The Hf/Ti ratio was precisely controlled at monolayer thickness using atomic partial layer deposition (APLD). HfxTi1−xO2 films with varying Hf concentrations were deposited by adjusting the pulse time of Hf precursors within a single atomic layer. Characterization using x-ray reflectivity, x-ray photoelectron spectroscopy, and spectroscopic ellipsometry confirmed the presence of Hf, Ti, and O in the films. Increasing the Hf content caused the binding energies of the O 1s peak to shift to higher values, indicating a chemical environment change from TiO2-like to HfO2-like. A higher Hf content also increased the relative atomic percentages of Hf, Ti, and O, altering the film properties. The mass density and optical properties were notably sensitive to changes in the Hf/Ti ratio at monolayer thickness. The potential of APLD to reduce dimensionality through precise control of both thickness and composition renders it especially appropriate for applications requiring highly specific material properties.

The TiO2- HfO2 oxides can be considered among the most promising cation combinations to create alloys. Ti1-xHfxO2 films have been prepared by a technique with which they had never been deposited before, spin coating. Silicon wafers were used as substrates; films were obtained upon mixing proper amounts of Ti and Hf solutions to have different Hf concentrations. Later films were annealed at 600°C. Structural characterization was performed with grazing incidence X-ray diffraction (GIXRD) and Raman spectroscopy. Polycrystalline films were obtained. Pure phases of anatase TiO2 and monoclinic HfO2 were identified at the extremes of the alloy. At x > 0.58, the crystalline phase changed from TiO2 anatase to an orthorhombic HfTiO4. An addendum to the phase diagrams of these systems is proposed adding the obtention of the HfTiO4 phase at a temperature of 600 °C. A Uniform film thickness of ~1 µm was found in all samples by SEM images. The atomic percentage obtained by XPS confirms the replacement of Ti atoms by Hf as the concentration of Hf increases. This work proves that it is possible to deposit films of the TiO2- HfO2 system through spin coating at relatively low temperature.

The potential of the III-nitride semiconductor materials for modern optoelectronic applications as diodes, transistors, LEDs, and photovoltaics has prompted the mechanical characterization of small volumes as thin films. In this paper, the load-displacement curves of cubic indium nitride (c-InN) obtained during the nanoindentation with a Berkovich indenter were investigated. c-InN was obtained by plasma-assisted molecular beam epitaxy growth on c-GaN/MgO (100). The thickness of the c-GaN buffer layer used in all the films studied was 350 nm to eliminate the substrate's effect on the material studied properties. The c-InN thickness is around 180 nm. The reflection high energy electron diffraction and the X-ray diffraction results show that the c-GaN buffer and c-InN grown layers had a high cubic zincblende phase with more than 97%. The obtained value of the hardness is 12.5 +/- 0.4 GPa, and the value for Young's modulus is 365.6 +/- 7 GPa with a Poisson's ratio of 0.3.

The epitaxial growth of cubic InxGa1-xN layers on GaN (0 0 1) buffer substrates is investigated using molecular dynamics simulation. The substrate temperature, flux ratio of In, Ga, and N, In concentration, and thermal annealing post-growth were simulated and studied. The dislocation, the critical thickness, and the incorporation of the hexagonal phase into the cubic structure for InxGa1-xN are discussed in detail. Theoretical model conditions were simulated by Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) free-source code; the simulated growths reproduce the experimental thermodynamic conditions for molecular beam epitaxy process during the nucleation and first layers deposited. We consider the Stillinger-Weber In-Ga-N-system potentials. We apply time-and-position-dependent boundary constraints that vary the ensemble treatments of the near-surface solid-phase and the bulk-like regions of the growing layer. The results demonstrate that the simulations are suitable for reproducing the experimental epitaxial growths of cubic phase InGaN alloys with In concentration with 0 < x < 0.5. The hexagonal inclusion is a maximum of 5% for In < 0.2, indicating a preferential pure cubic structure. For In >0.2, the RMS roughness surface increase due to the inclusion of hexagonal planes parallel (1 1 0), (1 1 1), and (1 1 2) in cubic matrix. The average error for cubic phase percentage in the InGaN layers is <1% for x < 0.3, whereas for x = 0.48, the error is 4.8% compared with experimental results.

