Organic material-based thermal switch is drawing much attention as one of the key thermal management devices in organic electronic devices. This study aims at tuning the switching temperature (T S) ...of thermal conductivity by using liquid crystalline block copolymers (BCs) with different order–order transition temperature (T tr) related to the types of mesogens in the side chain. The BC films with low T tr of 363 K and high T tr of 395 K exhibit reversible thermal conductivity switching behaviors at T S of ∼360 K and ∼390 K, respectively. The BC films also exhibit thermal conductivity variation originating from the anisotropy of the internal structures: poly(ethylene oxide) domains and liquid crystals. These results demonstrate that the switching behavior is attributed to an order–order transition between BC films with vertically arranged cylinder domains and the ones with ordered sphere domains. This highlights that BCs become a promising thermal conductivity switching material with tailored T S.
We investigated thermal conductivity of epitaxial germanane films: stacked structure of hydrogenated germanenes. It was confirmed that single crystalline germanane films were epitaxially grown on ...Ge(111). The films exhibited low out-of-plane thermal conductivity of 1.1 0.3 W m−1 K−1 which is lower than other layered materials composed of heavy atoms. This came from weak van der Waals interlayer interaction related to weak polarization in germanane composed of smaller atoms. This demonstrates that choice of small constituent atoms for weakening van der Waals interlayer interaction is a promising thermal conductivity reduction outline for developing ecofriendly high performance thermoelectric layered materials.
Toward drastic enhancement of thermoelectric power factor, quantum confinement effect proposed by Hicks and Dresselhaus has intrigued a lot of researchers. There has been much effort to increase ...power factor using step-like density-of-states in two-dimensional electron gas (2DEG) system. Here, we pay attention to another effect caused by confining electrons spatially along one-dimensional direction: multiplied 2DEG effect, where multiple discrete subbands contribute to electrical conduction, resulting in high Seebeck coefficient. The power factor of multiple 2DEG in GaAs reaches the ultrahigh value of ~100 μWcm
K
at 300 K. We evaluate the enhancement rate defined as power factor of 2DEG divided by that of three-dimensional bulk. The experimental enhancement rate relative to the theoretical one of conventional 2DEG reaches anomalously high (~4) in multiple 2DEG compared with those in various conventional 2DEG systems (~1). This proposed methodology for power factor enhancement opens the next era of thermoelectric research.
Layered silicene with deformed buckled structure attracts great interest as a next generation 2D Dirac thermoelectric material beyond conventional layered materials. However, the difficulty of ...modulating atomic positions in silicene prevents its realization. This study proposes a method to deform buckled structure in layered silicene by controlling the intercalated atoms, which can dramatically enhance its thermoelectric properties. Silicene buckled structure is deformed in epitaxial CaSi2 thin films, Ca‐intercalated layered silicenes, on Si(111) substrates, which is related to the composition of intercalated Ca. Therein, buckling height of silicene is changed. This CaSi2 film with deformed silicene exhibits not only metal‐like electrical conductivity but also three times larger Seebeck coefficient than the theoretically predicted value, resulting in ≈3000 times larger power factor (≈40 μW cm−1 K−2) than that of the reported CaSi2 film at room temperature. This result experimentally demonstrates that power factor can be greatly enhanced by deforming the silicene buckled structure.
Calcium‐intercalated layered silicene, CaSi2, is epitaxially grown on Si substrate. The silicene buckled structure is deformed through the control of the compositional ratio of Ca and Si. This deformation of silicene buckled structure can cause band convergence, enhancing Seebeck coefficient. As a result, thermoelectric power factor becomes ≈3000 times larger than that of the reported polycrystalline CaSi2 film.
