Abstract In this thesis work, crystal and phase structure, chemical composition and gas sensing properties of pulsed laser deposited vanadium oxide thin films were studied. Pulsed laser deposition was used to manufacture vanadium oxide thin films with various crystal structures, film morphologies and phase compositions. Both the well-known vanadium pentoxide V2O5, and a totally new stable phase in a solid-state thin-film form, V7O16, was produced. The existence of these phases was proven by several different characterization methods such as, X-ray diffraction, Raman spectroscopy, and X-ray photoelectron spectroscopy. The resistive gas sensing measurements of the films with pure V2O5 composition, and mixed phase compositions of V2O5 and V7O16, showed that behaviour of the electrical response to different gases at various measurement temperatures was dependent on the phase composition of the thin films. It was proved that in certain conditions the mixed phase films show p-type semiconducting gas sensing behaviour, instead of the pure n-type behaviour of V2O5. Both types of film compositions were shown to be highly sensitive to ammonia gas, down to 40 ppb-level. The mixed phase composition showed a higher response to ammonia compared to the pure V2O5 phase; however the pure V2O5 showed better long-term stability. Both sensing layer types also showed high selectivity to ammonia in comparison to NO and CO gases. Nanostructured pure V2O5 layers were successfully deposited on commercial microheater platforms and then used as a gas sensor. The V2O5 nanostructures were proven to be very promising candidates as gas sensor material to control the Selective Catalytic Reduction process used in the reduction of NOx gas emissions. The surface valence states of the thin film structures with various phase compositions were studied spectroscopically, and a clear connection between the valence states of the film surfaces and gas sensing properties was found. It was concluded that the pure V2O5 films also had some V4+ ions in the surface, and in the mixed phase thin films, the amount V4+ ions was already quite high, indicating a higher amount of oxygen vacancies in the thin film surface – another proof of the existence of V7O16 phase in the film composition. It is also suggested that the particular quantity of oxygen vacancies is one of the reasons for the high gas-sensing response of the thin films. / Tiivistelmä Tässä työssä tutkittiin pulssilaserkasvatettujen vanadiinioksidiohutkalvojen kide- ja faasirakenteita sekä ominaisuuksia kaasuantureina. Vanadiinioksidiohutkalvoja, jotka omaavat erilaiset kide- ja faasirakenteet, sekä erilaiset morfologiat valmistettiin pulssilaserkasvatuksella. Tunnetun V2O5 -faasin lisäksi myös V7O16 -faasi onnistuttiin valmistamaan ensimmäistä kertaa kiinteän aineen epäorgaanisena faasina ohutkalvorakenteeseen. Näiden erilaisten faasirakenteiden olemassaolo todistettiin käyttämällä useita menetelmiä kuten röntgendiffraktiota, Raman spektroskopiaa ja röntgenfotoelektronispektroskopiaa. Sekä ainoastaan V2O5 -faasia sisältäviä ohutkalvoja, että V2O5 ja V7O16 sekafaasirakenteen omaavia ohutkalvoja tutkittiin kaasuanturina, ja mittaustulokset osoittivat erilaisten kalvojen sähköisten kaasuanturivasteiden ominaisuuksien voimakkaan riippuvuuden kalvojen faasirakenteesta. Havaittiin myös, että sekafaasirakenne omaa tietyissä olosuhteissa p-tyyppisen puolijohteen sähkönjohtavuusmekanismin, toisin kuin puhdas V2O5-rakenne, joka on täysin n-tyyppinen. Molemmat ohutkalvotyypit todennettiin olevan erityisen herkkiä ammoniakki (NH3) kaasulle, jopa 40 miljardisosatasolle. Kalvo, jossa oli sekafaasirakenne, omasi korkeamman sähköisen kaasuvasteen kuin puhtaasta V2O5 faasista koostuva