IR-VASE at the Institute of Physical Chemistry of the Romanian Academy of Sciences in Bucarest

Short overview of the task at hand with IR spectral ellipsometry

By Dr. Mariuca Gartner, Head of Laboratory
Since August 2008, the Institute of Physical Chemistry has had an Infrared Spectroscopic Ellipsometer (IR - VASE) – built by J. A. Woollam (now available in updated configuration).  This is still a unique system in Romania. It has mainly been used to investigate optical, chemical, and vibrational properties of thin films obtained by chemical (sol-gel) and physical (sputtering, PLD) methods. These properties are analyzed as function of technological parameters of deposition (substrate, annealing, dopant concentrations and others).

The IR-VASE based studies (carried out over 1.7-30 µm wavelength range) offer increased sensitivity over FTIR spectroscopy and yield quantitative values for the optical constants n, and k. This technique has excellent sensitivity in regards to thin layer thickness and doping concentration, which is not seen using UV-VIS wavelengths.  

Compared with FTIR or Raman, IRSE can offer more information from a single measurement, like optical constants and chemical composition.  

Our institute performs the following studies:

  1. The vibrational bands‘ assignation can be made very quickly, directly from experimental IR spectra (from the inflexion points of the Ψ and Δ spectra) without any calculations [1].  Raman assignations confirm those obtained by IR-VASE.  
  2. The analysis of the dielectric functions evaluated from the IR-VASE spectra showed the formation of thin layers in nitrogen plasma implanted Si, which is identified as oxynitride with low N concentration.  The inclusion of N atoms in the Si-O network in different configurations was analyzed by IRSE, and the results were confirmed by XPS and VISSE spectroscopy [2].
  3. The vibrational spectra of the phonon modes E1(TO) and A1(LO) of different films (deposited on other substrates and by various preparation techniques) were analyzed [3-5]
  4. If we unify the data obtained from UV-VIS-NIR (0.193 - 1,7 µ) range with these from IR range (1.7-33 µ), we can have a large image of the optical constants and of the transmission on a very large scale from UV to IR (0.193 to 33µ) [6, 7].

References:

  1. M. Nicolescu, M. Anastasescu, J.M. Calderon-Moreno, A.V. Maraloiu, V.S. Teodorescu, S. Preda, L. Predoana, M. Zaharescu, M. Gartner, “Optical, microstructural and vibrational properties of sol–gel ITO films“, Optical Materials  114 (2021) 110999
  2. M. Gartner, A. Szekeres, S. Alexandrova, P. Osiceanu, M. Anastasescu, M. Stoica, A. Marin, E. Vlaikova, E. Halova, “Infrared ellipsometry as an investigation tool of thin layers grown into plasma immersion N+ implanted silicon“, Appl.Surf.Sci., 258, 7195– 7201(2012)]
  3. Nitrogen Amount on the Microstructural and Optical Properties of Thin r.f.-Sputtered ZnO Films Treated by Rapid Thermal Annealing“, Appl.Surf.Sci., 261, 815– 823 (2012)
  4. S. Bakalova, A. Szekeres, M. Anastasescu, M. Gartner, L. Duta, G. Socol, C. Ristoscu, I.N Mihailescu, „VIS/IR spectroscopy of thin AlN films grown by pulsed laser deposition at 400°C and 800°C and various N2 pressures“, Journal of Physics: Conference Series 514, 012001(2014)
  5. N. Dulgheru, M. Stoica,  J.M. Calderon-Moreno,  M. Anastasescu, M. Nicolescu, H. Stroescu, A. Szekeres, M. Gartner, „Influence of compositional variation on the optical and morphological properties of Ge-Sb-Se films for optoelectronics application“,  Infrared Physics and Technology 93 (2018) 260–270
  6. M. Nicolescu, M. Anastasescu, S. Preda, J. M. Calderon-Moreno, H. Stroescu, M. Gartner, V .S. Teodorescu, A.V. Maraloiu, V. Kampylafka, E. Aperathitis, M. Modreanu, “Surface topography and optical properties of nitrogen-doped ZnO thin films formed by radio frequency magnetron sputtering on fused silica substrates”, J. Optoelectron. Adv. Mater, 12 (6), 1343-1349 (2010)
  7. H.Stroescu, M.Anastasescu, S.Preda, M.Nicolescu, M.Stoica, N.Stefan, E. Aperathitis, M. Modreanu, M. Zaharescu, M. Gartner, „Influence of thermal treatment in N2 atmosphere on chemical, microstructural and optical properties of ITO and ITO: N sputtered thin films”, Thin Solid Films, 541,121-126 (2013)

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Thomas WagnerProduct Manager - Ellipsometry & Surface Science
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