In this study we have derived an exact framework for the calculation of the heat flux and its spectral decomposition in molecular dynamics (MD) for arbitrary many-body potentials. This work addresses several deficiencies and limitations of previous approaches and allows for the accurate computational study of thermal properties in a wide variety of many-body systems with MD. We have tested our modifications with Green-Kubo (GK) and nonequilibrium MD (NEMD) simulations for various two- and three-dimensional (2D and 3D) material systems using the Tersoff and Stillinger-Weber (SW) potentials as examples. The spectral decomposition of the heat current was also calculated for monolayer graphene (1LG) and MoS2, for different system lengths. Our results show that the heat current calculated by our method is consistently in agreement with the thermostat current in NEMD, while previous implementations can estimate quite poorly the thermal conductivity both under GK and NEMD simulations, and both for 2D and 3D materials. The decomposition of the heat current also sheds light on the contribution of different phonon modes to thermal conductivity and its dependence on length. Our methodology is implemented in the widely used LAMMPS code specifically for the Tersoff and SW potentials, and it is readily applicable to the vast majority of many-body MD potentials.

In this work, a thermal rectification ration of 18.5% was observed in partially perforated graphene with the use of Molecular Dynamics (MD) simulations to capture full phonon anharmonicity, exploring systems of up to 500 nm in total length. In all cases studied here, heat preferentially flows from the porous to the pristine region and both the thermal conductivity x and n increase upon increasing the length of the pristine region and upon decreasing the size of the pores. To interpret the results, the macroscopic "R-Series Model" is applied, attributing rectification to the different temperature-dependence of x of perforated and pristine graphene. According to the model, n is maximized when the two regions composing the structure have matching thermal resistances and mismatching temperature-dependence of x. The model agrees qualitatively with the MD results, indicating that the latter is the principal rectification mechanism, but it can significantly underestimate n. Phonon analysis further reveals the appearance of new 'defect' modes localized around and between pores, resulting in the emergence of a new prominent peak in the phonon Density of States at 520 cm-1 and contributing to further reduction of x. The study considers key geometric factors such as the length of the pristine region, and the pore size, shape, alignment, and orientation. Pore shape and alignment exert minimal influence on n, although alignment greatly influences x. Eventually, arranged pores are deemed more efficient than randomly distributed defects for increasing rectification.

In this work, we present a possibility of incorporating Nickel porphyrin and Iron porphyrin molecules into a semiconducting single-walled carbon nanotube to create an active layer for solar cell devices. The optoelectronic properties of the isolated Nickel/Iron porphyrin molecules and two different configurations of the hybrid system were investigated using density functional theory. The study reveals that the stability of the structure is attributed to the transfer of electrical charge between the Nickel/Iron porphyrin molecules and the nanotube. Nickel and Iron atoms were specifically chosen for their significant impact on the electronic properties of the hybrid systems, resulting in enhanced light absorption, improved charge separation, and higher power conversion efficiency in solar cell devices. We observed a shift in the fermi level of the nanotube after encapsulation, indicating a connection between the charge transfer of the metalloporphyrin molecules and the nanotube. These findings suggest that encapsulated systems with type II heterojunctions hold promise as efficient charge carriers and light absorbers in the active layer of organic solar cells based on filled single-walled carbon nanotubes. This research has the potential to contribute to the development of highly efficient organic solar cells using filled single-walled carbon nanotubes.

In this study, the classic double-slit experiment, originally developed for light waves is successfully adapted, to investigate the behavior of phonons in crystalline silicon. Through molecular dynamics (MD) simulations, how phonons can exhibit wave-like interference patterns when passing through two slits in a silicon block is explored. The results indicate that phonon waves behave similarly to photons, with slit distinct interference patterns. By manipulating geometric parameters such as slit width, distance, and length, in fringe distances that align with Young's double slit formula is observed to change. Key findings include the observation of phonon interference and the sensitivity of fringe distances to geometric configurations. Although some discrepancies with theory arose due to noise in the MD simulations, these results underscore the complexity of simulating phonon behavior in nanostructures. This study demonstrates that phonon behavior at the nanoscale can mirror classical wave interference phenomena, paving the way for future work that includes conducting physical experiments for validation and ultimately aiming to engineer devices that harness phononic interference for innovative applications in thermal management, microelectronics, and quantum computing.

