Laser cooling and control of excitations in superfluid helium

Superfluidity is an emergent quantum phenomenon which arises due to strong interactions between elementary excitations in liquid helium. These excitations have been probed with great success using techniques such as neutron and light scattering. However measurements to-date have been limited, quite generally, to average properties of bulk superfluid or the driven response far out of thermal equilibrium. Here, we use cavity optomechanics to probe the thermodynamics of superfluid excitations in real-time. Furthermore, strong light-matter interactions allow both laser cooling and amplification of the thermal motion. This provides a new tool to understand and control the microscopic behaviour of superfluids, including phonon-phonon interactions, quantised vortices and two-dimensional quantum phenomena such as the Berezinskii-Kosterlitz-Thouless transition. The third sound modes studied here also offer a pathway towards quantum optomechanics with thin superfluid films, including femtogram effective masses, high mechanical quality factors, strong phonon-phonon and phonon-vortex interactions, and self-assembly into complex geometries with sub-nanometre feature size.Comment: 6 pages, 4 figures. Supplementary information attache

Gold nanoparticles and chitosan encapsulation for therapy and sensing

Un sinfín de aplicaciones en el campo de la biomedicina se verían beneficiadas por el futuro uso de nanopartículas de oro (AuNPs). Sin embargo, a pesar de las miles de publicaciones científicas que destacan cada año las fabulosas propiedades de estas nanopartículas en este área, su empleo más allá del ámbito científico es testimonial, especialmente cuando hablamos de su uso con finalidades terapéuticas en el ámbito clínico. El objetivo principal de esta tesis consiste en mejorar la aplicabilidad de las nanopartículas de oro con diferentes geometrías mediante dos líneas de acción: 1) el estudio de la relación entre sus propiedades fisicoquímicas y su rendimiento para las aplicaciones de bio-detección y terapia fototérmica y 2) la búsqueda de una manera complementaria de mejorar sus propiedades intrínsecas para aplicaciones terapéuticas mediante su encapsulación en hidrogeles de quitosano. En la primera parte de esta tesis la inexistencia de una metodología clínica adecuada para la detección de miRNA nos ha llevado a buscar nuevas estrategias para su detección mediante el empleo de nanopartículas de oro como amplificadores de la señal de detección gracias a sus idóneas propiedades: elevada densidad, tamaño adecuado y facilidad para su funcionalización con diferentes proteínas. Además, para descubrir su utilidad en la detección de miRNA en condiciones similares a las necesarias en el ámbito clínico, se ha llevado a cabo un estudio comparativo empleando nanopartículas de oro con diversas geometrías y diferentes estrategias de biofuncionalización para su interacción con los miRNA. En la segunda parte de esta tesis se ha continuado con el estudio de la aplicación de diferentes geometrías de nanopartículas de oro para su uso en terapia fototérmica, centrándonos en sus propiedades ópticas, su interacción celular y eficacia, ya que hay una falta de conocimiento acerca de la importancia que tiene la forma de las nanopartículas en este tema. Gracias a las conclusiones extraídas durante este estudio concernientes a la baja internalización celular de los nanorods, hemos propuesto una estrategia innovadora consiste en su encapsulación en hidrogeles de quitosano motivada por las propiedades de adhesión celular del quitosano que han permitido una mejora remarcable de su eficacia. Finalmente se ha desarrollado una nueva metodología para la encapsulación de nanopartículas de oro en hidrogeles de quitosano empleando la tecnología de eyección automática de tinta o inkjet para mejorar su encapsulación, la cual permite que el proceso sea más fácil de escalar, efectivo y controlable. Esta tecnología ofrece una metodología automática para la producción continua de microcápsulas de quitosano que contengan las nanopartículas de oro en su interior, proporcionando biomateriales con propiedades muy interesante para las aplicaciones biomédicas. Como resultado, la investigación llevada a cabo durante esta tesis doctoral contribuye a ampliar nuestro conocimiento en la importancia del empleo de diferentes geometrías de nanopartículas de oro para las aplicaciones terapéuticas y de detección a la vez que proporciona nuevas herramientas para aumentar su aplicabilidad gracias a la funcionalización de su superficie y a su encapsulación en hidrogeles de quitosano. <br /

Incorporating nanomaterials with MEMS devices.

