Department of Mechanical engineering

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Author: search.filters.author.Roy, TribeniSubject: search.filters.subject.Molecular dynamics simulations

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Now showing 1 - 6 of 6
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    Study of side burr formation in steady-state nano-polishing of Si-wafer using molecular dynamics simulation
    (Sage, 2024-02) Roy, Tribeni
    With advancements in the semiconductor industry, it is required to have angstrom level surface finish on silicon wafers which is achieved by nano-polishing. However, side burr is formed due to material pile-up from material removal due to abrasive which becomes detrimental to achieving the high surface finish. This study employs molecular dynamics simulations to explore the mechanism underlying side burr formation during nano-polishing of mono-crystalline silicon (Si)-wafer. The study utilizes a diamond nano-abrasive grit to scratch the surface of the Si-wafer and investigates the formation of pile-ups during the steady-state process. It was observed that increasing the depth of cut by four times led to a 6.3-fold increase in the number of amorphous atoms, indicating greater bond breakage in the direction of scratching. As a result, the cutting force exceeds the thrust force at larger depths of the cut. The correlation between the side burr height and the depth of cut is also studied. Results show that the side burr height ratio increases with the depth of cut, indicating a higher sensitivity of side burr height to the depth of cut. The study suggests that to achieve a ductile mode of material removal and minimize the height of the side burr during nano-polishing of Si-wafers, it is crucial to maintain the depth of cut at or below half (≤0.5) of the abrasive radius and ensure an average friction coefficient below 0.6. The outcome of this study can be useful for the actual manufacturing of miniaturized sensors, actuators, and microsystems for microelectromechanical system devices where a high surface finish is crucial.
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    Mechanism of surface modification on monocrystalline silicon during diamond polishing at nanometric scale
    (Sage, 2023-11) Sharma, Anuj; Roy, Tribeni
    The demand for polished silicon wafers has increased significantly in recent years to cater to the development of the semiconductor industry. For example, polished silicon wafer has direct applications in integrated circuits, radio frequency amplifiers, micro-processors, micro-electromechanical systems, etc. To carry out mechanical polishing, lapping, grinding, or single-point diamond turning of silicon, diamond abrasives were extensively used before the implementation of chemo-mechanical polishing. During the diamond-based polishing, a few problems have already been identified, such as the formation of an amorphous phase, heat-affected zones, low material removal, etc. Some research work has also reported that nano-structured abrasives lead to a thin layer of the amorphous phase and a better material removal rate. In the same direction, a molecular dynamics simulation is carried out in this paper to investigate the mechanism of material removal from monocrystalline silicon during the diamond-abrasive-based polishing process. The present work is mainly focused on the dynamics of material removal phenomena near the abrasive particles at the nanometric scale by considering stress, lattice, cohesive energy, etc. This reveals that a higher value of indentation force results in surface buckling, which creates a zone of both compressive and tensile stresses, which increases the coordination number and forms β-silicon just ahead of the abrasive particle. This mechanism happens by developing a β-silicon phase on the surface with a thickness beyond a certain value of indentation force on the zone of compression. Buckling on this phase happens due to stress localisation in compression, as the flow stress of this phase is less than that of diamond cubic lattices. To avoid the mechanism of surface buckling and process silicon material on the surface, the indentation force needs to be maintained below a critical value. In the present case, it was found that the indentation force of less than or equal to 190 nN for the abrasive size of ϕ8 nm does the material removal by surface processing only without surface buckling. It was also found that surface processing helps to reduce the depth of the amorphous layer significantly without compromising the material removal rate or the generation of a wavy surface. Thus, the present mechanism will help in the polishing of silicon with minimum defects and reduce processing time for the final stage of polishing towards manufacturing ultra-smooth and planer surfaces.
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    Strain induced electrochemical behaviors of ionic liquid electrolytes in an electrochemical double layer capacitor: Insights from molecular dynamics simulations
    (AIP, 2023-12) Roy, Tribeni
    Electrochemical Double Layer Capacitors (EDLCs) with ionic liquid electrolytes outperform conventional ones using aqueous and organic electrolytes in energy density and safety. However, understanding the electrochemical behaviors of ionic liquid electrolytes under compressive/tensile strain is essential for the design of flexible EDLCs as well as normal EDLCs, which are subject to external forces during assembly. Despite many experimental studies, the compression/stretching effects on the performance of ionic liquid EDLCs remain inconclusive and controversial. In addition, there is hardly any evidence of prior theoretical work done in this area, which makes the literature on this topic scarce. Herein, for the first time, we developed an atomistic model to study the processes underlying the electrochemical behaviors of ionic liquids in an EDLC under strain. Constant potential non-equilibrium molecular dynamics simulations are conducted for EMIM BF4 placed between two graphene walls as electrodes. Compared to zero strain, low compression of the EDLC resulted in compromised performance as the electrode charge density dropped by 29%, and the performance reduction deteriorated significantly with a further increase in compression. In contrast, stretching is found to enhance the performance by increasing the charge storage in the electrodes by 7%. The performance changes with compression and stretching are due to changes in the double-layer structure. In addition, an increase in the value of the applied potential during the application of strain leads to capacity retention with compression revealed by the newly performed simulations.
