Projects

My research is focused at the intersection of physics, material science and ligt-matter interaction.

Carbon Doped Boron Nitride Nano-Coatings for Durable,Low Emissivity Glass Windows

Energy-eﬃcient, durable low-emissivity (low-E) glass windows are in demandfor reducing energy consumption and comfortable living environments.However, commercial low-E coating materials are expensive, proneto abrasion, and hence coated only on the interior side of windows, limitingtheir energy eﬃciency. Here, a new material is introduced, namely chemicallyinert and transparent carbon (C) doped boron nitride (BN) nano-coatingson glass surfaces at room temperature using pulsed laser deposition, thatshows promising long-wave infrared emissivity (𝝐LWIR ≈0.42). The hydrophilicC-BN coatings on glass show excellent environmental stability including hightemperature-high humidity degradation resistance, UV-light, thermal cycling,freezing condition, and saltwater resilience. Furthermore, the coating showspromising adhesion on the glass surface with full scratch protection. In anactual-sized building energy simulation for cold-climates, the intended exterior-side C-BN coated low-E glass shows 2.9% energy savings compared to theinterior-side coated commercial low-E glass. C-BN would be a useful coatingmaterial for durable and energy-eﬃcient low-E glass window technology.

Cultivation of In situ foam 3D-printing: Lightweight and flexible triboelectric nanogenerators employing polyvinylidene fluoride/graphene nanocomposite foams with superior EMI shielding and thermal conductivity

This work introduces in situ foam 3D-printing as a scalable approach to fabricate lightweight, stretchable PVDF/graphene nanocomposite foams for multifunctional electronics. By tuning graphene content and incorporating a foaming agent, the printed materials showed enhanced rheological behavior, improved electrical and thermal conductivity, and effective EMI shielding (up to 36 dB). The foamed nanocomposites also exhibited strong triboelectric performance, with output voltages up to 550 V, successfully powering 80 LEDs. These results highlight foam 3D-printing as a promising strategy for flexible energy harvesting and storage devices.

Effect of triangular pits on the mechanical behavior of 2D MoTe2: a molecular dynamics study

This study investigates how triangular pit defects influence the mechanical behavior of monolayer MoTe₂ using molecular dynamics simulations. By applying uniaxial and biaxial tensile loading, the researchers calculated Young’s modulus, fracture strain, ultimate tensile strength, and toughness. Results show that pit angle, edge length, and perimeter strongly affect fracture properties, with angle regulation enhancing uniaxial performance and perimeter variation improving biaxial behavior. Overall, defective MoTe₂ is more brittle than pristine sheets, offering insights for strain engineering and defect-tolerant design of TMD-based devices.

Strain Engineering of 2D TMDs

Tuning electrical properties of two-dimensional materials through mechanical strain has predominantly focused on n-type 2D materials like MoS2 and WS2, while p-type 2D materials such as WSe2 remain relatively unexplored. Here, we study the impact of controlled mechanical strain on the electron transport characteristics of both mono and bi-layer WSe2. Through coupling atomic force microscopy (AFM) nanoindentation techniques and conductive AFM, we demonstrate the ability to finely tune the electronic band structure of WSe2. Our research offers valuable mechanistic insights into understanding how WSe2's electronic properties respond to mechanical strain, a critical prerequisite for the development of flexible photoelectronic devices. We also observe that under high pressure, the AFM tip/monolayer WSe2/metal substrate junction transitions from Schottky to Ohmic contact, attributed to significant charge injection from the substrate to the WSe2. These findings are significant for designing efficient metal/semiconductor contact in thin and flexible PMOS (p-type Metal-Oxide-Semiconductor) devices.

Cyclic Wear of 2D Materials

Understanding wear, a critical factor impacting the reliability of mechanical systems, is vital for nano-, meso-, and macroscale applications. Due to the complex nature of nanoscale wear, the behavior of nanomaterials such as two-dimensional materials under cyclic wear and their surface damage mechanism is yet unexplored. In this study, we used atomic force microscopy coupled with molecular dynamic simulations to statistically examine the cyclic wear behavior of monolayer graphene, MoS2, and WSe2. We show that graphene displays exceptional durability and lasts over 3000 cycles at 85% of the applied critical normal load before failure, while MoS2 and WSe2 last only 500 cycles on average. Moreover, graphene undergoes catastrophic failure as a result of stress concentration induced by local out-of-plane deformation. In contrast, MoS2 and WSe2 exhibit intermittent failure, characterized by damage initiation at the edge of the wear track and subsequent propagation throughout the entire contact area. In addition to direct implications for MEMS and NEMS industries, this work can also enable the optimization of the use of 2D materials as lubricant additives on a macroscopic level.

