Search query: "Irina V Grigorieva"

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abstract: Research on black phosphorus has been experiencing a renaissance over the last years, after the demonstration that few layer crystals exhibit high carrier mobility and a thickness dependent bandgap. Black phosphorus is also known to be a superconductor under high pressure exceeding 10 GPa. The superconductivity is due to a structural transformation into another allotrope and accompanied by a semiconductor metal transition. No superconductivity could be achieved for black phosphorus in its normal orthorhombic form, despite several reported attempts. Here we describe its intercalation by several alkali metals (Li, K, Rb and Cs) and alkali earth Ca. All the intercalated compounds are found to be superconducting, exhibiting the same (within experimental accuracy) critical temperature of 3.8+ 0.1 K and practically identical characteristics in the superconducting state. Such universal superconductivity, independent of the chemical composition, is highly unusual. We attribute it to intrinsic superconductivity of heavily doped individual phosphorene layers, while the intercalated layers of metal atoms play mostly a role of charge reservoirs.
author_names: R Zhang

John Waters

Andre K Geim

Irina V Grigorieva
title: Intercalant independent transition temperature in superconducting black phosphorus
venue: Nature communications
year: 2017

abstract: Superconducting layered transition metal dichalcogenides (TMDs) stand out among other superconductors due to the tunable nature of the superconducting transition, coexistence with other collective electronic excitations (charge density waves) and strong intrinsic spin orbit coupling. Molybdenum disulfide (MoS2) is the most studied representative of this family of materials, especially since the recent demonstration of the possibility to tune its critical temperature, Tc, by electric field doping. However, just one of its polymorphs, band insulator 2H MoS2, has so far been explored for its potential to host superconductivity. We have investigated the possibility to induce superconductivity in metallic polytypes, 1T and 1T' MoS2, by potassium (K) intercalation. We demonstrate that at doping levels significantly higher than that required to induce superconductivity in 2H MoS2, both 1T and 1T' phases become superconducting with Tc 2.8 and 4.6 K, respectively. Unusually, K intercalation in this case is responsible both for the structural and superconducting phase transitions. By adding new members to the family of superconducting TMDs, our findings open the way to further manipulate and enhance the electronic properties of these technologically important materials.
author_names: Renyan Zhang

I -Ling Tsai

James Chapman

Ekaterina Khestanova

John Waters

Irina V Grigorieva
title: Superconductivity in Potassium Doped Metallic Polymorphs of MoS2.
venue: Nano letters
year: 2016

abstract: Using computer simulation, we have studied the random sequential adsorption of stiff linear segments (needles) onto a square lattice. Each such particle occupies $k$ adjacent lattice sites, thence, it is frequently called a $k$ mer. During deposition, the two mutually perpendicular orientations of the particles are equiprobable, hence, a macroscopically isotropic monolayer is formed. However, this monolayer is locally anisotropic, since the deposited particles tend to form so called `stacks' i.e. domains of particles with the same orientation. Using the `excluded area' concept, we have classified lattice sites into several types and examined how the fraction of each type of lattice site varies as the number of deposited particles increases. The behaviors of these quantities have allowed us to identify the following stages of stack formation (i) the emergence of stack seeds; (ii) the filling of stacks; (iii) densification of the stacks.
author_names: Mikhail Ulyanov

Yuri Yu Tarasevich

Andrei V Eserkepov

Irina V Grigorieva
title: Stack formation during random sequential adsorption of needles onto a square lattice
year: 2020

author_names: Irina V Grigorieva

Aynakul B Tumanova
title: From the conceptual analysis experience: free associative experiment
year: 2019

abstract: Despite graphene's long list of exceptional electronic properties and many theoretical predictions regarding the possibility of superconductivity in graphene, its direct and unambiguous experimental observation has not been achieved. We searched for superconductivity in weakly interacting, metal decorated graphene crystals assembled into so called graphene laminates, consisting of well separated and electronically decoupled graphene crystallites. We report robust superconductivity in all Ca doped graphene laminates. They become superconducting at temperatures (Tc) between 4 and 6 K, with Tc's strongly dependent on the confinement of the Ca layer and the induced charge carrier concentration in graphene. We find that Ca is the only dopant that induces superconductivity in graphene laminates above 1.8 K among several dopants used in our experiments, such as potassium, caesium and lithium. By revealing the tunability of the superconducting response through doping and confinement of the metal layer, our work shows that achieving superconductivity in free standing, metal decorated monolayer graphene is conditional on an optimum confinement of the metal layer and sufficient doping, thereby bringing its experimental realization within grasp.
author_names: James Chapman

