Effective Mean Free Path Research Articles

Resistivity scaling in epitaxial MAX-phase Ti4SiC3(0001) layers

In situ transport measurements on 5.8–92.1 nm thick epitaxial Ti4SiC3(0001) layers are used to experimentally verify the previously predicted low resistivity scaling. Magnetron co-sputtering from three elemental sources at 1000 °C onto 12-nm-thick TiC(111) nucleation layers on Al2O3(0001) substrates yields epitaxial growth with Ti4SiC3(0001) || Al2O3(0001) and Ti4SiC3(101¯0) || Al2O3(21¯1¯0), a low and thickness-independent surface roughness of 0.6 ± 0.2 nm, and a measured stoichiometric composition. The room-temperature resistivity ρ increases slightly with decreasing thickness, from ρ = 35.2 ± 0.4 to 37.5 ± 1.1 μΩ cm for d = 92.1–5.8 nm, and similarly from 9.5 ± 0.2 to 11.0 ± 0.4 μΩ cm at 77 K, indicating only a minor effect of electron surface scattering on ρ. Data analysis with the classical Fuchs–Sondheimer model yields a room-temperature bulk resistivity ρo = 35.1 ± 0.4 μΩ cm in the basal plane and suggests effective mean free paths λ = 1.1 ± 0.6 at 293 K and λ = 3.0 ± 2.0 nm at 77 K if assuming completely diffuse electron surface scattering. First-principles calculations predict an anisotropic Ti4SiC3 Fermi surface and a product ρoλ = 19.3 × 10−16 Ω m2 in the basal plane. This value is six times larger than that predicted previously and five times larger than the measured temperature-independent effective ρoλ = (3.8 ± 2.1) × 10−16 Ω m2. This deviation can be explained by a high experimental electron scattering specularity of p = 0.8 for Ti4SiC3(0001) surfaces. Air exposure causes a 4% room-temperature resistivity increase for d = 5.8 nm, indicating a decrease in the surface scattering specularity Δp = −0.19. The overall results show that Ti4SiC3 is not directly applicable as an interconnect material due to its relatively large ρo. However, the particularly small resistivity scaling with an effective λ that is more than an order of magnitude smaller than that of Cu confirms the potential of MAX phase materials for high-conductivity narrow interconnects.

Barriers to carriers: faults and recombination in non-stoichiometric perovskite scintillators

Tuning the efficiency and speed of charge carrier recombination in inorganic scintillators can potentially improve their performance in diverse applications. Recent work suggests that this maybe be achieved via a two-phase scintillator AB that naturally phase separates into A-rich and B-rich domains. In addition, a favorable electronic structure and band-edge alignment such that the charge carriers are confined or are thermodynamically driven to preferentially accumulate in one of the two domains, might lead to an improved radiative recombination rate. Here, we use density functional theory computations and ab initio molecular dynamics (AIMD), including non-adiabatic molecular dynamics (NAMD) simulations, to examine an alternative phase structure and its potential impact on recombination. Using a model perovskite SrTiO_3 system with one-, two- and three-dimensional Ruddlesden–Popper (RP) phases, we demonstrate that RP faults induce band structure changes in the material that can act as barriers to carrier transport. Our AIMD/NAMD simulations indicate competing effects of a lower mean free path (potentially enhancing the desired radiative recombination and overall scintillating efficiency) and faster non-radiative recombination (undesired) due to enhanced electron–phonon coupling in the faulted system. Full exploitation of such a rational design approach would require tuning of the effective scintillation efficiency by varying the perovskite chemistry using appropriate arrangements of RP faults in the bulk material. Finally, other effects, such as the tendency of point defects to segregate at the interface, that might affect the overall performance, are briefly discussed. We expect the basic results found here to apply to other nanostructured scintillators.Graphical

Thermo-mechanical properties of nitrogenated holey graphene (C2N): A comparison of machine-learning-based and classical interatomic potentials

