This work was supported by the Natural Science and Engineering Research Council of Canada (Discovery Grant No. 122795-2010) and the program of the Canada Research Chair in Quantum Semiconductors (JJD). The help provided by Xiaohuan Xuang, Mohamed Walid Hassen and technical assistance of Sonia Blais of the Universit&#233; de Sherbrooke Centre de caract&#233;risation de mat&#233;riaux (CCM) in collecting XPS data are greatly appreciated. NL acknowledges the Merit Scholarship Program for Foreign Student, Fonds de recherche du Qu&#233;bec - Nature et technologies, for providing a graduate student scholarship.

1. Préparation de l&#39;échantillon <ol><li> Utilisez un scribe de diamode pour cliver un type n (dopé P-) d&#39;un côté brillant tranche de silicium (résistivité 3,1 ~ 4,8 .m), qui est de 3 pouces de diamètre, 380 um d&#39;épaisseur, dans des échantillons de 12 mm x 6 mm; nettoyer les échantillons dans OptiClear, l&#39;acétone et l&#39;alcool isopropylique (5 min à chaque étape). </li><li> Échantillons gravure dans une solution de HF ~ 0,9% pendant 1 min à une distance de graver l&#39;oxyde initial; rincer à l&#39;eau DI et sec en haute pureté (99,999%) d&#39;azote (N 2). </li><li> Entreposer les échantillons préparés en N 2 sac de freiner leur oxydation à l&#39;air. </li></ol> 2. irradier les échantillons par ArF (λ = 193 nm) et KrF (λ = 248 nm) lasers. <ol><li> Placer les échantillons dans une grande chambre de 0,74 mm et puis sceller la chambre avec une fenêtre en verre de silice qui a une forte transmission dans l&#39;UV (≥90%). Remplir la chambre avec H 2 O 2 / H 2 O solution dans la gamme de 0,01 à 0,2% avec ou métha dégazénol en utilisant un canal microfluidique. </li><li> Irradier les échantillons avec des lasers ArF ou KrF homogénéisé à démagnification de 2,6 et 1,8, respectivement. Irradier seulement deux sites sur chaque échantillon en augmentant impulsions laser de 100 à 600 à l&#39;étape 100 impulsions à travers un masque circulaire (4 mm de diamètre). Irradier les échantillons de la même manière avec une &quot;feuille d&#39;érable&quot; (9 mm x 7,2 mm) de masque. </li><li> Échantillons rincer à l&#39;eau DI et secs, N 2 ras; placer les échantillons dans un récipient fermé, puis remplir rapidement ce conteneur avec N 2, afin d&#39;éviter l&#39;exposition à l&#39;air avant d&#39;autres expériences. </li></ol> 3. nanosphères Immobilisation de Bio-conjugués <ol><li> Diluer nanosphères de biotine conjugué à la fluorescéine et colorées 40 nm de diamètre dans une solution saline tamponnée au phosphate pH 7,4 (PBS, 1X) solution à 10 12 particules / ml à la température ambiante (~ 25 ° C). Immerger des échantillons de laser KrF ou ArF est irradié pendant 2 &amp;# 160; h dans cette solution à la température ambiante. </li><li> Échantillons Laver avec du PBS pour éliminer physiquement reliés fluorescéine nanosphères colorées sur la surface. </li></ol> Caractérisation 4. Surface <ol><li> L&#39;angle de contact (CA) mesure <ol><li> Effectuer des mesures de CA statiques avec un goniomètre dans un environnement de température ambiante et de l&#39;humidité ambiante. </li><li> Employer de l&#39;eau de haute pureté de DI (résistivité 17,95 MQ · cm) dans une micro-seringue; générer un volume similaire (~ 5 pi) tombe sur la surface de l&#39;échantillon par l&#39;abaissement de la micro-seringue à une hauteur similaire pour chaque mesure. </li><li> Capturer et enregistrer les gouttes d&#39;eau profil images par caméra CCD avec un logiciel. Mesurer indépendamment 4 différents sites ayant les mêmes conditions d&#39;irradiation. </li><li> Estimation et la moyenne des valeurs de CA en baisse module d&#39;analyse à partir du logiciel ImageJ; charger l&#39;image et le changer en niveaux de gris; lancer le plugin Dropsnake; placer environ quelques noeuds sur le contour de la goutte (~ 10 noeuds) de gauche àdroit à initialiser serpent; accepter la courbe reliant ces nœuds et évoluer la courbe en appuyant sur le bouton de serpent. Remarque: des angles de contact sont affichés dans l&#39;image et de la table. </li></ol></li><li> Mesure XPS <ol><li> Examiner modification chimique de la surface avec un spectromètre de XPS (pression de base 1x10 -9 Torr) équipé d&#39;une source de Al Ka de travail à 150 W: <ol><li> Charger les échantillons dans la chambre à vide. </li><li> Acquérir les données de l&#39;enquête de surface dans les modes d&#39;énergie constants de 50 eV l&#39;énergie de passer d&#39;une zone de 220 um x 220 um. </li><li> Acquérir des données de haute scans de résolution de la même zone analysée à 20 eV passent énergie. </li></ol></li><li> Processus XPS données spectres avec le logiciel de quantification de spectres XPS, comme référencé 25,26. </li></ol></li><li> Microscope à fluorescence imagerie <ol><li> Excite échantillons, qui ont été irradiés par &quot;feuille d&#39;érable&quot; masque et exposés à la fluorescéine nanosphères colorés, à l&#39;aideune source de lumière bleue (λ = 450 ~ 490 nm). </li><li> Respecter les images fluorescentes, émettant à 515 nm, avec un microscope inversé à fluorescence à un grossissement de 4X. </li><li> Caractériser la morphologie de surface de ces échantillons avec l&#39;AFM, comme référencé 27. </li></ol></li></ol>

