Determination of optical constants n and k of thin films from absorbance data using Kramers-Kronig relationship

Autor(es)

Rocha, W. R. M. ^[1] ; Pilling, S. ^[1]

Afiliação do(s) autor(es)

^[1] Univ Vale Paraiba, Sao Jose Dos Campos, SP - Brazil

• Tipo de documento: Artigo Científico
• Fonte: SPECTROCHIMICA ACTA PART A-MOLECULAR AND BIOMOLECULAR SPECTROSCOPY; v. 123, p. 436-446, APR 5 2014.
• Citações Web of Science: 13

Resumo

We present a code, called NKABS, to determine optical constants (complex refractive index) of thin films directly from the absorbance data in the infrared. The code is written in the Python language, which is more accurate and faster than previous methods in the literature. For solving the Kramers-Kronig relationship, we used the Maclaurin's methodology. Unlike other codes, which found convergence in 30-40 iterations, the NKABS reach the convergence in just 4 or 5 iterations. Additionally, to evaluate the error, this code calculates the MAPE (Mean Absolute Percentage Error) and the chi-square chi(2). The typical MAPE error obtained using NKABS is less than 1 x 10(-3)%. To illustrate the functionality of this code, we calculate the optical constants in the infrared spectral region of 28 different samples of astrophysical interest at different temperatures (10-300 K), which simulates molecules in space environments, mostly the ones called astrophysical ices. The samples were obtained from the condensation of pure gases (e.g. CO, CO2, NH3, SO2), from the sublimation in vacuum of pure liquids (e.g. water, acetone, acetonitrile, acetic acid, formic acid, ethanol and methanol) and from mixtures of different species (e.g. H2O:CO2, H2O:CO:NH3, H2O:CO2:NH3:CH4). Additionally films of solid biomolecules samples of astrochemistry/astrobiology interest (e.g. glycine, adenine) were probed. The code and the data-base obtained here are available on-line. The NKABS can also be employed to calculate refractive index of processed samples (by heating or radiation). Such data and the refractive index of virgin samples are required as input in several astrophysical models that calculate the radiative transfer in dusty astrophysical environments such as protoplanetary disks and circumstellar environments as well as dense molecular clouds. (C) 2013 Elsevier B.V. All rights reserved. (AU)

• Processo FAPESP: 13/07657-5 - Modelagem computacional do ambiente circum-estelar de protoestrelas empregando dados de gelos bombardeados por raios cósmicos simulados em laboratório.
• Beneficiário: Will Robson Monteiro Rocha
• Modalidade de apoio: Bolsas no Brasil - Doutorado
• Processo FAPESP: 09/18304-0 - Síntese e degradação de espécies moleculares pré-bióticas em atmosferas planetárias, cometas e gelos interestelares simulados
• Beneficiário: Sergio Pilling Guapyassu de Oliveira
• Modalidade de apoio: Auxílio à Pesquisa - Jovens Pesquisadores