arXiv subjects

Slava V. Rotkin

Publications and source records attributed to Slava V. Rotkin.

At least 19 recordsLinked to original sources

arXiv2026

Ultra-Confinement of Polaritons in Single Atomic Layer Ag Photonic Quantum Dots

Light scattering by two-dimensional (2D) van der Waals heterostructures (vdWHs) is immense, especially given their infinitesimal volume, thus enabling strong light-matter interactions. Surface 2D polariton waves manifest through large concentration of electromagnetic field in vertical direction, normal to their propagation. By confining vdWH materials into 2D photonic shapes, one can manipulate and compress light in lateral directions. Scattering-type scanning near-field optical microscopy is a perfect tool for direct imaging of the propagating polaritons and studying the properties of confined polaritons in nanostructures. Though, thus far the quantitative analysis, such the wavelength extraction, has been challenged for confined polaritons by incapability of mapping of the wave period on sub-wavelength scale and difficulty of identifying an adequate substrate's "background" to subtract. Here, an analytical approach is developed to reveal the local propagation constant of confined polaritons under abovementioned constraints and map it with the sub-wavelength resolution. Applied to analysis of the SiC/2D-Ag/EG (epitaxial graphene) photonic nanostructures, the technique uncovered that the polaritons are highly confined in both vertical ($\sim\lambda$/50) and lateral directions ($\sim\lambda$/40) by 2D metal.

cond-mat.mtrl-sci↗

arXiv2025

A copper sulfide-hydroxypropyl $\beta$-Cyclodextrin-reduced graphene oxide composite for highly sensitive electrochemical detection of 5-hydroxytryptamine in biological samples

The precise identification of neurotransmitters is essential for comprehending cerebral function, detecting neurological conditions, and formulating successful therapeutic approaches. The present work investigates the electrochemical detection of serotonin with the excellent hybrid electrocatalyst $Cu_2S/H{\beta}cd-rGO$. $Cu_2S$, with its significant features as improved catalytic activity and enhanced charge transfer when combined with $H{\beta}cd-rGO$, will enhance the performance. The integration of $Cu_2S$ with $H{\beta}cd-rGO$, regulated by the van der Waals force and the electrostatic interaction, makes it a stable catalyst without disrupting the composite structure. Also, the aggregation of the $Cu_2S/H{\beta}cd$ with the layered sheets of rGO can be highly reduced and resulting in the improvement of the conductivity. Thus, the above features resulted in the improved oxidation response current when fabricated over the glassy carbon electrode (GCE). The SR showed sensitive response at a broad linear range of 0.019 to 0.299 $\mu$M and 4.28 to 403.14 $\mu$M, resulting in a lower limit of detection (LOD) of 1.2 nM or 0.0012 $\mu$M and a sensitivity of about 15.9 $\mu$A ${\mu}M^{-1}$ $cm^{-2}$. The sensor demonstrated excellent selectivity against common interferents, including aminophenol, dopamine, epinephrine, hydroquinone, melatonin, and chlorine. The real sample studies in the biological samples show good recovery values, showing the effectiveness of the as-fabricated sensor. Thus, the cost-efficient and straightforward integration of $Cu_2S/H{\beta}cd-rGO$ will be an outstanding electrocatalyst for detecting SR.

cond-mat.mtrl-sci↗

arXiv2025

Metallic NbS2 one-dimensional van der Waals heterostructures

This study presents the experimental realization of metallic NbS2-based one-dimensional van der Waals heterostructures applying a modified NaCl-assisted chemical vapor deposition approach. By employing a "remote salt" strategy, precise control over NaCl supply was achieved, enabling the growth of high-quality coaxial NbS2 nanotubes on single-walled carbon nanotube-boron nitride nanotube (SWCNT-BNNT) templates. With the remote salt strategy, the morphologies of as synthesized NbS2 could be controlled from 1D nanotubes to suspended 2D flakes. Structural characterization via high-resolution transmission electron microscopy (HRTEM) and scanning transmission electron microscopy (STEM) confirms the formation of crystalline NbS2 nanotubes, revealing a distinct bi-layer preference compared to monolayer-dominated semiconducting transition metal dichalcogenide analogs. Optical analyses using UV-vis-NIR and FTIR spectroscopy highlight the metallic nature of NbS2. With Raman analysis, oxidation studies demonstrate relative higher degradation rate of 1D NbS2 under ambient conditions. Density functional theory (DFT) calculations further elucidate the stabilization mechanism of bi-layer NbS2 nanotubes, emphasizing interlayer charge transfer and Coulomb interactions. This work establishes a robust framework for synthesizing metallic 1D vdW heterostructures, advancing their potential applications in optoelectronics and nanodevices.