Efficient thermal transport across solid-liquid interfaces is critical for optimizing heat dissipation in modern technological applications. This study aims to investigate how surface functionalization affects heat transfer at the silica/water interface, with specific objectives: (i) to assess the impact of surface modification on interfacial thermal resistance (ITR) and (ii) to elucidate the physical mechanisms governing heat transfer on functionalized surfaces. We employ nonequilibrium molecular dynamics (NEMD) simulations of silica surfaces with varying concentrations of methyl and hydroxyl groups to quantify ITR and analyze the contribution of each functional group to the total heat flux. Results demonstrate that transitioning from methylated to hydroxylated groups leads to (i) an approximately 6-fold increase in adhesion energy, (ii) a reorientation of interfacial water molecules perpendicular to the surface normal, (iii) a reduction in liquid depletion length near the interface, (iv) a nonlinear decrease of ITR correlated with an increase in the number and strength of interfacial hydrogen bonds, and (v) enhanced dynamic stability of OH-mediated bonds, with OH-donor lifetimes exceeding those of CH3-donor bonds by a factor of 5-6 and showing peak persistence at intermediate hydroxylation levels (∼50%). These findings highlight that manipulating the concentrations of functional groups enables precise tailoring of interfacial thermal transport, offering new opportunities for optimizing heat transfer in silica-based systems.

Effective thermal management of electronic devices encounters substantial challenges owing to the notable power densities involved. Here, we propose layered MoS2 phononic crystals (PnCs) that can effectively reduce thermal conductivity (κ) with relatively small disruption of electrical conductivity (σ), offering a potential thermal management solution for nanoelectronics. These layered PnCs exhibit remarkable efficiency in reducing κ, surpassing that of Si and SiC PnCs with similar periodicity by ~100-fold. Specifically, in suspended MoS2 PnCs, we measure an exceptionally low κ down to 0.1 watts per meter kelvin, below the amorphous limit while preserving the crystalline structure. These findings are supported by molecular dynamics simulations that account for the film thickness, porosity, and temperature. We demonstrate the approach efficiency by fabricating suspended heat-routing structures that effectively confine and guide heat flow in prespecified directions. This study underpins the immense potential of layered materials as directional heat spreaders, thermal insulators, and active components for thermoelectric devices.

Hydrogen adsorption is a popular and flexible method to regulate the physical properties of two-dimensional (2D) materials, such as the recently synthesized biphenylene networks. In this study, the mechanical properties and the thermal conductivity (kappa) of a fully hydrogenated biphenylene network (HBPN) under strain were investigated systematically by molecular dynamics (MD) simulation and the wave-packet (WP) propagation method. It was found that HBPN could sustain an unusual strain as large as 28.8 and 34.5% along the zigzag and armchair directions, respectively, which were much larger than the other 2D buckling structures like silicene (about 19.5 and 17%, respectively). Besides, the kappa of HBPN exhibited an anomalous response to the uniaxial tensile strain. Different from its mother structure, like graphene, the kappa of HBPN had an increasing trend with strain, explained here with the phononic density of states (PDOS). The physical mechanism behind this nontrivial thermomechanical behavior of this planar sp(2) hybridized carbon allotrope was related to the following two factors: first, the increase of the number of phonons excited in a low-frequency region, which in general carried more energy, and second, the reduction of the number of higher frequency phonons, thus the weakening of the phonon-surface scattering, both helped increase the thermal conductivity under strain. Moreover, the strain-induced flattening of the structure was another reason to weaken the coupling between phonons with in-plane and curvature vibrational modes. The WP propagation method within MD was also employed to analyze the propagation of phonons inside the HBPN, and group velocities, phonon lifetimes, and mean free paths were obtained. Our research can provide an essential reference for the application of 2D materials in the field of electronic cooling devices and the modification of thermoelectric energy conversion efficiency of materials.

