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In this chapter the fundamentals of Density Functional Theory (DFT) are introduced. After presenting the Hohenberg-Kohn theorem, the most common concepts and approximations in DFT-calculations, namely the Kohn-Sham equations and the Local Density Approximation (LDA), are summarized. They allow mapping the many-body problem on a single particle system which ultimately enables numerical calculations...
Glasses exist in threegeneric elastic phases: flexible, intermediateand stressed-rigid, which are determined by the connectivity of their backbones. Measurements of glass transition temperatures (Tgs) using modulated-differential scanning calorimetry permits distinguishing these phases by their characteristic non-reversing enthalpies (ΔHnr) at Tgs. In Raman scattering,...
This chapter reviews what is currently known about the atomic structure of Ge-Sb-Te phase-change materials in the amorphous phase. An introduction is first given to aspects of structural order in amorphous solids at different length scales, and brief reviews of experimental techniques for structure determination and of computer-simulation methods are outlined. A discussion is then given of the available...
Phase-change materials and their crystallization behavior are qualitatively described. This crystallization behavior is important for the applicability of materials in optical and electrical recording. We describe an experimental method to determine the crystallization rate at ambient temperatures and as a result the archival life stability of recorded data. Furthermore, we explain two experimental...
Optical storage based on phase change materials has been so successful because the data density was increased from generation to generation. Phase Change Random Access Memory will only be a viable technology when this trend of increased storage density can continue for several future lithography generations. This chapter reviews the scaling properties of the phase change materials themselves and explores...
The classical theory of steady state crystal nucleation is discussed, as originally developed by Gibbs, Volmer, Weber, Becker, Döring, Turnbull and Fisher. A particular focus is drawn on the implications of heterogeneous nucleation sites, which can increase the homogeneous nucleation rate by many orders of magnitude. Classical theory of crystal growth is covered as well. In Sect. 7.2, these...
This chapter offers a brief historical review of phase change materials as well as an overview of more recent findings. The chapter mainly focuses on the prototypical phase change materials in the Ge-Sb-Te and doped Sb-Te systems as these are currently the two composition spaces that are being applied both in the current generation of optical storage as well as future generations of electrical memory...
Optical and electrical properties of the phase change material Ge2Sb2Te5 are reviewed for its three phases. Implications of these data for the energy distribution of the density of electron states in the vicinity of the band edges are described. Near-band edge optical data obtained from ellipsometry and optical absorption spectra have been fitted with dispersion equations to determine values of ∼...
In 1987, the breakthrough discovery of the GeTe-Sb2Te3 pseudo-binary alloys removed the difficulties that had inhibited phase-change materials from being used in practical applications. The keys issues that had to be solved were related to i) the material composition and ii) the conceptual change in designing materials for phase-change devices. The prominent features of GeTe-Sb2Te3 pseudo-binary alloys...
Recently, alternatives to conventional sputter deposition have emerged as novel routes to phase change materials. Applying chemical vapor deposition (CVD), electrodeposition, or solution-phase deposition to these materials offers potential advantages in fabrication of phase change memory cells or optical discs, yet each method brings its own challenges. In this chapter, we review the basics of each...
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