Novel Nano-OLED Based Probes for Very High Resolution Optical Microscopy.
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Abstract
Near-field scanning optical microscopy (NSOM) has been applied in the study of
nanomaterials, microelectronics, photonics, plasmonics, cells, and molecules. However,
conventional NSOM relies on optically pumped probes, suffering low optical transmission,
heating of the tip, and poor reproducibility of probe fabrication, increasing the cost,
impeding usability, reducing practical imaging resolution, and limiting NSOM’s utility.
In this thesis, I demonstrate a novel probe based on a nanoscale, electrically
pumped organic light-emitting device (OLED) formed on the tip of a low-cost, commercially
available atomic force microscopy (AFM) probe. I describe the structure, fabrication,
and principles of this novel probe’s operation, and discuss its potential to overcome
the limitations of conventional NSOM probes. The broader significance of this work in
the field of organic optoelectronics is also discussed.
Briefly, OLEDs consist of organic thin films sandwiched between two electrodes.
Under bias, electrons and holes are injected into the organic layers, leading to radiative
recombination. Depositing a small molecular OLED in vacuum onto a pyramid-tipped
AFM probe results in a laminar structure that is highly curved at the tip. Simple electrical
modeling predicts concentration of electric field and localized electron injection into the
organic layers at the tip, improving the local charge balance in an otherwise electronstarved
OLED. Utilizing an “inverted” OLED structure (i.e. cathode on the “bottom”),
light emission is localized to sub-200 nm sized, green light emitting regions on probe verxxv
tices; light output power in the range of 0.1-0.5 nanowatts was observed, comparable to
that of typical fiber based NSOM probes but with greater power efficiency. Massive arrays
of similar sub-micron OLEDs were also fabricated by depositing onto textured silicon
substrates, demonstrating the superior scalability of the probe fabrication process
(e.g. relative to pulled glass fibers).
The investigation of the effect of non-planar substrate geometry on charge injection,
transport and recombination provides broader insights into OLEDs made on rough
substrates, general understanding of OLED operation (e.g. filamentary charge conduction)
and degradation, and potentially helps to improve technologically important “inverted”
OLED structures.PhDMaterials Science and EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/77725/1/yiyingz_1.pd