Theoretical and Experimental Studies of Schottky Diodes That Use Aligned Arrays of Single Walled Carbon Nanotubes

We present theoretical and experimental studies of Schottky diodes that use aligned arrays of single walled carbon nanotubes. A simple physical model, taking into account the basic physics of current rectification, can adequately describe the single-tube and array devices. We show that for as grown array diodes, the rectification ratio, defined by the maximum-to-minimum-current-ratio, is low due to the presence of m-SWNT shunts. These tubes can be eliminated in a single voltage sweep resulting in a high rectification array device. Further analysis also shows that the channel resistance, and not the intrinsic nanotube diode properties, limits the rectification in devices with channel length up to ten micrometer.Comment: Nano Research, 2010, accepte

Integration of aligned arrays of single-walled carbon nanotubes in electronic devices

Aligned arrays of single-walled carbon nanotubes (SWNTs) are an attractive format for macroelectronics and RF analog electronics with exceptional electrical, mechanical and optical properties. Unlike isolated SWNT, the presence of many SWNTs in the aligned arrays increases the current output and statistical averaging in many SWNTs is expected to reduce the device to device variations. The SWNTs in aligned arrays do not intersect one another, unlike in networks of SWNTs. Hence, tube/tube contacts, which limit the transport in SWNT networks due to tunneling barriers or electrostatic screening at the contacts to prevent effective gate modulation at those specific points, are absent. Nonetheless, challenges still remain for these aligned arrays of SWNTs before their successful integration into electronic devices for large scale commercial use. The main challenges include (1) selective elimination of m-SWNTs, (2) increasing the density of SWNTs, (3) achieving electronic uniformity across devices fabricated and (4) understanding their mode of operation and the role of contacts in their operation. In this dissertation, I present a study that aims to tackle the 3rd and 4th challenges aforementioned. We integrated these arrays of SWNT thin films into field effect transistors to study the electronic uniformity of the devices. We examined the effect of variation in density and diameter distributions of the aligned arrays of SWNTs on the variation in the electrical performance of the transistors. We also analyzed the properties of the contacts at the SWNT/metal interface. We found Pd to be a good Ohmic contact and Ca to be a Schottky contact to the aligned arrays of SWNTs and went on to fabricate Schottky diodes. Using these Schottky diodes, we demonstrated light emitting diodes with aligned arrays of SWNTs which could be used in novel applications that require solid state and nano-scale infra-red emitters. Work done to selectively eliminate m-SWNTs (1st challenge) via selective laser ablation is also archived in this dissertation. These results represent important steps in understanding the device performance of transistors and Schottky diodes based on aligned arrays of SWNTs; which may have a large impact in large area RF analog electronics

Films of Carbon Nanomaterials for Transparent Conductors

The demand for transparent conductors is expected to grow rapidly as electronic devices, such as touch screens, displays, solid state lighting and photovoltaics become ubiquitous in our lives. Doped metal oxides, especially indium tin oxide, are the commonly used materials for transparent conductors. As there are some drawbacks to this class of materials, exploration of alternative materials has been conducted. There is an interest in films of carbon nanomaterials such as, carbon nanotubes and graphene as they exhibit outstanding properties. This article reviews the synthesis and assembly of these films and their post-treatment. These processes determine the film performance and understanding of this platform will be useful for future work to improve the film performance

Films of Carbon Nanomaterials for Transparent Conductors

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Biaxially stretchable silver nanowire transparent conductors

Biaxially stretchable silver nanowire transparent conductors are demonstrated. The silver nanowire film retains its electrical conductivity up to 10% applied strain. We examine the factors limiting stretchability and compare the mechanics of biaxially and uniaxially stretchable systems, which will be useful for exploring biaxially stretchable systems in future.Published versio

Characteristics and cytotoxicity of indoor fine particulate matter (PM2.5) and PM2.5-bound polycyclic aromatic hydrocarbons (PAHs) in Hong Kong

Organic components of fine particles, especially polycyclic aromatic hydrocarbons (PAHs), play an essential role in the toxicity of fine particulate matter (PM2.5). The chemical and bioreactive properties of PM2.5 in indoor environments were investigated from 2014 to 2016 in Hong Kong among 33 residential indoor environments. All analyzed components revealed higher concentrations in winter than in summer, except for organic carbon (OC). High molecular weight PAHs (4-6 rings) contributed higher total PAH compositions than low molecular weight PAHs (2-3 rings). The study results suggested that the major sources of indoor PM2.5 originated from outdoor vehicle emissions, indoor cooking activities, and incense burning. Cytotoxicity tests only revealed significant associations in winter. The cell viability demonstrated strong negative correlations between OC (r = - 0.8, p < 0.05), total PM2.5-bound PAHs (r = - 0.6, p < 0.05), and United States Environmental Protection Agency (US EPA) priority PAHs (r = - 0.7, p < 0.05). Cell lactate dehydrogenase (LDH) and 8-isoprostane were positively associated with OC (r = 0.8, p < 0.05; r = 0.7, p < 0.05), total PM2.5-bound PAH (r = 0.7, p < 0.05; r = 0.7, p < 0.05), and US EPA priority PAH (r = 0.6, p < 0.05; r = 0.5, p = 0.07) concentrations. IL-6 had the only positive association with OC (r = 0.5, p < 0.05). This study focused on indoor PM2.5 levels and the associated cytotoxicity in the absence of environmental tobacco smoke

Electrical and optical properties of hybrid transparent electrodes that use metal grids and graphene films

There have been efforts to develop alternative transparent conductors to replace indium tin oxide (ITO). A hybrid transparent conductor that integrates a metallic Cu grid and graphene film promises to be a suitable candidate. Flexibility, sheet resistance, and transmittance comparable to ITO have been demonstrated. Here, we show that the optical and electrical properties of the hybrid transparent conductor can be easily tuned by clever design of the metal grid. The outcome of our study provides unprecedented guidelines for future design of metal grids integrated in transparent conductors. We also find that the graphene film forms an effective barrier to retard the degradation of the copper grid when the hybrid transparent conductor is heated in air up to high temperatures for an extended period of time. Hence, a superior hybrid transparent conductor, which can be carefully engineered to display desirable properties, has been demonstrated.Published versio