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Density Functional Theory Calculations of Graphene based Humidity and Carbon Dioxide Sensors
KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF. (Anna Delin research group)ORCID iD: 0000-0002-8222-3157
2016 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Graphene has many interesting physical properties which makes it useful for plenty of applications. In this work we investigate the possibility of using graphene as a carbon dioxide and humidity sensor. Carbon dioxide and water adsorbates are modeled on top of the surface of a graphene sheet, which themselves lie on one of two types of silica substrates or sapphire substrate. We evaluate the changes in the electronic and structural properties of the graphene sheet in the presence of the described adsorbates as well as the accompanying substrate. We perform the study using ab-initio calculations based on density functional theory (DFT), that allows fast, accurate and efficient investigations. In particular, we focus our attention on investigating the effects of defects in the substrate and how it influences the properties of the graphene sheet. The defects of the substrate contribute with impurity bands leading to doping effects on the graphene sheet, which in turn together with the presence of the adsorbates result in changes of the electronic charge distribution in the system. We provide charge density difference plots to visualize these changes and also determine the relaxed minimum distances of the adsorbates from the graphene sheet together with the respective minimum energy configurations. We also include the density of states, Löwdin charges and work functions for further investigations.

Abstract [sv]

Grafen har många intressanta fysikaliska egenskaper, vilket gör det användbart för många  tillämpningar. I detta arbete har vi teoretiskt undersökt möjligheten att använda grafen som gassensor för koldioxid och fukt. Adsorberade koldioxid- och vattenmolekyler modelleras ovanför ytan av ett lager grafen, som i sig ligger ovanpå en av två typer av kiseldioxidsubstrat eller ett aluminiumoxidsubstrat. Vi har utvärderat förändringar i de elektroniska och strukturella egenskaperna hos grafenlagret i närvaro av de beskrivna molekylerna samt åtföljande substrat. Vi utför studien med ab-initio beräkningar baserade på täthetsfunktionalteori (DFT), som möjliggör snabba, korrekta och effektiva elektronstruktursberäkningar. Framför allt fokuserar vi på effekten av defekter i underlaget, och hur dessa påverkar egenskaperna hos grafenlagret. Defekter i underlaget bidrar genom att införa elektroniska band som leder till dopningseffekter i grafenlagret, vilket i sin tur tillsammans med närvaron av adsorbatmolekylerna leder till förändringar av den elektroniska laddningsfördelningen i systemet. Vi tillhandahåller s.k. laddningsdensitet-skillnadsfigurer som visualiserar dessa förändringar. Vi har även beräknat jämviktsavståndet mellan adsorbatmolekylerna och grafenlagret  tillsammans med respektive minimienergikonfigurationer för molekylerna, Vi åksa tillhandahåller täthet av stater, Löwdin laddningar och arbetsfunktion för fortsatta undersökningar.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2016. , xi, 20 p.
Series
TRITA-ICT, 2016:02
Keyword [en]
DFT, graphene, sensors, Quantum Espresso, ab-initio
National Category
Condensed Matter Physics
Research subject
Physics
Identifiers
URN: urn:nbn:se:kth:diva-180761ISBN: 978-91-7595-817-0 (print)OAI: oai:DiVA.org:kth-180761DiVA: diva2:896883
Presentation
2016-02-19, Sal/hall 205, Elektrum 229, Isafjordsgatan 22, KTH-ICT, Kista, 10:00 (English)
Opponent
Supervisors
Funder
Swedish e‐Science Research Center
Note

QC 20160218

Available from: 2016-01-28 Created: 2016-01-22 Last updated: 2016-02-12Bibliographically approved
List of papers
1. 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, 19099-19109 p.Article 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: 2017-12-01Bibliographically approved
2. Density functional theory 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 theory calculations of graphene-based humidity and carbon dioxide sensors: effect of silica and sapphire substrates
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(English)Manuscript (preprint) (Other academic)
Identifiers
urn:nbn:se:kth:diva-181089 (URN)
Note

QS 2016

Available from: 2016-01-28 Created: 2016-01-28 Last updated: 2016-01-28Bibliographically approved

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