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Graphene-based CO2 sensing and its cross-sensitivity with humidity
KTH, School of Information and Communication Technology (ICT), Electronics, Integrated devices and circuits.ORCID iD: 0000-0003-4637-8001
KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics. (KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF. KTH, Centres, SeRC - Swedish e-Science Research Centre.)ORCID iD: 0000-0002-8222-3157
KTH, School of Electrical Engineering (EES), Micro and Nanosystems.
RWTH Aachen, Otto-Blumenthal-Str., 52074 Aachen, Germany .ORCID iD: 0000-0003-4552-2411
Show others and affiliations
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. Vol. 7, p. 22329-22339
National Category
Nano Technology
Identifiers
URN: urn:nbn:se:kth:diva-206164DOI: 10.1039/C7RA02821KOAI: oai:DiVA.org:kth-206164DiVA, id: diva2:1091748
Note

QC 20170517

Available from: 2017-04-27 Created: 2017-04-27 Last updated: 2018-07-26
In thesis
1. Density Functional Theory Calculations for Graphene-based Gas Sensor Technology
Open this publication in new window or tab >>Density Functional Theory Calculations for Graphene-based Gas Sensor Technology
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
Keywords
graphene, ab-initio, humidity, carbon dioxide, substrate, DFT, vdW, first-principle, simulation, calculations
National Category
Condensed Matter Physics
Research subject
Physics
Identifiers
urn:nbn:se:kth:diva-221639 (URN)978-91-7729-660-7 (ISBN)
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
2. Integration of graphene into MEMS and NEMS for sensing applications
Open this publication in new window or tab >>Integration of graphene into MEMS and NEMS for sensing applications
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis presents a novel approach to integrate chemical vapor deposition (CVD) graphene into silicon micro- and nanoelectromechanical systems (MEMS/NEMS) to fabricate different graphene based MEMS/NEMS structures and explore mechanical properties of graphene as well as their applications such as acceleration sensing, humidity sensing and CO2 sensing. The thesis also presents a novel method of characterization of CVD graphene grain boundary based defects.

    The first section of this thesis presents a robust, scalable, flexible route to integrate double-layer graphene membranes to a silicon substrate so that large silicon masses are suspended by graphene membranes.

    In the second section, doubly-clamped suspended graphene beams with attached silicon masses are fabricated and used as model systems for studying the mechanical properties of graphene and transducer elements for NEMS resonators and extremely small accelerometers, occupying die areas that are at least two orders of magnitude smaller than the die areas occupied by the most compact state-of-the-art silicon accelerometers. An averaged Young’s modulus of double-layer graphene of ~0.22 TPa and non-negligible built-in stresses of the order of 200-400 MPa in the suspended graphene beams are extracted, using analytical and FEA models. In addition, fully clamped suspended graphene membranes with attached proof masses are also realized, which are used for acceleration sensing.

In the third section, CO2 sensing of single-layer graphene and the cross-sensitivity between CO2 and humidity are shown. The cross-sensitivity of CO2 is negligible at typical CO2 concentrations present in air. The properties of double-layer graphene when exposed to humidity and CO2 have been characterized, with similarly fast response and recovery behaviour but weak resistance responses, compared to single layer graphene.

In the fourth section, a fast and simple method for large-area visualization of grain boundaries in CVD graphene transferred to a SiO2 surface is demonstrated. The method only requires vapor hydrofluoric acid (VHF)-etching and optical microscope inspection and therefore could be useful to speed up the process of developing large-scale high quality graphene synthesis, and can also be used for analysis of the influence of grain boundaries on the properties of emerging graphene devices that utilize CVD graphene patches placed on a SiO2 substrate.

Place, publisher, year, edition, pages
KTH Royal Institute of Technology, 2018. p. 87
Series
TRITA-EECS-AVL ; 2018:43
Keywords
Micro-electromechanical systems (MEMS), Nano-electromechanical systems (NEMS), heterogeneous 3D integration, Graphene, single-layer graphene, double-layer graphene, bilayer graphene, chemical vapor deposition (CVD), suspended graphene beams, suspended graphene membranes, doubly clamped, fully clamped, silicon on insulator (SOI), vapor hydrofluoric acid (VHF), Young’s modulus, built-in stress, built-in tension, piezoresistivity, gauge factor, accelerometer, resonators, electromechanical sensing, advanced transducers, humidity, gas sensing, sensitivity, CO2 sensing, graphene grain boundary, line defects, optical microscopy, wire bonding
National Category
Nano Technology Engineering and Technology
Research subject
Electrical Engineering
Identifiers
urn:nbn:se:kth:diva-232557 (URN)978-91-7729-803-8 (ISBN)
Public defence
2018-08-24, Sal F3, Lindstedtsvägen 26, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20180726

Available from: 2018-07-26 Created: 2018-07-25 Last updated: 2018-07-26Bibliographically approved

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