cond-mat.mtrl-sci↗

arXiv2024

Low-Temperature Synthesis of Weakly Confined Carbyne inside Single-Walled Carbon Nanotubes

Carbyne, a one-dimensional (1D) carbon allotrope with alternating triple and single bonds, has the highest known mechanical strength but is unstable to bending, limiting synthesis to short linear chains. Encapsulation within carbon nanotubes (CNTs) stabilizes carbyne, forming confined carbyne (CC), thus enabling further research concerning attractive 1D physics and materials properties of carbyne. While CC has been synthesized in multi-walled CNTs (MWCNTs) using the arc-discharge method and in double-walled CNTs (DWCNTs) via high-temperature high-vacuum (HTHV) method, synthesis in single-walled CNTs (SWCNTs) has been challenging due to their fragility under such conditions. In this work, we report a low-temperature method to synthesize CC inside SWCNTs (CC@SWCNT). By annealing SWCNTs containing ammonium deoxycholate (ADC) at 400{\deg}C, ADC is converted into CC without damaging the SWCNTs. Raman spectroscopy revealed a strong CC phonon (CC-mode) peak at 1860-1870 cm^-1, much stronger than the SWCNT G-band peak, confirming a high fraction of CC in the resulting material. The Raman mapping result showed the uniformity of the CC-mode signal across the entire film sample, proving the high efficiency of this method in synthesizing CC in every SWCNT of appropriate size. Notably, the CC-mode peaks of CC@SWCNT (above 1860 cm^-1) are higher than those reported in previous CC@CNT samples (mostly less than 1856 cm^-1). This is attributed to larger SWCNT diameters (over 0.95 nm) used in this study, compared to the typical 0.6-0.8 nm range. Larger diameters result in reduced confinement, allowing carbyne to closely resemble free-standing carbyne while remaining stabilized. This low-temperature synthesis of long-chain, nearly free-standing carbyne within large-diameter SWCNTs offers new opportunities for exploring 1D physics and the unique properties of carbyne for potential applications.

physics.chem-ph↗

arXiv2024

Giant and Tunable Bosonic Quantum Interference Induced by Two-Dimensional Metals

Harnessing quantum interference among bosons provides significant opportunities as bosons often carry longer coherence time than fermions. As an example of quantum interference, Fano resonance involving phonons or photons describes the coupling between discrete and continuous states, signified by an asymmetric spectral lineshape. Utilizing photon-based Fano resonance, molecule sensing with ultra-high sensitivity and ultrafast optical switching has been realized. However, phonon-based Fano resonance, which would expand the application space to a vaster regime, has been less exploited because of the weak coupling between discrete phonons with continuous states such as electronic continuum. In this work, we report the discovery of giant phonon-based Fano resonance in a graphene/2D Ag/SiC heterostructure. The Fano asymmetry, being proportional to the coupling strength, exceeds prior reports by two orders of magnitude. This Fano asymmetry arises from simultaneous frequency and lifetime matching between discrete and continuous phonons of SiC. The introduction of 2D Ag layers restructures SiC at the interface and facilitates resonant scattering to further enhance the Fano asymmetry, which is not achievable with conventional Ag thin films. With these unique properties, we demonstrated that the phonon-based Fano resonance can be used for ultrasensitive molecule detection at the single-molecule level. Our work highlights strong Fano resonance in the phononic system, opening avenues for engineering quantum interference based on bosons. Further, our findings provide opportunities for advancing phonon-related applications, including biochemical sensing, quantum transduction, and superconductor-based quantum computing.