The critical thickness for the relaxation of cubic (beta) InxGa1-xN layers grown over (002) beta-GaN/MgO, with different indium content, particularly of 17, 44, and 70% have been determined experimentally. The layers were grown by plasma-assisted molecular beam epitaxy. In all the samples studied, the critical thickness (hc) of the pseudomorphic layer was measured with a frame-by-frame analysis of reflection high energy electron diffraction (RHEED) patterns. The growth mode transition during layer growth was identified via RHEED patterns, from layer by layer or 2D to 3D growth mode by gradually transitioning from a streaky to a spotty pattern. The experimental he value of beta-InxGa1-xN on beta-GaN was compared to values calculated from the Fisher model. For the indium concentration of x = 0.44, the self-assembling epitaxial nanostructures were successfully grown in the Stranski-Krastanov growth mode with a critical thickness of 1.8 +/- 0.7 nm. The beta-In0.44Ga0.56N nanostructures showed a variation in morphology and density depending on the deposition time; self-assembled nanodots and nano-bars were confirmed by atomic force microscopy. Photoluminescence spectra of beta-In0.44Ga0.56N nanostructures showed emissions associated with quantum confinement; these peaks indicate a blue shift with respect to the bulk.

The mechanical properties of gallium nitride thin films in the cubic phase (c-GaN) measured by Berkovich nanoindentation are reported here. The c-GaN thin films were grown on MgO (100) substrates by plasma-assisted molecular beam epitaxy. The X-ray diffraction results show that GaN thin films correspond to more than 99% cubic phase in all cases. Plastic transitions called pop-in events are observed during loading in some load-displacement curves at different depths. We believe that pop-in event is present when the tip interacts with defects encountered at different depths. The mean values of the hardness and Young's modulus of cubic GaN are 22 +/- 1 GPa, and 293 +/- 12, respectively.

We report the influence of the Mn atomic concentration (at.%) on the nanostructures formation and magnetic properties of GaAs:Mn layers grown by Molecular Beam Epitaxy at a relatively high substrate temperature of 530 degrees C varying the nominal Mn at% content from 0.01 to 0.2. It is shown that by modifying the Mn at.% different kind of nanostructures, ranging from 2D (such as islands and surface corrugation) to 3D microleave-and nanowire-like arrays, form on the surface layer. Samples produced with Mn contents ranging from 0.02 to 0.20 at.% show a significant room temperature ferromagnetic response that is attributed to the formation of MnAs nanocrystals as confirmed from X-ray diffraction analysis and magnetization measurements. The influence of MnAs clusters on the formation of the nanostructures observed is discussed.

The structural and electrical properties of Mg-doped cubic GaN epi-layers grown by plasma-assisted molecular beam epitaxy (PAMBE) near Ga rich conditions are investigated. The diffraction of high-energy reflected electrons (AHEM) in situ, in addition to structural studies of X-ray diffraction, show that the fraction of hexagonal and crystal twinning inclusions decreases when the Mg flux increases. The condition for the higher incorporation of Mg where the electrical properties are optimized is highly sensitive to the flow ratio Mg/Ga. The p-doping level steadily increases with increasing Mg flux. The Mg concentration obtained by secondary ion mass spectroscopy (SIMS) from samples grown at Mg temperatures from 200 degrees C to 700 degrees C are in a range between 2 x 10(19) to 2 x 10(20) atoms/cm(3). The highest mobility and p-type doping level achieved, determined from Hall measurements, were 28.2 cm(2)/V-s and 2 x 10(19) cm(-3), respectively. We corroborate that the Mg doped c-GaN films are suitable for the construction of optoelectronic devices based on cubic III-Nitrides.

This study presents an analysis of the photocatalytic efficiency in \(\hbox {TiO}_{2}\):N thin films grown by atomic layer deposition related to the film thickness. The nitriding process was carried out with nitrogen plasma by molecular nitrogen decomposition after \(\hbox {TiO}_{2}\) deposition. The study was performed using the time-dependent degradation of colour units for methylene-blue solutions and inactivation percentages for Escherichia coli bacteria, for potential applications in sewage purification. To determine the optoelectronic properties of the films, the optical, structural, surface and thickness characterizations were carried out by photoluminescence, Raman spectroscopy, atomic force microscopy and scanning electron microscopy, respectively.

