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Computational Studies of 2D Materials: Application to Energy Storage and Electron Transport in Nanoscale Devices
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, Materials Theory.
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The field of two-dimensional (2D) layered materials provides a new platform for studying diverse physical phenomena that are scientifically interesting and relevant for technological applications. Novel applications in electronics and energy storage harness the unique electronic, optical, and mechanical properties of 2D materials for design of crucial components. Atomically thin, with large surface to volume ratio, these materials are attractive for broad applications for hydrogen storage, sensing, batteries and photo-catalysis. Theoretical predictions from atomically resolved computational simulations of 2D materials play a pivotal role in designing and advancing these developments.

The central topic of this thesis is 2D materials studied using density functional theory and non-equilibrium Green’s function. The electronic structure and transport properties are discussed for several synthesized and predicted 2D materials, with diverse potential applications in nanoscale electronic devices, gas sensing, and electrodes for rechargeable batteries. Lateral and vertical heterostructures have been studied for applications in nanoscale devices such as graphene/hBN heterostructure nanogap for a potential DNA sequencing device, while in case of twisted bilayer black phosphorus nanojunction, where electronic and transport properties have been explored for diode-like characteristics device. We also have addressed the structural, electronic and transport properties of the recently synthesized polymorphs of 2D borons known as borophenes. We have explored the conventional methods of tuning the material’s properties such as strain in borophene and substitutional doping in black phosphorus with the further investigation of their gas sensing application.

A significant portion of this thesis is also dedicated to the energy storage applications of different 2D materials. Energy storage technologies arise with vital importance in providing effective ways to transport and commercialize the produced energy, aiming at rechargeable batteries with high energy and power density. In this context, first-principles simulations have been applied together with other theoretical tools to evaluate structural properties, ion intercalation kinetics, specific capacity and open circuit voltage of selected 2D materials at the atomic level. The simulation study supports the understanding while improving the properties of the materials to increase their efficiency in battery operation.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2019. , p. 101
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1761
Keywords [en]
Density functional theory, Non-equilibrium Green's function, 2D materials, Energy storage, Electron transport
National Category
Condensed Matter Physics Atom and Molecular Physics and Optics
Identifiers
URN: urn:nbn:se:uu:diva-369471ISBN: 978-91-513-0547-9 (print)OAI: oai:DiVA.org:uu-369471DiVA, id: diva2:1275373
Public defence
2019-03-01, 80101, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 13:00 (English)
Opponent
Supervisors
Available from: 2019-01-29 Created: 2019-01-05 Last updated: 2019-02-18
List of papers
1. Prospects of Graphene-hBN Heterostructure Nanogap for DNA Sequencing
Open this publication in new window or tab >>Prospects of Graphene-hBN Heterostructure Nanogap for DNA Sequencing
2017 (English)In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 9, no 46, p. 39945-39952Article in journal (Refereed) Published
Abstract [en]

Recent advances in solid-state nano-device-based DNA sequencing are at the helm of the development of a new paradigm, commonly referred to as personalized medicines. Paying heed to a timely need for standardizing robust nanodevices for cheap, fast, and scalable DNA detection, in this article, the nanogap formed by the lateral heterostructure of graphene and hexagonal boron nitride (hBN) is explored as a potential architecture. These heterostructures have been realized experimentally, and our study boasts the idea that the passivation of the edge of the graphene electrode with hBN will solve many of practical problems, such as high reactivity of the graphene edge and difficulty in controlled engineering of the graphene edge structure, while retaining the nanogap setup as a useful nanodevice for sensing applications. Employing first-principle density-functional-theory-based nonequilibrium Greens function methods, we identify that the DNA building blocks, nucleobases, uniquely couple with the states of the nanogap, and the resulting induced states can be attributed as leaving a fingerprint of the DNA sequence in the computed current-voltage (I-V) characteristic. Two bias windows are put forward: lower (1-1.2 V) and higher (2.7-3 V), where unique identification of all four bases is possible from the current traces, although higher sensitivity is obtained at the higher voltage window. Our study can be a practical guide for experimentalists toward development of a nanodevice DNA sensor based on graphene-hBN heterostructures.