ohutkalvo, joka taas toisaalta omasi paremman stabiiliuden pidemmällä aikavälillä. Molemmat kaasuanturimateriaalit havaittiin selektiiviseksi NH3 -kaasulle verrattuna NO- ja CO-kaasuihin. Puhdas V2O5 nanorakenne onnistuttiin myös kasvattamaan kaupalliselle anturialustalle, ja käyttämään menestyksekkäästi herkkänä NH3- kaasuanturina. Lisäksi puhtaan V2O5 nanorakenteen todennettiin olevan erittäin lupaava kaasuanturimateriaali hyödynnettäväksi NOx-kaasupäästöjen vähentämiseen käytettävän SCR-katalyysiprosessin (Selective Catalytic Reduction) ohjauksessa. Ohutkalvotyyppien pinnan sähköistä rakennetta tutkittiin röntgenspektroskopiamenetelmillä, ja selvä yhteys materiaalien pintojen valenssitilojen ja kaasuanturiominaisuuksien välillä havaittiin. Huomattiin, että myös puhdas V2O5 ohutkalvo omaa pinnallaan pienen määrän V4+ -ioneja, ja että ohutkalvossa, jossa on sekafaasirakenne, V4+ -ionien määrä on suuri, ollen yksi todiste lisää V7O16 faasin olemassaoloon kalvon rakenteessa. Tästä johtuva happivakanssien olemassaolo on yksi syy näiden ohutkalvojen korkeaan kaasuherkkyyteen.

Two-Dimensional (2D) materials often exhibit distinguished properties as compared to their 3D counterparts and offer great potential to advance technology. However, even graphene, the first synthesized 2D material, still faces several challenges, despite its high mobility and high thermal conductivity. Similarly, germanene and silicene face challenges due to readily available semiconducting properties to be used in electronics, photonics or photocatalysis applications. Here, we propose two approaches to tune the band gap: One is by forming nanoribbon and edge functionalization and another by doping using inorganic nanoparticle’s interaction with 2D nanomaterials. Edge functionalization of armchair germanene nanoribbons (AGeNRs) has the potential to achieve a range of band gaps. The edge atoms of AGeNRs are passivated with hydrogen (-H and -2H) or halogen (-F, -Cl,-OH, -2F,-2Cl) atoms. Using density functional theory calculations, we found that edge-functionalized AGeNRs had band gaps as small as 0.012 eV when functionalized by -2H and as high as 0.84 eV with -2F. Doping can change the semiconducting behavior of AGeNRs to metal due to the half-filled band making it useful for negative differential resistance (NDR) devices. In the case of zigzag germanene nanoribbons (ZGeNRs), single N or B doping transformed them from anti-ferromagnetic (AFM) semiconducting to ferromagnetic (FM) semiconductor or half-metal. Lastly, formation and edge free energy studies revealed the feasibility of chemical synthetization of edge-functionalized and doped germanene. Electronic, optical and transport properties of the graphene/ZnO heterostructure have been explored using first-principles density functional theory. The results show that Zn12O12 can open a band gap of 14.5 meV in graphene, increase its optical absorption by 1.67 times, covering the visible spectrum and extended to the infra-red (IR) range, and create slight nonlinear I-V characteristics depending on the applied bias. This agrees well with collaborative experimental measurement of a similar system. In conclusion, we have successfully studied the potential use of edge functionalization, band gap periodicity in nanoribbon width, and doping in germanene nanoribbons. Structural stability was also studied to investigate the feasibility for experimental synthesization. Inorganic nanoparticle’s interaction with graphene envisages the possibility of fabricating photo-electronic device covering visible spectrum and beyond. Finally, graphene complexes were merged with naturally available direct band gap of monolayer MoS2 to build efficient energy harvesting and photo detecting devices.

