Tunneling Lifetime Research Articles

Identification and Characterization of Tunneling Nanotubes for Intercellular Trafficking.

Tunneling nanotubes (TNTs) are thin membranous channels providing a direct cytoplasmic connection between remote cells. They are commonly observed in different cell cultures and increasing evidence supports their role in intercellular communication, and pathogen and amyloid protein transfer. However, the study of TNTs presents several pitfalls (e.g., difficulty in preserving such delicate structures, possible confusion with other protrusions, structural and functional heterogeneity, etc.) and therefore requires thoroughly designed approaches. The methods described in this protocol represent a guideline for the characterization of TNTs (or TNT-like structures) in cell culture. Specifically, optimized protocols to (1) identify TNTs and the cytoskeletal elements present inside them; (2) evaluate TNT frequency in cell culture; (3) unambiguously distinguish them from other cellular connections or protrusions; (4) monitor their formation in living cells; (5) characterize TNTs by a micropatterning approach; and (6) investigate TNT ultrastructure by cryo-EM are provided. Finally, this article describes how to assess TNT-mediated cell-to-cell transfer of cellular components, which is a fundamental criterion for identifying functional TNTs. © 2023 Wiley Periodicals LLC. Basic Protocol 1: Identification of tunneling nanotubes Alternate Protocol 1: Identifying the cytoskeletal elements present in tunneling nanotubes Alternate Protocol 2: Distinguishing tunneling nanotubes from intercellular bridges formed during cell division Basic Protocol 2: Deciphering tunneling nanotube formation and lifetime by live fluorescent microscopy Alternate Protocol 3: Deciphering tunneling nanotube formation using a live-compatible dye Basic Protocol 3: Assessing tunneling nanotubes functionality in intercellular transfer Alternate Protocol 4: Flow cytometry approach to quantify the rate of vesicle or mitochondria transfer Support Protocol: Controls to support TNT-mediated transfer Basic Protocol 4: Studies of tunneling nanotubes by cell micropatterning Basic Protocol 5: Characterization of the ultrastructure of tunneling nanotubes by cryo-EM.

Resonant tunneling of electrons in biased symmetric triangular double barrier nanostructure triodes

The present work investigates the resonant tunneling of electrons in symmetric triangular double barrier triodes composed of GaAs-Ga1-yAlyAs nanostructures under a step bias voltage. This work employs the complex energy method to compute the resonant tunneling energy and the associated lifetimes. In the mathematical analysis of this work, the matching conditions are taken at specific points on both lateral sides of the triangular barrier. Results showed decreasing the resonant tunneling energies for both the lowest and excited states by applying step bias voltage and disappearing the lowest energy states at a specific applied bias voltage. The resonant tunneling lifetimes of the present structure exhibited nearly constant behavior at constant values of both well half-width and barrier half-thickness although the enhancement of the bias voltage. Moreover, the lifetimes of both the lowest and the first excited states increased nearly non-linearly by increasing the aluminum concentration, with the enhancement of the lowest resonant lifetimes over those values associated with the first excited states. The results showed considerable agreement with the data published in the literature for both magnitude and tendency. The present work highlights the importance of employing the mass-mismatch condition in studying heterostructures. It is found from the present study that resonant tunneling energies and their related lifetimes are more affected by the variations of the aluminum concentration in the barrier region, barrier thickness, and well width, which can be adjusted to improve the performance of the resonant tunneling triangular triodes and other nanostructure devices.

Spin-resonant tunneling in ferromagnetic conductor/ semiconductor heterostructure for spin-filter application

Spin-dependent tunneling in a ferromagnetic conductor/ semiconductor is analyzed with zero external fields. The barrier transparency, dwell time, tunneling time of electrons through heterostructure and the degree of polarization efficiency are calculated in Fe/GaAs double barrier heterostructure. The polarization efficiency of Fe/GaAs and Fe/InAs double-barrier heterostructures are compared. The Fe/GaAs has a high degree spin-polarization than Fe/InAs structure. The barrier transparency peak is sharper at the high width of the barrier. The results show that the polarization efficiency is maximum when the barrier width is maximum. The tunneling lifetime of electrons is evaluated using Heisenberg’s uncertainty principle. The spin components are completely separated at high barrier width and hence can be used effectively as a spin filter.

