Showing papers on "Mean free path published in 2019"

Extremely high conductivity observed in the triple point topological metal MoP

Abstract: Weyl and Dirac fermions have created much attention in condensed matter physics and materials science. Recently, several additional distinct types of fermions have been predicted. Here, we report ultra-high electrical conductivity in MoP at low temperature, which has recently been established as a triple point fermion material. We show that the electrical resistivity is 6 nΩ cm at 2 K with a large mean free path of 11 microns. de Haas-van Alphen oscillations reveal spin splitting of the Fermi surfaces. In contrast to noble metals with similar conductivity and number of carriers, the magnetoresistance in MoP does not saturate up to 9 T at 2 K. Interestingly, the momentum relaxing time of the electrons is found to be more than 15 times larger than the quantum coherence time. This difference between the scattering scales shows that momentum conserving scattering dominates in MoP at low temperatures. Although novel topological quasiparticles have recently been evidenced, their electrical transport properties remain elusive. Here, the authors report ultra-low resistivity down to 6 nΩcm at 2 K in MoP with a large mean free path, which hints on the exotic properties of triple point fermions.

Physical, structural, optical and gamma radiation shielding properties of borate glasses containing heavy metals (Bi2O3/MoO3)

Abstract: In an attempt to develop a novel gamma radiation shielding glasses, we prepared borate glasses contains a high concentration of heavy metals like Bi2O3 and MoO3 with the composition of 20MoO3-(80-x)B2O3-xBi2O3, were x varied from 30 to 45 mol% using tradition melt-quenching-annealing method. A structural investigation such as XRD and FTIR were characterized to confirm the amorphous structure of the prepared glasses and prove the availability of all chemicals included in these compositions after the melting process. Furthermore, optical studies on these glasses were investigated to prove the transparency of the fabricated glasses. Attenuation characteristics (mass attenuation coefficients, radiation protection efficiency, and half value layer) of the prepared glasses with respect to gamma photons (in the range of 0.356–1.33 MeV) were investigated. The mass attenuation coefficients and radiation protection efficiency results increased with increasing the Bi2O3 content and this improves the attenuation ability for the prepared samples. The radiation protection efficiency also revealed that the glasses have the maximum capability in attenuation gamma photons at 0.356 MeV. The mean free path with the prepared glasses was compared with some concretes which is reported in the literature and with some commercial glasses to assess their potential for use in gamma radiation shielding products.

Physical, structural, optical investigation and shielding featuresof tungsten bismuth tellurite based glasses

Abstract: Ternary tellurite glasses with composition 20WO3-xBi2O3- (80-x) TeO2 (x = 10, 15, 20 and 25 mol%) were synthesized by conventional quenching method from pure oxides. Amorphous state of the prepared samples was checked by X-ray diffraction. The variation in the density values (ρ) and molar volume (Vm) oxygen packing density (OPD) and ion concentration (N) showed the influence of Bi2O3 on glass structure. The various optical properties such as optical band gap (Eopt), refractive index (n), molar refraction (Rm), cationic polarizability (αm) and optical basicity (∧) were calculated and are discussed in terms of structural changes. These optical properties have been observed to vary with Bi2O3 concentration. FTIR investigation shows the glasses contain TeO4, BiO6 and WO4 basic structural units. Additionally, different shielding parameters such as effective atomic number, radiation protection efficiency, mean free path, half value layer and exposure buildup factor were calculated in order to effectively use these glasses simultaneously in optical-based devices with high radiation shielding performance. The results showed that the mass attenuation coefficient and effective atomic number values of WTBi4 glass sample which contains the higher Bi2O3 concentration were the maximum at the selected energies. The mean free path of the prepared glasses was compared to different glasses, while the half value layer of the prepared glasses was compared to different types of concretes.

