fs-PLD (@ 800-400 nm) in HV or gaseous atmosphere

Antonio Santagata -

FemtoLAB

Tito Scalo (Pz)

By focusing a high power pulsed laser beam onto the surface of a solid (target) the ablation process is generated. This is characterized by the formation of a plasma containing a high density of electrons, atoms, ions and clusters, or also, when ultrashort fs pulsed lasers are used, nanoparticles (NPs), are ejected whose compositional features are typical of the ablated material. The technique can be applied for the "vaporization", in the form of plasma, of any material (e.g. oxides, carbides, nitrides, alloys such as quasicrystals, biocompatible materials, etc.) which, through their subsequent deposition, whose process is characterized by complex phenomena taking place and controlling the stoichiometric ratios of the various species present, allow the formation and growth of innovative thin films, or new nanostructures, that could be challenging to be obtained by other methods. The properties of the species deposited depend on the operating conditions employed such as the laser pulse duration as well as its energy density (fluence: J/cm2), the background gas present in the ablation chamber and its pressure, or otherwise vacuum, and the temperature of the substrate on which the ablated species are deposited. Two different laser pulses are available: one having pulse duration of 7ns and the other of 120 fs, which in turn allow the occurrence of different ablation processes. Although their description can be quite complex, these can roughly be distinguished in thermal and non-thermal ablation, respectively. In practical terms, fs laser pulses induce an ablation process that can be modeled in different ways (e.g. Coulomb explosion, photomechanical fragmentation etc.) leading to the formation of two components, 10-20% of plasma and 80-90% of hot NPs whose temperature can be determined, even at high temporal resolutions, by their blackbody-like Planck’s emission (Vis-NIR). On the contrary, when ns pulsed lasers are used just the plasma due to the radiative decay of the electronic excited species emitting in the UV-Vis region, takes place. Because of the laser ablation and deposition system apparatuses available, temporally characterizations of both the induced plasma and blackbody like emissions of the NPs produced, can be performed. It is, therefore, feasible to correlate them to the features of the thin films or nanostructured materials deposited.

TECHNICAL SPECIFICATIONS

Spectra Physics Ti:Sa “fs” Laser
Spitfire Pro - Regenerative Amplifier (120 fs; 1kHz; 4 mJ @ 800 nm; SH: 1.5 mJ @ 400 nm)
Quanta System Nd:YAG “ns” Laser
Prototype (7 ns; 10 Hz; 100 mJ @ 532 nm)
Time-resolved spectroscopy and imaging
- Andor iStar “Inductively Charge Couple Device – ICCD” camera (t ≥ 2 ns; Spectral range = 250-900 nm, Pixel_dim = 13 μm x 13 μm)
- ARC SpectraPro 300i monochromator (Spectral range = 200-1000 nm; ʎ/Δʎ = 10000)
Vacuum chamber
- p_min = 10^-7 mbar;
- Tmax (substrate holder) = 800 °C

AVAILABLE TECHNIQUES

Deposition at RT or high temperature (eg. (max 800°C) in HV or controlled gaseous environment (es. Ar, N₂, He, O₂) of various kind thin films and nanostructured inorganic materials:
- Carbides, oxides, nitrides, borides, etc.
- Noble metals (e.g. for plasmonic applications)

The PLD activities are also carried out in collaboration with the Physical-Chemistry Laser Laboratory of the University of Basilicata which expands the offer by the availability of other experimental equipments and techniques for characterizing the obtained deposits (e.g. HR-TEM).

SAMPLES

Solid and flat samples with side dimensions 10 mm x 10 mm (minimum) and 25 mm x 25 mm (maximum); thickness 20 mm (maximum).

USED FOR

Optoelectronics
Optical components
Thermoelectric devices
Tribological coatings
Magnetic devices
Semiconductors
Microbattery electrodes
Biosensors
Biocompatible coatings
Plasmonic systems
Superconductors
Thermionic systems

CASE STUDIES

Features of the NPs deposited by fs-PLD

The laser ablation and deposition performed by fs pulses allows the direct deposition of NPs:
* having an initial temperature of approximately 3500 K which decays exponentially over time;
* that during their flight towards the substrate onto which they deposit, a variation of their stoichiometry can take place as a consequence of a differential evaporative cooling of the involved species;
* form nanostructured deposits which, compared to the starting target, may miss part of the most volatile components;
* whose initial dimensions are centered around 5-10 nm giving rise, for long deposition times, to agglomerations having dimensions up to a few hundred nm
* which can give crystalline structures by increasing the substrate temperature although, however, it can affect to a further stoichiometry variation of the final deposit.

See: Angela, De Bonis et al. Appl. Surf. Sci. 258, 9198 (2012)
DOI: 10.1016/j.apsusc.2011.07.077

Deposition of Ag nanoparticles for SERS applications

The direct deposition of NPs by fs-PLD is immediately exploitable for getting nanostructured films which can be extremely beneficial for several applications. For instance, by fs-PLD of Ag, it has been demonstrated how the surfaces obtained, due to their localized surface plasmon resonance (LSPR) properties, are straightforward operating efficiently for enhancing the electromagnetic Raman scattering for the Surface Enhanced Raman Scattering (SERS) technique, whose signal amplification effect can exceed ten orders of magnitude.

See: Angela, De Bonis et al. Surf. Coat. Tech. 207, 279 (2012)
DOI: 10.1016/j.surfcoat.2012.06.084

Plasmonic angular tunability of Cu, Ag and Au nanoparticles generated by fs PLD

Noble metals NPs’ angular distribution induced by fs PLD plays a relevant role in providing spatially resolved NPs distribution on top of substrates and characterizing the resulting thin films' properties. As demonstrated by our published study, different grade of Au NPs’ agglomeration follows the NPs’ angular distribution which leads to spatially resolved plasmonic tunability of the obtained deposits offering new perspectives for their application in several fields such as biosensors and optoelectronic devices.

See: Maria Lucia, Pace et al., Appl. Surf. Sci. 374, 397 (2016)
DOI:10.1016/j.apsusc.2016.02.111

Contatto: Ambra Guarnaccio -

fs-PLD (@ 800-400 nm) in HV or gaseous atmosphere