Quasi-2D Bi_2O_2Se is part of an intensive materials research effort aimed at finding new semiconductors that outperform silicon-based electronics in terms of speed and power consumption. This material exhibits exceptionally high carrier mobility at low temperatures but mediocre mobility at 300 K. Its high mobility is generally associated with its high permittivity (ε_r 500), which is also associated with metallicity persisting down to very low carrier concentrations. This material exhibits a counterintuitive increase in carrier mobility as the concentration increases. The connection between low both carrier concentration and mobility in Se-rich conditions, and both high carrier concentration and mobility in Se-poor conditions suggests that the increase is related to native defects. We demonstrate that these defects can alter the effective mass of charge carriers. Specifically, substitutional Se(Bi) defects, which appear under Se-rich conditions, destroy the Bi_2O_2 channel and compromise charge transport properties. These defects increase the effective mass of charge carriers transforming the original semiconductor into a semimetal and introducing holes into charge transport. Additionally, we show that single crystals are generally inhomogeneous, particularly those grown under Se-rich conditions. Unlike Se-poor conditions, Se-rich conditions induce a higher concentration of dislocations and extraneous phases. These findings suggest that the perfection of the Bi_2O_2 channel is crucial for mobility, particularly at room temperature.

The properties of carbon-based materials with nanometric size support their use in numerous applications, such as optoelectronics and energy devices, bioimaging, photodetectors, and sensors. Among the various nanostructure fabrication methods, pulsed laser ablation in liquids (PLA) is widely recognized for its simplicity and rapid processing. It is considered an environmentally friendly synthesis, as it enables nanostructure fabrication in pure liquids without chemical reagents, activators, or vacuum systems, in line with the increasing interest in sustainable and green nanotechnologies. A great challenge of PLA is the reproducibility of the size and shape of the produced structure. This can be accomplished by selection of the proper laser parameters and characteristics of the used liquid. This study is focused on the comparison of the synthesis of graphene-based nanostructures by electric-field-assisted pulsed laser ablation of a graphite target immersed in distilled water and deionized water, used as separate liquid media, without the use of chemical reagents. This is an innovative and environmentally friendly approach for the production of graphene nanoparticles. The laser parameters were kept constant throughout the experiments, while different voltage values were applied between the electrodes immersed in the liquid medium. The applied electric field significantly influences plasma dynamics, cavitation bubble evolution, and post-ablation nanoparticle growth processes, enabling controlled tuning of nanoparticle size and morphology. The optical properties of the obtained suspensions were evaluated by UV-Vis and FTIR spectroscopies. Atomic force microscopy revealed the composition, morphology, and quality of the formed structures.

The Lorentz factor is a fundamental correction factor in quantitative analysis of X-ray diffraction experiments, enabling measured integrated peak intensities to be related to calculated structure factors. In this review, the physical origin of the Lorentz factor, its derivation and practical implementations are presented based on a unified approach, treating the Lorentz factor as the Jacobian relating the experimental measurement coordinates to the reciprocal-space volume element. This approach clarifies the trigonometric and wavelength-dependent contributions to the Lorentz factor and explains the origin of the commonly used `angular-velocity' formulation for rotational measurements. Equations for the Lorentz factor are derived systematically for a broad range of modern X-ray diffraction geometries, including single-crystal and powder diffraction, grazing-incidence diffraction methods, as well as small-angle X-ray scattering. Hereby it is demonstrated that the Lorentz factor sensitively depends not only on the experimental geometry, but also on the type of sample under investigation. In addition, we discuss how the Lorentz correction may be avoided by direct reciprocal-space integration, and the practical limitations of such approaches are pointed out. By providing a unified and comprehensive overview of the Lorentz factor, this review aims to support reliable and consistent intensity evaluation across various modern X-ray diffraction methods.

Mixed-halide perovskites (MHPs) offer good band-gap tunability via stoichiometry changes, and such tunability is an essential property for the creation of multijunction solar cells. However, under illumination halide ions in MHPs segregate and create I- and Br-rich regions, which decrease the efficiency of potential solar cells. In this work, a method for a detailed investigation of the distribution of halide ions within an MHP during and after illumination is introduced. Calculations of the strain field created by the halide segregation were performed, and the obtained local displacement of atoms was used to calculate the X-ray diffuse scattering. By fitting the experimental data measured on a thin polycrystalline layer of FA(0.83)Cs(0.17)Pb(I0.6Br0.4)(3) (where FA stands for formamidinium), the distribution of Br- and I- ions within an illuminated MHP was determined and the subsequent relaxation process of the segregation in the dark was tracked. The creation of highly Br-rich regions within a slightly I-rich volume during illumination was observed.

