M. Villanueva-Ibañez

Bio: M. Villanueva-Ibañez is an academic researcher from Polytechnic University of Puerto Rico. The author has contributed to research in topics: Fourier transform infrared spectroscopy & Thin film. The author has an hindex of 8, co-authored 19 publications receiving 264 citations. Previous affiliations of M. Villanueva-Ibañez include Centre national de la recherche scientifique & Claude Bernard University Lyon 1.

HfO2:X (X = Eu3+, Ce3+, Y3+) Sol Gel Powders for Ultradense Scintillating Materials

Abstract: Hafnium dioxide (HfO 2) presents a high crystalline density which makes it attractive for host lattice activated by rare earths for applications as scintillating materials. HfO 2 powders doped with Eu (3+) or Ce (3+) luminescent ions are prepared by sol gel process. The annealing temperature and the concentration of doping ions are optimized to provide the powder presenting the best scintillation yield. The powders are crystallized in monoclinic phase whatever annealing temperature above 800 degrees C. The emission spectra are characterized by a white broadband between 400 and 600 nm. After optimization, the most efficient composition, namely HfO 2:2.5% Eu 1% Y (molar percent) exhibits a scintillation yield about 31,000 photons/MeV, which is about 3.8 times that of the standard Bi 3Ge 5O 12 (BGO) commercial powder.

Elaboration, structural and spectroscopic properties of rare earth-doped yttrium–hafnium sol–gel oxide powders for scintillation applications

Abstract: Hafnium dioxide (HfO2) presents a high crystalline density (≈10 g/cm3) which makes it attractive for host lattice activated by rare earths (RE) for applications as scintillating materials. The potentiality to prepare Eu3+ and Tb3+ activated HfO2 sol–gel powders, with high scintillation yield, is explored. The powders are heat-treated at 1000 °C before analyses. The incorporation of yttrium (Y3+) in various concentrations is conducted to vary the lattice phase and to stabilize the trivalent terbium ions. The influence of Y3+ on the microstructure and then on the scintillation properties of the material is presented. A high concentration of Y3+ (20 mol%) stabilizes pure HfO2 tetragonal phase whatever RE (1 mol%) doping. The powders with the highest relative scintillation yield are Eu3+:HfO2 without Y3+ incorporation and crystallized into the monoclinic phase and Y3+ (20 mol%): Tb3+:HfO2 crystallized into the tetragonal phase. Sequential energy transfer process is assumed to explain these results.

31p-S-4 Giant Magnetoresistance in Magnetic Manganese Oxide with Intrinsic Antiferromagnetic Spin Structure

Abstract: Giant and isotropic magnetoresistance as huge as −53% was observed in magnetic manganese oxide La0.72Ca0.25MnOz films with an intrinsic antiferromagnetic spin structure. We ascribe this magnetoresistance to spin‐dependent electron scattering due to spin canting of the manganese oxide.

Scintillation detectors for x-rays

Abstract: Recent research in the field of phosphor and scintillator materials and related detectors is reviewed. After a historical introduction the fundamental issues are explained regarding the interaction of x-ray radiation with a solid state. Crucial parameters and characteristics important for the performance of these materials in applications, including the employed measurement methods, are described. Extended description of the materials currently in use or under intense study is given. Scintillation detector configurations are further briefly overviewed and selected applications are mentioned in more detail to provide an illustration.

Development of hafnium based high-k materials—A review

Abstract: The move to implement metal oxide based gate dielectrics in a metal-oxide-semiconductor field effect transistor is considered one of the most dramatic advances in materials science since the invention of silicon based transistors. Metal oxides are superior to SiO 2 in terms of their higher dielectric constants that enable the required continuous down-scaling of the electrical thickness of the dielectric layer while providing a physically thicker layer to suppress the quantum mechanical tunneling through the dielectric layer. Over the last decade, hafnium based materials have emerged as the designated dielectrics for future generation of nano-electronics with a gate length less than 45 nm, though there exists no consensus on the exact composition of these materials, as evolving device architectures dictate different considerations when optimizing a gate dielectric material. In addition, the implementation of a non-silicon based gate dielectric means a paradigm shift from diffusion based thermal processes to atomic layer deposition processes. In this report, we review how HfO 2 emerges from all likely candidates to become the new gold standard in the microelectronics industry, its different phases, reported electrical properties, and materials processing techniques. Then we use specific examples to discuss the evolution in designing hafnium based materials, from binary to complex oxides and to non-oxide forms as gate dielectric, metal gates and diffusion barriers. To address the impact of these hafnium based materials, their interfaces with silicon as well as a variety of semiconductors are discussed. Finally, the integration issues are highlighted, including carrier scattering, interface state passivation, phonon engineering, and nano-scale patterning, which are essential to realize future generations of devices using hafnium-based high- k materials.