Colloidal Phase-Change Materials: Synthesis of Monodisperse GeTe Nanoparticles and Quantification of Their Size-Dependent Crystallization

Yarema, Olesya; Perevedentsev, Aleksandr; Ovuka, Vladimir; Baade, Paul; Volk, Sebastian; Wood, Vanessa; Yarema, Maksym

doi:10.1021/acs.chemmater.8b02702

Cited by 30 publications

(68 citation statements)

References 38 publications

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“…Switching to NPs produced by chemical synthesis, only GeTe NPs have been studied in‐depth. [ 147,162–164 ] The dependence of T X on NPs size provides a consistent picture; see also Figure a. T X ‐values increase for decreasing NP size in a kind of exponential fashion.…”

Section: Phase‐change Materials In Nanoscale Dimensionssupporting

confidence: 57%

“…The general trend for thin films, nanowires, and nanoparticles indeed is that the melting temperature is reduced. [ 112,146,147 ] Still, the results do not appear too bad, since the melting temperatures of GeTe decreases from 725 °C (bulk value) to 600 °C when the film thickness is reduced to 2 nm; [ 112 ] see Figure 17d. Note that these GeTe films are sandwiched between SiO 2 and therefore the melting temperature reduction is probably more modest than for a free surface.…”

Section: Phase‐change Materials In Nanoscale Dimensionsmentioning

confidence: 99%

“…Reproduced with permission. [ 147 ] further permissions related to the material excerpted should be directed to the ACS. b,c) Crystallization temperature weakly decreases for decreasing Ge 2 Sb 2 Te 5 nanoparticle diameter.…”

Section: Phase‐change Materials In Nanoscale Dimensionsmentioning

confidence: 99%

“…In the most recent publication on GeTe NPs, two explanations for the observed size dependence of T X have been given. [ 147 ] One explanation is based on classical nucleation theory, using the argument that it is required to have one critical nucleus per NPs so that the density of critical nuclei N c is directly proportional to the volume of the NP ( V NP ), i.e. :

N_{c} = \frac{1}{V_{NP}} = \frac{6}{π d_{NP}^{3}}

.…”

Section: Phase‐change Materials In Nanoscale Dimensionsmentioning

confidence: 99%

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Chalcogenides by Design: Functionality through Metavalent Bonding and Confinement

2020

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unprecedented progress of the semiconductor industry and information technology. Yet, we have reached a stage where a simple evolution along established research lines might no longer bear much fruit. Advanced functional materials require increasingly complex and demanding property combinations. Their optimization would thus benefit from novel concepts. In thermoelectrics, which convert waste heat into electricity, for example, materials must show the unusual combination of high electrical and small thermal conductivity. This is demanding since a high electrical conductivity is usually accompanied by a high thermal conductivity. In phase change materials (PCMs) employed for data storage and processing, materials are required which possess a pronounced contrast in optical and/or electrical properties between two different states. Usually one of these states is a metastable one, which is typically amorphous, while the second state is then stable crystalline. The metastable state has to be stable at room temperature and slightly above for 10 years; but it should crystallize, i.e., return to the stable crystalline state in a few nanoseconds if heated to temperatures of typically around 500 °C. The combination of pronounced property contrast and hence presumably different atomic arrangements in the two different phases, yet rapid crystallization is indicative for an unusual correlation of chemical bonding, atomic arrangement, and resulting properties, including crystallization kinetics. Topological insulators, expected to help realize novel electronic functionalities, possess topologically protected spin-polarized surface states with high mobility. These states should govern the sample conductivity, if the bulk is insulating.This raises the question how these demanding requirements can be met and how superior materials can be identified. A number of different approaches have been developed in the past two decades to meet these needs. Combinatorial material synthesis, i.e., the fast preparation of stoichiometric libraries and their efficient analysis to identify superior compounds, has already been promoted over two decades ago. [1,2] While this scheme has indeed been successful in improving certain materials such as metal hydrides for hydrogen storage [3] and benchmarking electrocatalysts for solar water splitting, [4] for many material classes still empirical optimization schemes are employed. Machine learning is an emerging strategy to identify materials with a unique property portfolio. [5][6][7] This novel A unified picture of different application areas for incipient metals is presented. This unconventional material class includes several main-group chalcogenides, such as GeTe, PbTe, Sb 2 Te 3 , Bi 2 Se 3 , AgSbTe 2 and Ge 2 Sb 2 Te 5 . These compounds and related materials show a unique portfolio of physical properties. A novel map is discussed, which helps to explain these properties and separates the different fundamental bonding mechanisms (e.g., ionic, metallic, and covalent). The map also provides evidence ...

