In this thesis, the growth and fabrication of the self-assembly ordered porous alumina have been investigated. First, well-ordered honeycomb array can be obtained in large area under well-anodizing condition. The diameter of formed porous alumina was about 40 to 80 nm. Pore diameter can be tuned by different voltage and electrolyte. After we got such an ordered-arrangement porous alumina array, the following analysis of the material optical properties were characterized. In the luminescence behavior, photoluminescence (PL) measurements showed a strong PL peak in blue. The PL peak was at 420 nm excited by He-Cd laser. Material transmittance was also detected, the result showed that material was transparent above 400 nm. On the other hand, the porous alumina membrane can be used as a mask. For working as negative mask, we evaporated the metal such as Au or Ti into the membrane and the metal filled into the porous to adhere to the semiconductor substrate. After lifting-off the membrane, the metal nanadots was formed on the substrate. The size and the position of these metal nanodots were distinctly-controlled by the mask. For working as replica mask, we have used the membrane as an etching mask to transfer the pattern to the semiconductor substrate successfully. This technique has the advantages of low cost and large area for nano-fabrication.

High density, uniform GaN nanodot arrays with controllable size have been synthesized by using template-assisted selective growth. The GaN nanodots with average diameter 40nm, 80nm and 120nm were selectively grown by metalorganic chemical vapor deposition (MOCVD) on a nano-patterned SiO2/GaN template. The nanoporous SiO2 on GaN surface was created by inductively coupled plasma etching (ICP) using anodic aluminum oxide (AAO) template as a mask. This selective regrowth results in highly crystalline GaN nanodots confirmed by high resolution transmission electron microscopy. The narrow size distribution and uniform spatial position of the nanoscale dots offer potential advantages over self-assembled dots grown by the Stranski–Krastanow mode. / Singapore-MIT Alliance (SMA)

The application of membranes in liquid and gas separation is attractive because of their energy efficiency. Synthesis of membranes with well-defined nanostructure is necessary to achieve highly permeability and selectivity for separation processes. Recently, carbon nanomaterials such as graphene oxide nanoplatelets (GONPs) and carbon nanodots (CNDs) have emerged as an interesting class of nanomaterials due to their unique properties and tailorable functionalities. Incorporation of these nanomaterials in the membranes has been shown to improve membrane selectivity, mechanical robustness, and chemical stability. This dissertation elaborates on developing CNDs or GONPs embedded thin film composite (TFC) membranes using layer-by-layer (LbL) synthesis technique. Regarding the water desalination applications, GONPs were used to enhance the TFC membranes’ selectivity, chlorine resistant properties, and surface hydrophilicity. Incorporation of GONPs in the polyamide layer via LbL method resulted in an increase of surface hydrophilicity and salt rejection properties. Upon exposure to chlorine, GONPs embedded membranes retained salt rejection performance better than the pristine membranes (without GONPs). The LbL assembly was used to synthesize CNDs based TFC membranes for organic solvent nanofiltration (OSN) applications. Using the LbL framework, amineunctionalized CNDs were covalently crosslinked with trimesoyl chloride monomer to obtain nanoscale membranes. The synthesized membranes manifested high selectivity (up to 90%) when tested for dye molecules such as brilliant blue and disperse red in methanol. As the CNDs synthesized here are fluorescent under UV light, the resultant film is also fluorescent. This property can be harnessed for diagnostic purposes, such as tracking mechanical failure and fouling of the membranes. Based on the results, it can be concluded that the incorporation of carbon nanomaterials in the polymeric membranes has enhanced the hydrophilicity, mechanical stability, and chlorine resistant properties of the membranes. Overall, the LbL platform can be considered as a modular method in embedding nanoparticles in TFC membranes.

Title from first page of PDF document. Includes bibliographical references (p. 62-63).

Techn. Hochsch., Diss., 2006--Aachen.

No description available.

Understanding thermal transport in nanoscale is important for developing nanostructured thermolelectric materials and for heat management in nanoelectronic devices. This dissertation is devoted to understand thermal transport through SiGe based superlattices. First, we systematically studied the cross-plane thermal conductivity of SiGe superlattices by varying the thickness of Si(Ge) spacers thickness. The observed additive character of thermal resistance of the SiGe nanodot/planar layers allows us to engineer the thermal conductivity by varying the interface distance down to ~1.5 nm. Si-Ge intermixing driven by Ge surface segregation is crucial for achieving highly diffusive phonon scattering at the interfaces. By comparing the thermal conductivity of nanodot Ge/Si superlattices with variable nanodot density and superlattices with only wetting layers, we find that the effect of nanodots is comparable with that produced by planar wetting layers. This is attributed to the shallow morphology and further flattening of SiGe nanodots during overgrowth with Si. Finally, the experiments show that the interface effect on phonon transport can be weakened and even eliminated by reducing the interface distance or by enhancing Si-Ge intermixing around the interfaces by post-growth annealing. The results presented in this dissertation are expected to be relevant to applications requiring optimization of thermal transport for heat management and for the development of thermoelectric materials and devices based on superlattice structures. / Verständnis des thermischen Transport auf Nanoskala ist sowohl grundlegend für die Entwicklung nanostrukturierter Materialien, als auch für Temperaturkontrolle in nanoelektronischen Bauteilen. Diese Dissertation widmet sich der Erforschung des thermischen Transports durch SiGe basierenden Übergittern. Variationen, der Si(Ge) Schichtdicken, wurden zur systematischen Untersuchung der Normalkomponente zur Wachstumsrichtung der Wärmeleitfähigkeit, von SiGe Übergittern, genutzt. Die Beobachtung des additiven Charakters, des thermischen Widerstands, der SiGe Schichten, mit oder ohne Inselwachstum, ermöglicht die Erstellung von Strukturen mit bestimmter Wärmeleitfähigkeiten durch die Variation der Schichtdicken bis zu einer Minimaldistanz zweier Schichtübergänge von ~1.5nm. Die Ge Segregation führt zu einer Vermischung, von Si und Ge, welche eine essentielle Rolle zur diffusen Phononenstreuung spielt. Unsere Untersuchungen, von planaren Übergittern und Übergittern mit variabler Inseldichte, zeigen, dass Inseln und planare Schichten zu einer vergleichbaren Reduktion, der Wärmeleitfähigkeit, führen. Diese Beobachtung lässt sich, sowohl auf die flache Morphologie als auch die Abplattung der SiGe Inseln, aufgrund der Überwachsung mit Si, zurückführen. Die Experimente zeigen außerdem, dass sich der Barriereneffekt, der Schichtgrenzen, durch Reduktion der Schichtabstände und durch verstärkte Vermischung im Bereich der Schichtgrenzen, durch Erhitzung, eliminieren lässt. Die präsentierten Messungen sind sowohl, für die Entwicklung jener Bauteile, die eine Optimierung des thermischen Transports oder Temperaturmanagment erfordern, als auch von thermoelektrischen Matieralien und Bauteilen, basierend auf Übergittern, relevant.

