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Identifier

000426174

Title

Φασματοσκοπία πλάσματος επαγόμενου από λέιζερ υπεριώδους υπερβραχέων παλμών στο χαρακτηρισμό λεπτών υμενίων πολλαπλών επιστρώσεων

Alternative Title

UV - Femtosecond laseri induced breakdown spectroscopy for the characterization of multi-layered thin films

Author

Γιαννάκαρης, Νικόλαος Π.

Thesis advisor

Άγγλος, Δημήτριος

Reviewer

Παπάζογλου, Δημήτριος
Περγαντής, Σπυρίδων

Abstract

Performing compositional analysis and depth-resolved profiling of nanometer-scale multi-layered samples (thin films) is a demanding task and requires the use of sophisticated techniques. Furthermore, if this type of analysis is to be done in the context of a production line, in an industrial environment, additional requirements are imposed having to do with the speed of analysis and the ability to run such diagnostics in situ. For these reasons, Laser-Induced Breakdown Spectroscopy (LIBS) has been investigated as a potential technology for rapid analysis of materials at different depths of multi-layered thin film structures. The technique exploits the light emitted by a transient micro-plasma generated when a laser pulse is focussed on the surface of a solid substrate. The current work concentrates on the use of UV-Femtosecond-LIBS (λ = 248 nm, t_pulse = 450 fs) for the characterization of thin multi-layered samples, exploring critical measurement parameters and attempting to establish optimum conditions for performing minimally invasive depth-profile analysis. Our experiments demonstrate that UV-fs-LIBS enables selective detection of materials, both organic and inorganic, at different depths within nanometer-scale multi-layered samples (thickness: 10 nm - 250 nm) of relevance to industrial applications, in the semiconductors and solar cells fabrication sector. From the implementation standpoint, the method is straightforward, requires no sample preparation and is performed in ambient atmosphere, so it is quite promising for being applied for the rapid, in situ characterization of the thin film structures. A main challenge in this application is the need to achieve efficient analysis of each layered film with just a single sequence of pulses. This translates to the requirement of recording reliably good emission signals which arise from a single laser-plasma event that samples material volumes as low as (5 – 80) μm³ corresponding to elemental masses up to 7 picogram. In an effort to maximally exploit the optical energy of each laser pulse for generating an intense plasma, hence enhancing the analytical capacity of the proposed method, we have examined the possibility of performing Double-pulse LIBS (DP-LIBS) which involves ablation of the sample with a pair of pulses temporally separated by a few tens of picoseconds. Results on ITO films (thickness: 120 nm) indicate increase of the emission by as high as a factor of 3-10 depending on pulse energy and spectral transition properties. Furthermore DP-LIBS has been operated in lower energy regimes, where spectral information has not been observed in SP-LIBS, demonstrating that it can be an excellent choice for the characterisation of thin films. In addition, we have investigated the role of nanometer thin Al films overlaid (by use of pulsed laser deposition, PLD) on glass substrates in the context of studying the amplifying role thin metal films may have on LIBS spectra collected on transparent materials (nanofilm-enhanced LIBS, NE-LIBS).

Language

Greek

Subject

Depth profiling

In-situ DP-LIBS

LIBS

NE-LIBS

Διαστρωματική ανάλυση

Λεπτά υμένια

Πλάσμα

Issue date

2019-11-29