Photon Energy Dependence Research Articles

The impact of charge carrier dynamics on the outdoor performance of cesium-lead-halide perovskite photovoltaics

We investigated the optoelectronic characteristics of cesium-based perovskite using various techniques. The steady-state photoluminescence (PL) spectroscopy of this perovskite solar cell composition shows the presence of strong peaks at a wavelength of 759 nm, which that corresponds to a band gap energy 1.63 eV. This band gap energy was estimated using two complementary methods, the PL emission spectra and the UV–vis absorption spectra. The study describes the dependence of photon energy on wavelength using a Gaussian mathematical model. Real-outdoor performance testing was conducted in Ethiopia’s climate during the hottest seasons to study the device performance under outdoor conditions at varying irradiances. Moreover, we investigated power generation from the devices using current–time measurements and analyzed charge carrier dynamics through transient photocurrent measurements.

Evaluation of uncertainty in personal dose measured using CaSO4:Dy-based TLD badge at different workplaces.

The metrological quality of a measurement is characterised by evaluating the uncertainty in the measurement. In this paper, uncertainty in personal dose measured using individual monitoring CaSO4:Dy-based thermoluminescence dosimeter badge is evaluated by application of the guide to the expression of uncertainty in measurement method. The present dose reporting quantity, whole body dose (WBD) and the proposed quantity, personal dose equivalent, Hp(10) has been used as measurands. The influence of various input quantities on the measurement were analyzed through tests that conform to the requirements of the International Electrotechnical Commission IEC 62387. The study found that the expanded uncertainties for WBD and Hp(10) measurements were 63.4% and 41.4%, respectively, corresponding to a 95% coverage probability for workplace fields covering a wide photon energy range (33-1250keV). However, the uncertainty estimates were quite lower for the type of workplaces that are identified using the dose evaluation algorithm. The input quantities, namely, the response to a mixture of photon beam qualities and photon energy and angular dependence contribute the most to the total uncertainty.

Use of parametric X-ray radiation of electrons in crystals to determine the parameters of imaging-plates

Good agreement between experimental data and the results of calculations of the yield and angular distributions of parametric X-ray radiation of electrons in crystals within the framework of kinematic theory enables us to use the measurement results to determine the photon energy dependence of the sensitivity of X-ray plates. The results of measurements of the angular distributions of parametric X-ray radiation of electrons with an energy of 255 MeV in a Si crystal using imaging plates of several types were compared with the results of calculations that take into account all currently known experimental factors that influence the measurement results. The spectral dependence of the sensitivity of the studied X-ray plates was determined for photon energies of two orders of reflection and for the (111), (1̅1̅1), and (110) reflection planes.

Resonant Auger decay of dissociating CH3I near the I 4d threshold.

Resonant Auger processes provide a unique perspective on electronic interactions and excited vibrational and electronic states of molecular ions. Here, new data are presented on the resonant Auger decay of excited CH3I in the region just below the I 4d-1 ionization threshold. The resonances include the Rydberg series converging to the five spin-orbit and ligand-field split CH3I (I 4d-1) thresholds, as well as resonances corresponding to excitation from the I 4d5/2,3/2 orbitals into the σ* lowest unoccupied molecular orbital. This study focuses on participator decay that populates the lowest lying states of CH3I+, in particular, the X̃2E3/2 and 2E1/2 states, and on spectator decay that populates the lowest-lying (CH3I2+)σ* states of CH3I+. The CH3I (I 4d-1)σ* resonances are broad, and dissociation to CH3 + I competes with the autoionization of the core-excited states. Auger decay as the molecule dissociates produces a photoelectron spectrum with a long progression (up to v3+ ∼ 25) in the C-I stretching mode of the X̃2E3/2 and 2E1/2 states, providing insights into the shape of the dissociative core-excited surface. The observed spectator decay processes indicate that CH3I+ is formed on the repulsive wall of the lower-lying (CH3I2+)σ* potentials, and the photon-energy dependence of the processes provides insights into the relative slopes of the (4d-1)σ* and (CH3I2+)σ* potential surfaces. Data are also presented for the spectator decay of higher lying CH3I (I 4d-1)nl Rydberg resonances. Photoelectron angular distributions for the resonant Auger processes provide additional information that helps distinguish these processes from the direct ionization signal.

