HKUST-1 Thin Film Layer-by-Layer Liquid Phase Epitaxial Growth: Film Properties and Stability Dependence on Layer Number

The layer-by-layer epitaxial growth of HKUST-1 (Cu3(btc)2 where btc = 1,3,5-benzenetricarboxylate) thin films is measured by quartz crystal microbalance with dissipation monitoring (QCM-D), X-ray diffraction (XRD), and scanning electron microscopy (SEM) as a function of the number of layers (20–80 layers) for −OH and −COOH functionalized surfaces. Up to approximately 40 layers, the film growth proceeds by a layer-by-layer mode controlled by the chemical functionalization of the surface. For example, on hydroxylated SiO2, film growth is in the preferred [222] direction. Beyond 40 layers, for both −COOH and −OH functionalized surfaces, the crystallite grain size increases and ∼50–100 nm octahedral crystals are formed. Independent of the surface functional groups (−COOH and −OH), the octahedral crystals form with the {200} planes oriented parallel to the surface. By monitoring changes in mass and dissipation, the QCM data provides evidence for the change in growth behavior. The stability of the films, determ...