Submitted by CAMILA PAIXÃO SANTOS (camila.paixao@yahoo.com.br) on 2016-11-03T08:48:02Z No. of bitstreams: 1 DEFESA_FINAL.pdf: 1918396 bytes, checksum: 8ba642a529d4534993d8d024baa1c739 (MD5) / Rejected by Felipe Augusto Arakaki (arakaki@reitoria.unesp.br), reason: Solicitamos que realize uma nova submissão seguindo a orientação abaixo: O arquivo submetido está sem a ficha catalográfica. A versão submetida por você é considerada a versão final da dissertação/tese, portanto não poderá ocorrer qualquer alteração em seu conteúdo após a aprovação. Corrija esta informação e realize uma nova submissão com o arquivo correto. Agradecemos a compreensão. on 2016-11-10T12:39:58Z (GMT) / Submitted by CAMILA PAIXÃO SANTOS (camila.paixao@yahoo.com.br) on 2016-11-11T18:37:20Z No. of bitstreams: 1 DEFESA_FINAL.pdf: 2077990 bytes, checksum: 7c050271b8596995c2ed6deeef0aca4e (MD5) / Approved for entry into archive by LUIZA DE MENEZES ROMANETTO null (luizaromanetto@hotmail.com) on 2016-11-16T19:53:18Z (GMT) No. of bitstreams: 1 santos_cp_me_guara.pdf: 2077990 bytes, checksum: 7c050271b8596995c2ed6deeef0aca4e (MD5) / Made available in DSpace on 2016-11-16T19:53:18Z (GMT). No. of bitstreams: 1 santos_cp_me_guara.pdf: 2077990 bytes, checksum: 7c050271b8596995c2ed6deeef0aca4e (MD5) Previous issue date: 2016-09-03 / Não recebi financiamento / Este trabalho apresenta e discute o uso do óxido de cério na fabricação de filmes espessos por “screen printing” para aplicações em sensores de gás. Nesse estudo o CeO2 puro foi obtido pelo método dos precursores poliméricos utilizando como resina precursora o citrato de céria. O “puff” – espuma resultante da primeira fase do tratamento térmico da resina- foi calcinado a 550, 600, 700 e 750°C. O pó foi caracterizado por termogravimetria (TG) e as propriedades estruturais, morfológicas foram avaliadas por difratometria de raios X (DRX), espectroscopia Raman, área de superfície por isotermas Brunauer, Emmett e Taller (BET) e microscopia eletrônica de varredura (MEV). A resposta sensora foi estudada em uma câmara de teste construída no Laboratório de Catálise e Superfícies do Instituto de Ciência de Tecnologia de Materiais (INTEMA) da Universidade de Mar del Plata. A TG mostrou a formação de óxido de cério a 550°C, temperatura relativamente baixa quando comparada com outros métodos. Mediante DRX todas as amostras mostraram picos correspondentes à fase pura de CeO2 o qual cristaliza em uma estrutura cúbica do tipo fluorita, entretanto, maiores temperaturas de calcinação mostraram aumento da cristalinidade e tamanho do cristalito. No espectro Raman, um forte pico em torno do 461 cm-1 foi detectado, atribuído às vibrações simétricas do Ce-O. A área de superfície BET dos pós foi de 301, 77 m2/g o que evidencia a formação de partículas muito pequenas e altamente reativas. As micrografias obtidas por MEV mostram a presença de diferentes tamanhos na forma de aglomerados. A caracterização da resposta sensora mostrou que o sensor fabricado a partir de pós de CeO2 puro apresenta um bom tempo de resposta, alcançando a melhor performance com temperatura de trabalho de 400 °C, tanto em atmosferas redutoras e oxidantes. A característica principal observada foi que os resultados são dependentes dos ciclos anteriores, a reprodutibilidade do sistema é garantida quando se apaga a “memória” do sistema, expondo-o ao vácuo. / This paper presents and discusses the use of cerium oxide in the production of thick films for "screen printing" for applications in gas sensors. In this study the pure CeO2 was obtained by the polymeric precursor method using as a precursor resin citrate ceria. The "puff" - resulting foam from the first stage of thermal treatment of the resin-calcined at 550, 600, 700 and 750 °C. The powder was characterized by thermogravimetry (TG) and structural, morphological were evaluated by X-ray diffraction (XRD), Raman spectroscopy, isothermal Brunauer surface area, Emmett and Taller (BET) and scanning electron microscopy (SEM) . The sensor response was studied in a test chamber built in the Laboratory of Catalysis and Surface Materials Technology Institute of Science (INTEMA), University of Mar del Plata. The thermogravimetry showed the formation of cerium oxide at 550° C, relatively low temperature compared with other methods. Upon XRD all samples showed peaks corresponding to pure CeO2 phase which crystallizes in a cubic fluorite type structure, however, higher calcination temperatures showed increased crystallinity and crystallite size. In the Raman spectrum, a strong peak around 461 cm-1 was detected, assigned to symmetric vibrations of the Ce-O. The BET surface area of the powders was 301, 77 m2 /g which shows the formation of very small and highly reactive particles. The SEM micrographs show the presence of different sizes in the form of agglomerates. The characterization of the sensor response showed that the sensors manufactured from pure CeO2 powder has a good response time, achieving better performance at 400 °C working temperature in both reducing and oxidizing atmospheres. The main feature observed was that the results are dependent on previous cycles, the system reproducibility is guaranteed when it deletes the "memory" of the system, exposing it to vacuum.

