Questo lavoro è stato sostenuto dal programma D di MSIP / IITP (R0190-15-2040, Sviluppo di un sistema di gestione della configurazione contenuti e un simulatore per la stampa 3D utilizzando materiali intelligenti) R &amp; ICT.

Attenzione: Si prega di fare riferimento a tutte le pertinenti norme di sicurezza materiale prima dell&#39;uso. Molti dei prodotti chimici utilizzati nella fabbricazione di microchip sono altamente tossici e cancerogeni. Utilizzare tutte le pratiche di sicurezza appropriate quando si eseguono i processi fotolitografici e di attacco, compreso l&#39;uso di controlli tecnici (cappa, piastra calda, e allineatori) e dispositivi di protezione individuale (occhiali, guanti, camici, pantaloni full-length, e chiuso scarpe -toe). 1. Realizzazione della Microchannel PDMS <ol><li> Fabbricazione dello stampo microcanale dal processo fotolito <ol><li> Rimuovere completamente impurità sulla superficie 4 pollici wafer di Si con pulizia Piranha (Figura 1a). Miscela di acido solforico (H 2 SO 4) e perossido di idrogeno (H 2 O 2) in un rapporto di 3: 1 per rendere la soluzione Piranha nel piatto. Mescolare aggiungendo gradualmente piccole quantità di acido forte (H 2 O <sub&gt; 2) per l&#39;acido debole (H 2 SO 4); invertire questo ordine può provocare un&#39;esplosione a causa della forte acido altamente reattivo. </li><li> Immergere il wafer nella soluzione Piranha a 10 min. Successivamente, immergere il wafer in acqua deionizzata (DI) per 3 minuti per rimuovere la soluzione Piranha rimanente. Risciacquare il wafer con acqua corrente per 10 s DI. Ripetere la procedura di lavaggio 3 volte e asciugare con N 2 gas per rimuovere il residuo DI. </li><li> Posizionare il wafer su una piastra calda per 20 minuti a 180 ° C per disidratare ulteriormente wafer. </li><li> Versare 5 mL di fotoresist negativo sulla parte superiore della fetta e centrifuga cappotto per 45 s a 1.500 giri (Figura 1b); dopo rivestimento per rotazione, una perlina fotoresist viene creata sul bordo wafer a causa della relativamente alta viscosità del fotoresist. </li><li> Bilanciare il wafer photoresist rivestite da planarizzazione su un supporto livellante per 5 h. </li><li> Posizionare il wafer photoresist rivestite su una piastra calda per 12 min a 65° C, 35 min a 95 ° C e 12 min a 65 ° C (soft cottura). </li><li> Fissare la maschera pellicola sul supporto maschera e il wafer soft-cotta sulla scena substrato dell&#39;allineatore. Esporre alla luce ultravioletta (UV) per 43 s a 650 mJ / cm 2 per solidificare il fotoresist. </li><li> Posizionare il wafer sulla piastra calda per 5 minuti a 65 ° C, 15 min a 95 ° C e 5 min a 65 ° C (post-esposizione cottura). </li><li> Immergere il wafer nello sviluppatore photoresist per 30 minuti per rimuovere fotoresist solidificata. </li><li> Risciacquare il wafer con alcool isopropilico (IPA) e asciugare con N 2 gas per rimuovere il residuo IPA. </li></ol></li><li> Fabbricazione dei microcanali PDMS <ol><li> Trattare la superficie del wafer e lo stampo di fotoresist per 1 min a una potenza di 200 W utilizzando una macchina plasma atmosferico 25; i flussi di gas di CH 4 e dovrebbe essere 6 e 30 sccm, rispettivamente. Eseguire questo trattamento idrofobico di staccare facilmente il polydimethylsiloxane (PDMS) microcanali dalla superficie del wafer e muffa fotoresist (figura 1c). </li><li> Preparare la soluzione PDMS mescolando la base PDMS e agente indurente in un rapporto di 10: 1. Agitare la miscela per 2 min. </li><li> Posizionare il wafer in una piastra di Petri (150 mm x 15 mm) e aggiungere 100 ml di soluzione di PDMS. Rimuovere le bolle che sono stati creati da agitazione usando un essiccatore. </li><li> Porre la capsula di Petri in forno per 2 ore a 80 ° C per solidificare la soluzione PDMS (Figura 1d e h). </li><li> Tagliare lungo i contorni della microcanali PDMS con una lama di rasoio e staccarlo dal wafer; le PDMS fabbricate microcanale dovrebbero avere le seguenti dimensioni: lunghezza 13 mm, 300 micron di larghezza e 150 um alto (figure 1e, f, e i). NOTA: Due tipi di fori sono prodotte da un micropuntura per inserire la fibra monomodale (SMF) cavo e tubi (ingresso And uscita) sul PDMS microcanali (Figura 1g). Il cavo SMF viene utilizzato per emettere il fascio laser alla nanohole lavorato sul piatto d&#39;oro. Il tubo viene utilizzato per inserire / estrarre la soluzione particella a / da microcanali PDMS. </li><li> Forare ingresso 1,5 mm e fori di uscita a ciascuna estremità del microcanale PDMS. Perforare 0,3 mm foro del cavo SMF al centro del microcanale PDMS. </li></ol></li></ol> 2. processo di incisione del Gold Plate <ol><li> Preparare un piatto d&#39;oro disponibile in commercio con le dimensioni di 25 x 6,25 millimetri 2 (figura 2a). </li><li> Rimuovere eventuali sostanze estranee sul piatto d&#39;oro con le seguenti procedure di pulizia. Pulito nel seguente ordine immergendo in acetone, metanolo e acqua deionizzata per 5 minuti ciascuna. </li><li> Risciacquare il piatto d&#39;oro 3 volte con acqua deionizzata per 10 s e asciugare la piastra con N 2 gas per rimuovere l&#39;acqua residua DI. </li><li> Posizionare il piatto d&#39;oro su una piastra calda per20 min a 180 ° C per eliminare completamente l&#39;umidità residua. </li><li> Versare 0,5 mL di esametildisilazano (HMDS) sulla piastra di oro e cappotto centrifuga per 40 s a 3.000 rpm. </li><li> Versare 0,5 mL di photoresist positivo sopra le HMDS di spin-rivestito e cappotto centrifuga per 40 s a 3.000 rpm (Figura 2b). </li><li> Posizionare la piastra oro photoresist rivestite sulla piastra calda per 90 s a 110 ° C (soft cottura). </li><li> Fissare la maschera pellicola sulla fetta di vetro e posizionare la piastra oro morbido-cotta sulla scena substrato. Esporre alla luce UV per 4,5 s a 64 mJ / cm 2 per sciogliere il fotoresist. </li><li> Immergere il piatto d&#39;oro nello sviluppatore photoresist per 1 min per rimuovere il fotoresist disciolto (figura 2c). Risciacquare il piatto d&#39;oro con acqua deionizzata e asciugare con N 2 gas. </li><li> Immergere il piatto d&#39;oro nella Au mordenzante per 45 s ad una velocità di incisione di 28 Å / s per rimuovere l&#39;Au esposta (figura 2d). Sciacquare la piastra d&#39;oro con DI water e asciugare con N 2 gas. </li><li> Immergere il piatto d&#39;oro nel mordenzante Ti per 5 s ad una velocità di incisione di 25 Å / s per rimuovere il Ti esposta (figura 2e). Risciacquare il piatto d&#39;oro con acqua deionizzata e asciugare con N 2 gas. </li><li> Rimuovere il fotoresist rimanente sul piatto d&#39;oro