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In this critical review, we call attention to a widespread problem related to the vast disagreement in elastic moduli values reported by different authors for nanostructures made of the same material. As a particular example, we focus on ZnO nanowires (NWs), which are among the most intensively studied nanomaterials due to their remarkable physical properties and promising applications. Since ZnO NWs possess piezoelectric effects, many applications involve mechanical deformations. Therefore, there are plenty of works dedicated to the mechanical characterization of ZnO NWs using various experimental and computational techniques. Although the most of works consider exactly the same growth direction and wurtzite crystal structure, reported values of Young’s modulus vary drastically from author to author ranging from 20 to 800 GPa. Moreover, both – diameter dependent and independent – Young’s modulus values have been reported. In this work, we give a critical overview and perform a thorough analysis of the available experimental and theoretical works on the mechanical characterization of ZnO NWs in order to find out the most significant sources of errors and to bring out the most trustable results.

The results of first-principles calculations of the structural, electronic, elastic, vibrational, dielectric and optical properties, as well as the Raman and infrared (IR) spectra, of potassium hexafluorosilicate (K2SiF6; KSF) crystal are discussed. KSF doped with manganese atoms (KSF:Mn4+) is known for its ability to function as a phosphor in white LED applications due to the efficient red emission from Mn⁴⁺ activator ions. The simulations were performed using the CRYSTAL23 computer code within the linear combination of atomic orbitals (LCAO) approximation of the density functional theory (DFT). For the study of KSF, we have applied and compared several DFT functionals (with emphasis on hybrid functionals) in combination with Gaussian-type basis sets. In order to determine the optimal combination for computation, two types of basis sets and four different functionals (three advanced hybrid—B3LYP, B1WC, and PBE0—and one LDA functional) were used, and the obtained results were compared with available experimental data. For the selected basis set and functional, the above-mentioned properties of KSF were calculated. In particular, the B1WC functional provides us with a band gap of 9.73 eV. The dependencies of structural, electronic and elastic parameters, as well as the Debye temperature, on external pressure (0–20 GPa) were also evaluated and compared with previous calculations. A comprehensive analysis of vibrational properties was performed for the first time, and the influence of isotopic substitution on the vibrational frequencies was analyzed. IR and Raman spectra were simulated, and the calculated Raman spectrum is in excellent agreement with the experimental one. [ABSTRACT FROM AUTHOR]

The promise of two-dimensional (2D) rhenium diselenide (ReSe2) in electronics and optoelectronics has sparked considerable interest in this material. However, achieving the growth of high-quality ReSe2 thin films on a wafer scale remains a significant challenge. In this study, we adopted a two-step method to produce ReSe2 thin films by combining magnetron sputtering of Re and ReOx onto flat substrates with subsequent selenization via atmospheric pressure chemical vapor transport (CVT). After analyzing the produced films using X-ray diffraction to identify the crystalline phase in formed thin film and scanning electron microscopy (SEM) to examine surface morphology, it was determined that the suitable temperature range for the 15 min selenization process with CVT is 650 °C–750 °C. Further investigation of these optimally produced ReSe2 thin films included atomic force microscopy (AFM), X-ray photoelectron spectroscopy, and Raman spectroscopy. The bulk electrical analysis of these films and AFM and SEM surface morphology revealed a strong reliance on the type of precursor material used for their synthesis, whereas optical measurements indicated a potential for the films in non-linear optics applications, irrespective of the precursor or temperature used. This study not only provides a new pathway for the growth of ReSe2 films but also sheds light on the synthesis approaches of other 2D transition metal dichalcogenide materials. [ABSTRACT FROM AUTHOR]

