scholarly journals Experimental observation of localized interfacial phonon modes

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Zhe Cheng ◽  
Ruiyang Li ◽  
Xingxu Yan ◽  
Glenn Jernigan ◽  
Jingjing Shi ◽  
...  
Keyword(s):  
Experimental Observation ◽  
Thermal Transport ◽  
Interatomic Potential ◽  
High Energy ◽  
Scanning Transmission Electron Microscope ◽  
High Energy Resolution ◽  
Phonon Modes ◽  
Thermal Boundary Conductance ◽  
Scanning Transmission ◽  
Dynamics Simulations

AbstractInterfaces impede heat flow in micro/nanostructured systems. Conventional theories for interfacial thermal transport were derived based on bulk phonon properties of the materials making up the interface without explicitly considering the atomistic interfacial details, which are found critical to correctly describing thermal boundary conductance. Recent theoretical studies predicted the existence of localized phonon modes at the interface which can play an important role in understanding interfacial thermal transport. However, experimental validation is still lacking. Through a combination of Raman spectroscopy and high-energy-resolution electron energy-loss spectroscopy in a scanning transmission electron microscope, we report the experimental observation of localized interfacial phonon modes at ~12 THz at a high-quality epitaxial Si-Ge interface. These modes are further confirmed using molecular dynamics simulations with a high-fidelity neural network interatomic potential, which also yield thermal boundary conductance agreeing well with that measured in time-domain thermoreflectance experiments. Simulations find that the interfacial phonon modes have an obvious contribution to the total thermal boundary conductance. Our findings significantly contribute to the understanding of interfacial thermal transport physics and have impact on engineering thermal boundary conductance at interfaces in applications such as electronics thermal management and thermoelectric energy conversion.

Energy-Filtered CTEM Image of MgO Smoke Particles

1985 ◽  
Vol 43 ◽  
pp. 410-411
Author(s):  
Y. Kondo ◽  
T. Yoshioka ◽  
T. Oikawa ◽  
Y. Kokubo ◽  
M. Kersker
Keyword(s):  
Electron Microscope ◽  
Energy Resolution ◽  
Transmission Electron Microscope ◽  
High Energy ◽  
Scanning Transmission Electron Microscope ◽  
High Energy Resolution ◽  
Energy Analyzer ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Sector Type

The energy filtered imaging technique has so far been carried out in a scanning transmission electron microscope (STEM) fitted with a sector type energy analyzer. The STEM has a disadvantage of low beam parallelity because it uses a convergent beam, while the conventional transmission electron microscope (CTEM) allows good phase contrast and diffraction contrast to be obtained because of the high parallelity of the beam, and allows also high resolution images to be obtained. The technique to obtain energy filtered CTEM images has thus far been carried out by a Castaing-Henry type filter or an Ω type filter. However, these filters have the disadvantage of lower energy resolution than conventional sector type energy analyzer at the present time. This paper reports energy filtered CTEM images of MgO smoke, obtained using a new scanning CTEM image technique and a high energy resolution sector type energy analyzer which can resolve bulk and surface plasmon energy.

Toward Single Mode, Atomic Size Electron Vortex Beams

2014 ◽  
Vol 20 (3) ◽  
pp. 832-836 ◽  
Author(s):  
Ondrej L. Krivanek ◽  
Jan Rusz ◽  
Juan-Carlos Idrobo ◽  
Tracy J. Lovejoy ◽  
Niklas Dellby
Keyword(s):  
Single Mode ◽  
Practical Method ◽  
High Energy ◽  
Scanning Transmission Electron Microscope ◽  
High Energy Resolution ◽  
Narrow Slit ◽  
Angular Momenta ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Vortex Beams

AbstractWe propose a practical method of producing a single mode electron vortex beam suitable for use in a scanning transmission electron microscope (STEM). The method involves using a holographic “fork” aperture to produce a row of beams of different orbital angular momenta, as is now well established, magnifying the row so that neighboring beams are separated by about 1 µm, selecting the desired beam with a narrow slit, and demagnifying the selected beam down to 1–2 Å in size. We show that the method can be implemented by adding two condenser lenses plus a selection slit to a straight-column cold-field emission STEM. It can also be carried out in an existing instrument, the monochromated Nion high-energy-resolution monochromated electron energy-loss spectroscopy-STEM, by using its monochromator in a novel way. We estimate that atom-sized vortex beams with ≥20 pA of current should be attainable at 100–200 keV in either instrument.