Physical, structural, optical and gamma ray shielding behavior of (20+x) PbO – 10 BaO – 10 Na2O – 10 MgO – (50-x) B2O3 glasses

Abstract: Glass samples of composition (20 + x) PbO – 10 BaO – 10 Na2O – 10 MgO – (50-x) B2O3 (x = 0, 5, 10, 15 and 20 mol%) have been prepared by melt quenching technique. Density, molar volume, average boron-boron separation, ion concentration, polaron radius, inter-nuclear distance, field strength, oxygen packing density and oxygen molar volume have been determined to study the physical properties of the glasses. The presence of no sharp peak in the XRD spectra confirms the amorphous nature of the glasses. The structural properties of these glasses have been investigated using Fourier Transform Infrared (FTIR) spectroscopic techniques. The direct and indirect band gap energies, refractive index, dielectric constant, optical dielectric constant, molar fraction, reflection loss and metallization have been also investigated from the UV-VIS spectra. Besides, the radiation attenuation features for the prepared glasses have been calculated using XCOM program. The mass attenuation coefficient values and effective atomic numbers are found to increase with an increase in the PbO content. The radiation shielding study revealed that Pb40B30 and Pb20B50 glasses have the lowest and highest values of mean free path and half value layer values. This indicates that the Pb40B30 glass has the highest photon shielding competence.

Photon and neutron shielding performance of boron phosphate glasses for diagnostic radiology facilities

Abstract: This study focuses on radiation shielding characteristics of Li2O, Al2O3 and ZnO-doped boron phosphate glasses containing PbO and Bi2O3. Mass attenuation coefficient (μ/ρ) values of the glasses have been calculated using MCNPX code at various photon energies ranging from 60 to 120 keV and compared to those of XCOM software. The obtained results exhibited that MCNPX and XCOM are in good agreement at all energies. Some shielding parameters such as effective atomic number (Zeff), effective electron density (Nel), half value layer (HVL), mean free path (MFP) and Photon transmission factors (TF-photon) were determined using the obtained mass attenuation coefficients. Moreover, macroscopic effective removal cross sections (ΣR) and neutron transmission factors (TF-neutron) for fast neutrons have been evaluated. To simulate the attenuation properties of investigated glasses in a diagnostic radiology operation facility (control room), each boron phosphate glass sample was placed in front of a mathematical human head phantom namely SNYDER. For the glasses under examination, average photon flux in the eight detection points, which were located in different points of SNYDER head phantom, was calculated. Among the studied glasses, BPM4 sample has showed superior photon and neutron radiation shielding effectiveness. It can be concluded that boron-doped glasses are superior shielding materials for both gamma ray and neutrons.

An investigation on shielding properties of BaO, MoO3 and P2O5 based glasses using MCNPX code

Abstract: In the present work, some radiation shielding quantities (mass attenuation coefficients, effective atomic number, effective electron density, half value layer and mean free path) for various BaO–MoO3–P2O5 ternary glass systems have been determined within the 0.015–15 MeV energy range, using WinXCom program. Additionally, the mass attenuation coefficients of all the investigated glasses have been calculated using MCNPX simulation code (version 2.6.0) and compared to those of WinXCom results. Among the studied glasses, BaMoP8 glass sample with MoO3 content of 70% mol is found to have superior gamma-ray shielding characteristics. Moreover, the glasses studied in this paper possess better radiation shielding properties by providing shorter half value layer (HVL) than RS-253 G18 commercial glass and some concrete samples namely ordinary, hematite-serpentine and ilmanite-limonite.

Er2O3 effects on photon and neutron shielding properties of TeO2-Li2O-ZnO-Nb2O5 glass system

Abstract: In this study, a series of 75TeO2-5Li2O-10ZnO-(10-x)Nb2O5-(x)Er2O3 (where x = 0, 0.5, 1.0, 1.5, 2.0 and 2.8 mol%) glasses have been surveyed in terms of photon and neutron shielding characteristics. For this aim, 3 × 3 inch NaI(Tl) detector has been simulated in order to detect photons. Afterwards, the mass attenuation coefficients (μ/ρ) and some shielding quantities such as half-value layer (HVL), tenth value layer (TVL), mean free path (MFP), effective atomic number (Zeff), effective electron density (Nel), equivalent atomic number (Zeq) and exposure build-up factor (EBF) have been calculated. The obtained MCNPX results of all the glasses have been compared and approved with those of XCOM program. Also, their gamma ray buildup factors have been determined in a wide energy range of 0.02–20 MeV for penetration depths up to 15 mfp. Moreover, neutron attenuation abilities of glasses have been evaluated by estimating neutron total effective removal cross section. The results showed that Er2O3 partial replacement of Nb2O5 in 75TeO2-5Li2O-10ZnO-(10- x)Nb2O5-(x)Er2O3 glass system enhances photon and neutron attenuation characteristics. It can be deduced that obtained results from the present investigation can be useful to understanding of influence of Er2O3 on nuclear radiation shielding properties of tellurite glasses.