Excited state calculations are performed to predict the electronic structure and optical absorption characteristics of Cu-doped anatase Ti O 2  nanofilms, focusing on their (101) and (001) surface terminations. Using model structures that successfully represent the equilibrium positions of deposited Cu atoms on the Ti O 2  surface, a comprehensive analysis of the absorption spectra for each considered model is made. The proposed modeling reveals phenomena when photogenerated electrons from Ti O 2  tend to accumulate in the vicinity of the deposited Cu atoms exposed to photon energies surpassing the band gap of Ti O 2  (approximately 3.2 eV). The crucial transition states that are essential for the creation of potential photocatalytic materials are identified through detailed calculations of the excited states. These insights hold substantial promise for the strategic design of advanced photocatalytic materials. The obtained results provide a base for subsequent analyses, facilitating the determination of heightened surface reactivity, photostimulated water splitting, and antibacterial properties. [ABSTRACT FROM AUTHOR]

This study introduces a novel approach for fabricating ZnS/Al2O3/TaSe2 heterostructured core/shell nanowires (NWs) through the selenization of a metallic Ta thin film precursor. The synthesis process involves a meticulously designed four-step protocol: (1) generating ZnS NWs on an oxidized silicon substrate, (2) encapsulating these NWs with a precisely controlled thin Al2O3 layer via atomic layer deposition (ALD), (3) applying a Ta precursor layer by magnetron sputtering, and (4) annealing in a Se-rich environment in a vacuum-sealed quartz ampoule to transform the Ta layer into TaSe2, resulting in the final core/shell structure. The characterization of the newly produced NWs using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) was validated using the integrity and composition of the heterostructures. Our method not only establishes a new pathway for the synthesis of TaSe2-based core/shell NWs but also extends the potential for creating a variety of core/shell NW systems with chalcogenide shells by adapting the thin film metal precursor approach. This versatility opens the way for future advancements in nanoscale material applications, particularly in electronics and optoelectronics where core/shell geometries are increasingly important. [ABSTRACT FROM AUTHOR]

This study reveals a significant improvement in surface-enhanced Raman scattering (SERS) activity of Ag/ZrO2 substrates covered with a few-layer graphene preliminary exposed to ultraviolet (UV) light. The SERS-active substrates are formed by the "silver mirror" deposition of Ag nanoparticles on annealed zirconia blocks. The film composed of ~3 graphene layers is grown on copper foil by a chemical vapor deposition and then wet-transferred to the SERS-active substrates. The graphene-free Ag/ZrO2 samples are found to provide an enhancement of the Raman scattering from rhodamine 6G (R6G) at a micromolar concentration, which is associated with combined effects from the surface plasmon resonance in the Ag nanoparticles and a charge transfer facilitated by zirconium dioxide. It is revealed that the SERS signal from the analyte molecules can be suppressed by a UV exposure of the Ag/ZrO2 samples due to photocatalytic activity of the wide band gap semiconductor. However, if the samples are covered with a few-layer graphene (Gr/Ag/ZrO2) it prevents the dye molecule decomposition upon the UV treatment and improves SERS activity of the substrates. The 365 nm treatment leads to a 40% increase in the 10–6 M R6G SERS spectrum intensity, while the 254 nm irradiation causes it to rise by 47%, which is explained by different responses from the surface and bulk zirconia crystals to the short and long UV wavelengths. This enhancement is attributed to the distinct responses of surface and in-depth zirconia crystals to varied UV wavelengths and underscores the pivotal role of graphene as a protective and enhancing layer. [ABSTRACT FROM AUTHOR]

The aim of this study is to comprehensively examine the structural composition and properties of the AgAlS2 crystal during its high-pressure phase. This analysis delves into the second coordination environment of the crystal structure and elucidates the distinct transformations it undergoes during the phase transition. The band energy structure was calculated, and the origin of electronic levels was clarified. It is shown that the crystal becomes non-stratified during the phase transition. This study also determined the values of the crystal's carrier effective masses, underscoring its spatial anisotropy. It was found that the calculated optical functions are similar to the crystal in the chalcopyrite structure, and their differences are shown. Further, this study involved the calculation of the crystal's phonon spectrum, revealing the spectrum's transformation during the phase transition. The vibrational frequencies were also obtained, with a symmetrical classification of vibrational modes. Finally, this study derived the infrared and Raman spectra of the AgAlS2 crystal, thereby providing a comprehensive picture of the crystal during its high-pressure phase. [ABSTRACT FROM AUTHOR]

