Research Description:

RSOXS
Resonant soft X-ray scattering (RSOXS) is a useful new technique for characterizing the in-plane order in block copolymer thin films. In classical scattering of light, X-rays, or neutrons the relationship between the transmitted and incident beam fluxes Jx and J0 is given by Beer’s law:

where T is the transmission coefficient, µ is the absorption coefficient, and t the sample thickness. The optimal value of ?t for X-ray and neutron scattering experiments is unity; i.e. t=1/?. Samples with smaller thicknesses are sub-optimal due to lack of encounters between the incident beam and the scattering centers in the sample, while the incident and/or scattered beams from samples with larger thicknesses are heavily attenuated before they reach the detector.

The resonant enhancement in scattering intensity makes RSOXS a valuable for tool for characterization of lateral order in block copolymer thin films. By tuning X-rays to the absorption edge of a given chemical species in one of the block copolymer segments, sufficient scattering intensity is obtained to overcome the loss in scattering intensity associated with decreased sample thickness in thin film samples. This scattering intensity enhancement is caused by an abrupt change in the energy-dependent complex refractive index at an absorption edge. The relative difference between the complex refractive index of the two block copolymer segments at a given X-ray energy dramatically affects the resonant scattering intensity enhancement available at an adsorption edge.

Caption: A) Molecular orbital diagram of excitation of carbon K edge electron into ?* anti-bonding orbital. This excitation is the basis for the large increase in scattering intensity available at ?* resonances. B) RSOXS at the carbon K edge of a 50 nm PS-b-PI thin film. The indexed peaks (q*, v3q* and 2q*) confirm hexagonal packing of PS spheres in the PI matrix.

 

Organic Light Emitting Diode (OLED) Devices from Triplet Emitters
Self-assembly of a non-conjugated bipolar transport material is being studied as a first step in understanding the block copolymer structure to device performance relationship in OLED devices. By incorporating different electroactive functionalities into each block, the structure of hole and electron transporting regions can be controlled through self-assembly on the 10 nm length scale of exciton diffusion. Future work will incorporate recently developed Pt/Ir phosphorescent emitters in order to improve the conversion of charge carriers to useful light.

Caption: A) Scanning force micrograph of a cylinder-forming non-conjugated bipolar transport diblock copolymer self-assembled via solvent annealing in a thin film form. B) Transmission electron micrograph of a lamellae-forming non-conjugated bipolar transport diblock copolymer self-assembled via solvent casting in a bulk form.

 
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