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van der Waals topological insulators, characterized by their high-index dielectric response, offer a promising materials platform for nanophotonics. Among these materials, Bi2Te3 has one of the highest refractive indices and extinction coefficients. However, the precise determination of Bi2Te3 optical properties remains challenging owing to its complicated physical model, which includes an oxide layer, topological conducting states, and optical anisotropy. Here, we resolve this problem and develop an accurate optical model for Bi2Te3 in a broad (450–1500 nm) spectral range. Our study shows that an oxide layer plays a major role in optical model for these wavelengths, while the influence of topological conducting states and optical anisotropy is minimal. Our model allows us to obtain accurate Bi2Te3 optical constants and demonstrate their use in biosensors, thermal theranostics, and topological phase singularities. Moreover, we observe a polarization transition of topological phase singularity for Bi2Se3, which opens a new direction for the development of topological phase effects. Therefore, our results open new avenues for photonic applications of Bi2Te3 optical properties. [ABSTRACT FROM AUTHOR]

The nanosecond speed of information writing and reading is recognized as one of the main advantages of next-generation non-volatile ferroelectric memory based on hafnium oxide thin films. However, the kinetics of polarization switching in this material have a complex nature, and despite the high speed of internal switching, the real speed can deteriorate significantly due to various external reasons. In this work, we reveal that the domain structure and the dielectric layer formed at the electrode interface contribute significantly to the polarization switching speed of 10 nm thick Hf0.5Zr0.5O2 (HZO) film. The mechanism of speed degradation is related to the generation of charged defects in the film which accompany the formation of the interfacial dielectric layer during oxidization of the electrode. Such defects are pinning centers that prevent domain propagation upon polarization switching. To clarify this issue, we fabricate two types of similar W/HZO/TiN capacitor structures, differing only in the thickness of the electrode interlayer, and compare their ferroelectric (including local ferroelectric), dielectric, structural (including microstructural), chemical, and morphological properties, which are comprehensively investigated using several advanced techniques, in particular, hard X-ray photoelectron spectroscopy, high-resolution transmission electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, and electron beam induced current technique. [ABSTRACT FROM AUTHOR]

Metal-Organic CVD method (MOCVD) allows for deposition of ultrathin 2D transition metal dichalcogenides (TMD) films of electronic quality onto wafer-scale substrates. In this work, the effect of temperature on structure, chemical states, and electronic qualities of the MOCVD MoS2 films were investigated. The results demonstrate that the temperature increase in the range of 650 °C to 950 °C results in non-monotonic average crystallite size variation. Atomic force microscopy (AFM), transmission electron microscopy (TEM), and Raman spectroscopy investigation has established the film crystal structure improvement with temperature increase in this range. At the same time, X-Ray photoelectron spectroscopy (XPS) method allowed to reveal non-stoichiometric phase fraction increase, corresponding to increased sulfur vacancies (VS) concentration from approximately 0.9 at.% to 3.6 at.%. Established dependency between the crystallite domains size and VS concentration suggests that these vacancies are form predominantly at the grain boundaries. The results suggest that an increased Vs concentration and enhanced charge carriers scattering at the grains' boundaries should be the primary reasons of films' resistivity increase from 4 kΩ·cm to 39 kΩ·cm. [ABSTRACT FROM AUTHOR]

Manipulation of resonant dielectric nanostructures is of paramount importance for next-generation photonic devices. Traditionally, researchers use two-dimensional or phase-change materials for this purpose. However, the former leads to small efficiency, while the latter lacks continuous changes. Here, we provide an alternative approach through laser-induced modification. Specifically, via a laser ablation process we synthesized molybdenum disulfide (MoS2) nanoparticles (NPs), the composition of which we then controlled through laser fragmentation. It causes a transformation of MoS2 into its oxide MoO3−x, which, in turn, results in pronounced modification of the optical response, owing to a large difference between their optical constants. In addition, laser-fragmented NPs have a several times larger photothermal response, compared to the original MoS2 and classical silicon NPs. Thus, our MoS2-based laser-tunable NPs open up a new perspective for resonant nanophotonics, in particular, photothermal therapy. [ABSTRACT FROM AUTHOR]

