surface. In this case, the step faces provide the bonding sites and the deposited material grows along the steps, similar to the step-flow growth mechanism. In order to grow nanowires with a width of fifteen nanometers or less, the deposition temperature for both orientations should be chosen such that the mean free path of the adatoms on the surface is limited to a few nanometers. Experimental Development The ATLAS system was developed within the Applied Physics Group at the School of Physics, Trinity College, Dublin. The experimental procedure is relatively straightforward, when compared to lithography or other approaches, meaning that only standard equipment is needed. The set-up consists of an ultrahigh vacuum chamber (base pressure in the low 10−10 Torr range), with the sample mounted at a large working distance (40-100 cm) from the evaporation source. This large distance provides the high collimation required for the ATLAS technique. The sample itself is mounted on a rotation stage and can be tilted through 200° with a precision of ±0.5°. The substrate can be heated during deposition by either passing direct current through the sample for semiconductors or by driving current through a separate heating foil underneath the substrate for insulating oxides. Versatility The capabilities of the system were first tested by growing arrays of 10-30 nm wide metallic nanowires on two types of vicinal substrates, step-bunched Si(111) and α-Al2O3(0001). Deposition of Au and Ag onto these substrates yields arrays of wires with a width and height of 15 nm and 2 nm, and separated by approximately 30 nm. Since its introduction in 2008, ATLAS has been demonstrated as a simple technique to produce nanowires of a variety of materials down to a width of 15 nm and thickness of 2 nm, on several stepped substrates. Limitations Although ATLAS is a versatile technique, some limitations do exist. The initial growth of the nanowires is nucleated on certain preferential adsorption sites. This can form epitaxial seeds, which grow independently of each other, until they meet, which forms an overall polycrystalline wire. This polycrystallinity can affect the stability of the wire when exposed to air, and can increase the resistance due to its defective nature. It is an ongoing topic of research to increase the quality of nanowires by lattice matching, or increasing initial mobility through heating of the substrate. Despite these limitations, ATLAS's results of a 15 nm width is approximately a five-fold