Effective Mean Free Path Research Articles

Nuclear radiation shielding properties of calcium aluminum barium sodium borate glass samples doped with Dy3+ ions

Nuclear technology finds extensive application across various industries, medical physics, and research institutions, spanning fields such as agriculture and food technology. Despite its benefits, the pervasive use of ionizing radiation underscores the need for effective shielding materials to mitigate associated risks. Lead and concrete, traditionally favored for their attenuation properties, pose challenges due to weight, opacity, and toxicity concerns. In this context, calcium aluminum barium sodium borate glasses doped with Dy3+ ions emerge as promising alternatives for radiation shielding. This study investigates the ionizing electromagnetic radiation (gamma and X-ray) shielding capabilities of calcium aluminum barium sodium borate glasses doped with Dy3+ ions across a range of concentrations (0.1, 0.3, 0.5, and 1.0% mol). The mass attenuation coefficients and linear attenuation coefficients of four glass samples (S1 to S4) were determined using the software (Phy-X). Additionally, parameters such as effective atomic number (Zeff), half-value layer (HVL), tenth-value layer (TVL) and mean free path (mfp) were computed to assess shielding effectiveness.The results indicate that higher Dy3+ concentrations correlate with increased attenuation effectiveness, as evidenced by elevated μ and μm values. Glass sample S4, with the highest Dy3+ concentration, demonstrated superior shielding properties, attributed to its elevated density. Notably, the study elucidates the relationship between attenuation coefficients and photon energy, highlighting the dominance of photoelectric and Compton scattering effects. Furthermore, analysis of HVL, mfp, and Zeff values reveals the nuanced interplay between glass composition and radiation attenuation. Despite variations in composition, S4 consistently exhibited optimal shielding characteristics across photon energy ranges. The investigation also examines exposure and energy absorption buildup factors, indicating that higher Dy3+ concentrations lead to lower buildup values, indicative of enhanced shielding performance.In conclusion, the study underscores the potential of Dy3+ doped calcium aluminum barium sodium borate glasses as effective radiation shielding materials, offering insights into their composition-dependent attenuation properties. These findings contribute to the development of lead-free alternatives and advance the understanding of radiation shielding mechanisms in glass matrices, with implications for diverse applications in nuclear technology and beyond.

Air Leakages at Microvalves: Pressure Decay Measurements and Extended Continuum Modelling of Knudsen Flows

To improve the performance of valves in relation to the leakage rate, a comprehensive evaluation of the valve characteristics and behavior during pressure exposure is important. Often, these low gas flow rates below 0.1 cm3/min cannot be accurately measured with conventional flow sensors. This paper presents a small and low-cost test rig for measuring gas leakage rates accurately, even far below 0.1 cm3/min, with the pressure decay method. These leakage flows are substantiated with a flow model, where we demonstrate the feasibility of modeling those gas flows with an extended Navier–Stokes framework to obtain more accurate theoretical predictions. As expected, the comparison to the experimental results proves that the classical Navier–Stokes system is unsuitable for modeling Knudsen flows. Hence, self-diffusion of gas, a wall-slip boundary condition, and an effective mean free path model were introduced in a physically evident manner. In terms of the calculated mass flow, while self-diffusion and slip boundary conditions explain deviations from the classical Navier–Stokes equation for Knudsen numbers already smaller than 1, the effective mean free path model has an effect, especially when Kn > 1. For simplified conditions, an analytical solution was presented and compared to the results of an OpenFOAM CFD-solver for flow rates through more complex gap-flow geometries of the flap valve. Hereby, acceptable deviations between 10% and 20% were observed. A comparison with measurement results was carried out. The reproducibility of the measurement method was verified by comparing multiple measurements of one silicon microvalve sample to a state-of-the-art flow sensor. Three geometrically similar passive silicon microvalves were measured with air overpressure decreasing from 15 kPa relative to atmospheric pressure. Maximum gas volume flowing in a blocking direction of 1–26 µL/min with high reproducibility and marginal noise were observed.

