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The use of electric fields for edible coatings and films development and production : a review

Souza, B. W. S.; Cerqueira, M. A.; Teixeira, J. A.; Vicente, A. A.
Fonte: Springer Science ; Business Media, LLC Publicador: Springer Science ; Business Media, LLC
Tipo: Artigo de Revista Científica
Publicado em //2010 Português
Relevância na Pesquisa
581.13215%
Edible films and coatings can provide additional protection for food, while being a fully biodegradable, environmentally friendly packaging system. A diversity of raw materials used to produce edible coatings and films are extracted from marine and agricultural sources, including animals and plants. Electric fields processing holds advantage in producing safe, wholesome and nutritious food. Recently, the presence of a moderate electric field during the preparation of edible coatings and films was shown to influence their main properties, demonstrating its usefulness to tailor edible films and coatings for specific applications. This manuscript reviews the main aspects of the use of electric fields in the production of edible films and coatings, including the effect in their transport and mechanical properties, solubility and microstructure.; Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES), Brasil.; Fundação para a Ciência e a Tecnologia (FCT), Portugal.

Association of riboflavin in whey protein hydrogels produced through application of moderate electric field and cold induced gelation

Pereira, Ricardo; Altinok, Emir; Rodrigues, Rui M.; Ramos, Óscar L.; Malcata, F. X.; Ferrari, Giovanna; Teixeira, J. A.; Vicente, A. A.
Fonte: Universidade do Minho Publicador: Universidade do Minho
Tipo: Conferência ou Objeto de Conferência
Publicado em 15/10/2014 Português
Relevância na Pesquisa
895.02914%
Protein hydrogels are one of the most convenient and widely used matrix in food applications. Recently, cold gelation ability of whey protein isolate (WPI) is taking interest in protection and delivery of value-added bioactive compounds through micro and nano-association techniques. This study aims to combine an electro-heating treatment at moderate electric fields (MEF) together with cold gelation ability of whey proteins in order to reduce size of protein aggregates at nano-scale and improve association efficiency of riboflavin. Divalent iron cation assisted cold gelation of electro-heated WPI and effects of MEF on the produced hydrogels were reported and encouraged during this experimental research. Particle size was characterized, through dynamic light scattering. While spectrofluorimetric analyses were performed in order to examine the effects of MEF and cold induced gelation on the association of riboflavin within WPI hydrogel network structure. Under MEF application smaller sized particles were produced and riboflavin association efficiencies ranged from 40 to 60%. Results also show that MEF treatment allowed producing WPI nano-hydrogels with associated riboflavin less susceptible to light oxidation. This novel approach that combines electro-heating treatment together with cold gelation can be used to design and develop entirely biodegradable whey protein-based gels as potential devices for controlled release of riboflavin. MEF can be used to improve or create novel applications not only in food and bioprocessing industries...

Influence of moderate electric fields on gelation of whey protein isolate

Rodrigues, Rui M.; Martins, Artur J.; Ramos, Óscar L.; Malcata, F. X.; Teixeira, J. A.; Vicente, A. A.; Pereira, Ricardo
Fonte: Elsevier BV Publicador: Elsevier BV
Tipo: Artigo de Revista Científica
Publicado em //2015 Português
Relevância na Pesquisa
895.02914%
Proteins are one of the food constituents most affected by heating, and some of the changes involve their unfolding, denaturation and gelation. Ohmic heating has often been claimed to improve the quality of foodstuffs due to its uniform heating and (putative) presence of a moderate electric field (MEF). However, this is still subject to discussion, so it is important to determine the effect of ohmic heating and of its MEF upon food constituents. Hence, the aim of this work was to evaluate the effects of MEF on denaturation, aggregation and viscoelastic properties of whey protein isolate (WPI), and compare them with those obtained via conventional heating under identical treatment conditions (up to 30 min at 85 °C). Results have shown that MEF interferes with whey protein unfolding and aggregation pathways at relatively high temperatures. MEF treatments have resulted in WPI solutions possessing more 8 and 10% of native β-Lactoglobulin and α-Lactalbumin, respectively, after 30 s of heating at 85 °C, when compared with a conventional heating method. Protein aggregates from MEF-treated WPI solutions presented a maximum increase in size of 78 nm, whereas conventional heating produced an increase of 86 nm. Unlike in conventional heating...

