Diese Arbeit wurde im Rahmen des Center for Nanoscience Energie, Energy Frontier Research Center des US Department of Energy, Office of Science unter Verleihungsnummer DE-SC0001013 finanziert unterstützt. Wir wollen auch Dr. Max und Dr. Zhang Jianhua Yang von HP Labs für ihre Hilfe auf TiO 2 Film Sputtern und Brechungsindizes Mess danken.

1. Bereiten Sie die Blank Polydimethylsiloxan (PDMS) Substrat für Nanoimprint Mold <ol><li> Silizium-Wafer-Behandlung Prozess <ol><li> Reinigen einer 4 inch Siliziumwafer durch Spülen mit Aceton, Methanol und Isopropanol. </li><li> Blasen sie trocken mit dem Stickstoff gun. </li><li> Reinigen Sie es mit Piranha-Lösung (3: 1 Gemisch aus Schwefelsäure mit 30% Wasserstoffperoxid) durch Einweichen innerhalb 15 min. </li><li> Spülen Sie es mit DI-Wasser. Trocken blasen mit dem Stickstoff gun. </li><li> Legen Sie die Wafer in einem Glas Exsikkator. Fügen Sie einen Tropfen (20 Tropfen = 1 ml) der Trennmittel (Trichlorsilan) in den Exsikkator. </li><li> Abpumpen der Exsikkator, bis das Messgerät liest -762 Torr und warten Sie 5 Stunden. </li><li> Nehmen Sie die Wafer aus, die mit Trennmittel behandelt worden ist. </li></ol></li><li> Herstellung von PDMS Film (Wird als Mold in Nanoimprint) <ol><li> Ein Gewicht von 10 g Siliconelastomergrundstoff und 1 g des Härters. </li><li> Fügen Sie sie in der gleichen Becherglas. </li><li> Stir und mischen mit einem Glasstab für 5 min. </li><li> Die Mischung in einem Vakuum-Exsikkator bis das Manometer liest -762 Torr zu pumpen alle eingeschlossenen Luftblasen. </li><li> Verteile sie gleichmäßig auf die behandelte 4-Zoll-Siliziumwafer. </li><li> Backen Sie den Wafer mit PDMS oben im Vakuumofen für 7 h bei 80 ° C, um die PDMS Film zu härten. </li></ol></li></ol> 2. Bereiten Sie die Nanoimprint-Form (Vervielfältigung von der Master-Form) <ol><li> Spin zwölf Tropfen (20 Tropfen = 1 ml) von UV-härtbaren Resist (15,2%) auf eine saubere lassen Siliziumwafer für 30 Sekunden bei 1.500 Umdrehungen pro Minute. </li><li> Ziehen Sie vorsichtig ein Stück PDMS Folie von der behandelten Siliziumscheibe. </li><li> Legen Sie die PDMS-Film auf die UV-härtbaren widerstehen und lassen Sie es zu absorbieren die UV-Resist für 5 min dann abziehen. </li><li> Wiederholen 2,1-2,3 auf der gleichen PDMS-Film für zwei mal. Absorbieren die UV-Resist für 3 min und 1 min auf. </li><li> Legen Sie die PDMS-Film (nach dreimaliger UV widerAufnahme) auf ein Siliziummasterform. </li><li> Legen Sie es in eine Kammer mit Stickstoffumgebung. </li><li> Schalten Sie UV-Lampe, die Probe für 5 min zu heilen. </li><li> Ziehen Sie die PDMS-Film. Der ausgehärtete UV Resist auf dem PDMS wird die negative Muster der Master-Form zu halten. </li><li> Verwenden RF O2-Plasma, die PDMS-Form zu behandeln. (HF-Leistung: 30 W, Druck: 260 mTorr, Zeit: ca. 1 min) </li><li> Legen Sie die PDMS-Form in einer Vakuumkammer mit einem Tropfen (20 Tropfen = 1 ml) der Trennmittel für 2 Std. </li></ol> 3. Nanoimprint Musterübertragung <ol><li> Spin acht Tropfen (20 Tropfen = 1 ml) aus PMMA (996 T, 3,1%) auf das Substrat für 50 s bei 3.500 Upm eingedruckt. </li><li> Backen auf einer Heizplatte 5 min bei 120 ° C. </li><li> Warten Sie, bis die Probe zum Abkühlen. </li><li> Spin acht Tropfen (20 Tropfen = 1 ml) von UV-härtbaren Resist (3,9%) auf dem gleichen Substrat. </li><li> Legen Sie die PDMS-Form (in Schritt 2 hergestellt) auf die Probe (sowohl mit UV-widerstehen und PMMA). </li><li> Legen Sie es in eine Kammer mit Stickstoffumgebung.