Nanoscale Inhomogeneities Mapping in Ga-Modified Arsenic Selenide Glasses

Shpotyuk et al. Nanoscale Research Letters (2017) 12:88 DOI 10.1186/s11671-017-1887-1 NANO EXPRESS Open Access Nanoscale Inhomogeneities Mapping in GaModified Arsenic Selenide Glasses Ya. Shpotyuk1,2*, S. Adamiak1, A. Dziedzic1, J. Szlezak1, W. Bochnowski1 and J. Cebulski1 Abstract Nanoscale inhomogeneities mapping in Ga-modified As2Se3 glass was utilized exploring possibilities of nanoindentation technique using a Berkovitch-type diamond tip. Structural inhomogeneities were detected in Gax(As0.40Se0.60)100−x alloys with more than 3 at.% of Ga. The appeared Ga2Se3 nanocrystallites were visualized in Ga-modified arsenic selenide glasses using scanning and transmission electron microscopy. The Ga additions are shown to increase nanohardness and Young’s modulus, this effect attaining an obvious bifurcation trend in crystallization-decomposed Ga5(As0.40Se0.60)95 alloy. Keywords: Arsenic selenide glass, Nanoindentation, Crystallization, Phase separation Background Chalcogenide glasses (ChG), e.g., chemical compounds of chalcogens (S, Se, or Te, but not O) with some elements from IV–V groups of the Periodic table (such as As, Sb, Ge, Bi) prepared by rapid quenching from a melt have found widespread application in modern photonics and optoelectronics because of their superior transmittance in IR domain ranged from visible to nearly 20– 25 μm [1–3]. This important class of disordered materials sometimes distinguished as functional media of chalcogenide photonics [4] can be well-represented by several canonical systems (model glass-formers), where arsenic triselenide As2Se3 (i.e., As40Se60 as classified in specialized glass-chemistry terminology) in the form of meltquenched bulky rods, drawn fibers, deposited, or sputtered thin films, etc. plays a crucial role [1–4]. For a long time, these As2Se3-type ChG have been preferentially used as passive photonics elements, only transmitting light from one point to another. In the last decades, it was shown that due to purposeful rare-earth (RE) doping, these glasses could be also employed for a number of very important active device applications [3, 4]. In this case, the mid-IR light can be initiated by emission of excited RE ions (such as Pr3+, Er3+, Dy3+, Tb3+) on * Correspondence: 1 Center for Innovation and Transfer of Natural Sciences and Engineering Knowledge, Faculty of Mathematics and Natural Sciences, University of Rzeszow, 1, Pigonia Str., 35-959 Rzeszow, Poland 2 Department of Sensor and Semiconductor Electronics, Ivan Franko National University of Lviv, 107, Tarnavskoho Str., Lviv 79017, Ukraine different wavelengths, thus creating the remote sources of light [5–8]. From purely implementation point, it is important to achieve a high enough concentration of RE ions in ChG. One of best solutions relies on introducing Ga (or In) into ChG matrix, permitting dissolution of higher ratio of RE dopants [8–13]. However, the Ga additions may essentially restrict glass-forming ability in many ChG systems [8, 11, 13–15] provoking parasitic devitrification processes at a nanoscale through phase separation, crystallite nucleation, growth, and extraction (uncontrolled spontaneous crystallization). Thus, it was shown, that in case of glassy As2Se3 it is not possible to introduce more than 3 at.% of Ga without such intrinsic structural decomposition, which essentially influences the ChG functionality [8, 12, 14]. It is understandable that reliable experimental monitoring of such nanoscale inhomogeneities in Ga-modified ChG is very important problem in the engineering of modern chalcogenide photonics. In this work, such methodology based on nanoindentation mapping supported by a number of electron microscopy visualization techniques will be examined at the example of Ga-modified As2Se3 glasses. Methods Conventional melt-quenching technique was employed to prepare Gax(As0.40Se0.60)100−x (x = 0−5) samples using high purity commercial elemental precursors of Ga (7N), As (5N), and Se (5N) [12–14]. The As and Se were specially purified by distillation with low evaporation © The Author(s). 2017 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. Shpotyuk et al. Nanoscale Research Letters (2017) 12:88 rate to remove impurities such as oxygen, water, silica, and carbon. The appropriate amounts of initial elements with total weight of 30 g were introduced into a silica tube of 10 mm in diameter. The ampoule was sealed under vacuum and heated up to 900 °C in a rocking furnace for 10 h followed by quenching into water from 700 °C. After quenching, the samples were swiftly moved to preheated furnace for annealing for 5 h at the temperature of 10 °C below glass transition temperature (to remove mechanical strains induced by fast quenching). The obtained rods were cut into disks of ~2 mm in thickness and polished to high optical quality. The method of nanoindentation mapping [16] was probed as a tool to disclose possible nanoscale inhomogeneities caused by Ga additions in As40Se60 glass. The values of nanohardness (NHD) and reduced elastic modulus (the Young’s modulus E) were detected with a help of CSM nanoindentation instrument (CSM Instruments SA, Peseux, Switzerland) equipped with a pyramidal Berkovitch-type diamond tip with a radius of about 100 nm employing the known Oliver-Pharr method [17] for data analysis. The standard samples of fused silica with elastic modulus of 73 GPa and Poisson’s ratio of 0.17 were used for indenter calibration allowing reliable load and displacement resolution at the level of 10 nN and 0.1 nm, respectively. The trapezoidal load-displacement curves (as those shown in Fig. 1 for As40Se60 and Ga3(As0.40Se0.60)97 glasses) were detected simultaneously for maximal load of 10 mN and loading-unloading rate of 20 mN/min, the dwell time at maximal loading being set to 15 s. The tested sample’s surface was scanned within a uniform grid of nanoindentation series (incl. 7–10 separate measurements). Such arranged experimental measuring protocol allows a quite acceptable locality of each measuring test, eliminating an influence of indentation- Fig. 1 Nanoindentation load-displacement curves for As40Se60 and Ga3(As0.40Se0.60)97 ChG Page 2 of 5 size effects [18–20]. The values of NHD and Young’s modulus E were statistically averaged for each series and a whole sample’s surface in final. The surface morphology of fresh cut-sections of the prepared alloys was additionally visualized using scanning electron microscope (SEM) with energy-dispersive X-ray spectroscopy (EDS) analyzer FEI QUANTA 3D 200i. The transmission electron microscopy studies with primary electron beam accelera (...truncated)