Abstract Two-dimensional (2D) material is drawing considerable attention as a promising thermoelectric material. This study establishes the formation method of renewed Ca-intercalated group IV 2D ...materials, Ca(Ge 1− x Sn x ) 2 crystals including germanene-based 2D layers. The solid phase epitaxy allows us to form epitaxial Ca(Ge 1− x Sn x ) 2 on Si. Atomic force microscopy reveals that the Ca(Ge 1− x Sn x ) 2 has island structures. X-ray diffraction proved the epitaxial growth of the Ca(Ge 1− x Sn x ) 2 island structures and the increase of the c -axis lattice constant with Sn content increase. The formation of this renewed intermetallic compound including group IV 2D layer opens an avenue for high performance thermoelectric generator/Si.
ABSTRACT
A two‐dimensional walkaway vertical seismic profiling survey using distributed acoustic sensing was conducted at an onshore site in Japan. The maximum depth and the deviation of the ...observation well were more than 4,000 m and 81 degrees, respectively. Among the several methods for installing fibre optic cables, we adopted the inside coiled tubing method, in which coiled tubing containing a fibre optic cable is deployed. The signal‐to‐noise ratio of the raw shot gather was low, possibly due to poor coupling between the fibre optic cable and the subsurface formation resulting from the fibre optic cable deployment method and the existence of considerable tubewave noise. Nevertheless, direct P‐wave arrivals, P–P reflections and P–S converted waves exhibited acceptable signal‐to‐noise ratios after careful optimization of gauge length for distributed acoustic sensing optical processing and the application of carefully parameterized tubewave noise suppression. One of the challenges in current distributed acoustic sensing vertical seismic profile data processing is the separation of P‐ and S‐waves using only one‐component measurements. Hence, we applied moveout correction using two‐dimensional ray tracing. This process effectively highlights only reflected P‐waves, which are used in subsequent subsurface imaging. Comparison with synthetic well seismograms and two‐dimensional surface seismic data confirms that the final imaging result has a sufficiently high quality for subsurface monitoring. We acquired distributed acoustic sensing vertical seismic profile data under both flowing conditions and closed conditions, in which the well was shut off and no fluid flow was allowed. The two imaging results are comparable and suggest the possibility of subsurface imaging and time‐lapse monitoring using data acquired under flowing conditions. The results of this study suggest that, by adopting the inside coiled tubing method without drilling a new observation well, more affordable distributed acoustic sensing vertical seismic profile monitoring can be achieved in fields such as CO2 capture and storage and unconventional shale projects, where monitoring costs have to be minimized.
2-D electron gas (2DEG) is one of the promising approaches for high thermoelectric (TE) performance. However, high electrical resistance of the film originating from thin 2DEG conduction channel ...width and thick insulator layer is a bottleneck for obtaining high output power. In this study, we propose stacked GaAs 2DEG thermoelectric generator (TEG), which has a number of stacked channel structures for low electrical resistance. Our GaAs 2DEG TEGs with channels formed in triangular well exhibit ultrahigh TE power factor. In addition, the interfaces of the stacked 2DEG intensify phonon scatterings, resulting in the reduction of thermal conductivity. The stacked 2DEG TEGs exhibit nine times higher sheet electrical conductivity than the unstacked 2DEG one, resulting in ~7.5 times higher output power of stacked 2DEG TEGs (5.1 nW) than that of unstacked 2DEG ones. The cross-sectional TE efficiency factor of stacked 2DEG TEGs reaches <inline-formula> <tex-math notation="LaTeX">3.7~\mu </tex-math></inline-formula> W cm<inline-formula> <tex-math notation="LaTeX">^{-{2}} </tex-math></inline-formula> K<inline-formula> <tex-math notation="LaTeX">^{-{2}} </tex-math></inline-formula>. This value is the highest among various simple planar type film TEGs without cavities under the film. This TEG demonstration will open an avenue for the social application of 2DEG TEG.
Ca‐Intercalated Layered Silicene (CaSi2) with Deformed Buckled Structure
In article number 2101752, Tsukasa Terada, Yoshiaki Nakamura, and co‐workers reveal that in epitaxial film of Ca intercalated ...layered silicene, CaSi2 on Si substrate, the silicene buckled structure is deformed through the control of the Ca/Si ratio. This deformation causes giant enhancement of Seebeck coefficient due to band structure change, leading to high thermoelectric power factor.
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