A novel growth technique, called atomic partial layer deposition (APLD), has been proposed to expand the applications of, and the research in, atomic layer deposition (ALD). This technique allows the possibility for the fabrication of well-controlled alloys on a single atomic layer scale. To demonstrate the capabilities of this technique, samples of HfO2 and TiO2 were prepared as conventional ALD nanolaminates through the repeated exposure of the separated metal-precursor and reactant. Subsequently, HfO2-TiO2 APLD growth mode samples were obtained by varying the precursor doses and exposure times to obtain a fractional coverage in the monolayer of Hf and Ti. The thickness and structure of the samples were studied by X-ray reflectivity. The surface topography was studied using atomic force microscopy along with Kelvin probe force microscopy for surface potential mapping. Clear differences on the surface, compared with the conventional HfO2/TiO2 ALD nanolaminates, were observed, which confirmed the HfO2-TiO2 APLD growth. The films were analyzed using X-ray photoelectron spectroscopy (XPS) depth profile scans and angle resolved XPS, where well-defined HfO2 and TiO2 contributions were found for both the conventional and APLD mode samples, and an additional contribution, assigned to a ternary phase Hf-Ti-O, in the APLD grown films was observed. This result confirms that Hf and Ti form an alloy in a monolayer by APLD mode growth.

GaN thin films were grown on flexible metallic substrates by molecular beam epitaxy. MgO buffer layers were deposited by spin coating on Ni-Mo-Cr (Hastelloy C-276) alloy tapes that were used as substrates. The structural characterization of the GaN/MgO/hastelloy samples was performed by x-ray diffraction and Raman spectroscopy. The obtained nanometric films have the stable hexagonal phase (alpha-GaN) with an average crystallite size of 18 nm. The long and short range order of GaN decrease when the structure is bent. The most significant variations in the structural properties occur between 100 and 250 bending cycles.

Spectroscopic ellipsometry measurements of InXGa1-XN thin films were carried out in the photon energy range from 0.6 to 4.75eV. The samples were grown on cubic GaN/MgO (100) template substrates by plasma assisted molecular beam epitaxy. Optical properties as the energy gap, refractive index (η) and extinction coefficient (κ) were obtained from the analysis of experimental data by a parametric dielectric function model. Our results show that the behavior of the optical band gap of cubic InXGa1-XN fits Eg(x)=1.407x2−3.662x+3.2eV. The obtained bowing parameter of 1.4±0.1eV is in good agreement with reported calculated values around 1.37eV. The complex index of refraction dispersion relations η(ω) and κ(ω) are obtained for the 85–99% mostly cubic InXGa1-XN films for several In concentrations.

We investigate the influence of the MgO growth process on the bias dependence of the electrical spin injection from a Co-Fe-B=MgO spin injector into a GaAs-based light-emitting diode (spin LED). With this aim, textured MgO tunnel barriers are fabricated either by sputtering or molecular-beam-epitaxy (MBE) methods. For the given growth parameters used for the two techniques, we observe that the circular polarization of the electroluminescence emitted by spin LEDs is rather stable as a function of the injected current or applied bias for the samples with sputtered tunnel barriers, whereas the corresponding circular polarization decreases abruptly for tunnel barriers grown by MBE. We attribute these different behaviors to the different kinetic energies of the injected carriers linked to differing amplitudes of the parasitic hole current flowing from GaAs to Co-Fe-B in both cases.

Gallium nitride films were synthesized on GaAs (0 0 1) substrates at temperatures lower than the congruent sublimation temperature of GaAs. By controlling isothermal desorption of the substrate and setting experimental parameters in the early growth stage, the authors obtained cubic GaN films. No nitridation process or growth of a buffer layer was necessary prior to GaN growth of GaN. In situ reflection high-energy electron diffraction (RHEED) and ex situ high-resolution x-ray diffraction were used to study the crystalline qualities of the films. The measured pole diagram of cubic GaN at 2θ = 34.5° was consistent with RHEED results and confirmed the crystalline structure. Photoluminescence measurements showed a strong emission only at 3.21 eV.

We present a combined experimental and theoretical study of highly charged and excited electron-hole complexes in strain-free (111) GaAs/AlGaAs quantum dots grown by droplet epitaxy. We address the complexes with one of the charge carriers residing in the excited state, namely, the “hot” trions X^-* and X^+*, and the doubly negatively charged exciton X^2-. Our magneto-photoluminescence experiments performed on single quantum dots in the Faraday geometry uncover characteristic emission patterns for each excited electron-hole complex, which are very different from the photoluminescence spectra observed in (001)-grown quantum dots. We present a detailed theory of the fine structure and magneto-photoluminescence spectra of X^-*, X^+* and X^2- complexes, governed by the interplay between the electron-hole Coulomb exchange interaction and the heavy-hole mixing, characteristic for these quantum dots with a trigonal symmetry. Comparison between experiment and theory of the magneto-photoluminescence allows for precise charge state identification, as well as extraction of electron-hole exchange interaction constants and g-factors for the charge carriers occupying excited states.

