Low Temperature Relaxation And Optic Application Of Metallic Glasses

In terms of mechanism,the relaxation behavior of amorphous materials is the key to understand all kinds of physical phenomena in amorphous materials.The structure of metallic glasses(MGs)is simple due to the lack of side chains and groups.Therefore,metallic glass is an ideal model for studying glass-formers.The relaxation modes in the MGs are split near the glass transition temperature,?-and ?-relaxations respectively.The ? relaxations involves cooperation of a series of atoms and persists well below the glass transition temperature.Many studies show that the ? relaxations is related to deformation,plasticity and diffusion.After thermal treatment,the ? relaxations of MGs would be weakened,and the plasticity of the sample would be greatly reduced.However,the origin of the ? relaxations is not clear,which greatly hinders our understanding of the basic physics problems in glass-formers.In chapter 3 of this paper,the lowtemperature relaxation is studied from the perspective of overall relaxation behaviors,and the physical image from the near constant loss(NCL)to the ? relaxations is given preliminarily.In terms of application,compared with traditional metals,bulk MGs have higher hardness and strength,as well as good corrosion and wear resistance.On the other hand,MGs are easy to process and form due to the low viscosity in the supercooled liquid region.These excellent properties make it possible for MGs to replace traditional metallic materials in some fields in the future.At present,metallic glass has been widely used in high-frequency transformers,but the lack of tensile plasticity at room temperature is the bottleneck of the application.The micro-and nano-scale MGs can overcome this problem and can be precisely processed in large quantities.Therefore,low-dimensional MGs,including MGs with micro-nano structure and MG films,has attracted wide attention.Low-dimensional MGs have potential applications in many areas,such as medicine,optics,sensors and catalysis.In chapter 4,the surface Raman enhancement of MG films with nano-structure is explored.The following is a brief introduction of the two aspects of work:The NCL in relaxation spectra before ?-relaxations is a crucial dynamic phenomenon for glass-forming materials,while its underlying mechanism remains unclear and is hard to study due to the absence of characteristic time scale.We define a characteristic crossover point from both the dynamic mechanical measurements and the quasi-static tension experiments in the MGs,to study the transition regime,where the NCL dynamics terminates and evolves to the initiation of the ?-relaxation.It is found that such transition shows an apparent activation energy well below that of the ?-relaxation.Our results also show the concomitant change of the crossover points and the NCL with aging and provide a cursory physical picture on how the NCL occurs,decays and evolves to the ?-and ?-relaxations in MGs.The NCL involves in highly localized atomic motions existed in isolated,stochastic and reversible flow units persisted in the whole metallic glass.With the increase of temperature,the reversible ?-relaxation in which the atoms in flow units has escaped from their own cages and start to cooperate with each other appears.The surface-enhanced Raman spectroscopy(SERS)is a technique for the detection of analytes on the surface with an ultrahigh sensitivity down to the atomic-scale,yet the fabrication of SERS materials such as nanoparticles or arrays of coinage metals often involve multiple complex steps with the high cost and pollution,largely limiting the application of SERS.Here,we reported a complex hierarchical MG nanostructure by simply replicating the surface microstructure of butterfly wings through vapor deposition technique.The MG nanostructure displays an excellent SERS effect comparable to that of pure silver with similar structures,and moreover,a superhydrophilicity and self-cleaning behavior.The SERS effect of the MG nanostructure is attributed to the intrinsic nanoscale structural heterogeneities on the MG surface,which provide a large number of hotspots for the amplification of localized electromagnetic field and Raman scattering enhancement.Our works show that the MG could be a new potential SERS material with low cost and good durability,well extending the functional application of this kind material.