Plasmonic nanorods and nanoparticle-assemblies

Die vorliegenden Dissertation beschäftigt sich mit plasmonischen Nanopartikeln, deren Wechselwirkung mit Licht in einer Plasmonenschwingung resultiert. Suspensionen dieser Partikel zeigen kräftige Farben, da sich die Resonanzfrequenz der Plasmonenschwingung im sichtbaren Bereich des elektromagnetischen Spektrum befindet. Durch die Veränderung interner (Material, Größe, Form) oder externer Parameter (Brechungsindex der Umgebung, Abstand zu anderen plasmonischen Partikeln) lässt sich die Farbe der Partikel verändern, eine Verschiebung der Resonanzfrequenz kann beobachtet werden. Ihre Sensitivität gegenüber äußeren Bedingungen ist der Grund, weshalb plasmonische Nanopartikel als Sensoren eingesetzt werden können. Wichtig ist hierbei nicht nur, dass die Partikel eine hohe Sensitivität zeigen, sondern auch die Möglichkeit, reproduzierbar Partikel zu synthetisieren, die experimentellen Anforderungen entsprechen. In der vorliegenden Arbeit wird das Wachstum von reinen Gold- und mit Silber beschichteten Goldnanostäbchen untersucht. Des Weiteren werden plasmonische Nanopartikel als Orientierungs-, Brechungsindex- und Abstandssensoren verwendet. Die Synthese von Goldnanostäbchen erfolgt auf nasschemischen Weg, ihr anisotropes Wachstum aus isotropen Keimen wird durch zahlreiche Faktoren beeinflusst. In diesem Zusammenhang wurde ein Wachstumsmodell entwickelt, das neben dem Vorhandensein eines Stabilisators auch die Rolle von Bromid- und Silberionen herausstellt, die durch selektive Adsorption das Wachstum bestimmter Kristallflächen inhibieren. Zudem konnte gezeigt werden, dass die Potentialdifferenz zwischen Reduktions- und Oxidationsmittel klein sein muss, um ein langsames selektives Wachstum zu gewährleisten. rnDurch das Aufwachsen einer dünnen Silberschicht auf Goldnanostäbchen verbessert sich deren Qualität im Bezug auf die heterogene Linienbreite. Der “Plasmonic Focusing Effect”, die Änderung der Steigung des linearen Zusammenhangs von Plasmonenresonanz und Aspektverhältnis, konnte theoretisch berechnet und experimentell verifiziert werden. Durch die Aufnahme zeitaufgelöster Spektren und die Untersuchung des Verlaufs der Reaktion wurden sowohl Reaktionsordnung, als auch Aktivierungsenergie ermittelt. Das so gefundene kinetische Model erlaubt zudem die Vorhersage des Reaktionsprodukts zu verschiedenen Zeiten. rnEinzelne Goldnanostäbchen wurden in einer Gelmatrix bei verschiedenen Temperaturen untersucht, die Aufnahme der zeitlichen Variation der polarisationsabhängigen Streuintensität konnte genutzt werden, um den Kollaps des Gels zu charakterisieren. Neben der Verwendung einzelner plasmonischer Nanopartikel wurden auch Dimere, bestehend aus zwei Goldnanokugeln, untersucht. Nach der Kalibrierung der Resonanzfrequenz gegenüber des Abstandes der beiden Partikel durch externe Methoden (Lichtstreuung, Cryo- Elektronenmikroskopie) wurde der so gefundene exponentielle Zusammenhang verwendet, um sowohl den Brechungsindex der Umgebung, als auch den Abstand der beiden Goldnanokugeln zu bestimmen. Des Weiteren wurden Goldnanopartikeldimere benutzt, um ein als Linker verwendetes thermoresponsives Elastin-Polymer bei verschiedenen Temperaturen zu charakterisieren. Neben Aggregaten aus zwei Goldnanokugeln wurden auch so genannte “core-satellite” Strukturen synthetisiert, die um einen großen Goldnanopartikelkern viele kleine Goldnanopartikel tragen. Diese Partikel haben eine theoretisch vorhergesagte höhere Sensitivität gegenüber Brechungsindexänderungen, was in ersten Experimenten gezeigt werden konnte.

Efecto del riego deficitario controlado sobre el crecimiento vegetativo en plantaciones jóvenes de cerezo (Prunus avium L.)

