Abstract:Strain
engineering as a method to control functional properties
has seen in the last decades a surge of interest. Heterostructures
comprising 2D-materials and containing van der Waals(-like) gaps were
considered unsuitable for strain engineering. However, recent work
on heterostructures based on Bi
2
Te
3
, Sb
2
Te
3
, and GeTe showed the potential of a different
type of strain engineering due to long-range mutual strai… Show more
“…The corresponding targets were obtained from KTECH with a purity of 99.999%. The substrate cleaning method is described elsewhere . For the single layers of Sb 2 Te 3 and GeTe, first, a “seed” layer of 200 pulses (∼3 nm) film was grown at RT, followed by heating to 210 °C with a heating rate of 10 °C min –1 .…”
Over the past few decades, telluride-based chalcogenide multilayers, such as PbSeTe/PbTe, Bi 2 Te 3 /Sb 2 Te 3 , and Bi 2 Te 3 /Bi 2 Se 3 , were shown to be promising high-performance thermoelectric films. However, the stability of performance in operating environments, in particular, influenced by intermixing of the sublayers, has been studied rarely. In the present work, the nanostructure, thermal stability, and thermoelectric power factor of Sb 2 Te 3 /Ge 1+x Te multilayers prepared by pulsed laser deposition are investigated by transmission electron microscopy and Seebeck coefficient/electrical conductivity measurements performed during thermal cycling. Highly textured Sb 2 Te 3 films show p-type semiconducting behavior with superior power factor, while Ge 1+x Te films exhibit n-type semiconducting behavior. The elemental mappings indicate that the as-deposited multilayers have welldefined layered structures. Upon heating to 210 °C, these layer structures are unstable against intermixing of sublayers; nanostructural changes occur on initial heating, even though the highest temperature is close to the deposition temperature. Furthermore, the diffusion is more extensive at domain boundaries leading to locally inclined structures there. The Sb 2 Te 3 sublayers gradually dissolve into Ge 1+x Te. This dissolution depends markedly on the relative Ge 1+x Te film thickness. Rather, full dissolution occurs rapidly at 210 °C when the Ge 1+x Te sublayer is substantially thicker than that of Sb 2 Te 3 , whereas the dissolution is very limited when the Ge 1+x Te sublayer is substantially thinner. The resulting variations of the nanostructure influence the Seebeck coefficient and electrical conductivity and thus the power factor in a systematic manner. Our results shed light on a previously unreported correlation of the power factor with the nanostructural evolution of unstable telluride multilayers.
“…The corresponding targets were obtained from KTECH with a purity of 99.999%. The substrate cleaning method is described elsewhere . For the single layers of Sb 2 Te 3 and GeTe, first, a “seed” layer of 200 pulses (∼3 nm) film was grown at RT, followed by heating to 210 °C with a heating rate of 10 °C min –1 .…”
Over the past few decades, telluride-based chalcogenide multilayers, such as PbSeTe/PbTe, Bi 2 Te 3 /Sb 2 Te 3 , and Bi 2 Te 3 /Bi 2 Se 3 , were shown to be promising high-performance thermoelectric films. However, the stability of performance in operating environments, in particular, influenced by intermixing of the sublayers, has been studied rarely. In the present work, the nanostructure, thermal stability, and thermoelectric power factor of Sb 2 Te 3 /Ge 1+x Te multilayers prepared by pulsed laser deposition are investigated by transmission electron microscopy and Seebeck coefficient/electrical conductivity measurements performed during thermal cycling. Highly textured Sb 2 Te 3 films show p-type semiconducting behavior with superior power factor, while Ge 1+x Te films exhibit n-type semiconducting behavior. The elemental mappings indicate that the as-deposited multilayers have welldefined layered structures. Upon heating to 210 °C, these layer structures are unstable against intermixing of sublayers; nanostructural changes occur on initial heating, even though the highest temperature is close to the deposition temperature. Furthermore, the diffusion is more extensive at domain boundaries leading to locally inclined structures there. The Sb 2 Te 3 sublayers gradually dissolve into Ge 1+x Te. This dissolution depends markedly on the relative Ge 1+x Te film thickness. Rather, full dissolution occurs rapidly at 210 °C when the Ge 1+x Te sublayer is substantially thicker than that of Sb 2 Te 3 , whereas the dissolution is very limited when the Ge 1+x Te sublayer is substantially thinner. The resulting variations of the nanostructure influence the Seebeck coefficient and electrical conductivity and thus the power factor in a systematic manner. Our results shed light on a previously unreported correlation of the power factor with the nanostructural evolution of unstable telluride multilayers.
“…[12][13][14] For all these applications, it is important to understand the GeTe growth mechanisms. Several studies have shown and studied the possibility to grow high quality epitaxial GeTe using either molecular beam epitaxy or pulsed laser deposition techniques, enabling to grow ultrathin (down to 1 nm) epilayers for ferroelectricity applications 15,16 or strain engineering 17 for example. However, most studies that seek to investigate GeTe focus on the crystallization of an amorphous homogeneous stoichiometric, or near-stoichiometric, thin film.…”
In this work, solid-state α-GeTe growth is studied during the reactive diffusion of a polycrystalline thin film of hexagonal Te deposited on an amorphous Ge thin film (Te-on-Ge) using in...
“…Among the factors of strain engineering, the one with a high priority is how strain relaxes and behaves in thin films, which significantly affects the strain state of thin films. According to the bond hierarchy, the strain relaxation falls into two main strategies . (i) The strain gradually decays with the increase of film thickness, forming a strain gradient inside the thin film.…”
Strain engineering plays an important role in tuning the microstructure and properties of heterostructures. The key to implement the strain modulation to heterostructures is controlling the strain relaxation, which is generally realized by varying the thickness of thin films or changing substrates. Here, we show that interface polarity can tailor the behavior of strain relaxation in a hexagonal manganite film, whose strain state can be tuned to different extents. Using scanning transmission electron microscopy, a reconstructed atomic layer with elongated interlayer spacing and minor in-plane rotation is observed at the interface, suggesting that the bond hierarchy at interface transits from three-dimension to two-dimension, which accounts for the strain-free heteroepitaxy. Utilizing interface polarity to control the strain relaxation highlights a conceptually opt route to optimize the strain engineering and the realization of strain-free heteroepitaxy in such highly lattice-mismatched heterostructure also provides possibility to transform more bulklike functional oxides to low dimensionality.
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