immergendolo in acetone, metanolo e acqua deionizzata per 3 minuti ciascuno (figura 2f); immergere la piastra in ordine scritto. </li><li> Risciacquare il piatto d&#39;oro 3 volte con acqua deionizzata per 10 s. Secco con N 2 gas per rimuovere l&#39;acqua DI. </li><li> Posizionare la piastra d&#39;oro sulla piastra calda per 3 min a 120 ° C per rimuovere completamente l&#39;umidità; il blocco oro prodotto dovrebbe essere 400 x 150 um 2 (figura 2h). </li><li> Fresare una nanohole 400 nm usando un fascio ionico focalizzato (FIB) al centro del blocco oro che si fabbricata dopo l&#39;attacco (figure 2g e i). Creare un modello cerchio 370 nm a concentrarsi sul bl oroock con uno ione tensione di accelerazione di 30 kV a 28 pA per 3 s. </li></ol> 3. Montaggio della Microchip <ol><li> Trattare le due superfici del microcanale PDMS e la piastra d&#39;oro per 1 min con O 2 plasma per fissare insieme con un sistema plasma ad una potenza di 80 W ed una pressione di 825 mTorr 25. NOTA: E &#39;soprattutto difficile attaccarli con precisione perché il blocco di oro e PDMS a microcanali sono al livello micrometrico. Quindi, utilizzare un allineatore con una telecamera e una fase manuale. </li><li> Fissare il wafer in vetro che viene utilizzato per fissare la maschera pellicola al titolare maschera dell&#39;allineatore (Figura 3a). </li><li> Fissare i O 2 al plasma da trattati PDMS microcanale al wafer di vetro; perché il PDMS è idrofilo, sarà facilmente collegare al wafer vetro senza soluzione di adesione. Fissare la piastra d&#39;oro sulla scena substrato dell&#39;allineatore (Figura 3a). </li><li> Individuare i centri di the SMF foro del cavo e oro blocco, che sono allineati sullo stesso asse, utilizzando la telecamera sul allineatore. Sollevare la fase manuale di unire le due parti (figure 3b e c). </li></ol> 4. Miglioramento della Microchip Side rugosità di superficie con PDMS Coating NOTA: La piastra d&#39;oro con dimensioni fisse di 400 x 150 um 2 è relativamente più difficile da tagliare rispetto al materiale PDMS. Pertanto, per staccare il microcanale PDMS dal wafer, una lama di rasoio è utilizzata per tagliare un pezzo più grande della piastra dell&#39;oro. Dopo che unisce le due parti, la parte in eccesso del PDMS rispetto alla piastra oro devono poi essere tagliati in modo che l&#39;interno del canale può essere osservato dal lato utilizzando un microscopio (figura 4a). Tuttavia, la superficie di taglio, che viene utilizzato come una finestra, ha una elevata rugosità superficiale e produce quindi immagini nuvolosi delle particelle che fluiscono nel canale (Figura4b). Rivestimento con la soluzione di PDMS viene eseguito di nuovo per risolvere questo problema. <ol><li> Preparare la soluzione PDMS mescolando la base PDMS e agente indurente in un rapporto di 10: 1 ed agitare per 2 min. </li><li> Versare 2 ml della soluzione PDMS nella capsula Petri ed eseguire la spin coating per 30 s a 1.000 giri (Figura 4c). </li><li> Posizionare la superficie microchip che sta per essere situato sul microscopio sul piatto Petri (figura 4d). Porre la capsula di Petri in forno per 1 ora a 80 ° C per solidificare la soluzione PDMS. </li><li> Tagliare il bordo del microchip e PDMS usando una lama di rasoio e successivamente staccarlo dalla piastra di Petri (figure 4e, f). </li></ol> 5. Laser accoppiamento per inserire il cavo SMF alla Microchip NOTA: Per il sistema pinzette plasmonica, viene utilizzato un laser incidente fibra ottica con una lunghezza d&#39;onda 1.064 nm. Il cavo SMF viene utilizzato perché il diametro del incilaser Dent (5 mm) è troppo immenso per emettere il raggio laser sulla nanohole fresata sul blocco oro (400 x 150 um 2) nel microchip. Il diametro rivestimento del cavo SMF è di 125 um. Così, il laser incidente e il cavo SMF devono essere accoppiati. <ol><li> Collegare una lente obiettivo 40X all&#39;obiettivo microscopio montaggio sul accoppiatore SMF. Fissare il cavo SMF sul morsetto fibra dell&#39;accoppiatore SMF. Allineare il fascio laser incidente per riempire l&#39;apertura posteriore della lente obiettivo. </li><li> Focalizzare il fascio laser al nucleo del cavo SMF regolando la fase manuale a tre assi attrezzato al accoppiatore SMF. </li><li> Inserire l&#39;estremità opposta del cavo SMF nel foro cavo SMF del microchip. Misurare la potenza del laser prima dell&#39;inserimento al bordo del cavo in fibra, in quanto il cavo in fibra fissa al microchip non può essere rimosso. </li><li> Sigillare il foro cavo SMF utilizzando colla epossidica per bloccare la fuoriuscita della soluzione particella scorre dalla distanza tra la cabina SMFforo le (300 micron) e il rivestimento del cavo SMF (125 um); l&#39;estremità del cavo in fibra inserito non deve entrare nel microcanale per evitare il flusso di fluido. allineare manualmente il cavo in fibra con feedback visivo in modo che sia perpendicolare al blocco oro che ospita il nanohole. </li></ol> 6. particelle plasmoniche Cattura di singolo fluorescente polistirolo nel microchip <ol><li> Collegare la siringa, che viene riempito con la soluzione di particelle, ad una micropompa siringa. Posizionare il vetro di copertura sulla fase del campione del microscopio a fluorescenza. Raccordare tubi ai fori di entrata / uscita del microchip. Posizionare la superficie microchip PDMS rivestita sulla parte superiore del vetro di copertura. </li><li> Posizionare il microchip ortogonalmente immersione in acqua lente obiettivo 60X osservando l&#39;interno del canale con la fotocamera installata sul microscopio a fluorescenza. Utilizzare nastro trasparente per fissare il microchip al suo posto. Collegare il tubo di ingresso del microchip con la siringa needle. </li><li> Inserire la soluzione particella alla microchip controllando la micropompa a 20 um / s. In questo momento, confermano che la particella fluorescente può essere osservato anche nel canale quando la lampada fluorescente è accesa. </li><li> Attendere la soluzione particella esce dall&#39;uscita del microchip. Impostare la velocità a 3,4 micron / s. </li><li> Ruotare il dispositivo sorgente laser in modo che emette il laser nella nanohole; la particella fluorescente sarà intrappolato sul bordo della nanohole. </li><li> Rampa la velocità del fluido con incrementi di 0,4 um / s controllando la micropompa finché le fughe di particelle intrappolate. Misurare la velocità del fluido quando le particelle intrappolate fuga. Avere la forza di intrappolamento massimo per ciascuna intensità del laser che utilizza questo velocità del fluido misurata. </li></ol>