Phonon diffraction and interference patterns are observed at the atomic scale, using molecular dynamics simulations in systems containing crystalline silicon and nanometric obstacles, such as voids or amorphous inclusions. The diffraction patterns due to these nano-architectured systems of the same scale as the phonon wavelengths are similar to the ones predicted by the simple Fresnel–Kirchhoff integral. The few differences between the two approaches are attributed to the nature of the interface and the anisotropy of crystalline silicon. Based on the wave description of phonons, these findings can provide insights into the interaction of phonons with nano-objects and can have applications in smart thermal energy management.

This study proposes a promising candidate for organic solar cells through the creation of a novel nano-hybrid system composed of caffeine molecules encapsulated within a semiconducting single-walled carbon nanotube known as NT14 (14,0). The stability and optoelectronic properties of this hybrid system, designated as CA@NT14, were thoroughly investigated. We determined the optimal diameter for the NT14 nanotube using molecular mechanics, Density Functional Theory, spectral moment's method, and bond polarizability model, finding it to be approximately 1.18 nm. The encapsulation's impact on the Raman-active modes, specifically the radial breathing mode and tangential mode, was analyzed through Raman spectra calculations, revealing structural stability and charge transfer from CA to NT14. Notably, the NT14's Fermi level position increased upon encapsulation, indicating charge transfer and a type-II band alignment. The study further examined the bandgap characteristics of the hybrid system, finding that the encapsulation of CA within semiconducting NT14 nanotubes minimally impacts the nanotube's bandgap, thus retaining its excellent visible light absorption properties. Conversely, encapsulating CA within metallic nanotubes significantly reduces their bandgap, limiting their light absorption range. The nonresonant Raman responses of NT14 pre- and post-encapsulation corroborated the charge transfer between CA and NT14. Future research will focus on computing the electronic transport characteristics, transmission spectra, I-V characteristics, and yield of CA@NT14 using DFT and Non-Equilibrium Green's Function ( formalism. An experimental study will be conducted to validate these theoretical findings. These results indicate the potential of CA@NT14 hybrids as effective active layers in organic solar cells, highlighting their significance in advancing optoelectronic applications.

In light of the succefull use of Caffeine in perovskite solar cells, a novel nano- hybrid system comprised of caffeine packed in a metallic single-walled carbon nanotube is proposed as a viable candidate for organic solar cells. Investigations have been made on the stability of this hybrid system that has a single Cf molecule inside of NT8. In particular, the ideal diameter is found. The investigation’s findings show evidence of a charge transfer between the Cf molecules and the NT8 nanotube, which also attests to the stability of the structure. Electronic and optical computations are used to determine this Charge Transfer’s location in the Cf @NT8 hybrid system as well as its direction. The electronic computations and transmission spectra led us to the conclusion that a CT link from caffiene to carbone nanotube is implied by the increased fermi level position of carbone nanotube after encapsulation.

