Date of Award

Summer 2014

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Micro and Nanoscale Systems

First Advisor

Long Que

Abstract

In this dissertation, a hybrid nanomaterial, single-wall carbon nanotubes-copper sulfide nanoparticles (SWNTs-CuS NPs), was synthesized and its properties were analyzed. Due to its unique optical and thermal properties, the hybrid nanomaterial exhibited great potential for infrared (IR) sensing and energy harvesting.

The hybrid nanomaterial was synthesized with the non-covalent bond technique to functionalize the surface of the SWNTs and bind the CuS nanoparticles on the surface of the SWNTs. For testing and analyzing the hybrid nanomaterial, SWNTs-CuS nanoparticles were formed as a thin film structure using the vacuum filtration method. Two conductive wires were bound on the ends of the thin film to build a thin film device for measurements and analyses. Measurements found that the hybrid nanomaterial had a significantly increased light absorption (up to 80%) compared to the pure SWNTs. Moreover, the hybrid nanomaterial thin film devices exhibited a clear optical and thermal switching effect, which could be further enhanced up to ten times with asymmetric illumination of light and thermal radiation on the thin film devices instead of symmetric illumination. A simple prototype thermoelectric generator enabled by the hybrid nanomaterials was demonstrated, indicating a new route for achieving thermoelectricity. In addition, CuS nanoparticles have great optical absorption especially in the near-infrared region. Therefore, the hybrid nanomaterial thin films also have the potential for IR sensing applications.

The first application to be covered in this dissertation is the IR sensing application. IR thin film sensors based on the SWNTs-CuS nanoparticles hybrid nanomaterials were fabricated. The IR response in the photocurrent of the hybrid thin film sensor was significantly enhanced, increasing the photocurrent by 300% when the IR light illuminates the thin film device asymmetrically. The detection limit could be as low as 48mW mm-2. The dramatically enhanced sensitivity and detection limit were due to the temperature difference between the two junctions formed by the nanohybrid thin film and copper-wire electrodes under asymmetric IR illumination, and the difference between the effective Seebeck coefficient of the nanohybrid thin film and that of the Cu wires. The IR sensor embedded in polydimethylsiloxane (PDMS) layers was also fabricated and tested to demonstrate its potential application as a flexible IR sensor.

In another application, energy harvesting, a new type of thermoelectric microgenerator enabled with the SWNTs-CuS nanoparticles hybrid nanomaterial, was fabricated. This type of microgenerator did not require any cooling or heat sink element to maintain the temperature difference or gradient in the device. Instead, the integrated nanomaterials in the device enhanced the local temperature and thus produced and maintained an intrinsic temperature difference or gradient across the microgenerator, thereby converting light and heat directly into electricity. In order to enhance the maximum output voltage, the incoming light had to be focused on the thin film region. A tunable lens was fabricated to collect and focus the ambient light on the thin film to enhance the output voltage of the microgenerators. The tunable lens was fabricated with a flexible polymer, PDMS. Therefore, the focal length of the tunable lens can be adjusted by pumping oil into the lens chamber to deform a PDMS membrane, resulting in the changed focus of the lens. In order to enhance the output power, two different arrays of thermoelectric generators in series and in parallel were fabricated. A hybrid nanomaterial thin film was also used to enhance the temperature gradient of the thermoelectric generators. For the devices in series, the generated voltage of all thermoelectric generators was combined together to enhance the output voltage. With the device in parallel, it can be used to combine all of the current of thermoelectric generators together to enhance the output current.

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