A. W. Dunn

Manipulation of C60 molecules on a Si surface

We have used the tip of a scanning tunneling microscope to position individual C60 molecules on a Si(111) surface. It is possible to form simple patterns of molecules at room temperature using this technique.

(2×4)/c(2×8) to (4×2)/c(8×2) transition on GaAs(001) surfaces

We present scanning tunneling microscopy data illustrating the evolution of the decapped GaAs(001) surface following annealing in stages from 450 to 540 °C. After annealing at 450 °C a (2×4) reconstruction is formed by kinked rows of two As dimer unit cells. Following annealing in the 475–500 °C range small isolated regions of (4×2) reconstruction are visible, with a considerable increase in disorder of the remaining (2×4) reconstructed areas. Annealing at higher temperatures causes the (4×2) structure to become increasingly dominant. We have noted significant differences in the surface morphology as a function of annealing time. Our images of the (4×2) surface are similar to those recently reported by other groups but we propose a new structural model.

Room temperature manipulation of C60 molecules on a Si surface

The tip of a scanning tunnelling microscope is used to position individual C 60 molecules on an Si(111)-(7x7) surface. The molecules may be manipulated into simple patterns and we describe in addition how a molecule may be moved over a bilayer step between two terraces. We also discuss C 60 manipulation on an Si(111) surface with a submonolayer coverage of Ag.

Passivation of Si(111)‐7×7 by a C60 monolayer

C60 monolayers are formed on a Si(111)‐7×7 surface under ultrahigh vacuum (UHV) conditions. The effects of exposure to atmosphere (for 30 min) and water (for 30 s) are assessed by comparing images of the surface acquired using an UHV scanning tunneling microscope. Following exposure and/or immersion we are able to resolve the C60 molecules exhibiting hexagonal order in an arrangement which is essentially identical to that formed prior to withdrawal from the UHV system. Our results clearly show that deposition of one monolayer of C60 on a Si surface can inhibit chemical attack by water and atmospheric oxygen.

C60 manipulation and cluster formation using a scanning tunneling microscope

We have used the tip of an ultrahigh vacuum scanning tunneling microscope to induce displacements of C60 molecules on the Si(111)‐7×7 surface at room temperature. The manipulation is achieved by using a sweeping procedure we have developed which moves the tip closer to the surface and sweeps it across in a predetermined direction. Feedback control of the tunnel current is maintained throughout and the tip‐surface separation is adjusted by changing the sample bias and tunnel current. For a 0.007 monolayer (ML) coverage of C60, a sweeping area of 60 A×60 A was used to move individual C60 molecules, while for higher coverages (0.05–0.2 ML) a sweeping area of 216 A×216 A was used to move large groups of C60 molecules. We show an example at 0.2 ML coverage where we have removed C60 over an area 110 A×370 A resulting in the formation of a line of C60 molecules 20–30 A in width.

Molecular scale alignment strategies: An investigation of Ag adsorption on patterned fullerene layers

We have developed a procedure for atomic scale alignment with respect to macroscopic objects. Metallic and etched registration marks on clean reconstructed Si surfaces are used to guide the tip of a scanning tunnelling microscope. The metallic marks are formed from Ta and can withstand thermal cycling up to 1500 K. These procedures have been used to investigate the interaction of Ag with a patterned fullerene multilayer deposited on Si(111)-7×7.

Nanometer scale patterning of C60 multilayers using molecular manipulation

We show that the tip of a scanning tunneling microscope can be used to manipulate large groups of molecules and form lines in C60 multilayers that have widths of order 10 nm and lengths up to 1 μm. This modification is achieved by first moving the tip towards the surface and then sweeping it across a predetermined distance. This causes the second and higher layers of adsorbed C60 to accumulate in ordered islands that are several layers high and leaves exposed the first C60 layer, which is partially ordered in a hexagonal arrangement. Our results show that the first adsorbed C60 layer bonds strongly to the Si(111)–7×7 surface but that higher layers are bound much more weakly and can be routinely modified.

Adsorption of Sb on GaAs(111)B studied by photoemission and low energy electron diffraction

Abstract The surface structures resulting from the deposition of Sb on the GaAs(111)B-(2 × 2) surface at room temperature followed by annealing, have been studied by high-resolution soft X-ray photoemission (SXPS) and low energy electron diffraction (LEED). For depositions at room temperature with no subsequent anneal and for annealing temperatures up to 300°C, Sb islands are formed between which the As trimer-based (2 × 2) substrate reconstruction of the clean GaAs surface is observed. Annealing to temperatures between 350 and 475°C leads to the creation of Sb chain pairs coexisting with regions of Sb trimers. At 500°C an ordered surface is produced, associated with Sb trimers and an As vacancy.

STM investigation and manipulation of molecules adsorbed on an Si(111) surface

We have used an ultra-high-vacuum (UHV) scanning tunnelling microscope (STM) to image molecules adsorbed on a Si(111) surface. At low coverage ( monolayers) molecules are adsorbed at random sites. For coverages close to a monolayer they are partially ordered in a hexagonal arrangement. Second- and higher-layer islands, in which the molecules are clearly resolved, are observed at higher coverage. These islands may be desorbed by annealing in the range , leaving an Si surface terminated by a monolayer. This surface is stable to exposure to air and immersion in water. In addition, recent work on manipulation of molecules at various coverages is reviewed and results relating to tip alignment in UHV are discussed.

Investigation and manipulation of C60 on a Si surface using a scanning tunneling microscope

Abstract We have demonstrated that the tip of a scanning tunnelling microscope (STM) may be used to position individual C60 molecules on a Si(111) surface. This work is reviewed together with more recent results on STM modification of C60multilayers. The chemical passivation of Si(111) by a C60 monolayer is also discussed.