En cerezo, plantas con excesivo vigor son poco precoces, poco productivas y de difícil manejo. El exceso de vigor podría ser controlado con estrategias de riego deficitario controlado (RDC). Durante dos años se realizó un ensayo de RDC en un monte frutal comercial joven y de alto vigor de cerezos Bing, plantado en suelo árido poco profundo y regado por goteo. Se evaluó la respuesta a distintos regímenes de riego sobre el crecimiento de brotes terminales y vigorosos, área y peso seco foliar, y crecimiento de tronco. Los tratamientos de riego fueron: T1 = 100%, T2 = 75% y T3 = 50% de la evapotranspiración máxima (ETc full), respectivamente. Se midió periódicamente el estado hídrico de la planta a través del potencial agua del tallo a mediodía y el estado hídrico del suelo mediante gravimetría. En T3 disminuyó la longitud de brotes, número y longitud de entrenudos, número de hojas, área foliar y peso seco foliar, y área de tronco. En T2 disminuyó la longitud de brotes y entrenudos y el área de sección de tronco. El potencial hídrico del tallo a mediodía fue un buen indicador del estado hídrico de las plantas. En cerezos, un ajuste preciso del nivel de restricción hídrica puede ser una estrategia de manejo para controlar vigor y para ahorrar importantes cantidades de agua.

Analyzing size-symmetric vs. size-asymmetric and intra-vs. inter-specific competition in beech (Fagus sylvatica L.) mixed stands

In mixed stands, inter-specific competition can be lower than intra-specific competition when niche complementarity and/or facilitation between species prevail. These positive interactions can take place at belowground and/or aboveground levels. Belowground competition tends to be size symmetric while the aboveground competition is usually for light and almost always size-asymmetric. Interactions between forest tree species can be explored analyzing growth at tree level by comparing intra and inter-specific competition. At the same time, possible causes of niche complementarity can be inferred relating intra and inter-specific competition with the mode of competition, i.e. size-symmetric or sizeasymmetric. The aim of this paper is to further our understanding of the interactions between species and to detect possible causes of competition reduction in mixed stands of beech (Fagus sylvatica L.) with other species: pine?beech, oak?beech and fir?beech. To test whether species growth is better explained by size-symmetric and/or size-asymmetric competition, five different competition structures where included in basal area growth models fitted using data from the Spanish National Forest Inventory for the Pyrenees. These models considered either size-symmetry only (Reineke?s stand density index, SDI), size-asymmetry only (SDI of large trees or SDI of small trees), or both combined. In order to assess the influence of the admixture, these indices were introduced in two different ways, one of which was to consider that trees of all species compete in a similar way, and the other was to split the stand density indices into intra- and inter-specific competition components. The results showed that in pine?beech mixtures, there is a slightly negative effect of beech on pine basal area growth while beech benefitted from the admixture of Scots pine; this positive effect being greater as the proportion of pine trees in larger size classes increases. In oak?beech mixtures, beech growth was also positively influenced by the presence of oaks that were larger than the beech trees. The growth of oak, however, decreased when the proportion of beech in SDI increased, although the presence of beech in larger size classes promoted oak growth. Finally, in fir?beech mixtures, neither fir nor beech basal area growth were influenced by the presence of the other species. The results indicate that size-asymmetric is stronger than size-symmetric competition in these mixtures, highlighting the importance of light in competition. Positive species interactions in size-asymmetric competition involved a reduction of asymmetry in tree size-growth relationships.

The representation of the ipsilateral visual field in human cerebral cortex

Previous studies of cortical retinotopy focused on influences from the contralateral visual field, because ascending inputs to cortex are known to be crossed. Here, functional magnetic resonance imaging was used to demonstrate and analyze an ipsilateral representation in human visual cortex. Moving stimuli, in a range of ipsilateral visual field locations, revealed activity: (i) along the vertical meridian in retinotopic (presumably lower-tier) areas; and (ii) in two large branches anterior to that, in presumptive higher-tier areas. One branch shares the anterior vertical meridian representation in human V3A, extending superiorly toward parietal cortex. The second branch runs antero-posteriorly along lateral visual cortex, overlying motion-selective area MT. Ipsilateral stimuli sparing the region around the vertical meridian representation also produced signal reductions (perhaps reflecting neural inhibition) in areas showing contralaterally driven retinotopy. Systematic sampling across a range of ipsilateral visual field extents revealed significant increases in ipsilateral activation in V3A and V4v, compared with immediately posterior areas V3 and VP. Finally, comparisons between ipsilateral stimuli of different types but equal retinotopic extent showed clear stimulus specificity, consistent with earlier suggestions of a functional segregation of motion vs. form processing in parietal vs. temporal cortex, respectively.