Recent research suggests that photocatalytic activity toward water splitting of strontium titanate SrTiO3 (STO) is enhanced by creating multifaceted nanoparticles. To better understand the source of this activity, a previously designed model is used for two types of surfaces of this nanoparticle, flat and double‐stepped. Density functional theory calculations of water adsorption on these surfaces are performed to gain insight into water adsorption and proton migration processes, as well as thermodynamics of hydrogen evolution reaction within the framework of computational hydrogen electrode. It is concluded that ridges of single‐ and double‐stepped surfaces are nearly identical in terms of adsorption configurations and energetics. Also, it is demonstrated that protons have migration barriers lower than 0.7 eV and that surface morphology impacts catalytic activity toward hydrogen evolution reaction, with flat surface demonstrating higher catalytic activity. [ABSTRACT FROM AUTHOR]

Chalcopyrites are ternary semiconductor compounds with successful applications in photovoltaics. Certain chalcopyrites are well researched, yet others remain understudied despite showing promise. In this study, we use ab initio methods to study CuGaS2, AgGaS2, and CuGaSe2 chalcopyrites with a focus on their less studied solid solutions. We use density functional theory (DFT) to study the effects that atomic configurations have on the properties of a solid solution and we calculate the optical absorption spectra using a many-body perturbation theory. Our theoretical simulations predict that excess of In and Se in the solid solutions leads to narrowing of the band gap and to the broadening of the absorption spectra. Obtained results show promise for possible photovoltaic applications, as well as developed methodology can be used for further study of other promising chalcopyritic compounds. [ABSTRACT FROM AUTHOR]

Surface-enhanced Raman scattering (SERS) spectroscopy is used to investigate a composition of wash swabs from the Cu-TiO2/TiO2-modified filters with disinfecting ability. Macroporous Si chips coated with conformal 800 nm thick Ni layer and Ag particles (Ag/Ni) are engineered to act as SERS-active substrates. Such substrates are characterized by a moderate reflection band in the visible range and provide an improved heat dissipation from contaminants in wash swabs during SERS study. This prevents thermal-induced destruction of analyzing media for reliable assessment of its composition. The anatase Cu-TiO2 and TiO2 nanoparticles are synthesized using the sol-gel method and characterized via Raman spectroscopy and X-ray diffractometry. The filters are modified with Cu-TiO2/TiO2 nanoparticles and embedded in three-valve facial masks that are worn by a volunteer to breathe for 4 h. Comparative SERS analysis of the filters shows that they slightly destroy chemical bonds in the molecules constituting airborne contaminations upon ceiling day lights, which can be associated with Cu-TiO2 photocatalytic activity. The filters additionally exposed to near-ultraviolet light prominently decrease the intensity of Raman signatures of airborne contaminant due to the presence of pure TiO2. [ABSTRACT FROM AUTHOR]

Chloride is one of the most abundant ions in sea water, which is more available than fresh water. Due to lack of H 2 O adsorbate states near the valence band maximum (VBM) edge, the difficulty of water dissociation incidents has been reported on the rutile TiO 2 surface as the excitation energy is around the band gap energy of TiO 2 . It is interesting whether the extra chloride can be a benefit to the water dissociation or not. In this study, the models of chlorine adatoms placed on the rutile TiO 2 (110)/water interface are constructed using ab initio methods. The time-dependent spatial charges, bond-lengths of water molecules, and Hirshfeld charges are calculated by real-time time-dependent density functional theory and the Ehrenfest dynamics theory for investigating the excited state nonadiabatic dynamics of water dissociation. This study presents two photoinduced water-splitting pathways related to chlorine and analyzes the photogenerated hole along the reactions. The first step of water dissociation relies on the localized competition of oxygen charges between the dissociated water and the bridge site of TiO 2 for transforming the water into hydroxyl and hydrogen by photoinduced driving force. [ABSTRACT FROM AUTHOR]