Publications

Chemical vapor deposition growth of continuous monolayer antiferromagnetic CrOCl films

Interfacial Stress Transfer in a Graphene Monolayer Nanocomposite

Graphene is one of the stiffest known materials, with a Young's modulus of 1 TPa, making it an ideal candidate for use as a reinforcement in high-performance composites. However, being a one-atom thick crystalline material, graphene poses several fundamental questions: (1) can decades of research on carbon-based composites be applied to such an ultimately-thin crystalline material? (2) is continuum mechanics used traditionally with composites still valid at the atomic level? (3) how does the matrix interact with the graphene crystals and what kind of theoretical description is appropriate? We have demonstrated unambiguously that stress transfer takes place from the polymer matrix to monolayer graphene, showing that the graphene acts as a reinforcing phase. We have also modeled the behavior using shear-lag theory, showing that graphene monolayer nanocomposites can be analyzed using continuum mechanics. Additionally, we have been able to monitor stress transfer efficiency and breakdown of the graphene/polymer interface.

Substrate-aware computational design of two-dimensional materials

Two-dimensional materials have attracted considerable attention due to their remarkable electronic, mechanical and optical properties, making them prime candidates for next-generation electronic and optoelectronic applications. Despite their widespread use in combination with substrates in practical applications, including the fabrication process and final device assembly, computational studies often neglect the effects of substrate interactions for simplicity. This study presents a novel method for predicting the atomic structure of 2D materials on arbitrary substrates by combining an evolutionary algorithm, a lattice-matching technique, an automated machine learning interatomic potentials training protocol, and the ab initio thermodynamics approach for predicting the possible conditions of experimental synthesis of the predicted 2D structures. Using the Mo-S system on a c-cut sapphire substrate as a case study, we reveal several new stable and metastable structures, including previously known 1H-MoS2 and newly found Pmma Mo3S2, P-1 Mo2S, P21m Mo5S3, and P4mm Mo4S, where the Mo4S structure is specifically stabilized by interaction with the substrate. Electronic band structure calculations of Mo3S2, Mo2S, Mo5S3, and Mo4S showed their metallic behavior, while phonon properties calculations indicated their dynamic stability and substrate-induced modulation of the phonon density of states. Finally, we use the ab initio thermodynamics approach to predict the synthesis conditions of the discovered structures in the parameter space of the commonly used CVD technique. These results provide insights into computational substrate engineering, allowing one to study the substrate effect on the thermodynamic and dynamical stability of 2D materials and to modulate their electronic and phonon properties for their future applications, as well as to provide guide maps for their experimental synthesis.

Hexagonal Boron Nitride-Induced Lamellar-Structured Flexible Phase Change Film for Temperature-Controlled Information Storage and Wearable Thermal Regulation

The development of multifunctional composite phase change materials has emerged as a popular research field to achieve efficient thermal energy storage and management across diverse application scenarios. Herein, a novel flexible reversible thermochromic phase change film (TC-PCMs/nBN/OBC) has been proposed. The film comprises a thermochromic compound, hexagonal boron nitride (h-BN), and olefin block copolymers (OBC), and features a layered structure with h-BN embedded laterally in OBC. This design enhances thermal conductivity and confers reversible thermochromic ability, as well as excellent flexibility. The TC-PCMs/nBN/OBC film can perform multiple functions, including thermal storage, light-to-thermal conversion, and temperature-controlled information storage. Additionally, a sandwich-like structure of the multifunctional smart flexible device (TC-PCMs/10BN/OBC-CC) is fabricated using TC-PCMs/10BN/OBC and conductive cloth via easy layer-by-layer assembly. This flexible device is simple to prepare, retains the excellent comprehensive properties of TC-PCMs/nBN/OBC, and possesses high electric-to-thermal conversion efficiency (86.5%). Overall, the results demonstrate that TC-PCMs/10BN/OBC can meet diverse application requirements.

