Publications

Hetero-site nucleation for growing twisted bilayer graphene with a wide range of twist angles

Twisted bilayer graphene (tBLG) has recently attracted growing interest due to its unique twist-angle-dependent electronic properties. The preparation of high-quality large-area bilayer graphene with rich rotation angles would be important for the investigation of angle-dependent physics and applications, which, however, is still challenging. Here, we demonstrate a chemical vapor deposition (CVD) approach for growing high-quality tBLG using a hetero-site nucleation strategy, which enables the nucleation of the second layer at a different site from that of the first layer. The fraction of tBLGs in bilayer graphene domains with twist angles ranging from 0° to 30° was found to be improved to 88%, which is significantly higher than those reported previously. The hetero-site nucleation behavior was carefully investigated using an isotope-labeling technique. Furthermore, the clear Moiré patterns and ultrahigh room-temperature carrier mobility of 68,000 cm 2 V −1 s −1 confirmed the high crystalline quality of our tBLG. Our study opens an avenue for the controllable growth of tBLGs for both fundamental research and practical applications.

Inverse design of broadband antennas for terahertz devices based on two-dimensional materials

Graphene: New bridge between condensed matter physics and quantum electrodynamics

Graphene is the first example of truly two-dimensional crystals—it is just one layer of carbon atoms. It turns out to be a gapless semiconductor with unique electronic properties resulting from the fact that charge carriers in graphene demonstrate charge-conjugation symmetry between electrons and holes and possess an internal degree of freedom similar to “chirality” for ultrarelativistic elementary particles. It provides an unexpected bridge between condensed matter physics and quantum electrodynamics (QED). In particular, the relativistic Zitterbewegung leads to the minimum conductivity of the order of conductance quantum e 2 / h in the limit of zero doping; the concept of Klein paradox (tunneling of relativistic particles) provides an essential insight into electron propagation through potential barriers; vacuum polarization around charge impurities is essential for understanding of high electron mobility in graphene; an index theorem explains the anomalous quantum Hall effect.

ZnPSe$_3$ as ultrabright indirect bandgap system with microsecond excitonic lifetimes

We report an optical characterization of ZnPSe$_3$ crystals that demonstrates indirect band gap characteristics in combination with unusually strong photoluminescence. We found evidence of interband recombination from excitonic states with microsecond lifetimes. Through optical characterization, we reconstructed the electronic band scheme relevant for fundamental processes of light absorption, carrier relaxation and radiative recombination. The investigation of the radiative processes in the presence of magnetic field revealed spin polarization of fundamental electronic states. This observation opens a pathway towards controlling the spin of excitonic states in technologically relevant microsecond timescales.

Mechanism of Gold-Assisted Exfoliation of Centimeter-Sized Transition-Metal Dichalcogenide Monolayers

Exfoliation of large-area monolayers is important for fundamental research and technological implementation of transition-metal dichalcogenides. Various techniques have been explored to increase the exfoliation yield, but little is known about the underlying mechanism at the atomic level. Here, we demonstrate gold-assisted mechanical exfoliation of monolayer molybdenum disulfide, up to a centimeter scale. Detailed spectroscopic, microscopic, and first-principles density functional theory analyses reveal that strong van der Waals (vdW) interaction between Au and the topmost MoS2 layer facilitates the exfoliation of monolayers. However, the large-area exfoliation promoted by such strong vdW interaction is only achievable on freshly prepared clean and smooth Au surfaces, while rough surfaces and surfaces exposed to air for more than 15 min result in negligible exfoliation yields. This technique is successfully extended to MoSe2, WS2, WSe2, MoTe2, WTe2, and GaSe. In addition, electrochemical characterization reveals intriguing interactions between monolayer MoS2 and Au. A subnanometer-thick MoS2 monolayer strongly passivates the chemical properties of the underlying Au, and the Au significantly modulates the electronic band structure of the MoS2, turning it from semiconducting to metallic. This could find applications in many areas, including electrochemistry, photovoltaics, and photocatalysis.

Quenching of the Hall effect in localised high magnetic field regions

We report the suppression of the Hall effect in a mesoscopic Hall cross with a strong magnetic field only in the centre and vanishingly small outside. The local magnetic field is produced by placing Dy pillar on top of a structure with a high-mobility two-dimensional electron gas. The effect is found to be due to a sharp increase of the number of back-scattered and quasi-localised electron orbits. The possibility of localising electrons inside the magnetic inhomogeneity region is discussed.

