• Welcome at TFL!

    A bit of history...

    TFL was the pioneer in Italy in research on laser fabrication and thin films pulsed laser deposition (PLD). In 1966 the first CO2 laser in Sicily (and one of the firsts in Italy) was fabricated here by Prof. S. Riva Sanseverino and Prof. V. Daneu. The group has been working for thirty years in the field of thin films deposition, gaining a great and recognized expertise in the field. Some pioneering papers on laser film deposition are cited by the most important books on the subject (e.g. D.B. Chrisey, G.K. Hubler: “Pulsed Laser Deposition of Thin Films” (J. Wiley, New York, 1994).

    Description

    For several decades, in the former Laser techniques Laboratory of the Department of Electrical, Electronics and Telecommunication Engineering, now thin films laboratory of Palermo University, have been developed competencies in the growth and characterisation (both optical [6,10,24] and electrical) of thin films through laser radiation. Thin films have also been employed for the realisation of optics and electronics devices. It has been demonstrated that several dielectrics materials deposited by ablating the massive material through laser radiation, show excellent optical properties as well as some semiconductors materials show, together with good optical properties, also remarkable electrical properties, so that they can be used for the realisation of optoelectronics devices [22]. At the beginning it has been employed the radiation emitted by a CO2 (carbon dioxide) laser [1]; afterwards, interesting results have been achieved thanks to the radiation emitted by an Ar ion laser [9], then it has been used the radiation generated by an excimer laser [20] and finally it has been employed the radiation produced by a Nd:YAG laser triplicated in frequency [21,29]. The latter solution is advantageous because of the reduced length of the pulses and the easy focusing of the laser beam due to its quasi-gaussian transverse profile. Pulses length plays a fundamental role because by decreasing the pulse length there is a decrease of the probability of the dissociation of the material. Moreover, it has been demonstrated that, if the pulse length is small and the photon energy is larger than the gap energy of the material, the photoablation process occurs (i.e. the photon energy transforms itself directly into the emitted particles energy). This process is characterised by a strong directionality of the emitted material [20], which, very often, fluoresces in the visible region.

    For this kind of depositions two vacuum bells are available: they allow inserting and controlling precisely the pressure of a gas, which, in certain cases, can improve the quality of the deposited layers. These bells are equipped with electromechanics systems for handling the material to be ablated, a substrate heater, and electrical and optical feedthroughs. These latter allow the insertion into the bell of both the laser beam which ablates the material (usually a sintered pellet) and a low intensity laser used for controlling layers’ growth (i.e. layers thickness). By employing the systems described above, several dielectrics and semiconductors materials, such as cadmium sulphide [9,20] and indium tin oxide (ITO) [21] have been deposited. The latter is very used by the optoelectronics industry because of its high transparency and conductibility and it has been employed also for the realisation of organic LEDs [26]. Optical [24], electrical and mechanical analysis of the grown layers has given excellent results, comparable with those published by other researchers throughout the world. Moreover, it has been performed the spectroscopic analysis of the fluorescence (plume) of the photoablated ITO and it has been observed a dependence of the fluorescence both on the oxygen pressure used and the density of energy of the laser radiation [21,23,25].
    More recently it has been investigated the possibility of realising, by employing always the same photoablation techniques, zinc oxide layers [28] both n- and p-doped, in order to achieve p-n junctions suitable for the realisation of electroluminescent diodes in the violet region. The above described thin films deposition systems have also been employed for the realisation of multidielectrics mirrors with tuneable reflectivity profile [10,12,13,16,17,18,19]: they are normally used in laser resonators for generating beams of particular characteristics. A beam generated by an argon ion laser has been utilised for the selective removal of cadmium sulphide layers [7,8] in order to fabricate diffraction gratings for integrated optics [11,14,15].
    The emitted radiation from a CO2 laser working with giant pulses has been employed for investigating non linear effects in various crystals at the wavelength of 10 microns [2,3,4,5].
    Pulses generated by the Nd:YAG laser have also been used for the mobility measurements of the materials employed in the organic LEDs realised in the same laboratory [27].

