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Full-Text Articles in Nanoscience and Nanotechnology

Uncertainty Propagation In A Multiscale Model Of Nanocrystalline Plasticity, Marisol Koslowski, Alejandro Strachan Dec 2010

Uncertainty Propagation In A Multiscale Model Of Nanocrystalline Plasticity, Marisol Koslowski, Alejandro Strachan

PRISM: NNSA Center for Prediction of Reliability, Integrity and Survivability of Microsystems

We characterize how uncertainties propagate across spatial and temporal scales in a physicsbased model of nanocrystalline plasticity of fcc metals. Our model combines molecular dynamics (MD) simulations to characterize atomic level processes that govern dislocation basedplastic deformation with a phase field approach to dislocation dynamics (PFDD) that describes how an ensemble of dislocations evolve and interact to determine the mechanical response of the material. We apply this approach to a nanocrystalline Ni specimen of interest in micro-electromechanical (MEMS) switches. Our approach enables us to quantify how internal stresses that result from the fabrication process affect the properties of dislocations (using ...


Uncertainty Quantification Study For A Comprehensive Electrostatic Mems Switch Model, Michael G. Snow, Anil K. Bajaj Sep 2010

Uncertainty Quantification Study For A Comprehensive Electrostatic Mems Switch Model, Michael G. Snow, Anil K. Bajaj

PRISM: NNSA Center for Prediction of Reliability, Integrity and Survivability of Microsystems

This work presents an uncertainty analysis of a comprehensive model for an electrostatic MEMS switch. The goal is to elucidate the effects of parameter variations on certain performance characteristics. A sufficiently detailed model of an electrostatically actuated beam is developed. This model accounts for various physical effects, including the electrostatic fringing field, finite length of electrodes, squeeze film damping, and contact between the beam and the dielectric layer. The performance characteristics of immediate interest are the static and dynamic pull-in voltages for switch. Using Latin Hypercube and other sampling methods, the model is evaluated to find these performances characteristics when ...


Comprehensive Reduced-Order Models Of Electrostatically Actuated Mems Switches And Their Dynamics Including Impact And Bounce, Michael G. Snow, Anil K. Bajaj Aug 2010

Comprehensive Reduced-Order Models Of Electrostatically Actuated Mems Switches And Their Dynamics Including Impact And Bounce, Michael G. Snow, Anil K. Bajaj

PRISM: NNSA Center for Prediction of Reliability, Integrity and Survivability of Microsystems

As MEMS technology develops it is becoming better understood that MEMS designers must account for the large uncertainties characteristic of the relevant manufacturing processes. Uncertainty quantification tasks the designer with evaluating many different possible outcomes from the manufacturing process which creates a demand for models that are accurate and comprehensive, yet fast to evaluate. This work presents a comprehensive reduced-order model of electrostatically actuated switches incorporating a range of effects that are typically included only in FE modeling codes. Specifically, the model accounts for variable electrode geometry, stretching of centerline or large displacement effects, fringing field, squeeze film and rarefied ...


Simulation Of Sub-Micron Thermal Transport In A Mosfet Using A, James Loy, Druv Singh, Jayathi Y. Murthy Aug 2010

Simulation Of Sub-Micron Thermal Transport In A Mosfet Using A, James Loy, Druv Singh, Jayathi Y. Murthy

PRISM: NNSA Center for Prediction of Reliability, Integrity and Survivability of Microsystems

Self-heating has emerged as a critical bottleneck to scaling in modern transistors. In simulating heat conduction in these devices, it is important to account for the granularity of phonon transport since electron-phonon scattering occurs preferentially to select phonon groups. However, a complete accounting for phonon dispersion, polarization and scattering is very expensive if the Boltzmann transport equation (BTE) is used. Moreover, difficulties with convergence are encountered when the phonon Knudsen number becomes small. In this paper we simulate a two-dimensional bulk MOSFET hotspot problem using a partially-implicit hybrid BTE-Fourier solver which is significantly less expensive than a full BTE solution ...


Knudsen Force Modeling In Application To Microsystems, Jeremy S. Nabeth, Sruti Chigullapalli, Alina A. Alexeenko Jul 2010

Knudsen Force Modeling In Application To Microsystems, Jeremy S. Nabeth, Sruti Chigullapalli, Alina A. Alexeenko

PRISM: NNSA Center for Prediction of Reliability, Integrity and Survivability of Microsystems

At the microscale, even moderate temperature differences can result in significant Knudsen forces generated by the energy exchange between gas molecules and solids immersed in a gas. Creating, controlling and measuring Knudsen forces in microsystems can be an arduous task since only limited theory exists at present. This present study investigates the mechanism of Knudsen forces in detail based on numerical solution of the Boltzmann kinetic equation. The Knudsen force is shown, in general, to be a result of thermal nonequilibrium between gas and solid. The simulations are validated by comparison with experimental measurements that have been reported by Passian ...


