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Sally Jiao, 2018, Chemical and Biological Engineering

Crystallization of Thin Films Under Spatial Confinement
Loo Group, Chemical and Biological Engineering Department, Princeton University, Princeton, NJ
Lynn Loo, Professor, Chemical and Biological Engineering

In organic semiconductors, charge is transported from molecule to molecule along conjugated backbones. Understanding how various factors affect the arrangement of these molecules (i.e. how they crystallize) can help us build more efficient organic electronic devices. To that end, I researched the thin-film crystallization of TES-ADT (triethylsilylethynyl anthradithiophene), an organic semiconductor. TES-ADT films are disordered upon spincoating, but crystallize upon exposure to 1,2-dichloroethane vapor. My project focused on probing the relationship between the thickness of a TES-ADT film and its crystallization growth rate and nucleation density. I found no nucleation in films less than 50 nm, instantaneous nucleation with 0.3 nuclei/mm^2 in films 50-130 nm, and progressive nucleation with 1.6 nuclei/mm^2 in films 130-300 nm. I also found that the growth rate increases linearly with thickness across the whole range of film thicknesses tested. Tuning the film thickness could thus be an important tool in producing patterned films with desired properties for electronic device applications. In addition to developing and practicing the practical lab skills needed to carry out the experiments, I discovered the importance of meticulousness and patience in an academic lab setting. This internship reinforced my interest in materials science research with real world applications.