The growing family of two-dimensional crystals has been recognized as a promising platform for investigation of rich low-dimension physics and production of a variety of devices. Of particular interest are recently reported atomic sheets of non-van der Waals materials, which reshape our understanding of chemical bonds and enable heterostructures with novel functionality. Here, we study the structural and optical properties of ultrathin non-van der Waals InGaS3 sheets produced by standard mechanical cleavage. Our ab initio calculations reveal weak out-of-plane covalent bonds, responsible for the layered structure of the material. The energy required for isolation of a single layer is as low as ~50 meVÅ–2, which is comparable with the conventional van der Waals material's monolayer isolation energies of 20–60 meVÅ–2. A comprehensive study of the structural, vibrational, and optical properties of the material reveals its wide bandgap (2.73 eV), high refractive index (>2.5) and negligible losses in the visible and infrared spectral ranges. These properties make it a perfect candidate for visible-range all-dielectric nanophotonics. [ABSTRACT FROM AUTHOR]

Atomically thin molybdenum disulfide (MoS2) is a promising channel material for next-generation thin-body field-effect transistors (FETs), which makes the development of methods allowing for its controllable synthesis over a large area an essential task. Currently, one of the cost-effective ways of its synthesis is the sulfurization of preliminary grown oxide- or metallic film. However, despite apparent progress in this field, the electronic quality of the obtained MoS2 is inferior to that of exfoliated samples, making the detailed investigation of the sulfurized films' properties of great interest. In this work, we synthesized continuous MoS2 films with a thickness of ≈2.2 nm via the sulfurization of an atomic-layer-deposited MoO3 layer. X-ray photoelectron spectroscopy, transmission electron microscopy, and Raman spectroscopy indicated the appropriate chemical composition and microcrystalline structure of the obtained MoS2 films. The semiconductor quality of the synthesized films was confirmed by the fabrication of a field-effect transistor (FET) with an Ion/Ioff ratio of ≈40, which was limited primarily by the high contact resistance. The Schottky barrier height at the Au/MoS2 interface was found to be ≈1.2 eV indicating the necessity of careful contact engineering. Due to its simplicity and cost-effectiveness, such a technique of MoS2 synthesis still appears to be highly attractive for its applications in next-generation microelectronics. Therefore, further research of the electronic properties of films obtained via this technique is required. [ABSTRACT FROM AUTHOR]

Heterogeneous nanostructures composed of metastable tetragonal 1T-MoS 2 and stable hexagonal 2H-MoS 2 phases are highly promising for a wide range of applications, including catalysis and ion batteries, due to the high electrical conductivity and catalytic activity of the 1T phase. However, a controllable synthesis of stabilized 1T-MoS 2 films over the wafer-scale area is challenging. In this work, a metal-organic chemical vapor deposition process allowing us to obtain ultrathin MoS 2 films containing both 1T and 2H phases and control their ratio through rhenium doping was suggested. As a result, Mo 1- x Re x S 2 films with a 1T-MoS 2 fraction up to ≈30% were obtained, which were relatively stable under normal conditions for a long time. X-ray photoelectron spectroscopy and Raman spectroscopy also indicated that the 1T-MoS 2 phase fraction increased with rhenium concentration increase saturating at Re concentrations above 5 at. %. Also, its concentration was found to significantly affect the film resistivity. Thus, the resistivity of the film containing approximately 30% of the 1T phase was about 130 times lower than that of the film without the 1T phase., Competing Interests: The authors declare no competing financial interest., (© 2023 The Authors. Published by American Chemical Society.)

The influence of the bottom TiO 2 interfacial layer grown by atomic layer deposition on the ferroelectric properties of the TiN/Hf 0.5 Zr 0.5 O 2 /TiN capacitors is systematically investigated. We show that the integration of the TiO 2 layer leads to an increase in the polar orthorhombic phase content in the Hf 0.5 Zr 0.5 O 2 film. In addition, the crystalline structure of the Hf 0.5 Zr 0.5 O 2 film is highly dependent on the thickness of the TiO 2 inset, with monoclinic phase stabilization after the increase of TiO 2 thickness. Special attention in this work is given to the key reliability parameters-retention and endurance. We demonstrate that the integration of the TiO 2 inset induces valuable retention improvement. Using a novel approach to the depolarization measurements, we show that the depolarization contribution to the retention loss is insignificant, which leaves the imprint effect as the root of the retention loss in TiN/TiO 2 /Hf 0.5 Zr 0.5 O 2 /TiN devices. We believe that the integration of the insulator interfacial layer suppresses the scavenging effect from the bottom TiN electrode, leading to a decrease in the oxygen vacancy content in the Hf 0.5 Zr 0.5 O 2 film, which is the main reason for imprint mitigation. At the same time, although the observed retention improvement is very promising for the upcoming technological integration, the field cycling testing revealed the endurance limitations linked to the phase transitions in the TiO 2 layer and the rise of the effective electric field applied to the Hf 0.5 Zr 0.5 O 2 film., Competing Interests: The authors declare no competing financial interest., (© 2022 The Authors. Published by American Chemical Society.)