Charakterisierung funktionaler Nanomaterialien für biomagnetische Sensoren und Atemanalyse

The presented thesis is covering materials aspects for the development of magnetoelectric sensors for biomagnetic sensing and solid state sensors for breath monitoring. The electrophysiological signals of the human body and especially their irregularities provide extremely valuable information about the heart, brain or nerve malfunction in medical diagnostics. Similar and even more detailed information is contained in the generated biomagnetic fields which measurement offers improved diagnostics and treatment of the patients. A new type of room temperature operable magnetoelectric composite sensors is developed in the framework of the CRC1261 Magnetoelectric Sensors: From Composite Materials to Biomagnetic Diagnostics. This thesis focuses on the individual materials structure-property relations and their combination in magnetoelectric composite sensors studied by electron beam based techniques, at lengths scales ranging from micrometers to atomic resolution. The first part of this thesis highlights selected studies on the structural and analytic aspects of single phase materials and their composites using TEM as the primary method of investigation. With respect to the piezoelectric phase, alternatives to AlN have been thoroughly investigated to seek for improvement of specific sensor approaches. In this context, the alloying of Sc into the AlN matrix has been demonstrated to yield high quality films with improved piezoelectric and unprecedented ferroelectric properties grown under the control of deposition parameters. Lead-free titanate films with large piezo-coefficients at the verge of the morphotropic phase boundary as alternative to PZT films have been investigated in terms of crystal symmetry, defect structure and domains of cation ordering. New morphologies of ZnO and GaN semiconductors envisioned for a piezotronic-based sensor approach were subject of in-depth defect and analytical studies describing intrinsic defects and lattice strains upon deposition as well as hollow composite structures. When the dimensions of a materials are reduced, novel exciting properties such as in-plane piezoelectricity can arise in planar transition-metal dichalcogenides. Here, the turbostratic disorder in a few-layered MoSe2 film has been investigated by nanobeam electron diffraction and Fast Fourier Transformations. From the perspective of magnetic materials, the atomic structure of magnetostrictive multilayers of FeCo/TiN showing stability up to elevated temperatures has been analyzed in detail regarding the crystallographic relationship of heteroepitaxy in multilayer composites exhibiting individual layer thicknesses below 1 nm. Further, magnetic hard layers have been investigated in the context of exchange spring concepts and ME composites based on shape memory alloy substrates have been studied regarding structural changes implied by different annealing processes. The second part of this thesis introduces materials aspects and sensor studies on gas detection in the clinical context of breath analysis. The detection of specific vapors in the human breath is of medical relevance, since certain species can be enriched depending on the conditions and processes within the human body. Hence, they can be regarded as biomarkers for the patients condition of health. The selection of suitable materials and the gas measurement working principle are considered and selected studies on solid state sensors with different surface functionalization or targeted application on basis of ZnO or CuO-oxide and Fe-oxide species are presented

On the origin of uv laser-induced quantum well intermixing in iii-v semiconductor heterostructures