Temperature Dependent Fracture of 2D TMDs

Context

In this study, we investigated the mechanical responses of molybdenum ditelluride (MoTe2) using molecular dynamics (MD) simulations. Our key focus was on the tensile behavior of MoTe2 with trigonal prismatic phase (2H-MoTe2) which was investigated under uniaxial tensile stress for both armchair and zigzag directions. Crack formation and propagation were examined to understand the fracture behavior of such material for varying temperatures. Additionally, the study also assesses the impact of temperature on Young’s modulus and fracture stress–strain of a monolayer of 2H-MoTe2.

Method

The investigation was done using molecular dynamics (MD) simulations using Stillinger–Weber (SW) potentials. The tensile behavior was simulated for temperature for 10 K and then from 100 to 600 K with a 100-K interval. The crack propagation and formation of 10 K and 300 K 2H-MoTe2 for both directions at different strain rates was analyzed using Ovito visualizer. All the simulations were conducted using a strain rate of 10−4 ps−1. The results show that the fracture strength of 2H-MoTe2 in the armchair and zigzag direction at 10 K is 16.33 GPa (11.43 N/m) and 13.71429 GPa (9.46 N/m) under a 24% and 18% fracture strain, respectively. The fracture strength of 2H-MoTe2 in the armchair and zigzag direction at 600 K is 10.81 GPa (7.56 N/m) and 10.13 GPa (7.09 N/m) under a 12.5% and 12.47% fracture strain, respectively.

Atomically Thin Liquid Metal Oxides

Atomically thin, mechanically flexible, memory-functional, and power-generating crystals have a crucial role in advancing portable devices. However, their adoption faces challenges due to expensive and labor-intensive synthesis methods and the need for large-scale, mechanically stable, and air-stable materials. A recent development involves an instant-in-air liquid metal printing process using liquid bismuth (Bi), which produces naturally occurring, air-stable, atomically thin, and mechanically flexible nanogenerators and ferroelectric oxides. Despite the centrosymmetric nature of the monoclinic P21/c system in achieved α-Bi2O3-δ, the rapid kinetics of liquid metal synthesis results in the formation of vacancies that disrupt symmetry, as confirmed by density functional theory (DFT) calculations. Additionally, the polarization switching observed in these materials can be utilized for ferroelectric nanopatterning. These atomically thin multifunctional stable oxides possess remarkable attributes such as piezoelectricity, mechanical flexibility, and polarizability, offering significant opportunities for the development of nano-components that can seamlessly integrate into a wide range of devices.

Read more: Multi-functional Atomically thin Oxides from Bismuth Liquid Metal, Adv. Func Mat, https://onlinelibrary.wiley.com/doi/full/10.1002/adfm.202307348

Fatigue Behavior of Polymer Encapsulated Graphene

In flexible electronic devices, the weak van der Waals interface between graphene and stretchable polymeric substrates makes graphene prone to structural degradation from dynamic mechanical loads. To mitigate this, we used a polymer capping layer spin-coated onto graphene, effectively encapsulating it. Results demonstrate that capping layers significantly prevent fatigue damage in graphene, even after enduring 100 cycles at a 10% strain."

Fatigue Behavior of Polymer Encapsulated Graphene to Mitigate Interfacial Fatigue Damage, Advanced Engineering Materials, 2023, 2300336

