Abstract
With rapid advances occurring in terahertz (THz) radiation generation techniques, the interaction between matter and intense THz fields has become an important research topic. Among different types of THz radiation sources, the free electron laser (FEL) is a promising experimental tool that is expected to pave the way for new forms of material processing, control of phase transitions, and serve as a test bench for extreme operating conditions in high-speed small-size electrical and magnetic devices through the exploitation of strong THz electrical and magnetic fields without the presence of interband electronic excitation. In the current work, we irradiated Ge2Sb2Te5 phase change memory material with intense THz pulse trains from an FEL and observed THz-induced surface changes due to damage as a precursor to ablation and the formation of fine surface undulations whose spatial period is comparable to or slightly smaller than the wavelength of the excitation THz pulses in the material. The formation of undulations as well as the fact that no significant thermal effect was observed below the volume expansion threshold suggests that THz-induced effects mainly contributed to the observed changes. To the best of our knowledge, this is the first experimental observation of THz-induced undulations (so-called “LIPSS”), which are of potential importance for laser material processing.
Highlights
At the same time, intense THz radiation can be used as a test tool for high-speed electrical and magnetic device studies
Use of THz pulses goes beyond the limits of conventional measurements, enabling the application of instantaneous electrical and magnetic fields to a material or a device and can be used to replicate extreme operating conditions in high-speed electrical and magnetic devices in which their operation is induced by instantaneous high-intensity electrical or magnetic fields
We irradiated crystalline cubic Ge2Sb2Te5 phase change material samples with strong THz pulse trains generated by means of a free electron laser
Summary
Intense THz radiation can be used as a test tool for high-speed electrical and magnetic device studies. We report upon the effect of intense THz pulses derived from an FEL on two different crystalline Ge2Sb2Te5 (GST) phase change material samples with different electrical resistivities. The SET-RESET memory operation, known as crystalline-amorphous phase transition, is realized by application of electrical or optical pulses that induce thermal annealing or melt-quench disordering effects on the structure of GST. Since this structural phase transition results in significant differences in electrical resistivity and optical reflectivity, data storage can be realized. We confirmed that a bare Si substrate is not affected by THz pulse excitations for any fluence used in this experiment
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