Department of Mechanical engineering
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Item Study of side burr formation in steady-state nano-polishing of Si-wafer using molecular dynamics simulation(Sage, 2024-02) Roy, TribeniWith 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.Item Mechanism of surface modification on monocrystalline silicon during diamond polishing at nanometric scale(Sage, 2023-11) Sharma, Anuj; Roy, TribeniThe 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.Item Opportunities and challenges in machining of aluminium metal matrix composites using electrical discharge machining(Sage, 2023-11) Roy, TribeniThe machining of aluminium metal matrix composites (aluminium MMCs) presents a dynamic landscape of opportunities and challenges, with electrical discharge machining (EDM) emerging as a promising technique. This review article systematically navigates the intricate interplay between AMMCs’ unique characteristics and the EDM process. Through a comprehensive analysis of existing literature, we uncover the underlying mechanisms that govern the machining dynamics of AMMCs, exploring their compositional variations, reinforcement distribution and thermal properties. The article delves into the opportunities offered by EDM, such as precision machining of intricate geometries, inherent thermal control and the ability to navigate the varying hardness levels in AMMCs. Furthermore, the review addresses the challenges that arise, including electrode wear, surface integrity preservation and the influence of reinforcement particles on material removal rates. The authors highlight the role of parameter optimisation in achieving desirable machining outcomes, underlining the need to strike a balance between material removal efficiency and surface finish quality. Additionally, environmental considerations in EDM of AMMCs are discussed, emphasising sustainable machining strategies in line with contemporary ecological concerns. As the field of advanced materials and manufacturing continues to evolve, this review article provides valuable insights for researchers, engineers and industries seeking to harness the potential of EDM in machining AMMCs. By navigating the intricate landscape of opportunities and challenges, this article contributes to a holistic understanding of the nuanced relationship between EDM and AMMCs, laying the foundation for future advancements in precision machining of these composite materials.Item Strain induced electrochemical behaviors of ionic liquid electrolytes in an electrochemical double layer capacitor: Insights from molecular dynamics simulations(AIP, 2023-12) Roy, TribeniElectrochemical 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.Item Strain softening observed during nanoindentation of equimolar-ratio Co–Mn– Fe–Cr–Ni high entropy alloy(Sage, 2024-02) Roy, TribeniThis 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.Item Nano droplet behaviour on vibrating surfaces: atomistic simulations for bio-NEMS/MEMS applications(Taylor & Francis, 2024-04) Roy, TribeniRecent 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.Item Efficient fabrication of zero taper µ-electrode using novel dry µ-electrical discharge turning(Sage, 2025-01) Roy, TribeniMicromachining is essential for producing components smaller than 1000 µm and is increasingly significant due to the trend toward miniaturizing industrial products. Tool-based micromachining techniques like µ-turning, µ-grinding, µ-EDM, and µ-ECM offer benefits in productivity, efficiency, adaptability, and cost-effectiveness. Modern industrial products require high dimensional accuracy and superior surface finishes. µ-EDM is particularly promising for economically producing complex microfeatures with high precision. However, the high tool wear rate in µ-EDM requires on-machine microelectrode fabrication, which is essential for creating micro-sized holes and channels during µ-EDM operations. A major challenge lies in achieving high dimensional accuracy and minimal taper in microelectrodes. Additionally, there are health concerns related to hydrocarbons produced from liquid dielectrics. This research explores fabrication of microelectrodes using dry µ-ED Turning. Five machining strategies were employed, using stationary block electrical discharge turning (SB-EDT), moving block electrical discharge turning (MB-EDT), and their combinations to produce microelectrodes with improved surface finishes and minimal taper. Gaseous dielectrics significantly reduce harmful emissions and contamination, creating a safer working environment while minimizing environmental pollution. The taper issue was significantly mitigated in microelectrodes fabricated using MB-EDTd, achieving nearly zero taper with a surface finish of 2.04 µm. MB-EDTd also achieved highest material removal rate, producing a microelectrode with an average diameter of 428 µm. Scanning electron microscope (SEM) micrographs and surface finish analyses were conducted to examine the effects of various parameters, such as discharge currents and linear feed speed. The findings highlight the potential of