Graduate Student, Materials Chemistry
Department of Chemistry
University of Wisconsin-Madison
B.A. Williams College, Chemistry and Studio Art, 2006
PhD University of Wisconsin-Madison, 2006-Present
My project focuses on both developing synthetic strategies for tuning nanocrystal systems and characterizing their physical properties. My primary materials are colloidal EuS and PbSe nanocrystals.
As an intrinsic magnetic semiconductor, EuS is an appealing material for spintronic and magneto-optic applications. The utility of this material has been limited due to its low magnetic transition temperature (Curie temperature is 17 K). I study both element-specific and magnetism in EuS NCs. I measured the element specific magnetic properties of EuS NCs using X-ray absorbance spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD) and confirmed the Eu2+ ions are the source of ferromagnetic behavior.
Figure 1. Left: Magnetization of EuS NCs as function of applied field at 5 K, 100 K, and 300 K. Insets show HRTEM image of the EuS NCs (upper left) and field cooled/ zero field cooled magnetization scans (bottom right).
Right: : a) Experimental XMCD measured at 6 K and weighted sum of theoretical Eu2+ and Eu3+ XMCD multiplet spectra. b) Theoretical XMCD multiplet spectra for Eu2+ and Eu3+ ions. The drop-lines guide the eyes to the peaks in the experimental spectrum.
In addition, I have developed and characterized a library of novel single source europium and gadolinium dithiocarbamate precursors. Through simultaneous decomposition of a pair of these precursors I synthesized Gd doped EuS nanocrystals. To characterize the distribution of Gd ions within the EuS NCs, I performed scanning transmission electron microscopy (STEM) electron energy loss spectroscopy (EELS) mapping, powder X-ray diffraction (XRD) and ion coupled plasma atomic emission spectroscopy (ICP-AES) which were all consistent with a homogeneous distribution of dopants.
Figure 2. Left: STEM image showing the even distribution of Eu and Gd. a a) STEM image of Eu1-xGdxS NCs (x = 0.066) mapped using EELS (50 × 50 spectra); b) The average of all the EELS spectra present in the EELS map. The Eu M5 and Gd M5 edges used for examining elemental distribution are indicated. c) EELS map of Eu M5 edge intensity and d) EELS map of Gd M5 edge intensity.
Right: TC of Eu1-xGdxS NCs vs. Gd fraction for 0≤x≤0.2. Circles represent samples prepared from single injection reactions, squares indicate multiple injection reactions of M(Pytc)3Bipy (M = Eu, Gd), and triangles indicate syntheses using Eu(Ddtc)3Phen SSP.
Figure 3. TEM images of PbSe nanocrystals (left) and PbS nanocrystals (right)
PbSe and PbS are broadly quantum confineable in the near infrared. As a result the bandgaps of these materials can be easily tuned by changing the size of the particles. Given this tunability as well as high quantum efficiencies, these materials have appeal for photovoltaic applications. I am currently working to synthesize and characterize heterostructures of colloidal PbSe NCs on semiconductor nanowires. I am as working in collaboration with chemists specializing in surface characterization and modification and chemists specializing in multi dimensional spectroscopy to investigate these properties.
Publications and Presentations
1) Selinsky, R.S.; Ding, Q.; Faber, M.S.; Wright, J.C.; Jin, S.; Quantum Dot Nanoscale Heterostructures for Solar Energy Conversion, Chem. Soc. Rev., 2013, DOI: 10.1039/C2CS35374A.
2) Block, S.; Yurs, L.; Pakoulev, A.; Selinsky, R.S.; Jin, S.; Wright, J.; Multiresonant Multidimensional Spectroscopy of Surface-Trapped Excitons in PbSe Quantum Dots, J. Phys. Chem. Lett. 2012, 3, 2707-2712.
3) Selinsky, R. S. ; Shin, S.; Lukowski, M. A.; Jin, S.; Epitaxial Heterostructures of Lead Selenide Quantum Dots on Hematite Nanowires J. Phys. Chem. Lett. 2012, 3, 1649–1656.
4) DeGrave, Jack P.; Schmitt, Andrew L.; Selinsky, Rachel S.; Higgins, Jeremy; Keavney, David J.; Jin, Song; Spin Polarization Measurement of Homogeneously Doped Fe1-xCoxSi Nanowires by Andreev Reflection Spectroscopy, Nano. Lett, 11, 2011, 4431-4437.
5) Lurs, Lena; Block, Steven; Pakoulev, Andrei; Selinsky, Rachel S.; Jin, Song; Wright, John; Multiresonant Coherent Multidimensional Electronic Spectroscopy of Colloidal PbSe Quantum Dots, J. Phys. Chem., in press.
6) Clusters, Nanocrystals & Nanostructures. “Nanocrystal heterostructures for solar energy conversion and Gd doped EuS magnetic nanocrystals,” Selinsky, Rachel S.; Lukowski, M.; Keavney, D.; Shin, S.; Johns, R.; Han, J.H.; Jin, S.; Mount Holyoke, MA, July 2011 (poster)
7) Selinsky, Rachel S.; Han, Jae Hyo; Morales Perez, Elvin A.; Guzei, Ilia A.; Jin, Song; Synthesis and Magnetic Properties of Gd Doped EuS Nanocrystals with Enhanced Curie Temperatures, J. Am. Chem. Soc., 132, 2010,15997-16005.
8) Selinsky, Rachel; Keavney, David J.; Bierman, Matthew J.; Jin, Song; “Element-Specific Magnetometry of EuS Nanocrystals”Appl. Phys. Lett.,95, 2009, 202501.
9) 237th ACS National Meeting “Synthesis and magnetic properties of doped and ligand-exchanged EuS nanocrystals”, INOR 288, R.S. Selinsky, S. Jin, Salt Lake City, UT, March 23, 2009 (oral)
10) 237th ACS National Meeting “’Nano boot camp’ for high school students”, CHED 50, S. Jin, R.S.Selinsky, S.A. Morin, J. Rajkumar, Salt Lake City, UT, March 22 2009 (oral, presented for S. Jin)