scholarly journals Atypical thermal transport in Cu nanorods in the diffusive–ballistic crossover

2016 ◽  
Vol 94 (11) ◽  
pp. 1241-1244
Author(s):  
P.K. Karmakar ◽  
D. Mohanta
Keyword(s):  
Thermal Transport ◽  
Small Amplitude ◽  
Path Length ◽  
Heat Dissipation ◽  
Free Path Length ◽  
Mean Free Path ◽  
Hot Electrons ◽  
Axial Heat ◽  
Electron Mean Free Path ◽  
Electronic Scattering

We propose a simple theoretical calculation scheme based on the phenomenological Fourier heat-flow formalism to study thermal transport behaviors in nanoscale copper rods. The axial heat transport is characterized by a new super-oscillatory feature along with small-amplitude heat spikes. It is anticipated that these atypical spikes are generated by accumulation of localized “hotspots” that have low heat dissipation characteristics. In the case of radial transport, we witness the existence of three distinct heat regimes owing to buildup of hot electrons after experiencing ballistic scattering events. It is important to note that, even though the nanorod diameter is comparable to or smaller than the electron mean free path length, λmfp ∼ 30 nm; multiple ballistic electronic scattering from the outer surface of the nanorods and subsequent accrual into several layers through secondary collisional events has led to concentric heat zones. The hotspots disappear when the nanorod diameter exceeds λmfp.

Lattice Boltzmann Simulation of Rarefied Gas Flow Along Moving Rigid Objects in Micro-Cavities

2015 ◽  
Author(s):  
Weilin Yang ◽  
Hongxia Li ◽  
TieJun Zhang ◽  
Ibrahim M. Elfadel
Keyword(s):  
Free Path ◽  
Lattice Boltzmann ◽  
Path Length ◽  
Gas Flow ◽  
Rarefied Gas ◽  
Free Path Length ◽  
Mean Free Path ◽  
Fluid Simulation ◽  
Transition Flow ◽  
Rarefied Gas Flow

Rarefied gas flow plays an important role in the design and performance analysis of micro-electro-mechanical systems (MEMS) under high-vacuum conditions. The rarefaction can be evaluated by the Knudsen number (Kn), which is the ratio of the molecular mean free path length and the characteristic length. In micro systems, the rarefied gas flow usually stays in the slip- and transition-flow regions (10−3 < Kn < 10), and may even go into the free molecular flow region (Kn > 10). As a result, conventional design tools based on continuum Navier-Stokes equation solvers are not applicable to analyzing rarefaction phenomena in MEMS under vacuum conditions. In this paper, we investigate the rarefied gas flow by using the lattice Boltzmann method (LBM), which is suitable for mesoscopic fluid simulation. The gas pressure determines the mean free path length and Kn, which further influences the relaxation time in the collision procedure of LBM. Here, we focus on the problem of squeezed film damping caused by an oscillating rigid object in a cavity. We propose an improved LBM with an immersed boundary approach, where an adjustable force term is used to quantify the interaction between the moving object and adjacent fluid, and further determines the slip velocity. With the proposed approach, the rarefied gas flow in MEMS with squeezed film damping is characterized. Different factors that affect the damping coefficient, such as pressure of gas and frequency of oscillation, are investigated in our simulation studies.

Imaging of Metal/Semiconductor Interface by Ballistic-Electron-Emission Microscopy (Beem)

1992 ◽  
Vol 295 ◽  
Author(s):  
E. Y. Lee ◽  
B. R. Turnew ◽  
J. R. Jimenez ◽  
L. J. Schowalter
Keyword(s):  
Free Path ◽  
Spatial Resolution ◽  
Electron Emission ◽  
Path Length ◽  
Free Path Length ◽  
Mean Free Path ◽  
Ballistic Electron Emission Microscopy ◽  
Semiconductor Interface ◽  
Ballistic Electron ◽  
Emission Microscopy

