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Optical Imaging and Spectroscopy of Airborne Nanowires

Gompou, Eleni LU (2017) FYSM60 20161
Department of Physics
Abstract
Semiconductor nanowires are the potential base for building many future devices like solar cells and light emitting diodes. To reach the level of commercialization of such devices, mass production of NWs at low cost with reproducible high quality properties in terms of crystallinity, material and dimensions is a prerequisite. At Lund University a new technique, called Aerotaxy, which satisfies these characteristics, has been developed for continuous production of nanowires in the aerosol phase.
Further optimization of Aerotaxy process created the need for in situ, on line and on real time characterization of the aerosol NWs for a quick feedback during growth. For this purpose, I created a new set up for checking the feasibility of... (More)
Semiconductor nanowires are the potential base for building many future devices like solar cells and light emitting diodes. To reach the level of commercialization of such devices, mass production of NWs at low cost with reproducible high quality properties in terms of crystallinity, material and dimensions is a prerequisite. At Lund University a new technique, called Aerotaxy, which satisfies these characteristics, has been developed for continuous production of nanowires in the aerosol phase.
Further optimization of Aerotaxy process created the need for in situ, on line and on real time characterization of the aerosol NWs for a quick feedback during growth. For this purpose, I created a new set up for checking the feasibility of photoluminescence spectroscopy, absorption spectroscopy and imaging of the nanowire flow using the polarized and unpolarized scattered light. PL and absorption spectroscopy would be conducted for quality check of nanowires. Furthermore, absorption spectrum from aligned nanowires could possibly give information about their diameter and scattering from aligned nanowires would be tested for correlating the electric field strength used for aligning them to their length. Moreover, imaging of unpolarized scattered laser light would give us information on fluctuations in nanowire flow.
Due to insufficient set up components like fiber spectrometer, with poor signal collection efficiency and low quantum efficiency of the chip, in situ PL spectroscopy could not be performed. Scattering of laser light is successfully used for visualizing the nanowire flow which gives an immediate feedback on when the growth is taking place. Scattering experiments of polarized scattered light showed an effect on the direction of the nanowires but because of insufficient number of experiments no conclusions can be drawn. No conclusions also can be drawn for absorption experiments. (Less)
Popular Abstract
Light can take us where we cannot reach, light can show us what is beyond our sight. It reduces the distance to object which are huge but far away and it enhances the size of the object that’s close but tiny; none of which are eyes can see. Contrary to the astronomy, in which we use the light to track the motion of huge celestial object – for examples sun which has a diameter of 109m–, in this thesis we use the light to track the motion and get to know about properties of objects which are 109 times smaller than 1 meter. Nanowires are one such type of nano objects that are grown in flight in an Aerotaxy chamber. We use light to capture their flight.
NWs in Aerotaxy are carried from the growth chamber to a silicon substrate for deposition... (More)
Light can take us where we cannot reach, light can show us what is beyond our sight. It reduces the distance to object which are huge but far away and it enhances the size of the object that’s close but tiny; none of which are eyes can see. Contrary to the astronomy, in which we use the light to track the motion of huge celestial object – for examples sun which has a diameter of 109m–, in this thesis we use the light to track the motion and get to know about properties of objects which are 109 times smaller than 1 meter. Nanowires are one such type of nano objects that are grown in flight in an Aerotaxy chamber. We use light to capture their flight.
NWs in Aerotaxy are carried from the growth chamber to a silicon substrate for deposition using a carrier gases. Similar to dust particles in the air, nanowires in this carrier flow can scatter and absorb the light incident on it. We reproduce the same phenomena by shining the nanowires with an artificial light source of known wavelength to gather scientific information about their population or the material that they are made of. Additionally, these nanowires are made of semiconducting material which means that electrons inside the wires can absorb the light and emit photons with a different wavelength. These photons are then captured and their wavelengths are found to give information about the bandgap, which is a characteristic property of the semiconducting materials. Moreover, arranging them parallel to each other by external stimulation, which is the electric field, we can get information about their dimension from the absorbed and scattered light.
In this thesis we create a unique set up to observe and characterize the nanowires produced by Aerotaxy, when they are still ´´flying`` and before they are deposited on the substrate. This provides a feedback of our growth experiments which in some cases it is also real time. (Less)
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author
Gompou, Eleni LU
supervisor
organization
course
FYSM60 20161
year
type
H2 - Master's Degree (Two Years)
subject
language
English
id
8906421
date added to LUP
2017-05-04 13:46:26
date last changed
2017-05-04 13:46:26
@misc{8906421,
  abstract     = {Semiconductor nanowires are the potential base for building many future devices like solar cells and light emitting diodes. To reach the level of commercialization of such devices, mass production of NWs at low cost with reproducible high quality properties in terms of crystallinity, material and dimensions is a prerequisite. At Lund University a new technique, called Aerotaxy, which satisfies these characteristics, has been developed for continuous production of nanowires in the aerosol phase.
Further optimization of Aerotaxy process created the need for in situ, on line and on real time characterization of the aerosol NWs for a quick feedback during growth. For this purpose, I created a new set up for checking the feasibility of photoluminescence spectroscopy, absorption spectroscopy and imaging of the nanowire flow using the polarized and unpolarized scattered light. PL and absorption spectroscopy would be conducted for quality check of nanowires. Furthermore, absorption spectrum from aligned nanowires could possibly give information about their diameter and scattering from aligned nanowires would be tested for correlating the electric field strength used for aligning them to their length. Moreover, imaging of unpolarized scattered laser light would give us information on fluctuations in nanowire flow. 
Due to insufficient set up components like fiber spectrometer, with poor signal collection efficiency and low quantum efficiency of the chip, in situ PL spectroscopy could not be performed. Scattering of laser light is successfully used for visualizing the nanowire flow which gives an immediate feedback on when the growth is taking place. Scattering experiments of polarized scattered light showed an effect on the direction of the nanowires but because of insufficient number of experiments no conclusions can be drawn. No conclusions also can be drawn for absorption experiments.},
  author       = {Gompou, Eleni},
  language     = {eng},
  note         = {Student Paper},
  title        = {Optical Imaging and Spectroscopy of Airborne Nanowires},
  year         = {2017},
}