Nanoscale optical tomography with cathodoluminescence spectroscopy

Journal name:
Nature Nanotechnology
Year published:
Published online


Tomography has enabled the characterization of the Earth's interior, visualization of the inner workings of the human brain, and three-dimensional reconstruction of matter at the atomic scale. However, tomographic techniques that rely on optical excitation or detection are generally limited in their resolution by diffraction. Here, we introduce a tomographic technique—cathodoluminescence spectroscopic tomography—to probe optical properties in three dimensions with nanometre-scale spatial and spectral resolution. We first obtain two-dimensional cathodoluminescence maps of a three-dimensional nanostructure at various orientations. We then use the method of filtered back-projection to reconstruct the cathodoluminescence intensity at each wavelength. The resulting tomograms allow us to locate regions of efficient cathodoluminescence in three dimensions across visible and near-infrared wavelengths, with contributions from material luminescence and radiative decay of electromagnetic eigenmodes. The experimental signal can be further correlated with the radiative local density of optical states in particular regions of the reconstruction. We demonstrate how cathodoluminescence tomography can be used to achieve nanoscale three-dimensional visualization of light–matter interactions by reconstructing a three-dimensional metal–dielectric nanoresonator.

At a glance


  1. Metal–dielectric crescents.
    Figure 1: Metal–dielectric crescents.

    a, Schematic of a crescent consisting of a polystyrene (PS) core and a Au shell. b, Bright-field TEM image of an individual crescent. c, Wide-field TEM image of crescents.

  2. Cathodoluminescence line scans.
    Figure 2: Cathodoluminescence line scans.

    a, Schematic of the cathodoluminescence (CL) line scan, with the beam passing through the central z axis of the crescent (θ is the angle between the crescent's axis of symmetry and the electron beam). b, Experimental cathodoluminescence line scan of a crescent oriented at 90°, with darker colours corresponding to higher beam positions, as indicated in a. c, Cross-section of the scattered electric field intensity calculated by FDTD simulations for excitation with an x-polarized plane wave propagating in the −z direction at a wavelength of 874 nm (the peak in the extinction efficiency). d, Experimental sinogram of normalized cathodoluminescence intensity line scans at a wavelength of 850 nm for crescents at various angles, where the vertical axis corresponds to the excitation positions shown schematically in a. Owing to the reflection symmetry of the crescent, data from 0° to 165° are flipped and repeated for angles of 195° to 360°. A crescent at 180° was not available. The dashed-line overlay denotes the physical position of the centre of the gap between the tips of the crescent, derived from the crescent model.

  3. Two-dimensional cathodoluminescence maps.
    Figure 3: Two-dimensional cathodoluminescence maps.

    a, Schematics of crescents with orientations of (i) 90°, (ii) 120° and (iii) 150°. b, SEM images of crescents. c, Two-dimensional maps of the normalized cathodoluminescence (CL) intensity of crescents at a wavelength of 850 nm. Scale bar, 100 nm (all images).

  4. Three-dimensional TEM and cathodoluminescence reconstructions.
    Figure 4: Three-dimensional TEM and cathodoluminescence reconstructions.

    a, TEM tomogram based on a single projection. Panels (i) to (iv) correspond to different cross-sections through the reconstruction, as indicated by the coloured outlines. Panel (i) shows an xz cross-section of the reconstruction at the midpoint of the crescent, where the metal shell and the crescent geometry can be distinctly resolved. Panel (ii) shows an off-centre xz cross-section of the reconstruction for comparison. Panel (iii) is a horizontal xy cross-section of the reconstruction at the z position where the crescent tips come to a point, and panel (iv) is a xy cross-section of the reconstruction at the midpoint of the crescent, clearly showing the metal shell surrounding the inner core. b, Cathodoluminescence (CL) tomogram at 850 nm based on a single cathodoluminescence map (reconstruction in xy planes). c, Cathodoluminescence tomogram at 850 nm based on an experimental tilt series consisting of seven crescents (reconstruction in xz planes).

  5. Axial voxel cathodoluminescence spectra.
    Figure 5: Axial voxel cathodoluminescence spectra.

    a, Schematic of voxel positions within the crescent along its central axis. Darker colours correspond to higher z positions. b, Total Purcell factor (average of x, y and z components) calculated with FDTD (right axis), and average photoluminescence (PL) spectra of six individual crescents excited at 488 nm (blue curve, left axis). c, Voxel spectra from cathodoluminescence (CL) reconstruction based on a single cathodoluminescence map (reconstruction in xy planes). d, Voxel spectra from cathodoluminescence reconstruction based on an experimental tilt series consisting of seven crescents (reconstruction in xz planes).

  6. Cathodoluminescence spectroscopic tomography.
    Figure 6: Cathodoluminescence spectroscopic tomography.

    ah, Reconstructed cathodoluminescence (CL) signal based on a single cathodoluminescence map (reconstruction in xy planes) at different wavelengths. The reconstructed intensity corresponds to both the colour scale and the transparency of the figure. Scale bar, 100 nm (all images).


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Author information


  1. Department of Materials Science and Engineering, Stanford University, Stanford, California 94305, USA

    • Ashwin C. Atre,
    • Aitzol García-Etxarri &
    • Jennifer A. Dionne
  2. Center for Nanophotonics, FOM Institute AMOLF, Science Park 104, Amsterdam 1098 XG, The Netherlands

    • Benjamin J. M. Brenny,
    • Toon Coenen &
    • Albert Polman


A.C.A. fabricated samples and performed transmission electron microscopy, photoluminescence spectroscopy, tomographic reconstruction and electromagnetic simulations. A.C.A., B.J.M.B. and T.C. performed the cathodoluminescence microscopy, spectroscopy and scanning electron microscopy. A.G-E. performed boundary element method simulations. J.A.D. and A.P. guided and supervised the experiments and analysis. All authors analysed and interpreted the results and edited the manuscript.

Competing financial interests

A.P. is co-founder and co-owner of Delmic BV, a startup company that is developing a commercial product based on the cathodoluminescence system used in this work.

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