Search

Yttrium oxide thin films are deposited on silicon substrates using the ultrasonic spray pyrolysis technique from the thermal decomposition of a β-diketonate, yttrium acetylacetonate (Y(acac)3). The decomposition of Y(acac)3 was studied by thermogravimetry, differential scanning calorimetry, mass spectrometry, and infrared spectroscopy. It was found that a β-diketone ligand is lost during the initial steps of decomposition of the Y(acac)3. The rest of the complex is then dissociated or degraded partially until Y2O3 is obtained in the final step with the presence of carbon related residues. Then the Y(acac)3 was used to synthesize Y2O3 thin films using the spray pyrolysis technique. The films were deposited on silicon substrates at temperatures in the range of 400–550 °C. The films were characterized by ellipsometry, infrared spectroscopy, atomic force microscopy, and X-ray diffraction. The films presented a low surface roughness with an index of refraction close to 1.8. The crystalline structure of the films depended on the substrate temperature; films deposited at 400 °C were mainly amorphous, but higher deposition temperatures (450–550 °C), resulted in polycrystalline with a cubic crystalline phase. [ABSTRACT FROM AUTHOR]

Y2O3 films were deposited on c-Si substrates at temperatures in the 400–550 °C range, with no further thermal treatment given to these samples, using the spray pyrolysis technique. The spraying solution was yttrium acetilacetonate disolved N,N-dimethylformamide. In addition, a solution of H2O–NH4OH was sprayed in parallel during the deposition process to improve the optical, structural, and electrical properties of the deposited films. The growth of a SiO2 layer between the yttrium oxide and the Si substrate during this deposition process resulted in interface state density values as low as 1010 eV-1 cm-2. An effective refractive index value of 1.86, and deposition rates close to 1 Å/s were obtained. The Y2O3 films were polycrystalline with a crystalline cubic phase highly textured with the (400) direction normal to the Si surface. An effective dielectric constant up to 13, as well as a dielectric strength of the order of 0.2 MV/cm was obtained for ∼1000 Å thick as-deposited films incorporated in a metal-oxide-semiconductor structure. [ABSTRACT FROM AUTHOR]

In the present work, terbium-doped yttrium hydroxide was successfully synthesized by the microwave-assisted hydrothermal method using yttrium nitrate, terbium chloride, and lithium hydroxide as precursors; the study is based on samples with different terbium concentrations. X-ray diffraction indicates a pure hexagonal structure corresponding with the Y(OH)3 structure, as well as a preferential growth along (110) planes for the Tb-doped samples. FTIR confirms the presence of Y–OH bonds and no adsorbed nitrogen or N–O bonds. SEM images indicate the formation of rods smaller than 1 μm in length and diameters ranging from 80 to 55 nm while TEM images confirm the presence of large areas corresponding to (110) planes. The sample doped at 4 at.% presented the maximum photoluminescent intensity, though the sample doped at 2 at.% presented the highest values of quantum yield (23.5%). Quantum yield values decay with terbium concentration to a value of 7.89% for the 10 at.% concentration, such changes are attributed to a quenching effect and to differences in the photon-extraction efficiency. Photoluminescence decay time values decrease monotonically from 1.133 for the 2 at.% sample to 0.453 ms for the sample doped at 10 at.%, such behavior is attributed to a self-stimulated emission. [ABSTRACT FROM AUTHOR]

CsPbI 3 perovskite nanocrystals (NCs) are promising building blocks for photovoltaics and optoelectronics. However, they exhibit an essential drawback in the form of phase stability: α-phase, with a ∼1.80 eV bandgap, can easily experience a phase transition to a non-radiative orthorhombic δ-phase in an ambient environment. This leads to the need to carry out the CsPbI 3 -based device fabrication in an inert atmosphere, which is technologically inconvenient and expensive. One of the most successful approaches proposed to overcome this problem is synthesizing mixed halide CsPbBr 3- x I x NCs to improve the stability of the α-phase perovskite structure. However, the formation of high-quality thin films of CsPbBr 3- x I x NCs with high PLQY is challenging owing to the degradation of their optical properties after deposition on a substrate. This work presents spray coating to carry out a solid-state anion exchange in CsPbBr 3 NCs thin films at ambient conditions with low-demanding reaction conditions. This constitutes a novel open-air and annealing-free technology to manufacture CsPbBr 3- x I x NC thin films with high optical quality and record high photoluminescence quantum yields (PLQY) based on spray-driven halide (Br - to I - ) anion exchange in a solid-state phase. Besides, tunable emission wavelengths between 520 and 670 nm can be obtained from CsPbBr 3- x I x NC films using accurate tuning volumes of HI solution sprayed over the initial surface of CsPbBr 3 film to provide the halide exchange. The optical quality of the halide-exchanged PNCs films remains practically identical to that of initial Br-containing layers, with a remarkable PLQY enhancement after anion exchange, from ∼61% for CsPbBr 3 thin films emitting at 520 nm to ∼84% for mixed halide CsPbBr 3- x I x film emitting at 640 nm. The huge potential of the system is confirmed by demonstrating a low-threshold amplified spontaneous emission.