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The superconductor to normal metal phase transition induced by the in-plane magnetic field is studied in free-standing Pb(111) nanofilms. In the considered structures, the energy quantization induced by the confinement leads to the thickness-dependent oscillations of the critical field (the so-called 'shape resonances'). In this paper, we examine the influence of the orbital effect on the in-plane critical magnetic field in nanofilms. We demonstrate that the orbital term suppresses the critical field and reduces the amplitude of the thickness-dependent critical field oscillations. Moreover, due to the orbital effect, the slope [ABSTRACT FROM AUTHOR]

Similar to the cancelled Compound Semiconductor Week 2020 (CSW'2020), CSW'2021 was supposed to be an onsite conference in Stockholm but had to be rescheduled as a virtual event because of the prevailing worldwide pandemic situation. CSW thereby takes the role of providing all aspects of compound semiconductors and their applications in electronics, photonics and emerging fields. CSW'2021 was organized as a joint venue for the 47th International Symposium on Compound Semiconductors (ISCS) and the 32nd International Conference on Indium Phosphide and Related Materials (IPRM). [Extracted from the article]

The possibility of combining both optical transparency and high electrical conductivity in the same material makes transparent conducting oxides one of the most sought after materials in transparent electronics. This paper presents the investigations done on the conductivity mechanisms of n-type transparent conducting silver indium oxide thin films in different temperature ranges varying from 6 to 333 K. X-ray diffraction indicates the films to be amorphous, and the morphology of the films from scanning electron microscopy and atomic force microscopy shows agglomerations with average particle size ∼30 nm. X-ray photoelectron spectroscopy and energy-dispersive analysis of X-rays establish the films to be nearly stoichiometric with In/Ag at.% ratio in the range 1.1-1.2. The transmittance percentage obtained from optical transmittance and absorbance spectra is moderately high and the bandgap energy of the thin films is ∼3.5 eV. Transport parameters, such as carrier mobility ∼103 cm2/V s and carrier concentration ∼1018/cm3, are elucidated from Hall and thermopower data. [ABSTRACT FROM AUTHOR]

In this paper, temperature-dependent cathodoluminescence (CL) spectra of Er-implanted GaN thin films were measured. The effects of accelerating voltage and temperature on the CL spectra of Er-implanted GaN were investigated. In the near band-edge emission region, the competition mechanism between DAP and D0X was disclosed. A slight blue shift of the DAP emission peak with the increase of accelerating voltage was observed. The temperature dependence of the CL intensity of FX emission reveals a binding energy of ∼32 meV in Er-implanted GaN. Below 182 K, the 2H11/2 state of Er3+ is not thermally populated and the yellow band luminescence (YL) related to the defects was observed. At higher temperature, the thermal coupling between the two excited state levels of 2H11/2 and 4S3/2 of Er3+ is obvious and the YL is nearly invisible. Even at 373 K, a strong green emission at 537 nm can be observed, which indicates the Er-doped GaN is promising to be applied in high-temperature environments. [ABSTRACT FROM AUTHOR]

Cu2ZnSn(S,Se)4 (CZTS(e)) solar cells suffer from low-open-circuit voltages that have been blamed on the existence of band gap fluctuations, with different possible origins. In this paper, we show from both theoretical and experimental standpoints that disorder of Cu and Zn atoms is in all probability the primary cause of these fluctuations. First, quantification of Cu-Zn disorder in CZTS thin films is presented. The results indicate that disorder is prevalent in the majority of practical samples used for solar cells. Then, ab initio calculations for different arrangements and densities of disorder-induced [CuZn + ZnCu] defect pairs are presented and it is shown that spatial variations in band gap of the order of 200 meV can easily be caused by Cu-Zn disorder, which would cause large voltage losses in solar cells. Experiments using Raman spectroscopy and room temperature photoluminescence combined with in situ heat-treatments show that a shift in the energy of the dominant band-to-band recombination pathway correlates perfectly to the order-disorder transition, which clearly implicates Cu-Zn disorder as the cause of band gap fluctuations in CZTS. Our results suggest that elimination or passivation of Cu-Zn disorder could be very important for future improvements in the efficiency of CZTS(e)-based solar cells. [ABSTRACT FROM AUTHOR]

Physical features of titanium monoxide layers deposited on p-GaN(0001) substrate are reported in this paper. TiO was deposited under ultrahigh vacuum at room temperature. As revealed by scanning tunneling microscopy (STM) the deposit had grainy structure. The X-ray and ultraviolet photoelectron spectroscopy (XPS/UPS) studies have shown that, depending on the altered by annealing morphology of the TiO-based film, work function of the system underwent changes and electronic structure of the deposit displayed metallic character. The formation of specific TiN and ON bonds is confirmed by spectroscopic techniques. Electrical conductance of the TiO-based/p-GaN interface has been studied by current-sensing atomic force microscopy (CS-AFM) with Au-covered tip. Formation of ohmic nano-contacts on p-GaN surfaces was observed over whole probed surface. The contacts were homogeneous in contrast to the grainy structure of TiO-based film. The results suggest that TiO may be considered as an intermediate semiconducting layer (ISL) useful for p-GaN electrical contact engineering. [ABSTRACT FROM AUTHOR]

This paper reports the post-growth annealing effects of low-temperature grown Mg-doped InGaN. By using MOVPE, 1 μm-thick Mg-doped In xGa1- xN ( x ~ 0.36) films are grown at 570 °C. In order to activate the Mg acceptors, grown samples are treated by the conventional furnace annealing (FA) or the rapid thermal annealing (RTA). In the case of the FA at 650 °C for 20 min, the InGaN film is phase-separated. On the other hand, the RTA at a temperature higher than 700 °C enables us to get p-type samples. By using the RTA at 850 for 20 s, p-type samples with a hole concentration 1018-1019 cm−3 are successfully obtained without phase separation. [ABSTRACT FROM AUTHOR]

