Electrostatic Mechanism of Emission Enhancement in Hybrid Metal-semiconductor Light-emitting Heterostructures Page: 27
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Power-dependent PL simply entails using a neutral density filter mounted after
the doubler in Fig 3.5 to control the intensity of the laser incident on the sample. A
power meter was used to measure the incident power down to the nearest 0.1 mW. In
our experiments I varied the power between 1 and 100 mW.
3.6 Near-field PL
Near-field PL measurements involve measurements of the optical near-field
using either a fiber probe or a metal-coated AFM tip. The goal is to produce an optical
near-field at the end of the probe which can then interact directly with the sample. This
near-field is the evanescent field resulting from the interaction of photons with the metal-
coated AFM tip, or a sub-wavelength aperture in a metal-coated fiber probe. Due to the
nature of the optical near-field, there is no diffraction limit to the resolution of the
measurement, allowing sub-wavelength variations in emission properties of the sample
to be studied.
There are three possible "modes" of near-field measurement: illumination,
collection and illumination/collection. These refer to whether the excitation of the sample
and/or the measured spectrum is produced via near-field interaction with the sample.
Illumination mode involves excitation of the sample via a near-field source, and then
measurement of the resultant far-field emission from the sample. Collection involves
collection via near-field interaction of the emission resulting from excitation of the
sample using far-field illumination. Illumination/collection mode, then, involves both
illumination and collection in the near-field. Fiber-probe-based NSOM is capable of all
three modes of operation, but suffers in topographical resolution due to the size of the
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Llopis, Antonio. Electrostatic Mechanism of Emission Enhancement in Hybrid Metal-semiconductor Light-emitting Heterostructures, dissertation, May 2012; Denton, Texas. (digital.library.unt.edu/ark:/67531/metadc115113/m1/37/: accessed February 23, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; .