Plasmonic enhancement of Faraday rotation with gold nanodisks with low height-to-diameter aspect ratios

We investigate the Faraday rotation induced in gold nanodisks with low height-to-diameter aspect ratios. Through a systematic study, we analyze the phenomenon using electrostatic theory with the modified long-wavelength approximation. We show that the Faraday rotation is enhanced at the localized surface plasmon resonance when the nanodisk’s effective mean free path is equal to the mean free path of the conduction electrons in the bulk metal, where light absorption dominates over light scattering. We also show that the Faraday rotation is largely enhanced at shorter rather than longer wavelengths.

Impact of bismuth oxide on structural, optical and gamma-ray shielding properties of calcium-sodium-borate glasses.

In the present study, we have prepared six glass samples of bismuth borate using the melt-quenching method with the composition (70-x)B2O3-10CaO-20Na2O-xBi2O3; x=0, 3, 6, 9, 12 and 15mol%. The density of the prepared glasses was determined using Archimedes principle. The X-ray diffraction patterns provide confirmation of the amorphous nature of the prepared samples, whereas the Fourier transform infrared measurements pointed to the existence of structural units like BO3, BO4, BiO3 and BiO6 within the glass network. An assessment of the optical absorption spectra unveiled that with the increase in the bismuth oxide content, there was a decrease observed in both the direct and indirect band gap energies. Specifically, they decreased from 3.40 to 2.79eV and from 3.10 to 2.46eV, respectively. The properties related to gamma ray attenuation, including the mass attenuation coefficient (μm), effective atomic number (Zeff), half-value layer (HVL) and mean free path (MFP), were examined for all the glass samples. This investigation was carried out using the Phy-X/PSD software, covering the energy range from 0.511 to 1.332MeV. Out of all the samples, Bi-15, featuring the highest Bi2O3 content, demonstrated the highest μm, Zeff, the smallest HVL and MFP. These results suggest that the glass with 15mol% of Bi2O3 offers the most effective gamma radiation shielding performance. Moreover, the glasses examined in this study exhibit superior radiation shielding characteristics compared with specific concrete types, namely, ordinary concrete, Hematite serpentine concrete and barite concrete, as well as commercial glasses such as RS-360 and RS-253.

Insight into the TiO2 on transport behavior and heat transfer of the CaO–SiO2–FeO–MgO system at different basicities: Molecular dynamics simulation and thermodynamics

In order to promote the resource utilization of Ti-containing converter slag and reduce the loss of metallic Ti, it is necessary to clarify the relationship between the oxygen network structure and thermophysical properties of the slag. The present work uses classical molecular dynamics (CMD) simulation to study the effects of basicity (1.0–3.0) and TiO2 content (0%–10 %) on the local structural properties, viscosity, and thermal conductivity of the CaO–SiO2–FeO–MgO–TiO2 (CSFMT) system at 1873 K. The M − O (M = Ca, Si, Fe, Mg, and Ti) bond length calculated based on CMD is consistent with the experimental results, and the [SiO4] tetrahedron and [TiO6] octahedron are the basic structural units of the CSFMT system. The increase in basicity promotes the break of bridging oxygen (BO) Si–O–Si and the formation of non-bridging oxygen Si–O-M. The increase in TiO2 content promotes the formation of Ti–O–Si in the system. The basicity and TiO2 content affect the thermophysical properties of the CSFMT system by promoting and inhibiting the depolymerization of the oxygen network structure, respectively. The diffusion abilities of different atoms in the CSFMT system are in descending order of Fe > Mg > Ca > O > Si > Ti. The viscosity of the CSFMT system decreases with increasing basicity and increases with increasing TiO2 content. Increasing the proportion of BOs can weaken the anharmonicity in the polyhedral structural units and reduce phonon scattering. With increasing basicity and TiO2 content, the effective phonon mean free path decreases and increases, respectively, resulting in a decrease and an increase in the thermal conductivity of the CSFMT system. The changes in the microstructure properties of the CSFMT system can be reasonably explained by the changes in its thermodynamic properties such as enthalpy. It is worth noting that the basicity has a greater effect on the viscosity, while the TiO2 content has a more significant impact on the thermal conductivity of the CSFMT system.

