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Local mapping of piezoelectric response across grains with different crystal planes is crucial to enhance the level of understanding of the piezoelectric behavior of wurtzite hexagonal (WH) AlN thin films. To investigate this phenomenon, polycrystalline WH-AlN thin films were deposited by pulsed-DC magnetron sputtering using a mixture of argon (Ar) and nitrogen (N2) with varying N2 content as 5%, 10%, and 20% in the form of the AlN/Ti/Si (100) heterostructure. Piezo force microscopy (PFM) was used to establish a correlation among piezo-response (PR) phase contrast, polarity, and crystal planes constituting the film surface. A phenomenological model is also presented to correlate the distribution of interface sheet charges with polar (0002)-, semi-polar (10 1 ¯ 1)-, and non-polar (10 1 ¯ 0)-planes present on the film surface. This interdependence eventually regulates the phase between piezoelectric oscillations and modulation voltage, which is ultimately translated into a grain-wise contrast obtained from PR-phase images. [ABSTRACT FROM AUTHOR]

Tin oxide (SnO2) has garnered significant attention for its high spectral selectivity when used as an ultraviolet photodetector (PD). In this study, SnO2 nanosheets (NSs) were synthesized via a hydrothermal method, followed by spin-coating a layer of Ga2O3 thin film to construct a heterojunction photoelectrochemical ultraviolet PD (PEC UV PD). Initially, we investigated the effect of precursor composition on the properties of the Ga2O3 thin films. It was observed that the thickness of the films increased with higher precursor concentrations, while the optical bandgap decreased. Based on these findings, we successfully fabricated the SnO2 NSs-Ga2O3 PEC UV PD. Electrochemical analysis revealed that as the precursor concentration used for spin-coating Ga2O3 increased, the device's responsivity and detectivity initially increased and then decreased. After optimization, the device prepared with a 0.2 M Ga(NO3)3 solution spin-coated on SnO2 exhibited excellent spectral selectivity (R 265nm/ R 420nm ∼ 4472), a responsivity of 4.86 mA W−1, and a detectivity of 2.72 × 109 Jones. This study demonstrates that coating Ga2O3 is an effective approach to constructing high-performance SnO2-based UV PDs. [ABSTRACT FROM AUTHOR]

Tin oxide (SnO2) has garnered significant attention for its high spectral selectivity when used as an ultraviolet photodetector (PD). In this study, SnO2 nanosheets (NSs) were synthesized via a hydrothermal method, followed by spin-coating a layer of Ga2O3 thin film to construct a heterojunction photoelectrochemical ultraviolet PD (PEC UV PD). Initially, we investigated the effect of precursor composition on the properties of the Ga2O3 thin films. It was observed that the thickness of the films increased with higher precursor concentrations, while the optical bandgap decreased. Based on these findings, we successfully fabricated the SnO2 NSs-Ga2O3 PEC UV PD. Electrochemical analysis revealed that as the precursor concentration used for spin-coating Ga2O3 increased, the device's responsivity and detectivity initially increased and then decreased. After optimization, the device prepared with a 0.2 M Ga(NO3)3 solution spin-coated on SnO2 exhibited excellent spectral selectivity (R 265nm/ R 420nm ∼ 4472), a responsivity of 4.86 mA W−1, and a detectivity of 2.72 × 109 Jones. This study demonstrates that coating Ga2O3 is an effective approach to constructing high-performance SnO2-based UV PDs. [ABSTRACT FROM AUTHOR]

In contemporary optoelectronic devices, the transparent conductive oxides commonly demonstrate n-type conduction characteristics, with indium-doped tin oxide emerging as a prominent example. However, in applications involving fully invisible electronics that necessitate p-type conductive oxides, there exists a demand for a quintessential material possessing properties akin to its n-type counterpart. CuCrO2, a delafossite semiconductor based on copper, presently represents a notable compromise between optical and electrical attributes within the realm of p-type semiconductors. Despite numerous studies focusing on this material, the charge carrier transport regime within the material remains unclear. The commonly reported hole transport mechanism in CuCrO2 is the small polaron model. However, this work evidences several contradictions when this transport mechanism is assumed. Using the same methodology as previous studies, we investigated the holes' transport mechanism by the means of the measurement of electrical conductivity and the Seebeck coefficient at varying temperatures. Different charge transport models in high intrinsic defect doped CuCrO2 thin films are explored: small polarons, grain boundaries scattering in degenerate semiconductors, and variable range hopping with nearest neighbor hopping. The small polaron model does not provide conclusive results within the temperature range analyzed. Interestingly, no specific hole transport mechanism can be undoubtedly selected. The limitations of the models highlight the influence of peculiar defects within CuCrO2 thin films on the hole transport mechanism, particularly the adoption of well-ordered copper vacancies columns. [ABSTRACT FROM AUTHOR]

Cu2SnS3 (CTS) is expected to be an absorber material for next-generation solar cells because it is composed of nontoxic, low-cost elements and has an absorption coefficient of >104 cm−1. In this study, the effects of sulfurization in tin sulfide (Sn x S y) and S mixed vapors on various properties of CTS were investigated by using a 3-zone tube furnace to suppress carrier recombination at the grain boundaries and control the composition of the CTS. The CTS deposited via sulfurization in S vapor only (1-zone CTS) contained different monoclinic and tetragonal CTS structures. The grain size of the CTS thin films deposited via sulfurization in Sn x S y and S mixed vapors was not increased. On the other hand, crystal structure analysis revealed that the CTS had grown to single-phase monoclinic CTS. The results suggest that precipitation in Sn x S y and S mixed vapors contributes to the growth of monoclinic CTS with suitable power-generation characteristics. This finding is important for realizing high-efficiency CTS-based solar cells. [ABSTRACT FROM AUTHOR]

Cu2ZnSn(SSe)4 (CZTSSe) semiconductor is quite promising to solar cell applications, recently achieving a new record efficiency of 14.9%. Despite theoretical works have shown that efficiencies higher than 20% are possible in this technology, there are some critical points that should be carefully solved by the scientific community. In this review, it is presented a critical analysis on the state-of-the-art of Cu2ZnSn(SSe)4 solar cells. First, we summarize advantages and disadvantages of most used vacuum and non-vacuum thin film fabrication methods, followed by the most important results in solar cell fabrication along with key factors in performance improvement. Furthermore, the future experimental outlook is also analyzed with a particular focus on kesterite material engineering and its grading band-gap engineering. Likewise, the experimental state-of-the-art of CZTSSe device fabrication, a non-typical contribution of this work to the literature it is the presentation and discussion of most important theoretical results on solar cells. A particular attention is paid to results concerning numerical and analytical approaches for the study of Cu2ZnSn(SSe)4 solar cells. Finally, theoretical results concerning the potential use of nanostructured CZTSSe solar cells for achieving efficiencies higher than that of the Shockley–Queisser limit are presented and discussed. [ABSTRACT FROM AUTHOR]

