Evgeni S. Penev
Rice University
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Publication
Featured researches published by Evgeni S. Penev.
Nano Letters | 2012
Evgeni S. Penev; Somnath Bhowmick; Arta Sadrzadeh; Boris I. Yakobson
The structural stability and diversity of elemental boron layers are evaluated by treating them as pseudoalloy B(1-x)[hexagon](x), where [hexagon] is a vacancy in the close-packed triangular B lattice. This approach allows for an elegant use of the cluster expansion method in combination with first-principles density-functional theory calculations, leading to a thorough exploration of the configurational space. A finite range of compositions x is found where the ground-state energy is essentially independent of x, uncovering a variety of stable B-layer phases (all metallic) and suggesting polymorphism, in stark contrast to graphene or hexagonal BN.
Angewandte Chemie | 2013
Yuanyue Liu; Evgeni S. Penev; Boris I. Yakobson
Boron synthesis, in theory: Although two-dimensional boron sheets have attracted considerable interest because of their theoretically predicted properties, synthesis of such sheets remains a challenge. The feasibility of different synthetic methods for two-dimensional boron sheets was assessed using first-principles calculations, possibly paving the way towards its application in nanoelectronics.
Nano Letters | 2014
Yuanyue Liu; Fangbo Xu; Ziang Zhang; Evgeni S. Penev; Boris I. Yakobson
The deep gap states created by defects in semiconductors typically deteriorate the performance of (opto)electronic devices. This has limited the applications of two-dimensional (2D) metal dichalcogenides (MX2) and underscored the need for a new 2D semiconductor without defect-induced deep gap states. In this work, we demonstrate that a 2D mono-elemental semiconductor is a promising candidate. This is exemplified by first-principles study of 2D phosphorus (P), a recently fabricated high-mobility semiconductor. Most of the defects, including intrinsic point defects and grain boundaries, are electronically inactive, thanks to the homoelemental bonding, which is not preferred in heteroelemental system such as MX2. Unlike MX2, the edges of which create deep gap states and cannot be eliminated by passivation, the edge states of 2D P can be removed from the band gap by hydrogen termination. We further find that both the type and the concentration of charge carriers in 2D P can be tuned by doping with foreign atoms. Our work sheds light on the role of defects in the electronic structure of materials.
ACS Nano | 2010
Abhishek K. Singh; Evgeni S. Penev; Boris I. Yakobson
Complementary electronic properties and a tendency to form sharp graphene-graphane interfaces open tantalizing possibilities for two-dimensional nanoelectronics. First-principles density functional and tight-binding calculations show that graphane can serve as natural host for graphene quantum dots, clusters of vacancies in the hydrogen sublattice. Their size n, shape, and stability are governed by the aromaticity and interfaces, resulting in formation energies approximately 1/ radicaln eV/atom and preference to hexagonal clusters congruent with lattice hexagons (i.e., with armchair edge). Clusters exhibit large gaps approximately 15/ radicaln eV with size dependence typical for confined Dirac fermions.
Nano Letters | 2016
Evgeni S. Penev; Alex Kutana; Boris I. Yakobson
Two-dimensional boron is expected to exhibit various structural polymorphs, all being metallic. Additionally, its small atomic mass suggests strong electron-phonon coupling, which in turn can enable superconducting behavior. Here we perform first-principles analysis of electronic structure, phonon spectra, and electron-phonon coupling of selected 2D boron polymorphs and show that the most stable structures predicted to feasibly form on a metal substrate should also exhibit intrinsic phonon-mediated superconductivity, with estimated critical temperature in the range of Tc ≈ 10-20 K.