    Mission and expectations

    We are a small group of dynamic people with many and diverse competences in the field of photonics and optoelectronics. Our expertise comes from assorted experience made in several laboratory and research institutes around the world. We have two key missions:
    – Educating and training our students with a solid knowledge base which can allow them to be inserted in the photonic market (either industrial or research level), today the most exciting and advanced field of electronics. Our students are used to face whatever theoretical or practical subject with a problem solver approach: this allows matching a good knowledge of physics together with engineering skills. “Why?” and “How?” are the most used words in our classes!
    – Analysing and investigating advanced material thin films properties in order to fabricate novel devices for photonics and electronics. From this point of view, we consider our group continuously in progress (both competences, and objectives)!
    We are opened to new and stimulating research challenges, which also scatter in multi-issue fields. For the same reason, the laboratory is always in an open call state and enjoys any collaboration and partnership with industrial and/or government institutions for developing new and exciting projects or simple ideas. We expect not only to satisfy our scientific and intellectual curiosity, but also that the topics of our research be oriented to the final realisation of a system (component, device or a complex tool), useful to the human community.
  • List of publications relevant to the described activities:
    [1] C. Calì, V. Daneu, A. Orioli, S. Riva-Sanseverino: Flash evaporation of compounds with a pulsed-discharge CO2 laser - Appl. Opt., vol. 15, 1327 (1976).
    [2] I. M. Catalano, A. Cingolani, C. Calì, S. Riva-Sanseverino: Photondrag effect in polar crystals - Solid State Communications, vol. 25, 1, (1978).
    [3] I. M. Catalano, A. Cingolani, C. Calì, S. Riva-Sanseverino: CO2 laser induced photon drag effect in n-GaP - Solid State Communications vol. 29, 21, (1979).
    [4] I. M. Catalano, A. Cingolani, C. Calì, S. Riva-Sanseverino: Second harmonic generation in InSe - Solid State Communications, vol. 30, 585, (1979).
    [5] I. M. Catalano, A. Cingolani, C. Calì, S. Riva-Sanseverino: Experiments on the Photon Drag Effect in Polar Crystals - Digest of Technical Papers of XIth International Quantum Electronics Conference - June, 23-26, 1980, Boston, (USA), p. 640.
    [6] C. Calì, V. Daneu, S. Riva-Sanseverino: Use of a scanning laser beam for thin film control and characterization - Optica Acta, vol. 27, 1267, (1980).
    [7] C. Arnone, C. Calì, M. L. Rimicci, S. Riva-Sanseverino: Laser film thickness modulation and induced small pattern generation - Journal of Non-Crystalline Solids, vol. 47, 2 (1982), pp. 263-266.
    [8] C. Arnone, C. Calì, S. Riva-Sanseverino: Light-induced sublimation of Cadmium Sulfide - Springer Series in "Chemical Physics 39": "Laser Processing and Diagnostics", Ed: D. Bauerle, pag. 379-385, Springer-Verlag (1984).
    [9] C. Arnone, C. Calì, S. Riva-Sanseverino: Laser evaporation technique for CdS thin film deposition - Proc. of the 1984 IEEE International Workshop on Integrated Optical and Related Technologies for Signal Processing, Florence, Italy, 10-11 September 1984.
    [10] C. Calì: Lasers in thin films deposition - in "Laser Science and Technology", Plenum, p. 211 (1988).
    [11] G. Assanto, C. Calì and S. Riva Sanseverino: Laser direct-writing of gratings for integrated optics - SPIE Proceedings, Vol. 952 "Laser Technologies in Industry", p. 647, giugno 1988.