Quasi-Resonant Tunneling States in Triangular Double-Barrier Nanostructures

The quasi-resonant tunneling energies and lifetimes of symmetrical triangular double-barrier nanostructures fabricated from GaAs-Aly Ga1-yAs were investigated. The complex energy approach is used to calculate the resonant tunneling energy and its associated lifetime. The results show that decreasing the well width and increasing the aluminum concentration within the barrier material enhances the quasi-resonant tunneling energies for a fixed barrier thickness. Furthermore, increasing both the aluminum concentration and the barrier thickness results in longer resonant tunneling lifetimes. The current study's findings show that resonant tunneling energies and lifetimes closely match available data in the literature.

Study on Electron Tunneling Lifetime by Projected Green’s Function Approach in Single Quantum Well Semiconductor

The tunnelling lifetime of an electron in a single quantum well subject to an externally applied electric field is calculated using the Projected Green’s Function (PGF) approach. The lifetime in the biased single well decreases as a function of the electric field in good agreement with the previous result. The tunnelling lifetime is revealed with the behavior of the ground-state shift and the wave amplitude in the first well. As the electric field increases, the ground state energy shifts, leading to lessened constructive interference between the initial and reflected electron waves. Consequently, the study is essential to characterize the performance of high-speed quantum devices.

On the cosmological stability of the Higgs instability

The Standard Model Higgs potential becomes unstable at large Higgs field values where its quartic coupling becomes negative. While the tunneling lifetime of our current electroweak vacuum is comfortably longer than the age of the universe, quantum fluctuations during inflation might push the Higgs over the barrier, forming patches which might be lethal for our universe. We study the cosmological evolution of such regions and find that, at least in the thin wall approximation, they may be harmless as they collapse due to the backreaction of the Higgs itself. The presence of the Standard Model Higgs instability can provide a novel mechanism to end inflation and to reheat the universe through the evaporation of the black holes left over by the collapse of the Higgs bubbles. The bound on the Hubble rate during inflation may be therefore relaxed.

Resonant Tunneling of Electrons and Holes through the InxGa1−xN/GaN Parabolic Quantum Well/LED Structure

Models describing the tunneling of electrons and holes through parabolic InxGa1−xN/GaN quantum well/LED structures with respect to strain were developed. The transmission coefficient, tunneling lifetime, and efficiency of LED structures were evaluated by solving the Schrödinger equation. The effects of the mole fraction on the structure strain, resonant tunneling and tunneling lifetime, and LH–HH splitting were characterized. The value of LH–HH splitting increased and remained higher than the Fermi energy; therefore, only the HH band was dominant in terms of the valence band properties. The results indicate that an increase in the mole fraction can lead to efficiency droop.

Investigation of All-Oxide Thin-Film Solar Cell With p-SnOₓ as Absorber Layer

We propose an n-ZnO/p-SnO_<i>x</i> heterojunction solar cell as a novel pathway to realize all-oxide photovoltaics that offer attractive features such as stability, cost-effectiveness, and nontoxicity. TCAD device simulator was used to investigate the performance of n-ZnO/p-SnO_<i>x</i> thin-film solar cell using inputs on material parameters of SnO_<i>x</i> obtained experimentally. In this study, we considered the effects of SnO_<i>x</i> parameters, namely, bandgap and electron affinity on the performance of solar cell. Electrical transport models applied in modeling include the effects of interfacial recombination, tunneling, band discontinuity, and minority carrier lifetime. Our simulation results show that a maximum power conversion efficiency of &#x007E;15.5&#x0025; can be obtained in a window of an optimum combination of bandgap and electron affinity of SnO_<i>x</i> layer. Further enhancement in efficiency is achievable by improving the minority carrier lifetime.

Full-dimensional quantum mechanical calculations for the tunneling behavior of HOCO dissociation to H + CO2.