Thermal and mechanical properties of two-dimensional nanomaterials are commonly studied by calculating force constants using the density functional theory (DFT) and classical molecular dynamics (MD) simulations. Although DFT simulations offer accurate estimations, the computational cost is high. On the other hand, MD simulations strongly depend on the accuracy of interatomic potentials. Here, we investigate thermal conductivity and elastic modulus of nitrogenated holey graphene (C2N) using passively fitted machine-learning interatomic potentials (MLIPs), which depend on computationally inexpensive ab-initio molecular dynamics trajectories. Thermal conductivity of C2N is investigated via MLIP-based non-equilibrium molecular dynamics simulations (NEMD). At room temperature, the lattice thermal conductivity of 85.5 ± 3 W/m-K and effective phonon mean free path of 36.7 ± 1 nm are found. By carrying out uniaxial tension simulations, the elastic modulus, ultimate strength, and fractural strain of C2N are predicted to be 390 ± 3 GPa, 42 ± 2 GPa, and 0.29 ± 0.01, respectively. It is shown that the passively fitted MLIPs can be employed as an efficient interatomic potential to obtain the thermal conductivity and elastic modulus of C2N utilizing classical MD simulations. Moreover, the possibility of employing MLIPs to simulate C2N with point defects has been investigated. By training MLIP with point defect configurations, the mechanical properties of defective structures were studied. Although using the MLIP is more costly than classical interatomic potentials, it could efficiently predict the thermal and mechanical properties of 2D nanostructures.

The3He nuclear magnetic relaxation in nematically ordered Al2O3 aerogels: effects of 4He and nitrogen pre-plating

The results of 3He gas pulsed NMR spin–lattice relaxation study in high-porosity (84.9%–97.9%) nematically ordered Al2O3 aerogels at 1.5 and 4.2 K are presented. The linear dependence of T 1 on gas pressure is observed in aerogels that are pre-plated by helium-4. Nitrogen pre-plating prior to helium-4 pre-plating weakly decreases the 3He gas spin–lattice relaxation rate. A few possible mechanisms plausibly involved in 3He nuclear magnetic relaxation in aerogels are considered. The suggested nuclear spin–lattice relaxation model due to some magnetically ‘dirty’ aerogel fibers allows to estimate the effective mean free path of 3He atoms in aerogel.

Influence of the size effect on the generation and transport of charge carriers of phthalocyanines

In this work, on the surface of glass substrates with an ITO coating, solid phthalocyanine films with grain sizes of 40–50 nm were obtained by thermal evaporation in a vacuum, and nanowires with a cross-sectional area of ~ 5–7 nm and a thickness of 100 nm were synthesized by the method of gradient-temperature vapor deposition. The absorption spectra were measured in the visible range of the spectrum. It was found that the observed broadening of the bands and the shift of the peaks in the Q- and B-ranges in the absorption spectra of phthalocyanine nanowires are associated with the fact that the molecules in the nanowires are more densely packed compared to the films obtained by thermal evaporation, as a result of which their optical properties are complicated by intermolecular interactions. ITO/MPc/Al cells were prepared for photoelectrophysical measurements. The I–V characteristics of solid films and nanowires are measured. It is shown that in nanowires there is an increase in the maximum value of the I–V characteristic of phthalocyanines by 1.5 times and the open-circuit voltage by 0.1 V. The impedance spectra are measured. It was found that in nanowires, as compared to solid films, an increase (more than 10 times) in the effective mean free path of the charge, a decrease in the recombination resistance (by almost two orders of magnitude), and an increase in conductivity are observed. The results obtained can be used to improve the electrical transport characteristics of composite solar cells, organic light-emitting devices, and to develop sensitive elements for photoelectronic devices.

In-depth survey of nuclear radiation attenuation efficacies for high density bismuth lead borate glass system

