Name: seedless growth of bismuth nanowire array via vacuum thermal evaporation
Uploaded: 2015-12-21T13:00:00.000+00:00
Duration: 8 min 58 s
Description: Watch this Scientific Journal Video about Seedless Growth of Bismuth Nanowire Array via Vacuum Thermal Evaporation at JoVE.com

Research is carried out at the Center for Functional Nanomaterials, Brookhaven National Laboratory, which is supported by the U.S. Department of Energy, Office of Basic Energy Sciences, under Contract No. DE-SC0012704.

Attenzione: Si prega di consultare tutte le schede di sicurezza pertinenti (MSDS) prima dell&#39;uso. I nanomateriali possono avere rischi aggiuntivi rispetto alla loro controparte massa. Si prega di utilizzare tutte le pratiche di sicurezza appropriate quando si maneggiano i substrati nanomateriali coperte, compreso l&#39;uso di controlli tecnici (cappa) e dispositivi di protezione individuale (occhiali, guanti, camice, pantaloni a figura intera, chiuso-toe scarpe). 1. Lavori preparatori <ol><li> Preparazione del sistema di deposizione di vapore <ol><li> Sfiatare la camera di deposizione a pressione atmosferica e aprire la camera. La ventilazione avviene premendo il pulsante &quot;Start PC Ventilazione&quot; sull&#39;interfaccia software di controllo, che si avvia automaticamente una sequenza che la camera di sfogo di pressione atmosferica. Raggiunta la pressione atmosferica aprire la camera tirando la porta che accede anteriore. </li><li> Montare una barca evaporazione del tungsteno (allumina rivestito) tra una coppia di elettrodi evaporazione termica. Posizionare 1pellet g bismuto nella barca di evaporazione. </li><li> Montare un obiettivo di vanadio sputtering alla sorgente magnetron sputtering. Vedere il passo 1.1.4) per sistema di deposizione che non è dotato di una sorgente di sputtering. </li><li> (Opzionale, per sistema di deposizione che non è dotato di una sorgente di sputtering) Montare una barca evaporazione del tungsteno fra una coppia di elettrodi evaporazione termica. Mettere 0,5 g lumache vanadio nella barca evaporazione. </li><li> Collegare i connettori mini-banane (due per il riscaldamento / raffreddamento di alimentazione e due per sonda di temperatura) del controller di temperatura a circuito chiuso per il passante elettrico del sistema di deposizione. </li></ol></li><li> Preparazione di substrati di crescita Nota: La formazione di nanofili bismuto è insensibile al substrato di crescita di scelta. Risultati simili sono stati ottenuti dal vetrino, wafer di silicio, o lamiera. È raccomandato da che il substrato deve essere pulito immediatamente prima il vapore gli autoriprocesso di deposizione, al fine di ottenere un&#39;adesione coerente del sottostrato vanadio. Varie tecniche di pulizia substrato, compresa la pulizia al plasma e pulizia chimica umida, possono essere applicati e portano a risultati analoghi. <ol><li> Pulizia dei substrati di crescita di plasma di ossigeno <ol><li> Posizionare i substrati di crescita in un pulitore di plasma e pompare la camera, premendo il tasto &quot;VAC ON&quot;, per la sua pressione di base di 10 mTorr. </li><li> Aprire la valvola del gas di ossigeno e di introdurre il gas ossigeno nella camera premendo il tasto &quot;GAS&quot; sul pannello frontale e regolare la portata premendo i pulsanti &quot;DECR&quot; per il controllo della portata di gas &quot;INCR&quot; e per mantenere una pressione della camera di circa 100 mTorr. </li><li> Impostare la potenza del plasma a 20 W premendo i pulsanti &quot;DECR&quot; &quot;INCR&quot; e per il controllo del potere e accendere il plasma premendo il tasto &quot;RF ON&quot;. </li><li> Attendere 5 minuti prima di spegnere il plasma premendo il tasto &quot;; RF ON &quot;. Pulsante Vent camera premendo il pulsante&quot; BLEED &quot;e recuperare i substrati. </li></ol></li><li> Pulizia dei substrati di crescita con il metodo chimico bagnato <ol><li> Immergere i substrati di crescita in acetone contenute in un becher. Porre il bicchiere in un ultrasonicatore e sonicare per 2 minuti alla massima potenza. </li><li> Rimuovere i substrati dal bicchiere e sciacquare con un flusso di alcol assoluto da un flacone di lavaggio per 30 sec. </li><li> Essiccare i substrati in un flusso di azoto gassoso. </li></ol></li></ol></li><li> Substrato carico e sistema di deposizione di pompaggio <ol><li> Montare il gruppo di controllo temperatura del substrato al titolare substrato. </li><li> Utilizzare fermagli per montare i substrati di crescita sopra il gruppo refrigerante / riscaldamento Peltier. </li><li> Montare il supporto substrato completamente assemblato nella camera di deposizione di vapore, con i substrati di fronte alle sorgenti di deposizione. Collegare i passanti elettrici allaPeltier raffreddamento / gruppo riscaldante. </li><li> Chiudere l&#39;otturatore substrato per evitare la deposizione involontaria al substrato. </li><li> Iniziare