In this paper atomic-layer deposition (ALD) Hf xAl1- xO y thin films with a wide range of metal components concentrations ( x = 0.2−0.8) for metal-insulator-metal (MIM) capacitors were investigated with emphasis on the chemical properties and phase composition. It was shown by X-ray diffraction (XRD) that all films are amorphous. X-ray photoelectron spectroscopy (XPS) revealed the same energy position with respect to the valence-band maximum of Al2p and Hf4f lines and a continuous shift of O1s and O-KLL lines toward the higher binding energy (0.45 and 2.2 eV, respectively) with increase of Al content. Both the shape and position of O1s and O-KLL lines indicated the inability to deconvolute it on sublines related to the binary oxides. The calculated modified Auger parameter indicated the change of the ionicity of the bonding in Hf xAl1- xO y films with change of the composition. Thus, it was proposed that Hf xAl1- xO y films in all the studied composition range represent amorphous solid solutions. The continuous change of energy bandgap measured by reflected electron energy loss spectroscopy (REELS) from ∼6.5 eV for Al2O3 to ∼5.4 eV for HfO2 and XRD data do not contradict this assumption. Correlation between structural properties of Hf xAl1- xO y films and electrical properties of MIM capacitors based on them was also shown, that is, continuous change in capacitance density (from 3.1 to 7.4fF/µm2), leakage current density and quadratic voltage coefficient of capacitance with composition change was observed. [ABSTRACT FROM AUTHOR]

Chalcogenide glasses are interesting materials for their infrared transmitting properties and photo-induced effects. This paper reports the influence of light on the optical properties of Sb10S40Se50 thin films. The amorphous nature and chemical composition of the deposited film was studied by X-ray diffraction and energy dispersive X-ray analysis (EDAX). The optical constants, i.e., refractive index, extinction coefficient, and optical band gap as well as film thickness are determined from the measured transmission spectra using the Swanepoel method. The dispersion of the refractive index is discussed in terms of the single-oscillator Wemple-DiDomenico model. The dispersion energy parameter was found to be less for the laser-irradiated film, which indicates the laser-irradiated film is more microstructurally disordered as compared to the as-prepared film. It is observed that laser-irradiation of the films leads to decrease in optical band gap (photo-darkening) while increase in refractive index. The decrease in the optical band gap is explained on the basis of change in nature of films due to chemical disorderness and the increase in refractive index may be due to the densification of films with improved grain structure because of microstructural disorderness in the films. The optical changes are supported by X-ray photoelectron spectroscopy data. [ABSTRACT FROM AUTHOR]

Ultrathin Bi films have been theoretically predicted to be an elemental two-dimensional topological insulator recently. Investigation on phonon properties in topological insulators, especially down to a few-layer regime, is an interesting topic. In this paper, the evolution of structures and phonon properties of ultrathin Bi (111) films with thickness is studied from first-principles calculations by including spin-orbit coupling. The calculations of lattice dynamics show that both two Raman modes A1g and Eg in ultrathin Bi (111) films harden compared with those in bulk, which is contrary to other nanomaterials. The possible origin of this anomalous phonon behavior is discussed by considering the peculiar semimetallicity of Bi. With increasing thickness, the frequencies of these two Raman modes decrease gradually toward the values in the bulk. Our calculations also show that the softening and hardening of surface phonon modes coexist in ultrathin Bi films. [ABSTRACT FROM AUTHOR]

Herein, a mechanism is proposed as to how thin films formed from a Heusler compound can simultaneously have both perpendicular magnetic anisotropy (PMA) and be half‐metallic. It is proposed that a thin film formed from a half‐metallic full‐Heusler or half‐Heusler compound that is cubic in the bulk can undergo a tetragonal distortion by adopting the lattice constant of the underlayer material during the thin film deposition process. The value of this distortion can be tuned by using underlayer materials with different in‐plane lattice constants. The distortion can thereby be optimized so that it is large enough to give rise to sufficient PMA, while, simultaneously, small enough to retain the half‐metallic properties (and, therefore, high tunneling magnetoresistance properties) of the Heusler compound. Density functional theory (DFT) calculations that are carried out for 90 full‐Heuslers and 147 half‐Heuslers that have been identified in the literature as half‐metals show that of these, 14 full‐Heusler and 59 half‐Heusler compounds display both half‐metallicity and PMA for optimal tetragonal distortions. [ABSTRACT FROM AUTHOR]

Rare earth ions in the oxide semiconductors are commonly surrounded by oxygen (O) ligands which are the first nearest neighbors to rare earths. Intensities of the rare earth‐related luminescence are strongly influenced by crystal symmetry of the rare earth ions. Especially, distortion of the first nearest neighbor bonds is key to improving emission from these luminescent centers. In this paper, samarium (Sm) is doped into titanium dioxide (TiO2) with two different crystal structures, anatase and rutile, to investigate the influence of the different host crystal symmetries on the material optical properties. Sm‐related photoluminescence (PL) intensity from the samples, annealed at different temperatures reveals the optimal preparation condition. Also, X‐ray absorption fine structure (XAFS) spectra are measured, providing detailed information regarding the local fine structure around Sm. From these studies, the authors find that the optical properties of the TiO2:Sm are not only influenced by structural changes in the first nearest neighbor, O, but also the second nearest neighbor, Ti by annealing at different temperatures and/or crystal structure of TiO2. The authors discuss the connection between the enhanced PL intensity and the local fine structure around the Sm luminescent centers, including these changes in the second nearest neighbor, Ti. [ABSTRACT FROM AUTHOR]