Physical, mechanical and gamma-ray shielding properties of highly transparent ZnO-MoO3-TeO2 glasses

Abstract: Physical, mechanical and radiation shielding properties of ZnO-MoO3-TeO2 glasses were studied. Density, molar volume, oxygen molar volume, oxygen packing density were evaluated for the interpretation of physical properties. Mechanical properties were determined through Vickers hardness measurements. The shielding estimation was accomplished by studying linear attenuation coefficient (LACμ), mass attenuation coefficient (MAC), effective atomic number (Zeff), effective electron density (Neff), mean free path (mfp), exposure buildup factor (EBF) and energy absorption buildup factor (EABF). The glasses were irradiated by 133Ba radioactive source emitting gamma rays in the range of 79.61 keV to 383.80 keV to determine LACs and MACs. mfp values were calculated for present glasses and compared with various concretes and a commercial window glass in energy region 81–384 keV. The glass structure became stronger and mechanical properties showed an increment with increasing MoO3 content. Synthesized glasses have lower mfp values indicating better shielding properties than concretes and window glass.

Quasi-Ballistic Thermal Transport Across MoS2 Thin Films.

Abstract: Layered two-dimensional (2D) materials have highly anisotropic thermal properties between the in-plane and cross-plane directions. Conventionally, it is thought that cross-plane thermal conductivities (κz) are low, and therefore c-axis phonon mean free paths (MFPs) are small. Here, we measure κz across MoS2 films of varying thickness (20–240 nm) and uncover evidence of very long c-axis phonon MFPs at room temperature in these layered semiconductors. Experimental data obtained using time-domain thermoreflectance (TDTR) are in good agreement with first-principles density functional theory (DFT). These calculations suggest that ∼50% of the heat is carried by phonons with MFP > 200 nm, exceeding kinetic theory estimates by nearly 2 orders of magnitude. Because of quasi-ballistic effects, the κz of nanometer-thin films of MoS2 scales with their thickness and the volumetric thermal resistance asymptotes to a nonzero value, ∼10 m2 K GW–1. This contributes as much as 30% to the total thermal resistance of a 20 nm...

Gamma radiation shielding investigations for selected germanate glasses

Abstract: Radiation shielding characteristics of different germanate glasses with compositions of Nd doped Bi2O3–SiO2/GeO2–Nd2O3, Sm3+ doped B2O3–GeO2–Gd2O3, Tb3 doped GeO2–B2O3–SiO2–Ga2O3, TeO2–GeO2–Li2O and Na2O–GeO2–P2O5 glasses have been studied using XCOM program at several photon energies between 0.015 and 10 MeV. Dependencies of their photon attenuation properties with the photon energy and the composition have been investigated. The mass attenuation coefficient values and the effective atomic numbers for Nd doped Bi2O3–SiO2/GeO2–Nd2O3glasses are higher than those of the other samples. 69Bi2O3–30GeO2–1.0Nd2O3 has the highest mass attenuation coefficients among the selected samples. The Zeff results revealed that to increase the photon attenuation ability for the germanate glasses, high Z-elements (such as Bi, Te and Tb) in a suitable concentration must be included. The HVL results for the present germanate glasses suggested that the attenuation capacity of the gamma photons increases as the density of the sample increases, hence, the glass sample with high density must be considered for high attenuation ability. Also, the significant influence of modifier contents on the HVL values namely the attenuation ability has been noticed for Tb3 doped GeO2–B2O3–SiO2–Ga2O3 and TeO2–Li2O–GeO2 glasses. Moreover, the values of the mean free path for the selected samples have been compared with those of different radiation shielding glasses and concrete samples.

Investigation ofthe gamma ray shielding parameters of (100-x)[0.5Li2O–0.1B2O3–0.4P2O5]-xTeO2 glasses using Geant4 and FLUKA codes