In this work, unintentionally doped GaN thin films were successfully grown on (0001) c -, (11–20) a - and (10–10) m -plane GaN free-standing substrates using metal–organic chemical vapor deposition. Subsequently, Mg was introduced into the GaN thin films through ion implantation (I/I) to prepare Mg-doped GaN (GaN:Mg). Compared with the c -plane substrate, non-polar a - and m -plane substrates were found to effectively enhance the concentration of MgGa acceptors while reducing the concentration of nitrogen vacancy-related clusters in I/I GaN:Mg. The origins of the ultraviolet luminescence peak, green luminescence band and blue luminescence band were analyzed by photoluminescence (PL) spectra. Two acceptor energy levels of Mg in I/I GaN:Mg were calibrated by measuring low-temperature PL spectra in the range of 5 K to 50 K. [ABSTRACT FROM AUTHOR]

The immobilization design strategy plays an important role in biosensor development and its sensing performance. Both adsorption (physisorption) and cross-linker functionalization (chemisorption) are common approaches for immobilizing a bioreceptor layer. In this work, these two approaches were studied and compared, envisaging a functional and strongly attached bioreceptor layer onto sputtered Au–TiO2 thin films. DSP cross-linker (Lomant's reagent) was used in the thin film's functionalization, and the effect of different concentrations on the development of an adhesion layer was investigated. Surface morphology analysis of functionalized thin films suggested the development of uniformly coated self-assembled layers. However, DSP islands with a fractal structure were found for a concentration of 4 mg ml−1. Infrared spectroscopy confirmed the cross-linker functionalization at the thin film's surface. Confocal microscopy of immobilized fluorescent antibodies revealed that DSP islands improve the chemical surface area available for bioreceptor immobilization. Moreover, an immunoassay using mouse IgG interaction with fluorescent anti-mouse IgG (Fab specific), working as capture and detection antibody, respectively, showed that DSP functionalization favors antibodies orientation and adhesion strength to the surface, when compared to physisorption. [ABSTRACT FROM AUTHOR]

We report the presence of electron-spin-phonon interactions in half-metallic ferromagnetic Sr2FeMoO6 (SFMO) double perovskite thin films using temperature-dependent Raman spectroscopy. A series of SFMO thin films have been prepared on LaAlO3 (001) single-crystal substrate using the Pulsed Laser Deposition technique. These depositions have been made in different gas-conditions such as in vacuum, and under nitrogen and oxygen gas pressures. At room temperature, Raman spectra manifest a Fano feature which indicates the presence of electron-phonon coupling in the films. The electron-phonon coupling strength further changes with a change in deposition conditions. Magnetization results show that the SFMO film grown in vacuum has the highest saturation magnetization which suggests better cation ordering as compared to the other films. For enhanced understanding, Raman spectra were recorded at varied temperatures and the data were analyzed by theoretical model fittings. A parameter quantifying temperature-dependent anharmonic nature of phonons has been derived using Balkanski model fits. This parameter shows a drastic deviation in the vicinity of Curie temperatures, manifesting a spin-phonon coupling in SFMO films. We further show that the spin-phonon coupling strengthens with improved Fe–Mo ordering. Any experimental observation of spin-phonon coupling has not been reported for SFMO systems till date. The magnetization data corroborate well with these observations made by Raman measurements. Our results of Raman spectroscopy, magnetization and resistivity collectively suggest that the SFMO films exhibit electron-spin-phonon interactions, which are influenced by the cation ordering. We also devised out the method of relating the anharmonic nature of Raman modes with the degree of Fe–Mo ordering and spin-phonon coupling in double-perovskite materials. [ABSTRACT FROM AUTHOR]

Nickel (II) oxide, NiO, is a wide band gap Mott insulator characterized by strong Coulomb repulsion between d-electrons and displays antiferromagnetic order at room temperature. NiO has gained attention in recent years as a very promising candidate for applications in a broad set of areas, including chemistry and metallurgy to spintronics and energy harvesting. Here, we report on the fabrication of polycrystalline NiO using spray-pyrolysis technique, which is a deposition technique able to produce quite uniform films of pure and crystalline materials without the need of high vacuum or inert atmospheres. The composition and structure of the NiO thin films were then studied using x-ray diffraction, and atomic force and scanning electron microscopies (SEM). The phononic and magnonic properties of the NiO thin films were also studied via Raman spectroscopy, and the ultrafast electron dynamics by using optical pump probe spectroscopy. We found that the NiO samples display the same phonon and magnon excitations expected for single crystal NiO at room temperature, and that electron dynamics in our system is like those of previously reported NiO mono- and polycrystalline systems synthesized using different techniques. These results prove that spray-pyrolysis can be used as affordable and large-scale fabrication technique to synthesize strongly correlated materials for a large set of applications. [ABSTRACT FROM AUTHOR]

TiO2 thin films were prepared by sol-gel spin-coating (SGSC) and electron beam-physical vapor deposition (EB-PVD) methods and annealed at different temperatures (Ta). X-ray diffraction spectroscopy (XRD) results show that the TiO2 films prepared by the SGSC method transformed from the anatase single phase to the coexistence of anatase and rutile with the increase of Ta. However, TiO2 films prepared by the EB-PVD method existed only in the anatase phase, and the crystalline strength was enhanced with the increase of Ta. Meanwhile, particles of TiO2 targets annealed at different Ta showed a rutile phase for TiO2 target particles in the EB-PVD method. The results indicate that the EB-PVD method hinders the nucleation growth and phase transformation of TiO2 films. Scanning electron microscopy and atomic force microscopy also show that the grain size and R ms of TiO2 thin films prepared by the SGSC method increased with the increase of Ta, and the grain size becomes inhomogeneous when the rutile phase is formed. Ultraviolet–visible results show that the forbidden bandwidth and light absorption capacity increase with increasing Ta. For the EB-PVD method, the grain size and surface roughness gradually increased when the Ta of the films was less than 800 °C, while annealing at 800 °C changed the direction of growth and nucleation, and also produced surface cracks; XRD verified the hypothesis that the EB-PVD method hinders the nucleation growth as well as the phase transition of the films. Weak differences in the optical absorption properties and bandgap values of the films also indicate that the EB-PVD method hinders the phase transformation of TiO2 films. Finally, the results of degradation of methylene blue (MB) under simulated visible light showed that the films prepared by the SGSC method gradually improved the photocatalytic performance with the enhancement of the crystalline strength of the anatase phase. The TiO2 films prepared by the EB-PVD method improved the photocatalytic performance with the increase of the active area. [ABSTRACT FROM AUTHOR]

This paper reports the systematic study on the structure, magnetic properties and magnetoelastic properties for the Fe100− x Ga x (001) thin films epitaxially grown on the different substrates of GaAs(001) and MgO(001) using the sputtering technique. The alloy composition dependence of effective magnetoelastic coupling coefficient B eff along the FeGa [110] direction indicated that the largest magnetoelastic coupling was obtained for the Fe–Ga layer with x = 30 grown on the MgO substrate, which was evaluated to be B eff = − 9.4 × 107 erg cm−3. Considering the results of structural analysis and magnetization measurement, the different crystallite sizes depending on the kind of substrate may give rise to the different magnetoelastic coupling strengths between the Fe–Ga layers on the MgO and the GaAs. The magnetostriction along the Fe–Ga [111] direction λ 111 was also estimated with the assumption of plausible elastic property of Fe–Ga, and showed the values comparable to the reported value of bulk Fe–Ga. This means the large magnetostriction can be obtained even for the Fe–Ga thin films epitaxially grown not only on the GaAs(001) but also on the MgO(001). The findings in this work will give a guideline for designing spintronic applications with a Fe–Ga layer exhibiting a large magnetoelastic coupling. [ABSTRACT FROM AUTHOR]

