Hole Lifetime Research Articles

Fast plasma production by intense femtosecond extreme ultraviolet and x-ray pulses

We develop a semiempirical model to describe the creation of an electron plasma in matter at extreme conditions, as excited by high-intensity, extreme ultraviolet (EUV) or x-ray radiation pulses currently available at free-electron laser (FEL) facilities. In typical FEL experiments, EUV and x-ray pulses are used to investigate highly excited states of matter produced by optical pump pulses. The pump pulses, promoting electrons from delocalized valence band states, excite the system often through multiphoton absorption processes and/or shock wave propagation. Instead, the use of FEL radiation as a pump allows triggering electron transitions from bound, core states to nearly free levels above the Fermi energy, promptly generating a highly excited state, toward the warm dense matter regime. We model such an excitation process starting from the optical properties of the analyzed materials and first-principle considerations, with the aim of motivating further studies in this scheme. We apply our model to predict the differences in the plasma creation process in insulators and metals, at varying exciting pulse wavelength and fluence, and we interpret the results in terms of the different nature of the investigated systems. Furthermore, we explore the effect of the finite core hole lifetime on the plasma formation and relaxation dynamics. We show the model is suited for the interpretation of real experimental data obtained from a prototypical insulating crystal (LiF) in a EUV FEL pump–optical transmission probe experiment. Published by the American Physical Society 2025

From the perspective of photo-induced holes lifetime: Application of anionic and cationic co-embedded carbon nitride in marine

From the perspective of photo-induced holes lifetime: Application of anionic and cationic co-embedded carbon nitride in marine

Visible Light-Driven Photocatalysis of Al-Doped SrTiO3: Experimental and DFT Study.

Environmental problems associated with water pollution caused by organic dyes have raised serious concerns. In this context, photocatalytic processes have proven to be promising and environmentally friendly methods for water purification utilising abundant solar energy. In this study, a SrTiO3-based photocatalyst was modified by doping with Al ions and the deposition of dual co-catalysts (Rh/Cr2O3 and CoOOH) to enhance the photocatalytic decomposition efficiency of methylene blue (MB). Pure perovskite SrTiO3 was synthesised by chemical precipitation followed by calcination at 1100 °C. Al-doped SrTiO3 with deposited co-catalysts showed 3.2 times higher photocatalytic activity compared to unalloyed SrTiO3 with co-catalysts in MB decomposition under visible radiation. This study highlights the effectiveness of using dual co-catalysts and low-valence metal doping to enhance the efficiency of the photocatalytic decomposition of organic pollutants. The density functional theory analysis results show that the Al doping of SrTiO3 improves charge separation and increases the lifetime of photogenerated electrons and holes while maintaining the size of the forbidden band, which confirms its effectiveness for enhancing photocatalytic activity.

Probing modified Hawking evaporation with gravitational waves from the primordial black hole dominated universe

It has been recently proposed that Hawking evaporation might slow down after a black hole has lost about half of its mass. Such an effect, called “memory burden”, is parameterized as a suppression in the mass loss rate by negative powers n of the black hole entropy and could considerably extend the lifetime of a black hole. We study the impact of memory burden on the Primordial Black Hole (PBH) reheating scenario. Modified PBH evaporation leads to a significantly longer PBH dominated stage. Requiring that PBHs evaporate prior enough to Big Bang Nucleosynthesis shrinks the allowed PBH mass range. Indeed, we find that for n > 2.5 the PBH reheating scenario is not viable. The frequency of the Gravitational Waves (GWs) induced by PBH number density fluctuations is bound to be larger than about a Hz, while the amplitude of the GW spectrum is enhanced due to the longer PBH dominated phase. Interestingly, we show that, in some models, the slope of the induced GW spectrum might be sensitive to the modifications to Hawking evaporation, proving it may be possible to test the “memory burden” effect via induced GWs. Lastly, we argue that our results could also apply to general modifications of Hawking evaporation.