Exfoliation Mechanism of 2D Materials and their Applications

Due to the strong in-plane but weak out-of-plane bonding, it is relatively easy to separate nanosheets of two-dimensional (2D) materials from their respective bulk crystals. This exfoliation of 2D materials can yield large 2D nanosheets, hundreds of micrometers wide, that can be as thin as one or a few atomic layers thick. However, the underlying physical mechanisms unique to each exfoliation technique can produce a wide distribution of defects, yields, functionalization, lateral sizes, and thicknesses, which can be appropriate for specific end applications. The five most commonly used exfoliation techniques include micromechanical cleavage, ultrasonication, shear exfoliation, ball milling, and electrochemical exfoliation. In this review, we present an overview of the field of 2D material exfoliation and the underlying physical mechanisms with emphasis on progress over the last decade. The beneficial characteristics and shortcomings of each exfoliation process are discussed in the context of their functional properties to guide the selection of the best technique for a given application. Furthermore, an analysis of standard applications of exfoliated 2D nanosheets is presented including their use in energy storage, electronics, lubrication, composite, and structural applications. By providing detailed insight into the underlying exfoliation mechanisms along with the advantages and disadvantages of each technique, this review intends to guide the reader toward the appropriate batch-scale exfoliation techniques for a wide variety of industrial applications.

Appl. Phys. Rev. 9, 041301 (2022); doi: 10.1063/5.0090717

Mechanical Reliability of Atomically Thin 2D Materials

Mechanical reliability reflects the survival (or equivalently, failure) probability of materials under loading and is critical for their long-term and device-scale applications. So far, the mechanical reliability of two-dimensional (2D) materials remains elusive and largely unexplored, especially in long-term loading conditions. Here, through more than 300 nanomechanical experiments and 1,200 molecular dynamics simulations, we evaluate the mechanical reliability of monolayer (1L) MoS2 and WSe2 under both monotonic tension and long-term static fatigue loading conditions. Weibull statistics reveal their mechanical reliability to resemble that of common engineering ceramics and soda-lime glass. We uncover that the observed low reliability results from the synergistic effect of thermal fluctuations, variations in defect configuration, and defect density. Finally, we establish that proof testing can be an effective approach to improve the mechanical reliability of 2D monolayers in practical applications.

Mechanical Reliability of Monolayer MoS2 and WSe2, Matter 5, 1-15, 2022

Solvent-free exfoliation by compressible flows for scalable production of low defect 2D nanomaterials

The existence of structural disorders in 2D nanomaterials (i.e., graphene, hexagonal boron nitride (hBN), and molybdenum disulfide) strongly affects its electrical, mechanical, chemical, thermal, and optical properties. The level and nature of the defects are introduced into the 2D nanomaterials while separating from the bulk materials and strongly depend on the exfoliation methods. Here we report a detailed analysis of structural disorders of graphene that are induced during the exfoliation process using our recently conceived compressible flow exfoliation (CFE) method. We found the decoupled exfoliation process from the suspension stabilization process induces comparatively low structural irregularities in graphene as compared to the state-of-the-art exfoliation processes. (Ongoing Project. In collaboration with UCLA, USA and University of Heidelberg, Germany)

Graphene-based anti-corrosive coating on steel for reinforced concrete infrastructure applications: Challenges and potential

Steel corrosion has been a major perpetual issue of concern for durability and structural integrity of steel and reinforced concrete infrastructure. Polymeric, zinc-galvanic and chromate conversion coatings are commonly applied to protect typical steel materials such as structural steel, reinforcing steel bar (rebar), mild steel and light gauge steel used in infrastructure. Yet, due to physical integrity, long-term performance and environmental concerns, their applications have been limited. In recent years, graphene has garnered considerable attention in the field of anti-corrosive coatings and substantial progress has been achieved in the development of particular graphene-based monolithic (single/few-layer graphene and graphene oxides) as well as laminate and nanocomposite coatings.

Read more: Construction and Building Materials 351 (2022) 128947

High‐Throughput Continuous Production of Shear‐Exfoliated 2D Layered Materials using Compressible Flows

2D materials have raised immense interest among the scientific community because of their unprecedented properties such as high electrical conductivity, light transparency, high mechanical strength and high insulating properties. Although several methods to exfoliate/synthesis the layered materials have been reported, a high throughput-continuous process was still missing. We have shown through our work in Advanced Materials journal that these layered materials can be exfoliated using high shear rate. In our process, we pass compressed He gas into a material chamber and then through a swagelock needle valve. The high shear rate generated in the CD nozzle causes the layers of the materials to exfoliate into thin sheets of 2D nano materials.

High Throughput Continuous Production of Shear Exfoliated 2D Materials using Compressible Flows, Advanced Materials, 2018, 1800200

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