TY - JOUR
T1 - Magnesium fluoride as low-refractive index material for near-ultraviolet filters applied to optical sensors
AU - Silva, M.F.
AU - Pimenta, S.
AU - Rodrigues, J.A.
AU - Freitas, J.R.
AU - Ghaderi, M.
AU - Goncalves, L.M.
AU - de Graaf, G.
AU - Wolffenbuttel, R.F.
AU - Correia, J.H.
PY - 2020
Y1 - 2020
N2 - This article describes the fabrication of MgF2 and MgO thin-film-based optical filters and compares the optical transmission of the filters over UV. The MgF2 thin-films were deposited by use of an e-beam technique and their optical properties were characterised by ellipsometry. The effect of substrate temperature on the optical properties was studied. The MgF2 optimum refractive indices were obtained with a substrate temperature between 200 °C and 300 °C. Optical simulations were performed to compare the performance of MgF2 and MgO in the fabrication of near-UV narrow bandpass optical filters. While MgO-based optical filters result in a higher transmittance peak intensity, especially at 350 nm, the MgF2 optical filters are narrower, present lower values of FWHM, a mean value of 20 nm. This feature could be especially relevant for specific applications on fluorescent optical sensors. Finally, a Fabry-Perot based on a MgF2/TiO2 optical filter was deposited, using an e-beam technique for the MgF2 thin-films and RF-sputtering technique for the TiO2 thin-films. The MgF2/TiO2 optical filter peak transmittance is approximately 70% close to 400 nm, as expected. The results are discussed with focus on applications in fluorescent optical sensors for peaks at 350, 370, 380 and 400 nm, respectively.
AB - This article describes the fabrication of MgF2 and MgO thin-film-based optical filters and compares the optical transmission of the filters over UV. The MgF2 thin-films were deposited by use of an e-beam technique and their optical properties were characterised by ellipsometry. The effect of substrate temperature on the optical properties was studied. The MgF2 optimum refractive indices were obtained with a substrate temperature between 200 °C and 300 °C. Optical simulations were performed to compare the performance of MgF2 and MgO in the fabrication of near-UV narrow bandpass optical filters. While MgO-based optical filters result in a higher transmittance peak intensity, especially at 350 nm, the MgF2 optical filters are narrower, present lower values of FWHM, a mean value of 20 nm. This feature could be especially relevant for specific applications on fluorescent optical sensors. Finally, a Fabry-Perot based on a MgF2/TiO2 optical filter was deposited, using an e-beam technique for the MgF2 thin-films and RF-sputtering technique for the TiO2 thin-films. The MgF2/TiO2 optical filter peak transmittance is approximately 70% close to 400 nm, as expected. The results are discussed with focus on applications in fluorescent optical sensors for peaks at 350, 370, 380 and 400 nm, respectively.
KW - Electron beam
KW - Ellipsometry
KW - Energy-dispersive X-ray spectroscopy
KW - Magnesium fluoride
KW - Near-ultraviolet range
KW - Optical sensors
KW - Optical transmittance
KW - RF sputtering
KW - Scanning electron microscopy
KW - Thin-film optical filters
UR - http://www.scopus.com/inward/record.url?scp=85090480273&partnerID=8YFLogxK
U2 - 10.1016/j.vacuum.2020.109673
DO - 10.1016/j.vacuum.2020.109673
M3 - Article
AN - SCOPUS:85090480273
SN - 0042-207X
VL - 181
SP - 1
EP - 7
JO - Vacuum
JF - Vacuum
M1 - 109673
ER -