</li><li> Schalten Sie die UV-Lampe für 5 min zu heilen. </li><li> Schälen Sie die PDMS-Form aus der Probe und das Muster auf der PDMS-Form wird auf die Probe übertragen. </li></ol> 4. Cr Abhebeprozeß <ol><li> Reactive Ion Etching Restschicht von UV-widerstehen und PMMA Hinweis: Die SOP für ICP Maschine kann bei https://www.nanocenter.umd.edu/equipment/fablab/sops/etch-07/Oxford%20Chlorine%20Etcher%20SOP.pdf gefunden werden <ol><li> Melden Sie sich an ICP RIE-Maschine. </li><li> Legen Sie eine leere 4-Zoll-Siliziumwafer. Führen Sie das saubere Rezept für 10 min. </li><li> Nehmen Sie die leeren Siliziumwafer aus. </li><li> Montieren Sie die Probe auf einem anderen sauberen Siliziumwafer und laden Sie es in die Maschine. </li><li> Führen Sie die UV Resistätzen Rezept für 2 min (das Rezept können in Tabelle 1 zu finden). </li><li> Nehmen Sie die Probe aus. Legen Sie eine leere 4-Zoll-Siliziumwafer. Führen Sie den sauberen Rezept für 10 min (in Tabelle 1 zu finden). </li><li> Montieren Sie die Probe auf einem sauberen Siliziumwaferund laden Sie es in die Maschine. </li><li> Führen Sie das PMMA Ätzen Rezept (in Tabelle 1 aufgeführt) für 2 min. Anmerkung: Nun wird die Restresist geätzt wurde, und das Substrat freigelegt wird. </li></ol></li><li> Cr Elektronenstrahlbedampfung <ol><li> Melden Sie sich e-beam Verdampfer. </li><li> Laden Sie die Cr Metallquelle und Probe in die Kammer. </li><li> Stellen Sie die Dicke (20 nm) und Abscheidungsrate (0,03 nm / s). </li><li> Pumpen Sie die Kammer, bis erforderliche Vakuum (10 -7 Torr) erreicht ist. </li><li> Starten Sie den Abscheidungsprozess. </li><li> Nehmen Sie die Probe aus, nachdem die Ablagerung beendet. </li></ol></li><li> CR Lift-off Verfahren <ol><li> Tauchen Sie die Probe in Aceton mit Ultraschallbewegung für 5 min. </li><li> Reinigen Sie die Probe durch Spülen mit Aceton, Methanol und Isopropanol. Hinweis: Der Cr verdampft auf dem Resist wird abgehoben, und eine Cr-Maske zum Substrat Ätzen gebildet. </li></ol></li></ol> 5. TiO 2 Deposition <ol><li> Lastprobe. </li><li> Stellen Sie die Parameter für die Gleichstrom-Magnetron-Sputter-Maschine <ol><li> Verwenden einen Kammerdruck von 1,5 mTorr Ar-Strom von 100 sccm und einer Sputterleistung von 130 W. </li><li> Verwenden eine Temperatur von 27 ° C und eine Stufe Drehzahl von 20 Upm. </li></ol></li><li> Starten Sie das Sputter-Verfahren und stoppen an der gewünschten Dicke. </li><li> Nehmen Sie die Probe aus und glühen die TiO 2 -Schicht in Sauerstoffumgebung bei 300 ° C für 3 Stunden. </li></ol> 6. High Contrast Grating Etching <ol><li> Log in der induktiv gekoppelten Plasma (ICP) reaktives Ionenätzen (RIE) Maschine. </li><li> TiO 2 Ätzen <ol><li> Legen Sie eine leere 4-Zoll-Siliziumwafer. </li><li> Starten und die saubere Rezept für 10 min (in Tabelle 1 zu finden). </li><li> Entladen Sie laden den Rohling Wafer und laden Sie die Probe mit Cr-Maske. </li><li> Stellen Ätzzeit. Starten TiO 2 Ätzen Rezept. Der Ätzprozess wird automatischtisch zu stoppen. </li><li> Entladen Sie die Probe. </li></ol></li><li> SiO 2 Etching <ol><li> Wiederholen Sie Schritt 5.2 nur geben Sie den SiO 2 Ätzen Rezept. </li></ol></li></ol> 7. Reflexionsmessung <ol><li> Melden Sie sich an und schalten Sie das Messsystem. </li><li> Setzen Sie den Reflexionsstandard Spiegel auf dem Probenhalter und richten Sie den optischen Weg. </li><li> Kalibrierung des Systems für die 100% Reflexion. </li><li> Nehmen Sie die Reflexionsstandard Spiegel und setzen Sie die HCG. </li><li> Messen des Reflexionsvermögens des HCG. </li><li> Speichern Sie die Daten und melden Sie sich aus dem Messsystem. </li></ol>