The multiferroic properties of BiCrO3 (BCO) bulk and thin films are investigated for the first time using a microscopic model. The influence of ion doping on the multiferroic properties of BCO is also studied because the doping process changes the physical properties and can be used for potential applications in magnetoelectronic devices. The magnetization M increases by Mn and decreases by Ga‐ion doping whereas the Néel temperature TN decreases in both cases. There are some discrepancies by polarization whether it is ferroelectric or antiferroelectric. It is shown that bulk pure BCO is antiferroelectric because the electric field dependence of polarization P shows a double hysteresis loop and the dielectric constant has no anomalies at TN. In Ga‐, Mn‐ or Ti‐doped BCO a ferroelectric polarization appears. The specific heat shows a peak at TN for BCO. By Ga doping, this peak vanishes with increasing x. The multiferroic behavior of BCO is demonstrated in the magnetic field dependence of the dielectric constant. In BCO thin films, ferroelectric and ferromagnetic behavior is observed. [ABSTRACT FROM AUTHOR]

This paper reports the research of the electrical transport properties of Cr‐doped Bi2Se3 thin films. The films with a uniform Cr distribution exhibit the same structure as undoped Bi2Se3 thin film. At low temperatures, both the weak antilocalization (WAL) and the electron–electron interaction (EEI) effects are observed. From the WAL effect, the dephasing length and the number of the transport channels are extracted. The temperature dependence of the extracted dephasing length can be described by both the Nyquist electron–electron and the electron–phonon scatterings. With increasing time in vacuum, the resistances of the thin films exhibit a transition from the negative to the positive temperature coefficient, with an increase in electron density. Unexpectedly, the number of the transport channels extracted from the WAL effect is found to increase with increasing time, which is further confirmed by analyzing the EEI effect. This observation can be attributed to the presence of two‐dimensional electron gas on the surface of films, which is likely to be formed through the surface reaction with water. [ABSTRACT FROM AUTHOR]

Herein, pulsed DC sputtering of the AlN film on top of the Si (111) substrate is reported on. First, major articles on the reactive sputtering of AlN film on top of Si (111) substrate that were published in the past 30 years are tabulated. Then, a sputtering recipe to produce a consistent and high‐crystal‐quality (as measured by the full width at half maximum [FWHM] of rocking curve) AlN film across varying substrate temperatures (250–450 °C) and sputtering powers (1200–2400 W) is proposed. In addition, the influence of both parameters to in‐plane stress is demonstrated, in agreement with similar trends that have been reported in the literature for AlN films on other substrates. The best sample is produced at a substrate temperature of 350 °C and sputtering power of 1800 W, resulting in FWHM of rocking curve of 1.84°, surface roughness of 1 nm, and in‐plane stress of +300 MPa. The recipe herein is beneficial for integration of AlN thin film in complementary metal–oxide–semiconductor and micro‐electromechanical system processes. [ABSTRACT FROM AUTHOR]

Recent advances in optoelectronics are often based on thin‐film organic semiconductors. Interesting organic semiconductors are given by squaraines, small molecules that show excitonic coupling with visible light and are thus suitable for applications in solar cells and light sensors. While such squaraine thin films have already been proven to be suitable for stimulation of neuronal model cells, the integration into, e.g., the human eye to support blind people necessitates forming thin layers on seamless substrates. Herein, squaraine films are spin‐coated on electrospun nanofiber mats and nanomembranes, prepared from polyacrylonitrile, and made conductive by spin coating with poly(3,4‐ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS). The fibrous non‐woven texture of the nanofiber mats and membranes alters the thin film formation of the squaraine compound considerably compared with preparation on planar, nonsoaking substrates such as glass and polyethylene terephthalate (PET) foil demanding further engineering regarding material's choice and processing conditions. [ABSTRACT FROM AUTHOR]

The structural, optical, and nonlinear optical absorption properties of ZnO polycrystalline thin films are investigated. Energy bandgap values are obtained with linear absorption spectrum and depending on either sole doping of Al or co‐doping, bandgap energies shift toward higher or lower energies. With Al‐only doping, bandgap of the ZnO thin film shifts toward higher energies which can be attributed to Moss–Burstein effect, and with co‐doping (Al–Cu or Al–Co) bandgap energies shift toward lower energies due to defect states residing within the bandgap. Urbach energies and grain sizes are calculated to study the effect of defect states on the nonlinear absorption, and these calculations indicate that co‐doping drastically reduces the grain size thereby increasing the contribution to the defect density by means of boundary defects. To analyze the transmission in open aperture Z‐scan data, a theoretical model incorporating one‐photon, two‐photon, and free‐carrier absorptions as well as their saturations is used. By this modeling, saturation intensity thresholds and effective nonlinear absorption coefficients are extracted from fitting of the experimental data. Highest saturation intensity threshold and effective nonlinear absorption coefficient are found for ZnO:(Al, Co) and ascribed to having the smallest bandgap energy and highest Urbach energy. [ABSTRACT FROM AUTHOR]

To study the effect of Cu concentration on morphological, structural, linear and nonlinear optical properties, copper‐doped ZnO thin films are grown by sol–gel/spin‐coating technique on the glass substrates. Scanning electron microscopy (SEM) images reveal that the surface morphology is homogeneous with good adhesion to the glass substrate. The energy dispersive X‐ray spectroscopy (EDS) spectra confirm that Zn, O, and Cu elements are present in ZnO films. The X‐ray diffraction (XRD) pattern of Cu‐doped ZnO is dominated by (002) peak, indicating an upstanding ZnO nanorods array growing along the c‐axis. The optical bandgap of Cu‐doped ZnO thin films, calculated from optical transmission spectra, is found to decrease with the increase in copper concentration. The refractive index dispersion curve of ZnO films is subjected to the single‐oscillator model. The optical dispersion parameters Eo, Ed, and n∞, the nonlinear refractive index, and nonlinear optical susceptibility are calculated and interpreted. [ABSTRACT FROM AUTHOR]