Phonon localization is a phenomenon that influences numerous material properties in condensed matter physics. Anderson localization brings rise to localized atomic-scale phonon interferences in disordered lattices with an influence limited to high-frequency phonons having wavelengths comparable to the size of a randomly perturbed unit cell. Here we theoretically reveal a new form of phonon localization induced by augmenting a crystalline material with intrinsic phonon nanoresonators with feature sizes that can be smaller or larger than the phonon wavelengths but must be relatively small compared to the phonon mean free paths. This mechanism is deterministic and takes place within numerous discrete narrow-frequency bands spread throughout the full spectrum with central frequencies controlled by design. For demonstration, we run molecular dynamics simulations of all-silicon nanopillared membranes at room temperature, and apply to the underlying thermalized environment narrowband wave packets as an excitation at precisely the frequencies where resonant hybridizations are evident in the anharmonic phonon band structure. Upon comparison to other frequency ranges where the nanostructure does not exhibit local resonances, significant intrinsic spatial phonon localization along the direction of transport is explicitly observed. Furthermore, the energy exchange with external sources is minimized at the resonant frequencies. We conclude by making a direct comparison with Anderson localization highlighting the superiority of the resonant phonons across both sides of the interference frequency limit.

In this work, we have studied the phonon properties of multi-layered graphene with the use of Molecular Dynamics (MD) simulations and the k-space Autocorrelation Sequence (k-VACS) method. We calculate the phonon dispersion curves, densities of states and lifetimes τ of few-layered graphene of 1-5 layers and graphite. Γ-point phonon energies and lifetimes are investigated for different temperatures ranging from 80 K to 1000 K. The study focuses on the impact of the interlayer interaction and temperature on the energies and lifetimes of the Γ-point phonons, as well as the type of interlayer potential used. For the later we used the Kolmogorov-Crespi (KC) and the Lennard-Jones (LJ) potentials. We have found that the number of layers N has little effect on the intra-layer (ZO and G) mode energies and greater effect on the inter-layer (Layer Shearing and Layer Breathing) modes, while τ is generally affected by N for all modes, except for the Layer Shear mode. The trend of N on the lifetimes was also found to independent of the type of potential used. For the Raman-active G phonon, our calculations show that the lifetime increase with N and that this increase is directly connected to the strength of the interlayer coupling and how this is modelled.

This research discusses incorporating a single magnesium porphyrin molecule into a semiconducting single‐walled carbon nanotube (SWCNT) for solar cell applications. Using density functional theory (DFT), the study examines the optical and electronic properties of the isolated magnesium porphyrin molecule and two configurations of the hybrid system. Results show structural stability due to charge transfer between the molecule and the nanotube. Different exchange‐correlation functionals (GGA and HSE06) yield varied bandgap results, affecting light absorption. Integration of the molecule into the SWCNT reduces the bandgap. Encapsulation of the molecule influences absorption and stability under irradiation. These encapsulated systems exhibit type II heterojunction characteristics, making them promising for organic solar cells based on SWCNTs, offering potential for highly efficient solar cells.

Recently, nanostructuration has been proposed to improve the performance of phase change memories. This is the case of superlattices composed of amorphous carbon and crystalline germanium telluride, which we have investigated by molecular dynamics. For this, a modified Stillinger–Weber potential is adapted to reproduce their stiffness contrast/impedance ratio. In order to study the effect of the interface interaction, two sets of parameters are used to model the interfaces with different interactions between the two materials using the properties of the softer material or the average properties between the two creating an adaptation of impedance across the layers. The effects of interface roughness and carbon diffusion at grain boundaries are studied. Using equilibrium molecular dynamics as well as the propagation of wave-packets, we show first that without impedance adaptation, the anisotropy is high, and the roughness has a marked impact on the properties. However, the introduction of impedance adaptation destroys those effects on the thermal conductivity. Finally, we show that the periodic texturing of the interface increases the transmission of in-plane transverse phonons.