We present a study of the properties related to the magnetization reversal process in two thin-film samples with magnetic stripe domains: Fe0.82Ga0.18 (Fe–Ga) and Ni0.81Fe0.19 (permalloy). In Fe–Ga thin films, we focus on magnetization reversal driven by thermal activation by considering the magnetic viscosity behavior. The results suggest that the reversal process occurs gradually, where the magnetization switches direction via ∼ 10 nm-long jumps of the magnetic domain walls. On the other hand, vectorial hysteresis loops were performed in permalloy thin films with the aim to study the behavior of the transverse magnetization component (perpendicular to the applied field) during the magnetization reversal process. We show that the measurement of the transversal magnetization component shows a much higher sensitivity for the determination of the in-plane magnetic anisotropy than the usual hysteresis loops where the magnetization is parallel to the applied field. Moreover, this allows to highlight the competition between the intrinsic and rotatable anisotropies in thin films that present stripe domains. [ABSTRACT FROM AUTHOR]

Unintentionally doped carbon impurities from organometallic precursors are primary sources of carrier compensation and mobility degradation in wide bandgap semiconductors, leading to lowered performance of power electronic devices. To address this challenge, carbon-free α- Ga2O3 single-crystalline thin films were heteroepitaxially grown on sapphire substrates by using gallium inorganic precursors through a mist chemical vapor deposition technique. Determined through a temperature dependence of growth rates, three distinct growth regimes are identified: the surface reaction limited regime below 480 °C, the mid-temperature mass-transport limited regime (480 °C–530 °C) and the high temperature limited regime related to desorption or phase transition. With an optimized around 530 °C, the densities of screw and edge dislocations are reduced to 7.17 × 106 and 7.60 × 109 cm−2, respectively. Notably, carbon incorporation was eliminated in the α -Ga2O3 grown by inorganic GaCl3, as evidenced by the absence of carbon-related vibrational bands in Raman scattering analysis, while crystalline quality was comparable to that grown with organometallic precursors. The high solubility of GaCl3 in water is expected to enable the rapid growth of high purity α -Ga2O3 with improved electronic transport performances. [ABSTRACT FROM AUTHOR]

In this study, we present a systematic analysis of the relation between the structural properties and magnetic anisotropies of as-grown and heat-treated polycrystalline Fe 1 − x Ga x (0.11 < x < 0.19) thin films deposited on glass and Si(100) substrates. The results show that the crystallographic texture of the films has a significant impact on the evolution of the magnetic anisotropies. The samples grown on glass do not exhibit a preferred texture while, for samples grown on Si(100), the appearance of a weak in-plane fourfold magnetic anisotropy is reported. Such anisotropy is enhanced and better defined in the heat treated samples. Via a phenomenological model we show that this anisotropy has a microstructural origin. These findings demonstrate the possibility of tuning magnetic anisotropies by growing on different substrates and/or performing thermal treatments, which in turn reinforces the possibility of developing smart magnetic switching materials for electronic applications. [ABSTRACT FROM AUTHOR]

The first asymmetric mode (A1 mode) lamb wave resonator (LWR) with a resonant frequency of 6 GHz based on Z-cut lithium niobate (LN) films is presented. An asymmetric electrode structure with different-sized electrode pads in the center and edged regions has been proposed, which can be used to optimize the distribution of the electric field and decrease acoustic impedance mismatch to improve the target mode. Experiment results reveal that LWRs with an asymmetric electrode structure can successfully enhance the A1 mode, achieving a high effective electromechanical coefficient ( k eff 2 ) of 26%, a quality factor (Q) of 1123, and an excellent figure-of-merit (FOM = k eff 2 ∙ Q) of 262. It demonstrates that asymmetric electrode structure provides a new way to suppress the spurious modes for LWRs and shows a great application prospect in wide-bandwidth and low-loss filters used in the sub-6 G frequency range. [ABSTRACT FROM AUTHOR]

Experimentally it is shown that without any oxygen manipulation for TiO2, a strong room temperature ferromagnetism could be expected only in ultra-thin films, with the ideal thickness below 100 nm. Both bulks and nano-powders of TiO2 are diamagnetic, indicating that the surface and its nano-sublayers play very important roles in tailoring the magnetic properties in this type of compound. To shed a new light on the defect-related magnetism in the typical case of anatase TiO2 surfaces, we have performed a series of quantum-mechanical calculations for TiO2 slabs containing Ti or O vacancies in different distances from the (001) surface. The lowest formation energies were obtained for the Ti vacancies in the first sub-surface layer and the O vacancies within the surface. The computed magnetic states reflect complicated structural relaxations of atoms influenced by both the surface and vacant atomic positions. O atoms cannot contribute much to magnetic moment when Ti vacancies are isolated and far from the surface. Ti vacancies in TiO2 are only metastable. The formation energy of Ti interstitials is lower than for Ti vacancies since high-temperature annealing, especially with a lot of O2 available that would fill up O-related defects, and as a result, eliminate most of Ti vacancies. Lower temperatures, less O2, and shorter exposure times may enable not only partial elimination of Ti vacancies but also can facilitate their diffusion into different states of aggregations. In the ferromagnetic films (i.e. thin films below 100 nm), it looks like that the O atoms are located closer to the Ti vacancies. [ABSTRACT FROM AUTHOR]

In this work, the conduction mechanism and dielectric nonlinearity of undoped and Mn-doped Na0.5Bi0.5TiO3 (NBT) films were investigated. The potential conduction mechanism in relatively low electric fields should be dominated by hopping conduction rather than typical Ohmic conduction. In the high electric field region, the conduction mechanism is dominated by Poole–Frenkel emission and Schottky emission. The enhancement of electrical insulation of NBT films after Mn doping was shown to result from a decrease in oxygen vacancies and elevation of the conduction energy barrier. Furthermore, significant improvements in the nonlinearity of both the dielectric constant and polarization of Mn-doped NBT films were observed, as indicated by the results of Rayleigh fitting and first-order reversal curve distributions. Such enhancements were attributed to the reduction in domain wall pinning, decreased interference from electrostatic potential and improved leakage characteristics. [ABSTRACT FROM AUTHOR]

We present a method to model the gas permeation through silicon-oxide thin film coatings that are afflicted with nanoscale defects. With it, we are able to give an estimation of the diffusion coefficient in bulk by subtracting the influence of the defects. The model is based on data obtained from positron annihilation spectroscopy, which is processed to yield possible defect allocation patterns of the coatings. For a systematic evaluation of these patterns, a path through the coating is calculated and then subjected to in-depth analysis to evaluate the used approach as well as to interpret the results for insights on the permeation mechanisms. The model appears to function as intended and no unexpected behaviour is observed. The defect volume share is overestimated, which can be retraced to the underlying algorithm, and a correction method is applied to the resulting bulk diffusion coefficient. The model gives reasonable results both for oxygen and water vapor permeation. These results can be used in following works that build on the presented model. [ABSTRACT FROM AUTHOR]

