Mechanical Engineering Commons^™

Characteristic Of The Dynamics Of Disorder In Crystalline And Amorphous Materials, Amir Behbahanian

All Graduate Theses and Dissertations, Spring 1920 to Summer 2023

This work provides the evidence to apply simulation methods that are applicable to systems with structural randomness to simulate crystalline materials at high temperatures. My work not only open the avenue to expand the simulation capability of materials but also provides insight to the physics of vibrations of atoms under different temperature and for different types of materials. I have also evaluated the reliability of Molecular Dynamics simulations at the frequency level and found that theses types of simulations, despite the previous belief, are reliable at low temperatures but up to a measurable frequency. In addition, the result of my …

Mechanical Strength Of Germanium Doped Low Oxygen Concentration Czochralski Silicon And The Effect Of Oxygen On Nitrogen Dissociation In Silicon, Junnan Wu

McKelvey School of Engineering Theses & Dissertations

During the Czochralski growth of silicon, it is inevitable for oxygen to be incorporated into the silicon crystal from the quartz crucible. Interstitial oxygen improves the mechanical strength of silicon by pinning and locking dislocations, but also generates thermal donors during device processes, shifting the electrical resistivity. For silicon wafers used in radio frequency (RF) applications, it is important to ensure the high resistivity of the substrates for good RF characteristics. Therefore, the oxygen level in these high resistivity silicon wafers is kept very low (< 2.5 × 1017 atoms/cm3) by carefully controlling the Czochralski growth conditions, in order to reduce the thermal donor concentration to an acceptable level. Silicon on insulator (SOI) substrates made from high resistivity wafers have been widely used for RF applications. SOI manufacturing includes multiple high temperature thermal cycles (1000 – 1100 °C), during which the high resistivity wafers are prone to slip and warpage. Therefore, it is technologically important to recover some of the lost mechanical strength due to the lack of oxygen by introducing electrically inactive impurities to suppress the dislocation generation and mobility in silicon. Germanium (Ge) as an isovalent impurity is 4% larger in size and forms a solid solution with silicon in the entire concentration range. Previous works have shown Ge doping at high concentrations above 6 × 1019 atoms/cm3 increased mechanical strength of silicon with high oxygen concentration (~ 1 × 1018 atoms/cm3). In this work, we explore the effect of Ge doping (7 - 9 × 1019 atoms/cm3) on the mechanical strength of low oxygen concentration (< 2 × 1017 atoms/cm3) silicon, where the oxygen associated dislocation locking and pinning are very low. A mechanical bending test was used to study the average dislocation migration velocity and the critical shear stress of dislocations motion at 600 – 750 °C for Ge doped, nitrogen doped, and undoped low oxygen samples, as well as nitrogen doped float-zone and un-doped high oxygen concentration samples. Next, we fabricated SOI substrates using these high resistivity wafers and compared their slip generation rates and the slip-free epitaxial grow temperature windows after the high temperature thermal cycles (> 1000 °C). Our results indicate at lower temperature Ge doesn’t affect the dislocation mobility …

Characterization Of Flexible Hybrid Electronics Using Stretchable Silver Ink And Ultra-Thin Silicon Die, Joshua A. Ledgerwood

Master's Theses

Flexible Hybrid Electronics (FHEs) offer many advantages to the future of wearable technology. By combining the dynamic performance of conductive inks, and the functionality of ultra-thinned, traditional IC technology, new FHE devices allow for development of applications previously excluded by relying on a specific type of electronics technology.

The characterization and reliability analysis of stretchable conductive inks paired with ultra-thin silicon die in theµm range was conducted. A silver based ink designed to be stretchable was screen printed on a TPU substrate and cured using box oven, conveyor convection oven, and photonic curing processes. Reliability tests were conducted including a …

Laser Direct Written Silicon Nanowires For Electronic And Sensing Applications, Woongsik Nam

Open Access Dissertations

Silicon nanowires are promising building blocks for high-performance electronics and chemical/biological sensing devices due to their ultra-small body and high surface-to-volume ratios. However, the lack of the ability to assemble and position nanowires in a highly controlled manner still remains an obstacle to fully exploiting the substantial potential of nanowires. Here we demonstrate a one-step method to synthesize intrinsic and doped silicon nanowires for device applications. Sub-diffraction limited nanowires as thin as 60 nm are synthesized using laser direct writing in combination with chemical vapor deposition, which has the advantages of in-situ doping, catalyst-free growth, and precise control of position, …

