Observation of Filamentous Nanostructures in Organic-Inorganic Composite Thin Films Deposited by Co-Evaporation

• Published in: Advanced functional materials 2013-05, Vol.23 (17), p.2130-2136
• Main Authors: Donhauser, Daniela, Pfannmöller, Martin, Dieterle, Levin, Schultheiß, Katrin, Schröder, Rasmus R., Kowalsky, Wolfgang, Kröger, Michael
• Format: Article
• Language: English
• Subjects: Agglomeration; composites; doping; Evaporative cooling; Filaments; Nanocomposites; Nanomaterials; Nanostructure; nanostructures; organic electronics; Thin films; Three dimensional; transmission electron microscopy
• ISSN: 1616-301X; 1616-3028
• DOI: 10.1002/adfm.201202089

Nanostructures are important for a wide area of applications, but are very often difficult to fabricate. A novel and basic approach for controlled nanofilament growth in an organic/inorganic composite material is demonstrated. Thin films of MoO3‐doped 4′‐bis(N‐carbazolyl)‐1,1′‐biphenyl are grown via vacuum sublimation and analyzed using advanced electron microscopy and spectroscopy techniques. Using electron spectroscopic imaging in the core‐loss and low‐loss regime, MoO3 agglomerations are identified for different doping concentrations. A 3D reconstruction of the thin film yielded by electron tomography reveals a filamentous structure of MoO3 within the organic matrix. These filaments are preferentially oriented along the growth direction and are only a few nanometers in diameter. Furthermore, control of the filament growth is possible by changing the substrate temperature because for composites grown on substrates cooled to 120 K MoO3 agglomeration cannot be detected. Organic‐inorganic composites fabricated via co‐evaporation of two materials reveal a filamentous nanostructure with filaments preferentially oriented perpendicular to the substrate plane. This growth process can be controlled by changing the substrate temperature so that for films evaporated on cooled substrates no filament growth can be detected.