cond-mat.mtrl-sci↗

arXiv2021

Multidimensional imaging reveals mechanisms controlling label-free biosensing in vertical 2DM-heterostructures

Two-dimensional materials and their van der Waals heterostructures enable a large range of applications, including label-free biosensing. Lattice mismatch and work function difference in the heterostructure material result in strain and charge transfer, often varying at nanometer scale, that influence device performance. In this work, a multidimensional optical imaging technique is developed in order to map sub-diffractional distributions for doping and strain and understand the role of those for modulation of electronic properties of the material. As an example, vertical heterostructure comprised of monolayer graphene and single layer flakes of transition metal dichalcogenide MoS$_2$ is fabricated and used for biosensing. Herein, an optical label-free detection of doxorubicin, a common cancer drug, is reported via three independent optical detection channels (photoluminescence shift, Raman shift and Graphene Enhanced Raman Scattering). Non-uniform broadening of components of multimodal signal correlates with the statistical distribution of local optical properties of the heterostructure. Multidimensional nanoscale imaging allows one to reveal the physical origin for such a local response and propose the best strategy for mitigation of materials variability and future device fabrication.

cond-mat.mes-hall↗

arXiv2020

One-dimensional van der Waals heterojunction diode

The synthesis of one-dimensional van der Waals heterostructures was realized recently, which opens up new possibilities for prospective applications in electronics and optoelectronics. The even reduced dimension will enable novel properties and further miniaturization beyond the capabilities of its two-dimensional counterparts have revealed. The natural doping results in p-type electrical characteristics for semiconducting single-walled carbon nanotubes, while n-type for molybdenum disulfide with conventional noble metal contacts. Therefore, we demonstrate here a one-dimensional heterostructure nanotube of 11-nm-wide, with the coaxial assembly of semiconducting single-walled carbon nanotube, insulating boron nitride nanotube, and semiconducting molybdenum disulfide nanotube which induces a radial semiconductor-insulator-semiconductor heterojunction. When opposite potential polarity was applied on semiconducting single-walled carbon nanotube and molybdenum disulfide nanotube, respectively, the rectifying effect was materialized.

cond-mat.mes-hall↗

arXiv2015

Two-color spectroscopy of UV excited ssDNA complex with a single-wall nanotube probe: Fast nucleobase autoionization mechanism

DNA autoionization is a fundamental process wherein UV-photoexcited nucleobases dissipate energy by charge transfer to the environment without undergoing chemical damage. Here, single-wall carbon nanotubes (SWNT) are explored as a photoluminescent reporter for studying the mechanism and rates of DNA autoionization. Two-color photoluminescence spectroscopy allows separate photoexcitation of the DNA and the SWNTs in the UV and visible range, respectively. A strong SWNT photoluminescence quenching is observed when the UV pump is resonant with the DNA absorption, consistent with charge transfer from the excited states of the DNA to the SWNT. Semiempirical calculations of the DNA-SWNT electronic structure, combined with a Green's function theory for charge transfer, show a 20 fs autoionization rate, dominated by the hole transfer. Rate-equation analysis of the spectroscopy data confirms that the quenching rate is limited by the thermalization of the free charge carriers transferred to the nanotube reservoir. The developed approach has a great potential for monitoring DNA excitation, autoionization, and chemical damage both {\it in vivo} and {\it in vitro}.

cond-mat.mes-hall↗

arXiv2015

Low B Field Magneto-Phonon Resonances in Single-Layer and Bilayer Graphene

Many-body effects resulting from strong electron-electron and electron-phonon interactions play a significant role in graphene physics. We report on their manifestation in low B field magneto-phonon resonances in high quality exfoliated single-layer and bilayer graphene encapsulated in hexagonal boron nitride. These resonances allow us to extract characteristic effective Fermi velocities, as high as $1.20 \times 10^6$ m/s, for the observed "dressed" Landau level transitions, as well as the broadening of the resonances, which increases with Landau level index.

