Open Access

Andreas Schaller

• The spatially controlled attachment of crystals on a prepared surface is of major concern in current research fields such as biomineralization and metal-organic frameworks (MOF). In both cases substrate preparation mostly employs established self-assembled monolayers (SAM) to generate a surface with specific chemical moieties. However, recently it was shown that plasma-enhanced chemical vapor deposition (PE CVD) can also be used to produce thin coatings with tunable surface chemistry suitable for crystallization experiments. This work connects three main subjects: plasma coatings deposited via PE CVD and the site-selective synthesis of calcium carbonate and metal-organic frameworks. First several modifications of the employed plasma deposition device were necessary to improve the chemical properties of the plasma coatings – mainly the hydrophobicity. The basic coating consists of two subsequent layers, the first layer is made of propionic acid and the second layer is deposited fromThe spatially controlled attachment of crystals on a prepared surface is of major concern in current research fields such as biomineralization and metal-organic frameworks (MOF). In both cases substrate preparation mostly employs established self-assembled monolayers (SAM) to generate a surface with specific chemical moieties. However, recently it was shown that plasma-enhanced chemical vapor deposition (PE CVD) can also be used to produce thin coatings with tunable surface chemistry suitable for crystallization experiments. This work connects three main subjects: plasma coatings deposited via PE CVD and the site-selective synthesis of calcium carbonate and metal-organic frameworks. First several modifications of the employed plasma deposition device were necessary to improve the chemical properties of the plasma coatings – mainly the hydrophobicity. The basic coating consists of two subsequent layers, the first layer is made of propionic acid and the second layer is deposited from n-heptane. The resulting coatings were then characterized in detail and the improvements were verified by biomimetic crystallization experiments with calcium carbonate. Calcite was grown site-selectively on a multilayer plasma polymer coating featuring an alternating hydrophobic and hydrophilic pattern, which is introduced by UV lithographic etching. Through the etching process the upper, hydrophobic layer is removed from fixed spots revealing the hydrophilic layer underneath. Incorporating a third layer, which works as a coupling agent layer between the inorganic substrate and the subsequent plasma polymer layer, further improves the properties of the multilayer plasma coatings. These coatings possess sufficient chemical stability to endure the harsh reaction conditions which are required for solvothermal MOF synthesis. Hence, MFU-4 and MFU-4l are grown site-selectively on two multilayer plasma polymer substrates, having different hydrophobic top layers deposited from either n-heptane or from trifluoromethane. Analysis of the MOF crystals reveals that the MFU-4l crystals adhere preferentially with <1 0 0> orientation on the surface. Further investigations lead to a model concept of the MOF crystals attaching to the substrate surface.…