Herein, the possibility of changing the conductivity of thin‐film systems consisting of two metals separated by an insulator (metal–insulator–metal, MIM) is shown. The electrophysical properties are studied in three systems: Fe/MgO/Ni, Fe/MgO/Co, and Fe/MgO/Fe + C (Fe doped with carbon). The resulting inhomogeneity in thickness of the dielectric layer over the junction area promotes the appearance of local conduction regions. This makes it possible to change the type of conductivity from tunneling to semiconducting. As a result, a region with negative differential resistance is observed in I–V characteristics of MIM systems. The processes of electromigration during the alloying of one of the metal layers are considered. Presence of such processes is confirmed by the results of dynamic and static measurements of conductivity and corresponding assessments. Exposure of the sample in laboratory atmosphere at room temperature for several tens of days provides asymmetrical I–V characteristics. This indicates the rectifying properties of the contact—characteristic of the conductivity of the Schottky diode. The use of MIM systems with the described properties is considered promising for application in modern electronic devices as basic elements and memory cells. [ABSTRACT FROM AUTHOR]

The molecular dynamics method is used to study the process of development of dynamic instability of a thin film, leading to its destruction. The calculations are performed for a thin aluminum film using the interatomic interaction potential tested by comparing the numerical results with the analytical ones from the elasticity theory. An original approach which allows one to calculate the dispersion law of long‐wave phonons in ultrathin films is developed. The temperatures (<600 K) at which the system remains stable for 0.6 ns are found. This makes it possible to analyze the low‐frequency part of the spectrum down to the minimum frequency νmin = 0.0166 THz, and to determine the vibration frequency of the longest bending wave ν0 = 0.033 THz which decreases with increasing temperature, and therefore, its period grows. Once the vibration period becomes comparable with the time of simulation, there occurs a continuous increase in the amplitude of this mode which will be referred to as "retarded mode." It is shown that the film destruction begins with the attainment of a certain critical value of the bending wave amplitude. [ABSTRACT FROM AUTHOR]

Herein, a simple, low‐cost, and scalable process is developed to prepare the reduced graphene oxide (rGO) thin films (TFs) with strong optical nonlinearity. To do so, a chemical reduction method (using inorganic agent hydroiodic acid) and drop‐casting technique are used. Optical nonlinearity of the prepared thin rGO film is measured by the Z‐scan technique at low light intensity (continuous‐wave wavelength of 632 nm). The result of optical nonlinearity responses is illustrated by a remarkable nonlinear refraction index (n2 ≈ 10−4 cm2 W−1) as well as a considerable nonlinear absorption coefficient (β = 1.43 × 10−8 cm2 W–1) compared with similar reported results. Moreover, experimental results show that the prepared film enjoys a positive nonlinear refractive index with strong optical nonlinearity. Results also confirm that the changes made in optical absorption of rGO TFs are due to state filling effects and the optical nonlinearity proportional to the carriers' density is in fact due to thermal effects of SiO2 substrate. [ABSTRACT FROM AUTHOR]

Anisotropies often arise in the context of on‐lattice simulations of deposition processes. For instance, the density of simulated thin films depends on the orientation of the substrate and the particle flux with respect to the simulation cell axes, which is known as "grid effect". Although being the reason for a variety of unphysical results obtained in on‐lattice simulations, less attention is paid to such anisotropies. Herein, the grid effect is studied on the example of the glancing angle deposition (GLAD) technique. GLAD is a physical vapor deposition process that is characterized by a material flux arriving with a highly oblique incidence angle at the substrate. Due to self‐shadowing, a highly porous thin film consisting of separated nanostructures is formed by this method. It is shown that all on‐lattice simulations that contain substrate rotation, beam divergence, or a varying angle of incidence are affected by the grid effect. A method utilizing cluster particles is presented, to reduce the grid effect in on‐lattice simulations. Finally, it is demonstrated that the on‐lattice simulation of GLAD films utilizing cluster particles matches with experimentally deposited silicon films. [ABSTRACT FROM AUTHOR]

Organic and hybrid thin film materials are of high relevance in many fields of optics, electronics, and biomedicine. An IR spectroscopic study of manipulations of characteristic vibrational bands is presented by Karsten Hinrichs et al. (article number 1900490). In contrast, the s-polarized reflection exhibits material specific fingerprints, and spectra resemble the in-plane absorption properties of the material. [Extracted from the article]

Herein, the magnetoelectric (ME) performance of epitaxial multilayer composite films built from nanometer‐thick layers of multiferroic BiFeO3 and ferroelectric BaTiO3 is reviewed. A successful implementation of shadow‐mask pulsed laser deposition considerably reduces the interface and surface roughness of the multilayers. In dependence of double‐layer thickness and the degree of structural perfection, the multilayers show high ME voltage coefficients up to 480 V cm−1 Oe−1 at 300 K and 0 T bias magnetic field. With decreasing double‐layer thickness, an interface‐driven effect critically enhances the ME coupling in this strain and charge–comediated system. Interestingly, the characteristics of temperature and DC magnetic field dependencies of magnetoelectric voltage coefficients change with the transition from the 2D to 3D character of the single layers, i.e., for BiFeO3 layers thicker than 5 nm within the multilayers. These changes are attributed to variations of the contributing ME coupling mechanisms. Furthermore, scanning transmission electron microscopy (STEM) with energy‐dispersive X‐ray (EDX) spectroscopy mapping‐based nanoanalysis indicates that chemical effects at the interfaces play an important role for the ME performance of the BiFeO3–BaTiO3 multilayer thin films. [ABSTRACT FROM AUTHOR]

The crystallographic polarity of AlN grown on Si(111) by plasma‐assisted molecular beam epitaxy is intentionally inverted from N‐polar to Al‐polar at a planar boundary. The position of the inversion boundary is controlled by a two‐step growth process that abruptly changes from Al‐rich to N‐rich growth conditions. The polarity inversion is induced by the presence of Si, which is incorporated from an Al–Si eutectic layer that forms during the initial stages of AlN growth and floats on the AlN surface under Al‐rich growth conditions. When the growth conditions change to N‐rich, the Al and Si in the eutectic react with the additional N‐flux and are incorporated into the solid AlN film. Relatively low levels of Al–Si eutectic formation combined with lateral variations in the Si incorporation lead to nonuniformity in the polarity inversion and formation of surprisingly narrow, vertical inversion domains. The results suggest that intentional incorporation of uniform layers of Si may provide a method for producing polarity engineered nitride structures. [ABSTRACT FROM AUTHOR]