a pompare lungo la camera di deposizione. Il pompaggio avviene premendo il pulsante &quot;Start PC pompaggio&quot; sull&#39;interfaccia software di controllo, che si avvia automaticamente una sequenza che pompa la camera per la sua pressione di base. </li></ol></li></ol> 2. Crescita di bismuto Nanofili Nota: L&#39;esperimento non si muove al passo successivo fino alla pressione di base della camera di deposizione ha raggiunto 2 × 10 -6 Torr o inferiore. <ol><li> La deposizione di sottostrato vanadio Nota: La migliore riproducibilità sperimentale si ottiene quando il sottostrato vanadio viene depositato dal metodo magnetron sputtering. In assenza di una fonte di sputtering, alta riproducibilità può essere ancora ottenuto depositando sottostrato vanadio con metodo di evaporazione termica, a condizione che il sistema di deposizione hasa bassa pressione di base (≤ 5 × 10 -7 Torr). Fare riferimento al punto 3.1.2 per i dettagli. <ol><li> Vanadium deposizione con una sorgente magnetron sputtering. <ol><li> Inizia flusso argon nell&#39;origine sputtering. Impostare la velocità di flusso di 40 sccm. </li><li> Regolare la velocità di rivoluzione della pompa turbomolecolare per una pressione della camera di 2,5 mTorr. </li><li> Mentre la camera sta raggiungendo gradualmente la sua pressione stato stazionario, impostare i fattori di calibrazione spessore al QCM. Per vanadio, la densità è 5.96 g / cm 3 e Z-fattore è 0.530. </li><li> Accendere la sorgente sputtering DC e impostare la potenza 200-250 W. Per il sistema di deposizione operata dagli autori, la velocità di deposizione è di circa 0,4 A / sec a questa potenza. Senza aprire l&#39;otturatore substrato, mantenere la sorgente corsa per 2 min. NOTA: Tramite questo passo l&#39;ossido nativo sulla fonte di vanadio è rimosso, esponendo la superficie di vanadio fresco. </li><li> Aprire l&#39;otturatore substrato per iniziare Depositio vanadion. Nel frattempo, ripristinare lo spessore accumulato della QCM a zero. </li><li> Continuare deposizione fino uno spessore apparente di 20 nm è accumulato, per lettura QCM. Chiudere l&#39;otturatore substrato. </li><li> Gradualmente diminuire la potenza polverizzazione a zero. Spegnere la sorgente. </li><li> Chiudere il flusso di argon. Riportare la pompa turbomolecolare per tutta la sua potenza. </li></ol></li><li> (Opzionale, per sistema di deposizione che non è dotato di una sorgente di sputtering) Vanadio deposizione con una sorgente di evaporazione termica. <ol><li> Dato l&#39;elevato punto di fusione di vanadio (1.910 ° C) e la sua disponibilità all&#39;ossidazione, si raccomanda che la sua evaporazione termica per essere condotta ad una pressione di base di 5 × 10 -7 Torr o inferiore. </li><li> Impostare i fattori di calibrazione spessore al QCM. Per vanadio, la densità è 5.96 g / cm 3 e Z-fattore è 0.530. </li><li> Accendere evaporazione termica alimentazione alla fonte di vanadio.Lentamente aumentare la potenza di riscaldamento alla barca tungsteno fino a quando i proiettili vanadio fondono. </li><li> Con l&#39;otturatore substrato mantenuta chiusa, lentamente aumentare la potenza di riscaldamento fino a una velocità di deposizione di 2 Å / s si ottiene, per la lettura QCM. Aprire l&#39;otturatore substrato per iniziare la deposizione di vanadio. Nel frattempo, ripristinare lo spessore accumulato della QCM a zero. </li><li> Continuare fino a quando un deposito di spessore apparente di 50 nm è accumulato. Chiudere l&#39;otturatore substrato. </li><li> Gradualmente diminuire la potenza evaporazione termica a zero. Spegnere la sorgente. </li></ol></li></ol></li><li> La deposizione di nanofili bismuto <ol><li> Per la deposizione di bismuto a temperatura superiore o inferiore RT, impostare il valore desiderato per il regolatore di temperatura. Attendere fino al raggiungimento della temperatura desiderata. </li><li> Impostare i fattori di calibrazione spessore al QCM. Per bismuto, la densità è 9.78 g / cm 3 e Z-fattore è 0,790. </li><li> Accendere il evaporazione termica supplicare alla sorgente di bismuto. Lentamente aumentare la potenza di riscaldamento alla barca tungsteno fino a quando la velocità di deposizione di 2 Å / s si ottiene, per la lettura QCM. </li><li> Aprire l&#39;otturatore substrato per iniziare la deposizione di bismuto. Nel frattempo, ripristinare lo spessore accumulato della QCM a zero. </li><li> Continuare fino a quando un deposito di spessore apparente di 50 nm è accumulato. Chiudere l&#39;otturatore substrato. </li><li> Gradualmente diminuire la potenza evaporazione termica a zero. Spegnere la sorgente. </li><li> Spegnere alimentazione del dispositivo di raffreddamento / riscaldamento elettrico termico. </li><li> Sfiatare la camera di deposizione a pressione atmosferica e aprire la camera. Recuperare il supporto substrato e raccogliere i nanofili bismuto substrati coperti. </li></ol></li></ol>