This dissertation demonstrates an elegant method, known as \u27micro-origami\u27 or strain architecture to design and fabricate three-dimensional MEMS structures which are assembled using actuation of a metal-oxide bilayer with conventional planar lithography. Folding allows creating complex, robust, three-dimensional shapes from two-dimensional material simply by choosing folds in the right order and orientation, small disturbances of the initial shape may also be used to produce different final shapes. These are referred to as pop-up structures in this work. The scope of this work presented the deposition of colloidal gold nanoparticles (GNPs) into conformal thin films using a microstenciling technique. Results illustrated that the gold nanoparticle deposition process can easily be integrated into current MEMS microfabrication processes. Thin films of GNPs deposited onto the surfaces of siliconbased bistable MEMS and test devices were shown to have a significant effect on the heating up of microstructures that cause them to fold. The dissertation consists of four chapters, covering details of fabrication methods, theoretical simulations, experimental work, and existing and potential applications. Chapter II illustrates how control of the folding order can generate complex three-dimensional objects from metal-oxide bilayers using this approach. By relying on the fact that narrower structures are released from the substrate first, it is possible to create multiaxis loops and interlinked objects with several sequential release steps, using a single photomask. The structures remain planar until released by dry silicon etching, making it possible to integrate them with other MEMS and microelectronic devices early in the process. Chapter III depicts the fabrication process of different types of bistable structures. It describes the principle of functioning of such structures, and simulations using CoventorWare are used to support the concept. We talk over about advantages and disadvantages of bistable structures, and discuss possible applications. Chapter IV describes fabrication procedure of nanoparticle-MEMS hybrid device. We introduce a convenient synthesis of GNPs with precisely controlled optical absorption in the NIR region by a single step reaction ofHAuCl4 and Na2S203. We take a look at different techniques to pattern gold nanoparticles on the surface of MEMS structures, and also provide a study of their thermal properties under near IR stimulation. We demonstrate the first approach of laser-driven bistable MEMS actuators for bioapplications. Finally, in Conclusion discuss the contributions of this dissertation, existent limitations and plans of the future work

Photothermal experiments on condensed phase samples of agricultural interest : optical and thermal characterization

