Micro- and Nano-scale Thermal Fluid Lab. (MNTF Lab)
- Long-term Projects
Modeling for Semiconductor Manufacturing Processes using Molecular Dynamics
Modeling and process simulation for semiconductor manufacturing processes (material specialization, etching, spin coating, etc.) require molecular-level precision, and classical methods using mathematical approaches through continuum-based differential formulations are not valid. However, recent studies have shown that modeling of various transport phenomena via classical continuity equations can still be used in a modified way even in limited spaces of 1 nm, i.e. the space corresponding to three or four atoms. Based on these results, it may be possible to advance global chip development technology if classical mathematical modeling approaches to chip design, process modeling, and simulation are still valid. This requires setting up a computational model of the system and then performing MD simulations to track the positions, velocities, and forces of atoms and molecules and analyze the results. The multi-scale modeling method of the semiconductor manufacturing process is a technology that increases the efficiency of the manufacturing process by studying nanoscale behavior and phenomena around 1 nm using MD (molecular dynamics) simulation technology.
Molecular Transport Phenomena for the Next Generation Fuel Cell
For the future energy system, the fundamental goal in the field of nano-scale transport research is to present innovative approaches for energy conversion systems such as integrated Fuel Cells. In particular, the phenomenon of molecular-level transport of mass and energy between the bulk and the interface is a key factor for the performance of the integrated energy conversion systems in the future.
Thermal Transport in Solidification Process for Additive Manufacturing
Additive manufacturing (AM), also known as 3D printing, has gained a blossoming of research due to its advantages and wide range of applications. AM is transforming every aspect of product development from product design and manufacturing to quality control and qualification, by offering the opportunity to quantify errors and correct them in-process. In addition to that, AM enables the manufacture of multi-material, and functionally graded material components. In metal 3D printing, melting and solidification of metal or alloy substrates are very important process, and need to be actively investigated in order to optimize the operation efficiency. By utilizing the electron or UV laser beam, the metallic powder is molten and deposited to the successive layers, which are typically solidified, until the entire target object is created. Under such condition, not only the solid/liquid interface, but also the mismatch of orientation, translation, and composition between crystals are important issues as well. For such cases, micro- nano- scale heat management becomes a key problem. Therefore, we put our particular attention to investigate the thermal transport in melting and solidification of solid materials to provide a model with in-depth understanding. To address this, molecular dynamics (MD) simulation is utilized, since it is possible to directly access to the independent molecular motion, which is very difficult in most of experimental works.
Structural and Interfacial Analysis for Enhanced Micro-/nano-scale Fluidic Transport
Many physical effects (e.g., the discrete water molecule effect near the solid surface) are neglected in continuum hypotheses. As a result, the classical models fail to predict many experimental and atomistic simulation results. We develop a theoretical tool for prediction of nanocapillary liquid rise using the Lucas-Washburn theory. Molecular dynamics simulations were employed to investigate the effects of surface forces on the viscosity of liquid water. This provides an update to the modified LW equation that considered only a nanoscale slip length. It was found that the liquid layering in the vicinity of the solid surface induces a higher density and viscosity, leading to a slower simulation-measured uptake of fluid into the capillaries than was theoretically predicted. Considering the effects of both the interface viscosity and slip length of the fluid, we successfully predicted the fluid rise in the nanotubes.
Nanoscale Liquid Flow and Heat Transfer
For the theoretical investigation of nanoscale heat transfer and interface thermal resistance, molecular structure of the liquid and surfaces, and their interactions at the atomistic length scales play a key role, and hence, Molecular Dynamics (MD) emerges as a viable approach for investigation of the flow physics in such scales. Using parametric studies, the interface thermal resistance will be investigated as a function of the liquid/solid interaction strength (i.e., surface wettability) and the crystal bonding stiffness. I have developed a Navier type thermal boundary condition for predicting the interface thermal resistance and temperature jump on the wall/fluid interface. Also, We have verified that Kapitza length (thermal resistance length) for “simple liquids” can be achieved in nano-channels as small as 3.24 nm. Moreover, recent experimental measurements of Kapitza length vary between 3 nm to 6 nm for aluminum, and 10 nm to 12 nm for gold. These values are similar to my published results. Using the developed Navier type thermal boundary condition, effects of interface structure and chemistry on nanoscale thermal transport will be systematically investigated with different coating materials (e.g. Au, Al, Ti). Particular emphasis will be placed on the analysis of the Kapitza lengths at hydrophobic and hydrophilic interfaces. The Kapitza length at hydrophobic interfaces (10-12 nm) is a factor of 2-3 larger than the Kapitza length at hydrophilic interfaces (3-6 nm). Encouraged by the success of our previous work, the thermal transport in solid/liquid interface on nano-probe will be investigated with full implementation of comprehensive theoretical and experimental work.
Nanoscale Gas Flow
Most MEMS and nano-technology applications working in gaseous environments require an acute understanding of gas transport in the slip, transition and free molecular flow regimes, as well as the molecule-surface interactions. Although the rarefaction effects are studied extensively, molecule-surface interactions are not studied with adequate detail. In order to overcome a deficiency in macroscopic theory for gas flows in nanoscale confinements, i.e., its inability to include the van der Waals interactions between the gas and surface molecules, and other surface physics effects, we are investigating the non-equilibrium surface effects in nano-scale confined gas flows using MD. This is indeed a new and open area for further growth and funding potential from the nano-electronics industry.
Molecular Dynamics Simulations for Biological System
Biological systems consist of a variety of cells and molecules capable of harnessing organic energy to accomplish specific tasks with a remarkable and optimized efficiency. These cells and molecules act together in a dynamic and complex network that may be disrupted by the entrance of nanomaterials in the human body. Capturing the dynamics of the interactions between cellular systems and the nanoparticles is indeed a challenging task. My objective of this research topic is to investigate the interactions of nanomaterials with human cells for the purpose of developing and validating new nanotechnology based therapies. The biological cell membrane contains a broad mixture of biological atomic structures (proteins and lipids) and serves as intracellular cytoskeleton and the extracellular cell walls. The complexity of biological cell surface is a challenging problem for the cell modeling. Biological cell membranes, consisting of protein structures and lipid bilayers, are now a popular research topic for MD simulations. The validity of constructed cell membrane system will be tested with experimental results (e.g., area per lipid, area compressibility modulus and chain disorder and hydration of the water/lipid interface) which are already available in the published literature. The significance of these computer models is to provide predictive tools for nanoparticle and human cell interactions that will improve the structural and functionality design of nanomaterials. A series of experiments and measurements are also need to be supplied for generating data for code validation purposes.
Last Updated on Nov 27, 2023