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Il cavo SMF è stato inserito nel foro cavo SMF sul microchip, come mostrato nella puntino rettangolare di figura 6a. Poiché il foro del cavo SMF è maggiore del diametro del cavo, colla epossidica è stato utilizzato per chiudere l&#39;apertura di bloccare la fuoriuscita della soluzione particella fluente. Prima dell&#39;applicazione di colla epossidica, il blocco oro e bordo cavo devono essere allineati coassialmente a mano con un microscopio. Anche se è ideale per il bordo cavo inserito ed il nanoh...

La capacità di manipolare oggetti microscala è un elemento indispensabile per vari esperimenti micro / nano. manipolazioni contatto diretto può danneggiare gli oggetti manipolati. Rilasciando gli oggetti precedentemente detenute è anche difficile a causa di problemi stiction. Per superare questi problemi,, 8 sono stati proposti diversi metodi indiretti utilizzando fluidico 1, 2 elettrico, magnetico 3, o forze fotonici 4, 5, 6, 7. Pinzette plasmoniche che utilizzano forze fotonici sono basati sulla fisica di straordinari campo valorizzazione diversi ordini superiori dell&#39;intensità incidente 9. Questo estremamente forte amplificazione di campo consente l&#39;intrappolamento di piccolissime nanoparticelle. Ad esempio, è stato dimostrato per immobilizzare e manipolare nanoscalaoggetti, come particelle di polistirene 7, 10, 11, 12, 13, 14, 15 catene polimeriche, proteine, 16 punti quantici 17, e le molecole di DNA 8, 18. Senza pinzette plasmoniche, è difficile intercettare nanoparticelle perché scompaiono rapidamente prima che vengano effettivamente esaminate o perché sono danneggiati a causa dell&#39;elevata intensità del laser. Molti studi plasmoniche hanno usato varie strutture d&#39;oro a nanoscala. Possiamo classificare le strutture d&#39;oro come sporgenti tipi nanodisk 12, 13, 14, 15, 19 <sup&gt;, 20, 21 o soppresse tipi nanohole 7, 8, 10, 11, 22, 23. In termini di convenienza di imaging, i tipi nanodisk sono più adatti rispetto ai tipi nanohole perché, per quest&#39;ultimo, i substrati oro può ostacolare la vista di osservazione. Inoltre, l&#39;intrappolamento plasmonica si verifica in prossimità della struttura plasmonica e rende osservazione ancora più difficile. Per quanto a nostra conoscenza, cattura plasmoniche sui tipi nanohole è stata verificata solo tramite segnali di scattering indiretti. Tuttavia, nessun osservazioni dirette di successo, come ad esempio immagini microscopiche, sono stati segnalati. Pochi studi hanno descritto la posizione di particelle intrappolate. Un tale risultato è stato presentato da Wang et al. Hanno creato un pilastro oro su un substrato d&#39;oro e osservati il ​​pmovimento articolo usando un microscopio a fluorescenza 24. Tuttavia, questo è efficace solo per monitorare movimenti laterali non nella direzione parallela all&#39;asse del fascio. In questo lavoro, si introduce nuove procedure di progettazione e di fabbricazione di microchip fluidici. Utilizzando questo chip, dimostriamo il monitoraggio di particelle intrappolate plasmonically, sia in direzioni parallele e ortogonali alla nanostruttura plasmonica. Inoltre, si misura la forza massima della particella immobilizzato aumentando la velocità del fluido per trovare la velocità ribaltamento nel microchip. Questo studio è unico perché la maggior parte degli studi sulla pinzette plasmoniche non possono mostrare quantitativamente le forze di cattura massimi utilizzati nei loro apparati sperimentali.