Keywords
DNA sequencing, graphene-hBN heterostructure, nonequilibrium Green's function, density functional theory, I-V characteristics
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-343317 (URN)10.1021/acsami.7b06827 (DOI)000416614600012 ()
Funder
Swedish Research CouncilStandUpCarl Tryggers foundation
Available from: 2018-03-13 Created: 2018-03-13 Last updated: 2019-01-05Bibliographically approved
2. Rectifying properties in 90º rotated bilayer black phosphorus nanojunction: A first principle study
Open this publication in new window or tab >>Rectifying properties in 90º rotated bilayer black phosphorus nanojunction: A first principle study
(English)Manuscript (preprint) (Other academic)
National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-369469 (URN)
Available from: 2018-12-13 Created: 2018-12-13 Last updated: 2019-01-05
3. Strain controlled electronic and transport anisotropies in two-dimensional borophene sheets
Open this publication in new window or tab >>Strain controlled electronic and transport anisotropies in two-dimensional borophene sheets
2018 (English)In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 20, no 35, p. 22952-22960Article in journal (Refereed) Published
Abstract [en]

Two recent reports on realization of an elemental 2D analogue of graphene:borophene (Science, 2015, 350, 1513-1516; Nat. Chem., 2016, 8, 563-568) focus on the inherent anisotropy and directional dependence of the electronic properties of borophene polymorphs. Achieving stable 2D borophene structures may lead to some degree of strain in the system because of the substrate-lattice mismatch. We use first principles density functional theory (DFT) calculations to study the structural, electronic and transport properties of (12) and -borophene polymorphs. We verified the directional dependency and found the tunable anisotropic behavior of the transport properties in these two polymorphs. We find that strain as low as 6% brings remarkable changes in the properties of these two structures. We further investigate current-voltage (I-V) characteristics in the low bias regime after applying a strain to see how the anisotropy of the current is affected. Such observations like the sizeable tuning of transport and I-V characteristics at the expense of minimal strain suggest the suitability of 2D borophene for futuristic device applications.

Place, publisher, year, edition, pages
Royal Society of Chemistry, 2018
National Category
Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-363428 (URN)10.1039/c8cp03815e (DOI)000445220500055 ()30156222 (PubMedID)
Funder
Swedish Research CouncilSwedish National Infrastructure for Computing (SNIC), SNIC2017-11-28 SNIC2017-5-8 SNIC2017-1-237
Available from: 2018-10-18 Created: 2018-10-18 Last updated: 2019-01-05Bibliographically approved
4. Toward the Realization of 2D Borophene Based Gas Sensor
Open this publication in new window or tab >>Toward the Realization of 2D Borophene Based Gas Sensor
Show others...
2017 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 121, no 48, p. 26869-26876Article in journal (Refereed) Published
Abstract [en]

To the league of rapidly expanding 2D materials, borophene is a recent addition. Herein, a combination of ab initio density functional theory (DFT) and nonequilibrium Green's function (NEGF) based methods is used to estimate the prospects of this promising elemental 2D material for gas sensing applications. We note that the binding of target gas molecules such as CO, NO, NO2, NH3, and CO2 is quite strong on the borophene surface. Interestingly, our computed binding energies are far stronger than several other reported 2D materials like graphene, MoS2, and phosphorene. Further rationalization of stronger binding is made with the help of charge transfer analysis. The sensitivity of the borophene for these gases is also interpreted in terms of computing the vibrational spectra of the adsorbed gases on top of borophene, which show dramatic shift from their gas phase reference values. The metallic nature of borophene enables us to devise a setup considering the same substrate as electrodes. From the computation of the transmission function of system (gas + borophene), appreciable changes in the transmission functions are noted compared to pristine borophene surface. The measurements of current-voltage (I-V) characteristics unambiguously demonstrate the presence and absence of gas molecules (acting as ON and OFF states), strengthening the plausibility of a borophene based gas sensing device. As we extol the extraordinary sensitivity of borophene, we assert that this elemental 2D material is likely to attract subsequent interest.

Place, publisher, year, edition, pages
AMER CHEMICAL SOC, 2017
National Category
Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-340255 (URN)10.1021/acs.jpcc.7b09552 (DOI)000417671500032 ()
Funder
Swedish National Infrastructure for Computing (SNIC)Swedish Research CouncilCarl Tryggers foundation StandUp
Available from: 2018-01-30 Created: 2018-01-30 Last updated: 2019-04-13Bibliographically approved
5. Ultrahigh-sensitive gas sensors based on doped phosphorene: A First-principles investigation
Open this publication in new window or tab >>Ultrahigh-sensitive gas sensors based on doped phosphorene: A First-principles investigation
Show others...
2019 (English)In: Applied Surface Science, ISSN 0169-4332, E-ISSN 1873-5584, Vol. 497, article id UNSP 143660Article in journal (Other academic) Published
Abstract [en]

Recent significant advancements have been made in demonstrating the usage of phosphorene to detect the presence of gases leading to a new breed of gas sensor device. Based on pristine phosphorene, the devices can detect a small concentration of adsorbed molecules with high sensitivity at room temperature. In this work, we propose doping silicon and sulfur impurity atoms into phosphorene to drastically improve its gas sensing performance. We use a combination of density functional theory and non-equilibrium Green's function method to evaluate the sensitivity and selectivity of doped phosphorene nanosensors for four gases (NO, NO2, NH3, and CO). Both devices demonstrate a prominent distinction in conductance when the gas molecules are exposed to the sensor surface. We suggest the doped phosphorene may present advantages over the device based purely on phosphorene due to the ability to discriminate different gases controlled by types of dopants.

