arXiv subjects

Yonatan Calahorra

Publications and source records attributed to Yonatan Calahorra.

5 recordsLinked to original sources

arXiv2022

Magnetic properties of nickel electrodeposited on porous GaN substrates with infiltrated and laminated connectivity

We studied the magnetic properties of ferromagnetic-semiconductor composites based on nickel and porous-GaN, motivated by the effort to couple magnetic and semiconductor functionality. Nickel-infiltrated and nickel-coated (laminated thin-film) porous GaN structures were fabricated by electrodeposition, and their magnetic properties were subsequently examined collectively, by vibrating sample magnetometry and on the nanoscale, by magnetic force microscopy. We successfully demonstrated the ability to realize nickel infiltrated porous GaN, where the magnetic properties were dominated by the infiltrated material without a measurable surface contribution. We found that the structure and magnetization of electrodeposited porous-GaN/Ni composites depended on GaN degree of porosity and the amount of deposited nickel. The magnetization evolves from a nearly isotropic response in the infiltrated structures, to a shape-anisotropy controlled magnetic thin-film behaviour. Furthermore, both infiltrated and thin-film nickel electrodeposited on porous GaN were found to have low (< 0.1%) strain and corresponding low coercivity: < 6.4 and < 2.4 kA/m for infiltrated and thin-film, correspondingly. The most likely cause for the lowered strain is increased compliance of the porous GaN compared to bulk. These results encourage deeper investigation of magnetic nanostructure property tuning and of magnetic property coupling to GaN and similar materials.

cond-mat.mtrl-sci↗

arXiv2019

Time-Resolved Open-Circuit Conductive Atomic Force Microscopy for Quantitative Analysis of Nanowire Piezoelectricity and Triboelectricity

Piezoelectric nanowires are promising materials for sensing, actuation and energy harvesting, due to their enhanced properties at the nanoscale. However, quantitative characterization of piezoelectricity in nanomaterials is challenging due to practical limitations and the onset of additional electromechanical phenomena, such as the triboelectric and piezotronic effects. Here, we present an open-circuit conductive atomic force microscopy (cAFM) methodology for quantitative extraction of the axial piezoelectric coefficients of nanowires. We show, both theoretically and experimentally, that the standard short-circuit cAFM mode is inadequate for piezoelectric characterization of nanowires, and that such measurements are governed by competing mechanisms. We introduce an alternative open-circuit configuration, and employ time-resolved electromechanical measurements, to extract the piezoelectric coefficients. This method was applied to GaAs, an important semiconductor, with relatively low piezoelectric coefficients. The results obtained for GaAs,~0.4-1 pm/V, are in good agreement with existing knowledge and theory. Our method represents a significant advance in understanding the coexistence of different electromechanical effects, and in quantitative piezoelectric nanoscale characterization. The easy implementation will enable better understanding of electromechanics at the nanoscale.

cond-mat.mes-hall↗

arXiv2019

Highly sensitive piezotronic pressure sensors based on undoped GaAs nanowire ensembles

Semiconducting piezoelectric materials have attracted considerable interest due to their central role in the emerging field of piezotronics, where the development of a piezo-potential in response to stress or strain can be used to tune the band structure of the semiconductor, and hence its electronic properties. This coupling between piezoelectricity and semiconducting properties can be readily exploited for force or pressure sensing using nanowires, where the geometry and unclamped nature of nanowires render them particularly sensitive to small forces. At the same time, piezoelectricity is known to manifest more strongly in nanowires of certain semiconductors. Here, we report the design and fabrication of highly sensitive piezotronic pressure sensors based on GaAs nanowire ensemble sandwiched between two electrodes in a back-to-back diode configuration. We analyse the current-voltage characteristics of these nanowire-based devices in response to mechanical loading in light of the corresponding changes to the device band structure. We observe a high piezotronic sensitivity to pressure, of ~7800 meV/MPa. We attribute this high sensitivity to the nanowires being fully depleted due to the lack of doping, as well as due to geometrical pressure focusing and current funneling through polar interfaces.

physics.app-ph↗

arXiv2016

Localized electromechanical interactions in ferroelectric P(VDF-TrFE) nanowires investigated by scanning probe microscopy

We investigate the electromechanical interactions in individual P(VDF-TrFE) nanowires in response to localized electrical poling via a conducting atomic force microscope tip. Spatially resolved measurements of piezoelectric coefficients and elastic moduli before and after poling reveal a striking dependence on the polarity of the poling field, notably absent in thin films of the same composition. These observations are attributed to the unclamped nature of the nanowires and the inherent asymmetry in their chemical and electrical interactions with the tip and underlying substrate. Our findings provide insights into the mechanism of poling/switching in polymer nanowires critical to ferroelectric device performance.

cond-mat.mtrl-sci↗

arXiv2014

On the diameter dependence of metal-nanowire Schottky barrier height

Bardeen's model for the non-ideal metal-semiconductor interface was applied to metal-wrapped cylindrical nanowire systems; a significant effect of the nanowire diameter on the non-ideal Schottky barrier height was found. The calculations were performed by solving Poisson's equation in the nanowire, self-consistently with the constraints set by the non-ideal interface conditions; in these calculations the barrier height is obtained from the solution, and it is not a boundary condition for Poisson's equation. The main finding is that thin nanowires are expected to have tens of meV higher Schottky barriers compared to their thicker counterparts. What lies behind this effect is the electrostatic properties of metal-wrapped nanowires; in particular, since depletion charge is reduced with nanowire radius, the potential drop on the interfacial layer, is reduced - leading to the increase of the barrier height with nanowire radius reduction.

cond-mat.mes-hall↗