<table><tbody><tr><td>Negative photoresist&amp;nbsp;</td><td>MicroChem</td><td>SU-8 2075</td><td></td></tr><tr><td>Developer</td><td>MicroChem</td><td>SU-8 Developer</td><td></td></tr><tr><td>Positive photoresist&amp;nbsp;</td><td>Merck Ltd.</td><td>AZ GXR-601</td><td></td></tr><tr><td>AZ Photoresist Developers</td><td>Merck Ltd.</td><td>AZ 300 MIF</td><td></td></tr><tr><td>HMDS</td><td>Merck Ltd.</td><td>AZ Adhesion Promoter</td><td></td></tr><tr><td>Aligner</td><td>Midas System</td><td>MDA 400M</td><td></td></tr><tr><td>Atmospheric plasma machine&amp;nbsp;</td><td>Atmospheric Process&lt;br/&gt; Plasma Co.</td><td>IDP-1000</td><td></td></tr><tr><td>Polydimethylsiloxane (PDMS)</td><td>Dow Corning</td><td>Sylgard 184 A/B</td><td></td></tr><tr><td>Gold coated test slides</td><td>EMF Co.</td><td>TA124(Ti/Au)</td><td></td></tr><tr><td>Au etchant&amp;nbsp;</td><td>Transene Inc.</td><td>TFA</td><td></td></tr><tr><td>Ti etchant&amp;nbsp;</td><td>Transene Inc.</td><td>TFT</td><td></td></tr><tr><td>40X objective lens&amp;nbsp;</td><td>Edmund Optics</td><td>40X DIN</td><td></td></tr><tr><td>60X water immersion&lt;br/&gt; objective lens&amp;nbsp;</td><td>Olympus</td><td>LUMPLFLN 60XW</td><td></td></tr><tr><td>Optical fiber incident laser&amp;nbsp;</td><td>IPG Photonic</td><td>YLR 10</td><td></td></tr><tr><td>SMF coupler</td><td>Thorlabs</td><td>MBT612D/M</td><td></td></tr><tr><td>Syringe micropump</td><td>Harvard</td><td>PC2 70-4501</td><td></td></tr><tr><td>Fluorescent microscope&amp;nbsp;</td><td>Olympus</td><td>IX-51</td><td></td></tr><tr><td>Plasma system</td><td>Femto Science Inc</td><td>CUTE-MPR</td><td></td></tr></tbody></table>

plasmonic trapping and release of nanoparticles in a monitoring environment

pinzette plasmoniche utilizzano polaritoni plasmon di superficie per confinare oggetti nanoscala polarizzabili. Tra i vari disegni di pinzette plasmoniche, solo pochi possono osservare particelle immobilizzate. Inoltre, un numero limitato di studi hanno misurata sperimentalmente le forze esercitabile sulle particelle. I disegni possono essere classificati come tipo di nanodisk sporgenti o il tipo nanohole soppressa. Per questi ultimi, osservazione microscopica è estremamente impegnativo. In questo documento, un nuovo sistema pinzetta plasmonica viene introdotto per monitorare particelle, sia in direzioni parallele e ortogonali all&#39;asse simmetrica di una struttura nanohole plasmonico. Questa caratteristica permette di osservare il movimento di ogni particella vicino al bordo del nanohole. Inoltre, possiamo stimare quantitativamente le forze massime di cattura usando un nuovo canale fluidico.

Il processo di fabbricazione del microcanale e oro nanohole piastra PDMS è mostrata nelle figure 1 e 2. Il metodo per combinare le due parti e il microchip effettivo è mostrato in figura 3. Il PDMS è stato tagliato per rivelare l&#39;interno del canale dal lato del microchip. Tuttavia, è stato difficile osservare le particelle che fluiscono nel canale a causa della rugosità superficiale del piano di taglio. Pertanto, abbiamo introdo...

Watch this Scientific Journal Video about Plasmonic Trapping and Release of Nanoparticles in a Monitoring Environment at JoVE.com

Plasmonic Trapping and Release of Nanoparticles in a Monitoring Environment

Un processo di fabbricazione di microchip che incorpora pinzette plasmoniche è presentato qui. Il microchip permette l&#39;imaging di una particella intrappolata per misurare forze di cattura massime.

Plasmonico cattura e rilascio di nanoparticelle in un ambiente di monitoraggio

Plasmonic tweezers use surface plasmon polaritons to confine polarizable nanoscale objects. Among the various designs of plasmonic tweezers, only a few ...

plasmonic-trapping-release-nanoparticles-monitoring

Universidad de Cartagena UDEC

Research

JoVE Journal

Engineering

7.5K Views.  Korea Basic Science Institute (KBSI).  Un processo di fabbricazione di microchip che incorpora pinzette plasmoniche è presentato qui. Il microchip permette l'imaging di una particella intrappolata per misurare forze di cattura massime. 