Upconverted electroluminescence via Auger scattering of interlayer excitons in van der Waals heterostructures

The intriguing physics of carrier-carrier interactions, which likewise affect the operation of light emitting devices, stimulate the research on semiconductor structures at high densities of excited carriers, a limit reachable at large pumping rates or in systems with long-lived electron-hole pairs. By electrically injecting carriers into WSe$_2$/MoS$_2$ type-II heterostructures which are indirect in real and k-space, we establish a large population of typical optically silent interlayer excitons. Here, we reveal their emission spectra and show that the emission energy is tunable by an applied electric field. When the population is further increased by suppressing the radiative recombination rate with the introduction of an hBN spacer between WSe$_2$ and MoS$_2$, Auger-type and exciton-exciton annihilation processes become important. These processes are traced by the observation of an up-converted emission demonstrating that excitons gaining energy in non-radiative Auger processes can be recovered and recombine radiatively.

Interfacial H‐bond Network/Concentration Fields/Electric Fields Regulation Achieved by D‐Valine Anions Realizes the Highly Efficient Aqueous Zinc Ion Batteries

Uncontrolled mobile anions and proton transport result in many issues, including interfacial anion depletion, irregular multi‐physics fields fluctuations, space charge layer‐induced interfacial Zn dendrites, and hydrogen evolution reaction (HER), which seriously exacerbates the cycling stability of zinc‐ion batteries. Herein, this work constructs an efficient D‐valine anion interface structure to reversely regulate the Zn2+/H+ dynamic chemistry and unlocks the multiple regulation effects of this anionic interface by investigating interfacial proton transport and complex concentration/electric fields distribution of Zn anode through dynamic in‐situ spectroscopy analysis, static energy calculations, and molecular dynamics simulation. We unravel core factors affecting complicated interfacial HER processes and the generation of the space charge layer. This anionic interfacial layer severs proton hopping transport by rupturing the initial water‐water hydrogen bond, which effectively restrains uncontrolled HER processes. Further, the anion‐immobilized interfacial layer accelerates Zn2+ transfer to optimize the interfacial concentration fields. Also, the anionic interface restrains the formation of the anion depletion layer by relieving rapid Zn2+ ions exhaustion and strengthening the uniformity of interfacial electrical field distribution, which suppresses space charges‐induced Zn dendrite growth. Consequently, Zn||Zn symmetric cells deliver an ultra‐long cycle life of 4150 h. Importantly, the multiple regulation effects enable Zn||I2 cells exhibit long‐term stable life.

Marcus-Hush Theory Revealed by Electron Tunneling Through Hexagonal Boron Nitride

Marcus-Hush theory of electron transfer is one of the pillars of modern electrochemistry with a large body of supporting experimental evidence presented to date. However, some predictions, such as the electrochemical behavior at microdisk electrodes, remain unverified. Herein, we present a study of electron tunneling across a hexagonal boron nitride barrier between a graphite electrode and redox levels in a liquid solution. This was achieved by the fabrication of microdisk electrodes with a typical diameter of 5 µm. Analysis of voltammetric measurements, using two common redox mediators, yielded several electrochemical parameters, including the electron transfer rate constant, limiting current, and transfer coefficient. They show a significant departure from the Butler-Volmer behavior in a clear manifestation of the Marcus-Hush theory of electron transfer. In addition, our system provides a novel experimental platform, which could be applied to address a number of scientific problems such as identification of reaction mechanisms, surface modification, or long-range electron transfer.

Chiral tunnelling and the Klein paradox in graphene

No abstract is provided for this article.

DNA‐rGO Aerogel Bioanodes with Microcompartmentalization for High‐Performance Bioelectrochemical Systems

