Energetic Cluster Ion Research Articles

STM investigation of energetic carbon cluster ion penetration depth into HOPG

We present an STM study of fullerene cluster ion induced damage on HOPG surfaces resulting from 0.5–23 keV impact. Some impact events show up as uniform protrusions some as hillocks comprising craters. The diameters of the surface defects are discussed in terms of a thermal spike model. Oxidation of the irradiation defects leads to formation of holes with depths depending on ion energy. Mean energy loss is found to be about 2200 eV per carbon layer, independent of impact energy over the investigated range.

On the dyeing of ion tracks in polymers

Latent ion tracks in polymers can incorporate dyes at high concentrations. This is of interest in a number of applications. Dyes may also be used as sensitive probes to study the fine structure of latent ion tracks. In this work, we discuss the dependence of dye uptake on both time and mean transferred electronic energy density, and also consider the depth distribution of dyes along ion tracks. Special attention is paid to dye uptake in tracks created by energetic carbon cluster ions.

SPUTTERING WITH GAS CLUSTER-ION BEAMS

A high-current (~100 nA) cluster-ion-beam equipment with a new mass filter has been developed to study the energetic cluster-bombardment effects on solid surfaces. A dramatic reduction of Cu concentration on silicon surfaces has been achieved by 20-keV Ar cluster (N~3000) ion bombardment. The removal rate of Cu with cluster ions is two orders of magnitude higher than that with monomer ions. A significantly higher sputtering yield is expected for cluster-ion irradiation. An energetic cluster-ion beam is quite suitable for removal of metal.

Irradiation Effects of Ar-Cluster Ion Beams on Si Surfaces

ABSTRACTThe effects of energetic Ar cluster ion impacts on Si(111) surfaces have been studied for cluster energies up to l5keV. The mean cluster size was about 1000 atoms, and the smaller sizes could be systematically excluded. Si samples irradiated at different cluster ion energies were analyzed by RBS, ellipsometry, and differential reflectometry. Implantation of Ar in samples irradiated with cluster ions was found by RBS to be detectable, but very small in comparison with samples irradiated with monomer ions of the same energy. The thickness of the damage layer as measured by both ellipsometry and differential reflectometry was also much smaller in the cluster ion irradiated samples.

Thin films from energetic cluster impact; experiment and molecular dynamics simulations

Thin film formation by energetic metal cluster ions (Al, Ti, Cu, Mo, and Ta) is studied. The clusters are electrically accelerated, separated from the neutral ones, and deposited on a surface. If the kinetic energy is higher than about 5 keV for a cluster of about 1000 atoms, highly reflecting, strongly adhering thin films are formed on room temperature substrates. The film morphology does not fit the structure zone model of Movchan, Demchishin and Thornton. Langevin molecular dynamics simulations give the following physical picture: a tiny, very high temperature spot is formed at each impact. This anneals the area around the impact zone and gives rise to near epitaxial growth. The main advantage of the method seems to be that dense films without columnar voids can be produced on room temperature substrates. The abbreviation ECI for energetic cluster impact is proposed for this method.

Molecular Dynamics Simulation of the Effects of Energetic Cluster Ion Impact on Solid Surface

ABSTRACTBeams of energetic clusters may provide a unique tool for surface modification. Experimental data on the effects of cluster bombardment are still scarce but Molecular Dynamics Simulation may help guide the research in most promising directions. We modeled Ar cluster impact on gold surface and compared the calculated sputtering yield with the available experimental data at 30 keV. The results confirm the uniqueness of cluster impacts characterized by deposition of very high energy density at the surface.

Mass distributions of ions sputtered by cluster impacts on carbon, copper and gold targets

Results of sputtering studies of carbon, copper and gold surfaces with energetic water cluster ions are presented. Secondary ion products were determined using quadrupole mass analysis of ions generated in the cluster impact process. Clusters containing as many as nearly 3000 water molecules with energies up to 240 keV were used as projectiles. Ion yields in cluster sputtering were shown to be a very small fraction of the total sputtered product. Very similar distributions of secondary ions were determined with a wide range of cluster sizes and energies. Relatively large yields of energetic atomic ions and smaller yields of polyatomic ions with much lower kinetic energies are consistent with a sputtering mechanism with minimal cooling by thermal conduction prior to the sputtering process.

