A. Maker è stato sostenuto da una Fondazione Annenberg Graduate Research Fellowship, e questo lavoro è stato sostenuto dal National Science Foundation [085281 e 1028440].

1. Microsfera Fabrication <ol><li> Selezionare una piccola quantità (circa 5 pollici) di fibra ottica, strip ~ 1.5 &quot;rivestimento da una estremità e pulire sia con metanolo o etanolo (Figura 1a, b). </li><li> Se disponibile, attaccatevi alla fine con una mannaia in fibra ottica. Se non disponibile, tagliato con tronchesi o forbici tali che ~ 0.5 &quot;è a sinistra. Il vantaggio di utilizzare una fibra ottica mannaia è che produce molto liscia, taglio uniforme come in figura 1b. Rugosità eccessiva o difetti di un taglio può causare reflow irregolare, abbassando il fattore di qualità delle sfere risultanti. </li><li> Esporre l&#39;estremità della fibra pulita per 3W di potenza del laser CO 2 focalizzato a una dimensione del diametro di 500μm ~ ~ posto per 1 secondo (Figura 1c, d, e). Questo produce sfere ~~~HEAD=NNS 200μm di diametro, tuttavia, la dimensione può essere regolata aumentando o diminuendo il diametro della fibra ottica. Leggermente regolando l&#39;intensità del laser può anche be necessario sfere reflow più o meno grandi. </li></ol> 2. Microtoroid Fabrication <ol><li> Progettare e realizzare una fotomaschera con scuri, cerchi pieni, nella spaziatura e il diametro della vostra scelta. È importante notare che i prodotti toroidi sarà 25-30% inferiore dei cerchi sulla maschera. Ad esempio, un cerchio pieno con un diametro di 100 micron produrrà un toroide con un diametro di circa 75 micron. Inoltre, si raccomanda di lasciare almeno 1-2mm di spazio tra ogni cerchio e di almeno 5 mm di spazio tra le matrici di cerchio e attorno ai bordi della maschera. Poiché i wafer campioni deve essere maneggiato con attenzione con una pinzetta, è importante per lasciare spazio per le pinze per afferrare senza danneggiare i toroidi. Lo spazio extra fornisce anche spazio per una fibra ottica rastremata coppia di luce nei dispositivi finiti, e consente di campioni di essere tagliati in piccoli array più facilmente. Per questa procedura, abbiamo usato una maschera con file di 160 micron dicerchi di diametro compreso ~ 1 millimetro di distanza, con ~ 5 mm di spazio tra una fila di cerchi. I toroidi sono finiti circa 110 micron di diametro. </li><li> Inizia con wafer di silicio con uno strato di 2 micron di spessore di silicio cresciuto termicamente. Fendere i wafer per adattarsi al modello desiderato microfloppy sulla maschera fotolitografia, lasciando spazio per photoresist bordo del tallone. Si noti che all&#39;inizio di fabbricazione, di solito è più conveniente per incidere più array di cerchi su grandi pezzi di wafer di silicio (~ diversi cm x cm diversi). Wafer più grandi consentono fotolitografia e incisione BOE di più campioni alla volta, e sono più facilmente trattato con una pinzetta. Più tardi, prima della fase 2 XEF attacco, si raccomanda di fendere i wafer più grandi in piccoli array per consentire un rapido, più uniforme XEF 2 incisione. </li><li> In un fumehood, pulire accuratamente i wafer risciacquando con acetone, metanolo, isopropanolo e acqua deionizzata. Soffiare i campioni asciugare con un azoto o comp filtrataressed fucile ad aria compressa, e metterli su una piastra calda impostata a 120 ° C per almeno 2 minuti per asciugarsi. </li><li> Dopo aver fatto raffreddare i wafer, metterli in un infiammabili / solvente fumehood ed esporre a HMDS per 2 minuti con il metodo di deposizione del vapore. Un semplice metodo di deposizione del vapore: mettere alcune gocce di HMDS in un bicchiere da 10 ml piccola e quindi coprire i wafer e piccolo becher con un contenitore di vetro più grande per contenere il vapore. </li><li> Porre un campione su un filatore con un supporto di dimensioni adeguate. Utilizzo di un contagocce o siringa e filtro, applicare photoresist al campione. Spin cappotto photoresist S1813 su ogni campione per 5 secondi a 500rpm, seguiti da 45 secondi a 3000rpm. Bordo rimozione tallone non è necessaria se il wafer è sufficientemente grande in modo che il tallone bordo non interferisce con il patterning. </li><li> Morbida cuocere il fotoresist su una piastra calda a 95 ° C per 2 minuti. </li><li> Utilizzando un allineatore maschera UV e la fotomaschera desiderato, esporre il fotoresist coperti campioni ad untotale di 80mJ/cm 2 di radiazioni UV. </li><li> Porre