The formation of Ge nanowires in V-grooves has been studied experimentally as well as theoretically. As substrate oxide covered Si V-grooves were used formed by anisotropic etching of (001)Si wafers and subsequent oxidation of their surface. Implantation of 1E17 Ge+ cm^-2 at 70 keV was carried out into the oxide layer covering the V-grooves. Ion irradiation induces shape changes of the V-grooves, which are captured in a novel continuum model of surface evolution. It describes theoretically the effects of sputtering, redeposition of sputtered atoms, and swelling. Thereby, the time evolution of the target surface is determined by a nonlinear integro-differential equation, which was solved numerically for the V-groove geometry. A very good agreement is achieved for the predicted surface shape and the shape observed in XTEM images. Surprisingly, the model predicts material (Si, O, Ge) transport into the V-groove bottom which also suggests an Ge accumulation there proven by STEM-EDX investigations. In this Ge rich bottom region, subsequent annealing in N2 atmosphere results in the formation of a nanowire by coalescence of Ge precipitates shown by XTEM images. The process of phase separation during the nanowire growth was studied by means of kinetic 3D lattice Monte-Carlo simulations. These simulations also indicate the disintegration of continuous wires into droplets mediated by thermal fluctuations. Energy considerations have identified a fragmentation threshold and a lower boundary for the droplet radii which were confirmed by the Monte Carlo simulation. The here given results indicate the possibility of achieving nanowires being several nanometers wide by further growth optimizations as well as chains of equally spaced clusters with nearly uniform diameter.

Nous avons développé un nano-fil conducteur, constitué uniquement de protéines et bio-inspiré des nano-fils bactériens conducteurs. Pour cela, une protéine chimère a été créée par l'association d'une protéine prion capable de s'auto-assembler en fibre et d'une métalloprotéine, une rubrédoxine, capable d'effectuer des transferts d'électrons. Comme montré par des techniques de microscopies et de spectroscopies (absorbance UV-visible et RPE), la protéine chimère est capable de former des fibres à la surface desquelles on retrouve les rubrédoxines. Les propriétés électroniques des nano-fils ont été caractérisées par des mesures courant-tension sur des échantillons secs et par électrochimie. Les mesures courant-tension ont montré que la conduction se faisait par plusieurs mécanismes. Les acides aminés aromatiques présents au centre du domaine prion semblent impliqués dans un des mécanismes de conduction. Les mesures électrochimiques ont quant à elles montré une conduction par sauts entre rubrédoxines. De plus, nous avons utilisé les nano-fils comme interface entre une enzyme, la laccase, et une électrode. Un courant électrocatalytique dû à la réduction de l'oxygène a été obtenu prouvant ainsi la capacité de nos nano-fils à agir comme médiateurs d'électrons. Les nano-fils conducteurs faits de protéines sont une structure intéressante pour comprendre le transport de charges dans les systèmes biologiques et sont également très prometteurs pour le développement de la bioélectronique et plus particulièrement de biocapteurs et de biopiles enzymatiques / The discovery of bacterial nanowires able to transport electrons on long range within biofilms and transfer them to electrodes is very promising for the development of bioelectronics and bio-electrochemical interfaces. However, their assembling process, their molecular composition and the electron transport mechanism are not fully understood yet. We took inspiration from bacterial nanowires to design conductive protein nanowires. We fused the sequence of a rubredoxin, an electron transfer iron-sulfur protein, to the sequence of HET-s(218-289), a prion domain that forms amyloid fibril by self-assembling under well-defined conditions. The resulting chimeric protein forms amyloid fibrils and displays redox proteins organized on the surface as shown by microscopy techniques and UV-Vis and EPR spectroscopy. Electron transfer mechanisms were studied in “dry state” current-voltage (I-V ) measurements and as hydrated film by electrochemistry. Dry state measurements allowed to evidence several conduction pathways with a possible role of aromatic residues in the conduction. Electrochemistry revealed electron transport by hopping between adjacent redox centers. This property allowed the use of our protein as mediator between a multicopper enzyme (laccase) and an electrode for electrocatalytic reduction of oxygen. These protein nanowires are interesting structures for the study of charge transport mechanisms in biological systems but are also very promising for the design of biosensors and enzymatic biofuel cells.

