Glass - Back to the Future!

Presenting Author:
Raluca Iordanescu

article posted 4 April 2016

Raluca Iordanescu is a Research Scientist at National Institute R&D for Optoelectronics INOE 2000, Optospintronics Department; doctor in Physics. The authors main activities: Thin films obtaining by PLD (Pulsed Laser Deposition) technique, sol-gel films obtaining by spin-coating method; advanced materials characterization by FTIR, Raman, UV-Vis and fluorescence spectroscopy.

Spin coating depositions from sol-gel rare-earth doped boron-phosphate systems

B.A. Sava1, L. Boroica1, M. Elisa2, R.C.C. Monteiro3, O. Shikimaka4, D. Grabco4, I. Belei4, R. Iordanescu2*, S. Brajnicov1, V. Kuncher5

Even phosphate glasses show usefulness as fast ion conductors, waveguides, optical switches, fibres, and also bio and agricultural materials, their applications are often hampered by their low chemical durability. The addition of trivalent oxides such as boron oxide (B2O3) will improve their chemical durability. Moreover, the mechanical parameters, as hardness, Youngs modulus and fracture toughness, demonstrate higher values with the addition of B2O3. Rare-earth doping ions introduce interesting opto-electronic, luminescence and magneto-optical properties.
Dysprosium Dy3+ and terbium Tb3+ ions-codoped boron-phosphate glasses (BPM6) were obtained as powders and thin films by sol-gel route.
The chosen precursors were phosphoric acid and triethilphosphate for phosphorus oxide (P2O5), boric acid, boron oxide and triethilborate for B2O3 and Dy and Tb chlorides for Dy3+ and Tb3+. Several gelation and drying treatments were tested and the gelation occurred between 80 and 150C, in the case of doped and un-doped samples, prepared at several pH and concentrations.
Spin coating technique was chosen for thin films deposition on silicon and boro-silicate glass substrates (BS ref), using rotation speeds between 1500 and 4500 rotations per minute (RPM). Since the thickness of the films influences the magneto-optical properties, five to ten layers (totalizing about 1 m thickness) were successively deposited on the substrates.>br> The films were thermally treated at 600800C and then investigated by Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD).
XRD results (Fig.1, left) show that the films (I3), obtained at pH=2 and (I1) obtained at pH=1 are amorphous, both deposited on boro-silicate glass and treated at 600C.

Figure 1. XRD analysis of I1 and I3 films (left) and SEM image of I1 film (right) SEM observation of the cross section of I1 film (Fig. 1, right) shows not very regular film thickness, the values of measured thickness being around 977nm

Figure 2. AFM image of the film prepared at pH=1, deposited on silicon

The AFM image on the sample obtained at pH 1, deposited on Si, treated at 800C is presented in Figure 2 showing a roughness of about 1 nm.
For the rare earth doped glasses (BPM6), an important Faraday rotation was observed (up to 017 min/cm/Oe at 400 nm and 006 min/cm/Oe at 600 nm). Only films deposited by rf sputtering presents enough uniform surfaces (over the focal area) in order to observe magneto-optical effects. Such films deposited on Si surfaces present an enhanced (three times higher) Faraday rotations as compared to the bulk case (e.g. 02 min/cm/Oe at 600 nm). Taking into account that the thickness of Ce3+ and Tb3+-doped silico-phosphate films is 18 m and 27 m, respectively, the Verdet constant deduced from the relationships from Figure 1 is 33710-2 min/Oe/cm and 210-4 min/Oe/cm, respectively, at the wavelength of 635 nm

1 National Institute of R & D for Optoelectronics, INOE 2000, Magurele-Bucharest, 77125, Romania
2 National Institute for Laser, Plasma and Radiation Physics, Magurele-Bucharest, 077125, Romania
3 Department of Materials Science, CENIMAT/I3N, Faculty of Sciences and Technology, New University of Lisbon, 2825-516 Caparica, Portugal
4 Institute of Applied Physics, Academy of Sciences of Moldova, Chisinau, Republic of Moldova
5 National Institute of Materials Physics, Magurele-Bucharest, 077125, Romania