i campioni in MF-321 sviluppatore per rimuovere il fotoresist che è stato esposto a luce UV. Durante lo sviluppo, strettamente guardare il fotoresist viene rimosso dal wafer e disciolto. È importante agitare / swish il contenitore costantemente durante questo processo per assicurare il fotoresist viene rimosso uniformemente. Per i parametri indicati, il photoresist impiega circa 30 secondi per lo sviluppo. </li><li> Quando la maggior parte del photoresist indesiderato si è dissolta nello sviluppatore, lavare i campioni accuratamente sotto acqua corrente, soffiare delicatamente asciugare i campioni utilizzando una pistola ad aria o di azoto, e ispezionare i campioni con un microscopio per assicurare tutti i photoresist indesiderato è stato rimosso. Se necessario, i campioni possono essere immersi nuovamente in sviluppatore, tuttavia, si dovrebbe stare attenti a non overdevelop i campioni, come i modelli di photoresist desiderati potrebbe essere danneggiato. (Se i modelli desiderati sono danneggiato o difettoso, il fotoresist può essererimosso con acetone e gradini 2,1-2,9 può essere ripetuto). </li><li> Dopo aver sviluppato, risciacquare accuratamente i campioni in acqua corrente, soffiare delicatamente asciugare i campioni, e duro li cuocere su una piastra calda a 110 ° C per 2 minuti. Questo passaggio riscalda il fotoresist di sopra della sua temperatura di transizione vetrosa, reflow il fotoresist e rugosità parzialmente riparazione che durante il processo di sviluppo. </li><li> Utilizzando Teflon contenitori e dispositivi di protezione necessari, immergere i campioni in miglioramento tamponata ossido di mordenzante (BOE). BOE contiene HF, che incide la silice non coperta da fotoresist per formare pastiglie circolari silice sul wafer di silicio (Figura 2a-c). Migliorata tamponata HF produce un più agevole etch, riducendo al minimo ruvidità nei circoli di silice che ne derivano. Mentre è possibile mescolare tamponata HF iniziano 49% HF, questo può portare a risultati altamente variabili come tipicamente solo piccole quantità sono fatti. </li><li> Dopo circa 15-20 minuti (depending sulle dimensioni dei campioni, i modelli e numero di campioni), togliere i campioni dal BOE con Teflon pinzette. Sciacquare accuratamente i campioni in acqua corrente. La silice è stato rimosso quando i campioni diventano idrofobo. </li><li> Dopo incisione, risciacquo e asciugatura dei campioni, li ispezionare utilizzando un microscopio ottico. Verificare che i modelli desiderati sono stati incisi completamente e tutta la silice indesiderato è stato rimosso. Se necessario, restituire i campioni al BOE per l&#39;incisione ulteriormente. Bisogna stare attenti a non overetch i campioni, i modelli circolari o sotto il photoresist potrebbe essere danneggiato. </li><li> Una volta incisione BOE è completo, sciacquare i campioni in acqua deionizzata e asciugare. Se i campioni sono grandi pezzi di wafer di silicio, si raccomanda anche di tagliarli (utilizzando una sega a dadi o scriba diamante) in piccoli pezzi con singole righe di cerchi di silice. Singole righe di cerchi sono incise più rapidamente e uniformemente nel XEF2 fase di attacco (2.16). La polvere di silicio prodotta dal taglio viene rimosso durante la pulizia nel passaggio successivo. </li><li> Rimuovere il fotoresist lavando con acetone, metanolo, isopropanolo, e acqua deionizzata, e asciugare i campioni utilizzando una pistola azoto e riscaldamento a 120 ° C piastra calda per almeno 2 minuti. </li><li> Utilizzando un incisore XEF 2, inferiori al silicio sotto le pastiglie di silice circolari per formare minidischi di silice (Figura 2d-f). L&#39;importo inciso dovrebbe essere circa 1/3 della dimensione del cerchio di silice, in modo che il pilastro microfloppy risultante è di circa 1/3-1/2 del diametro totale del disco, come determinato mediante ispezione con un microscopio ottico. Il numero di impulsi XEF 2 e la durata di ciascun impulso dipende dalla quantità di silicio nella camera e il tipo di XEF 2 incisore utilizzato. </li><li> Dopo XEF 2 acquaforte, esporre i campioni ad un concentrato raggio laser CO 2 a circa 1Intensità di 2W per ~ 3 secondi o fino a quando si forma toroidale liscia (Figura 2 g-i). A seconda delle dimensioni esatte del disco e la quantità di XEF 2 inferiori, una intensità leggermente superiore o inferiore e il tempo di esposizione può essere necessario per formare un microtoroid. È