Hole diffusion length and mobility of a long wavelength infrared InAs/InAsSb type-II superlattice nBn design

We demonstrated high-performance 8.9 μm cutoff wavelength nBn InAs/InAsSb type-II strained-layer superlattice (T2SL). These detectors exhibit a long minority carrier (hole) lifetime of 1.2 μs at 80 K, high quantum efficiency of 40% for back-side illuminated devices without antireflection coating, and low dark current density of 4.6 × 10−6 A/cm2 at 80 K. We measured absorption, minority carrier (hole) lifetime, quantum efficiency, and spectral response as a function of the temperature and applied bias. We investigated the temperature dependence of the hole diffusion length and mobility and found that their values increase with temperature from 1.3 μm and 6.5 cm2/Vs at 30 K to 6.5 μm and 36 cm2/Vs at T = 90 K. We compared the measured diffusion length and mobility of holes in long-wavelength infrared (LWIR) T2SL with these parameters of a high-performance mid-wavelength infrared (MWIR) T2SL. Unexpectedly, hole mobility in LWIR T2SL was found to be higher than in MWIR that is contrary to the theoretical predictions.

Hole and electron spin lifetime in lightly n-doped silicon at low temperatures

We report on photoinduced inverse spin-Hall effect (ISHE) measurements as a function of the incident photon energy in the 4–50 K temperature range for a Pt/n-doped Si junction. Optical spin injection allows generating a spin-oriented population of electrons and holes around the Δ valleys and Γ point of the Si Brillouin zone, respectively. Spin-polarized carriers cross the Pt/Si contact and then enter the Pt overlayer, where spin-to-charge conversion occurs by means of spin-dependent scattering with Pt nuclei. For temperatures T up to 20 K, most of the dopants are not ionized, so that the electric field, stemming from the contact potential between Pt and Si, extends to the whole Si substrate, which becomes insulating, and only spin-oriented holes reach the Pt layer and contribute to the ISHE spectra. For T>20 K, donors are partially ionized, and the resulting space charge close to the Pt/Si interface leads to the formation of a Schottky contact where the electric field rapidly vanishes within a few micrometers. As a consequence, also spin-polarized electrons enter Pt by means of thermionic emission, contributing to the ISHE signal. We numerically solve the one-dimensional spin drift-diffusion equations for holes and electrons and estimate the temperature dependence of the spin lifetime in Si for both populations, demonstrating that Si may serve as a versatile platform for spintronic applications, able to leverage both electrons and holes.

Time-resolved cathodoluminescence measurement of the effects of α -particle-related damage on minority hole lifetime in free-standing n-GaN

Time-resolved cathodoluminescence using 30 keV ultrafast electron pulses has been used to perform direct measurements of the minority hole lifetime τh as a function of 3.7 MeV α-particle fluence in high-quality free-standing n-type GaN substrates. The lifetime damage factor K calculated from these measurements was found to monotonically decrease from 6.9 × 10−2 to 6.4 × 10−4 cm2 s−1 ion−1 with increasing α-fluence from 108 to 1012 cm−2, implying a reduction in trap cross section and/or an aggregation of α-induced traps. The small, ∼200–300 nm, hole diffusion length estimated from the minority hole lifetime for the highest α-fluence necessitates the deployment of α-voltaic device strategies and architectures that emphasize depletion and drift over diffusion for effective charge collection and optimal power conversion efficiency.

The use of low-frequency current fluctuations in measuring the mobility of holes in the MEH-PPV polymer

A diagnostic method based on the evaluation of low-frequency current fluctuation spectra is presented. When measuring the current through a p-type MEH-PPV sample, the occurrence of fluctuation is observable which can be measured with an AC amplifier. A model has been proposed that proves that the fluctuations originate from the interaction between the valence band and the band gap traps. The mean value of the amplitudes of these fluctuations increases linearly with decreasing frequency with a slope from which the product of mobility and lifetime of current carriers µpτp= (9 ± 3) × 10−15 cm2V−1 was obtained. The hole lifetime of (0.27 ± 0.01) ns was evaluated from the luminescence relaxation using the time-correlated single photon counting (TCSPC) technique. The mobility value (3 ± 1) × 10−5 cm2 V−1s−1 calculated using the above methods was compared with the mobility 1.8 × 10−5 cm2 V−1s−1 determined by the CELIV method (Charge extraction by linearly increasing voltage) and good agreement was obtained.

Facet-Engineered BiVO4 Photocatalysts for Water Oxidation: Lifetime Gain Versus Energetic Loss.