National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-372109 (URN)10.1016/j.apsusc.2019.143660 (DOI)000487849800050 ()
Available from: 2019-01-05 Created: 2019-01-05 Last updated: 2019-10-25Bibliographically approved
6. The Curious Case of Two Dimensional Si2BN: A High-capacity Battery Anode Material
Open this publication in new window or tab >>The Curious Case of Two Dimensional Si2BN: A High-capacity Battery Anode Material
2017 (English)In: Nano Energy, ISSN 2211-2855, E-ISSN 2211-3282, Vol. 41, p. 251-260Article in journal (Refereed) Published
Abstract [en]

The ubiquity of silicon in the semiconductor industry and its unique charge transport features has consistently fueled interest in this element and recent realization 2D silicene is a new feather in its cap. In what could be considered as opening up the Pandora's box with many possible virtues, buckled silicene, planar graphene and a host of other newly discovered 2D materials have redefined a whole new paradigm of research. To this end, the quest for new 2D materials and finding potential applications, particularly to the realm of energy storage, is a curiosity driven task. From first principle density functional theory studies, a newly reported graphene like 2D material Si2BN is investigated as a probable anode material for Li and Na ion batteries. In contrast to pristine silicene, which is inherently buckled, the material Si2BN is planar. However, an interesting transition from planar to buckled structure takes place upon subsequent adsorption of Li and Na ions. Concomitantly, this transition is associated with superior specific capacity (1158.5 and 993.0 mA h/g respectively for Li and Na) which is significantly higher than several other 2D analogues. Furthermore, the substrate Si2BN regains the planar structure on subsequent desorption of ions and stability of the material remains intact, as evidenced from ab initio molecular dynamics simulations. As we delve deep into the electronic structure and compute the diffusion pathways and barriers, it is observed that the ionic diffusion is very fast with significantly lesser barrier heights, particularly for Na-ion. These findings suggest that for the 2D Si2BN, there is no diminution in order to be a potential anode material for Li and Na ion batteries.

National Category
Nano Technology
Identifiers
urn:nbn:se:uu:diva-330765 (URN)10.1016/j.nanoen.2017.09.026 (DOI)000415302600027 ()
Funder
StandUpSwedish Research CouncilCarl Tryggers foundation Swedish National Infrastructure for Computing (SNIC), SNIC-2017-11-28 SNIC-2017-1-237
Available from: 2017-10-03 Created: 2017-10-03 Last updated: 2019-01-05Bibliographically approved
7. Borophane as a Benchmate of Graphene: A Potential 2D Material for Anode of Li and Na-Ion Batteries
Open this publication in new window or tab >>Borophane as a Benchmate of Graphene: A Potential 2D Material for Anode of Li and Na-Ion Batteries
2017 (English)In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 9, no 19, p. 16148-16158Article in journal (Refereed) Published
Abstract [en]

Borophene, single atomic-layer sheet of boron (Science 2015, 350, 1513), is a rather new entrant into the burgeoning class of 2D materials. Borophene exhibits anisotropic metallic properties whereas its hydrogenated counterpart borophane is reported to be a gapless Dirac material lying on the same bench with the celebrated graphene. Interestingly, this transition of borophane also rendered stability to it considering the fact that borophene was synthesized under ultrahigh vacuum conditions on a metallic (Ag) substrate. On the basis of first-principles density functional theory computations, we have investigated the possibilities of borophane as a potential Li/Na-ion battery anode material. We obtained a binding energy of -2.58 (-1.08 eV) eV for Li (Na)-adatom on borophane and Bader charge analysis revealed that Li(Na) atom exists in Li+(Na+) state. Further, on binding with Li/Na, borophane exhibited metallic properties as evidenced by the electronic band structure. We found that diffusion pathways for Li/Na on the borophane surface are anisotropic with x direction being the favorable one with a barrier of 0.27 and 0.09 eV, respectively. While assessing the Li-ion anode performance, we estimated that the maximum Li content is Li0.445B2H2, which gives rises to a material with a maximum theoretical specific capacity of 504 mAh/g together with an average voltage of 0.43 V versus Li/Li+. Likewise, for Na-ion the maximum theoretical capacity and average voltage were estimated to be 504 mAh/g and 0.03 V versus Na/Na+, respectively. These findings unambiguously suggest that borophane can be a potential addition to the map of Li and Na-ion anode materials and can rival some of the recently reported 2D materials including graphene.

