Publications

Limits on Charge Carrier Mobility in Suspended Graphene due to Flexural Phonons

The temperature dependence of the mobility in suspended graphene samples is investigated. In clean samples, flexural phonons become the leading scattering mechanism at temperature $T \gtrsim 10\,\,$K, and the resistivity increases quadratically with $T$. Flexural phonons limit the intrinsic mobility down to a few $\text{m}^2/\text{Vs}$ at room $T$. Their effect can be eliminated by applying strain or placing graphene on a substrate.

Selenolaurite, RuSe₂, a new mineral from the Ingul gold placer, South Urals, Russia

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Mineral Forms of Tungsten at the Porokhovskoe and Yugo-Konevskoe Deposits (Southern Urals)

Ore hand specimens and technological ore samples from the greisen-type Porokhovskoe and Yugo-Konevskoe tungsten deposits in the Southern Urals were studied. The major tungsten minerals in primary ores of both deposits are hübnerite and scheelite. Secondary and accessory minerals are pyrite, chalcopyrite and molybdenite; rare minerals are sphalerite, galena, bismuthinite, aikinite, unidentified Bi chalcogenides and sulfosalts, magnetite, rutile, ilmenite, titanite, and columbite. Veins are mainly composed by quartz–muscovite aggregate with secondary (calcite, dolomite, and fluorite), minor (chlorite and amphibole), and accessory (zircon, apatite, and uraninite). No distinct zonation in the distribution pattern of wolframite with varying Fe content relative to the Yugo-Konevsky granite pluton is identified. However, wolframites from the Northern area of the Porokhovskoe deposit are enriched in Fe compared to those from the Central area and Yugo-Konevskoe deposit. Along with through vein wolframite and scheelite, the oxidized ores also contain Fe and Mn oxyhydroxides, malachite, pyromorphite, and bromargyrite. Tungsten enters the composition of Mn and Fe oxyhydroxides, which replace wolframite and less often sulfides. The WO3 content in pseudomorphs of Mn and Fe oxyhydroxides after hübnerite reaches 18 wt %. Single grains of stolzite and russellite are found. According to the results of phase chemical analysis of technological samples, the amount of tungstite in oxidized ores is minor. Due to this, all ores of both deposits can be ascribed to primary technological type.

Photogating-assisted tunneling boosts the responsivity and speed of heterogeneous WSe2/Ta2NiSe5 photodetectors

Photogating effect is the dominant mechanism of most high-responsivity two-dimensional (2D) material photodetectors. However, the ultrahigh responsivities in those devices are intrinsically at the cost of very slow response speed. In this work, we report a WSe

Constructing custom thermodynamics using deep learning

One of the most exciting applications of artificial intelligence is automated scientific discovery based on previously amassed data, coupled with restrictions provided by known physical principles, including symmetries and conservation laws. Such automated hypothesis creation and verification can assist scientists in studying complex phenomena, where traditional physical intuition may fail. Here we develop a platform based on a generalized Onsager principle to learn macroscopic dynamical descriptions of arbitrary stochastic dissipative systems directly from observations of their microscopic trajectories. Our method simultaneously constructs reduced thermodynamic coordinates and interprets the dynamics on these coordinates. We demonstrate its effectiveness by studying theoretically and validating experimentally the stretching of long polymer chains in an externally applied field. Specifically, we learn three interpretable thermodynamic coordinates and build a dynamical landscape of polymer stretching, including the identification of stable and transition states and the control of the stretching rate. Our general methodology can be used to address a wide range of scientific and technological applications.

All-electrical perpendicular switching of chiral antiferromagnetic order

All-2D Material Inkjet-Printed Capacitors: Toward Fully Printed Integrated Circuits

A well-defined insulating layer is of primary importance in the fabrication of passive (e.g. capacitors) and active (e.g. transistors) components in integrated circuits. One of the most widely known 2-Dimensional (2D) dielectric materials is hexagonal boron nitride (hBN). Solution-based techniques are cost-effective and allow simple methods to be used for device fabrication. In particular, inkjet printing is a low-cost, non-contact approach, which also allows for device design flexibility, produces no material wastage and offers compatibility with almost any surface of interest, including flexible substrates. In this work we use water-based and biocompatible graphene and hBN inks to fabricate all-2D material and inkjet-printed capacitors. We demonstrate an areal capacitance of 2.0 \pm 0.3 nF cm^(-2) for a dielectric thickness of \sim 3 \mu m and negligible leakage currents, averaged across more than 100 devices. This gives rise to a derived dielectric constant of 6.1 \pm 1.7. The inkjet printed hBN dielectric has a breakdown field of 1.9 \pm 0.3 MV cm^(-1). Fully printed capacitors with sub-/mu m hBN layer thicknesses have also been demonstrated. The capacitors are then exploited in two fully printed demonstrators: a resistor-capacitor (RC) low-pass filter and a graphene-based field effect transistor.