This study examines the influence of niobium and oxygen on phase stability, crystal structure, and martensitic transformation pathways in Ti-Nb-O alloys. A series of Ti-(8-28)Nb-(0-3)O (at. A 2D-XRD orientation simulation approach was applied to distinguish all 12 crystallographically equivalent α" martensitic variants originating from a single prior β grain, enabling detailed diffraction analysis. This method further allowed quantitative evaluation of the atomic shuffle parameter y, describing the β" transformation. The results demonstrate that Nb primarily governs α" martensite evolution. Increasing Nb stabilizes the β phase and shifts the α" structure toward higher symmetry, as reflected by systematic changes in lattice parameters and increasing shuffle parameter y, indicating suppression of transformation toward the hexagonal α' phase. Oxygen, in contrast, modifies transformation pathways. At lower Nb contents, it suppresses the ω phase formation and promotes β" transformation, while at higher Nb levels it inhibits long-range martensitic transformation, resulting in retained β or competing ω phase. These effects are attributed to local lattice distortions induced by interstitial oxygen.

In this study, we describe the preparation of carbon dots (CDs) from natural charcoal by laser ablation in a liquid. A continuum wave (CW) laser diode operating at a wavelength of 450 nm, hitting a solid carbon target placed into a biocompatible liquid, constituted of a phosphate-buffered saline (PBS) solution and distilled water, was used for the generation of the CDs suspension. Exploring the practical applications of carbon dots, it was observed that the luminescence of the produced CDs can be used as bioimaging in living organisms, environmental monitoring, chemical analysis, targeted drug delivery, disease diagnosis, therapy, and others. The CDs’ luminescence can be induced by UV irradiation and, as demonstrated in this study, by energetic MeV proton beams. The fluorescence was revealed mainly at 480 nm when UV illuminated the CDs, and also in the region at 514–642 nm when the CDs were irradiated by energetic proton ions. Atomic force microscopy (AFM) of the CD films revealed their spherical shape with a size of about 10 nm. The significance of the manuscript lies in the use of CDs produced by laser ablation exhibiting luminescence under irradiation of an energetic proton beam.

Bi2O2Se belongs to a group of quasi-2D semiconductors that can replace silicon in future high-speed/lowpower electronics. However, the correlation between crystal/band structure and other physical properties still eludes understanding: carrier mobility increases non-intuitively with carrier concentration; the observed T2 temperature dependence of resistivity lacks explanation. Moreover, a very high relative out-of-plane permittivity of about 150 has been reported in the literature. A proper explanation for such a high permittivity is still lacking. We have performed infrared (IR) reflectivity and Raman scattering experiments on a large perfect single crystal with defined mosaicity, carrier concentration, and mobility. Five of the eight phonons allowed by factor group theory have been observed and their symmetries determined. The IR spectra show that the permittivity measured in the tetragonal plane is as high as epsilon r approximate to 500, and this high value is due to a strong polar phonon with a low frequency of '34 cm-1 ('1 THz). Such an unusually high permittivity allows the screening of charge defects, leading to the observation of high electron mobility at low temperatures. It also allows effective modulation doping providing a platform for high-performance 2D electronics. DFT calculations suggest the existence of a very low-frequency acoustic phonon '14 cm-1 ('0.4 THz). Both the low-frequency phonons cause anomalous phonon DOS, which is reflected in the unconventional temperature dependence of the heat capacity, Cp approximate to T3.5. The temperature-dependent, two-component group velocity is proposed to explain the unusual temperature dependence of the thermal conductivity, kappa approximate to T1.5.

