19 research outputs found
Electrical Spin Injection in a Ferromagnetic / Tunnel Barrier/ Semiconductor Heterostructure
We demonstrate experimentally the electrical ballistic electron spin
injection from a ferromagnetic metal / tunnel barrier contact into a
semiconductor III-V heterostructure. We introduce the Oblique Hanle Effect
technique for reliable optical measurement of the degree of injected spin
polarization. In a CoFe / Al2O3 / GaAs / (Al,Ga)As heterostructure we observed
injected spin polarization in excess of 8 % at 80K.Comment: 5 pages, 4 figure
Highly efficient room temperature spin injection in a metal-insulator-semiconductor light emitting diode
We demonstrate highly efficient spin injection at low and room temperature in
an AlGaAs/GaAs semiconductor heterostructure from a CoFe/AlOx tunnel spin
injector. We use a double-step oxide deposition for the fabrication of a
pinhole-free AlOx tunnel barrier. The measurements of the circular polarization
of the electroluminescence in the Oblique Hanle Effect geometry reveal injected
spin polarizations of at least 24% at 80K and 12% at room temperature
An innovative and viable routre for the realization of ultra-thin supercapacitor electrodes assembled with carbon nanotubes
Electrochemical Double Layer Capacitors (EDLC), also known as supercapacitors, have been fabricated
using Single Walled Carbon Nanotubes (SWCNTs) as active material for electrode assembling.
In particular a new way of fabrication of ultra-thin electrodes (â€25 m) directly formed on the
separator has been proposed, and a prototype of EDLC has been realized and tested. For such
devices the specific capacitance is in the range 40â45 F/g and the internal resistances in the range
6â8 ·cm2, at current density of 2 mA·cmâ2.
Keywords: Carbon Nanotube, Supercapacito
Spin diffusion and injection in semiconductor structures: Electric field effects
In semiconductor spintronic devices, the semiconductor is usually lightly
doped and nondegenerate, and moderate electric fields can dominate the carrier
motion. We recently derived a drift-diffusion equation for spin polarization in
the semiconductors by consistently taking into account electric-field effects
and nondegenerate electron statistics and identified a high-field diffusive
regime which has no analogue in metals. Here spin injection from a ferromagnet
(FM) into a nonmagnetic semiconductor (NS) is extensively studied by applying
this spin drift-diffusion equation to several typical injection structures such
as FM/NS, FM/NS/FM, and FM/NS/NS structures. We find that in the high-field
regime spin injection from a ferromagnet into a semiconductor is enhanced by
several orders of magnitude. For injection structures with interfacial
barriers, the electric field further enhances spin injection considerably. In
FM/NS/FM structures high electric fields destroy the symmetry between the two
magnets at low fields, where both magnets are equally important for spin
injection, and spin injection becomes locally determined by the magnet from
which carriers flow into the semiconductor. The field-induced spin injection
enhancement should also be insensitive to the presence of a highly doped
nonmagnetic semiconductor (NS) at the FM interface, thus FM/NS/NS
structures should also manifest efficient spin injection at high fields.
Furthermore, high fields substantially reduce the magnetoresistance observable
in a recent experiment on spin injection from magnetic semiconductors
Spin injection into a ballistic semiconductor microstructure
A theory of spin injection across a ballistic
ferromagnet-semiconductor-ferromagnet junction is developed for the Boltzmann
regime. Spin injection coefficient is suppressed by the Sharvin
resistance of the semiconductor , where is the
Fermi-surface cross-section. It competes with the diffusion resistances of the
ferromagnets , and in the absence of contact
barriers. Efficient spin injection can be ensured by contact barriers. Explicit
formulae for the junction resistance and the spin-valve effect are presented.Comment: 5 pages, 2 column REVTeX. Explicit prescription relating the results
of the ballistic and diffusive theories of spin injection is added. To this
end, some notations are changed. Three references added, typos correcte
Spintronics: Fundamentals and applications
Spintronics, or spin electronics, involves the study of active control and
manipulation of spin degrees of freedom in solid-state systems. This article
reviews the current status of this subject, including both recent advances and
well-established results. The primary focus is on the basic physical principles
underlying the generation of carrier spin polarization, spin dynamics, and
spin-polarized transport in semiconductors and metals. Spin transport differs
from charge transport in that spin is a nonconserved quantity in solids due to
spin-orbit and hyperfine coupling. The authors discuss in detail spin
decoherence mechanisms in metals and semiconductors. Various theories of spin
injection and spin-polarized transport are applied to hybrid structures
relevant to spin-based devices and fundamental studies of materials properties.
Experimental work is reviewed with the emphasis on projected applications, in
which external electric and magnetic fields and illumination by light will be
used to control spin and charge dynamics to create new functionalities not
feasible or ineffective with conventional electronics.Comment: invited review, 36 figures, 900+ references; minor stylistic changes
from the published versio
Nanocomposite Si/diamond layers: room temperature visible-light emitting systems
Visible-light emitting nanocomposite Si/diamond polycrystalline layers, produced by means of a hybrid CVD/powder-flowing technique, have been investigated by atomic force microscopy (AFM),reflection high energy electron diffraction (RHEED), Raman spectroscopy, photoluminescence(PL), and electron spin resonance (ESR). The room temperature emission of the layers at 1.7 eV and 2.0-2.4 eV is dominated by the optical properties of the inserted Si nanoparticles (mean diameter 3.3 +/- 0.5 nm). The density of the ESR active centers is N = (4 +/- 2) x 10(19) cm(-3) with g = 2.0025 (T = 300 K). A study of the temperature-dependent changes in the nature and localization of paramagnetic centers has been carried out by comparing the ESR signals taken at 300 K, 30 K, and 4.2 K. The ESR results suggest that the active centers originate from the dangling bonds induced in sp(3)-coordinated C atoms by insertion of the Si nanoparticles. The g-factor anisotropy, detected at 4.2 K, is consistent with the peculiarities of dipole-dipole interactions in structures with low dimensionality
Electron spin resonance study of poly(ortho-anisidine)/single-walled carbon nanotube composite films: spin dynamics and effects of physisorption processes
Poly(ortho-anisidine) (POA)/single-walled carbon nanotubes (SWCNTs) composite films have
been prepared by means of oxidative potentiostatic electropolymerization of the monomer
(ortho-anisidine) in the presence of purified SWCNTs. The magnetic properties of the obtained
films have been investigated by electron spin resonance (ESR) (Μ
âŒ=
9.4GHz; temperature range
10â300K) and compared with those of pure POA films in the same oxidation state. The similarity
of the ESR signals and the dependence on temperature of the ESR line features suggest
a polaron origin of the paramagnetic states. A strong increase of the ESR integral intensity has
been detected for composite samples kept for 72 h in hydrogen atmosphere at room temperature.
Under the same conditions, a less pronounced increase in the intensity has been detected
in the case of pure polymer films. The kinetics of the hydrogen adsorptionâdesorption processes
in the nanocomposite samples has been investigated and interpreted in the frame of
an H-physisorption mechanism. The comparison between the H-induced effects in POA and
nanocomposite POA/SWCNTs films has been carried out taking into account the structure of
the samples and the presence of defects
Superparamagnetic resonance of Ni nanoparticles in single-walled carbon nanotubes systems
The paper has been also selected for the publication on Virtual J on Nanoscale Science and Technology (2007) vol 15