<ol>
	<li>Horne, S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+Solid+500+Sun+Compound+Concentrator+PV+Design.">A Solid 500 Sun Compound Concentrator PV Design.</a> Photovoltaic Energy Conversion, Conference Record of the 2006 IEEE 4th World Conference on. , 694-697 (2006).</li><li>Guter, W., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Current-matched+triple-junction+solar+cell+reaching+41.1%+conversion+efficiency+under+concentrated+sunlight.">Current-matched triple-junction solar cell reaching 41.1% conversion efficiency under concentrated sunlight.</a> Applied Physics Letters. 94, 223504 (2009).</li><li>Shockley, W., Queisser, H. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Detailed+Balance+Limit+of+Efficiency+of+p-n+Junction+Solar+Cells.">Detailed Balance Limit of Efficiency of p-n Junction Solar Cells.</a> Journal of Applied Physics. 32, 510-519 (1961).</li><li>Green, M. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Potential+for+low+dimensional+structures+in+photovoltaics.">Potential for low dimensional structures in photovoltaics.</a> Materials Science and Engineering: B. 74, 118-124 (2000).</li><li>Karagodsky, V., Chang-Hasnain, C. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Physics+of+near-wavelength+high+contrast+gratings.">Physics of near-wavelength high contrast gratings.</a> Opt. Express. 20, 10888-10895 (2012).</li><li>Chou, S. Y., Krauss, P. R., Renstrom, P. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nanoimprint+lithography.">Nanoimprint lithography.</a> Journal of Vacuum Science &amp; Technology B: Microelectronics and Nanometer Structures. 14, 4129-4133 (1996).</li><li>Namiki, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+new+FDTD+algorithm+based+on+alternating-direction+implicit+method.+Microwave+Theory+and+Techniques.">A new FDTD algorithm based on alternating-direction implicit method. Microwave Theory and Techniques.</a> IEEE Transactions on. 47, 2003-2007 (1999).</li><li>Moharam, M. G., Gaylord, T. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Rigorous+coupled-wave+analysis+of+planar-grating+diffraction.">Rigorous coupled-wave analysis of planar-grating diffraction.</a> J. Opt. Soc. Am. 71, 811-818 (1981).</li><li>Yao, Y., Liu, H., Wu, W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Spectrum+splitting+using+multi-layer+dielectric+meta-surfaces+for+efficient+solar+energy+harvesting.">Spectrum splitting using multi-layer dielectric meta-surfaces for efficient solar energy harvesting.</a> Appl. Phys. A. 115, 713-719 (2014).</li><li>Yao, Y., Liu, H., Wu, W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fabrication+of+high-contrast+gratings+for+a+parallel+spectrum+splitting+dispersive+element+in+a+concentrated+photovoltaic+system.">Fabrication of high-contrast gratings for a parallel spectrum splitting dispersive element in a concentrated photovoltaic system.</a> Journal of Vacuum Science &amp; Technology B. 32, 06FG04-06FG04-6 (2014).</li><li>Solak, H. H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Sub-50+nm+period+patterns+with+EUV+interference+lithography.">Sub-50 nm period patterns with EUV interference lithography.</a> Microelectronic Engineering. 67, 56-62 (2003).</li><li>Li, Z., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Hybrid+nanoimprint&#8722;+soft+lithography+with+sub-15+nm+resolution.">Hybrid nanoimprint&#8722; soft lithography with sub-15 nm resolution.</a> Nano letters. 9, 2306-2310 (2009).</li><li>Yu, Z., Chen, L., Wu, W., Ge, H., Chou, S. Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fabrication+of+nanoscale+gratings+with+reduced+line+edge+roughness+using+nanoimprint+lithography.">Fabrication of nanoscale gratings with reduced line edge roughness using nanoimprint lithography.</a> Journal of Vacuum Science &amp; Technology B. 21, 2089-2092 (2003).</li></ol>

The authors have nothing to disclose.