The authors have nothing to disclose.

Nous avons proposé un protocole d&#39;irradiation UV de laser de tranche de Si dans une chambre remplie de microfluidique faible concentration en H 2 O 2 solution pour induire une surface de Si superhydrophile, ce qui est principalement dû à la génération de liaisons Si-OH. Photolyse UV de laser de H 2 O 2 était censé former chargés négativement OH - les radicaux. En outre, l&#39;effet photoélectrique laser UV conduit à la formation d&#39;une surface 37 chargée pos...

Les propriétés électroniques et chimiques remarquables ainsi que sa haute résistance mécanique ont fait silicium (Si) un choix idéal pour les dispositifs microélectroniques et biomédicales puces 1. Le contrôle de zone désignée de la surface Si a reçu beaucoup d&#39;attention pour les applications impliquant microfluidiques et des appareils de laboratoire sur puce 2,3 .Cet est souvent obtenu soit par modification nano-échelle de la rugosité de surface ou par traitement chimique de la surface 4. La rugosité de surface ou de motifs pour produire des structures de surface désordonnés ou commandés sur la surface Si comprennent la photolithographie 5, faisceau d&#39;ions lithographie 6 et 7 techniques laser. Par rapport à ces méthodes, processus de texturation de surface laser est signalé à être moins compliqué avec le potentiel de produire des microstructures à haute résolution spatiale 8. Cependant, comme Si a un seuil de texturation élevée, nécessitant une irradiation par impulsions à la fluenceinduisent texturation de surface au-delà de son seuil d&#39;ablation (~ 500 MJ / cm 2) 9, la texturation de surface Si a souvent été aidé en employant des atmosphères de gaz réactifs, tels que celui d&#39;une haute pression SF 6 environnement 4,7,8. Par conséquent, pour modifier la mouillabilité de la surface de Si, de nombreux travaux ont porté sur le traitement chimique par dépôt de couches organiques 10 et inorganiques 2, ou l&#39;utilisation de plasma ou faisceau d&#39;électrons traitement de surface 11,12. Il est admis que le caractère hydrophile de Si provenant de l&#39;existence de groupes OH singulier et associés sur sa surface pourrait être réalisé en le faisant bouillir dans une solution de H 2 O 2 à 100 ° C pendant 13 plusieurs minutes. Cependant, les hydrophobes états de surface de silicium, dont la plupart sont dus à la présence de liaisons Si-H ou Si-O-CH 3 groupes, peuvent être obtenus par traitement chimique par voie humide impliquant la gravure avec une solution d&#39;acide fluorhydrique ou de revêtement avec photoresist 13-15. Pour obtenir un contrôle sélectif de la zone de mouillabilité de Si, étapes de structuration complexes sont généralement nécessaires, y compris le traitement dans des solutions chimiques 16. La réactivité chimique élevée d&#39;UV rayonnement laser a également été utilisé pour traiter la zone sélective organique film substrats solides enrobés et modifier leur mouillabilité 17. Cependant, une quantité limitée de données est disponible sur la modification assistée par laser de Si mouillabilité par irradiation d&#39;échantillons immergés dans des solutions chimiques différentes. Dans notre recherche précédente, UV irradiation laser de semi-conducteurs III-V dans l&#39;air 18-20 et NH 3 21 a été utilisé avec succès pour modifier la composition chimique de la surface de GaAs, InP et InGaAs. Nous avons établi que l&#39;irradiation laser UV de semiconducteurs III-V en désionisée (DI) de l&#39;eau diminue les oxydes et carbures de surface, tandis que l&#39;eau adsorbée sur la surface de semi-conducteur augmente 22. Une surface de Si fortement hydrophobe (AR ~ 103 °) a été obtenu par ArF irradiation laser d&#39;échantillons Si dans le méthanol dans notre récent travail 23. Comme cela est indiqué par la spectroscopie photoélectronique à rayons X (XPS), ceci est principalement dû à la capacité du laser ArF à photodissociate CH 3 OH. Nous avons également utilisé des lasers KrF et ArF à irradier Si (001) dans un 0,01% de H 2 O 2 dans de l&#39;eau DI. Cela nous a permis d&#39;atteindre formation de zone sélective de la surface superhydrophile de Si (001) caractérisé par le CA de près de 15 °. Les résultats XPS suggèrent que ceci est dû à la génération de liaisons Si-OH sur la surface irradiée 24. Une description détaillée de cette nouvelle technique utilisant KrF et lasers ArF pour zone sélectif modification in situ de la surface hydrophile / hydrophobe de surface de Si dans une faible concentration de H 2 O 2 / H 2 O et des solutions de methanol est mise en évidence dans cet article. Les détails fournis ici devraient être suffisantespour permettre à des expériences similaires à exécuter par les chercheurs intéressés.