Video: Plasmonic Trapping and Release of Nanoparticles in a Monitoring Environment

Polycrystalline Silicon Thin-film Solar cells with Plasmonic-enhanced Light-trapping

One of major approaches to cheaper solar cells is reducing the amount of semiconductor material used for their fabrication and making cells thinner. To compensate for lower light absorption such physically thin devices have to incorporate light-trapping which increases their optical thickness. Light scattering by textured surfaces is a common technique but it cannot be universally applied to all solar cell technologies. Some cells, for example those made of evaporated silicon, are planar as produced and they require an alternative light-trapping means suitable for planar devices. Metal nanoparticles formed on planar silicon cell surface and capable of light scattering due to surface plasmon resonance is an effective approach.
The paper presents a fabrication procedure of evaporated polycrystalline silicon solar cells with plasmonic light-trapping and demonstrates how the cell quantum efficiency improves due to presence of metal nanoparticles.
To fabricate the cells a film consisting of alternative boron and phosphorous doped silicon layers is deposited on glass substrate by electron beam evaporation. An Initially amorphous film is crystallised and electronic defects are mitigated by annealing and hydrogen passivation. Metal grid contacts are applied to the layers of opposite polarity to extract electricity generated by the cell. Typically, such a ~2 &mu;m thick cell has a short-circuit current density (Jsc) of 14-16 mA/cm2, which can be increased up to 17-18 mA/cm2 (~25% higher) after application of a simple diffuse back reflector made of a white paint.
To implement plasmonic light-trapping a silver nanoparticle array is formed on the metallised cell silicon surface. A precursor silver film is deposited on the cell by thermal evaporation and annealed at 23&deg;C to form silver nanoparticles. Nanoparticle size and coverage, which affect plasmonic light-scattering, can be tuned for enhanced cell performance by varying the precursor film thickness and its annealing conditions. An optimised nanoparticle array alone results in cell Jsc enhancement of about 28%, similar to the effect of the diffuse reflector. The photocurrent can be further increased by coating the nanoparticles by a low refractive index dielectric, like MgF2, and applying the diffused reflector. The complete plasmonic cell structure comprises the polycrystalline silicon film, a silver nanoparticle array, a layer of MgF2, and a diffuse reflector. The Jsc for such cell is 21-23 mA/cm2, up to 45% higher than Jsc of the original cell without light-trapping or ~25% higher than Jsc for the cell with the diffuse reflector only.
Introduction
Light-trapping in silicon solar cells is commonly achieved via light scattering at textured interfaces. Scattered light travels through a cell at oblique angles for a longer distance and when such angles exceed the critical angle at the cell interfaces the light is permanently trapped in the cell by total internal reflection (Animation 1: Light-trapping). Although this scheme works well for most solar cells, there are developing technologies where ultra-thin Si layers are produced planar (e.g. layer-transfer technologies and epitaxial c-Si layers) 1 and or when such layers are not compatible with textures substrates (e.g. evaporated silicon) 2. For such originally planar Si layer alternative light trapping approaches, such as diffuse white paint reflector 3, silicon plasma texturing 4 or high refractive index nanoparticle reflector 5 have been suggested.
Metal nanoparticles can effectively scatter incident light into a higher refractive index material, like silicon, due to the surface plasmon resonance effect 6. They also can be easily formed on the planar silicon cell surface thus offering a light-trapping approach alternative to texturing. For a nanoparticle located at the air-silicon interface the scattered light fraction coupled into silicon exceeds 95% and a large faction of that light is scattered at angles above critical providing nearly ideal light-trapping condition (Animation 2: Plasmons on NP). The resonance can be tuned to the wavelength region, which is most important for a particular cell material and design, by varying the nanoparticle average size, surface coverage and local dielectric environment 6,7. Theoretical design principles of plasmonic nanoparticle solar cells have been suggested 8. In practice, Ag nanoparticle array is an ideal light-trapping partner for poly-Si thin-film solar cells because most of these design principle are naturally met. The simplest way of forming nanoparticles by thermal annealing of a thin precursor Ag film results in a random array with a relatively wide size and shape distribution, which is particularly suitable for light-trapping because such an array has a wide resonance peak, covering the wavelength range of 700-900 nm, important for poly-Si solar cell performance. The nanoparticle array can only be located on the rear poly-Si cell surface thus avoiding destructive interference between incident and scattered light which occurs for front-located nanoparticles 9. Moreover, poly-Si thin-film cells do not requires a passivating layer and the flat base-shaped nanoparticles (that naturally result from thermal annealing of a metal film) can be directly placed on silicon further increases plasmonic scattering efficiency due to surface plasmon-polariton resonance 10.
The cell with the plasmonic nanoparticle array as described above can have a photocurrent about 28% higher than the original cell. However, the array still transmits a significant amount of light which escapes through the rear of the cell and does not contribute into the current. This loss can be mitigated by adding a rear reflector to allow catching transmitted light and re-directing it back to the cell. Providing sufficient distance between the reflector and the nanoparticles (a few hundred nanometers) the reflected light will then experience one more plasmonic scattering event while passing through the nanoparticle array on re-entering the cell and the reflector itself can be made diffuse - both effects further facilitating light scattering and hence light-trapping. Importantly, the Ag nanoparticles have to be encapsulated with an inert and low refractive index dielectric, like MgF2 or SiO2, from the rear reflector to avoid mechanical and chemical damage 7. Low refractive index for this cladding layer is required to maintain a high coupling fraction into silicon and larger scattering angles, which are ensured by the high optical contrast between the media on both sides of the nanoparticle, silicon and dielectric 6. The photocurrent of the plasmonic cell with the diffuse rear reflector can be up to 45% higher than the current of the original cell or up to 25% higher than the current of an equivalent cell with the diffuse reflector only.