Recently, methane has been demonstrated as an effective n -type dopant for ZnO thin films deposited using the RF-magnetron sputtering method. It was shown that the major electrical doping effect of methane is caused by hydrogen released during methane decomposition. This work investigates the origin of the observed increase in conductivity of methane-doped ZnO films with the increase in thickness. The study is aimed at describing the nature of this thickness-dependent effect through a detailed analysis of the thickness-dependent morphology and crystalline structure. A combination of structural, electrical, and optical characterization revealed a transition from fine-grained films with a random orientation at early stages to partially (002)-textured films with columnar grains at later stages of growth. It is demonstrated that grain/sub-grain boundaries increase the electrical conductivity and that the contribution of such buried inner boundaries increases with increasing thickness. It is proposed that hydrogen diffuses along the grain and sub-grain boundaries during growth, leading to continuous doping of the buried interfaces. This hydrogen diffusion mechanism results in an apparent 'additional doping' of thicker films. The results provide new insights into the thickness-dependent conductivity of doped polycrystalline ZnO films mediated by hydrogen diffusion along internal interfaces. [ABSTRACT FROM AUTHOR]

We propose a simple approach to locally modify the conductance of molybdenum oxide thin films with thermal annealing in oxygen atmosphere at relatively low temperature for constructing a visible-blind ultraviolet photoconductor. The amorphous MoO x is grown by remote plasma enhanced atomic layer deposition (RPALD), and then crystallized into α -MoO x at 500 °C in argon atmosphere, which exhibits good conductance with resistivity of 3.9 × 10−3 Ω cm due to the formation of oxygen vacancies. Good ohmic contact between Ti and the crystallized MoO x is demonstrated with specific contact resistance of 9.74 × 10−4 Ω cm2. The lateral Au/Ti-MoO x -Ti/Au structures are defined and the conductance of the exposed MoO x channel is significantly modified by thermal annealing in oxygen atmosphere to form a photodetector, which shows obvious photoresponse at the wavelength of less than 372 nm with low dark current of 0.9 pA at 5 V, and the remarkable responsivity of 0.75 mA W−1 at 280 nm is achieved with a high ultravoilet/visible rejection ratio. The low dark current and incredible responsivity can be attributed to the good ohmic contacts of untreated MoO x and the reduction of number of oxygen vacancies in the MoO x channel. The key role of oxygen vacancy on the conductance of MoO x has been demonstrated. Those results suggest that the MoO x thin films are promising candidate for visible-blind ultraviolet photodetectors in a simple complementary metal oxide semiconductor (CMOS)-compatible process. [ABSTRACT FROM AUTHOR]

Metal halide perovskite materials have received significant attention in recent years due to their promising properties and potential applications, particularly their use as scintillator detectors, which is rapidly emerging due to their promising advantages as detectors, such as low costs, fast response, high quantum yield, strong absorption, scalability, flexibility, and emission wavelength tunability. Given the effectiveness of perovskites as α particle detectors and the potential of 10B as a neutron converter, in this paper a 10B converting layer was coupled with an all-inorganic lead halide perovskite (CsPbBr3) layer aiming to create a thermal neutron detector. Specifically, a 1 µ m thin film of 10B and a 1 µ m thin layer of CsPbBr3 were deposited on a suitable substrate using a laser ablation process. The fabricated detector was subjected to a comprehensive characterization, including structural, morphological, and detection properties. As output, the films exhibit macroscopically uniform behavior and good adhesion to the substrate. In terms of thermal neutron efficiency, an efficiency of (7.9 ± 0.3)% was determined with respect to a commercial detector (EJ-426), which corresponds to an intrinsic efficiency of (2.5 ± 0.1)%. Also, Monte Carlo simulations were conducted, and the optimum value of the 10B layer thickness was found to be 2.5 µ m. [ABSTRACT FROM AUTHOR]

In search of novel conducting oxide heterointerfaces, we previously uncovered an distinctive quasi two-dimensional electron gas (q-2DEG) type behaviour in non-stoichimetric CaxTayO3-δ/SrTiO3 heterostructure. However, the underlying mechanism remained enigmatic. In this study, we delve into the intricate interplay of growth conditions, stoichiometry, and transport properties of these heterostructures. Using (Ca0.5TaO3)2 Target and the pulsed laser deposition technique, we grow the epitaxial thin films while systematically varying growth parameters, inculding laser energy density, oxygen pressures, and post-deposition annealing. Structural analysis unveiled a notable presence of oxygen vacancies in the as-grown films, while annealed samples exhibited an oxygen surplus. Building upon these findings, our comprehensive charge transport measurements revealed that while oxygen vacancies do contribute to conductivity, the polar catastrophe model takes precedence as the primary source of interfacial conductance in these heterostructures. This study provides valueable insights into the behavior of these innovative heterostructures, paving the way for future advancements in the field. [ABSTRACT FROM AUTHOR]

In search of novel conducting oxide heterointerfaces, we previously uncovered an distinctive quasi two-dimensional electron gas (q-2DEG) type behaviour in non-stoichimetric CaxTayO3-δ/SrTiO3 heterostructure. However, the underlying mechanism remained enigmatic. In this study, we delve into the intricate interplay of growth conditions, stoichiometry, and transport properties of these heterostructures. Using (Ca0.5TaO3)2 Target and the pulsed laser deposition technique, we grow the epitaxial thin films while systematically varying growth parameters, inculding laser energy density, oxygen pressures, and post-deposition annealing. Structural analysis unveiled a notable presence of oxygen vacancies in the as-grown films, while annealed samples exhibited an oxygen surplus. Building upon these findings, our comprehensive charge transport measurements revealed that while oxygen vacancies do contribute to conductivity, the polar catastrophe model takes precedence as the primary source of interfacial conductance in these heterostructures. This study provides valueable insights into the behavior of these innovative heterostructures, paving the way for future advancements in the field. [ABSTRACT FROM AUTHOR]

Molybdenum disulfide (MoS2) has been considered as a promising candidate material for photodetectors due to its unrivaled transistor behavior and strong light absorption. However, due to the ultra-thin nature of monolayer or few-layer MoS2, it exhibits a low optical cross-section, resulting in a very weak light–matter interaction and accordingly limiting the photoelectric conversion efficiency. In this work, we report a facile method to prepare single-layer gold (Au) nanoparticles with ultra-high area density according to the annealing of thin Au films. By transferring the single-layer Au nanoparticle film onto a prefabricated MoS2 photodetector, we demonstrate a photodetector with a responsivity as high as 1120 A W−1. Moreover, it is found that the response time is not affected by the Au nanoparticle decoration. This method provides an easy but effective way to fabricate high-performance two-dimensional material-based photodetectors. [ABSTRACT FROM AUTHOR]

