Modelling of tunnelling-based static random access memory (TSRAM) architecture with conjugated molecules and nanocrystals:
Computer simulations have been used to determine the performance required for molecular electronic devices to be useful in computer circuits. One of the possible applications of molecular electronics in combination with silicon technology is for the refresh of DRAM cells. The simulations show that no molecules with resonant electrical properties published so far in the literature have suitable properties for this particular application. Thus the aim should be to find molecules which show NDR at lower applied voltages and lower current levels than the molecules published so far.
Fabrication of gold nanogaps using shadow evaporation, and self-assembly and current-voltage measurements of nanocrystals or short conjugated molecules within them:
The edge of one layer of gold shadows the region next to it from gold atoms evaporated at an angle, forming a gap of a controllable size, usually between 2 and 6 nm. CdSe nanocrystals with dithiol linker molecules, or short conjugated molecules with thiol end groups, were self-assembled in this gap. The I-V characteristics of some of these samples showed a staircase structure (at 4K), indicative of the quantised energy levels or of Coulomb blockade of single-electron tunnelling.
Physical and electrical characterisation of conjugated molecules and nanocrystals on gold and silicon surfaces using a low-temperature UHV scanning tunnelling spectroscopy:
Selected molecules and nanocrystals have been investigated by scanning tunnelling spectroscopy with regard to their electrical properties and their suitability for an application in nanoelectronic devices. I-V characteristics collected at different molecules or nanocrystals have been measured and interpreted. The I-V characteristics on semiconductor substrates are found to be strongly dependent on whether the substrate is doped heavily p- or n-type.
Development of selectively-etched nanogaps (size about 5nm) on silicon wafers, and incorporation and current-voltage measurements of nanocrystals within them; use of such gaps as a template for metal:
The SiO(2) oxide in a conventional MOSFET structure is etched away, leaving a gap between highly doped silicon electrodes. The size of the gap (~5nm) can be tailored to the length of the molecule or diameter of the nanocrystal. We have observed reproducible negative differential resistance (NDR) when CdSe nanocrystals are incorporated into such gaps. We have developed a technique of forming a silicide on the nanogap surfaces, and have shown that molecules with thiol end groups will self-assemble on such surfaces. We have also used the selectively etched gap as a template for the formation of a gap between metal electrodes. These two techniques offer the prospect of easy attachment of molecules to a silicon device.