Recently SnSe, a layered chalcogenide material, has attracted a great deal of attention for its excellent p-type thermoelectric property showing a remarkable ZT value of 2.6 at 923 K. For ...thermoelectric device applications, it is necessary to have n-type materials with comparable ZT value. Here, we report that n-type SnSe single crystals were successfully synthesized by substituting Bi at Sn sites. In addition, it was found that the carrier concentration increases with Bi content, which has a great influence on the thermoelectric properties of n-type SnSe single crystals. Indeed, we achieved the maximum ZT value of 2.2 along b axis at 733 K in the most highly doped n-type SnSe with a carrier density of -2.1 × 10
cm
at 773 K.
Owing to the continuous increase in the damage to farms due to wild animals’ destruction of crops in South Korea, various methods have been proposed to resolve these issues, such as installing ...electric fences and using warning lamps or ultrasonic waves. Recently, new methods have been attempted by applying deep learning-based object-detection techniques to a robot. However, for effective training of a deep learning-based object-detection model, overfitting or biased training should be avoided; furthermore, a huge number of datasets are required. In particular, establishing a training dataset for specific wild animals requires considerable time and labor. Therefore, this study proposes an Extract–Append data augmentation method where specific objects are extracted from a limited number of images via semantic segmentation and corresponding objects are appended to numerous arbitrary background images. Thus, the study aimed to improve the model’s detection performance by generating a rich dataset on wild animals with various background images, particularly images of water deer and wild boar, which are currently causing the most problematic social issues. The comparison between the object detector trained using the proposed Extract–Append technique and that trained using the existing data augmentation techniques showed that the mean Average Precision (mAP) improved by ≥2.2%. Moreover, further improvement in detection performance of the deep learning-based object-detection model can be expected as the proposed technique can solve the issue of the lack of specific data that are difficult to obtain.
Chemical treatment using bis(trifluoromethane) sulfonimide (TFSI) was shown to be particularly effective for increasing the photoluminescence (PL) of monolayer (1L) MoS2, suggesting a convenient ...method for overcoming the intrinsically low quantum yield of this material. However, the underlying atomic mechanism of the PL enhancement has remained elusive. Here, we report the microscopic origin of the defect healing observed in TFSI-treated 1L-MoS2 through a correlative combination of optical characterization and atomic-scale scanning transmission electron microscopy, which showed that most of the sulfur vacancies were directly repaired by the extrinsic sulfur atoms produced from the dissociation of TFSI, concurrently resulting in a significant PL enhancement. Density functional theory calculations confirmed that the reactive sulfur dioxide molecules that dissociated from TFSI can be reduced to sulfur and oxygen gas at the vacancy site to form strongly bound SMo. Our results reveal how defect-mediated nonradiative recombination can be effectively eliminated by a simple chemical treatment method, thereby advancing the practical applications of monolayer semiconductors.
The formation of semiconductor heterojunctions and their high-density integration are foundations of modern electronics and optoelectronics. To enable two-dimensional crystalline semiconductors as ...building blocks in next-generation electronics, developing methods to deterministically form lateral heterojunctions is crucial. Here we demonstrate an approach for the formation of lithographically patterned arrays of lateral semiconducting heterojunctions within a single two-dimensional crystal. Electron beam lithography is used to pattern MoSe2 monolayer crystals with SiO2, and the exposed locations are selectively and totally converted to MoS2 using pulsed laser vaporization of sulfur to form MoSe2/MoS2 heterojunctions in predefined patterns. The junctions and conversion process are studied by Raman and photoluminescence spectroscopy, atomically resolved scanning transmission electron microscopy and device characterization. This demonstration of lateral heterojunction arrays within a monolayer crystal is an essential step for the integration of two-dimensional semiconductor building blocks with different electronic and optoelectronic properties for high-density, ultrathin devices.
The two-dimensional electron gas (2DEG) formed at the oxide heterointerface between LaAlO
3
(LAO) and SrTiO
3
(STO) has gained significant attention due to its exotic physical properties and ...interfacial conductivity. However, the 2DEG resides in a weakly dispersive Ti-d band, resulting in relatively low mobility. This limitation hampers its practical applications in future oxide electronics. To enhance the mobility of the 2DEG, we propose the use of BaSnO
3
(BSO) as a novel host material with a highly dispersive conduction Sn-5 s band. The s orbitals in BSO are significantly more delocalized than d orbitals, leading to a higher dispersion of the conduction band. Our first-principles density functional theory (DFT) calculations reveal that a high-mobility n-type 2DEG can indeed be formed near the PbZr
0.5
Ti
0.5
O
3
/BSO interface. The polar field of the ferroelectric PbZr
0.5
Ti
0.5
O
3
generates an interfacial conducting state in BSO, resulting in a high-mobility n-type 2DEG within the highly dispersive Sn-5 s band.