A limiting factor to the efficiency of water Oxygen Evolution Reaction (OER) in metal oxide nanoparticle photocatalysts is the rapid recombination of holes and electrons. Facet-engineering can effectively improve charge separation and, consequently, OER efficiency. However, the kinetics behind this improvement remain poorly understood. This study utilizes photoinduced absorption spectroscopy to investigate the charge yield and kinetics in facet-engineered BiVO4 (F-BiVO4) compared to a non-faceted sample (NF-BiVO4) under operando conditions. A significant influence of preillumination on hole accumulation is observed, linked to the saturation and, thus, passivation of deep and inactive hole traps on the BiVO4 surface. In DI-water, F-BiVO4 shows a 10-fold increase in charge accumulation (∼5 mΔOD) compared to NF-BiVO4 (∼0.5 mΔOD), indicating improved charge separation and stabilization. With the addition of Fe(NO3)3, an efficient electron acceptor, F-BiVO4 demonstrates a 30-fold increase in the accumulation of long-lived holes (∼45 mΔOD), compared to NF-BiVO4 (∼1.5 mΔOD) and an increased half-time, from 2 to 10 s. Based on a simple kinetic model, this increase in hole accumulation suggests that facet-engineering causes at least a 50-100 meV increase in band bending in BiVO4 particles, thereby stabilizing surface holes. This energetic stabilization/loss results in a retardation of OER relative to NF-BiVO4. This slower catalysis is, however, offset by the observed increase in density and lifetime of photoaccumulated holes. Overall, this work quantifies how surface faceting can impact the kinetics of long-lived charge accumulation on metal oxide photocatalysts, highlighting the trade-off between lifetime gain and energetic loss critical to optimizing photocatalytic efficiency.

Nano‐Size Effects on Decay Dynamics of Photo‐Excited Polarons in CeO2

AbstractThe study of polaron dynamics in complex materials has garnered significant attention owing to its implications for various technological applications, including catalysis, solid‐state devices, and energy storage. This paper investigates the photo‐excited electron and hole polaron dynamics in cerium dioxide (CeO2) using time‐resolved X‐ray absorption spectroscopy, with an emphasis on the nano‐size effect. Additionally, density functional theory and multiplet calculations have been utilized to reveal the photo‐excited polaron dynamics in CeO2 single crystal (SC) and nanocrystal (NC). The electron polaron is observed to decay into a deep trap site with a short duration of ≈5 ps, while electrons in the traps stay for more than 1400 ps. The most significant observation is the behavior of holes in NC, which tends to stay longer (≈150 ps) compared to SC (<10 ps) suggesting hole existence more at the surface than at bulk. The fast dissociation of the electron polarons the prolonged lifetime of the electrons above the Fermi level and the enhanced hole lifetime at the surface are proposed to be among the various factors that influence the high reactivity of CeO2.

Effects of non-commutative geometry on black hole properties

In this study, we investigate the signatures of a non-commutative black hole solution. Initially, we calculate the thermodynamic properties of the system, including entropy, heat capacity, and Hawking radiation. For the latter quantity, we employ two distinct methods: surface gravity and the topological approach. Additionally, we examine the emission rate and remnant mass within this context. Remarkably, the lifetime of the black hole, after reaching its final state due to the evaporation process, is expressed analytically up to a grey-body factor. We estimate the lifetime for specific initial and final mass configurations. Also, we analyze the tensorial quasinormal modes using the 6th-order WKB method. Finally, we study the deflection angle, i.e., gravitational lensing, in both the weak and strong deflection limits.

Four STU black holes shadows

Abstract In this work, we examine the optical behaviors and thermodynamic phase structures using shadow analysis for four S T U black holes. The study is conducted for four cases of charge configurations on the parameter space M ( q 1 , q 2 , q 3 , q 4 ) . As a matter of fact, both the electric charge as a parameter and the parameter space M ( q 1 , q 2 , q 3 , q 4 ) affect the geometry of the black hole shadow, particularly the size of the shadow. We also introduce a constraint on the charge of the black hole from the observational results of the M87 ⋆ and Sgr A ⋆ shadow. Furthermore, we show that the electric charge and the parameter space M ( q 1 , q 2 , q 3 , q 4 ) have a non-trivial impact on the variation of the energy emission rate. Interestingly enough, we find novel scenarios in which the evaporation is slower, which causes the lifetime of the black holes to be considerably elongated. On the other side, the phase structure of four S T U black holes is explored for two cases of electric charge configuration. The findings show a perfect correlation between the shadow and event horizon radii. This correlation is, in fact, helpful in discovering the phase transition in terms of the shadow radius. In addition, the microstructure is being analyzed in terms of shadow analysis, providing similar behavior to the ordinary situation of the Ruppeiner formalism.

