Modeling Electron-Phonon Nonequilibrium in Gold Films Using Boltzmann Transport Model

2009 ◽  
Vol 131 (8) ◽  
Author(s):  
Arvind Pattamatta ◽  
Cyrus K. Madnia
Keyword(s):  
Film Thickness ◽  
Pulse Duration ◽  
Laser Fluence ◽  
Laser Heating ◽  
Gold Film ◽  
Transport Model ◽  
Melting Time ◽  
Gold Films ◽  
Boltzmann Transport ◽  
Energy Carriers

Ultrashort-pulsed laser irradiation on metals creates a thermal nonequilibrium between electrons and the phonons. Previous computational studies used the two-temperature model and its variants to model this nonequilibrium. However, when the laser pulse duration is smaller than the relaxation time of the energy carriers or when the carriers’ mean free path is larger than the material dimension, these macroscopic models fail to capture the physics accurately. In this paper, the nonequilibrium between energy carriers is modeled via a numerical solution of the Boltzmann transport model (BTM) for electrons and phonons, which is applicable over a wide range of lengths and time scales. The BTM is solved using the discontinuous Galerkin finite element method for spatial discretization and the three-step Runge–Kutta temporal discretization. Temperature dependent electron-phonon coupling factor and electron heat capacity are used due to the strong electron-phonon nonequilibrium considered in this study. The results from the proposed model are compared with existing experimental studies on laser heating of macroscale materials. The model is then used to study laser heating of gold films, by varying parameters such as the film thickness, laser fluence, and pulse duration. It is found that the temporal evolution of electron and phonon temperatures in nanometer size gold films is very different from the macroscale films. For a given laser fluence and pulse duration, the peak electron temperature increases with a decrease in the thickness of the gold film. Both film thickness and laser fluence significantly affect the melting time. For a fluence of 1000 J/m2, and a pulse duration of 75 fs, gold films of thickness smaller than 100 nm melt before reaching electron-phonon equilibrium. However, for the film thickness of 2000 nm, even with the highest laser fluence examined, the electrons and phonons reach equilibrium and the gold film does not melt.

Electron-Phonon Non-Equilibrium in Nanoscale Gold Films

2008 ◽  
Author(s):  
Arvind Pattamatta ◽  
Cyrus K. Madnia
Keyword(s):  
Film Thickness ◽  
Pulse Duration ◽  
Laser Fluence ◽  
Laser Heating ◽  
Gold Film ◽  
Melting Time ◽  
Gold Films ◽  
Energy Carriers ◽  
Wide Range ◽  
Non Equilibrium

Ultrashort-pulsed laser irradiation on metals creates a thermal non-equilibrium between electrons and the phonons. Previous computational studies used the two-temperature model and its variants to model this non-equilibrium. However, when the laser pulse duration is smaller than the relaxation time of the energy carriers or when the carriers mean free path is larger than the material dimension, these macroscopic models fail to capture the physics accurately. In this paper, the non-equilibrium between energy carriers is modeled via numerical solution of the Boltzmann Transport Model (BTM) for electrons and phonons which is applicable over a wide range of length and time scales. The BTM is solved using the Discontinuous Galerkin Finite Element Method for spatial discretization and the three-step Runge Kutta temporal discretization. Temperature dependant electron-phonon coupling factor and electron heat capacity are used due to the strong electron-phonon non-equilibrium considered in this study. The results from the proposed model is compared with existing experimental studies on laser heating of macroscale materials. The model is then used to study laser heating of gold films, by varying parameters such as the film thickness, laser fluence and pulse duration. It is found that the temporal evolution of electron and phonon temperatures in nanometer size gold films are very different from the macroscale films. For a given laser fluence and pulse duration, the peak electron temperature increases with a decrease in the thickness of the gold film. Both film size as well as laser fluence significantly affect the melting time. For a fluence of 5000 J/m2, and a pulse duration of 75 fs, gold films of thickness smaller than 200 nm melt before reaching electron-phonon equilibrium. However, for the film thickness of 2000 nm, even with the highest laser fluence examined, the electrons and phonons reach equilibrium and the gold film does not melt.