The production of hydrogen fuel through sunlight-driven water splitting has the potential to harness and store large quantities of solar energy in a clean and scalable chemical state, suitable for later use in a range of energy applications. Silicon (Si) possesses many of the required properties to be used effectively as a photoelectrochemical (PEC) water-splitting photoanode. However, its sensitivity to corrosion during the oxygen evolution reaction limits its performance in photoanode applications, thus requiring additional overlayer materials to protect the underlying Si substrate. Nickel oxide (NiO) is one material that acts as an effective protective layer, being transparent, suitably conductive and stable. In this work, we present NiO deposition via state-of-the-art atomic layer deposition and photoemission studies to grow and characterize NiO and Ni–metal protective films. Early-stage nucleation of deposited thin films is illustrated along with the effects of post-deposition annealing and argon milling on depth profile information. Previous reports on the effects of slow argon milling are explored and counter arguments are proposed. Protective films are subjected to PEC testing, which shows enhancement of stability and photocurrent output as a result of the deposited films and plasma annealing on these thin films. [ABSTRACT FROM AUTHOR]

We report the observation of angular-dependent antisymmetric magnetoresistance (MR) in artificially deformed Co-Tb Hall bar structures with perpendicular magnetization. Simultaneous transport measurements and domain imaging show that the antisymmetric MR results from the generation of a single domain wall (DW) inclination due to the restricted geometry and is further proportional to the inclination-associated geometry factor. The results are well described by a theoretical model that is supported by analytic and numerical calculations of the nonequilibrium current and Hall voltage distribution in the vicinity of the inclined DW. This finding provides a straightforward and effective approach to control DW geometries, leading to various DW-based spintronic device applications. [ABSTRACT FROM AUTHOR]

Charge recombination is one of the critical factors that influences the performance of thin film polymer solar cells (TFPSCs). In this investigation, metal, plasmonic nano-particles are employed to suppress charge recombination and energy loss in TFPSC. Trimetallic nano-composite (NC) was successfully synthesized and composed of copper, nickel, and silver (Cu/Ni/Ag) using wet chemistry. The NC was incorporated into polymer-based solar absorber layers at different concentrations. The absorber layer is a fullerene-based bulk-heterojunction design using poly-3-hexylthiophene (P3HT) donor polymer. The results show that the power conversion efficiency of the device doped with NC has improved by 85% compared to the undoped one. The incorporation of tri-metallic NC into the polymer blend solar absorber resulted in enhanced optical absorption and improved collection of photo-current as reflected by the recorded high short circuit current density (J s c ) and fill factor. The enhancement of the performance is due to the occurrence of local surface plasmon resonances in the polymer medium. The experiment indicated that there is some increment in an open circuit voltage, which is attributed to the low energy losses as a result of improved exciton dissociation, charge carrier transport, and collection. [ABSTRACT FROM AUTHOR]

The competition between shape and perpendicular magnetic anisotropies in magnetic thin films gives rise to unusual magnetic behaviors. In ferromagnetic thin films, the presence of an out-of-plane component of the magnetic anisotropy may induce a transition from planar to stripe-like magnetic domains above a critical thickness, t c . In this article, we present a detailed study of the magnetization switching mechanism in FePt thin films, where this phenomenon is observed. Using micromagnetic simulations and experiments, we found that below t c the reversal mechanism is well described by the two-phase model while above this thickness the magnetization within each stripe reverses by coherent rotation. We also analyzed the out-of-plane component of the magnetic anisotropy and its temperature dependence, probing that substrate-induced strains are responsible for the abnormal coercive field behavior observed for FePt films with t > t c . [ABSTRACT FROM AUTHOR]

Silver thin films have wide-ranging applications in optical coatings and optoelectronic devices. However, their poor wettability to substrates such as glass often leads to an island growth mode, known as the Volmer–Weber mode. This study demonstrates a method that utilizes a low-energy ion beam (IB) treatment in conjunction with magnetron sputtering to fabricate continuous silver films as thin as 6 nm. A single-beam ion source generates low-energy soft ions to establish a nominal 1 nm seed silver layer, which significantly enhances the wettability of the subsequently deposited silver films, resulting in a continuous film of approximately 6 nm with a resistivity as low as 11.4 µ Ω.cm. The transmittance spectra of these films were found to be comparable to simulated results, and the standard 100-grid tape test showed a marked improvement in adhesion to glass compared to silver films sputter-deposited without the IB treatment. High-resolution scanning electron microscopy images of the early growth stage indicate that the IB treatment promotes nucleation, while films without the IB treatment tend to form isolated islands. X-ray diffraction patterns indicate that the (111) crystallization is suppressed by the soft IB treatment, while growth of large crystals with (200) orientation is strengthened. This method is a promising approach for the fabrication of silver thin films with improved properties for use in optical coatings and optoelectronics. [ABSTRACT FROM AUTHOR]

Large area manufacturing processes of thin films such as large-area vacuum roll-to-roll coating of dielectric and gas permeation barrier layers in industry require a precise control of e.g. film thickness, homogeneity, chemical compositions, crystallinity and surface roughness. In order to determine these properties in real time, hyperspectral imaging is a novel, cost-efficient, and fast tool as in-line technology for large-area quality control. We demonstrate the application of hyperspectral imaging to characterize the thickness of thin films of the multilayer system ZTO/Ag/ITO produced by roll-to-roll magnetron sputtering on 220 mm wide polyethylene terephthalate substrate. X-ray reflectivity measurements are used to determine the thickness gradients of roll-to-roll produced foils with sub nanometer accuracy that serve as ground truth data to train a machine learning model for the interpretation of the hyperspectral imaging spectra. Based on the model, the sub-layer thicknesses on the complete substrate foil area were predicted which demonstrates the capabilities of this approach for large-scale in-line real-time quality control for industrial applications. [ABSTRACT FROM AUTHOR]

In this work we present a model explaining the properties of magnetoelastic waves propagation in the heterostructure containing an antiferromagnetic layer on a non-magnetic elastic substate. Horizontally polarized shear surface waves (SH-waves) propagating in thin film are Love waves. The dispersion characteristic of magnetoelastic waves in such structure was obtained, and the effect of variation of the thickness of the antiferromagnetic layer and the external magnetic field on the frequency of the magnetoelastic resonance was also studied. It was found that an increase in the magnetic field magnitude leads to the increase in the magnetoelastic resonance frequency, and, on the contrary, with an increase in the thickness of the AFM layer the magnitude of the magnetoelastic resonance frequency decreases. The obtained results can be used to develop devices for generating and processing signals in the GHz and THz frequency ranges. [ABSTRACT FROM AUTHOR]

Second-harmonic Hall voltage (SHV) measurement method has been widely used to characterize the strengths of spin–orbit torques (SOTs) in heavy metal/ferromagnet thin films saturated in the single-domain regime. Here, we show that the magnetic anisotropy of a W/Pt/Co trilayer can be robustly tuned from in-plane to out-of-plane by varying W, Pt, or Co thicknesses. Moreover, in samples with easy-cone anisotropy, SHV measurements exhibit anomalous 'humps' in the multidomain regime accessed by applying a nearly out-of-plane external magnetic field. These hump features can only be explained as a result of the formation of Néel-type domain walls, efficiently driven by nevertheless small SOTs in this double heavy metal heterostructure with canceling spin Hall angles. [ABSTRACT FROM AUTHOR]