<table border="0" cellpadding="0" cellspacing="0">
	<tbody>
		<tr>
			<td>fluorescein stained nanospheres</td>
			<td>Invitrogen</td>
			<td>F8795</td>
			<td></td>
		</tr>
		<tr>
			<td>OptiClear</td>
			<td>National Diagnostics</td>
			<td>OE-101</td>
			<td></td>
		</tr>
		<tr>
			<td>ArF laser (&#955;=193 nm)</td>
			<td>Lumonics</td>
			<td>pulse master 800</td>
			<td></td>
		</tr>
		<tr>
			<td>KrF laser (&#955;=248 nm)</td>
			<td>Lumonics</td>
			<td>pulse master 800</td>
			<td></td>
		</tr>
		<tr>
			<td>XPS</td>
			<td>Kratos Analytical</td>
			<td>AXIS Ultra DLD</td>
			<td></td>
		</tr>
		<tr>
			<td>Fluorescence microscope</td>
			<td>Olympus</td>
			<td>IX71</td>
			<td></td>
		</tr>
		<tr>
			<td>XPS quantitification software</td>
			<td>CasaXPS</td>
			<td>2.3.15</td>
			<td></td>
		</tr>
	</tbody>
</table>

selective area modification of silicon surface wettability by pulsed uv laser irradiation in liquid environment