importante che il centro del fascio laser e il centro del microfloppy sono allineate, in modo che la silice microfloppy formerà una superficie liscia, microtoroid circolare. </li></ol> 3. Risultati rappresentativi I dispositivi di microsfere e microtoroid possono essere esposte utilizzando sia la microscopia ottica e la microscopia elettronica a scansione (Figura 1d 2h, elettronici e Figura, I). In tutte le immagini, l&#39;uniformità della superficie del dispositivo è evidente. Per verificare che l&#39;approccio dettagliato crea ultra-high-Q dispositivi, si caratterizza anche il fattore Q di più dispositivi eseguendo un (Δλ) linewidth di misurazione e di calcolo del caricoQ dalla semplice espressione: Q = λ / Δλ = ωτ, dove λ = lunghezza d&#39;onda di risonanza, ω = frequenza, e τ = vita fotone. Spettri rappresentativa di ciascun dispositivo fabbricato utilizzando le procedure precedentemente dettagliate 1,9 e un grafico di confronto diversi dispositivi è mostrato in Figura 3. I fattori di qualità di tutti i dispositivi sono superiori a 10 milioni, con la maggioranza di essere superiore a 100 milioni di euro. Lo spettro della microsfera era una sola risonanza, che indica che la luce sia accoppiata in senso orario o antiorario modalità di propagazione ottica. Tuttavia, lo spettro del toroide mostrato una risonanza scissione, indicando che la luce accoppiata in entrambe le modalità in senso orario e antiorario contemporaneamente. Questo fenomeno si verifica quando vi è una leggera imperfezione nel sito di accoppiamento. Inserendo lo spettro di una doppia Lorentzian, il fattore Q di entrambe le modalità può essere determinato. La scissione fenomeno di risonanzana può verificarsi sia in sfera e risonatori toroide, ma è più frequentemente osservata in toroidi quanto sono più sensibili alle imperfezioni e avere un minor numero di modalità di ottiche rispetto a sfere. <img src="/files/ftp_upload/4164/4164fig1.jpg" alt="Figura 1"/> Figura 1. Diagramma di flusso del processo di fabbricazione microsfera cavità. a) Rendering e b) micrografia ottica di una fibra ottica pulito e tagliato. c) al microscopio Rendering, d) ed e ottica), la scansione al microscopio elettronico di un microspere risonatore. <img src="/files/ftp_upload/4164/4164fig2.jpg" alt="Figura 2"/> Figura 2. Diagramma di flusso del processo di fabbricazione microtoroid cavità. a) Rendering, b) vista dall&#39;alto micrografia ottica e c) vista laterale micrografia elettronica a scansione di ossido di pad circolare, come definito dalla fotolitografia e incisione BOE. Nota la leggera cuneo del ossido che è formato dal BOE. d) Rendering, e) vista dall&#39;altoal microscopio ottico e f) vista laterale scansione al microscopio elettronico del pad di ossido dopo la fase di incisione 2 XEF. Si noti che il disco ossido mantiene a cuneo periferia. g) Rendering, h) top-view al microscopio ottico e i) laterale vista al microscopio elettronico a scansione della cavità microtoroid. <img src="/files/ftp_upload/4164/4164fig3.jpg" alt="Figura 3"/> Figura 3. Qualità spettri rappresentativa del fattore a) microsfera eb) microtoroid cavità risonanti come determinato usando il metodo di misurazione della larghezza di riga. In molto elevate dispositivi Q, si può osservare la modalità di suddivisione o un doppio picco, in cui la luce riflessa un piccolo difetto e circola in entrambe le direzioni in senso orario e antiorario. c) Confronto grafico che mostra i fattori Q di microsfere diverse e microtoroid cavità risonanti. <a href="http://www.jove.com/files/ftp_upload/4164/4164fig3large.jpg" target="_blank">Clicca qui per ingrandire la figura</a> . Figura 4. Schematica del reflow laser CO 2 set-up. Il raggio laser CO 2 (linea continua blu) viene riflessa e poi focalizzata sul campione. Esso passa attraverso i 10,6 um / 633 nm fascio di combinazione, che trasmette 10,6 um e riflette 633 nm. Le immagini colonna ottiche il riflesso del campione fuori del combinatore di fascio, pertanto, l&#39;immagine è leggermente rosso. Un elenco dei componenti necessari per questa impostazione è in Tabella 4. <img src="/files/ftp_upload/4164/4164fig5.jpg" alt="Figura 5"/> Figura 5. Correttamente rifluire a) eb microsfere) microtoroid cavità risonanti. Grazie al posizionamento scorretto all&#39;interno del fascio, il dispositivo è mal-formato. c) Come risultato di una fotomaschera scarsa o litografia poveri, il toroide è luna forma.