Nature inspired biomimetic growth of anisotropic, hierarchical nanostructures could offer insight into new and exciting crystalline properties for advanced multifunctional applications. Our study demonstrates diethanolamine-mediated mesoscopic self-assembly of semiconducting ZnO Quantum Dots (3–5 nm) into lattice-aligned, symmetrical superstructures (40–50 nm) via non-classical oriented attachment (OA) crystal growth observed in various biomineralization processes. Multifunctional nanocomposite thin films of self-assembled nanostructures and polymethyl methacrylate were spin-coated onto plasma-treated Si wafers and the surface and interfacial properties were rigorously studied. HR-TEM images depicted the OA growth process with neighboring nano-crystals having perfectly aligned lattices. Preferential orientation of the thin films along <100> direction was evident from the XRD data. Quantum confinement in ZnO QDs and surface defect originating sharp green PL emission were examined through UV–Vis absorption and Photoluminescence spectra respectively. DLS and Zeta potential studies of surface-engineered colloidal superstructures established excellent long-term physico–chemical stability with no agglomeration or transparency loss observed in ZnO mesocrystal suspension even after 6 months. Diethanolamine, due to its dual functionality radically enhanced the interaction between polar ZnO and non-polar PMMA matrix resulting in highly stable thin films (Class II hybrids) with enhanced surface and interfacial properties as evident from the extremely low surface roughness and homogenous nanofiller dispersion observed in AFM and FE-SEM studies. Chemical interactions at the interface were also established quantitatively by XPS binding energy measurements which suggested hydrogen bonds and covalent bonds between organic-inorganic phases promoted via diethanolamine surface engineering. [ABSTRACT FROM AUTHOR]

Pressure bulge testing is one of the standard techniques for characterizing the mechanical properties of thin films, whereas it is far less often used to characterize the mechanical properties of 2D materials. In the present work, the effectiveness of bulge testing on determining the mechanical properties of 2D materials is systematically investigated using numerical analysis. After assuming 2D materials as continuum thin films, we start by simulating the relationship between the pressure difference across the suspended film and the film deflection, and then fit the results with analytical models to extract the elastic modulus of the film. It should be noted that the clamped, pre-stretched film widely assumed in the existing analytical model is not appropriate for atomically thin materials; instead, freestanding 2D materials are actually slack in bulge testing due to the delamination of their adhesive boundary condition. Therefore, the initially unstressed flat films, pre-stretched films and slack films are investigated in the present work, and the Poisson's ratio effect is considered to investigate the effectiveness of bulge testing for most 2D materials. It is found that bulge testing can be an effective approach to characterize the mechanical properties of 2D materials. [ABSTRACT FROM AUTHOR]

Plasma synthesis of thin films by physical vapour deposition (PVD) enables the creation of materials that drive significant innovations in modern life. High value manufacturing demand for tighter quality control and better resource utilisation can be met by a digital twin capable of modelling the deposition process in real time. Optical emission spectroscopy (OES) was combined with process parameters to monitor all stages of both high power impulse magnetron sputtering and conventional magnetron sputtering processes to provide a robust method of determining process repeatability and a reliable means of process control for quality assurance purposes. Strategies and physics-based models for the in-situ real-time monitoring of coating thickness, composition, crystallographic and morphological development for a CrAlYN/CrN nanoscale multilayer film were developed. Equivalents to the ion-to-neutral ratio and metal-to-nitrogen ratios at the substrates were derived from readily available parameters including the optical emission intensities of Cr I, N2 (C–B) and Ar I lines in combination with the plasma diffusivity coefficient obtained from the ratio of substrate and cathode current densities. These optically-derived equivalent parameters identified the deposition flux conditions which trigger the switch of dominant crystallographic texture from (111) to (220) observed in XRD pole figures and the development of coating morphology from faceted to dense for a range of magnetron magnetic field configurations. OES-based strategies were developed to monitor the progress of chamber evacuation, substrate cleaning and preventative chamber wall cleaning to support process optimisation and equipment utilisation. The work paves the way to implementation of machine learning protocols for monitoring and control of these and other processing activities, including coatings development and the use of alternative deposition techniques. The work provides essential elements for the creation of a digital twin of the PVD process to both monitor and predict process outcomes such as film thickness, texture and morphology in real time. [ABSTRACT FROM AUTHOR]

In the current work, thin film (∼55 nm) of n-type Ga2O3 (n-Ga2O3) is deposited on silicon (p-Si) substrate by using radio-frequency (RF) sputtering technique with systematic substrate temperature variations (room temperature to 700 °C). The structural, optical properties and chemical states of elements of the deposited films are observed to depend significantly on the deposition temperatures. The chemical composition and oxidation states, optical properties, defect states and structural quality of the deposited films are investigated in detail by employing x-ray photoelectron spectroscopy, energy dispersive x-ray, spectroscopic ellipsometry, Raman, photoluminescence and atomic force microscopy images. X-ray diffraction result reveals a polycrystalline nature of monoclinic β -phase of Ga2O3 with (403) dominant plane. The work functions are calculated from the ultraviolet photo-electron spectroscopy for all the deposited films and Ga2O3/Si heterojunction properties are investigated by using currentâ€"voltage (I â€" V) and capacitanceâ€"voltage (C â€" V) measurements. Among all the fabricated heterojunctions, 600 °C deposited Ga2O3 film exhibits superior performance in terms of energy bandgap, work function, refractive index, barrier height, rectification ratio and effective carrier concentrations. The current transport mechanism is analysed using the appropriate energy band diagram of Ga2O3 and Si. Therefore, the study suggests that 600 °C deposition temperatures is the optimum temperature for developing a high quality Ga2O3 thin film on Si by using RF sputtering technique and corresponding Ga2O3 thin film/Si heterojunction can be a potential candidate for developing several electronic and optoelectronic devices. [ABSTRACT FROM AUTHOR]

Al-doped ZnO (AZO) thin films were deposited on p-type silicon (p-Si) substrates by radio frequency magnetron sputtering technology. The crystal structure, morphology characterization and elemental analysis show that AZO film grows along the c -axis (002) orientation without other impurities. The currentâ€"voltage and current-time characteristics under different illumination conditions demonstrate that the Au/AZO/p-Si diode has typical rectification behavior, excellent stability and repeatability. The photocurrent is proportional to the intensity of ultraviolet (UV) irradiation, and the photocurrent reaches 110 ÎĽ A at a bias voltage of 5 V under 11.75 mW cmâˆ'2 UV light irradiation. By calculating the conduction band and valence band offset values of AZO/p-Si heterojunction, the energy band diagrams at different bias states are constructed to explain the photoelectric response behavior. These results will be helpful for the design of high-performance photodiodes. [ABSTRACT FROM AUTHOR]