Production of whey protein cold-set hydrogels through application of moderate electric fields

Rodrigues, Rui M.; Ramos, Óscar L.; Teixeira, J. A.; Vicente, A. A.; Pereira, Ricardo
Fonte: Sociedade Portuguesa de Química Publicador: Sociedade Portuguesa de Química
Tipo: Conferência ou Objeto de Conferência
Publicado em //2014 Português
Relevância na Pesquisa
487.94457%
ISBN 978-989-98541-5-4; Whey, a liquid by-product from dairy industry is now recognized as a functional food due to the presence of bioactive and highly nutritional components, such as globular whey proteins. Denaturation and aggregation kinetic behavior of these proteins is of particular relevance when properly engineered and controlled, as it results in the production of novel micro and nano-systems with many potential uses in food compositions. Application of moderate electric fields (MEF) during heating process at relatively high temperatures has the potential to interfere with the secondary structure of globular whey proteins networks [1], eventually forming gels. However, the heat needed to produce these gels limits their application to formulations that do not contain heat-sensitive compounds [2]. The objective of this study is producing cold-set hydrogels from purified β-lactoglobulin and whey ingredients through combined application thermal and MEF treatment and salt induced gelation. Protein dispersions (3 % w/v and pH=3) were heated with and without presence of MEF treatments (0, 3 and 10 V/cm) at temperatures of 90 °C. Cold gelation was then induced through addition of different quantities of FeSO4 at 24 ºC. Nano-scale aggregation phenomena during the initial steps of whey protein aggregation as affected by the thermal treatment and applied electric field were assessed by dynamic light scattering (DLS). Rheological measurements were performed using a controlled stress rheometer with concentric cylinder geometry in order to assess the effects of MEF on macroscopic properties of the WPI hydrogels produced. Results shows that the extent of protein aggregation decreased both with the purity of the whey product used and the increase of the intensity of the applied MEF treatment. MEF treatments at 10 V/cm applied on whey protein isolate originated average mean particle sizes at nano-scale range...

Effect of moderate electric field in the physical and transport properties of chitosan coatings

Souza, B. W. S.; Cerqueira, M. A.; Casariego, A.; Martins, Joana; Teixeira, J. A.; Vicente, A. A.
Fonte: Universidade do Minho Publicador: Universidade do Minho
Tipo: Conferência ou Objeto de Conferência
Publicado em 22/10/2009 Português
Relevância na Pesquisa
806.0595%
Edible films and coatings can provide additional protection for food, while being a fully biodegradable, environmentally friendly packaging system. Preliminary works have shown that the presence of a moderate electric field during the preparation of chitosan coating solutions may influence e.g. their transport properties. The aim of this work was to determine the effect of field strength on functional properties of chitosan coatings (obtained from lobster of the Cuban coasts). Four different field strengths (50,100,150, 200 V·cm-1) were applied during the preparation of the film forming solution, films were cast and, for each electric treatment, the water vapor, O2 and CO2 permeabilities of the films were determined, together with their solubility in water. The films were also analysed using scanning electron microscopy (SEM) and X-ray diffractometry (XRD).The results showed that the electric field has statistically significant effects on films transport properties (which e.g. for water vapour permeability, varied from 0.3228 to 0.2667(g.(m.day.atm)-1)) and structure, a positive correlation having been found between the water vapor, O2 and CO2 permeability coefficients and the applied field strength. XRD indicated that when electrically treated...

