Thermal Conductivity of α-Tetragonal Boron Nanoribbons

2009 ◽  
Author(s):  
Scott W. Waltermire ◽  
Juekuan Yang ◽  
Deyu Li ◽  
Terry T. Xu
Keyword(s):  
Thermal Conductivity ◽  
Thermal Transport ◽  
Room Temperature ◽  
High Hardness ◽  
Mean Free Path ◽  
Good Oxidation Resistance ◽  
Elemental Boron ◽  
Past Half Century ◽  
Materials Research ◽  
Low Dimensional

Elemental boron has many interesting properties, such as high melting point, low density, high hardness, high Young’s modulus, good oxidation resistance, resulting from its complex crystalline structure from its electron-deficient nature. Boron forms complex crystalline structures according to the various arrangements of B12 icosahedra in the lattice, such as α (B12)- and β (B105)-rhombohedral and α (B50)- and β (B196)-tetragonal boron polymorphs, among others. Even though considerable materials research has been conducted over the past half century on boron and boron-based compounds, investigating their unique structures and corresponding properties, our understanding of this complex class of materials is still poor, compared to some other well-studied materials with much simpler structures such as silicon. Thermal transport studies through bulk boron have been performed mainly on β-rhombohedral and amorphous boron, because of the difficulty to grow high quality bulk α-rhombohedral boron samples [1–3]. Some efforts have been made to measure B12As2, B12P2, AlB12 samples that have an α-rhombohedral form [2,3]. There is almost no information available on α-tetragonal boron. However, Slack predicted the thermal conductivity of α-boron should be ∼200 W/m-K at room temperature, which is 1/2 that of copper. Large phonon mean free path has been predicted for α-boron (from ∼200 nm at room temperature to 6 nm at the Debye temperature), which could lead to interesting thermal transport properties for low dimensional boron structures.

Electrohydrodynamic Flow in Thick Liquid Crystal Cells

1989 ◽  
Vol 177 ◽  
Author(s):  
David H. Van Winkle ◽  
Jit Gurung ◽  
Rand Biggers
Keyword(s):  
Thermal Conductivity ◽  
Liquid Crystal ◽  
Thermal Transport ◽  
Room Temperature ◽  
Liquid Crystal Cell ◽  
Optical Observations ◽  
Constant Voltage ◽  
Maximum Enhancement ◽  
Flowing Liquid ◽  
Crystal Cells

ABSTRACTThe thermal transport across a thick (0.66 cm) liquid crystal cell has been measured versus applied ac voltage and frequency. These measurements are correlated with the optically observed onset of flow and turbulence in cells as identical as practicable to those used for the thermal transport measurements. In addition, the measurements are compared with reported observations in thin cells. The thermal transport across the liquid crystal is characterized by an effective thermal conductivity Kf. It was found that Kf increases with increasing frequency, at constant voltage, to a maximum enhancement at about 40 Hz at room temperature. Optical observations on thick cells indicate that dynamic columnar domains of flowing liquid crystal are the primary mode of heat transport, as determined by correlating the structure and characteristic lifetime of such domains as a function of voltage and frequency. Optical observations at low voltages suggest that Williams Domains do not exist in these thick cells, and that all observed responses are functions of electric field strength, not applied voltage (as in thin Williams Domain cells).

Built-in-polarization field effect on intrinsic and extrinsic thermal conductivities of AlN/GaN/AlN quantum well

2015 ◽  
Vol 29 (21) ◽  
pp. 1550149 ◽  
Author(s):  
A. Pansari ◽  
V. Gedam ◽  
B. K. Sahoo
Keyword(s):  
Thermal Conductivity ◽  
Relaxation Time ◽  
Quantum Well ◽  
Room Temperature ◽  
Mean Free Path ◽  
Polarization Field ◽  
Polarization Mechanism ◽  
Negative Effect ◽  
Phonon Velocity ◽  
Thermal Conductivities