ADVERTISEMENT RETURN TO ISSUEPREVEnergy FocusNEXTNanomaterials and SustainabilityGary P. Wiederrecht*Gary P. WiederrechtCenter for Nanoscale Materials, Argonne National Laboratory, Lemont, Illinois 60439, United States*[email protected]More by Gary P. Wiederrechthttps://orcid.org/0000-0001-8821-932X, Renaud Bachelot*Renaud BachelotLight, Nanomaterials & Nanotechnologies Laboratory (L2n), Université de Technologie de Troyes and CNRS EMR7004, 10004 Troyes Cedex, France*[email protected]More by Renaud Bachelothttps://orcid.org/0000-0003-1847-5787, Hui XiongHui XiongMicron School of Materials Science and Engineering, Boise State University, Boise, Idaho 83725, United StatesCenter for Advanced Energy Studies, Idaho Falls, Idaho 83415, United StatesMore by Hui Xionghttps://orcid.org/0000-0003-3126-1476, Konstantinos TermentzidisKonstantinos TermentzidisUniversité Claude Bernard Lyon, CNRS, INSA-Lyon, CETHIL UMR5008, F-69621 Villeurbanne, FranceMore by Konstantinos Termentzidishttps://orcid.org/0000-0002-8521-7107, Alexandre NominéAlexandre NominéInstitut Jean Lamour, UMR CNRS-UL 7198, 54011 Nancy, FranceLORIA, UMR CNRS-UL-INRIA 7503, 54506 Vandoeuvre-lès-Nancy, FranceGaseous Electronics, Jožef Stefan Institute, Jamova cesta 39, SI-1000 Ljubljana, SloveniaMore by Alexandre Nominé, Jier HuangJier HuangDepartment of Chemistry and Schiller Institute for Integrated Science and Society, Boston College, Chestnut Hill, Massachusetts 02467, United StatesMore by Jier Huanghttps://orcid.org/0000-0002-2885-5786, Prashant V. KamatPrashant V. KamatRadiation Laboratory, Department of Chemistry and Biochemistry, and Department of Chemical and Biomolecular Engineering, University of Notre Dame, Notre Dame, Indiana 46556, United StatesMore by Prashant V. Kamathttps://orcid.org/0000-0002-2465-6819, Elena A. RozhkovaElena A. RozhkovaCenter for Nanoscale Materials, Argonne National Laboratory, Lemont, Illinois 60439, United StatesMore by Elena A. Rozhkovahttps://orcid.org/0000-0001-8498-8228, Anirudha SumantAnirudha SumantCenter for Nanoscale Materials, Argonne National Laboratory, Lemont, Illinois 60439, United StatesMore by Anirudha Sumanthttps://orcid.org/0000-0002-6028-0038, Michele OstraatMichele OstraatPajarito Powder, Albuquerque, New Mexico 87109, United StatesMore by Michele Ostraat, Prashant K. JainPrashant K. JainDepartment of Chemistry and Materials Research Laboratory, University of Illinois Urbana−Champaign, Urbana, Illinois 61801, United StatesMore by Prashant K. Jainhttps://orcid.org/0000-0002-7306-3972, Chris HeckleChris HeckleMaterials Manufacturing Innovation Center (MMIC), Argonne National Laboratory, Lemont, Illinois 60439, United StatesMore by Chris Heckle, Jie LiJie LiMaterials Engineering Research Facility (MERF), Argonne National Laboratory, Lemont, Illinois 60439, United StatesMore by Jie Lihttps://orcid.org/0000-0002-3416-7787, and Krzysztof Z. PupekKrzysztof Z. PupekMaterials Engineering Research Facility (MERF), Argonne National Laboratory, Lemont, Illinois 60439, United StatesMore by Krzysztof Z. PupekCite this: ACS Energy Lett. 2023, 8, 8, 3443–3449Publication Date (Web):July 18, 2023Publication History Received29 June 2023Accepted11 July 2023Published online18 July 2023Published inissue 11 August 2023https://pubs.acs.org/doi/10.1021/acsenergylett.3c01303https://doi.org/10.1021/acsenergylett.3c01303newsACS PublicationsCopyright © Published 2023 by American Chemical Society. This publication is available under these Terms of Use. Request reuse permissions This publication is free to access through this site. Learn MoreArticle Views2826Altmetric-Citations1LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail PDF (3 MB) Get e-AlertscloseSUBJECTS:Materials,Nanomaterials,Nanostructures,Plasmonics,Sustainability Get e-Alerts