We study current-induced domain wall dynamics in a thin ferromagnetic nanowire. We derive the effective equations of domain wall motion, which depend on the wire geometry and material parameters. We describe the procedure to determine these parameters by all-electric measurements of the time-dependent voltage induced by the domain wall motion. We provide an analytical expression for the time variation of this voltage. Furthermore, we show that the measurement of the proposed effects is within reach with current experimental techniques. We also show that a certain resonant time-dependent current moving a domain wall can significantly reduce the Joule heating in the wire, and thus it can lead to a novel proposal for the most energy efficient memory devices. We discuss how Gilbert damping, non-adiabatic spin transfer torque, and the presence of Dzyaloshinskii-Moriya interaction can effect this power optimization. Furthermore, we propose a new nanodot magnetic device. We derive a specific time-dependent current that is needed to switch the magnetization of the nanodot the most efficiently.

Understanding thermal transport in nanoscale is important for developing nanostructured thermolelectric materials and for heat management in nanoelectronic devices. This dissertation is devoted to understand thermal transport through SiGe based superlattices. First, we systematically studied the cross-plane thermal conductivity of SiGe superlattices by varying the thickness of Si(Ge) spacers thickness. The observed additive character of thermal resistance of the SiGe nanodot/planar layers allows us to engineer the thermal conductivity by varying the interface distance down to ~1.5 nm. Si-Ge intermixing driven by Ge surface segregation is crucial for achieving highly diffusive phonon scattering at the interfaces. By comparing the thermal conductivity of nanodot Ge/Si superlattices with variable nanodot density and superlattices with only wetting layers, we find that the effect of nanodots is comparable with that produced by planar wetting layers. This is attributed to the shallow morphology and further flattening of SiGe nanodots during overgrowth with Si. Finally, the experiments show that the interface effect on phonon transport can be weakened and even eliminated by reducing the interface distance or by enhancing Si-Ge intermixing around the interfaces by post-growth annealing. The results presented in this dissertation are expected to be relevant to applications requiring optimization of thermal transport for heat management and for the development of thermoelectric materials and devices based on superlattice structures. / Verständnis des thermischen Transport auf Nanoskala ist sowohl grundlegend für die Entwicklung nanostrukturierter Materialien, als auch für Temperaturkontrolle in nanoelektronischen Bauteilen. Diese Dissertation widmet sich der Erforschung des thermischen Transports durch SiGe basierenden Übergittern. Variationen, der Si(Ge) Schichtdicken, wurden zur systematischen Untersuchung der Normalkomponente zur Wachstumsrichtung der Wärmeleitfähigkeit, von SiGe Übergittern, genutzt. Die Beobachtung des additiven Charakters, des thermischen Widerstands, der SiGe Schichten, mit oder ohne Inselwachstum, ermöglicht die Erstellung von Strukturen mit bestimmter Wärmeleitfähigkeiten durch die Variation der Schichtdicken bis zu einer Minimaldistanz zweier Schichtübergänge von ~1.5nm. Die Ge Segregation führt zu einer Vermischung, von Si und Ge, welche eine essentielle Rolle zur diffusen Phononenstreuung spielt. Unsere Untersuchungen, von planaren Übergittern und Übergittern mit variabler Inseldichte, zeigen, dass Inseln und planare Schichten zu einer vergleichbaren Reduktion, der Wärmeleitfähigkeit, führen. Diese Beobachtung lässt sich, sowohl auf die flache Morphologie als auch die Abplattung der SiGe Inseln, aufgrund der Überwachsung mit Si, zurückführen. Die Experimente zeigen außerdem, dass sich der Barriereneffekt, der Schichtgrenzen, durch Reduktion der Schichtabstände und durch verstärkte Vermischung im Bereich der Schichtgrenzen, durch Erhitzung, eliminieren lässt. Die präsentierten Messungen sind sowohl, für die Entwicklung jener Bauteile, die eine Optimierung des thermischen Transports oder Temperaturmanagment erfordern, als auch von thermoelektrischen Matieralien und Bauteilen, basierend auf Übergittern, relevant.