Final Activity Report Summary - NANOBIOSIC (Atomic structure, selectivity and nanostructuring of biomolecules on Silicon Carbide surfaces)
Nanometer-scale patterning of surfaces is a topic of growing interest for a broad variety of potential applications, ranging from selective host-guest interactions, molecular sensing and catalysis to magnetic surface layers. The self-assembly of semiconductor or organic molecule ligands to achieve such nano-architectures is a very attractive strategy, both for its efficiency as well as for the high structural quality that can be achieved. The interaction of bio-related molecules on silicon carbide surfaces, the development of molecular nanostructures and the study of their atomic and electronic properties under the aspect of future biotechnology and medical applications of silicon carbide (SiC) were the main goal of this proposal.
We recently discovered a successful method to prepare a homogeneous large area graphene layer on the SiC(0001) surface, which no one had succeeded to construct earlier. Graphene was a single layer of graphite and had unique electronic and magnetic properties in comparison to bulk graphite. This opened up possibilities and opportunities for graphene-SiC based electronic devices. Surface patterning lithography of large area graphene was also possible since the graphene surface was very inert in the atmospheric ambient and had good chemical resistance. Because of its intriguing electronic properties, graphene was also of interest for sensor applications and studies of adsorption phenomena ranging from atoms to biomolecules.
In addition, we discovered that arrays of silicon (Si) nanowires could be formed by Si deposition on to SiC(1-102) substrates at temperatures in the 830 °C to 900 °C range and that they produced a two times one surface reconstruction. A surface state originating from these Si nanowires was revealed and a one-dimensional behaviour was observed, since dispersion was demonstrated only along the Si chains but not in the perpendicular direction. Based on our experimental findings a structural model for this two times one reconstructed surface could be suggested, which contained alternating stripes of Si adatom rows and double bonded Si dimers. This Si nanowire array could be used as a future template for synthesising metallic or molecular chain structures on top of a large band gap semiconductor with possible applications in nano-sized devices or biological sensors.
Studies of organic molecules on metal surface, such as (2)catenane on Ag(111), were also performed, in collaboration with other research groups. The (2)catenane consisted of interlocked cyclic components and represented a promising candidate for the development of nanoscale mechanical and electronic devices. The interlocked parts might undergo relative rotations, or motions, through external stimuli, such as modifications of the chemical potential or light exposures. This system was therefore selected for studies and was successfully deposited on Ag(111) surfaces at a relatively high substrate temperature without chemical degradation. Once the (2)catenane molecules were adsorbed on the Ag(111) surface an in situ copper (Cu) complexation induced a complete rearrangement of the system. The two interlocking rings of the compound could glide within one another to completely accommodate the rearranged species. This study exemplified a first step towards molecular mechanical machines working at surface supports. Studies of tetracyanoquinodimethane (TCNQ) on Cu(100) and collaborative studies of TMA adsorbed on Cu(110) were also carried out.
From the abovementioned experience we gained a perspective that we transferred onto SiC surfaces or graphene-SiC. This experience transfer was underway by the time of the project completion.
We recently discovered a successful method to prepare a homogeneous large area graphene layer on the SiC(0001) surface, which no one had succeeded to construct earlier. Graphene was a single layer of graphite and had unique electronic and magnetic properties in comparison to bulk graphite. This opened up possibilities and opportunities for graphene-SiC based electronic devices. Surface patterning lithography of large area graphene was also possible since the graphene surface was very inert in the atmospheric ambient and had good chemical resistance. Because of its intriguing electronic properties, graphene was also of interest for sensor applications and studies of adsorption phenomena ranging from atoms to biomolecules.
In addition, we discovered that arrays of silicon (Si) nanowires could be formed by Si deposition on to SiC(1-102) substrates at temperatures in the 830 °C to 900 °C range and that they produced a two times one surface reconstruction. A surface state originating from these Si nanowires was revealed and a one-dimensional behaviour was observed, since dispersion was demonstrated only along the Si chains but not in the perpendicular direction. Based on our experimental findings a structural model for this two times one reconstructed surface could be suggested, which contained alternating stripes of Si adatom rows and double bonded Si dimers. This Si nanowire array could be used as a future template for synthesising metallic or molecular chain structures on top of a large band gap semiconductor with possible applications in nano-sized devices or biological sensors.
Studies of organic molecules on metal surface, such as (2)catenane on Ag(111), were also performed, in collaboration with other research groups. The (2)catenane consisted of interlocked cyclic components and represented a promising candidate for the development of nanoscale mechanical and electronic devices. The interlocked parts might undergo relative rotations, or motions, through external stimuli, such as modifications of the chemical potential or light exposures. This system was therefore selected for studies and was successfully deposited on Ag(111) surfaces at a relatively high substrate temperature without chemical degradation. Once the (2)catenane molecules were adsorbed on the Ag(111) surface an in situ copper (Cu) complexation induced a complete rearrangement of the system. The two interlocking rings of the compound could glide within one another to completely accommodate the rearranged species. This study exemplified a first step towards molecular mechanical machines working at surface supports. Studies of tetracyanoquinodimethane (TCNQ) on Cu(100) and collaborative studies of TMA adsorbed on Cu(110) were also carried out.
From the abovementioned experience we gained a perspective that we transferred onto SiC surfaces or graphene-SiC. This experience transfer was underway by the time of the project completion.