What Determines Knudsen Force At The Microscale, Jeremy S. Nabeth, Sruti Chigullapalli, Alina A. Alexeenko Jul 2010

What Determines Knudsen Force At The Microscale, Jeremy S. Nabeth, Sruti Chigullapalli, Alina A. Alexeenko

PRISM: NNSA Center for Prediction of Reliability, Integrity and Survivability of Microsystems

Knudsen forces arise in microscale systems when there is a thermal gradient with a characteristic length scale comparable to the molecular mean free path of the ambient gas. These forces are sometimes referred as radiometric or thermo-molecular forces [1] and have been recently measured experimentally in a microscale configuration using heated atomic force microscopy (AFM) probes [2]. The Knudsen force on microstructures with thermal gradients can provide a novel actuation mechanism for mass detection, thermogravimetry, and very high-resolution heat flux measurements. While measuring such forces precisely at microscale can be an arduous task especially since only limited analytical results exist ...


Numerical Approach For Quantification Of Epistemic Uncertainty, John Jakeman, Michael Eldred, Dongbin Xiu Jun 2010

Numerical Approach For Quantification Of Epistemic Uncertainty, John Jakeman, Michael Eldred, Dongbin Xiu

PRISM: NNSA Center for Prediction of Reliability, Integrity and Survivability of Microsystems

In the field of uncertainty quantification, uncertainty in the governing equations may assume two forms: aleatory uncertainty and epistemic uncertainty. Aleatory uncertainty can be characterised by known probability distributions whilst epistemic uncertainty arises from a lack of knowledge of probabilistic information. While extensive research efforts have been devoted to the numerical treatment of aleatory uncertainty, little attention has been given to the quantification of epistemic uncertainty. In this paper, we propose a numerical framework for quantification of epistemic uncertainty. The proposed methodology does not require any probabilistic information on uncertain input parameters. The method only necessitates an estimate of the ...


Puremd Manual (Purdue Reactive Molecular Dynamics Program), Hasan Metin Aktulga Jun 2010

Puremd Manual (Purdue Reactive Molecular Dynamics Program), Hasan Metin Aktulga

PRISM: NNSA Center for Prediction of Reliability, Integrity and Survivability of Microsystems

No abstract provided.


Strain Rate Sensitivity Of Nanocrystalline Au Films At Room Temperature, K Jonnalagadda, N Karanjgaokar, Joo Lien Chee, Dimitrios Peroulis Jun 2010

Strain Rate Sensitivity Of Nanocrystalline Au Films At Room Temperature, K Jonnalagadda, N Karanjgaokar, Joo Lien Chee, Dimitrios Peroulis

PRISM: NNSA Center for Prediction of Reliability, Integrity and Survivability of Microsystems

The effect of strain rate on the inelastic properties of nanocrystalline Au films was quantified with 0.85 and 1.76 lm free-standing microscale tension specimens tested over eight decades of strain rate, between 6 106 and 20 s1. The elastic modulus was independent of the strain rate, 66 ± 4.5 GPa, but the inelastic mechanical response was clearly rate sensitive. The yield strength and the ultimate tensile strength increased with the strain rate in the ranges 575–895 MPa and 675–940 MPa, respectively, with the yield strength reaching the tensile strength at strain rates faster than 101 s1 ...


Nanoscale Metal-Metal Contact Physics From Molecular Dynamics: The Strongest Contact Size, Hojin Kim, Alejandro Strachan May 2010

Nanoscale Metal-Metal Contact Physics From Molecular Dynamics: The Strongest Contact Size, Hojin Kim, Alejandro Strachan

PRISM: NNSA Center for Prediction of Reliability, Integrity and Survivability of Microsystems

Using molecular dynamics we find that the tensile strength of the contacts between two clean platinum surfaces with nanoscale asperities is strongly size dependent with a maximum strength for contact lengths of approximately 5 nm. This is the first time a strongest size is observed in single crystals. The strengthening with decreasing size down to 5 nm results from a decrease in the initial density of mobile dislocations available for plastic deformation and the subsequent weakening originates from a reduction in the constraint to mechanical deformation inside the contact by the bulk.