Electronic Thermal Conduction in Thin Gold Films

2003 ◽  
Author(s):  
Basil T. Wong ◽  
M. Pinar Mengu¨c¸
Keyword(s):  
Heat Transfer ◽  
Monte Carlo ◽  
Thermal Conduction ◽  
Gold Film ◽  
Boltzmann Transport Equation ◽  
Gold Films ◽  
Temperature Profiles ◽  
Boltzmann Transport ◽  
Fourier Law ◽  
Thin Gold Film

In this work, electronic thermal conduction in thin gold film is modeled via the Boltzmann Transport Equation (BTE). The BTE is solved using a Monte Carlo Method (MCM). Temperature profiles for various film thicknesses are computed. Results show that the electronic thermal transport in gold is still diffusion-like at film thicknesses as small as 100 nm, implying that the Fourier law of conduction can be applied at this scale to predict the steady-state thermal heat transfer without comprising the physics. However, the Fourier law does not predict the temperature profiles accurately if the film thickness is reduced to 10 nm or below.

Modeling Carrier-Phonon Nonequilibrium Due to Pulsed Laser Interaction With Nanoscale Silicon Films

2010 ◽  
Vol 132 (8) ◽  
Author(s):  
Arvind Pattamatta ◽  
Cyrus K. Madnia
Keyword(s):  
Laser Pulse ◽  
Pulse Duration ◽  
Laser Fluence ◽  
Laser Heating ◽  
Acoustic Phonon ◽  
Pulsed Laser ◽  
Silicon Films ◽  
Laser Pulse Duration ◽  
Computational Studies ◽  
Phonon Coupling

Ultrashort-pulsed laser irradiation on semiconductors creates a thermal nonequilibrium between carriers and phonons. Previous computational studies used the “two-temperature” model and its variants to model this nonequilibrium. However, when the laser pulse duration is smaller than the relaxation time of the carriers or phonons or when the carriers’ or phonons’ mean free path is larger than the material dimension, these macroscopic models fail to capture the physics accurately. In this article, the nonequilibrium between carriers and phonons in silicon films is modeled via numerical solution of the Boltzmann transport model (BTM), which is applicable over a wide range of length and time scales. The BTM is solved using the discontinuous Galerkin finite element method for spatial discretization and the three-stage Runge–Kutta temporal discretization. The BTM results are compared with previous computational studies on laser heating of macroscale silicon films. The model is then used to study laser heating of nanometer size silicon films, by varying parameters such as the laser fluence and pulse duration. From the laser pulse duration study, it is observed that the peak carrier number density, and maximum carrier and phonon temperatures are the highest for the shortest pulse duration of 0.05 ps and decreases with increasing pulse duration. From the laser fluence study, it is observed that for fluences equal to or higher than 1000 J/m2, due to the Auger recombination, a second peak in carrier temperature is observed. The use of carrier-acoustic phonon coupling leads to equilibrium phonon temperatures, which are approximately 400 K higher than that of carrier-optical phonon-acoustic phonon coupling. Both the laser pulse duration and fluence are found to strongly affect the equilibrium time and temperature in Si films.

Structural and electronic characterization of 355 nm laser-crystallized silicon: Interplay of film thickness and laser fluence

2014 ◽  
Vol 115 (16) ◽  
pp. 163503 ◽  
Author(s):  
Matthew R. Semler ◽  
Justin M. Hoey ◽  
Srinivasan Guruvenket ◽  
Cody R. Gette ◽  
Orven F. Swenson ◽  
...  
Keyword(s):  
Film Thickness ◽  
Laser Fluence

Fabrication of periodic microscale stripes of silver by laser interference induced forward transfer and their SERS properties

2021 ◽  
Author(s):  
Huijuan Shen ◽  
Yaode Wang ◽  
Liang Cao ◽  
Ying Xie ◽  
Lu Wang ◽  
...  
Keyword(s):  
Film Thickness ◽  
Laser Fluence ◽  
Nano Particles ◽  
Good Resolution ◽  
Laser Interference ◽  
Ag Nps ◽  
Wide Range ◽  
Forward Transfer ◽  
Stripe Structure ◽  
Average Size