Bioelectrochemical systems (BES) have garnered significant attention for their applications in renewable energy, microbial fuel cells, biocatalysis, and bioelectronics. In BES, bioelectrodes are used to facilitate extracellular electron transfer among microbial biocatalysts. This study is focused on enhancing the efficiency of these processes through microcompartmentalization, a technique that strategically organizes and segregates microorganisms within the electrode, thereby bolstering BES output efficiency. The study introduces a deoxyribonucleic acid (DNA)‐based reduced graphene oxide (rGO) aerogel engineered as a bioanode to facilitate microorganism compartmentalization while providing an expanded biocompatible surface with continuous conductivity. The DNA‐rGO aerogel is synthesized through the self‐assembly of graphene oxide and DNA, with thermal reduction imparting lightweight structural stability and conductivity to the material. The DNA component serves as a hydrophilic framework, enabling precise regulation of compartment size and biofunctionalization of the rGO surface. To evaluate the performance of this aerogel bioanode, measurements of current generation are conducted using Shewanella oneidensis MR‐1 bacteria as a model biocatalyst. The bioanode exhibits a current density reaching up to 1.5 A·m⁻ 2 , surpassing the capabilities of many existing bioanodes. With its abundant microcompartments, the DNA‐rGO demonstrates high current generation performance, representing a sustainable approach for energy harvesting without reliance on metals, polymers, or heterostructures.

Cross-sectional imaging of individual layers and buried interfaces of graphene-based heterostructures and superlattices

No abstract is provided for this article.

Fundamental limits of few-layer NbSe$_2$ microbolometers at terahertz frequencies

The rapid development of infrared spectroscopy, observational astronomy, and scanning near-field microscopy has been enabled by the emergence of sensitive mid- and far-infrared photodetectors. Owing to their exceptional signal-to-noise ratio and fast photoresponse, superconducting hot-electron bolometers (HEBs) have become a critical component in these applications. While superconducting HEBs are traditionally made from sputtered superconducting thin films like Nb or NbN, the potential of layered van der Waals (vdW) superconductors is untapped at THz frequencies. Here, we report the fabrication of superconducting HEBs out of few-layer NbSe$_2$ microwires. By improving the interface between NbSe$_2$ and metal leads connected to a broadband antenna, we overcome the impedance mismatch between this vdW superconductor and the radio frequency (RF) readout circuitry that allowed us to achieve large responsivity THz detection over the range from 0.13 to 2.5 THz with minimum noise equivalent power of 7~pW$\sqrt{Hz}$. Using the heterodyne sub-THz mixing technique, we reveal that NbSe$_2$ superconducting HEBs are relatively fast and feature a characteristic response time in the nanosecond range limited by the slow heat escape to the bath through a SiO$_2$ layer, on which they are assembled, in agreement with energy relaxation model. Our work expands the family of materials for superconducting HEBs technology, reveals NbSe$_2$ as a promising platform, and offers a reliable protocol for the in-lab production of custom bolometers using the vdW assembly technique.

pH-dependent water permeability switching and its memory in 1T' MoS$_2$ membranes

Intelligent transport of molecular species across different barriers is critical for various biological functions and is achieved through the unique properties of biological membranes. An essential feature of intelligent transport is the ability to adapt to different external and internal conditions and also the ability to memorise the previous state. In biological systems, the most common form of such intelligence is expressed as hysteresis. Despite numerous advances made over previous decades on smart membranes, it is still a challenge for a synthetic membrane to display stable hysteretic behaviour for molecular transport. Here we show the memory effects and stimuli regulated transport of molecules through an intelligent phase changing MoS$_2$ membrane in response to external pH. We show that water and ion permeation through 1T' MoS$_2$ membranes follows a pH dependent hysteresis with a permeation rate that switches by a few orders of magnitude. We demonstrate that this phenomenon is unique to the 1T' phase of MoS$_2$ due to the presence of surface charge and exchangeable ions on the surface. We further demonstrate the potential application of this phenomenon in autonomous wound infection monitoring and pH-dependent nanofiltration. Our work significantly deepens understanding of the mechanism of water transport at the nanoscale and opens an avenue for developing neuromorphic applications, smart drug delivery systems, point-of-care diagnostics, smart sensors, and intelligent filtration devices.

