Research

   M.Sc. Research (2022-2024)                                                                          

Predicting Intrinsic and Interfacial Thermal Transport in Sn/hBN van der Waals Heterostructure (M.Sc. Thesis)

Supervisor: Dr. AKM Monjur Morshed, Professor, Dept. of ME, BUET

In collaboration with: Dr. Titan C. Paul, Department of Mathematical Science, University of South Carolina Aiken

• Calculated interfacial thermal resistance (ITR) and in-plane phonon thermal conductivity (PTC) of Stanene/Hexagonal Boron Nitride (Sn/h-BN) heterostructures using molecular dynamics simulations.

• Provided molecular-level insights into the impacts of nanosheet size, defect engineering, system temperature, interlayer interaction, and tensile strain on nanoscale heat conduction in Sn/h-BN van der Waals heterostructures for energy-efficient nanoelectronics applications.

Abstract

Recently, the stanene (Sn)/hexagonal boron nitride (h-BN) van der Waals heterostructure (vdW) has garnered significant attention among the scientific community due to its distinctive electrical, optical, and thermal characteristics. Despite the promising potential of this heterostructure, the interfacial thermal resistance (ITR) between the Sn and h-BN layers remains unexplored. Understanding and modulating this ITR are essential steps towards harnessing the maximum potential of these materials in practical nanodevices. This study aims to investigate the interfacial thermal resistance (ITR) between the Sn and h-BN layers through the use of conventional molecular dynamics (MD) simulation. The transient pump-probe heating technique, commonly referred to as the Fast Pump Probe (FPP) approach, is utilized to analyze the ITR of the Sn/h-BN heterostructure. The estimated ITR value of a 30 × 10 nm2 Sn/h-BN nanosheet is found to be around ~ 7 × 10-8 K.m2/W at room temperature. This study comprehensively investigates the impact of various internal and external parameters, including nanosheet size, system temperature, contact pressure, vacancy concentration, and mechanical tensile strain (uniaxial and biaxial) on ITR, providing an extensive understanding of how these factors collectively affect the thermal resistance between Sn and h-BN layers. The simulation results demonstrate a consistent decline in ITR by approximately ~ 93 %, ~45 %, ~65 %, and ~ 33 % with the increasing system size, temperature, contact pressure, and defect concentration, respectively. In contrast, increasing mechanical strain leads to a substantial enhancement in ITR, with a maximum increase of approximately ~ 47 % under uniaxial tensile strain and almost ~ 99 % under biaxial tensile strain. Moreover, the pristine Sn/h-BN heterostructure exhibits no significant thermal rectification effect. The Phonon Density of States (PDOS) profile of the Sn and h-BN layer is calculated to elucidate this underlying behavior of ITR. The PDOS analysis reveals that heat is transported from h-BN to the Sn layer through efficient coupling of low-frequency flexural phonons between these two materials. This work will provide both theoretical support and logical guidelines for modulating thermal resistance across diverse dissimilar material interfaces, which will be necessary for the development of advanced nanodevices used in next generation nanoelectronics, nanophotonic, and optoelectronics applications.

  M.Sc. Research (2022-2024)

Data-Driven Machine and Deep Learning-Based Prediction of Interfacial Thermal Resistance Using High-Fidelity Molecular Dynamics Simulations 

Supervisor: Dr. AKM Monjur Morshed, Professor, Dept. of ME, BUET

In collaboration with: Dr. Titan C. Paul, Department of Mathematical Science, University of South Carolina Aiken  

• Generated over 1,000 datasets from high-throughput molecular dynamics simulations, with temperature, defect concentration, strain, and van der Waals interaction strength as input features and interfacial thermal resistance value between Sn and h-BN layer as the output feature. 

• Employed various Machine learning models (Linear Regression, Polynomial Regression, Random Forest, Support Vector Machine) and Artificial Neural Networks (ANN) to predict interfacial thermal resistance (ITR) between Sn and h-BN layers with 98% accuracy.

 M.Sc. Research (2022-2024)

Graph Neural Network Accelerated Molecular Dynamics: Simple Argon Case study.      

