Electrochromic writing and erasing on tungsten oxide films in air by scanning tunneling microscopy

H. Qiu, Y. F. Lu, Z. H. Mai

Research output: Contribution to journalArticlepeer-review

18 Scopus citations


The scanning tunneling microscope (STM) was used for both spot coloring and bleaching on α-WO3-x thin films. By wetting the STM tip with 1 M KOH solutions or de-ionized water before the tip approached, and keeping the humidity higher than 40%, the electrochemical reaction occurred at the tip-surface gap while the electrochromic reactions took place at the film surface. With a constant negative sample bias and grounded tip, a brown color circle or a light blue disk was formed on the surface with an enlarged diameter. The circle and disk formations were attributed to the production of alkali and hydrogen tungsten bronzes. By applying a positive sample bias with a grounded tip, the color of the hydrogen tungsten bronze could be bleached. The cathodic reduction of W6+ forms a color center at the W5+ site, while the anodic reaction removes an electron from the color center W5+ state. Raman spectroscopy indicated that for the colored state, the frequency for the W-O bond stretching mode increased, while for the WO bonds it decreased.

Original languageEnglish (US)
Pages (from-to)440-443
Number of pages4
JournalJournal of Applied Physics
Issue number1
StatePublished - Jan 1 2002
Externally publishedYes

ASJC Scopus subject areas

  • Physics and Astronomy(all)

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