MCNPX, Geant4 and FLUKA codes are employed to compute mass attenuation coefficients (μ/ρ) for 20Bi2O3-(80-x)B2O3-xPbO (x = 0, 20, 30, 40 and 60 mol%) glasses at 20, 30, 40 and 60 KeV, 133Ba (81, 161, 223, 276, 303, 356 and 384 keV), 57Co (122 and 136 KeV), 22Na (511 and 1275 keV),137Cs (662 keV),54Mn (835 keV), 60Co (1173 and 1333 keV) and 42K (1524 keV) photon peaks where 20, 30, 40 and 60 KeV energies are utilized for Mammography, Dental, General and Computed tomography (CT) scanning accordingly, in this study. All simulated μ/ρ outcomes accuracy was verified by WinXCOM and Phy-X/PSD programs’ μ/ρ findings and we noticed a satisfactory agreement among them. From μ/ρ and linear attenuation coefficient (μ) values effective atomic number (Zeff), effective electron density (Neff), half-value layer (HVL), tenth-value layer (TVL) and mean free path (MFP) have been determined. 20Bi2O3-20B2O3-60PbO (mol%) glass HVL and MFP have been compared with some commercial glasses, alloys, polymers, concretes and lead and ceramics corresponding values. Later equivalent atomic numbers (Zeq) and applying geometric progression (G–P) fitting method at 1 – 40 mfp penetration depths (PDs) at 0.015–15 MeV energy range exposure buildup factors (EBFs) and energy absorption buildup factors (EABFs) were estimated. At all selected twenty energies derived radiation protection efficiency (RPE) results confirmed studied samples’ excellent efficacy for low energy photons absorption. Moreover, applying SRIM codes mass stopping powers (MSPs) and projected ranges (PRs) for protons and α-particles and utilizing ESTAR database electron MSPs and continuous slowing down approximation (CSDA) range for electrons were determined at kinetic energy (KE) range of 0.015–15 MeV. Further fast neutron removal cross-sections (ΣR), for 0.0253 eV energy neutrons coherent and incoherent scattering cross-sections (σcs and σics), absorption cross-section (σA) and total cross-section (σT) quantities were evaluated. Derived ΣR was changed at 0.1166–0.123 cm−1 range depending on PbO addition in chosen samples. 20Bi2O3-80B2O3 (mol%) glass has larger σT (23.094 cm−1) in all studied samples for thermal neutron absorption while 20Bi2O3-20B2O3-60PbO (mol%) sample shows superior attenuation factors for photons and fast neutrons signifying included PbO positive effect.

Heat conduction below diffusive limit in amorphous superlattice structures

Advanced means to further reduce the thermal conductivity of dense amorphous materials by nanostructuring is important for thermal management in future electronic and optical devices. While the works so far have realized the reduction by scattering propagons, here, we demonstrate that nanostructures can in addition inhibit transport of diffusons, by measuring the thermal conductivity of amorphous-silicon/amorphous-silica superlattices with a periodicity ranging from 4.5 nm to 29.3 nm at room temperature. The measurements show that thermal conductivity of the superlattice with periodicity below 9.5 nm is significantly below the amorphous diffusive limit (~1 W/m K). The measured thermal conductivity can be reproduced using a combination of the phonon-gas kinetics model and Allen-Feldmann theory without any fitting parameters, with the interfacial transmittance of propagons and diffusons obtained by atomistic Green’s function. In addition to the known reduction of propagon transport, the effective mean free paths of diffusons are reduced from that of the bulk (1–3 nm) to several angstroms or even atomistic by extreme boundary scattering at the interfaces in the superlattice, giving rise to a significant tunability of the amorphous thermal conductivity using truly nanoscale structures. The influence of interface scattering on the diffusion transport can be effectively described by the Boltzmann transport equation, and in this sense, propagons and diffusons do not fundamentally differ. All data needed to evaluate the conclusions in the paper are present in the paper and/or the Supplementary Materials. Additional data related to this paper may be requested from the authors.

Gamma ray interaction studies of the PbCl2–SnCl2–P2O5 bioactive glass system for applications in nuclear medicine

Studies of bioactive glasses give an advanced roadbook to realize radiation applications in nuclear medicine and other medical applications. This paper aims to investigate the gamma ray interaction parameters of the PbCl2–SnCl2–P2O5 glass system. The mass attenuation coefficients (μm) of the selected bioactive glasses have been obtained using XCOM and dosimetry Phy-X/PSD programs in the photon energy range 10–150 keV and also correlated with those simulated through MCNP5 code. The other parameters, such as the effective atomic number (Zeff), electron density (Ne), and mean free path (MFP), tenth-value layer (TVL), and half-value layer (HVL) values have also been computed. Among all the selected bioactive glasses, the S4 bioactive glass has the lowest MFP, HVL, and TVL, showing that it is highly effective in absorbing gamma rays. The values of MFP of all samples (S1–S8) are also compared to the RS 253G18 and RS 360 commercial glasses at energy 150 keV. The fast neutron removal cross-sections have been obtained to study the fast neutron absorption behavior with the selected bioactive glasses.

