The Atomic Force Microscope (AFM) is a tool for imaging surfaces at the microand nano meter scale. The microscope senses the force acting between a surfaceand a tip positioned at the end of a micro-cantilever, forming an image of the surface topography. Image contrast however, arises not only from surface topography, but also from variation in material composition. Improved material contrast, and improved interpretation of that contrast are two issues central to the further development of AFM. This thesis studies dynamic AFM where the cantilever is driven at multiple frequencies simultaneously. Due to the nonlinear dependence of the tip-surface force on the tip’s position, the cantilever will oscillate not only at the driven frequencies, but also at harmonics and at mixing frequencies of the drives, so-called intermodulation products. A mode of AFM called Intermodulation AFM (ImAFM) is primarily studied, which aims to make use of intermodulation products centered around the resonance frequency of the cantilever. With proper excitation many intermodulation products are generated near resonance where they can be measured with large signal-to-noise ratio. ImAFM is performed on samples containing two distinct domains of different material composition and a contrast metric is introduced to quantitatively evaluate images obtained at each response frequency. Although force sensitivity is highest on resonance, we found that weak intermodulation response off resonance can show larger material contrast. This result shows that the intermodulation images can be used to improve discrimination of materials. We develop a method to obtain material parameters from multifrequency AFM spectra by fitting a tip-surface force model. Together with ImAFM, this method allows high resolution imaging of material parameters. The method is very generalas it is not limited to a specific force model or particular mode of multifrequency AFM. Several models are discussed and applied to different samples. The parameter images have a direct physical interpretation and, if the model is appropriate, they can be used to relate the measurement to material properties such as the Young’s modulus. Force reconstruction is tested with simulations and on measured data. We use the reconstructed force to define the location of the surface so that we can address the issue of separating topographic contrast and material contrast. / Svepkraftmikroskop (eller atomkraftmikroskop från engelskans atomic forcemicroscope, AFM) är ett instrument för att avbilda ytor på mikro- och nanometer skalan. Mikroskopet känner av kraften som verkar mellan en yta och en spetsplacerad längst ut på ett mikrometerstort fjäderblad och kan därigenom skapa en topografisk bild av ytans form. Bildkontrast uppstår dock inte bara från ytans form utan även från variation i material. Förbättrad materialkontrast och förbättrad tolkning av denna kontrast är två centrala mål i vidareutvecklingen av AFM. Denna avhandling berör dynamisk AFM där fjädern drivs med flera frekvensersamtidigt. På grund av det ickelinjära förhållandet i yt-spets-kraften som funktion av spetsens position så kommer fjädern inte bara att svänga på de drivna frekvenserna utan också på övertoner och blandfrekvenser, så kallade intermodulationsprodukter. Vi undersöker primärt Intermodulation AFM (ImAFM) som ämnar att utnyttja intermodulationsprodukter nära fjäderns resonansfrekvens. Med en lämplig drivsignal genereras många intermodulationsprodukter nära resonansen, där de kan mätas med bra signal till brus förhållande. ImAFM utförs på ytor bestående av två distinkta domäner av olika material ochen kontrastmetrik introduceras för att kvantitativt utvärdera bilderna som skapas vid varje frekvens. Trots att känsligheten för kraftmätningen är högst på resonans-frekvensen, så fann vi att svaga intermodulationsprodukter bortanför resonansen kan visa hög materialkontrast. Detta resultat visar att intermodulationsbilderna kan användas för att bättre särskilja olika material. Vi har utvecklat en metod för att rekonstruera yt-spets-kraften från multifrekventa AFM spektra genom modellanpassning i frekvensrymden. Tillsammans med ImAFM leder detta till högupplösta bilder av materialparametrar. Metoden är generell och är applicerbar för olika kraftmodeller och AFM-varianter. Parametrarna har en direkt fysikalisk tolkning och, om lämpliga modeller används, kan egenskaper så som materialets elasticitetsmodul mätas. Metoden har testats på simulerat såvälsom experimentellt data, och den har också används för att särskilja topografisk kontrast från materialkontrast. / <p>QC 20150209</p>

Thesis (Ph. D.)--Ohio State University, 2007. / Title from first page of PDF file. Includes bibliographical references (p. 104-107).