This work reviews some fundamental issues that are relevant for the fabrication of stable‐phase strontium ferromolybdate thin films. The main challenges for strontium ferromolybdate thin film deposition arise from the sensitivity of the material's magnetic properties to point defect formation: i) Antisite defect formation and oxygen nonstoichiometry should be avoided by precise composition control during film manufacturing; ii) a highly ordered state of the correct phase and B‐site cation valence will be obtained only in a very narrow window of growth conditions; iii) to avoid additional antisite disorder with decreasing synthesis temperature, the effective temperature at the film surface should be increased by an energy flux to the growing film surface. Since thin film deposition is nonequilibrium in nature, the review starts with the consideration of equilibrium phase stability. Cation and oxygen stoichiometries are analyzed with regard to their effect on key magnetic properties. Film strain formed due to thermal and lattice mismatch is of great concern since it influences the choice of the substrate. Finally, thin film deposition techniques are valued for their benefits in strontium ferromolybdate thin film technology. [ABSTRACT FROM AUTHOR]

The growth and crystalline structure of ultrathin Mn films are studied in terms of thickness and temperature by scanning tunneling microscopy (STM) as well as medium‐ and low‐energy electron diffraction. We show that the Mn films deposited at room temperature exhibit a thickness‐dependent growth behavior with a layer‐by‐layer growth mode up to 5.3 monolayers. Two transitions in the growth mode can be observed in this range. Atomically resolved STM images of a submonolayer of Mn on Ni(111) reveal a lateral lattice distortion which becomes less significant after the islands form a wetting layer at room temperature. The low‐temperature‐deposited wetting layer shows a metastable lattice distortion which vanishes after annealing to room or higher temperatures. This phenomenon may be attributed to a temperature‐dependent metastable arrangement of the Mn adlayer as well as the distinct interaction strength between Mn–Mn and Mn–Ni atoms. Low‐temperature‐grown thick Mn films exhibit a Stranski–Krastanov growth mode with a stable ( 3 × 3 ) R 30° reconstruction, which remains stable up to room temperature. [ABSTRACT FROM AUTHOR]

Among the many applications of chalcogenide glasses, their involvement as an active layer in redox‐conductive‐bridge‐memory (CBRAM) devices triggers particular interest because of their potential to replace CMOS‐based NAND and flash memory. In these devices the chalcogenide glass film is in contact with a silver film, and it is of a practical interest to understand how a beam of protons can influence this dual layer structure in order to identify how the performance of the CBRAM devices will be affected. In this work we studied the influence of proton beam irradiation over a Ge40Se60/Ag film stack. Various methods of analysis including scanning atomic force microscopy (AFM), Raman spectrometry, Rutherford backscattering spectrometry (RBS), X‐ray diffraction (XRD), and X‐ray photoelectron spectrometry (XPS) have been applied to study the structure, topography, composition, bonding configurations, diffusion kinetics, and molecular evolution of thin films related to the active sections of CBRAM devices, and quantitative analysis of material parameters and changes is reported. The results reveal silver surface deposition and germanium oxidation, as well as change in the films chemistry as a result of proton irradiation. [ABSTRACT FROM AUTHOR]

Titanium dioxide (TiO2) powder in anatase phase is thermally evaporated by physical vapor deposition (PVD) on glass substrates. Different‐thickness TiO2 thin films are deposited on glass slides. The samples are then optically and structurally investigated using optical absorption (ABS) and Raman scattering (RS). Optical absorption spectroscopy shows that Urbach energy (EU) related to the width of the long‐wavelength tail decreased from 212 to 176 meV as the film thickness increased from 143 to 221 nm, respectively. The grain size, which depends on thickness of the film, a00nd the grain size distribution are evaluated by fitting the absorption coefficient α experimental data to a model of α as a function of energy E. Absorption edge energy (ER) is also calculated, it decreases by 165 meV as the film thickness increases from 143 to 221 nm. The energies of band gap transitions are also determined from the observed data of absorption. There are two types of transitions, i.e., direct and indirect transitions, in the TiO2 compound. The phonon confinement model is used to interpret the size effect in Raman scattering. Relative to the Raman active Eg mode of bulk TiO2 crystal, a size‐dependent blue shift is noticed in the Raman bands for the first and second Eg modes ( E g ( 1 ) : ≈144 cm−1 and E g ( 2 ): 197 cm−1, respectively). In this study, the results of Raman scattering and optical absorption are combined together in order to investigate the grain size effect, structural disorder, and thickness‐dependent strain. In ABS spectroscopy, it is noticed that (at certain wavelength) the intensity of the transmitted light for the thinner sample is higher than that for the thicker one, which is compatible with the relation I = I0e−αt, where α is the absorption coefficient and t is the thickness. [ABSTRACT FROM AUTHOR]

The stability of charges trapped by the single‐contact and repeated‐contact modes with atomic force microscopy (AFM) probe for polystyrene/cruciformed spiro [fluorene‐9,9′‐xanthene] (PS/SFXs) electret films is detected by Kelvin probe force microscopy (KPFM). The influences of the contact duration and number of contacts on the trapped charges are explored. We found that the contact duration and number of contacts are important factors to improve the trapping property. The repeated contacts between the AFM probe and the sample are a promising way to improve the stability of trapped charges in PS/SFXs. The possible mechanisms for improving storage properties are also discussed. [ABSTRACT FROM AUTHOR]

