A multi-technique approach to study the microstructural properties of tin-based transparent conductive oxides

Transparent conductive oxides (TCOs) are semiconductor-like materials that exhibit high electrical conductivity and high optical transparency combined. They are adopted in various applications ranging from gas sensors, to electrochromic windows, to photovoltaic cells. Indium-based TCOs represent the industry standard. Nevertheless, indium is among the less abundant elements in the earth crust and forecasts based on its current consumption envisage an urgent need to replace it. Tin-based TCOs are a promising alternative, since their opto- electronic characteristics mimic the ones of indium-based materials. This thesis aims to investigate the link between optoelectronic and microstructural properties of tin dioxide and zinc tin oxide (ZTO) with a composition Zn0.05Sn0.30O0.65 and their stability when submitted to thermal treatments. Indeed, lots of practi- cal applications require the TCO to operate in high temperature conditions. To conduct this study, a combination of analytical techniques, such as transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), X- ray diffraction (XRD), electron paramagnetic resonance (EPR) and differential scanning calorimetry (DSC) was employed. Amorphous SnO2 and ZTO were deposited by RF sputtering and annealed up to 1050°C in different atmospheres. The influence of annealing temperature and atmosphere were decoupled and led us to an in-depth comprehension of the mechanisms governing the optoelectronic properties of both materials. When annealed in air, between room temperature and 300°C, ZTO exhibits increased mobility and carrier concentration with respect to the as-deposited state. This increase, investigated with DSC, was ascribed to a structural relaxation that allows point defects to release electrons in conduction band. Between 300°C and 500°C atmospheric oxygen passivates oxygen vacancies, drastically decreasing the carrier concentration and therefore causing a large drop of the conductivity. EPR experiments allowed to ascribe the drop in conductivity to the decrease of carrier concentration, which occurs slightly before the phase change. At 570°C (and 930°C for the case of vacuum annealing) the phase change occurs and the ZTO crystallizes in the rutile form of SnO2. The material becomes completely insulating. When the temperature is increased to 1050°C, evaporation of zinc is observed. In order to improve the electrical conductivity of ZTO at high temperature, a doping strategy was implemented starting from DFT calculations conducted by a partner group, who screened among the entire periodic table, which elements are the best candidates to act as n-dopants for ZTO. Bromine and iodine were retained, since they were found to be the most energetically favorable to become substitutional defects for a tin site. An exploratory doping route is therefore presented and the treated samples analyzed with TEM, EDX and UV-VIS-IR spectroscopy. Finally, the structural properties of an indium-based TCO (zirconium-doped indium oxide) were investigated and used as a benchmark to propose a crystallization model for the tin-based, as well as the indium-based materials. The influence of pa- rameters such as the material thickness, annealing atmosphere and temperature and deposition pressure are discussed for both materials

The burden of skin disease in the United States

Since the publication of the last US national burden of skin disease report in 2006, there have been substantial changes in the practice of dermatology and the US health care system. These include the development of new treatment modalities, marked increases in the cost of medications, increasingly complex payer rules and regulations, and an aging of the US population. Recognizing the need for up-to-date data to inform researchers, policy makers, public stakeholders, and health care providers about the impact of skin disease on patients and US society, the American Academy of Dermatology produced a new national burden of skin disease report. Using 2013 claims data from private and governmental insurance providers, this report analyzed the prevalence, cost, and mortality attributable to 24 skin disease categories in the US population. In this first of 3 articles, the presented data demonstrate that nearly 85 million Americans were seen by a physician for at least 1 skin disease in 2013. This led to an estimated direct health care cost of $75 billion and an indirect lost opportunity cost of$11 billion. Further, mortality was noted in half of the 24 skin disease categories

Contribution of health care factors to the burden of skin disease in the United States

The American Academy of Dermatology has developed an up-to-date national Burden of Skin Disease Report on the impact of skin disease on patients and on the US population. In this second of 3 manuscripts, data are presented on specific health care dimensions that contribute to the overall burden of skin disease. Through the use of data derived from medical claims in 2013 for 24 skin disease categories, these results indicate that skin disease health care is delivered most frequently to the aging US population, who are afflicted with more skin diseases than other age groups. Furthermore, the overall cost of skin disease is highest within the commercially insured population, and skin disease treatment primarily occurs in the outpatient setting. Dermatologists provided approximately 30% of office visit care and performed nearly 50% of cutaneous surgeries. These findings serve as a critical foundation for future discussions on the clinical importance of skin disease and the value of dermatologic care across the population