page_title: Scanning electron microscope
section_title: Cathodoluminescence
hierarchical_section_title: Scanning electron microscope / Cathodoluminescence
caption_attribution_description: English: Indium-gallium nitride is a semiconductor alloy that emits light when irradiated by energetic particles. A small crystal cluster has accidentally grown during the w:MOVPE process. The lightness corresponds to its standard w:SEM image, whereas the colour overlayers were added according to the light emitted under the electron beam. Blue and green channels are roughly natural colours, while red encodes the ultraviolet emission. The image demonstrates that InGaN/GaN structures are highly anisotropic, and so are their cathodoluminescence properties.Image taken in the Institute of Physics, Czech Academy of Sciences, using Philips XL30 ESEM equipped with custom color-resolved cathodoluminescence photomultiplier setup. Author acknowledges the great help of R. Horešovksý. Čeština: Nitrid india a gallia je polovodičová slitina, která jasně svítí při dopadu částic ionizujícího záření. Drobná krystalová drúza vznikla omylem během růstu metodou w:cz:MOVPE. Světlost odpovídá obvyklému elektronovému w:SEM obrazu, zatímco barevné vrstvy byly přeloženy na základě světla emitovaného pod elektronovým paprskem. Modrý a zelený kanál odpovídají zhruba přirozeným barvám, kdežto červený kanál odpovídá ultrafialovému záření. Obrázek ukazuje silnou anizotropii struktur na bázi InGaN, která se projevuje i na jejich katodoluminiscenčním chování.
context_page_description: A scanning electron microscope is a type of electron microscope that produces images of a sample by scanning the surface with a focused beam of electrons. The electrons interact with atoms in the sample, producing various signals that contain information about the surface topography and composition of the sample. The electron beam is scanned in a raster scan pattern, and the position of the beam is combined with the intensity of the detected signal to produce an image. In the most common SEM mode, secondary electrons emitted by atoms excited by the electron beam are detected using a secondary electron detector. The number of secondary electrons that can be detected, and thus the signal intensity, depends, among other things, on specimen topography. SEM can achieve resolution better than 1 nanometer.
  Specimens are observed in high vacuum in conventional SEM, or in low vacuum or wet conditions in variable pressure or environmental SEM, and at a wide range of cryogenic or elevated temperatures with specialized instruments.
context_section_description: Cathodoluminescence, the emission of light when atoms excited by high-energy electrons return to their ground state, is analogous to UV-induced fluorescence, and some materials such as zinc sulfide and some fluorescent dyes, exhibit both phenomena. Over the last decades, cathodoluminescence was most commonly experienced as the light emission from the inner surface of the cathode ray tube in television sets and computer CRT monitors. In the SEM, CL detectors either collect all light emitted by the specimen or can analyse the wavelengths emitted by the specimen and display an emission spectrum or an image of the distribution of cathodoluminescence emitted by the specimen in real color.
caption: Color cathodoluminescence overlay on SEM image of an InGaN polycrystal. The blue and green channels represent real colors, the red channel corresponds to UV emission.
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