei LAO / STO nanostruttura. (B) disposizione precisa di nanostrutture utilizzando un open-source di grafica vettoriale scalabile (SVG) montaggio. <img alt="Figura 4" src="/files/ftp_upload/51886/51886fig4highres.jpg" /> Figura 4. (A) litografia pannello anteriore per c-AFM patterning. (B) la posizione e la tensione di punta c-AFM Screenshot dal simulatore 3D che mostra.w.jove.com/files/ftp_upload/52058/52058fig4large.jpg &quot;target =&quot; _blank &quot;&gt; Clicca qui per vedere una versione più grande di questa figura. <img alt="Figura 5" src="/files/ftp_upload/51886/51886fig5highres.jpg" /> Figura 5. (A) LAO / STO nanostruttura essendo inserito in diluizione frigorifero. (B) Controllo di resistenza campione viene raffreddato da 300 K a 50 mK. (C) Controllo di conduttanza differenziale a quattro terminali di dispositivo in funzione della Vsg tensione cancello laterale e tensione ai capi del dispositivo (V4T). Grafico di intensità visualizzato in unità di siemens (S), e le tensioni sono visualizzati in unità di volt (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.

Scrittura e bassa temperatura Caratterizzazione di nanostrutture di ossido

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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Engineering

9.9K Views.  University of Pittsburgh. Oxide nanostructures provide new opportunities for science and technology. The interfacial conductivity between LaAlO3 and SrTiO3 can be controlled with near-atomic precision using a conductive atomic force microscopy technique. The protocol for creating and measuring conductive nanostructures at LaAlO3/SrTiO3 interfaces is demonstrated.

Video: Writing and Low-Temperature Characterization of Oxide Nanostructures

Angle-resolved Photoemission Spectroscopy At Ultra-low Temperatures

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

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

Angolo-spettroscopia di fotoemissione risolta A ultra-basse temperature

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

Ricerca

Ingegneria

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.

Fabbricazione di nano-ingegneria trasparenti Ossidi Conducting da 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, ...

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.

Fabbricazione di ossidi complessi spazialmente confinati

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.

Modelli atomicamente definiti per epitassiale crescita di ossido Complex Thin Films

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

Chimica

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.

Preparazione e reattività di gasless Nanostrutturati materiali energetici

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.

Atomicamente tracciabile nanostrutture

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.

Metodi sperimentali avanzati per bassa temperatura magnetotrasporto Misura di nuovi materiali

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.

Crescita ed elettrostatico/chimica proprietà di metallo/LaAlO3/SrTiO3 eterostrutture

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.

Massa e sintesi di Film sottile di ossidi compositivamente varianti entropia-stabilizzato

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.

Regolazione delle proprietà dell'ossido mediante il controllo del vuoto di ossigeno durante la crescita e la ricottura

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