Fundamental Effects of Boundary Structure on Nano-Scale Conductive Heat Transfer

2002 ◽  
Author(s):  
Nicole Aitcheson ◽  
Dan Fickes ◽  
John R. Lloyd
Keyword(s):  
Energy Transport ◽  
Bulk Material ◽  
Boundary Surface ◽  
Boundary Region ◽  
Phonon Transport ◽  
Boundary Structure ◽  
Conductive Heat ◽  
Low Dimensional ◽  
Boundary Characteristics ◽  
Structural Boundary

Modeling of energy transport in nanostructures is very different from that in larger scaled materials. Researchers have reported considerably lower “thermal conductivity” in nano-scaled materials compared to the corresponding bulk material property. This observation is most often attributed to phonon-boundary interactions. However, in-depth explanations of this phenomenon are lacking. This study defines the fundamentals of low-dimensional phonon transport by relating the structural boundary characteristics of a material with the mechanisms of phonon transport. The structural boundary of a material controls phonon transport, creating a “boundary region” rather than a boundary surface, resulting in apparent differences in energy transport efficiency between the bulk material and the nano thin materials.

Grain Boundary Structures in High-Purity Al2O3 Bicrystals Grown From the Melt

1985 ◽  
Vol 60 ◽  
Author(s):  
P.A. Morris ◽  
R.L. Coble
Keyword(s):  
Grain Boundary ◽  
High Purity ◽  
Ceramic Materials ◽  
Boundary Region ◽  
Boundary Structure ◽  
Second Phase ◽  
Stem Analysis ◽  
Tilt Boundaries ◽  
Boundary Characteristics ◽  
Structure Investigations

AbstractThe clean room processing, firing and crystal growth techniques required to produce high-purity Al2O3 crystals and bicrystals with [2110] tilt boundaries near low Σ misorientations are described. The chemical analysis requirements for high-purity ceramic materials are discussed. The boundary characteristics of the θ=33.2°, near Σ = 11, misorientation and the applicability of the CSL model to describe the observed facet planes is determined. The periodicity of the dislocations present in the boundary is 21 nm. STEM analysis of the grain boundary region indicates no second phase or detectable impurity concentrations. The importance of gra in boundary structure investigations in high-purity materials and of chemically well-characterized boundaries is discussed.

Guided Acoustic Phonon Modes in Layered Anisotropic Nanowires

2003 ◽  
Author(s):  
Osama M. Mukdadi ◽  
Subhendu K. Datta ◽  
Martin L. Dunn
Keyword(s):  
Thermal Conductivity ◽  
Acoustic Phonon ◽  
Energy Transport ◽  
Bulk Material ◽  
Rectangular Cross Section ◽  
Critical Role ◽  
Acoustic Phonons ◽  
Phonon Modes ◽  
Low Velocity ◽  
Analysis Technique

Acoustic phonons play a critical role in energy transport in nanostructures. The dispersion of acoustic phonons strongly influences thermal conductivity. Recent observations show lower values of thermal conductivity in finite dimensional nanostructures than in the bulk material. In this work, we will present results for guided acoustic phonon modes in (a) a bilayered GaAs-Nb nanowire of rectangular cross section and (b) a trapezoidal Si nanowire. The former has been used for phonon counting in a nanocalorimeter for measuring thermal conductivity and the latter is commonly used in MEMS applications. A semi-analytical finite element (SAFE) analysis technique has been used to investigate the effects of layering, anisotropy, and boundaries on the dispersion of modes of propagation. Many interesting features of group velocities are found that show confinements around the corners, in the low velocity layer, and coupling of the longitudinal and flexural modes. These would strongly influence thermal conductivity and might provide means of nondestrutive evaluation of mechanical properties.

