Characterisation of Nanoparticles using Advanced Electron Microscopy

Transcription

1 Wright State University CORE Scholar Special Session 5: Carbon and Oxide Based Nanostructured Materials (2013) Special Session Characterisation of Core@Shell Nanoparticles using Advanced Electron Microscopy Andrew Wheatley Follow this and additional works at: Part of the Physics Commons Repository Citation Wheatley, A. (2013). Characterisation of Core@Shell Nanoparticles using Advanced Electron Microscopy.. This Presentation is brought to you for free and open access by the Special Session 5 at CORE Scholar. It has been accepted for inclusion in Special Session 5: Carbon and Oxide Based Nanostructured Materials (2013) by an authorized administrator of CORE Scholar. For more information, please contact corescholar@

2 Characterisation of nanoparticles using advanced electron microscopy Dr. Andrew Wheatley Chemical Laboratories, University of Cambridge, Lensfield Road, Cambridge, CB2 1EW, UK

3 Magnetic Nanoparticles Dual functionality Oxidative Stability Functionalisable Tuneable Recoverable Inexpensive Catalytically active Magnetic Low Cost Oxidatively stable Applications in Magnetic separation Catalysis Drug delivery Magnetic hyperthermia

4 Synthesis of particles Sequential reduction/decomposition Simultaneous reduction/decomposition Heat Heat Heat A + B A + B Core@shell Heterodimer Segregated mixture Intermixed (alloyed)

5 Characterisation of heterostructures Powder XRD Can identify phases present Sherrer equation gives particle size Bulk technique Peaks broadened by small crystalliites Size information only relevant to the smallest particles Particles may be polycrystalline XRD of 3 O 4 Bright-field TEM Particle forms directly observed Lattice fringes give information on phase Core@shell structure may be visible Increase in particle size could be caused by aggregation Beam damage can occur Core@shell structure may not be visible Suffers from lens abberations Au@Fe 3 O 4 Fe 3 O S. Sun, C. Wang, S. Peng and L.-M. Lacroix, Nano Research, 2009, 2, J. Gallo, I. García, D. Padro, B. Arnáiz and S. Penadés, J. Mater. Chem., 2010, 20, 10010

6 Characterisation of heterostructures High-angle annular dark-field (HAADF) STEM Z-contrast is high Poor signal-to-noise ratio Reduced image resolution Spatially resolved EDS and EELS Produces elemental line scans Maps individual particles EDX best for high Z, EELS best for low Z Energy Filtered (EF) TEM Electrons with a particular energy loss are selected Selection based on core losses for specific elements Composite images for element mapping Poor signal-to-noise ratio Electron diffraction and fast Fourier Transforms Requires less material than XRD Bulk technique Suffers from lens abberations

7 Synthesis of particles Co 2 (CO) 8 1) PPh 3, 2) OA, 1) ex. Fe(CO) 5, 120 ºC, 3)185 ºC 2) 180 ºC, 3) 250 ºC EtOH DCB monodisperse 8 nm Co particles monodisperse 14 nm particles 30nm 20nm 30nm OA = cis-me(ch 2 ) 7 CH=CH(CH 2 ) 7 CO 2 H H. T. Yang, C. M. Shen, Y. G. Wang, Y. K. Su, T. Z. Yang and H. J. Gao, Nanotechnology, 2004, 15, S. Sun, C. Wang, S. Peng and L.-M. Lacroix, Nano Research, 2009, 2,

8 HRTEM analysis of the product Mean = ± 1.2 nm 25 Frequency nm Particle size (nm) Mean particle size = 13.6 ± 1.2 nm Core@shell structure clear Inner shell and outer shell? 20 nm Background of small (<2 nm) particles

9 High Resolution TEM Co (220) 5 nm Fe 3 O 4 (311) Metallic Co core Polycrystalline shell Partial oxidation in the shell

10 Comparing bulk and individual particle analysis SAED and FFT combine bulk and individual particle analysis Metallic Co core Partially oxidised shell

11 Reconstructing particle images 2 nm nm -1 2 nm -1 2 nm -1 5 nm -1 5 nm -1 5 nm -1 5 nm -1 Inverse-FFT regenerates the particle image from the diffraction pattern

12 Elemental characterisation by line scans llu l~u... ~ luu :I 0 8U u bu I I,, '' \ I I I LO '... ',,, _ 20 " :,.,,'/ ' '.. ~ I \ I f". /...,' ; /'.J \..,,, \.....w: " " // '-/- _:. -.. ~_,,,-;.~,,.,.,,, ' -~\ Co L ed!\e... F" l " ~ ti" o Ked11e..._ \ u -r--=-=-~-:...:: -~'~~~~..-~~~~~~~~~~~'~.::..::: nm c;.. ~ ~ 8., ~ L <: v " 3 2, II Co _ ed5e Fe L edse 0 s ;:);, UNIVERSITY OF -; - CAMBRIDGE

13 Confirming the oxidation states EELS line scans EELS data obtained for the L 2,3 edge of Fe 95 particles scanned Calibrated with respect to the Co L 2 edge Comparison of data from shell, core and reference materials confirms that shell is closest in nature to Fe 3 O 4

14 Verifying the location of carbon EELS point scans Fe-rich background (2 nm particles) Fe 3 O 4 shell must act to retain both C and Co

15 Conclusions and further work structre and metal oxidation states established Knappett et al., Nanoscale, 2013, 5, Monocrystalline Co core, polycrystalline Fe 3 O 4 outer-shell formed by agglomeration of background Fe 3 O 4? Presence of C inner-shell confirmed Possibility of lowering epitaxial constraints at the core-shell interface C may help protect the Co core Vary core size/material, outer-shell thickness, and capping to tune stability and properties

16 Acknowledgements Synthesis Benjamin Knappett Pavel Abdulkin Analysis Dr. David Jefferson Dr. Emilie Ringe (Materials Science, Cambridge) Dr. Sergio Lozano-Perez (Materials Science, Oxford) Drs. Asunción Fernández and Christina Rojas (Ciencia de Materiales de Sevilla) Drs. Christian Kübel and Di Wang (KMNF, Germany) Funding

17 Characterisation of nanoparticles using advanced electron microscopy Dr. Andrew Wheatley Chemical Laboratories, University of Cambridge, Lensfield Road, Cambridge, CB2 1EW, UK