Electrical contact to molecules in semiconductor structures established for the first time

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A new method is said to allow electrical contact to be established with simple molecules on a conventional silicon chip.

The technique could bring advances in sensor technology and medicine, as reported in the journal Nature by chemists from the University of Basel and researchers from IBM Research - Zurich in Rüschlikon.

To further develop semiconductor technology, the field of molecular electronics is seeking to manufacture circuit components from individual molecules instead of silicon. Due to their unique electronic properties, molecules are suited to applications that cannot be implemented using conventional silicon technology. However, this requires reliable and inexpensive methods for creating electrical contacts at the two ends of a molecule.

Researchers from the University of Basel and IBM Research – Zurich, say that thousands of stable metal-molecule-metal components can be produced simultaneously by depositing a film of nanoparticles onto the molecules, without compromising the properties of the molecules. The approach was demonstrated using alkane-dithiol compounds, which are made up of carbon, hydrogen, and sulfur.

The researchers used a type of sandwich construction in which an interlayer of molecules is brought into contact with metallic electrodes from above and below. The lower electrode consists of a layer of platinum, which is coated with a layer of non-conducting material. Tiny pores are then etched into this layer to produce arbitrary patterns of compartments of different sizes, inside which there is an electrical contact with the platinum electrode.

The researchers then took advantage of the ability of certain molecules to self-assemble. Onto the pattern of pores, they applied a solution containing alkane-dithiol molecules, which self-assemble into the pores, forming a densely packed monolayer film.

Within this film, the individual molecules exhibit a regular arrangement and an electrical connection with the lower platinum electrode, says the team. Electrical contact with the molecular layer is established via an upper electrode made of gold nanoparticles.

According to the researchers, their technique largely resolves the issues that previously hampered the creation of electrical contacts to molecules - such as high contact resistance or short circuits by filaments penetrating the film. Building blocks fabricated by this method can be operated under standard conditions and provide long-term stability.

Moreover, the team says the method can be applied to a variety of other molecular systems and opens up new avenues for integrating molecular compounds into solid-state devices.