Résumé : Les circuits photoniques intégrés qui combinent des dispositifs photoniques pour la génération, la détection, la modulation, l'amplification, la commutation et le transport de la lumière dans une puce, ont été rapportés comme étant une innovation technologique importante qui simplifie la conception du système optique et qui réduit l'espace et la consommation de l'énergie en améliorant ainsi la fiabilité. La capacité de modifier la bande interdite des zones sélectives des différents dispositifs photoniques à travers la puce est la clé majeure pour le développement de circuits photoniques intégrés. Comparé à d'autres méthodes d’épitaxie, l’interdiffusion de puits quantiques a attiré beaucoup d'intérêt en raison de sa simplicité et son efficacité en accordant la bande interdite durant le processus de post-épitaxie. Cependant, l’interdiffusion de puits quantiques a subi des problèmes reliés au manque de précision pour modifier convenablement la bande interdite ciblée et à l’incontrôlabilité de l’absorption des impuretés au cours du processus qui peut dégrader la qualité du matériel interdiffusé. Dans cette thèse, nous avons utilisé les lasers excimer pour créer des défauts à proximité de la surface (~ 10 nm) des microstructures à base de puits quantiques III-V (par exemple InP et GaAs) et pour induire l’interdiffusion après le recuit thermique. L'irradiation par les lasers excimer (ArF et KrF) des microstructures à puits quantiques a été réalisée dans différents environnements, y compris l'air, l'eau déionisée, les couches diélectriques (SiO2 et Si3N4) et les couches d’InOx. Pour proposer un bon contrôle de la technique d’interdiffusion de puits quantiques par laser excimer, nous avons étudié la génération et la diffusion de défauts de surface en utilisant différentes méthodes de caractérisation de surface/interface, comme l'AFM, SEM, XPS et SIMS qui ont été utilisées pour analyser la modification de la morphologie de surface/interface et la modification chimique de la microstructure de ces puits quantiques. La qualité des microstructures à puits quantiques étudiées a été représentée par des mesures de photoluminescence et de luminescence des diodes lasers ainsi fabriqués. Les résultats montrent que le laser excimer induit des quantités d'oxydes de surface dans les surfaces des microstructure à puits quantiques InP/InGaAs/InGaAsP dans l'air et des impuretés d'oxygène des couches d'oxydes diffusées dans la région active de la microstructure lors du recuit, ce qui améliore l’interdiffusion, mais réduit l'intensité de la photoluminescence. Par contre, l’irradiation dans un environnement d'eau déionisée n’a pas démontré de diffusion des impuretés évidentes d'un excès d'oxygène vers les régions actives, mais la stœchiométrie de surface a été restaurée après l’interdiffusion. L’InOx a été trouvé avec un grand coefficient de dilatation thermique dans la microstructure interdiffusée qui était supposée d’augmenter la contrainte de compression dans la région active et ainsi d’augmenter l'intensité de photoluminescence de 10 fois dans l’échantillon irradié dans l'eau déionisée. Concernant les microstructures avec une couche diélectrique, la modification de la bande interdite a été toujours réalisée sur des échantillons dont les couches diélectriques ont été irradiées et la surface de InP a été modifiée par le laser excimer. Pour l'échantillon avec une couche de 243 nm de SiO2, les variations de la photoluminescence ont été mesurées sans l’ablation de cette couche de SiO2 lors de l'irradiation par le laser KrF. Cependant, la morphologie de l'interface d’InP a été modifiée, les oxydes d'interface ont été générés et les impuretés d'oxygène se sont diffusées à l'intérieur des surfaces irradiées. Les améliorations de l’interdiffusion dans les deux surfaces non irradiées et irradiés de l'échantillon couvert de couche d’InOx ont démontré l'importance des oxydes dans l’interdiffusion des puits quantiques. Les diodes laser fabriquées à partir d’un matériau interdiffusé par un laser KrF ont montré un seuil de courant comparable à celui des matériaux non interdiffusés avec un décalage de photoluminescence de 100 nm. En combinant un masque d'aluminium, nous avons créé un déplacement uniforme de photoluminescence de 70 nm sur une matrice rectangulaire de 40 μm x 200 μm ce qui présente un potentiel d’application de l’interdiffusion des puits quantiques par les lasers excimer dans les circuits