Ionized cluster beam deposition: Modeling, cluster size measurement and applications

Clusters are aggregations of atoms or molecules, generally intermediate in size between individual atoms and aggregates that are large enough to be called bulk matter. Clusters can also be called nanoparticles, because their size is on the order of nanometers or tens of nanometers. A new field has begun to take shape called nanostructured materials which takes advantage of these atom clusters. The ultra-small size of building blocks leads to dramatically different properties and it is anticipated that such atomically engineered materials will be able to be tailored to perform as no previous material could.^ The idea of ionized cluster beam (ICB) thin film deposition technique was first proposed by Takagi in 1972. It was based upon using a supersonic jet source to produce, ionize and accelerate beams of atomic clusters onto substrates in a vacuum environment. Conditions for formation of cluster beams suitable for thin film deposition have only recently been established following twenty years of effort. Zinc clusters over 1,000 atoms in average size have been synthesized both in our lab and that of Gspann. More recently, other methods of synthesizing clusters and nanoparticles, using different types of cluster sources, have come under development.^ In this work, we studied different aspects of nanoparticle beams. The work includes refinement of a model of the cluster formation mechanism, development of a new real-time, in situ cluster size measurement method, and study of the use of ICB in the fabrication of semiconductor devices.^ The formation process of the vaporized-metal cluster beam was simulated and investigated using classical nucleation theory and one dimensional gas flow equations. Zinc cluster sizes predicted at the nozzle exit are in good quantitative agreement with experimental results in our laboratory.^ A novel in situ real-time mass, energy and velocity measurement apparatus has been designed, built and tested. This small size time-of-flight mass spectrometer is suitable to be used in our cluster deposition systems and does not suffer from problems related to other methods of cluster size measurement like: requirement for specialized ionizing lasers, inductive electrical or electromagnetic coupling, dependency on the assumption of homogeneous nucleation, limits on the size measurement and non real-time capability. Measured ion energies using the electrostatic energy analyzer are in good accordance with values obtained from computer simulation. The velocity (v) is measured by pulsing the cluster beam and measuring the time of delay between the pulse and analyzer output current. The mass of a particle is calculated from m = (2E/v$\sp2).$ The error in the measured value of background gas mass is on the order of 28% of the mass of one N$\sb2$ molecule which is negligible for the measurement of large size clusters. This resolution in cluster size measurement is very acceptable for our purposes.^ Selective area deposition onto conducting patterns overlying insulating substrates was demonstrated using intense, fully-ionized cluster beams. Parameters influencing the selectivity are ion energy, repelling voltage, the ratio of the conductor to insulator dimension, and substrate thickness. ^

Influence des conditions climatiques sur la croissance du sapin baumier et de l'épinette noire

L’effet du climat sur la croissance de la végétation est depuis longtemps un fait acquis. Les changements climatiques globaux ont entrainé une augmentation des efforts de recherche sur l’impact de ces changements en milieux naturels, à la fois en termes de distribution et d’abondance des espèces, mais également à travers l’étude des rendements des espèces commerciales. La présente étude vise à déterminer, à travers l’utilisation de relevés dendrochronologiques, les effets de variables climatiques sur la croissance de l’épinette noire et du sapin baumier à l’échelle de la forêt boréale du Québec. Le but est d’identifier les principaux modificateurs climatiques responsables de la croissance des peuplements boréaux en fonction de leur âge et de leur localisation. Se focalisant sur un modèle non-linéaire des moindres carrés incorporant les modificateurs climatiques et un modificateur d’âge, la modélisation de la croissance en surface terrière en fonction de ces critères a permis de détecter des différences entre le sapin baumier et l’épinette noire. Les résultats montrent que les deux espèces réagissent surtout à la longueur de la saison de croissance et aux températures estivales maximales. L’épinette noire semble également plus sensible aux conditions de sécheresse. Les modèles basés sur l’âge ainsi que sur la localisation le long d’un gradient nord-sud révèlent quelques différences, notamment concernant la réaction plus prononcée des jeunes peuplements au climat, en particulier aux températures, tandis que les vieux peuplements sont sensibles au rayonnement solaire. L’étude démontre tout de même une relative indépendance de l’épinette vis-à-vis du gradient latitudinal, à l’inverse du sapin. Les résultats permettent de discuter des modifications de productivité de ces espèces liées à l’allongement de la saison de croissance (gain pour les deux essences) et aux températures croissantes en conjonction avec les précipitations (perte due à la sécheresse pour l’épinette), dans un contexte de changements climatiques.