A rapidly increasing number of photothermal (PT) techniques has had a considerable impact on agriculture and environmental sciences in the last decade. It was the purpose of the work described here to develop and apply new PT techniques in this specific field of research.Chapter I is a general introduction with an overview of PT techniques used in this research. Two different photoacoustic (PA) techniques used for optical characterization of a variety of condensed phase samples are discussed in chapters 2 and 3. The possibilities for thermal characterization of samples are described in chapter 4.In chapter 2 classical PA spectroscopy with microphone detection was used to obtain spectra in the visible region (350-700 nm) of powdered (light scattering) food samples such as flours, coffee and spices (chapter 2.1). The outcome of these experiments suggest the feasibility of PA spectroscopy for quality control in the food-processing industry. Another PA cell was designed (chapter 2.2) and used in the IR region (10 μm). The final PA experiment was concerned with study of various carboxylic acids, alcohols and alkanes at 3.39 μm (chapter 2.3).The feasibility of optothermal window (OW) method, an elegant approach to determine the optical absorption coefficient of condensed phase samples is described in chapter 3. The method was not only extended to 9-11 μm but also proved capable of investigating opaque samples (liquids and gel) which are otherwise not amenable to conventional IR spectroscopies.The content of trans fatty acids in several margarine samples was measured with the OW technique and its performance compared to that of GLC, GLC + TLC and FTIR. The data obtained with the different methods were generally in a good agreement. The improved OW cell resulting in substantial reduction of the background signal, was then used to study extra virgin olive oil (chapter 3.2) adulterated by known adulterants (sunflower oil (4.5%) and safflower oil (6%)). The achieved limit of detection (LOD) was comparable to those reported in literature for other techniques (FTIR-ATR, GLC, HPLC and mass spectroscopy).Many biological samples contain water that itself exhibits a strong absorption in IR. Quantitative measurements on such specimens are all but trivial. The new OW sensor was shown capable of direct and quantitative measurements (chapter 3.3 and 3.4) of lactose, corn starch and sulfate in water. The performance of the OW method was slightly inferior to that of FTIR. On the other hand, unlike the OW method, FTIR-ATR could only provide quantitative results for corn starch samples. As to the study of sulfate in water, the limit of detection (I mmolL -1) achieved with the OW method is one order of magnitude better than that of ATR.In the fourth and last chapter, two different PT techniques (photopyroelectric method and photothermal beam deflection) were used for thermal characterization of a candy (a model for a glassy sugar system) and different packaging materials. The thermal diffusivity of a candy at room temperature found by PPE and PTBD was 14.7 x10 -8and 12.0 x10 -8m 2S -1respectively. In addition, the PPE technique in the standard configuration, was used to measure temperature dependence of the thermal diffusivity in the -30°C to 70°C temperature range. The glass-rubber transition, underwent by the sample in this temperature range was observed and compared to the results obtained by differential scanning calorimetry (DISC).The PPE technique was also used to obtain the temperature behaviour of thermal diffusivity of low density polyethylene and polyvinylchloride foils (used for packaging purposes). Such behavior was found dependent on the thermal history of the sample. The "untreated' foils exhibit values for thermal diffusivity that were consistently lower (7-20%) than those obtained for the same samples when heated to 70°C. The increase in thermal diffusivity is associated with structural changes (i.e. glass transitions) taking place in the material during thermal annealing. Additional measurements by differential scanning calorimetry (DSC) confirmed the validity of PPE results. It was shown that the PPE method is more sensitive than the standard DSC in detecting changes in thermal parameters.Finally, the PPE method allows one in principle to obtain the temperature behavior of all static and dynamic thermal parameters provided one of the remaining thermal parameters (thermal conductivety, thermal effusivity and volume specific heat) is available at a given temperature.OutlookResults of a research described in this thesis show the feasibility of PT techniques for applications to a wide range of condensed phase samples. The methods used here constitute only a part of techniques developed and used in our laboratory. The low-cost and compact OW device is easy to handle and moreover offers the possibility for on-line studies of optically opaque and thermally thick samples that are normally not accessible by other techniques. It is anticipated that development of infrared diode lasers will increase the potential of the OW method because desired wavelengths characterized by the highest spectral contrast will become available. The sensitivity of the OW method was shown comparable to that of FTIR and therefore additional developments might eventually make the OW approach a candidate technique for quantitative analysis throughout the entire infrared region. The analytical potential of PT schemes becomes more obvious when they are used as detectors in combination with separation techniques such as GLC, HPLC or capillary electrophoresis.The potential of photopyroelectric technique was demonstrated by obtaining thermal diffusivity values for different kind of samples. The PPE method is able to provide data on aging effect, structural stability and crystaline polymorphism. The technique is fast, sensitive and reproducible, requires small amounts of sample for analysis while providing more information than existing, classical methods used currently in thermal research. The only drawback of PPE is the necessity for good thermal contact between sample and sensor. When one is interested to obtain thermal diffusivity data in a non-contact manner the photothermal beam deflection (zero crossing method) is a valuable tool. Accurate (5% error determination of thermal diffusivity is achievable due to intrinsically low errors in measurement of frequency and of zero crossing position.In conclusion, based on the results of the work described here, one can anticipate that in the years to come the PT methods, alone or combined with existing techniques, will most likely play a more important role for variety of applications in agricultural and environmental sciences

Characterization of a home-built low temperature scanning probe microscopy system

