Baowen Li

Baowen Li
National University of Singapore | NUS · Centre for Computational Science and Engineering

About

381
Publications
60,231
Reads
How we measure 'reads'
A 'read' is counted each time someone views a publication summary (such as the title, abstract, and list of authors), clicks on a figure, or views or downloads the full-text. Learn more
21,594
Citations

Publications

Publications (381)
Preprint
We develop a unified theory for the second sound in two dimensional materials. Previously studied drifting and driftless second sound are two limiting cases of the theory, corresponding to the drift and diffusive part of the energy flux, respectively. We find that due to the presence of quadratic flexural phonons the drifting second sound does not...
Article
Full-text available
Hotspot is a ubiquitous phenomenon in micro/nanoscale chips. Here, it is found that the thermal conductivity is not a constant in such a homogeneous system. The hotspots in homogeneous 2D disk/3D sphere and graphene disk are studied based on phonon Boltzmann transport equation. Instead a constant value, a graded thermal conductivity is observed eve...
Article
Full-text available
The reciprocity principle governs the symmetry in transmission of electromagnetic and acoustic waves, as well as the diffusion of heat between two points in space, with important consequences for thermal management and energy harvesting. There has been significant recent interest in materials with time-modulated properties, which have been shown to...
Article
We numerically investigated the phenomenon of non-Gaussian normal diffusion of a Brownian colloidal particle in a periodic array of planar counter-rotating convection rolls. At high Péclet numbers, normal diffusion is observed to occur at all times with non-Gaussian transient statistics. This effect vanishes with increasing the observation time. Th...
Preprint
Full-text available
The reciprocity principle governs the symmetry in transmission of electromagnetic and acoustic waves, as well as the diffusion of heat between two points in space, with important consequences for thermal management and energy harvesting. There has been significant recent interest in materials with time-modulated properties, which have been shown to...
Article
The demand for sophisticated tools and approaches in heat management and control has triggered the fast development of fields that include conductive thermal metamaterials, nanophononics, and far-field and near-field radiative thermal management. In this Review, we offer a unified perspective on the control of heat transfer, summarizing complementa...
Article
Full-text available
The microscopic mechanism of thermal transport in liquids and amorphous solids has been an outstanding problem for a long time. There have been several approaches to explain the thermal conductivities in these systems, for example, Bridgman's formula for simple liquids, the concept of the minimum thermal conductivity for amorphous solids, and the t...
Preprint
Full-text available
Hotspot is a ubiquitous phenomenon in microdevices/chips. In homogeneous nanoscale graphene disk with a hotspot, a graded thermal conductivity is observed previously even when the system size is fixed. However, the underlying physical mechanism is not clear. In this work, the hotspots in homogeneous 2D disk/3D ball and graphene disk are studied bas...
Preprint
The demand for sophisticated tools and approaches in heat management and control has triggered fast development of emerging fields including conductive thermal metamaterials, nanophononics, far-field and near-field radiative thermal management, etc. In this review, we cast a unified perspective on the control of heat transfer, based on which the re...
Preprint
The thermal transport mechanisms in both liquids and amorphous solids remain unclear due to the lack of successful theories. Several models have been proposed to explain the thermal conductivity, for example, the Bridgman's model for liquids with simple molecules, the minimum thermal conductivity model for amorphous solids, and the thermal resistan...
Article
We report the thermal conductivity of π-stacked Metallophthalocyanine nanowires using thermal bridge method. In temperature range of 20-300K, the thermal conductivity of copper Phthalocyanine nanowires (CuPc NWs) and iron Phthalocyanine nanowires (FePc NWs) increases with temperature and reaches a peak value at around T = 40K, then decreases at hig...
Article
We report phonon renormalization induced by an external electric field E in ferroelectric poly(vinylidene fluoride–trifluoroethylene) [P(VDF-TrFE)] nanofibers through measuring the E-dependent thermal conductivity. Our experimental results are in excellent agreement with the theoretical ones derived from the lattice dynamics. The renormalization is...
Article
Full-text available
The discovery of graphene has stimulated the search for and investigations into other 2D materials because of the rich physics and unusual properties exhibited by many of these layered materials. Transition metal dichalcogenides (TMDs), black phosphorus, and SnSe among many others, have emerged to show highly tunable physical and chemical propertie...