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Authors have nothing to disclose.

La crescita di nanofili bismuto deve essere condotta in un sistema di deposizione da vapore fisico con almeno due fonti di deposizione, uno per bismuto e un&#39;altra per vanadio. Si raccomanda che una delle fonti è una sorgente magnetron sputtering, per la deposizione di vanadio. Alto vuoto si ottiene un pompe turbomolecolari sostenuta da una pompa di scorrimento a secco. Il sistema di deposizione di vapore è dotato di una microbilancia al quarzo calibrata (QCM) per il monitoraggio in situ spessore. Il siste...

Nanowires limitano il trasporto di portatori di carica e altri quasiparticelle, come fotoni e plasmoni in una dimensione. Di conseguenza, nanofili di solito presentano nuove proprietà elettriche, magnetiche, ottiche e chimiche, che accordano loro potenziale pressoché infinita per applicazioni in micro / nano elettronica, fotonica, tecnologie biomedicali, ambientali ed energetiche. 1,2 Nel corso degli ultimi due decenni, numerosi top-down e bottom-up sono stati sviluppati per la sintesi di una vasta gamma di metalli o semiconduttori nanofili di alta qualità a livello di laboratorio. 3-6 Nonostante questi sviluppi, ogni approccio si basa su alcune proprietà uniche del prodotto finale per il suo successo. Per esempio, il metodo popolare vapore-liquido-solido (VLS) è migliore misura per i materiali semiconduttori che hanno punti di fusione più alti e formano lega eutettica con corrispondenti &quot;semi&quot; catalitici. 7 Di conseguenza, la sintesi di un nanofilomateriale di particolare interesse non può essere coperta da tecniche esistenti. Come un semimetallo con piccola sovrapposizione indiretta banda (-38 meV a 0 K) e portatori di carica insolitamente leggeri, bismuto è un esempio. Il materiale si comporta radicalmente diverso in dimensioni ridotte rispetto al loro volume, il confinamento quantistico potrebbe girare nanofili bismuto o film sottili in una stretta banda proibita semiconduttori. 8-12 Nel frattempo, la superficie di un metallo bismuto forme quasi-bidimensionale che è significativamente più metallico di suo ingombro. 13,14 È stato mostrato che la superficie di bismuto raggiunge una mobilità elettronica di 2 × 10 4 cm -1 2 V sec -1 e contribuisce fortemente alla sua termoelettrica in forma nanofili. 15 Come tale, ci sono interessi significativi di studio nanofili bismuto per elettronica e in particolare le applicazioni termoelettriche. 12-16 Tuttavia, a causa di bismuto molto bassopunto di fusione (544 K) e la disponibilità per l&#39;ossidazione, essa rimane una sfida di sintesi di alta qualità e singole nanofili bismuto cristallino con tecniche tradizionali di fase in fase di vapore o la soluzione. In precedenza, è stato riportato da alcuni gruppi che monocristallino nanofili bismuto crescono a bassa resa durante vuoto deposizione di film sottili di bismuto, che è attribuito al rilascio di stress incorporato nel film. 17-20 Recentemente, abbiamo scoperto un romanzo tecnica che si basa sulla evaporazione termica di bismuto sotto alto vuoto e porta alla formazione scalabile singoli nanofili bismuto cristallino ad alta resa. 21 Confrontando precedentemente riferito metodi, la caratteristica più unica di questa tecnica è che il substrato di crescita è appena rivestito con un sottile strato di nanoporoso vanadio prima bismuto deposizione. Durante evaporazione termica di quest&#39;ultimo, vapore bismuto infiltra nella struttura nanoporoso del furgonepellicola Adium e condensa lì come nanodomini. Dal momento che il vanadio risulti umido per bismuto condensata, i domini infiltrate vengono successivamente espulsi dalla matrice di vanadio a rilasciare la loro energia di superficie. È l&#39;espulsione continua delle nanodomini bismuto che formano nanofili bismuto verticali. Poiché i domini bismuto sono solo 1-2 nm di diametro, sono soggetti alla soppressione significativa punto di fusione, che li rende quasi fuso a RT. Come risultato, la crescita nanofili procede con il substrato presso RT. D&#39;altra parte, come la migrazione dei domini bismuto viene attivato termicamente, la lunghezza e la larghezza dei nanofili possono essere sintonizzati in un ampio intervallo, semplicemente controllando la temperatura del substrato di crescita. Questo protocollo dettagliato video è destinato per aiutare i nuovi operatori del settore evitare vari problemi comuni associati con deposizione di vapore fisico di film sottili sotto vuoto spinto, ambiente privo di ossigeno.