The rapidly growing demand for high-performance and low-power electronic and photonic devices has driven attention towards novel two-dimensional (2D) layered materials. In this regard, 2D layered materials, including graphene, molybdenum disulfide (MoS2), and newly discovered phosphorene, have the potential to take over the existing semiconductor industry due to their intriguing features, such as excellent electrical conductivity, strong lightâ€"matter interaction, and especially the ability to scale down the resulting device to the atomic level. However, to explore the full potential of these materials in various technological applications, it is essential to develop a large-scale synthesis method that can provide uniform, defect-free thin film. The chemical vapor deposition (CVD) technique has been proven to produce large-scale and less defective 2D crystals with reasonably good quality and uniformity compared to other elaboration techniques, such as molecular beam epitaxy. This article discusses whether CVD may improve 2D layered materials growth, including graphene and MoS2, and whether it can be used to grow phosphorene. Only a few attempts have been made using CVD-like methods to grow phosphorene directly on the substrate. Still, one has to go long to establish a proper CVD method for phosphorene synthesis. [ABSTRACT FROM AUTHOR]

Combining the experimental characterization with the large-scale density functional theory calculations based on finite-element discretization (DFT-FE), we address the stabilization of polar orthorhombic phases (o-HfO2) in Al:HfO2 nanofilms by means of the atomic registry distortions and lattice deformation caused by Al substitutional defects (AlHf) and Schottky defects (2AlHf + VO) in tetragonal phases (t-HfO2) or monoclinic phases (m-HfO2). The phase transformation directly from the t-HfO2 into polar o-HfO2 are also elucidated within a heterogeneous distribution of Al dopants in both t-HfO2 bulk crystal structure and Al:HfO2 nanofilm. It is revealed using large-scale DFT calculations that the Al substitutional defects (AlHf) or the Schottky defect (2AlHf + VO) could induce the highly extended atomic registry distortions or lattice deformation in the t- and m-HfO2 phases, but such effects are greatly diminished in ferroelectric orthorhombic phase. By purposely engineering the multiple AlHf defects to form dopant-rich layers in paraelectric t-HfO2 nanofilm or bulk crystal, the induced extended lattice distortions surrounding the defect sites exhibit the shearing-like atomic displacement vector field. The large-scale DFT calculations further predicted that the shearing-like microscopic lattice distortions could directly induce the phase transformation from the t-HfO2 into polar orthorhombic phase in both Al:HfO2 bulk crystal and nanofilms, leading to the large remanent polarization observed in Al:HfO2 nanofilms with the presence of Al-rich layers. The current study demonstrates that the ferroelectricity of HfO2 bulk crystal or thin film can be optimized and tuned by delicately engineering both the distribution and concentration of Al dopants in atomic layer deposition without applying the top capping electrode, providing the extra flexibility for designing the HfO2 based electronic devices in the future. [ABSTRACT FROM AUTHOR]

The scandium (Sc) and aluminum (Al) co-doped antimony-selenium (Sb45Se25Sc7Al23) thin film was fabricated and systematically investigated in this study. The results reveal that our examined Sb45Se25Sc7Al23 thin film has good thermal stability (the failure temperature for ten years data retention ∼103 °C) and the fast phase change speed (5 ns) at same time. Besides, the Sb45Se25Sc7Al23 thin film shows no multiple phase change, which derives from the fact that no formation of new Sc or Al related phases that are able to trigger multiple states in the thin film. However, it is found that more Sb precipitation is formed by the increase of dopants, which may increase the tendency of multiple phase change. All results suggest Sb45Se25Sc7Al23 thin film would be a good candidate used for phase change random access memory applications. [ABSTRACT FROM AUTHOR]

Zirconium nitride (ZrN) is a candidate for contact metal and diffusion barrier in ohmic contacts for GaN-based devices due to its superior electrical conductivity and corrosion resistance. This paper reported ZrN films deposited on GaN/Si templates using metal-organic chemical vapor deposition (MOCVD) and analyzed the effect of substrate temperature (T s) on its growth mode, film stress, as well as electrical properties. Firstly, the surface morphology and film roughness of the resultant ZrN epilayers were investigated, which were found to vary dramatically with T s. Then, a temperature-dominated crystal formation process was reasonably proposed, revealing the transfer from the island to layer growth mode and the augmentation of the growth rate of ZrN with elevated T s. Stress information was obtained from the position of XRD diffraction peaks, indicating large in-plane lattice stretching in ZrN film and the presence of compressive stress in the GaN/Si template. The stress states can be related to island merger and thermal mismatch between ZrN and GaN, which proved satisfyingly advantageous in preventing the GaN layer from cracking during the subsequent preparation procedure. In addition, XPS surface and interface investigations were performed to identify the chemical state and the atomic content of the ZrN film, which also implied a relatively clear interface between the ZrN epilayer and GaN/Si template. Furthermore, Hall tests proved the resistivity of ZrN thin film can reach a minimum of 2.28 Ă— 10âˆ'4 Ω cm, owing to the grain boundary chaining and flat film surface at high temperatures. Overall, it appears to have promising prospects for its application in the contact layer and diffusion barrier of ohmic contact in GaN-based devices. [ABSTRACT FROM AUTHOR]

We investigated the Ge-composition (Îł) dependence of the saturation magnetization of Co2Fe(Ga, Ge) (CFGG) thin films and the magnetoresistance (MR) ratio of CFGG-based current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) devices together with first-principles calculations of the electronic states of CFGG. Theoretical calculations showed that spin polarization is highest at the stoichiometric composition Îł = 0.56 in Co2Fe1.03Ga0.41Ge Îł and that it decreases in off-stoichiometric CFGG, mainly due to the formation of CoFe antisites for Ge-deficient compositions and FeCo antisites for Ge-rich compositions, where CoFe (FeCo) indicates that Co (Fe) atoms replace the Fe (Co) sites. The saturation magnetic moment (ÎĽ s) per formula unit decreased monotonically as Îł increased from 0.24 to 1.54 in Co2Fe1.03Ga0.41Ge Îł. The ÎĽ s was closest to the Slaterâ€"Pauling value predicted for half-metallic CFGG at the stoichiometric composition Îł = 0.56, indicating that stoichiometric CFGG has a half-metallic nature. This is consistent with the result for the theoretical spin polarization. In contrast, the MR ratio of CFGG-based CPP-GMR devices increased monotonically as Îł increased from 0.24 to 1.10 and reached an MR ratio of 87.9% at the Ge-rich composition Îł = 1.10. Then, the MR ratio decreased rapidly as Îł increased from 1.10 to 1.48. Possible origins for the slight difference between the Ge composition at which the highest MR ratio was obtained (Îł = 1.10) and that at which the highest spin polarization was obtained (Îł = 0.56) are improved atomic arrangements in a Ge-rich CFGG film and the reduction of effective Ge composition due to Ge diffusion in the GMR stacks. [ABSTRACT FROM AUTHOR]

