Phase-change like process through bond switching in distorted and resonantly bonded crystal

Abstract

Although some methods to improve phase-change memory efficiency have been proposed, an effective experimental approach to induce a phase-change like process without external heat energy has not yet been reported. Herein we have shown that GeTe is a prototype phase-change material, which can exhibit a non-thermal phase-change-like process under uniaxial stress. Due to its structural characteristics like directional structural instability and resonance bonding under 1% uniaxial stress, we observed that bond switching in the GeTe film between short and long bonds is possible. Due to this phase change, GeTe displays the same phase-change as crystal layer rotation. Crystal layer rotation has not been observed in the conventional phase change process using intermediate states, but it is related to the structural characteristics required for maintaining local coordination. Moreover, since the resonance bonding characteristics are effectively turned off upon applying uniaxial stress, the high-frequency dielectric constant can be significantly decreased. Our results also show that the most significant process in the non-thermal phase transition of phase-change materials is the modulation of the lattice relaxation process after the initial perturbation, rather than the method inducing the perturbation itself. Finally, these consequences suggest that a new type of phase-change memory is possible through changes in the optical properties under stress.

Elastic organic semiconducting single crystals for durable all-flexible field-effect transistors: insights into the bending mechanism

“…Despite the demonstration of mobility values as low as 10 −4 cm 2 V −1 s −1 from the strained flexible devices fabricated from DPP-diEt, it is important to note that these measurements have been reliable over a number of devices (at least 3 devices) and such values of low mobility are not uncommon in solution processed organic semiconductors. 41,43 Although it has been observed that the single crystals of DPP-diMe can withstand strains up to 3–6%, we still observed a decrease in μ FET , for much lower strains in the device (strain range: 0.7–1.25%). This behaviour can be attributed to several factors such as the difference in strain between the layers involved in device fabrication, development of micro-cracks in the dielectric layer and the metal contacts with the crystal.…”

“…The paucity of the reported DFT strain–energy data on elastically deformable molecular crystals limits our ability to compare these findings to the uniaxial strain behaviour of other elastically bendable molecular crystals. However, comparable periodic DFT calculations on rhombohedral crystalline GeTe ( r -GeTe) suggests 41 that the minimum in the strain-energy curve need not always be at zero strain, and in the case of r -GeTe it is as high as 2.47% uniaxial strain for its phase 2 structure. For DPP-diMe, the DFT results are in excellent agreement with the results of the experimental mechanical bending tests (see ESI, Fig.…”