Thin films of amorphous Ga 2 S 3 and rare-earth sulphides M. Popescu a , A. Lőrinczi a , F. Sava a,n , A. Velea a , I.D. Simandan a , P. Badica a , M. Burdusel a , A.C. Galca a , G. Socol b , F. Jipa b , M. Zamfirescu b a National Institute of Materials Physics, Atomistilor 105bis, RO-077125, P.O. Box M.G. 7, Magurele-Ilfov, Romania b National Institute for Laser, Plasma and Radiation Physics, Atomistilor 409, RO-077125, P.O. Box M.G. 36, Magurele-Ilfov, Romania article info Article history: Received 18 September 2014 Accepted 4 December 2014 Available online 13 December 2014 Keywords: Amorphous thin films Spark Plasma Sintering Pulsed Laser Deposition Femtosecond laser irradiation abstract The aim of this research is to prepare amorphous thin films of undoped gallium sulphide and doped with rare-earth sulphides, of rare-earth sulphides and to investigate their physical properties. We have prepared thin amorphous films of Ga 2 S 3 , EuS, Er 2 S 3 , Gd 2 S 3 , and Ga 2 S 3 doped with rare-earth sulphides (Ga 2 S 3 :EuS, Ga 2 S 3 :Er 2 S 3 , Ga 2 S 3 :Gd 2 S 3 ) by Pulsed Laser Deposition (PLD). The corresponding targets for preparation of amorphous thin films were obtained by Spark Plasma Sintering (SPS) from commercially available powders of binary sulphides. The structural results for the undoped and doped Ga 2 S 3 thin films indicate a packing of disordered layers similar to that of amorphous As 2 S 3 . Femtosecond laser irradiation of the Ga 2 S 3 thin films shows a photoexpansion effect at low laser power (85–100 mW) and an ablation effect at higher laser power (above 105 mW). The threshold between low power and high power pulses is situated at higher value for Ga 2 S 3 (100 mW) in comparison with the case of As 2 S 3 thin films (20 mW). & 2014 Elsevier B.V. All rights reserved. 1. Introduction Chalcogenide glasses based on Ga 2 S 3 have interesting applica- tions in optics and optoelectronics [1] such as infrared and mid- infrared lasers [2], fiber optics amplifiers [3]. They can be drawn into optical fibers [4], can form waveguides [5] or can be doped by high concentrations of RE-ions [6]. Sulphide glasses are wide band gap semiconductors (1.5–3.6 eV) making them promising candi- dates for optoelectronics and photovoltaics. The best known RE gallium-sulphides glasses are the gallium– lanthanum-sulphide glasses which have been proposed as RE hosts for 1.3 μm optical amplification devices [7]. Recently Pom- pilian et al. [8] have prepared and investigated amorphous thin films of Er- and Pr-doped Ga–La-S. Using the same techniques (SPS and PLD), Yang et al. [9] have obtained high-quality crystalline thin films of the ferromagnetic insulator europium (II) sulphide (EuS). We report in this paper the preparation and properties of amorphous thin films based on undoped gallium sulphides and doped by rare-earth sulphides, and on rare-earth sulphides. 2. Materials and methods Ga 2 S 3 (purity 99.99%) and rare-earth sulphides powders (Alpha- AESAR and CHEMOS GmbH) were used to prepare mixtures under ambient conditions by manually grinding for 360 s in an agate mortar. These mixtures with compositions of (Ga 2 S 3 ) 0.95 (Re x S y ) 0.05 at%, (where Re x S y ¼ EuS, Er 2 S 3 and Gd 2 S 3 ) were used to prepare disc-shaped bulk samples by SPS. Using the same technique, additional disc-shaped bulk samples of EuS, Er 2 S 3 and Gd 2 S 3 have been prepared. For Spark Plasma Sintering we have used a commercial SPS machine FCT Systeme GmbH—HP D 5, Germany. In the SPS tech- nique a pulsed current and a uniaxial pressure on punches of a mould system are simultaneously applied. The initial vacuum in the SPS furnace was 40 Pa. The uniaxial pressure applied on punches was 60 MPa. The heating rate was 100 1C/min and the temperature rise up to 900 1C when this temperature was main- tained for 5 min. A pulsed current pattern of 12-on/2-off pulses was applied, with a 3 ms period. The total time of one sequence was  0.04 s. The operating voltage and the peak current were up to 5 V and 1600 A, respectively. The sintered ceramic disks have been used as targets for Pulsed Laser Deposition (PLD) of thin films. During the laser ablation process, the glass and silicon substrates were kept at room temperature and continuously rotated. The targets were irradiated with a KrF n laser, model COMPexPro 205, Lambda Physics- Coherent (λ ¼ 248 nm, τ FWHM ¼ 25 ns) that operated at a repetition rate of 10 Hz and at a fluence of 3 J/cm 2 . The thin films have been studied by X-ray diffraction (XRD), atomic force microscopy (AFM), ellipsometry, and optical absorp- tion spectroscopy. To obtain the X-ray diffraction curves of the thin films we used a Bruker A8 Advanced diffractometer provided with CuKα target tube, scintillation counter, Göbell mirror and Asymmetric Channel-cut (ACC) Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/matlet Materials Letters http://dx.doi.org/10.1016/j.matlet.2014.12.028 0167-577X/& 2014 Elsevier B.V. All rights reserved. n Corresponding author. Tel.: þ40 213690170. E-mail address: fsava@infim.ro (F. Sava). Materials Letters 142 (2015) 229–231