Hole Energy Research Articles

Enhancement the intensity of optical transitions in the germanium/silicon nanosystem with germanium quantum dots

It is shown that in a germanium/silicon nanosystem with germanium quantum dots, the hole leaving the germanium quantum dot causes the appearance of the hole energy level in the bandgap energy in a silicon matrix. The dependences of the energies of the ground state of a hole and an electron, as well as spatially indirect excitons on the radius of the germanium QD and on the depth of the potential well for holes in the germanium QD are obtained. It is found that as a result of a direct electron transition in real space between the electron level, located in the conduction band of the silicon matrix, and the hole level located in the bandgap of the silicon matrix, the radiative recombination intensity in the germanium/silicon nanosystem with germanium quantum dots increases significantly.

The newborn black hole in GRB 191014C proves that it is alive

A multi-decade theoretical effort has been devoted to finding an efficient mechanism to use the rotational and electrodynamical extractable energy of a Kerr-Newman black hole (BH), to power the most energetic astrophysical sources such as gamma-ray bursts (GRBs) and active galactic nuclei. We show an efficient general relativistic electrodynamical process which occurs in the “inner engine” of a binary driven hypernova. The inner engine is composed of a rotating Kerr BH of mass M and dimensionless spin parameter α, a magnetic field of strength B0 aligned and parallel to the rotation axis, and a very low-density ionized plasma. Here, we show that the gravitomagnetic interaction between the BH and the magnetic field induces an electric field that accelerates electrons and protons from the environment to ultrarelativistic energies emitting synchrotron radiation. We show that in GRB 190114C the BH of mass M = 4.4 M⊙, α = 0.4, and B0 ≈ 4 × 1010 G can lead to a high-energy (≳GeV) luminosity of 1051 erg s−1. The inner engine parameters are determined by requiring (1) that the BH extractable energy explains the GeV and ultrahigh-energy emission energetics, (2) that the emitted photons are not subjected to magnetic-pair production, and (3) that the synchrotron radiation timescale agrees with the observed high-energy timescale. We find for GRB 190114C a clear jetted emission of GeV energies with a semi-aperture angle of approximately 60° with respect to the BH rotation axis.

Stability of horizon with pressure and volume of d-dimensional charged AdS black holes with cloud of strings and quintessence

In this paper, the thermodynamics and the stability of horizon of the charged AdS black hole surrounded by quintessence and cloud of strings in d-dimensional spacetime are studied via the scalar field scattering and the charged particle absorption. The cosmological constant is interpreted as the thermodynamic pressure in the black hole. During the study, we consider the case where the energy of the particle (scalar field) is related to the internal energy of the black hole. Furthermore, we also consider another assumption, which is proposed in Hu et al. (2019). This assumption considers that the energy of the particle (scalar field) is related to the enthalpy of the black hole. In addition, we compare and discuss the results obtained under these two assumptions. At the same time, we also consider the effect of the dimension. The thermodynamics of black holes in different dimensions has also been studied and compared.

Quantum chemical designing of banana-shaped acceptor materials with outstanding photovoltaic properties for high-performance non-fullerene organic solar cells

Non-Fullerene acceptors (NFAs) are getting a huge attention from the researchers across the globe to develop bulk-heterojunction organic solar cells (BHJ-OSC). In contrast with fullerene counterparts, the electronic energy levels as well as their optical properties can be tuned easily which ultimately helps to further enhance the power conversion efficiency of BHJ-OSC devices. By considering this crucial phenomenon of NFAs in OSCs, here we have designed a series of new banana-shaped NFAs (BS1-BS5) by doing end-capped modifications of BDTP-4F (R). Structural-property relationship, photo-physical, and optoelectronic properties of newly designed molecules are extensively studied by using density functional theory (DFT) and time dependent-density functional theory (TD-DFT). Furthermore, some geometric parameters like frontier molecular orbitals (FMOs), excitation and binding energy, hole-electron overlap, density of states, molecular electrostatic potential, open circuit voltage, transition density matrix, and reorganizational energy of electron and hole are also studied and compared with BDTP-4F (R). All of the designed materials (BS1-BS5) showed a red-shifting in absorption spectrum, higher electronic charge mobility, while, lower binding and excitation energies in-contrast to BDTP-4F. Much narrower HOMO-LUMO energy gaps (Eg= 1.89–1.98 eV) has been observed among all of the newly designed materials, suggesting their higher charge shifting behavior from HOMO to LUMO. In last, complex study of PTB7-Th/BS2 and PM6/BS2 also investigated in order to understand the charge shifting between donor and acceptor molecules. From all reported analysis, we concluded that our theoretical designed molecules are better than BDTP-4F (R), thus we recommend these molecules to experimentalist for future development of highly-efficient OSCs devices.

