RESUMO
Finding suitable p-type dopants, as well as reliable doping and characterization methods for the emerging wide bandgap semiconductor [Formula: see text]-[Formula: see text] could strongly influence and contribute to the development of the next generation of power electronics. In this work, we combine easily accessible ion implantation, diffusion and nuclear transmutation methods to properly incorporate the Cd dopant into the [Formula: see text]-[Formula: see text] lattice, being subsequently characterized at the atomic scale with the Perturbed Angular Correlation (PAC) technique and Density Functional Theory (DFT) simulations. The acceptor character of Cd in [Formula: see text]-[Formula: see text] is demonstrated, with Cd sitting in the octahedral Ga site having a negative charge state, showing no evidence of polaron deformations nor extra point defects nearby. The possibility to determine the charge state of Cd will allow assessing the doping type, in particular proving p-type character, without the need for ohmic contacts. Furthermore, a possible approach for contactless charge mobility studies is demonstrated, revealing thermally activated free electrons for temperatures above [Formula: see text] 648 K with an activation energy of 0.54(1) and local electron transport dominated by a tunneling process between defect levels and the Cd probes at lower temperatures.
RESUMO
Highly ordered anodic hafnium oxide (AHO) nanoporous or nanotubes were synthesized by electrochemical anodization of Hf foils. The growth of self-ordered AHO was investigated by optimizing a key electrochemical anodization parameter, the solvent-based electrolyte using: Ethylene glycol, dimethyl sulfoxide, formamide and N-methylformamide organic solvents. The electrolyte solvent is here shown to highly affect the morphological properties of the AHO, namely the self-ordering, growth rate and length. As a result, AHO nanoporous and nanotubes arrays were obtained, as well as other different shapes and morphologies, such as nanoneedles, nanoflakes and nanowires-agglomerations. The intrinsic chemical-physical properties of the electrolyte solvents (solvent type, dielectric constant and viscosity) are at the base of the properties that mainly affect the AHO morphology shape, growth rate, final thickness and porosity, for the same anodization voltage and time. We found that the interplay between the dielectric and viscosity constants of the solvent electrolyte is able to tailor the anodic oxide growth from continuous-to-nanoporous-to-nanotubes.
RESUMO
Inorganic-polymer composites have become promising materials to be processed by printing technologies because of their unique properties that allow the fabrication of flexible wearable electronics at reduced manufacturing costs. In the present work, a complete methodological process of assembling a flexible microthermoelectric generator based on inorganic-polymer materials is presented. The used microparticles were prepared by a top-down approach beginning with a previously prepared material by solid-state reaction and later scaled down through the use of ball milling. It was found that the necessity to proceed with a chemical treatment with HCl to reduce Bi2O3 present on the surface of the microparticle leads to a power factor (PF) of 2.29 µW K-2 m-1, which is two times higher than that of the untreated sample. On the fabrication of flexible inorganic-organic thermoelectric thick films based on Bi2Te3 microparticles (<50 µm) and the poly(vinyl alcohol) (PVA) polymer with different thicknesses ranging from 11 to 265 µm and with different Bi2Te3 weight percentages (wt %), we found that PVA allowed achieving a homogeneous dispersion of the parent inorganic thermoelectric materials, while still maintaining their high performance. The best produced ink was obtained with 25 wt % of PVA and 75 wt % of chemically treated Bi2Te3 micropowder with a Seebeck coefficient of -166 µV K-1 and a PF of 0.04 µW K-2 m-1. For this optimized concentration, a flexible thermoelectric device was fabricated using n-type thermoelectric inks, which constitutes a major advantage to be applied in printing techniques because of their low curing temperature. The device architecture was composed of 10 stripes with 0.2 × 2.5 cm2 each in a one-leg configuration. This prototype yielded a power output up to â¼9 µW cm-2 with a 46 K temperature gradient (Δ T), and the results were combined with numerical simulations showing a good match between the experimental and the numerical results. The thermoelectric devices studied in this work offer easy fabrication, flexibility, and an attractive thermoelectric output for specific power requirements such as for environmental health monitoring.
RESUMO
Recent developments have led to an enormous increase of publicly available large genomic data, including complete genomes. The 1000 Genomes Project was a major contributor, releasing the results of sequencing a large number of individual genomes, and allowing for a myriad of large scale studies on human genetic variation. However, the tools currently available are insufficient when the goal concerns some analyses of data sets encompassing more than hundreds of base pairs and when considering haplotype sequences of single nucleotide polymorphisms (SNPs). Here, we present a new and potent tool to deal with large data sets allowing the computation of a variety of summary statistics of population genetic data, increasing the speed of data analysis.