SiOx nanowires grown through the VLS mechanism were electrophoretically deposited on top of Au electrodes. GOx was immobilized using APTES and the EDC-NHS chemistry. Cyclic Voltammetry was used as the method to characterize the electrodes through their processing steps, and CV was also used to detect glucose in a PBS based solution. Ferro-Ferri Cyanide couple was used as the mediator.

The precise determination of the type and concentration of gases is of increasing importance in numerous applications. Despite the diverse operating principles of today´s gas sensors, technological trends can be summarized with the keyword miniaturization, because of the resulting benefits such as integrability and energy efficiency. This work deals with the development and fabrication of novel nanowire based gas sensors, which in comparison to conventional devices have an advantageous combination of high sensitivity and selectivity with low power consumption and small size. On the basis of grown silicon nanowires, sensors based on the functional principle of classical Schottky barrier field effect transistors with abrupt metal-semiconductor contacts are fabricated. The sensing performance of the devices is investigated with respect to the detection of ammonia. Ammonia concentrations down to 170 ppb are measured with a sensor response of more than 160 % and a theoretical limit of detection of 20 ppb is determined. Selectivity investigations show that no cross sensitivity to most common solvents occurring in living spaces exists. Moisture influences on the device are studied and reveal that the sensor responds within seconds, making it potentially suitable as humidity sensor. Moreover, it is shown that a higher relative humidity and higher temperatures decrease the sensor sensitivity. In terms of possible applications, it is a great advantage that the maximum sensitivity is achieved at 25 °C. With respect to sensitivity and selectivity an enhancement is demonstrated compared to most nanosensors known from the literature. Hence, the technology offers the potential to complement conventional measurement systems in future sensor technology especially in portable applications. / Die präzise Bestimmung der Art und Konzentration von Gasen erlangt in zahlreichen Anwendungsgebieten zunehmend an Bedeutung. Trotz der vielfältigen Wirkprinzipien heutiger Gassensoren lassen sich die technologischen Trends mit dem Schlagwort Miniaturisierung zusammenfassen, da sich daraus entscheidende Vorteile wie Integrierbarkeit und Energieeffizienz ergeben. Diese Arbeit beschäftigt sich mit der Entwicklung und Herstellung neuartiger nanodrahtbasierter Gassensoren, welche im Vergleich zu klassischen Sensoren eine vorteilhafte Kombination von hoher Sensitivität und Selektivität bei geringem Stromverbrauch und geringer Größe aufweisen. Auf der Grundlage gewachsener Silizium-Nanodrähte werden Sensoren mit abrupten Metall-Halbleiter-Kontakten hergestellt, welche auf dem Funktionsprinzip klassischer Schottkybarrieren-Feldeffekttransistoren beruhen. Die Eignung der Sensoren wird in Bezug auf die Detektion von Ammoniak untersucht. Dabei kann eine minimale Ammoniakkonzentration von 170 ppb mit einer Signaländerung von mehr als 160 % gemessen werden, wobei die theoretische Nachweisgrenze mit 20 ppb ermittelt wird. Selektivitätsuntersuchungen zeigen, dass keine Querempfindlichkeit gegenüber den am häufigsten in Wohnräumen vorkommenden Lösungsmitteln besteht. Feuchtigkeitseinflüsse auf den Sensor werden untersucht und es wird nachgewiesen, dass der Sensor Ansprechzeiten im Sekundenbereich besitzt, was ihn zu einem potenziell geeigneten Feuchtigkeitssensor macht. Darüber hinaus wird gezeigt, dass eine höhere relative Luftfeuchtigkeit und höhere Umgebungstemperaturen die Sensorsensitivität verringern. In Bezug auf mögliche Einsatzgebiete stellt die maximale Empfindlichkeit bei 25 °C einen großen Vorteil da. Bezogen auf Sensitivität und Selektivität wird somit eine Verbesserung im Vergleich zu den meisten aus der Literatur bekannten Nanosensoren demonstriert. Damit bietet die Technologie das Potential, konventionelle Messsysteme in zukünftiger Sensorik vor allem in portablen Anwendungen zu ergänzen.

