Publications

In this work a microfabricated 6 meter long gas chromatography column has been integrated with a platinum resistive heater and installed in an ion-trap mass spectrometer. The system is for the detection and identification of volatile organic compounds. The system was demonstrated to separate a mixture of sixteen volatile organic compounds with a maximum temperature of 150 ºC.

No abstract is provided for this article.

This work depicts an electrochemical hydrogel–eutectic gallium indium alloy interface for the detection of tick-borne encephalitis (TBE) virus. This interface allows recording of nonlinear current–voltage responses, depending on the composition of the hydrogel. The current–voltage data for the machine learning model are trained by a multilayer perceptron. This model accurately recognizes the TBE antibody, antigen, and an antibody–antigen complex in mixture with interfering bovine serum albumin with 93% accuracy. Thus, this interface can be used as a convenient method for expressed viruses and pathogens detection.

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.

Accelerated materials discovery is an urgent demand to drive advancements in fields such as energy conversion, storage, and catalysis. Property-directed generative design has emerged as a transformative approach for rapidly discovering new functional inorganic materials with multiple desired properties within vast and complex search spaces. However, this approach faces two primary challenges: data scarcity for functional properties and the multi-objective optimization required to balance competing tasks. Here, we present a multi-property-directed generative framework designed to overcome these limitations and enhance site symmetry-compliant crystal generation beyond P1 (translational) symmetry. By incorporating Wyckoff-position-based data augmentation and transfer learning, our framework effectively handles sparse and small functional datasets, enabling the generation of new stable materials simultaneously conditioned on targeted space group, band gap, and formation energy. Using this approach, we identified previously unknown thermodynamically and lattice-dynamically stable semiconductors in tetragonal, trigonal, and cubic systems, with bandgaps ranging from 0.13 to 2.20 eV, as validated by density functional theory (DFT) calculations. Additionally, we assessed their thermoelectric descriptors using DFT, indicating their potential suitability for thermoelectric applications. We believe our integrated framework represents a significant step forward in generative design of inorganic materials.

Distributions and atomic sites of transition metals and gold on suspended graphene were investigated via high-resolution scanning transmission electron microscopy, especially using atomic resolution high angle dark field imaging. All metals, albeit as singular atoms or atom aggregates, reside in the omni-present hydrocarbon surface contamination; they do not form continuous films, but clusters or nanocrystals. No interaction was found between Au atoms and clean single-layer graphene surfaces, i.e., no Au atoms are retained on such surfaces. Au and also Fe atoms do, however, bond to clean few-layer graphene surfaces, where they assume T and B sites, respectively. Cr atoms were found to interact more strongly with clean monolayer graphene, they are possibly incorporated at graphene lattice imperfections and have been observed to catalyze dissociation of C-C bonds. This behavior might explain the observed high frequency of Cr-cluster nucleation, and the usefulness as wetting layer, for depositing electrical contacts on graphene.

When two-dimensional crystals are brought into close proximity, their interaction results in strong reconstruction of electronic spectrum and local crystal structure. Such reconstruction strongly depends on the twist angle between the two crystals and has received growing attention due to new interesting electronic and optical properties that arise in graphene and transitional metal dichalcogenides. Similarly, novel and potentially useful properties are expected to appear in insulating crystals. Here we study two insulating crystals of hexagonal boron nitride (hBN) stacked at a small twist angle. Using electrostatic force microscopy, we observe ferroelectric-like domains arranged in triangular superlattices with a large surface potential that is independent on the size and orientation of the domains as well as the thickness of the twisted hBN crystals. The observation is attributed to interfacial elastic deformations that result in domains with a large density of out-of-plane polarized dipoles formed by pairs of boron and nitrogen atoms belonging to the opposite interfacial surfaces. This effectively creates a bilayer-thick ferroelectric with oppositely polarized (BN and NB) dipoles in neighbouring domains, in agreement with our modelling. The demonstrated electrostatic domains and their superlattices offer many new possibilities in designing novel van der Waals heterostructures.

Two-dimensional (2D) materials, graphene, hexagonal boron nitride (h-BN) and transition metal dichalcogenides (TMD) have been investigated by means of Scanning Transmission Electron Microscopy (STEM), in particular via High Angle Annular Dark Field (HAADF) imaging technique. They are compared in terms of their structure and durability under intense electron beams.

We exploit the low density of electronic states of graphene to modulate the tunnel current flowing perpendicular to the atomic layers of a multi-layer graphene-boron nitride device. This is achieved by using the electric field effect to raise the Fermi energy of the graphene emitter layer and thereby reduce the effective barrier height for tunneling electrons. We discuss how the electron charge density in the graphene layers and the properties of the boron nitride tunnel barrier determine the device characteristics under operating conditions and derive expressions for carrier tunneling in these highly anisotropic layered heterostructures.

During the last years, giant optical anisotropy demonstrated its paramount importance for light manipulation which resulted in numerous applications ranging from subdiffraction light guiding to switchable nanolasers. In spite of recent advances in the field, achieving continuous tunability of optical anisotropy remains an outstanding challenge. Here, we present a solution to the problem through chemical alteration of the ratio of halogen atoms (X = Br or Cl) in single-crystal CsPbX$_3$ halide perovskites. It turns out that the anisotropy originates from an excitonic resonance in the perovskite, which spectral position and strength are determined by the halogens composition. As a result, we manage to continually modify the optical anisotropy by 0.14. We also discover that the halide perovskite can demonstrate optical anisotropy up to 0.6 in the visible range -- the largest value among non-van der Waals materials. Moreover, our results reveal that this anisotropy could be in-plane and out-of-plane, depending on perovskite shape -- rectangular and square. Hence, it can serve as an additional degree of freedom for anisotropy manipulation. As a practical demonstration, we created perovskite anisotropic nanowaveguides and show a significant impact of anisotropy on high-order guiding modes. These findings pave the way for halide perovskites as a next-generation platform for tunable anisotropic photonics.

We prepare twist-controlled resonant tunneling transistors consisting of monolayer and Bernal bilayer graphene electrodes separated by a thin layer of hexagonal boron nitride. The resonant conditions are achieved by closely aligning the crystallographic orientation of graphene electrodes, which leads to momentum conservation for tunneling electrons at certain bias voltages. Under such conditions, negative differential conductance can be achieved. Application of in-plane magnetic field leads to electrons acquiring additional momentum during the tunneling process, which allows control over the resonant conditions.

Abstract Atomically thin transition metal dichalcogenides (TMDCs) present a promising platform for numerous photonic applications due to excitonic spectral features, possibility to tune their constants by external gating, doping, or light, and mechanical stability. Utilization of such materials for sensing or optical modulation purposes would require a clever optical design, as by itself the 2D materials can offer only a small optical phase delay – consequence of the atomic thickness. To address this issue, we combine films of 2D semiconductors which exhibit excitonic lines with the Fabry-Perot resonators of the standard commercial SiO2/Si substrate, in order to realize topological phase singularities in reflection. Around these singularities, reflection spectra demonstrate rapid phase changes while the structure behaves as a perfect absorber. Furthermore, we demonstrate that such topological phase singularities are ubiquitous for the entire class of atomically thin TMDCs and other high-refractive-index materials, making it a powerful tool for phase engineering in flat optics. As a practical demonstration, we employ PdSe2 topological phase singularities for a refractive index sensor and demonstrate its superior phase sensitivity compared to typical surface plasmon resonance sensors.