טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentArmon Eran
SubjectNovel Surface Sputtering Processes Induced By the Impact
of Large Polyatomic Projectile
DepartmentDepartment of Chemistry
Supervisor Professor Eliezer Kolodney


Abstract

When a solid surface is bombarded with energetic ions (energy range from hundreds eV to tens of keV), it undergoes fast erosion on the nano-scale. Surface atoms are emitted and the morphology of the surface is modified. This phenomenon is referred to as "surface sputtering" and is the key to various industrial and fundamental surface processes.  The basic sputtering mechanisms using large polyatomic projectiles (as oppose to mono-atomic ion projectile) and specifically those leading to the formation and emission of large clusters, represent one of the crucial open questions in the field of ion-solid interactions. A direct experimental evidence for a novel sputtering phenomenon which was not yet observed either experimentally or computationally is presented. The results are rationalized in terms of a novel sputtering mechanism where an outgoing, moving precursor, is the source of the emitted clusters.


The main achievements reported in this work are:

-          Direct experimental observation of a novel sputtering phenomenon - Inspection of KEDs for surface emitted cluster ions following impact of 14 keV  reveal that the most probable energies Emp are gradually shifted to higher values with increase in cluster size, and the distributions are getting broader with cluster size. These trends are in sharp contrast to the behavior of KEDs obtained under bombardment atomic projectiles (Ar and Cs). It was found that all secondary clusters emitted following C60- impact share nearly the same velocity.

-          A novel sputtering mechanism - (precursor model) is proposed where an outgoing, moving precursor, is the source of the emitted clusters.

-          The general nature of the new mechanism is exhibited by studying the emission characteristics for a variety of target materials: refractory metals carbide TanCn (n≤10) and NbnCn (n≤18), coinage metals Cun (n≤11), Agn (n≤9), Aun (n≤11) and post transition metals Bin (n≤7), Inn (n≤23). The new emission mechanism and distributions which are getting broader with cluster size, were observed in all the studied materials with the exception of small indium clusters (n≤10). 

Generation and emission of large pure carbon clusters (contain up to several hundreds atoms), induced by prolonged bombardment of the post transition metals (Bi, In, Sn, Pb) surfaces with 14 keV C60-. Inspection of the mass spectra of these cluster ions reveal distinct bimodal mass distribution. The mass distribution is very similar to the laser ablation mass spectra, for great variety of carbon based materials, as reported in the literature, typical of emission of giant fullerenes.