Filling-Factor-Dependent Magnetophonon Resonance with Circularly Polarized Phonons in Graphene Revealed by High-Field Magneto-Raman Spectroscopy

We perform polarization-resolved Raman spectroscopy on graphene in magnetic fields up to 45T. This reveals a filling-factor-dependent, multi-component anticrossing structure of the Raman G peak, resulting from magnetophonon resonances between magnetoexcitons and E$_{2g}$ phonons. This is explained with a model of Raman scattering taking into account the effects of spatially inhomogeneous carrier densities and strain. Random fluctuations of strain-induced pseudo-magnetic fields lead to increased scattering intensity inside the anti-crossing gap, consistent with the experiment.

Antropogenic supergenic mineral of verhne arshinskoe lead zinc deposit (Bashkortostan)

No abstract is provided for this article.

Large-Scale Self-Assembly of anisotropic graphene oxide films via blade Coating: Sustainable design and Stimuli-Responsive performance for biomimicry

Sustainable structural design, utilizing material to imitate natural biological systems, presents both promise and challenges. By avoiding interfacial problems encountered in composite counterparts, such designs offer self-adaptive materials for smart housing and green architecture, etc. In this study, we demonstrate the feasibility of large-scale self-assembly of graphene oxide (GO) flakes into anisotropic films through a simple blade coating technique. Through the application of blade coating to a highly concentrated nematic GO suspension, we successfully fabricate GO films with morphological gradient and patterning. Additionally, we propose a statistical analysis method utilizing scanning electron microscopy (SEM) images for the characterization of materials with macroscopic surface morphology. Furthermore, we explore the application of these GO films as low-dimensional soft actuators, revealing their outstanding stimuli-responsive performance and self-adaptation to environment. Such robust and flexible films can be used as integral building elements in the bioinspired design of sustainable smart housing facilitating remote robotization and sensing capabilities.

Magneto-phonon resonance in graphene

No abstract is provided for this article.

Precious metal mineralogy of the Murtykty gold deposit, South Urals

Ore mineralogy of the Murtykty gold deposit is presented in the paper and main attention is paid to the mode of occurrence of precious metals. Ores are pyrite-bearing quartz-chlorite (±sericite, ±carbonate of the dolomite-ankerite series) metasomatites with variable ratios between rock-forming minerals. Pyrite is the major sulfde; sphalerite, galena and chalcopyrite are secondary in abundance. Rare minerals include pyrrhotite, arsenopyrite, altaite, coloradoite, hessite, petzite, calaverite, volynskite, rucklidgeite, and native gold. The Ag content of native gold ranges from 6.11 to 35.32 wt. %. Signifcant amount of Au and Ag occurs in a telluride form: hessite Ag2Te, petzite Ag3AuTe2, calaverite AuTe2, and volynskite AgBiTe2. The refractory features of sulfde ores are caused by diverse modes of occurrences of precious metal.

Multifunctional van der Waals PdSe2 for light detection, guiding and modulation

Modern optoelectronic devices demand materials that can perform multiple, often conflicting functions, such as acting as metals for interconnects, dielectrics for waveguides, and semiconductors for light emission and detection. The integration of these materials is challenging, slowing industry progress and increasing costs. It inspired an intensive search for an optoelectronic response within a single material. Here, we reveal that palladium diselenide (PdSe₂) provides an answer to this quest owing to its band structure. It exhibits a semimetallic band structure with a large bandgap for interband transitions responsible for semiconductor-metallic nature. This duality enables PdSe₂ to function as both a photodetector and a waveguide, integrating two traditionally incompatible responses. As a result, our findings provide a full picture of PdSe₂ optoelectronic properties, paving the way for its use in multifunctional optoelectronic applications.

Imaging of Bernal stacked and misoriented graphene and boron nitride: experiment and simulation

Experimental atomic resolution bright and high angle dark field transmission electron microscopy images of mono- and few-layer graphene and boron nitride, as well as of turbostratic arrangements in both materials, are compared to their simulated counterparts. Changes in the images according to defocus, layer number and accelerating voltage are discussed. It emerges that simulations with realistic microscope parameters accurately depict experimental graphene and boron nitride images and present a reliable tool for their interpretation.

