Tuning electronic properties of graphene heterostructures by amorphous-to-crystalline phase transitions

Abstract

The remarkable ability of phase change materials (PCM) to switch between amorphous and crystalline states on a nanosecond time scale could provide new opportunities for graphene engineering. We have used density functional calculations to investigate the structures and electronic properties of heterostructures of thin amorphous and crystalline films of the PCM GeTe (16Å thick) and Ge2Sb2Te5 (20Å) between graphene layers. The interaction between graphene and PCM is very weak, charge transfer is negligible, and the structures of the chalcogenide films differ little from those of bulk phases. A crystalline GeTe (111) layer induces a band gap opening of 80 meV at the Dirac point. This effect is absent for the amorphous film, but the Fermi energy shifts down along the Dirac cone by −60 meV. Ge2Sb2Te5 shows similar features, although inherent disorder in the crystalline rocksalt structure reduces the contrast in band structure from that in the amorphous structure. These features originate in charge polarization within the crystalline films, which show electromechanical response (piezoelectricity) upon compression, and show that the electronic properties of graphene structures can be tuned by inducing ultra-fast structural transitions within the chalcogenide layers. Graphene can also be used to manipulate the structural state of the PCM layer and its electronic and optical properties.

Hydrogen evolution descriptors of 55-atom PtNi nanoclusters and interaction with graphite

“…Except for Pt 55 , both Ni and Pt spin down states show significantly larger weight than spin up states near the Fermi level (energy of the highest occupied state), in agreement with the calculated ground state magnetic moments. Graphite DOS should exhibit zero-gap (and zero-weight) at the Fermi energy [78], but we observe a 0.16 eV HOMO-LUMO gap in our model. This is due to the limited k-space sampling as we only sample in the Γ-point.…”

Research Advances in Amorphous‐Crystalline Heterostructures Toward Efficient Electrochemical Applications

“…[38][39] Intriguingly, several pioneering researches have recently pointed out that it is attractive to construct the amorphouscrystalline heterostructure by introducing amorphous nanomaterial into the traditional crystalline-crystalline heterostructure, which would expectedly offer greater opportunities to enrich the hetero interface structures and further improve the electrocatalysis performance, showing considerable advances in comparison with traditional crystalline-crystalline heterostructure. [40][41][42][43] This novel amorphous-crystalline heterostructure has rapidly drawn intensive interest and be one of the most hot research topic since its emergence. [44][45] Nevertheless, in contrast to the massive review works for traditional crystalline-crystalline heterostructures, [46][47][48][49][50] the origins, positive effects, and applications of such new amorphous-crystalline heterostructures have not been systematically collected, classified, and summarized.…”

Electronic Structures of Ge2Sb2Te5/Co2FeX (X: Al, Si) Interfaces for Phase Change Spintronics

“…Recently, the use of the phase change mechanism to tune the electronic properties of graphene as the electrode(s) has been proposed. 16,17 A second example is the ITO/PCM/ITO structure for phase change optoelectronics, as proposed by Hosseini et al 4 Indium tin oxide (ITO) is a special type of electrode, both metallic and transparent to visible light, making electrically switchable color pixels possible. PCMs actively tailor the optical reflectivity/refractivity of this structure through the phase change mechanism.…”

“…An example is the metal/PCM/metal sandwich structure for PCRAMs, in which the metal electrodes provide suitable electrical contact with the PCM interlayer which actively tailors the electrical conductivity of the device through the phase change mechanism. Recently, the use of the phase change mechanism to tune the electronic properties of graphene as the electrode(s) has been proposed. , A second example is the ITO/PCM/ITO structure for phase change optoelectronics, as proposed by Hosseini et al Indium tin oxide (ITO) is a special type of electrode, both metallic and transparent to visible light, making electrically switchable color pixels possible. PCMs actively tailor the optical reflectivity/refractivity of this structure through the phase change mechanism.…”