Resistivity size effect in epitaxial face-centered cubic Co(001) layers

Metastable face-centered cubic (fcc) Co layers are deposited by reactive magnetron sputtering in 5 mTorr N2 at 400 °C followed by vacuum annealing at 500 °C. The resulting phase-pure Co(001)/MgO(001) layers contain negligible nitrogen and exhibit a surface roughness <0.8 nm and a cube-on-cube epitaxial relationship with the substrate with Co[100]ǁMgO[100]. The measured resistivity vs thickness d = 10–1000 nm indicates a bulk resistivity ρo = 6.4 ± 0.3 μΩ cm for fcc Co at room temperature and ρo = 1.3 ± 0.1 μΩ cm at 77 K, and an effective electron phonon mean free path λ = 27 ± 2 nm and 79 ± 6 nm at 295 and 77 K, respectively. The resulting ρo × λ benchmark quantity is 3–5 times larger than that predicted from first principles, suggesting a breakdown of the Fuchs–Sondheimer model at small dimensions. The overall results indicate that fcc Co exhibits no intrinsic conductance benefit over stable hcp Co nor conventional Cu for narrow interconnects. The developed method for growth of epitaxial fcc Co(001) layers provides opportunities to study this metastable material for potential spintronic applications.

High-harmonic spectroscopy of low-energy electron-scattering dynamics in liquids

High-harmonic spectroscopy is an all-optical nonlinear technique with inherent attosecond temporal resolution. It has been applied to a variety of systems in the gas phase and solid state. Here we extend its use to liquid samples. By studying high-harmonic generation over a broad range of wavelengths and intensities, we show that the cut-off energy is independent of the wavelength beyond a threshold intensity and that it is a characteristic property of the studied liquid. We explain these observations with a semi-classical model based on electron trajectories that are limited by the electron scattering. This is further confirmed by measurements performed with elliptically polarized light and with ab-initio time-dependent density functional theory calculations. Our results propose high-harmonic spectroscopy as an all-optical approach for determining the effective mean free paths of slow electrons in liquids. This regime is extremely difficult to access with other methodologies, but is critical for understanding radiation damage to living tissues. Our work also indicates the possibility of resolving subfemtosecond electron dynamics in liquids offering an all-optical approach to attosecond spectroscopy of chemical processes in their native liquid environment.

Frequency response and transient analysis of through glass packaging vias using matrix-rational approximation (MRA) technique for three-dimensional ICs

In this paper, a computationally efficient matrix rational approximation (MRA) technique is developed to analyze the electrical behaviour of through packaging vias in glass interposer (TGVs). Using MRA technique, the electrical behaviour of TGVs utilizing differential multi-bit configuration, filled with composite copper-mixed carbon nanotube bundle (Cu-mCNTB), is investigated. A temperature-dependent π-type equivalent circuit of such differential multi-bit (DM) composite TGVs is developed using partial-element equivalent-circuit technique. The effective complex conductivity of Cu-mCNTB is also derived by appropriately considering the effects of temperature-dependent mean free path in CNTs. The frequency dependent differential- and common-mode impedances are obtained up to 100 GHz through PEEC technique. It is analyzed that composite DM-TGVs outperform silicon via counterparts in terms of reduced insertion loss using proposed MRA technique and verified through high-frequency structure simulator (HFSS). The transient analysis including crosstalk-induced propagation delay, peak crosstalk, and peak timing of coupled Cu-mCNTB/composite DM-TGVs is determined through the proposed MRA model, which exhibits error within 1% compared to the SPICE. The robustness of proposed model is examined under a wide variety of test cases including the proposed 5-Cu-mCNTB composite TGV array. For the transient analysis, the CPU runtime using the MRA model is 18.57 × faster than the SPICE. To the best of the authors’ knowledge, it is for the first time that temperature-dependent modeling and crosstalk analysis of coupled TGV structures is reported using MRA technique.