Is the binding energy of galaxies related to their core black hole mass?

Most of the large galaxies host a supermassive black hole, but their origin is still not well understood. In this paper, we look at a possible connection between the gravitational binding energies of large galaxies, etc., and the masses of their central black holes. Using this relation (between the gravitational binding energy of the host structure and the black hole energy), we argue why globular clusters are unlikely to harbour large black holes and why dwarf galaxies, if they have to host black holes, should have observed mass-to-light ratios of ~100.

CFRP drilling under throttle and evaporative cryogenic cooling and micro-lubrication

Hole-making in CFRP plates has been unsustainable due to poor hole quality, high specific energy consumption, a trade-off between shortened drill life and low productivity, and high processing cost. This experimental study investigates the effects of using throttle and evaporative cryogenic fluids, actualized by applying compressed carbon dioxide and liquid nitrogen, respectively, and micro-lubrication on hole quality (roughness, coaxiality, and circularity), production economy (tool damage and process cost), structural intactness (delamination and uncut fibers), energy consumption, and machining forces. Additionally, the effects of applying drill pecking and cutting speed are also quantified. Based on the experimental results, micro-lubrication is found to have outperformed dry drilling and the two cryogenic coolants regarding the measures associated with process viability, such as tool wear, process cost, energy consumption, and machining forces. Throttle cryogenic cooling, on the other hand, yielded the best results in respect of the work quality measures, which includes hole quality and structural intactness. Pecking yielded disappointing results regarding most of the measures, whereas the high level of cutting speed yielded favorable results in respect of specific cutting energy and process cost.

End‐Capped Molecular Engineering of S‐Shaped Hepta‐Ring‐Containing Fullerene‐Free Acceptor Molecules with Remarkable Photovoltaic Characteristics for Highly Efficient Organic Solar Cells

Nonfullerene acceptor materials are getting more and more attention from the scientific community because of their various applications in photovoltaic energy devices. Herein, a series of eight new S‐shaped nonfullerene acceptors (SY1–SY8) with end‐capped molecular modeling of IDTP‐4F (R) is designed. These designed materials are theoretically characterized along with the reference molecule R to investigate their structural‐property relationship, photophysical, and optoelectronic properties with density functional theory and time dependent calculations. Moreover, the geometric specifications such as alignments of frontier molecular orbitals, excitation and binding energy, hole‐electron overlap, density of states, overlap density of states, molecular electrostatic potential, open circuit voltage, transition density matrix, and reorganizational energy of electron and hole have also been investigated and compared with the experimentally synthesized reference molecule R. A highly red‐shifting behavior along, with a high charge mobility of electrons is realized after these end‐capped modifications in all designed molecules. Moreover, all designed molecules have lower binding and excitation energies as compared to reference molecule R. After these analyses, it is realized that the newly designed molecules (SY1‐SY8) are better than R, thus these molecules are recommended to experimentalists for the future development of highly efficient OSCs.

Intensity of Radiative Recombination in the Germanium/Silicon Nanosystem with Germanium Quantum Dots

It is shown that in a germanium/silicon nanosystem with germanium quantum dots, the hole leaving the germanium quantum dot causes the appearance of the hole energy level in the bandgap energy in a silicon matrix. The dependences of the energies of the ground state of a hole and an electron are obtained as well as spatially indirect excitons on the radius of the germanium quantum dot and on the depth of the potential well for holes in the germanium quantum dot. It is found that as a result of a direct electron transition in real space between the electron level that is located in the conduction band of the silicon matrix and the hole level located in the bandgap of the silicon matrix, the radiative recombination intensity in the germanium/silicon nanosystem with germanium quantum dots increases significantly.