Effects of moderate electric fields on aggregation of whey protein solutions and properties of edible films made thereof

Pereira, Ricardo; Souza, B. W. S.; Cerqueira, M. A.; Teixeira, J. A.; Vicente, A. A.
Fonte: Universidade do Minho Publicador: Universidade do Minho
Tipo: Conferência ou Objeto de Conferência
Publicado em 20/07/2010 Português
Relevância na Pesquisa
497.39043%
Thermal processing may result in disruption of the native conformation of whey proteins, thus affecting their structure and functional properties. The aim of this work was to evaluate the effects of moderate electric fields on thermal aggregation of whey proteins and its subsequent effects on properties of edible films made from ohmic heated whey protein film forming solutions. Thermal aggregation of whey protein isolate was studied at 85 ºC up to 30 min through ohmic heating, under the presence of moderate electric fields ranging from 4 to 20 V/cm; these treatments were compared with conventional heating under identical temperature profiles. Unfolding and exposure of sulphydryls initially buried inside the macromolecules was measured through reactivity of free thiol groups. Results show that whey protein aggregation (measured by dynamic light scattering in terms of aggregate size) was found to decrease with the increase of electric field applied during ohmic heating; a maximum increase in whey protein aggregation of 45 nm was observed for treatments at 18 V/cm, while treatments at 4 V/cm and 0 V/cm (conventional heating) produced a maximum increase of 70 nm and 75 nm, respectively. Furthermore, ohmic heating led to lower reactivity of free sulphydryls when compared with conventional heating. Edible films prepared from ohmic heated film forming solutions present a decrease of about 10 %...

Phagocytic clearance of electric field induced ‘apoptosis-mimetic’ cells

Tekle, E.; Wolfe, M.D; Oubrahim, H.; Chock, P.B
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
582.5908%
Cells undergoing apoptosis lose lipid asymmetry that is often manifested by the exposure of phosphatidylserine (PS) to the outer surface of the cell membrane. Macrophages and other cell types recognize externalized PS to signal phagocytosis, thereby eliciting a non-inflammatory response. PS exposure is obligatory in the recognition and clearance of apoptotic cells. Here, we find that externally applied moderate electric field induces PS externalization in a mouse B cell (FOX-NY) membrane without procaspase-3 activation, a major characteristic of apoptotic cells. The field induced PS inversion is caused as a result of electroporation and/or a process involving membrane reorganizations and recovery that ensues following field exposure. Using a mouse macrophage cell line (J7444A.1) from the same strain, we show phagocytic clearance of PS expressing B cells and demonstrate that this is in part due to the apoptosis mimicry of the field exposed cells.

Compression and self-entanglement of single DNA molecules under uniform electric field

Tang, Jing; Du, Ning; Doyle, Patrick S.
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
592.31234%
We experimentally study the effects of a uniform electric field on the conformation of single DNA molecules. We demonstrate that a moderate electric field (∼200 V/cm) strongly compresses isolated DNA polymer coils into isotropic globules. Insight into the nature of these compressed states is gained by following the expansion of the molecules back to equilibrium after halting the electric field. We observe two distinct types of expansion modes: a continuous molecular expansion analogous to a compressed spring expanding, and a much slower expansion characterized by two long-lived metastable states. Fluorescence microscopy and stretching experiments reveal that the metastable states are the result of intramolecular self-entanglements induced by the electric field. These results have broad importance in DNA separations and single molecule genomics, polymer rheology, and DNA-based nanofabrication.

Comparative analysis of electric field influence on the quantum wells with different boundary conditions: II. Thermodynamic properties

Olendski, Oleg
Fonte: BlackWell Publishing Ltd Publicador: BlackWell Publishing Ltd
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
490.31816%
Thermodynamic properties of the one-dimensional (1D) quantum well (QW) with miscellaneous permutations of the Dirichlet (D) and Neumann (N) boundary conditions (BCs) at its edges in the perpendicular to the surfaces electric field are calculated. For the canonical ensemble, analytical expressions involving theta functions are found for the mean energy and heat capacity for the box with no applied voltage. Pronounced maximum accompanied by the adjacent minimum of the specific heat dependence on the temperature T for the pure Neumann QW and their absence for other BCs are predicted and explained by the structure of the corresponding energy spectrum. Applied field leads to the increase of the heat capacity and formation of the new or modification of the existing extrema what is qualitatively described by the influence of the associated electric potential. A remarkable feature of the Fermi grand canonical ensemble is, at any BC combination in zero fields, a salient maximum of observed on the T axis for one particle and its absence for any other number N of corpuscles. Qualitative and quantitative explanation of this phenomenon employs the analysis of the chemical potential and its temperature dependence for different N. It is proved that critical temperature of the Bose-Einstein (BE) condensation increases with the applied voltage for any number of particles and for any BC permutation except the ND case at small intensities what is explained again by the modification by the field of the interrelated energies. It is shown that even for the temperatures smaller than the total dipole moment may become negative for the quite moderate . For either Fermi or BE system...

