Philosophiae Doctor - PhD / When the amorphous silicon (a-Si) dangling bonds are bonded to hydrogen the concentration of the dangling bond is decreased. The resulting film is called hydrogenated amorphous silicon (a-Si:H). The reduction in the dangling bonds concentration improves the optoelectrical properties of the film. The improved properties of a-Si:H makes it possible to manufacture electronic devices including a solar cell.A solar cell device based on the hydrogenated amorphous silicon (a-Si:H) was fabricated using the Hot-Wire Chemical Vapour Deposition (HWCVD). When an n-i-p solar cell configuration is grown, the norm is that the p-doped layer is deposited from a mixture of silane (SiH4) gas with diborane (B2H6). The boron atoms from diborane bonds to the silicon atoms and because of the number of the valance electrons, the grown film becomes a p-type film. Aluminium is a group 3B element and has the same valence electrons as boron, hence it will also produce a p-type film when it bonds with silicon.In this study the p-doped layer is grown from the co-deposition of a-Si:H from SiH4 with aluminium evaporation resulting in a crystallized, p-doped thin film. When this thin film is used in the n-i-p cell configuration, the device shows photo-voltaic activity.The intrinsic layer and the n-type layers for the solar cell were grown from SiH4 gas and Phosphine (PH3) gas diluted in SiH4 respectively. The individual layers of the solar cell device were characterized for both their optical and electrical properties. This was done using a variety of experimental techniques. The analyzed results from the characterization techniques showed the films to be of device quality standard. The analysed results of the ptype layer grown from aluminium showed the film to be successfully crystallized and doped.A fully functional solar cell was fabricated from these layers and the cell showed photovoltaic activity.

Volatile organic compounds (VOCs) in the indoor air have adverse effects on the dwellers residing in a building or a vehicle. One of these effects is called sick building syndrome (SBS). SBS refers to situations in which the users of a building develop acute health effects and discomfort depending on the time they spend inside some buildings without having any specific illness. Furthermore, monitoring volatile organic compounds could lead to early diagnosis of specific illnesses through breath analysis. Among those VOCs formaldehyde, acetaldehyde can be listed. In this thesis, VOC detecting thin film sensors have been investigated. Such sensors have been manufactured using semiconducting metal oxides, ligand activated gold nanoparticles and Graphene/TiO2 mixtures. Advanced gas deposition unit, have been used to produce NiO thin films and Au nanoparticles. DC magnetron sputtering has been used to produce InSnO and VO2 thin film sensors. Graphene/TiO2 sensors have been manufactured using doctor-blading. While presenting the results, first, material characterization details are presented for each sensor, then, gas sensing results are presented. Morphologies, crystalline structures and chemical properties have been analyzed using scanning electron microscopy, X-ray diffraction and X-ray photo electron spectroscopy. Furthermore, more detailed analyses have been performed on NiO samples using extended X-ray absorption fine structure method and N2 adsorption measurements. Gas sensing measurements were focused on monitoring formaldehyde and acetaldehyde. However, responses ethanol and methane were measured in some cases to monitor selectivity. Graphene/TiO2 samples were used to monitor NO2 and NH3. For NiO thin film sensors and Au nano particles, fluctuation enhanced gas sensing is also presented in addition to conductometric measurements.

In this study, we used UV-ozone Ar sputtering, X-ray photoelectron and ultra-violet photoelectron spectroscopies and sputtering based depositions of RuO2 and Se nano-layers on indium tin oxides (ITOs). We elucidated the effect of Ar sputtering on the composition and chemistry of Sn rich ITO surface. We demonstrated that while a combination of UV-ozone radiation and Ar sputtering removes most of the hydrocarbons responsible for degrading the work function of ITO, it also removes significant amount of the segregated SN at the ITO surface that's responsible for its reasonable work function of 4.7eV. We also demonstrated for the first time that sputtering cleaning ITO surface leads to the reduction of the charge state of Sn from Sn4+ to Sn2+ that adds to the degradation of the work function. For the nano-layers coverage of ITO studies, we evaluated both RuO2 and Se. For RuO2 coated ITO, XPS showed the formation of a Ru-Sn-O ternary oxide. The RuO2 nano-layer reduced the oxidation state of Sn in the Sn-rich surface of ITO from +4 to +2. The best work function obtained for this system is 4.98eV, raising the effective work function of ITO by more than 0.5 eV. For the Se coated ITO studies, a systematic study of the dependence of the effective work function on the thickness of Se overage and its chemistry at the Se/ITO interface was undertaken. XPS showed that Se reacts with Sn at the Sn-rich surface of ITO determined the presence of both negative and positive oxidation state of Se at the Se/ITO interface. The Se also reduced the oxidation state of Sn from Sn4+ to Sn2+ in the Sn-rich ITO surface. The highest effective work function obtained for this system is 5.06eV. A combination of RuO2/Se nanoscale coating of optimally cleaned ITO would be a good alternative for device applications that would provide work function tuning in addition to their potential ability to act as interface stabilizers and a barrier to reaction and inter-diffusion at ITO/active layers interfaces responsible for long term stability of devices and especially organic solar cells and organic light emitting diodes.

