University of Calgary PRISM: University of Calgary's Digital Repository Graduate Studies The Vault: Electronic Theses and Dissertations 2017 Origins of Unconventional Magnetism in Coinage Metal Nanomaterials Marenco, Armando J. Marenco, A. J. (2017). Origins of Unconventional Magnetism in Coinage Metal Nanomaterials (Unpublished doctoral thesis). University of Calgary, Calgary, AB. doi:10.11575/PRISM/27233 http://hdl.handle.net/11023/3610 doctoral thesis University of Calgary graduate students retain copyright ownership and moral rights for their thesis. You may use this material in any way that is permitted by the Copyright Act or through licensing that has been assigned to the document. For uses that are not allowable under copyright legislation or licensing, you are required to seek permission. Downloaded from PRISM: https://prism.ucalgary.ca UNIVERSITY OF CALGARY Origins of Unconventional Magnetism in Coinage Metal Nanomaterials by Armando J. Marenco A DISSERTATION SUBMITTED TO THE FACULTY OF GRADUATE STUDIES IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY GRADUATE PROGRAM IN CHEMISTRY CALGARY, ALBERTA January, 2017 c Armando J. Marenco 2017 Abstract The studies presented in the dissertation focused on the unconventional magnetic properties of coinage metals - Cu, Ag, and Au - nanomaterials synthesized in the gas phase by sputtering. Unlike other common synthetic methods, gas-phase synthe- sis creates nanoparticles and thin films free of capping ligands allowing for pristine surface studies. The two types of nanomaterials synthesized were sub-12 nm diame- ter nanoparticles and thin films. These three parameters, namely the nature of the coinage metal, unmodified surfaces, and nanodimensionality, were the core effects independently studied. The unconventional magnetism of Cu nanomaterials has been studied in highly- pure and capping-ligand-free nanoparticles and thin films. Superconducting quantum interference device (SQUID) room-temperature (300 K) measurements displayed no size correlation to the ferromagnetic behavior observed in Cu nanoparticles ranging from 4.5 ± 1.0nmto9.0± 1.8 nm in diameter. Moreover, magnetic quartz crystal microbalance (MQCM) in situ tests of 4.5 ± 1.0 nm nanoparticles under vacuum con- ditions showed magnetic behavior only after the onset of oxidation. SQUID analysis conducted on Cu thin films exposed to several heat treatments demonstrated minor oxidation inducing higher ferromagnetic responses compared to extended oxidation. i Further analysis of nanomaterial samples exhibiting the highest magnetic responses indicated an atomic ratio of ∼3-5:1 Cu:O suggesting non-stoichiometric oxidation as the source of the ferromagnetic signature. Similar ferromagnetic results were obtained for Ag nanomaterials. No size cor- relation to magnetism in Ag nanoparticles ranging from 3.3 ± 0.9nmto7.8± 1.3 nm was determined by SQUID magnetometry. Additionally, MQCM under vacuum conditions of 3.3 ± 0.9 nm Ag NPs shows magnetic behaviour only after the onset of oxidation. The trend in SQUID magnetometry shows a higher saturation mag- netization for samples exposed to oxygen compared to inert atmospheres, which is opposite to the Cu findings. However, this also indicates non-stoichiometric oxida- tion at the surface as the reason for the observed magnetism as supported by an ∼8:1 Ag:O ratio from MQCM measurements. Finally, heat-treated Ag thin films present a lower saturation magnetization compared to those kept in oxygen without heating. This latter observation could be the result of driving the oxidation to stoichiometric surface oxides AgO and Ag2O which are known to be diamagnetic. For Au nanomaterials, our findings show some promise but are inconclusive. A single diameter was synthesized at 3.9 ± 1.7 nm. Unlike the MQCM studies observed for Cu and Ag, Au NPs show no significant signal change which could be interpreted as ferromagnetic behaviour. However, SQUID magnetometry does provide a clear ferromagnetic signal. Further studies are required to determine for certain if oxidation plays a role in Au nanomaterials as determined for Cu and Ag. Acknowledgements First and foremost, I would like to thank my supervisors Prof. Simon Trudel and Dr. David B. Pedersen for their guidance, encouragement, and support throughout this lengthy and successful process. Also, I would like to thank the members of my committee Prof. George K. H. Shimizu and Prof. Venkataraman Thangadurai whom provided me with excellent advise during the entirety of my program. Additionally, I am thankful to Prof. Colin Dalton and to Prof. Andrew P. Grosvenor for reviewing my thesis and providing helpful comments. I am grateful to our collaborators Prof. Jillian M. Buriak at the University of Alberta, Prof. Frank C. J. M. van Veggel at the