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Density Functional Theory Calculations for Graphene-based Gas Sensor Technology
KTH, School of Engineering Sciences (SCI), Applied Physics. SeRC (Swedish e-Science Research Center). (Anna Delin's research group)ORCID iD: 0000-0002-8222-3157
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Nowadays, electronic devices span a diverse pool of applications, especially when getting smaller and smaller satisfying the more than Moore paradigm. To further develop this, studies focusing on material design toward electronic devices are crucial. Accordingly, we present a theoretical study investigating the possibility of graphene as a promising material for such electronic devices design. We focus on graphene and graphene-based sensors. Graphene is known to have outstanding electronic and mechanical properties making it a game changer in the electronic design in the so-called 'post-silicon' industry. It is stronger than steel yet the thinnest material ever known while overstepping copper regarding electronic conductivity.

In this thesis, we perform first-principle ab-initio density functional theory (DFT) calculations of graphene in different sensing ambient conditions, which allows fast, accurate and efficient investigations of the electronic structure properties. Principally, we centre our attention on the arising interactions between the adsorbates on top of the graphene sheet and the underlying substrates' surface defects. The combined effect of the impurity bands arising from these defects and the adsorbates reveals a doping influence within the graphene sheet. This doping behaviour is responsible for different equilibrium distances and binding energies for different adsorbate types as well as substrates. Moreover, we briefly investigate the same effect on double layered graphene under the same ambient conditions.

We extend the studies to involve various types of substrates with different surface conditions and different adhesion nature to graphene. We take into consideration the governing van der Waals interactions in describing the electronic structure properties taking place at the graphene sheet interfacing both with the substrates below and the adsorbates above. Furthermore, we investigate the possibility of passivating such action of graphene sensing towards adsorbates to inhibit the graphene's sensing action as devices passivation becomes a necessity for the ultimate purpose of achieving more than Moore applications. Which in turn result in the optimal integration of graphene-based devices with different other devices functionalities on the same resultant chip.

In summary, graphene, by means of first-principle calculations verification, shows a promising behaviour in the sensor functionality enabling more than Moore applications for further advances.

Abstract [sv]

Elektroniska komponenter används i allt vidare utsträckning, och deras användning ökar i takt med att de blir mindre och mindre samtidigt som deras prestanda ökar, enligt det paradigm som brukar kallas ''more than Moore''. För att att göra ytterligare framsteg i denna riktning är grundläggande studier som fokuserar på materialdesign och tillverkning av nya typer av elektroniska komponenter avgörande. I den här avhandlingen presenteras teoretiska studier av grafen-baserade komponenter. Grafen är ett mycket intressant material för framtidens elektroniska komponenter. Specifikt fokuserar vi på grafenbaserade gas-sensorer. Grafen är känt för att ha mycket ovanliga elektroniska och mekaniska egenskaper som gör det till ett unikt material för "post-silicon"-design av elektronik. Det är starkare än stål och är samtidigt världens tunnaste material. Samtidigt har det bättre elektrisk ledningsförmåga än koppar.

Täthetsfunktionalsteori (DFT) har använts för att beräkna hur den elektroniska strukturen hos grafen ändras som funktion av substratmaterial och typ av molekyler som adsorberats på grafenets yta. DFT är en beräkningsmetod som medger simuleringar med hög precision samtidigt som den är relativt snabb. I studierna har DFT kombinerats med olika modeller för van der Waals-interaktionen.En viktig aspekt i de studier vi presenterar här är interaktionen mellan adsorbat-molekylerna ovanpå grafenet och ytdefekterna hos det underliggande substratet. De orenhetsband som härrör från defekterna, i kombination med adsorbat-molekylerna, skapar en slags dopningseffekt som ändrar elektronstrukturen hos grafenet. Därmed kan även de elektriska transportegenskaperna ändras hos grafenet, vilket möjliggör elektrisk detektion av molekylerna.

Vi har även studerat sensorer byggda med dubbelskiktad grafen. Dessutom har vi gjort en systematisk studie av hur grafen binder till ett stort antal substrat samt även hur man kan passivisera grafen så att den elektriska ledningsförmågan inte ändras vid molekyladsorption. Detta sista är viktigt för "more than Moore"-tillmämpningar, där ett centralt designkriterium är att kunna integrera många funktioner på samma chip.