La mouillabilité de silicium (Si) est un des paramètres importants de la technologie de fonctionnalisation de surface de ce matériau et de fabrication de dispositifs de biodétection. Nous rapportons un protocole à l&#39;aide de lasers KrF et ArF irradiation de Si (001) échantillons immergés dans un milieu liquide avec un faible nombre d&#39;impulsions et fonctionnant à des fluences d&#39;impulsions modérément basses pour induire une modification de la mouillabilité de Si. Wafers immergés jusqu&#39;à 4 h dans un 0,01% de H 2 O 2 / H 2 O solution ne montrent pas de changement mesurable dans leur angle de contact initial (CA) ~ 75 °. Cependant, le 500 impulsions KrF et lasers ArF irradiation de ces pastilles dans une microchambre rempli avec 0,01% de H 2 O 2 / H 2 O solution à 250 et 65 mJ / cm 2, respectivement, a diminué le CA à près de 15 °, indiquant la formation d&#39;une surface superhydrophile. La formation de Si à terminaison OH (001), sans changement mesurable de la morphologie de surface de la tranche, aété confirmée par rayons X et la spectroscopie photoélectronique des mesures de force microscopie atomique. Les échantillons irradiés zone désignée ont ensuite été immergées dans une solution de biotine-conjugué à la fluorescéine nanosphères taché pendant 2 heures, ce qui entraîne une immobilisation réussie des nanosphères dans la zone non irradiée. Ceci illustre le potentiel de la méthode pour biofonctionnalisation de zone désignée et de fabrication de pointe de biodétection architectures à base de Si. Nous décrivons également un protocole similaire d&#39;irradiation de plaquettes immergées dans du méthanol (CH 3 OH) à l&#39;aide de laser ArF fonctionnant à impulsion fluence de 65 mJ / cm 2 et la formation in situ d&#39;une surface fortement hydrophobe de Si (001) avec l&#39;AC de 103 °. Les résultats indiquent XPS induite par laser ArF formation de Si- (OCH 3) x composés responsables de l&#39;hydrophobie observé. Cependant, aucun de ces composés ont été trouvés par XPS sur la surface irradiée par laser Si KrF dans du methanol, ce qui démontrel&#39;incapacité du laser KrF à photodissociate methanol et de créer des radicaux -OCH 3.

Ces résultats représentatifs ont été présentés dans notre travail publié précédente 23,24. La figure 1 montre le CA vs N (nombre d&#39;impulsions) sur les sites irradiée par laser KrF à 250 mJ / cm 2 en DI H 2 O pour différentes concentrations de H 2 O 2 / H 2 O solutions (par ex., 0,01, 0,02, 0,05 et 0,2%). L&#39;AC diminue avec l&#39;augmentation du nombre d&#39;impulsions pour tout le H 2 O 2 solutions. ...

Watch this Scientific Journal Video about Selective Area Modification of Silicon Surface Wettability by Pulsed UV Laser Irradiation in Liquid Environment at JoVE.com

Selective Area Modification of Silicon Surface Wettability by Pulsed UV Laser Irradiation in Liquid Environment

Nous rapportons un processus d&#39;une altération in situ de HF traitée Si surface (001) dans un état ​​hydrophile ou hydrophobe en irradiant les échantillons dans des chambres microfluidiques remplis de H 2 O 2 / H 2 O solution (0,01% -0,5%) ou des solutions de méthanol en utilisant pulsé laser UV d&#39;une faible fluence rapport d&#39;impulsions.

Selective Area Modification de la Silicon mouillabilité de surface par irradiation laser pulsé UV en milieu liquide

The wettability of silicon (Si) is one of the important parameters in the technology of surface functionalization of this material and fabrication of ...

selective-area-modification-silicon-surface-wettability-pulsed-uv

Research

JoVE Journal

Engineering

8.2K vues.  Université de Sherbrooke.  Nous rapportons un processus d'une altération in situ de HF traitée Si surface (001) dans un état ​​hydrophile ou hydrophobe en irradiant les échantillons dans des chambres microfluidiques remplis de H 2 O 2 / H 2 O solution (0,01% -0,5%) ou des solutions de méthanol en utilisant pulsé laser UV d'une faible fluence rapport d'impulsions. 

Vidéo: Selective Area Modification of Silicon Surface Wettability by Pulsed UV Laser Irradiation in Liquid Environment

Characterization of Surface Modifications by White Light Interferometry: Applications in Ion Sputtering, Laser Ablation, and Tribology Experiments