Abstract: In the present work, the radiation shielding proeprties of lithium borophosphtellurite glass system with the composition of (100-x) [0.5Li2O-0.1B2O3–0.4P2O5]-xTeO2 (x = 0, 10, 20, 30 and 40 mol%) were reported. The mass attenuation coefficient (μ/ρ) of the selected glass system (LiBPTe0, LiBPTe10, LiBPTe20, LiBPTe30 and LiBPTe40) was calculated at 356 keV, 662 keV, 1173 keV and 1330 keV photon energies by using Geant4 and FLUKA codes and the results were compared to the values obtained theoretically using WinXcom software. The correlation theory has been used to calculate the correlation coefficients (R2) between the results from WinXcom and the both simulations codes (Geant4 and FLUKA) for each sample. Moreover, some other radiation shielding parameters such as effective atomic number, photon transmission, mean free path and half value layer were calculated. The gamma photon transmission results showed that the transmission values of the 356 keV photons are lower than those of energies 662, 1173 and 1330 keV. At 356 keV, the transmission value for LiBPTe0 (at 6 cm thickness) is found to be 0.245 while at the same energy and thickness the transmission value is 0.088 for LiBPTe40. Out of all the glasses considered in present work, LiBPTe40 possesses the highest values of effective atomic number (Zeff). The Zeff values for the present glasses are 8.02, 9.55, 11.16, 12.85 and 14.64 for LiBPTe0, LiBPTe10, LiBPTe20, LiBPTe30 and LiBPTe40 respectively at 356 keV. The mass attenuation coefficient and effetive atomic number results showed that utilization 40% mol of TeO2 significantly improves the gamma ray shielding properties of the selected glass system. The shielding effectiveness of the selected samples was compared with other reference materials namely two radiation shielding glasses and four concretes used in different shielding purposes in terms of the mean free path (MFP) at 356 keV. The results revealed that the MFP of RS-253-G18 is lower than LiBPTe0sample. Moreover, the MFP of ordinary concrete is higher than the MFP of all glasses under examination, thus the investigated tellurite glasses have better attenuation features than the ordinary concrete.

Evaluation of photon attenuation and optical characterizations of bismuth lead borate glasses modified by TiO 2

Abstract: A study of photon attenuation and optical properties was performed for (20Bi2O3–60B2O3–(20-y)PbO–yTiO2), where y = 0.0, 1.0, 2.5, 5.0, 7.5, and 10.0 wt%) glassy system. UV–Vis absorption measurements for the glasses in the range of 90–1100 nm wavelengths have been recorded. Based on the absorption spectra, the band gap of optical energy for each glass sample has been evaluated using absorbance spectrum fitting ( $$E_{\text{Optical}}^{\text{ASF}}$$ ) and derivative absorbance spectrum fitting ( $$E_{\text{Optical}}^{\text{DASF}}$$ ) models and compared with those obtained by Tauc’s method. $$E_{\text{Optical}}^{\text{ASF}}$$ varies from 2.405 to 2.008 eV, while $$E_{\text{Optical}}^{\text{DASF}}$$ takes values from 3.000 to 2.914 eV. Indeed, different optical parameters such as refractive index, molar polarizability, molar refractivity, metallization criterion, dielectric constants, optical transmission, reflection loss, band gap of optical energy-based metallization criterion, and refractive index-based metallization criterion have been evaluated. Moreover, several shielding parameters such as mass attenuation coefficients, linear attenuation coefficient, half-value layer, tenth-value layer, mean free path, effective atomic numbers, and effective electron densities have been evaluated using the WinXCOM program in the energy range 0.010–15 MeV for the prepared glass system. At 1 MeV photon energy, the half value layer for the investigated glasses takes values from 2.03 to 2.15 cm. The results showed that the studied glasses can be applied as candidate for radiation shielding materials according to their coefficients of mass attenuation and HVL values, especially the composition with the highest value of PbO (20 wt%), which introduced good nuclear radiation shielding.

Photon and neutron shielding characteristics of samarium doped lead alumino borate glasses containing barium, lithium and zinc oxides determined at medical diagnostic energies

Abstract: In the present work, we studied the radiation shielding parameters such as mass attenuation coefficients, effective atomic number, half value layer, mean free path, macroscopic effective removal cross-sections and neutron transmission function for samarium doped lead alumino borate glasses containing barium, lithium and zinc oxides at medical diagnostic energies (between 20 and 150 keV) using MCNPX code. The results showed that the photon attenuation depends on the type of modifier used (i.e. ZnO, BaO or Li2O) and also, upon the energy of the photon. The higher mass attenuation coefficients were found for the glass containing BaO. The results also revealed that the glass containing Li2O has the maximum effective atomic number between 20 and 40 keV. In addition, some important neutron shielding parameters such as macroscopic effective removal cross-sections (ΣR) and neutron transmission function (N/N0) have been calculated for investigated glass samples.