Precision measurement of the muonium hyperfine interaction in mesoporous silica and aerogel

Precise measurements of the muonium (Mu) hyperfine interaction versus temperature are reported in a silica aerogel and mesoporous silica SBA-15 using a fast-timing spectrometer to detect the precession frequencies of Mu in a magnetic field of 1.14 T. The observed signals are a sensitive monitor of dynamics associated with the binding and unbinding of Mu from the silica surface. Above 100 K the Mu is effectively off the surface. Significant differences are observed in the way the lines show motional narrowing, and are attributed to differences in sample morphology. At room temperature the effective mean free path appears longer in SBA-15, suggesting it may offer advantages over aerogel as a source of Mu in vacuum.

INVESTIGATIONS OF GAMMA RAY SHIELDING PROPERTIES OF MoO3 MODIFIED P2O5-SiO2-K2O-MgO-CaO GLASSES

The aim of this paper is to investigate the gamma radiation shielding properties of P2O5- SiO2-K2O-MgO-CaO-MoO3 glasses. The mass attenuation coefficients (μm) have been computed via Photon Shielding and Dosimetry (Phy-X/PSD) software in the energy range 0.015-15 MeV. The other shielding factors are also computed as the effective atomic number (Zeff), electron density (Ne), and mean free path (MFP) values, exposure (EBF) and energy absorption (EABF) buildup factors for a penetration depths 20 mfp. The values of the shielding parameters are strongly dependent on energy and chemical composition. The PSKMCM6 possesses the lowest value of MFP and highest value of µm and Zeff, among the glasses. The glass sample PSKMCM6 has minimum value of EBF and EABF as compared to other samples.

Resistivity Size Effect in Epitaxial Rh(001) and Rh(111) Layers

Rh(001) and Rh(111) layers with thickness d = 8-181 nm are sputter deposited onto MgO(001) and Al2O3(112̅0) substrates and their resistivity ρ measured in situ and ex situ at room temperature and 77 K in order to quantify the resistivity size effect. Rh(001) layers are epitaxial single crystals and show a resistivity increase with decreasing d that is well described with the classical Fuchs and Sondheimer model, indicating an effective electron mean free path λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">eff</sub> = 9.5 ± 0.8 nm at 295 K. Rh(111) layers exhibit an epitaxial microstructure with two 60°-rotated domains with a lateral width of 19 ± 2 nm, as determined from the X-ray coherence length. The grain boundaries between the domains cause a thickness-independent resistivity contribution Δρ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">gb</sub> = 0.74 and 0.59 μΩcm at 295 and 77 K, indicating an electron reflection coefficient R = 0.16 ± 0.03 for a boundary characterized by a 60° rotation about the (111) axis. Air exposure causes a nearly negligible (<; 6%) resistivity increase which suggests a possible reduction in the surface scattering specularity by Δp <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> = -0.3 ± 0.2 during surface oxidation. The overall results yield a temperature-independent product of the bulk resistivity times the electron mean free path ρ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</sub> λ = (4.5 ± 0.4) × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-16</sup> Ωm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . This is 1.4 times larger than previously predicted from first principles, but 33%, 55%, 63%, and 11% smaller than for Cu, W, Co, and Ru, respectively, suggesting great promise for Rh as an alternative metal for narrow interconnects.