Zunächst ist die Qualität des TiO 2 -Films sehr entscheidend für den HCG Leistung. Der Reflexionspeak wird höher sein, wenn die TiO 2 -Schicht hat einen geringeren Verlust und Oberflächenrauhigkeit. Der TiO 2 -Film mit einem höheren Brechungsindex ist auch günstig, weil der optische Modenführung wird durch einen höheren Kontrast im Index, was zu einer flacheren und breiteren Reflexionsbande in HCG geben kann verbessert werden. Zweitens werden die Her...

Unsere moderne Gesellschaft nicht ohne einen erheblichen Teil des Energieverbrauchs auf erneuerbare Energiequellen zu überleben. Um dies zu ermöglichen, müssen wir einen Weg, um erneuerbare Energien zu einem Preis niedriger als auf Erdöl basierenden Energiequellen in naher Zukunft ernten zu finden. Solarenergie ist die am häufigsten vorkommende erneuerbaren Energien auf der Erde. Trotz, dass viele Fortschritte haben in Solarenergieernte erzielt wurden, ist es immer noch sehr schwierig, mit Erdöl basierenden Energiequellen konkurrieren. Zur Verbesserung der Effizienz von Solarzellen ist eine der effizientesten Methoden, um die Systemkosten der Nutzung von Sonnenenergie zu senken. Optische Linsen und Reflektoren Schale werden üblicherweise in den meisten konzentrierten Photovoltaik (CPV) 1 verwendet, um eine hohe Konzentration von Sonnenenergie Einfall auf die kleinflächige Solarzellen zu erreichen, so dass es wirtschaftlich sinnvoll zu teuren Tandem Multi-Junction-Solarzellen 2 in auszunutzen CPV-Systeme, und eine angemessene pflegenKosten zugleich. Für die meisten nicht-konzentrierten Photovoltaik, die in der Regel großflächig Rate von Solarzellen, die mit hohen Kosten Tandem-Solarzellen nicht eingebunden werden können, obwohl sie in der Regel einen größeren Sonnenspektrums Antwort und einen höheren Gesamtumwandlungswirkungsgrad als die Einzelsolarzellen 3. In jüngster Zeit mit Hilfe der parallelen Spektrum Teilungsoptik (dh dispersive Element), der parallel Spektrum Spalt Photovoltaik 4 hat es möglich gemacht, daß eine ähnliche oder bessere Spektrum Abdeckung und Umwandlungseffizienz ohne Verwendung der teuren Tandemsolarzellen erreicht werden. Das Sonnenspektrum in verschiedene Bänder aufgeteilt werden und jede Band kann absorbiert und Strom von den Facheinzelsolarzellen werden. Auf diese Weise können die teuren Tandemsolarzellen in CPV-Systeme durch eine parallele Verteilung der Single-Junction-Solarzelle ersetzt werdens, ohne Kompromisse bei der Leistung. Das dispersive Element, das in diesem Bericht entworfen wurde, kann in einer reflektierenden CPV-System (die auf Teller Reflektoren basiert), um parallel Spektrum Aufspaltung für die verbesserte Solarstromumwandlungseffizienz und reduzierten Kosten zu realisieren angewendet werden. Mehrschicht hohen Kontrast Gitter (HCG) 5 als dispersives Element durch die Gestaltung jeder Schicht HCG verwendet, um als ein optisches Bandspiegel funktionieren. Strukturen und Parametern des dispersiven Elements numerisch optimiert. Darüber hinaus ist die Herstellung von Hochkontrastgittern zum dispersiven Elements durch Verwendung von dielektrischen (TiO 2) Sputtern Nanoimprintlithografie 6 und reaktives Ionenätzen untersucht und nachgewiesen.