Synergistic effect of La2O3 on mass stopping power (MSP)/projected range (PR) and nuclear radiation shielding abilities of silicate glasses

Abstract: Photon and neutron attenuation properties of La2O3 based Li2O-SiO2-La2O3 glass system have been evaluated through MCNPX (2.6.0) Monte Carlo code at some photon energies of 0.256–1.33 MeV. In order to control the accuracy of the data, the estimated MCNPX of mass attenuation coefficients have been compared to those of WinXCOM software. The half value layer (HVL), tenth value layer (TVL) and mean free path (MFP) values of the selected glass system exhibited that the shielding performance of the gamma photons is related to the density of glass, thus, the inclusion of TeO2 to Li2O-SiO2 improves the capacity of the glass system to attenuate more photons. In addition, the effective removal cross-section (ΣR) calculations have been done. Further, Mass sopping power (MSP) and Projected range (PR) are calculated for proton particles (H1) and alpha particles (He+2). It may be deduced that La4 glass among the studied samples may be kept in view as a superior glass in terms of shielding for photon and neutron while La0 glass can be considered as a best shielding material against to alpha and proton particles. The results of this study may be useful for shielding optimization of medical and industrial facilities.

First-principles study of thermal transport properties in the two- and three-dimensional forms of Bi2O2Se.

Abstract: Recently, an air-stable layered semiconductor Bi2O2Se has been synthesized [Nat. Nanotechnol., 2017, 12, 530; Nano Lett. 2017, 17, 3021]. It possesses ultrahigh mobility, semiconductor properties, excellent environmental stability and easy accessibility. Here, we report on the thermal transport properties in monolayer (ML), bilayer (BL), and bulk forms of Bi2O2Se using density-functional theory and the Boltzmann transport approach. The results show that the ML exhibits better thermal transport properties than the BL and bulk. The intralayer opposite phonon vibrations greatly suppress the thermal transport and lead to an ultralow lattice thermal conductivity of ∼0.74 W m−1 K−1 in the ML, which has a large band gap of ∼2.12 eV, a low value of average acoustic group velocity of ∼0.76 km s−1, low-lying optical modes of ∼0.54 THz, strong optical-acoustic phonon coupling, and large Gruneisen parameters of ∼5.69. The size effect for all three forms is much less sensitive due to their short intrinsic phonon mean free path (MFP).

The effective role of La 2 O 3 contribution on zinc borate glasses: radiation shielding and mechanical properties

Abstract: In this theoretical study, the zinc borate glasses have been modified with lanthanum oxide (La2O3) in a different amount (0, 1, 2, 3 and 4%).The mechanical and shielding properties change after adding of lanthanum oxide in zinc borate glasses depending on the bond compression and Makishima-Mackenzie models. The mass attenuation coefficients have been calculated using the XCOM program and MCNPX simulation code. The results present that La2O3 increment in the glass density modifies the glass mechanical properties and improves the radiation attenuation performances. The variations in the mechanical properties are resulting from the formation of bridging oxygen. The density of the ZnO–B2O3–La2O3 glass system is proportional to La2O3 concentration, which is attributable to the highest molecular weight of La2O3 than those of ZnO and B2O3. Furthermore, the mass attenuation coefficients, effective atomic numbers and effective removal cross-section of the glasses increases as La2O3 contains increase. The half-value layer, tenth value layer, mean free path, buildup factors and mass stopping power of the glasses decrease as La2O3 contain increases. Present results explained the characteristic of ZnO–B2O3–La2O3 glass as a novel nominee for radiation attenuation barrier in the chosen energy zone.

Resistivity scaling and electron surface scattering in epitaxial Co(0001) layers

Abstract: In situ and ex situ transport measurements on epitaxial Co(0001)/Al2O3(0001) layers with thickness d = 7–300 nm are used to quantify the resistivity ρ scaling due to electron surface scattering. Sputter deposition at 300 °C followed by in situ annealing at 500 °C leads to single-crystal layers with smooth surfaces (<1 nm roughness) and an epitaxial relationship: Co[0001]‖Al2O3[0001] and Co[ 101¯0]‖Al2O3[ 112¯0]. The measured ρ vs d data are well described by the classical expression by Fuchs and Sondheimer at both 295 and 77 K, yielding a temperature-independent product of the bulk resistivity times the mean free path ρo × λ and an effective room temperature λ = 19.5 ± 1.0 nm. The resistivity increases by 9%–24% upon air exposure for layers with d ≤ 21 nm, indicating a transition from partially specular (p = 0.55 ± 0.05) to completely diffuse (p = 0) surface scattering during native oxide formation. The overall results suggest that Co exhibits a resistivity scaling that is comparable to W and approximately 2× smaller than that of Cu and that the resistance of narrow Co lines can be reduced considerably by engineering the Co-liner interface to facilitate specular electron scattering.