Advances in ultrafast laser structuring of materials at the nanoscale

Abstract Laser processing implies the generation of a material function defined by the shape and the size of the induced structures, being a collective effect of topography, morphology, and structural arrangement. A fundamental dimensional limit in laser processing is set by optical diffraction. Many material functions are yet defined at the micron scale, and laser microprocessing has become a mainstream development trend. Consequently, laser microscale applications have evolved significantly and developed into an industrial grade technology. New opportunities will nevertheless emerge from accessing the nanoscale. Advances in ultrafast laser processing technologies can enable unprecedented resolutions and processed feature sizes, with the prospect to bypass optical and thermal limits. We will review here the mechanisms of laser processing on extreme scales and the optical and material concepts allowing us to confine the energy beyond the optical limits. We will discuss direct focusing approaches, where the use of nonlinear and near-field effects has demonstrated strong capabilities for light confinement. We will argue that the control of material hydrodynamic response is the key to achieve ultimate resolution in laser processing. A specific structuring process couples both optical and material effects, the process of self-organization. We will discuss the newest results in surface and volume self-organization, indicating the dynamic interplay between light and matter evolution. Micron-sized and nanosized features can be combined into novel architectures and arrangements. We equally underline a new dimensional domain in processing accessible now using laser radiation, the sub-100-nm feature size. Potential application fields will be indicated as the structuring sizes approach the effective mean free path of transport phenomena.

Effect of lead oxide on the optical properties and radiation shielding efficiency of antimony-sodium-tungsten glasses

This paper reports the effect of lead oxide (PbO) on the optical properties and radiation shielding efficiency of Sb2O3–Na2O–WO3–PbO glasses. The optical properties of the glasses were tested by estimating molar refraction (Rm), molar polarizability (αm), metallization principle (M), optical transmission (T), dielectric coefficients (static and optical), and reflection loss (RL). Additionally, the gamma radiation shielding efficiency of the glasses was evaluated via the Monte Carlo method (Geant4 simulations) and the XCOM program. The mass attenuation coefficient (µ/ρ) and other related factors such as effective atomic number (Zeff), half-value layer (HVL), and mean free path (MFP) were calculated at the energy range of 0.25–1.25 meV. Furthermore, the dependence of radiation protection efficiency (RPE) on the thickness of glasses was discussed in detail. The results revealed that at 40 mol% of PbO, the optical transmission was 0.7774 and the reflection loss was 1.1997. A notable increase in RPE as the thickness of the glass changes from 0.5 to 2 cm. The gamma shielding efficiency of the glasses was compared with those of commonly used shields. The reported glasses showed superior properties to apply for radiation shielding applications.

Effect of Surface Force on Nanoconfined Shale-Gas Flow in Slit Channels

Summary A model for gas transport in nanoscale channels in shale-gas reservoirs (SGRs) is proposed using a new effective mean free path (MFP) model, which considers the effects of surface/gas interaction and the geometrical termination of a nanochannel boundary. In addition, the influences of the nanochannel dimension, formation-burial depth, surface type, and gas type on nanoconfined gas flow in slit channels are addressed. The nanoconfined gas-flow behavior is investigated for a wide range of temperature and pressure in this work because of the large prospects of shale gas in deep and ultradeep formations with pressure up to 100 MPa and temperature up to 480 K. The newly developed effective MFP model and the gas-flow-rate model are successfully validated with data from molecular dynamics (MD) simulations and experiments. Results show that the effect of surface force reduces the MFP and gas-flow capacity, which increases with a decreasing pressure, a decreasing channel size, and an increasing temperature; that the nanoconfinement effect has weaker influence on gas-transport capacity as the formation-burial depth increases and greater influence as formation pressure decreases during hydrocarbon production from SGRs; that a surface type affects the gas transport, and the gas-flow capacity in carbon (C) channels (organic channels) is stronger than that in silicon (Si) channels (inorganic channels) with the same size; and that the differences among the transport capacities of nitrogen (N2), argon (Ar), and methane (CH4) are not obvious, while the transport capacities of helium (He) are greatly lower compared with CH4 at both the SGR temperature and the laboratory temperature.

