Cemal Basaran

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Professor of Engineering Mechanics

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Unified Mechanics Theory

Springer eBooks, 2021

Thermodynamics

Springer eBooks, 2021

A Review of Damage, Void Evolution, and Fatigue Life Prediction Models

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Experimental Damage Mechanics of Microelectronic Solder Joints Under Fatigue Loading

Fatigue damage is a progressive process of material degradation. The objective of this study is t... more Fatigue damage is a progressive process of material degradation. The objective of this study is to experimentally qualify the damage mechanism in solder joints in electronic packaging under thermal fatigue loading. Another objective of this paper is to show that damage mechanism under thermal cycling and mechanical cycling is very different. Elastic modulus degradation under thermal cycling, which is considered as a physically detectable quantity of material degradation, was measured by Nano-indenter. It was compared with tendency of inelastic strain accumulation of solder joints in Ball Grid Array (BGA) package under thermal cycling, which was measured by Moire´ interferometry. Fatigue damage evolution in solder joints with traditional load-drop criterion was also investigated by shear-strain hysteresis loops from strain-controlled cyclic shear testing of thin layer solder joints. Load-drop behavior was compared with elastic modulus degradation of solder joints under thermal cycling. Following conventional Coffin-Manson approach, S-N curve was obtained from isothermal fatigue testing with load-drop criterion. Coffin-Manson curves obtained from strain controlled mechanical tests were used to predict fatigue life of solder joints. In this paper it is shown that this approach underestimates the fatigue life by an order of magnitude. Results obtained in this project indicate that thermal fatigue and isothermal mechanical fatigue are completely different damage mechanism for microstructurally evolving materials.

Unified Mechanics of Metals under High Electrical Current Density: Electromigration and Thermomigration

High current density electron wind forces in metallic graphene nanoribbons

Nanotechnology, Jun 16, 2020

In this study the electric current-induced wind forces on a unit lattice of a 10-dimer zigzag gra... more In this study the electric current-induced wind forces on a unit lattice of a 10-dimer zigzag graphene nanoribbon (ZGNR) are calculated under different magnitudes of electric field and temperatures. Wind forces are calculated using a semi-classical method where quantum mechanics is integrated into Ensemble Monte Carlo (EMC) simulations by considering energy and momentum conservation in both transverse and longitudinal directions of GNR during the electron-phonon scattering process. First order perturbation theory using the Deformation Potential Approximation (DPA) has been used in the calculation of the scattering rates. Results show that under the same electric field, Joule heating power in 10-dimer ZGNR is around 3 magnitudes higher than metallic single-walled carbon nanotubes and the wind forces are 1 magnitude higher. According to the calculated results, the wind force in 10-dimer ZNGR is in the order of 0.0073 eV/Å2 under 20 kV at 300K and it is much lower than the fracture strength of ZGNR from the results of Molecular Dynamics simulations. Thus the failure of GNR under electric current is considered to be mainly due to the Joule heating.

<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mi>β</mml:mi><mml:mtext>-Sn</mml:mtext></mml:mrow></mml:math>grain-boundary structure and self-diffusivity via molecular dynamics simulations

Physical Review B, Apr 26, 2010

ABSTRACT The self-diffusion properties of several β-Sn symmetric tilt grain boundaries are examin... more ABSTRACT The self-diffusion properties of several β-Sn symmetric tilt grain boundaries are examined using molecular dynamics simulations. The boundary types examined—(101), (201), (401), (310)-Σ5, and (410)—are chosen from those observed in experiment and from arbitrary Miller planes, giving a variety of tilt angles and interface properties. Planar structure factor and diffusivity profiles for each boundary are computed and a grain-boundary width, δGB, is measured from these profiles. Larger diffusive widths (δGB) are exhibited by higher excess potential energy grain boundaries. Diffusivities (DGB) in the directions parallel to the interface plane are computed and activation energies are found with the Arrhenius relation. DGB (as δGBDGB normalized by δGB) is shown to agree well with experiment. We also investigate the anisotropic diffusive behavior of the (401) grain boundary and find that the low energy grain boundary exhibits very low activation energy diffusion, due to the development of diffusive channels.