<table border="0" cellpadding="0" cellspacing="0">
	<tbody>
		<tr>
			<td>184 SILICONE ELASTOMER KIT</td>
			<td>SYLGARD</td>
			<td></td>
			<td>Polydimethylsiloxane (PDMS)</td>
		</tr>
		<tr>
			<td>4-inch silicon wafer</td>
			<td>Universitywafer</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>4-inch fused silica wafer</td>
			<td>Universitywafer</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Poly(methyl methacrylate)</td>
			<td>SIGMA-ALDRICH</td>
			<td align="right">182265</td>
			<td></td>
		</tr>
		<tr>
			<td>UV-curable resist</td>
			<td></td>
			<td></td>
			<td>Nor available on market</td>
		</tr>
		<tr>
			<td>PlasmaLab System 100</td>
			<td>Oxford Instruments</td>
			<td></td>
			<td>ICP IRE machine</td>
		</tr>
		<tr>
			<td>UV curing system for nanoimprint fabrication</td>
			<td></td>
			<td></td>
			<td>Not available on market</td>
		</tr>
		<tr>
			<td>Ocean Optics HR-4000&#160;</td>
			<td>Ocean Optics</td>
			<td>HR-4000</td>
			<td>Spectrometer with normal detector</td>
		</tr>
		<tr>
			<td>Lambda 950 UV / VIS</td>
			<td>PerkinElmer</td>
			<td></td>
			<td>spectrometer with hemisphere intergration detector</td>
		</tr>
		<tr>
			<td>JSM-7001F-LV</td>
			<td>JEOL</td>
			<td></td>
			<td>Field emission SEM</td>
		</tr>
		<tr>
			<td>DC magnetron sputtering machine</td>
			<td></td>
			<td></td>
			<td>Equipment is in HP labs, who helped us to sputter the TiO2</td>
		</tr>
		<tr>
			<td>Metal e-beam evaporator</td>
			<td>Temescal</td>
			<td>BJD-1800</td>
			<td></td>
		</tr>
	</tbody>
</table>

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.

Abbildung 1 zeigt die Durchführung des dispersiven Elements (Multilayer hohen Kontrast Gitter (HCG)) in konzentrierter Photovoltaikanlage. Die Sonne Licht wird zuerst durch den Primärspiegel reflektiert und trifft auf den reflektierenden dispersiven Element, wo der Strahl reflektiert und in verschiedenen Banden unterschiedlicher Wellenlängen aufgespalten. Jedes Band wird auf eine bestimmte Stelle auf der Solarzellenanordnung für die beste Absorption und Umwandlung in Elektrizität auftreffen. Der Sc...

Watch this Scientific Journal Video about Fabrication of High Contrast Gratings for the Spectrum Splitting Dispersive Element in a Concentrated Photovoltaic System at JoVE.com

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

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.

Herstellung von High Contrast Roste für die Spectrum Splitting dispersives Element in einer konzentrierten Photovoltaik-Anlage

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

fabrication-high-contrast-gratings-for-spectrum-splitting-dispersive

Research

JoVE Journal

Engineering

10.6K Aufrufe.  University of Sothern California. 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. 

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

Electron Channeling Contrast Imaging for Rapid III-V Heteroepitaxial Characterization

Misfit dislocations in heteroepitaxial layers of GaP grown on Si(001) substrates are characterized through use of electron channeling contrast imaging (ECCI) in a scanning electron microscope (SEM). ECCI allows for imaging of defects and crystallographic features under specific diffraction conditions, similar to that possible via plan-view transmission electron microscopy (PV-TEM). A particular advantage of the ECCI technique is that it requires little to no sample preparation, and indeed can use large area, as-produced samples, making it a considerably higher throughput characterization method than TEM. Similar to TEM, different diffraction conditions can be obtained with ECCI by tilting and rotating the sample in the SEM. This capability enables the selective imaging of specific defects, such as misfit dislocations at the GaP/Si interface, with high contrast levels, which are determined by the standard invisibility criteria. An example application of this technique is described wherein ECCI imaging is used to determine the critical thickness for dislocation nucleation for GaP-on-Si by imaging a range of samples with various GaP epilayer thicknesses. Examples of ECCI micrographs of additional defect types, including threading dislocations and a stacking fault, are provided as demonstration of its broad, TEM-like applicability. Ultimately, the combination of TEM-like capabilities &#8211; high spatial resolution and richness of microstructural data &#8211; with the convenience and speed of SEM, position ECCI as a powerful tool for the rapid characterization of crystalline materials.

The use of electron channeling contrast imaging in a scanning electron microscope to characterize defects in III-V/Si heteroexpitaxial thin films is described. This method yields similar results to plan-view transmission electron microscopy, but in significantly less time due to lack of required sample preparation.

