Ultrafast goes localMarc Achermann
Taschenbuch
This thesis demonstrates the remarkable performance of a technique that connects the ultrafast, femtosecond regime with the local, nanometer world. The combination of the ultrafast pump-probe technique with near-field scanning optical . microscopy ( N S O M) allows to perform optical spectroscopy with simultaneous femtosecond-scale temporal and nanometer-scale spatial resolution. Such spatiotemporal resolution obtained with the ultrafast N S O M is crucial for transport studies in nanostructured materials, for the study of carrier dynamics in single nanostructures as well as for the characterization of inhomogeneities in nanostructured ensembles. With respect to transport measurements spatiotemporal diffusion dynamics is studied in single quantum well : Samples, Iocally patterned by focused ion-beam implantation. With the femtosecond N S O M one can disentangle even more complex transport dynamics that involve both carrier drift and carrier diffusion. Such dynamics occurs in metal-semiconductor composite materials, where buried Schottky contacts and built-in electric fields are formed at the semiconductor-, metal interface. Beside transport measurements, studies of single nanostructures, such as low-dimensional systems, are one of the most important applications of the femtosecond N S O M technique. Such studies allow one to gain insight into the intrinsic properties of nanostructures, unperturbed by spatial averaging over an ensemble of structures. Moreover, growth· inhomogeneities in nanostructured materials can be characterized. As an example, experiments on single one-dimensional semiconductor quantum wires ( Q W Rs) are discussed.
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