Neste trabalho, foram desenvolvidos filmes finos de composição SrTi1-xFexO3 (0,00≤ x ≤0,150) nanoestruturados visando sua aplicação como sensor de gás ozônio. Os filmes finos foram depositados através da técnica de deposição por feixe de elétrons (EBD) cujo alvo utilizado foram pastilhas obtidas a partir do pó cristalino SrTi1-xFexO3 (0,00≤ x ≤0,150) sintetizadas através do método dos precursores poliméricos. Foi observado a partir das analises termogravimétrica e térmica diferencial que a incorporação de ferro no sistema diminui a temperatura de queima do pó precursor, sugerindo que o ferro atua como catalisador na cadeia polimérica. Os filmes depositados por DFE apresentam-se no estado amorfo sendo necessário um tratamento térmico ex-situ para que a fase cristalina desejada seja obtida. Todos os filmes apresentaram uma boa aderência aos diferentes tipos de substratos utilizados. Após o processo de cristalização, os filmes depositados sobre diferentes substratos foram caracterizados através das técnicas de difração de raios-X, espectroscopia UV-Vis e microscopia de força atômica (MFA). Foi observado que um aumento na temperatura de tratamento térmico dos filmes leva a um aumento no grau de cristalização e a uma diminuição no valor da energia de gap, calculada a partir dos espectros UV-VIS. A analise por MFA mostrou que a mudança do tipo de substrato utilizado não influencia as propriedades estruturais e microestruturais dos filmes. Através da realização de medidas de resistência elétrica, observou-se que os filmes cristalinos submetidos a um tratamento térmico ex-situ a 500oC por 4 horas apresentaram uma boa sensibilidade ao gás ozônio sendo possível detectar a presença de até 75 ppb de ozônio. / In this study, nanostructured thin films of SrTi1-xFexO3 (0.00 ≤ x ≤ 0.150) compositions were prepared looking their application as ozone gas sensor. The thin films were deposited using the technique of electron beam deposition (EBD) whose targets were obtained from polycrystalline SrTi1-xFexO3 (0.00 ≤ x ≤ 0.150) powders synthesized by the polymeric precursor method. It was observed from the thermogravimetric and differential thermal analysis that the incorporation of iron in the system decreases the calcination temperature of the precursor powders, suggesting that the iron acts as a catalyst in the polymer chain. The as obtained films deposited by EBD present an amorphous state being necessary a ex-situ heat treatment to obtain the desired crystalline phase. All films showed good adhesion to different substrates. After the crystallization process, the films deposited on different substrates were characterized through X-ray diffraction, UV-Vis spectroscopy and atomic force microscopy (AFM) trechniques. It was observed that an increase in the annealing temperature of the film results in an increase in the degree of crystallization and a decrease in the value of band gap energy, which was calculated from the UV-VIS spectra. The AFM analysis showed that changing the type of substrate does not influence the structural properties and microstructure of the films. By carrying out measurements of electrical resistance, it was observed that the crystalline films subjected to a ex-situ heat treatment at 500oC for 4 hours showed a good sensitivity to the ozone gas being possible to detect the presence of up to 75 ppb ozone.