京都大学 / 新制・課程博士 / 博士(理学) / 甲第24871号 / 理博第4981号 / 新制||理||1711(附属図書館) / 京都大学大学院理学研究科化学専攻 / (主査)准教授 武田 和行, 教授 堀毛 悟史, 教授 北川 宏 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

Quantum cascade lasers (QCLs) operate due to population inversion on intersubband in unipolar mutiple-quantum-well (MQW) heterostructure. QCLs are considered one of the most flexible and powerful light semiconductor sources in the mid- and far-infrared (IR) wavelength range, covering most of the critical spectral regions relevant to IR applications. InGaAs/InAlAs/InP QCLs are the only semiconductor lasers capable of continuous wave (CW) operation at room temperature (RT) in the spectral range 3.4-12 micron. This dissertation details the development of RT QCLs based on passive nonlinear coupled-quantum-well structures monolithically integrated into mid-IR QCLs to provide a giant nonlinear response for the pumping frequency. The primary focus of short-wavelength approach in this dissertation is to develop of RT InGaAs/InAlAs/InP QCLs for lamda=2.5-3.7 micron region, based on quasi-phase-matched intracavity second harmonic generation (SHG) associated with intersubband transition. Intersubband optical transition can be engineered by the choice of quantum well and barrier thicknesses to provide the appropriate energy levels, optical dipole matrix elements, and electron scattering rates amongst other parameters. Thus, aside from their linear optical properties, resonant intersubband transitions in coupled QW's can also be designed to produce nonlinear optical medium with giant nonlinear optical susceptibilities. In long-wavelength region, at high temperature, the population inversion is reduced between the upper and lower laser levels due to the longitudinal optical (LO) phonon scattering of thermal carriers in the upper laser state and the thermal backfilling of carriers into the lower laser level from the injector state. This dissertation aims to improve an alternative approach for THz QCL sources based on intra-cavity difference frequency generation (DFG) in dual-wavelength mid-IR QCLs with a passive nonlinear structure, designed for giant optical nonlinearity. Further studies describe that Cerenkov DFG scheme allows for extraction of THz radiation along the whole length of the laser waveguide and provides directional THz emission in 1.2-4.5 THz range. An important requirement for many applications, like chemical sensing and molecular spectroscopy, is single-mode emission. We demonstrate single-mode RT DFG THz QCLs operation in 1-5 THz region by employing devices as integrated dual-period DFB lasers, where efficient solid state RT sources do not exist. / text

La détection et quantification d’agent biologique occupe une place prépondérante dans la prévention et la détection des dangers possibles pour la santé publique (épidémie ou pandémie), l’environnement ainsi que d’autres risques contextuelles (bioterrorisme, armes biologique ou chimiques…etc.). Par conséquent, le développement d’un système portable et à moindre coût permettant de détecter ces dangers constitue l’axe de recherche pluridisciplinaire de la collaboration entre différents laboratoires de l’UPMC (Paris 6) et « RWTH university » à Aachen en Allemagne. Dans ce projet, nous avons étudié les aspects pluridisciplinaires d’un microsystème (LoC) électromagnétique de détection immunologique basé sur l’utilisation de nanoparticules magnétiques (MNP). En raison de leur extractabilité et de leur triabilité, les MNP sont adaptées à l'examen d'échantillons biologiques, servant de marqueurs pour des réactions biochimiques. La plupart des techniques classiques de détection existantes sont basées sur des méthodes colorimétrique, fluorescence ou électrochimique qui souffrent en majorité de problème de temps d’analyse et de sensibilité. A cet égard, Les méthodes d’immuno-détection