Polycrystalline silicon thin-film solar cells on glass are fabricated by deposition of boron and phosphorous doped silicon layers followed by crystallisation, defect passivation and metallisation. Plasmonic light-trapping is introduced by forming Ag nanoparticles on the silicon cell surface capped with a diffused reflector resulting in ~45% photocurrent enhancement.

Celle in silicio policristallino solari a film sottile con plasmoniche-enhanced Light-trapping

One of major approaches to cheaper solar cells is reducing the amount of semiconductor material used for their fabrication and making cells thinner. To ...

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Optical Trapping of Nanoparticles

Optical trapping is a technique for immobilizing and manipulating small objects in a gentle way using light, and it has been widely applied in trapping and manipulating small biological particles. Ashkin and co-workers first demonstrated optical tweezers using a single focused beam1. The single beam trap can be described accurately using the perturbative gradient force formulation in the case of small Rayleigh regime particles1. In the perturbative regime, the optical power required for trapping a particle scales as the inverse fourth power of the particle size. High optical powers can damage dielectric particles and cause heating. For instance, trapped latex spheres of 109 nm in diameter were destroyed by a 15 mW beam in 25 sec1, which has serious implications for biological matter2,3.
A self-induced back-action (SIBA) optical trapping was proposed to trap 50 nm polystyrene spheres in the non-perturbative regime4. In a non-perturbative regime, even a small particle with little permittivity contrast to the background can influence significantly the ambient electromagnetic field and induce a large optical force. As a particle enters an illuminated aperture, light transmission increases dramatically because of dielectric loading. If the particle attempts to leave the aperture, decreased transmission causes a change in momentum outwards from the hole and, by Newton's Third Law, results in a force on the particle inwards into the hole, trapping the particle. The light transmission can be monitored; hence, the trap can become a sensor. The SIBA trapping technique can be further improved by using a double-nanohole structure.
The double-nanohole structure has been shown to give a strong local field enhancement5,6. Between the two sharp tips of the double-nanohole, a small particle can cause a large change in optical transmission, thereby inducing a large optical force. As a result, smaller nanoparticles can be trapped, such as 12 nm silicate spheres7 and 3.4 nm hydrodynamic radius bovine serum albumin proteins8. In this work, the experimental configuration used for nanoparticle trapping is outlined. First, we detail the assembly of the trapping setup which is based on a Thorlabs Optical Tweezer Kit. Next, we explain the nanofabrication procedure of the double-nanohole in a metal film, the fabrication of the microfluidic chamber and the sample preparation. Finally, we detail the data acquisition procedure and provide typical results for trapping 20 nm polystyrene nanospheres.

The following setup approach details low power optical trapping of dielectric nanoparticles using a double-nanohole in metal film.

Trapping ottica di nanoparticelle

Optical trapping is a technique for immobilizing and manipulating small objects in a gentle way using light, and it has been widely applied in trapping ...

Construction of a High Resolution Microscope with Conventional and Holographic Optical Trapping Capabilities

High resolution microscope systems with optical traps allow for precise manipulation of various refractive objects, such as dielectric beads 1 or cellular organelles 2,3, as well as for high spatial and temporal resolution readout of their position relative to the center of the trap. The system described herein has one such "traditional" trap operating at 980 nm. It additionally provides a second optical trapping system that uses a commercially available holographic package to simultaneously create and manipulate complex trapping patterns in the field of view of the microscope 4,5 at a wavelength of 1,064 nm. The combination of the two systems allows for the manipulation of multiple refractive objects at the same time while simultaneously conducting high speed and high resolution measurements of motion and force production at nanometer and piconewton scale.

The system described herein employs a traditional optical trap as well as an independent holographic optical trapping line, capable of creating and manipulating multiple traps. This allows for the creation of complex geometric arrangements of refractive particles while also permitting simultaneous high-speed, high-resolution measurements of the activity of biological enzymes.

Costruzione di un microscopio ad alta risoluzione con convenzionali e Holographic Capabilities intrappolamento ottico

High resolution microscope systems with optical traps allow for precise manipulation of various refractive objects, such as dielectric beads 1 or cellular ...

Utilization of Plasmonic and Photonic Crystal Nanostructures for Enhanced Micro- and Nanoparticle Manipulation

A method to manipulate the position and orientation of submicron particles nondestructively would be an incredibly useful tool for basic biological research. Perhaps the most widely used physical force to achieve noninvasive manipulation of small particles has been dielectrophoresis(DEP).1 However, DEP on its own lacks the versatility and precision that are desired when manipulating cells since it is traditionally done with stationary electrodes. Optical tweezers, which utilize a three dimensional electromagnetic field gradient to exert forces on small particles, achieve this desired versatility and precision.2 However, a major drawback of this approach is the high radiation intensity required to achieve the necessary force to trap a particle which can damage biological samples.3 A solution that allows trapping and sorting with lower optical intensities are optoelectronic tweezers (OET) but OET's have limitations with fine manipulation of small particles; being DEP-based technology also puts constraint on the property of the solution.4,5
This video article will describe two methods that decrease the intensity of the radiation needed for optical manipulation of living cells and also describe a method for orientation control. The first method is plasmonic tweezers which use a random gold nanoparticle (AuNP) array as a substrate for the sample as shown in Figure 1. The AuNP array converts the incident photons into localized surface plasmons (LSP) which consist of resonant dipole moments that radiate and generate a patterned radiation field with a large gradient in the cell solution. Initial work on surface plasmon enhanced trapping by Righini et al and our own modeling have shown the fields generated by the plasmonic substrate reduce the initial intensity required by enhancing the gradient field that traps the particle.6,7,8 The plasmonic approach allows for fine orientation control of ellipsoidal particles and cells with low optical intensities because of more efficient optical energy conversion into mechanical energy and a dipole-dependent radiation field. These fields are shown in figure 2 and the low trapping intensities are detailed in figures 4 and 5. The main problems with plasmonic tweezers are that the LSP's generate a considerable amount of heat and the trapping is only two dimensional. This heat generates convective flows and thermophoresis which can be powerful enough to expel submicron particles from the trap.9,10 The second approach that we will describe is utilizing periodic dielectric nanostructures to scatter incident light very efficiently into diffraction modes, as shown in figure 6.11 Ideally, one would make this structure out of a dielectric material to avoid the same heating problems experienced with the plasmonic tweezers but in our approach an aluminum-coated diffraction grating is used as a one-dimensional periodic dielectric nanostructure. Although it is not a semiconductor, it did not experience significant heating and effectively trapped small particles with low trapping intensities, as shown in figure 7. Alignment of particles with the grating substrate conceptually validates the proposition that a 2-D photonic crystal could allow precise rotation of non-spherical micron sized particles.10 The efficiencies of these optical traps are increased due to the enhanced fields produced by the nanostructures described in this paper.

