Linear and NLO spectroscopy of GaSe and InSe nanoparticles formed via laser ablation A. Pashayev a , B. Tunaboylu b,c , K. Allahverdiyev ∗a,b , E. Salayev d , B. Tagiyev a,d a National Aviation Academy, Bina 25 th km St., Baku, Azerbaijan 1045; b Turkish Scientific and Technological Research Council, Marmara Research Centre, 1 Dr. Z. Acar St., Gebze/Kocaeli, Turkey 41470; c Istanbul Sehir University, Kustepe St., Uskudar, Istanbul, Turkey 34662; d Azerbaijan National Academy of Sciences, Institute of Physics, 33 H. Javid St., Baku, Azerbaijan 1143 ABSTRACT Nanoparticles of layered GaSe, InSe were fabricated by laser ablation (LA) method (KrF laser, λ = 248 nm, 50 Hz, maximum energy 200 mJ, τ = 4 ns) and characterized by: •XRF; •GDOES; •SEM and TEM; •UV-, VIS-, and IR- absorption; •Raman and PL spectroscopy (also in confocal geometry). Results are discussed in relation to the particle size. Absorption spectra of particles with diameter 20 nm and less turned out to be blue shifted and is consisted with a weak confinement effect on Wannier-Mott type excitons. It is shown, that with decreasing the particle size the energy position of the low-frequency Raman active phonons in both compounds are shifted to lower frequencies (21 and 18 cm -1 in bulk GaSe and InSe and 8 and 7 cm -1 in particles with sizes 5 and 7 nm, respectively). From the low frequency Raman data, decrease of the force constants ca. 25 % (for GaSe) due to the formation of the nanoparticles are estimated, and the origin is suggested. Second harmonic generation (SHG) with 1064 nm line of a mode locked Nd : YAG laser was observed for nanoparticles ablated on different substrates. Potential for using these structures for laser light visualizators are discussed. Keywords: Nanoparticles, layered crystals, gallium selenide, indium selenide, Raman scattering, PL, SHG, absorption 1. INTRODUCTION Semiconductor nanostructures are promising building blocks for future electronic and photonic devices. Nanostructures based on layer-type semiconductors, such as GaSe- type (GaS, InSe, GaTe) are of particular interest in terms of the optical, non-linear optical (NLO), solar, X- ray and particles detection applications 1-4 . GaSe and InSe have two main advantages over other semicondutors (GaAs, CdS, CdSe etc.), i.e. the large exciton binding energy (19.5 and 16.9 meV at 300 K, for GaSe and InSe, respectively) and the availability to perform the van der Waals homo-, and hetero- epitaxy growth for highly lattice-mismatched system 5 . Reduced dimensionality has a profound effect on the electronic, optical and NLO properties of material. The strong bonding inside the layers is thought to be covalent, with some ionic contribution 1-7 . At the same time the inter-layer bonding is much weaker, and is mainly of the van der Waals type. Because of this, easy cleavage occurs parallel to layers (perpendicular to the direction of the optical c- axis) into plane parallel slabs with mirror like surfaces. The hierarchy of weak forces and the ability of these materials for easy cleavage together with the low density of electronic states on freshly cleaved surfaces (does not exceed ∼ 10 10 cm -2 , water absorbs on a surface without any reaction and forms 3- D clusters on the (0001) planes)) and existence of different polytypes and other unique properties- is one of the main reason why GaSe-type layered semiconductors were extensivley investigated since about 1960th up to the present time 1-3 . Both in GaSe and InSe all polytypes have the same stacking unit of the covalently bonded Se – Ga(In) – Ga(In) – Se layer with average thickness of 0.797 nm (GaSe) and 0.669 nm (InSe) 1 . Difference between different polytypes are the stacking sequence and/or the stacking periodicity 1 . For GaSe and InSe- 4 and 3 polytypes were reported, respectively: (GaSe- β (D 6h 4 ); γ (C 3v 5 ); ε (D 3h 1 ); δ (C 6v 4 ) and InSe- β (D 6h 4 ); γ (C 3v 5 ); ε (D 3h 1 ) 1 . For both compounds the noncentrosymmetric ε- modification is the main component obtained from melt 1-3 . It contains 2 layers per unir cell. The indirect 1.96 eV (1.2 eV for InSe) and the direct 2.1 eV band gaps (1.32 eV for InSe) have been reported for GaSe single crystals 1,2 . Melting points of GaSe and InSe T m = 960 o C and T m = 600 o C, respectively (density: InSe 5.80 g/cm 3 and GaSe 5.03 g/cm 3 ) 1 . International Conference on Atomic and Molecular Pulsed Lasers XII, edited by Victor F. Tarasenko, Andrey M. Kabanov, Proc. of SPIE Vol. 9810, 981017 · © 2015 SPIE CCC code: 0277-786X/15/$18 · doi: 10.1117/12.2225218 Proc. of SPIE Vol. 9810 981017-1 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 01/29/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx