Atomic Layer Deposition of

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Atomic Layer Deposition of Visible Light Active
Photocatalytic TiO2 Viljami Pore, Jaana Saarni,
Markku Leskelä, Mikko Ritala Department of
Chemistry, University of Helsinki Sami
Areva Department of Physical Chemistry, Åbo
Akademi University
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Research Objectives at IC/UH (i) development
of self-cleaning photocatalytic TiO2 based
coatings which operate at visible light (ii)
supply of well reproducible model surfaces for
various surface phenomena studies carried
out by the other partners of the consortia
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Atomic Layer Deposition (ALD) excellent
conformality atomic level control of film
composition large area uniformity
reproducibility accurate and easy film
thickness control down to an atomic level
ZrxSiyOz - ZrxTiyOz nanolaminate
Al2O3
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BASIC PRINCIPLE OF ALD
Self-limiting film growth via alternate saturative
surface reactions.
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ALD MATERIALS CURRENTLY AVAILABLE AT IC/UH
Oxides Dielectric Al2O3, TiO2, ZrO2, HfO2,
Ta2O5, Nb2O5, MgO, Cr2O3, SrTiO3, BaTiO3
Transparent conductors In2O3, In2O3Sn,
In2O3Zr, SnO2, ZnO, ZnOAl Nitrides
Semiconductors/Dielectric AlN, Ta3N5
Metallic TiN, Ti-Al-N, TaN, NbN, MoN Metals
Ru, Pt, Ir II-VI compounds ZnS, ZnS1-xSex,
CaS, SrS, BaS, SrS1-xSex CdS, CdTe OTHER
MATERIALS BY - E-BEAM EVAPORATION (widest
variety) - ELECTRODEPOSITION and SILAR
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Earlier work 1. Testing of photocatalytic
characterization methods and selection of
the most convenient ones for further use ?
methylene blue (aquoeus solution), stearic acid
(solid) 2. Demonstration of the photocatalytic
activity of ALD TiO2
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Degradation of methylene blue under UV
light -comparison of TiO2 samples
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Degradation of stearic acid under UV
light -comparison of TiO2 samples
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• Band gap narrowing by doping
• TiO2S and TiO2N
• ALD-cycles
• X x (TiCl4 H2S) Y x (TiCl4 H2O)
• -X x (TiCl4 NH3) Y x (TiCl4 H2O)
• -growth temperature 500 C

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Degradation of stearic acid by UV and visible
light
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Degradation of stearic acid by visible light
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XRD
best VIS activity
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Sulfur content by SIMS (ÅA)
no sulfur was detected by EDX or TOF-ERDA ?
sulfur content lt 1 at-
best VIS activity
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Band gap determination -bulk values anatase 3,2
eV, rutile 3,0 eV -ALD TiO2 3,3 - 3,4 eV
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Band gap determination
(best VIS activity)
3,15 eV
3,15 eV
2,85 eV
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TiO2N -nitrogen was detected by elemental
analysis (TOF-ERDA, 0-9 at- depending on XY
cycle ratio) -NH3 caused the films to be
anatase(001) oriented -no visible light activity
in the destruction of stearic acid -UV activity
was also poor -surprisingly good results from D.
Geothermalis -biofilm experiments (ACM/UH)
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• Conclusions
• Sol-gel and ALD films had comparable
• photocatalytic activity under UV irradiation
• Band gap narrowing of ALD TiO2 was achieved
• by sulfur doping
• TiO2S film with a TiCl4/H2S TiCl4/H2O ALD
  cycle
• ratio of 11 showed the best visible light
  activity