Three-dimensional electronic structure of the superconductor Sn4Sb3 by angle-resolved photoemission spectroscopy

The layered material Sn4Sb3 exhibits superconductivity with 1.47 K and is proposed to be a topological superconductor candidate. In this study, we investigate the electronic structure of Sn4Sb3 using angle-resolved photoemission spectroscopy and density functional theory (DFT) calculations. Despite its layered structure, the band structure of Sn4Sb3 shows strong kz dependence, leading to the formation of a three-dimensional Fermi surface. The electronic bands exhibit three-fold symmetry at most kz planes and six-fold symmetry at the Γ and Z planes. These observations are consistent with DFT calculations, except for the presence of additional flat-like bands located 500 meV below the Fermi level. The photon energy dependence measurement show noticeable kz dispersion in one of the splitted branches, suggesting a bulk origin of the feature, and negligible kz dispersion in another branch, implying the surface origin of the state.

Photon energy dependence of graphene oxide reduction by soft X-ray irradiation and atomic hydrogen annealing

The effects of soft X-ray irradiation and atomic hydrogen annealing on the reduction of graphene oxide (GO) to obtain graphene were investigated. To clarify the interaction between soft X-rays and GO, soft X-rays of 300 eV and 550 eV were used for C 1s and O 1s inner-shell electron excitation, respectively at the NewSUBARU synchrotron radiation facility. Low-temperature reduction of the GO film was achieved by using soft X-ray at temperatures below 150 °C at 300 eV, and 60 °C at 550 eV. O-related peaks in X-ray photoelectron spectroscopy, such as the C–O–C peak, were smaller at 550 eV than those at 300 eV. This result indicates that excitation of the core–shell electrons of O enhances the reduction of GO. Soft X-rays preferentially break C–C and C–O bonds at 300 and 550 eV, respectively.

Photon energy dependence of photoneutron production from heavy targets

The double differential cross-sections (DDXs) of photoneutron production via the photonuclear reaction on tantalum, tungsten, and bismuth for 13 and 17 MeV linearly polarized photon beams were measured using the time-of-flight method at the NewSUBARU-BL01 facility. Polarized photons were obtained by the Laser Compton backscattering (LCS) technique. Two distinct components were observed on the spectra: the lowenergy component up to 4 MeV and the high-energy above 4 MeV. The angular distribution of the low-energy component was isotropic, whereas the high-energy was distributed anisotropically and influenced by the angle between direction of photon polarization and neutron emission, especially for 17 MeV photon energy. These phenomena were similar to those of 197Au target observed in the previous studies. The low-energy neutron distributions at 13 and 17 MeV photon energies were almost identical for all three targets. The DDX energy integration was calculated and compared among the three targets for two-photon energies. Given the horizontal polarization (plane parallel to the x-axis) of the incident photons, the emission angles of 90° on the x-axis and y-axis recorded the maximum and minimum photoneutron yield, respectively. The differences between these two positions were minor for 181Ta and natW at 13 MeV photon energy and noticeable for other cases. An underestimation of the TENDL nuclear data library was observed on the photoneutron DDXs compared to the experimental results for 181Ta and 209Bi.