scholarly journals Acoustic phonon lifetimes limit thermal transport in methylammonium lead iodide

2018 ◽  
Vol 115 (47) ◽  
pp. 11905-11910 ◽  
Author(s):  
Aryeh Gold-Parker ◽  
Peter M. Gehring ◽  
Jonathan M. Skelton ◽  
Ian C. Smith ◽  
Dan Parshall ◽  
...  
Keyword(s):  
Lattice Dynamics ◽  
Acoustic Phonon ◽  
Optoelectronic Devices ◽  
High Energy ◽  
High Energy Resolution ◽  
Phonon Coupling ◽  
Lead Iodide ◽  
Phonon Modes ◽  
Electron Phonon Coupling ◽  
Methylammonium Lead Iodide

Hybrid organic–inorganic perovskites (HOIPs) have become an important class of semiconductors for solar cells and other optoelectronic applications. Electron–phonon coupling plays a critical role in all optoelectronic devices, and although the lattice dynamics and phonon frequencies of HOIPs have been well studied, little attention has been given to phonon lifetimes. We report high-precision momentum-resolved measurements of acoustic phonon lifetimes in the hybrid perovskite methylammonium lead iodide (MAPI), using inelastic neutron spectroscopy to provide high-energy resolution and fully deuterated single crystals to reduce incoherent scattering from hydrogen. Our measurements reveal extremely short lifetimes on the order of picoseconds, corresponding to nanometer mean free paths and demonstrating that acoustic phonons are unable to dissipate heat efficiently. Lattice-dynamics calculations using ab initio third-order perturbation theory indicate that the short lifetimes stem from strong three-phonon interactions and a high density of low-energy optical phonon modes related to the degrees of freedom of the organic cation. Such short lifetimes have significant implications for electron–phonon coupling in MAPI and other HOIPs, with direct impacts on optoelectronic devices both in the cooling of hot carriers and in the transport and recombination of band edge carriers. These findings illustrate a fundamental difference between HOIPs and conventional photovoltaic semiconductors and demonstrate the importance of understanding lattice dynamics in the effort to develop metal halide perovskite optoelectronic devices.

Thermal boundary conductance between Al films and GaN nanowires investigated with molecular dynamics

2014 ◽  
Vol 16 (20) ◽  
pp. 9403-9410 ◽  
Author(s):  
Xiao-wang Zhou ◽  
Reese E. Jones ◽  
Patrick E. Hopkins ◽  
Thomas E. Beechem
Keyword(s):  
Molecular Dynamics ◽  
Molecular Dynamics Simulations ◽  
Thermal Transport ◽  
Thermal Boundary Conductance ◽  
Gan Nanowires ◽  
System P ◽  
Dynamics Simulations ◽  
Important System

Using molecular dynamics simulations, we studied the thermal boundary conductance between GaN nanowires and Al films and showed how it may be possible to enhance interfacial thermal transport in this important system.

scholarly journals Single-atom vibrational spectroscopy in the scanning transmission electron microscope

Science ◽  
2020 ◽  
Vol 367 (6482) ◽  
pp. 1124-1127 ◽  
Author(s):  
F. S. Hage ◽  
G. Radtke ◽  
D. M. Kepaptsoglou ◽  
M. Lazzeri ◽  
Q. M. Ramasse
Keyword(s):  
Electron Microscope ◽  
Vibrational Spectroscopy ◽  
Materials Science ◽  
Scanning Transmission Electron Microscope ◽  
Atomic Scale ◽  
Single Atom ◽  
Phonon Modes ◽  
Resonant States ◽  
Resolution Electron ◽  
Scanning Transmission

Single-atom impurities and other atomic-scale defects can notably alter the local vibrational responses of solids and, ultimately, their macroscopic properties. Using high-resolution electron energy-loss spectroscopy in the electron microscope, we show that a single substitutional silicon impurity in graphene induces a characteristic, localized modification of the vibrational response. Extensive ab initio calculations reveal that the measured spectroscopic signature arises from defect-induced pseudo-localized phonon modes—that is, resonant states resulting from the hybridization of the defect modes and the bulk continuum—with energies that can be directly matched to the experiments. This finding realizes the promise of vibrational spectroscopy in the electron microscope with single-atom sensitivity and has broad implications across the fields of physics, chemistry, and materials science.