Selective growth of carbon nanotubes on bare silicon : MWNT sinthesys on patterned substrates without predeposition of metal catalyst

Carbon nanotubes (CNTs) are expected to become the ideal constituent of many technologes, in particular for future generation electronics. This considerable interest is due to their unique electrical and mechanical properties. They show indeed super-high current-carrying capacity, ballistic electron transport and good field-emission properties. Then, these superior features make CNTs the most promising building blocks for electronic devices, as organic solar cells and organic light emitting devices (OLED). By using Focused Ion Beam (FIB) patterning it is possible to a obtain a high control on position, relative distances and diameter of CNTs. The present work shows how to grow three-dimensional architecture made of vertical-aligned CNTs directly on silicon. Thanks to the higher activity of a pre-patterned surface the synthesis process results very quick, cheap and simple. Such large area growths of CNTs could be used in preliminary test for application as electrodes for organic solar cells.

An MMP13-selective inhibitor delays primary tumor growth and the onset of tumor-associated osteolytic lesions in experimental models of breast cancer

We investigated the effects of the matrix metalloproteinase 13 (MMP13)-selective inhibitor, 5-(4-{4-[4-(4-fluorophenyl)-1,3-oxazol-2-yl]phenoxy}phenoxy)-5-(2-methoxyethyl) pyrimidine-2,4,6(1H,3H,5H)-trione (Cmpd-1), on the primary tumor growth and breast cancer-associated bone remodeling using xenograft and syngeneic mouse models. We used human breast cancer MDA-MB-231 cells inoculated into the mammary fat pad and left ventricle of BALB/c Nu/Nu mice, respectively, and spontaneously metastasizing 4T1.2-Luc mouse mammary cells inoculated into mammary fat pad of BALB/c mice. In a prevention setting, treatment with Cmpd-1 markedly delayed the growth of primary tumors in both models, and reduced the onset and severity of osteolytic lesions in the MDA-MB-231 intracardiac model. Intervention treatment with Cmpd-1 on established MDA-MB-231 primary tumors also significantly inhibited subsequent growth. In contrast, no effects of Cmpd-1 were observed on soft organ metastatic burden following intracardiac or mammary fat pad inoculations of MDA-MB-231 and 4T1.2-Luc cells respectively. MMP13 immunostaining of clinical primary breast tumors and experimental mice tumors revealed intra-tumoral and stromal expression in most tumors, and vasculature expression in all. MMP13 was also detected in osteoblasts in clinical samples of breast-to-bone metastases. The data suggest that MMP13-selective inhibitors, which lack musculoskeletal side effects, may have therapeutic potential both in primary breast cancer and cancer-induced bone osteolysis.

Size- and orientation-selective Si nanowire growth : thermokinetic effects of naeoscale plasma chemistry

A multiscale, multiphase thermokinetic model is used to show the effective control of the growth orientation of thin Si NWs for nanoelectronic devices enabled by nanoscale plasma chemistry. It is shown that very thin Si NWs with [110] growth direction can nucleate at much lower process temperatures and pressures compared to thermal chemical vapor deposition where [111]-directed Si NWs are predominantly grown. These findings explain a host of experimental results and offer the possibility of energy- and matter-efficient, size- and orientation-controlled growth of [110] Si NWs for next-generation nanodevices.

Energy and matter-efficient size-selective growth of thin quantum wires in a plasma

It is shown that plasmas can minimize the adverse Gibbs-Thompson effect in thin quantum wire growth. The model of Si nanowirenucleation includes the unprecedented combination of the plasma sheath, ion- and radical-induced species creation and heating effects on the surface and within an Au catalyst nanoparticle. Compared to neutral gas thermal processes, much thinner, size-selective wires can nucleate at the same temperature and pressure while much lower energy and matter budget is needed to grow same-size wires. This explains the experimental observations and may lead to energy- and matter-efficient synthesis of a broader range of one-dimensional quantum structures.

Low-temperature growth of large area, vertically aligned carbon nanotubes for field emission applications

Large area, highly uniform vertically aligned carbon nanotips (VACNTP) and other nanostructures have been grown on silicon (100) substrates with Ni catalyst in the low-temperature, low-frequency, high-density inductively coupled plasmas (ICP) of methane-hydrogen-argon gas mixtures. The control strategies for the morphology, crystalline structure and chemical states of the resulting nanostructures by varying the growth conditions are proposed. XRD and Roman analyses confirm that the nanotips are well graphitized, which is favorable for the field emission applications.