Distinctive Features of Mesa‐Type Metal/Dielectric Surface Grating Structures Assisting Resonant Enhancement of Thermal Emission at Longitudinal–Optical Phonon Energy

Previously, a longitudinal optical (LO) phonon resonant emission (LORE) at 8.5 THz from Au‐GaAs surface microstructures at 630 K is reported. This emission ascribed to thermally generated electric dipoles by the coherently vibrating charges at Au/GaAs/Au interfaces shows no dependence of the emission photon energy on the emission direction, which is different from the property of surface phonon polaritons. Herein, the advantage of surface grating structures with high mesa and narrow window width is shown. The experimental emission properties of samples with 1.4–6.0 μm window width and mesa height up to 2.7 μm and finite difference time domain simulations reveal the increase in mesa height increases the electric dipole moment, while it augments the reabsorption of LORE and the background radiation subject to Planck's law for a wide window width of 6 μm. Reabsorption and the background emission can be reduced by adopting high mesa and narrow windows, which is due to the reduction of both the wire‐grid polarizer function and the distribution of the electric field beyond the LO‐phonon coherence inside the GaAs wafer. Theoretical simulation results suggest that a structure with a window width of 0.75 μm and a mesa height of 2 μm is an effective countermeasure.

Higher-Order Harmonics in Hexagonal Graphene Quantum Dots

We have considered the high-order harmonic generation in plane graphene quantum dots of hexagonal shape by the independent quasiparticle approximation-tight binding model. We have investigated how such a nonlinear effect is affected by a strong optical wave field, quantum dot typical band gap and lateral size, and dephasing processes. The equation of motion for the density matrix is solved by performing the time integration with the eight-order Runge–Kutta algorithm. If the optical wave frequency is much less than the quantum dot intrinsic band gap, the main aspects of multiphoton high harmonic emission in quantum dots are revealed. In such case dependence of the cutoff photon energy on the strength of the optical pump wave is almost linear. But when the wave frequency is comparable to the bandgap of the quantum dot, the cutoff photon energy shows saturation behavior with an increase in the wave field strength.

A coherent phonon-induced hidden quadrupolar ordered state in Ca2RuO4

Ultrafast laser excitation provides a means to transiently realize long-range ordered electronic states of matter that are hidden in thermal equilibrium. Recently, this approach has unveiled a variety of thermally inaccessible ordered states in strongly correlated materials, including charge density wave, ferroelectric, magnetic, and intertwined charge-orbital ordered states. However, more exotic hidden states exhibiting higher multipolar ordering remain elusive owing to the challenge of directly manipulating and detecting them with light. Here we demonstrate a method to induce a dynamical transition from a thermally allowed to a thermally forbidden spin-orbit entangled quadrupolar ordered state in Ca2RuO4 by coherently exciting a phonon that is strongly coupled to the order parameter. Combining probe photon energy-resolved coherent phonon spectroscopy measurements with model Hamiltonian calculations, we show that the dynamical transition is manifested through anomalies in the temperature, pump excitation fluence, and probe photon energy dependence of the strongly coupled phonon. With this procedure, we introduce a general pathway to uncover hidden multipolar ordered states and to control their re-orientation on ultrashort timescales.

Enhanced vacuum ultraviolet photoemission from graphene nanoribbons

Photon-energy dependence of photoemission from seven-atoms-wide armchair graphene nanoribbons (GNRs) is studied experimentally and theoretically up to eV. A strong photon energy dependence of the normal emission from the valence band maximum (VB1) is observed, sharply peaked at eV. The detailed analysis of the light-polarization dependence of the photoemission from VB1 unambiguously characterizes the symmetry of the state. The experimental observations are analyzed based on ab initio one-step theory of photoemission. Off-normal emission is studied in detail and its relation to the standing-wave character of the valence band states is discussed. Excellent agreement with the earlier experiment (Senkovskiy et al 2018 2D Mater. 5 035007) is obtained. Rapid variations of the intensity with the ribbon-transverse photoelectron momentum are predicted from the ab initio theory, which are at variance with the prediction of the tight-binding rigid-wall model. These findings can help interpret angle-resolved photoemission measurements of similar systems. Moreover, the strong enhancement of the photoyield could trigger the GNR application as narrow-band photodetectors and contribute to the design of novel photocathodes for vacuum ultraviolet photodetection.