µ-EDM with gaseous dielectrics to enhance microelectrode fabrication process.Item Insights of zinc ion storage in chilli-stem derived porous carbon enabling ultrastability and high energy density of zinc-ion hybrid supercapacitors(ACS, 2024-12) Roy, TribeniAqueous zinc ion hybrid supercapacitors (ZIHSCs) are promising as low-cost and safe energy storage devices for next-generation applications. Still, their energy-power performance and durability are far from satisfactory. Here, we present an energy-dense, and ultrastable ZIHSC realized using activated porous carbons derived from chilli-stems. KOH activation resulted in a high specific surface area of 1710 m2/g, abundant mesoporous structure, and oxygen functionalities, which helped the KOH-activated carbon (CSK) to yield an impressive specific capacity and energy density of 192 mA h/g and 172 W h/kg, respectively, and makes it the top-performing ZIHSC in recent times. ZIHSC’s cycling performance is exceptional, retaining over 90% capacity even after 50,000 charge–discharge cycles. Molecular dynamics simulations reveal easy Zn ion diffusion through interconnected channels and subsequent pore fillings within the carbon electrodes, rendering impressive performance. Simulations further reveal important atomic interactions, demonstrating that higher currents drawn from the device cause partial filling of pores and blockages in the channels and result in a decrease in the device’s specific capacity. Benefitted by CSK’s impressive performance, the aqueous Zn@pCu//CSK full-cell device has demonstrated good energy-power densities (57.7 W h/kg and 4.5 k W/kg) and durability over tens of thousands of cycles, further substantiating ZIHSCs’ application prospects in real life.Item Insights into interlayer dislocation augmented zinc-ion storage kinetics in MOS2 nanosheets for rocking-chair zinc-ion batteries with ultralong cycle-life(Wiley, 2025-01) Roy, TribeniIncreasing attention to sustainability and cost-effectiveness in energy storage sector has catalyzed the rise of rechargeable Zinc-ion batteries (ZIBs). However, finding replacement for limited cycle-life Zn-anode is a major challenge. Molybdenum disulfide (MoS2), an insertion-type 2D layered material, has shown promising characteristics as a ZIB anode. Nevertheless, its high Zn-ion diffusion barrier because of limited interlayer spacing substantiates the need for interlayer modifications. Here, N-doped carbon quantum dots (N-CQDs) are used to modify the interlayers of MoS2, resulting in increased interlayer spacing (0.8 nm) and rich interlayer dislocations. MoS2@N-CQDs attain a high specific capacity (258 mAh g−1 at 0.1 A g−1), good cycle life (94.5% after 2000 cycles), and an ultrahigh diffusion coefficient (10−6 to 10−8 cm2 s−1), much better than pristine MoS2. Ex situ Raman studies at charge/discharge states reveal that the N-CQDs-induced interlayer expansion and dislocations can reversibly accommodate the volume strain created by Zn-ion diffusion within MoS2 layers. Atomistic insight into the interlayer dislocation-induced Zn-ion storage of MoS2 is unveiled by molecular dynamic simulations. Finally, rocking-chair ZIB with MoS2@N-CQDs anode and a ZnxMnO2 cathode is realized, which achieved a maximum energy density of 120.3 Wh kg−1 and excellent cyclic stability with 97% retention after 15 000 cycles.Item Role of artificial intelligence in the design and discovery of next-generation battery electrolytes(AIP, 2025-03) Roy, TribeniAdverse climate change, global warming, and energy security have emerged as global challenges, demanding advancements in high-performance battery technologies to drive sustainability. In this scenario, developing electrolytes has gained significant momentum among various innovations, given their critical role in determining battery safety and performance. However, the conventional trial-and-error approach to electrolyte discovery is costly, complex, time-consuming, and often inefficient. Recent advancements in artificial intelligence (AI) over the past decade have catalyzed innovations across diverse fields, ranging from nanotechnology to space explorations, and are now emerging as a powerful tool for materials discovery. Numerous studies have demonstrated the effectiveness of AI in screening and characterizing next-generation electrolytes. This review offers a comprehensive outlook on the transformative role of AI in designing novel electrolytes. Examination of various electrolytes and their key parameters that influence the electrochemical performance of batteries is conducted. The challenges and opportunities in using AI to design electrolytes with tailored properties are explored. Furthermore, a futuristic vision for integrating science-driven AI-based approaches with existing experimental and theoretical methods to accelerate electrolyte discovery is presented. By offering such a comprehensive understanding, this review aims to provide researchers, industries, and policymakers with insights into how AI can be leveraged to design next-generation electrolytes, paving the way toward transformative progress in battery technology.