Using Thermomechanical Properties to Reassess Particles' Dispersion in Nanostructured Polymers: Size vs. Content.

Nanoparticle-filled polymers (i.e., nanocomposites) can exhibit characteristics unattainable by the unfilled polymer, making them attractive to engineer structural composites. However, the transition of particulate fillers from the micron to the nanoscale requires a comprehensive understanding of how particle downsizing influences molecular interactions and organization across multiple length scales, ranging from chemical bonding to microstructural evolution. This work outlines the advancements described in the literature that have become relevant and have shaped today's understanding of the processing-structure-property relationships in polymer nanocomposites. The main inorganic and organic particles that have been incorporated into polymers are examined first. The commonly practiced methods for nanoparticle incorporation are then highlighted. The development in mechanical properties-such as tensile strength, storage modulus and glass transition temperature-in the selected epoxy matrix nanocomposites described in the literature was specifically reviewed and discussed. The significant effect of particle content, dispersion, size, and mean free path on thermomechanical properties, commonly expressed as a function of weight percentage (wt.%) of added particles, was found to be better explained as a function of particle crowding (number of particles and distance among them). From this work, it was possible to conclude that the dramatic effect of particle size for the same tiny amount of very small and well-dispersed particles brings evidence that particle size and the particle weight content should be downscaled together.

Effect of the Spatially-Varied Electron Mean Free Path on Vortex Matter in a Superconducting Pb Island Grown on Si (111)

In this work we report theoretical calculations of a superconducting island in a strong vortex confinement regime. The obtained results reveal the evolution of the superconducting condensate with an applied magnetic field, depending on the spatial profile of the electron mean-free path in the sample. The results of this study provide an insight about the emergent superconducting properties under such conditions, using the Ginzburg-Landau numerical simulations where spatial variation of thickness of the island and the corresponding variation of the mean free path, omnipresent in similar structures of Pb grown on Si (111), are taken into account. These results offer a new route to tailor superconducting circuits by nanoengineered mean free path, using for example the controlled ion-bombardment on thin films, benefiting from the here shown impact of the spatially-varying mean free path on the vortex distribution, phase of superconducting order parameter, and the critical fields.

Delay characterization of multilayer graphene nanoribbon interconnects in presence of scattering and thermal effects

AbstractScattering source‐based mean free path (MFP) and circuit modeling are proposed for three different configurations of undoped multilayer graphene nanoribbon (U‐MLGNR) (viz. horizontal top‐contact (HTC), horizontal side‐contact (HSC), and vertical top‐contact (VTC)). A similar analysis is carried out for doped HTC‐MLGNR (D‐HTC‐MLGNR) considering dopants viz. Li, FeCl3, and AsF5, for a temperature range of 300–500 K. The optimistic intrinsic‐phonon limited (Λeff,1(T)) and realistic scattering limited (Λeff,2(T)) effective MFP models are considered to derive the equivalent resistance of MLGNR. The performance of MLGNR variants, considering Λeff,1(T) and Λeff,2(T), is compared to copper (Cu) (with smooth and rough surface) in terms of coupled line crosstalk‐induced delay (XT‐D). The results show that the MLGNR variants outperform Cu interconnects in terms of XT‐D, for Λeff,1(T). However, structural edge roughness being the dominant scattering source in Λeff,2(T), severely degrades the performance of MLGNR variants in comparison to Cu counterparts. Moreover, for Λeff,1(T) and Λeff,2(T), Li‐D HTC‐MLGNR outperforms other MLGNR variants. Also, among the MLGNR variants, U‐VTC‐MLGNR exhibits a minimum average relative penalty of 21.58 × 102% in terms of XT‐D, when Λeff,2(T) is considered as against Λeff,1(T). Li‐D HTC‐MLGNR with optimized width exhibits 10.59× lower XT‐D and 8.85× higher XT‐D for Λeff,1(T) and Λeff,2(T), respectively, compared to smooth Cu. The optimized Li‐D HTC‐MLGNR demonstrates a reduction of 85.48% and 74.67% in XT‐D values for Λeff,1 (T) and Λeff,2 (T), respectively, when compared to mixed carbon nanotube (MCNT) bundle interconnects.