The continuing advancement of technology is the driving force behind science and fundamental research. Scanning probe instruments still have a major impact in nanoscience and technology, because they provide a link between the macroscopic world and the atomic scale. The key to a reliable performance of experiments at the nanometer scale is the instrumentation, that allows probe positioning ranging from micrometers to Ångstroms with sub atomic precisions. A new type of scanning probe microscopy (SPM) system operating in ultra high vacuum (UHV) and at liquid Helium (LHe) temperature was developed. This offers the advantages that even reactive surfaces remain clean over time periods of several days, permitting long time experiments. Moreover, these experiments this low temperature scanning probe microscopy (LTSPM) system is the implementation of a focussing Fabry Perot interferometer (fFPi) that allows the following features: - Small amplitude operations and stiff cantilevers require sensors with high deflection sensitivity. With the fFPi in this low temperature SPM system, a deflection sensitivity of 4fm/ sqrt(Hz) at 1MHz can be obtained. - Wide detection bandwidth (DC-10MHz) enables the operation of higher flexural oscillation modes as well as the torsional modes of the cantilever. - A laser spot size of 3µm allows the use of ultra small cantilevers with the dimensions 1/10 of conventional cantilevers. - Photothermal excitation of cantilevers avoids undesirable mechanical vibrations near the cantilever resonance frequency. - Simultaneous flexural and torsional force detection provides quantitative studies of frictions and thus, atom manipulations by atomic force microscopy (AFM). - The combination of both types of microscopes (simultaneous AFM/STM) reveals more information than a scanning tunneling microscopy (STM) or AFM alone. A series of measurements on Si(111)7x7, herringbone superstructure of Au(111) and highly oriented pyrolytic graphite (HOPG) provides information regarding imaging performance of the system. Among these performance tests are atomically resolved scans at three different operating temperatures in STM mode. In non-contact atomic force microscopy (nc-AFM) mode, imaging was performed with the cantilever driven at the fundamental and 2nd oscillation mode. Additional measurements were performed with the fFPi in order to quantify the impact of the laser cooling effects (radiation pressure and photothermal effects) on the oscillating cantilever at three different operating temperatures. The aim of this work is the development, implementation and characterization of a new low temperature scanning probe microscope with an ultra sensitive and high bandwidth fFPi deflection sensor, suitable for nc-AFM operations with small, simultaneous flexural and torsional cantilever oscillation modes. Furthermore, expected upgrades will allow simultaneous nc-AFM/STM operations. Keywords: low temperature home-built simultaneous STM/ nc-AFM, tip-sample gap stability, PLL and self-excitation, highly oriented pyrolytic graphite (HOPG), reconstructed Si(111)7x7, herringbone superstructure, focussing Fabry-Perot interferometer, cantilever cooling, radiation pressure and photothermal effects. Der kontinuierliche, technologische Fortschritt ist die treibende Kraft hinter Wissenschaft und Grundlagenforschung. Rasterkraft und -tunnel Instrumente haben immer noch einen bedeutenden Einfluss auf die Nanotechnologie und -wissenschaft, weil sie eine Verbindung zwischen der makroskopischen Welt und den atomaren Massstäben darstellen. Der Schlüssel für eine zuverlässige Ausführung von Experimenten mit Nanometer Massstäben ist die Instrumentierung, die eine Spitzenpositionierung von Mikrometer bis Ångstroms mit subatomarer Präzision erlaubt. Ein neuartiges Rasterspitzen Mikroskop (SPM) System wurde entwickelt, das im Ultra Hoch Vakuum (UHV) und bei flüssig Helium Temperaturen arbeitet. Dies bietet Vorteile