Influence of the Ion Mass in the Radial to Orbital Transition in Weakly Collisional Low-Pressure Plasmas Using Cylindrical Langmuir Probes

This paper presents an experimentally observed transition from the validity of the radial theories to the validity of the orbital theories that model the ion current collected by a cylindrical Langmuir probe immersed in low-pressure, low-temperature helium plasma when it is negatively biased with respect to the plasma potential, as a function of the positive ion-neutral collision mean free path to the Debye length ratio Λ=λ+/λD. The study has been also conducted on argon and neon plasmas, which allows a comparison based on the mass of the ions, although no transition has been observed for these gases. As the radial or orbital behavior of the ions is essential to establish the validity of the different sheath theories, a theoretical analysis of such a transition not only as a function of the parameters Λ and β=T+/Te, T+ and Te being the positive ion and electron temperature, respectively, but also as a function of the ion mass is provided. This study allows us to recognize the importance of the mass of the ion as the parameter that explains the transition in helium plasmas. Motivated by these theoretical arguments, a novel set of measurements has been performed to study the relationship between the Λ and β parameters in the transition that demonstrate that the effect of the ion mean free path cannot be completely ignored and also that its influence on the ion current collected by the probe is less important than the effect of the ion temperature.

Study on Degradation Mechanisms of Thermal Conductivity for Confined Nanochannel in Gate-All-Around Silicon Nanowire Field-Effect Transistors

In this article, an analytical thermal conductivity model for confined nanochannel in gate-all-around silicon nanowire field-effect transistors (GAA SiNW FETs) is developed by considering the limitations caused by the cross section and length. A geometry dependence of phonon mean free path (MFP) is established for quantitatively analyzing the influence of cross-sectional dimension. Furthermore, the length-induced degradation mechanism is revealed by employing the transverse transportation phonon effective MFP. The results calculated by the model which was verified by published data indicate that the thermal conductivity of confined nanochannel in the GAA SiNW FETs is suffering from a severe degradation compared to that of ultrathin silicon in fully depleted (FD) silicon-on-insulator (SOI) MOSFETs. In addition to the suppression caused by the cross-sectional boundaries, the impact of the channel length should be taken into consideration during the modeling of thermal conductivity for accurately evaluating the self-heating effects (SHEs) in GAA SiNW FETs.

Theory for High‐Angular‐Resolution Photoelectron Holograms Considering the Inelastic Mean Free Path and the Formation Mechanism of Quasi‐Kikuchi Band

In recent years, highly accurate measurements of photoelectron holograms have become possible through the development of electron energy analyzers with an energy range of 300–1000 eV. Effects of the inelastic mean free path (IMFP) and thermal vibration became apparent in the hologram pattern. For example, the quasi‐Kikuchi band is clearly observed, which cannot be explained by conventional multiple scattering theories. Herein, the theory of photoelectron holograms is summarized, considering the inelastic scattering (IES) and thermal vibration effects. Furthermore, the simulated hologram is compared with a diamond hologram measured at a kinetic energy of 563.4 eV. It is also shown that the formation mechanism of the quasi‐Kikuchi band differs from that of the normal Kikuchi band.

Reckoning of nuclear radiation attenuation capabilities for binary GeO2-Tl2O, GeO2-Bi2O3, and ternary GeO2-Tl2O–Bi2O3 glasses utilizing pertinent theoretical and computational approaches

Abstract In this work, a total of eight thallium germanate, bismuth germanate, and bismuth thallium germanate glasses were explored for nuclear radiation shielding purposes. By employing the WinXCOM dependent Phy-X/PSD program, linear attenuation coefficient (μ) and mass attenuation coefficient (μ/ρ) values have been figured out within γ-ray energy range of 0.015–15 MeV and acquired μ/ρ quantities are in well accord with simulated Geant4 and Penelope codes μ/ρ results, accordingly. Some other relevant γ-ray attenuation parameters like effective atomic number (Zeff), effective electron density (Neff), half-value layer (HVL), tenth-value layer (TVL), and mean free path (MFP) were evaluated with the aid of Phy-X/PSD μ/ρ results. All μ/ρ, Zeff, Neff, HVL, TVL, and MFP parameters rely upon both samples' chemical composition and γ-ray energy. In place of GeO2, the inclusion of Tl2O and/or Bi2O3 in all selected samples demonstrates the enhanced γ-ray attenuation capacity with increasing Zeff and lower HVL, TVL, and MFP values. Besides, utilizing geometric progression (G‒P) fitting approach, within 0.015–15 MeV γ-ray energy range exposure buildup factors (EBFs) and energy absorption buildup factors (EABFs) have been estimated at discrete penetration depths (up to 40 mfp) and larger EBFs and EABFs are attained at higher energies with greater penetration depths. The ternary 16GeO2-62Tl2O–22Bi2O3 (mol%) glass, among all the tested samples, by owing comparatively larger μ, μ/ρ, and Zeff, lower HVL, TVL, MFP, EBFs, and EABFs, validate its' superior γ-ray attenuation ability as even HVL and MFP quantities of this sample are lower than some of the commercial shielding glasses, alloys, polymers, and concretes respective values when compared. Additionally, for all samples, neutron total cross-section (σT) values are derived within the neutron energy range of 10−8‒10 MeV by exerting Geant4 code. At 10−8 and 10 MeV neutron energies, the obtained ‘σT’ values are varied within 0.3589–0.4245 cm−1 and 0.13–0.1439 cm−1 ranges, respectively, for all studied glasses.