In this paper, the effect of built-in-polarization field on lattice thermal conductivity of AlN/GaN/AlN quantum well (QW) has been theoretically investigated. The built-in-polarization field at the hetero-interface of GaN/AlN modifies elastic constant, phonon velocity and Debye temperature of GaN QW. The relaxation time of acoustic phonons (AP) in various scattering processes in GaN with and without built-in-polarization field has been computed at room temperature. The result shows that combined relaxation time of AP is enhanced by built-in-polarization field and implies a longer mean free path. The revised intrinsic and extrinsic thermal conductivities of GaN have been estimated. The theoretical analysis shows that up to a certain temperature the polarization field acts as negative effect and reduces the thermal conductivities. However, after this temperature both thermal conductivities are significantly contributed by polarization field. This gives the idea of temperature dependence of polarization effect which signifies the pyro-electric character of GaN. The intrinsic thermal conductivity at room temperature for with and without polarization mechanism is found to be 491 Wm -1 K -1 and 409 Wm -1 K -1, respectively i.e., 20% enhancement. However, the extrinsic thermal conductivity at room temperature for with and without polarization mechanism is found to be 280 Wm -1 K -1 and 245 Wm -1 K -1, respectively i.e., 13% enhancement. The method we have developed may be taken into account during the simulation of heat transport in optoelectronic nitride devices to minimize the self-heating processes and in polarization engineering strategies to optimize the thermoelectric performance of GaN alloys.

scholarly journals Tuning the Anisotropic Thermal Transport in {110}-Silicon Membranes with Surface Resonances

Nanomaterials ◽  
2021 ◽  
Vol 12 (1) ◽  
pp. 123
Author(s):  
Keqiang Li ◽  
Yajuan Cheng ◽  
Maofeng Dou ◽  
Wang Zeng ◽  
Sebastian Volz ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Thermal Transport ◽  
Heat Dissipation ◽  
Mean Free Path ◽  
Dynamic Simulations ◽  
Resonant Structures ◽  
Thermoelectric Energy ◽  
Thin Membranes ◽  
The Mean ◽  
Equilibrium Molecular Dynamic

Understanding the thermal transport in nanostructures has important applications in fields such as thermoelectric energy conversion, novel computing and heat dissipation. Using non-homogeneous equilibrium molecular dynamic simulations, we studied the thermal transport in pristine and resonant Si membranes bounded with {110} facets. The break of symmetry by surfaces led to the anisotropic thermal transport with the thermal conductivity along the [110]-direction to be 1.78 times larger than that along the [100]-direction in the pristine structure. In the pristine membranes, the mean free path of phonons along both the [100]- and [110]-directions could reach up to ∼100 µm. Such modes with ultra-long MFP could be effectively hindered by surface resonant pillars. As a result, the thermal conductivity was significantly reduced in resonant structures, with 87.0% and 80.8% reductions along the [110]- and [100]-directions, respectively. The thermal transport anisotropy was also reduced, with the ratio κ110/κ100 decreasing to 1.23. For both the pristine and resonant membranes, the thermal transport was mainly conducted by the in-plane modes. The current work could provide further insights in understanding the thermal transport in thin membranes and resonant structures.

Elephant ivory: A low thermal conductivity, high strength nanocomposite

2006 ◽  
Vol 21 (1) ◽  
pp. 287-292 ◽  
Author(s):  
Michael B. Jakubinek ◽  
Champika J. Samarasekera ◽  
Mary Anne White
Keyword(s):  
Thermal Conductivity ◽  
Room Temperature ◽  
High Strength ◽  
Mean Free Path ◽  
Boundary Scattering ◽  
Low Thermal Conductivity ◽  
Recent Interest ◽  
Elephant Ivory ◽  
Nanocomposite Structures ◽  
Structure Properties

There has been much recent interest in heat transport in nanostructures, and alsoin the structure, properties, and growth of biological materials. Here we present measurements of thermal properties of a nanostructured biomineral, ivory. The room-temperature thermal conductivity of ivory is anomalously low in comparison with its constituent components. Low-temperature (2–300 K) measurements ofthermal conductivity and heat capacity reveal a glass-like temperature dependenceof the thermal conductivity and phonon mean free path, consistent with increased phonon-boundary scattering associated with nanostructure. These results suggest that biomineral-like nanocomposite structures could be useful in the design of novel high-strength materials for low thermal conductivity applications.

Thermal Transport in Few-Quintuple Bi2Te3 Thin Films and Nanoribbons

2011 ◽  
Author(s):  
Bo Qiu ◽  
Xiulin Ruan
Keyword(s):  
Thin Films ◽  
Thermal Conductivity ◽  
Molecular Dynamics ◽  
Temperature Dependence ◽  
Thermal Transport ◽  
Room Temperature ◽  
Phonon Scattering ◽  
Md Simulations ◽  
Boundary Scattering ◽  
Nanoporous Films

In this work, thermal conductivity of perfect and nanoporous few-quintuple Bi2Te3 thin films as well as nanoribbons with perfect and zig-zag edges is investigated using molecular dynamics (MD) simulations with Green-Kubo method. We find minimum thermal conductivity of perfect Bi2Te3 thin films with three quintuple layers (QLs) at room temperature, and we believe it originates from the interplay between inter-quintuple coupling and phonon boundary scattering. Nanoporous films and nanoribbons are studied for additional phonon scattering channels in suppressing thermal conductivity. With 5% porosity in Bi2Te3 thin films, the thermal conductivity is found to decrease by a factor of 4–6, depending on temperature, comparing to perfect single QL. For nanoribbons, width and edge shape are found to strongly affect the temperature dependence as well as values of thermal conductivity.