Effect of moderate electric fields in the permeation properties of chitosan coatings

Souza, B. W. S.; Cerqueira, M. A.; Casariego, A.; Lima, A. M. P.; Teixeira, J. A.; Vicente, A. A.
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
Publicado em /12/2009 Português
Relevância na Pesquisa
811.5106%
Edible films and coatings can provide additional protection for food, while being a fully biodegradable, environmentally friendly packaging system. Preliminary works have shown that the presence of a moderate electric field during the preparation of chitosan coating solutions may influence e.g. their transport properties. If such effect is confirmed, moderate electric fields could be used to tailor edible films and coatings for specific applications. The aim of this work was to determine the effect of field strength on functional properties of chitosan coatings (obtained from lobster from the Cuban coasts). Four different field strengths were tested (50, 100, 150, 200 V cm−1) and, for each electric field treatment, the water vapor, oxygen and carbon dioxide permeabilities of the films formed were determined, together with their color, opacity and solubility in water. The surface microstructure of the films was analyzed using atomic force microscopy (AFM). The results showed that ohmic heating had statistically significant effects on film's physical properties and structure. In general, the most pronounced effect of the field strength was observed for treatments made at 100 V cm−1 or higher, a positive correlation being found between the water vapor...

Reversible Control of Magnetic Interactions by Electric Field in a Single Phase Material

Ryan, P. J.; Kim, J. -W.; Birol, T.; Thompson, P.; Lee, J. -H.; Ke, X.; Normile, P. S.; Karapetrova, E.; Schiffer, P.; Brown, S. D.; Fennie, C. J.; Schlom, D. G.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 22/06/2012 Português
Relevância na Pesquisa
490.31816%
Intrinsic magnetoelectric coupling describes the interaction between magnetic and electric polarization through an inherent microscopic mechanism in a single phase material. This phenomenon has the potential to control the magnetic state of a material with an electric field, an enticing prospect for device engineering. We demonstrate 'giant' magnetoelectric cross-field control in a single phase rare earth titanate film. In bulk form, EuTiO3 is antiferromagnetic. However, both anti and ferromagnetic interactions coexist between different nearest neighbor europium ions. In thin epitaxial films, strain can be used to alter the relative strength of the magnetic exchange constants. Here, we not only show that moderate biaxial compression precipitates local magnetic competition, but also demonstrate that the application of an electric field at this strain state, switches the magnetic ground state. Using first principles density functional theory, we resolve the underlying microscopic mechanism resulting in the EuTiO3 G-type magnetic structure and illustrate how it is responsible for the 'giant' cross-field magnetoelectric effect.

Spin-dependent phenomena in semiconductors in strong electric fields

Golub, L. E.; Ivchenko, E. L.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 24/05/2013 Português
Relevância na Pesquisa
486.19188%
We develop a theory of spin-dependent phenomena in the streaming regime characterized by ballistic acceleration of electrons in the moderate electric field until they achieve the optical phonon energy and abruptly emit the phonons. It is shown that the Dyakonov-Perel spin relaxation is drastically modified in this regime, the current-induced spin orientation remarkably increases, reaches a high value ~2% in the electric field ~1kV/cm and falls with the further increase in the field. The spin polarization enhancement is caused by squeezing of the electron momentum distribution in the direction of drift. We also predict field-induced oscillatory dynamics of spin polarization of the photocarriers excited into the conduction band by a short circularly-polarized optical pulse.; Comment: 15 pages, 3 figures, submitted to the focus issue of New J. Phys. on "The Rashba effect"

Multivalley spin relaxation in $n$-type bulk GaAs in the presence of high electric fields