Electron Channeling Contrast Imaging Rapid III-V heteroepitaktischen Charakterisierung

Misfit dislocations in heteroepitaxial layers of GaP grown on Si(001) substrates are characterized through use of electron channeling contrast imaging ...

Forschung

Ingenieurwesen

Energy Dispersive X-ray Tomography for 3D Elemental Mapping of Individual Nanoparticles

Energy dispersive X-ray spectroscopy within the scanning transmission electron microscope (STEM) provides accurate elemental analysis with high spatial resolution, and is even capable of providing atomically resolved elemental maps. In this technique, a highly focused electron beam is incident upon a thin sample and the energy of emitted X-rays is measured in order to determine the atomic species of material within the beam path. This elementally sensitive spectroscopy technique can be extended to three dimensional tomographic imaging by acquiring multiple spectrum images with the sample tilted along an axis perpendicular to the electron beam direction.
Elemental distributions within single nanoparticles are often important for determining their optical, catalytic and magnetic properties. Techniques such as X-ray tomography and slice and view energy dispersive X-ray mapping in the scanning electron microscope provide elementally sensitive three dimensional imaging but are typically limited to spatial resolutions of &gt; 20 nm. Atom probe tomography provides near atomic resolution but preparing nanoparticle samples for atom probe analysis is often challenging. Thus, elementally sensitive techniques applied within the scanning transmission electron microscope are uniquely placed to study elemental distributions within nanoparticles of dimensions 10-100 nm.
Here, energy dispersive X-ray (EDX) spectroscopy within the STEM is applied to investigate the distribution of elements in single AgAu nanoparticles. The surface segregation of both Ag and Au, at different nanoparticle compositions, has been observed.

The use of energy dispersive X-ray tomography in the scanning transmission electron microscope to characterize elemental distributions within single nanoparticles in three dimensions is described.

Energieröntgentomografie für 3D-Elementar Zuordnung einzelner Nanopartikel

Energy dispersive X-ray spectroscopy within the scanning transmission electron microscope (STEM) provides accurate elemental analysis with high spatial ...

Writing Bragg Gratings in Multicore Fibers

Fiber Bragg gratings in multicore fibers can be used as compact and robust filters in astronomical and other research and commercial applications. Strong suppression at a single wavelength requires that all cores have matching transmission profiles. These gratings cannot be inscribed using the same method as for single-core fibers because the curved surface of the cladding acts as a lens, focusing the incoming UV laser beam and causing variations in exposure between cores. Therefore we use an additional optical element to ensure that the beam shape does not change while passing through the cross-section of the multicore fiber. This consists of a glass capillary tube which has been polished flat on one side, which is then placed over the section of the fiber to be inscribed. The laser beam enters the fiber through the flat surface of the capillary tube and hence maintains its original dimensions. This paper demonstrates the improvements in core-to-core uniformity for a 7-core fiber using this method. The technique can be generalized to larger multicore fibers.

We describe a technique for inscribing identical fiber Bragg gratings into each core of a multicore fiber. This is achieved by introducing an additional surface into the optical path to mitigate lensing by the curved surface of the fiber cladding.

Schreiben-Bragg-Gitter in Multicore- Fibers

Fiber Bragg gratings in multicore fibers can be used as compact and robust filters in astronomical and other research and commercial applications. Strong ...

Fabrication of Fully Solution Processed Inorganic Nanocrystal Photovoltaic Devices

We demonstrate a method for the preparation of fully solution processed inorganic solar cells from a spin and spray coating deposition of nanocrystal inks. For the photoactive absorber layer, colloidal CdTe and CdSe nanocrystals (3-5 nm) are synthesized using an inert hot injection technique and cleaned with precipitations to remove excess starting reagents. Similarly, gold nanocrystals (3-5 nm) are synthesized under ambient conditions and dissolved in organic solvents. In addition, precursor solutions for transparent conductive indium tin oxide (ITO) films are prepared from solutions of indium and tin salts paired with a reactive oxidizer. Layer-by-layer, these solutions are deposited onto a glass substrate following annealing (200-400 &#176;C) to build the nanocrystal solar cell (glass/ITO/CdSe/CdTe/Au). Pre-annealing ligand exchange is required for CdSe and CdTe nanocrystals where films are dipped in NH4Cl:methanol to replace long-chain native ligands with small inorganic Cl- anions. NH4Cl(s) was found to act as a catalyst for the sintering reaction (as a non-toxic alternative to the conventional CdCl2(s) treatment) leading to grain growth (136&#177;39 nm) during heating. The thickness and roughness of the prepared films are characterized with SEM and optical profilometry. FTIR is used to determine the degree of ligand exchange prior to sintering, and XRD is used to verify the crystallinity and phase of each material. UV/Vis spectra show high visible light transmission through the ITO layer and a red shift in the absorbance of the cadmium chalcogenide nanocrystals after thermal annealing. Current-voltage curves of completed devices are measured under simulated one sun illumination. Small differences in deposition techniques and reagents employed during ligand exchange have been shown to have a profound influence on the device properties. Here, we examine the effects of chemical (sintering and ligand exchange agents) and physical treatments (solution concentration, spray-pressure, annealing time and annealing temperature) on photovoltaic device performance.

