Institute of Electronics, Bulgarian Academy of Sciences, Space reliability of the new superconducting and carbon based materials S.S. Tinchev Institute of Electronics, Bulgarian Academy of Sciences, Sofia 1784, Bulgaria

SUPERCONDUCTING MATERIALS Superconductors have the ability to conduct electricity without the loss of energy

Below the superconducting transition temperature, the resistivity of a material is exactly zero

Magnetic flux exclusion - the Meissner Effect

The SQUID, an acronym for Superconducting QUantum Interference Device, is the most sensitive detector known to science

M. Klinger, J.H. Hinken and S.S. Tinchev, First space test of high-Tc SQUIDs, IEEE Trans. Appl. Superconductivity, 5, No. 2 (1995), 2759-2760.

SQUID pattern (Sample F599-44) made after the flight on November 9, 1993

CARBON-BASED MATERIALS The carbon-based materials have contrasting and complementary electronic properties, which could be combined to form electronic devices

Diamond: Wide gap material (5 Diamond: Wide gap material (5.5 eV), very high resistivity, excellent thermal conductivity, electron emission, radiation-hard, chemically inert Graphite: High in-plane mobility, can be intercalated giving high conductivity

Carbon nanotubes (CNTs): Semiconducting or metallic, interesting structural properties and dimensions, electron emission Diamond like carbon (DLC): Metastable form of amorphous carbon, n and p-type, but modest mobility, multilayers possible Polymers: Low-cost plastic electronics, fabricated in a continuous printing process as opposed to photolithography

Diamond Like Carbon (DLC) Diamond like carbon is the most important carbon-based material used in electronics today DLC is a wide gap semiconductor with high mechanical hardness, chemical inertness and optical transparency DLC films have already widespread applications as protective coating in magnetic storage disks, in solar cells and in supercapacitors

a-C:H absorber layer for solar cells matched to solar spectrum (S. S a-C:H absorber layer for solar cells matched to solar spectrum (S.S. Tinchev, P.I. Nikolova, J.T. Dyulgerska, G. Danev, Tz. Babeva, Solar Energy Materials & Solar Cells, 86 (2005) 421–426 One of the most interesting properties of amorphous carbon is the ability to vary the optical band gap by simply varying the sp2/sp3 relation Deposition of DLC thin films by plasma enhanced chemical vapor deposition (PECVD)

Optical transmittance of a-C:H films formed under different DC voltage

Optical gaps can be extracted from the absorption coefficient  and Tauc relation: ( E)1/2 = B (E - Eg), Here Eg is the optical gap, E is the photon energy and B is a constant. One can estimate the sp2 amount using the familiar relation between the optical gap and sp2 content z:

Variation of optical bandgap - Eg and sp2 - fraction for a-C:H thin films with DC voltage

Real (n) and imaginary part (k) of refractive index at 632 Real (n) and imaginary part (k) of refractive index at 632.8 nm for a-C:H film made with different DC voltage

Raman spectra of the DLC film decomposited with two Gaussian peaks: D-peak (disordered ) at 1350 cm-1 and G-peak (graphite) at 1540 cm-1

Comparison of solar radiation spectrum and absorption of a-C:H multilayer

a-C:H films with tunable optical gap have been fabricated by varying only the bias voltage in a DC PECVD system. An absorber layer composed of five a-C:H layers with different band gaps deposited at different bias voltages was proposed and tested. The performance of this system can be tailored quite well to the solar spectrum and can be used in solar cell as well as in thermal solar absorbers

PROPOSAL ESA SURE ANNOUNCEMENT OF OPPORTUNITY “SPACE APPLICATION RELIABILITY OF DIAMOND – LIKE CARBON FILMS”

Scientific objectives: to find changes in mechanical, optical and electrical properties of DLC films after exposure to space environment. to extract structural rearrangements, carbon and hydrogen losses of DLC films caused by solar particle bombardments, irradiation, high vacuum and temperature changes in space . to propose possible ideas for improving the space – relevant properties of DLC films.

Expected results: to identify these space application, where DLC materials can be used. to find possible changes of material properties of DLC film. to propose some ideas for improving the space reliability of diamond – like carbon films. to improve DLC film fabrication technology according to the obtained results.

DLC films are very attractive for space application DLC films are very attractive for space application. Possible areas of space-relevant applications are: DLC films as solid lubricants - extremely low coefficient of friction in vacuum (lower than 0.01) DLC films as anti-could welding for holding the satellite solar panel DLC protective layers for space sensors - high mechanical hardness and scratch resistance Scratch resistance lenses and windows Gas barriers properties of the DLC films on plastics in solar cells for space as protective and antireflection coating.

However, in almost all space applications such films are exposed to the rough space environment: solar particles bombardment, solar light radiation, sudden and big temperature changes and high vacuum. In these hard conditions DLC films can deteriorate, therefore we plan to investigate how the DLC film properties are changed after certain time spend in space.

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