Abstract Transition metal dichalcogenide (TMD) materials crystalize in a layered structure with a stoichiometry MX₂ where M is a transition metal (Mo, W, Tc, Re, V, Nb, Ta, Ti, Zr, Hf) and X is a chalcogen (S, Se, Te). While there is a strong covalent bond between the chalcogen and the metal atoms in each 2-dimensional (2D) sheet, the bulk 3-dimensional crystals are held together by weak van der Waals forces acting on the adjacent 2D sheets allowing for micromechanical and liquid phase exfoliation into nanostructures composed of either a single layer or a few layers. Since the electronic band structure depends not only on the chemistry but also on the number of layers, a whole new range of metal, semimetal and semiconductor materials may be achieved. These properties, among many other advantages (e.g. tunable band structure, high mobility of carriers, easy intercalation with ions), make TMDs appealing and timely for applications in solar cells and photodetectors, heterogeneous catalysis, electrocatalytic electrodes, energy storage and in (electro) chemical sensing. Motivated by the anticipated fascinating properties of TMDs, this research work focuses on the synthesis, characterization and application of a novel hybrid WS₂ nanomaterial. While the original goal of the research work was to develop a simple method to synthesize WS₂ nanowires, it became clear that instead of nanowires a hybrid nanowire-nanoflake (NW-NF) structure could be synthesized by a simple thermal sulfurization of hydrothermally grown WO₃ nanowires. The structure, morphology and composition of the new materials were analyzed by X-ray diffraction, Raman spectroscopy, electron microscopy and X-ray photoelectron spectroscopy. Temperature dependent electrical measurements carried out on random networks of the nanostructures showed nonlinear characteristics and a negative temperature coefficient of resistance indicating that the hybrids were semiconducting. Resistive gas sensors were prepared and exposed to H₂S, CO, NH₃, H₂ and NO and to which the devices displayed ultra-high sensitivity (0.043 ppm⁻¹) towards H₂S with a detection limit of 20 ppb. The results suggest further exploration of gas sensing with TMDs as potential competitive alternatives to the classical metal oxide based devices. Moreover, photodetector devices with excellent visible light response were also demonstrated using an individual WS₂ NW-NF hybrid as well as its random networks having photoresponsivity of up to 400 mAW⁻¹. This was two orders of magnitude higher than that measured for other 2D materials based devices. Overall, the WS₂ nanowire-nanoflake hybrid is a truly multipurpose and multifunctional semiconductor making it a promising material for advanced micro, nano and optoelectronics devices. / Tiivistelmä Siirtymämetallidikalkogenidistä (transition metal dichalcogenide, TMD) olevat materiaalit kiteytyvät kerroksittaisiksi rakenteiksi, joiden stoikiometria on MX₂, missä M on siirtymämetalli (Mo, W, Tc, Re, V, Nb, Ta, Ti, Zr, Hf) ja X on kalkogeeni (S, Se, Te). 2-ulotteisessa (2D) tasossa kalkogeenin ja metallin välillä on voimakas kovalenttinen sidos, mutta suuremmassa kolmiulotteisessa kiteessä viereisiä tasoja sitoo toisiinsa vain heikot van der Waals-voimat, jolloin tasot on mahdollista erottaa mikromekaanisesti ja nestefaasikuorinnalla yksittäisiksi tai muutamasta kerroksesta koostuvaksi nanorakenteeksi. Koska elektronivyörakenne ei riipu ainoastaan kemiallisesta koostumuksesta vaan myös kerrosten lukumäärästä, voidaan muodostaa täysin uusia metallisia, puolimetallisia tai puolijohdemateriaaleja. Nämä ominaisuudet monien muiden lisäksi (esim. räätälöity