Abstract The micro-stripe structure was prepared by laser interference induced forward transfer (LIIFT) technique, composed of Ag nano-particles (NPs). The effects of the film thickness with the carbon nano-particles mixed polyimide (CNPs@PI), Ag film thickness, and laser fluence were studied on the transferred micro-stripe structure. The periodic Ag micro-stripe with good resolution was obtained in a wide range of CNPs@PI film thickness from ~ 0.5 μm to ~ 1.0 μm for the Ag thin film ~ 20 nm. The distribution of the Ag NPs composing the micro-stripe was compact. Nevertheless, the average size of the transferred Ag NPs was increased from ~ 41 nm to ~ 197 nm with the change of the Ag donor film from ~ 10 nm to ~ 40 nm. With the increase of the laser fluence from 102 mJ•cm-2 to 306 mJ•cm-2 per-beam, the transferred Ag NPs became aggregative, improving the resolution of the corresponding micro-stripe. Finally, the transferred Ag micro-stripe exhibited the significant surface enhanced Raman scattering (SERS) property for rhodamine B (RhB). While the concentration of the RhB reached 10-10 mol•L-1, the Raman characteristic peaks of the RhB were still observed clearly at 622 cm-1, 1359 cm-1, and 1649 cm-1. These results indicate that the transferred Ag micro-stripe has potential application as a SERS chip in drug and food detection.

Interplay Between Thermoelectric and Thermionic Effects in Heterostructures

2000 ◽  
Author(s):  
Taofang Zeng ◽  
Gang Chen
Keyword(s):  
Film Thickness ◽  
Free Path ◽  
Thermionic Emission ◽  
Approximate Solutions ◽  
Mean Free Path ◽  
Boltzmann Transport ◽  
Thermoelectric Effects ◽  
Double Heterojunction ◽  
The Mean ◽  
Electron Mean Free Path

Abstract When electrons sweep through a double-heterojunction structure, there exist thermionic effects at the junctions and thermoelectric effects in the film. While both thermoelectric and thermionic effects have been studied for refrigeration and power generation applications separately, their interplay in heterostructures is not understood. This paper establishes a unified model including both thermionic and thermoelectric processes based on the Boltzmann transport equation for electrons, and the nonequilibrium interaction between electrons and phonons. Approximate solutions are obtained, leading to the electron temperature and Fermi level distributions inside heterostructures and discontinuities at the interfaces as a consequence of the highly nonequilibrium transport when the film thickness is much smaller than the electron mean free path. It is found that when the film thickness is smaller than the mean free path of electrons, the transport of electrons is controlled by thermionic emission. The coexistence of thermoelectric and thermionic effects may increase the power factor when the electron mean free path is comparable to the film thickness.

Critical Laser Fluence Observed in (111) Texture, Grain Size and Mobility of Laser Crystallized Amorphous Silicon

1993 ◽  
Vol 297 ◽  
Author(s):  
R.I. Johnson ◽  
G.B. Anderson ◽  
J.B. Boyce ◽  
D.K. Fork ◽  
P. Mei ◽  
...  
Keyword(s):  
Grain Size ◽  
Film Thickness ◽  
Substrate Temperature ◽  
Amorphous Silicon ◽  
Laser Fluence ◽  
Laser Energy ◽  
X Ray ◽  
Peak Intensity ◽  
Silicon Materials ◽  
The Relationship

This paper describes new results on the relationship between the grain size, mobility, and Si (111) x-ray peak intensity of laser crystallized amorphous silicon as a function of the laser fluence, shot density, substrate temperature, and film thickness. These observations include an unexpected narrow peak found in the silicon (111) x- ray peak intensity, which occurs at a specific laser fluence for a given film thickness and substrate temperature. Amorphous silicon materials processed at laser energy densities defined by this peak exhibit exceptionally large grain sizes and electron mobilities that cannot be obtained at any other energy and shot density combination above or below the energy at which the Si (111) x-ray peak intensity maximum occurs.

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