Mr. Nyasha Joseph Suliali Profile

Nyasha Joseph Suliali

Student at Nelson Mandela University

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Proceedings Article | 24 January 2019 Paper

Effect of increasing etchant concentration to accelerate synthesis of 9-µm-long TiO2 nanotubes

Nyasha Suliali, William Goosen, Johannes Botha

Proceedings Volume 11043, 110430Q (2019) https://doi.org/10.1117/12.2327083

KEYWORDS: Etching, Oxides, Titanium, Titanium dioxide, Scanning electron microscopy, Ions, Nanostructures, X-rays, Physics, Chemical reactions

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During electro-deposition of a TiO₂ film on titanium foil, an etching agent supplies ionic species that create the desired morphology by chemical dissolution of the oxide layer. The etchant ions attack both titanium ions and the oxide film to form hexafluorotitanate complexes, water and hydroxyl species. In this study, an attempt was made to reduce the duration of a TiO₂ film electro-deposition process by increasing the chemical dissolution rate. Two 127 μm-thick titanium foil substrates were anodised for different durations in an anhydrous polar organic solvent containing different amounts of an etchant. This yielded 9 μm-long nanotubes. Anodisation current density measurements for a two hour process showed slow chemical dissolution when the amount of etchant was low. In an attempt to speed-up the electro-deposition process, the amount of etchant was increased and anodisation carried out for only an hour. This yielded films (consisting of nanotube arrays) that are equal in thickness to that obtained in the two hour process. However, scanning electron microscopy revealed un-etched regions of the film between the tubes when the etchant concentration is high. These fragments are dimensional irregularities in an otherwise uniform tubular structure and hence are defect sites that could reduce charge transport efficiency. The study shows that the nanotube array quality is reduced when the duration of the anodisation process is shortened by an increased etch rate, without further optimisation of the anodisation parameters.

Proceedings Article | 26 June 2017 Paper

Development of a low-cost, 11 µm spectral domain optical coherence tomography surface profilometry prototype

Nyasha Suliali, Peter Baricholo, Pieter Neethling, Erich Rohwer

Proceedings Volume 10329, 103292Q (2017) https://doi.org/10.1117/12.2268064

KEYWORDS: Optical coherence tomography, Prototyping, Interferometers, Detection and tracking algorithms, Interferometry, Profilometers, Michelson interferometers, Metrology, Optical components, Light sources, Light emitting diodes, Mirrors

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A spectral-domain Optical Coherence Tomography (OCT) surface profilometry prototype has been developed for the purpose of surface metrology of optical elements. The prototype consists of a light source, spectral interferometer, sample fixture and software currently running on Microsoft® Windows platforms. In this system, a broadband light emitting diode beam is focused into a Michelson interferometer with a plane mirror as its sample fixture. At the interferometer output, spectral interferograms of broadband sources were measured using a Czerny-Turner mount monochromator with a 2048-element complementary metal oxide semiconductor linear array as the detector. The software performs importation and interpolation of interferometer spectra to pre-condition the data for image computation. One dimensional axial OCT images were computed by Fourier transformation of the measured spectra. A first reflection surface profilometry (FRSP) algorithm was then formulated to perform imaging of step-function-surfaced samples. The algorithm re-constructs two dimensional colour-scaled slice images by concatenation of 21 and 13 axial scans to form a 10 mm and 3.0 mm slice respectively. Measured spectral interferograms, computed interference fringe signals and depth reflectivity profiles were comparable to simulations and correlated to displacements of a single reflector linearly translated about the arm null-mismatch point. Surface profile images of a double-step-function-surfaced sample, embedded with inclination and crack detail were plotted with an axial resolution of 11 μm. The surface shape, defects and misalignment relative to the incident beam were detected to the order of a micron, confirming high resolution of the developed system as compared to electro-mechanical surface profilometry techniques.

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