    [12] S. De Silvestri, P. Laporta, V. Magni, O. Svelto, C. Arnone, C. Calì, S. Sciortino, C. Zizzo: Nd:Yag laser with multidielectric variable reflectivity output coupler - Opt. Communication, 67, 229 (1988).
    [13] C. Zizzo, C. Arnone, C. Calì, S. Sciortino: Fabrication and characterization of tuned gaussian mirrors for the visible and the near infrared - Optics Lett. 13, 342 (1988).
    [14] M. Bertolotti, F. Michelotti, C. Sibilia, G. Assanto, C. Calì: Nonlinear coupling with CdS grating in waveguide - SPIE vol. 1273, Nonlinear Optical Materials III (1990), p. 185-190.
    [15] M. Bertolotti, F. Michelotti, C. Nisio, E. Fazio, G. Assanto, C. Calì: Nonlinear CdS Grating Coupler: cw and Pulsed Operation - Proc. 'Nonlinear Guided-Wave Phenomena' Top. Meeting, Tech.Digest Series, Vol.15, p.312 (1991).
    [16] C. Calì, F. Mezzolla, C. Pace, M. R. Perrone, P. Rejfir: Characterization of an unstable gaussian-reflectivity resonator in a XeCl laser - Optics Comm., vol. 81, 301, (1991).
    [17] M. R. Perrone, F. Mezzolla, C. Calì, C. Pace: Super-Gaussian Reflectivity Unstable Resonator for Excimer Lasers - Appl. Phys. Lett., vol. 59, 1153 (1991).
    [18] M. R. Perrone, C. Calì, C. Pace: Performance of a XeCl laser with super-gaussian reflectivity unstable resonators - Optics Comm., vol. 92, 93-98, (1992).
    [19] C. Pace, E. Nava, C. Calì: A simple GRM design for tunable Ti:Sapphire laser - Pure Appl. Opt. 3 (1994) 441-447.
    [20] C. Calì, F. La Rosa, G. Targia, D. Robba: Study of film growth from excimer laser-induced evaporation of CdS - J. Appl. Phys., Vol. 78 (10), pag. 6265, (1995).
    [21] C. Calì, M. Mosca, G. Targia: Deposition of Indium Tin Oxide films by laser ablation: processing and characterization - Solid-State Electronics 42, 877 (1998).
    [22] C. Calì, M. Mosca: Indium Tin Oxide Films for Optical Sensors - Published in "Optical Sensors and Microsystems", Edited by S.Martellucci, A.N.Chester and A.G.Mignani, Kluwer Academic / Plenum Publishers, p.79, 2000.
    [23] C. Calì, R. Macaluso, M. Mosca: In-Situ Monitoring of Pulsed Laser Indium-Tin-Oxide Film Deposition by Optical Emission Spectroscopy - Spectrochimica Acta Part B: Atomic Spectroscopy, Vol. 56, pp. 743-751 (2001).
    [24] C. Calì, M. Mosca, G. Targia: A simple apparatus for the determination of the optical constants and thickness of absorbing thin films - Opt.Comm., 191 (2001) 295-298.
    [25] C. Calì, R. Macaluso, M. Mosca: Effects of the process conditions on the plume of a laser-irradiated indium-tin-oxide target - Opt.Comm., 197 (2001) 341-354.
    [26] P. Cusumano, F. Buttitta, A. Di Cristofalo, C. Calì: Effect of driving method on the degradation of organic light emitting diodes - Synthetic Metals 139 (2003) 657-661.
    [27] S. Gambino, P. Cusumano, C. Calì: Measurement of drift mobilities in amorphous organic films using the time of flight method - SPIE Europe, 26-30 April 2004, Conference Proceeding, 5464-59, p. 222 (2004).
    [28] Mosca M, Cali' C., Butte' R., Nicolay S., Grandjean N.: Growth of device-quality ZnO films by pulsed-laser deposition - Proceedins of EL-2008: 14th International Workshop on Inolganic and Organic Electroluminescence & 2008 International Conference on the Science and Technology of Emissive Displays and Lighting [4-03-PO], pag.229-231.
    [29] Calì C., Cornacchia F., Di Lieto A., Marchetti F., Tonelli M.: Nd:YVO4 crystalline film grown by pulsed laser deposition - Optical Materials 31 (2009), pag. 1331-1333.


University of Palermo  -  Department of Energy, Information engineering and Mathematical models (DEIM)
viale delle Scienze, Building 9  -  I-90128  Palermo (Italy)