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Come con qualsiasi struttura ottica, mantenere la pulizia ad ogni passo del processo di fabbricazione è di importanza critica. Come ci sono numerosi libri di testo scritti sul tema della litografia e di fabbricazione, i suggerimenti che seguono non intendono essere esaustivi, ma mettere in evidenza alcuni dei problemi più comuni, i ricercatori hanno dovuto affrontare. 19-20 Poiché l&#39;uniformità della periferia del microtoroid è determinata dalla uniformità del disco inizi...

<table border="1"><tbody><tr><td> Nome della parte </td><td> Azienda </td><td> Numero di catalogo </td><td> Comments </td></tr><tr><td> Fiber scriba </td><td> Newport </td><td> F-RFS </td><td> Opzionale </td></tr><tr><td> Fibra ottica </td><td> Newport </td><td> F-SMF-28 </td><td> Qualsiasi tipo di fibra ottica può essere utilizzata. </td></tr><tr><td> Fiber Rivestimento stripper </td><td> Newport </td><td> F-STR-175 </td><td> Spelafili può anche essere usato </td></tr><tr><td> Etanolo </td><td> Ogni vendor </td><td> Solvente-livello di purezza </td><td> Metanolo o isopropanolo sono sostituti </td></tr></tbody></table> Tabella 1. Materiali di fabbricazione microsfere. <table border="1"><tbody><tr><td> Nome del reattivo </td><td> Azienda </td><td> &lt;strong&gt; Numero di catalogo </td><td> Comments </td></tr><tr><td> Wafer di silicio con 2μm silice cresciuto termicamente </td><td> WRS Materiali </td><td> n / a </td><td> Usiamo intrinseca 8, &lt;100&gt;, 4 &quot;diametro </td></tr><tr><td> HMDS (esametildisilazano) </td><td> Aldrich </td><td> 440191 </td><td></td></tr><tr><td> Photoresist </td><td> Shipley </td><td> S1813 </td><td></td></tr><tr><td> Sviluppatore </td><td> Shipley </td><td> MF-321 </td><td></td></tr><tr><td> Tamponata HF - Migliorata </td><td> Transene </td><td> n / a </td><td> Il miglioramento HF tamponata dà fluida e, di migliore qualità rispetto alla semplice etch BOE o HF </td></tr><tr><td> Acetone, metanolo, isopropanolo </td><td> Ogni vendor </td><td> 99,8% di purezza </td><td></td></tr></tbody></table> Tabella 2. MicrMateriali di fabbricazione otoroid. <table border="1"><tbody><tr><td> Attrezzature Nome </td><td> Fabbricante </td><td> Numero di catalogo </td><td> Comments </td></tr><tr><td> Spinner </td><td> Solitec </td><td> 5110-ND </td><td> Qualsiasi filatore può essere utilizzato. </td></tr><tr><td> Aligner </td><td> Suss Microtec </td><td> MJB 3 </td><td> Ogni allineatore può essere utilizzato. </td></tr><tr><td> XEF 2 incisore </td><td> Advanced Communication Devices, Inc. </td><td> # ADCETCH2007 </td><td></td></tr></tbody></table> Tabella 3. Apparecchiature di fabbricazione Microtoroid. <table border="1"><tbody><tr><td> Nome della parte </td><td> Azienda </td><td> Numero di catalogo </td><td> Comments </td></tr><tr><td> CO 2 </sub&gt; Laser </td><td> Synrad </td><td> Series 48 </td><td></td></tr><tr><td> 3-Axis stage </td><td> OptoSigma </td><td> 120-0770 </td><td> Disponibile da altri fornitori pure. </td></tr><tr><td> Si Reflector 1 &quot;di diametro) </td><td> II-VI </td><td> 308325 </td><td> Disponibile da altri fornitori pure. </td></tr><tr><td> Cinematica staffa di montaggio (per Si riflettore) </td><td> Thor Labs </td><td> KX1G </td><td> Disponibile da altri fornitori pure. </td></tr><tr><td> Larghezza combinatore (1 &quot;di diametro) </td><td> Meller Optics </td><td> L19100008-B0 </td><td> Disponibile da altri fornitori pure. </td></tr><tr><td> 4 &quot;Obiettivo Lunghezza focale (1&quot; di diametro) </td><td> Ottica Meller o II-VI </td><td></td><td> Disponibile da altri fornitori, come pure </td></tr><tr><td> Messaggi assortiti, monta lenti </td><td> Labs Thor, Newport, Edmund Optics o Optosigma </td><td></td><td></td></tr><tr><td> Zoom 6000 Sistema di visione artificiale </td><td> Navitar </td><td> n / a </td><td> Richiede generico USB della fotocamera e il computer per imaging in tempo reale. Questo è acquistato come kit. </td></tr><tr><td> Focheggiatore per il sistema Zoom 6000 </td><td> Edmund Optics </td><td> 54-792 </td><td> Disponibile da altri fornitori pure. </td></tr><tr><td> Posizionatori Axis XZ per il 6000 Zoom </td><td> Parker Daedal </td><td> CR4457, CR4452, 4499 </td><td> CR4457 è asse X, CR4452 è Z, 4499 è staffa di montaggio. </td></tr></tbody></table> Tabella 4. Reflow laser CO 2 Set-up.