<table><tbody><tr><td>Bismuth</td><td>Sigma-Aldrich</td><td>556130</td><td>Granular, 99.999%</td></tr><tr><td>Vanadium Slug</td><td>Alfa Aesar</td><td>42829</td><td>3.175&amp;nbsp;mm (0.125&amp;nbsp;in) dia x 6.35&amp;nbsp;mm (0.25&amp;nbsp;in) length, 99.8%</td></tr><tr><td>Vanadium Sputtering Target</td><td>Kurt J. Lesker</td><td>EJTVXXX253A2</td><td>3.00&quot; Dia. x 0.125&quot; Thick, 99.5%</td></tr><tr><td>Acetone</td><td>Sigma-Aldrich</td><td>179124</td><td>&gt;99.5%</td></tr><tr><td>Ethanol</td><td>Alfa Aesar</td><td>33361</td><td>Anhydrous</td></tr><tr><td>Silicon Wafer</td><td>University Wafers</td><td></td><td>300 microns in thickness, (100) orientation</td></tr><tr><td>Silver Filled Epoxy</td><td>Circuit Works</td><td>CW2400</td><td>Two part conductive epoxy resin</td></tr><tr><td>Tungsten Boat, Alumina Coated</td><td>R. D. Mathis</td><td>S9B-AO-W</td><td>For bismuth thermal evaporation</td></tr><tr><td>Tungsten Boat</td><td>R. D. Mathis</td><td>S4-.015W</td><td>For vanadium thermal evaporation</td></tr><tr><td>RIE Plasma</td><td>Nordson March</td><td>CS-1701</td><td></td></tr><tr><td>PVD 75 Vapor Deposition Platform</td><td>Kurt J. Lesker</td><td>PEDP75FTCLT001</td><td>Equipped with three thermal evaporation source and one DC magnetron sputtering source</td></tr><tr><td>Thermoelectric Temperature Controller</td><td>LairdTech</td><td>MTTC-1410</td><td></td></tr><tr><td>PT1000 RGD</td><td>LairdTech</td><td>340912-01</td><td>Temperature sensor for MTTC-1410</td></tr><tr><td>Thermoelectric Module</td><td>LairdTech</td><td>56910-502</td><td></td></tr><tr><td>Ultrasonicator</td><td>Crest Ultrasonics</td><td>Tru-Sweep 175</td><td></td></tr></tbody></table>

seedless growth of bismuth nanowire array via vacuum thermal evaporation

Ecco una tecnica senza semi e senza modello è dimostrato scalably crescere nanofili di bismuto, per evaporazione termica in alto vuoto a temperatura ambiente. Convenzionalmente riservato per la fabbricazione di film sottili metallici, depositi evaporazione termica bismuto in un array di nanofili verticali monocristallino su una sottile pellicola piatta di vanadio tenuto a RT, che è appena depositato mediante sputtering o evaporazione magnetron termico. Controllando la temperatura del substrato di crescita la lunghezza e la larghezza dei nanofili possono essere sintonizzati in un ampio intervallo. Responsabile di questo romanzo è una tecnica finora sconosciuta meccanismo di crescita nanowire che radici nella la porosità mite del film sottile di vanadio. Infiltrata nei pori vanadio, i domini bismuto (~ 1 nm) trasportano eccessiva energia superficiale che sopprime il loro punto di fusione e li espelle continuamente dalla matrice di vanadio per formare nanofili. Questa scoperta dimostra la fattibilità del vapore scalabile fase di synthESIS di elevata purezza nanomateriali senza l&#39;uso di catalizzatori.

Le immagini a sezione trasversale SEM di sottostrati vanadio formate da magnetron sputtering e metodi evaporazione termica sono presentati nella Figura 2. Microscopia elettronica a scansione (SEM) immagini sono rappresentati per nanofili bismuto formate a diverse temperature del substrato (Figura 3). La struttura cristallina dei nanofili bismuto viene determinata tramite microscopia elettronica a trasmissione (TEM), selettivo zona diffrazione di elettroni (SAED), e diff...

