The density of the amorphous phase of metals is generally thought to be related to glass formation, but this correlation has not been demonstrated experimentally to date. In this work, systematic deflection measurements using microcantilevers and a combinatorial deposition method show a correlation between glass-forming ability and the density change upon crystallization over a broad compositional range in the copper-zirconium binary system. Distinct peaks in the density of the amorphous phase were found to correlate with specific maxima in the critical thickness for glass formation. Our findings provide quantitative data for the development of structural models of liquids that are readily quenched to the amorphous state. The experimental method developed in this work can facilitate the search for new glass-forming alloys. Metallic glasses are amorphous metals that do not have a structure with longrange atomic order like crystalline materials do, but have pronounced short-and medium-range order at the atomic scale. Because of their very different properties as compared to those of their crystalline counterparts, metallic glasses are very promising materials for future structural, chemical, and magnetic applications (1, 2). The packing density of the amorphous phase is a key consideration in studying the formation of metallic glasses (2-5). A liquid of high packing density (6-8) has a low free volume content and a correspondingly low atomic mobility (9-11). Upon quenching, such a liquid is expected to have a strong kinetic constraint on nucleation and the subsequent growth of crystals. This has been the basis for recent theoretical studies (12, 13) of structural models of metallic glasses, in which a correlation between compositions having especially dense packing and compositions that are known to quench to the glassy state at relatively low cooling rates was sought, but not obtained. Earlier studies of the density of glasses, based on the Archimedes method, have been mostly limited to relatively narrow compositional ranges of ternary and quaternary alloys with large critical sample sizes for glass formation (14-16), and no correlation between density and the ease of glass formation has been demonstrated.We have developed a method for the measurement of density changes, using microfabricated Si-rich silicon nitride (SiN) cantilevers (17). Owing to the small size and close spacing of the cantilevers, the deposition of alloy films with compositions that varied in a controlled way from cantilever to cantilever allowed a combinatorial approach to measurements of density changes for a broad range of compositions, with high compositional resolution. This process is schematically illustrated in fig. S1. Heatinginduced crystallization of the initially amorphous Cu-Zr films causes an increase in density (a decrease in volume) that causes an upward deflection of the cantilevers, as a result of the tensile elastic mismatch strain developed at the interface between the film and the cantilever. By measuring the magnitude of ...

Ex situ atomic force microscopy in combination with a high-precision furnace has been employed for a systematic study of crystallization kinetics of sputtered amorphous Ag0.055In0.065Sb0.59Te0.29, Ge4Sb1Te5, and Ge2Sb2Te5 thin films used for optical data storage. Direct observation of crystals enabled us to establish the temperature dependence of the crystal nucleation rate and crystal growth velocity around 150°C. While these alloys exhibited similar crystal growth characteristics, the crystal nucleation behavior of Ag0.055In0.065Sb0.59Te0.29 differed significantly from that of Ge4Sb1Te5 and Ge2Sb2Te5. These observations provide an explanation for the different recrystallization mechanisms observed upon laser heating of amorphous marks.

Sputtered amorphous Ge4Sb1Te5, Ge1Sb2Te4, Ge2Sb2Te5, and Ag0.055In0.065Sb0.59Te0.29 thin films were studied by differential scanning calorimetry. Upon continuous heating, heat release due to structural relaxation of the amorphous phase between 0.5 and 1.0 kJ/mol was observed. This value depends on the thermal history of the sample. Preannealing of the amorphous phase revealed the glass transition temperature Tg within 10 K of the crystallization temperature upon continuous heating at 40 K/min.