In materials science and engineering it is often necessary to obtain quantitative measurements of surface topography with micrometer lateral resolution. From the measured surface, 3D topographic maps can be subsequently analyzed using a variety of software packages to extract the information that is needed.
In this article we describe how white light interferometry, and optical profilometry (OP) in general, combined with generic surface analysis software, can be used for materials science and engineering tasks. In this article, a number of applications of white light interferometry for investigation of surface modifications in mass spectrometry, and wear phenomena in tribology and lubrication are demonstrated. We characterize the products of the interaction of semiconductors and metals with energetic ions (sputtering), and laser irradiation (ablation), as well as ex situ measurements of wear of tribological test specimens.
Specifically, we will discuss:
<ol class="lroman">
	<li>Aspects of traditional ion sputtering-based mass spectrometry such as sputtering rates/yields measurements on Si and Cu and subsequent time-to-depth conversion.</li>
	<li>Results of quantitative characterization of the interaction of femtosecond laser irradiation with a semiconductor surface. These results are important for applications such as ablation mass spectrometry, where the quantities of evaporated material can be studied and controlled via pulse duration and energy per pulse. Thus, by determining the crater geometry one can define depth and lateral resolution versus experimental setup conditions.</li>
	<li>Measurements of surface roughness parameters in two dimensions, and quantitative measurements of the surface wear that occur as a result of friction and wear tests.</li>
</ol>
Some inherent drawbacks, possible artifacts, and uncertainty assessments of the white light interferometry approach will be discussed and explained.

White light microscope interferometry is an optical, noncontact and quick method for measuring the topography of surfaces. It is shown how the method can be applied toward mechanical wear analysis, where wear scars on tribological test samples are analyzed; and in materials science to determine ion beam sputtering or laser ablation volumes and depths.

Caractérisation des modifications de surface par interférométrie en lumière blanche: Applications de pulvérisation ionique, ablation laser, tribologie et expériences

In materials science and engineering it is often necessary to obtain quantitative measurements of surface topography with micrometer lateral resolution. ...

Recherche

Ingénierie

Fabrication of Nano-engineered Transparent Conducting Oxides by Pulsed Laser Deposition

Nanosecond Pulsed Laser Deposition (PLD) in the presence of a background gas allows the deposition of metal oxides with tunable morphology, structure, density and stoichiometry by a proper control of the plasma plume expansion dynamics. Such versatility can be exploited to produce nanostructured films from compact and dense to nanoporous characterized by a hierarchical assembly of nano-sized clusters. In particular we describe the detailed methodology to fabricate two types of Al-doped ZnO (AZO) films as transparent electrodes in photovoltaic devices: 1) at low O2 pressure, compact films with electrical conductivity and optical transparency close to the state of the art transparent conducting oxides (TCO) can be deposited at room temperature, to be compatible with thermally sensitive materials such as polymers used in organic photovoltaics (OPVs); 2) highly light scattering hierarchical structures resembling a forest of nano-trees are produced at higher pressures. Such structures show high Haze factor (&gt;80%) and may be exploited to enhance the light trapping capability. The method here described for AZO films can be applied to other metal oxides relevant for technological applications such as TiO2, Al2O3, WO3 and Ag4O4.

We describe the experimental method to deposit nanostructured oxide thin films by nanosecond Pulsed Laser Deposition (PLD) in the presence of a background gas. By using this method Al-doped ZnO (AZO) films, from compact to hierarchically structured as nano-tree forests, can be deposited.

Fabrication de nano-oxydes conducteurs transparents conçus par ablation laser

Nanosecond Pulsed  Laser Deposition (PLD) in the presence of a background gas allows the deposition  of metal oxides with tunable morphology, structure, ...

Visualization of High Speed Liquid Jet Impaction on a Moving Surface

Two apparatuses for examining liquid jet impingement on a high-speed moving surface are described: an air cannon device (for examining surface speeds between 0 and 25 m/sec) and a spinning disk device (for examining surface speeds between 15 and 100 m/sec). The air cannon linear traverse is a pneumatic energy-powered system that is designed to accelerate a metal rail surface mounted on top of a wooden projectile. A pressurized cylinder fitted with a solenoid valve rapidly releases pressurized air into the barrel, forcing the projectile down the cannon barrel. The projectile travels beneath a spray nozzle, which impinges a liquid jet onto its metal upper surface, and the projectile then hits a stopping mechanism. A camera records the jet impingement, and a pressure transducer records the spray nozzle backpressure. The spinning disk set-up consists of a steel disk that reaches speeds of 500 to 3,000 rpm via a variable frequency drive (VFD) motor. A spray system similar to that of the air cannon generates a liquid jet that impinges onto the spinning disc, and cameras placed at several optical access points record the jet impingement. Video recordings of jet impingement processes are recorded and examined to determine whether the outcome of impingement is splash, splatter, or deposition. The apparatuses are the first that involve the high speed impingement of low-Reynolds-number liquid jets on high speed moving surfaces. In addition to its rail industry applications, the described technique may be used for technical and industrial purposes such as steelmaking and may be relevant to high-speed 3D printing.