The thermal stress effect on the structure of phase change memory materials, namely single films and double stacked films of GeTe and SnSe, is evaluated. The crystallization temperatures of GeTe and SnSe single films are 138 °C and 292 °C, respectively. The films are amorphous before annealing and crystallize in rhombohedral and orthorhombic structures afterwards. Ge is tetrahedrally bonded and Se is bivalent after deposition. Both Ge and Se have an octahedral configuration after annealing. The double stacked structure is studied in the as‐deposited state and after annealing at temperatures of 100, 210, and 350 °C. Pulsed laser deposition produces the crystallization of both as‐deposited layers when stacked, mostly of SnSe, but also some crystalline GeTe is present. GeTe fully crystallizes after annealing at 210 °C, in the face‐centred cubic structure. Annealing at 350 °C leads to the evaporation of a significant quantity of Se and to the formation of a cubic Ge0.75Sn0.25Te solid solution. Ge has an octahedral coordination, while Se is tetrahedrally bonded as a result of a combination of bivalent amorphous Se and octahedral Se from crystalline SnSe. The study shows that diffusion between layers at high annealing temperatures might suppress the memory property and determines the formation of irreversible solid solutions. [ABSTRACT FROM AUTHOR]

Poly(3,4‐ethylenedioxythiophene):poly(4‐styrenesulfonate) (PEDOT:PSS) is a promising candidate for terahertz (THz) metamaterial devices. Its dielectric properties can be changed by the dopant dimethylsulfoxide (DMSO). In this study, the dielectric properties of DMSO‐doped‐PEDOT:PSS films are investigated using terahertz time‐domain spectroscopy (THz‐TDS) measurements. The values of the carrier density and mobility are also determined by fitting the dielectric permittivity to the Drude–Smith model. A simple THz frequency selective surface (FSS) is designed based on these DMSO‐doped‐PEDOT:SS films. Strong band rejection can be achieved at resonant frequencies. These results may inspire the development of new materials for manipulating THz waves in future studies. [ABSTRACT FROM AUTHOR]

A simple procedure for the fabrication of colloidal silver films on the surface of flexible polymer substrates, such as polypropylene and polyethylene, with the use of only polyelectrolyte pre‐treatment is presented. The optical properties of these films depend on the number of predeposited polyelectrolyte layers and salt concentration. The uncharged nature of the polymer surface allows to alternate the first polyelectrolyte layer (positively or negatively charged). The proposed method of silver deposition can be used for manufacturing silver films of different density on the polymer surfaces. This approach is low‐cost, does not require special equipment and allows to control the surface properties of the films. Using an average salt concentration (0.5 M) during the deposition of polyelectrolytes allowed to produce the densest films. [ABSTRACT FROM AUTHOR]

Epitaxial NixO thin films were grown on c‐plane (0001) sapphire substrates by ion beam sputtering (IBS) of a Ni metal target in a mixed argon and oxygen atmosphere. The composition of the film was varied systematically by varying the O2:Ar ratio in the IBS process. Structural characterization was carried out by X‐ray diffraction and scanning electron microscopy. All the NixO samples grew (111)‐oriented out‐of‐plane and with a defined two‐fold in‐plane orientation relationship relative to the crystalline substrate. The surface morphologies of the samples were very similar. The chemical bonding information of the films was examined by X‐ray photoelectron spectroscopy showing that the composition x could be varied in a wide range of x ≈ 0.9 to 1.5. Optical characterization yielded a strong dependence of the spectral dispersion of the refractive index and the band gap of NixO on composition for this otherwise structurally very similar series of samples. The dependence of the refractive index of NixO on composition x contributes significantly to the wide range of values reported for NixO in literature. [ABSTRACT FROM AUTHOR]

One of the most frequently used methods for characterizing thin films is UV–Vis absorption. The near‐edge region can be fitted to a simple expression where the intercept gives the band gap and the fitting exponent identifies the electronic transition as direct or indirect. [See Tauc et al., Physica Status Solidi 15, 627 (1966); naturally, these are usually called “Tauc” plots.] In earlier work, we found that direct band gaps fitted using Tauc's method can be quite accurate, to ∼1% [see Viezbicke et al., Phys. Status Solidi B 252, 1700 (2015)]. Still, slopes of these Tauc plots are less frequently quantified, even though the slopes are directly rooted in key band‐structure parameters. In this study, we examine the reproducibility of Tauc plot slopes for ZnO as a model direct‐gap material and compare these experimental values with the theoretically derived slope. In contrast to the band gap accuracy, the experimental slope values varied by several orders of magnitude. The histogram of slope values was significantly more compact for Tauc plots exhibiting less Urbach tail contribution. In these cases, the Tauc slopes can provide an order‐of‐magnitude quantification of other key band characteristics such as carrier effective mass. [ABSTRACT FROM AUTHOR]

Magnetic and nonmagnetic shape memory alloys (SMAs) exhibit thermoelastic martensitic transformations (MTs) which are hysteretic due to their first‐order nature. According to the thermodynamic Landau theory of phase transitions, which assumes ideal thermoelastic equilibrium at each point of the MT interval, the hysteresis is explained by the different limits of stability for austenite and martensite in the phase diagram. No interactions on the phase boundaries are taken into account. In the real alloys, the hysteresis of MT is related not only to the stability intervals of two phases but also to the processes of nucleation and growth of the resultant phase inside the parent phase. In turn, the features of these processes are related to the heights of energy barriers caused by the incompatibility of austenitic and martensitic lattices, crystal defects and some other physical factors. However, the defects, normally, play a minor role in the width of MT hysteresis if compared to the thermodynamic and crystallographic factors. A reduction of hysteresis of MT in SMAs, being crucial for technology, presents a challenging problem for science. A decrease of hysteresis width of MT was observed recently for the single crystals of ferromagnetic SMAs such Ni–Fe(Co)–Ga and Fe–Pd on approaching of their transformation paths to the critical point in stress–temperature phase diagram. Moreover, the superelastic and shape memory properties characterized by the nearly‐zero hysteresis width were observed in the postcritical transformational regime. Here we show that both the Landau‐type theory of ferroelastic phase transitions and neutron diffraction experiments carried out under axial compression describe the essential features of these properties. We also interpret the experimentally observed anhysteretic phenomena in Ni–Mn–Ga thin films and nanobeam actuators in terms of their postcritical state. [ABSTRACT FROM AUTHOR]