Watch this Scientific Journal Video about Seedless Growth of Bismuth Nanowire Array via Vacuum Thermal Evaporation at JoVE.com

Seedless Growth of Bismuth Nanowire Array via Vacuum Thermal Evaporation

A protocol for seedless and high yield growth of bismuth nanowire arrays through vacuum thermal evaporation technique is presented.

Crescita senza semi di bismuto Nanowire Array via Vacuum evaporazione termica

Here a seedless and template-free technique is demonstrated to scalably grow bismuth nanowires, through thermal evaporation in high vacuum at RT. ...

seedless-growth-bismuth-nanowire-array-via-vacuum-thermal

Universidad San Sebastian

Research

JoVE Journal

Engineering

8.3K Views.  Brookhaven National Laboratory. A protocol for seedless and high yield growth of bismuth nanowire arrays through vacuum thermal evaporation technique is presented. 

Video: Seedless Growth of Bismuth Nanowire Array via Vacuum Thermal Evaporation

Fabrication, Densification, and Replica Molding of 3D Carbon Nanotube Microstructures

The introduction of new materials and processes to microfabrication has, in large part, enabled many important advances in microsystems, lab-on-a-chip devices, and their applications. In particular, capabilities for cost-effective fabrication of polymer microstructures were transformed by the advent of soft lithography and other micromolding techniques 1, 2, and this led a revolution in applications of microfabrication to biomedical engineering and biology. Nevertheless, it remains challenging to fabricate microstructures with well-defined nanoscale surface textures, and to fabricate arbitrary 3D shapes at the micro-scale. Robustness of master molds and maintenance of shape integrity is especially important to achieve high fidelity replication of complex structures and preserving their nanoscale surface texture. The combination of hierarchical textures, and heterogeneous shapes, is a profound challenge to existing microfabrication methods that largely rely upon top-down etching using fixed mask templates. On the other hand, the bottom-up synthesis of nanostructures such as nanotubes and nanowires can offer new capabilities to microfabrication, in particular by taking advantage of the collective self-organization of nanostructures, and local control of their growth behavior with respect to microfabricated patterns. 
Our goal is to introduce vertically aligned carbon nanotubes (CNTs), which we refer to as CNT "forests", as a new microfabrication material. We present details of a suite of related methods recently developed by our group: fabrication of CNT forest microstructures by thermal CVD from lithographically patterned catalyst thin films; self-directed elastocapillary densification of CNT microstructures; and replica molding of polymer microstructures using CNT composite master molds. In particular, our work shows that self-directed capillary densification ("capillary forming"), which is performed by condensation of a solvent onto the substrate with CNT microstructures, significantly increases the packing density of CNTs. This process enables directed transformation of vertical CNT microstructures into straight, inclined, and twisted shapes, which have robust mechanical properties exceeding those of typical microfabrication polymers. This in turn enables formation of nanocomposite CNT master molds by capillary-driven infiltration of polymers. The replica structures exhibit the anisotropic nanoscale texture of the aligned CNTs, and can have walls with sub-micron thickness and aspect ratios exceeding 50:1. Integration of CNT microstructures in fabrication offers further opportunity to exploit the electrical and thermal properties of CNTs, and diverse capabilities for chemical and biochemical functionalization 3.

We present methods for fabrication of patterned microstructures of vertically aligned carbon nanotubes (CNTs), and their use as master molds for production of polymer microstructures with organized nanoscale surface texture. The CNT forests are densified by condensation of solvent onto the substrate, which significantly increases their packing density and enables self-directed formation of 3D shapes.

Molding Fabrication, densificazione e Replica di microstrutture 3D Nanotubi di carbonio

The introduction of new materials and processes to microfabrication has, in large part, enabled many important advances in microsystems, lab-on-a-chip ...

Ricerca

Ingegneria

Dry Oxidation and Vacuum Annealing Treatments for Tuning the Wetting Properties of Carbon Nanotube Arrays

In this article, we describe a simple method to reversibly tune the wetting properties of vertically aligned carbon nanotube (CNT) arrays. Here, CNT arrays are defined as densely packed multi-walled carbon nanotubes oriented perpendicular to the growth substrate as a result of a growth process by the standard thermal chemical vapor deposition (CVD) technique.1,2 These CNT arrays are then exposed to vacuum annealing treatment to make them more hydrophobic or to dry oxidation treatment to render them more hydrophilic. The hydrophobic CNT arrays can be turned hydrophilic by exposing them to dry oxidation treatment, while the hydrophilic CNT arrays can be turned hydrophobic by exposing them to vacuum annealing treatment. Using a combination of both treatments, CNT arrays can be repeatedly switched between hydrophilic and hydrophobic.2 Therefore, such combination show a very high potential in many industrial and consumer applications, including drug delivery system and high power density supercapacitors.3-5
The key to vary the wettability of CNT arrays is to control the surface concentration of oxygen adsorbates. Basically oxygen adsorbates can be introduced by exposing the CNT arrays to any oxidation treatment. Here we use dry oxidation treatments, such as oxygen plasma and UV/ozone, to functionalize the surface of CNT with oxygenated functional groups. These oxygenated functional groups allow hydrogen bond between the surface of CNT and water molecules to form, rendering the CNT hydrophilic. To turn them hydrophobic, adsorbed oxygen must be removed from the surface of CNT. Here we employ vacuum annealing treatment to induce oxygen desorption process. CNT arrays with extremely low surface concentration of oxygen adsorbates exhibit a superhydrophobic behavior.