Two experimental devices for examining liquid jet impingement on a high-speed moving surface are described: an air cannon device and a spinning disk device. The apparatuses are used to determine optimal approaches to the application of liquid friction modifier (LFM) onto rail tracks for top-of-rail friction control.

Visualisation de High Speed ​​Liquid Jet impaction sur une surface en mouvement

Two apparatuses for examining liquid jet impingement on a high-speed moving surface are described: an air cannon device (for examining surface speeds ...

Integration of Light Trapping Silver Nanostructures in Hydrogenated Microcrystalline Silicon Solar Cells by Transfer Printing

One of the potential applications of metal nanostructures is light trapping in solar cells, where unique optical properties of nanosized metals, commonly known as plasmonic effects, play an important role. Research in this field has, however, been impeded owing to the difficulty of fabricating devices containing the desired functional metal nanostructures. In order to provide a viable strategy to this issue, we herein show a transfer printing-based approach that allows the quick and low-cost integration of designed metal nanostructures with a variety of device architectures, including solar cells. Nanopillar poly(dimethylsiloxane) (PDMS) stamps were fabricated from a commercially available nanohole plastic film as a master mold. On this nanopatterned PDMS stamps, Ag films were deposited, which were then transfer-printed onto block copolymer (binding layer)-coated hydrogenated microcrystalline Si (&#181;c-Si:H) surface to afford ordered Ag nanodisk structures. It was confirmed that the resulting Ag nanodisk-incorporated &#181;c-Si:H solar cells show higher performances compared to a cell without the transfer-printed Ag nanodisks, thanks to plasmonic light trapping effect derived from the Ag nanodisks. Because of the simplicity and versatility, further device application would also be feasible thorough this approach.

A viable transfer printing-based methodology to introduce plasmonic metal nanostructures in solar cells is described. Using nanopillar poly(dimethylsiloxane) stamps, an Ag-based ordered nanodisk array was integrated with standard hydrogenated microcrystalline Si solar cells, which led to improved device performances due to plasmonic light trapping.

Intégration de la Lumière de piégeage argent Nanostructures dans hydrogénée microcristalline cellules solaires en silicium par impression par transfert

One of the potential applications of metal nanostructures is light trapping in solar cells, where unique optical properties of nanosized metals, commonly ...

Automation of Mode Locking in a Nonlinear Polarization Rotation Fiber Laser through Output Polarization Measurements

When a laser is mode-locked, it emits a train of ultra-short pulses at a repetition rate determined by the laser cavity length. This article outlines a new and inexpensive procedure to force mode locking in a pre-adjusted nonlinear polarization rotation fiber laser. This procedure is based on the detection of a sudden change in the output polarization state when mode locking occurs. This change is used to command the alignment of the intra-cavity polarization controller in order to find mode-locking conditions. More specifically, the value of the first Stokes parameter varies when the angle of the polarization controller is swept and, moreover, it undergoes an abrupt variation when the laser enters the mode-locked state. Monitoring this abrupt variation provides a practical easy-to-detect signal that can be used to command the alignment of the polarization controller and drive the laser towards mode locking. This monitoring is achieved by feeding a small portion of the signal to a polarization analyzer measuring the first Stokes parameter. A sudden change in the read out of this parameter from the analyzer will occur when the laser enters the mode-locked state. At this moment, the required angle of the polarization controller is kept fixed. The alignment is completed. This procedure provides an alternate way to existing automating procedures that use equipment such as an optical spectrum analyzer, an RF spectrum analyzer, a photodiode connected to an electronic pulse-counter or a nonlinear detecting scheme based on two-photon absorption or second harmonic generation. It is suitable for lasers mode locked by nonlinear polarization rotation. It is relatively easy to implement, it requires inexpensive means, especially at a wavelength of 1550 nm, and it lowers the production and operation costs incurred in comparison to the above-mentioned techniques.

A protocol to detect and automate mode locking in a pre-adjusted nonlinear polarization rotation fiber laser is presented. The detection of a sudden change in the output polarization state when mode locking occurs is used to command the alignment of an intra-cavity polarization controller in order to find mode-locking conditions.