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A key to solar cells with lower environmental impact is higher efficiency and reduced material usages. Bifacial solar cells may have a higher efficiency as light can enter from two directions and tandem solar cells may use a larger part of the incoming solar spectrum, increasing the efficiency. However, both these applications require transparent and conducting contacts. This thesis aimed to investigate how suitable the transparent conductive oxides aluminum doped zinc oxide (AZO) and indium doped tin oxide (ITO) are as contacts in bifacial CIGS cells or CIGS/Silicon tandem cells. The contacts must remain stable when CIGS is deposited on top of it, meaning that they have to endure first 500°C and then 600°C in combination with copper, indium, gallium and selenium vapours. A thin layer of AZO topped with ITO and pure ITO films of different thicknesses were deposited by RF- and DC-sputtering, varying the oxygen flow. Opto-electrical characterization showed that the transparency in the infrared was balanced against high conductivity due to a shift in the plasmon peak's position. No great difference was seen between pure ITO samples and AZO/ITO samples, so only the first where further processed. The ITO films were annealed to 500°C in the CIGS deposition chamber, exposed to selenium vapour. The films' sheet resistances dropped drastically, which was mainly attributed to activation of tin donors. ITO produced with low oxygen flows also appeared more crystalline according to x-ray diffraction measurements. Photon absorption in the ITO was used to estimate the current loss in bifacial and tandem applications and graphs with current loss and sheet resistance can be used to select an ITO deposition process. Commercial ITO was exposed to 100s of the CIGS deposition process but only during selenium and gallium vapour. A layer of gallium selenide could be identified on the surface, but the ITO appeared to remain stable. Sodium fluoride pre deposition treatment lowered the samples absorption for all wavelengths compared to non-treated samples.

