During this PhD thesis I researched the conditions to obtain a controlled electrodeposition of bismuth metal and bismuth selenide and the standardless determination of the thickness of electrodeposited thin films by means of a quantification method based on Monte Carlo simulations. The first part of this thesis was dedicated to the development of a new quantification method for the thickness determination of electroplated samples since the high variability of alloys makes impossible to use specific standards with a consequent lowering of the accuracy. The specimens were prepared with materials and features that made this study focused on the application in the electroplating sector. For this reason, films of varying thicknesses of nickel, palladium and gold have been deposited on copper and brass substrates. The study was conducted using EDS and XRF techniques and the results were compared with measurements of weight, SEM and XRF (current quantification method). Certified samples were also used as a comparison. The proposed method consists in constructing a calibration curve using simulated standards obtained from Monte Carlo algorithm in which the single electrons, or photons, interact with the substrate. The intensities are then normalized with respect to the pure elements (the only required standards to be measured) to minimize possible instrumental deviations; the calibration curve is used to derive the thickness of the samples. Taking into account that the current XRF quantification technique predicts an error of about 5 %, the results were encouraging for both techniques. In fact, a deviation from the expected values of about 9 % was obtained with EDS using DTSA-II software (consistent with results obtained with measured standards) while one of only about 4 % was obtained with XRF using XMI-MSIM software. The two different techniques are complementary and allow to analyse very different ranges of thicknesses. Beyond the accuracy, this procedure does not require standards of known thickness: therefore, its advantages consist in being very low-cost and it would allow to virtually analyse any type of coating having only available bulk samples of the pure elements to be identified. Regarding the electrodeposition processes, I have investigated the conditions for bismuth and bismuth selenide deposition since these materials have numerous properties that make them attractive for their use in technological devices. Currently, the films of these materials are obtained through vapour phase techniques to have good control over the deposition but the use of techniques in liquid phase, at ambient temperature and pressure, could considerably reduce the production costs. I found the conditions for an underpotential deposition to control the deposition of monolayer fractions on monocrystalline silver electrode. In this way both single layer and multilayer samples of bismuth and bismuth selenide were prepared. In addition to synthesise these compounds I tried to measure their thickness with the previously developed standardless method to obtain a better characterization of the deposits.

Electrodeposition and characterization of thin films / Walter Giurlani. - (2020).

Electrodeposition and characterization of thin films

Walter Giurlani
2020

Abstract

During this PhD thesis I researched the conditions to obtain a controlled electrodeposition of bismuth metal and bismuth selenide and the standardless determination of the thickness of electrodeposited thin films by means of a quantification method based on Monte Carlo simulations. The first part of this thesis was dedicated to the development of a new quantification method for the thickness determination of electroplated samples since the high variability of alloys makes impossible to use specific standards with a consequent lowering of the accuracy. The specimens were prepared with materials and features that made this study focused on the application in the electroplating sector. For this reason, films of varying thicknesses of nickel, palladium and gold have been deposited on copper and brass substrates. The study was conducted using EDS and XRF techniques and the results were compared with measurements of weight, SEM and XRF (current quantification method). Certified samples were also used as a comparison. The proposed method consists in constructing a calibration curve using simulated standards obtained from Monte Carlo algorithm in which the single electrons, or photons, interact with the substrate. The intensities are then normalized with respect to the pure elements (the only required standards to be measured) to minimize possible instrumental deviations; the calibration curve is used to derive the thickness of the samples. Taking into account that the current XRF quantification technique predicts an error of about 5 %, the results were encouraging for both techniques. In fact, a deviation from the expected values of about 9 % was obtained with EDS using DTSA-II software (consistent with results obtained with measured standards) while one of only about 4 % was obtained with XRF using XMI-MSIM software. The two different techniques are complementary and allow to analyse very different ranges of thicknesses. Beyond the accuracy, this procedure does not require standards of known thickness: therefore, its advantages consist in being very low-cost and it would allow to virtually analyse any type of coating having only available bulk samples of the pure elements to be identified. Regarding the electrodeposition processes, I have investigated the conditions for bismuth and bismuth selenide deposition since these materials have numerous properties that make them attractive for their use in technological devices. Currently, the films of these materials are obtained through vapour phase techniques to have good control over the deposition but the use of techniques in liquid phase, at ambient temperature and pressure, could considerably reduce the production costs. I found the conditions for an underpotential deposition to control the deposition of monolayer fractions on monocrystalline silver electrode. In this way both single layer and multilayer samples of bismuth and bismuth selenide were prepared. In addition to synthesise these compounds I tried to measure their thickness with the previously developed standardless method to obtain a better characterization of the deposits.
2020
Massimo Innocenti, Alessandro Lavacchi
Walter Giurlani
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Utilizza questo identificatore per citare o creare un link a questa risorsa: https://hdl.handle.net/2158/1186460
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