This protocol describes the synthesis and solution deposition of inorganic nanocrystals layer by layer to produce thin film electronics on non-conductive surfaces. Solvent-stabilized inks can produce complete photovoltaic devices on glass substrates via spin and spray coating following post-deposition ligand exchange and sintering.

Die Herstellung von Voll Lösung verarbeitet Anorganische Nanokristalline Photovoltaik-Anlagen

We demonstrate a method for the preparation of fully solution processed inorganic solar cells from a spin and spray coating deposition of nanocrystal ...

Recombination Dynamics in Thin-film Photovoltaic Materials via Time-resolved Microwave Conductivity

A method for investigating recombination dynamics of photo-induced charge carriers in thin film semiconductors, specifically in photovoltaic materials such as organo-lead halide perovskites is presented. The perovskite film thickness and absorption coefficient are initially characterized by profilometry and UV-VIS absorption spectroscopy. Calibration of both laser power and cavity sensitivity is described in detail. A protocol for performing Flash-photolysis Time Resolved Microwave Conductivity (TRMC) experiments, a non-contact method of determining the conductivity of a material, is presented. A process for identifying the real and imaginary components of the complex conductivity by performing TRMC as a function of microwave frequency is given. Charge carrier dynamics are determined under different excitation regimes (including both power and wavelength). Techniques for distinguishing between direct and trap-mediated decay processes are presented and discussed. Results are modelled and interpreted with reference to a general kinetic model of photoinduced charge carriers in a semiconductor. The techniques described are applicable to a wide range of optoelectronic materials, including organic and inorganic photovoltaic materials, nanoparticles, and conducting/semiconducting thin films.

A Time Resolved Microwave Conductivity technique for investigating direct and trap-mediated recombination dynamics and determining carrier mobilities of thin film semiconductors is presented here.

Rekombinationsdynamik in Dünnschicht-Photovoltaik-Materialien über zeitaufgelöste Mikrowellenleitfähigkeit

A method for investigating recombination dynamics of photo-induced charge carriers in thin film semiconductors, specifically in photovoltaic materials ...

Challenges in Rheological Characterization of Highly Concentrated Suspensions &#8212; A Case Study for Screen-printing Silver Pastes

A comprehensive rheological characterization of highly concentrated suspensions or pastes is mandatory for a targeted product development meeting the manifold requirements during processing and application of such complex fluids. In this investigation, measuring protocols for a conclusive assessment of different process relevant rheological parameters have been evaluated. This includes the determination of yield stress, viscosity, wall slip velocity, structural recovery after large deformation and elongation at break as well as tensile force during filament stretching.
The importance of concomitant video recordings during parallel-plate rotational rheometry for a significant determination of rheological quantities is demonstrated. The deformation profile and flow field at the sample edge can be determined using appropriate markers. Thus, measurement parameter settings and plate roughness values can be identified for which yield stress and viscosity measurements are possible. Slip velocity can be measured directly and measuring conditions at which plug flow, shear banding or sample spillover occur can be identified clearly. 
Video recordings further confirm that the change in shear moduli observed during three stage oscillatory shear tests with small deformation amplitude in stage I and III but large oscillation amplitude in stage II can be directly attributed to structural break down and recovery. For the pastes investigated here, the degree of irreversible, shear-induced structural change increases with increasing deformation amplitude in stage II until a saturation is reached at deformations corresponding to the crossover of G' and G'', but the irreversible damage is independent of the duration of large amplitude shear. 
A capillary breakup elongational rheometer and a tensile tester have been used to characterize deformation and breakup behavior of highly filled pastes in uniaxial elongation. Significant differences were observed in all experiments described above for two commercial screen-printing silver pastes used for front side metallization of Si-solar cells.

