Search results for "Thin films."

Physical properties of ferroelectric film with continuous space charge distribution

2014

We present a theory of ferroelectric phase transitions in a film with a homogeneously distributed space charge leading to the so-called built-in polarization. On the base of our complete solution of the problem of continuous space charge distribution in a ferroelectric film, we calculate the ferroelectric phase transition temperature , spatial polarization distribution in paraelectric and ferroelectric phases as well as hysteresis loop in the ferroelectric phase. We have shown that the presence of continuous space charge in a film inhibits the ferroelectricity in it: it lowers the ferroelectric phase transition temperature and coercive field. Our estimates of these differences show that the…

Order-Order Phase Transitions Induced by Supercritical Carbon Dioxide in Triblock Copolymer Thin Films

2019

We study the influence of supercritical carbon dioxide (scCO2) on the phase behavior of a cylinder-forming polystyrene-block-polybutadiene-b-polystyrenetriblock copolymer thin film. Solvent annealing with scCO2 can produce patterns with long-range order but these structures become unstable for thin films with small thicknesses. These results are in good agreement with self-consistent mean field calculations, which indicate that a drying transition occurs for thicknesses below the radius of gyration of the molecule.After decompression and solvent extraction, the initially swollen polymer nanostructure suffers a strong reduction in the average domain spacing, which has a deleterious effect on…

Photocurrent Spectroscopy Applied to the Characterization of Compositionally and Structurally Graded Materials: from Thin Films to Nanostructures

2010

Low-Temperature Atomic Layer Deposition of Crystalline and Photoactive Ultrathin Hematite Films for Solar Water Splitting

2015

We developed a low-temperature atomic layer deposition route to deposit phase pure and crystalline hematite (alpha-Fe2O3) films at 230 degrees C without the need for postannealing. Homogenous and conformal deposition with good aspect ratio coverage was demonstrated on a nanostructured substrate and analyzed by transmission electron microscopy. These as-deposited alpha-Fe2O3 films were investigated as photoanodes for photoelectrochemical water oxidation and found to be highly photoactive. Combined with a TiO2 underlayer and a low-cost Ni(OH)(2) catalyst, hematite films of less than 10 nm in thickness reached photocurrent densities of 0.3 mA cm(-2) at 1.23 V vs RHE and a photocurrent onset po…

Correlation between Zn vacancies and photoluminescence emission in ZnO films.

2006

Photoluminescence and positron annihilation spectroscopy have been used to characterize and identify vacancy-type defects produced in ZnO films grown on sapphire by metal-organic chemical-vapor deposition. The photoluminescence of the samples in the near band edge region has been studied, paying particular attention to the emission at 370.5 nm (3.346 eV). This emission has been correlated to the concentration of Zn vacancies in the films, which has been determined by positron annihilation spectroscopy. Jesus.Zuniga@uv.es Vicente.Munoz@uv.es

Optical characterization of Mg-doped GaN films grown by metalorganic chemical vapor phase deposition

2000

Scanning electron microscopy, micro-Raman, and photoluminescence (PL) measurements are reported for Mg-doped GaN films grown on (0001) sapphire substrates by low-pressure metalorganic chemical vapor phase deposition. The surface morphology, structural, and optical properties of GaN samples with Mg concentrations ranging from 1019 to 1021 cm−3 have been studied. In the scanning micrographs large triangular pyramids are observed, probably due to stacking fault formation and three-dimensional growth. The density and size of these structures increase with the amount of magnesium incorporated in the samples. In the photoluminescence spectra, intense lines were found at 3.36 and 3.31 eV on the tr…

Modulation of the electronic properties of GaN films by surface acoustic waves

2003

We report on the interaction between photogenerated electron-hole pairs and surface acoustic waves (SAW) in GaN films grown on sapphire substrates. The spatial separation of photogenerated carriers by the piezoelectric field of the SAW is evidenced by the quenching of the photoluminescence (PL) intensity. The quenching levels in GaN are significantly smaller than those measured in GaAs under similar conditions. The latter is attributed to the lower exciton ionization efficiency and carrier separation probabilities mediated by the piezoelectric effect. The PL spectra also evidence energy shifts and broadenings of the electronic transitions, which are attributed to the band gap modulation by …

Bis(arylimidazole) Iridium Picolinate Emitters and Preferential Dipole Orientation in Films

2018

The straightforward synthesis and photophysical properties of a new series of heteroleptic iridium(III) bis(2-arylimidazole) picolinate complexes are reported. Each complex has been characterized by nuclear magnetic resonance, UV-vis, cyclic voltammetry, and photoluminescent angle dependency, and the emissive properties of each are described. The preferred orientation of transition dipoles in emitter/host thin films indicated more preferred orientation than homoleptic complex Ir(ppy)3.

Photocatalysis of rhodamine B and methyl orange degradation under solar light on ZnO and Cu2O thin films

2020

We report the photocatalytic properties of ZnO and Cu2O thin films deposited on glass substrates at room temperature by DC sputtering and pulsed laser deposition. The photoactivity of the films was investigated through the degradation of rhodamine B (RhB) and methyl orange (MO) under solar light. In order to select the most suitable film of ZnO for the of RhB and MO degradation, the relationship between the characteristics (e.g. energy levels and defects concentration) of ZnO films and their effectiveness in the photocatalytic yield of RhB and MO been studied, where several films were deposited by using different oxygen partial pressures (PO2: 0.05–1.3 mbar), while Cu2O films were grown und…

Si:O Alloys for Photovoltaics: Optical and Electrical Properties from Quantum Dots to Thin Films

2010

In current Si based PV devices the sun-light-electricity conversion rarely exceeds the 20% in efficiency, stimulating significant efforts towards new solutions and technologies for giving a boost to Si for PV. One of the most promising routes for the 21st century is exploiting the quantum confinement effect in reduced dimensionality systems, with the aim to harvest the full solar spectrum. Recently, it has been proposed that a certain modulation of the optical bandgap (EG OPT) can be attained by changing the size of Si quantum dots (QDs), which should allow for a large absorption of the solar photon flux [1]. By this way, an “all-Si” tandem solar cell could be fabricated, by stacking solar …