Surface Dynamics/Ion Deposition System
Quick Specs
- Produces positive or negative ions
- Molecular beam dosing from 1 to 100,000 monolayers
- Temperature-programmed desorption from 30 K to 2000 K
This mass-selected ion beam source for "soft-landing" deposition is designed to produce either positive or negative ions, including ions that depend on ion-neutral reactions (e.g., H3O+ and NH4+). (See Cowin et al. 1999 for a discussion of such ions.) Soft-landing deposition of molecular ions on various surfaces is important to studying aqueous ion interactions, making exotic radicals, and modeling electrochemical double layers. Examples follow.
- Environmental cleanup efforts at many sites require a thorough understanding of ionic reactions, at water-mineral interfaces, in separations or analytical chemistry, or in materials chemistry (as for long-term storage of dangerous wastes). At PNNL and elsewhere, novel experiments for modeling aqueous interfaces are being performed using thin film-ices. A versatile low-energy ion source such as EMSL's permits flexible exploration of ionic processes.
- A source of pure radicals is very helpful to unravel surface chemical mechanisms. An ion beam such as EMSL's can be used, if after deposition onto a surface they can be neutralized, either spontaneously on a conductor surface, via photodetachment, or by using an electron beam. Many radical species can be made in their mass-selected positive or negative ion forms. Negative ions can be superior to positive ions, as the former often neutralize to the ground state, while positive ions will often neutralize to excited electronic states.
- There have been extensive efforts to model the electrochemical double layer in a vacuum. Vacuum experiments offer more control on the adlayer, and more probes to study the properties of and processes in the adlayer. However, most studies involving ions have been only able to put ions into near-equilibrium states, limiting the kinetic information that can be obtained. The ions studied have been typically those few that spontaneously form at the surface from conveniently dosed neutral parents, such as alkali ions, hydronium, or halide ions. With a soft-landing ion beam like EMSL's, one can provide a wider array of ions, put them in situations far from equilibrium so as to clearly observe critical kinetics, and even "sculpt" the z-dependent ion profiles that constitute the electrochemical double layer or are important in redox couples.
Electron transfers are important in many of the applications above, as well as for electronics and life processes. EMSL's ion source provides an excellent way to apply biases to model thin film systems to explore electron transfers.
System Configuration
| EMSL's Surface Dynamics/Ion Deposition System | |
| Ion Source | 1 to 30 nA of ions like NH4+, H3O+, D3O+, Cs+, Na+, C6H6+. C6H5-, OH-, etc. at 1 eV typically, to 1000 eV maximum. |
| Molecular beam dosing (including amorphous glass/supercooled liquid films: 3-methypentane, decalin, water, etc.) | From 1 to 100,000 monolayers. |
| Thin-film growth of oxide crystalline and glass films | |
| Ultrahigh vacuum surface analysis system | 2 × 10-10 Torr |
| Temperature-programmed desorption | From T = 30 to 2000 K |
| Kelvin probe measure of surface potential, film voltages, etc. | |
| Auger Spectrometry | |
Individuals may use this instrument independently for their research, with training provided by the equipment custodian.
