arXiv subjects

Gregory Burwell

Publications and source records attributed to Gregory Burwell.

3 recordsLinked to original sources

arXiv2023

The effect of direct electron beam patterning on the water uptake and ionic conductivity of Nafion thin films

We report the effect of electron-beam patterning on the water uptake and ionic conductivity of Nafion films using a combination of x-ray photoelectron spectroscopy, quartz crystal microbalance studies, neutron reflectometry, and AC impedance spectroscopy. The aim was to more fully characterize the nature of the nanoscale patterned Nafion structures recently used as a key element in novel ion-to-electron transducers by Gluschke et al. To enable these studies, we develop the electron beam patterning process for large areas, achieving patterning speeds approaching 1 cm$^{2}$/hr, and patterned areas as large as 7 cm$^{2}$ for the neutron reflectometry studies. We ultimately show that electron-beam patterning affects both the water uptake and the ionic conductivity, depending on film thickness. We see Type-II adsorption isotherm behaviour for all films. For thick films (~230 nm), we see a strong reduction in water uptake with electron-beam patterning. In contrast, for thin films (~30 nm), electron-beam patterning enhances water uptake. Notably, we find that for either thickness the reduction in ionic conductivity arising from electron-beam patterning is kept to less than an order of magnitude. We propose mechanisms for the observed behaviour based on the known complex morphology of Nafion films to motivate future studies of electron-beam processed Nafion.

cond-mat.soft↗

arXiv2023

The Thermodynamic Limit of Indoor Photovoltaics Based on Energetically-Disordered Molecular Semiconductors

Due to their tailorable optical properties, organic semiconductors show considerable promise for use in indoor photovoltaics (IPVs), which present a sustainable route for powering ubiquitous "Internet-of-Things" devices in the coming decades. However, owing to their excitonic and energetically disordered nature, organic semiconductors generally display considerable sub-gap absorption and relatively large nonradiative losses in solar cells. To optimize organic semiconductor-based photovoltaics, it is therefore vital to understand how energetic disorder and non-radiative recombination limit the performance of these devices under indoor light sources. In this work, we explore how energetic disorder, sub-optical gap absorption, and non-radiative open-circuit voltage losses detrimentally affect the upper performance limits of organic semiconductor-based IPVs. Based on these considerations, we provide realistic upper estimates for the power conversion efficiency. The energetic disorder, inherently present in molecular semiconductors, is generally found to shift the optimal optical gap from 1.83 eV to ~1.9 eV for devices operating under LED spectra. Finally, we also describe a methodology (accompanied by a computational tool with a graphical user interface) for predicting IPV performance under arbitrary illumination conditions. Using this methodology, we estimate the indoor PCEs of several photovoltaic materials, including the state-of-the-art systems PM6:Y6 and PM6:BTP-eC9.

physics.app-ph↗

arXiv2017

Image sensor array based on graphene-CMOS integration

Integrated circuits based on CMOS (complementary metal-oxide semiconductors) are at the heart of the technological revolution of the past 40 years, as these have enabled compact and low cost micro-electronic circuits and imaging systems. However, the diversification of this platform into applications other than microcircuits and visible light cameras has been impeded by the difficulty to combine other semiconductors than silicon with CMOS. Here, we show for the first time the monolithic integration of a CMOS integrated circuit with graphene, operating as a high mobility phototransistor. We demonstrate a high-resolution image sensor and operate it as a digital camera that is sensitive to UV, visible and infrared light. The demonstrated graphene-CMOS integration is pivotal for incorporating 2d materials into the next generation microelectronics, sensor arrays, low-power integrated photonics and CMOS imaging systems covering visible, infrared and even terahertz frequencies.. The demonstrated graphene-CMOS integration is pivotal for incorporating 2d materials into the next generation microelectronics, sensor arrays, low-power integrated photonics and CMOS imaging systems covering visible, infrared and even terahertz frequencies.

cond-mat.mes-hall↗