Charge Relaxation Dynamics Research Articles

Investigation of Sr doping effect on oxygen ion de-localization in Gd2Ti2O7 pyrochlore system and its influence on charge relaxation dynamics and ionic conductivity: as electrolyte for IT-SOFCs

Investigation of Sr doping effect on oxygen ion de-localization in Gd2Ti2O7 pyrochlore system and its influence on charge relaxation dynamics and ionic conductivity: as electrolyte for IT-SOFCs

Structural and electrical study of novel Ba3SrNb2O9 triple perovskite based solid electrolyte for LT-SOFCs

Solid Electrolytes (SOE) with high ionic conductivity highly desirable in order to improve the efficiency of SOFCs at lower functioning temperature range) (350–500 °C). Triple perovskite Ba3SrNb2O9 based proton ion conductor have up-and-coming to enhance ionic conductivity at Low temperature range (LT) (350–500 °C). With this motivation we have successfully synthesized Ba3SrNb2O9 (BSNO) by solgel combustion method. Powder X-ray diffraction (XRD) confirms the formation of Triclinic crystal structure having space group P1, having lattice dimensions (a = 5.89340 Å, b = 5.88760 Å, c = 7.27360 Å). Rietveld Refinement of XRD data was carried out to get detail structural information by Full-Prof suite software. Electrical performance of the BSNO system were systematically studied by Electrochemical Impedance spectroscopy at functioning temperature 350–500 °C with interval of 50 °C. BSNO system exhibit conductivity of the order of 5.8 × 10−3 Scm−1 at 500 °C with the activation energy of the range of 0.48 eV. Charge Relaxations phenomenon very systematically explored by impedance loss spectra and it is very correlate with Modulus (M’’) as a function of frequency at several temperatures which used to clarify the charge relaxation dynamics in proton ion conducting BSNO material.

Impurity level substitution of Cr and Ni in CaBaCo4O7 – a dielectric study

The fascinating physical characteristics of the 114-cobaltate, CaBaCo4O7, like alternate stacking of two-dimensional layers of CoO4 tetrahedra in triangular and kagomé patterns, geometrical frustration, and magnetoelectric coupling have attracted several studies in the magneto-structural and dielectric sectors. But the study of electrical conduction dynamics remains practically unknown. Here we have presented dc conduction studies and ac dielectric spectroscopy intending to understand the charge conduction and charge carrier relaxation dynamics of CaBaCo4O7, along with two chemically substituted derivatives – CaBaCo3.96Cr0.04O7 and CaBaCo3.96Ni0.04O7, of impurity level (1%) substitutions. We observe that dc conduction at low temperatures is mediated by variable range polaron hopping, while the ac conduction study points out small-polaron-tunneling across strongly localized states. Electric modulus obeys the Havriliak-Negami equation, with parameters α and γ significantly less than unity, indicating strong distribution in relaxation times; and its non-exponential nature, pointing out the cooperative motion of charge carriers. Imaginary electric modulus is not scaled to a single master curve for the three samples, signifying differences in charge relaxation dynamics.

Separation and Quantum Tunneling of Photo-generated Carriers Using a Tribo-Induced Field

Tribo-induced potential at a metal-insulator-semiconductor sliding junction results in very high interfacial electric field E (∼107–108 V/m). Such fields are used to separate photo-generated electron-hole pairs that transport through the junction via quantum tunneling. We show that this phenomenon can generate direct current with high current density J. The strong synergetic effect between the photo-excitation and the interfacial electronic excitation at the MIS sliding contact boosts the photocurrent output in Si-based Schottky solar cell by ∼50 times and the triboelectric power output by ∼28 times. Charge relaxation dynamics calculations agree well with conductive atomic force microscopy results and show the coupling effect between the photo- and the tribo-induced electric fields. Experimental observation of the tribo-photovoltaic effect provides new fundamental understanding of electromechanical coupling, and thus offers a new direction for future solar-mechanical energy co-harvesting.

