STM studies of charge transfer and transport through metal-molecule complexes on ultrathin insulating films
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The Ohio State University / OhioLINK
2011
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ndltd-OhioLink-oai-etd.ohiolink.edu-osu12995255152021-08-03T06:01:44Z STM studies of charge transfer and transport through metal-molecule complexes on ultrathin insulating films Choi, Taeyoung Physics Scanning tunneling microscopy Spectroscopy Ultrathin insulating layer Cu2N Spin IETS Charge transport Charge transfer Kondo Single molecule Switch Spin excitation Traditional electronic and memory devices face a fundamental limit as their size shrinks to an order of one nanometer. An understanding of the electronic and magnetic properties of single atoms and molecules is needed for their incorporation into passive or active components of such devices. Ultrathin insulating films comprising only a few atomic layers are useful materials for building nanostructures from atoms and molecules and for controlling their electronic and magnetic coupling at the nanoscale. Scanning Tunneling Microscopy (STM) is used to study the geometric and electronic structure of an ultrathin insulating film, Cu2N, grown on a Cu(100) surface. We find that the Cu2N lattice is incommensurate with the Cu(100) lattice, suggesting that the resulting strain contributes to the self-assembly of Cu2N into square shaped, ~25nm2 islands. Atomically resolved STM images enable us to register Cu and N atoms within the islands and reveal a contrast reversal with voltage that is similar to that for the GaAs(110) surface. Scanning Tunneling Spectroscopy (STS) indicates that the Cu2N islands suppress the local density of state (LDOS) of Cu(100) within a range from +2eV to -4eV and thus act as an insulator. We study single magnetic atoms (Fe and Co) and clusters on the Cu2N islands grown on Cu(100). Our tunneling spectra show step-like features which are due to the opening of inelastic tunneling channels. The inelastic conductance originates from excitations among spin states (spin-IETS). We observe the evolution of magnetic moments as a function of the number of atoms in clusters or chains. Transition metal ion (M=V, Mn, Co, and Fe)-tetracyanoethylene (TCNE, C6N4) compounds (e.g. V(TCNE)2) are well known organic semiconductors exhibiting ferromagnetism above room temperature. As a bottom-up approach, we studied single TCNE molecules on Cu(111). The single molecules display five distinct configurations which are reversibly switchable by voltage pulses from the STM tip. One of states shows a Kondo resonance in tunneling spectroscopy. Our density functional theory calculation suggests that molecular deformation is responsible for a rearrangement of molecular orbitals, such that unpaired spin in an orbital activates the Kondo resonance. We also study single TCNE molecules on Cu2N and successfully demonstrate the formation of single atom-molecule complexes (Fe-, Co-, and Cu-tetracyanoethylene) on Cu2N via atomically controlled manipulation. We find that the magnetic moments of metal atoms in these complexes change due to bonding with TCNE. The variation in spin-IETS could be useful for quantifying the degree of charge transfer and understanding spin-spin interactions in organic magnets. In order to realize charge/spin transport through a single molecule, we studied azobenzene and alkanedithiol molecules on Cu2N. Molecules bridging Co atoms on Cu2N and the Cu(100) substrate act as an additional pathway for current flow. This pathway is evidenced as a change in the Co Kondo resonance lineshape from a positive Lorentzian, to a more derivative-like Fano resonance. 2011-03-21 English text The Ohio State University / OhioLINK http://rave.ohiolink.edu/etdc/view?acc_num=osu1299525515 http://rave.ohiolink.edu/etdc/view?acc_num=osu1299525515 unrestricted This thesis or dissertation is protected by copyright: all rights reserved. It may not be copied or redistributed beyond the terms of applicable copyright laws. |
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NDLTD |
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English |
| sources |
NDLTD |
| topic |
Physics Scanning tunneling microscopy Spectroscopy Ultrathin insulating layer Cu2N Spin IETS Charge transport Charge transfer Kondo Single molecule Switch Spin excitation |
| spellingShingle |
Physics Scanning tunneling microscopy Spectroscopy Ultrathin insulating layer Cu2N Spin IETS Charge transport Charge transfer Kondo Single molecule Switch Spin excitation Choi, Taeyoung STM studies of charge transfer and transport through metal-molecule complexes on ultrathin insulating films |
| author |
Choi, Taeyoung |
| author_facet |
Choi, Taeyoung |
| author_sort |
Choi, Taeyoung |
| title |
STM studies of charge transfer and transport through metal-molecule complexes on ultrathin insulating films |
| title_short |
STM studies of charge transfer and transport through metal-molecule complexes on ultrathin insulating films |
| title_full |
STM studies of charge transfer and transport through metal-molecule complexes on ultrathin insulating films |
| title_fullStr |
STM studies of charge transfer and transport through metal-molecule complexes on ultrathin insulating films |
| title_full_unstemmed |
STM studies of charge transfer and transport through metal-molecule complexes on ultrathin insulating films |
| title_sort |
stm studies of charge transfer and transport through metal-molecule complexes on ultrathin insulating films |
| publisher |
The Ohio State University / OhioLINK |
| publishDate |
2011 |
| url |
http://rave.ohiolink.edu/etdc/view?acc_num=osu1299525515 |
| work_keys_str_mv |
AT choitaeyoung stmstudiesofchargetransferandtransportthroughmetalmoleculecomplexesonultrathininsulatingfilms |
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1719429673376546816 |