Understandings heat transfer across a solid/liquid interface is crucial for establishing novel thermal control pathways in a range of energy applications. One of the major problems raised in this context is the impact of the three-phase contact line between solid, liquid, and gas on heat flux perturbations at the nanoscale. The focus of this research is the thermal transport via nanosized meniscus restricted between two solid walls. The molecular dynamics approach was used to consider different wetting states of the meniscus by varying the interaction potential between atoms of the substrate and the liquid. The influence of the meniscus size on the energy exchange between two solid walls was also studied. It was discovered that possessing a three-phase contact line reduces the interfacial boundary resistance between solid and liquid. Furthermore, the finite element method was employed to connect atomistic simulations with continuum mechanics. We show that the wetting angle and interfacial boundary resistance are essential important parameters for multiscale analysis of thermal engineering issues with precise microscale parametrization.

In modern electrical circuits overheating is an issue and techniques enabling efficient heat dissipation are critical. One potential solution to dissipate excess heat away from critical electronic components are 2D materials, due to their high thermal anisotropy and possibility of directing the heat flow. Here, we propose heat routing structures based on few-layer, nanopatterned MoS2 to confine and guide the heat flow in a pre-specified in-plane direction. In such structures heat can be evacuated away from hotspots through a predefined path without affecting adjacent structures, a functionality which is limited in the standard materials for heat spreading. Our designs result from experimental and theoretical study of the in-plane thermal conductivity (κ) as a function of thickness, porosity, and temperature in both pristine (κ) and nanopatterned (κp) MoS2 membranes. Reduction factors R (κ/κp) greater than 10 and 80 are obtained after nanopatterning a square lattice of ~100-nm diameter holes with periods of 500 and 300 nm, respectively. Notably, the R for nanopatterned MoS2 is 10 times larger than for materials such as silicon with a similar periodicity. These results highlight the potential use of MoS2 for thermal management applications as directional in-plane heat dissipators, for instance in three-dimensional integrated circuits.

With wave-packet propagation simulations and heat flux estimation via molecular dynamics, we show that the heat flux radial distribution in silicon nanowires can be described by a mesoscopic model, the hydrodynamic heat equation. We observe Poiseuille like heat flux profile, that cannot be described by a simple kinetic model such as the Fuchs-Sondheimer model, in both pristine and core/shell nanowires. The addition of a shell does not change the shape of the radial heat flux distribution, but just modifies the maximum of the heat flux in the center of the nanowire. These results show that there is a heat flux depletion length for pristine or core shell nanowires, 1-2 nm away from the boundary of the crystalline part. The parameters of the mesoscopic model are discussed in terms of microscopic properties, including the phonon mean free path as function of frequency and the partial vibrational density of states in the different regions of the nanowire. (c) 2022 Elsevier Ltd. All rights reserved.

In this proceeding, we show diverse non Fourier effects that have been obtained with Molecular Dynamics simulations using silicon nanostructures and nanostructured materials. First, thermal rectification is observed in silicon nanowires with asymmetric amorphous shells. We then show that it is possible to design a pass band filter for phonons using a similar structure. Finally, phonon diffraction is obtained using two crystalline silicon blocks connected by silicon nanochannels.

Phonons diffraction and interference patterns are observed at the atomic scale, using molecular dynamics simulations in systems containing crystalline silicon and nanometric obstacles as voids or amorphous-inclusions. The diffraction patterns caused by these nano-architectured systems of the same order as the phonon wavelengths are similar to the ones predicted by a simple Fresnel-Kirchhoff integral, with a few differences due to the nature of the obstacle and the anisotropy of crystalline silicon. These findings give evidence of the wave nature of phonons, can help to a better comprehension of the interaction of phonons with nanoobjects and at long term can be useful for intelligent thermal management and phonon frequency filtering at the nanoscale.