We investigated the structural, vibrational, and magnetic properties of CrCl3 plate-like nanocrystals on Si/SiO2 substrates, synthesized via vapor transport, across a broad temperature range (2-300 K) to elucidate structural and magnetic phase transitions. X-ray diffraction analysis identified rhombohedral and monoclinic phases, with temperature-variable ratio. Unexpectedly, the high-temperature (monoclinic) phase persisted in coexistence with the low-temperature (rhombohedral) phase down to the lowest accessed temperature. Magnetic susceptibility measurements under different magnetic field orientations (B||c and Bic) showed distinct features at 14 K and 17 K, confirming a two-step magnetic ordering. Polarization-resolved Raman spectroscopy under varying temperature revealed significant changes in the peak positions, full-width at half maximum (FWHM), and intensity ratios, which was consistent with the proposed structural and magnetic phase transitions. Analysis of the polarization ratio highlighted anisotropic contributions linked to the structural phase transitions, showing a gradual transformation from the rhombohedral to the monoclinic phase with temperature, as corroborated by the X-ray diffraction study. The observed temperature dependence of the structural, magnetic and vibrational properties underscores the interplay between structural phase transitions and spin-lattice coupling in CrCl3. In particular, the high temperature phase persists far below the magnetic ordering temperature in the nanocrystals (the ratio of the monoclinic to the rhombohedral phase below 10 K is still about 2:3, as revealed by the X-ray diffraction analysis). Our findings offer a comprehensive understanding of the structural-magnetic correlation in CrCl3 and point to the possibility of the phase coexistence in the chromium trihalides in the form of plate-like nanocrystals.

Bi2O2Se belongs to a group of quasi-2D semiconductors that can replace silicon in future high-speed/low-power electronics. However, the correlation between crystal/band structure and other physical properties still eludes understanding: carrier mobility increases non-intuitively with carrier concentration; the observed T^2 temperature dependence of resistivity lacks explanation. Moreover, a very high relative out-of-plane permittivity of about 150 has been reported in the literature. A proper explanation for such a high permittivity is still lacking. We have performed infrared (IR) reflectivity and Raman scattering experiments on a large perfect single crystal with defined mosaicity, carrier concentration and mobility. Five of the eight phonons allowed by factor group theory have been observed and their symmetries determined. The IR spectra show that the permittivity measured in the tetragonal plane is as high as ε_r≈500, and this high value is due to a strong polar phonon with a low frequency of 34 cm^-1 ( 1 THz). Such an unusually high permittivity allows the screening of charge defects, leading to the observation of high electron mobility at low temperatures. It also allows effective modulation doping providing a platform for high performance 2D electronics. DFT calculations suggest the existence of a very low frequency acoustic phonon 14 cm^-1 ( 0.4 THz). Both the low frequency phonons cause anomalous phonon DOS, which is reflected in the unconventional temperature dependence of the heat capacity, c_M≈T^3.5. The temperature-dependent, two-component group velocity is proposed to explains the unusual temperature dependence of the thermal conductivity, κ≈T^1.5

Bi2O2Se is a semiconductor that is being intensively studied due to its many extraordinary properties. Since about 2010, research on polycrystals has focused on thermoelectric materials. For the last 10 years, single crystal research has been driven by its quasi 2D structure with unexpectedly high permittivity (epsilon r approximate to 500), which promotes high electron mobility. Bi2O2Se thus outperforms other 2D materials in many parameters. However, the high permittivity is also responsible for the extremely low critical concentration of the metal-insulator transition (n approximate to 1015 cm-3). Thus, Bi2O2Se is so far only available as an n-type semiconductor largely with metal-like properties, although the electron concentration can range over 6 orders of magnitude (n approximate to 1015-1021 cm-3), reportedly due to the very high concentration of selenium vacancies or selenium antisites on the Bi site. In this paper, we consider Mn doping in Bi2O2Se, Bi2-xMnxO2Se. The Mn doping leads to a decrease in the electron concentration and, for the first time, to a transition of the material to p-type conductivity. A thermal gap (approximate to 0.9 eV) can be deduced from the temperature dependence of the electrical conductivity. The p-type transition is related to the interaction of Mn with the defect structure of Bi2O2Se. Our experiments suggest that the most abundant defects, besides the Se vacancies VSe, are the substitutional defect Se atom at the Bi site, SeBi and the O atom at the Se site. From high resolution XRD analysis, we conclude that Mn reduces its concentration and brings the structure to the p-type state. From DFT calculations and magnetic data we infer the substitution of Bi by Mn (MnBi, in a high spin state, mu congruent to 5 mu B), although all experiments indicate a very low solubility nMn = 2.67 x 1018 cm-3 based on magnetic data.

