Research ArticlePHYSICS

Water nanostructure formation on oxide probed in situ by optical resonances

See allHide authors and affiliations

Science Advances  25 Oct 2019:
Vol. 5, no. 10, eaax6973
DOI: 10.1126/sciadv.aax6973
  • Fig. 1 The evanescent field of resonant light in a microtube cavity is sensitive to surface molecular layers and/or nanoclusters.

    (A) The bottom panel shows schematically a microtube cavity being excited by a laser beam. The top panel shows a schematic of resonant light propagating in the tube wall and the surface molecular layer, being scattered by molecular clusters. (B) Measured optical resonant mode spectrum labeled by mode numbers m = 36 to 39. The inset shows an individual mode where the mode shift characterizes the thickness of the molecular layer, and the variation of the mode width (δλ) characterizes the light scattering by the surface clusters. (C) Electric field profile of mode m = 38 taken to quantify the resonant mode shift induced by adsorbed molecular layers. a.u., arbitrary units.

  • Fig. 2 Evolution of resonant mode position throughout the water layer growth and desorption processes.

    (A) Optical mode (m = 38) shift during water layer growth (blue plus symbols) and desorption (red cross symbols) processes triggered by decreasing and increasing the temperature, respectively. The adsorption/desorption rate deduced from the differential derivative of the adsorption/desorption curve is shown in the left-bottom/right-top inset. (B) Mode (m = 38) shift induced by surface water layer (h) calculated by perturbation theory. The insets show the schematic of the resonant mode shift (top left) due to the presence of a molecular layer on the tube surface (bottom right).

  • Fig. 3 Water layer growth dynamics probed during decreasing system temperature.

    (A) Four regions (I to IV) are identified by the comparison between Q factor variation (blue triangle symbols) and mode shift (black dashed line). The error bars represent the SEs in fitting the mode measured at different temperatures. The inset (top) shows a schematic of nanoclusters and planar layer formed by the same amount of adsorbed molecules. While the two morphologies result in the same spectral mode shift, the nanoclusters lead to a broadened peak (decreased Q factor), and the smoothing planar layer results in a narrowed peak (increased Q factor). (B) Free energy in nanocluster (red curve) and planar (green curve) morphology as a function of average layer thickness. The adsorption selects the growth mode with the lowest energy in each region. Schematic of the water layer structure in region II (clustering growth), region III (turning to planar growth after reaching the transition point), and region IV (formation of a planar layer).

  • Fig. 4 Water layer desorption dynamics probed during increasing system temperature.

    (A) Four regions (I′ to IV′) are identified by the comparison between Q factor variation (red triangle symbols) and mode shift (black dashed line). The error bars represent the SEs in fitting the mode measured at different temperatures. The inset shows a nonlinear mode shift in the range of 80 to 140 K. (B) Upon heating up, the water film rearranges from the planar morphology in region IV′ to the cluster morphology in region III′ and eventually desorbs in region II′.

  • Fig. 5 Overview of water layer dynamics in the growth and desorption processes.

    The dynamics of water layer growth/desorption processes are detected in situ over different temperature regimes. RT, room temperature.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/5/10/eaax6973/DC1

    Section S1. Perturbation theory analysis

    Section S2. Quality factor variation versus surface roughness

    Section S3. Surface morphology of HfO2

    Fig. S1. Measured and simulated WGM resonances in a microtubular cavity.

    Fig. S2. Quality factor variation (QT/Q0) as a function of surface roughness.

    Fig. S3. Surface morphology of HfO2 characterized by SEM and AFM.

    Reference (35)

  • Supplementary Materials

    This PDF file includes:

    • Section S1. Perturbation theory analysis
    • Section S2. Quality factor variation versus surface roughness
    • Section S3. Surface morphology of HfO2
    • Fig. S1. Measured and simulated WGM resonances in a microtubular cavity.
    • Fig. S2. Quality factor variation (QT/Q0) as a function of surface roughness.
    • Fig. S3. Surface morphology of HfO2 characterized by SEM and AFM.
    • Reference (35)

    Download PDF

    Files in this Data Supplement:

Stay Connected to Science Advances

Navigate This Article