The inelastic scattering of the primary electrons in the crystal leads to the emission of secondary electrons, Auger electrons and X-rays, which in turn can scatter as well, which leads to up to 103 secondary electrons per incident electron.[1]

Sketch of a cathodoluminescence system: The electron beam passes through a small aperture in the parabolic mirror which collects the light and reflects it into the spectrometer. A charge-coupled device (CCD) or photomultiplier (PMT) can be used for parallel or monochromatic detection, respectively. An electron beam-induced current (EBIC) signal may be recorded simultaneously. Credit: Pv42.{{free media}}
Color cathodoluminescence overlay on a scanning electron microscope (SEM) image of an InGaN polycrystal, where the blue and green channels represent real colors and the red channel corresponds to UV emission. Credit: FDominec.{{free media}}

These secondary electrons can excite valence electrons into the conduction band when they have a kinetic energy about three times the band gap energy of the material .[2]

The primary advantages to the electron microscope based technique is its spatial resolution, where the attainable resolution is on the order of a few ten nanometers,[3] while in a (scanning) transmission electron microscope, nanometer-sized features can be resolved.[4]

An optical cathodoluminescence microscope benefits from its ability to show actual visible color features directly through the eyepiece, where more recently developed systems try to combine both an optical and an electron microscope to take advantage of both these techniques.[5]

Cathodoluminescence performed in electron microscopes is also being used to study surface plasmon resonances in metallic nanoparticles.[6] Surface plasmons in metal nanoparticles can absorb and emit light, though the process is different from that in semiconductors. Similarly, cathodoluminescence has been exploited as a probe to map the local density of states of planar dielectric photonic crystals and nanostructured photonic materials.[7]

See also edit

References edit

  1. Mitsui, T; Sekiguchi, T; Fujita, D; Koguchi, N. (2005). "Comparison between electron beam and near-field light on the luminescence excitation of GaAs/AlGaAs semiconductor quantum dots". Jpn. J. Appl. Phys. 44 (4A): 1820–1824. doi:10.1143/JJAP.44.1820. 
  2. Klein, C. A. (1968). "Bandgap dependence and related features of radiation ionization energies in semiconductors". J. Appl. Phys. 39 (4): 2029–2038. doi:10.1063/1.1656484. 
  3. Lähnemann, J.; Hauswald, C.; Wölz, M.; Jahn, U.; Hanke, M.; Geelhaar, L.; Brandt, O. (2014). "Localization and defects in axial (In,Ga)N/GaN nanowire heterostructures investigated by spatially resolved luminescence spectroscopy". J. Phys. D: Appl. Phys. 47 (39): 394010. doi:10.1088/0022-3727/47/39/394010. 
  4. Zagonel (2011). "Nanometer Scale Spectral Imaging of Quantum Emitters in Nanowires and Its Correlation to Their Atomically Resolved Structure". Nano Letters 11 (2): 568–73. doi:10.1021/nl103549t. PMID 21182283. 
  5. "What is Quantitative Cathodoluminescence?". 2013-10-21. Retrieved 2013-10-21.
  6. García de Abajo, F. J. (2010). "Optical excitations in electron microscopy". Reviews of Modern Physics 82 (1): 209–275. doi:10.1103/RevModPhys.82.209. 
  7. Sapienza, R.;Coenen, R.; Renger, J.; Kuttge, M.; van Hulst, N. F.; Polman, A (2012). "Deep-subwavelength imaging of the modal dispersion of light". Nature Materials 11 (9): 781–787. doi:10.1038/nmat3402. PMID 22902895. 

External links edit

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