We propose a simple fabrication method of thin film hybrid solar cells by combining single‐walled carbon nanotubes (SWCNTs) and poly(3,4‐ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) with hydrogenated amorphous silicon (a‐Si:H). Electrically conductive polymer PEDOT:PSS introduced in a randomly oriented network of SWCNTs forms a coupled continuous heterojunction between PEDOT:PSS–SWCNT and a‐Si:H. We fabricated and compared the performance of SWCNT/a‐Si:H, PEDOT:PSS/a‐Si:H and PEDOT:PSS–SWCNT/a‐Si:H solar cells. The PEDOT:PSS–SWCNT/a‐Si:H solar cells resulted to have an efficiency of 1.6% with state‐of‐the‐art fill factor and open circuit voltage of 54% and 0.803 V, respectively. [ABSTRACT FROM AUTHOR]

We have systematically investigated the electrical transport properties of a series of In [ABSTRACT FROM AUTHOR]

Surface-sensitive UV Raman spectroscopy is used to analyze the crystallinity of silicon films less than 20 nm thick directly on silicon wafers. The 325-nm excitation has a Raman detection thickness of only 13 nm within the silicon film, thus eliminating signal from the substrate. We demonstrate measured crystallinities of microcrystalline silicon thin films that are consistent with the microstructure observed in transmission electron microscopy. Comparison is also made to ellipsometry, which is less able to accurately determine crystallinity than UV Raman spectroscopy. The UV Raman approach is particularly useful for layers grown on substrates of the same material but with different microstructure, and can be extended to non-silicon materials. [ABSTRACT FROM AUTHOR]

The electrical properties of an n-type GaN wafer and epitaxial layer were evaluated using terahertz time-domain spectroscopic ellipsometry (THz-TDSE). The electrical properties, such as carrier density and mobility, were determined by fitting the reflective spectra of the sample using the Drude model. The measured properties of the GaN by THz-TDSE are consistent with those obtained by conventional Hall methods. For the GaN epitaxial layer on sapphire substrates, the thickness was obtained by THz-TDSE and compared with other measurements. THz-TDSE has shown to be a suitable technique for evaluating the electrical properties of n-type GaN materials non-destructively and without contacts. [ABSTRACT FROM AUTHOR]

Single phase nickel-cobalt-titanate thin films with a formula A1+2 xTi1− xO3, where A is Ni2+,Co2+, and −0.25 < x < 1, were grown by pulsed laser deposition on sapphire substrates. There is a large window in which Ni/Co ratio and x can be chosen independently, allowing a control of properties by the synthesis. In the prototype ilmenite and corundum structures one third of the octahedra are vacant. The reported structure is obtained by filling vacant octahedra ( x > 0) or emptying filled octahedra ( x < 0). Films with x = 1 have all octahedra filled. X-ray photoelectron spectroscopy, X-ray diffraction measurements and Raman scattering techniques were applied to address the structure as a function of x. Data collected on samples with x ≈ 1 are interpreted in terms of hexagonal P63/ mmc space group. The hexagonal structure was obtained when films contained both Ni and Co: pure cobalt oxide thin films possessed the spinel structure. Two factors controlling the magnetism and crystal distortion are identified: a direct overlap between the adjacent cation d-orbitals resulting in a bond formation and magnetic interactions, and x controlling the cation shift toward the vacant octahedron. The displacement decreases and the symmetry increases with increasing x. When x ≈ 1 the cations prefer octahedron center positions. [ABSTRACT FROM AUTHOR]

Polarized Raman spectra of the epitaxial Ba0.4Sr0.6TiO3 film grown on MgO substrate with thickness of 600 nm were studied in a broad temperature range of 80-600 K and the phase transition from paraelectric to tetragonal ferroelectric phase was observed at about 500 K. This critical temperature is substantially higher than that calculated from the lattice-mismatch strain theory. In addition, the predicted from the theory low-temperature orthorhombic and rhombohedral phases were not observed. We ascribe the strengthening of the tetragonal ferroelectric phase to the effect of the interface-induced build-in electric field resulted from the interface-accumulated charges. [ABSTRACT FROM AUTHOR]

The ferromagnetic material MnSb can exist in two polymorphs in epitaxial thin-film form, namely niccolite n-MnSb and cubic c-MnSb. We investigate the behavior of these polymorphs using grazing incidence depth-dependent in-plane X-ray diffraction. The in-plane lattice parameter evolution of a nominal 3000 Å thin film reveals a small near-surface compression of [ABSTRACT FROM AUTHOR]

The chemical solution process of MoS2 on high- k oxide films has been systematically investigated. The source solution used in this work is made of (NH4)2MoS4 powder dissolved in N-methyl-2-pyrrolidone. We have spin-coated the solution on various kinds of dielectric oxide films and shown that the coating properties strongly depend on the kind of dielectric, which can be understood by surface energy analysis, following this, the growth of high quality of MoS2 film is confirmed by Raman scattering spectroscopy and X-ray diffraction. It is demonstrated that the MoS2 film can be grown on Nb doped ZrO2 using a solution with a two-step annealing process, where the first annealing is performed at 450 °C in H2/Ar (5:95) atmosphere for 20 min and the second annealing at 1000 °C in Ar atmosphere with S vapor for 20 min. In addition, conformal growth of a MoS2 layered structure on the curved surface of the oxide film is confirmed by transmission electron microscope observations. A further conclusion is that the thickness of MoS2 can be controlled by the concentration of a source solution and that two-layer MoS2 is obtained when the concentration of source solution is 0.00625 mol kg−1. The measured Hall mobility of the solution-derived MoS2 film, annealed at 1000 °C is approximately 25 cm2 V−1s−1. [ABSTRACT FROM AUTHOR]

