Magnetologic devices fabricated by nanostencil lithography.

We present magnetic quantum cellular automata (MQCA), fabricated by means of nanostencil lithography, i.e., using a resistless shadow masking technique in ultra-high vacuum. The nanostencil tool allows the fabrication and in situ investigation of structures using atomic force microscopy (AFM) and magnetic force microscopy (MFM). We analyze the error distribution within the structures to shed light on the performance and challenges of magnetic cellular logic devices. Simulations are performed to corroborate an improved concept for these devices which makes use of fourfold magnetic anisotropy.

Photon emission at molecular resolution induced by a scanning tunneling microscope.

The tip-surface region of a scanning tunneling microscope (STM) emits light when the energy of the tunneling electrons is sufficient to excite luminescent processes. These processes provide access to dynamic aspects of the local electronic structure that are not directly amenable to conventional STM experiments. From monolayer films of carbon-60 fullerenes on gold(110) surfaces, intense emission is observed when the STM tip is placed above an individual molecule. The diameter of this emission spot associated with carbon-60 is approximately 4 angstroms. These results demonstrate the highest spatial resolution of light emission to date with a scanning probe technique.

Single crystals of single-walled carbon nanotubes formed by self-assembly.

We report the self-assembly of single crystals of single-walled carbon nanotubes (SWCNTs) using thermolysis of nano-patterned precursors. The synthesis of these perfectly ordered, single crystals of SWCNTs results in extended structures with dimension on the micrometer scale. Each crystal is composed of an ordered array of tubes with identical diameters and chirality, although these properties vary between crystals. The results show that SWCNTs can be produced as a perfect bulk material on the micrometer scale and point toward the synthesis of bulk macroscopic crystalline material.

Direct determination of the energy required to operate a single molecule switch.

Using a noncontact atomic-force and scanning-tunneling microscope in ultrahigh vacuum, we have measured the switching energy of a single molecule switch based on the rotation of a di-butyl-phenyl leg in a Cu-tetra-3,5 di-tertiary-butyl-phenyl porphyrin. The mechanics and intramolecular conformation of the switched leg is controlled by the tip apex of the noncontact atomic-force microscope. The comparison between experimental and calculated force curves shows that the rotation of the leg requires an energy less than 100 x 10(-21) J, which is 4 orders of magnitude lower than state-of-the-art transistors.