Resonant bonding in crystalline phase-change materials

Shportko, K.; Kremers, Stephan; Woda, Michael; Lencer, Dominic; Robertson, John; Wuttig, Matthias

doi:10.1038/nmat2226

Cited by 1,006 publications

(988 citation statements)

References 27 publications

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“…For example, the dielectric constants of PbTe and Bi 2 Te 3 (||) are 33 and 50, respectively, while for Si the value is 11.76 (refs 20-22). In a similar way, certain electronic properties of thermoelectric and phase-change materials have also been explained by invoking resonant bonding 12,15 . Matsunaga et al 23 used experimental observations of low frequency of transverse optical (TO) phonons, so-called soft TO mode (a feature that is clear in the phonon dispersion to be shown later), to make a connection between resonant bonding and the small differences in the thermal conductivities of crystalline and amorphous phases of GST.…”

Section: Resultsmentioning

confidence: 93%

“…This description of resonant bonding is based on IV-VI compounds and their isoelectronic V elements for simplicity, but the resonant bonding exists in even more complicated materials such as V 2 -VI 3 and many alloys of IV-VI and V 2 -VI 3 materials 14 . In general, the unsaturated covalent bonding by p-electrons with rocksalt-like crystal structures can be regarded as resonant bonding 15 .…”

Section: Resultsmentioning

confidence: 99%

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Resonant bonding leads to low lattice thermal conductivity

et al. 2014

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Understanding the lattice dynamics and low thermal conductivities of IV-VI, V 2 -VI 3 and V materials is critical to the development of better thermoelectric and phase-change materials. Here we provide a link between chemical bonding and low thermal conductivity. Our first-principles calculations reveal that long-ranged interaction along the /100S direction of the rocksalt structure exist in lead chalcogenides, SnTe, Bi 2 Te 3 , Bi and Sb due to the resonant bonding that is common to all of them. This long-ranged interaction in lead chalcogenides and SnTe cause optical phonon softening, strong anharmonic scattering and large phase space for three-phonon scattering processes, which explain why rocksalt IV-VI compounds have much lower thermal conductivities than zincblende III-V compounds. The new insights on the relationship between resonant bonding and low thermal conductivity will help in the development of better thermoelectric and phase change materials.

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Section: Resultsmentioning

confidence: 93%

Section: Resultsmentioning

confidence: 99%

Resonant bonding leads to low lattice thermal conductivity

et al. 2014

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“…One of the most useful properties of GST materials is the huge difference of refractive index between amorphous and crystallized states in near-infrared region 31 . This allows on-demand writing of dielectric metamaterial patterns with resonances at near-infrared frequencies where the available spatial resolution is sufficient to write non-diffracting two-dimensional arrays of sub-wavelength meta-molecules.…”

Section: A Dielectric Metamaterialsmentioning

confidence: 99%

“…We used a Ti:Sapphire laser with single femtosecond pulse fluence up to 600 mJ/cm 2 at the wavelength of 730 nm. When changing phase from amorphous to crystalline, the complex refractive index of the film 3 changes from = 3.9 + 4.2 to = 4.3 + 2.0 (at a wavelength of 730 nm) 31 , which results in the formation of bright marks in reflection images. The written patterns were observed and recorded by a CCD camera with LED illumination at 633 nm using a lens of NA= 0.7.…”

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confidence: 99%

Optically reconfigurable metasurfaces and photonic devices based on phase change materials

