Lithography and doping in strained Si towards atomically precise device fabrication.

We investigate the ability to introduce strain into atomic-scale silicon device fabrication by performing hydrogen lithography and creating electrically active phosphorus δ-doped silicon on strained silicon-on-insulator (sSOI) substrates. Lithographic patterns were obtained by selectively desorbing hydrogen atoms from a H resist layer adsorbed on a clean, atomically flat sSOI(001) surface with a scanning tunnelling microscope tip operating in ultra-high vacuum. The influence of the tip-to-sample bias on the lithographic process was investigated allowing us to pattern feature-sizes from several microns down to 1.3 nm. In parallel we have investigated the impact of strain on the electrical properties of P:Si δ-doped layers. Despite the presence of strain inducing surface variations in the silicon substrate we still achieve high carrier densities (>1.0 × 10(14) cm(-2)) with mobilities of ∼100 cm(2) V(-1) s(-1). These results open up the possibility of a scanning-probe lithography approach to the fabrication of strained atomic-scale devices in silicon.

Fabrication and properties of free-standing c60 membranes.

Van der Waals forces that bind C(60) molecular solids are found to be sufficiently strong to allow the reproducible fabrication of free-standing C(60) membranes on (100) silicon wafers. Membranes, 2000 to 6000 angstroms thick, were fabricated by a modified silicon micro-machining process and were found to be smooth, flat, and mechanically robust. An important aspect of the silicon-compatible fabrication procedure is the demonstration that C(60) films can be uniformly and nondestructively thinned in a CF(4) plasma. Young's modulus and fracture strength measurements were made on membranes with areas larger than 6 millimeters by 6 millimeters. It may be possible to use C(60), membranes for physical property measurements and applications.