Mass selected energy distributions of sputtered atoms and molecules from AgBr, AgF, CdI2 and PbI2 have been measured using a time of flight method. The analysis of experimental data shows a complex character of the sputtering which can be explained by a simultaneous appearance of three different processes: collision cascade, thermal spike and thermal evaporation of decomposed target material. The analytical expressions for energy distributions given by the three sputtering mechanisms are in very good agreement with the experimental spectra. Physical parameters of the energy distributions: E b (surface binding energy), T sp (mean temperature of the spike) and T (macroscopic surface temperature) are obtained and their physical meaning is discussed. A comparison between existing sputtering theories and results of the investigations is presented.

The sputtering processes during 6 kev Xe ion beam bombardment of halides

Condensed gas layers of H2O, NH3 and CO at 15–20 K have been bombarded by 6 keV H+2 and 3 keV He+ and Ar+ ions. Mass spectra of the neutral species sputtered from these layers have been measured. There is a substantial yield of products which originally were not in the target material, and which have thus been formed in chemical reactions induced by the ion bombardment. The relative yields of some of the products have been found to increase with decreasing incident ion mass. This is mainly attributed to the larger amount of energy deposited by electronic stopping in such situations. From CO a nonvolatile residue is left after ion irradiation. From a layer of H2O frozen on top of the CO-residue H2CO was detected.

Reactive sputtering of simple condensed gases by keV ions II: Mass spectra

The trapping of potassium atoms by a polycrystalline tungsten surface as a function of energy and angle of incidence

Negative ion formation in alkali-atom-molecule collisions is a powerful method to study the dynamic properties of negative ions. By studying a collision with an electron donor such as an alkali atom one has access to the electron affinity of the molecule as it is manifested in the collision. The electron affinities obtained depend on the conditions of the collision and do not have to be identical to electron affinities obtained by other means. In this way adiabatic, vertical and reactive electron affinities can be discerned. Moreover if the collision energy is in the eV region one can probe the vibrational dynamics of a negative molecular ion on a 10 fs timescale. As a theoretical introduction to negative ion formation by electron transfer in atom-molecule collisions the curve crossing model and the collision dynamics of the atom-atom case are briefly reviewed. A short survey of the experimental methods used is presented. Measurements of total, differential and double-differential cross sections as a function of the collision energy and different collision partners are discussed. In atom-molecule collisions stretching of the bond of the molecular negative ion during the collision is among the most relevant consequences of the internal degrees of freedom of the molecule. The collision dynamics explored in this way not only gives insight into the properties of negative ions, but also into the dynamics of elementary processes occurring in chemical reactions.

https://iopscience.iop.org/article/10.1088/0953-4075/34/14/201/pdf

Negative ion formation in alkali-atom-molecule collisions

Bombardment of condensed Kr and Xe by 2–8 keV noble gas ions results in very high sputtering yields. A considerable fraction (10–30%) of the sputtered particles consists of Van der Waals clusters, with Kr 2 , Kr 3 , Xe 2 , XeKr, XeKr 2 and ArKr having been observed. The kinetic energy distributions of the sputtered monomer-species are in agreement with a collision cascade mechanism. However, at the low energy side an excess yield is observed. This is explained by a model which takes into account the large sputtering yields and the damage of the surface during the sputtering process. The energy distributions of the dimers and trimers are satisfactorily explained by a statistical model. It is concluded that the dimer and trimer species are sputtered during an early stage of the cascade.

Sputtering of condensed noble gases by keV heavy ions

An apparatus has been developed for producing an atomic beam of potassium in the energy range of 0.2 to 45 eV (1000–15 000 m/sec). The technique used here is cathode sputtering. With a velocity selector (spread, 6.7%; maximum rotational speed, 48 000 rpm), both the signal of a Pt‐W detector and an energy independent one are measured as a function of the velocity of the beam particles.

P. K. Rol

Papers

Atomic Beam Source for the Energy Range of 0.2–45 eV