Automatisation du mode de verrouillage dans un Nonlinear Polarisation Rotation fibre laser par Polarisation sortie Mesures

When a laser is mode-locked, it emits a train of ultra-short pulses at a repetition rate determined by the laser cavity length. This article outlines a ...

Emission Spectroscopic Boundary Layer Investigation during Ablative Material Testing in Plasmatron

Ablative Thermal Protection Systems (TPS) allowed the first humans to safely return to Earth from the moon and are still considered as the only solution for future high-speed reentry missions. But despite the advancements made since Apollo, heat flux prediction remains an imperfect science and engineers resort to safety factors to determine the TPS thickness. This goes at the expense of embarked payload, hampering, for example, sample return missions. 
Ground testing in plasma wind-tunnels is currently the only affordable possibility for both material qualification and validation of material response codes. The subsonic 1.2MW Inductively Coupled Plasmatron facility at the von Karman Institute for Fluid Dynamics is able to reproduce a wide range of reentry environments. This protocol describes a procedure for the study of the gas/surface interaction on ablative materials in high enthalpy flows and presents sample results of a non-pyrolyzing, ablating carbon fiber precursor. With this publication, the authors envisage the definition of a standard procedure, facilitating comparison with other laboratories and contributing to ongoing efforts to improve heat shield reliability and reduce design uncertainties.
The described core techniques are non-intrusive methods to track the material recession with a high-speed camera along with the chemistry in the reactive boundary layer, probed by emission spectroscopy. Although optical emission spectroscopy is limited to line-of-sight measurements and is further constrained to electronically excited atoms and molecules, its simplicity and broad applicability still make it the technique of choice for analysis of the reactive boundary layer. Recession of the ablating sample further requires that the distance of the measurement location with respect to the surface is known at all times during the experiment. Calibration of the optical system of the applied three spectrometers allowed quantitative comparison. At the fiber scale, results from a post-test microscopy analysis are presented.

Development of new ablative materials and their numerical modeling requires extensive experimental investigation. This protocol describes procedures for material response characterization in plasma flows with the core techniques being non-intrusive methods to track the material recession along with the chemistry in the reactive boundary layer by emission spectroscopy.

Investigation de la couche d&#39;émission spectroscopique Boundary au cours d&#39;essai des matériaux ablatif dans Plasmatron

Ablative Thermal Protection Systems (TPS) allowed the first humans to safely return to Earth from the moon and are still considered as the only solution ...

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.

Fabrication à haute température de nanostructurés yttriée-Zircon (YSZ) par scellants<em&gt; In Situ</em&gt; Carbon Templating xérogels

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

Orientational Transition in a Liquid Crystal Triggered by the Thermodynamic Growth of Interfacial Wetting Sheets

In liquid crystal (LC) physical chemistry, molecules near the surface play a great role in controlling bulk orientation. Thus far, mainly to achieve desired molecular orientation states in LC displays, the "static" surface property of LCs, so-called surface anchoring, has been intensively studied. As a rule of thumb, once the initial orientation of LCs is "locked" by specific surface treatments, such as rubbing or treatment with a specific alignment layer, it hardly changes with temperature. Here, we present a system exhibiting an orientational transition upon temperature variation, which conflicts with the consensus. Right on the transition, the bulk LC molecules experience the orientational rotation, with 90&#176; between the planar (P) orientation at high temperatures and the vertical (V) orientation at low temperatures in the first-order transitional manner. We have tracked thermodynamic surface anchoring behavior by means of polarizing optical microscopy (POM), dielectric spectroscopy (DS), high-resolution differential scanning calorimetry (HR-DSC), and grazing incidence X-ray diffraction (GI-XRD) and reached a plausible physical explanation: that the transition is triggered by a growth of surface wetting sheets, which impose the V orientation locally against the P orientation in the bulk. This landscape would provide a general link explaining how the equilibrium bulk orientation is affected by surface-localized orientation in many LC systems. In our characterization, POM and DS are advantageous by offering information on the spatial distribution of the orientation of LC molecules. HR-DSC gives information about the precise thermodynamic information on transitions, which cannot be addressed by conventional DSC instruments due to limited resolution. GI-XRD provides information on surface-specific molecular orientation and short-range orderings. The goal of this paper is to present a protocol for preparing a sample that exhibits the transition and to demonstrate how the thermodynamic structural variation, both in the bulk and on surfaces, can be analyzed through the abovementioned methods.