Para-hydrodynamics from weak surface scattering in ultraclean thin flakes

Electron hydrodynamics typically emerges in electron fluids with a high electron–electron collision rate. However, new experiments with thin flakes of WTe2 have revealed that other momentum-conserving scattering processes can replace the role of the electron–electron interaction, thereby leading to a novel, so-called para-hydrodynamic regime. Here, we develop the kinetic theory for para-hydrodynamic transport. To this end, we consider a ballistic electron gas in a thin three-dimensional sheet where the momentum-relaxing (lmr) and momentum-conserving (lmc) mean free paths are decreased due to boundary scattering from a rough surface. The resulting effective mean free path of the in-plane components of the electronic flow is then expressed in terms of microscopic parameters of the sheet boundaries, predicting that a para-hydrodynamic regime with lmr ≫ lmc emerges generically in ultraclean three-dimensional materials. Using our approach, we recover the transport properties of WTe2 in the para-hydrodynamic regime in good agreement with existing experiments.

Influence of turbulence on Ly α scattering

ABSTRACT We develop a Monte Carlo radiative transfer code to study the effect of turbulence with a finite correlation length on scattering of Ly α photons propagating through neutral atomic hydrogen gas. We investigate how the effective mean free path, the emergent spectrum, and the average number of scatterings that Ly α photons experience change in the presence of turbulence. We find that the correlation length is an important and sensitive parameter that has an influence on physically relevant properties of Ly α radiative transfer. In particular, it can significantly, by orders of magnitude, reduce the number of scattering events that the average Ly α photon undergoes before it escapes the turbulent cloud.

Anisotropic Resistivity Size Effect in Epitaxial Mo(001) and Mo(011) Layers

Mo(001) and Mo(011) layers with thickness d = 4-400 nm are sputter-deposited onto MgO(001) and α-Al2O3(112¯0) substrates and their resistivity is measured in situ and ex situ at room temperature and 77 K in order to quantify the resistivity size effect. Both Mo(001) and Mo(011) layers are epitaxial single crystals and exhibit a resistivity increase with decreasing d due to electron surface scattering that is well described by the classical Fuchs and Sondheimer model. Data fitting yields room temperature effective electron mean free paths λ*= 14.4 ± 0.3 and 11.7 ± 0.3 nm, respectively, indicating an anisotropy with a smaller resistivity size effect for the Mo(011) orientation. This is attributed to a smaller average Fermi velocity component perpendicular to (011) surfaces, causing less surface scattering and a suppressed resistivity size effect. First-principles electronic structure calculations in combination with Boltzmann transport simulations predict an orientation dependent transport with a more pronounced resistivity increase for Mo(001) than Mo(011). This is in agreement with the measurements, confirming the effect of the Fermi surface shape on the thin-film resistivity. The predicted anisotropy λ001*/λ011* = 1.57 is in reasonable agreement with 1.66 and 1.23 measured at 77 and 295 K. The overall results indicate that the resistivity size effect in Mo is relatively small, with a measured product of the bulk resistivity times the effective electron mean free path ρoλ* = (7.7 ± 0.3) and (6.2 ± 0.2) × 10-16 Ωm2 for Mo(001) and Mo(011) layers. The latter value is in excellent agreement with the first-principles-predicted ρoλ = 5.99 × 10-16 Ωm2 and is 10% and 40% smaller than the reported measured ρoλ for Cu and W, respectively, indicating the promise of Mo as an alternate conductor for narrow interconnects.