Tong, H.; Wu, M. W.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 22/11/2011 Português
Relevância na Pesquisa
496.34133%
Multivalley spin relaxation in $n$-type bulk GaAs in the presence of high electric field is investigated from the microscopic kinetic spin Bloch equation approach with the $\Gamma$ and $L$ valleys included. We show that the spin relaxation time decreases monotonically with the electric field, which differs from the two-dimensional case and is recognized due to to the cubic form of the Dresselhauss spin-orbit coupling of the $\Gamma$ valley in bulk. In addition to the direct modulation of the spin relaxation time, the electric field also strongly influences the density and temperature dependences of the spin relaxation. In contrast to the monotonic decrease with increasing lattice temperature in the field-free condition, the spin relaxation time is shown to decrease more slowly under the influence of the electric field and even to increase monotonically in the case with small electron density and high electric field. We even predict a peak in weakly doped samples under moderate electric field due to the anomalous lattice-temperature dependence of the hot-electron temperature. As for the $L$ valleys, we show that instead of playing the role of a "drain" of the total spin polarization as in quantum well systems, in bulk they serve as a "momentum damping area"...

Comparative analysis of electric field influence on the quantum wells with different boundary conditions. II. Thermodynamic properties

Olendski, O.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
490.31816%
Thermodynamic properties of the one-dimensional (1D) quantum well (QW) with miscellaneous permutations of the Dirichlet (D) and Neumann (N) boundary conditions (BCs) at its edges in the perpendicular to the surfaces electric field $\mathscr{E}$ are calculated. For the canonical ensemble, analytical expressions involving theta functions are found for the mean energy and heat capacity $c_V$ for the box with no applied voltage. Pronounced maximum accompanied by the adjacent minimum of the specific heat dependence on the temperature $T$ for the pure Neumann QW and their absence for other BCs are predicted and explained by the structure of the corresponding energy spectrum. Applied field leads to the increase of the heat capacity and formation of the new or modification of the existing extrema what is qualitatively described by the influence of the associated electric potential. A remarkable feature of the Fermi grand canonical ensemble is, at any BC combination in zero fields, a salient maximum of $c_V$ observed on the $T$ axis for one particle and its absence for any other number $N$ of corpuscles. Qualitative and quantitative explanation of this phenomenon employs the analysis of the chemical potential and its temperature dependence for different $N$. It is proved that critical temperature $T_{cr}$ of the Bose-Einstein (BE) condensation increases with the applied voltage for any number of particles and for any BC permutation except the ND case at small intensities $\mathscr{E}$ what is explained again by the modification by the field of the interrelated energies. It is shown that even for the temperatures smaller than $T_{cr}$ the total dipole moment $\langle P\rangle$ may become negative for the quite moderate $\mathscr{E}$. For either Fermi or BE system...

Ab initio molecular dynamics study of dissociation of water under an electric field

Saitta, A. Marco; Saija, Franz; Giaquinta, Paolo V.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 05/04/2012 Português
Relevância na Pesquisa
489.13566%
The behavior of liquid water under an electric field is a crucial phenomenon in science and engineering. However, its detailed description at a microscopic level is difficult to achieve experimentally. Here we report on the first ab initio molecular-dynamics study on water under an electric field. We observe that the hydrogen-bond length and the molecular orientation are significantly modified at low-to-moderate field intensities. Fields beyond a threshold of about 0.35 V/\AA are able to dissociate molecules and sustain an ionic current via a series of correlated proton jumps. Upon applying even more intense fields (1.0 V/\AA), a 15-20% fraction of molecules are instantaneously dissociated and the resulting ionic flow yields a conductance of about 7.8 $\Omega^{-1}cm^{-1}$, in good agreement with experimental values. This result paves the way to quantum-accurate microscopic studies of the effect of electric fields on aqueous solutions and, thus, to massive applications of ab initio molecular dynamics in neurobiology, electrochemistry and hydrogen economy.; Comment: 5 pages, 4 figures. Supplementary material available upon request. To be published in Phys. Rev. Lett. http://prl.aps.org/accepted/

Nonequilibrium dynamics of the Holstein polaron driven by external electric field