Developing materials that can lead to compact versions of artificial neurons (neuristors) and synapses (memristors) is the main aspiration of the nascent neuromorphic materials research field. Oscillating circuits are interesting as neuristors, as they emulate the firing of action potentials. Here we present room-temperature self-oscillating devices fabricated from epitaxial thin films of semiconducting TbMnO3. We show that the negative differential resistance regime observed in these devices, orginates from transitions across the electronic band gap of the semiconductor. The intrinsic nature of the mechanism governing the oscillations gives rise to a high degree of control and repeatability. Obtaining such properties in an epitaxial perovskite oxide opens the way towards combining self-oscillating properties with those of other piezoelectric, ferroelectric, or magnetic perovskite oxides in order to achieve hybrid neuristor-memristor functionality in compact heterostructures. [ABSTRACT FROM AUTHOR]

Low-temperature N2/NH3/SiH4 discharge is used to deposit hydrogenated silicon nitride films (SiN x H y). In this process, the main factor influencing the improvement of film quality is the active species, such as SiH x and NH x radicals, which are responsible for surface reactions. The change in plasma chemistry under different operating conditions affects the production of active species in the bulk plasma region. In the conventional N2/NH3/SiH4 discharge for SiN x H y thin-film deposition, the information required to explain the correlation between the generation of active species and the process parameters was insufficient. In particular, it was difficult to completely understand the relationship between the generation of SiH x and NH x radicals using the experimental results based on the measured thin-film properties. Therefore, a numerical model was prepared to understand the mechanism of each radical. To improve the efficiency of material processing and enhance process controllability, an inductively coupled plasma N2/NH3/SiH4 model was introduced and investigated. This work provides an overview of the generation of each active species in the N2/NH3/SiH4 discharge. In particular, the effects of the gas pressure and N2/NH3/SiH4 gas mixture ratio are discussed. Moreover, the principle of the N2/NH3/SiH4 plasma process for the production of active species (N, NH x, SiH x, amino-silane complexes) was analyzed; it was found that the generation density of specific particles is affected by the spatial distribution of electrons based on the pressure and gas composition ratio. [ABSTRACT FROM AUTHOR]

Polar vortex domains have recently become an emergent research field due to the abundant physical phenomena and potential applications in high-density memories. Here, we explore the mechanisms of creating polar vortex domains in the BiFeO3 (BFO) membranes subjected to different boundary conditions using phase-field simulations. A major difference is that the vortex in membrane can be stabilized even under short-circuit electrical boundary conditions compared to vortex in other systems, such as thin film or superlattice. We found that (a) the formation of polar vortex domains at the membrane interior under bending is mainly driven by the reduction of elastic energy under short-circuit boundary condition, and the vortex chirality (namely, clockwise and counterclockwise) could be identified by n-shape and u-shape bending; (b) in the unbent open-circuit BFO membrane case, exotic trapezoid-shaped vortex nanodomains form at the terminations of 109° domain walls (DWs) and partially charged 71° DWs, which is driven by the local depolarization field and the interplay among electrostatic, elastic, and gradient and Landau energies. We also examine Kittel's law by establishing the dependence of vortex periods on the membrane thickness. These results give further understanding of the effect of boundary conditions on the formation of polar vortex domains, guiding experimental designs of vortex-based high-density memories. [ABSTRACT FROM AUTHOR]

The ultrafast carrier dynamics in SnSe2 film and their influencing factors are studied using femtosecond transient absorption (TA) spectroscopy. Nano-scale SnSe2 sample films are prepared by pulsed laser deposition on the SiO2 substrate. The observed carrier dynamics are influenced by the film thickness and pulse energy. All carrier ultrafast dynamics can be perfectly fitted with a tri-exponential decay model, which means that the carriers have undergone the process of carrier scattering, carrier recombination and diffusion. The influence of the surface reorganization process and the deep defect state in the material makes the carrier lifetime longer in the thicker film. Moreover, the defect state intensifies the state filling effect, leading to the production of bleaching signal in thin thinner film. With the increase of the pump pulse energy, the carrier lifetime becomes longer. This is due to the influence of the pulse energy on the carrier concentration and the temperature difference between the carrier temperature and the lattice temperature. And the influence of pump pulse energy of band gap reconstruction makes the peak in TA spectrum move with the change of pulse energy. The results reveal the carrier dynamics in SnSe2 thin film at different pump pulse energy and identify the critical role of the pump pulse in photo-generated phenomena. [ABSTRACT FROM AUTHOR]

Magnetic vortex as one of the quintessentially non-uniform magnetic structure that can be found to commonly exist in micrometer or submicrometer sized ferromagnetic thin films. Here, we present that the vortex core can be efficiently expelled from the central region and excited into gyrotropic motion by using a voltage induced strain in bi-component magnetic nanodisks. In particular, the polarity can be deterministic switched by proper modulation the amplitude and frequency of applied voltage. The related results of micromagnetic simulations indicated that the magnetic vortex polarity is reversed through the nucleation-annihilation process of topological vortex-antivortex pairs or rotation-fusion edge soliton pairs. This voltage-controlled low-power vortex polarity switching scheme has the ability to accurately address individual magnets in dense arrays and also is compatible with integrated circuit techniques, which provides an additional route for the design of vortex-based on-chip devices. [ABSTRACT FROM AUTHOR]

Epitaxial NbO2 (1 1 0) films, 20 nm thick, were grown by pulsed laser deposition on Al2O3 (0 0 0 1) substrates. The Ar/O2 total pressure during growth was varied to demonstrate the gradual transformation between NbO2 and Nb2O5 phases, which was verified using x-ray diffraction, x-ray photoelectron spectroscopy, and optical absorption measurements. Electric resistance threshold switching characteristics were studied in a lateral geometry using interdigitated Pt top electrodes in order to preserve the epitaxial crystalline quality of the films. Volatile and reversible transitions between high and low resistance states were observed in epitaxial NbO2 films, while irreversible transitions were found in the case of Nb2O5 phase. Electric field pulsed current measurements confirmed thermally-induced threshold switching.

The study presents the synthesis of epitaxial V2O3 thin films on c-plane Al2O3 substrates by reactive high-power impulse (HiPIMS) and direct current (dcMS) magnetron sputtering. The results reveal that for fixed deposition conditions and discharge power, well defined epitaxial layers can be attained using both HiPIMS and dcMS. For dcMS we observe the formation of these epitaxial films down to flow rate values of 1.3 sccm while for HiPIMS we observe an extended operation window down to much lower oxygen flow of 0.5 sccm without sacrificing the structural quality of the films. Furthermore, the effect of varying HiPIMS discharge parameters i.e. repetition frequency and average power for fixed O2 flow setting, were explored in order to determine their effect on the structural quality and electrical characteristics of the films. The magnitude of the metal–insulator transition (MIT) and the transition temperature is correlated to the film stoichiometry which can be fine-tuned by mapping the HiPIMS discharge parameters, displaying a total change in resistance of ∼7 decades over the studied temperature range. The MIT temperature and magnitude obtained for films fabricated by HiPIMS, even for low O2 flow settings (down to 0.6–0.5 sccm), displayed superior characteristics compared to films fabricated by dcMS where a minimum O2 flow of 1.3 sccm was needed. [ABSTRACT FROM AUTHOR]