AbstractStudies in ballistic-electron-emission spectroscopy (BEES) have enabled precise energy measurements of Schottky barrier heights with excellent spatial resolution and, more recently, it was shown that even scattering at the metal/semiconductor interface affects the BEES spectrum [1]. Monte Carlo simulations have been done to predict the spatial resolution of ballistic-electron-emission microscopy (BEEM) [2]. In this paper, we will discuss the experimental spatial resolution of BEEM, and we will also give some of our BEES results for Au/Si and for Au/PtSi/Si. Our experimental BEEM studies indicate that, for Au/Si, hot electron transport is diffusive rather than ballistic, because the inelastic mean free path length (∼100 nm) is much larger than the elastic mean free path length (∼10 nm). This is in agreement with existing theories and with the literature on the internal photoemission method of studying the transport. Even in this diffusive regime, the spatial resolution of BEEM is still expected to be very good, being on the order of 10 nm [2]. Our preliminary work on PtSi shows that it has an attenuation length of 4 nm, which differs significantly from that of Au.

A STUDY ON PENETRATION DEPTH OF POLARIZATION IMAGING

2010 ◽  
Vol 03 (03) ◽  
pp. 177-181 ◽  
Author(s):  
RAN LIAO ◽  
NAN ZENG ◽  
DONGZHI LI ◽  
TIANLIANG YUN ◽  
YONGHONG HE ◽  
...  
Keyword(s):  
Penetration Depth ◽  
Free Path ◽  
Path Length ◽  
Free Path Length ◽  
Mean Free Path ◽  
Optical Measurements ◽  
Degree Of Polarization ◽  
Polarization Imaging ◽  
Optical Clearing ◽  
Different Response

Optical clearing improves the penetration depth of optical measurements in turbid tissues. Polarization imaging has been demonstrated as a potentially promising tool for detecting cancers in superficial tissues, but its limited depth of detection is a major obstacle to the effective application in clinical diagnosis. In the present paper, detection depths of two polarization imaging methods, i.e., rotating linear polarization imaging (RLPI) and degree of polarization imaging (DOPI), are examined quantitatively using both experiments and Monte Carlo simulations. The results show that the contrast curves of RLPI and DOPI are different. The characteristic depth of DOPI scales with transport mean free path length, and that of RLPI increases slightly with g. Both characteristic depths of RLPI and DOPI are on the order of transport mean free path length and the former is almost twice as large as the latter. It is expected that they should have different response to optical clearing process in tissues.

Mean free-path length theory of predator–prey interactions: Application to juvenile salmon migration

2005 ◽  
Vol 186 (2) ◽  
pp. 196-211 ◽  
Author(s):  
James J. Anderson ◽  
Eliezer Gurarie ◽  
Richard W. Zabel
Keyword(s):  
Free Path ◽  
Path Length ◽  
Free Path Length ◽  
Mean Free Path ◽  
Juvenile Salmon ◽  
Predator Prey

scholarly journals A new regime of nanoscale thermal transport: Collective diffusion increases dissipation efficiency

2015 ◽  
Vol 112 (16) ◽  
pp. 4846-4851 ◽  
Author(s):  
Kathleen M. Hoogeboom-Pot ◽  
Jorge N. Hernandez-Charpak ◽  
Xiaokun Gu ◽  
Travis D. Frazer ◽  
Erik H. Anderson ◽  
...  
Keyword(s):  
Integrated Circuits ◽  
Free Path ◽  
Thermal Management ◽  
Thermal Transport ◽  
Heat Dissipation ◽  
Mean Free Path ◽  
Heat Sources ◽  
Nanoscale Systems ◽  
Nanoscale Thermal Transport ◽  
Thermal Therapies