Assessment of gamma-rays and fast neutron beam attenuation features of Er2O3-doped B2O3–ZnO–Bi2O3 glasses using XCOM and simulation codes (MCNP5 and Geant4)

Abstract: The authors aim to study the gamma-rays and neutron beam shielding capabilities of zinc bismuth borate glasses doped with erbium ions. Mass attenuation coefficient (MAC) (μ/ρ) values were computed employing XCOM and two different simulation codes, MCNP5 and Geant4, within 0.015–15 MeV photon energy, which showed good agreement within the derived values. The effective atomic number (Zeff), electron density (Ne), half-value layer (HVL) and mean free path (MFP) values were derived using MAC values. To account on the scattering effects of photons from the samples, exposure buildup factor (EBF) were determined, applying geometric progression (G-P) method, within 0.015–15 MeV photon energy and penetration depth of 1–40 mfp (intervals: 1, 5, 10, 15, and 40 mfp). The high MAC, Zeff values and low HVL, MFP values of 16.93B2O3‒22.57ZnO‒60Bi2O3‒0.5Er2O3 (mol%) glass optimized its shielding effects against gamma-rays. The macroscopic effective removal cross-section for fast neutron (ΣR) values lie within the range of 0.1142–0.1232 cm−1 for the selected Er2O3-doped samples. The studied parameters of the experimented glasses revealed their dominant radiation shielding features compared to commercial shielding glasses, concretes, and alloys.

Structural, optical, and shielding investigations of TeO 2 –GeO 2 –ZnO–Li 2 O–Bi 2 O 3 glass system for radiation protection applications

Abstract: Glass gained much attention to be utilized in various applications, for this reason different kinds of glass compositions was the subject of investigation. In this work, we successfully fabricated a series of tellurite–germanate glasses with a composition of (70-x)TeO2–10GeO2–10ZnO–10Li2O–xBi2O3, where x = 0, 5, 10 and 15 (all in mol%). Ordinary melt-quenching was used to synthesize the mentioned glass series with 975 °C as a melting temperature for 30 min and 300 °C for annealing to release the internal stress. To study the structural properties of these glasses, X-ray diffraction (XRD) was used to confirm the glassy structure of these glasses. Regarding that, XRD profiles were recorded in ranges between 10° and 80° for all samples. Moreover, FTIR was employed to study the functional groups of all elements, which were used in the composition with the range of 4000–400 cm−1. Optical absorption was used to investigate the cutoff wavelength and optical band gap. Optical absorption was measured at the range of 200–800 nm. The variation of the attenuation properties for the tested tellurite–germanate glasses has been investigated using WinXcom software for photon energy ranges between 0.015 and 15 MeV. The examined attenuation properties include linear and mass attenuation coefficients, half value layer and mean free path, and effective atomic number of the radiation shielding glass. The present results suggest the utilization of the new prepared glass samples in radiation shielding applications.

The lifetime of interlayer breathing modes of few-layer 2H-MoSe2 membranes

Abstract: A time-resolved observation of coherent interlayer longitudinal acoustic phonons in thin layers of 2H-MoSe2 is reported. A femtosecond pump–probe technique is used to investigate the evolution of the energy loss of these vibrational modes in a wide selection of MoSe2 flakes with different thicknesses ranging from bilayer up to the bulk limit. By directly analysing the temporal decay of the modes, we can clearly distinguish an abrupt crossover related to the acoustic mean free path of the phonons in a layered system, and the constraints imposed on the acoustic decay channels when reducing the dimensionality. For thicker samples, the main acoustic attenuation mechanism is attributed to the scattering of the acoustic modes with thermal phonons. For samples thinner than ∼20 molecular layers, the predominant damping mechanism is ascribed to the effects of surface asperity. Losses intrinsic to the low dimensionality of single or few layer materials impose critical limitations for their use in optomechanical and optoelectronic devices.