Article
Full-text available
The ability to control monochromatic and coherent phonons is crucial for many phonon-related applications but remains very challenging. Here, we demonstrate a promising phonon nanocapacitor for storing and emitting phonons, built by the carbon schwarzite based host-guest system (HGS). This phonon nanocapacitor takes advantage of the inherently stro...
Preprint
We theoretically investigate the energy relaxation rate of magnons and phonons near the resonance points to clarify the underlying mechanism of heat transport in ferromagnetic materials. We find that the simple two-temperature model is valid for the one-phonon/one-magnon process, as the rate of energy exchange between magnons and phonons is proport...
Article
Full-text available
While numerous studies have been carried out to characterize heat transport behaviours in various crystalline silicon nanostructures, the corresponding characteristics of amorphous one-dimension system have not been well understood. In this study, we amorphize crystalline silicon by means of helium-ion irradiation, enabling the formation of a compl...
Preprint
We report phonon renormalization induced by an external electric field E in ferroelectric poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] nanofibers through measuring the E-dependent thermal conductivity. Our experimental results are in excellent agreement with the theoretical ones derived from the lattice dynamics. The renormalization is...
Article
The heat transfer from nanoparticles (NPs) to gas of photothermal effect is investigated by taking into account both conduction and radiation. The steady-state and unsteady-state heat transfer processes are studied analytically and numerically, respectively. In contrast to the photothermal effect in liquid with metal NPs, in which the radiation is...
Article
Understanding, quantifying and predicting market fluctuation has become increasingly important in recent decades. Volatility and volume are the two commonly used quantities to study the market dynamics and the relationship between these two has been modeled and debated for years with several hypothesis been put forward. Using empirical data, we inv...
Article
Topological materials attract enormous attention due to their unique physical properties and thermoelectric applications. ZrTe5, a semimetal material, is proposed to be a new topological material and shows interesting thickness‐dependent electrical transport properties. Here, the in‐plane thermal conductivity and power factor in exfoliated few‐laye...
Article
Since the advent of transformation optics and scattering cancelling technology, a plethora of unprecedented metamaterials, especially invisibility cloaks, have been successfully demonstrated in various communities, e.g., optics, acoustics, elastic mechanics, dc electric field, dc magnetic field, and thermotics. A long‐held captivation is that trans...
Preprint
Full-text available
Black phosphorus (BP) has emerged as a promising candidate for next generation electronics and optoelectronics among the 2D family materials due to its extraordinary electrical/optical/optoelectronic properties. Interestingly, BP shows strong anisotropic transport behaviour because of its puckered honeycomb structure. Previous studies have demonstr...
Article
Active control of heat flow is one of the important concepts in phononic devices, among which thermal diode is a fundamental building block. The long-standing bottleneck is the relevant experiments lagging far behind theoretical results. In this paper, we experimentally demonstrated considerable thermal rectification in the Y-junction carbon nanotu...
Article
Through non-equilibrium molecular dynamics simulations, we report the direct numerical evidence for the coherent phonons participating in thermal transport at room temperature in graphene phononic crystal (GPnC) structure, and evaluate their contribution to thermal conductivity based on the two-phonon model. With decreasing period length in GPnC, t...
Article
Full-text available
The mechanism of thermal conductivity in amorphous polymers, especially polymer fibers, is unclear in comparison with that in inorganic materials. Here, we report the observation of a crossover of heat conduction behavior from three dimensions to quasi-one dimension in polyimide nanofibers at a given temperature. A theoretical model based on the ra...
Article
Full-text available
Lattice thermal conductivities κL of type-I clathrates encapsulating “off-center” guest atoms behave in a way that is sharply different from those of conventional crystals such as on-center type-I clathrates. The latter decreases with increasing temperature according to 1/T above a few tens K, while κL of off-center clathrates increase T linearly a...
Article
Full-text available
Due to substantial phonon scattering induced by various structural defects, the in‐plane thermal conductivity (K) of graphene films (GFs) is still inferior to the commercial pyrolytic graphite sheet (PGS). Here, the problem is solved by engineering the structures of GFs in the aspects of grain size, film alignment, and thickness, and interlayer bin...
