Crystal Growth in Se–Te Chalcogenides: Overview of the Growth/Relaxation/Viscosity Interplay for Bulk Glasses and Thin Films

Abstract

Crystal growth in 1 μm Se(1–y)Te y thin films (for y = 0, 7, 10, and 17) deposited on the Kapton, SiO2 glass, and white glass substrates was researched and quantified by means of a unique combination of direct joint microscopic and calorimetric measurements. As a general feature, the crystal growth in the Se–Te thin films deposited on a Kapton tape was very close to the native/bulk crystal growth. Deposition on the inorganic glassy substrates largely accelerated the crystal growth in the Se–Te thin films due to the build-up of internal tension originating from the large difference in thermal expansion coefficients between the film and the substrate. An additional increase in the crystal growth rate was also caused by the diffusion of Na+ ions from the white glass substrate into the Se–Te films. Almost perfect correspondence was found for the activation energies of crystal growth determined by various measurement techniques (calorimetry and microscopy) and for various Se–Te sample forms (thin films, bulk glass, powdered bulk glass). A very good agreement was found also between the activation energies of viscous flow and structural relaxation at the glass transition temperature T g. At higher temperatures, the Se–Te thin films exhibit a minor-to-moderate breach of the Stokes–Einstein law, as expressed by the value of Ediger’s decoupling parameter ξ ≈ 0.80 ± 0.05. At lower temperatures near the glass transition, the violation of the Stokes–Einstein relation deepens for the thin films with higher Te content. An explanation was proposed based on the potential interconnection between the below-T g relaxation kinetics and above-T g connectivity of the undercooled liquid domains (resulting either in changes of the effective hydrodynamic radius during the self-diffusion or in the tendency to create structural inhomogeneities via thermal fluctuations).

Native Crystal Growth Revealed by a Joint Microscopy–Calorimetry Technique in (GeS2)0.1(Sb2S3)0.9 Thin Amorphous Films: A Critical Role of Internal Stress and Mechanical Defects

“…All depicted u r −T dependences are very similar, differing within half an order of magnitude. This is well consistent with the concept of different substrates having only a low impact on the crystals growing from the free surface�contrary to, e.g., Se y Te 1−y thin films, 37 where the substrate-caused differences in u r were almost 2 orders of magnitude large (due to the Se y Te 1−y nucleation and crystal growth initiating at the film/substrate interface). The subtle trends resulting from Figure 6A are as follows: (1) u r slightly decreases with decreasing film thickness; (2) apart from high T, u r is slightly lower for the growth in the films deposited on the glass substrate; and (3) at higher T, u r in thin films is lower than that in the bulk glass.…”

“…For the present thin films, the glass transition temperature T g varied between ∼180−210 °C (in the 1−10 °C•min −1 range of q + ; measured during a single heating scan in the as-deposited state). Contrary to the recently studied Se−Te thin films, 37 the T g of the as-deposited (GeS 2 ) 0.1 (Sb 2 S 3 ) 0.9 thin film is significantly lower compared to that for the bulk glass (225− 230 °C in the 1−10 °C•min −1 range). This may be understandable from the structural point of view, where the bulk glass is significantly more compact (prepared by rapid cooling of a liquid) compared to the vapor-deposited thin film, in which individual structural units were deposited and stacked in a low-density, nonrelaxed regime with higher free volume and/or porosity.…”

“…38 It is immediately apparent that the macroscopic manifestation of the crystal growth is very similar for both as-deposited films, regardless of the underlying substrate (Kapton or white glass). Interestingly, at high q + , it is the films on the Kapton substrate that exhibits faster crystallization (contrary to what was observed for the Se−Te glasses 37 ). The crystallization rate of the 1 μm film on the white glass substrate is at high q + , even close to that of the 20− 50 μm powdered bulk material.…”

Direct comparison of surface crystal growth kinetics in chalcogenide glass measured by microscopy and DSC

“…Some authors also focused their attention on the combined study of the kinetics of crystal growth of chalcogenide glasses by microscopy and DSC 30–33 . The crystal growth rate in thin chalcogenide films was calculated using a correlation between DSC data (described by the JMAK model) and microscopy data 29,34,35 . However, to our knowledge, there are not as many articles that provide a model for the direct calculation of crystal growth data from DSC measurements 36 …”

“…[30][31][32][33] The crystal growth rate in thin chalcogenide films was calculated using a correlation between DSC data (described by the JMAK model) and microscopy data. 29,34,35 However, to our knowledge, there are not as many articles that provide a model for the direct calculation of crystal growth data from DSC measurements. 36 This paper quantitatively compares the surface crystal growth kinetics in a chalcogenide glass measured by microscopy and DSC.…”