Mound or pit formation for different tip and surface materials and tip polarity.

1<p>: Element determination by scanning Auger microprobe spectra.</p>2<p>: For triangular voltage pulse. Rectangular pulse used elsewhere.</p>3<p>: Nonconducting liquid between tip and surface.</p>4<p>: Au, Ag, In, Si, Pt, W, C, SiO, MoS or BiSrCaCuO.</p>5<p>: Pit created at larger tip-surface distance, mound at smaller.</p

Radial dipole force on an adatom obtained from equation (23)using nm and nm and our values of and for two different voltages 6.5 V.

<p>Increasing all the distances , and and the voltage by a factor of 10 yields a reduction of the force to 1/10. The radial van der Waals force calculated using equation (7) is barely visible in the figure at this “large” nm.</p

Radial van der Waals force from equation (7) and radial electric forces (El) from equation (23) for different tip voltages, at as a function of tip-to-surface distance .

<p> nm.</p

Histogram of the resistance (Ω) distribution of twenty different gold nanobelts, calculated from measured IV data.

<p>Histogram of the resistance (Ω) distribution of twenty different gold nanobelts, calculated from measured IV data.</p

Radial van der Waals force on an adatom from simulations of a parabolic and a spherical tip respectively as a function of the distance from the centrum under the tip to the adatom using numerical integration of equation (1).

<p>Also plotted in the figure is equation (7) and (8). nm and nm. Even the curve of a point model has been added. We see that equation (7) agrees well with the simulated curves close under the tip but underestimates the van der Waals force somewhat for larger where the approximation of the tip as a sphere becomes too crude. The simpler formula equation (8) assuming overestimates the force compared with the simulations in the figure. However, even this equation should underestimate the force for even larger because the assumption of the tip as a sphere that both equation (7) and (8) uses breaks down. That the simulated value for the parabolic tip tend to sink below the curve from equation (8) at nm is probably due to the limited size of the tip used in the simulation. In deriving equation (5), that equation (7) and (8) uses, we assume that the tip is extended to infinity.</p

Radial dipole force on an adatom obtained from equation (23) using nm and nm and our values of and for two different voltages , one above and one below 3.7 V.

<p>The van der Waals force has been calculated using equation (7) and plotted in the figure using nm. For nm the van der Waals force becomes important for the radial force on the adatoms.</p

Phase diagram showing STM induced surface modifications at different tip voltage and different tip-to-surface distance mainly constructed using ref. [5], [12] and ref. [17].

<p>In drawing the lines for mound formation we have assumed that it is the electric field that decides if some particular kind of mound will be formed. Mounds will form at positive voltages, area A. From our model assuming field induced diffusion of adatoms we can calculate the threshold electric field for mound formation for area A to 2 V/nm. In area B we have transfer of tip materials to the surface making a mound of tip material on the surface. For pits, area C, we have assumed that they are formed at constant independent of the tip-to-surface distance in agreement with Kondo <i>et al. </i><a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0030106#pone.0030106-Kondo1" target="_blank">[17]</a>. At short distances and low electric fields, area D, the van der Waals force will contribute in creating a mound <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0030106#pone.0030106-Erts1" target="_blank">[22]</a>. Close to the U-axis (not shown) at electrical fields above 20–50 V/nm field evaporation will occur <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0030106#pone.0030106-Tsong2" target="_blank">[18]</a>.</p

SEM of gold nanobelts, showing small (A) and large (B) magnifications.

<p>SEM of gold nanobelts, showing small (A) and large (B) magnifications.</p

Calculation of van der Waals force on an adatom by a massive paraboloid tip with radius of curvature at the apex.

<p>For a adatom sitting off-axis on the surface the distance to the tip is . The letters denoting distances, and are placed at the midpoint of the distances they represent.</p

SEM of ZnO nanowires grown on gold nanobelt patterns at low (A) and high (B) magnification; and TEM of the ZnO nanowire (C).

<p>The black dot in the TEM images is an artifact for imaging.</p