A model of ballistic helium transport during helium-induced fuzz growth in tungsten

Ballistic helium transport in tungsten during fuzz growth was investigated to provide insight into the helium-induced nanostructuring process which adversely affects the near-surface properties of tungsten plasma-facing components. An analytical model of helium ion transport in the vacuum region within the fuzz layer was developed, whereby He ions are assumed to move in straight-line trajectories with mean free paths determined from fuzz/nanotendril dimensions. Reflection of ions from tendril sides was considered, with He ions allowed to implant into the bulk at the base of the fuzz layer if they maintain ≥5eV of energy necessary to overcome the He-W surface barrier potential, resulting in an increase in the effective He mean free path. Using the model results for helium implantation in the bulk, a helium fluence-fuzz thickness relation was achieved, which matches well with experimental data in the literature, and implies that the fuzz growth rate is consistent with ballistic implantation into the bulk through the growing porous fuzz layer.

Investigation of gamma shielding parameters of some silica borotellurite glasses with different amount of Bi[formula omitted]O[formula omitted] at energies between 10 and 150 keV

A newly developed computer code GRASP to calculate some gamma ray shielding parameters has been introduced. Mass attenuation coefficients, effective atomic numbers, half-value layers and mean free paths of TeO2-B2O3-SiO2 glasses with different amounts of Bi2O3 have been studied in detail for photon energies between 10 and 150 keV. The mass attenuation coefficients determined with GRASP are in good agreement with the ones calculated with XCOM. GRASP can be used to determine various shielding parameters as an alternative to the existing programs. All the parameters calculated with GRASP suggest that gamma shielding capability of the glasses studied gets better as the amount of Bi2O3 in the glass increases.

Self-transport of swimming bacteria is impaired by porous microstructure

Motility is a fundamental survival strategy of bacteria to navigate porous environments, where they mediate essential biogeochemical processes in quiescent wetlands and sediments. However, a comprehensive understanding of the mechanisms regulating self-transport in the confined interstices of porous media is lacking, and determining the interactions between cells and surfaces of the solid matrix becomes paramount. Here, we precisely track the movement of bacteria (Magnetococcus marinus) through a series of microfluidic porous media with broadly varying geometries and show how successive scattering events from solid surfaces decorrelate cell motion. Ordered versus disordered media impact the cells’ motility over short ranges, but their large-scale transport properties are regulated by the cutoff of their persistent motility. An effective mean free path is established as the key geometrical parameter controlling cell transport, and we implement a theoretical model that universally predicts the effective cell diffusion for the diverse geometries studied here. These results aid in our understanding of the physical ecology of swimming cells, and their role in environmental and health hazards in stagnant porous media.

Resistivity scaling in CuTi determined from transport measurements and first-principles simulations

The resistivity size effect in the ordered intermetallic CuTi compound is quantified using in situ and ex situ thin film resistivity ρ measurements at 295 and 77 K, and density functional theory Fermi surface and electron–phonon scattering calculations. Epitaxial CuTi(001) layers with thickness d = 5.8–149 nm are deposited on MgO(001) at 350 °C and exhibit ρ vs d data that are well described by the classical Fuchs and Sondheimer model, indicating a room-temperature effective electron mean free path λ = 12.5 ± 0.6 nm, a bulk resistivity ρo = 19.5 ± 0.3 μΩ cm, and a temperature-independent product ρoλ = 24.7 × 10−16 Ω m2. First-principles calculations indicate a strongly anisotropic Fermi surface with electron velocities ranging from 0.7 × 105 to 6.6 × 105 m/s, electron–phonon scattering lengths of 0.8–8.5 nm (with an average of 4.6 nm), and a resulting ρo = 20.6 ± 0.2 μΩ cm in the (001) plane, in excellent agreement (7% deviation) with the measurements. However, the measured ρoλ is almost 2.4 times larger than predicted, indicating a break-down of the classical transport models. Air exposure causes a 6%–30% resistivity increase, suggesting a transition from partially specular (p = 0.5) to completely diffuse surface scattering due to surface oxidation as detected by x-ray photoelectron spectroscopy. Polycrystalline CuTi layers deposited on SiO2/Si substrates exhibit a 001 texture, a grain width that increases with d, and a 74%–163% larger resistivity than the epitaxial layers due to electron scattering at grain boundaries. The overall results suggest that CuTi is a promising candidate for highly scaled interconnects in integrated circuits only if it facilitates liner-free metallization.