Plasmonic tweezers and photonic crystal nanostructures are shown to produce useful enhancements in the efficiency and orientation control of optically trapping micro- and nano-particles.

L&#39;utilizzo di nanostrutture di cristallo plasmoniche e fotonici per Enhanced manipolazione micro e nanoparticelle

A method to manipulate the position and orientation of submicron particles nondestructively would be an incredibly useful tool for basic biological ...

Bioingegneria

Analyzing the Movement of the Nauplius 'Artemia salina' by Optical Tracking of Plasmonic Nanoparticles

We demonstrate how optical tweezers may provide a sensitive tool to analyze the fluidic vibrations generated by the movement of small aquatic organisms. A single gold nanoparticle held by an optical tweezer is used as a sensor to quantify the rhythmic motion of a Nauplius larva (Artemia salina) in a water sample. This is achieved by monitoring the time dependent displacement of the trapped nanoparticle as a consequence of the Nauplius activity. A Fourier analysis of the nanoparticle&#39;s position then yields a frequency spectrum that is characteristic to the motion of the observed species. This experiment demonstrates the capability of this method to measure and characterize the activity of small aquatic larvae without the requirement to observe them directly and to gain information about the position of the larvae with respect to the trapped particle. Overall, this approach could give an insight on the vitality of certain species found in an aquatic ecosystem and could expand the range of conventional methods for analyzing water samples.

Analyzing the Movement of the Nauplius 'Artemia salina' by Optical Tracking of Plasmonic Nanoparticles

We use optical tracking of plasmonic nanoparticles to probe and characterize the frequency movements of aquatic organisms.

Analizzando il movimento del Nauplius &#39;<em&gt; Artemia salina</em&gt; &#39;Di monitoraggio ottico di nanoparticelle plasmoniche

We demonstrate how optical tweezers may provide a sensitive tool to analyze the fluidic vibrations generated by the movement of small aquatic organisms. A ...

Fabrication and Operation of a Nano-Optical Conveyor Belt

The technique of using focused laser beams to trap and exert forces on small particles has enabled many pivotal discoveries in the nanoscale biological and physical sciences over the past few decades. The progress made in this field invites further study of even smaller systems and at a larger scale, with tools that could be distributed more easily and made more widely available. Unfortunately, the fundamental laws of diffraction limit the minimum size of the focal spot of a laser beam, which makes particles smaller than a half-wavelength in diameter hard to trap and generally prevents an operator from discriminating between particles which are closer together than one half-wavelength. This precludes the optical manipulation of many closely-spaced nanoparticles and&#160;limits the&#160;resolution of optical-mechanical systems. Furthermore, manipulation using focused beams requires beam-forming or steering optics, which can be very bulky and expensive. To address these limitations in the system scalability of conventional optical trapping our lab has devised an alternative technique which utilizes near-field optics to move particles across a chip. Instead of focusing laser beams in the far-field, the optical near field of plasmonic resonators produces the necessary local optical intensity enhancement to overcome the restrictions of diffraction and manipulate particles at higher resolution. Closely-spaced resonators produce strong optical traps which can be addressed to mediate the hand-off of particles from one to the next in a conveyor-belt-like fashion. Here, we describe how to design and produce a conveyor belt using a gold surface patterned with plasmonic C-shaped resonators and how to operate it with polarized laser light to achieve super-resolution nanoparticle manipulation and transport. The nano-optical conveyor belt chip can be produced using lithography techniques and easily packaged and distributed.

The scalability and resolution of conventional optical manipulation techniques are limited by diffraction. We circumvent the diffraction limit and describe a method of optically transporting nanoparticles across a chip using a gold surface patterned with a path of closely spaced C-shaped plasmonic resonators.

Fabbricazione e funzionamento di un nano-ottica Nastro trasportatore

The technique of using focused laser beams to trap and exert forces on small particles has enabled many pivotal discoveries in the nanoscale biological ...

Construction and Operation of a Light-driven Gold Nanorod Rotary Motor System

The possibility to generate and measure rotation and torque at the nanoscale is of fundamental interest to the study and application of biological and artificial nanomotors and may provide new routes towards single cell analysis, studies of non-equilibrium thermodynamics, and mechanical actuation of nanoscale systems. A facile way to drive rotation is to use focused circularly polarized laser light in optical tweezers. Using this approach, metallic nanoparticles can be operated as highly efficient scattering-driven rotary motors spinning at unprecedented rotation frequencies in water.
In this protocol, we outline the construction and operation of circularly-polarized optical tweezers for nanoparticle rotation and describe the instrumentation needed for recording the Brownian dynamics and Rayleigh scattering of the trapped particle. The rotational motion and the scattering spectra provides independent information on the properties of the nanoparticle and its immediate environment. The experimental platform has proven useful as a nanoscopic gauge of viscosity and local temperature, for tracking morphological changes of nanorods and molecular coatings, and as a transducer and probe of photothermal and thermodynamic processes.