Preprint
Full-text available
Lattice thermal conductivities $\kappa_{\rm L}$ of type-I clathrates encapsulating "off-center" guest atoms behave in a way that is sharply different from those of conventional crystals such as on-center type-I clathrates. The latter decreases with increasing temperature according to 1/$T$ above a few tens\,K. While, $\kappa_{\rm L}$ of off-center...
Article
The applications of polymers and their nanocomposites for thermal dissipation/management are limited by their low thermal conductivity and inferior thermal stability due to their disordered molecular chains. In this paper, we experimentally demonstrate the high thermal conductivity in individual suspended PMDA/ODA nanofibers which are fabricated by...
Article
Full-text available
Establishment of a new technique or extension of an existing technique for thermal and thermoelectric measurements to a more challenging system is an important task to explore the thermal and thermoelectric properties of various materials and systems. The bottleneck lies in the challenges in measuring the thermal contact resistance. In this work, w...
Article
Full-text available
In the regime of strong nonlinearity, the validity of conventional perturbation based phonon transport theories is questionable. In particular, the renormalized phonons instead of phonons are responsible for heat transport in nonlinear lattices. In this work, we directly study the temperature and frequency dependent Mean Free Path (MFP) of renormal...
Article
Full-text available
Composite materials, which consist of organic and inorganic components, are widely used in various fields because of their excellent mechanical properties, resistance to corrosion, low-cost fabrication, etc. Thermal properties of organic/inorganic composites play a crucial role in some applications such as thermal interface materials for micro-elec...
Article
Polymers are considered to be thermal insulator and their applications are limited by the relatively low thermal conductivity which is in the order of ~0.1 Wm-1K-1. The low thermal conductivity of polymer is accepted to be one of the major reasons for the thermal failure in electronic devices. Fortunately, recent studies show that polymer hold surp...
Article
Full-text available
Modifying phonon thermal conductivity in nanomaterials is important not only for fundamental research but also for practical applications. However, the experiments on tailoring the thermal conductivity in nanoscale, especially in two-dimensional materials, are rare due to technical challenges. In this work, we demonstrate in-situ thermal conduction...
Article
Full-text available
Metal oxide based polymer nanocomposites find diverse applications as functional materials and in particular thiol-ene/TiO2 nanocomposites are promising candidates for dental restorative materials. The important mechanical and thermal properties of the nanocomposites, however, are still not well understood. In this study, the elastic modulus and th...
Article
For a nonperiodic system, a bamboo Si1−xGex nanowire with axially degraded components, it is impossible to obtain its phonon dispersion relations through lattice dynamic or the first principle calculation. Therefore, we present a simple and available method to solve this problem. At first, the Si1−xGex nanowire with axially degraded component is di...
Article
Full-text available
Type-I clathrate compounds with off-center guest ions can be used to realize the concept of phonon-glass electron-crystal because they exhibit lattice thermal conductivities κL that are almost identical to those observed in network-forming glasses. This is in contrast with type-I clathrates with on-center guest ions, which show κL of conventional c...
Article
Porous materials provide a large surface to volume ratio, thereby providing a knob to alter fundamental properties in unprecedented ways. In thermal transport, porous nanomaterials can reduce thermal conductivity by not only enhancing phonon scattering from the boundaries of the pores and therefore decreasing the phonon mean free path, but also by...
Article
Full-text available
To explore energy transfer in the nonequilibrium spin-boson model (NESB) from weak to strong system-bath coupling regimes, we propose a polaron-transformed nonequilibrium Green’s function (NEGF) method. By combining the polaron transformation, we are able to treat the system-bath coupling nonperturbatively, thus in direct contrast to conventionally...
Article
Full-text available
The ability to engineer the thermal conductivity of materials allows us to control the flow of heat and derive novel functionalities such as thermal rectification, thermal switching, and thermal cloaking. While this could be achieved by making use of composites and metamaterials at bulk scales, engineering the thermal conductivity at micro- and nan...
Article
Supported graphene on a standard SiO2 substrate exhibits unsatisfactory heat dissipation performance that is far inferior to the intrinsic ultrahigh thermal conductivity of a suspended sample. A suitable substrate for enhancing thermal transport in supported graphene is highly desirable for the development of graphene devices for thermal management...