Quantum capacitance measurements of electron-hole asymmetry and next-nearest-neighbor hopping in graphene

The next-nearest-neighbor hopping term ${t}^{\ensuremath{'}}$ determines a magnitude, and, hence, the importance of several phenomena in graphene that include self-doping due to broken bonds and the Klein tunneling, which in the presence of ${t}^{\ensuremath{'}}$, is no longer perfect. Theoretical estimates for ${t}^{\ensuremath{'}}$ vary widely, whereas a few existing measurements by using polarization-resolved magnetospectroscopy have found surprisingly large ${t}^{\ensuremath{'}}$, close to or even exceeding the highest theoretical values. Here, we report dedicated measurements of the density of states in graphene by using high-quality capacitance devices. The density of states exhibits a pronounced electron-hole asymmetry that increases linearly with energy. This behavior yields ${t}^{\ensuremath{'}}$ \ensuremath{\approx} \ensuremath{-}0.3 eV\ifmmode\pm\else\textpm\fi{}15$%$, in agreement with the high end of theory estimates. We discuss the role of electron-electron interactions in determining ${t}^{\ensuremath{'}}$ and overview phenomena, which can be influenced by such a large value of ${t}^{\ensuremath{'}}$.

Probing the Twist-Controlled Interlayer Coupling in Artificially Stacked Transition Metal Dichalcogenide Bilayers by Second-Harmonic Generation

Interlayer coupling plays a critical role in the electronic band structures and optoelectronic properties of van der Waals (vdW) materials and heterostructures. Here, we utilize optical second-harmonic generation (SHG) measurements to probe the twist-controlled interlayer coupling in artificially stacked WSe2/WSe2 homobilayers and WSe2/WS2 and WSe2/MoS2 heterobilayers with a postannealing procedure. In the large angle twisted WSe2/WSe2 and WSe2/WS2, the angular dependence of the SHG intensity follows the interference relations up to angles above 10°. For lower angles, the SHG is significantly suppressed. Furthermore, for the twisted WSe2/MoS2 the SHG intensity largely deviates from the coherent superposition model and shows consistent quenching for all the stacking angles. The suppressed SHG in twisted transition metal dichalcogenide (TMDC) bilayers is predominantly attributed to the interlayer coupling between the two adjacent monolayers. The evolution of the interlayer Raman mode in WSe2 demonstrates that the interlayer coupling in the twisted WSe2/WSe2 and WSe2/WS2 is highly angle-dependent. Alternatively, the interlayer coupling generally exists in the twisted WSe2/MoS2, regardless of the different angles. The interlayer coupling is further confirmed by the quenching and red-shift of the photoluminescence of WSe2 in the twisted TMDC bilayers. Combined with density functional theory calculations, we reveal that the stacking-angle-modulated interlayer coupling originates from the variation of the interlayer spacing and the binding energy in the twisted TMDC bilayers.

Ultrafast non-thermal electron dynamics in single layer graphene

The impulsive optical excitation of carriers in graphene creates an out-of-equilibrium distribution, which thermalizes on an ultrafast timescale [1-4]. This hot Fermi-Dirac (FD) distribution subsequently cools via phonon emission within few hundreds of femtoseconds. While the relaxation mechanisms mediated by phonons have been extensively investigated, the initial stages, ruled by fundamental electron-electron (e-e) interactions still pose a challenge.

Correction to Photoelectrochemistry of Pristine Mono- and Few-Layer MoS₂

ADVERTISEMENT RETURN TO ISSUEPREVAddition/CorrectionNEXTORIGINAL ARTICLEThis notice is a correctionCorrection to Photoelectrochemistry of Pristine Mono- and Few-Layer MoS2Matěj Velický*, Mark A. Bissett, Colin R. Woods, Peter S. Toth, Thanasis Georgiou, Ian A. Kinloch, Kostya S. Novoselov, and Robert A. W. Dryfe*Cite this: Nano Lett. 2016, 16, 12, 8035Publication Date (Web):November 14, 2016Publication History Published online14 November 2016Published inissue 14 December 2016https://doi.org/10.1021/acs.nanolett.6b04704Copyright © 2016 American Chemical SocietyRIGHTS & PERMISSIONSACS AuthorChoicewith CC-BYlicenseArticle Views857Altmetric-Citations-LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (161 KB) Get e-Alerts Get e-Alerts

Engineering electrical properties of graphene: chemical approaches

To ensure the high performance of graphene-based devices, it is necessary to engineer the electrical properties of graphene with enhanced conductivity, controlled work function, opened or closed bandgaps, etc. This can be performed by various non-covalent chemical approaches, including molecular adsorption, substrate-induced doping, polymerization on graphene, deposition of metallic thin films or nanoparticles, etc. In addition, covalent approaches such as the substitution of carbon atoms with boron or nitrogen and the functionalization with hydrogen or fluorine are useful to tune the bandgaps more efficiently, with better uniformity and stability. In this review, representative examples of chemically engineered graphene and its device applications will be reviewed, and remaining challenges will be discussed.

