Deposition of mass-selected cluster ions using a pulsed arc cluster-ion source

A PACIS (pulsed arc cluster-ion source) developed for high average cluster-ion currents is presented. The performance of the PACIS at different operational modes is described, and the suitability for cluster-deposition experiments is discussed in comparison with other cluster-ion sources. Maximum currents of mass-selected cluster ions of 3–6 nA of small Si_n ^- (n=4–10) clusters and 0.3–0.5 nA of large Al_n ^+/- (n=20–70) clusters are achieved. The mass-selected cluster ions are soft-landed on a substrate at residual kinetic energies lower than 1 eV/atom, and the samples are characterized by X-ray photoelectron spectroscopy and scanning tunneling microscopy. First results on the soft landing of “magic” Si₄ ^- clusters on graphite are presented. Received: 30 May 2001 / Accepted: 14 June 2001 / Published online: 2 October 2001     

Electrochromic switching of WO3 nanostructures and thin films

We present transmission measurements through tungsten tri-oxide nanostructures and thin films prepared by sol–gel process on micro-contact printed substrates. Identical electrochromic switching times are found for both the nanostructures and the bulk films with equal thicknesses upon intercalation of H⁺ ions. We attribute the large change in the transmission through nanostructures at 632 nm, which can not be solely explained by absorption, to diffraction effects. PACS 73.40.Cg; 73.40.Mr; 78.20.-e; 78.67.n     

Electrical field induced growth of triangular nanometer structures on WSe2

We report on the conditions for the growth of triangular structures on WSe₂ surfaces in scanning tunneling experiments with a vertical dimension of one layer (Se-W-Se) and up to 200 nm in horizontal direction. Experiments carried out in different atmospheres (ambient air, dry N₂, dry O₂) suggest that the growth is directly related to the presence of a thin physisorbed water layer on the surface of WSe₂. Furthermore examinations under different scanning and bias conditions show that the electric field of the tip induces the growth of these nanometer structures.     

The influence of tip–sample interaction on step fluctuations on Ag(111)

The fluctuations of the position of monatomic steps on Ag(111) are investigated by scanning tunneling microscopy (STM). We analyze the influence of tip–sample interaction by varying the gap impedance over more than two orders of magnitude. For tunneling tips providing a weak tip–sample interaction, we show that the step position autocorrelation function remains essentially unaltered. In this unperturbed case, the kinetics of step fluctuations are found to be dominated by one-dimensional mass transport. For larger variations of the tip–sample distance or for less favorable tip configurations, we observe a tip-induced increase of the step fluctuations. Our measurements suggest that this effect is caused rather by short-range forces than by the electric field in the tunneling gap.     

Size-dependent self-organization of colloidal particles on chemically patterned surfaces

A study of the self-organization of colloidal particles during the evaporation of particle solutions on chemically patterned surfaces is presented. On a surface with hydrophilic and hydrophobic regions, colloidal particles form compact structures on the hydrophilic sites. When a colloidal solution containing a mixture of particles with a variation in size is used, the number density of each type of particle deposited on the hydrophilic islands after evaporation decreases with increasing particle size. This makes it possible to produce a concentration gradient of the particles on islands of different sizes. It is shown that this technique could allow for particle separation.     

Bubble nucleation and pressure generation during laser cleaning of surfaces

with a pressure pulse width of . Additionally, the phase of an acoustic pulse is observed to change upon reflection at the liquid–solid interface if bubbles are present, providing a direct proof for laser-induced bubbles. Received: 5 December 1996/Accepted: 6 January 1997     

Two-dimensional pressure measurements with nanosecond time resolution

An optical setup for the measurement of acoustic shock waves is demonstrated experimentally. This sensor, which is based on surface plasmon excitation, provides ns time resolution as well as 7m lateral resolution. Initial experiments with laser-induced plasma generation in a water cell already show that in a simple geometry high lateral resolution gives new insight into the ongoing processes.