Nature Communications | 2014
Vasilii I. Artyukhov; Evgeni S. Penev; Boris I. Yakobson
Carbon nanotubes hold enormous technological promise. It can only be harnessed if one controls their chirality, the feature of the tubular carbon topology that governs all the properties of nanotubes-electronic, optical, mechanical. Experiments in catalytic growth over the last decade have repeatedly revealed a puzzling strong preference towards minimally chiral (near-armchair) tubes, challenging any existing hypotheses and making chirality control ever more tantalizing, yet leaving its understanding elusive. Here we combine the nanotube/catalyst interface thermodynamics with the kinetic growth theory to show that the unusual near-armchair peaks emerge from the two antagonistic trends at the interface: energetic preference towards achiral versus the faster growth kinetics of chiral nanotubes. This narrow distribution is inherently related to the peaked behaviour of a simple function, xe(-x).
Nature Chemistry | 2016
Zhuhua Zhang; Evgeni S. Penev; Boris I. Yakobson
Early theories suggested the possibility of atomically thin boron layers, but electron-deficient boron favours multicentre bonds and assembles into various polymorphs, making the synthesis of such layers challenging. Now, in two independent experiments, the deposition of atomic boron has offered this long-sought material on a silver platter.
Advanced Functional Materials | 2017
Zhuhua Zhang; Yang Yang; Evgeni S. Penev; Boris I. Yakobson
We study the mechanical properties of two-dimensional (2D) boron, borophenes, by first-principles calculations. The recently synthesized borophene with 1/6 concentration of hollow hexagons (HH) is shown to have in-plane modulus C up to 210 N/m and bending stiffness as low as D = 0.39 eV. Thus, its Foppl-von Karman number per unit area, defined as C/D, reaches 568 nm-2, over twofold higher than graphenes value, establishing the borophene as one of the most flexible materials. Yet, the borophene has a specific modulus of 346 m2/s2 and ideal strengths of 16 N/m, rivaling those (453 m2/s2 and 34 N/m) of graphene. In particular, its structural fluxionality enabled by delocalized multi-center chemical bonding favors structural phase transitions under tension, which result in exceptionally small breaking strains yet highly ductile breaking behavior. These mechanical properties can be further tailored by varying the HH concentration, and the boron sheet without HHs can even be stiffer than graphene against tension. The record high flexibility combined with excellent elasticity in boron sheets can be utilized for designing composites and flexible systems.
ACS Nano | 2011
Elena Pigos; Evgeni S. Penev; Morgana A. Ribas; Renu Sharma; Boris I. Yakobson; Avetik R. Harutyunyan
In situ observation of the carbon nanotube nucleation process accompanied by dynamic reconstruction of the catalyst particle morphology is considered within a thermodynamic approach. It reveals the driving force for the detachment of the sp(2)-carbon cap, so-called lift-off-a crucial event in nanotube growth. A continuum model and detailed atomistic calculations identify the critical factors in the lift-off process: (i) catalyst surface energy, affected by the chemisorbed carbon atoms at the exterior surface of the catalyst, exposed to the carbon feedstock; and (ii) the emergence of a pristine, high-energy facet under the sp(2)-carbon dome. This further allows one to evaluate the range of carbon feedstock chemical potential, where the lift-off process occurs, to be followed by emergence of single-walled nanotube, and provides insights into observed catalyst morphology oscillations leading to formation of multiwalled carbon nanotubes.
Advanced Materials | 2012
Evgeni S. Penev; Vasilii I. Artyukhov; Feng Ding; Boris I. Yakobson
Recent research progress in nanostructured carbon has built upon and yet advanced far from the studies of more conventional carbon forms such as diamond, graphite, and perhaps coals. To some extent, the great attention to nano-carbons has been ignited by the discovery of the structurally least obvious, counterintuitive, small strained fullerene cages. Carbon nanotubes, discovered soon thereafter, and recently, the great interest in graphene, ignited by its extraordinary physics, are all interconnected in a blend of cross-fertilizing fields. Here we review the theoretical and computational models development in our group at Rice University, towards understanding the key structures and behaviors in the immense diversity of carbon allotropes. Our particular emphasis is on the role of certain transcending concepts (like elastic instabilities, dislocations, edges, etc.) which serve so well across the scales and for chemically various compositions.