Wavelength-Sensitive Superconducting Single-Photon Detectors on Thin Film Lithium Niobate Waveguides.

Lithium niobate, because of its nonlinear and electro-optical properties, is one of the materials of choice for photonic applications. The development of nanostructuring capabilities of thin film lithium niobate (TFLN) permits fabrication of small footprint, low-loss optical circuits. With the recent implementation of on-chip single-photon detectors, this architecture is among the most promising for realizing on-chip quantum optics experiments. In this Letter, we report on the implementation of superconducting nanowire single-photon detectors (SNSPDs) based on NbTiN on 300 nm thick TFLN ridge nano-waveguides. We demonstrate a waveguide-integrated wavelength meter based on the photon energy dependence of the superconducting detectors. The device operates at the telecom C- and L-bands and has a footprint smaller than 300 × 180 μm2 and critical currents between ∼12 and ∼14 μA, which ensures operation with minimum heat dissipation. Our results hold promise for future densely packed on-chip wavelength-multiplexed quantum communication systems.

Photon Energy‐Dependent Optical Spin‐Orbit Torque in Heavy Metal–Ferromagnet Bilayers

AbstractThe manipulation of magnetization through optically generated ultrafast spin currents is a fascinating area that needs a thorough understanding for its potential future applications. In this work, a comprehensive investigation of helicity‐driven optical spin‐orbit torque in heavy metal/ferromagnetic metal heterostructures is presented, specifically cobalt capped with gold or platinum, subject to laser pumping at different wavelengths. The results demonstrate up to tenfold enhancement in optical spin‐orbit torque quantum efficiency for gold compared to platinum of the same thickness when pumped with a visible laser. Additionally, the study provides the first experimental analysis of the photon energy dependence of optical spin‐orbit torque and derives the optical spin orientation spectra for both gold/cobalt and platinum/cobalt heterostructures. A key insight gained from the study is the impact of photon energy‐dependent spin transport in the system, which suggests the use of a high photon energy pump for efficient spin transport. These findings highlight the potential of spin current generation and manipulation in gold/ferromagnet heterostructures for a wide range of applications such as all‐optical magnetization switching, spin‐wave generation and control, and spintronic terahertz emission.

On the Wavelength-Dependent Photochemistry of the Atmospheric Molecule CF3COCl.

The wavelength control of photochemistry usually results from ultrafast dynamics following the excitation of different electronic states. Here, we investigate the CF3COCl molecule, exhibiting wavelength-dependent photochemistry both via (i) depositing increasing internal energy into a single state and (ii) populating different electronic states. We reveal the mechanism behind the photon-energy dependence by combining nonadiabatic ab initio molecular dynamics techniques with the velocity map imaging experiment. We describe a consecutive mechanism of photodissociation where an immediate release of Cl taking place in an excited electronic state is followed by a slower ground-state dissociation of the CO fragment. The CO release is subject to an activation barrier and is controlled by excess internal energy via the excitation wavelength. Therefore, a selective release of CO along with Cl can be achieved. The mechanism is fully supported by both the measured kinetic energy distributions and anisotropies of the angular distributions. Interestingly, the kinetic energy of the released Cl atom is sensitively modified by accounting for spin-orbit coupling. Given the atmospheric importance of CF3COCl, we discuss the consequences of our findings for atmospheric photochemistry.