cond-mat.mes-hall↗

arXiv2015

Raman spectroscopy as probe of nanometer-scale strain variations in graphene

Confocal Raman spectroscopy is a versatile, non-invasive investigation tool and a major workhorse for graphene characterization. Here we show that the experimentally observed Raman 2D line width is a measure of nanometer-scale strain variations in graphene. By investigating the relation between the G and 2D line at high magnetic fields we find that the 2D line width contains valuable information on nanometer-scale flatness and lattice deformations of graphene, making it a good quantity for classifying the structural quality of graphene even at zero magnetic field.

cond-mat.mes-hall↗

arXiv2010

Theoretical and Experimental Studies of Schottky Diodes That Use Aligned Arrays of Single Walled Carbon Nanotubes

We present theoretical and experimental studies of Schottky diodes that use aligned arrays of single walled carbon nanotubes. A simple physical model, taking into account the basic physics of current rectification, can adequately describe the single-tube and array devices. We show that for as grown array diodes, the rectification ratio, defined by the maximum-to-minimum-current-ratio, is low due to the presence of m-SWNT shunts. These tubes can be eliminated in a single voltage sweep resulting in a high rectification array device. Further analysis also shows that the channel resistance, and not the intrinsic nanotube diode properties, limits the rectification in devices with channel length up to ten micrometer.

cond-mat.mes-hall↗

arXiv2010

Scattering of the near field of an electric dipole by a single-wall carbon nanotube

The use of carbon nanotubes as optical probes for scanning near-field optical microscopy requires an understanding of their near-field response. As a first step in this direction, we investigated the lateral resolution of a carbon nanotube tip with respect to an ideal electric dipole representing an elementary detected object. A Fredholm integral equation of the first kind was formulated for the surface electric current density induced on a single-wall carbon nanotube (SWNT) by the electromagnetic field due to an arbitrarily oriented electric dipole located outside the SWNT. The response of the SWNT to the near field of a source electric dipole can be classified into two types, because surface-wave propagation occurs with (i) low damping at frequencies less than ~ 200-250 THz and (ii) high damping at higher frequencies. The interaction between the source electric dipole and the SWNT depends critically on their relative location and relative orientation, and shows evidence of the geometrical resonances of the SWNT in the low-frequency regime. These resonances disappear when the relaxation time of the SWNT is sufficiently low. The far-field radiation intensity is much higher when the source electric dipole is placed near an edge of SWNT than at the centroid of the SWNT. The use of an SWNT tip in scattering-type scanning near-field optical microscopy can deliver a resolution less than ~ 20 nm. Moreover, our study shows that the relative orientation and distance between the SWNT and the nanoscale dipole source can be detected.

cond-mat.mes-hall↗

arXiv2009

An essential mechanism of heat dissipation in carbon nanotube electronics

Excess heat generated in integrated circuits is one of the major problems of modern electronics. Surface phonon-polariton scattering is shown here to be the dominant mechanism for hot charge carrier energy dissipation in a nanotube device fabricated on a polar substrate, such as $SiO_2$. Using microscopic quantum models the Joule losses were calculated for the various energy dissipation channels as a function of the electric field, doping, and temperature. The polariton mechanism must be taken into account to obtain an accurate estimate of the effective thermal coupling of the non-suspended nanotube to the substrate, which was found to be 0.1-0.2 W/m.K even in the absence of the bare phononic thermal coupling.

cond-mat.mtrl-sci↗

arXiv2008

Optical Identification of a DNA-Wrapped Carbon Nanotube: Signs of Helically Broken Symmetry