Towards Graphene-Based Electronics

Abstract : During the last year, we have published more than 20 research papers including 2 Science papers, 4 papers in Nature Physics and Nature Communications and 5 Phys. Rev. Letters. The most important technological result probably was the development of fabrication procedures to encapsulate graphene between boron-nitride crystals, which allows us to routinely achieve mobilities above 100,000 cm2/Vs and demonstrate room-temperature ballistic transport at micron scale (Nano Lett. 11, 2396, 2011). This development also led to the first double-layer graphene heterostructures, in which we reported interesting interaction phenomena (Nature Phys. online 2011) and which continue to be in the focus of our attention offering a wealth of new physics and potential applications. Interaction phenomena have also been studied in suspended devices made from graphene and its bilayer (Science 333, 860, 2011; Nature Phys. 7, 701, 2011) and by using the nonlocal geometry (Science 332, 328, 2011). As a result we can now routinely make and investigate complex graphene-BN heterostructures with mobilities 10 times higher than for graphene on the standard Si substrates. For suspended graphene devices, we achieve mobilities well above a million, that is, 100 times higher than for graphene on a Si substrate. Another important development over the last year was the demonstration of a graphene-based derivative, fluorographene that is a two-dimensional version of Teflon (Small 6, 2877, 2010). In all these publications, the PIs have gratefully acknowledged the AFOSR support. As concerns the entire 3-year project, it resulted in 4 Science research papers and dozens of reports in Nature series magazines, Phys. Rev. Letters, Nano Letters and other high-quality research journals. Despite the short reported period, our research has already caused very high impact that can be quantified by the number of citations for the papers supported by the AFOSR grant.

Graphene plasmonics

No abstract is provided for this article.

Synergetic hydrogen-bond network of functionalized graphene and cations for enhanced atmospheric water capture

Water molecules at the solid-liquid interface display intricate behaviours sensitive to small changes. The presence of different interfacial components, such as cations or functional groups, shape the physical and chemical properties of the hydrogen bond network. Understanding such interfacial hydrogen-bond networks is essential for a large range of applications and scientific questions. To probe the interfacial hydrogen-bond network, atmospheric water capture is a powerful tool. Here, we experimentally observe that a calcium ion on a calcium-intercalated graphene oxide aerogel (Ca-GOA) surface captures 2.7 times more water molecules than in its freestanding state. From density functional theory (DFT) calculations, we uncover the synergistically enhanced hydrogen-bond network of the calcium ion-epoxide complex due to significantly larger polarizations and hydrogen bond enthalpies. This study reveals valuable insights into the interfacial water hydrogen-bond network on functionalized carbon-cation complexed surfaces and potential pathways for future atmospheric water generation technologies.

Functional nanocarbons from waste plastics for energy storage applications

Out-of-equilibrium criticalities in graphene superlattices

In thermodynamic equilibrium, current in metallic systems is carried by electronic states near the Fermi energy whereas the filled bands underneath contribute little to conduction. Here we describe a very different regime in which carrier distribution in graphene and its superlattices is shifted so far from equilibrium that the filled bands start playing an essential role, leading to a critical-current behavior. The criticalities develop upon the velocity of electron flow reaching the Fermi velocity. Key signatures of the out-of-equilibrium state are current-voltage characteristics resembling those of superconductors, sharp peaks in differential resistance, sign reversal of the Hall effect, and a marked anomaly caused by the Schwinger-like production of hot electron-hole plasma. The observed behavior is expected to be common for all graphene-based superlattices.

Nature-Inspired Living Materials for Health, Energy, and Sustainability

Nature serves as an inexhaustible source of inspiration for advanced material design. While nature-inspired nonliving materials exhibit exceptional properties, they typically lack the dynamic functionalities of living systems, such as self-healing and environmental responsiveness. To bridge this gap, living materials, which integrate living cells (e.g., bacteria, fungi, algae) within abiotic matrices, have emerged as transformative platforms. These materials harness cellular functions (e.g., biomineralization, programmable metabolism) to achieve unprecedented adaptability and sustainability. In this review, we categorized living materials into two distinct types based on the role of the cells: (1) cells acting as platforms for material synthesis and (2) cells integrated as components of materials for functionalization. We summarized the characteristics of living and nonliving materials inspired by nature, with applications of living materials in energy, medicine, catalysis, concrete, and soft robotics. We further discussed advanced manufacturing techniques for living materials. We envision that the design principles of living materials will advance health, energy, and sustainability.