Nicolae TOMOZEIU

    In the field of thin films characterization, the VIS optical spectroscopy is an important tool. The method here presented has been extensively described by us elsewhere (J. Coat. Technol. Res. (2019), https://doi.org/10.1007/s11998-019-00218-1)

The aim of this work is to briefly  introduce to the reader an extraordinary powerful tool. Because, as a Hawaian proverb says: “no rain, no rainbow!”.

     The Automatic Scanning Absorptometer (ASA) is a modern version of the Bristow method and is used to characterize the liquid absorption into thin porous media. The method of measurement is described in this work. Once the measurement started, the ASA software will take over and life the transferred liquid volume normalized to the contact area (TLV/A) will be displayed as a function of square root of the contact time.
     The liquid properties (surface tension, viscosity, contact angle, etc) and the characteristics of the porous material (porosity, surface energy, fibrous or granular internal structure) defines the liquid absorption dynamics.

(this work was made in Océ Technologies, R&D, published  in  Che. Eng. Sci. https://doi.org/10.1016/j.ces.2017.12.024)

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   The IR spectroscopy revealed the increasing of the Si-O bonds' number and the Raman investigations showed the increase of the Si-Si number when the SiO_x sample has been laser irradiated. Increasing the energy delivered into the material, more oxygen-rich and silicon-rich material has been detected. Increasing more the energy delivered to the SiO_x it is possible to induce the phase separation (silicon and SiO₂ ) together with the phase transformation: from amorphous into crystalline silicon.

       (this work was made in Océ Technologies, R&D, published  in Optoelectronics - Materials and Techniques:DOI: 10.5772/20156) 

      Optical Emission Spectroscopy (OES) was employed to study the plasma used in silicon suboxides SiO_x depositions. Theoretical calculations performed in the frame of electron impact excitation mechanism for argon and atomic oxygen corroborated with electron impact dissociation of the molecular oxygen have shown the strong influence of the electron temperature on the rate coefficients of photons' production.
     Correlation functions between the OES signals assigned to silicon and oxygen atoms from plasma (gas phase) and the SiO_x layer composition (infrared and energy dispersive X-ray investigated) have been found. Based on these functions, the OES plasma monitoring is proposed as a tool to control in-situ and in direct time the SiO_x layer composition.

             (this work was made in Utrecht University, prof. FHPM Habraken 2002 and continued at Océ Technologies B.V. 2005) 

     During plasma deposition of a-C:H thin films, carbon atoms can form sp³, sp² and sp¹ sites; the chemical and physical properties of the a-C:H films are determined by the fractions of these sites.
     In this work we report on an investigation of a magnetic- multipole system to confine the plasma targeting the increase of sp³ sites specific to “diamond like” carbon (DLC). The mechanical and tribological properties, the photoluminescence as well as the electron field emission from a-C:H layers are dependent on the sp³/sp² ratio. Interesting results concerning the magnetic field effect on both plasma parameters and film properties are here revealed.

                              (this work was made in Cambridge  University, Engineering Depart. prof. Bill Milne 1997) 

OMS techniques were used to study the a-SiC:H alloys with different carbon content. The energy distribution of the localized states into the band-tails as well as those as dangling bonds (DB) as deep states. The room temperature measurements allow us to determine the position of the DB states in the energy gap. The experimental results are fitted with Gaussian distributions for D⁰ and D^-. An increase in the transition energies involving D⁰ and D^- states and the conduction band has been determined for alloys with two different r values.

From the experimental data fit, the Fermi level and the quasi-Fermi levels positions are dedtermined. A good agreement with optical measurement of the energy gap was found. 

                                        (this work was made in KU Leuven, prof. G. Adriaenssens and prof. W.  Grevendonk, 1994) 

The photoconductivity of hydrogenated amorphous silicon (a-Si:H) thin films is still of interest. A variety of models have been proposed to investigate the steady-state photoconductivity in the samples obtained under various physical conditions. The photo-generation of carriers combined with the electron trapping and recombination kinetics have been treated in the frame of the classical photoconductivity theory; different models have been elaborated considering the kinetic equations for electron and hole capture as well as the thermal emission. However, in the quoted works a peculiar attention has been devoted to the behavior of the lux-ampere characteristics, these curves being generally approximated by some straight lines with various slopes in a definite temperature range. 

                        his work was  developed during my  PhD studies in Bucharest University prof I. Munteanu, prof  I. Licea, 1994)