Magnetic Nanocrystals


Times Beacon Record Article

Prof. Dickerson has been featured in a recent article, entitled BNL's James Dickerson: facilitating nanotechnology.  Check it out!

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Prof. Dickerson just recently Guest Edited the Journal of the Electrochemical Society’s Focus Issue on Electrophoretic Deposition (http://jes.ecsdl.org/content/162/11.toc).  This collection of articles on EPD features many of the cutting-edge trends in the field.

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Monolayer Ticker

A new article on nanoparticle monolayer formation, led by Alex Krejci, was published in ACS Applied Materials and Interfaces.

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Shalom and Jyotishka have had their manuscript on electrochemical separation of carbon nanotube films published by the Journal of the Electrochemical Society. Congratulations Jyotishka and Shalom!

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Our article on iron oxide nanoparticle monolayer formation by electrophoretic deposition was published by ACS Materials and Interfaces.

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1

Hardcover versions of Electrophoretic Deposition of Nanomaterials can be accessed via the 'Read Article' link below.

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2

The Spring 2012 MRS Conference was a great success.  Prof. Dickerson presented an Invited Talk on our Rare Earth Nanoparticles.  He also will be the Editor of the YY:Rare-Earth-Materials Section of the MRS Conference Proceedings.

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3

Article on graphene oxide films published in ACS Nano.

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4

Weidong He has finished his PhD with us. Congratulations, Weidong, and best of luck at Pacific Northwest National Laboratory!

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5

Dr. Suseela Somarajan successfully defends her PhD dissertation. Congratulations Suseela!

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Prof. Dickerson is awarded a National Science Foundation CAREER Award!

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Synopsis:

We have explored the size-dependent behavior of europium (Eu) chalcogenide (anti-)ferromagnetic nanoparticles [EuX, X = sulfur (S), selenium (Se), or tellurium (Te)], particularly the transition between ferromagnetic behavior and superparamagnetic behavior in sub-20 nm nanoparticles.  Such investigations can provide considerable information about fundamental nanoscale magnetism that can be exploited for applications like telecommunications and spintronics.  Further, we investigated magnetism within random ensembles (powders) and arrangements (electrophoretically deposited films) of iron oxide (FeO/Fe3O4 core/shell and Fe3O4) nanocrystals.

Major Achievements:

a) Magnetization reversal in ultra-small, sub-2.0 nm nanomaterials; a) Synthesis of ultra-small EuX nanoparticles; c) Verwey transition in core/shell iron oxide nanocrystals.  A portion of this research is the subject of a patent application.

Publicity:

The Virtual Journal of Nanoscience and Nanotechnology.

Detailed Discussion:

For a number of years, bulk forms of EuX have been studied for their optical and magneto-optical properties and for their robust ferromagnetic (FM), ferrimagnetic (FIM), and antiferromagnetic (AFM) properties (Table 1), primarily in bulk crystal form.54-61 Europium chalcogenides are called f-block compounds because the 4f electron orbital in the lanthanide, which are strongly bound to the lanthanide ion, govern the magnetic properties of the compounds.  Further, the size of the 4f orbital is relatively small; thus, the orbital overlap between neighboring lanthanide ions is minimal in the bulk semiconductor crystals.  However, as the material’s size diminishes in the nanoscale, surface strain can alter the atomic arrangement and can alter the orbital overlap between nn lattice sites and nnn sites.  This can dramatically affect J1 and J2.

To conduct a comprehensive investigation of the correlation among the size, the atomic arrangement, and the magnetic and magneto-optical properties of nanocrystals, we synthesized EuS and EuTe nanocrystals, which possess different lattice constants, magnetic ordering, and optical transitions.  To illustrate the aforementioned correlation in these materials, we compared high resolution electron microscopy with magnetic studies, specifically magnetization hysteresis, which can reveal the magnitude and type of magnetic ordering within a nanocrystal.  Slide 1 shows images of the world’s smallest EuS NCs, imaged via high-angle annular dark-field (HAADF), aberration-corrected, atomic number contrast, scanning transmission electron microscopy (Z-STEM), with bright image intensities representing Eu atoms.5 The chosen imaging conditions limit the visibility of sulfur and carbon atoms due to the large difference in the atomic numbers for Eu (Z=63), S (Z=16) and C (Z=6). The STEM analysis revealed highly crystalline face‑centered cubic nanocrystals (encircled), the majority of which has dimensions well below 2 nm (quantum-confined).  For example, in Slide 4 two nanocrystals with nominal diameters of 1.10 ± 0.20 nm and 0.72 ± 0.13 nm are encircled.  The detection of isolated Eu atoms dispersed on the carbon support film (marked by arrows) indicates atomic resolution and single atom sensitivity during the STEM experiments.  In many areas of the sample, non‑crystalline aggregates of Eu atoms (likely in conjunction with sulfur atoms) were observed.  Slide 7 illustrates larger NCs synthesized by our technique (nanocrystalline).  For the sub-2.0 nm EuS, HAADF data provide direct evidence for the size and crystallinity of the NCs and first indication of size-induced atomic rearrangement in EuX NCs.

Reference Articles:

1. W. He and J.H. Dickerson, Insight into Thermally Driven Isotropic Crystallinity Breaking: The 1D Assembly of Europium Chalcogenide Nanoparticles with Oleate Ligands, accepted, Applied Physics Letters, 2011.
2. W. He, S. Somarajan, D.S. Koktysh, and J.H. Dickerson, Superantiferromagnetic EuTe Nanoparticles: Room Temperature Colloidal Synthesis, Structural Characterization, and Magnetic Properties, Nanoscale 3, 184, 2011.
3. M.A. Harrison, S. Somarajan, S.V. Mahajan, D.S. Koktysh, K. van Benthem, and J.H. Dickerson, Template Assisted Synthesis of EuS Nanotubes, Materials Letters 65, 420, 2011.
4. D.S. Koktysh, S. Somarajan, W. He, M.A. Harrison, S.A. McGill, and J.H. Dickerson, EuS nanocrystals: a novel synthesis for the generation of monodisperse nanocrystals with size-dependent optical properties, Nanotechnology 21, 415601, 2010.
5. A.M. Thron, C.S. Bonifacio, N. Erdman, M.A. Harrison, S. Somarajan, J.H. Dickerson, and K. van Benthem, Characterization of EuS Nanotubes in Quantum Confinement, Microscopy and Microanalysis 15, 1178, 2009
6. M.L. Redígolo, D.S. Koktysh, K. van Benthem, S.J. Rosenthal, and J.H. Dickerson, Europium Sulfide Nanoparticles in the Sub-2nm Size Regime, Materials Chemistry & Physics 115 (2-3), 526, 2009.
7. M. L. Redigolo, D. S. Koktysh, S. J. Rosenthal, J. H. Dickerson, Z. Gai, L. Gao, and J. Shen, Magnetization Reversal in Europium Sulfide Nanocrystals, Applied Physics Letters 89 222501, 2006.

 

 


© Copyright 2017 by James H. Dickerson II.

James H. Dickerson

Brown University