Effects of bubble-induced strain on the magnetic properties of van der Waals ferromagnet CrBr₃

Two-dimensional materials provide with ability to control their properties with a number of methods. One of such methods is using strain and compression. In this work, we investigated the influence of locally induced strain through bubbles in thin ferromagnetic CrBr 3 using low-temperature magnetic force microscopy. As a result, domain pinning and higher coercive and saturation fields were observed in the bubble. In addition, nontrivial spin arrangements are allowed to take place in a non-homogeneously strained area, leading to different responses to the external magnetic field in comparison to a non-strained region. Finally, Raman spectroscopy and magneto-photoluminescence spectroscopy were performed to show alternation of the magnetic properties of the sample under mechanical deformation.

Electrochemistry of the Basal Plane versus Edge Plane of Graphite Revisited

The electrochemical activity of the basal plane and edge plane of graphite has long been a subject of an extensive debate. While significant advances have been made, several gaps still exist in our understanding of this issue, namely, the relative differences in the electrochemical activity of the perfect basal plane and perfect edge plane and the dependence of measurable electrochemical quantities on the edge/defect density of the basal plane. In this work, we employ a microdroplet electrochemical cell technique and atomic force microscopy to measure localized electrochemical properties of the graphitic surface with known edge coverage. The electron transfer rate, capacitance, and density of electronic states of the perfect basal plane and perfect edge plane are estimated, and a qualitative model is proposed for the dependence of the electrochemical quantities on the defect density of the basal plane.

The Music of Every Day

Wonderchaos, pp. 21-24 (2025) No AccessThe Music of Every DayKate Daudy and Kostya NovoselovKate Daudy and Kostya Novoselovhttps://doi.org/10.1142/9789819806430_0002Cited by:0 (Source: Crossref) PreviousNext AboutFiguresReferencesRelatedDetailsPDF/EPUB ToolsAdd to favoritesDownload CitationsTrack CitationsRecommend to Library ShareShare onFacebookTwitterLinked InRedditEmail Cite Recommend Abstract: The companionship and inspiration brought to me by becoming friends with Kostya Novoselov has been a turning point in the way I see things. We met a few years ago when I was looking for truth in the field of science, and our enjoyment of one another's spirit has become a pillar of my everyday happiness. Science, art and nature bring richer colours and depth alongside any true friend. One is set free to engage with the everyday sublime. Learning through the prism of physics and mathematics I have felt myself a piece of white paper upon which new ideas were being written… We recommendIdentity Authentication Based on Music-Induced Autobiographical Memory EEGXin Xu, Journal of Circuits, Systems and Computers, 2022Altered EEG Oscillatory Brain Networks During Music-Listening in Major DepressionYongjie Zhu, International Journal of Neural Systems, 2020Recognition and Classification of Depression under Deep Neural Network and Rehabilitation Effect of Music TherapyXueting Li, Journal of Mechanics in Medicine and Biology, 2022Validation of the HOSPITAL score as predictor of 30-day potentially avoidable readmissions in a Brazilian population: retrospective cohort studyNayara Cristina da Silva, Journal of Circuits, Systems and Computers, 2022Discussion on Y. Zhu, X. Wang, K. Mathiak, P. Toiviainen, T. Ristaniemi, J. Xu, Y. Chang and F. Cong, Altered EEG Oscillatory Brain Networks During Music-Listen...Milena B. Čukić Radenković, International Journal of Neural Systems, 2021Monoclonal Antibodies for the Treatment of COVID-19—Every Day You Fight Like You're Running Out of Time Erin K. McCreary, JAMA Network Open, 2023Failures at every level: breakdown of the epigenetic machinery of aging Dongxin Zhao, Life Medicine, 2022The Lake Wobegon Effect—Where Every Medicare Advantage Plan Is "Above Average" Joan M. Teno, JAMA Health Forum, 2022Health Reform: The Music Didn't Stop a Second Time Andrew B. Bindman, JAMA Health Forum, 2012Judgment Day for the Affordable Care Act? Larry Levitt, JAMA Health Forum, 2014Powered by Privacy policyGoogle Analytics settings FiguresReferencesRelatedDetailsNone Recommended Recommended Good Sunshine Day, Good Shopping Day?Kiasunomics©2Every Day is a BirthdayRainbow after DuskEvery Child CountsYou Know the Glory, Not the StoryLost in MusicPete's Bogus JourneyTHE SOUND OF MUSICABHIJIT NAGInspirations of a NationA Reason to Wake Up Every MorningMany DawnsFIRST DAY AT WORKServing SingaporeThe Passing of a DaySay Pin TANSingapore Teachers WonderchaosMetrics Downloaded 0 times History PDF download