Tumor Regression with 5-Aminolevulinic Acid (5-ALA)-Mediated Radiodynamic Therapy (RDT) Using Different Megavoltage Energies

5-aminolevulinic acid (5-ALA) accumulates in target tumor cells, where it is metabolized to a photosensitizer - protoporphyrin IX (PpIX). Cherenkov light induced by high-energy photon beams effectively activates the PpIX due to the Soret band. The activated photosensitizers lead to cellular toxicities to kill malignant tumor cells by converting surrounding tissue oxygens into singlet oxygens. Radiodynamic therapy (RDT) utilizes cellular damage caused by both radiation dose and activated photosensitizer. The emission of Cherenkov light was observed higher with higher energy irradiation in phantom and ex-vivo tissues. Therefore, using an in-vivo mouse model, this study aimed to investigate the efficacy and energy dependency of RDT combined with 5-ALA and different ranges of megavoltage photon irradiation. In order to investigate individual and synergistic effects of 5-ALA administration and radiation treatment, the tumors (n = 344) were randomized into eight groups: control (untreated), 5-ALA only, 6-, 15-, and 45-MV conventional radiation treatment (RT) only, 6-, 15-, and 45-MV RDT. 4 Gy in a single fraction was delivered to the tumors using three different energy photons for RT only and RDT groups. 5-ALA was systemically injected into 5-ALA only and RDT groups at 100 mg/kg by tail-vein 4 hours before irradiation for endogenous PpIX accumulation in the tumor. Tumor growth was measured using a 1.5 T MR scanner on the day of treatment (prior to the treatment), 3, 7, and 14 days post-treatment. Two-way repeated ANOVA with Bonferroni correction was used to compare each treatment group to determine the statistically significant difference in tumor growth. A total of 45 MV RDT resulted in the most significant decrease in tumor growth by 58.8 ± 3.4 %, 58.0 ± 3.0 %, and 55.0 ± 3.0 % compared to 5-ALA, 45 MV RT, and control group on 7 days post-treatment (P<0.001), respectively. Moreover, a synergistic effect of 45 MV RDT causes a 47.1-54.1 % additional decrease in tumor growth toward the effective treatment outcome. Compared to the different energies, 45 MV RDT resulted in a 52.2 ± 3.1 % and 19.7 ± 7.2 % decrease in tumor growth compared to 6 MV RDT and 15 MV RDT on 7 days post-treatment, respectively (P<0.001), whereas the conventional RT was not. Radiodynamic therapy using 5-ALA administration and 45MV photon beam irradiation resulted in the most significant tumor growth control. A photon energy dependency was observed in radiodynamic therapy. 45MV photon beams showed greater in activating PpIX, improving the synergistic effects of radiation dose and activated photosensitizer than the other energies. The preliminary results provide a foundation for new innovative treatment strategies that have the potential to improve cancer treatment.

Simple extension of the plane-wave final state in photoemission: Bringing understanding to the photon-energy dependence of two-dimensional materials

Simple extension of the plane-wave final state in photoemission: Bringing understanding to the photon-energy dependence of two-dimensional materials

Soft x-ray photoelectron momentum microscope for multimodal valence band stereography

The photoelectron momentum microscope (PMM) in operation at BL6U, an undulator-based soft x-ray beamline at the UVSOR Synchrotron Facility, offers a new approach for μm-scale momentum-resolved photoelectron spectroscopy (MRPES). A key feature of the PMM is that it can very effectively reduce radiation-induced damage by directly projecting a single photoelectron constant energy contour in reciprocal space with a radius of a few Å−1 or real space with a radius of a few 100 μm onto a two-dimensional detector. This approach was applied to three-dimensional valence band structure E(k) and E(r) measurements (“stereography”) as functions of photon energy (hν), its polarization (e), detection position (r), and temperature (T). In this study, we described some examples of possible measurement techniques using a soft x-ray PMM. We successfully applied this stereography technique to μm-scale MRPES to selectively visualize the single-domain band structure of twinned face-centered-cubic Ir thin films grown on Al2O3(0001) substrates. The photon energy dependence of the photoelectron intensity on the Au(111) surface state was measured in detail within the bulk Fermi surface. By changing the temperature of 1T-TaS2, we clarified the variations in the valence band dispersion associated with chiral charge-density-wave phase transitions. Finally, PMMs for valence band stereography with various electron analyzers were compared, and the advantages of each were discussed.