The tunneling behavior during HOCO dissociation to H + CO2 was investigated by full-dimensional quantum mechanical calculations based on an accurate global potential energy surface. The tunneling lifetimes for the low-lying 1500 vibrational states were calculated using the low-storage filter diagonalization method after a 1 million-step Chebyshev propagation. In the calculated energy range, the lifetimes of different vibrational states with similar energy are found to differ by 3-4 orders of magnitude, and the lower limit for these tunneling lifetimes is consistent with the experimental results reported by Continetti et al. For the given vibrational progressions, the lifetime of the vibrational states decreases with the increasing energy level, which is consistent with the results of 1D simulation calculations reported by Bowman, but the declining curve obviously fluctuates, and the declining slope is significantly different from that obtained by 1D simulation. Due to a difference in the effective barrier width, the mode-specific behavior of the tunneling effect is manifested in that the O-C-O' and H-O-C bend modes lead to the largest enhancement and an inhibitory effect on the tunneling process, respectively.

Photolysis dynamics of m- and o-fluorophenol: Substitution effects on tunneling mechanism

The photolysis dynamics of m-fluorophenol (m-FPhOH) and o-fluorophenol (o-FPhOH) have been investigated with time-resolved velocity map imaging (TR-VMI) and time-resolved ion-yield (TR-IY) techniques. Following excitation to the origin of S1 (ππ∗) state of m- and o-FPhOH, H atoms elimination mediated by tunneling through the potential barrier under the S1 (ππ∗)/S2 (πσ∗) conical intersection (CI) has been observed as a Gaussian feature signal centered at a total kinetic energy release (TKER) of ∼6000 cm−1 for both molecules. The quantum tunneling mechanism has been identified as the main decay pathway of S1 state for m-FPhOH, and the tunneling lifetime of 2.1 ns has been obtained from the TR-VMI measurements of H fragments. This tunneling mechanism is further confirmed by the studies on the selective O–H deuterated species, m-FPhOD, and consolidated by our theoretical calculations. However, the photolysis dynamics is quite different for the photoexcited o-FPhOH. The much lower yield of the H atoms originating from tunneling hinders the extraction of a reliable tunneling lifetime for o-FPhOH. Our theoretical calculations exhibit a broader and higher potential barrier exists beneath the S1/S2 CI of o-FPhOH, which increase the difficulty for tunneling. Furthermore, the special existence of intramolecular hydrogen bond in o-FPhOH is probably also the key factor that affects the tunneling rate, which would restrict the O–H stretch motion.

Carrier transport and recombination dynamics of InAs/GaAs sub-monolayer quantum dot near infrared photodetector

Here, we present a relative study of tunnel-induced photocarrier escape processes in a laterally coupled InAs sub-monolayer quantum dot-based photodetector (SML QD-PD) as a function of fractional coverage from 0.4 ML to 0.8 ML. Both by simulation and experiment, we have quantitatively described the temperature dependent interband photoresponse spectrally tuned in the near infrared region (835 nm–890 nm) on the basis of mutual competition between the interband carrier recombination and interdot tunneling lifetime with varying SML coverage. The progressively increasing recombination lifetime and decreasing interdot tunneling lifetime with increasing SML coverage has attributed to a faster photoresponse and greater responsivity. At higher coverage fraction, tunnel induced fast speed photocarrier transit through lateral array of SML QDs has been found to be capable of offering a faster temporal response (100 µs) with faithful reproducibility up to higher frequencies (1.3 KHz). Here, we report a powerful strategy to simultaneously tune responsivity, speed of time response and detectivity by externally controlling the SML coverage. This time response is measured to be nine times faster than a conventional SK QD photodetector. With increased coverage, inhibition of dark current due to trapping of injected charge carriers up to higher temperatures have resulted in high sustainable photodetectivity of 8 × 1011 cm Hz1/2 w−1 at ~250 K that offers near room temperature photodetection.

Effect of pressure and temperature on spin-dependent tunneling in InAs/GaAs heterostructure with Dresselhaus spin-orbit interaction

Abstract Using the transfer matrix, spin-dependent electron tunneling was studied in InAs/GaAs double barrier symmetrical heterostructure. The effect of Dresselhaus spin-orbit interaction in this system was analysed as a function of pressure and temperature. Both pressure and temperature influences the polarization efficiency, barrier transparency and dwell time of electrons. The increasing pressure increases polarization efficiency, tunneling life time and dwell time of electrons, where as the increasing temperature decreases the same parameters. The results might be helpful for the fabrication of spin-devices.