photoniques intégrés. En outre, les lasers excimer ont été utilisés pour créer des structures de nano-cônes auto-organisées sur des surfaces de microstructure de InP/InGaAs/InGaAsP en augmentant l'intensité de PL par ~ 1.4 fois. Les lasers excimer ont été aussi utilisés pour modifier la mouillabilité sélective des zones d’une surface de silicium par une modification chimique de surface induite par laser dans différents milieux liquides. Ainsi, la fluorescence des nanosphères a été réussie pour des fonctions de configuration spécifique avec une surface de silicium. // Abstract : Photonic integrated circuits (PICs) which combine photonic devices for generation, detection, modulation, amplification, switching and transport of light on a chip have been reported as a significant technology innovation that simplifies optical system design, reduces space and power consumption, improves reliability. The ability of selective area modifying the bandgap for different photonic devices across the chip is the important key for PICs development. Compared with other growth methods, quantum well intermixing (QWI) has attracted amounts of interest due to its simplicity and effectiveness in tuning the bandgap in post-growth process. However, QWI has suffered problems of lack of precision in achieving targeted bandgap modification and uncontrollable up-taking of impurities during process which possibly degrade the quality of intermixed material. In this thesis, we have employed excimer laser to create surface defects in the near surface region (~ 10 nm) of III-V e.g. InP and GaAs, based QW microstructure and then annealing to induce intermixing. The irradiation by ArF and KrF excimer lasers on the QW microstructure was carried out surrounded by different environments, including air, DI water, dielectric layers (SiO2 and Si3N4) and InOx coatings. To propose a more controllable UV laser QWI technique, we have studied surface defects generation and diffusion with various surface/interface characterization methods, like AFM, SEM, XPS and SIMS, which were used to analyse the QW surface/interface morphology and chemical modification during QWI. The quality of processed QW microstructure was represented by photoluminescence measurements and luminescence measurements of fabricated laser diodes. The results shows that excimer laser induced amounts of surface oxides on the InP/InGaAs/InGaAsP microstructure surface in air and the oxygen impurities from oxides layer diffused to the active region of the QW microstructure during annealing, which enhance intermixing but also reduce the PL intensity. When irradiated in DI water environment, no obvious excessive oxygen impurities were found to diffuse to the active regions and the surface stoichiometry has been restored after intermixing. InOx with large coefficient of thermal expansion was found inside the intermixed QW microstructure, which was supposed to increase the compressive strain in active region and enhance the PL intensity to maximum 10 times on sample irradiated in DI water. On microstructure coated with dielectric layers, bandgap modifications were always found on samples whose dielectric layers were ablated and InP surface was modified by excimer laser. On sample coated with 243 nm SiO2 layer, the PL shifts were found on sample without ablation of the SiO2 layer when irradiated by KrF laser. However, the InP interface morphology was modified, interface oxides were generated and oxygen impurities have diffused inside on the irradiated sites. The enhancements of interdiffusion on both non irradiated and irradiated sites of sample coated with InOx layer have verified the importance of oxides in QWI. The laser diodes fabricated from KrF laser intermixed material have shown comparable threshold current density with as grown material with PL shifted by 133 nm. Combined aluminum mask, we have created uniform 70 nm PL shifts on 40 μm x 200 μm rectangle arrays which presents UV laser QWI potential application in PICs. In addition, excimer lasers have been used to create self organized nano-cone structures on the surface of InP/InGaAs/InGaAsP microstructure and enhance the PL intensity by ~1.4x. Excimer lasers have selective area modified wettability of silicon surface based on laser induced surface chemical modification in different liquid environments. Then the fluorescence nanospheres succeeded to specific pattern functions with silicon surface

