Electrochromic writing and erasing on tungsten oxide films in air by scanning tunneling microscopy
Qiu, H. Lu, Y.F. Mai, Z.H.
Qiu, H.
Mai, Z.H.
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Abstract
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. © 2002 American Institute of Physics.
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Journal of Applied Physics
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Date
2002-01-01
DOI
10.1063/1.1424053
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Article