The hexagonal ferrite h-YbFeO3 grown on YSZ(111) by pulsed laser deposition is foreseen as a promising single multiferroic candidate where ferroelectricity and antiferromagnetism coexist for future applications at low temperatures. We studied in detail the microstructure as well as the temperature dependence of the magnetic properties of the devices by comparing the heterostructures grown directly on YSZ(111) (i.e., YbPt_Th0nm) with h-YbFeO3 films deposited on substrates buffered with platinum Pt/YSZ(111) and in dependence on the Pt underlayer film thickness (i.e., YbPt_Th10nm, YbPt_Th40nm, YbPt_Th55nm, and YbPt_Th70nm). The goal was to deeply understand the importance of the crystal quality and morphology of the Pt underlayer for the h-YbFeO3 layer crystal quality, surface morphology, and the resulting physical properties. We demonstrate the relevance of homogeneity, continuity, and hillock formation of the Pt layer for the h-YbFeO3 microstructure in terms of crystal structure, mosaicity, grain boundaries, and defect distribution. The findings of transmission electron microscopy and X-ray diffraction reciprocal space mapping characterization enable us to conclude that an optimum film thickness for the Pt bottom electrode is ThPt = 70 nm, which improves the crystal quality of h-YbFeO3 films grown on Pt-buffered YSZ(111) in comparison with h-YbFeO3 films grown on YSZ(111) (i.e., YbPt_Th0nm). The latter shows a disturbance in the crystal structure, in the up-and-down atomic arrangement of the ferroelectric domains, as well as in the Yb–Fe exchange interactions. Therefore, an enhancement in the remanent and in the total magnetization was obtained at low temperatures below 50 K for h-YbFeO3 films deposited on Pt-buffered substrates Pt/YSZ(111) when the Pt underlayer reached ThPt= 70 nm.

The structure and the chemical composition of individual layers as well as of interfaces belonging to the two heterostructures M1 (BaFe12O19/YbFeO3/YSZ) and M2 (YbFeO3/BaFe12O19/YSZ) grown by pulsed laser deposition on yttria-stabilized zirconia (YSZ) substrates are deeply characterized by using a combination of methods such as high-resolution X-ray diffraction, transmission electron microscopy (TEM), and atomic-resolution scanning TEM with energy-dispersive X-ray spectroscopy. The temperature-dependent magnetic properties demonstrate two distinct heterostructures with different coercivity, anisotropy fields, and first anisotropy constants, which are related to the defect concentrations within the individual layers and to the degree of intermixing at the interface. The heterostructure with the stacking order BaFe12O19/YbFeO3, i.e., M1, exhibits a distinctive interface without any chemical intermixture, while an Fe-rich crystalline phase is observed in M2 both in atomic-resolution EDX maps and in mass density profiles. Additionally, M1 shows high c-axis orientation, which induces a higher anisotropy constant K1 as well as a larger coercivity due to a high number of phase boundaries. Despite the existence of a canted antiferromagnetic/ferromagnetic combination (T < 140 K), both heterostructures M1 and M2 do not reveal any detectable exchange bias at T = 50 K. Additionally, compressive residual strain on the BaM layer is found to be suppressing the ferromagnetism, thus reducing the Curie temperature (Tc) in the case of M1. These findings suggest that M1 (BaFe12O19/YbFeO3/YSZ) is suitable for magnetic storage applications.

The morphology and crystal structure of Pt films grown by pulsed laser deposition (PLD) on yttria-stabilized zirconia (YSZ)at high temperatures Tg = 900 °C was studied for four different film thicknesses varying between 10 and 70 nm. During the subsequent growth of the capping layer, the thermal stability of the Pt was strongly influenced by the Pt film’s thickness. Furthermore, these later affected the film morphology, the crystal structure and hillocks size, and distribution during subsequent growth at Tg = 900 °C for a long duration. The modifications in the morphology as well as in the structure of the Pt film without a capping layer, named also as the as-grown and encapsulated layers in the bilayer system, were examined by a combination of microscopic and scattering methods. The increase in the thickness of the deposited Pt film brought three competitive phenomena into occurrence, such as 3D–2D morphological transition, dewetting, and hillock formation. The degree of coverage, film continuity, and the crystal quality of the Pt film were significantly improved by increasing the deposition time. An optimum Pt film thickness of 70 nm was found to be suitable for obtaining a hillock-free Pt bottom electrode which also withstood the dewetting phenomena revealed during the subsequent growth of capping layers. This achievement is crucial for the deposition of functional bottom electrodes in ferroelectric and multiferroic heterostructure systems.

Light-induced ion demixing in mixed-halide perovskites is simulated numerically using the phenomenological Cahn-Hilliard equation. In the model we consider the energy of local elastic deformation as well as the contribution of free carriers, assuming both the polaron and the bandgap-fluctuation models. The simulation shows that elastic deformation suppresses the demixing while free carriers promote it, however both effects lead to different ion distributions. The free-carrier-induced demixing appears only for larger starting random fluctuations of the ion concentration.