vyörakenne, korkeanliikkuvuuden varauksen kuljettajat, helppo ionien interkelaatio) tekevät TMD-materiaaleista kiinnostavia ja ajankohtaisia aurinkokennoihin, valokennoihin, heterogeeniseen katalyysiin, sähkökatalyyttisiin elektrodeihin, energiavarastoihin ja sähkökemiallisiin antureihin. TDM-materiaalien oletettavasti kiehtovien ominaisuuksien motivoimana tämä tutkimus keskittyy uusien hybridi-WS₂-nanomateriaalien synteesiin, karakterisoimiseen ja sovellutuksiin. Tutkimuksen alkuperäinen tavoite oli kehittää yksinkertainen menetelmä WS₂-nanolankojen syntetisoimiseksi, mutta kävi ilmi että nanolankojen sijaan syntyi nanolanka-nanohiutale -hybridirakenne (nanowire-nanoflake, NW-NF), kun hydrotermisesti kasvatettuja WO₃-nanolankoja rikitettiin termisesti. Näiden uusien materiaalien rakenne, morfologia ja koostumus on analysoitu röntgendiffraktiolla, Raman-spekstrokopialla, elektronimikroskoopilla ja röntgenfotoelektronispektroskopialla. Valikoimattomista nanorakenteista koostuvien verkostojen lämpötilasta riippuvien sähköisten ominaisuuksien mittaukset osoittavat epälineaarisia piirteitä ja negatiivinen resistanssin lämpötilakerroin viittaa hybridien puolijohtavuuteen. Materiaalista valmistettiin resistiivisiä kaasuantureita, jotka altistettiin H₂S:lle, CO:lle, NH₃:lle, H₂:lle ja NO:lle, näistä anturi osoitti erittäin suurta herkkyyttä H₂S:lle (0.043 ppm) havaintorajan ollessa 20 ppb. Tulokset kannustavat TMD-materiaalien kaasuanturisovellutusten jatkotutkimukseen tarjoten potentiaalisesti kilpailukykyisen vaihtoehdon perinteisille metallioksidi-pohjaisille laitteille. Lisäksi, yksittäisillä WS₂-nanolanka-nanohiutalepartikkeleilla sekä valikoimattomilla nanolanka-nanohiutalehybridiverkostoilla demonstroitiin valokenno, jonka vaste näkyvään valoon oli jopa 400 mAW⁻¹ ollen kaksi kertaluokkaa korkeampi kuin muilla 2D-materiaaleihin perustuvilla kennoilla. Kaiken kaikkiaan, WS₂-nanolanka-nanohiutalehybridi on todella monikäyttöinen ja monipuolinen puolijohde ollen lupaava materiaali kehittyneille mikro-, nano- ja optoelektronisille laitteille.

This diploma thesis discusses the gas sensor preparation via anodic oxidation. It names sensor types, deals with the sensing principle of electrochemical sensors in detail and submits sensor parameters. It describes preparation technology and characterization technology methods. In the experimental part, it focuses on both the measurement methodology and the electrochemical oxygen sensor covered with titanium dioxide nanocolumns fabrication. Not the least it discusses acquired research results.

The design, construction and optimization of a low power-high temperature heated ceramic sensor to detect leaking of halogen gases in refrigeration systems are presented. The manufacturing process was done with microelectronic assembly and the Low Temperature Cofire Ceramic (LTCC) technique. Four basic sensor materials were fabricated and tested: Li2SiO3, Na2SiO3, K2SiO3, and CaSiO3. The evaluation of the sensor material, sensor size, operating temperature, bias voltage, electrodes size, firing temperature, gas flow, and sensor life was done. All sensors responded to the gas showing stability and reproducibility. Before exposing the sensor to the gas, the sensor was modeled like a resistor in series and the calculations obtained were in agreement with the experimental values. The sensor response to the gas was divided in surface diffusion and bulk diffusion; both were analyzed showing agreement between the calculations and the experimental values. The sensor with 51.5%CaSiO3 + 48.5%Li2SiO3 shows the best results, including a stable current and response to the gas.