Sputtering by cluster ions

Using the Monte Carlo simulation code DYACAT, the sputtering by cluster ions (more than 100 atoms) has been investigated. In the DYACAT program which is based on the binary collision approximation, trajectories of ions and recoil atoms are followed dynamically. In order to simulate the nonlinear cascade development, three types of collision events are taken into account, i.e., between two moving particles, between a moving atom and a target atom and between a moving particle and an interstitial. The time-dependent material change is also followed. The energetic cluster ions, 100 eV/atom (Ar) n ( n being 10 to 200), have been bombarded on a carbon target. It is found that the energy spectra of slowing down ions which are spread until 200 eV is much different from those of a monatomic ion. Although the incident energy is in the near-threshold region, nonhnearity in sputtering is clear for large n.

Energetic Cluster Ion Impacts on Carbon and Gold/Carbon Films

Mass analyzed beams of accelerated cluster ions have been used to study energy transfer processes on impact with solid surfaces. Singly-charged water molecule clusters containing between 20 and 150 water molecules and one proton have been accelerated to kinetic energies as high as 300 kV and collided with 10 nm films of carbon or carbon covered with 2 μg/cm2 evaporated gold. Alterations in the structure of these films have been studied by transmission electron microscopy.Carbon films bombarded with water clusters of 25 and 100 molecules accelerated to 300 kV are shown in Fig. 1. The use of 100 water molecules produced craters about 7-8 nm in diameter and even 50 molecules produced craters about 1.5-2 nm in diameter; however, 25 molecules failed to produce any detectable alterations in the film. The bombardment of a gold-covered film by similar clusters is shown in Fig. 2. In these cases, gold grains were removed to form voids about 10-20 nm in diameter, even by the clusters as small as 25 molecules, which produced no craters in pure carbon.

Time-of-flight spectroscopy of sub-MeV cluster ions in the mass range of 1–106 atoms per charge

A time-of-flight spectrometer has been developed for ions in the mass and energy range of 1–106 atoms per charge and 100 keV–1 MeV, respectively. The ion beam is chopped by electrostatic deflection plates, the gate function being step-like. The instrument has been used to measure velocity spectra of intense energetic cluster-ion beams made of hydrogen.

Cluster-ion bombardment of thin films

Energetic cluster ion impact on solid surfaces can be used to deposit large quantities of kinetic energy in small assemblies of atoms in the surface. Extremely high transient pressures and increases in the density of surface atoms are produced by these impact processes. Significant alteration of surface structure is expected. We have investigated the effects of bombardment of thin carbon films with singly charged clusters of argon atoms and protonated water molecules accelerated to energies as high as 300 kV. Clusters were generated in weakly ionized plasmas produced by a corona discharge at atmospheric pressure in helium carrier gas. The singly charged seed ions in this discharge served as nuclei in the expanding gas mixture that was introduced into a high vacuum system through a super sonic nozzle and a differentially pumped skimmer.

The production of charged fragments of energetic hydrogen cluster ions by interaction with an H 2O gas target

Hydrogen duster ions of 800 keV were passed through an H 2O gas target. The production and destruction of charged fragments was followed as a function of the target thickness. The comparison of the experimental results with those of a model calculation shows that the dominant process for fragment production is most probably the evaporation of H 2 molecules. Indications of the luminescence of clusters after electron impact are found from a background signal.

Production and beam analysis of energetic small hydrogen cluster ions for study of their interaction with targets and of their structure

Using magnetic deflection mass selected hydrogen cluster ion beams having mass number 2 n + 1, 0 ⩽ n ⩽ 7, were produced within the energy range of 25 to 700 keV. The secondary electron yield of metal surfaces bombarded by energetic cluster ions was measured, for the three target materials Au, Mo and stainless stell, as a function of the projectile mass and the kinetic energy. The latter ranged from 25 to 700 keV, while the mass range covered the odd numbers from 1 to 9.

Production and beam analysis of energetic small hydrogen cluster ions for study of their interaction with targets and of their structure

Production and beam analysis of energetic small hydrogen cluster ions for study of their interaction with targets and of their structure

A Bisection Break-Up Theory for Cluster Ions and Its Application to the Design of Mean Specific Size Controllers

The most important condition for additional heating of high temperature plasmas and refuelling of fusion reactors using energetic cluster ions is to give the proper energy to each constituent atom. This can be done by controlling their specific sizes and by accelerating the cluster ions by an appropriate voltage. A bisection break-up theory, in which cluster ions are assumed to be divided into two equal fragments by electrostatic repulsion arising from multiple ionization by electron impact is proposed for the first time. The purpose of this theory is to obtain the relation between the mean specific size and the electron current. The theory gives good agreement between the theoretical and the experimental values of the mean specific size of nitrogen cluster ions, demonstrating its applicability to the design of mean specific size controllers.