Resonance-Frequency Modulation for Rapid, Point-of-Care Ebola-Glycoprotein Diagnosis with a Graphene-Based Field-Effect Biotransistor

Recent outbreaks of Ebola-virus infections in several countries demand a rapid point-of-care (POC) detection strategy. Here we report an innovative pathway founded on electronic-resonance-frequency modulation to detect Ebola glycoprotein (GP), on the basis of a carrier-injection-trapping-release-transfer mechanism and the standard antibody-antigen interaction principle within a dielectric-gated reduced graphene oxide (rGO) field-effect transistor (GFET). The sensitivity of Ebola detection can be significantly enhanced by monitoring the device’s electronic-resonance frequency, such as its inflection frequency, where the phase angle reaches a maximum. In addition to an excellent selectivity, a sensitivity of ~36-160 % and ~17-40 % for 0.001-3.401 mg/L Ebola GP can be achieved at high and low inflection resonance frequencies, respectively, which are several orders of magnitude higher than those from other electronic parameters (e.g., resistance-based sensitivity). Using equivalent circuit modeling for contributions from channel and contact, analytical equations for resonance shifts have been generalized. When matching with the incoming ac-measurement signal, electronic resonance from the phase-angle spectrum evolves from various relaxation processes (e.g., trap and release of injected charges at surface-trap sites of the channel-gate oxide and channel-source or drain interfaces) that are associated with a characteristic emission frequency. Using charge relaxation dynamics, a high-performance bio-FET sensing platform for healthcare is realized through resonance shifting. Figure 1

Resonance-Frequency Modulation for Rapid, Point-of-Care Ebola-Glycoprotein Diagnosis with a Graphene-Based Field-Effect Biotransistor.

Recent outbreaks of Ebola-virus infections in several countries demand a rapid point-of-care (POC)-detection strategy. This paper reports on an innovative pathway founded on electronic-resonance-frequency modulation to detect Ebola glycoprotein (GP), on the basis of a carrier-injection-trapping-release-transfer mechanism and the standard antibody-antigen-interaction principle within a dielectric-gated reduced graphene oxide (rGO) field-effect transistor (GFET). The sensitivity of Ebola detection can be significantly enhanced by monitoring the device's electronic-resonance frequency, such as its inflection frequency ( fi), where the phase angle reaches a maximum (θmax). In addition to excellent selectivity, a sensitivity of ∼36-160% and ∼17-40% for 0.001-3.401 mg/L Ebola GP can be achieved at high and low inflection-resonance frequencies, respectively, which are several orders of magnitude higher than the sensitivity from other electronic parameters (e.g., resistance-based sensitivity). Using equivalent circuit modeling for contributions from channel and contact, analytical equations for resonance shifts have been generalized. When matching with the incoming ac-measurement signal, electronic resonance from the phase-angle spectrum evolves from various relaxation processes (e.g., trap and release of injected charges at surface-trap sites of the channel-gate oxide and channel-source or drain interfaces) that are associated with a characteristic emission frequency. Using charge-relaxation dynamics, a high-performance bio-FET sensing platform for healthcare and bioelectronic applications is realized through resonance shifting.

Control of Charge Carriers Trapping and Relaxation in Hematite by Oxygen Vacancy Charge: Ab Initio Non-adiabatic Molecular Dynamics.

Ultrafast charge recombination in hematite (α-Fe2O3) severely limits its applications in solar energy conversion and utilization, for instance, in photoelectrochemical water splitting. We report the first time-domain ab initio study of charge relaxation dynamics in α-Fe2O3 with and without the oxygen vacancy (Ov) defect, using non-adiabatic molecular dynamics implemented within time-dependent density functional theory. The simulations show that the hole trapping is the rate-limiting step in the electron-hole recombination process for both neutral and ionized Ov systems. The electron trapping is fast, and the trapped electron are relatively long-lived. A similar asymmetry is found for the relaxation of free charge carriers: relaxation of photoholes in the valence band is slower than relaxation of photoelectrons in the conduction band. The slower dynamics of holes offers an advantage to water oxidation at α-Fe2O3 photoanodes. Notably, the neutral Ov defect accelerates significantly the charge recombination rate, by about a factor of 30 compared to the ideal lattice, due to the stronger electron-vibrational coupling at the defect. However, the recombination rate in the ionized Ov defect is decreased by a factor of 10 with respect to the neutral defect, likely due to expansion of the local iron shell around the Ov site. The Ov defect ionization in α-Fe2O3 photoanodes is important for increasing both electrical conductivity and charge carrier lifetimes. The simulations reproduce well the time scales for the hot carrier cooling, trapping and recombination available from transient spectroscopy experiments, and suggest two alternative mechanisms for the Ov-assisted electron-hole recombination. The study provides a detailed atomistic understanding of carrier dynamics in hematite, and rationalizes the experimentally reported activation of α-Fe2O3 photoanodes by incorporation of Ov defects.