Plasmonic gold nanorods can be trapped in liquids and rotated at kHz frequencies using circularly-polarized optical tweezers. Introducing tools for Brownian dynamics analysis and light scatteringspectroscopy leads to a powerful system for research and application in numerous fields of science.

Costruzione e funzionamento di un sistema motore basato su luce oro Nanorod Rotary

The possibility to generate and measure rotation and torque at the nanoscale is of fundamental interest to the study and application of biological and ...

Trapping of Micro Particles in Nanoplasmonic Optical Lattice

The plasmonic optical tweezer has been developed to overcome the diffraction limits of the conventional far field optical tweezer. Plasmonic optical lattice consists of an array of nanostructures, which exhibit a variety of trapping and transport behaviors. We report the experimental procedures to trap micro-particles in a simple square nanoplasmonic optical lattice. We also describe the optical setup and the nanofabrication of a nanoplasmonic array. The optical potential is created by illuminating an array of gold nanodiscs with a Gaussian beam of 980 nm wavelength, and exciting plasmon resonance. The motion of particles is monitored by fluorescence imaging. A scheme to suppress photothermal convection is also described to increase usable optical power for optimal trapping. Suppression of convection is achieved by cooling the sample to a low temperature, and utilizing the near-zero thermal expansion coefficient of a water medium. Both single particle transport and multiple particle trapping are reported here.

We describe a procedure to optically trap micro-particles in nanoplasmonic optical lattice.

Intrappolamento delle Micro particelle in grata ottica Nanoplasmonic

The plasmonic optical tweezer has been developed to overcome the diffraction limits of the conventional far field optical tweezer. Plasmonic optical ...

Monitoring Conformational Dynamics of Single Unmodified Proteins using Plasmonic Nanotweezers

Current single-molecule techniques to characterize proteins typically require labels, tethers, or the use of non-native solution conditions. Such changes can alter protein biophysics and reduce the usefulness of the data acquired. Plasmonic nanotweezers is a technique that uses localized surface plasmon resonance (LSPR) on gold nanostructures to enhance the electric field within a confined hotspot region. This field enhancement allows for the use of low laser powers to trap single nanoparticles far smaller than conventional optical tweezers, down to only a few nanometers in diameter, such as single proteins. Trapping of single protein molecules within the hotspot region induces a shift in the local refractive index (nprotein &#62; nwater), altering light scattering as a product of the molecule&#39;s polarisability, which is affected by its volume, shape anisotropy, and refractive index. An avalanche photodiode (APD) collects the subsequent changes in light scattering. These alterations can then be analyzed to determine changes in the trapped molecule, including its size, global conformation, and dynamics of conformational change over time. The incorporation of microfluidics within the system allows for controlled environmental changes and real-time monitoring of their subsequent effects on the molecule. In this protocol, we demonstrate the steps to trap single protein molecules, alter their environmental solution conditions, and monitor their corresponding conformational changes using a plasmonic nanotweezers system.

Plasmonic nanotweezers use localized surface plasmon resonance in gold nanostructures to trap single nanoparticles, including proteins, within a nanometer-scale optical field. Changes in the scattered signal reveal protein presence and conformational dynamics, enabling monitoring without fluorophore modifications or surface tethering.

Monitoraggio della dinamica conformazionale di singole proteine non modificate mediante Nanotweezers plasmonici

Current single-molecule techniques to characterize proteins typically require labels, tethers, or the use of non-native solution conditions. Such changes ...

Optical Trapping of Plasmonic Nanoparticles for In Situ Surface-Enhanced Raman Spectroscopy Characterizations

Surface-enhanced Raman spectroscopy (SERS) enables the ultrasensitive detection of analyte molecules in various applications due to the enhanced electric field of metallic nanostructures. Salt-induced silver nanoparticle aggregation is the most popular method for generating SERS-active substrates; however, it is limited by poor reproducibility, stability, and biocompatibility. The present protocol integrates optical manipulation and SERS detection to develop an efficient analytical platform to address this. A 1064 nm trapping laser and a 532 nm Raman probe laser are combined in a microscope to assemble silver nanoparticles, which generate plasmonic hotspots for in situ SERS measurements in aqueous environments. Without aggregating agents, this dynamic plasmonic silver nanoparticle assembly enables an approximately 50-fold enhancement of the analyte molecule signal. Moreover, it provides spatial and temporal control to form the SERS-active assembly in as low as 0.05 nM analyte-coated silver nanoparticle solution, which minimizes the potential perturbation for in vivo analysis. Hence, this optical trapping-integrated SERS platform holds great potential for efficient, reproducible, and stable molecular analyses in liquids, especially in aqueous physiological environments.

Optical Trapping of Plasmonic Nanoparticles for In Situ Surface-Enhanced Raman Spectroscopy Characterizations

The present protocol describes a convenient approach to integrating optical trapping and surface-enhanced Raman spectroscopy (SERS) to manipulate plasmonic nanoparticles for sensitive molecular detection. Without aggregating agents, the trapping laser assembles plasmonic nanoparticles to enhance the SERS signals of target analytes for in situ spectroscopic measurements.

Intrappolamento ottico di nanoparticelle plasmoniche per la caratterizzazione della spettroscopia Raman potenziata dalla superficie in situ

Surface-enhanced Raman spectroscopy (SERS) enables the ultrasensitive detection of analyte molecules in various applications due to the enhanced electric ...

Plasmonico cattura e rilascio di nanoparticelle in un ambiente di monitoraggio

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