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Section: Phase‐change Materials In Nanoscale Dimensionssupporting

confidence: 57%

Section: Phase‐change Materials In Nanoscale Dimensionsmentioning

confidence: 99%

Section: Phase‐change Materials In Nanoscale Dimensionsmentioning

confidence: 99%

N_{c} = \frac{1}{V_{NP}} = \frac{6}{π d_{NP}^{3}}

.…”

Section: Phase‐change Materials In Nanoscale Dimensionsmentioning

confidence: 99%

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Chalcogenides by Design: Functionality through Metavalent Bonding and Confinement

2020

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“…A practical limitation of PCMs is the requirement of dedicated, costly fabrication tools and experience in the deposition process for achieving high material quality. Here, cheaper, solution‐based processing would facilitate the fabrication and may enable a more widespread adoption of PCM‐based metasurfaces . Another challenge is the integration of PCMs to guarantee a large number of reversible cycling of adaptive metasurfaces.…”

Section: Adaptive Metasurfacesmentioning

confidence: 99%

Optical Metasurfaces: Evolving from Passive to Adaptive

Hail

Michel

Poulikakos

et al. 2019

Advanced Optical Materials

123

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of ultrathin, artificial surfaces, so-called metasurfaces, for manipulating the propagation of light at will. [1,2] Metasurfaces control the propagation of light by abruptly changing its phase, amplitude, polarization, or spectrum at a surface and within a thin (quasi-2D) layer using large arrays of optical scatterers with subwavelength separation. Ideally, each scatterer can be independently engineered in order to locally influence the wavelets of the impinging light, and therefore, arbitrarily reform the wavefront. This concept has been exploited to create a variety of flat optical elements such as beam deflectors, [3][4][5] lenses, [6][7][8] and holograms. [9,10] As compared to bulky refraction-based optical elements, these surfaces are of subwavelength or wavelength-scale thickness, which enables their integration into compact devices. A main feature of the majority of such flat optical elements is that they are passive, and once fabricated, their optical functionalities are invariable. A beam deflector of this kind will direct light of a certain wavelength and direction always into the same direction, or a lens will focus light always to the same focal point. A broad range of new applications could be enabled if it were possible to actively and reversibly change the functionality of metasurfaces after their fabrication. With such "adaptive" metasurfaces beam deflectors with adjustable angle of deflection, metalenses with variable focal length or dynamic holograms may be realized. Advances toward such active devices are highly relevant for applications such as light detection and ranging [11] (LIDAR) sensing for driverless cars, dynamic zoom lenses for miniaturized camera systems [12] (e.g., in smartphones), or holographic displays for augmented reality devices. [13] An adaptive metasurface allows for the dynamic adjustment of an optical functionality of the surface. As shown in Figure 1, for the specific case of a metalens, these surfaces can be categorized based on their degree of dynamic adaptivity. While a passive surface has a fixed functionality, a switchable metasurface allows for switching back and forth between two (or more) predefined states (e.g., switching between different focal lengths, deflection angles, or hologram images). A continuously tunable metasurface enables continuous adjustment of a property within a range (e.g., tunable focal length or deflection angle). Finally, a freely tunable metasurface allows for continuous, arbitrary adjustment of a property, for example, 3D adjustment of the focal point of the metalens shown in Figure 1. Adaptive functionalities can be added to metasurfaces with different methods, for example, by mechanically rearranging the scatterers on the surface with respect to each other, or modifying

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Trends in GeTe Thermoelectrics: From Fundamentals to Applications

Li,

Shi,

Chen

2024

Adv Funct Materials

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Germanium telluride (GeTe) with ultrafast ferroelectric transition, Rashba‐like electronic transport, and anomalous phonon anharmonicity are historically studied for potential memorizing and thermoelectric applications. Due to recent breakthroughs in spintronics, valleytronics, orbitronics, pre‐eminent GeTe thermoelectrics have re‐attracted enormous interest from both academia and industries, with increasing reports of significant figure‐of‐merit over 2.7 and the maximum efficiency of up to 17.0%. Here, the emerging trends in advancing GeTe thermoelectrics, starting from fundamentals of phase transformation, crystal structure, bonding mechanisms, and transport characteristics, with a highlight on the roles of Ge_4s2 lone pairs, are timely overviewed. Technical insights in synthesis, characterization, property measurement, and computation are then summarized. After that, several innovative strategies for increasing the figure‐of‐merit, including entropy engineering, nanostructuring, and hybridization, which will further benefit near‐room‐temperature and n‐type performance, are examined. Moreover, high‐density and high‐efficiency devices with broad working temperatures are discussed as a result of rational configurational and interfacial design. In the end, perspective remarks on the challenges and outlook envisaging for next‐generation GeTe thermoelectrics, which will play a prominent role in future energy and environmental landscapes, are provided.

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Colloidal Phase-Change Materials: Synthesis of Monodisperse GeTe Nanoparticles and Quantification of Their Size-Dependent Crystallization

Cited by 30 publications

References 38 publications

Chalcogenides by Design: Functionality through Metavalent Bonding and Confinement

Chalcogenides by Design: Functionality through Metavalent Bonding and Confinement

Optical Metasurfaces: Evolving from Passive to Adaptive

Trends in GeTe Thermoelectrics: From Fundamentals to Applications

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