Presentation on theme: "Student: Peter Knapp Research Advisor: Professor Jeremiah Abiade"— Presentation transcript:
1Student: Peter Knapp Research Advisor: Professor Jeremiah Abiade Analysis of Ferromagnetic-Multiferroic interfaces in Epitaxial Multilayers of LSMO and BFOStudent: Peter KnappResearch Advisor: Professor Jeremiah Abiade
2OverviewBilayers were fabricated from ferromagnetic (FM) LSMO (La0.7Sr0.3MnO3) and anti-ferromagnetic (AFM) BFO (BiFeO3) via Pulsed Laser Deposition (PLD)Layers were analyzed using TEM (Transmission Electron Microscopy), XRD (X-ray Diffraction), and XPS (X-ray Photoelectron Spectroscopy) in order to confirm composition and observe structural detiails
3Motivation For Project Need to control the structure of oxide thin films and multilayersUnderstand effects of structure & layering on magnetic interactionPreliminary work for future experiments on properties of ferromagnetic/ferroelectric systems
4Introduction to Multiferroic Bilayers Materials where electric polarization influences ferromagnetic polarization, allowing manipulation of electric/magnetic order1Contemporary research focuses on bilayers of FM and AFM materialsThese structures demonstrate exchange bias (EB), exchange enhancement (EE), and exchange coupling (EC)
5Particular Interest in LSMO and BFO On their own LSMO and BFO possess useful characteristicsCombined they clearly exhibit exchange interactions that characterize multiferroic systemsAdditional advantages include common perovskite structure and a close lattice parameter(A)(B)All Perovskites have the same basic chemical formula: ABO3
6Interfacial EffectsResearchers know little about how interfacial effects impact magnetic effectsIt is known that there is lattice mismatch and diffusion between LSMO and BFO layers.It is necessary to understand how these phenomena can effect film propertiesLattice Mismatch
7Controlling Structure These experiments will focus on achieving structural control during depositionSubstrate will be varied between LaAlO3 or SrTiO3The thickness of the layers will be variedLayer order will be varied
8Potential Applications of Work Could help demonstrate novel uses for materials like LMSO and BFO in memory devices and sensors, for instance Hard Drives and SQUIDs (superconducting quantum interference devices)Development of novel heterostructures for unusual uses i.e. LMSO as electrode for ferroelectric filmsTailor structures to realize multicomponent multiferroic systems (e.g. electrical control of magnetism)
9Experimental Procedures PLD for synthesis of the Bilayers.TEM to observe local characteristicsXRD to observe interlayer interaction and structural characteristicsXPS to confirm composition
10Pulsed Laser Deposition Physical Vapor Deposition TechniqueHigh Powered (Excimer Laser) focused on target (material to be deposited) in vacuumMaterial is vaporized into plasma plume which extends from targetProceeds to land on substrate forming a thin filmHighly Advantageous
11Transmission Electron Microscopy Beam of Electrons fired through specimenElectrons interact with material in filmImage created on photographic film or a CCD camera
12II. X-Ray ReflectivityMeasurement: Specular reflection as a function of angle of incidence.Result: electron density profile along substrate normalThickness and average electron density of the film.Thickness and electron density can be used to infer roughness and structural defects like diffusion and lattice mismatchX-ray techniques can also be used to analyze strain in the filmsThin Film or MultilayerThin Film or Multilayer
13III. X-ray Photoelectron Spectroscopy XPS = X-Ray Photoelectron SpectroscopyKinetic Energy and Intensity of electrons emitted from material irradiated with X-Rays is measuredYields elemental composition, empirical formula, chemical state, and electronic stateXPS Mechanism
14PLD Results: Films Deposited Target Substrate Distance=4.5 cmDeposition Temp=6500 CelsiusO2 Background=0.02 TorrPulse Frequency=5 HzLaser Fluence =1.5 Jcm-2Wavelength=248 nmUsed KrF Excimer LaserThickness LSM0 (nm)Pulses for LSMO DepositionThickness BFO (nm)Pulses for BFO DepositionOrder of layers on substrate (bottom/top)15010,580BFOBFO/LSMO20014,10025017,630LSMOLSMO/BFOFilms deposited on both LaAlO3 and SrTiO3
16TEM Results – Contd. Unknown LaAlO3 BFO Glue Clean Diffraction Pattern Indicates highly crystalline filmGrowth rate of BFO twice what was expected