Thermal Transport in Nanostructured Solid-State Cooling Devices

2005 ◽  
Vol 127 (1) ◽  
pp. 108-114 ◽  
Author(s):  
Deyu Li ◽  
Scott T. Huxtable ◽  
Alexis R. Abramson ◽  
Arun Majumdar
Keyword(s):  
Thermal Conductivity ◽  
Solid State ◽  
Nanostructured Materials ◽  
Thermal Transport ◽  
Experimental Studies ◽  
Phonon Transport ◽  
Peltier Effect ◽  
Cooling Devices ◽  
Low Dimensional ◽  
Solid State Cooling

Low-dimensional nanostructured materials are promising candidates for high efficiency solid-state cooling devices based on the Peltier effect. Thermal transport in these low-dimensional materials is a key factor for device performance since the thermoelectric figure of merit is inversely proportional to thermal conductivity. Therefore, understanding thermal transport in nanostructured materials is crucial for engineering high performance devices. Thermal transport in semiconductors is dominated by lattice vibrations called phonons, and phonon transport is often markedly different in nanostructures than it is in bulk materials for a number of reasons. First, as the size of a structure decreases, its surface area to volume ratio increases, thereby increasing the importance of boundaries and interfaces. Additionally, at the nanoscale the characteristic length of the structure approaches the phonon wavelength, and other interesting phenomena such as dispersion relation modification and quantum confinement may arise and further alter the thermal transport. In this paper we discuss phonon transport in semiconductor superlattices and nanowires with regards to applications in solid-state cooling devices. Systematic studies on periodic multilayers called superlattices disclose the relative importance of acoustic impedance mismatch, alloy scattering, and crystalline imperfections at the interfaces. Thermal conductivity measurements of mono-crystalline silicon nanowires of different diameters reveal the strong effects of phonon-boundary scattering. Experimental results for Si/SiGe superlattice nanowires indicate that different phonon scattering mechanisms may disrupt phonon transport at different frequencies. These experimental studies provide insight regarding the dominant mechanisms for phonon transport in nanostructures. Finally, we also briefly discuss Peltier coolers made from nanostructured materials that have shown promising cooling performance.

Thermometry and Thermal Transport in Micro/Nanoscale Solid-State Devices and Structures

2001 ◽  
Vol 124 (2) ◽  
pp. 223-241 ◽  
Author(s):  
David G. Cahill ◽  
Kenneth Goodson ◽  
Arunava Majumdar
Keyword(s):  
Thermal Conductivity ◽  
Carbon Nanotubes ◽  
Single Crystal ◽  
Time Resolution ◽  
Thermal Transport ◽  
Room Temperature ◽  
Lateral Resolution ◽  
Small Range ◽  
Single Crystal Films ◽  
Crystal Films

We review recent advances in experimental methods for high spatial-resolution and high time-resolution thermometry, and the application of these and related methods for measurements of thermal transport in low-dimensional structures. Scanning thermal microscopy (SThM) achieves lateral resolutions of 50 nm and a measurement bandwidth of 100 kHz; SThM has been used to characterize differences in energy dissipation in single-wall and multi-wall carbon nanotubes. Picosecond thermoreflectance enables ultrahigh time-resolution in thermal diffusion experiments and characterization of heat flow across interfaces between materials; the thermal conductance G of interfaces between dissimilar materials spans a relatively small range, 20<G<200 MW m−2K−1 near room temperature. Scanning thermoreflectance microscopy provides nanosecond time resolution and submicron lateral resolution needed for studies of heat transfer in microelectronic, optoelectronic and micromechanical systems. A fully-micromachined solid immersion lens has been demonstrated and achieves thermal-radiation imaging with lateral resolution at far below the diffraction limit, <2 μm. Microfabricated metal bridges using electrical resistance thermometry and joule heating give precise data for thermal conductivity of single crystal films, multilayer thin films, epitaxial superlattices, polycrystalline films, and interlayer dielectrics. The room temperature thermal conductivity of single crystal films of Si is strongly reduced for layer thickness below 100 nm. The through-thickness thermal conductivity of Si-Ge and GaAs-AlAs superlattices has recently been shown to be smaller than the conductivity of the corresponding alloy. The 3ω method has been recently extended to measurements of anisotropic conduction in polyimide and superlattices. Data for carbon nanotubes measured using micromachined and suspended heaters and thermometers indicate a conductivity near room temperature greater than diamond.