Phase transitions in D-dimensional Gauss–Bonnet–Born–Infeld AdS black holes

In this paper, we have investigated the phase transition in black holes when Gauss-Bonnet corrections to the spacetime curvature and Born-Infeld extension in stress-energy tensor of electromagnetic field are considered in a negative cosmological constant background. It is evident that the black hole undergoes a phase transition as the specific heat capacity at constant potential shows discontinuities. Further, the computation of the free energy of the black hole, the Ehrenfest scheme and the Ruppeiner state space geometry analysis are carried out to establish the second order nature of this phase transition. The effect of non-linearity arising from Born-Infeld electrodynamics is also evident from our analysis. Our investigations are done in general D-spacetime dimensions with D > 4, and specific computations have been carried out in D = 5, 6, 7 spacetime dimensions.

Wandering of the central black hole in a galactic nucleus and correlation of the black hole mass with the bulge mass

Abstract We investigate a mechanism for a super-massive black hole at the center of a galaxy to wander in the nucleus region. A situation is supposed in which the central black hole tends to move by the gravitational attractions from the nearby molecular clouds in a nuclear bulge but is braked via the dynamical frictions from the ambient stars there. We estimate the approximate kinetic energy of the black hole in an equilibrium between the energy gain rate through the gravitational attractions and the energy loss rate through the dynamical frictions in a nuclear bulge composed of a nuclear stellar disk and a nuclear stellar cluster as observed from our Galaxy. The wandering distance of the black hole in the gravitational potential of the nuclear bulge is evaluated to get as large as several 10 pc, when the black hole mass is relatively small. The distance, however, shrinks as the black hole mass increases, and the equilibrium solution between the energy gain and loss disappears when the black hole mass exceeds an upper limit. As a result, we can expect the following scenario for the evolution of the black hole mass: When the black hole mass is smaller than the upper limit, mass accretion of the interstellar matter in the circumnuclear region, causing the AGN activities, makes the black hole mass larger. However, when the mass gets to the upper limit, the black hole loses the balancing force against the dynamical friction and starts spiraling downward to the gravity center. From simple parameter scaling, the upper mass limit of the black hole is found to be proportional to the bulge mass, and this could explain the observed correlation of the black hole mass with the bulge mass.

Monte Carlo Solution of High Electric Field Hole Transport Processes in Avalanche Amorphous Selenium.

Amorphous selenium lacks the structural long-range order present in crystalline solids. However, the stark similarity in the short-range order that exists across its allotropic forms, augmented with a shift to non-activated extended-state transport at high electric fields beyond the onset of impact ionization, allowed us to perform this theoretical study, which describes the high-field extended-state hole transport processes in amorphous selenium by modeling the band-transport lattice theory of its crystalline counterpart trigonal selenium. An in-house bulk Monte Carlo algorithm is employed to solve the semiclassical Boltzmann transport equation, providing microscopic insight to carrier trajectories and relaxation dynamics of these non-equilibrium “hot” holes in extended states. The extended-state hole–phonon interaction and the lack of long-range order in the amorphous phase is modeled as individual scattering processes, namely acoustic, polar and non-polar optical phonons, disorder and dipole scattering, and impact ionization gain, which is modeled using a power law Keldysh fit. We have used a non-parabolic approximation to the density functional theory calculated valence band density of states. To validate our transport model, we calculate and compare our time of flight mobility, impact ionization gain, ensemble energy and velocity, and high field hole energy distributions with experimental findings. We reached the conclusion that hot holes drift around in the direction perpendicular to the applied electric field and are subject to frequent acceleration/deceleration caused by the presence of high phonon, disorder, and impurity scattering. This leads to a certain determinism in the otherwise stochastic impact ionization phenomenon, as usually seen in elemental crystalline solids.