Ground state depletion with individual molecule return (GSDIM) super-resolution microscopy is used to interrogate the location of individual fluorescence bursts from two different nanoparticle-fluorophore systems. The first system consists of fluorophore-labeled DNA molecules on gold nanowire surfaces. In this system carboxytetramethyl rhodamine-labeled double-stranded DNA molecules were bound to the surface of gold nanowires via gold-thiol linkages. The second system focuses on mesoporous silica coated nanorods with dye embedded into the silica coating. The dye molecule, Rhodamine 6G, was incorporated into the silica shell during the nanorod coating procedure. Individual fluorescence bursts were spatially localized using point spread function fitting and used to reconstruct the image of the underlying nanowire or nanorod. / text

Steps on a high index metal or semiconductor surface may play a fundamental role for electronic structure, adsorption, film growth, chemical reaction and catalysis. The surface atomic and electronic structures of stepped W(110) surfaces have been investigated by a few research groups during the past 20 years. But there is still a lot of controversy. We use high resolution core level photoemission to study several different stepped tungsten surfaces. Curve fittings of the spectra permit tests of core-level binding- energy shift models that relate local atomic coordination to binding -energy differences associated with terrace and step-edge atoms. For the first time we find a well resolved W4f₂/₇ peak associated with step edge atoms. We attribute previous failure to directly detect the step-edge effects in core level photoemission to contamination by hydrogen. The well resolved peaks for surface atoms with different coordinations can serve as a “finger print” for specific atoms. Experiments in which stepped surfaces are systematically dosed by H₂ clarify the role played by H contamination. We also grow Ag nanowires on the stepped W(110) surface and use angle resolved photoemission to study the band structure. We find distinct dispersion for the nanowires along the step edge direction while there is only little dispersion perpendicular to the wires. The second part of the research is core level photoemission study on Cesium film growth on Cu(100) surface. We study the phonon broadening effect for Cs at different temperatures. We compare our data with previous theoretical models and get good results on surface and bulk Debye temperatures and zero temperature phonon broadening. The binding energy shifts for the Cs 5p₂/₇ at different temperatures have also been investigated. The results fit the lattice expansion model very well except at temperature higher than 200 K. The higher temperature deviation is caused by thermal evaporation of Cs films. This conclusion is checked by the following coverage dependent core level peaks study on the Cs/Cu(100) system. / text

Pattern formation in buckled membranes was studied along with the morphology of flowers formed at the tip of silicon nanowires and ripples formed in suspended graphene sheets. Nash's perturbation method was tested for a simple case where initial and final metrics embed smoothly and there is a smooth path from one surface to another and was found to work successfully. The method was tested in more realistic conditions where a smooth path was not known and the method failed. Cylindrical flower-like membranes with a metric of negative Gaussian curvature were simulated in three and four dimensions. These four dimensional flowers had 2 orders of magnitude less energy than their three dimensional counterparts. Simulations were used to show that the addition of a fourth spatial dimension did not relieve all bending energy from the cylindrical membranes. Patterns formed at the tip of silicon nanowires were studied and found to be of the Dense Branching Morphology type. The rate of branching is dependent on the curvature of the gold bubble on which they are grown. Graphene was simulated using the modified embedded atom method potential and buckles were found to form if the carbon bonds were stretched. An energy functional was found for the energy of a sheet with a metric different from that of flat space. / text

ZnO nanostructures have been investigated for quite a long time. However, only recently they triggered much interest due to advances in materials synthesis and characterization, as well as emerging demand for new nanostructured materials in novel device implementations. A large part of the work was devoted to exploring new methodology for patterning growth sites and controlling nanowires morphology using the deposition methods that are compatible with integrated circuits (IC) processing. Microcontact printing was used to pattern the seeding layer, and, subsequently, ZnO nanowires through a resistless soft lithography process. When considering hydrothermal growth of ZnO nanowires in the framework of IC compatible techniques, it is favorable to keep the chemistry of the process constant, while tailoring morphological properties of ZnO nanowires through other means. Therefore, control over morphology of ZnO nanowires was realized by setting the physical properties of seeding layers. Atomic Layer Deposition (ALD) was used to deposit seeding layer required for hydrothermal growth and the effect of the physical properties of ALD thin films on resultant ZnO nanowires was studied. Opto-electrochemical properties of ZnO nanowires were studied in various electrolytes and performance of ZnO nanowires as an electrode material for multifunctional applications was investigated. Also, bulk nucleation and growth of novel aster-like nanostructures was investigated. These nanostructures may prove useful for creation of mechanically reinforced biocompatible polymers. Another key objective of the present work was to create strategies for controlled growth of ZnO nanowires on substrates previously unavailable for conventional hydrothermal growth of ZnO nanowires. The newly developed approach greatly facilitates growth of ZnO nanowires in confined microstructures, which greatly enhances the possibilities for the usage of ZnO nanowires in applications where they act as a porous electrode. These novel techniques open wide possibilities for improving performance of devices such as dye sensitized solar cells or supercapacitors.