Article
Full-text available
Type-I cathrate compounds with off-center guest ions realize the phonon-glass electron-crystal concept by exhibiting almost identical lattice thermal conductivities $\kappa_{\rm L}$ to those observed in network-forming glasses. This is in contrast with type-I clathrates with on-center guest ions showing $\kappa_{\rm L}$ of conventional crystallines...
Article
We study the 3D dynamics of an elastic dimer consisting of an active swimmer bound to a passive cargo, both suspended in a Couette flow. Using numerical simulations, we determine the diffusivity of such an active dimer in the presence of long-range hydrodynamic interactions for different values of its self-propulsion speed and the Couette flow. We...
Article
Thermal conductance of a homogeneous 1D nonlinear lattice system with neareast neighbor interactions has recently been computationally studied in detail by Li et al [Eur. Phys. J. B {\bf 88}, 182 (2015)], where its power-law dependence on temperature $T$ for high temperatures is shown. Here, we address its entire temperature dependence, in addition...
Article
Full-text available
The needs for efficient heat removal and superior thermal conduction in nano/micro devices have triggered tremendous studies in low-dimensional materials with high thermal conductivity. Hexagonal boron nitride (h-BN) is believed to be one of the candidates for thermal management and heat dissipation due to its novel physical properties, i.e. therma...
Article
Full-text available
The mechanism of thermal conductivity in amorphous polymers, especially polymer fibers, is unclear in comparison with that in inorganic materials. Here, we report the observation of across over of heat conduction behavior from three dimensions (3D) to quasi-one dimension (1D) in Polyimide(PI) nanofibers at a given temperature. A theoretical model b...
Article
Full-text available
The effects of defect and isotopic doping with different ratios on the thermal conductivity of graphene are investigated by using non-equilibrium molecular dynamics simulations and normal mode analysis method. In contrast to the persisted size dependent thermal conductivity in the pristine graphene, thermal conductivity of defected graphene quickly...
Article
Full-text available
Copper based materials are potential candidates for commercial thermoelectric materials due to their abundance, non-toxicity and good performance. In this paper, we incorporate multi-band Boltzmann transport equations with first principle calculations to theoretically investigate the thermoelectric properties of Cu-based chalcopyrite including quate...
Article
Full-text available
Article
An active swimmer can tow a passive cargo by binding it to form a self-propelling dimer. The orientation of the cargo relative to the axis of the active dimer’s head is determined by the hydrodynamic interactions associated with the propulsion mechanism of the latter. We show how the tower-cargo angular configuration greatly influences the dimer’s...
Article
A novel approachis proposed to enhance the thermal rectification ratio, namely, arranging two thermal rectifiers in series. Through theoretical analysis and molecular dynamics simulations on graphene/phononic crystal structures, the results show that the series thermal rectifiers enhance thermal rectification ratio significantly, compared to a sing...
Article
We theoretically propose a new kind of hybrid thermoelectric material in which metallic nanowireswith high electrical conductivity are embedded in insulating polymer with low thermal conductivity. The electrical conductivity of this hybrid material can be controlled by the volumetric fraction of metallic nanowires due to electron percolation while...
Article
Full-text available
We propose a feasible and effective approach to study quantum thermal transport through anharmonic systems. The main idea is to obtain an {\it effective} harmonic Hamiltonian for the anharmonic system by applying the self-consistent phonon theory. Using the effective harmonic Hamiltonian we study thermal transport within the framework of nonequilib...
Article
Type-I clathrate compounds exhibit glasslike thermal/dynamic properties due to symmetry breaking of guest-atom positions in tetrakaidecahedron cages. All of these features are associated with the phonon dynamics in the THz region, for which we perform large-scale numerical simulations by highlighting the difference between type-I clathrates Ba8Ga16...
Article
For heat conduction in one-dimensional (1D) nonlinear Hamiltonian lattices, it has been known that conserved quantities play an important role in determining the actual heat conduction behavior. In closed or microcanonical Hamiltonian systems, the total energy and stretch are always conserved. Depending on the existence of external on-site potentia...