University of Victoria, and to Prof. Mark J. MacLachlan at the University of British Columbia. Our collaborations allowed me to greatly expand my knowledge on magnetism. The acknowledgments could not be completed without thanking current and past members of the Trudel Group, specially to Raphael Dong, Jennifer Emara, Luvdeep Bhandari, and Casey Platnich. I am grateful to my parents, my siblings and their families for all their support. Finally, I would like to thank the entire support personnel in the Department of the Chemistry at the University of Calgary. iii Dedicated to my nieces and nephews. Contents Abstract .................................... i Acknowledgements .............................. iii Contents..................................... v ListofTables.................................. viii ListofFigures.................................. ix ListofSymbols................................. xi 1 Introduction................................ 1 1.1Originofmagnetism........................... 1 1.2Classificationofmagneticmaterials................... 4 1.2.1 Diamagnetism........................... 4 1.2.2 Paramagnetism.......................... 7 1.2.3 Collective Magnetism . 9 1.3ExchangeInteractions.......................... 15 1.3.1 Exchange............................. 15 1.3.2 DirectExchangeInteraction................... 18 1.3.3 IndirectExchangeInteractions.................. 19 1.4 Conventional and Unconventional Magnetism . 22 1.4.1 Conventionalmagnetism..................... 22 1.4.2 Unconventionalmagnetism.................... 25 1.5 Unconventional Magnetism in Coinage Metals . 26 1.6Nanomaterials............................... 31 1.6.1 Nanoparticles........................... 32 1.6.2 Thinfilms............................. 33 1.7Sputteringprocess............................ 33 1.7.1 Sputteringtheory......................... 34 1.7.2 Gas-phasenanoparticlegeneration................ 36 1.8 Research goal . 38 1.8.1 Importanceofmagnetism.................... 41 1.9Outlineofthesis.............................. 42 2 Experimentaldetails........................... 44 2.1Nanomaterialsynthesisinthegasphase................ 44 2.1.1 Nanoparticlepreparation..................... 45 v 2.1.2 Thinfilmpreparation....................... 51 2.2Opticalsetup............................... 55 2.3 Magneto-optical Kerr effect setup . 55 2.4 Superconducting quantum interference device magnetometry . 57 2.5 Magnetic quartz crystal microbalance . 61 2.5.1 In situ MQCM.......................... 63 2.6X-rayphotoelectronspectroscopy.................... 66 2.7Atomicforcemicroscopy......................... 66 2.8Scanningelectronmicroscopy...................... 66 2.9PowderX-raydiffraction......................... 67 2.10 Experimental methodology for Cu nanomaterials . 67 2.11 Experimental methodology for Ag nanomaterials . 68 3 Opticalstudiesofsilvernanomaterials................. 71 3.1Introduction................................ 71 3.2 Magneto-optical effects . 72 3.2.1 Faradayeffect........................... 72 3.2.2 Kerreffect............................. 75 3.3 Magneto-optical Kerr effect . 79 3.4 An alternative to direct measurement of the Kerr rotation . 82 3.5Resultsanddiscussion.......................... 83 3.5.1 Preliminaryopticalexperiments................. 83 3.5.2 MOKEmeasurements...................... 90 3.6Conclusion................................. 95 4 Inducing ferromagnetic behaviour in Cu nanomaterials . 96 4.1Introduction................................ 96 4.2Experimental............................... 99 4.3Results................................... 99 4.3.1 CuNPs.............................. 99 4.3.2 Cufilms.............................. 102 4.3.3 Cu NPs - in situ MQCMmeasurements............ 103 4.4Discussion................................. 115 4.4.1 Sizedependence.......................... 115 4.4.2 Oxidation............................. 116 4.4.3 Our magnetic system compared to other systems . 116 4.5Conclusion................................. 120 5 On the origin of ferromagnetic signature in Ag nanomaterials . 122 5.1Introduction................................ 122 5.2Experimental............................... 126 5.3Results................................... 126 5.3.1 AgNPs.............................. 126 5.3.2 Agfilms.............................. 129 5.3.3 Ag NPs: In Situ OxidationEffects............... 131 5.3.4 SurfaceAnalysis......................... 136 5.4Discussion................................. 138 5.4.1 SurfaceSpeciesCharacterization................. 138 vi 5.4.2 OriginofferromagnetisminAgNPs.............. 147 5.5Conclusion................................. 150 6 Preliminarystudiesongold....................... 151 6.1Introduction................................ 151 6.2Experimental..............................