Date of Award

2018-01-01

Degree Name

Doctor of Philosophy

Department

Material Science and Engineering

Advisor(s)

Anupama B. Kaul

Abstract

In monolayers of two-dimensional (2-D) layered materials, the motion of electrons is confined to a 2-D plane yielding a "zero" effective thickness with regard to the electrons. These monolayers are commonly obtained by exfoliating membranes from the bulk crystal to overcome the weak interplanar Van der Waals bonding using the so-called top-down approach. The bottom-up approach is another avenue to realize these materials, where atoms and molecules coalesce together into increasingly larger assemblies for the realization of the bulk three-dimensional (3-D) crystal. The unique properties of many of these 2-D materials make them highly sought out candidates for advancing conventional electronics that is currently based on Silicon, in addition to flexible electronics, optoelectronics and sensing devices. Graphene was the first 2-D material to be isolated more than a decade ago using mechanical exfoliation. It is now being explored as an attractive material for interconnects and contacts for optoelectronic devices, given its ballistic electron transport, metal-like character and enhanced chemical and structural stability. In order to construct electronic devices, there is also a need to expand the suite of materials from metallic systems by exploring semiconducting and dielectric 2-D layered materials. In this regard, substantial interest has also been cast on tungsten disulfide (WS2) which exhibits tunable semiconducting properties, where an indirect-to-direct band gap transition is observed in going from the bulk to monolayers. Another 2-D material of great interest is hexagonal boron nitride (h-BN) which finds its potential as an excellent dielectric for electronics and optoelectronics given its superb structural integrity devoid of trapped charges, its atomic super-flat surface morphology, and its high-temperature stability.

In this work, 2-D materials are obtained by chemical exfoliation which refers to the breaking of layered 3-D materials into single or few-layer nanosheets in suitable solvents. Inkjet-printing is used as a material-conserving deposition technique for printing graphene, WS2, and h-BN nanosheets. Different avenues for formulating inks of nanomaterials, specifically graphene, WS2, and h-BN, for electronic and optoelectronic devices using scalable, low-cost, additive manufacturing approaches have been explored and optimized. Inkjet-printed graphene/WS2 based photodetector with rise and decay time of less than 50 ms, responsivity of up to ~ 0.86 A/W and detectivity up to ~ 1013 cmHz-1/2W-1 and graphene/h-BN based photosensitive capacitor with leakage current density as low as 0.072 µA/mm2 and capacitance density as high as 24 fF/µm2 are fabricated. Temperature-dependent Raman spectroscopy was performed to demonstrate the high-temperature stability of inkjet printed patterns. Optoelectronic properties of different materials and devices are studied using optical microscopy, scanning electron microscopy (SEM), UV-vis spectroscopy, current-voltage, current-time, capacitance-time and capacitance-frequency measurements.

Language

en

Provenance

Received from ProQuest

File Size

187 pages

File Format

application/pdf

Rights Holder

Jay Amrish Desai

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