As-based chalcogenides as holographic recording media

Amorphous chalcodenide materials are semiconducting compounds formed by VI. A group elements (excluding oxygen) in combination with each other or with other elements. The glass forming region decreases with increasing mass of used atoms [22] and with decreasing amount of chalcodenide [22,23] With increasing cooling speed the glass forming region increases. Amorphous system As$_x$S$_{100-x}$ shows only the short range order, it consist of various structural units corresponding to As$_{40}$S$_{60}$, As$_{28}$S$_{72}$ [24], in sulfur rich systems also S$_8$ [24]. In the As rich compounds can also be observed As-As bonds (e.g. in As$_4$S$_4$ units [25]) In the thermally evaporated thin layers can be found low-mass fragments as As$_4$S$_4$, As$_4$S$_3$, As$_4$S$_8$ and others [26]. Thin layers are heterogeneous and thermodynamically unstable systems which can exhibit a wide variety of changes of their physical properties particularly when exposed to light or annealed. Difference in structure of bulk sample and thermally evaporated thin layer was proven by many authors [27,28,29]