TITLE:
Optical Properties of Tetrahedral Amorphous Carbon Films and Their Potential for Lab-on-a-Chip
AUTHORS:
Katja Guenther, Frank Sonntag, Teja Roch, Andrés Fabián Lasagni
KEYWORDS:
Tetrahedral Amorphous Carbon, Pulsed Laser Deposition, Thin Films, Diamond-Like Carbon, Lab-on-a-Chip
JOURNAL NAME:
Materials Sciences and Applications,
Vol.6 No.5,
May
27,
2015
ABSTRACT: In this study, tetrahedral amorphous carbon (ta-C) films with thicknesses between several 100 nm
and several micrometers have been deposited onto polished tungsten carbide and steel substrates
by pulsed laser deposition (PLD) using an excimer laser (248 nm wavelength). We investigate the
optical properties (e.g. the refractive index (n) and extinction coefficient (k) in the visible and
near-infrared wavelength range) of these layers in dependence of the used laser ablation fluence
on the target. It is shown that n of ~2000 nm thick ta-C films can be tuned, depending on the
sp3-content, between n = 2.5 and 2.8 at a wavelength of 632 nm. Besides of this k reduces with the
sp3-content and is as low as 0.03 at sp3-contents of more than 75%. We proof that this gives the
opportunity to prepare coating with tailored optical properties. Furthermore, it is shown that the
ta-C films have low background fluorescence in the wavelengths range of 380 - 750 nm, which
make this thin films attractive for certain optical, medical and biotechnological applications. We
present for the first time that one possible application is the use in Lab-on-a-Chip-systems (LOC).
Within these systems, the ultrasensitive detection of fluorescence markers and dyes is a challenge.
In order to increase the signal-to-noise-ratio, a setup was developed, that used the specific optical
properties of ta-C films produced by PLD. We used the ta-C film as an integrated reflector that
combined low background fluorescence, a low reflectivity at the excitation wavelength and the
high reflectivity at the emission wavelength. We prove that this setup improves the detection of
fluorescence photons.