Ternary III-N-V semiconductor alloys are interesting and complex materials. GaNAs is one such material that has been studied extensively; however, the accurate determination of the N content within this material in which the growth conditions significantly increases the amount of interstitial N has not yet been reported. To address this problem, GaNAs layers (100 nm) were prepared using molecular beam epitaxy at temperatures between 400 and 600 °C with a high nominal N concentration (3%). The N content was determined using high resolution x-ray diffraction (HRXRD), secondary ion mass spectrometry (SIMS), and low-temperature photoluminescence (PL). The N concentration determined using these techniques was compared. Additionally, the relationship between the growth temperature and N concentration is discussed. The incorporation of N into interstitial sites resulted in significant variations in the N content as estimated by SIMS, HRXRD, and PL.

In self assembled III-V semiconductor quantum dots, valence holes have longer spin coherence times than the conduction electrons, due to their weaker coupling to nuclear spin bath fluctuations. Prolonging hole spin stability relies on a better understanding of the hole to nuclear spin hyperfine coupling which we address both in experiment and theory in the symmetric (111) GaAs/AlGaAs droplet dots. In magnetic fields applied along the growth axis, we create a strong nuclear spin polarization detected through the positively charged trion X^+ Zeeman and Overhauser splittings. The observation of four clearly resolved photoluminescence lines - a unique property of the (111) nanosystems - allows us to measure separately the electron and hole contribution to the Overhauser shift. The hyperfine interaction for holes is found to be about five times weaker than that for electrons. Our theory shows that this ratio depends not only on intrinsic material properties but also on the dot shape and carrier confinement through the heavy-hole mixing, an opportunity for engineering the hole-nuclear spin interaction by tuning dot size and shape.

Light emission in the three primary colors was achieved in cubic GaN/InGaN/GaN heterostructures grown by molecular beam epitaxy on MgO substrates in a single growth process. A heterostructure with four quantum wells with a width of 10nm was grown; this quantum wells width decrease the segregation effect of In. Photoluminescence emission produced four different emission signals: violet, blue, green-yellow and red. Thus, we were able to tune energy transitions in the visible spectrum modifying the In concentration in cubic InxGa1−xN ternary alloy.

We combine linear and nonlinear optical spectroscopy at 4 K with ab initio calculations to study the electronic bandstructure of MoSe2 monolayers. In one-photon photoluminescence excitation (PLE) and reflectivity we measure a separation between the A- and B-exciton emission of 220 meV, in good agreement with our calculations. In two-photon PLE we detect for the A- and B-exciton the 2p state 180 meV above the respective 1s state. In second harmonic generation (SHG) spectroscopy we record an enhancement by more than two orders of magnitude of the SHG signal at resonances of the charged exciton and the 1s and 2p neutral A- and B-exciton. Our post-density functional theory calculations show in the conduction band along the K–Γ direction a local minimum at the Λ-point that is energetically and in k-space close to the global minimum at the K-point. The influence of this local minimum on exciton transitions is discussed.

Conventional approaches to bone regeneration rarely use multiwall carbon nanotubes (MWCNTs) but instead use polymeric matrices filled with hydroxyapatite, calcium phosphates and bioactive glasses. In this study, we prepared composites of MWCNTs/polycaprolactone (PCL) for bone regeneration as follows: (a) MWCNTs randomly dispersed on PCL, (b) MWCNTs aligned with an electrical field to determine if the orientation favors the growing of human dental pulp stem cells (HDPSCs), and (c) MWCNTs modified with β-glycerol phosphate (BGP) to analyze its osteogenic potential. Raman spectroscopy confirmed the presence of MWCNTs and BGP on PCL, whereas the increase in crystallinity by the addition of MWCNTs to PCL was confirmed by X-ray diffraction and differential scanning calorimetry. A higher elastic modulus (608 ± 4.3 MPa), maximum stress (42 ± 6.1 MPa) and electrical conductivity (1.67 × 10−7 S/m) were observed in non-aligned MWCNTs compared with the pristine PCL. Cell viability at 14 days was similar in all samples according to the live/dead assay, but the 21 day cell proliferation, measured by MTT was higher in MWCNTs aligned with BGP. Von Kossa and Alizarin red showed larger amounts of mineral deposits on MWCNTs aligned with BGP, indicating that at 21 days, this scaffold promotes osteogenic differentiation of HDPSCs.