New mass window for primordial black holes as dark matter from the memory burden effect

The mass ranges allowed for primordial black holes (PBHs) to constitute all of dark matter (DM) are broadly constrained. However, these constraints rely on the standard semiclassical approximation which assumes that the evaporation process is self-similar. Quantum effects such as memory burden take the evaporation process out of the semiclassical regime latest by the time the black hole loses half of its mass. What happens beyond this time is currently not known. However, theoretical evidence based on prototype models indicates that the evaporation slows down, thereby extending the lifetime of a black hole. This modifies the mass ranges constrained, in particular, by big bang nucleosynthesis (BBN) and cosmic microwave background spectral distortions. We show that previous constraints are largely relaxed when the PBH lifetime is extended, making it possible for PBHs to constitute all of DM in previously excluded mass ranges. In particular, this is the case for PBHs lighter than 109 g that enter the memory burden stage before BBN and are still present today as DM. Published by the American Physical Society 2024

Electromagnetic ion cyclotron emission from ion-scale magnetic holes

Ion-scale magnetic holes are nonlinear plasma structures commonly observed in the solar wind and Earth's magnetosphere. These holes are characterized by the magnetic field depletion filled by hot, transversely anisotropic ions and electrons and are likely formed during the nonlinear stage of ion mirror instability. Due to the plasma thermal anisotropy within magnetic holes, they serve as a host of electromagnetic ion cyclotron waves, whistler-mode waves, and electron cyclotron harmonic waves. This makes magnetic holes an important element of the Earth's inner magnetosphere, where electromagnetic waves generated within may strongly contribute to energetic ion and electron scattering. Such scattering, however, will modify the hot-ion distribution that is trapped within magnetic holes and responsible for the magnetic field stress balance. Therefore, hot ion scattering within magnetic holes likely determines the hole lifetime. In this study, we investigate how ion scattering by electromagnetic waves affects the stress balance and lifetime of magnetic holes. For illustration, we used typical characteristics of magnetic holes, ion populations, and ion cyclotron waves observed in the Earth's magnetosphere. We have demonstrated that ion distribution isotropization via scattering by waves does not change significantly magnetic hole magnitude, but ion losses due to scattering into the atmosphere may limit the hole life-times to 10–30 min in the Earth's inner magnetosphere.

Effects of thermal fluctuations on the evaporation of AdS Schwarzschild scalar tensor vector gravity black hole

The Hawking evaporation process has important implications for our understanding of the universe, as it suggests that black holes are not eternal and can eventually evaporate away completely. We evaluate the Hawking evaporation process of AdS Schwarzschild scalar-tensor-vector gravity black hole by using Stefan-Boltzmann law and find out that Hawking evaporation rate depends on the AdS radius l and deviation parameter α of the scalar-tensor-vector gravity. We analyze that for small values of AdS radius l and positive deviation parameter α black hole evaporates quickly. While there is exponential increase in lifetime of the black hole for large AdS radius l and negative deviation parameter α. Moreover, we find out thermodynamical quantities like Helmholtz free energy, internal energy, pressure, enthalpy, Gibbs free energy and specific heat and show that how deviation parameter α and the correction parameter ζ of the first order corrected entropy play vital role on the stability and phase transitions of the black holes.

Radiationless decay spectrum of O 1s double core holes in liquid water.

We present a combined experimental and theoretical investigation of the radiationless decay spectrum of an O 1s double core hole in liquid water. Our experiments were carried out using liquid-jet electron spectroscopy from cylindrical microjets of normal and deuterated water. The signal of the double-core-hole spectral fingerprints (hypersatellites) of liquid water is clearly identified, with an intensity ratio to Auger decay of singly charged O 1s of 0.0014(5). We observe a significant isotope effect between liquid H2O and D2O. For theoretical modeling, the Auger electron spectrum of the central water molecule in a water pentamer was calculated using an electronic-structure toolkit combined with molecular-dynamics simulations to capture the influence of molecular rearrangement within the ultrashort lifetime of the double core hole. We obtained the static and dynamic Auger spectra for H2O, (H2O)5, D2O, and (D2O)5, instantaneous Auger spectra at selected times after core-level ionization, and the symmetrized oxygen-hydrogen distance as a function of time after double core ionization for all four prototypical systems. We consider this observation of liquid-water double core holes as a new tool to study ultrafast nuclear dynamics.

