Foreign Collaborators

Dr. Fomin took part in the activity of the ICRCCM, ASA (Atmospheric Spectroscopy Application) and IPCC (Intergovernmental Panel on Climate Change) working groups and has good contacts with foreign scientists from these groups.

№ - 0175 Ultra Thin Superstrong Carbon Foils by Sputter Processes

Full Title:	Ultra Thin Superstrong Diamond-Like Carbon Foils by Sputter Processes
Technology Field(s):	MAT-CER: Materials / Ceramics PHY-PFA: Physics / Particles, Fields and Accelerator Physics

Contributors

Vitaly Kh Liechtenstein	Russian Research Center "Kurchatov Institute" (RRC KI) 1, Kurchatov sq., Moscow, 123182, Russia Phone: 7+095+1969183 Fax: 7+095+9430073 liechten@qq.nfi.kiae.su
Mikhail I Martynov	Russian Research Center "Kurchatov Institute" (RRC KI) 1, Kurchatov sq., Moscow, 123182, Russia Phone: 7+095+1967807 Fax: 7+095+9430073 mart_m@qq.nfi.kiae.su
Eugeny D Olshansky	Russian Research Center "Kurchatov Institute" (RRC KI) 1, Kurchatov sq., Moscow, 123182, Russia Phone: 7+095+1969973 Fax: 7+095+1964588

Present Status of Research

Brief Description of Research

Ultra thin (5-15 nm) foils are mainly needed for efficient stripping of electrons from the high energy negative ion beams in the terminal of tandem accelerators and for fast ion timing by use of secondary-electron emission in time-of-flight spectrometers as well. These foils have traditionally been prepared by thermal deposition of carbon and frequently last hours to days when stripping low Z ions.However, the foils typically fail within 6 to 10 minutes when a beam of heavier ions (e.g. I^- or U^-) is stripped because of irradiation damage, sputtering and thermal stresses. The accelerator must be shut down to replenish the stripper foils. Concerning time-of-flight spectrometers, their both sensivity and energy resolution are often limited by the emitting foil properties.

From a theoretical point of view, diamond shows great promise as a target foil material. Diamond’s high carbon-to carbon bond strength should mitigate primary knock-on effects as well as collision cascade effects and sputtering. Diamond’s very high thermal conductivity and low mass density should also mitigate thermal gradients created by deposited ion beam power. In addition, diamond is well suited as an thin secondary electron emitter material owing to its negative electron affinity and high tensile strength.. But to apply all these values of diamond for targetry, only amorphous diamond-like (DLC) films are suitable, since policrystalline diamond films are composed of relatively large grains (0.1-1 m) and therefore can not be produced sufficiently thin.

The objective of this research is to establish a controllable process for large-scale producing of improved ultra thin diamond-like carbon target foils to fulfill demands of heavy ion tandem accelerators and time-of-flight spectrometers nowadays. Specific ion beam deposition and glow discharge sputtering techniques, originally developed at RRC “Kurchatov Institute” to produce hard DLC protective coatings, offer an efficient means of preparation free-standing DLC films of required properties. The important features of latter sputter technique are follows: i) substrates are cooled down to liquid nitrogen temperature; ii) base pressure is about 10^-5 Pa; iii) only neutral sputtered atoms are selected to produce the film. This technique has been used successfully for DLC layers with hardness and electrical resistivity close to natural diamond. Preliminary work has proved the feasibility of producing ultra thin DLC foils by these techniques with enhanced mechanical strength and essentially (at least 5 times) improved lifetimes under heavy ion irradiations as compared to conventional carbon foils. It is shown also that use of ultra thin DLC emitting foil instead of conventional one enables significant increasing of energy resolution of time-of flight spectrometer due to reduced energy straggling in the foil. These promising results were obtained during common irradiation experiments which have been carried out at the Tandem Accelerator Facilities of Brookhaven National Laboratory, NewYork (USA), Max-Planck-Institut fr Kernphysik, Heidelberg (Germany), and Paul Scherrer Institute, Zrich (Switzerland).

Legal Aspects The proposed method to produce DLC target foils by specific sputter deposition is covered by Patent in Russia.

Special Facilities A) Several oil free high vacuum systems for fabrication of ultra thin DLC films by DC glow discharge sputtering at low pressures and low temperatures. B) High intensity ion beam sputtering system for large-scale fabtrication of thicker DLC films at low temperatures and high deposition rates.