Device engineering of organic field-effect transistors toward complementary circuits

Organic complementary circuits are attracting significant attention due to their high power efficiency and operation robustness, driven by the demands for low-cost, large-area and flexible devices. Previous demonstrations of organic complementary circuits often show high operating voltage, small noise margins, low dc gain, and electrical instability such as hysteresis and threshold voltage shifts. There are two obstacles to developing organic complementary circuits: the lack of high-performance n-channel OFET devices, and the processing difficulty of integrating both n- and p-channel organic field-effect transistors (OFETs) on the same substrate. The operating characteristics of OFETs are often governed by the boundary conditions imposed by the device architecture, such as interfaces and contacts instead of the properties of the semiconductor material. Therefore, the performance of OFETs is often limited if either of the essential interfaces or contacts next to the semiconductor and the channel are not optimized. This dissertation presents research work performed on OFETs and OFET-based complementary inverters in an attempt to address some of these knowledge issues. The objective is to develop high-performance OFETs, with a focus on n-channel OFETs through interface engineering both at the interface between the organic semiconductor and the source/drain electrodes, and at the interface between the organic semiconductor and gate dielectric. Through interface engineering, both p- and n-channel high-performance low-voltage OFETs are realized with high mobilities, low threshold voltages, low subthreshold slopes, and high on/off current ratios. Optimization at the gate dielectric/semiconductor also gives OFET devices excellent reproducibility and good electrical stability under multiple test cycles and continuous electrical stress. Finally, with the interfaces and contacts optimized for both p- and n-channel charge transport, the integration of n- and p-channel OFETs with comparable performance are demonstrated in complementary inverters. The research achieves inverters with a high-gain, a low operation voltage, good electrical stability (absence of hysteresis), and a high switching-speed. A preliminary study of the encapsulation of OFETs and inverters with an additional protective layer is also presented to validate the practicality of organic devices containing air-sensitive n-channel transport.Ph.D.Committee Chair: Kippelen, Bernard; Committee Member: Brand, Oliver; Committee Member: Graham, Samuel; Committee Member: Rohatgi, Ajeet; Committee Member: Shen, Shyh-Chian

The Political (Un)conscious: Rethinking Aesthetics from a Cross-Cultural Perspective

In her article, The Political (Un)conscious: Rethinking Aesthetics from a Cross-Cultural Perspective, Xiaohong Zhang adopts a cross-cultural perspective, examining the cultural-specific nuances of critical terms like race, class and gender, all of which have bearings on our perception and conception of aesthetics. Drawing on Emory Elliot\u27s groundbreaking book, Aesthetics in a Multicultural Age (2002), the paper probes into the aesthetic experience whose primary effect is to depragmatize. Along this line of thinking, the author draws attention to the aesthetic impetus of two Nobel laureates, Mo Yan and Gao Xingjian, whose rewriting of Western classics demonstrates Chinese authors\u27 shared predilection for Western modernity in general and for modernist and postmodernist aesthetics in particular

Frailty among older adults in the community: insight in the complexity of frailty

The thesis is divided into three parts. Part 1 focuses on the measurement of frailty and the factors that contribute to it. The main outcome is the development of a questionnaire to measure frailty, including physical, psychological, social and environmental domains, which is suitable for a Chinese context. The Frailty Index (FI-35) is a self-reported screening instrument to measure frailty in the elderly and consists of 35 items in four domains: physical, psychological, social and environmental, and 11 subdomains. The FI-35 score ranges from zero to one, with a score closer to one indicating a person being more frail. In part 2 of the thesis, it is established that it is important not only to look at the total score of frailty, but also to look at the different items of frailty and how they increase with increasing frailty in order to provide tailored care. Finally, part 3 examines whether a dance intervention can improve the frailty of older people. For this purpose, a randomized controlled experimental study was conducted in a local community in Hebei, China. The project illustrated that dance was a feasible and effective intervention to improve the frailty status of older people in communities

Generalized estimating equations for clustered survival data

Although time to event data is traditionally analyzed assuming independent responses, it is common to encounter correlated time to event data in the form of repeated measurements on subjects or clusters of subjects formed by genetic or social relationships. The objective of this research is to develop estimation procedures for clustered survival data that improve efficiency in estimating regression coefficients in Cox proportional hazards model without imposing overwhelming computational burdens;A commonly used method for clustered survival data obtains parameter estimates from the partial likelihood score equations based on a model that incorrectly assumes independent observations. This independent working model (IWM) approach provides consistent estimators with asymptotic Gaussian distribution and a robust covariance estimator provides a consistent estimator of the covariance matrix of the parameter estimates. The availability of the software in most statistical packages has led to the wide use of this methodology for correlated survival data. Because of the potential loss of efficiency when within cluster correlation is strong, we examine two alternative methods to improve efficiency;We first considered a simplified approach to estimate weights in the weighted estimating equations proposed by Cai and Prentice (1997). This approach reduces the computational burden of the Cai and Prentice methodology. We also consider a new set of weighted estimating equations obtained by inserting weight matrices into the IWM score equations in a different manner. Another set of estimating equations is developed by applying a generalized estimating equation (GEE) approach using approximate Poisson distributions for counting process differentials. The bootstrap procedure is used to estimate the covariance matrix of the parameter estimates;Simulation studies are used to assess bias, variance and relative efficiency of the proposed estimators. Results show that the biases of all of the estimators are small and comparable, but there may be substantial gains in efficiency by incorporating weight matrices into estimating equations when the within cluster correlation is strong and the censoring rate is low. Simulation studies confirm that the bootstrap procedure provides accurate standard errors for estimates of regression coefficients and confidence intervals with appropriate coverage probabilities