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Deep and Shallow TiO2Gap States on Cleaved Anatase Single Crystal (101) Surfaces, Nanocrystalline Anatase Films, and ALD Titania Ante and Post Annealing

Reckers, Philip and Dimamay, Mariel and Klett, Joachim and Trost, Sara and Zilberberg, Kirill and Riedl, Thomas and Parkinson, Bruce A. and Brötz, Joachim and Jaegermann, Wolfram and Mayer, Thomas (2015):
Deep and Shallow TiO2Gap States on Cleaved Anatase Single Crystal (101) Surfaces, Nanocrystalline Anatase Films, and ALD Titania Ante and Post Annealing.
In: The Journal of Physical Chemistry C, 119 (18), American Chemical Society, pp. 9890-9898, ISSN 1932-7447,
[Online-Edition: http://dx.doi.org/10.1021/acs.jpcc.5b01264],
[Article]

Abstract

Using photoelectron spectroscopy (PES), deep (around 1.2 eV below Fermi level) and shallow (around 0.2 eV below Fermi level) gap states are investigated in differently prepared TiO2 samples: In situ cleaved single anatase crystal TiO2 (101) surface, sintered slurry of nanocrystalline anatase, amorphous atomic layer deposited (ALD) titania, and nanocrystalline anatase transformed by annealing from ALD titania. Deep gap states are generally attributed to under-coordinated Ti atoms due to oxygen defects. The origin of shallow gap states is unclear. PES on in situ cleaved anatase TiO2 (101) surfaces show in part no or weak emission from deep, but always weak emission from shallow gap states. Amorphous ALD titania initially is free of gap states, but deep gap states are easily induced by exposure to synchrotron radiation, while shallow gap states do not form. Exposure to synchrotron radiation also induced deep gap states in in situ cleaved single crystal (101) surfaces and in the nanoporous anatase films, whereas emission from shallow gap states stays constant. Amorphous ALD films transform to anatase nanocrystals by annealing as shown by XRD and AFM and show deep and shallow gap state emissions similar to the nanoporous anatase films prepared by sintering spin coated anatase slurry. Atomic force microscopy (AFM) reveals the presence of terraces on the cleaved (101) surfaces. The comparison of the data collected on the differently prepared anatase and amorphous titania samples suggest assigning shallow gap states to under-coordinated Ti atoms located at edge sites. Conformal amorphous films that show no edges in AFM, accordingly have no shallow gap states.

Item Type: Article
Erschienen: 2015
Creators: Reckers, Philip and Dimamay, Mariel and Klett, Joachim and Trost, Sara and Zilberberg, Kirill and Riedl, Thomas and Parkinson, Bruce A. and Brötz, Joachim and Jaegermann, Wolfram and Mayer, Thomas
Title: Deep and Shallow TiO2Gap States on Cleaved Anatase Single Crystal (101) Surfaces, Nanocrystalline Anatase Films, and ALD Titania Ante and Post Annealing
Language: English
Abstract:

Using photoelectron spectroscopy (PES), deep (around 1.2 eV below Fermi level) and shallow (around 0.2 eV below Fermi level) gap states are investigated in differently prepared TiO2 samples: In situ cleaved single anatase crystal TiO2 (101) surface, sintered slurry of nanocrystalline anatase, amorphous atomic layer deposited (ALD) titania, and nanocrystalline anatase transformed by annealing from ALD titania. Deep gap states are generally attributed to under-coordinated Ti atoms due to oxygen defects. The origin of shallow gap states is unclear. PES on in situ cleaved anatase TiO2 (101) surfaces show in part no or weak emission from deep, but always weak emission from shallow gap states. Amorphous ALD titania initially is free of gap states, but deep gap states are easily induced by exposure to synchrotron radiation, while shallow gap states do not form. Exposure to synchrotron radiation also induced deep gap states in in situ cleaved single crystal (101) surfaces and in the nanoporous anatase films, whereas emission from shallow gap states stays constant. Amorphous ALD films transform to anatase nanocrystals by annealing as shown by XRD and AFM and show deep and shallow gap state emissions similar to the nanoporous anatase films prepared by sintering spin coated anatase slurry. Atomic force microscopy (AFM) reveals the presence of terraces on the cleaved (101) surfaces. The comparison of the data collected on the differently prepared anatase and amorphous titania samples suggest assigning shallow gap states to under-coordinated Ti atoms located at edge sites. Conformal amorphous films that show no edges in AFM, accordingly have no shallow gap states.

Journal or Publication Title: The Journal of Physical Chemistry C
Volume: 119
Number: 18
Publisher: American Chemical Society
Divisions: 11 Department of Materials and Earth Sciences > Material Science > Surface Science
11 Department of Materials and Earth Sciences > Material Science > Structure Research
11 Department of Materials and Earth Sciences > Material Science
11 Department of Materials and Earth Sciences
Date Deposited: 21 Jan 2016 12:12
Official URL: http://dx.doi.org/10.1021/acs.jpcc.5b01264
Identification Number: doi:10.1021/acs.jpcc.5b01264
Funders: For financial support, we would like to thank the Deutsche Forschungsgemeinschaft (DFG) for Grants RI1551/4-1 and MA 21041/2-1., SoLiAS was financed by the German Ministry for Science and Education BMBF under Project No.05K-SIRD1/0 and BESSY beam time under Grant No. O5ES3XBA/5., We thank Helmholtz Zentrum Berlin (HZB) for the allocation of synchrotron radiation beamtime and the group of Christian Pettenkofer for their support at BESSY II., B.P. wishes to acknowledge the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Division of Chemical Sciences, Geosciences and Biosciences, for financial support through Grant DE-FG03-96ER14625.
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