magnétiques constituent une alternative prometteuse. Cette détection est effectuée à l’aide des MNP qui sont spécifiquement bio-fonctionnalisés en surface afin d’être liée à la cible (virus, anticorps…etc). La nouvelle méthode magnétique de mélange de fréquence permet la détection et la quantification de ces MNP avec une grande dynamique. Dans cette thèse, l’effort est dirigé vers la miniaturisation de ce système. Pour ce faire, nous avons développé un ensemble d’outils analytiques et de simulations multiphysiques afin d’optimiser les dimensions des parties électromagnétique (bobines planaires) et microfluidiques. Par la suite, des prototypes de cette structure de détection à partir de bobines en circuits imprimés et de réservoirs microfluidiques en PDMS sont dimensionnés et réalisés. Les performances de ces prototypes ont été évaluées en termes de limite de détection de MNP, linéarité et plage dynamique. En outre, ces prototypes ont permis de valider les outils de dimensionnement réalisés. Une limite de détection de nanoparticules magnétiques de 15ng/mL a été mesurée avec un volume d'échantillon de 14 μL correspondant à une goutte de sang. Finalement, la validation du système quant à l’immuno-détection est abordée avec un état de l’art et le développement d’une procédure de fonctionnalisation biochimique de surface ainsi que des premiers tests pour sa validation. / The detection and quantification of a biological agent or entity has become paramount to anticipate a possible health threat (epidemic or pandemic), environmental threat or to combat other contextual threats (bioterrorism, chemical and biological weapons, drugs). Consequently, developing a portable cost effective device that could detect and quantify such threats is the research focus of the joint multidisciplinary project between UPMC (Paris 6) laboratories and RWTH university in Aachen, Germany. In the framework of this project, we have studied the multidisciplinary aspects of an electromagnetic microsystem for immunologic detection based on magnetic nanoparticles (MNP) in a microfluidic lab-on-chip (LoC). Because of their extractability and sortability, magnetic nanoparticles are adapted for examination of biological samples, serving as markers for biochemical reactions. So far, the final detection step is mostly achieved by well-known immunochemical or fluorescence-based techniques which are time consuming and have limited sensitivity. Therefore, magnetic immunoassays detecting the analyte by means of magnetic markers constitute a promising alternative. MNP covered with biocompatible surface coating can be specifically bound to analytes, cells, viruses or bacteria. They can also be used for separation and concentration enhancement. The novel frequency mixing magnetic detection method allows quantifying magnetic nanoparticles with a very large dynamic measurement range. In this thesis, emphasis is put on the miniaturized implementation of this detection scheme. Following the development of analytical and multiphysics simulations tools for optimization of both excitation frequencies and detection planar coils, first multilayered printed circuit board prototypes integrating all three different coils along with an adapted microfluidic chip has been designed and realized. These prototypes have been tested and characterized with respect to their performance for limit of detection (LOD) of MNP, linear response and validation of theoretical concepts. Using the frequency mixing magnetic detection technique, a LOD of 15ng/mL for 20 nm core sized MNP has been achieved with a sample volume of 14 μL corresponding to a drop of blood. Preliminary works for biosensing have also been achieved with a state of the art of surface functionalization and a developed proposed biochemical immobilization procedure and preliminary tests of its validation.