Here, we present a protocol to trigger an orientational transition of a liquid crystal in response to temperature. Methodologies are described for preparing a sample in order to observe the transition and the detailed transitional evolution.

Transition orientale dans un cristal liquide déclenché par la croissance thermodynamique des feuilles de mouillage interfaciales

In liquid crystal (LC) physical chemistry, molecules near the surface play a great role in controlling bulk orientation. Thus far, mainly to achieve ...

Preparation of Liquid Crystal Networks for Macroscopic Oscillatory Motion Induced by Light

A strategy based on doped liquid crystalline networks is described to create mechanical self-sustained oscillations of plastic films under continuous light irradiation. The photo-excitation of dopants that can quickly dissipate light into heat, coupled with anisotropic thermal expansion and self-shadowing of the film, gives rise to the self-sustained deformation. The oscillations observed are influenced by the dimensions and the modulus of the film, and by the directionality and intensity of the light. The system developed offers applications in energy conversion and harvesting for soft-robotics and automated systems.
The general method described here consists of creating free-standing liquid crystalline films and characterizing the mechanical and thermal effects observed. The molecular alignment is achieved using alignment layers (rubbed polyimide), commonly used in the display manufacturing industry. To obtain actuators with large deformation, the mesogens are aligned and polymerized in a splay/bend configuration, i.e., with the director of the liquid crystals (LCs) going gradually from planar to homeotropic through the film thickness. Upon irradiation, the mechanical and thermal oscillations obtained are monitored with a high-speed camera. The results are further quantified by image analysis using an image processing program.

The goal of the protocol is to create liquid crystalline polymer films that can mechanically oscillate under continuous light irradiation. We describe in great detail the conception of free-standing films, from the liquid crystal alignment method to the photo-actuation. The experimental protocol applied to prepare this material is broadly applicable.

Préparation des réseaux de cristaux liquides pour macroscopique mouvement oscillatoire induite par la lumière

A strategy based on doped liquid crystalline networks is described to create mechanical self-sustained oscillations of plastic films under continuous ...

Quantitative Analysis of Vacuum Induction Melting by Laser-induced Breakdown Spectroscopy

Vacuum induction melting is a popular method for refining high purity metal and alloys. Traditionally, standard process control in metallurgy involves several steps, include drawing samples, cooling, cutting, transport to the laboratory, and analysis. The whole analysis process requires more than 30 minutes, which hinders on-line process control. Laser-induced breakdown spectroscopy is an excellent on-line analysis method that can satisfy the requirements of vacuum induction melting because it is fast and noncontact and does not require sample preparation. The experimental facility uses a lamp-pumped Q-switched laser to ablate melted liquid steel with an output energy of 80 mJ, a frequency of 5 Hz, a FWHM pulse width of 20 ns, and a working wavelength of 1,064 nm. A multi-channel linear charge coupled device (CCD) spectrometer is used to measure the emission spectrum in real time, with a spectral range from 190 to 600 nm and a resolution of 0.06 nm at a wavelength of 200 nm. The protocol includes several steps: standard alloy sample preparation and an ingredient test, smelting of standard samples and determination of the laser breakdown spectrum, and construction of the elements concentration quantitative analysis curve of each element. To realize the concentration analysis of unknown samples, the spectrum of a sample also needs to be measured and disposed with the same process. The composition of all main elements in the melted alloy can be quantitatively analyzed with an internal standard method. The calibration curve shows that the limit of detection of most metal elements ranges from 20-250 ppm. The concentration of elements, such as Ti, Mo, Nb, V, and Cu, can be lower than 100 ppm, and the concentrations of Cr, Al, Co, Fe, Mn, C, and Si range from 100-200 ppm. The R2 of some calibration curves can exceed 0.94.

During vacuum induction melting, laser-induced breakdown spectroscopy is used to perform real-time quantitative analysis of the main-ingredient elements of a molten alloy.

Analyse quantitative de la fusion par induction sous vide par spectroscopie de répartition induite par laser

Vacuum induction melting is a popular method for refining high purity metal and alloys. Traditionally, standard process control in metallurgy involves ...