Band Edge Energetics of Heterostructured Nanorods: Photoemission Spectroscopy and Waveguide Spectroelectrochemistry of Au-Tipped CdSe Nanorod Monolayers

Ramanan Ehamparam, Nicholas G. Pavlopoulos, Michael W. Liao, Lawrence J. Hill, Neal R Armstrong, Dong-Chul Pyun, Steven S Saavedra

Research output: Contribution to journalArticle

17 Scopus citations

Abstract

Conduction and valence band energies (E<inf>CB</inf>, E<inf>VB</inf>) for CdSe nanorods (NRs) functionalized with Au nanoparticle (NP) tips are reported here, referenced to the vacuum scale. We use (a) UV photoemission spectroscopy (UPS) to measure E<inf>VB</inf> for NR films, utilizing advanced approaches to secondary electron background correction, satellite removal to enhance spectral contrast, and correction for shifts in local vacuum levels; and (b) waveguide-based spectroelectrochemistry to measure E<inf>CB</inf> from onset potentials for electron injection into NR films tethered to ITO. For untipped CdSe NRs, both approaches show E<inf>VB</inf> = 5.9-6.1 eV and E<inf>CB</inf> = 4.1-4.3 eV. Addition of Au tips alters the NR band edge energies and introduces midgap states, in ways that are predicted to influence the efficiency of these nanomaterials as photoelectrocatalysts. UPS results show that Au tipping shifts E<inf>VB</inf> closer to vacuum by up to 0.4 eV, shifts the apparent Fermi energy toward the middle of the band gap, and introduces additional states above E<inf>VB</inf>. Spectroelectrochemical results confirm these trends: Au tipping shifts E<inf>CB</inf> closer to vacuum, by 0.4-0.6 eV, and introduces midgap states below E<inf>CB</inf>, which are assigned as metal-semiconductor interface (MSI) states. Characterization of these band edge energies and understanding the origins of MSI states is needed to design energy conversion systems with proper band alignment between the light absorbing NR, the NP catalyst, and solution electron donors and acceptors. The complementary characterization protocols presented here should be applicable to a wide variety of thin films of heterogeneous photoactive nanomaterials, aiding in the identification of the most promising material combinations for photoelectrochemical energy conversion.

Original languageEnglish (US)
Pages (from-to)8786-8800
Number of pages15
JournalACS Nano
Volume9
Issue number9
DOIs
StatePublished - Sep 22 2015

Keywords

  • band edge energies
  • electron transfer
  • metal nanoparticle
  • semiconductor nanorods
  • spectroelectrochemistry
  • UV photoemission

ASJC Scopus subject areas

  • Engineering(all)
  • Materials Science(all)
  • Physics and Astronomy(all)

Fingerprint Dive into the research topics of 'Band Edge Energetics of Heterostructured Nanorods: Photoemission Spectroscopy and Waveguide Spectroelectrochemistry of Au-Tipped CdSe Nanorod Monolayers'. Together they form a unique fingerprint.

  • Cite this