Supervisor: AKM Monjur Morshed, Professor, Dept. of ME, BUET

• Developed a Graph Neural Network to predict intermolecular forces between atoms, taking positions of atoms as inputs to accelerate molecular dynamics simulations, reducing simulation time significantly for simple argon liquids.

M.Sc. Research (2022-2024)

Investigation of the thermo-mechanical of Graphene/MoTe2 vertical heterostructure: A molecular dynamics study (ongoing)    

Supervisor: AKM Monjur Morshed, Professor, Dept. of ME, BUET

Collaborators: S. S. H. Tuhin, Md. Jishan 

• Calculated the thermomechanical properties of Gr/MoTe2 van der Waals heterostructure nanosheet to understand their mechanical behavior and thermal conductivity at the atomic level.

M.Sc. Research (2022-2024)

Data-Driven Design of Metal-Foam Heat Sink  

Supervisor: AKM Monjur Morshed, Professor, Dept. of ME, BUET

• Analyzed thermal-hydraulic performance of metal-foam heat sinks using machine learning models (KNN, Random Forest, XGBoost, SVR, ANN), performing model comparison, hyperparameter tuning, and evaluation with statistical metrics.

• The dataset was taken from a previously published paper.

M.Sc. Research (2022-2024)

Effect of Surrounding Liquid Medium on the Thermal Conductivity of van der Waals Heterostructure: Implications for Thermal Management

Supervisor: AKM Monjur Morshed, Professor, Dept. of ME, BUET

• Conducted Atomistic Simulation to understand the effect of the surrounding liquid medium on the thermal conductivity of Sn/h-BN nanosheet at various nanosheet sizes.

  B.Sc. Research (2017-2022)

Effect of Surface Wettability on Specific Heat Capacity of Nano-confined Liquid (NCLs)

(Undergraduate Thesis)

Supervisor: AKM Monjur Morshed, Professor, Dept. of ME, BUET

• Conducted MD simulations to examine the influence of wall wettability and nanogap thickness on the size-dependent molar heat capacity (Cv) of liquid argon confined between two copper (Cu) walls.

• Revealed that increased hydrophobicity leads to a reduction in maximum molar heat capacity (Cv)(max) and critical nanogap thickness,     with Cv converging to bulk values as the nanogap widens.                                                                                                                                               

Abstract

Equilibrium Molecular Dynamics (EMD) simulations are carried out to investigate the effects of wall wettability and nanogap thickness (ℎ) on the constant volume molar heat capacity (𝐶𝑣) of liquid argon entrapped between two solid copper walls at a fixed temperature of 100 K. Lennard-Jones (LJ) potential is employed to model the interaction between atoms, with nanogap thickness (ℎ) varying between 0.585 nm to 5.85 nm. To characterize interfacial surface wettability as hydrophobic or hydrophilic, the solid-liquid interaction potential has been altered, and its effect on molar heat capacity (𝐶𝑣) has been evaluated. Simulation results reveal three key findings. As the surface becomes more hydrophobic (i) Both maximum heat capacity (𝐶𝑣,𝑚𝑎𝑥) and critical nanogap thickness (ℎ𝑐 ) (nanogap thickness at which maximum heat capacity is obtained) decrease; (ii) the range of nanogap thickness where the heat capacity of nanoconfined liquid surpasses that of bulk liquid diminishes;(iii) the heat capacity of nanoconfined liquid tends to match its bulk equivalent. This anomalous behavior of heat capacity with changing wall wettability is explained by variation in both vibrational (mode of phonon transportation) and configurational (density oscillation near the wall, thermal boundary resistance, molecular mobility, etc.) contribution of nanoconfined liquid.

 B.Sc. Research (2017-2022)

Thermal Properties of Liquid entrapped between hybrid wettability surface

Supervisor: AKM Monjur Morshed, Professor, Dept. of ME, BUET

In collaboration with: Titan C. Paul, Department of Mathematical Science, University of South Carolina Aiken, Aiken, SC 29801, USA

• Explored the effects of hybrid wettability surface on the thermal properties of nano-confined liquid, revealing enhanced heat capacity and decreased thermal conductivity with increased hydrophilic surface areas.