Charge Relaxation Dynamics of an Electrolytic Nanocapacitor.

Understanding ion relaxation dynamics in overlapping electric double layers (EDLs) is critical for the development of efficient nanotechnology-based electrochemical energy storage, electrochemomechanical energy conversion, and bioelectrochemical sensing devices as well as the controlled synthesis of nanostructured materials. Here, a lattice Boltzmann (LB) method is employed to simulate an electrolytic nanocapacitor subjected to a step potential at t = 0 for various degrees of EDL overlap, solvent viscosities, ratios of cation-to-anion diffusivity, and electrode separations. The use of a novel continuously varying and Galilean-invariant molecular-speed-dependent relaxation time (MSDRT) with the LB equation recovers a correct microscopic description of the molecular-collision phenomena and enhances the stability of the LB algorithm. Results for large EDL overlaps indicated oscillatory behavior for the ionic current density, in contrast to monotonic relaxation to equilibrium for low EDL overlaps. Further, at low solvent viscosities and large EDL overlaps, anomalous plasmalike spatial oscillations of the electric field were observed that appeared to be purely an effect of nanoscale confinement. Employing MSDRT in our simulations enabled modeling of the fundamental physics of the transient charge relaxation dynamics in electrochemical systems operating away from equilibrium wherein Nernst–Einstein relation is known to be violated.

Plasmon Induced Resonant Energy Transfer and Hot Electron Injection in Plasmon Enhanced Photocatalysis

Localized surface plasmon resonance (LSPR) is ideal for improving solar energy harvesting because of the strong, tunable absorption and scattering cross sections. The energy stored in the collective electron oscillations can be transferred to a semiconductor, allowing photoconversion at wavelengths near and above the band edge of the semiconductor. In this presentation we will investigate the mechanisms and optimization of plasmon enhanced photocatalysis using a combined transient absorption and action spectrum/IPCE analysis. Specifically, by controlling the spectral overlap, energy band alignment, and thickness of insulating barriers in metal@semiconductor nanostructures the two possible energy transfer pathways, hot electron injection and plasmon induced resonant energy transfer, are mapped out as well as the corresponding charge relaxation dynamics. A connection is made between the initial plasmonic energy transfer measured on ultrafast time scales to the resulting enhancement in photocatalysis, guiding the efficient design of plasmon enhanced photocatalysts.

Ultrafast Spin-Resolved Spectroscopy Reveals Dominant Exciton Dynamics in Conducting Polymer Polyaniline

The conducting polymer polyaniline (PANI) has a wide range of optoelectronic applications due to its unique electronic and optical characteristics. Although extensive works have been performed to understand the equilibrium properties, the nature of the charge type that governs its nonequilibrium optical response has been barely understood; a number of studies have debated the nature of photogenerated charge type in PANI, specifically whether it is polaron or exciton based. Here, we report experimental evidence that the charge relaxation dynamics of PANI are dominated by excitons. Utilizing ultrafast spin-resolved pump–probe spectroscopy, we observed that PANI charge dynamics are strongly spin-polarized, exhibiting a spin Pauli-blocking effect. Investigations including both spin-independent and spin-dependent dynamics reveal that there is no spin-flip process involved in charge relaxation. This provides compelling evidence of an exciton-dominated photoresponse in PANI.