Infrared photodetection in graphene-based heterostructures: bolometric and thermoelectric effects at the tunneling barrier

Graphene/hBN/graphene tunnel devices offer promise as sensitive mid-infrared photodetectors but the microscopic origin underlying the photoresponse in them remains elusive. In this work, we investigated the photocurrent generation in graphene/hBN/graphene tunnel structures with localized defect states under mid-IR illumination. We demonstrate that the photocurrent in these devices is proportional to the second derivative of the tunnel current with respect to the bias voltage, peaking during tunneling through the hBN impurity level. We revealed that the origin of the photocurrent generation lies in the change of the tunneling probability upon radiation-induced electron heating in graphene layers, in agreement with the theoretical model that we developed. Finally, we show that at a finite bias voltage, the photocurrent is proportional to the either of the graphene layers heating under the illumination, while at zero bias, it is proportional to the heating difference. Thus, the photocurrent in such devices can be used for accurate measurements of the electronic temperature providing a convenient alternative to Johnson noise thermometry.

Graphene Based Spin Valve Devices

Graphene is a name given to an atomic layer of carbon atoms densely packed into a benzene-ring structure with a nearest-neighbour distance of ~1.4Aring. This theoretical material is widely used in the description of the crystal structure and properties of graphite, large fullerenes and carbon nanotubes. As a first approximation, graphite is made of graphene layers relatively loosely stacked on top of each other with a fairly large interlayer distance of ~3.4Aring . Carbon nanotubes are usually thought of as graphene layers rolled into hollow cylinders. Graphene films are made by repeated peeling of small (mm-sized) mesas of highly-oriented pyrolytic graphite (HOPG). The exfoliation continues until flakes that are nearly invisible in an optical microscope are obtained. A simple spin valve structure has been fabricated from such films using electron beam lithography. This is based on a symmetrical electrode structure and relies on imperfections in the two ferromagnetic electrodes to give different switching fields for each electrode. Despite this highly non-optimised structure we observed a 10% change in resistance at 300 K as the applied field is swept between +450 G and -450 G. The 10% change in resistance is much larger than can be attributed to MR effects in the individual permalloy electrodes (2.5% maximum), giving confidence that it is due to the spin valve effect with the graphene acting as the non-magnetic conductor. Although spin valve effects have been observed in carbon nanotubes this is the first observation of this effect in planar graphene.

НАБЛЮДЕНИЕ СПИНОВОГО И ДОЛИННОГО РАСЩЕПЛЕНИЯ УРОВНЕЙ ЛАНДАУ ПРИ МАГНИТОТУННЕЛИРОВАНИИ В ГРАФЕН/НИТРИД БОРА/ГРАФЕН СТРУКТУРАХ, "Письма в Журнал экспериментальной и теоретической физики"

Исследовано резонансное магнитотуннелирование в гетероструктурах с однослойными листами гра-фена, разделенными барьером из гексагонального нитрида бора, и двумя затворами в сильном магнитном поле, что позволило наблюдать переходы между расщепленными по спину и долине уровнями Ландау с различными индексами, принадлежащими разным графеновым слоям. Неожиданный рост межслоевой туннельной проводимости для переходов между уровнями Ландау в сильных магнитных полях при повышении температуры оказался необъяснимым в рамках известных теорий.

(Invited) Stationary Phase Coatings for a Microfabricated GC Column Integrated with Low Power Ion Trap Mass Spectrometer for Analysis of Volatile Organic Compounds

Miniature gas chromatography (GC) columns of length 6m were fabricated in silicon using eutectic bonding to achieve a column with improved temperature control. The micro GC column includes an integrated platinum thin film heater and temperature sensors for closed loop temperature programing. In order to achieve low power operation the GC column was mounted inside the vacuum chamber of an ion-trap mass spectrometer. This approach provides much lower power consumption than a laboratory instrument. The ion trap electronics were miniaturized and operate at lower power, to demonstrate a portable instrument able to operate at with less than 25W, including vacuum pumps. This instrument will have a range of applications from environmental monitoring, to food safety and medical diagnostics, including breath analysis. Static coating of the stationary phase in the microfabricated column was carried out by injection using a solvent and extraction at reduced pressure to improve resolution. This paper reports the results of different stationary phases investigated to separate mixtures of volatile organic compounds, specifically OV-1 and OV-215. The properties of the stationary phases where characterized using a novel probe mixture for microcolumn evaluation and six McReynolds probes to identify the Kovats indices and the polarity of the column. The dependence of polarity on the coating technique and temperature of the column during analysis was also investigated. Results are presented with both an FID and ion-trap mass spectrometer to achieve rapid temperature programmed analysis of mixtures of up to 18 organic compounds.