Vidmar, Lev; Bonca, Janez; Mierzejewski, Marcin; Prelovsek, Peter; Trugman, Stuart A.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
495.6956%
This work represents a fundamental study of a Holstein polaron in one dimension driven away from the ground state by a constant electric field. Taking fully into account quantum effects we follow the time-evolution of the system from its ground state as the constant electric field is switched on at t = 0, until it reaches a steady state. At weak electron phonon coupling (EP) the system experiences damped Bloch oscillations (BO) characteristic for noninteracting electron band. An analytic expression of the steady state current is proposed in terms of weak EP coupling and large electric field. For moderate values of EP coupling the oscillations are almost critically damped and the system reaches the steady state after a short time. In the strong coupling limit weakly damped BO, consistent with nearly adiabatic evolution within the polaron band, persist up to extremely large electric fields. A traveling polaron under the influence of the electric field leaves behind a trail of phonon excitations absorbing the excess energy gained from the electric field. The shape of the traveling polaron is investigated in details.

Electric field induced narrowing of exciton line width

Ponomarev, I. V.; Deych, L. I.; Lisyansky, A. A.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
491.81797%
Considering effects of electric field on the low temperature absorption line of quantum well excitons, we show that, for moderate strength of the electric field, the main contribution to the field dependence of the line-width results from field induced modifications of inhomogeneous broadening of excitons. We find that the strength of the random potential acting on quantum well excitons due to alloy disorder and interface roughness can either decrease or increase with field depending upon the thickness of the well. This means that under certain conditions one can observe counterintuitive narrowing of exciton spectral lines in electric field.; Comment: RevTeX4, 4 pages, 1 figure; submitted to Phys. Rev. Lett

Saturated Sodium Chloride Solution under an External Static Electric Field: a Molecular Dynamics Study

Ren, Gan; Wang, Yanting
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 02/05/2015 Português
Relevância na Pesquisa
484.44625%
The behavior of saturated aqueous sodium chloride solutions under a constant external electric field (E) was studied by molecular dynamics (MD) simulation. Our dynamic MD simulations have indicated that the irreversible nucleation process towards crystallization is accelerated by a moderate E, but retarded or even prohibited under a stronger E, which can be understood by the competition between self-diffusion and drift motion. The former increases with E resulting in the acceleration of the nucleation process, and the latter tears oppositely charged ions more apart under a stronger E leading to the deceleration of nucleation. Moreover, our steady-state MD simulations have indicated that a first-order phase transition happens in saturated solutions only when the applied E is below a certain threshold Ec, and the ratio of crystallized ions does not change with the electric field. The magnitude of Ec increases with concentration, because larger clusters are easy to form in a more concentrated solution and require a stronger E to dissociate them.; Comment: 19 pages, 4 tables, 10 figures, and 41 references

Spin diffusion and injection in semiconductor structures: Electric field effects

Yu, Z. G.; Flatte, M. E.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 17/06/2002 Português
Relevância na Pesquisa
493.16637%
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...

Effect of giant electric fields on the optical properties of GaN quantum wells

González de la Cruz,G; Herrera,H; Calderón Arenas,A
Fonte: Sociedad Mexicana de Física Publicador: Sociedad Mexicana de Física
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/08/2007 Português
Relevância na Pesquisa
584.5534%
Spontaneous and piezoelectric fields are known to be the key to understanding the optical properties of nitride heterostructures. This effect modifies the electronic states in the quantum well (QW) and the emission energy in the photoluminescence (PL) spectrum. These fields induce a reduction in the oscillator strength of the transition energy between the confined electron and hole states in GaN/Al xGa1-xN QWs, and dramatically increase the carrier lifetime as the QW thickness increases. In this work, we solve analytically the Schrodinger equation for moderate electric fields when the electron-hole transition energy in the QW is larger than the energy gap of the GaN. Furthermore, the large redshifts of the PL energy position and the spatial separation of the electrons and holes several greater times than the Bohr radius caused by the strong piezoelectric fields are explained using a triangular potential, instead of a square one, in the Schrodinger equation. The transition energy calculations between the electron-hole pair as a function of the well width with the electric field as a fitting parameter are in agreement with the measured photoluminescence energy peaks.