17TEM - ResultsPLD Allowed for deposition of films that are highly crystallineAt the interface there is a slight rotation (30o to 40o) between the crystalline plane of the substrate and filmGrowth Rate of BFO is twice that of LSMO
18Rigaku-ATXG diffractometer XRD Preliminary WorkSlit Collimation Geometry S1 = 0.5 mm (h) 2 mm (v) S2 = 0.1 mm (h) 2 mm (v) S3 and X Replaced with Soller Slit to lock out reflection from excess crystal planes/substrate Sample : 5mmX5mmX0.5mm substratesXS3S2S1Rigaku-ATXG diffractometer
19Crystallinity Scans Hold Omega at 0.5 degrees Scan 2Theta from 20o to 600If resulting graph hasSingle Peak Single CrystalMultiple Peaks PolycrystallineNo clear Peaks AmorphousAmorphousPolycrystallineNanocrystaline
20Approaching Single Crystal Sample ScansApproaching Single CrystalAmorphousPolycrystallineNanocrystaline
21Crystallinity Scan Contd. AmorphousNanocrystalline or AmorphousNanoctystalline or AmorphousPolycrystaline
22Crystallinity Scans Contd. AmorphousAmorphousAmorphousAmorphous or Nanocrystalline
24Crystallinity Scans Contd. AmorphousAmorphous or NanocrystallineResultsMajority of Films are amorphousSeveral Films appear to be Polycrystalline or NanocrystallineNew BFO film created with alternate deposition parameters
25Nanocrystaline Samples Film (radians)B(2)(radians)Crystallite Width(nm)150nm_BFO_SrTiO30.2630.1115150nm_LSMO_SrTiO30.2560.08038150nm_BFO_150nm_LSMO_LaAlO30.265200nm_BFO_150nm_LSMO_SrTiO30.2590.09866250nm_LSMO_150nm_BFO_SrTiO30.2540.116Possible to determine the size of crystallites using the Scherrer Eqn.B(2) = Peak Width (radians)λ = nmL = Crystallite Width (nm) = d-spacing (radians)K = Scherrer Constant (Assumed to be 1)
26New 150 nm BFO Film on SrTiO3Used standard Laser Fluence and Pulse FrequencyModified Annealing ProcessDeposition at 670o C at .02 TorrCool to 390o C, anneal for 1 hourCool to room temperature at 5o C/minData indicates Amorphous film. XPS analysis used to confirm composition allowing us to draw a more accurate conclusion.
27Crystallinity Scans - Results Majority of films are amorphous with some polycrystalline and nanocrystalline samplesLikely due to diffusion of oxygen during annealingIndicated deposition process still requires optimization
28X-Ray Reflectivity 150nm_BFO_150nm_LSMO_SrTiO3 GE111 Compressor Crystal S1 = 0.5 mm (h) 2 mm (v) S2 = 0.1 mm (h) 2 mm (v) S3 = 0.2 mm (h) 5 mm (v) X = 0.2 mm (h) Flux: ~ 2.1*106 photons/s Sample : 5mmX5mmX0.5mm substratesLayerThickness (Å)SLD (Real)SLD (Imaginary)Roughness (Å)AirINFResidue84.34.27*10-63.32*10-830.1BFO14506.57*10-57.90*10-677.5LSMO15505.09*10-51.59*10-551.5SrTiO3 Substrate4.49*10-51.95*10-649.8
29Conclusion - XRRThickness and SLD data seems reasonable but contrasts with data on growth rate from TEMUnfitted drop results from having a high roughness film and low X-ray intensity during scanningTop residue Layer is Likely a Combination of organics and silver particles from adhesive
30XPS Analysis Peak Position BE (eV) FWHM (eV) Raw Area (CPS) RSF Atomic MassAtomic Conc. (%)Mass Conc. (%)Bi 4f1562.7679.140208.982168Fe 2p7084.5722.95755.8461917O 1s5273.1620.78015.996015XPS Results for original 150nm_BFO_SrTiO3: Proper Stoichiometry ObservedPeakPosition BE (eV)FWHM (eV)Raw Area (CPS)RSFAtomic MassAtomic Conc. (%)Mass Conc. (%)Bi 4f1572.8819.140208.982474Fe 2p7085.0992.95755.8461311O 1s5273.3800.78015.996315XPS Results for New 150nm_BFO_SrTiO3: Proper Stoichiometry not Observed
31XPS - Results Stoichiometry of films very similar to target material Currently no explanation for iron deficiency in the new BFO film
32Summary/ConclusionWhile the constructed films were not epitaxial many were highly crystallineThe Stoichiometry of films examined by XPS was consistent with the target materialXRR indicated the films have a large roughnessThe deposition process for LSMO and BFO still requires optimization.
33AcknowledgementsThe financial support from the National Science Foundation, EEC-NSF Grant # is gratefully acknowledged. I would like to thank Professors Jursich and Takoudis for organizing the REU Program. I would like to thank the LORE lab in general and Professor Jeremiah Abiade specifically for providing me with the opportunity to work in their lab.
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