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Wetting Behavior of Cerium Oxide Films Grown by Pulsed Laser Deposition. Daniel Li, UIUC Advisor Dr. Jeremiah Abiade NSF-REU Symposium University of Illinois at Chicago Chicago, IL 8/1/2013. Daniel Li dli22@illinois.edu. Purpose and Motivation.
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Wetting Behavior of Cerium Oxide Films Grown by Pulsed Laser Deposition • Daniel Li, UIUC • Advisor Dr. Jeremiah AbiadeNSF-REU Symposium • University of Illinois at Chicago • Chicago, IL • 8/1/2013 Daniel Li dli22@illinois.edu
Purpose and Motivation Build upon research that investigate the intrinsic hydrophobic properties of REOs Robust, hydrophobic coating compatible with existing facilities Daniel Li dli22@illinois.edu 15Azimi, Gisele, Rajeev Dhiman, Kwon Hyuk-Min, Adam T. Paxton, and Kripa K. Varanasi. "Hydrophobicity of Rare-earth Oxide Ceramics." Nature Materials 12.4 (2013): 315-20. Nature Publishing Group, 20 Jan. 2013.
Wetting Behavior • Water Contact Angle • Surface energy • Hydrophobicity and hydrophilicity Daniel Li dli22@illinois.edu 9 Quéré, David. "Wetting and Roughness." Annual Review of Materials Research 38.1 (2008): 71-99. Review in Advance. Annual Review of Materials Research, 7 Apr. 2007.
Applications of Hydrophobic Materials • Waterproofing and Lubrication • Corrosion Prevention • Condensation • Self Cleaning Materials • Heat Transfer/Cooling Systems [1] http://geography.swansea.ac.uk/hydrophobicity/soil_hydrophobicity.htm[2] http://meanderinglanes.blogspot.com/2010/09/rain-on-windshield.html Daniel Li dli22@illinois.edu [3] http://www.aeconline.ae/qatar-s-deputy-prime-minister-to-inaugurate-world-2s-largest-district-cooling-24893/news-files/dc2_main.jpg [4] http://www.criticalend.com/wp-content/uploads/2009/03/balepsycho.jpg
Cerium Oxide Polymer Additives • Chemically Stable • High Adhesiveness • Thermal Transfer • Durability/Wear Resistance • Relatively Low Cost Hydrophobic Properties diminish substantially from thermal, mechanical, and chemical attack Daniel Li dli22@illinois.edu [1,2] http://www.rustoleum.com/product-catalog/consumer-brands/neverwet/neverwet-kit/ [3]http://www.netl.doe.gov/newsroom/features/12-2010.html
Pulsed Laser Deposition (PLD) Process1. Laser is focused onto a target in high vacuum or ambient gas2. Target material is vaporized and a plasma plume is created3. Gaseous target deposits onto substrate, thin film develops Thin Films • Thin = less than one micron (1000 nm) • Film = layer of material on a substrate Daniel Li dli22@illinois.edu [1,2] http://tfy.tkk.fi/aes/AES/projects/prlaser/pld.htm
PLD Factors • KrFExcimer Laser Fluence • Target-substrate distance • Number of pulses and frequency • Deposition temperature • Basal and gas pressure Advantages:- stoichiometry is preserved- multiple targets allowable- easily controlled growth rateDisadvantages:- limited uniformity, requires small substrate Daniel Li dli22@illinois.edu [1] https://rt.grc.nasa.gov/main/rlc/pulsed-laser-deposition-laboratory/
Experimentation Pulsed laser deposition of thin film cerium oxide (ceria) on Si at varying oxygen partial pressures and deposition temperature WCA measurements over time with and without UV irradiation (4 microliters, DI water) III. X-ray photoelectron spectroscopy (XPS) characterization Daniel Li dli22@illinois.edu
PLD Thin Films • Controls • Cerium Oxides onto Silicon wafer • Target-Substrate Distance: 6.2 cmKrFExcimer Laser: • Wavelength: 248 nm (UV) • Laser Fluence 4.5 J/cm2, 22 kV, 500 mJ • 5000 Pulses at 5 Hz • Independent Variables • Oxygen Partial Pressure • 2 main Cerium oxidation states: +3, +4 • Temperature (RT, 300, 700 degrees Celsius) Daniel Li dli22@illinois.edu [1] http://www.kruss.de/en/products/contact-angle/drop-shape-analysis-system
PLD Depositions Daniel Li dli22@illinois.edu
WCA as a function of Deposition Temperature Oxygen Pressure(Torr) 3.0 E-2 5.0 E-2 No Oxygen Photo provided courtesy of Sin Pui Fu, UIC Daniel Li dli22@illinois.edu
Oxygen Pressure(Torr) Daniel Li dli22@illinois.edu
Retreatment of Previous Samples with UV over time Oxygen Pressure(Torr) Oxygen Pressure(Torr) Resistance to UV: smaller drop in WCA Daniel Li dli22@illinois.edu
UV Treatment of Room Temperature Samples over Time Oxygen Pressure(Torr) Daniel Li dli22@illinois.edu
WCA over Time (after 120 minutes of UV Irradiation)Samples were kept in the dark Variation in recovery to pre- UV levels Daniel Li dli22@illinois.edu
X-Ray Photoelectron Spectroscopy (XPS) Sample is irradiated by X-rays - emitted electrons are measured Useful for determining stoichiometry- oxidation states- empirical formula Daniel Li dli22@illinois.edu
XPS Data 2.1 E-3 T, 700 C 7.5 E-3 T, 700 C • XPS analyzed valency of Ce ions at the surface • Ce(III)Oxide is present in higher amounts in higheroxygen pressures than Ce (IV) Oxide • Stoichiometry: cerium and oxygen is independent of temperature Daniel Li dli22@illinois.edu
Conclusions and Discussion • Water contact angles vary initially but eventually increase and plateau to ~ 90 degrees over a week • UV treatment causes a significant drop in WCA but most samples recover to pre-UV levels • Samples that have been treated previously with UV have a greater resistance (smaller WCA drop) than those treated for the first time; likewise for recovering to pre-UV treatment levels • More observed uniformity in samples created at 700 degrees, though XPS indicates temperature has little effect on oxidation states Daniel Li dli22@illinois.edu
Further Work • Run standard scan on pure cerium to determine remaining peak features; XPS of additional samples • Additional characterization of surface morphology with AFM and TEM • Ultra clean storage inbetween measurements to account for hydrocarbon contamination Daniel Li dli22@illinois.edu
Acknowledgements • EEC-NSF Grant # 1062943 • Advisor Jeremiah Abiade • RiadAlzeghier • Jelani Hannah • Dr. Takoudis and Dr. Jursich • REU Staff Daniel Li dli22@illinois.edu
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Atomic Force Microscopy: Cerium (IV) oxide on Si No oxygen, 200 degrees C Roughness: 4.61 nm WCA: 95 degrees 5 E-2, 200 degrees CRoughness: 4.91 nmWCA: 44 degrees • PLD process doesn’t seems to yield different surface morphologies • Very different water contact angles Images provided by Sin-Pui Fu, UIC Daniel Li dli22@illinois.edu
XPS DataCerium 7.5 E-3, 700 C 2.5 E-3, RT 2.1 E-3, 700 C Stoichiometry:7.5 E-3 torr at 700 C Ce:O 15:1 2.1 E-3 torr at 700 C Ce:O 32:1 Intensity A.u. Binding Energy eV Daniel Li dli22@illinois.edu