Surface acoustic wave (SAW) sensors detect chemical and biological species by monitoring the shifts in frequency of surface acoustic waves generated on piezoelectric substrates. Incorporation of nanomaterials having increased surface area as sensing layer have been effective in improving the sensitivity as well as miniaturization of SAW sensors. Selectivity, sensitivity and speed of response are the three primary aspects for any type of sensor. This dissertation focuses on design and development of SAW devices with novel transducer configurations employing nanomaterial sensing layers for enhanced sensing, improved selectivity, and speed of response. The sensing mechanism in these SAW sensors is a complex phenomenon involving interactions across several different length and time scales. Surface acoustic wave propagation at the macro-scale is influenced by several kinetic phenomena occurring at the molecular scale such as adsorption, diffusion, reaction, and desorption which in turn depend on the properties of nanomaterials. This suggests the requirement of a multi-scale model to effectively understand and manipulate the interactions occurring at different length scales, thereby improving sensor design. Sensor response modeling at multiple time and length scales forms part of this research, which includes perturbation theories, and simulation techniques from finite element methods to molecular-level simulations for interpreting the response of these surface acoustic wave chemical and biosensors utilizing alloy nanostructures as sensing layers. Molecular modeling of sensing layers such as transition metal alloy nanoclusters and nanowires is carried out to gain insights into their thermodynamic, structural, mechanical and dynamic properties. Finite element technique is used to understand the acoustic wave propagation at the macroscale for sensing devices operating at MHz frequencies and with novel transducer designs. The findings of this research provide insights into the design of efficient surface acoustic wave sensors. It is expected that this work will lead to a better understanding of surface acoustic wave devices with novel transducer configurations and employing nanomaterial sensing layers.

In this thesis, a systematic study has been carried out on the synthesis, characterization and applications of microcrystalline diamond (MCD) and nanocrystalline diamond (NCD) thin films deposited by the chemical vapor deposition (CVD) method. Firstly, an overview of diamond films synthesized from carbon-containing gas plasmas is presented. A parameter study was performed to grow diamond thin films. The transition from micro- to nanocrystallinity of diamond grains was achieved by controlling the Ar/Hydrogen gas ratio. The nanocrystallinity is the result of a new growth mechanism which involves the insertion of carbon dimmer into carbon-carbon and carbon-hydrogen bonds. Secondly, characterization of diamond films has been carried out by different techniques including electron microscopy, near edge X-ray absorption fine structure (NEXAFS), nanoindentation, and Raman spectroscopy. Unique properties of NCD, compared to those of MCD grown by conventional hydrogen rich plasma, have been observed and investigated. Thirdly, various applications of diamond films are discussed: a). Well-adhered MCD coatings have been deposited on WC-Co substrates with proper surface pretreatment. A diffusion barrier Cr/CrN/Cr was deposited on the cemented carbide substrate and the substrate was short peened with 150 micron friable diamond powders to achieve higher nucleation density and stronger adhesion strength; b). A nitrogen doped NCD based biosensor was fabricated for glucose sensing. Carboxyl functional group and conducting polymer (polyaniline) have been utilized respectively to electrochemically functionalize the diamond surface. A linear response to glucose concentration has been obtained from the electrode with good sensitivity and stability; c). A novel approach to synthesize NCD wires has been developed for the first time. The NCD coating was successfully coated on Si nanowires (SiNWs) to form NCD wire with diameter around a few microns. This study opens a whole new area for applications based on diamond wires such as neural transmission electrodes, field emission emitters, and electrochemical electrodes with improved properties