Place, publisher, year, edition, pages
AMER CHEMICAL SOC, 2017
Keywords
borophene, borophane, Dirac material, Li-ion battery, Na-ion battery, Li/Na-diffusion
National Category
Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-327151 (URN)10.1021/acsami.7b01421 (DOI)000401782500026 ()28443653 (PubMedID)
Funder
Swedish Research CouncilStandUpCarl Tryggers foundation
Available from: 2017-08-25 Created: 2017-08-25 Last updated: 2019-01-05Bibliographically approved
8. Borophene's tryst with stability: exploring 2D hydrogen boride as an electrode for rechargeable batteries
Open this publication in new window or tab >>Borophene's tryst with stability: exploring 2D hydrogen boride as an electrode for rechargeable batteries
2018 (English)In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 20, no 34, p. 22008-22016Article in journal (Refereed) Published
Abstract [en]

Graphene's emergence can be viewed as a positive upheaval in 2D materials research. Along the same line, the realization of a related elemental 2D material, borophene, is another breakthrough. To circumvent the stability issues of borophene, which is reported to have been synthesized on metallic substrates under extreme conditions, hydrogenation of borophene (otherwise called as borophane or hydrogen boride or boron hydride) has been a plausible solution, but only proposed computationally. A recent report (H. Nishino, T. Fujita, N. T. Cuong, S. Tominaka, M. Miyauchi, S. Iimura, A. Hirata, N. Umezawa, S. Okada, E. Nishibori, A. Fujino, T. Fujimori, S. Ito, J. Nakamura, H. Hosono and T. Kondo, J. Am. Chem. Soc., 2017, 139(39), 13761-13769) brings to fore its experimental realization. Our current study delves into the possibilities of employing this intriguing 2D hydrogen boride as anodes in Li/Na ion batteries. Using first-principles density functional theory methods, we computed relevant properties such as the ion (Li/Na) adsorption behavior, the possible pathways of ionic diffusion with the estimation of barriers as well as the theoretical specific capacities and average voltages to uniquely demonstrate that this material is of particular significance for battery applications. It is noted that the use of hydrogen boride leads to a high specific capacity of 861.78 mA h g(-1) for Li ions, which is remarkably higher than the value reported in relation to its computationally predicted structure. Furthermore, Na ion intercalation leads to negative voltage profiles, implying the unsuitability of 2D hydrogen boride for this particular ion. Our findings are timely and pertinent towards adding insightful details relevant to the progress of applications of 2D materials for energy storage.

Place, publisher, year, edition, pages
ROYAL SOC CHEMISTRY, 2018
National Category
Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-369513 (URN)10.1039/c8cp03686a (DOI)000449394100021 ()30109880 (PubMedID)
Funder
Swedish Research CouncilCarl Tryggers foundation StandUp
Available from: 2018-12-17 Created: 2018-12-17 Last updated: 2019-01-05Bibliographically approved
9. Modeling High-performing Batteries with Mxenes: The case of S-functionalized two- Dimensional Nitride Mxene Electrode
Open this publication in new window or tab >>Modeling High-performing Batteries with Mxenes: The case of S-functionalized two- Dimensional Nitride Mxene Electrode
Show others...
2019 (English)In: Nano Energy, ISSN 2211-2855, E-ISSN 2211-3282, Vol. 58, p. 877-885Article in journal (Refereed) Published
Abstract [en]

Recent upsurge in the two-dimensional (2D) materials have established their larger role on energy storage applications. To this end, Mxene represent a new paradigm extending beyond the realm of oft-explored elemental 2D materials beginning with graphene. Here in, we employed first principles modelling based on density functional theory to investigate the role of S-functionalized Nitride Mxenes as anodes for Li/Na ion batteries. To be specific, V2NS2 and Ti2NS2 have been explored with a focus on computing meaningful descriptors to quantify these 2D materials to be optimally performing electrodes. The Li/Na ion adsorption energies are found to be high (> -2 eV) on both the surfaces and associated with significant charge transfer. Interestingly, this ion intercalation can reach up to multilayers which essentially affords higher specific capacity for the substrate. Particularly, these two 2D materials (V2NS2 and Ti2NS2) have been found to be more suitable for Li-ion batteries with estimated theoretical capacities of 299.52 mAh g(-1) and 308.28 mAh g(-1) respectively. We have also probed the diffusion barriers of ion migration on these two surfaces and these are found to be ultrafast in nature. All these unique features qualify these Mxenes to be potential anode materials for rechargeable batteries and likely to draw imminent attention.

National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-372108 (URN)10.1016/j.nanoen.2019.02.007 (DOI)000461433600100 ()
Funder
Swedish National Infrastructure for Computing (SNIC)Swedish Research Council
Available from: 2019-01-05 Created: 2019-01-05 Last updated: 2019-04-04Bibliographically approved

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