Photoinduced mass-transport based holographic recording of surface relief gratings in amorphous selenium films

Abstract

Surface relief gratings formation in amorphous selenium thin films in two recording configurations with light intensity modulation were studied in situ by real-time atomic force microscopy and diffraction efficiency measurements. We report observation of mass transport effect in films induced by band-gap irradiation when the light polarization of the recording beams has a component along the light intensity gradient ("p-p" scheme of recording) that allows obtaining giant stable gratings in this versatile chalcogenide material. On the contrary, only a pure scalar weak grating caused by photoinduced volume shrinkage is obtained in the "s-s" recording configuration, even for long-term irradiation. Chalcogenide glasses (ChG) are known to exhibit a rich variety of photoinduced changes when illuminated with near bandgap light including changes in mechanical properties, termed as photoplastic effects.1 Among them, the effect of light induced surface deformation and direct fabrication of surface relief gratings (SRGs) in ChG is intensively studied over the last decade both experimentally 2-10 and theoretically.11 Two main types of SRG induced by holographic recording, due to the excitation intensity modulation, with near band-gap light in ChG can be distinguished according to their formation mechanism and their properties:10 (1) small scalar SRG induced by either volume expansion or shrinkage due to different response of the material in the bright and dark zones of the interference pattern formed and (2) giant vectorial SRG induced by lateral mass transport in the case where the light polarization of the recording beams has a component along the light intensity gradient.Experiments have shown that only few compositions of ChG demonstrate both types of SRG. For example, vectorial SRG have been observed only for Se-rich films in the binary As-Se system (As 20 Se 80 ) 10 and for the compositions close to As 40 S 60 in As-S glasses 3 while scalar SRGs are common to all glass compositions of As-S and As-Se glasses. While for As-S glass the above observation (lack of vectorial SRG) could be accounted for by considering the photo-induced polymerization effect in S-rich compositions, 12 in the case of As-Se glasses the effect is not yet well understood. Although elemental amorphous Se (a-Se) is a model glass-former in chalcogenide science, no systematic studies of SRG formation have been carried out up to now, while investigations of other photoinduced effects abound. 13 A fact that perplexes studies of SRG formation relates to the photoinduced crystallization of a-Se (Ref. 14) under band-gap illumination, thus preventing the formation of advanced surface relief stable in time.Few papers report the formation of surface relief induced by holographic recording for a-Se films. 2,5,15 In an early study, Haro-Poniatowski et al.,15 employing phase conjugation, haveshown that small (20 nm in height) photoinduced surface relief gratings appears in 4 lm-thick films with the same spatial period. Slightly higher reliefs ($ 40 nm) formed a...

Light-induced mass transport in amorphous chalcogenides/gold nanoparticles composites

“…5). Due to the fact that the direction of photoinduced mass transport in amorphous selenium is opposite to As 20 Se 80 composition [16], the material accumulates in the places of the local minimum of light (Figs 5b and 5c). This results in a significant reduction in surface roughness of the sample under irradiation with light: from RMS of 1.33 nm for reference surface (Fig.…”

“…Amorphous Se (a-Se) and As 20 Se 80 were selected as the film forming compositions. The presence of significant mass-transport in As 20 Se 80 films [15] served as a criterion for its choice; while a-Se film was of interest due to the fact that it is the only ChG composition with the opposite direction of motion of the material (away from light) [16].…”

Electron beam-induced mass transport in As–Se thin films: compositional dependence and glass network topological effects

“…direct light-induced fabrication of surface relief (SR) by lateral mass transport on ChG films, have been widely studied for several selected composition, including As 0.4 S 0.6 , As 0.2 Se 0.8 , Se [9][10][11][12] and appropriate mechanisms were proposed recently [13,14]. More detailed study reveals the influence of chalcogen content on this process.…”

Coexistence of fast photodarkening and slow photobleaching in Ge_19As_21Se_60 thin films

“…Besides the fundamental interest in PD/PB in CG, these effects find useful technological applications in high bit rate waveguide writing, dense holographic recording, etc. [3][4][5][6]. PD in As-based CG has been investigated for many years and is believed to originate from photoinduced structural transformations.…”