Research ArticleChemistry

Backside absorbing layer microscopy: Watching graphene chemistry

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Science Advances  12 May 2017:
Vol. 3, no. 5, e1601724
DOI: 10.1126/sciadv.1601724
  • Fig. 1 Principle of BALM and example of images of 2D materials.

    (A) Representation of the BALM geometry: The image is obtained in reflected light microscopy; immersion oil avoids parasitic reflections between the objective and the transparent window. The near-ARA layer (here, a gold layer) is represented in yellow. The contrast is enhanced for the part of the sample that is very close to the surface and the half-space on the top remains accessible. (B) The AR property of a layer comes from the interferences between all reflected beams, as shown on the three schemes representing different situations for AR layers at the air/glass interface. From left to right: nonabsorbing AR layer (i), absorbing AR layer lighted from air (ii), and absorbing AR layer lighted from the glass (iii). In the first case (i), the AR condition is obtained for a layer of thickness of one-quarter of the wavelength (so-called quarter-wave layer). In the second case (ii), for the absorbing layer, it was previously shown that the layer must be thicker than quarter-wave (3638); with highly absorbing materials, the absorption by the layer becomes so high that the light cannot reach the lower interface anymore and the destructive interferences are lost. In the third case (iii), by contrast, we demonstrate in the Supplementary Materials that the thickness of AR must be sub–quarter-wave and must become thinner as the layer material becomes more absorbing; the overall absorption of the layer remains low, and the light can always go through. Therefore, only the third configuration allows to make AR layers out of strongly absorbing materials. (C) BALM image of GO deposited on near-ARA and imaged in air (green channel, full contrast). Inset: Light intensity as a function of the number of layers. a.u., arbitrary units. (D) BALM image of GO obtained in water (RGB image with topographical representation of the total reflected intensity). (E and F) Images realized in air of MoS2 and MoS2 on GO; GO is still observable by transparency under the MoS2 crystals. The purple structures on the MoS2 triangles correspond to multilayers that start to grow on the monolayers.

  • Fig. 2 Contrast between GO and r-GO.

    (A) BALM image of r-GO flakes. (B and C) BALM images (red channel) of r-GO flakes with GO deposited on top. (D) Light intensity profile showing GO and r-GO from (C).

  • Fig. 3 Adsorption of Fe3O4 nanoparticles on r-GO.

    BALM images of r-GO (green channel and color scale “orange hot” of ImageJ software) flakes before (A) and after (B) the deposition of the 5-nm Fe3O4 nanoparticles. The particles tend to accumulate along the wrinkles of the r-GO flakes. (C) BALM image after rinsing the nanoparticles. (D) Enlargement of the area enclosed in blue rectangle in (B) showing the nanoparticle distribution along the wrinkles of r-GO.

  • Fig. 4 Adsorption kinetics of a pyrene derivative on GO.

    (A to D) Evolution of intensity upon trimethyl-(2-oxo-2-pyrene-1-yl-ethyl)-ammonium bromide adsorption and intercalation [extracted from each image from the red channel on different areas of the gold surface and of the mono-, bi-, and trilayers as a function of time (black dots) and fit of the curves using an exponential decay function (red lines)]. (E) Raw RGB image of the GO flakes and areas used to extract the plotted data. (F to H) Plot of the fit parameters of the exponential decay function Yn(t) = Yn(0) + An[1 − exp(−tn)]. Red lines in (F) and (G) are linear fits.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/3/5/e1601724/DC1

    Demonstration of the formulae for antireflective layers made of absorbing materials

    fig. S1. BALM-coupled electrochemical setup for real-time imaging of the electrochemical deposition of copper.

    fig. S2. Comparison between BALM, AFM, and SEM images of GO.

    fig. S3. Additional example of the difference of contrast between GO and r-GO.

    fig. S4. Numerical simulations of contrast and intensity change of various stacks of GO/r-GO on an Au layer.

    fig. S5. Images of the deposition and washing of nanoparticles on graphene.

    fig. S6. Original image of the GO flakes used for pyrene adsorption experiments.

  • Supplementary Materials

    This PDF file includes:

    • Demonstration of the formulae for antireflective layers made of absorbing materials
    • fig. S1. BALM-coupled electrochemical setup for real-time imaging of the electrochemical deposition of copper.
    • fig. S2. Comparison between BALM, AFM, and SEM images of GO.
    • fig. S3. Additional example of the difference of contrast between GO and r-GO.
    • fig. S4. Numerical simulations of contrast and intensity change of various stacks of GO/r-GO on an Au layer.
    • fig. S5. Images of the deposition and washing of nanoparticles on graphene.
    • fig. S6. Original image of the GO flakes used for pyrene adsorption experiments.

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