Photon energy dependence of the photoelectron spectra of the anthracene anion: On the influence of autodetaching states.

Vibrationally resolved photoelectron spectra of anthracene anions have been measured for photon energies between 1.13 and 4.96eV. In this energy range, photoemission mostly occurs via autodetaching electronically excited states of the anion, which strongly modifies the vibrational excitation of the neutral molecule after electron emission. Based on the observed vibrational patterns, eight different excited states could be identified, seven of which are resonances known from absorption spectroscopy. Distinctly different photon energy dependencies of vibrational excitations have been obtained for different excited states, hinting at strongly different photoemission lifetimes. Unexpectedly, some resonances seem to exhibit bimodal distributions of emission lifetimes, possibly due to electronic relaxation processes induced by the excitation of specific vibrational modes.

Triphasic CoFe2O4/ ZnFe2O4 / CuFe2O4 nanocomposite for water treatment applications

In the recent years, ferrites have been extending their application niche from the traditional field of soft magnetics to various other fields, including catalysis, gas sensors, energy, biomedicine, and water decontamination. Most of these applications are geared toward single-phase ferrites and their mixtures are rarely investigated. Here, we report on the first study of a triphasic spinel ferrite nanocomposite containing CoFe2O4, ZnFe2O4 and CuFe2O4 and synthesized using citrate auto-combustion. Detailed characterization of the composite in comparison with its three constitutive ferrites is provided. Interestingly, many of the physical properties of the triphasic nanocomposite are more conducive to adsorption of heavy metals than those of any of the three individual ferrites. These properties include experimental density, surface area and roughness, and microstrain, which were all highest in the nanocomposite. For example, the triphasic nanocomposite displayed a twice higher surface roughness and three times higher surface area than those of CuFe2O4. Further, due to heterogeneous structuring of grain boundaries, the band gap of the nanocomposite was at 2.21 eV lower than that of any individual ferrites comprising it (2.31 – 2.62 eV). Consequently, at 6 × 1010 S-1, the maximum of the optical conductivity versus photon energy dependence was higher and the dielectric constant was lower for the nanocomposite than for any of its constitutive ferrites. The suitability of the nanocomposite to act as an adsorbent of toxic heavy metals was tested on the lead ion. The adsorption of lead increased with pH due to the effects on terminal group configuration, dispersion stability and metal ion speciation. The sorption also increased with the contact time, reaching saturation at 89% of the removal efficiency after 50 min. Adsorption isotherm fitting demonstrated that the ions adsorbed as monolayers on the surface of the nanocomposite. The adsorption process also followed the pseudo-second order kinetic model, with chemisorption as the dominant form of surface binding. The study confirms the potential of the triphasic ferrite nanocomposite to serve as an adsorbent material, given the promising removal efficiencies exhibited under the ambient conditions. This opens the door to a wide range of applications, not restricted to wastewater treatments alone, but also extending to the fields of antimicrobials, dye removal, and photocatalysis.

Origin of the Liquid/Gaseous Water Binding Energy Splitting Measured via X-ray Photoelectron Spectroscopy

Ambient-pressure X-ray photoelectron spectroscopy (APXPS) provides an effective way of tackling the challenge of detecting chemical states within complex systems. Here a fundamental understanding of the core-level shift (CLS) of water in the liquid/gas phase observed via APXPS is obtained with computational modeling at the molecular and electronic levels. The CLS value of ∼2 eV derived from experiments is reproduced by modeling in terms of the total shift and photon energy dependence. The contributions of collective electrical effects, including electrostatic potential, orbital deformation, and electronic polarization, to the CLS were further analyzed and discussed. Our results show that the CLS is dominated by the final state effect due to electronic polarization of the surrounding molecules following photoionization, while the peak broadening is mainly determined by the electrostatic potential, which belongs to an initial state effect. The physical insights and computational approaches could be further applied to study more complex molecules or materials.