This article describes a simple method to fabricate vertically aligned carbon nanotube arrays by CVD and to subsequently tune their wetting properties by exposing them to vacuum annealing or dry oxidation treatment.

Ossidazione a secco e vuoto ricottura Trattamenti per accordare le proprietà di bagnabilità di matrici di nanotubi di carbonio

In this article, we describe a simple method to reversibly  tune the wetting properties of vertically aligned carbon nanotube (CNT) arrays.  Here, CNT ...

Ultrahigh Density Array of Vertically Aligned Small-molecular Organic Nanowires on Arbitrary Substrates

In recent years &pi;-conjugated organic semiconductors have emerged as the active material in a number of diverse applications including large-area, low-cost displays, photovoltaics, printable and flexible electronics and organic spin valves. Organics allow (a) low-cost, low-temperature processing and (b) molecular-level design of electronic, optical and spin transport characteristics. Such features are not readily available for mainstream inorganic semiconductors, which have enabled organics to carve a niche in the silicon-dominated electronics market. The first generation of organic-based devices has focused on thin film geometries, grown by physical vapor deposition or solution processing. However, it has been realized that organic nanostructures can be used to enhance performance of above-mentioned applications and significant effort has been invested in exploring methods for organic nanostructure fabrication.	
A particularly interesting class of organic nanostructures is the one in which vertically oriented organic nanowires, nanorods or nanotubes are organized in a well-regimented, high-density array. Such structures are highly versatile and are ideal morphological architectures for various applications such as chemical sensors, split-dipole nanoantennas, photovoltaic devices with radially heterostructured "core-shell" nanowires, and memory devices with a cross-point geometry. Such architecture is generally realized by a template-directed approach. In the past this method has been used to grow metal and inorganic semiconductor nanowire arrays. More recently &pi;-conjugated polymer nanowires have been grown within nanoporous templates. However, these approaches have had limited success in growing nanowires of technologically important &pi;-conjugated small molecular weight organics, such as tris-8-hydroxyquinoline aluminum (Alq3), rubrene and methanofullerenes, which are commonly used in diverse areas including organic displays, photovoltaics, thin film transistors and spintronics.	
Recently we have been able to address the above-mentioned issue by employing a novel "centrifugation-assisted" approach. This method therefore broadens the spectrum of organic materials that can be patterned in a vertically ordered nanowire array. Due to the technological importance of Alq3, rubrene and methanofullerenes, our method can be used to explore how the nanostructuring of these materials affects the performance of aforementioned organic devices. The purpose of this article is to describe the technical details of the above-mentioned protocol, demonstrate how this process can be extended to grow small-molecular organic nanowires on arbitrary substrates and finally, to discuss the critical steps, limitations, possible modifications, trouble-shooting and future applications.

We report a simple method for fabricating an ultrahigh density array of vertically ordered small-molecular organic nanowires. This method allows for synthesis of complex heterostructured hybrid nanowire geometries, which can be inexpensively grown on arbitrary substrates. These structures have potential applications in organic electronics, optoelectronics, chemical sensing, photovoltaics and spintronics.

Altissima densità Array of allineato verticalmente Nanofili organici piccola molecolari su substrati arbitrarie

In  recent years &pi;-conjugated  organic semiconductors have emerged as the active material in a number of  diverse applications including large-area, ...

Analysis of Contact Interfaces for Single GaN Nanowire Devices

Single GaN nanowire (NW) devices fabricated on SiO2 can exhibit a strong degradation after annealing due to the occurrence of void formation at the contact/SiO2 interface. This void formation can cause cracking and delamination of the metal film, which can increase the resistance or lead to a complete failure of the NW device. In order to address issues associated with void formation, a technique was developed that removes Ni/Au contact metal films from the substrates to allow for the examination and characterization of the contact/substrate and contact/NW interfaces of single GaN NW devices. This procedure determines the degree of adhesion of the contact films to the substrate and NWs and allows for the characterization of the morphology and composition of the contact interface with the substrate and nanowires. This technique is also useful for assessing the amount of residual contamination that remains from the NW suspension and from photolithographic processes on the NW-SiO2 surface prior to metal deposition. The detailed steps of this procedure are presented for the removal of annealed Ni/Au contacts to Mg-doped GaN NWs on a SiO2 substrate.

