Structure and photo-induced effects in elemental chalcogens: a review on Raman scattering

Abstract

Much progress has been made over a long period, spanning more than a century, in understanding the atomic arrangement on various length scales of non-crystalline chalcogens and their transitions upon certain external stimuli. However, it is broadly admitted that there are still several unsettled issues that call for proper rationalization. The current review presents an assessment of Raman scattering studies of non-crystalline phases of elemental chalcogens and their mixtures. First, a few remarks on the analysis of Raman data, related to polarization details and spectra reduction are presented. The effect of temperature, pressure and irradiation on the structure of chalcogens is reviewed in detail. As only selenium can form a stable glass at ambient conditions, the interest on sulfur and tellurium has been placed in the melt and the amorphous phase, respectively, whereas reference is also made to the sporadic structural studies of glassy sulfur at low temperatures. It is shown how Raman scattering can be exploited to explore unique phenomena emerging in the liquid state of sulfur, offering valuable information on the details of λ−transition including various thermodynamic-related properties. The subtle nature of this transition in selenium is also discussed. Tellurium is not only impossible to be prepared in the bulk glassy state, but also forms a very liable to crystallization amorphous film. Therefore, the emphasis is placed on light-induced nanostructuring and effects related to photo-amorphization and photo-oxidation. 2 IntroductionNon-crystalline chalcogenides, either as bulk glasses or amorphous films, have attracted extensive interest since their discovery, not only from the viewpoint of fundamental science but in addition owing to the technological potential that these materials exhibit over diverse sectors of active and passive applications [1,2]. Structure on the atomic scale is the decisive factor that determines macroscopic properties and ultimately function of the material. In addition, photoinduced effects, a hallmark of non-crystalline chalcogenides, depend on composition since structural arrangement must be suitable to allow photoinduced transformations on various length scales [3,4]. Understanding structure will not only allow identifying why a material behaves macroscopically in a certain manner, but will make feasible to establish structure-property relations. The latter are central to progress from serendipitous discoveries of functional materials to a rational design of materials with tailored properties. Disorder abolishes all the amenities accompanying the crystal periodicity, which render the role of structure-property relationships indispensable to disordered media.Resolving structure in the amorphous state is per se a formidable task. This is true even for simple systems, e.g. monoatomic chalcogens, let alone for multicomponent materials. Research for applications in non-crystalline chalcogenides has since the beginning of their discovery moved to studies of multicomponent systems, i.e....

Density functional and classical simulations of liquid and glassy selenium

“…The FF calculations at 350 K and 500 K show ring structures with up to 20 atoms, the most prominent being five-membered rings. DF calculations also give ring structures with five and more atoms, but the number of eight-membered rings is vanishingly small, except at the highest simulation temperature 773 K. This is very surprising, since an equilibrium between Se 8 rings and chains has been postulated for more than 60 years as a possible structure for a-Se [16,18,20].…”

“…There are three atoms in the unit cell and nine phonon branches, and the identification of the acoustic branches with torsional vibrations, and the optical branches with bending (∼13 meV) and stretching (∼30 meV) nodes, has been carried over to the disordered phases as well. The low-frequency modes (∼5 meV) have been attributed to interchain interactions (see [16] and references therein).…”

“…In spite of these structural regularities and the miscibility for all concentrations of S-Se, S-Te (with a gap [12,13]), and Se-Te [14,15], the disordered phases of S, Se, and Te differ greatly, as emphasized in a recent review [16]. It has been known for over a century [17] that the viscosity of liquid S increases by several orders of magnitude near 160 • C. This is usually attributed to the ring-opening polymerization of S 8 units [18], and very recent combined density, x-ray diffraction, and Raman scattering measurements in sulfur indicate * r.jones@fz-juelich.de the presence of a liquid-liquid first-order phase transition and critical point at pressures up to 3 GPa [19].…”

Direct-write laser-induced self-organization and metallization beyond the focal volume in tellurite glass

“…170 cm -1 is attributed to Te-Te homopolar bonds in amorphous tellurium (a-Te). As reported by others, Te-Te homopolar bonds are not stable and crystallize above 285 K, however, they can be found up to 473 K [35,38,39]. This result indicates the existence of a chain-like structure within the amorphous phase after femtosecond pulses irradiation.…”

“…As their intensity gradually increases towards the center, the main peaks assigned to structures in the glass vanish in Figure 5(c). Raman spectra are deconvoluted into Gaussian bands and accordingly, the peaks at 119, 139, 170, 220, 264 and 355 cm -1 are observed at the center of modified region (peak assignment is performed based on [37][38][39][40][41][42][43][44]). Peaks at 119, 139, 220 and 260 cm -1 belong to a crystallized trigonal tellurium (t-Te) phase.…”