Influence of defects on dissipative transport in graphene nanoribbons tunnel field-effect transistor

Nanotechnology, Oct 25, 2019

The impact of electrostatic doping level on the dissipative transport of Armchair GNR-TFET is stu... more The impact of electrostatic doping level on the dissipative transport of Armchair GNR-TFET is studied using the Quantum Perturbation Theory (QPT) with the Extended Lowest Order Expansion (XLOE) implementation method. Results show that the doping level of the source and drain sides of the GNR-TFET has a significant impact on the phonon contribution to the carrier transport process. Unlike in other similar studies, where phonons are believed to have a constant detrimental influence on the ION/IOFF ratio and Subthreshold Swing (SS) of the TFET devices due to the phonon absorption-assisted tunneling, we show that by a proper engineering of the doping level in the source and drain, the phonon absorption assisted tunneling can be effectively inhibited. We also show that as temperature increase, the device switching property deteriorates in both the ballistic and dissipative transport regimes, and there exists a temperature-dependent critical doping level where the device has optimal switching behavior.

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Shear Strength of Square Graphene Nanoribbons beyond Wrinkling

Journal of Electronic Materials, Apr 6, 2018

Atomistic modeling of armchair and zigzag graphene nanoribbons (GNRs) has been performed to inves... more Atomistic modeling of armchair and zigzag graphene nanoribbons (GNRs) has been performed to investigate the post-wrinkling behavior under in-plane (x-y) shear deformation. Simulations were performed at 300 K for square GNRs with size ranging from 2.5 nm to 20 nm. Shear stresses led only to diagonal tension, and wrinkling was not accompanied by any diagonal compressive force. Once the diagonal tension reached its ultimate elastic level, three major stress-relaxing phenomena were observed. The type of stressrelaxing phenomenon involved greatly affected the mechanical behavior in terms of the slope of the stress-strain diagram beyond the elastic range. The results showed that the average slope of the stress-strain relation beyond the ultimate elastic stress decreased with the increase of the GNR size. Moreover, the slope of the shear stress-strain curve beyond the ultimate elastic stress was always greater for armchair than for zigzag GNRs. GNRs can sustain very high plastic shear strains beyond 100% before failure. The ultimate elastic stress can range from 20 GPa to 50 GPa, occurring at shear strain ranging from 52% to 19%. The ultimate elastic stress and strain were inversely proportional to the size of the GNR with a power factor ranging from 0.261 for armchair GNRs to 0.354 for zigzag GNRs due to the decrease in the effective width for diagonal tension.

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Impact of electrostatic doping level on the dissipative transport in graphene nanoribbons tunnel field-effect transistors

Carbon, Nov 1, 2019

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Aspect ratio effect on shear modulus and ultimate shear strength of graphene nanoribbons

Diamond and Related Materials, Apr 1, 2017

This paper focuses on shear modulus and shear deformation behavior of Graphene Nano Ribbons (GNR)... more This paper focuses on shear modulus and shear deformation behavior of Graphene Nano Ribbons (GNR) post wrinkling initiation taking into account size effect. Atomistic modeling of armchair and zigzag GNR were performed at 300 o K for GNR with a constant 10 nm width and lengths ranging from 2.5 nm to 25 nm. Results show that ridge formation is oriented at 45 degrees for GNR with an aspect ratio less than one and that the number of ridges is equal to the reciprocal of the aspect ratio, while for aspect ratios higher than one, the ridge formation direction coincides with the diagonal direction of the GNR and only one ridge is formed. Once the diagonal tension reached its ultimate elastic level, three major stress-relaxing phenomena are reported. Results show that the average slope of the stress-strain curve beyond the ultimate elastic stress decreases with increasing GNR length. Moreover, the slope of the shear stress-strain curve in that region is always greater in armchair GNR than in Zigzag GNR. GNR can sustain very high plastic shear strains beyond 400% before failure for wide GNR. It is observed that the shear modulus is inversely proportional to the aspect ratio of the GNR.