Abstract:

Molecular dynamics (MD) simulations were conducted to investigate the impact of hybrid wettability on thermal properties, specifically focusing on the constant volume molar heat capacity and thermal conductivity of Nano-confined liquid (NCL). The simulation domain, maintained at a temperature of 100K, consisted of a ∼ 3 nm—thin film of liquid argon entrapped between two solid copper surfaces with hybrid wettability. Hybrid wettability surfaces were produced by varying the solid-liquid interaction parameter and applying two different wettability factors (𝜇) to the same surface. In this study, key findings pertaining to the influence of hybrid wettability on heat capacity and thermal conductivity include: (i) The heat capacity of liquid confined within hybrid wettability surfaces surpasses the heat capacity of the liquid in its bulk form. The heat capacity of bulk argon liquid is 20 J/mol k, but the liquid confined in the Hybrid I surface has a maximum heat capacity of roughly ∼53.2 J/mol k, which is 2.3 times higher. (ii) Remarkably, liquid confined in patterned wettability surfaces exhibited higher maximum heat capacity compared to the liquid confined inside uniform (Fully hydrophobic or hydrophilic) surfaces. The maximal heat capacity of liquid confined in Hybrid I surface is approximately ∼53.2 J/mol K, while the heat capacity of confined argon in a fully hydrophilic surface is around ∼30 J/mol K. (iii) Moreover, the heat capacity exhibits intriguing patterns. As the proportion of hydrophilic regions on the hybrid surfaces rose, there was a corresponding increase in heat capacity up to a specific threshold, beyond which the heat capacity dropped. (iv) Unlike Heat capacity, thermal conductivity exhibits a consistent behavior. A gradual decrease of thermal conductivity in the liquid region is observed as hydrophilic portions of the hybrid surface increase. The incorporation of hybrid wettability surfaces transforms the behavior of nano-confined liquid, inducing both structural and dynamic changes. These structural and dynamic variations result in the division of the entire simulation domain into two distinct zones: (i) Solid-like nanolayer zones located near the walls and (ii) Liquid zones located further away from the wall. The behavior of argon molecules in these two zones is completely different. Argon molecules in the solid-like layer exhibit increased density, higher potential energy, less translational motion, and vigorous vibration over a frequency range of ∼0 to ∼ 3 THz. Conversely, the argon molecules in the liquid layer mostly exhibit translational motion.

 However, this translational motion is hindered as the hydrophilic area of the surface increases resulting in a reduction in overall molecular mobility. The observed variations in heat capacity and thermal conductivity of the Nano-confined liquid were elucidated by taking into account the combined influence of structural modifications of argon molecules occurring in solid-like nanolayer regions and the dynamic alterations of argon molecules in liquid regions. The findings of this study will provide valuable insights for improving cooling systems in electronic chips and nanoscale memory devices, advancing energy storage systems with potential applications in various biological domains in the future.

 B.Sc. Research (2017-2022)

Desalination Performance of Nanoporous MoS2 membrane for different Salts of Saline Water: A molecular Dynamics Study.

Supervisor: AKM Monjur Morshed, Professor, Dept. of ME, BUET

• Investigated the desalination potential of nano-porous MoS2​ membranes for various salts (NaCl, MgCl2 ​, and CaSO4​) through molecular dynamics simulations.

• Achieved water flux in MoS2​ membranes two to five orders of magnitude higher than conventional nanoporous membranes, with high over-salt rejection for MgCl2​ and CaSO4​.

 B.Sc. Research (2017-2022)

Coalescence-Induced Jumping of Unequal Droplets on Superhydrophobic Surfaces in High Ohnesorge Number Regime: A Molecular Dynamics Study

Supervisor: AKM Monjur Morshed, Professor, Dept. of ME, BUET

• Investigated the jumping behavior of unequal-sized nanodroplets (4 nm, 5 nm, 6 nm) through molecular dynamics simulations, identifying critical size differences and key factors affecting droplet dynamics at high Ohnesorge numbers.

B.Sc. Research (2017-2022)

Investigation of Phonon Thermal Conductivity of Partial Periodic Si/Ge Superlattice Nanowire

Supervisor: AKM Monjur Morshed, Professor, Dept. of ME, BUET

• Calculated the reduction of thermal conductivity (30-40%) in partial periodic Si/Ge superlattice nanowires through the controlled placement of Ge bands for enhanced thermoelectric efficiency.