A Reactive Molecular Dynamics Simulation Of The Silica-Water Interface, Joseph C. Fogarty, Hasan Metin Aktulga, Ananth Y. Grama, Adri C. T. Van Duin, Sagar A. Pandit May 2010

A Reactive Molecular Dynamics Simulation Of The Silica-Water Interface, Joseph C. Fogarty, Hasan Metin Aktulga, Ananth Y. Grama, Adri C. T. Van Duin, Sagar A. Pandit

PRISM: NNSA Center for Prediction of Reliability, Integrity and Survivability of Microsystems

We report our study of a silica-water interface using reactive molecular dynamics. This first-of-its-kind simulation achieves length and time scales required to investigate the detailed chemistry of the system. Our molecular dynamics approach is based on the ReaxFF force field of van Duin [J. Phys. Chem. A 107, 3803 (2003)]. The specific ReaxFF implementation (SERIALREAX) and force fields are first validated on structural properties of pure silica and water systems. Chemical reactions between reactive water and dangling bonds on a freshly cut silica surface are analyzed by studying changing chemical composition at the interface. In our simulations, reactions involving silanol ...


An Experimental Investigation On Viscoelastic Behavior In Tunable, Hao-Han Hsu, Dimitrios Peroulis May 2010

An Experimental Investigation On Viscoelastic Behavior In Tunable, Hao-Han Hsu, Dimitrios Peroulis

PRISM: NNSA Center for Prediction of Reliability, Integrity and Survivability of Microsystems

Abstract—In this paper, the viscoelastic behavior of a tunable RF-MEMS resonator and its impacts are studied by means of direct RF measurements for the first time. This tunable resonator consists of one λ/2 coplanar waveguide (CPW) resonator and two nanocrystalline-Ni RF-MEMS varactors. S-parameters of this tunable resonator have been measured for 80 hours under a bi-state bias condition of 0 and 40 V. It is demonstrated that the resonant frequency is shifted by 90 MHz and the varactor deformed by 0.12 μm over the 80 hour period. The gap of the loaded varactor is extracted from the ...


Uncertainty Quantification Models For Micro-Scale Squeeze-Film Damping, Xiaohui Guo, Jia Li, Dongbin Xiu, Alina Alexeenko Apr 2010

Uncertainty Quantification Models For Micro-Scale Squeeze-Film Damping, Xiaohui Guo, Jia Li, Dongbin Xiu, Alina Alexeenko

PRISM: NNSA Center for Prediction of Reliability, Integrity and Survivability of Microsystems

Two squeeze-film gas damping models are proposed to quantify uncertainties associated with the gap size and the ambient pressure. Modeling of gas damping has become a subject of increased interest in recent years due to its importance in micro-electro-mechanical systems (MEMS). In addition to the need for gas damping models for design of MEMS with movable micro-structures, knowledge of parameter dependence in gas damping contributes to the understanding of device-level reliability. In this work, two damping models quantifying the uncertainty in parameters are generated based on rarefied flow simulations. One is a generalized polynomial chaos (gPC) model, which is a ...


A Continuum Plasticity Model That Accounts For Hardening And Size Effects In Thin Films, Abigail Hunter, Hariharanath Kavuri, Marisol Koslowski Mar 2010

A Continuum Plasticity Model That Accounts For Hardening And Size Effects In Thin Films, Abigail Hunter, Hariharanath Kavuri, Marisol Koslowski

PRISM: NNSA Center for Prediction of Reliability, Integrity and Survivability of Microsystems

We conducted three-dimensional finite element simulations of the mechanical response of passivated single crystal copper thin films with a continuum crystal plasticity model. The model introduces the formation of high density dislocation layers close to the substrate and passivation interfaces obtained from dislocation dynamics simulations. These dislocation structures are responsible for an increase in strain hardening as the film thickness decreases. The model predicts an increase in strain hardening as the film thickness decreases in agreement with experimental observation in films with thickness in the range 0.2 to 2μm.


Bdf-Like Methods For Nonlinear Dynamic Analysis, S. Dong Jan 2010

Bdf-Like Methods For Nonlinear Dynamic Analysis, S. Dong

PRISM: NNSA Center for Prediction of Reliability, Integrity and Survivability of Microsystems

We present several time integration algorithms of second-order accuracy that are numerically simple and effective for nonlinear elastodynamic problems. These algorithms are based on a general four-step scheme that has a resemblance to the backward differentiation formulas. We also present an extension to the composite strategy of the Bathe method. Appropriate values for the algorithmic parameters are determined based on considerations of stability and dissipativity, and less dissipative members of each algorithm have been identified. We demonstrate the convergence characteristics of the proposed algorithms with a nonlinear dynamic problem having analytic solutions, and test these algorithms with several three-dimensional nonlinear ...


Reactive Molecular Dynamics: Numerical Methods And Algorithmic Techniques, Hasan Metin Aktulga, Shailaja Pandit, Adri C. T. Van Duin, Ananth Y. Grama Jan 2010

Reactive Molecular Dynamics: Numerical Methods And Algorithmic Techniques, Hasan Metin Aktulga, Shailaja Pandit, Adri C. T. Van Duin, Ananth Y. Grama

PRISM: NNSA Center for Prediction of Reliability, Integrity and Survivability of Microsystems

Modeling atomic and molecular systems requires computation-intensive quantum mechanical methods such as, but not limited to, density functional theory (DFT) [11]. These methods have been successful in predicting various properties of chemical systems at atomistic detail. Due to the inherent nonlocality of quantum mechanics, the scalability of these methods ranges from O(N3) to O(N7) depending on the method used and approximations involved. This significantly limits the size of simulated systems to a few thousands of atoms, even on large scale parallel platforms. On the other hand, classical approximations of quantum systems, although computationally (relatively) easy to implement, yield ...