abstract: Global industrialization and urbanization have led to increased levels of air pollution. The costs to society have come in the form of environmental damage, healthcare expenses, lost productivity, and premature mortality. Measuring pollutants is an important task for identifying its sources, warning individuals about dangerous exposure levels, and providing epidemiologists with data to link pollutants with diseases. Current methods for monitoring air pollution are inadequate though. They rely on expensive, complex instrumentation at limited fixed monitoring sites that do not capture the true spatial and temporal variation. Furthermore, the fixed outdoor monitoring sites cannot warn individuals about indoor air quality or exposure to chemicals at worksites. Recent advances in manufacturing and computing technology have allowed new classes of low-cost miniature gas sensor to emerge as possible alternatives. For these to be successful however, there must be innovations in the sensors themselves that improve reliability, operation, and their stability and selectivity in real environments. Three novel gas sensor solutions are presented. The first is the development of a wearable personal exposure monitor using all commercially available components, including two metal oxide semiconductor gas sensors. The device monitors known asthma triggers: ozone, total volatile organic compounds, temperature, humidity, and activity level. Primary focus is placed on the ozone sensor, which requires special circuits, heating algorithm, and calibration to remove temperature and humidity interferences. Eight devices are tested in multiple field tests. The second is the creation of a new compact optoelectronic gas sensing platform using colorimetric microdroplets printed on the surface of a complementary-metal-oxide-semiconductor (CMOS) imager. The nonvolatile liquid microdroplets provide a homogeneous, uniform environment that is ideal for colorimetric reactions and lensless optical measurements. To demonstrate one type of possible indicating system gaseous ammonia is detected by complexation with Cu(II). The third project continues work on the CMOS imager optoelectronic platform and develops a more robust sensing system utilizing hydrophobic aerogel particles. Ammonia is detected colorimetrically by its reaction with a molecular dye, with additives and surface treatments enhancing uniformity of the printed films. Future work presented at the end describes a new biological particle sensing system using the CMOS imager. / Dissertation/Thesis / Doctoral Dissertation Materials Science and Engineering 2020

In this study, gas sensing systems that are based on piezoelectric smart material and structures are proposed, designed, developed, and tested, which are mainly aimed to address the temperature dependent CO2 gas sensing in a real environment. The state-of-the-art of gas sensing technologies are firstly reviewed and discussed for their pros and cons. The adsorption mechanisms including physisorption and chemisorption are subsequently investigated to characterize and provide solutions to various gas sensors. Particularly, a QCM based gas sensor and a C-axis inclined zigzag ZnO FBAR gas sensor are designed and analyzed for their performance on room temperature CO2 gas sensing, which fall into the scope of physisorption. In contrast, a Langasite (LGS) surface acoustic wave (SAW) based acetone vapor sensor is designed, developed, and tested, which is based on the chemisorption analysis of the LGS substrate. Moreover, solid state gas sensors are characterized and analyzed for chemisorption-based sensitive sensing thin film development, which can be further applied to piezoelectric-based gas sensors (i.e. Ca doped ZnO LGS SAW gas sensors) for performance enhanced CO2 gas sensing. Additionally, an innovative MEMS micro cantilever beam is proposed based on the LGS nanofabrication, which can be potentially applied for gas sensing, when combined with ZnO nanorods deposition. Principal component analysis (PCA) is employed for cross-sensitivity analysis, by which high temperature gas sensing in a real environment can be achieved. The proposed gas sensing systems are designated to work in a high temperature environment by taking advantage of the high temperature stability of the piezoelectric substrates.

This thesis deals with one-dimensional (1D) and two-dimensional nanomaterials (2D) in terms of their utilization for new types of gas sensors. Thesis focuses on study of sensing elements for gas sensors based on semiconductor metal oxide materials (MOX) and their manufacturing technology. The objective of the thesis is the design and implementation of a sensing elements formed by selected nanomaterials based on the structure of interdigital electrodes. The result of the practical part of the thesis is the characterization and comparison of materials in terms of their detection parameters in the presence of selected test gases. The first part of thesis hierarchically defines chemoresistive gas sensor, characterizes and explains its operation principle. Second part studies 1D and 2D nanomaterials of sensing elements for MOX chemoresistive gas sensors, contains a research of their properties and describes their methods of manufacturing and implementation. The last part deals with the implementation of the sensitive layer of the sensor with selected nanomaterials, characterizes and compares their detection properties.