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Effect of SrTiO <sub/>3</sub> oxygen vacancies on the conductivity of LaTiO <sub/>3</sub> /SrTiO <sub/>3</sub> heterostructures
摘要： In this work, we report the formation of a conductive layer through oxygen vacancies in an underlying SrTiO3 (STO) layer due to the growth of LaTiO3 (LTO) and the resulting LTO thickness-dependent conductivity of the LTO/STO system. Crystalline LTO films were grown by molecular beam epitaxy on TiO2-terminated STO(001) single-crystal substrates and 8-unit-cell (u.c.) STO template layers grown on Ge(001), under partial pressures of molecular oxygen ranging from 10?10 to 10?7 Torr. Film crystallinity was studied by in situ reflection high-energy electron diffraction, ex situ X-ray diffraction, and ex situ transmission electron microscopy. Film composition and the existence of oxygen vacancies were confirmed by in situ X-ray photoelectron spectroscopy. LTO films grown on STO substrates at oxygen partial pressures of 10?10 Torr were optimally oxidized (1:1:3 La:Ti:O). However, LTO films grown on 8-u.c. templates of STO on Ge with oxygen partial pressures less than 10?7 Torr showed extensive reduction of the Ti oxide and desorption of Sr/SrO in the STO layer. LTO films began to over-oxidize when grown on STO single-crystal substrates at oxygen partial pressures greater than 10?10 Torr but were nearly optimally oxidized when grown on STO templates on Ge at oxygen partial pressures of 10?7 Torr. Electrical characterization showed a dependence of conductivity on the thickness of the LTO films, with sheet carrier densities reaching ～5 × 1016 cm?2 for 20-u.c. (8-nm-thick) LTO/STO grown at 10?10 Torr of oxygen, suggesting that significant conduction occurred throughout the STO substrate due to the formation of oxygen vacancies.
关键词： oxygen vacancies,conductivity,SrTiO3,molecular beam epitaxy,LaTiO3/SrTiO3 heterostructures
更新于2025-09-10 09:29:36
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Spectroscopic signature of trimer Mott insulator and charge disproportionation in
摘要： We have measured the re?ectivity spectra of the barium iridate 9R BaIrO3, the crystal structure of which consists of characteristic Ir3O12 trimers. In the high-temperature phase above the transition temperature Tc (cid:2) 180 K, we ?nd that the optical conductivity involves two temperature-dependent optical transitions with an ill-de?ned Drude response. These features are reminiscent of the optical spectra in the organic dimer Mott insulators, implying a possible emergence of an unusual electronic state named trimer Mott insulator in BaIrO3, where the carrier is localized on the trimer owing to the strong Coulomb repulsion. Along with a pronounced splitting of the phonon peak observed below Tc, which is a hallmark of charge disproportionation, we discuss a possible phase transition from the trimer Mott insulator to a charge-ordered insulating phase in BaIrO3.
关键词： phase transition,charge disproportionation,BaIrO3,optical conductivity,trimer Mott insulator
更新于2025-09-10 09:29:36
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Anharmonic stabilization and lattice heat transport in rocksalt <i>β</i> -GeTe
摘要： Peierls-Boltzmann transport equation, coupled with third-order anharmonic lattice dynamics calculations, has been widely used to model lattice thermal conductivity (jl) in bulk crystals. However, its application to materials with structural phase transition at relatively high temperature is fundamentally challenged by the presence of lattice instabilities (imaginary phonon modes). Additionally, its accuracy suffers from the absence of higher-than-third-order phonon scattering processes, which are important near/above the Debye temperature. In this letter, we present an effective scheme that combines temperature-induced anharmonic phonon renormalization and four-phonon scattering to resolve these two theoretical challenges. We apply this scheme to investigate the lattice dynamics and thermal transport properties of GeTe, which undergoes a second-order ferroelectric phase transition from rhombohedral a-GeTe to rocksalt b-GeTe at about 700 K. Our results on the high-temperature phase b-GeTe at 800 K con?rm the stabilization of b-GeTe by temperature effects. We ?nd that considering only three-phonon scattering leads to signi?cantly overestimated jl of 3.8 W/mK at 800 K, whereas including four-phonon scattering reduces jl to 1.7 W/mK, a value comparable with experiments. To explore the possibility to further suppress jl, we show that alloying b-GeTe with heavy cations such as Pb and Bi can effectively reduce jl to about 1.0 W/mK, whereas particle size needs to be around 10 nm through nanostructuring to achieve a comparable reduction in jl.