Correlating activities and defects in (photo)electrocatalysts using in-situ multi-modal microscopic imaging

Photo(electro)catalysts use sunlight to drive chemical reactions such as water splitting. A major factor limiting photocatalyst development is physicochemical heterogeneity which leads to spatially dependent reactivity. To link structure and function in such systems, simultaneous probing of the electrochemical environment at microscopic length scales and a broad range of timescales (ns to s) is required. Here, we address this challenge by developing and applying in-situ (optical) microscopies to map and correlate local electrochemical activity, with hole lifetimes, oxygen vacancy concentrations and photoelectrode crystal structure. Using this multi-modal approach, we study prototypical hematite (α-Fe2O3) photoelectrodes. We demonstrate that regions of α-Fe2O3, adjacent to microstructural cracks have a better photoelectrochemical response and reduced back electron recombination due to an optimal oxygen vacancy concentration, with the film thickness and extended light exposure also influencing local activity. Our work highlights the importance of microscopic mapping to understand activity, in even seemingly homogeneous photoelectrodes.

Quasinormal modes, and different aspects of Hawking radiation within the metric-affine bumblebee gravity framework

We consider a static and spherically symmetric black hole metric that emerges from the vacuum solution of the traceless metric-affine bumblebee model. Our study focuses on the possible implications of the modifications induced by the model on various astrophysical observables that include quasinormal modes, ringdown waveforms, Hawking radiation spectrum, sparsity of that radiation, and the lifetime of a black hole. We explore the impact of the Lorentz symmetry-breaking (LSB) parameter α on the quasinormal modes with the help of the 6th-order WKB method. Our inquisition reveals that the emission frequency and decay rate initially decreases with α and then grows up. As a result, the LSB becomes critically important for maintaining the stability of the system after being exposed to perturbation. The convergence of the WKB method for various orders is also studied here. We then analyze the Hawking temperature, radiation spectrum, and sparsity in this modified gravity framework that provides valuable insights into the thermal radiation emitted by black holes. It points out that the Hawking temperature, the peak of the power spectrum, and the total power emitted initially decreases and then increases with α. However, The variation of the sparsity with α follows a reverse trend. Finally, we obtain the analytical expression of the ‘lifetime’ of black holes and scrutinize the effect of α on it.

Kerr–Newman black holes in Weyl–Cartan theory: Shadows and EHT constraints

With the recent release of the black hole image of Sgr A* alongside the earlier image of M87*, one can achieve an in-depth understanding of gravitational physics at the horizon scale. According to the Event Horizon Telescope (EHT) collaboration, the observed image is consistent with the expected appearance of a Kerr black hole. In the present work, we consider Kerr–Newman black holes in Weyl–Cartan theory as a supermassive black hole (BH) and evaluate the parameters of the model with shadow size estimates done by the observations of M87* and Sgr A* from EHT. Such a study can be a possible way to distinguish Weyl–Cartan theory from general relativity and ensure the validity of the idea. Besides, we calculate the energy emission rate for the corresponding BH and discuss how the model’s parameters affect the emission of particles around the black hole. With this investigation, we are able to examine the time evolution and lifetime of the black hole in such a theory of gravity.

Improved temporal performance and optical quantum efficiency of avalanche amorphous selenium for low dose medical imaging.

Active matrix flat panel imagers (AMFPIs) with thin-film transistor arrays experience image quality degradation by electronic noise in low-dose radiography and fluoroscopy. One potential solution is to overcome electronic noise using avalanche gain in an amorphous selenium (a-Se) (HARP) photoconductor in indirect AMFPI. In this work, we aim to improve temporal performance of HARP using a novel composite hole blocking layer (HBL) structure and increase optical quantum efficiency (OQE) to CsI:Tl scintillators by tellurium (Te) doping. Two different HARP structures were fabricated: Composite HBL samples and Te-doped samples. Dark current and optical sensitivity measurements were performed on the composite HBL samples to evaluate avalanche gain and temporal performance. The OQE and temporal performance of the Te-doped samples were characterized by optical sensitivity measurements. A charge transport model was used to investigate the hole mobility and lifetime of the Te-doped samples in combination with time-of-flight measurements. The composite HBL has excellent temporal performance, with ghosting below 3% at 10mR equivalent exposure. Furthermore, the composite HBL samples have dark current and achieved an avalanche gain of 16. Te-doped samples increased OQE from 0.018 to 0.43 for 532nm light. The addition of Te resulted in 2.1% first-frame lag, attributed to hole trapping within the layer. The composite HBL and Te-doping can be utilized to improve upon the limitations of previously developed indirect HARP imagers, showing excellent temporal performance and increased OQE, respectively.