Thermal transport manipulated by vortex domain walls in bulk h-ErMnO3

Topological defects such as structural vortex domain walls (DWs), which induce many intriguing properties and associated physical phenomena in multiferroics, also provide a platform for manipulating thermal transport. Here, we employ time-domain thermoreflectance (TDTR) to study the thermal conductivity of bulk h-ErMnO3 single crystals with different vortex DWs over a wide temperature range. We find that the vortex DWs can effectively and synergistically suppress the thermal conductivity along (κc) and perpendicular (κab) to the c-axis of h-ErMnO3 single crystals. A phonon scattering model is utilized to explain the mechanism of thermal transport manipulated by vortex DWs. This model yields the intrinsic thermal conductivity and the effective phonon mean free path (MFP) of h-ErMnO3. The model also manifests that vortex DWs achieve a maximum reduction of ∼28% for the room-temperature thermal conductivity against the single-domain case. The reduction becomes more significant with decreasing temperature due to the longer effective MFP at lower temperatures, both proved experimentally by the cryogenic experiment and theoretically based on the proposed phonon scattering model. These findings not only provide an essential understanding of heat transport in multiferroics with vortex DWs but also pave the way for their application in next-generation ferroelectric devices.

Regulation of thermal conductivity of bilayer graphene nanoribbon through interlayer covalent bond and tensile strain

The interlayer bonding of graphene is a method of modifying graphene, which can change the mechanical property and conductivity of graphene, but also affect its thermal properties. In this paper, the non-equilibrium molecular dynamics method is used to study the thermal conductivity of bilayer graphene nanoribbon which is local carbon sp<sup>3</sup> hybridization (covalent bond formed between layers) under different concentration and angle of interlayer covalent bond chain and different tensile strain. The mechanism of the change of the thermal conductivity of bilayer graphene nanoribbon is analyzed through the density of phonon states. The results are as follows. The thermal conductivity of bilayer graphene nanoribbon decreases with the increase of the interlayer covalent bond concentration due to the intensification of phonon scattering and the reduction of phonon group velocities and effective phonon mean free path. Moreover, the decrease rate of thermal conductivity depends on the distribution angle of covalent bond chain. With the increase of interlayer covalent bond concentration, when the interlayer covalent bond chain is parallel to the direction of heat flow, the thermal conductivity decreases slowest because the heat transfer channel along the heat flow direction is gradually affected; when the interlayer covalent bond chain is at an angle with respect to the direction of heat flow, the thermal conductivity decreases more rapidly, and the larger the angle, the faster the thermal conductivity decreases. The rapid decline of thermal conductivity is due to the formation of interfacial thermal resistance at the interlayer covalent bond chain, where strong phonon-interface scattering occurs. In addition, it is found that the thermal conductivity of bilayer graphene nanoribbon with interlayer bonding will be further reduced by tensile strain due to the intensification of phonon scattering and the reduction of phonon group velocity. The results show that the thermal conductivity of bilayer graphene nanoribbon can be controlled by interlayer bonding and tensile strain. These conclusions are of great significance in designing and thermally controlling of graphene based nanodevices.