(II) thin films were synthesized and compared to the pure telluride Ge 2 Sb 2 Te 5 . In situ X-ray diffraction (XRD) and in situ transmission electron microscopy (TEM) investigations revealed a remarkably increased stability of the as-deposited amorphous phase and crystalline phases, which is increased by a factor of 100 for compound (II) compared to established phase change materials.

Thin film samples of Ge 9 SnSb 2 Te 9 Se 4 , Ge 4.5 SnSb 2 Te 4.5 Se 4 , Ge 2.5 SnSb 2 Te 2.5 Se 4 , and GeSnSb 2 TeSe 4 were prepared via co-sputtering of GeTe and SnSb 2 Se 4 and compared to the well-investigated phase change material GeTe. All samples were obtained in an amorphous state. Temperature-dependent in situ X-ray diffraction experiments reveal a crystallization temperature that increases with an increasing SnSb 2 Se 4 content, leading to a higher stability of the amorphous phase. The electrical contrast between the amorphous and metastable crystalline state investigated via the van der Pauw method is as large as 4 orders of magnitude up to a 4.5:1 GeTe:SnSb 2 Se 4 ratio. Increasing the SnSb 2 Se 4 content leads to a decrease in the electrical contrast. Investigations of the samples by applying Fourier transform infrared spectroscopy and variable incident angle spectroscopic ellipsometry show that the optical properties of the amorphous phase are not affected by changes in stoichiometry. In striking contrast, the impact of SnSb 2 Se 4 on the optical properties of the crystalline phases is significant: all optical constants decrease because of the reduction in the level of resonant bonding, which leads to a reduced absolute reflectivity of the crystalline phase resulting in a decrease in the optical contrast. These results support the assumption that resonant bonding is crucial for successful optical phase change memory materials.

Thin films of (Ge 1-x Sn x ) 8 Sb 2 Te 11 are prepared to study the impact of Snsubstitution on properties relevant for application in phase-change memory, a next-generation electronic data storage technology. It is expected that substitution decreases the crystallization temperature, but it is not known how the maximum crystallization rate is affected. Ge 8 Sb 2 Te 11 is chosen from the (GeTe) y (Sb 2 Te 3 ) 1-y system of phase-change materials as a starting point due to its higher crystallization temperature as compared to the common material Ge 2 Sb 2 Te 5 . In situ X-ray diffraction at 5 K min −1 heating rate is performed to determine the crystallization temperature and the resulting structure. To measure the maximum crystallization rate, femtosecond optical pulses that heat the material repetitively and monitor the resulting increase of optical reflectance are used. Glasses over the entire composition range are prepared using a melt-quenching process. While at x = 0, 97, subsequent pulses are required for crystallization, one single pulse is enough to achieve the same effect at x = 0.5. The samples are further characterized by optical ellipsometry and calorimetry. The combined electrical and optical contrast and the ability to cycle between states with single femtosecond pulses renders Ge 4 Sn 4 Sb 2 Te 11 promising for photonics applications.