fabrication of silica ultra high quality factor microresonators

Whispering gallery resonant cavities confine light in circular orbits at their periphery.1-2 The photon storage lifetime in the cavity, quantified by the quality factor (Q) of the cavity, can be in excess of 500ns for cavities with Q factors above 100 million. As a result of their low material losses, silica microcavities have demonstrated some of the longest photon lifetimes to date1-2. Since a portion of the circulating light extends outside the resonator, these devices can also be used to probe the surroundings. This interaction has enabled numerous experiments in biology, such as single molecule biodetection and antibody-antigen kinetics, as well as discoveries in other fields, such as development of ultra-low-threshold microlasers, characterization of thin films, and cavity quantum electrodynamics studies.3-7
The two primary silica resonant cavity geometries are the microsphere and the microtoroid. Both devices rely on a carbon dioxide laser reflow step to achieve their ultra-high-Q factors (Q&gt;100 million).1-2,8-9 However, there are several notable differences between the two structures. Silica microspheres are free-standing, supported by a single optical fiber, whereas silica microtoroids can be fabricated on a silicon wafer in large arrays using a combination of lithography and etching steps. These differences influence which device is optimal for a given experiment.
Here, we present detailed fabrication protocols for both types of resonant cavities. While the fabrication of microsphere resonant cavities is fairly straightforward, the fabrication of microtoroid resonant cavities requires additional specialized equipment and facilities (cleanroom). Therefore, this additional requirement may also influence which device is selected for a given experiment.
Introduction
An optical resonator efficiently confines light at specific wavelengths, known as the resonant wavelengths of the device. 1-2 The common figure of merit for these optical resonators is the quality factor or Q. This term describes the photon lifetime (&tau;o) within the resonator, which is directly related to the resonator's optical losses. Therefore, an optical resonator with a high Q factor has low optical losses, long photon lifetimes, and very low photon decay rates (1/&tau;o). As a result of the long photon lifetimes, it is possible to build-up extremely large circulating optical field intensities in these devices. This very unique property has allowed these devices to be used as laser sources and integrated biosensors.10
A unique sub-class of resonators is the whispering gallery mode optical microcavity. In these devices, the light is confined in circular orbits at the periphery. Therefore, the field is not completely confined within the device, but evanesces into the environment. Whispering gallery mode optical cavities have demonstrated some of the highest quality factors of any optical resonant cavity to date.9,11 Therefore, these devices are used throughout science and engineering, including in fundamental physics studies and in telecommunications as well as in biodetection experiments. 3-7,12
Optical microcavities can be fabricated from a wide range of materials and in a wide variety of geometries. A few examples include silica and silicon microtoroids, silicon, silicon nitride, and silica microdisks, micropillars, and silica and polymer microrings.13-17 The range in quality factor (Q) varies as dramatically as the geometry. Although both geometry and high Q are important considerations in any field, in many applications, there is far greater leverage in boosting device performance through Q enhancement. Among the numerous options detailed previously, the silica microsphere and the silica microtoroid resonator have achieved some of the highest Q factors to date.1,9 Additionally, as a result of the extremely low optical loss of silica from the visible through the near-IR, both microspheres and microtoroids are able to maintain their Q factors over a wide range of testing wavelengths.18 Finally, because silica is inherently biocompatible, it is routinely used in biodetection experiments.
In addition to high material absorption, there are several other potential loss mechanisms, including surface roughness, radiation loss, and contamination loss.2 Through an optimization of the device size, it is possible to eliminate radiation losses, which arise from poor optical field confinement within the device. Similarly, by storing a device in an appropriately clean environment, contamination of the surface can be minimized. Therefore, in addition to material loss, surface scattering is the primary loss mechanism of concern.2,8
In silica devices, surface scattering is minimized by using a laser reflow technique, which melts the silica through surface tension induced reflow. While spherical optical resonators have been studied for many years, it is only with recent advances in fabrication technologies that researchers been able to fabricate high quality silica optical toroidal microresonators (Q&gt;100 million) on a silicon substrate, thus paving the way for integration with microfluidics.1
The present series of protocols details how to fabricate both silica microsphere and microtoroid resonant cavities. While silica microsphere resonant cavities are well-established, microtoroid resonant cavities were only recently invented.1 As many of the fundamental methods used to fabricate the microsphere are also used in the more complex microtoroid fabrication procedure, by including both in a single protocol it will enable researchers to more easily trouble-shoot their experiments.

Watch this Scientific Journal Video about Fabrication of Silica Ultra High Quality Factor Microresonators at JoVE.com

Fabrication of Silica Ultra High Quality Factor Microresonators

Si descrivono l&#39;uso di una tecnica di anidride carbonica reflow laser per fabbricare cavità risonanti silice, incluse autoportante microsfere e on-chip microtoroids. Il metodo di reflow rimuove le imperfezioni della superficie, che consente lunghi tempi di vita dei fotoni all&#39;interno di entrambi i dispositivi. I dispositivi ultra risultanti hanno fattori di alta qualità, consentendo applicazioni che vanno dalle telecomunicazioni alla rilevazione di agenti biologici.

Fabbricazione di Microrisonatori silice Ultra High Quality Factor

Whispering gallery resonant cavities confine light in circular orbits at their periphery.1-2 The photon storage lifetime in the cavity, quantified by the ...

fabrication-of-silica-ultra-high-quality-factor-microresonators

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16.0K Views.  University of Southern California. Si descrivono l'uso di una tecnica di anidride carbonica reflow laser per fabbricare cavità risonanti silice, incluse autoportante microsfere e on-chip microtoroids. Il metodo di reflow rimuove le imperfezioni della superficie, che consente lunghi tempi di vita dei fotoni all'interno di entrambi i dispositivi. I dispositivi ultra risultanti hanno fattori di alta qualità, consentendo applicazioni che vanno dalle telecomunicazioni alla rilevazione di agenti biolog...

Video: Fabrication of Silica Ultra High Quality Factor Microresonators

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 ...