Anisotropic diffusion in Cyphochilus white beetle scales

Cyphochilus white beetles possess an exceptional ability to scatter visible light from their scales, which have anisotropic nanofibrillar network structures. We discover a striking effect that diffusely incident light on the beetle scales is preferentially channeled sideways and scattered backward on the average after traversing a vertical distance corresponding to only two scattering events. For normally incident light, the scattering is only slightly forward, resulting in close proximity between two optical characteristic lengths: scattering mean free path (1.78 µm) and effective transport mean free path (1.85 µm). We have used effective transport mean free path to properly describe the scattering strength in anisotropic random media. For improved description of light scattering in beetle scales, we apply complete solutions to the anisotropic diffusion equation, where the solution approach made use of optical boundary layer theory. Our method enables highly accurate determination of mean free paths and extrapolation length in the white beetle scales.

TeO2–B2O3–ZnO–La2O3 glasses: γ-ray and neutron attenuation characteristics analysis by WinXCOM program, MCNP5, Geant4, and Penelope simulation codes

γ-ray, fast and thermal neutrons shielding features for five Pb-free {[(TeO2)0.70(B2O3)0.30]0.7 (ZnO)0.30}(1-x)(La2O3)x (x = 0.01, 0.02, 0.03, 0.04, and 0.05 mol%) glasses have been inspected in this work. For all samples, within the photon energy range of 0.015–15 MeV, linear attenuation coefficients (μ) and mass attenuation coefficients (μ/ρ) were estimated using WinXCOM program (theoretical approach), and obtained μ/ρ values are in fine agreement with computed μ/ρ results of respective MCNP5, Geant4, and Penelope codes. By utilizing μ/ρ values of WinXCOM, γ-ray attenuation parameters like effective atomic number (Zeff), effective electron density (Neff), half-value layer (HVL), and mean free path (MFP) were assessed within 0.015–15 MeV photon energy range, for all samples. Additionally, exposure buildup factors (EBFs) and energy absorption buildup factors (EABFs) were calculated for all samples by applying a five parameter geometric progression (G‒P) fitting method as a function of various penetration depths (1, 5, 10, 15, 20, 25, 30, 35, and 40 mfp) within 0.015–15 MeV photon energy range. The derived radiation protection efficiency (RPE) results indicate all samples' effective attenuation competence for lower energy γ-rays. Among all glasses, 46.55TeO2-19.95B2O3-28.5ZnO–5La2O3 (mol%) sample, by having relatively bigger μ/ρ and Zeff, minimal HVL and MFP, and lowest EBF and EABF, endorse its' excellent γ-ray shielding effectiveness. Further, neutron shielding parameters such as macroscopic removal cross-section for fast neutrons (ΣR), coherent and incoherent scattering cross-sections (σcs & σics), absorption cross-section (σA), and total cross-section (σT) for thermal neutrons were explored. By using the Geant4 code, ‘σT’ values have been deduced within 10−4‒10−8 MeV neutron energy range. The 46.55TeO2-19.95B2O3-28.5ZnO–5La2O3 (mol%) glass owns relatively larger ΣR (0.1474 cm−1) for fast neutrons attenuation and ‘σT’ (10.1444 cm−1 at 0.0253 eV neutron energy, 15.9824 cm−1 → 0.551 cm−1 from 1 × 10−8 MeV →1 × 10−4 MeV neutron energy) for thermal neutrons absorption, respectively, revealing its' superior neutrons shielding ability.