The spatial orientation of α lamellae in a metastable β-Ti matrix of Timetal LCB (Ti–6.8 Mo–4.5 Fe–1.5 Al in wt%) was examined and the orientation of the hexagonal close-packed α lattice in the α lamella was determined. For this purpose, a combination of methods of small-angle X-ray scattering, scanning electron microscopy and electron backscatter diffraction was used. The habit planes of α laths are close to {111}β, which corresponds to (1320)α in the hexagonal coordinate system of the α phase. The longest α lamella direction lies approximately along one of the 〈110〉β directions which are parallel to the specific habit plane. Taking into account the average lattice parameters of the β and α phases in aged conditions in Timetal LCB, it was possible to index all main axes and faces of an α lath not only in the cubic coordinate system of the parent β phase but also in the hexagonal system of the α phase.

Defect control is critical to achieve long carrier lifetimes in semiconductors. SnS is a promising thermoelectric and photovoltaic material, in which native defects play a detrimental role, particularly in photovoltaics. In this study, we investigated the Fe-doping of SnS and the interaction of Fe impurities with native defects in a series of single crystals of Sn1-xFexS up to concentrations of x = 0.05. Although the doped single crystals appear rather disordered, the hole mobility is very high (similar to 8500 cm(2)V(-1)s(-1) at 30 K for Sn0.99Fe0.01S), suggesting that holemediated charge transport in this material is largely insensitive to extrinsic impurities. Charge transport analysis suggests that the incorporation of Fe atoms leads to the healing of the intrinsic defect structure and the exclusion of minority electrons from charge transport, allowing the observation of high hole mobility.

ZnO nanopillars were implanted with Au-400 keV and Ag-252 keV ions with ion fluences from 1 x 1015 cm-2 to 1 x 1016 cm-2. We compared ZnO nanopillars solely implanted with Au-ions and dually-implanted with Au and Ag-ions. Rutherford Back-Scattering spectrometry (RBS) confirmed Ag and Au embedded in ZnO nanopillar layers in a reasonable agreement with theoretical calculations. A decreasing thickness of the ZnO nanopillar layer was evidenced with the increasing ion implantation fluences. Spectroscopic Ellipsometry (SE) showed a decrease of refractive index in the nanopillar parts with embedded Au, Ag-ions. XRD discovered vertical domain size decreasing with the proceeding radiation damage accumulated in ZnO nanopillars which effect was preferably ascribed to Au-ions. SE and diffuse reflectance spectroscopy (DRS) showed optical activity of the created nanoparticles at wavelength range 500 - 600 nm and 430 - 700 nm for the Au-implanted and Au, Ag-implanted ZnO nanopillars, respectively. Photoluminescence (PL) features linked to ZnO deep level emission appear sub-stantially enhanced due to plasmonic interaction with metal nanoparticles created by Ag, Au-implantation. Photocatalytic activity seems to be more influenced by the nanoparticles presented in the layer rather than the surface morphology. Dual implantation with Ag, Au-ions enhanced optical activity to a larger extent without significant morphology deterioration as compared to the solely Au-ion implanted nanopillars.

The possibility to engineer (GeTe)m (Sb2 Te3 )n phase-change materials to co-host ferroelectricity is extremely attractive. The combination of these functionalities holds great technological impact, potentially enabling the design of novel multifunctional devices. Here an experimental and theoretical study of epitaxial (GeTe)m (Sb2 Te3 )n with GeTe-rich composition is presented. These layered films feature a tunable distribution of (GeTe)m (Sb2 Te3 )1 blocks of different sizes. Breakthrough evidence of ferroelectric displacement in thick (GeTe)m (Sb2 Te3 )1 lamellae is provided. The density functional theory calculations suggest the formation of a tilted (GeTe)m slab sandwiched in GeTe-rich blocks. That is, the net ferroelectric polarization is confined almost in-plane, representing an unprecedented case between 2D and bulk ferroelectric materials. The ferroelectric behavior is confirmed by piezoresponse force microscopy and electroresistive measurements. The resilience of the quasi van der Waals character of the films, regardless of their composition, is also demonstrated. Hence, the material developed hereby gathers in a unique 2D platform the phase-change and ferroelectric switching properties, paving the way for the conception of innovative device architectures.