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$Research paper thumbnail of The effects of vacancy defect on the fracture behaviors of zigzag graphene nanoribbons$

The effects of vacancy defect on the fracture behaviors of zigzag graphene nanoribbons

International Journal of Damage Mechanics, Sep 28, 2016

Zigzag graphene nanoribbons with and without single vacancy defect are strained under uniaxial te... more Zigzag graphene nanoribbons with and without single vacancy defect are strained under uniaxial tension using molecular dynamics simulations. In order to understand the influence of vacancy defect on the damage mechanics, the graphene nanoribbons are categorized into six groups based on their width, ranging from 2.5 nm to 15 nm. In each group, the length of GRNGNR also varied from 2.5 nm to 15 nm. The comparison of the stress–strain relationship and the fracture behavior of pristine and defective graphene nanoribbon demonstrate that single vacancy defect has little influence on the elastic modulus and the ultimate strength of graphene nanoribbons. However, size effect does have an influence on the ultimate failure stress of the graphene nanoribbon.

Mechanical and electronic properties of graphene nanomesh heterojunctions

Computational Materials Science, Oct 1, 2018

Abstract It is well known that introducing periodic holes into graphene can be used to obtain sem... more Abstract It is well known that introducing periodic holes into graphene can be used to obtain semiconducting graphene nanomeshes (GNM). Using Molecular Dynamics (MD) simulations as well as semi-empirical Extended Huckel (EH) method, the mechanical and electronic properties of GNM heterojunction are studied. In this study the mechanical and electronic properties of graphene nanoribbons with different hole sizes and different hole shapes (circular, square and equilateral triangle) were studied. Midgap states were observed near the Fermi level, which are also affected by the geometries of the holes. Dependence of the properties on the density (ρ) was also investigated for each geometry. It has been found that GNM is significantly brittle compared to pristine graphene nanoribbons. It is observed that the relationship between the hole shape and size and the band gap is different for armchair and zigzag chirality.

Unraveling mechanics of armchair and zigzag graphene nanoribbons

International Journal of Damage Mechanics, Mar 1, 2017

The unraveling process of armchair and zigzag graphene nanoribbons (GNRs) was studied with molecu... more The unraveling process of armchair and zigzag graphene nanoribbons (GNRs) was studied with molecular dynamics simulations using the Adaptive Intermolecular Reactive Empirical Bond Order Potential for carbon-carbon bond. Simulations were performed at 300 K, with GNR length and width varying from 2.5 nm to 15 nm in 2.5 nm increments. In these simulations, the unraveling of the GNRs was started from two positions; the corner or the middle of the top side. Force-displacement relationship was analyzed for the terminal atom of the unraveling chains. For armchair GNRs (AGNRs) that were unraveled from the corner, the force required for the onset of the unraveling is in the range of 4.279-5.045 eV/Å , and the observed failure force in the carbon chain is in the range of 5.553-5.963 eV/Å. Unraveling will not happen when AGNRs are unraveled from the middle, and zigzag GNRs (ZGNRs) are unraveled either from corner or middle. For the latter cases, the bond between the terminal atom and GNR sheet breaks under the stretching force, and only one carbon atom can be pulled out from the GNR sheet. The size effect of width and length on the unraveling process was also studied. Simulations show that size has a trivial effect on unraveling. Comparison between unraveling of AGNRs and ZGNRs indicates that AGNRs are perfect structure to produce Monatomic Carbon Chains, while ZGNRs are more stable and are good candidate for graphene nanodevices that are free from unraveling disintegration.

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$Research paper thumbnail of Comparison of fracture behavior of defective armchair and zigzag graphene nanoribbons$

Comparison of fracture behavior of defective armchair and zigzag graphene nanoribbons

International Journal of Damage Mechanics, Mar 27, 2018

Molecular dynamics simulations of armchair graphene nanoribbons and zigzag graphene nanoribbons w... more Molecular dynamics simulations of armchair graphene nanoribbons and zigzag graphene nanoribbons with different sizes were performed at room temperature. Double vacancy defects were introduced in each graphene nanoribbon at its center or at its edge. The effect of defect on the mechanical behavior was studied by comparing the stress-strain response and the fracture toughness of each pair of pristine and defective graphene nanoribbon. Results show that the effect of vacancies in zigzag graphene nanoribbon is more profound than in armchair graphene nanoribbon. Also, the effect of double vacancy defect on the ultimate failure stress is greater in zigzag graphene nanoribbons than in armchair graphene nanoribbon due to bond orientation with respect to loading direction. Strength reduction can be as high as 17.5% in armchair graphene nanoribbon with no significant difference between single and double vacancies, while for zigzag graphene nanoribbon, the strength reduction is up to 30% for single vacancy and 43% for double vacancy defects. It is observed that for zigzag graphene nanoribbon with double vacancy at the edge, the direction of the failure plane is oriented at AE30 with respect to the loading direction while it is always perpendicular to the direction of loading in armchair graphene nanoribbon. Results have been verified through studying the fracture toughness parameters in each case as well.