Enhancement in the Photovoltaic Properties of Hole Transport Materials by End‐Capped Donor Modifications for Solar Cell Applications

Efficient hole transport materials for solar cell applications are gained huge intension of every scientist. Hole transport materials play a dominant role in solar cells as they provide high power conversion efficiency along with low cost, less toxic, and easy synthesis routs. Motivates from valuable literature, here efforts are being made to designed new novel hole transport materials for solar cell applications. Five new and highly efficient hole transport molecules (BT1–BT5) are designed after end‐capped donor modifications of recently synthesizedB3(R) molecule. The photovoltaic, optoelectronic, and structural‐property relationship of all designed molecules are extensively studied while using density functional theory and time‐dependent density functional theory at MPW1PW91/6‐31G(d,p) basis set. Low reorganizational energy of hole is observed in all designed molecules as compared to reference molecule which suggested that designed molecules have high hole mobility as compared toRmolecule. Red‐shifting in absorption spectrum of designed molecules (as compared to reference molecule) is also seen which offer high power conversion efficiency and high excited highest occupied molecular orbital to lowest unoccupied molecular orbital charge shifting. Low binding and excitation energies are observed in designed molecules. Molecular electrostatic potential, transition density matrix, hole–electron overlap as heat map, open circuit voltage, density of states, and complex study ofBT5:PC61BMis also performed for all studied molecule. After all analysis, we believed that our theoretical designed molecules are superior toRmolecule, thus we recommend these molecules to experimentalist for future development of highly‐efficient solar cells.

Bounds on warm dark matter from Schwarzschild primordial black holes

We consider light dark matter candidates originated from the evaporation of Schwarzschild primordial black holes, with masses in the range 10^{-5}–10^9 g. These candidates are beyond standard model particles with negligible couplings to the other particles, so that they interact only gravitationally. Belonging to the category of warm dark matter, they nevertheless spoil structure formation, with a softer impact for increasing values of the candidate spin. Requiring such candidates to fully account for the observed dark matter, we find that the scenario of black hole domination is ruled out for all spin values up to 2. For the scenario of radiation domination, we derive upper limits on the parameter beta (the primordial black hole energy density at formation over the radiation one), which are less stringent the higher the candidate spin is.

How Does Bridging Core Modification Alter the Photovoltaic Characteristics of Triphenylamine-Based Hole Transport Materials? Theoretical Understanding and Prediction.

Perovskite solar cells have gained immense interest from researchers owing to their good photophysical properties, low-cost production, and high power conversion efficiencies. Hole transport materials (HTMs) play a dominant role in enhancing the power conversion efficiencies (PCEs) and long diffusion length of holes and electrons in perovskite solar cells. In hole transport materials, modification of π-linkers has proved to be an efficient approach for enhancing the overall PCE of perovskite solar cells. In this work, π-linker modification of a recently synthesized H-Bi molecule (R) is achieved with novel π-linkers. After structural modifications, ten novel HTMs (HB1-HB10) with a D-π-D backbone are obtained. The structure-property relationship, and optoelectronic and photovoltaic characteristics of these newly designed hole transport materials are examined comprehensively and compared with reference molecules. In addition, different geometric parameters are also examined with the assistance of density functional theory (DFT) and time-dependent DFT. All the designed molecules exhibit narrow HOMO-LUMO energy gaps (Eg =2.82-2.99 eV) compared with the R molecule (Eg =3.05 eV). The designed molecules express redshifting in their absorption spectra with low values of excitation energy, which in return offer high power conversion efficiencies. Further, density of states and molecular electrostatic potential analysis is performed to locate the different charge sites in the molecules. The reorganizational energies of holes and electrons are found to have good values, suggesting that these novel designed molecules are efficient hole transport materials for perovskite solar cells. In addition, the low binding energy values of the designed molecules (compared with R) offer high current charge density. Finally, complex study of HB9:PC61 BM is also undertaken to understand the charge transfer between the molecules of the complex. The results of all analyses advocate that these novel designed HTMs are promising candidates for the construction of future high-performance perovskite solar cells.

Theoretical investigations about the effect of electron-withdrawing groups on proprieties of A-π-D-π-A type small molecules donor for organic solar cells.

