One of the most current and also most promising fields of research in solid state physics is that of nano-structured materials. In particular, there is a great interest in nanostructured semiconductors, thanks to the latest developments in preparation techniques. These techniques allow to prepare nano-sized semiconductors with excellent crystalline structure and most often also with epitaxially determined orientations with respect to a template. The interest in nano-structures is triggered by the discovery that their physical properties (electronic, optical, thermodynamical) are different from those of the corresponding bulk material due to confinement. Consequently, the size becomes a new design parameter for new electronic and optoelectronic devices, for example. The goal of this work is to study nano-structures by optical methods, especially by Raman spectroscopy. 1-dimensional nano-structures are the main focus because of their recently intensively investigated and improved growth mechanisms. This research enables the synthesis of nano-materials of high crystalline quality, controlled orientation and size. To obtain measurements from 1- dimensional (quantum wires, nanorods, nanotubes) and 0-dimensional nanostructures (quantum dots)—in contrast to well-investigated 2- dimensional quantum wells—an additional requirement for the measurement technique is that the probe must provide lateral resolution in the nanometer range. This requirement excludes or limits many of the standard surface science techniques and is especially true for the standard optical tools with diffraction limited spatial resolution in the sub-micrometer range. If possible, samples with modified growth process parameters are chosen in order to reduce the spatial density of the nanostructures in a way that only one structure is contained in the probing area. The goal is to exclude averaging of their properties by summing contributions from different structures. This is achieved also by using confocal microscopy spectroscopy providing diffraction limited spatial resolution in the micrometer range (~ 1μm). Confocal micro Raman measurements are performed on low dimensional semiconductor structures such as Si, GaAs, AlGaAs, SnO2 and ZnO nanowires. Another important goal of this work is to design and build a new experimental set-up in order to extend the spatial resolution to the nanometer range, exploiting near field optics in combination with scanning probe microscopy (Scanning Tunnelling Microscopy and Atomic Force Microscopy). This enables simultaneous measurements of topography and spectroscopy, thus permitting direct correlation of morphological and optical properties. Moreover the internal structure of nano-samples can be made accessible by optical spectroscopy. For this purpose an apertureless scanning near field optical microscope (a-SNOM) set-up was developed. Scanning Probe Microscopy (SPM) equipment was integrated into a confocal Raman spectroscopy apparatus and preliminary test measurements are performed.

Speiser, E. (2008). Raman spectroscopy on nanostructures.

Raman spectroscopy on nanostructures

SPEISER, EUGEN
2008-07-30

Abstract

One of the most current and also most promising fields of research in solid state physics is that of nano-structured materials. In particular, there is a great interest in nanostructured semiconductors, thanks to the latest developments in preparation techniques. These techniques allow to prepare nano-sized semiconductors with excellent crystalline structure and most often also with epitaxially determined orientations with respect to a template. The interest in nano-structures is triggered by the discovery that their physical properties (electronic, optical, thermodynamical) are different from those of the corresponding bulk material due to confinement. Consequently, the size becomes a new design parameter for new electronic and optoelectronic devices, for example. The goal of this work is to study nano-structures by optical methods, especially by Raman spectroscopy. 1-dimensional nano-structures are the main focus because of their recently intensively investigated and improved growth mechanisms. This research enables the synthesis of nano-materials of high crystalline quality, controlled orientation and size. To obtain measurements from 1- dimensional (quantum wires, nanorods, nanotubes) and 0-dimensional nanostructures (quantum dots)—in contrast to well-investigated 2- dimensional quantum wells—an additional requirement for the measurement technique is that the probe must provide lateral resolution in the nanometer range. This requirement excludes or limits many of the standard surface science techniques and is especially true for the standard optical tools with diffraction limited spatial resolution in the sub-micrometer range. If possible, samples with modified growth process parameters are chosen in order to reduce the spatial density of the nanostructures in a way that only one structure is contained in the probing area. The goal is to exclude averaging of their properties by summing contributions from different structures. This is achieved also by using confocal microscopy spectroscopy providing diffraction limited spatial resolution in the micrometer range (~ 1μm). Confocal micro Raman measurements are performed on low dimensional semiconductor structures such as Si, GaAs, AlGaAs, SnO2 and ZnO nanowires. Another important goal of this work is to design and build a new experimental set-up in order to extend the spatial resolution to the nanometer range, exploiting near field optics in combination with scanning probe microscopy (Scanning Tunnelling Microscopy and Atomic Force Microscopy). This enables simultaneous measurements of topography and spectroscopy, thus permitting direct correlation of morphological and optical properties. Moreover the internal structure of nano-samples can be made accessible by optical spectroscopy. For this purpose an apertureless scanning near field optical microscope (a-SNOM) set-up was developed. Scanning Probe Microscopy (SPM) equipment was integrated into a confocal Raman spectroscopy apparatus and preliminary test measurements are performed.
A.A. 2007/2008
Fisica
20.
Raman spectroscopy; phonon confinement; Nearfield optics; apertureless SNOM; semiconductor nanostructures
Settore FIS/03 - Fisica della Materia
English
Tesi di dottorato
Speiser, E. (2008). Raman spectroscopy on nanostructures.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/2108/566
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