Spectroscopic and electrochemical study of TiO2/Si photocathode

  • This thesis focuses on the deposition of thin TiO2 films on p-type Si using atomic layer deposition (ALD) technique, on the study of the electronic proprieties of the grown films and on the electrochemical characterization of TiO2/Si photoelectrodes. The deposition parameters, electronic properties and electrochemical performance and stability of the TiO2/Si samples are correlated. The ALD technique is used to deposit TiO2 with two different precursors namely Titanium isopropoxide and Titanium methoxide onto Si substrates. Laboratory as well as synchrotron based X-ray spectroscopy techniques are used to characterize these films. The growth quality of the TiO2 ALD films is determined by analyzing X-Ray photoelectron spectroscopy (XPS) data in terms of stoichiometry, defect states and Ti3+:Ti4+ ratios. The ALD technique was modified with different heating arrangements to obtain various polymorphs of TiO2. The ALD and anatase TiO2 films are characterized using synchrotron radiation to study their electronic properties and theseThis thesis focuses on the deposition of thin TiO2 films on p-type Si using atomic layer deposition (ALD) technique, on the study of the electronic proprieties of the grown films and on the electrochemical characterization of TiO2/Si photoelectrodes. The deposition parameters, electronic properties and electrochemical performance and stability of the TiO2/Si samples are correlated. The ALD technique is used to deposit TiO2 with two different precursors namely Titanium isopropoxide and Titanium methoxide onto Si substrates. Laboratory as well as synchrotron based X-ray spectroscopy techniques are used to characterize these films. The growth quality of the TiO2 ALD films is determined by analyzing X-Ray photoelectron spectroscopy (XPS) data in terms of stoichiometry, defect states and Ti3+:Ti4+ ratios. The ALD technique was modified with different heating arrangements to obtain various polymorphs of TiO2. The ALD and anatase TiO2 films are characterized using synchrotron radiation to study their electronic properties and these films are compared with single crystal rutile TiO2. X-ray absorption spectroscopy (XAS) and resonant photoelectron spectroscopy (res-PES) measurements are performed with synchrotron radiation. XAS measurements are used to determine the polymorphs as well as the electronic structure of TiO2. Res-PES measurements are conducted at the O1s and Ti2p edges to study multiple hole Auger decay processes and polaronic and charge transfer states as well as to determine the electronic band gap of the TiO2 layers. One of the main findings of this thesis is the determination of the partial density of states (pDOS) of O and Ti in the conduction and valence band. The combination of the pDOS and the band edge positions obtained from res-PES measurements are used to calculate the charge neutrality level of the TiO2 polymorphs. The photoelectrochemical measurements are conducted on bare-Si and TiO2/Si photoelectrodes. The electrochemical performance of these photoelectrodes is studied in electrolytes having pH values ranging from 1 to 13. The deposition of TiO2 on Si enhances the photoelectrochemical performance of the Si photoelectrode. The TiO2 increases the stability of the photoelectrode in all electrochemical media over 12 hours of experimental condition. Moreover, it is also observed that the TiO2/Si photoelectrode is less responsive to the pH value of the electrolyte. The electrochemical findings are explained on the basis of the electronic properties of the TiO2 layer. The electronic band gap obtained from spectroscopic measurement and the photoelectrochemical measurements are used to explain the performance and stability of the TiO2/Si photoelectrodes. The thesis also addresses the stability of Si microstructured photoelectrodes (SiMPs) prepared by an electrochemical method. The stability of the SiMPs deteriorates more rapidly than that one of the planar Si photoelectrode. However, using a protective ALD TiO2 layer on these SiMPs the overall performance is even more enhanced than on the TiO2/planar Si system.show moreshow less

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Metadaten
Author: Chittaranjan DasORCiD
URN:urn:nbn:de:kobv:co1-opus4-36924
URL:https://opus4.kobv.de/opus4-btu/frontdoor/index/index/docId/3692
Document Type:Doctoral thesis
Language:English
Year of publication:2015
Tag:Atomic layer deposition (ALD); Photocathodes; TiO2; X-Ray absorption spectroscopy (XAS); X-Ray photoelectron spectroscoopy (XPS)
Number of pages:135
Faculty/Chair:Fakultät 1 MINT - Mathematik, Informatik, Physik, Elektro- und Informationstechnik / FG Angewandte Physik und Halbleiterspektroskopie
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