Scanning Thermal Microscopy of Carbon Nanotubes

2000 ◽  
Author(s):  
Li Shi ◽  
Sergei Plyasunov ◽  
Adrian Bachtold ◽  
Paul L. McEuen ◽  
Arunava Majumdar
Keyword(s):  
Carbon Nanotubes ◽  
Thermal Imaging ◽  
Heat Dissipation ◽  
Energy Transport ◽  
Imaging Technique ◽  
Mechanical Deformation ◽  
Phonon Transport ◽  
Scanning Thermal Microscopy ◽  
Thermal Microscopy ◽  
Nanoelectronic Circuits

Abstract This paper reports the use of scanning thermal microscopy (SThM) for studying heat dissipation and phonon transport in nanoelectronic circuits consisting of carbon nanotubes (CNs). Thermally designed and batch fabricated SThM probes were used to resolve the phonon temperature distribution in the CN circuits with a spatial resolution of 50 nm. Heat dissipation at poor metal-CN contacts could be readily found by the thermal imaging technique. Important questions regarding energy transport in nanoelectronic circuits, such as where is heat dissipated, whether the electrons and phonons are in equilibrium, how phonons are transported, and what are the effects of mechanical deformation on the transport and dissipation properties, are addressed in this work.

Disruption of Dislocation Cores at Grain Boundary in Nb-Doped SrTiO3 Bicrystals

2007 ◽  
Vol 558-559 ◽  
pp. 869-872
Author(s):  
S.Y. Choi ◽  
J.P. Buban ◽  
Naoya Shibata ◽  
Takahisa Yamamoto ◽  
Yuichi Ikuhara
Keyword(s):  
Grain Boundary ◽  
Tilt Angle ◽  
Structural Changes ◽  
Boundary Region ◽  
Boundary Structure ◽  
Regular Array ◽  
Density Of Dislocations ◽  
Discrete Dislocation ◽  
Grain Boundary Structure ◽  
Oriented Region

Bicrystals of Nb-doped SrTiO3, having tilt angles of 4o~18 o with respect to [001], were prepared by joining two single crystals at 1873 K and then investigated to identify the effect of tilt angle on the grain boundary structure. The boundaries consisted of a regular array of dislocations but the positioning of cores along the boundary was found to be changed from a line to a zigzag as a tilt angle was increased up to 10o. The 14° - tilted boundary exhibited two kinds of boundary region exist at the same grain boundary; (1) the discrete cores region as observed in 4° ~ 10° - tilted boundaries and (2) the randomly oriented region as found in the 18° boundary. Thus it was observed that the structure of low-angle tilt boundary changed from the discrete dislocation structure to the randomly oriented structure as a tilt angle increases. These structural changes at the grain boundaries are considered to be related to a minimization of strain due to the high density of dislocations.

Enhanced Photoluminescence Properties of Low-Dimensional Eu3+-Activated Y4Al2O9 Phosphor Compared to Bulk for Solid-State Lighting Applications and Latent Fingerprint Detection-Based Forensic Applications

2019 ◽  
Vol 25 (6) ◽  
pp. 1422-1430
Author(s):  
Antika Das ◽  
Subhajit Saha ◽  
Karamjyoti Panigrahi ◽  
Uttam Kumar Ghorai ◽  
Kalyan Kumar Chattopadhyay
Keyword(s):  
Solid State ◽  
Bulk Material ◽  
Optical Excitation ◽  
Superior Performance ◽  
Solvothermal Reaction ◽  
Latent Fingerprint ◽  
Light Emitting ◽  
Enhanced Photoluminescence ◽  
Improved Performance ◽  
Low Dimensional

AbstractIn recent years, nanoscale phosphors have become vital in optoelectronic applications and to understand the improved performance of nanophosphors over bulk material, detailed investigation is essential. Herein, trivalent europium-activated Y4Al2O9 phosphors were developed by solid-state reaction and solvothermal reaction methods and their performance as a function of their dimension was studied for various applications. Under 394 nm optical excitation, the photoluminescence (PL) emission, excited state lifetime of the nanophosphor, exhibits greater performance than its bulk counterpart. The homogeneous spherical structure of the nanophosphors as compared with solid lumps of bulk phosphors is the basis for almost 40% of the enhancement in nanophosphors' intense red emission compared to the bulk. Moreover, the thermal stability of the nanophosphor is much better than the bulk phosphor, which clearly indicates a key advantage of nanophosphor. The superior performance of Eu3+-doped Y4Al2O9 nanophosphors over their bulk counterparts has been demonstrated for industrial phosphor-converted light-emitting diodes and visualization of latent fingerprint.