Unusual Scaling Obsrvations In The Quality Factors Of Cantilevered Carbon Nanotube Resonators, Ajit K. Vallabhaneni, Jeffrey F. Rhoads, Xiulin Ruan, Jayathi Y. Murthy Jan 2010

Unusual Scaling Obsrvations In The Quality Factors Of Cantilevered Carbon Nanotube Resonators, Ajit K. Vallabhaneni, Jeffrey F. Rhoads, Xiulin Ruan, Jayathi Y. Murthy

PRISM: NNSA Center for Prediction of Reliability, Integrity and Survivability of Microsystems

This work examines the quality factors (Q factors) of resonance associated with the axial and transverse vibrations of single-wall carbon nanotube (SWCNT) resonators through the use of molecular dynamics (MD) simulation. Specifically, the work investigates the effect of device length, diameter, and chirality, as well as temperature, on the resonant frequency and quality factor of these devices, and benchmarks the results of MD simulation against classical theories of energy dissipation. Of note are the facts that the quality factors associated with transverse vibration decrease with increasing device diameter and are largely insensitive to chirality. Additionally, quality factors increase with increasing ...


Real-Time Monitoring Of Contact Behaviour Of Rf Mems Switches With A Very Low Power Cmos Capactive Sensor Interface, Adam Fruehling, Mohammad Abu Khater, Byunghoo Jung, Dimitrios Peroulis Jan 2010

Real-Time Monitoring Of Contact Behaviour Of Rf Mems Switches With A Very Low Power Cmos Capactive Sensor Interface, Adam Fruehling, Mohammad Abu Khater, Byunghoo Jung, Dimitrios Peroulis

PRISM: NNSA Center for Prediction of Reliability, Integrity and Survivability of Microsystems

This paper presents the first ultra-low power, fully electronic methodology for real-time monitoring of the dynamic behavior of RF MEMS switches. The measurement is based on a capacitive readout circuit composed of 67 transistors with 105 µm x 105 µm footprint consuming as little as 60 µW. This is achieved by accurately sensing the capacitance change around the contact region at sampling rates from 10 kHz to 5 MHz. Experimental and simulation results show that times of not only the first contact event but also all subsequent contact bounces can be accurately measured with this technique without interfering with the ...


A Viscoelastic-Aware Experimentally-Derived Model For Analog Rf Mems Varactors, Hao-Han Hsu, Dimitrios Peroulis Jan 2010

A Viscoelastic-Aware Experimentally-Derived Model For Analog Rf Mems Varactors, Hao-Han Hsu, Dimitrios Peroulis

PRISM: NNSA Center for Prediction of Reliability, Integrity and Survivability of Microsystems

In this paper we present, for the ¯rst time, an experimentally-extracted model for the spring con- stant and tuning range of an analog RF-MEMS var- actor that includes viscoelastic e®ects in RF-MEMS devices. By utilizing a bi-state bias condition with one state lasting 60 minutes and the other 1 minute, this model focuses on capturing the true electrome- chanical behavior of the varactor. An experimental setup with very high long-term accuracy is created to measure capacitance of the varactor up to 1,370 hours. The impact of these e®ects and the e®ective- ness of the model are ...


Weighted Matrix Ordering And Parallel Banded Preconditioners For Iterative Linear System Solvers, Murat Manguoglu, Mehmet Koyuturk, Ahmed Sameh, Ananth Y. Grama Jan 2010

Weighted Matrix Ordering And Parallel Banded Preconditioners For Iterative Linear System Solvers, Murat Manguoglu, Mehmet Koyuturk, Ahmed Sameh, Ananth Y. Grama

PRISM: NNSA Center for Prediction of Reliability, Integrity and Survivability of Microsystems

The emergence of multicore architectures and highly scalable platforms motivates the development of novel algorithms and techniques that emphasize concurrency and are tolerant of deep memory hierarchies, as opposed to minimizing raw FLOP counts. While direct solvers are reliable, they are often slow and memory-intensive for large problems. Iterative solvers, on the other hand, are more efficient but, in the absence of robust preconditioners, lack reliability. While preconditioners based on incomplete factorizations ( whenever they exist) are effective for many problems, their parallel scalability is generally limited. In this paper, we advocate the use of banded preconditioners instead and introduce a ...