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    Strain softening observed during nanoindentation of equimolar-ratio Co–Mn– Fe–Cr–Ni high entropy alloy
    (Sage, 2024-02) Roy, Tribeni
    This research article presents an atomistic study on the cyclic nanoindentation of an equimolar-ratio Co–Mn–Fe–Cr–Ni high-entropy alloy (HEA) using molecular dynamics simulation. The study investigated the effects of indentation depth on the cyclic load versus the indentation depth of the HEA. The results showed that the cyclic response exhibits a pronounced shift towards plasticity with pile-up formation instead of sinking behavior at higher indentation depths. Within the realm of molecular dynamics simulations, the simulated hardness value reached up to 16 GPa for the initial indentation cycle. A steep drop in the load–displacement curve was observed during the elastic–plastic transition, signifying substantial strain softening of the substrate. It was found that the densely clustered stacking faults undergo a reverse transition during cyclic loading, contributing to the backpropagation phase responsible for elastic recovery despite subsequent strain hardening. The study provides important insights into the underlying mechanisms governing the cyclic mechanical behavior of HEAs to guide their improved micromanufacturing.
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    Nano droplet behaviour on vibrating surfaces: atomistic simulations for bio-NEMS/MEMS applications
    (Taylor & Francis, 2024-04) Roy, Tribeni
    Recent advancement in nanoengineered technologies that use surface acoustic waves of variable frequency and amplitude have sparked significant interest among researchers in the field of bio nano electromechanical systems (Bio-NEMS/MEMS). The increased fascination with vibrating surfaces due to their acoustic streaming possibilities, is the driving force behind this research. These surfaces have outstanding physiochemical characteristics that make them extremely adaptable for a variety of applications, including fluidics, tissue engineering, targeted drug delivery, enhanced oil recovery, etc. In the present work, the study of the vibrating nano platinum surface has been carried out to analyze the effect of surface wettability, resistance force, and mean square displacements to obtain the desired performance using molecular dynamics simulations (MDS). A modified Lennard-Jones (LJ) potential was used to control the mobility of water molecules using a solid–liquid. The optimum performance of the nano surface for the desired application is obtained at higher amplitude (5 Å) and frequency (300 GHz) respectively. The average resistance force (FR) for high configuration surface vibrations increased to 80.14% i.e. from 4.4394 × 1014 kJ/mol/m, compared to 8.818 × 1013 kJ/mol/m at amplitude (2 Å) and frequency (50 GHz) configuration. This shows that the present work has substantial implications for applications towards nano technologies.
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    Mechanistic insights into nanoscale heat transfer on platinum surfaces using molecular dynamics simulations
    (Elsevier, 2025-04) Roy, Tribeni
    Cooling microelectronics devices is challenging, and phase change heat transfer at the nanoscale is considered an effective method to overcome this. However, designing heat transfer at the nanoscale requires a mechanistic understanding of the solid–liquid interface at the molecular level. Hence, this study focuses on investigating the interactions between liquid coolant (water nanodroplets) and solid surface (platinum) using molecular dynamics simulations, focusing on how varying energy coefficients (α) influence heat transfer. The simulation results indicate that the wettability of the platinum surface is significantly affected by variations in energy coefficients. At a high energy coefficient (α = 3.0), the contact angle is 49.09˚, indicating higher wettability, while a low energy coefficient (α = 0.1) results in lower wettability. Improved wettability indirectly corresponds to enhanced heat transfer, as higher wettability indicates a better surface area for heat transfer. Further, potential energy analysis conducted as part of the work shows a decreasing trend with increasing energy coefficient value, indicating the reason for improved wettability. From the study, it was also observed that higher wettability has contributed towards better heat transfer, and this has been analyzed using the changes in the heat flux concerning increasing energy coefficient values. From the results, an increasing trend in the values of average heat flux with a higher value of 1.6 × 10−5 Wm−2 for α = 3.0 and a lesser value of −4.40 × 10−7 Wm−2 for α = 0.1 was observed. This confirms that heat transfer is better at higher energy coefficients. This study highlights the pivotal role of energy coefficients in optimizing heat transfer at the nanoscale, providing valuable insights for designing advanced thermal management systems.