METALLIC AND SEMICONDUCTOR HALL MICROPROBES FOR WIDE TEMPERATURE RANGE APPLICATIONS

We report on mesoscopic Hall sensors allowing accurate magnetization studies of submicron or nanometer-sized samples over a wide temperature range. Even at 300 K, the probes can reliably resolve local changes in dc field of ≈ 1 G with spatial resolution of ≈ 1 μm, which corresponds to a flux sensitivity of less than 0.1 ϕ 0 (ϕ 0 =h/e is a flux quantum). The resolution increases 100 times at temperatures below 80 K. The capabilities of new micromagnetometers are demonstrated by measuring nm-scale movements of individual domain walls in a ferromagnet.

Composite super-moiré lattices in double-aligned graphene heterostructures

When two-dimensional atomic crystals are brought into close proximity to form a van der Waals heterostructure, neighbouring crystals can start influencing each others electronic properties. Of particular interest is the situation when the periodicity of the two crystals closely match and a moir\'e pattern forms, which results in specific electron scattering, reconstruction of electronic and excitonic spectra, crystal reconstruction, and many other effects. Thus, formation of moir\'e patterns is a viable tool of controlling the electronic properties of 2D materials. At the same time, the difference in the interatomic distances for the two crystals combined, determines the range in which the electronic spectrum is reconstructed, and thus is a barrier to the low energy regime. Here we present a way which allows spectrum reconstruction at all energies. By using graphene which is aligned simultaneously to two hexagonal boron nitride layers, one can make electrons scatter in the differential moir\'e pattern, which can have arbitrarily small wavevector and, thus results in spectrum reconstruction at arbitrarily low energies. We demonstrate that the strength of such a potential relies crucially on the atomic reconstruction of graphene within the differential moir\'e super-cell. Such structures offer further opportunity in tuning the electronic spectra of two-dimensional materials.

Atomic and Electronic Structure of Defects in hBN: Enhancing Single-Defect Functionalities

Defect centers in insulators play a critical role in creating important functionalities in materials: prototype qubits, single-photon sources, magnetic field probes, and pressure sensors. These functionalities are highly dependent on their midgap electronic structure and orbital/spin wave function contributions. However, in most cases, these fundamental properties remain unknown or speculative due to the defects being deeply embedded beneath the surface of highly resistive host crystals, thus impeding access through surface probes. Here, we directly inspected the atomic and electronic structures of defects in thin carbon-doped hexagonal boron nitride (hBN:C) by using scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS). Such investigation adds direct information about the electronic midgap states to the well-established photoluminescence response (including single-photon emission) of intentionally created carbon defects in the most commonly investigated van der Waals insulator. Our joint atomic-scale experimental and theoretical investigations reveal two main categories of defects: (1) single-site defects manifesting as donor-like states with atomically resolved structures observable via STM and (2) multisite defect complexes exhibiting a ladder of empty and occupied midgap states characterized by distinct spatial geometries. Combining direct probing of midgap states through tunneling spectroscopy with the inspection of the optical response of insulators hosting specific defect structures holds promise for creating and enhancing functionalities realized with individual defects in the quantum limit. These findings underscore not only the versatility of hBN:C as a platform for quantum defect engineering but also its potential to drive advancements in atomic-scale optoelectronics.

Te-canfieldite from the lunnoe au-u deposit (Aldan region, Republic of Yakutiya)

Te-canfeldite was found in assemblage with pyrite, marcasite, hessite, and Tl sulfosalts in the ores of the Fedorovskaya vein zone of the Lunnoe Au-U deposit, Aldan shield (Yakutia). The mineral forms anhedral inclusions in vein matrix. Its refection spectrum is characterized by weak normal dispersion, the dispersion curve is almost parallel to the canfeldite curve, but the refectivity value is signifcantly higher. A sustained S:Te ratio of Te-canfldite is consistent with the analytical data for most mineral localities (Lengenbach, Sirotan, Nikolayevskoye, Uryakh). It is suggested that Te-canfeldite is formed in a wide range of geological settings.