No abstract

No abstract

Three elastic phases of covalent networks, (I) floppy, (II) isostatically rigid and (III) stressed-rigid have now been identified in glasses at specific degrees of cross-linking (or chemical composition) both in theory and experiments.Here we use size-increasing cluster combinatorics and constraint counting algorithms to study analytically possible consequences of self-organization. In the presence of small rings that can be locally I, II or III, we obtain two transitions instead of the previously reported single percolative transition at the mean coordination numberr = 2.4, one from a floppy to an isostatic rigid phase, and a second one from an isostatic to a stressed rigid phase. The width of the intermediate phase ∆r and the order of the phase transitions depend on the nature of medium range order (relative ring fractions). We compare the results to the Group IV chalcogenides, such as Ge-Se and Si-Se, for which evidence of an intermediate phase has been obtained, and for which estimates of ring fractions can be made from structures of high T crystalline phases.

Network glasses are the physical prototype for many self-organized systems, ranging from proteins to computer science. Conventional theories of gases, liquids, and crystals do not account for the strongly material-selective character of the glass-forming tendency, the phase diagrams of glasses, or their optimizable properties. A new topological theory, only 25 years old, has succeeded where conventional theories have failed. It shows that (probably all slowly quenched) glasses, including network glasses, are the result of the combined effects of a few simple mechanisms. These glass-forming mechanisms are topological in nature, and have already been identified for several important glasses, including chalcogenide alloys, silicates (window glass, computer chips), and proteins."Some four thousand years ago man discovered glass in the embers of a fire built somewhere in the deserts of the Near East. A few years from now ultratransparent glass fibers will be transmitting [much, much, much!] more information than copper wires"[1]. As foreseen 25 years ago, the Internet has indeed revolutionized our world. In this article certain phrases will appear in {}s: the interactive reader will find background on the quoted topics with his Internet Browser. What was unforeseeable 25 years ago was the discovery of an important new class of electronic glasses, doped cuprates, exhibiting not only high temperature superconductivity (~ 100K), but also "strange metal" transport anomalies right up to the annealing temperature (700 K) -a sure sign of electronic glassy arrest. Theory has identified two new topological phase transitions in network glasses,

An increasingly important issue in semiconductor device physics is understanding of how departures from ideal bonding at silicon-dielectric interfaces generate electrically active defects that limit performance and reliability. Building on previously established criteria for formation of low defect density glasses, constraint theory is extended to crystalline silicon-dielectric interfaces that go beyond Si-SiO 2 through development of a model that quantifies average bonding coordination at these interfaces. This extension is validated by application to interfaces between Si and stacked silicon oxide/nitride dielectrics demonstrating that as in bulk glasses and thin films, an average coordination, N av , greater than three yields increasing defective interfaces.