Study of deep level defects in InGaP/InGaAs-GaAsP/InGaAsN quantum well based multi-junction solar cell using finite element analysis

Degradation analysis of a quantum well-dilute nitride based multi-junction solar cell is presented using a 2D numerical device simulator: APSYS. By taking carrier removal effects into consideration, the proposed device exhibits strong electric field uniformity within the intrinsic region of the p-i-n middle cell. The electron traps are defined in the top InGaP and bottom InGaAsN base region considering 1 MeV electron irradiation in geostationary orbits. Considering thermionic emission, tunneling and SRH lifetime an effective lifetime value of 16.7 ps is considered in the middle MQW region. A record efficiency value of 38% and 44% is obtained at 1-sun and 500-sun AM0 spectrum respectively. The same efficiency value dropped by 4% by introducing a realistic SRV (1 × 104 cm s−1) and trap concentration values (1 × 1016 cm−3). Finally, we illustrate the influence of traps and lifetime on overall cell Jsc, Voc, η, and power density.

Up to a Sign. The Insidious Effects of Energetically Inaccessible Conical Intersections on Unimolecular Reactions.

It is now well established that conical intersections play an essential role in nonadiabatic radiationless decay where their double-cone topography causes them to act as efficient funnels channeling wave packets from the upper to the lower adiabatic state. Until recently, little attention was paid to the effect of conical intersections on dynamics on the lower state, particularly when the total energy involved is significantly below that of the conical intersection seam. This energetic deficiency is routinely used as a sufficient condition to exclude consideration of excited states in ground state dynamics. In this account, we show that, this energy criterion notwithstanding, energy inaccessible conical intersections can and do exert significant influence on lower state dynamics. The origin of this influence is the geometric phase, a signature property of conical intersections, which is the fact that the real-valued electronic wave function changes sign when transported along a loop containing a conical intersection, making the wave function double-valued. This geometric phase is permitted by an often neglected property of the real-valued adiabatic electronic wave function; namely, it is determined only up to an overall sign. Noting that in order to change sign a normalized, continuous function must go through zero, for loops of ever decreasing radii, demonstrating the need for an electronic degeneracy (intersection) to accompany the geometric phase. Since the total wave function must be single-valued a compensating geometry dependent phase needs to be included in the total electronic-nuclear wave function. This Account focuses on how this consequence of the geometric phase can modify nuclear dynamics energetically restricted to the lower state, including tunneling dynamics, in directly measurable ways, including significantly altering tunneling lifetimes, thus confounding the relation between measured lifetimes and barrier heights and widths, and/or completely changing product rotational distributions. Some progress has been made in understanding the origin of this effect. It has emerged that for a system where the lower adiabatic potential energy surface exhibits a topography comprised of two saddle points separated by a high energy conical intersection, the effect of the geometric phase can be quite significant. In this case topologically distinct paths through the two adiabatic saddle points may lead to interference. This was pointed out by Mead and Truhlar almost 50 years ago and denoted the Molecular Aharonov-Bohm effect. Still, the difficulty in anticipating a significant geometric phase effect in tunneling dynamics due to energetically inaccessible conical intersections leads to the attribute insidious that appears in the title of this Account. Since any theory is only as relevant as the prevalence of the systems it describes, we include in this Account examples of real systems where these effects can be observed. The accuracy of the reviewed calculations is high since we use fully quantum mechanical dynamics and construct the geometric phase using an accurate diabatic state fit of high quality ab initio data, energies, energy gradients, and interstate couplings. It remains for future work to establish the prevalence of this phenomenon and its deleterious effects on the conventional wisdom discussed in this work.

Multidimensional WKB approximation for particle tunneling.

