Search results for "NANOWIRE"
showing 10 items of 382 documents
Optical phonon modes of wurtzite InP
2013
Optical vibration modes of InP nanowires in the wurtzite phase were investigated by Raman scattering spectroscopy. The wires were grown along the [0001] axis by the vapor-liquid-solid method. The A1(TO), E2h, and E1(TO) phonon modes of the wurtzite symmetry were identified by using light linearly polarized along different directions in backscattering configuration. Additionally, forbidden longitudinal optical modes have also been observed. Furthermore, by applying an extended 11-parameter rigid-ion model, the complete dispersion relations of InP in the wurtzite phase have been calculated, showing a good agreement with the Raman experimental data.
Current-driven periodic domain wall creation in ferromagnetic nanowires
2016
We predict the electrical generation and injection of domain walls into a ferromagnetic nano-wire without the need of an assisting magnetic field. Our analytical and numerical results show that above a critical current $j_{c}$ domain walls are injected into the nano-wire with a period $T \sim (j-j_{c})^{-1/2}$. Importantly, domain walls can be produced periodically even in a simple exchange ferromagnet with uniaxial anisotropy, without requiring any standard "twisting" interaction like Dzyaloshinskii-Moriya or dipole-dipole interactions. We show analytically that this process and the period exponents are universal and do not depend on the peculiarities of the microscopic Hamiltonian. Finall…
Nonlinear thermovoltage and thermocurrent in quantum dots
2013
Quantum dots are model systems for quantum thermoelectric behavior because of their ability to control and measure the effects of electron-energy filtering and quantum confinement on thermoelectric properties. Interestingly, nonlinear thermoelectric properties of such small systems can modify the efficiency of thermoelectric power conversion. Using quantum dots embedded in semiconductor nanowires, we measure thermovoltage and thermocurrent that are strongly nonlinear in the applied thermal bias. We show that most of the observed nonlinear effects can be understood in terms of a renormalization of the quantum-dot energy levels as a function of applied thermal bias and provide a theoretical m…
Quantum size effects in a one-dimensional semimetal
2006
We study theoretically the quantum size effects in a one-dimensional semimetal by a Boltzmann transport equation. We derive analytic expressions for the electrical conductivity, Hall coefficient, magnetoresistance, and the thermoelectric power in a nanowire. The transport coefficients of semimetal oscillate as the size of the sample shrinks. Below a certain size the semimetal evolves into a semiconductor. The semimetal-semiconductor transition is discussed quantitatively. The results should make a theoretical ground for better understanding of transport phenomena in low-dimensional semimetals. They can also provide useful information while studying low-dimensional semiconductors in general.
Role of B diffusion in the interfacial Dzyaloshinskii-Moriya interaction inTa/Co20Fe60B20/MgOnanowires
2015
We report on current-induced domain wall motion in $\mathrm{Ta}/\mathrm{C}{\mathrm{o}}_{20}\mathrm{F}{\mathrm{e}}_{60}{\mathrm{B}}_{20}/\mathrm{MgO}$ nanowires. Domain walls are observed to move against the electron flow when no magnetic field is applied, while a field along the nanowires strongly affects the domain wall motion velocity. A symmetric effect is observed for up-down and down-up domain walls. This indicates the presence of right-handed domain walls, due to a Dzyaloshinskii-Moriya interaction (DMI) with a DMI coefficient $D=+0.06\phantom{\rule{0.16em}{0ex}}\mathrm{mJ}/{\mathrm{m}}^{2}$. The positive DMI coefficient is interpreted to be a consequence of B diffusion into the Ta bu…
Correlation between spin structure oscillations and domain wall velocities (presentation video)
2014
Magnetic sensing and logic devices based on the motion of magnetic domain walls rely on the precise and deterministic control of the position and the velocity of individual magnetic domain walls. Varying domain wall velocities have been predicted to result from intrinsic effects such as oscillating domain wall spin structure transformations and extrinsic pinning due to imperfections. We use direct dynamic imaging of the nanoscale spin structure to directly check these predictions. We find a new regime of oscillating domain wall motion even below the Walker breakdown correlated with periodic spin structure changes and we show that the extrinsic pinning from defects in the nanowire only affec…
Quantification of Competing Magnetic States and Switching Pathways in Curved Nanowires by Direct Dynamic Imaging.
2020
For viable applications, spintronic devices based, for example, on domain wall motion need to be highly reliable with stable magnetization states and highly reproducible switching pathways transforming one state to another. The existence of multiple stable states and switching pathways in a system is a definitive barrier for device operation, yet rare and stochastic events are difficult to detect and understand. We demonstrate an approach to quantify competing magnetic states and stochastic switching pathways based on time-resolved scanning electron microscopy with polarization analysis, applied to the technologically relevant control of vortex domain wall chirality via field and curvature …
Topological Defects in Nanostructures—Chiral Domain Walls and Skyrmions
2016
In this chapter, spin structures with particular topologies in confined geometries are presented. Domain walls in nanowires exhibit a spin structure that depends on the material and geometry while in discs Skyrmions can be stabilized by different competing interactions. The topologies of these spin structures can be characterized by a Skyrmion or Winding number that governs the dynamics and stability.
Nanoscale X-ray detectors based on individual CdS, SnO2 and ZnO nanowires
2021
Abstract The development of nanoscale X-ray sensors is of crucial importance to achieve higher spatial resolution in many X-ray-based techniques playing a key role in materials science, healthcare, and security. Here, we demonstrate X-ray detection using individual CdS, SnO 2 , and ZnO nanowires (NWs). The NWs were produced via vapor–liquid–solid technique and characterized using X-ray diffraction, scanning, and transmission electron microscopy . Electrical measurements were performed under ambient conditions while exposing two-terminal NW-based devices to X-rays generated by a conventional tungsten anode X-ray tube. Fast and stable nanoampere-range X-ray beam induced current (XBIC) in resp…
Exciton Gas Compression and Metallic Condensation in a Single Semiconductor Quantum Wire
2008
4 páginas, 5 figuras.-- PACS numbers: 78.67.Lt, 71.30.+h, 71.35. -y.-- Comunicación presentada a la International Conference on the Physics of Semiconductors (ICPS) celebrada en Rio de Jqaneiro (Brasil/2008).