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Effects of Rock Layering on Dynamic Response of a Gravity Dam

Geo-Congress 2019, Mar 21, 2019

Hot Phonons Contribution to scattering rates in Single-Walled Carbon Nanotubes

TechConnect Briefs, May 12, 2013

The influence of hot phonons on the electron-phonon scattering rates is studied via an Ensemble M... more The influence of hot phonons on the electron-phonon scattering rates is studied via an Ensemble Monte Carlo(EMC) simulation with step by step update of the phonon occupation number to account for the generation of hot phonons in metallic armchair (10, 10) carbon nanotubes. EMC simulations are carried out at different temperatures ranging from 300 to 1800 K and at electric field forces ranging from 5KV/cm to 20 KV/cm. The energy dispersion relation is calculated using a tight binding formulation while the phonon dispersion relation is calculated using the Fourth nearest neighbor interactions between atoms. The hot phonon contribution to the scattering rates appears to be a function of applied electric force field at room temperature, while it becomes independent of the applied electric force field for higher temperatures.

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Modeling and simulating thermomigration in power electronics

Miniaturization of electronics to nanoscale leads to significantly higher current density levels ... more Miniaturization of electronics to nanoscale leads to significantly higher current density levels and larger thermal gradients in electronics packaging. Laboratory test data show that thermomigration plays a significant role in high current density induced failure in solder joints and interconnects. In this paper, a computational damage mechanics model for thermomigration process is proposed and implemented in finite element method. This model is based on thermodynamics and formulated by continuum mechanics equations, mass transport principals and heat transfer equations. A damage evolution model using entropy production rate as a metric is utilized to evaluate the degradation in solder joints subjected to high temperature gradients.

Electrostatic Doping-Based All GNR Tunnel FET: An Energy-Efficient Design for Power Electronics

IEEE Transactions on Electron Devices, Apr 1, 2019

Electrostatic doping (ED)-based graphene nanoribbon (GNR) tunneling field-effect transistor (TFET... more Electrostatic doping (ED)-based graphene nanoribbon (GNR) tunneling field-effect transistor (TFET) with trigate design is studied. The transfer and output characteristics of the GNR-TFET are explored using extended Hückel semiempirical method. An ION/IOFF ratio as high as 10¹ is obtained with the ON-state current on the order of 10 A/m. A sub-60 mv/decade subthreshold swing is also observed (35 mv/decade). Armchair GNR with widths of 11 and 9 dimmers is found to be the best geometry to obtain a high ION/IOFF ratio, and channel length of greater than 6.9 nm suppresses short-channel effect. The scaling behavior of the ED-based GNR-TFET is also studied. It is observed that a smaller gate-to-gate distance facilitate large ON-state current and small OFF-state current. Moreover, it is shown that for a high-quality switching performance, the lowest required built-in gate voltage must provide enough energy differential E between the source-and drain-side energy bands.

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Impact of geometry on transport properties of armchair graphene nanoribbon heterojunction

Carbon, Nov 1, 2017

Electron transport properties of undoped armchair Graphene Nanoribbon Heterojunction (GNRHJ) has ... more Electron transport properties of undoped armchair Graphene Nanoribbon Heterojunction (GNRHJ) has been studied using semi-empirical extended Hückel method (EH). A two-probe configuration device utilizing armchair GNRHJ has been proposed. It is shown that a potential barrier was formed at the heterojunction interface between semiconductor and semi-metal, which resemble the conventional Schottky barrier at the interface of semiconductor/metal. Transmission spectrum was analyzed at finite bias; and current-bias voltage characteristic relations were established. Results show that the IeV characteristics of the heterojunction have rectifying nature, with its rectification ratio affected by the geometric asymmetry of the heterojunction.

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