Challenges in Rheological Characterization of Highly Concentrated Suspensions &amp;#8212; A Case Study for Screen-printing Silver Pastes

A protocol for a robust and application relevant rheological characterization of highly concentrated suspensions is presented. Silver pastes used for screen-printing application in solar cell production are employed as model systems.

Herausforderungen in rheologische Charakterisierung von hochkonzentrierten Suspensionen - Eine Fallstudie für Serigrafie Silberpasten

A comprehensive rheological characterization of highly concentrated suspensions or pastes is mandatory for a targeted product development meeting the ...

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.

Hochtemperatur Herstellung von Nanostrukturierte Yttrium-stabilisiertes Zirkonoxid (YSZ) Scaffolds durch<em&gt; In Situ</em&gt; Carbon-Templating Xerogele

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

Detecting the Water-soluble Chloride Distribution of Cement Paste in a High-precision Way

To improve the accuracy of the chloride distribution along the depth of cement paste under cyclic wet-dry conditions, a new method is proposed to obtain a high-precision chloride profile. Firstly, paste specimens are molded, cured, and exposed to cyclic wet-dry conditions. Then, powder samples at different specimen depths are grinded when the exposure age is reached. Finally, the water-soluble chloride content is detected using a silver nitrate titration method, and chloride profiles are plotted. The key to improving the accuracy of the chloride distribution along the depth is to exclude the error in the powderization, which is the most critical step for testing the distribution of chloride. Based on the above concept, the grinding method in this protocol can be used to grind powder samples automatically layer by layer from the surface inward, and it should be noted that a very thin grinding thickness (less than 0.5 mm) with a minimum error less than 0.04 mm can be obtained. The chloride profile obtained by this method better reflects the chloride distribution in specimens, which helps researchers to capture the distribution features that are often overlooked. Furthermore, this method can be applied to studies in the field of cement-based materials, which require high chloride distribution accuracy.

A protocol for obtaining a water-soluble chloride profile by using a high precision milling method is presented.

Die wasserlöslichen Chlorid Verteilung der Zementleim erkennen auf präzise Weise

To improve the accuracy of the chloride distribution along the depth of cement paste under cyclic wet-dry conditions, a new method is proposed to obtain a ...

Method for Recording Broadband High Resolution Emission Spectra of Laboratory Lightning Arcs

Lightning is one of the most common and destructive forces in nature and has long been studied using spectroscopic techniques, first with traditional camera film methods and then digital camera technology, from which several important characteristics have been derived. However, such work has always been limited due to the inherently random and non-repeatable nature of natural lightning events in the field. Recent developments in lightning test facilities now allow the reproducible generation of lightning arcs within controlled laboratory environments, providing a test bed for the development of new sensors and diagnostic techniques to understand lightning mechanisms better. One such technique is a spectroscopic system using digital camera technology capable of identifying the chemical elements with which the lightning arc interacts, with these data then being used to derive further characteristics. In this paper, the spectroscopic system is used to obtain the emission spectrum from a 100 kA peak, 100 &#181;s duration lightning arc generated across a pair of hemispherical tungsten electrodes separated by a small air gap. To maintain a spectral resolution of less than 1 nm, several individual spectra were recorded across discrete wavelength ranges, averaged, stitched, and corrected to produce a final composite spectrum in the 450 nm (blue light) to 890 nm (near infrared light) range. Characteristic peaks within the data were then compared to an established publicly available database to identify the chemical element interactions. This method is readily applicable to a variety of other light emitting events, such as fast electrical discharges, partial discharges, and sparking in electrical equipment, apparatus, and systems.

Emission spectroscopy techniques have traditionally been used to analyze inherently random lightning arcs occurring in nature. In this paper, a method developed to obtain the emission spectroscopy from reproducible lightning arcs generated within a laboratory environment is described.

Verfahren zur Aufzeichnung von Breitband-Emissionsspektren von Laborblitzen

Lightning is one of the most common and destructive forces in nature and has long been studied using spectroscopic techniques, first with traditional ...

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.

Flow-gestützte Dielektrophorese: Eine kostengünstige Methode für die Herstellung von Hochleistungs-Lösung-verarbeitbare Nanodraht-Geräte

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