<p> Volatile organic compounds (VOCs) are byproducts of metabolic processes that can be uniquely dysregulated by various medical conditions and are expressed in biological samples. Therefore, VOCs expressed in breath, urine and other sample types may be utilized for noninvasive, rapid, and accurate diagnostics in a point-of-care setting. Currently, the most common methods for VOC detection include gas chromatography-mass spectrometry (GC-MS) and electronic noses (E-noses) that integrate nanosensors. Both methods present important advantages and challenges that allow their implementation for different applications. While GC-MS can be used to directly identify VOCs in complex matrices, it is a non-portable and high-cost instrument. On the other hand, E-noses are portable and user-friendly VOC detectors, but they do not allow for direct VOC identification or quantification. Among different VOC rich sample types, breath offers the advantage of being a virtually limitless source of endogenous biomarkers that can be implemented for noninvasive VOC detection.</p> <p><br></p> <p>The presented thesis focuses on the optimization of the operating parameters (heater and sensor voltages) of a metal oxide (MOX) sensor and breath sampling techniques (sensor casing, breath fractionation, and exhalation volume) for their implementation in exhaled VOC analysis. In parallel, an in-house feature extraction algorithm was developed and implemented for the optimization of a MOX sensor composed of a tin oxide (SnO2) sensing layer. The optimized sensor parameters (heater voltage equal to 2 V and sensor voltage equal to 0.8 V) and breath sampling protocol (24 L of whole breath analyzed using the in-house sensor casing design) were tested with exhaled breath samples from distinct volunteers which could be successfully separated with 100% accuracy. The sensor response also showed a high degree of intrasubject reproducibility (RSD < 6%). Additionally, the sensor performance was further validated under ambient conditions, and sensor degradation was studied over the course of 3 months. Finally, sensor response to synthetic VOC profiles and individual VOC standards was explored. Optimized SnO2 sensors distinguished between VOC mixtures regardless of variations in relative humidity (RH) levels. Furthermore, the characteristic sensor response to VOC standards indicates that the sensors are most sensitive toward isopropanol by a factor of 1.15 in 45% RH and a factor of 3.58 in 85% RH relative to isoprene. </p> <p><br></p> <p>To translate the potential of MOX sensors to point-of-care biomedical applications, there first exists the need to establish a reference of sensor baseline signals corresponding to exhaled breath samples from healthy individuals. SnO2 sensors and breath sampling methods were implemented for the collection of individual samples from 109 relatively healthy volunteers. 10 of these volunteers provided 9 additional samples over the course of six months. In parallel, exhaled breath samples were also analyzed by GC-MS to comprehensively profile VOCs present in the samples. The results from these experiments not only aid in the identification of the healthy breath signal baseline but also allow the exploration of VOC reproducibility over time. High variation between samples from distinct volunteers was observed, but samples longitudinally collected across volunteers could not be distinguished, alluding to the existence of a universal range of sensor signals that could describe the composition of exhaled breath from healthy subjects. Finally, results were compared with relevant confounding variables to better understand how VOCs are impacted by an array of factors that are not directly correlated to disease diagnosis. Sensor signals were significantly elevated in breath samples from male volunteers compared to samples from female subjects (p-value = 0.044). Interestingly, isoprene signals resulting from the GC-MS analysis were also higher in male subjects relative to females. No other relationships were identified between sensor signals and the confounding variables of interest. </p> <p><br></p> <p>Future work would require a deeper understanding of sensor degradation and life cycle, along with sensor testing using a broader range of individual VOC standards and more complex VOC profiles. Additionally, further comparison between sensor signal and GC-MS signal of relevant VOC biomarkers present in breath would be beneficial. Nonetheless, the presented be leveraged in future investigations aiming to identify biomarkers for different medical conditions. Finally, the findings disclosed in the deposited thesis suggest the ability of a SnO2 nanosensor array to be implemented for breath analysis, providing a noninvasive, easy to use, and reliable diagnostic device in a point-of-care setting. </p>

No description available.

No description available.

The primary objective of this thesis is to develop a process for fabricating integrated circuits based on thin-film transistors (TFTs) using zinc tin oxide (ZTO) as the channel layer. ZTO, in contrast to indium- or gallium-based amorphous oxide semiconductors (AOS), is perceived to be a more commercially viable AOS choice due to its low cost and ability to be deposited via DC reactive sputtering. In the absence of an acceptable ZTO wet etch process, a plasma-etching process using Ar/CH₄ is developed for both 1:1 and 2:1 ZTO compositions. An Ar/CH₄ plasma etch process is also designed for indium gallium oxide (IGO), indium gallium zinc oxide (IGZO), and indium tin oxide (ITO). Ar/CH₄ dry etches have excellent selectivity with respect to SiO₂, providing a route for obtaining patterned ZTO channels. A critical asset of ZTO process integration involves removing polymer deposits after ZTO etching without active layer damage. A ZTO process is developed for the fabrication of integrated circuits which use ZTO channel enhancement-mode TFTs. Such ZTO TFTs exhibit incremental and average mobilities of 23 and 18 cm²V⁻¹s⁻¹, respectively, turn-on voltages approximately 0 to 1.5 V and subthreshold swings below 0.5 V/dec when annealed in air at 400 °C for 1 hour. Several types of ZTO TFT circuits are realized for the first time. Despite large parasitic capacitances due to large gate-source and gate-drain overlaps, AC/DC rectifiers are fabricated and found to operate in the MHz range. Thus, they are usable for RFID and other equivalent-speed applications. Finally, a ZTO process for simultaneously fabricating both enhancement-mode and depletion-mode TFTs on a single substrate using a single target and anneal step is developed. This dual-channel process is used to build a high-gain two-transistor enhancement/depletion inverter. At a rail voltage of 10 V, this inverter has a gain of 10.6 V/V, the highest yet reported for an AOS-based inverter. This E/D inverter is an important new functional block which will enable the realization of more complex digital logic circuits. / Graduation date: 2009

