Light-enhanced sensors of oxidizing gases based on single-layer CVD graphene
Kuupäev
2024-11-01
Autorid
Ajakirja pealkiri
Ajakirja ISSN
Köite pealkiri
Kirjastaja
Abstrakt
Edendatud funktsionaalsete omadustega (suur tundlikkus, selektiivsus ja stabiilsus; väike võimsustarve) gaasisensorid on vajalikud erinevate looduslikest või inimtekkelistest allikatest pärinevate gaaside tuvastamisel. Grafeeni, ainult ühest süsinikuaatomite kihist koosneva materjali avastamine lõi ideaalse aluse uute gaasisensorite loomiseks, sest selle materjali kogu pind on avatud mõõdetavale keskkonnale.
Käesolev doktoritöö on fokusseeritud ultravioletse (UV) valguse mõju uurimisele grafeenil põhinevate hapniku (O₂) ja lämmastikdioksiidi (NO₂) sensorite funktsionaalsetele omadustele.
Töö esimeses osas uuriti UV-valguse mõju keemilise aurufaassadestusega valmistatud grafeeni elektrilistele omadustele ja nende hapnikutundlikkusele. Demonstreeriti, et UV-valgus muudab algul praktiliselt inertse grafeenisensori tundlikuks õhuhapniku suhtes ja kiirendab oluliselt sensori signaali koste- ja taastumiskiirust.
Järgmisena uuriti grafeenisensorite omadusi ühe olulisima ja juba väikeses koguses tervist kahjustava õhusaastegaasi, NO₂, detekteerimisel; seejuures kasutati lisaks puhtale grafeenile ka funktsionaliseeritud grafeeni. Viimane materjal oli valmistatud laserablatsiooni meetodiga: grafeenile oli kantud üliõhuke, vaid mõne aatomi paksune oksiidi- (ZrO₂, TiO₂) või metallikiht (Ag). Tulemusena saavutati grafeenisensorite tundlikkuse oluline tõus, mis võimendus UV-valguse kasutamisega. Suurim tundlikkus saadi titaanoksiidiga kaetud grafeenisensoritega, millel testiti gaasikontsentratsioone kuni 10 ppb (10 osa miljardi kohta) ning hinnati detekteerimisläveks 0,03 ppb. Lisaks demonstreeriti grafeen/TiO₂ sensori suurepärast selektiivsust, kuna signaalikosted NO₂ korral ületasid oluliselt teiste saastavate gaaside (CO, SO₂ ja NH₃), aga ka niiskuse mõjul tekkivaid kosteid.
Kokkuvõttes näidati, et grafeeni ja sellel põhinevate sensormaterjalide kasutamine väikese võimsusega UV-valguse (365 nm) mõju all võimaldab märkimisväärselt suurendada nende tundlikkust uuritavate gaaside suhtes ning suurendada koste- ja taastumiskiirust nii, et kõik funktsionaalsed parameetrid on rakenduste jaoks sobivas vahemikus toatemperatuuril töötavate sensorite korral.
Gas sensors with improved functional properties (high sensitivity, selectivity, and stability; low power consumption) are needed to detect a wide variety of gases originating from both natural and anthropogenic sources. Graphene, a material consisting of a single layer of carbon atoms, has emerged as an ideal building foundation for gas sensors since its entire surface can act as a sensing area. This thesis focuses on investigating the influence of ultraviolet (UV) light on the functional properties of graphene-based sensors towards two oxidizing gases – oxygen (O₂) and nitrogen dioxide (NO₂). The first part of the thesis focuses on studying the light irradiation effect on pristine chemical vapor deposited (CVD) graphene. For that, the electrical properties of graphene were investigated, as well as the influence of UV light on O₂ sensing. The results demonstrated a highly beneficial effect of irradiation, which led to the activation of an initially inert sensor, making it sensitive to oxygen concentration changes and improving response and recovery speed. As a next step, both pristine and modified CVD graphene were tested as sensors for NO₂, a highly toxic polluting gas causing millions of premature deaths per year in the whole world. For graphene modification, pulsed laser deposition was used to grow thin layers of oxides (ZrO₂, TiO₂) or metal (Ag) on top of graphene. The highest sensitivity was obtained with titania-coated graphene sensors under UV light. Gas concentrations down to 10 ppb (10 parts per billion) were investigated with the estimated level of detection of 0.03 ppb. Additionally, the excellent selectivity of the graphene/TiO₂ sensor was showcased, as NO₂ results significantly overperformed those for other polluting gases (CO, SO₂, and NH₃), as well as the humidity. Overall, it was demonstrated that the irradiation with low-power UV light (365 nm) allowed a considerable increase in the sensitivity towards the studied gases and increased the response and recovery rates so that all functional parameters became within the range of real-world applications for the sensors operated at room temperature.
Gas sensors with improved functional properties (high sensitivity, selectivity, and stability; low power consumption) are needed to detect a wide variety of gases originating from both natural and anthropogenic sources. Graphene, a material consisting of a single layer of carbon atoms, has emerged as an ideal building foundation for gas sensors since its entire surface can act as a sensing area. This thesis focuses on investigating the influence of ultraviolet (UV) light on the functional properties of graphene-based sensors towards two oxidizing gases – oxygen (O₂) and nitrogen dioxide (NO₂). The first part of the thesis focuses on studying the light irradiation effect on pristine chemical vapor deposited (CVD) graphene. For that, the electrical properties of graphene were investigated, as well as the influence of UV light on O₂ sensing. The results demonstrated a highly beneficial effect of irradiation, which led to the activation of an initially inert sensor, making it sensitive to oxygen concentration changes and improving response and recovery speed. As a next step, both pristine and modified CVD graphene were tested as sensors for NO₂, a highly toxic polluting gas causing millions of premature deaths per year in the whole world. For graphene modification, pulsed laser deposition was used to grow thin layers of oxides (ZrO₂, TiO₂) or metal (Ag) on top of graphene. The highest sensitivity was obtained with titania-coated graphene sensors under UV light. Gas concentrations down to 10 ppb (10 parts per billion) were investigated with the estimated level of detection of 0.03 ppb. Additionally, the excellent selectivity of the graphene/TiO₂ sensor was showcased, as NO₂ results significantly overperformed those for other polluting gases (CO, SO₂, and NH₃), as well as the humidity. Overall, it was demonstrated that the irradiation with low-power UV light (365 nm) allowed a considerable increase in the sensitivity towards the studied gases and increased the response and recovery rates so that all functional parameters became within the range of real-world applications for the sensors operated at room temperature.
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