et al. 2015

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Photonic components with adjustable parameters, such as variable-focal-length lenses or spectral filters, that can change functionality upon optical stimulation, could offer numerous useful applications. Tuning of such components is conventionally achieved by either micro-or nano-mechanical actuation of their constitutive parts, by stretching or heating. Here we report a new type of dielectric metasurface for making reconfigurable optical components that are created with light in a non-volatile and reversible fashion. Such components are written, erased and re-written as two-dimensional binary or grey-scale patterns into a nanoscale film of phase change material by inducing a refractive-index-changing phase-transition with tailored trains of femtosecond pulses. We combine germanium-antimony-tellurium-based films with a sub-wavelength-resolution optical writing process to demonstrate a variety of devices: visible-range reconfigurable bi-chromatic and multi-focus Fresnel zone-plates, a super-oscillatory lens with sub-wavelength focus, a grey-scale hologram and a dielectric metamaterial with on-demand reflection and transmission resonances.A metasurface made of carefully designed discrete metallic or dielectric elements can exhibit interesting abilities for directing the flow of electromagnetic radiation across the entire electromagnetic spectrum with similar capabilities to planar holograms in optics 1,2,3,4,5,6,7,8,9,10 . As substantial efforts are now focused on developing metamaterials with switchable 11, 12 and reconfigurable metadevices 13 driven by thermal 14,15 , electrostatic 16 and magnetic forces 17,18 and stretching 19 , and we are witnessing the emergence of concepts of randomly accessible reconfigurable metamaterials in the microwave 20,21,22 and optical regions of the spectrum 23, 24 thus making reconfigurable photonic devices 2 controllable by external signals a realistic possibility. Here we introduce and demonstrate dynamic photonic components written into a dielectric film that can be randomly and reversibly reconfigured with light. Recent work demonstrated control of a metamaterial with light 25 . In contrast, the technique reported here allows random and non-volatile two-dimensional control of optical properties of the film with diffraction-limited resolution and in a femtosecond (fs) time-frame. This provides much more flexibility and allows the creation of various photonic functions difficult or impossible with the above mentioned technologies. The randomly reconfigurable metasurface uses phase-change material and is written, erased and re-written as a two-dimensional binary or grey-scale pattern into a nanoscale thin film by inducing a refractive-index-changing phase-transition with tailored trains of femtosecond pulses.We use phase-change medium, the chalcogenide compound Ge 2 Sb 2 Te 5 (GST), which is widely exploited in rewritable optical disk storage technology and non-volatile electronic memories due to its good thermal stability, high switching speed and large number of achievable rewr...

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“…Moreover, the lateral optical force is reversibly altered, through a switchable tuning of the DQ-FR wavelength achieved by varying the state of Ge 2 Sb 2 Te 5 between amorphous and crystalline. 51 Consequently, it can change the sign of DQ-FR-induced transverse force at a fixed wavelength, hence moving the particle in the opposite direction. This advantage leads to a reversible manipulation of nanoparticles at linearly polarized plane wave incidence.…”

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confidence: 99%

Controlling Lateral Fano Interference Optical Force with Au–Ge₂Sb₂Te₅ Hybrid Nanostructure

et al. 2016

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We numerically demonstrate that a pronounced dipole− quadrupole (DQ) Fano resonance (FR) induced lateral force can be exerted on a dielectric particle 80 nm in radius (R sphere = 80 nm) that is placed 5 nm above an asymmetric bow-tie nanoantenna array based on Au/ Ge 2 Sb 2 Te 5 dual layers. The DQ-FR-induced lateral force achieves a broad tuning range in the mid-infrared region by changing the states of the Ge 2 Sb 2 Te 5 dielectric layer between amorphous and crystalline and in turn pushes the nanoparticle sideways in the opposite direction for a given wavelength. The mechanism of lateral force reversal is revealed through optical singularity in the Poynting vector. A thermal−electric simulation is adopted to investigate the temporal change of the Ge 2 Sb 2 Te 5 film's temperature, which demonstrates the possibility of transiting the Ge 2 Sb 2 Te 5 state by electrical heating. Our mechanism by tailoring the DQ-FR-induced lateral force presents clear advantages over the conventional nanoparticle manipulation techniques: it possesses a pronounced sideways force under a low incident light intensity of 10 mW/μm 2 , a fast switching time of 2.6 μs, and a large tunable wavelength range. It results in a better freedom in flexible nanomechanical control and may provide a new means of biomedical sensing and nano-optical conveyor belts.

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Resonant bonding in crystalline phase-change materials

Cited by 1,006 publications

References 27 publications

Resonant bonding leads to low lattice thermal conductivity

Resonant bonding leads to low lattice thermal conductivity

Optically reconfigurable metasurfaces and photonic devices based on phase change materials

Controlling Lateral Fano Interference Optical Force with Au–Ge₂Sb₂Te₅ Hybrid Nanostructure

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Resonant bonding in crystalline phase-change materials

Cited by 1,006 publications

References 27 publications

Resonant bonding leads to low lattice thermal conductivity

Resonant bonding leads to low lattice thermal conductivity

Optically reconfigurable metasurfaces and photonic devices based on phase change materials

Controlling Lateral Fano Interference Optical Force with Au–Ge2Sb2Te5 Hybrid Nanostructure

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Product

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Controlling Lateral Fano Interference Optical Force with Au–Ge₂Sb₂Te₅ Hybrid Nanostructure