Taking the reporting donor SM0 as reference, three new A-π-D-π-A type small molecules donors (SM1, SM2, and SM3) were designed via replacing acceptor moieties. The molecular proprieties affecting the cell performance, such as, frontier molecular orbital, open circuit voltage (Voc), absorption spectrum, vertical and adiabatic ionization potential, vertical and adiabatic electronic affinity, and energy driving force ΔEL-L were investigated through the density functional theory (DFT) and the time dependent density functional theory (TD-DFT). All new designed molecules exhibit reduced energy gap, show a red shift absorption band, small energy binding Eb, moderate Voc, and improve the creation of hole and electron as compared to SM0, which demonstrate that these new designed molecules could be used as a promising donors materials for organic solar cell. Additionally, the three new designed molecules present a larger amount charge transfer qCT, a longer length charge transfer DCT than SM0 and have a smaller reorganization energy of hole λ(h) which improve the charge carrier mobilities.

Electron-phonon coupling in the magnetic Weyl semimetal ZrCo2Sn

Electron-phonon coupling in $\mathrm{Zr}{\mathrm{Co}}_{2}\mathrm{Sn}$ is investigated within the density-functional theory and linear-response approach in the mixed-basis pseudopotential representation. Phonon-induced scattering is analyzed for excited electrons (holes) in two majority bands, which form the topological Weyl state. Although the electron-phonon coupling in the energy range under consideration demonstrates some dependence on the available phase space, the strength of the phonon-mediated scattering, $\ensuremath{\lambda}$, changes rather weakly with the hole (electron) energy and momentum, varying between 0.1 and 0.3. The momentum-averaged value of $\ensuremath{\lambda}$ ranges from 0.25 to 0.45. The phonon-mediated scattering of electrons near the Weyl point is found to be weak enough to warrant well-defined quasiparticles. Most of the modes actively involved in electron scattering are middle- and high-frequency lattice vibrations, while the participation of low-energy acoustic phonons is significantly suppressed by electron-phonon matrix elements. Of the long-wavelength optical phonons, only the ${T}_{2g}$ Raman active modes generated by opposite vibrations of Co atoms make a noticeable contribution to the scattering of electrons.

Magnetic reconnection as a mechanism for energy extraction from rotating black holes

Spinning black holes store rotational energy that can be extracted. When a black hole is immersed in an externally supplied magnetic field, reconnection of magnetic field lines within the ergosphere can generate negative energy (relative to infinity) particles that fall into the black hole event horizon while other particles escape stealing energy from the black hole. We show analytically that energy extraction via magnetic reconnection is possible when the black hole spin is high (dimensionless spin $a\sim1$) and the plasma is strongly magnetized (plasma magnetization $\sigma_0>1/3$). The parameter space region where energy extraction is allowed depends on the plasma magnetization and the orientation of the reconnecting magnetic field lines. For $\sigma_0 \gg 1$, the asymptotic negative energy at infinity per enthalpy of the decelerated plasma that is swallowed by a maximally rotating black hole is found to be $\epsilon^\infty_- \simeq - \sqrt{\sigma_0/3}$. The accelerated plasma that escapes to infinity and takes away black hole energy asymptotes the energy at infinity per enthalpy $\epsilon^\infty_+ \simeq \sqrt{3\sigma_0}$. We show that the maximum power extracted from the black hole by the escaping plasma is $P_{\rm extr}^{\rm max} \sim 0.1 M^2\sqrt{\sigma_0}\,w_0$ (here, $M$ is the black hole mass and $w_0$ is the plasma enthalpy density) for the collisionless plasma regime and one order of magnitude lower for the collisional regime. Energy extraction causes a significant spindown of the black hole when $a \sim 1$. The maximum efficiency of the plasma energization process via magnetic reconnection in the ergosphere is found to be $\eta_{\rm max} \simeq 3/2$. Since fast magnetic reconnection in the ergosphere should occur intermittently in the scenario proposed here, the associated emission within a few gravitational radii from the black hole is expected to display a bursty nature.

