Physics of Amorphous Materials,
Dynamical Heterogeneities in undercooled Melts
and Relaxation Phenomena

A material is referred to a "glass", if it has an amorphous structure in the solid state and undergoes a glass transition when heating into an undercooled melt. Bulk metallic glasses are often composed of many components. Appearance and some properties of such glasses are similar to that of crystalline metals, but their mechanical (rheological) behaviour is completely different. Using dynamical mechanically spectroscopy we analyse the excitation processes and compare with simulation data on the microscopic (nanometer) scale.

Sample preparation

The samples can be prepared by rapid quenching from the melt using various techniques:
  • Splat-Quenching: The liquid sample is quenched between two copper pistons.
  • Melt-spinning: This method, which is commonly used commercially, produces narrow ribbons by quenching the melt on a rotating copper wheel.
  • Mold-Casting: Solidification in a cooled copper mold yields bulk samples.
  • Vapor deposition of glass forming alloys onto a cold substrate under UHV-conditions yields amorphous thin films.

  • Mechanical Spectroscopy

    Mechanical spectroscopy on different time scales offers a way to measure elastic constants, viscosity of liquids, polymers, biological systems and glasses as well as to investigate loss mechanisms in those complex fluids.
    For low frequencies (0.1-50 Hz) and a temperature range of -100°C to 1000°C, we use a dynamic mechanical analyzer (DMA) to apply static and dynamic forces on the sample.
    For the kHz range (about 5.4 kHz), the double paddle oscillator (DPO) is a very sensitive tool. Operated at its resonance frequency, it allows for the analysis of mechanical properties of thin films.
    For low temperatures (Room temperature down to 2 K) a pulse echo ultrasound measurement unit (USO) is used, which can detect very small changes in the elastic moduli for a given frequency in the MHz range.
    Most recently an Acoustic Atomic Force Microscope (AFAM) was built with the help of W. Arnold, which allows also local spectroscopy at surfaces.

    AG Samwer
    Fig. 1: Loss spectroscopy as a function of temperature: Identification of the ?-process (wing) in the loss spectra of PdCuSi

    For a deeper understanding of the connection of microscopic and macroscopic behaviour of glasses, the correlation between α- und β-relaxation as seen in loss spectra needs further explanation. At the moment, we discuss the α-process in the context of shear transformation zones (STZ) and the β-process with chain like excitations (strings). The former dominates the liquid above Tg, the latter below Tg. At high temperatures (T > Tg) both merge. Using higher mechanical forces we recently demonstrate the interaction of (vectorial) mechanical forces with the (scalar) temperature and identify local avalanches as the main relaxation process in creep and stress-strain curves.

    To examine microscopic processes which are not accessible experimentally, molecular dynamics simulations are employed for comparisons, which are done in collaboration with several colleagues. The great progress achieved recently in the description of the primary (α-) and secondary (β-) relaxation as well as in the avalanche dynamics is supported by the results of computer simulations.

    The thermophysical properties of semiconductor melts are investigated in an international project with experiments in microgravity environment (parabola flights, International Space Station). The samples are processed in an electromagnetic levitator in UHV and can be analysed with contactless techniques to measure thermal expansion, surface tension and viscosity. The connection of fragility and thermal expansion is now also mathematically established.


    1.) Local elastic properties of a metallic glass, H. Wagner, D. Bedorf, S. Küchemann, M. Schwabe, B. Zhang, W. Arnold and K. Samwer, , Nature Materials 2011, 10, 439.
    2.) Dynamic Singularity in Multicomponent Glass-Forming Metallic Liquids, S.M. Chathoth, B. Damaschke, M.M. Koza, and K. Samwer, Phys. Rev. Lett. 2008, 101, 037801
    3.) Anelastic to Plastic Transition in Metallic Glass-Forming Liquids, J.S. Harmon, M.D. Demetriou, W.L. Johnson, K. Samwer, Phys. Rev. Lett. 2007, 99, 135502
    4.) A universal criterion for plastic yielding of metallic glasses with a (T/Tg)2/3 temperature dependence, W.L. Johnson, K. Samwer, Phys. Rev. Lett. 2005, 95, 195501
    5.) Interatomic repulsion softness directly controls the fragility of supercooled metallic melts, J. Krausser, K. Samwer and A. Zaccone, PNAS 2015, 10.1073/1503741112
    6.) Unified Criterion for temperature-Induced and Strain-Driven Glass Transitions in Metallic Glasses, H.B. Yu, R. Richert, R. Maass, K. Samwer, Phys. Rev. Lett. 2015, 115, 135701
    7.) Strain induced fragility transition in metallic glass, H.B. Yu, R. Richert, R. Maass, K. Samwer, Nature Communications 2015, 6, 7179
    8.) Crossover from random three-dimensional avalanches to correlated nano shear bands in metallic glasses, J.-O. Krisponeit, S. Pitikaris, K.E. Avila, S. Kuechemann, A. Krueger, K. Samwer, Nature Communications 2014, 5, 3616