Place, publisher, year, edition, pages
Stockholm, Sweden, 2018: KTH Royal Institute of Technology, 2018. , p. 75
Series
TRITA-SCI-FOU ; 2018:01
Keyword [en]
graphene, ab-initio, humidity, carbon dioxide, substrate, DFT, vdW, first-principle, simulation, calculations
National Category
Condensed Matter Physics
Research subject
Physics
Identifiers
URN: urn:nbn:se:kth:diva-221639ISBN: 978-91-7729-660-7 (print)OAI: oai:DiVA.org:kth-221639DiVA, id: diva2:1175594
Public defence
2018-02-09, Ka-Sal C (Sal Sven-Olof Öhrvik), Electrum 229 16440 Kista, Stockholm, Stockholm, 09:00 (English)
Opponent
Supervisors
Note

QC 20180118

Available from: 2018-01-18 Created: 2018-01-18 Last updated: 2018-01-19Bibliographically approved
List of papers
1. Density functional calculations of graphene-based humidity and carbon dioxide sensors: effect of silica and sapphire substrates
Open this publication in new window or tab >>Density functional calculations of graphene-based humidity and carbon dioxide sensors: effect of silica and sapphire substrates
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2017 (English)In: Surface Science, ISSN 0039-6028, E-ISSN 1879-2758, Vol. 663, p. 23-30Article in journal (Refereed) Published
Abstract [en]

We present dispersion-corrected density functional calculations of water and carbon dioxide molecules adsorption on graphene residing on silica and sapphire substrates. The equilibrium positions and bonding distances for the molecules are determined. Water is found to prefer the hollow site in the center of the graphene hexagon, whereas carbon dioxide prefers sites bridging carbon-carbon bonds as well as sites directly on top of carbon atoms. The energy differences between different sites are however minute - typically just a few tenths of a millielectronvolt. Overall, the molecule-graphene bonding distances are found to be in the range 3.1-3.3 (A) over circle. The carbon dioxide binding energy to graphene is found to be almost twice that of the water binding energy (around 0.17 eV compared to around 0.09 eV). The present results compare well with previous calculations, where available. Using charge density differences, we also qualitatively illustrate the effect of the different substrates and molecules on the electronic structure of the graphene sheet.

Place, publisher, year, edition, pages
Elsevier, 2017
Keyword
Graphene, DFT, Sensor, Humidity, Carbon dioxide
National Category
Theoretical Chemistry
Identifiers
urn:nbn:se:kth:diva-211313 (URN)10.1016/j.susc.2017.04.009 (DOI)000405043300004 ()2-s2.0-85018431677 (Scopus ID)
Funder
Swedish e‐Science Research CenterSwedish Research Council, VR 2015-04605The Royal Swedish Academy of SciencesKnut and Alice Wallenberg FoundationCarl Tryggers foundation , CTS 14:105 CTS KF16:2Swedish Energy Agency, STEM P40147-1Swedish Foundation for Strategic Research , SSF EM11-0002
Note

QC 20170802

Available from: 2017-08-02 Created: 2017-08-02 Last updated: 2018-01-18Bibliographically approved
2. Adsorption of carbon dioxide and water molecules on graphene on top of silica substrates: dispersion corrected density functional calculations
Open this publication in new window or tab >>Adsorption of carbon dioxide and water molecules on graphene on top of silica substrates: dispersion corrected density functional calculations
(English)Manuscript (preprint) (Other academic)
Abstract [en]

We report on systematic computational studies of carbon dioxide and water molecule adsorption on graphene, with the graphene layer deposited on top of a substrate. Specifically, we address the influence of cristobalite and quartz substrates, i.e. two different types of silicon dioxide. The computations are based on density functional theory (DFT), with a nonempirical nonlocal van der Waals density functional included to account for dispersion forces.We calculate the binding energies and equilibrium positions of the molecules, as well as charge transfer and how the charge density of the graphene layer changes due to the interactions with the substrate and the molecules. The molecule-graphene bonding distances are found to be in the range 3.3-3.4 Å, and the graphene-substrate bonding distances around 3.6 Å. These values are slightly larger than what we have found previously, using an empirical expression for the van der Waals density functional. At the same time, the values for the binding energies are increased, compared to what we have obtained in a previous study. We find, in all cases, a net electron transfer from the adsorbed molecule to the graphene+substrate system. For quartz, the total charge transfer is between 0.1 and 0.2 electrons per adsorbed molecule. For cristobalite, it is only about a tenth of that. Our findings are consistent with earlier calculations as well as experimental data.