Thermal Conductivity Measurement of Graphene Exfoliated on Silicon Dioxide

2010 ◽  
Author(s):  
Jae Hun Seol ◽  
Arden L. Moore ◽  
Insun Jo ◽  
Zhen Yao ◽  
Li Shi
Keyword(s):  
Thermal Conductivity ◽  
Silicon Dioxide ◽  
Thermal Transport ◽  
Heat Dissipation ◽  
Electronic Materials ◽  
Conductivity Measurement ◽  
Heat Transfer Analysis ◽  
Suspended Graphene ◽  
Numerical Heat Transfer ◽  
Low Dimensional

Since graphene was first exfoliated from graphite, the monatomic layer of carbon atoms has attracted great interest for fundamental studies of unique two dimensional transport phenomena. Meanwhile, graphene is being explored for nanoelectronic applications because of the superior electron mobility and mechanical strength as well as compatibility with existing planar silicon-based microelectronics. The ultrahigh thermal conductivity suggested recently for suspended graphene is another attractive feature that may potentially address the increasingly severe heat dissipation problems in nanoelectronic devices. However, little is known about thermal transport properties of supported graphene that is used in most graphene device configurations. To better understand thermal transport in supported graphene, we have developed a device to measure the thermal conductivity of graphene exfoliated on a silicon dioxide beam. The obtained peak thermal conductivity is about 600 W/m-K near room temperature. This value is lower than the basal plane values for graphite and suspended graphene, but still considerably higher than common electronic materials. The measurement results at low temperatures further reveal intriguing low dimensional behaviors. Here, we present a detailed analytical and numerical heat transfer analysis of the thermal measurement method.

Thickness-dependent in-plane thermal conductivity of suspended MoS2 grown by chemical vapor deposition

Nanoscale ◽  
2017 ◽  
Vol 9 (7) ◽  
pp. 2541-2547 ◽  
Author(s):  
Jung Jun Bae ◽  
Hye Yun Jeong ◽  
Gang Hee Han ◽  
Jaesu Kim ◽  
Hyun Kim ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Chemical Vapor Deposition ◽  
Free Path ◽  
Vapor Deposition ◽  
Room Temperature ◽  
Chemical Vapor ◽  
Mean Free Path

We observe that the Fuchs–Sondheimer model works for the thickness-dependent thermal conductivity of MoS2 down to 10 nm in thickness at room temperature, yielding a phonon mean free path of 17 nm for bulk.

Thermal Transport in Thorium Dioxide

2017 ◽  
Author(s):  
Jungkyu Park ◽  
Eduardo B. Farfán ◽  
Christian Enriquez ◽  
Nicholas Kinder ◽  
Matthew Greeson
Keyword(s):  
Thermal Conductivity ◽  
Thermal Transport ◽  
Low Temperatures ◽  
Nuclear Reactors ◽  
Mean Free Path ◽  
Thorium Dioxide ◽  
Long Wavelength ◽  
Fuel Pellets ◽  
Different Temperatures ◽  
Non Equilibrium Molecular Dynamics

Thorium is more abundant in nature than uranium and thorium fuels can breed fissile U-233 fuel that can be used in various types of nuclear reactors. Moreover, thorium dioxide has drawn interest from researchers due to its relatively superior thermal properties when compared to conventional uranium dioxide fuel pellets. In this study, thermal transport in thorium dioxide is investigated using reverse non-equilibrium molecular dynamics. The thermal conductivity of bulk thorium dioxide was measured to be 20.8 W/m-K and the phonon mean free path was estimated to be between 7 ∼ 8.5 nm at 300 K. It was also observed that the thermal conductivity of thorium dioxide has a strong dependency on temperature; the thermal conductivity decreases with an increase in the temperature. Moreover, by simulating thorium dioxide structures with different lengths at different temperatures, it was also identified that short wavelength phonons dominate thermal transport in thorium dioxide at high temperatures, resulting in decreased intrinsic phonon mean free paths and minimal effect of boundary scattering while long wavelength phonons dominate the thermal transport in thorium dioxide at low temperatures.

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