关键词： rocksalt β-GeTe,lattice heat transport,thermal conductivity,phonon scattering,anharmonic stabilization
更新于2025-09-10 09:29:36
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Attaining reduced lattice thermal conductivity and enhanced electrical conductivity in as-sintered pure n-type Bi2Te3 alloy
摘要： Undoped n-type Bi2Te3 bulks were prepared via the liquid state manipulation (LSM) with subsequent ball milling and spark plasma sintering processes. The sample with LSM obtains higher carrier concentration and larger effective mass compared with that without LSM, exhibiting favourable electrical transport properties. More importantly, a much reduced lattice thermal conductivity * 0.47 W m-1 K-1 (decreased by 43%) is obtained, due to the enhanced multiscale phonon scattering from hierarchical microstructures, including boundaries, nanograins and lattice dislocations. Additionally, due to the increased carrier concentration and enlarged band gap, the bipolar effect is effectively suppressed in sample BT-LSM. Consequently, zTmax * 0.66 is achieved in the sample with LSM at higher temperature of 475 K, almost 22% improvement compared with that of the contrast.
关键词： spark plasma sintering,thermoelectric,electrical conductivity,thermal conductivity,liquid state manipulation,ball milling,Bi2Te3
更新于2025-09-09 09:28:46
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On the thermal conductivity of AgSbTe <sub/>2</sub> and Ag <sub/>0.82</sub> Sb <sub/>1.18</sub> Te <sub/>2.18</sub>
摘要： The temperature dependencies of the thermal conductivity of AgSbTe2 and Ag0.82Sb1.18Te2.18 were studied in the temperature range of 5–320 K. The obtained results are compared with quantitative calculations based on a theoretical model of generalized conductivity of heterogeneous systems. It was shown that a rather low value of thermal conductivity of AgSbTe2 and Ag0.82Sb1.18Te2.18 is associated with the disordering of the crystal structure, as well as phonon scattering by point defects and structural components. The presence of the second phase of Ag2Te leads to an increase in the thermal conductivity of AgSbTe2.
关键词： crystal structure disordering,AgSbTe2,thermal conductivity,Ag0.82Sb1.18Te2.18,phonon scattering
更新于2025-09-09 09:28:46
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Charge transport in GaAs nanowires: Interplay between conductivity through the interior and surface conductivity
摘要： The charge transport through GaAs nanowires, partially p-doped and partially intrinsic, is analyzed by four-point resistance profiling along freestanding nanowires using a multip-STM. The charge transport channel in the undoped segment is assigned to the surface conductivity, while the interior of the nanowire is the conductance channel in the p-doped segment. The convoluted interplay between conduction through the interior of the nanowire and surface state conduction is studied in detail. Measurements of the I-V curves along the nanowires provide the experimental basis for the proposed charge transport model for the transition of the conduction from the interior to the surface of the nanowire. A voltage drop along the surface state conduction channel leads to an upward shift of the band edges at the surface. This results, for higher applied voltages, in the removal of the depletion layer and an opening of a conductance channel between the interior of the nanowire and the surface states.
关键词： GaAs nanowires,surface conductivity,multip-STM,charge transport,four-point resistance profiling
更新于2025-09-09 09:28:46
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Electron-phonon anharmonicity and low thermal conductivity in phosphorous chalcogenide ferroelectrics
摘要： The dependence of thermal conductivity with temperature has been studied for Sn(Pb)2P2S(Se)6 ferroelectrics-semiconductors, showing an ultra-low (0.5 W/m K) thermal conductivity above 250 K and the possibility to tune it at lower temperatures playing with the dopant concentration. This behavior has been explained taking into account the combination of different physical mechanisms: hopping heat conductivity in a lattice with strong electron-phonon anharmonicity linked to the stereoactivity of tin and lead cations electron lone pairs together with valence fluctuations in P2S(Se)6 groups. Besides, the presence of an incommensurate phase in the more covalent compounds, the location of tricritical points near 250 K and the peculiarities of the chemical bonding have all been correlated with the experimental behavior observed.