weil sogar reaktive Oberflächen über eine Dauer von einigen Tagen sauber bleiben, was eine längere Experimentierphase zulässt. Zusätzlich zeigen diese Experimente bei tiefen Temperaturen weitere Vorteile wie kleine Driftwerte und tiefe Piezo Kriechraten. Der Ansatz bei diesem Tieftemperatur Rasterspitzen Mikroskop System ist die Implementierung eines fokussierenden Fabry Perot Interferometers das die folgenden Eigenschaften vorweist: - Der Betrieb bei kleinen Amplituden und mit steifen Cantilever setzt Sensoren mit einer hohen Ablenkempfindlichkeit voraus. Mit diesem fokussierenden Fabry Perot Interferometer (fFPi) kann eine Ablenkempfindlichkeit von 4fm/ sqrt(Hz) bei 1MHz erreicht werden. - Detektion mit einer grossen Bandbreite (DC-10MHz) erlauben einen Betrieb von Cantilever mit flexuralen und torsionalen Oszillation Modi. - Ein Laser mit einem Brennpunkt von 3µm lässt einen Betrieb mit einem ultra kleinen Cantilever zu, der 1/10 so gross ist wie ein konventioneller Cantilever. - Photothermische Anregung eines Cantilevers vermeidet unerwünschte mechanische Vibrationen rund um die Resonanzfrequenz. - Gleichzeitige flexural und torsional Kraftdetektion erlauben quantitative Untersuchungen von Reibungen und daher atomare Manipulationen mit Rasterkraft Mikroskopie (AFM). - Die Kombination und simultanen Betrieb von beiden Rasterspitzen Mikroskopen (AFM/STM) zeigen mehr Information als ein Raster Tunnel Mikroskop (STM) alleine. Eine Serie von Messungen mit Si(111)7x7, Herringbone Superstrukturen auf Au(111) und Highly Oriented Pyrolytic Graphite (HOPG) geben Information bezüglich der Leistungen des Systems preis. Einige dieser Leistungstests sind atomar aufgelöste Abbildungen bei drei unterschiedlichen Betriebstemperaturen im STM Betriebsart. Im nicht-Kontakt AFM (nc-AFM) Betriebsart, Abbildungen sind ausgeführt worden auf der Grundschwingung und der zweiten Oberschwingung. Zusätzliche Messungen wurden mit dem fFPi ausgeführt um den Einfluss der Laserkühlung auf den oszillierenden Cantilever bei drei unterschiedlichen Betriebstemperaturen zu quantifizieren. Das Ziel dieser Arbeit ist die Entwicklung, Implementation und Charakterisierung eines neuen Tieftemperatur Rasterspitzen Mikroskops mit einem ultra-empfindlichen und Breitband fokussierenden Fabry Perot Interferometer Ablenk Sensor, geeignet für den nicht-Kontakt AFM Betrieb mit kleinen, simultanen flexural und torsional Cantilever Schwingungsmodi. Naheliegende Erweiterungen des Systems gewährleisten einen simultan nc-AFM/STM Betrieb. Schlüsselwörter: Tieftemperatur simultan nc-AFM/STM aus Eigenbau, Spitzen-Probe Spalt Stabilität, PLL und Eigenanregungsbetrieb, Highly Oriented Pyrolytic Graphite (HOPG), reconstrukturiertes Si(111)7x7, Herringbone Superstruktur, fokussierenden Fabry Perot Interferometer, Cantilever Kühlung, Strahlendruck und photothermische Effekte

High-sensitivity monitoring of micromechanical vibration using optical whispering gallery mode resonators

The inherent coupling of optical and mechanical modes in high finesse optical microresonators provide a natural, highly sensitive transduction mechanism for micromechanical vibrations. Using homodyne and polarization spectroscopy techniques, we achieve shot-noise limited displacement sensitivities of 10^(-19) m Hz^(-1/2). In an unprecedented manner, this enables the detection and study of a variety of mechanical modes, which are identified as radial breathing, flexural and torsional modes using 3-dimensional finite element modelling. Furthermore, a broadband equivalent displacement noise is measured and found to agree well with models for thermorefractive noise in silica dielectric cavities. Implications for ground-state cooling, displacement sensing and Kerr squeezing are discussed.Comment: 25 pages, 8 figure

Doped ZnO nanoparticles in biomedicine: their role as stimuli-responsive anticancer agents

L'abstract è presente nell'allegato / the abstract is in the attachmen