National Category
Other Materials Engineering
Research subject
Physics
Identifiers
urn:nbn:se:kth:diva-221086 (URN)
Note

QC 20180115

Available from: 2018-01-12 Created: 2018-01-12 Last updated: 2018-01-18Bibliographically approved
3. Graphene adhesion on surfaces: a van der Waals density functional study
Open this publication in new window or tab >>Graphene adhesion on surfaces: a van der Waals density functional study
(English)Manuscript (preprint) (Other academic)
Abstract [en]

We present a van der Waals density functional (vdW-DF) calculations study of graphene adhesion to different types of substrates with different surface conditions. The study expands to both metal and semiconductor substrates with different surface endings. All substrate surfaces were the 111 surfaces where they have hexagonal lattice parameters perfectly matching with the graphene's. Adsorption geometries, energies, bader charges, dipole moments and electronic structure in terms of density of states are investigated. The results are showing a general agrement with both experimental results as well as theoritical findings done with similar setup. The results reveal that the degree of adhesive of graphene to different surfaces can affect the electronic structure of graphene ending in having different applications when designing graphene in building nano-electronic devices.

National Category
Other Materials Engineering
Research subject
Physics
Identifiers
urn:nbn:se:kth:diva-221087 (URN)
Note

QC 20180116

Available from: 2018-01-12 Created: 2018-01-12 Last updated: 2018-01-18Bibliographically approved
4. Resistive graphene humidity sensors with rapid and direct electrical readout
Open this publication in new window or tab >>Resistive graphene humidity sensors with rapid and direct electrical readout
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2015 (English)In: Nanoscale, ISSN 2040-3364, E-ISSN 2040-3372, Vol. 7, no 45, p. 19099-19109Article in journal (Refereed) Published
Abstract [en]

We demonstrate humidity sensing using a change of the electrical resistance of single-layer chemical vapor deposited (CVD) graphene that is placed on top of a SiO2 layer on a Si wafer. To investigate the selectivity of the sensor towards the most common constituents in air, its signal response was characterized individually for water vapor (H2O), nitrogen (N-2), oxygen (O-2), and argon (Ar). In order to assess the humidity sensing effect for a range from 1% relative humidity (RH) to 96% RH, the devices were characterized both in a vacuum chamber and in a humidity chamber at atmospheric pressure. The measured response and recovery times of the graphene humidity sensors are on the order of several hundred milliseconds. Density functional theory simulations are employed to further investigate the sensitivity of the graphene devices towards water vapor. The interaction between the electrostatic dipole moment of the water and the impurity bands in the SiO(2)d substrate leads to electrostatic doping of the graphene layer. The proposed graphene sensor provides rapid response direct electrical readout and is compatible with back end of the line (BEOL) integration on top of CMOS-based integrated circuits.

Place, publisher, year, edition, pages
Royal Society of Chemistry, 2015
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:kth:diva-179618 (URN)10.1039/c5nr06038a (DOI)000364852500035 ()26523705 (PubMedID)2-s2.0-84947265250 (Scopus ID)
Funder
Swedish Research Council, E0616001 D0575901Knut and Alice Wallenberg FoundationSwedish Energy Agency
Note

QC 20160111

Available from: 2016-01-11 Created: 2015-12-17 Last updated: 2018-01-18Bibliographically approved
5. Graphene-based CO2 sensing and its cross-sensitivity with humidity
Open this publication in new window or tab >>Graphene-based CO2 sensing and its cross-sensitivity with humidity
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2017 (English)In: RSC Advances, ISSN 2046-2069, E-ISSN 2046-2069, Vol. 7, p. 22329-22339Article in journal (Refereed) Published
Abstract [en]

We present graphene-based CO2 sensing and analyze its cross-sensitivity with humidity. In order to assess the selectivity of graphene-based gas sensing to various gases, measurements are performed in argon (Ar), nitrogen (N2), oxygen (O2), carbon dioxide (CO2), and air by selectively venting the desired gas from compressed gas bottles into an evacuated vacuum chamber. The sensors provide a direct electrical readout in response to changes in high concentrations, from these bottles, of CO2, O2, nitrogen and argon, as well as changes in humidity from venting atmospheric air. From the signal response to each gas species, the relative graphene sensitivity to each gas is extracted as a relationship between the percentage-change in graphene's resistance response to changes in vacuum chamber pressure. Although there is virtually no response from O2, N2 and Ar, there is a sizeable cross-sensitivity between CO2 and humidity occurring at high CO2 concentrations. However, under atmospheric concentrations of CO2, this cross-sensitivity effect is negligible – allowing for the use of graphene-based humidity sensing in atmospheric environments. Finally, charge density difference calculations, computed using density functional theory (DFT) are presented in order to illustrate the bonding of CO2 and water molecules on graphene and the alterations of the graphene electronic structure due to the interactions with the substrate and the molecules.