High-Efficiency Three-Dimensional Visualization of Complex Microstructures via Multidimensional STEM Acquisition and Reconstruction

2020 ◽  
Vol 26 (2) ◽  
pp. 240-246 ◽  
Author(s):  
Kevin G. Field ◽  
Benjamin P. Eftink ◽  
Chad M. Parish ◽  
Stuart A. Maloy
Keyword(s):  
High Efficiency ◽  
3D Visualization ◽  
Accurate Determination ◽  
Three Dimensional ◽  
High Energy ◽  
Scanning Transmission Electron Microscope ◽  
Chromium Steel ◽  
Transmission Electron ◽  
Scanning Transmission

AbstractComplex material systems in which microstructure and microchemistry are nonuniformly dispersed require three-dimensional (3D) rendering(s) to provide an accurate determination of the physio-chemical nature of the system. Current scanning transmission electron microscope (STEM)-based tomography techniques enable 3D visualization but can be time-consuming, so only select systems or regions are analyzed in this manner. Here, it is presented that through high-efficiency multidimensional STEM acquisition and reconstruction, complex point cloud-like microstructural features can quickly and effectively be reconstructed in 3D. The proposed set of techniques is demonstrated, analyzed, and verified for a high-chromium steel with heterogeneously situated features induced using high-energy neutron bombardment.

Role of Edge Chirality and Isotope Doping in Thermal Transport and Thermal Rectification in Graphene Nanoribbons

2011 ◽  
Author(s):  
Yan Wang ◽  
Xiulin Ruan
Keyword(s):  
Thermal Conductivity ◽  
Thermal Transport ◽  
Graphene Nanoribbons ◽  
Mass Density ◽  
Transport Processes ◽  
Phonon Modes ◽  
Cross Sectional ◽  
Thermal Rectification ◽  
The Difference ◽  
Dynamics Simulations

Thermal transport processes in graphene nanoribbons (GNRs) within and beyond the linear response regime has been studied using classical molecular dynamics simulations. Zigzag-edged GNRs have higher thermal conductivities than armchair-edged ones, and the difference diminishes with increasing width. Analysis on the cross-sectional distribution of heat flux reveals that edge atoms cannot transport thermal energy as efficiently as interior ones. Edge localization of phonon modes reduces thermal transport through edge carbon atoms, especially on armchair edges, which results in a lower thermal conductivity. Isotope (13C) doping can reduce the thermal conductivity of GNRs by 30%–40% by an addition of only ∼20% isotope atoms. The significant reduction in thermal conductivity is partially attributed to phonon localization induced by isotope defects, which is confirmed by phonon mode participation ratio analysis. We also demonstrate that a GNR asymmetric in edge chirality or mass density can generate considerable thermal rectification, which is essential for developing GNR-based thermal management devices.

scholarly journals Recent developments in the structure of high temperature oxide melts

2014 ◽  
Vol 70 (a1) ◽  
pp. C1332-C1332
Author(s):  
Chris Benmore ◽  
Lawrie Skinner ◽  
Oliver Alderman ◽  
Anthony Tamalonis ◽  
J.K. Weber ◽  
...  
Keyword(s):  
High Temperature ◽  
Interatomic Potential ◽  
Standard Technique ◽  
High Energy ◽  
Oxidation Reactions ◽  
Recent Developments ◽  
High Temperature Oxide ◽  
Temperature Oxide ◽  
Dynamics Simulations ◽  
Oxide Melts

Aerodynamic levitation with laser heating has now become a standard technique for studying the structure of oxide melts on synchrotron and neutron beamlines. Here we summarize the results of a growing number of findings that show a distinct decrease in the local cation-oxygen coordination number, for liquid state single and binary oxides, compared to their crystalline forms. This phenomenon is often correlated with a significant decrease in density upon melting and diffraction measurements show a distribution of lower coordinated polyhedra. The diffraction data allow us to refine interatomic potential parameters within molecular dynamics simulations to obtain very good agreement between the structural models and experiments. The feasibility of very high temperature experiments around and above 3000 degrees Celsius, as well as the safety aspects associated with measuring radioactive samples will be discussed. Future prospects on changing the oxidation state of high temperature oxide melts through reduction-oxidation reactions will also be considered. The photograph below shows a Uranium dioxide pellet being loaded into the aerodynamic levitator on a high energy x-ray beam line at the APS prior to melting.

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