C: Molecular Nanostructures

Top-down semiconductor fabrication has reached the 14-nm-node. Smaller functional structures necessitate radically different materials/approaches. As an example, a collaboration between CFN Research Areas B and C recently demonstrated bridging of sub-5nm gaps in metallic single-walled carbon nanotubes (SWNT) with single electroluminescent molecules. Existing methods now allow the positional mapping of every atom in such a device. The fabrication of arrays of functional molecular nanodevices with positional control to within atomic dimensions has advanced to a realistic mid-term goal. Research area C contributes to realizing this vision by designing, preparing and characterizing nanosystems/devices based on molecular building blocks with size-tunable and addressable primary functions – in particular electrical, optical/photonic, magnetic, mechanical/structural, and chemical.

Arguably, large-scale molecular fabrication will still rely on semiconductor chip fabrication methods. Therefore building blocks should ideally be sublimable and stable at elevated temperatures. However, some of the most promising molecular structures can only be processed in (contamination prone) liquids. Nevertheless, even the semiconductor industry is beginning to experiment with solution/dispersion processing steps for fabrication on length scales below 10 nm. Overall, size-tunable, homologous series of chemically inert molecules that can be processed both in solution and gas-phase appear particularly attractive as building blocks. Some of the most obvious candidates are the sp²-nanocarbons (e.g., fullerenes and carbon nanotubes). However, the periodic table provides essentially limitless opportunities for improvement. Therefore, we design, synthesize, and characterize new functional molecules (e.g., homologous series of luminescent clusters).

The past years have seen proof-of-principle demonstrations of molecular devices, which realize some of the above individual functions. However, this goes only part of the way towards applications. For those, the field must advance along three directions. First, our understanding of the chemical physics issues involved with molecular-device functions must be improved – eventually enabling computational prescreening of operating nanosystems. Second, components must be found that manifest sufficient chemical and thermal robustness to allow for high-yield processing (e.g., of “on-top” passivation layers) and long-term operation. Third, better approaches towards large-scale molecular fabrication are required.

Molecular fabrication will rely on processing at surfaces. Consequently, our near-term efforts are directed towards developing surface-based molecular nanosystems with the long-term goal of extending device architectures into the third dimension. Research area C brings together efforts from chemistry, physics and biology towards developing the scientific underpinning for atomically precise devices based on individual molecules in contact with nanostructured substrates. Predictive-level theory plays a critical role by prescreening structures and properties, thus facilitating the design of viable device heterostructures. Research area C is organized into: C1: Synthesis and Structural Characterization of Molecule-Based Nanostructures where functional building blocks are prepared and characterized, C3: Properties of Molecule-Based Nanostructures in which chemico-physical properties of building blocks are theoretically predicted and compared with experiment, C4: Molecular Nanostructures on Surfaces where switchable building blocks are positioned and assembled into functional devices, and C5: Frameworks and Containers on the Nanoscale, which explores programmable self-assembly for 3D fabrication with sub-nm spatial resolution.