A technique was developed that removes Ni/Au contact metal films from their substrate to allow for the examination and characterization of the contact/substrate and contact/NW interfaces of single GaN nanowire devices.

Analisi di contatto Interfacce semplici dispositivi GaN nanowire

Single GaN nanowire (NW) devices fabricated on SiO2 can exhibit  a strong degradation after annealing due to the  occurrence of void formation at the ...

Monolayer Contact Doping of Silicon Surfaces and Nanowires Using Organophosphorus Compounds

Monolayer Contact Doping (MLCD) is a simple method for doping of surfaces and nanostructures1. MLCD results in the formation of highly controlled, ultra shallow and sharp doping profiles at the nanometer scale. In MLCD process the dopant source is a monolayer containing dopant atoms.
In this article a detailed procedure for surface doping of silicon substrate as well as silicon nanowires is demonstrated. Phosphorus dopant source was formed using tetraethyl methylenediphosphonate monolayer on a silicon substrate. This monolayer containing substrate was brought to contact with a pristine intrinsic silicon target substrate and annealed while in contact. Sheet resistance of the target substrate was measured using 4 point probe. Intrinsic silicon nanowires were synthesized by chemical vapor deposition (CVD) process using a vapor-liquid-solid (VLS) mechanism; gold nanoparticles were used as catalyst for nanowire growth. The nanowires were suspended in ethanol by mild sonication. This suspension was used to dropcast the nanowires on silicon substrate with a silicon nitride dielectric top layer. These nanowires were doped with phosphorus in similar manner as used for the intrinsic silicon wafer. Standard photolithography process was used to fabricate metal electrodes for the formation of nanowire based field effect transistor (NW-FET). The electrical properties of a representative nanowire device were measured by a semiconductor device analyzer and a probe station.

A detailed procedure for surface doping of Silicon interfaces is provided. The ultra-shallow surface doping is demonstrated by using phosphorus containing monolayers and rapid annealing process. The method can be used for doping of macroscopic area surfaces as well as nanostructures.

Monostrato Contatto doping di silicio superfici e nanofili Uso organofosforici Composti

Monolayer Contact Doping (MLCD) is a simple method for doping of surfaces and nanostructures1. MLCD results in the formation of highly controlled, ultra ...

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

Fabrication of Carbon Nanotube High-Frequency Nanoelectronic Biosensor for Sensing in High Ionic Strength Solutions

The unique electronic properties and high surface-to-volume ratios of single-walled carbon nanotubes (SWNT) and semiconductor nanowires (NW) 1-4 make them good candidates for high sensitivity biosensors. When a charged molecule binds to such a sensor surface, it alters the carrier density5 in the sensor, resulting in changes in its DC conductance. However, in an ionic solution a charged surface also attracts counter-ions from the solution, forming an electrical double layer (EDL). This EDL effectively screens off the charge, and in physiologically relevant conditions ~100 millimolar (mM), the characteristic charge screening length (Debye length) is less than a nanometer (nm). Thus, in high ionic strength solutions, charge based (DC) detection is fundamentally impeded6-8.
We overcome charge screening effects by detecting molecular dipoles rather than charges at high frequency, by operating carbon nanotube field effect transistors as high frequency mixers9-11. At high frequencies, the AC drive force can no longer overcome the solution drag and the ions in solution do not have sufficient time to form the EDL. Further, frequency mixing technique allows us to operate at frequencies high enough to overcome ionic screening, and yet detect the sensing signals at lower frequencies11-12. Also, the high transconductance of SWNT transistors provides an internal gain for the sensing signal, which obviates the need for external signal amplifier.
Here, we describe the protocol to (a) fabricate SWNT transistors, (b) functionalize biomolecules to the nanotube13, (c) design and stamp a poly-dimethylsiloxane (PDMS) micro-fluidic chamber14 onto the device, and (d) carry out high frequency sensing in different ionic strength solutions11.

We describe the device fabrication and measurement protocol for carbon nanotube based high frequency biosensors. The high frequency sensing technique mitigates the fundamental ionic (Debye) screening effect and allows nanotube biosensor to be operated in high ionic strength solutions where conventional electronic biosensors fail. Our technology provides a unique platform for point-of-care (POC) electronic biosensors operating in physiologically relevant conditions.

Fabbricazione di Nanotubi di carbonio ad alta frequenza Nanoelectronic biosensore per la rilevazione in alta forza ionica Solutions

The unique electronic properties and high surface-to-volume ratios of single-walled carbon nanotubes (SWNT) and semiconductor nanowires (NW) 1-4 make them ...