High intrinsic mobility and small, biologically-compatible size make single-walled carbon nanotubes (SWNTs) in demand for the next generation of electronic devices. Further, the wide range of available bandgaps due to changes in diameter and symmetry give SWNTs greater versatility than traditional semiconductors. Single-stranded DNA has been employed to make these desirable properties accessible for large scale fabrication of devices. Because single-stranded DNA can helically wrap a SWNT, forming a stable hybrid structure, DNA/polymer wrapping has been used to disperse bundles of intrinsically hydrophobic SWNTs into individual tubes in aqueous solution. The ability to isolate individual tubes, make them soluble, and separate them according to symmetry would enable fabrication of SWNT optoelectronic devices that benefit from the unique electronic properties of specific nanotube structures. Envisioning optoelectronic applications of nanotubes, we investigate whether the optical properties of DNA-wrapped SWNT materials are different than those of pristine SWNTs. Our previous work found that bandstructures of DNA-SWNTs were indeed affected by the charged wrap. That is, the direct optical bandgap, $E_{11}$, decreases, but changes are fairly small. This is consistent with the available experimental data in standard experimental geometry in which incident light is polarized along the SWNT axis. Here we consider optical absorption of light with perpendicular (or circular) polarization with respect to the tube axis, which has been measured experimentally for SWNTs dispersed using a surfactant. In this geometry we find qualitative changes in the absorption spectra of SWNTs upon hybridization with DNA, including strong optical circular dichroism in non-chiral SWNTs.

cond-mat.mtrl-sci↗

arXiv2006

Gate Capacitance Coupling of Singled-walled Carbon Nanotube Thin-film Transistors

The electrostatic coupling between singled-walled carbon nanotube (SWNT) networks/arrays and planar gate electrodes in thin-film transistors (TFTs) is analyzed both in the quantum limit with an analytical model and in the classical limit with finite-element modeling. The computed capacitance depends on both the thickness of the gate dielectric and the average spacing between the tubes, with some dependence on the distribution of these spacings. Experiments on transistors that use sub-monolayer, random networks of SWNTs verify certain aspects of these calculations. The results are important for the development of networks or arrays of nanotubes as active layers in TFTs and other electronic devices.

cond-mat.mtrl-sci↗

arXiv2005

Metal-Semiconductor Transition in Armchair Carbon Nanotubes by Symmetry Breaking

The electronic band structure of armchair carbon nanotubes may be considerably modified by potentials with angular dependence. Different angular modes V_q ~ cos(q*theta) have been studied within a tight-binding scheme. Using symmetry arguments, we demonstrate a bandgap opening in these metallic nanotubes when certain selection rules are satisfied for both potential and nanotube structure. We estimate the bandgap opening as a function of both the external potential strength and the nanotube radius and suggest an effective mechanism of metal-semiconductor transition by combination of different forms of perturbations.

cond-mat.mtrl-sci↗

arXiv2005

Metal-Semiconductor Transition and Fermi Velocity Renormalization in Metallic Carbon Nanotubes

Angular perturbations modify the band structure of armchair (and other metallic) carbon nanotubes by breaking the tube symmetry and may induce a metal-semiconductor transition when certain selection rules are satisfied. The symmetry requirements apply for both the nanotube and the perturbation potential, as studied within a nonorthogonal $π$-orbital tight-binding method. Perturbations of two categories are considered: an on-site electrostatic potential and a lattice deformation which changes the off-site hopping integrals. Armchair nanotubes are proved to be robust against the metal-semiconductor transition in second-order perturbation theory due to their high symmetry, but can develop a nonzero gap by extending the perturbation series to higher orders or by combining potentials of different types. An assumption of orthogonality between $π$ orbitals is shown to lead to an accidental electron-hole symmetry and extra selection rules that are weakly broken in the nonorthogonal theory. These results are further generalized to metallic nanotubes of arbitrary chirality.

cond-mat.mes-hall↗

arXiv2004

Transport in Nanotubes: Effect of Remote Impurity Scattering

Theory of the remote Coulomb impurity scattering in single--wall carbon nanotubes is developed within one--electron approximation. Boltzmann equation is solved within drift--diffusion model to obtain the tube conductivity. The conductivity depends on the type of the nanotube bandstructure (metal or semiconductor) and on the electron Fermi level. We found exponential dependence of the conductivity on the Fermi energy due to the Coulomb scattering rate has a strong dependence on the momentum transfer. We calculate intra-- and inter--subband scattering rates and present general expressions for the conductivity. Numerical results, as well as obtained analytical expressions, show that the degenerately doped semiconductor tubes may have very high mobility unless the doping level becomes too high and the inter--subband transitions impede the electron transport.

cond-mat.mtrl-sci↗