Piezotronic Bicrystals and Hexagonal Nano-Platelets: A TEM Study on Structure and Chemistry of Functionalized Zinc Oxide

TEM and SEM investigations of piezotronic ZnO bicrystals were conducted with the aim to study the relationship between interface structure and electrical properties. In this context, the term “piezotronic” refers to the manipulation and tuning of electrostatic potential barriers at doped varistor-type grain boundaries via piezoelectric charges generated upon mechanical load. To this end, varistor-type inversion-boundary bicrystals were synthesized in tail-to-tail (000-1)|(000-1) or head to head (0001)|(0001) orientation with respect to the c axis, providing an optimized piezotronic response for load applied in directions. Different synthesis methods are compared and specific tilt configurations as well as undoped reference bicrystals were examined. Furthermore, ZnO nanocrystals, i.e., hexagonal platelets and rod shaped twins, were investigated, as both the bicrystals and the nanocrystals hold a large potential for functionalization and the development of novel devices. Finally, the dopant-related varistor-effect itself, which underlies the piezotronic applications, is – despite decades of research – still not completely elucidated and the examined bicrystals are well suited model systems for respective studies on specific dopant/grain-boundary situations. Since the varistor-effect is attributed to potential barriers at doped grain-boundaries, respective interfaces were investigated by atomic-resolution HAADF STEM; the main method in this thesis, capable of delivering structural as well as chemical information. These measurements were complemented with conventional TEM, ABF STEM, electron diffraction and EDS methods in order to fully characterize the bicrystals as well as control and verify their successful synthesis. The TEM results were interpreted with respect to the findings from corresponding electrical measurements. In doing so, the focus laid upon the successful doping with bismuth, which is essential to obtain varistor behavior and hence, for the subsequent piezotronic manipulation. As a main result, it was found that doping with Bi, being insoluble in ZnO, is by no means trivial and demands appropriate synthesis procedures and/or bicrystal configurations, which provide suitable segregation sites. Otherwise, Bi retracts from the interfaces and forms electrically inactive secondary phases. The presence of such segregation sites was found to be related to the respective structural coherence of the grain boundary. While highly coherent interfaces did not feature any significant Bi doping, semi- or incoherent interfaces exhibited a clear Bi decoration, which was also reflected by the electrical measurements revealing the absence or occurrence of varistor behavior, respectively. The required incoherency could be introduced either via a special synthesis procedure (epitaxial solid-state transformation) leading to a strongly curved defect-rich interface or by applying specific tilt configurations to diffusion-bonded bicrystals with a flat interface. The latter comprises two different cases: Semi-coherent configurations, where a coincidence-site lattice (CSL) is formed and CSL points act as semi-periodic segregation sites, and highly incoherent situations, where the interface structure is strongly and irregularly disordered. In addition to the structural characterization, thermodynamic aspects were considered, indicating that all three types of Bi-segregation (curved, flat semicoherent, flat incoherent) can be explained qualitatively by applying Gibbs adsorption isotherm, which describes the lowering of surface or interface energies depending on the decoration by impurity atoms. Due to the special case of an insoluble dopant, which is available in a quasi-infinite reservoir with respect to the limited amount of segregation sites, the segregation of Bi depends only on a) the energy difference between the undecorated and decorated interface, and b) the actual quantity of segregation sites. Both a) and b) are higher for incoherent interfaces and approach zero for the case of maximum coherency. The TEM results as well as the thermodynamic considerations were found to be not only in perfect agreement with previous ZnO bicrystal studies but also with comparable situations in other, completely different material systems. In consequence, they are considered to be applicable to all cases of interfacial segregation of insoluble dopants. The main goal behind the synthesis of the hexagonal ZnO platelets is their self-assembled tessellation upon Langmuir-Blodgett deposition. However, a synthesis route needed to be established first. TEM investigations were performed in order to characterize the obtained mineralization products and provide feedback for the optimization of the synthesis. In doing so, the same methods as for the bicrystals could be employed, in particular, ABF STEM and NBED for determining the absolute direction of the c-axis. This was an important issue for both the hexagonal platelets, where inversion twinning needed to be ruled out, as well as for the rod shaped twins, whose twinning character could be identified this way. In addition, the TEM investigations revealed a surface coverage of the hexagonal facets by residuals from the precipitation process. In consequence, an additional calcination step was added to the synthesis procedure, which was shown to successfully remove this coverage and simultaneously increase the quality of the surfaces from rough to almost atomically flat. Regarding the rod-shaped twins, actually a side-product of the synthesis experiments, the TEM findings revealed a situation similar to the piezotronic inversion-boundary bicrystals. In all cases, the crystallites were found to be accurate tail-to-tail inversion twins with anti-parallel c-axes and a disordered interface, probably capable of incorporating dopants such as Bi. In consequence, they are seen as holding potential for further development in their own right, especially against the background that the original “piezotronics” were established based on ZnO nanocrystals (nanowires)

In Situ X-ray Scattering Studies of Ultrathin Epitaxial Metal Oxide Films

This work combines electrochemical studies of thin epitaxial metal and metal oxide films with advanced in situ and operando surface X-ray diffraction (SXRD). This combination enables the correlation of reactive processes with the structure of the interfaces at which they occur. In the focus of our studies are Co oxides which are promising candidates for the precious-metal-free catalysis of the oxygen evolution reaction (OER). In a first attempt to grow thin epitaxial metal oxide film catalysts, the anodic oxidation of Co deposited on Au(111) was investigated. A different approach, in which Co3O4 and CoOOH were directly electrodeposited on Au(111) substrates, produced well defined oxide films. These films were structurally characterized under operation conditions, i.e. under strong gas evolution and current densities of up to 150 mA/cm^2. Aside from the OER motivated studies, magnetic Pd/Co/Au(111) stacks were investigated. Furthermore, transmission surface diffraction (TSD), a novel high-energy SXRD technique, was developed

Solid State Division progress report for period ending March 31, 1997

This report covers research progress in the Solid State Division from April 1, 1995, through March 31, 1997. During this period, the division conducted a broad, interdisciplinary materials research program in support of Department of Energy science and technology missions. The report includes brief summaries of research activities in condensed matter theory, neutron scattering, synthesis and characterization of materials, ion beam and laser processing, and the structure of solids and surfaces. An addendum includes listings of division publications and professional activities

Microscopy Conference 2017 (MC 2017) - Proceedings

Das Dokument enthält die Kurzfassungen der Beiträge aller Teilnehmer an der Mikroskopiekonferenz "MC 2017", die vom 21. bis 25.08.2017, in Lausanne stattfand

Microscopy Conference 2017 (MC 2017) - Proceedings

Das Dokument enthält die Kurzfassungen der Beiträge aller Teilnehmer an der Mikroskopiekonferenz "MC 2017", die vom 21. bis 25.08.2017, in Lausanne stattfand