Fabrication of Microdevices with Integrated Nanowires for Investigating Low-Dimensional Phonon Transport

Nano Letters ◽  
2010 ◽  
Vol 10 (11) ◽  
pp. 4341-4348 ◽  
Author(s):  
Kedar Hippalgaonkar ◽  
Baoling Huang ◽  
Renkun Chen ◽  
Karma Sawyer ◽  
Peter Ercius ◽  
...  
Keyword(s):  
Phonon Transport ◽  
Low Dimensional

Electron Correlation and Shake up Effects on Energy Bands of Low Dimensional Carbon Systems

2010 ◽  
Vol 163 ◽  
pp. 72-75 ◽  
Author(s):  
Edward Rówiński
Keyword(s):  
Electron Correlation ◽  
Bulk Material ◽  
Niti Alloy ◽  
Carbon Films ◽  
Core Particle ◽  
Energy Bands ◽  
Tetrahedral Amorphous Carbon ◽  
Auger Spectra ◽  
Low Dimensional ◽  
Niti Matrix

The electron correlation and shake up effects on energy band structures in the diamond and tetrahedral amorphous carbon films (both on the substrate of NiTi alloy), the graphite (thin film) and precipitates of the titanium carbide (in the NiTi matrix) were studied by the Auger electron spectroscopy. The description of carbon spectrum is based on the convolution of two-conduction particles and one-core particle spectral densities. It was concluded that the comparisons of the experimental and theoretical Auger spectra were determined the quantitative assessment of the electron correlation and shake up effects in the carbon systems. We also discuss the electron correlations in a quantum wire/dot or bulk material.

scholarly journals Elemental Mapping at Grain Boundaries in Alloy X-750 by EFTEM

1997 ◽  
Vol 3 (S2) ◽  
pp. 975-976 ◽  
Author(s):  
J. Bentley ◽  
N. D. Evans ◽  
E. A. Kenik
Keyword(s):  
Grain Boundary ◽  
Base Alloy ◽  
Boundary Migration ◽  
Analytical Electron Microscopy ◽  
Boundary Region ◽  
Heat Treatment Condition ◽  
Boundary Structure ◽  
Phase Identification ◽  
Elemental Mapping ◽  
Nickel Base

Alloy X-750 is a γ -strengthened, nickel-base alloy used in demanding high-temperature applications. The HTH commercial heat treatment condition provides excellent strength and good corrosion resistance. However, the resultant precipitate structure is complex with fine (˜20 nm) intragranular γ' phase and copious intergranular precipitation of at least four phases (γ', M23C6, M23B6, and TiN). The intergranular precipitation causes localized grain boundary migration and results in a convoluted grain boundary structure. Such complex grain boundary microstructures increase the difficulty of phase identification and interfacial composition measurements by traditional analytical electron microscopy methods. Elemental mapping by EFTEM is a useful additional or alternative technique for characterizing such structures. A Gatan Imaging Filter (GIF) on a Philips CM30 (LaB6) was used in the current investigation. Experimental details have been summarized elsewhere.Elemental maps of Cr, Ti, and Ni (net L23 intensities) are presented in Fig. la-c for a typical grain boundary region of a HTH heat treated specimen.

Atomic structure of undoped Σ=5 symmetrical-tilt grain boundary in strontium titanate

1993 ◽  
Vol 51 ◽  
pp. 986-987
Author(s):  
V. Ravikumar
Keyword(s):  
Grain Boundary ◽  
Strontium Titanate ◽  
Atomic Structure ◽  
Processing Parameters ◽  
Boundary Region ◽  
Boundary Structure ◽  
Reference Structure ◽  
Structure Changes ◽  
Symmetrical Tilt ◽  
Tilt Grain Boundary

Strontium titanate is an important electroceramic material which, under appropriate processing and dopant additions exhibits both varistor and Grain Boundary Layer Capacitor (GBLC) behavior. The presence of electrically active grain boundaries is essential for obtaining these properties. The first step towards correlating the grain boundary structure to properties is to determine the detailed atomic structure of the boundary, which includes its geometric structure, chemistry and electronic structure. We present here our TEM investigation of the atomic structure of an undoped (“pristine”) symmetrical tilt grain boundary in SrTiO3. This provides the basic reference structure, changes to which can be studied as a function of doping and/or processing parameters, and correlated to electrical and dielectric properties.Self-supported TEM samples were made from bicrystals of SrTiO3 through the conventional sample preparation route. Fig. 1 shows a high resolution electron micrograph (Hitachi H9000) of a representative grain boundary region in the sample.

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