Deformation and hyperfine structures of dendrimers investigated by scanning tunneling microscopy

Christopher J. Fleming, Ying X. Liu, Zhao Deng, Gang-yu Liu

Research output: Contribution to journalArticle

11 Scopus citations

Abstract

Scanning tunneling microscopy (STM) is known to provide the highest spatial resolution in real space imaging of materials, and its applications are most common among conductive and semiconductive systems. The high tunneling barrier of insulators diminishes the tunneling probability and thus compromises STM's resolution. This work introduces a simple method to approach this problem, by using STM for high-resolution imaging of insulating materials such as the fourth and fifth generations of poly(amidoamine) hydroxyl-terminated dendrimers. The tunneling barrier is lowered by precoordination with Cu(II) or Pt(II) ions, enabling intramolecular hyperfine features be resolved with 0.2 nm resolution. The spatial distribution, size, and overall number of hyperfine features are consistent with the location of dendrimer termini. The immobilization process deforms dendrimers from the spherical geometry in solution phase to asymmetrical domes in ambient. The ultrahigh vacuum (UHV) environment leads to a higher degree of deformation with reduction of volume. The high-resolution images enable the determination of fundamental parameters of individual dendrimers, including axis, height, asymmetry, and volume. From STM spectroscopy and prior knowledge of dendritic systems, the STM imaging mechanism under UHV is consistent with metal(0) nanoparticles encapsulated by dendrimers, while ambient imaging is most likely via metal-ion-facilitated charge transport. The results from this investigation bring us one step closer toward structural characterization at atomistic level and should enable direct comparison of dendrimer structures with simulations, and deepen our understanding of charge transport in dendrimer systems.

Original languageEnglish (US)
Pages (from-to)4168-4174
Number of pages7
JournalJournal of Physical Chemistry A
Volume113
Issue number16
DOIs
StatePublished - Apr 23 2009

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry

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