Reproducible and label-free biosensor for the selective extraction and rapid detection of proteins in biological fluids

Erythropoietin (EPO), a glycoprotein hormone of ∼34 kDa, is an important hematopoietic growth factor, mainly produced in the kidney and controls the number of red blood cells circulating in the blood stream. Sensitive and rapid recombinant human EPO (rHuEPO) detection tools that improve on the current laborious EPO detection techniques are in high demand for both clinical and sports industry. A sensitive aptamer-functionalized biosensor (aptasensor) has been developed by controlled growth of gold nanostructures (AuNS) over a gold substrate (pAu/AuNS). The aptasensor selectively binds to rHuEPO and, therefore, was used to extract and detect the drug from horse plasma by surface enhanced Raman spectroscopy (SERS). Due to the nanogap separation between the nanostructures, the high population and distribution of hot spots on the pAu/AuNS substrate surface, strong signal enhancement was acquired. By using wide area illumination (WAI) setting for the Raman detection, a low RSD of 4.92% over 150 SERS measurements was achieved. The significant reproducibility of the new biosensor addresses the serious problem of SERS signal inconsistency that hampers the use of the technique in the field. The WAI setting is compatible with handheld Raman devices. Therefore, the new aptasensor can be used for the selective extraction of rHuEPO from biological fluids and subsequently screened with handheld Raman spectrometer for SERS based in-field protein detection.

Developmental and growth controls of tillering and water-soluble carbohydrate accumulation in contrasting wheat (Triticum aestivum L.) genotypes: can we dissect them?

In wheat, tillering and water-soluble carbohydrates (WSCs) in the stem are potential traits for adaptation to different environments and are of interest as targets for selective breeding. This study investigated the observation that a high stem WSC concentration (WSCc) is often related to low tillering. The proposition tested was that stem WSC accumulation is plant density dependent and could be an emergent property of tillering, whether driven by genotype or by environment. A small subset of recombinant inbred lines (RILs) contrasting for tillering was grown at different plant densities or on different sowing dates in multiple field experiments. Both tillering and WSCc were highly influenced by the environment, with a smaller, distinct genotypic component; the genotypeenvironment range covered 350750 stems m(2) and 25210mg g(1) WSCc. Stem WSCc was inversely related to stem number m(2), but genotypic rankings for stem WSCc persisted when RILs were compared at similar stem density. Low tilleringhigh WSCc RILs had similar leaf area index, larger individual leaves, and stems with larger internode cross-section and wall area when compared with high tilleringlow WSCc RILs. The maximum number of stems per plant was positively associated with growth and relative growth rate per plant, tillering rate and duration, and also, in some treatments, with leaf appearance rate and final leaf number. A common threshold of the red:far red ratio (0.390.44; standard error of the difference0.055) coincided with the maximum stem number per plant across genotypes and plant densities, and could be effectively used in crop simulation modelling as a ocut-off' rule for tillering. The relationship between tillering, WSCc, and their component traits, as well as the possible implications for crop simulation and breeding, is discussed.

Selective growth of ZnO nanoneedles by thermal oxidation of Zn microstructures

Zinc film containing hexagonal plate stack and tower-like micro structures were grown on Si substrates at high temperature by thermal evaporation. Thermal oxidation studies on these micro structures have shown that ZnO nanoneedles selectively grow from the facets of the zinc microstructure at temperature above 300 degrees C in atmosphere TEM analysis showed that single crystalline and bicrystalline nanoneedles were formed in this oxidation process and the growth direction of these nanoneedles was identified along the [1 1 (2) overbar 0]. Based on the structural studies and morphological observation, we have proposed a possible mechanism for the selective growth of ZnO nanoneedles during thermal oxidation.

Selective growth of single phase VO2(A, B, and M) polymorph thin films

We demonstrate the growth of high quality single phase films of VO2(A, B, and M) on SrTiO3 substrate by controlling the vanadium arrival rate (laser frequency) and oxidation of the V atoms. A phase diagram has been developed (oxygen pressure versus laser frequency) for various phases of VO2 and their electronic properties are investigated. VO2(A) phase is insulating VO2(B) phase is semi-metallic, and VO2(M) phase exhibits a metal-insulator transition, corroborated by photoelectron spectroscopic studies. The ability to control the growth of various polymorphs opens up the possibility for novel (hetero) structures promising new device functionalities. (C) 2015 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.