Exploring the electron-hole transport nature and optoelectronic properties of 4-nitro-4′-amino-azobenzene-based dyes

Charge transport and electronic properties of 4-nitro-4′-amino-azobenzene compounds with donor-acceptor backbone were examined at the molecular level. Optical properties of all the studied six azobenzene dyes were also explored at the solid-state bulk level, i.e., dielectric constants, conductivity, refractive index, and extinction coefficient values. The introduction of benzyl group enhances whereas propanenitrile diminishes the values for real and imaginary dielectric functions. Moreover, the substitution of 3-methoxy-3-oxopropyl and propanenitrile at amino group decreases the real conductivity values; however, bis(3-methoxy-3-oxopropyl) improves these values. These 4-nitro-4′-amino-azobenzene compounds showed good refractive indices in the energy range 0–2 eV which revealed that these dyes would be efficient to generate healthier outputs with lower energy inputs. The effect of substituents was also investigated on transfer integrals, frontier molecular orbitals (FMOs), reorganization energies, electron affinity (EA), and ionization energy (IE). The ground-state geometries were optimized by density functional theory at B3LYP/6-31G** level to probe the molecular level properties. The same level of theory was used for the cation and anion optimizations. The hole and electron transfer nature of azo dyes was investigated by evaluating the electron/hole transfer integrals (Velectron/Vhole) as well as hole and electron reorganization energy values. The results exposed that superior Vhole values of Azo2 and Azo4 might lead to these dyes as p-type contenders. Moreover, larger Velectron values of Azo1, Azo3, Azo5, and Azo6 might lead to these dyes as n-type competitors. These results revealed that inspected Azo dyes would be able to serve as competent hole and electron transfer materials within versatile organic semiconductors.

Theoretical research of time-dependent density functional on initiated photo-dissociation of some typical energetic materials at excited state

Nitro explosive is a main type of energetic material which can release a large amount of energy when detonated under extreme conditions. Further study of the excited state dynamics of photo-induced nitro explosive can provide an effective method to understand the complex process of ultrafast detonation physics. In this paper, the initial step of photodissociation at the first excited electron state of some typical nitro explosives including nitromethane (NM), cyclotrimethylenetrinitramine (RDX) and triaminotrinitrobenzene (TATB) is studied using the time-dependent density functional theory and the molecular dynamic method. The transient structures of energetic molecules and time evolutions of excited energy levels are observed. It is found that the structural relaxation of energetic molecules occurs immediately after the electronic excitation, and the entire photoexcitation process comes into being within a range of 200 fs. At the same time, the positions of molecular energy levels change to various degrees with the oscillations of different frequencies, such as the overlap between HOMO and LUMO, which is related to the obvious change of molecular configuration, indicating that the energy of excited carriers transfers to atoms in the form of heat through electron-phonon coupling, and the energy is redistributed through vibration relaxation in the initial stage of photodissociation which causes the chemical bonds of C—H, N—N and N—N to rupture, and the hydrogen atoms dissociated from methyl, methylene or amino groups, and the nearest nitro group to form some new intermediate states. In this process, the energy levels near the excited electron and hole energy also change significantly with time, suggesting that the coupling between electron and electron also plays a role in the dissociation process. Comparing with NM and RDX, the evolution of the excited energy level of TATB has obvious lower-frequency (phonon frequency) oscillations, showing that the coupling between electronic state and phonon of TATB is weak and thus makes it more difficult to dissociate. Our study can deepen the understanding of the structural relaxation of excited states and the time evolution of excitation energy levels in energetic materials, and provide a new understanding of the photoinduced reaction and the initial steps of laser ignition in energetic materials.

Фотопроводимость и поглощение инфракрасного излучения в квантовых ямах p-GaAs/AlGaAs

The spectra of low-temperature impurity-assisted far and mid-infrared photoconductivity and absorption in nanostructure with multiple GaAs/AlGaAs quantum wells doped with acceptors are investigated. The experimentally obtained absorption and photoconductivity spectra correlate well with each other. According to the hole and acceptor state energy spectrum calculations the spectral features related to the optical hole transitions from the ground acceptor state to the delocalized states of valence subbands, to the excited acceptor states and to the delocalized states above the quantum well (photoionization) are identified in the absorption and photoconductivity spectra.