Bioingegneria

Synthesis of Substrate-Bound Au Nanowires Via an Active Surface Growth Mechanism

Advancing synthetic capabilities is important for the development of nanoscience and nanotechnology. The synthesis of nanowires has always been a challenge, as it requires asymmetric growth of symmetric crystals. Here, we report a distinctive synthesis of substrate-bound Au nanowires. This template-free synthesis employs thiolated ligands and substrate adsorption to achieve the continuous asymmetric deposition of Au in solution at ambient conditions. The thiolated ligand prevented the Au deposition on the exposed surface of the seeds, so the Au deposition only occurs at the interface between the Au seeds and the substrate. The side of the newly deposited Au nanowires is immediately covered with the thiolated ligand, while the bottom facing the substrate remains ligand-free and active for the next round of Au deposition. We further demonstrate that this Au nanowire growth can be induced on various substrates, and different thiolated ligands can be used to regulate the surface chemistry of the nanowires. The diameter of the nanowires can also be controlled with mixed ligands, in which another &#34;bad&#34; ligand could turn on the lateral growth. With the understanding of the mechanism, Au nanowire-based nanostructures can be designed and synthesized.

We report a solution-based method to synthesize substrate-bound Au nanowires. By tuning the molecular ligands used during the synthesis, the Au nanowires can be grown from various substrates with different surface properties. Au nanowire-based nanostructures can also be synthesized by adjusting the reaction parameters.

Sintesi di nanofili Au associato a substrato tramite un meccanismo di crescita superficiale attiva

Advancing synthetic capabilities is important for the development of nanoscience and nanotechnology. The synthesis of nanowires has always been a ...

A Standard and Reliable Method to Fabricate Two-Dimensional Nanoelectronics

Two-dimensional (2D) materials have attracted huge attention due to their unique properties and potential applications. Since wafer scale synthesis of 2D materials is still in nascent stages, scientists cannot fully rely on traditional semiconductor techniques for related research. Delicate processes from locating the materials to electrode definition need to be well controlled. In this article, a universal fabrication protocol required in manufacturing nanoscale electronics, such as 2D quasi-heterojunction bipolar transistors (Q-HBT), and 2D back-gated transistors are demonstrated. This protocol includes the determination of material position, electron beam lithography (EBL), metal electrode definition, et al. A step by step narrative of the fabrication procedures for these devices are also presented. Furthermore, results show that each of the fabricated devices has achieved high performance with high repeatability. This work reveals a comprehensive description of process flow for preparing 2D nano-electronics, enables the research groups to access this information, and pave the way toward future electronics.

The article aims to introduce a standard and reliable fabrication procedure for the development of future low dimensional nanoelectronics.

Un metodo Standard e affidabile per fabbricare nanoelettronica bidimensionale

Two-dimensional (2D) materials have attracted huge attention due to their unique properties and potential applications. Since wafer scale synthesis of 2D ...

Fabrication of Schottky Diodes on Zn-polar BeMgZnO/ZnO Heterostructure Grown by Plasma-assisted Molecular Beam Epitaxy

Heterostructure field effect transistors (HFETs) utilizing a two dimensional electron gas (2DEG) channel have a great potential for high speed device applications. Zinc oxide (ZnO), a semiconductor with a wide bandgap (3.4 eV) and high electron saturation velocity has gained a great deal of attention as an attractive material for high speed devices. Efficient gate modulation, however, requires high-quality Schottky contacts on the barrier layer. In this article, we present our Schottky diode fabrication procedure on Zn-polar BeMgZnO/ZnO heterostructure with high density 2DEG which is achieved through strain modulation and incorporation of a few percent Be into the MgZnO-based barrier during growth by molecular beam epitaxy (MBE). To achieve high crystalline quality, nearly lattice-matched high-resistivity GaN templates grown by metal-organic chemical vapor deposition (MOCVD) are used as the substrate for the subsequent MBE growth of the oxide layers. To obtain the requisite Zn-polarity, careful surface treatment of GaN templates and control over the VI/II ratio during the growth of low temperature ZnO nucleation layer are utilized. Ti/Au electrodes serve as Ohmic contacts, and Ag electrodes deposited on the O2 plasma pretreated BeMgZnO surface are used for Schottky contacts.

Attainment of high-quality Schottky contacts is imperative for achieving efficient gate modulation in heterostructure field effect transistors (HFETs). We present the fabrication methodology and characteristics of Schottky diodes on Zn-polar BeMgZnO/ZnO heterostructures with high-density two dimensional electron gas (2DEG), grown by plasma-assisted molecular beam epitaxy on GaN templates.

Fabbricazione di diodi Schottky su Zn-polar eterostruttura BeMgZnO/ZnO cresciuto di epitassia da fasci molecolari assistita da Plasma

Heterostructure field effect transistors (HFETs) utilizing a two dimensional electron gas (2DEG) channel have a great potential for high speed device ...