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Synthesis and Microdiffraction at Extreme Pressures and Temperatures

High pressure compounds and polymorphs are investigated for a broad range of purposes such as determine structures and processes of deep planetary interiors, design materials with novel properties, understand the mechanical behavior of materials exposed to very high stresses as in explosions or impacts. Synthesis and structural analysis of materials at extreme conditions of pressure and temperature entails remarkable technical challenges. In the laser heated diamond anvil cell (LH-DAC), very high pressure is generated between the tips of two opposing diamond anvils forced against each other; focused infrared laser beams, shined through the diamonds, allow to reach very high temperatures on samples absorbing the laser radiation. When the LH-DAC is installed in a synchrotron beamline that provides extremely brilliant x-ray radiation, the structure of materials under extreme conditions can be probed in situ. LH-DAC samples, although very small, can show highly variable grain size, phase and chemical composition. In order to obtain the high resolution structural analysis and the most comprehensive characterization of a sample, we collect diffraction data in 2D grids and combine powder, single crystal and multigrain diffraction techniques. Representative results obtained in the synthesis of a new iron oxide, Fe4O5 1 will be shown.

The laser heated diamond anvil cell combined with synchrotron micro-diffraction techniques allows researchers to explore the nature and properties of new phases of matter at extreme pressure and temperature (PT) conditions. Heterogeneous samples can be characterized in situ under high pressure by 2D mapping and combined powder, single-crystal and multigrain diffraction approaches.

Sintesi e microdiffrazione a pressioni e temperature estreme

High pressure compounds and polymorphs are investigated for a broad range of purposes such as determine structures and processes of deep planetary ...

Convergent Polishing: A Simple, Rapid, Full Aperture Polishing Process of High Quality Optical Flats &amp; Spheres

Convergent Polishing is a novel polishing system and method for finishing flat and spherical glass optics in which a workpiece, independent of its initial shape (i.e., surface figure), will converge to final surface figure with excellent surface quality under a fixed, unchanging set of polishing parameters in a single polishing iteration. In contrast, conventional full aperture polishing methods require multiple, often long, iterative cycles involving polishing, metrology and process changes to achieve the desired surface figure. The Convergent Polishing process is based on the concept of workpiece-lap height mismatch resulting in pressure differential that decreases with removal and results in the workpiece converging to the shape of the lap. The successful implementation of the Convergent Polishing process is a result of the combination of a number of technologies to remove all sources of non-uniform spatial material removal (except for workpiece-lap mismatch) for surface figure convergence and to reduce the number of rogue particles in the system for low scratch densities and low roughness. The Convergent Polishing process has been demonstrated for the fabrication of both flats and spheres of various shapes, sizes, and aspect ratios on various glass materials. The practical impact is that high quality optical components can be fabricated more rapidly, more repeatedly, with less metrology, and with less labor, resulting in lower unit costs. In this study, the Convergent Polishing protocol is specifically described for fabricating 26.5 cm square fused silica flats from a fine ground surface to a polished ~&#955;/2 surface figure after polishing 4 hr per surface on a 81 cm diameter polisher.

A novel optical polishing process, called &#8220;Convergent Polishing&#8221;, which enables faster, lower cost polishing, is described. Unlike conventional polishing processes, Convergent Polishing allows a glass workpiece to be polished in a single iteration and with high surface quality to its final surface figure without requiring changes to polishing parameters.

Convergent lucidatura: A Simple, Rapid, massima apertura lucidatura processo di alta qualità ottica Flats &amp; Spheres

Convergent Polishing is a novel polishing system and method for finishing flat and spherical glass optics in which a workpiece, independent of its initial ...

Fabrication of High Contrast Gratings for the Spectrum Splitting Dispersive Element in a Concentrated Photovoltaic System

High contrast gratings are designed and fabricated and its application is proposed in a parallel spectrum splitting dispersive element that can improve the solar conversion efficiency of a concentrated photovoltaic system. The proposed system will also lower the solar cell cost in the concentrated photovoltaic system by replacing the expensive tandem solar cells with the cost-effective single junction solar cells. The structures and the parameters of high contrast gratings for the dispersive elements were numerically optimized. The large-area fabrication of high contrast gratings was experimentally demonstrated using nanoimprint lithography and dry etching. The quality of grating material and the performance of the fabricated device were both experimentally characterized. By analyzing the measurement results, the possible side effects from the fabrication processes are discussed and several methods that have the potential to improve the fabrication processes are proposed, which can help to increase the optical efficiency of the fabricated devices.

The fabrication of high contrast gratings as the parallel spectrum splitting dispersive element in a concentrated photovoltaic system is demonstrated. Fabrication processes including nanoimprint lithography, TiO2 sputtering and reactive ion etching are described. Reflectance measurement results are used to characterize the optical performance.

Fabbricazione di Grigliati un forte contrasto per la suddivisione Spectrum Dispersive elemento in un sistema fotovoltaico a concentrazione

High contrast gratings are designed and fabricated and its application is proposed in a parallel spectrum splitting dispersive element that can improve ...

