Editing Cathodoluminescence (section)

=== Cathodoluminescence from a scanning electron microscope ===

[[File:Cl-scheme.svg|thumb|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.]]

[[File:AllalinDesign.png|thumb|Sketch of a cathodoluminescence objective inserted in a SEM column]]

In [[scanning electron microscope]]s a focused beam of electrons impinges on a sample and induces it to emit light that is collected by an optical system, such as an elliptical mirror.  From there, a [[optical fiber|fiber optic]] will transfer the light out of the microscope where it is separated into its component wavelengths by a [[monochromator]] and is then detected with a [[photomultiplier]] tube.  By scanning the microscope's beam in an X-Y pattern and measuring the light emitted with the beam at each point, a map of the optical activity of the specimen can be obtained (cathodoluminescence imaging). Instead, by measuring the wavelength dependence for a fixed point or a certain area, the spectral characteristics can be recorded (cathodoluminescence spectroscopy).  Furthermore, if the photomultiplier tube is replaced with a [[CCD camera]], an entire [[spectrum]] can be measured at each point of a map ([[hyperspectral imaging]]). Moreover, the optical properties of an object can be correlated to structural properties observed with the electron microscope.

The primary advantages to the electron microscope based technique is its spatial resolution. In a scanning electron microscope, the attainable resolution is on the order of a few ten nanometers,<ref>{{cite journal|doi=10.1088/0022-3727/47/39/394010|arxiv=1405.1507|bibcode=2014JPhD...47M4010L|title= Localization and defects in axial (In,Ga)N/GaN nanowire heterostructures investigated by spatially resolved luminescence spectroscopy
|journal=J. Phys. D: Appl. Phys.|volume=47|issue=39|pages=394010|year=2014|last1=Lähnemann|first1=J.|last2=Hauswald|first2=C.|last3=Wölz|first3=M.|last4=Jahn|first4=U.|last5=Hanke|first5=M.|last6=Geelhaar|first6=L.|last7=Brandt|first7=O.|s2cid=118314773 }}</ref> while in a (scanning) [[transmission electron microscope]] (TEM), nanometer-sized features can be resolved.<ref>{{cite journal|last1=Zagonel|title=Nanometer Scale Spectral Imaging of Quantum Emitters in Nanowires and Its Correlation to Their Atomically Resolved Structure|journal=Nano Letters|volume=11|issue=2|pages=568–73|year=2011|doi=10.1021/nl103549t|display-authors=etal|pmid=21182283|arxiv = 1209.0953 |bibcode = 2011NanoL..11..568Z |s2cid=18003378 }}</ref> Additionally, it is possible to perform nanosecond- to picosecond-level time-resolved measurements if the electron beam can be "chopped" into nano- or pico-second pulses by a beam-blanker or with a pulsed electron source. These advanced techniques are useful for examining low-dimensional semiconductor structures, such a [[quantum well]]s or [[quantum dots]].

While an electron microscope with a cathodoluminescence detector provides high magnification, an optical cathodoluminescence microscope benefits from its ability to show actual visible color features directly through the eyepiece. More recently developed systems try to combine both an optical and an electron microscope to take advantage of both these techniques.<ref>{{cite web
 |title        = What is Quantitative Cathodoluminescence?
 |url          = http://www.attolight.com/technology/cathodoluminescence-principles/
 |date         = 2023-08-23
 }}</ref>