关键词： Ferroelectricity,Bonding,Thermal Conductivity,Structure–Property Relationship,Temperature Dependence
更新于2025-09-09 09:28:46
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Decoupling the contributions to the enhancement of electrical conductivity in transparent silver nanowire/zinc oxide composite electrodes
摘要： Electrical properties of silver nanowire (AgNW)-based transparent electrodes have been improved without transmittance loss by forming a composite with zinc oxide (ZnO). Here, we identified the dominant effect responsible for the improvement of electrical conductivity of the transparent AgNW:ZnO composite electrodes by fabricating the AgNW:ZnO composite electrodes with different architectures and theoretically calculating the overall resistance of their equivalent circuits. Specifically, when we compared the overall resistances of the AgNW:ZnO electrodes with various architectures by experiment, the electrode with only the electrical bridge effect showed the lowest electrical resistance. In addition, while the theoretical overall resistances were comparable on changing the interconnect resistances between the silver nanowires in the equivalent circuits of all architectures, they decreased dramatically with the decreasing ZnO bridging resistance. Thus, it was concluded that the electrical bridge effect is more important than the capillary force effect which decreases the interconnect resistance between the silver nanowires for the enhancement of the electrical properties of AgNW:ZnO composite electrodes. It was also found that the AgNW:ZnO electrodes with only the electrical bridge effect showed better device performances when applied to optoelectronic devices such as organic photovoltaics.
关键词： electrical conductivity,silver nanowire,electrical bridge effect,zinc oxide,capillary force effect
更新于2025-09-09 09:28:46
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Electronic transport properties of (Se80Te20)100?xZnx (2?≤?x?≤?6) chalcogenide alloys
摘要： The bulk chalcogenide (Se80Te20)100-xZnx (2≤x≤6) alloys are prepared using melt quenching technique and electronic transport properties are studied in the frequency range 50 Hz–500 KHz and temperature range 400-520 K. The sharp peaks observed in X-ray diffraction pattern indicate the polycrystalline nature of prepared compositions. The measured dielectric properties and a.c. conductivity reveal the significant influence of Zn doping on the properties of the Se-Te matrix. The a.c. conductivity obeys Jonscher power law as ~ w s (s<1). To describe the conduction mechanism, the experimental results are analyzed in the framework of various theoretical models. The correlated barrier hopping (CBH) model successfully describe the observed frequency, temperature and composition response of ac conductivity.
关键词： a.c. conductivity,electronic transport properties,Chalcogenide alloys,dielectric constant,dielectric loss,X-Ray diffraction
更新于2025-09-09 09:28:46
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Electric-field modulation of linear dichroism and Faraday rotation in few-layer phosphorene
摘要： Electro-optical modulators, which use an electric voltage (or an electric field) to modulate a beam of light, are essential elements in present-day telecommunication devices. Using a self-consistent tight-binding approach combined with the standard Kubo formula, we show that the optical conductivity and the linear dichroism of few-layer phosphorene can be modulated by a perpendicular electric field. We find that the field-induced charge screening plays a significant role in modulating the optical conductivity and the linear dichroism. Distinct absorption peaks are induced in the conductivity spectrum due to the strong quantum confinement along the out-of-plane direction and to the field-induced forbidden-to-allowed transitions. The field modulation of the linear dichroism becomes more pronounced with increasing number of phosphorene layers. We also show that the Faraday rotation is present in few-layer phosphorene even in the absence of an external magnetic field. This optical Hall effect is induced by the reduced lattice symmetry of few-layer phosphorene. The Faraday rotation is greatly influenced by the field-induced charge screening and is strongly dependent on the strength of perpendicular electric field and on the number of phosphorene layers.
关键词： electric field modulation,linear dichroism,optical conductivity,Faraday rotation,electro-optical modulators,few-layer phosphorene
更新于2025-09-09 09:28:46