Search

In the past few decades, digital technologies have profoundly altered virtually every aspect of human life. While the direct impact of digital technologies on individuals' economic welfare or personal behaviors has attracted considerable attention, the interplay of digital technologies with social connections remains underexplored. Indeed, regardless of whether formed offline or online, social connections in the form of personal ties and affiliations that have long been the bedrock of human society continue to shape human behaviors and outcomes. To the extent that digitization will only continue to grow in scale and scope, an understanding of such effects is important for scholars, practitioners, and policymakers. I address two overarching research questions in my dissertation: (1) Whether, and to what extent digital technologies affect individuals' economic welfare and habituated behavior, and (2) How social connections such as personal ties and affiliations condition the impact of the digital technologies. My studies are conducted in two distinct contexts: mobile interventions for health, and computer ownership for social and economic welfare. Drawing on diverse bodies of literature and using various econometric methods, I seek to answer questions related to how interventions orchestrated on mobile platforms help individuals form healthy behaviors, and how computer ownership affects long-term income mobility. In the first essay, I show that a social norms intervention on a mobile platform is effective in increasing individuals' physical activity. In the second study, I investigate how the motivational incentive of reciprocity can be leveraged to promote healthy behavior. Finally, in my third essay, I show that computer ownership generates both private and social returns (IT spillovers) on individuals' income mobility. All three papers then consider how individuals' social connections condition the direct effects of digital technologies. The first two studies explore how online social ties and social relationships moderate the impact of mobile interventions, and the third study examines how caste groups affect the positive spillover effects of computer ownership. Collectively, the three studies advance our understanding of the heterogeneous effects of digital technologies on individuals and provide implications for researchers and practitioners. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]

Over the past few decades, electronics and photonics have made significant impacts on every aspect of our daily life. Importantly, as the technology advancing and moving forward, the development of these devices not only relies on deeper fundamental understanding but also requires novel materials with unique properties as well as new device architecture to achieve higher performance with more diverse functionalities. In this regards, low dimensional materials inherently possess properties that are conceptually different from those of bulk materials in most aspects. The capability to tailor these nanomaterials as well as their unique properties is essential to achieve unconventional devices with revolutionary impacts. In this dissertation work, our aim is to develop novel nanoelectronics and nanophotonics by exploiting the extraordinary characteristics of purely two-dimensional (2D) monolayer graphene and its heterostructures. Firstly, we design and propose the dual-gate graphene ambipolar transistor that can operate as either common mode or differential mode amplifier by properly tuning the gate biases. Our device can also achieve high noise rejection amplification with common mode rejection ration (CMRR) as high as 80 dB, which is comparable to a commercial operational amplifier (op-amp). Secondly, we demonstrate the hyperbolic metamaterials (HMMs) by using precisely controlled periodic graphene-dielectric multilayer nanostructures to investigate the optical topological transition from elliptical to hyperbolic dispersion in mid-infrared regime. Thirdly, we propose the graphene-SOI heterojunction broadband photodetector design to improve the device on-off operation speed, strengthen the photo-gating effect, as well as minimize the dark current. We further fabricate the single pixels into 32 x 32 matrix arrangement to demonstrate the proof-of-concept image array readout, opening up the development of graphene-based ultra-broadband image sensor array applications. Lastly, we propose the all-graphene transparent photodetector design for light-field imaging and demonstrate the proof-of-concept one-dimensional (1D) ranging by using two stacked single-pixel transparent photodetectors. The results should lay the stepping stones and foundation for the new generation of graphene-based light-field photodetectors and image sensors.