We have demonstrated scanning internal photoemission microscopy to characterize the degradation of Au/amorphous In-Ga-Zn-O Schottky contacts. After applying a reverse voltage stress of −30 V, the current-voltage characteristics became leaky and a local degradation of the contacts was clearly visualized in a photocurrent image, while no symptom of the degradation was observed in the optical microscope image. In addition, it was found that Schottky barrier height decreased by 0.1 eV in the degraded region. Thus, we conclude that this method gives quantitative and visual information on the underlying thin-film transparency metal/semiconductor interfaces. [ABSTRACT FROM AUTHOR]

Copper-containing thin films were synthesized by a citrate sol-gel method using ethylene glycol. The evolution of the shape and local atomic structure of the copper-containing fractal crystallites at different stages of growth was investigated by the combination of experimental and theoretical techniques. A surface morphological study of the deposited film samples was carried out using SEM. It revealed the evolution of the crystallite structures as a function of annealing temperature. To describe this mechanism diffusion-limiting aggregation and cluster-cluster models were used. X-ray absorption spectroscopy (XANES) was applied to show the dynamics of the local atomic structure of Cu ion and the copper oxidation state at different stages of crystallites formation. It was found that at temperatures up to 250 °C the Cu2Cl(OH)3 (atacamite phase) and chelate complex are formed. With temperature increases changes in the local atomic structure as well as in morphology take place and at 500 °C CuO formed. As a result of these processes, the fractal organization of the other level was observed. [ABSTRACT FROM AUTHOR]

Dealloying has been widely employed lately for the fabrication of nanoporous metals. However, in case of thin films, the impact of the initial morphology on the final porosity is still not well understood. In this work, we report on the influence of the initial morphology of silver-aluminum (Ag-Al) thin films on the dealloying process in hydrochloric acid. The films deposition was performed by a DC co-sputtering process of silver and aluminum targets in a cofocal geometry using pure argon plasma; by tuning the deposition conditions such as the electrical powers applied to the targets and the deposition temperature, films with various compositions and morphologies can be obtained. The dealloying is then carried out using a free corrosion process applied in diluted (2 wt.%) hydrochloric acid in order to leach preferentially aluminum leaving behind a nanoporous skeleton of silver. We show that the dealloying process becomes faster when decreasing the initial silver content within the films. We further demonstrate that the dealloying kinetic is also dependent on the initial morphology of the Ag-Al films: it increases when decreasing the size of the columns forming the Ag-Al films. Top-view SEM image of Ag-Al alloy thin film with 23 at.% of initial Ag content dealloyed for 5 min in 2 wt.% hydrochloric acid. [ABSTRACT FROM AUTHOR]

Electrostatic charging of nanostructured N2 films was studied employing optical and a current set of emission spectroscopy methods: cathodoluminescence CL, thermally and photon-stimulated exoelectron emission TSEE, PSEE as well as thermally and photon-stimulated luminescence TSL, PSL. Concurrently with thermally stimulated yield of electrons the yield of nitrogen particles was detected, so-called 'postdesorption.' An enhancement of the optical emission stemmed from the neutralization reaction N4+ + e → N2* + N2* → N2 + N2 + hν was observed with an exposure to an electron beam. The experiments performed with a variable voltage applied to an electrode for current detection demonstrated significant accumulation of negative charge. The TSEE current in the low-temperature range was detected at negative voltages up to −30 V. An accumulation of trapped electrons (up to 1016 cm−3) was detected. A possible contribution of N3− in electrostatic charging was assumed. Thermally stimulated yield of negatively charged particles from a N2 film subjected to an electron beam. [ABSTRACT FROM AUTHOR]

Phase-change materials (PCM) show remarkable property-contrast from amorphous to crystalline phase that forms the basis for high-speed non-volatile memory device applications. Despite understanding the local structure and physical properties of these phases, a systematic study on the phase-change behavior is essential. Here, we used in situ UV-Vis-NIR spectroscopic measurements to study a systematic evolution of optical band gap ( Eg) and the local disorder described by Tauc parameter ( B), for the temperatures from 90 to 480 K on amorphous and cubic phases of Ge1Sb4Te7 thin films. It has been found that the Eg of amorphous phase decreases with increasing temperature from 90 to 400 K, while the disorder as exemplified by B, increases owing to thermal vibrations. At 420 K, a rapid decrease in the Eg from 0.47 to 0.33 eV and also a sharp reduction of ∼13% in the value of B1/2 is observed evidencing the signature of amorphous-to-cubic phase transition. Furthermore, the hexagonal phase is more disordered compared to cubic phase. The Raman results are consistent with optical measurements, which indicate that the degree of disorder reduces from amorphous to cubic phase, while hexagonal phase with an increased disorder is attributed to elongated bonds. [ABSTRACT FROM AUTHOR]

Conductive bridge resistance change (CBRAM) memory devices are one of the premier emerging technologies for non-volatile memory. The application of these devices could overlap possible situations where they are expected to perform in environments containing X-ray radiation. This poses the question, how X-ray radiation affects the materials comprised within these devices, as well as the performance of the CBRAM devices. In this work, we studied the structural changes caused by a wide range X-ray radiation over thin Ge-Se films with composition ranging from Se rich to Ge rich, as well as X-ray induced Ag diffusion within these films. The results show that after the cessation of radiation, the Ge rich films undergo considerable structural modification while the other compositions did not exhibit substantial changes. X-ray stimulated Ag diffusion with formation of Ag-Se by-products occurred predominantly in the Se and Ge rich films. These effects influence the performance of the CBRAM devices, based on these films and their I-V characteristics, threshold voltage and endurance are presented and discussed in the context of the materials characterization findings of this work, performed by Raman spectroscopy, Energy dispersion spectroscopy and X-ray diffraction. [ABSTRACT FROM AUTHOR]