Made available in DSpace on 2017-07-21T20:42:31Z (GMT). No. of bitstreams: 1 Herve Stangler Irion.pdf: 4493069 bytes, checksum: 2fe9398c9c2006313a4b148ad265c9dd (MD5) Previous issue date: 2006-03-30 / In this work it was investigated the influence the in influence of the doping Pr6O11 in the electrical conductivity and in the microstructural properties in the basic ternary system (98,95 – x)%Sn02 1,0% Co0 0,05%Ta205. The used concentration of the doping Pr6011 had varied in 0,05%, 0.5% in mol, remaining constant the concentrations for the Co0 and Ta205. The processing applied was the conventional method of mixture of oxides in ambient atmosphere. The samples had been conformed in 50 MPa and sintered in 1350°C for 2 hours. After the sintering the densification of ceramics was verified with a value of 93,63% for the system with 0,1% in mol of Pr6011. The study of the electrical properties for the varistor system Sn02.Co0.Ta205 Pr6011 was carried out in continuous current in the ambient temperature and in function of the temperature. It was observed that the variation in the concentration of Pr6011 modifies the electrical behavior of the ceramics. The electrical parameters found are of [alfa]= 8,0, Er= 319 volts/cm and Vb= 0,66 volts/barrier for basic ternary system and [alfa]= 17,0 Er= 853 volts/cm and Vb= 1,15 volts/barrier with the addition of 0,10% in mol of Pr6011. The system with 0,05% mol 0.1% in mol Pr6011 presents the same value of the non linearity coefficient of the system with 0,1% in mol, however, with lower values of rupture tension and barrier tension (Er= 708 volts/cm and Vb= 0,98 volts/barrier). To concentration above of 0,1% in mol of Pr6011, the increase of the concentration of this doping, starts to be deleterious to the varistor characteristics. This effects is due to the increase in the concentration of the stannate of praseodymium phase (Pr2Sn207). This crystalline phase with the cassiterita phase (Sn02)was characterized by DRX and EDS and quantified by the refinement of Rietveld. / Neste trabalho investigou-se a influência do dopante Pr6O11 na condutividade elétrica e nas propriedades microestruturais no sistema ternário básico (98,95-x)%SnO2.1,0%CoO.0,05%Ta2O5. As concentrações utilizadas do dopante Pr6O11 variaram em 0,05%, 0,1%, 0,3% e 0,5% em mol, mantendo-se constante as concentrações para o CoO e Ta2O5 . O processamento empregado foi o método convencional de mistura dos óxidos. As amostras foram conformadas a 50 MPa e, sinterizadas a 1350ºC por 2 horas em atmosfera ambiente. Após a sinterização verificou-se densificação das cerâmicas, com valor de 93,63% para o sistema com 0,1% em mol de Pr6O11. O estudo das propriedades elétricas para o sistema varistor SnO2.CoO.Ta2O5 Pr6O11 foi realizado em corrente contínua a temperatura ambiente e, em função da temperatura. Observou-se que a variação na concentração de Pr6O11 altera o comportamento elétrico das cerâmicas. Os parâmetros elétricos encontrados são de [alfa] = 8,0, Er= 319 volts/cm e Vb= 0,66 volts/barreira para o sistema ternário básico e, [alfa] = 17,0, Er= 853 volts/cm e Vb = 1,15 volts/barreira com a adição de 0,10% em mol de Pr6O11. O sistema com 0,05% em mol de Pr6O11 apresenta o mesmo valor do coeficiente de não linearidade do sistema com 0,1 % em mol, entretanto, com valores menores de tensão de ruptura e tensão de barreira (Er= 708 volts/cm e Vb= 0,98 volts/barreira). Para concentrações acima de 0,1% em mol de Pr6O11, o aumento da concentração desse dopante, passa a ser deletério para as características varistoras. Esse efeito é devido ao aumento na concentração da fase cristalina estanato de praseodímio (Pr2Sn2O7). Essa fase cristalina, juntamente com a fase cassiterita (SnO2), foi caracterizada por DRX e por EDS e, quantificadas pelo refinamento de Rietveld.