High-Throughput Mechanical Characterization Methods For Composite Electrodes And In-Situ Analysis Of Li-Ion Batteries, Luize Scalco De Vasconcelos

Open Access Theses

Electrodes in commercial rechargeable batteries are microscopically heterogeneous materials. The constituents often have large variation in their mechanical properties, making the characterization process a challenging task. In addition, the mechanical properties and mechanical behaviors of electrodes are closely coupled with the electrochemical processes of lithium insertion and extraction. There is an urgent need to develop an experimental platform to characterize the chemomechanical response of electrodes under the in-situ conditions of charge and discharge.

In the first part of this thesis, instrumented grid indentation is employed to determine the elastic modulus and hardness of the constituent phases of a composite cathode. …

Design And Optimization Of Lithium Ion Battery For High Temperature Applications, Khalid Abdullitife Ababtain

Wayne State University Dissertations

With massive commercial success of lithium ion batteries, the ability to operate at

and above 70 °C still a crucial issue and a safety concern to combat ever-increasing

global warming and to extend applications beyond portable electronics. Among various

components of battery, anode and electrolyte and the passivation layer formed between

them is crucial towards the development of Li-ion batteries for extendable temperature

range. In this regard, room temperature ionic liquids (RTILs) have the capability to

tackle thermal stability issues of lithium ion batteries but their poor compatibility with

traditional graphite anodes limits their practical application. Towards addressing this

issue, …

Heat Transfer Analysis Of Slot Jet Impingement Onto Roughened Surfaces, Rashid Ali Alshatti

USF Tampa Graduate Theses and Dissertations

The effect of surface roughness on jet impingement heat transfer was investigated in this research. A numerical analysis was conducted for free surface slot jet impinging normally onto a heated plate. Six different geometries and three different plate materials were investigated. The cooling fluid used for the analysis was water, and the flow was laminar with a range of Reynolds number (Re) from 500 to 1000. Temperature distribution, local and average heat transfer coefficient, and local and average Nusselt number were presented for each case.

The steady state heat transfer results show that the increase in Reynolds number (Re) increases …

Continuous Electrowetting In Passivating And Non-Passivating Systems, Mehdi Khodayari

USF Tampa Graduate Theses and Dissertations

Electrowetting is an electromechanical response that can be used to change the equilibrium

shape of droplets on a surface through the application of an electric potential. By applying this potential asymmetrically to a droplet, the droplet can be moved. Typical electrowetting devices use an electrode covered by a dielectric to reduce electrochemical interactions. Successful electrowetting requires electrodes and dielectric layers that can resist damage through many cycles of voltage.

Continuous Electrowetting (CEW) is performed on high resistivity silicon wafers. In this process, when an electric potential difference is applied between the substrate ends, the droplet on the substrate moves towards …

Silicon Wafer Temperature Distribution, Daniel Gonzalez, Nathan Jones, Dylan Justice

Mechanical Engineering

Applied Materials is a global company that designs equipment for use in the semiconductor manufacturing industry. The scope of this project covers process chambers used for depositing thin chemical films onto silicon wafers. These processes must take place in particularly specific environments– including extremely low pressures and high temperatures. One challenge engineers face when designing these processes is carefully controlling the thermal behavior of silicon wafers. Typically, behavior is predicted using time consuming and computationally expensive CFD simulations. We have been asked to address this issue with a simpler, faster model which will allow engineers to reduce the total number …

The Composition And Distribution Of Coal-Ash Deposits Under Reducing And Oxidizing Conditions From A Suite Of Eight Coals, David R. Brunner

Theses and Dissertations

Eighteen elements, including: carbon, oxygen, sodium, magnesium, aluminum, silicon, phosphorus, sulfur, chlorine, potassium, calcium, titanium, chromium, manganese, iron, nickel, strontium, and barium were measured using a scanning electron microscope with energy dispersive spectroscopy from deposits. The deposits were collected by burning eight different coals in a 160 kWth, staged, down-fired, swirl-stabilized combustor. Both up-stream and down-stream deposits from an oxidizing region (equivalence ratio 0.86) and reducing region (equivalence ratio 1.15) were collected. Within the deposits, the particle size and morphology were studied. The average particle cross-sectional area from the up-stream deposits ranged from 10 - 75 µm2 and had a …