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Terahertz Conductivities and Optical Constants of High-Entropy Alloys and Their Applications
High entropy alloys
Metallic materials always play an important role to our life. In the past, we have tried to enhance the certain characteristics of the metal, so we would have used one of the main metal with smaller amounts of other elements to change its original properties for more applications in many fields. However, the experiments showed that the higher mixing make higher difficulty, even make the materials easier to become brittle. In recent years, there is a novel material called High-Entropy Alloys(HEAs) that has opened up the whole new developments to the world. In physics, Entropy indicated some kinds of chaos. As more other elements increase, the chaos of the principal element becomes more confusing. HEAs is defined as five or more than five elements, but widely it can also be three or four principal elements. HEAs can not only synthesize bulks but also synthesize thin films. Due to advanced technology, there are two types of HEAs. One is that each element has an equal atomic ratio, the other is unequal. The difference between them that is the latter provides the higher capabilities. Different kinds of elements,proportions, scales can produce different attributes. For instance, high density,corrosion resistance, high temperature resistance, wear resistance, high toughness, magnetic properties, formability…etc. Nowadays, many optical information can be obtained quickly in THz spectroscopy. For instance, refractive index, photoconductivity, mobility…etc. High entropy alloys come in a variety of types. In order to improve the measurement efficiency, THz is used to explore the properties of this HEAs. The advantage of THz measurement are non-contact, low photon energy(4.1meV) and even more fast. For non-uniform HEAs, the traditional contact measurement method may destroy the material structure in the measurement process, so it can be measured by THz TDS. Even though THz has a strong reflection on metals, in this paper we used nano-scale NbMoTaW film with DC magnetron sputtering method to deposit on high resistivity silicon substrate as a sample, and to measure different thickness. And then the THz wave is passed through the sample by normal incident. We can see the change of phase and amplitude of the signal. Finally take the data and analyze. The conductivity, transmittance and properties of the signal are calculated.
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