Place, publisher, year, edition, pages
Royal Society of Chemistry, 2017
National Category
Nano Technology
Identifiers
urn:nbn:se:kth:diva-206164 (URN)10.1039/C7RA02821K (DOI)
Note

QC 20170517

Available from: 2017-04-27 Created: 2017-04-27 Last updated: 2018-04-05
6. Humidity and CO2 gas sensing properties of double-layer graphene
Open this publication in new window or tab >>Humidity and CO2 gas sensing properties of double-layer graphene
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2018 (English)In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 127, p. 576-587Article in journal, Editorial material (Refereed) Published
Abstract [en]

Graphene has interesting gas sensing properties with strong responses of the graphene resistance when exposed to gases. However, the resistance response of double-layer graphene when exposed to humidity and gasses has not yet been characterized and understood. In this paper we study the resistance response of double-layer graphene when exposed to humidity and CO2, respectively. The measured response and recovery times of the graphene resistance to humidity are on the order of several hundred milliseconds. For relative humidity levels of less than ~ 3% RH, the resistance of double-layer graphene is not significantly influenced by the humidity variation. We use such a low humidity atmosphere to investigate the resistance response of double-layer graphene that is exposed to pure CO2 gas, showing a consistent response and recovery behaviour. The resistance of the double-layer graphene decreases linearly with increase of the concentration of pure CO2 gas. Density functional theory simulations indicate that double-layer graphene has a weaker gas response compared to single-layer graphene, which is in agreement with our experimental data. Our investigations contribute to improved understanding of the humidity and CO2 gas sensing properties of double-layer graphene which is important for realizing viable graphene-based gas sensors in the future.

Place, publisher, year, edition, pages
Netherlands: Elsevier, 2018
Keyword
Graphene, humidity, gas sensing, CO2
National Category
Other Engineering and Technologies not elsewhere specified
Research subject
Electrical Engineering; Materials Science and Engineering
Identifiers
urn:nbn:se:kth:diva-218275 (URN)10.1016/j.carbon.2017.11.038 (DOI)000418095900026 ()2-s2.0-85034837689 (Scopus ID)
Projects
M&MWaveGraphGEMS
Funder
EU, European Research Council, 277879VINNOVA, 2016-01655Swedish Research Council, 2015-05112
Note

QC 20171127

Available from: 2017-11-25 Created: 2017-11-25 Last updated: 2018-02-20Bibliographically approved
7. Toward Effective Passivation of Graphene to Humidity Sensing Effects
Open this publication in new window or tab >>Toward Effective Passivation of Graphene to Humidity Sensing Effects
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2016 (English)In: 2016 46TH EUROPEAN SOLID-STATE DEVICE RESEARCH CONFERENCE (ESSDERC), IEEE, 2016, p. 299-302Conference paper, Published paper (Refereed)
Abstract [en]

Graphene has a number of remarkable properties which make it well suited for both transistor devices as well as for sensor devices such as humidity sensors. Previously, the humidity sensing properties of monolayer graphene on SiO2 substrates were examined - showing rapid response and recovery over a large humidity range. Further, the devices were fabricated in a CMOS compatible process which can be incorporated back end of the line (BEOL). We now present a way to selectively passivate graphene to suppress this humidity sensing effect. In this work, we experimentally and theoretically demonstrate effective passivation of graphene to humidity sensing - allowing for future integration with other passivated graphene devices on the same chip.

Place, publisher, year, edition, pages
IEEE, 2016
Series
Proceedings of the European Solid-State Device Research Conference, ISSN 1930-8876
Keyword
Graphene, Sensors, Humidity, Passivation, DFT, BEOL, Integration
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-197022 (URN)10.1109/ESSDERC.2016.7599645 (DOI)000386655900071 ()2-s2.0-84994429440 (Scopus ID)978-1-5090-2969-3 (ISBN)
Conference
46th European Solid-State Device Research Conference (ESSDERC) / 42nd European Solid-State Circuits Conference (ESSCIRC), SEP 12-15, 2016, Lausanne, SWITZERLAND
Note

QC 20161209

Available from: 2016-12-09 Created: 2016-11-28 Last updated: 2018-04-05

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