Bragg reflection waveguides (BRW) or one-dimensional photonic bandgap structures have been demonstrated for phase-matching chi(2) nonlinearities in AlxGa1-xAs. The method exploits strong modal dispersion of a Bragg mode and total internal reflection modes co-propagating inside the waveguide. It is shown that phase-matching is attained among the lowest order modes of interacting harmonics, which allows maximizing the utilization of harmonics powers for nonlinear interactions. As our first demonstration, we report second-harmonic generation (SHG) of a 2-ps telecommunication pump in a 2.4 mm long slab BRW. The conversion efficiency is estimated as 2.0 %/W.cm^2 with a generated SH power of 729 nW. This efficiency has been considerably improved by introducing lateral confinement of optical modes in ridge structures. Characterizations denote that efficiency of SHG in ridge BRWs can increase by over an order of magnitude in comparison to that of the slab device. Also, we report continuous-wave SHG in BRWs. Using a telecommunication pump with a power of 98 mW, the continuous-wave SH power of 23 nW is measured in a 2.0 mm long device. Significant enhancements of chi(2) interactions is obtained in the modified design of matching-layer enhanced BRW (ML-BRW). For the first time, we report type-II SHG in ML-BRW, where the second-harmonic power of 60 µW is measured for a pump power of 3.3 mW in a 2.2 mm long sample. Also, we demonstrate the existence of type-0 SHG, where both pump and SH signal have an identical TM polarization state. It is shown that the efficiency of the type-0 process is comparable to type-I and type-II processes with the phase-matching wavelengths of all three interactions lying within a spectral window as small as 17 nm. ML-BRW is further reported for sum-frequency and difference-frequency generations. For applications requiring high pump power, a generalized ML-BRW design is proposed and demonstrated. The proposed structure offsets the destructive effects of third-order nonlinearities on chi(2) processes when high power harmonics are involved. This is carried out through incorporation of larger bandgap materials by using high aluminum content AlxGa1-xAs layers without undermining the nonlinear conversion efficiency. Theoretical investigations of BRWs as integrated sources of photon-pairs with frequency correlation properties are discussed. It is shown that the versatile dispersion properties in BRWs enables generation of telecommunication anti-correlated photon-pairs with bandwidth tunablity between 1 nm and 450 nm.

Bragg reflection waveguides (BRW) or one-dimensional photonic bandgap structures have been demonstrated for phase-matching chi(2) nonlinearities in AlxGa1-xAs. The method exploits strong modal dispersion of a Bragg mode and total internal reflection modes co-propagating inside the waveguide. It is shown that phase-matching is attained among the lowest order modes of interacting harmonics, which allows maximizing the utilization of harmonics powers for nonlinear interactions. As our first demonstration, we report second-harmonic generation (SHG) of a 2-ps telecommunication pump in a 2.4 mm long slab BRW. The conversion efficiency is estimated as 2.0 %/W.cm^2 with a generated SH power of 729 nW. This efficiency has been considerably improved by introducing lateral confinement of optical modes in ridge structures. Characterizations denote that efficiency of SHG in ridge BRWs can increase by over an order of magnitude in comparison to that of the slab device. Also, we report continuous-wave SHG in BRWs. Using a telecommunication pump with a power of 98 mW, the continuous-wave SH power of 23 nW is measured in a 2.0 mm long device. Significant enhancements of chi(2) interactions is obtained in the modified design of matching-layer enhanced BRW (ML-BRW). For the first time, we report type-II SHG in ML-BRW, where the second-harmonic power of 60 µW is measured for a pump power of 3.3 mW in a 2.2 mm long sample. Also, we demonstrate the existence of type-0 SHG, where both pump and SH signal have an identical TM polarization state. It is shown that the efficiency of the type-0 process is comparable to type-I and type-II processes with the phase-matching wavelengths of all three interactions lying within a spectral window as small as 17 nm. ML-BRW is further reported for sum-frequency and difference-frequency generations. For applications requiring high pump power, a generalized ML-BRW design is proposed and demonstrated. The proposed structure offsets the destructive effects of third-order nonlinearities on chi(2) processes when high power harmonics are involved. This is carried out through incorporation of larger bandgap materials by using high aluminum content AlxGa1-xAs layers without undermining the nonlinear conversion efficiency. Theoretical investigations of BRWs as integrated sources of photon-pairs with frequency correlation properties are discussed. It is shown that the versatile dispersion properties in BRWs enables generation of telecommunication anti-correlated photon-pairs with bandwidth tunablity between 1 nm and 450 nm.