Understanding thermal transport from nanoscale heat sources is important for a fundamental description of energy flow in materials, as well as for many technological applications including thermal management in nanoelectronics and optoelectronics, thermoelectric devices, nanoenhanced photovoltaics, and nanoparticle-mediated thermal therapies. Thermal transport at the nanoscale is fundamentally different from that at the macroscale and is determined by the distribution of carrier mean free paths and energy dispersion in a material, the length scales of the heat sources, and the distance over which heat is transported. Past work has shown that Fourier’s law for heat conduction dramatically overpredicts the rate of heat dissipation from heat sources with dimensions smaller than the mean free path of the dominant heat-carrying phonons. In this work, we uncover a new regime of nanoscale thermal transport that dominates when the separation between nanoscale heat sources is small compared with the dominant phonon mean free paths. Surprisingly, the interaction of phonons originating from neighboring heat sources enables more efficient diffusive-like heat dissipation, even from nanoscale heat sources much smaller than the dominant phonon mean free paths. This finding suggests that thermal management in nanoscale systems including integrated circuits might not be as challenging as previously projected. Finally, we demonstrate a unique capability to extract differential conductivity as a function of phonon mean free path in materials, allowing the first (to our knowledge) experimental validation of predictions from the recently developed first-principles calculations.

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.

ALTERNATIVE EXPERIMENTAL DETERMINATION OF WEAK LOCALIZATION OF LIGHT IN NANOSTRUCTURED MATERIALS

2002 ◽  
Vol 11 (03) ◽  
pp. 261-274 ◽  
Author(s):  
KOEN CLAYS ◽  
KURT WOSTYN ◽  
YUXIA ZHAO ◽  
ANDRÉ PERSOONS
Keyword(s):  
Random Walk ◽  
Free Path ◽  
Nanostructured Materials ◽  
Path Length ◽  
Dwell Time ◽  
Colloidal Crystals ◽  
Weak Localization ◽  
Free Path Length ◽  
Mean Free Path

An alternative experimental technique for the determination of weak localization of light in partially ordered nanostructured materials is proposed. The technique is based on the criterion for weak localization of light that the transport mean free path length of multiply scattered photons is reduced down to shorter than the wavelength of the light. This mean free path is calculated from the experimental dwell time of the photons in the scattering structure and by applying the photon random walk model using the diffusion approximation. The dwell time is experimentally determined by multifrequency phasefluorimetry. This technique is capable of providing corroborative intensity demodulation data that can be linked to the wavelength dependent transmission (optical bandgap) of colloidal crystals.

scholarly journals Simulation of Z-Shaped Graphene Geometric Diodes Using Particle-In-Cell Monte Carlo Method in theQuasi-Ballistic Regime

Nanomaterials ◽  
2021 ◽  
Vol 11 (9) ◽  
pp. 2361
Author(s):  
John Stearns ◽  
Garret Moddel
Keyword(s):  
Monte Carlo ◽  
Free Path ◽  
Path Length ◽  
Ballistic Transport ◽  
Free Path Length ◽  
Simulation Method ◽  
Mean Free Path ◽  
Device Performance ◽  
Ballistic Regime ◽  
Particle In Cell

Geometric diodes are planar conductors patterned asymmetrically to provide electrical asymmetry, and they have exhibited high-frequency rectification in infrared rectennas. These devices function by ballistic or quasi-ballistic transport in which the transport characteristics are sensitive to the device geometry. Common methods for predicting device performance rely on the assumption of totally ballistic transport and neglect the effects of electron momentum relaxation. We present a particle-in-cell Monte Carlo simulation method that allows the prediction of the current–voltage characteristics of geometric diodes operating quasi-ballistically, with the mean-free-path length shorter than the critical device dimensions. With this simulation method, we analyze a new diode geometry made from graphene that shows an improvement in rectification capability over previous geometries. We find that the current rectification capability of a given geometry is optimized for a specific mean-free-path length, such that arbitrarily large mean-free-path lengths are not desirable. These results present a new avenue for understanding geometric effects in the quasi-ballistic regime and show that the relationship between device dimensions and the carrier mean-free-path length can be adjusted to optimize device performance.

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