The Evolution of Silica Nanoparticle-polyester Coatings on Surfaces Exposed to Sunlight

Corrosion of metallic surfaces is prevalent in the environment and is of great concern in many areas, including the military, transport, aviation, building and food industries, amongst others. Polyester and coatings containing both polyester and silica nanoparticles (SiO2NPs) have been widely used to protect steel substrata from corrosion. In this study, we utilized X-ray photoelectron spectroscopy, attenuated total reflection infrared micro-spectroscopy, water contact angle measurements, optical profiling and atomic force microscopy to provide an insight into how exposure to sunlight can cause changes in the micro- and nanoscale integrity of the coatings. No significant change in surface micro-topography was detected using optical profilometry, however, statistically significant nanoscale changes to the surface were detected using atomic force microscopy. Analysis of the X-ray photoelectron spectroscopy and attenuated total reflection infrared micro-spectroscopy data revealed that degradation of the ester groups had occurred through exposure to ultraviolet light to form COO&#903;, -H2C&#903;, -O&#903;, -CO&#903; radicals. During the degradation process, CO and CO2 were also produced.

Two types of surfaces, polyester-coated steel and polyester coated with a layer of silica nanoparticles, were studied. Both surfaces were exposed to sunlight, which was found to cause substantial changes in the chemistry and nanoscale topography of the surface.

L&#39;evoluzione di silice Coatings nanoparticelle-poliestere su superfici esposte al sole

Corrosion of metallic surfaces is prevalent in the environment and is of great concern in many areas, including the military, transport, aviation, ...

High Temperature Fabrication of Nanostructured Yttria-Stabilized-Zirconia (YSZ) Scaffolds by In Situ Carbon Templating Xerogels

We demonstrate a method for the high temperature fabrication of porous, nanostructured yttria-stabilized-zirconia (YSZ, 8 mol% yttria - 92 mol% zirconia) scaffolds with tunable specific surface areas up to 80 m2&#183;g-1. An aqueous solution of a zirconium salt, yttrium salt, and glucose is mixed with propylene oxide (PO) to form a gel. The gel is dried under ambient conditions to form a xerogel. The xerogel is pressed into pellets and then sintered in an argon atmosphere. During sintering, a YSZ ceramic phase forms and the organic components decompose, leaving behind amorphous carbon. The carbon formed in situ serves as a hard template, preserving a high surface area YSZ nanomorphology at sintering temperature. The carbon is subsequently removed by oxidation in air at low temperature, resulting in a porous, nanostructured YSZ scaffold. The concentration of the carbon template and the final scaffold surface area can be systematically tuned by varying the glucose concentration in the gel synthesis. The carbon template concentration was quantified using thermogravimetric analysis (TGA), the surface area and pore size distribution was determined by physical adsorption measurements, and the morphology was characterized using scanning electron microscopy (SEM). Phase purity and crystallite size was determined using X-ray diffraction (XRD). This fabrication approach provides a novel, flexible platform for realizing unprecedented scaffold surface areas and nanomorphologies for ceramic-based electrochemical energy conversion applications, e.g. solid oxide fuel cell (SOFC) electrodes.

High Temperature Fabrication of Nanostructured Yttria-Stabilized-Zirconia YSZ Scaffolds by In Situ Carbon Templating Xerogels

A protocol for fabricating porous, nanostructured yttria-stabilized-zirconia (YSZ) scaffolds at temperatures between 1,000 &#176;C and 1,400 &#176;C is presented.

Fabbricazione ad alta temperatura di Nanostrutturati di ossido di ittrio stabilizzato-Zirconia (YSZ) Ponteggi da<em&gt; In Situ</em&gt; Carbon Templating xerogel

We demonstrate a method for the high temperature fabrication of porous, nanostructured yttria-stabilized-zirconia (YSZ, 8 mol% yttria - 92 mol% zirconia) ...

Scalable Solution-processed Fabrication Strategy for High-performance, Flexible, Transparent Electrodes with Embedded Metal Mesh

Here, the authors report the embedded metal-mesh transparent electrode (EMTE), a new transparent electrode (TE) with a metal mesh completely embedded in a polymer film. This paper also presents a low-cost, vacuum-free fabrication method for this novel TE; the approach combines lithography, electroplating, and imprint transfer (LEIT) processing. The embedded nature of the EMTEs offers many advantages, such as high surface smoothness, which is essential for organic electronic device production; superior mechanical stability during bending; favorable resistance to chemicals and moisture; and strong adhesion with plastic film. LEIT fabrication features an electroplating process for vacuum-free metal deposition and is favorable for industrial mass production. Furthermore, LEIT allows for the fabrication of metal mesh with a high aspect ratio (i.e., thickness to linewidth), significantly enhancing its electrical conductance without adversely losing optical transmittance. We demonstrate several prototypes of flexible EMTEs, with sheet resistances lower than 1 &#937;/sq and transmittances greater than 90%, resulting in very high figures of merit (FoM) &#8211; up to 1.5 x 104 &#8211; which are amongst the best values in the published literature.

This protocol describes a solution-based fabrication strategy for high-performance, flexible, transparent electrodes with fully-embedded, thick metal mesh. Flexible transparent electrodes fabricated by this process demonstrate among the highest reported performances, including ultra-low sheet resistance, high optical transmittance, mechanical stability under bending, strong substrate adhesion, surface smoothness, and environmental stability.

