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Sun, Tao 2015-09-29T20:50:06Z 2015-09-29T20:50:06Z 2017-09-30T09:15:18Z 2015-08 2015-07-17 The interactions of ambient molecules with graphene-based devices, espe- cially sensors, is of great importance as such interactions could impact the operation of the device, often producing unpredictable effects. In this project, we focus on a graphene humidity sensor based on capacitance measurement to uncover fundamental physical mechanisms governing the operation of the de- vice. Using molecular dynamics (MD) and density functional theory (DFT) simulations, we show that ambient molecules (mainly O 2 and H 2 O) can ap- pear on the top of graphene, and get intercalated between graphene and the substrate (Hf O 2 ). Both of these phenomena can have large effects on graphene sensing behavior. When the device is in vacuum, the oxygen va- cancies (VOs) on the surface of the substrate can induce n-type doing effect to graphene. Then the device is brought into dry air, where O 2 molecules will enter between graphene and the substrate and fill the vacancies, which eliminates the n-type doping effect. O 2 molecules also appear on the top of graphene, acting as electron acceptors and causing p-type doping effect on graphene. After that the device is brought into the atmosphere, and the intercalation of H 2 O molecules underneath graphene is observed. The inter- facial distance between graphene and the substrate is enlarged, thus changing the measured capacitance. At the same time, H 2 O molecules appear above graphene will displace some of the originally existing O 2 molecules, which causes graphene to be less p-type doped than before. Our simulations un- cover how a capacitance-based graphene humidity sensor works, which is due to change of the interlayer distance caused by intercalated water molecules underneath graphene. Also through the interactions between graphene sensor system and ambient molecules, we understand the doping effect on graphene during the operation process. Submission published under a 24 month embargo labeled 'U of I only', the embargo will last until 2017-08-01 The student, Tao Sun, accepted the attached license on 2015-07-16 at 13:08. The student, Tao Sun, submitted this Thesis for approval on 2015-07-16 at 13:12. This Thesis was approved for publication on 2015-07-17 at 12:12. DSpace SAF Submission Ingestion Package generated from Vireo submission #8499 on 2015-09-29 at 15:00:04 Made available in DSpace on 2015-09-29T20:50:06Z (GMT). No. of bitstreams: 2 SUN-THESIS-2015.pdf: 7465082 bytes, checksum: 058900aba8eaffcf57ab44d3d002576d (MD5) LICENSE.txt: 4204 bytes, checksum: e05025a5369760b8039dfbc2785f1146 (MD5) Previous issue date: 2015-07-17 Embargo set by: Seth Robbins for item 89483 Lift date: 2017-09-29T20:50:34Z Reason: Author requested U of Illinois access only (OA after 2yrs) in Vireo ETD system U of I Only Restriction Lifted for Item 89483 on 2017-09-30T09:15:18Z. application/pdf http://hdl.handle.net/2142/88203 en Copyright 2015 Tao Sun graphene capacitance humidity molecular dynamics (MD) density functional theory (DFT) Physical mechanism of a capacitance-based graphene humidity sensor text text 2015-8 Mechanical Science & Engineering Mechanical Engineering University of Illinois at Urbana-Champaign Thesis M.S.