Abstract Since the discovery of two-dimensional electron gas at the LaAlO 3 /SrTiO 3 interface, its intriguing physical properties have garnered significant interests for device applications. Yet, ...understanding its response to electrical stimuli remains incomplete. Our in-situ transmission electron microscopy analysis of a LaAlO 3 /SrTiO 3 two-dimensional electron gas device under electrical bias reveals key insights. Inline electron holography visualized the field-induced modulation of two-dimensional electron gas at the interface, while electron energy loss spectroscopy showed negligible electromigration of oxygen vacancies. Instead, atom-resolved imaging indicated that electric fields trigger polar distortion in the LaAlO 3 layer, affecting two-dimensional electron gas modulation. This study refutes the previously hypothesized role of oxygen vacancies, underscoring the lattice flexibility of LaAlO 3 and its varied polar distortions under electric fields as central to two-dimensional electron gas dynamics. These findings open pathways for advanced oxide nanoelectronics, exploiting the interplay of polar and nonpolar distortions in LaAlO 3 .
Piezoelectricity crystallographically exists only in the in-plane direction in two-dimensional transition metal dichalcogenides. Here, we demonstrated flexoelectricity-tunable out-of-plane ...piezoelectricity in semiconducting 2H-MoTe2 flakes by creating surface corrugation. In particular, the strong out-of-plane piezoelectricity and its spatial variation depending on local flexoelectricity was observed even though crystallographically there exists only in-plane piezoelectricity. Surface corrugation-mediated flexoelectricity tuning can be applied to other two-dimensional or thin-layered materials and, furthermore, the results could provide useful information on the interweaving nature between mechanical stimulus and electric dipole in low-dimensional materials.
Topotactic phase transformation enables structural transition without losing the crystalline symmetry of the parental phase and provides an effective platform for elucidating the redox reaction and ...oxygen diffusion within transition metal oxides. In addition, it enables tuning of the emergent physical properties of complex oxides, through strong interaction between the lattice and electronic degrees of freedom. In this communication, the electronic structure evolution of SrFeOx epitaxial thin films is identified in real‐time, during the progress of reversible topotactic phase transformation. Using real‐time optical spectroscopy, the phase transition between the two structurally distinct phases (i.e., brownmillerite and perovskite) is quantitatively monitored, and a pressure–temperature phase diagram of the topotactic transformation is constructed for the first time. The transformation at relatively low temperatures is attributed to a markedly small difference in Gibbs free energy compared to the known similar class of materials to date. This study highlights the phase stability and reversibility of SrFeOx thin films, which is highly relevant for energy and environmental applications exploiting the redox reactions.
Topotactic phase transformation coupled with the metal–insulator transition in SrFeOx epitaxial thin films is studied using real‐time optical spectroscopy. The oxygen‐content‐dependent phase transition leads to a pressure–temperature phase diagram of the topotactic transformation. The transformation at relatively low temperatures is ascribed to a markedly small Gibbs' free energy difference between the two structurally distinctive phases.
Abstract
Exsolution of excess transition metal cations from a non-stoichiometric perovskite oxide has sparked interest as a facile route for the formation of stable nanoparticles on the oxide ...surface. However, the atomic-scale mechanism of this nanoparticle formation remains largely unknown. The present in situ scanning transmission electron microscopy combined with density functional theory calculation revealed that the anti-phase boundaries (APBs) characterized by the
a
/2 < 011> type lattice displacement accommodate the excess B-site cation (Ni) through the edge-sharing of BO
6
octahedra in a non-stoichiometric ABO
3
perovskite oxide (La
0.2
Sr
0.7
Ni
0.1
Ti
0.9
O
3-δ
) and provide the fast diffusion pathways for nanoparticle formation by exsolution. Moreover, the APBs further promote the outward diffusion of the excess Ni toward the surface as the segregation energy of Ni is lower at the APB/surface intersection. The formation of nanoparticles occurs through the two-step crystallization mechanism, i.e., the nucleation of an amorphous phase followed by crystallization, and via reactive wetting on the oxide support, which facilitates the formation of a stable triple junction and coherent interface, leading to the distinct socketing of nanoparticles to the oxide support. The atomic-scale mechanism unveiled in this study can provide insights into the design of highly stable nanostructures.
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