Y Su

Christopher A Howard

Dmytro Kundys

Alexander N Grigorenko

Francisco Guinea

Andre K Geim

Irina V Grigorieva

Rahul R Nair
title: Superconductivity in Ca doped graphene laminates
venue: Scientific reports
year: 2016

abstract: Despite being only one atom thick, defect free graphene is considered to be completely impermeable to all gases and liquids 1 10 This conclusion is based on theory 3 8 and supported by experiments 1 9 10 that could not detect gas permeation through micrometre size membranes within a detection limit of 10 5 to 10 6 atoms per second. Here, using small monocrystalline containers tightly sealed with graphene, we show that defect free graphene is impermeable with an accuracy of eight to nine orders of magnitude higher than in the previous experiments. We are capable of discerning (but did not observe) permeation of just a few helium atoms per hour, and this detection limit is also valid for all other gases tested (neon, nitrogen, oxygen, argon, krypton and xenon) except for hydrogen. Hydrogen shows noticeable permeation, even though its molecule is larger than helium and should experience a higher energy barrier. This puzzling observation is attributed to a two stage process that involves dissociation of molecular hydrogen at catalytically active graphene ripples, followed by adsorbed atoms flipping to the other side of the graphene sheet with a relatively low activation energy of about 1.0 electronvolt, a value close to that previously reported for proton transport 11 12 Our work provides a key reference for the impermeability of two dimensional materials and is important from a fundamental perspective and for their potential applications. Graphene is shown to be impermeable to helium and several other gases, except for hydrogen, which is attributed to the strong catalytic activity of ripples in the graphene sheet.
author_names: P Z Sun

Q Yang

Wenjun Kuang

Yury V Stebunov

Wei Xiong

J Yu

Rahul R Nair

Mikhail I Katsnelson

Shengjun Yuan

Irina V Grigorieva

Marcelo Lozada-Hidalgo

F C Wang

Andre K Geim
title: Limits on gas impermeability of graphene
venue: Nature
year: 2020

author_names: Olga Vygovskaya-Kazarina

Nataliya M Shlenskaya

Elena A Golubovskaya

Natalia Mekeko

I G Grigorieva
title: EDUCATIONAL PRINCIPLES IN LANGUAGE LEARNING: TRAINING OF MEDIA TEXT SLANG TRANSLATION
year: 2018

abstract: Raman spectroscopy is an ideal tool for the characterization of strained graphene. Biaxial strain, in particular, allows for more reliable calculation of the Gruneisen parameters than uniaxial strain. However, the application of biaxial strain is rather difficult to achieve experimentally, so all previous studies reported on graphene subjected to relatively small biaxial strains (0.1% 1% in contrast to uniaxial strain above 10% Here, we report a simple fabrication technique to produce pressurized and stable graphene membranes that can support differential pressures up to 14 bar, corresponding to a reversible strain up to ~2% We find that the Gruneisen parameters remain constant even for the largest strains achieved, in agreement with the theoretical predictions. However, for strains above 1% a distinctive broadening of both the G and 2D peaks was observed for biaxial strain. We attribute this to the nanoscale variations of strain in the membrane within an area comparable with the laser spot size.
author_names: Yuyoung Shin

Marcelo Lozada-Hidalgo

J L Sambricio

Irina V Grigorieva

Andre K Geim

Cinzia Casiraghi
title: Raman spectroscopy of highly pressurized graphene membranes
year: 2016

abstract: We report on an extensive investigation to figure out the origin of room temperature ferromagnetism that is commonly observed by SQUID magnetometry in highly oriented pyrolytic graphite (HOPG) Electron backscattering and X ray microanalysis revealed the presence of micron size magnetic clusters (predominantly Fe) that are rare and would be difficult to detect without careful search in a scanning electron microscope in the backscattering mode. The clusters pin to crystal boundaries and their quantities match the amplitude of typical ferromagnetic signals. No ferromagnetic response is detected in samples where we could not find such magnetic inclusions. Our experiments show that the frequently reported ferromagnetism in pristine HOPG is most likely to originate from contamination with Fe rich inclusions introduced presumably during crystal growth.
author_names: Margherita Sepioni

Rahul R Nair

I -Ling Tsai

Andre K Geim

Irina V Grigorieva
title: Revealing common artifacts due to ferromagnetic inclusions in highly oriented pyrolytic graphite
year: 2012

abstract: Trapped substances between a 2D crystal, such as graphene, and an atomically flat substrate, for example, hexagonal boron nitride, give rise to the formation of bubbles. We show that the size, shape and internal pressure inside these bubbles are determined by the competition between van der Waals attraction of a 2D crystal to the substrate and the elastic energy needed to deform the atomically thin layer. This presents opportunities to use bubbles to study the elasticity of 2D materials as well as the conditions of confinement, yet none of these have been explored so far, either theoretically or experimentally. We have created a variety of bubbles formed by monolayers of graphene, hBN and MoS2 mechanically exfoliated onto hBN, graphite and MoS2 substrates. Their shapes, analyzed using atomic force microscopy, are found to exhibit universal scaling with well defined aspect ratios, in agreement with theoretical analysis based on general properties of membranes. We also measured the pressure induced by the confinement, which increased with decreasing bubble's size and reached tens on MPa inside submicron bubbles. This agrees with our theory estimates and suggests that for bubbles with radii 10 nm hydrostatic pressures can reach close to 1 GPa, which may modify the properties of a trapped material.
author_names: Ekaterina Khestanova

Francisco Guinea

Laura Fumagalli

Andre K Geim

Irina V Grigorieva
title: Graphene bubbles on a substrate Universal shape and van der Waals pressure
year: 2016