Strategia di Fabbricazione elaborata in soluzione scalabile per elettrodi ad alte prestazioni, flessibili e trasparenti con maglia metallica incorporata

Here, the authors report the embedded metal-mesh transparent electrode (EMTE), a new transparent electrode (TE) with a metal mesh completely embedded in a ...

Fabrication of Ultra-thin Color Films with Highly Absorbing Media Using Oblique Angle Deposition

Ultra-thin film structures have been studied extensively for use as optical coatings, but performance and fabrication challenges remain.&#160; We present an advanced method for fabricating ultra-thin color films with improved characteristics. The proposed process addresses several fabrication issues, including large area processing. Specifically, the protocol describes a process for fabricating ultra-thin color films using an electron beam evaporator for oblique angle deposition of germanium (Ge) and gold (Au) on silicon (Si) substrates.&#160; Film porosity produced by the oblique angle deposition induces color changes in the ultra-thin film. The degree of color change depends on factors such as deposition angle and film thickness. Fabricated samples of the ultra-thin color films showed improved color tunability and color purity. In addition, the measured reflectance of the fabricated samples was converted into chromatic values and analyzed in terms of color. Our ultra-thin film fabricating method is expected to be used for various ultra-thin film applications such as flexible color electrodes, thin film solar cells, and optical filters. Also, the process developed here for analyzing the color of the fabricated samples is broadly useful for studying various color structures.

We present a detailed method for fabricating ultra-thin color films with improved characteristics for optical coatings. The oblique angle deposition technique using an electron beam evaporator allows improved color tunability and purity. Fabricated films of Ge and Au on Si substrates were analyzed by reflectance measurements and color information conversion.

Fabbricazione di film ultra-sottile di colore con altamente assorbente Media mediante deposizione di angolo obliquo

Ultra-thin film structures have been studied extensively for use as optical coatings, but performance and fabrication challenges remain.&#160; We present ...

Flow-assisted Dielectrophoresis: A Low Cost Method for the Fabrication of High Performance Solution-processable Nanowire Devices

Flow-assisted dielectrophoresis (DEP) is an efficient self-assembly method for the controllable and reproducible positioning, alignment, and selection of nanowires. DEP is used for nanowire analysis, characterization, and for solution-based fabrication of semiconducting devices. The method works by applying an alternating electric field between metallic electrodes. The nanowire formulation is then dropped onto the electrodes which are on an inclined surface to create a flow of the formulation using gravity. The nanowires then align along the gradient of the electric field and in the direction of the liquid flow. The frequency of the field can be adjusted to select nanowires with superior conductivity and lower trap density. 
In this work, flow-assisted DEP is used to create nanowire field effect transistors. Flow-assisted DEP has several advantages: it allows selection of nanowire electrical properties; control of nanowire length; placement of nanowires in specific areas; control of orientation of nanowires; and control of nanowire density in the device. 
The technique can be expanded to many other applications such as gas sensors and microwave switches. The technique is efficient, quick, reproducible, and it uses a minimal amount of dilute solution making it ideal for the testing of novel nanomaterials. Wafer scale assembly of nanowire devices can also be achieved using this technique, allowing large numbers of samples for testing and large-area electronic applications.

In this paper, flow assisted dielectrophoresis is demonstrated for the self-assembly of nanowire devices. The fabrication of a silicon nanowire field effect transistor is shown as an example.

Flusso-assistita dielettroforesi: Un metodo a basso costo per la realizzazione di dispositivi ad alte prestazioni soluzione-processable Nanowire

Flow-assisted dielectrophoresis (DEP) is an efficient self-assembly method for the controllable and reproducible positioning, alignment, and selection of ...

Determination of Aggregate Surface Morphology at the Interfacial Transition Zone (ITZ)

Here, we present a comprehensive method to illustrate the uneven distribution of the interfacial transition zone (ITZ) around the aggregate and the effect of aggregate surface morphology on the formation of ITZ. First, a model concrete sample is prepared with a spherical ceramic particle in roughly the central part of the cement matrix, acting as a coarse aggregate used in common concrete/mortar. After curing until the designed age, the sample is scanned by X-ray computed tomography to determine the relative location of the ceramic particle inside the cement matrix. Three locations of the ITZ are chosen: above the aggregate, on the side of the aggregate, and below the aggregate. After a series of treatments, the samples are scanned with a SEM-BSE detector. The resultant images were further processed using a digital image processing method (DIP) to obtain quantitative characteristics of the ITZ. The surface morphology is characterized at the pixel level based on the digital image. Thereafter, K-means clustering method is used to illustrate the effect of surface roughness on ITZ formation.

Determination of Aggregate Surface Morphology at the Interfacial Transition Zone ITZ

Hereby, we proposed a protocol to illustrate the effect of aggregate surface morphology on the ITZ microstructure. The SEM-BSE image were quantitatively analyzed to obtain ITZ's porosity gradient via digital image processing and a K-means clustering algorithm was further employed to establish a relationship between porosity gradient and surface roughness.

Determinazione della morfologia di superficie aggregata nella zona di transizione interfacciale (IT)

Here, we present a comprehensive method to illustrate the uneven distribution of the interfacial transition zone (ITZ) around the aggregate and the effect ...