In this paper we present a method for obtaining the WKB approximation for non-separable multidimensional potentials. At its leading order one has to solve the classical Hamilton-Jacobi equation with zero energy for which a very efficient method is proposed. The essence of this method lies in the recognition that in the vicinity to the potential minimum the solution of Schrödinger equation has to approach that of coupled harmonic oscillators. Quantum corrections to the semiclassical result are then obtained very easily and to an arbitrarily high order. The method is applied to the calculation of the tunneling splitting and tunneling lifetime. We show that classical turning points are part of the dynamical problem; they could not be determined simply from looking at the form of the potential, but are obtained from the solution of the pertinent equations of motion.

Improved projected Green's function approach to electron tunneling lifetime calculations in quantum wells

We demonstrate that the use of an optimal initial state of a wave function generated using Lanczos method allows the previously proposed projected Green's function approach to predict the tunneling lifetime of a particle crossing a double quantum well with a considerably improved accuracy. It is further revealed that the electron tunneling lifetime of such system depends linearly or quadratically on the barrier thickness or the well width. We also investigate the asymmetric double quantum well structure and find that the electron tunneling lifetime in it is strongly dependent on barrier thickness. Finally, we discuss the possible experimental designs to observe the above-mentioned tunneling features.

Tunneling lifetimes of electrons escaping from atoms under a static electric field.

The tunneling lifetime of an electron escaping from an atom is calculated using a projected Green's function method, combining with the radial potential of the atom which is obtained from density functional theory. Results of the calculated electron tunneling lifetimes in model systems such as a quantum dot are shown to be comparable with other theoretical studies. For the first time, we have obtained the tunneling lifetimes of electrons escaping from a series of atoms (He, Ne, Ar, Kr, H, Li, Na, K) under a static electric field. Dependent on both the barrier width/height and the bound strength of the ground state electron, the calculated tunneling lifetime under a static electric field spans from femtosecond level to picosecond level, consistent with the attosecond-level results in experiments using a time-dependent external field.

Hydrogen bond network rearrangement dynamics in water clusters: Effects of intermolecular vibrational excitation on tunneling rates.

Theoretical studies of hydrogen bond network rearrangement (HBNR) dynamics in liquid water have indicated that librational motions initiate the hydrogen bond breaking/formation processes. We present the results of using a simple time evolution method to extract and compare the tunneling lifetimes for motions that break and reform the hydrogen bond for the water dimer, trimer, and pentamer from the experimentally measured tunneling splittings in the ground and excited intermolecular vibrational states. We find that the specific nature of the intermolecular vibrational excitation does not significantly influence the tunneling lifetime of the dimer, but that only excitations to a librational vibration affect the water trimer and pentamer lifetimes. The specific enhancement of bifurcation tunneling in larger clusters relative to the dimer also indicates that hydrogen bond cooperativity is a vital element of these dynamics.

Effect of magnetic field on spin-dependent hole transport through a type-I Cd1-xMnxTe/CdTe double barrier heterostrucutre

We study the effect of the magnetic field on the spin-dependent hole transport through a diluted magnetic semiconductor double barrier heterostrucutre such as Cd1-x Mn x Te/CdTe. Using the transfer matrix, the barrier transparency, polarization efficiency and tunneling lifetime of a light hole and a heavy hole are calculated. The spin separation is found out and is observed that it is the same for both the light and the heavy hole. The heavy hole takes more time to travel in the heterostrucutre than the light hole. The effect of the magnetic field influences the tunneling lifetime. The results give the basic idea about the spin-dependent transport of light and heavy holes.

Constructive and Destructive Interference in Nonadiabatic Tunneling via Conical Intersections.

As a manifestation of the molecular Aharonov-Bohm effect, tunneling-facilitated dissociation under a conical intersection (CI) requires the inclusion of the geometric phase (GP) to ensure a single-valued adiabatic wave function encircling the CI. In this work, we demonstrate using a simple two-dimensional model that the GP induces destructive interference for vibrational states with even quanta in the coupling mode, but it leads to constructive interference for those with odd quanta. The interference patterns are manifested in tunneling wave functions and clearly affect the tunneling lifetime. It is further shown that the inclusion of the diagonal Born-Oppenheimer correction is necessary for agreement with exact results.