Electroluminescence from ZnO Nanostructure Synthesizes between Nanogap

This thesis presents the investigation of a nanoscale light-emitting diode (LED) device. The nanoscale LED has a great potential to be used as a light source for biomedical screening and fluorescence lifetime spectroscopy. It can also be developed to a single photon emitter for the application of quantum computing. The nano-LED has the electrical structure of a metal-semiconductor-metal (MSM) junction. The MSM junction has been formed on the nanogap device that is fabricated on a SOI wafer by optical lithography and KOH solution silicon etching. The Ni evaporated on the surface of the nanogap device performs the metal contact for the junction. The ZnO made by evaporation and thermal oxidation of Zn serves as the semiconductor part to realize efficient excitonic emission. Photon emission phenomenon has been observed when bias is applied to the nano-LED device. The measured IV curve has confirmed the junction structure. The electroluminescence spectrum of the light has been obtained by using monochromator and CCD camera. The spectrum shows broad visual band wavelengths that are believed to result from some intrinsic defects of ZnO. The electroluminescence mechanisms are explained by the recombination of electrons and holes injected through thermionic emission, field emission, and thermionic-field emission

Suspended Nanoscale Field Emitter Devices for High-Temperature Operation

In this work, we demonstrate suspended two- and four-terminal field emission devices for high-temperature operation. The planar structures were fabricated with tungsten on a 200-nm silicon nitride membrane. The insulator in the vicinity of the terminals was removed to minimize undesirable Frenkel–Poole emission and increase the resistance of leakage current pathways. The effects of temperatures up to 450 °C on Fowler–Nordheim emission characteristics and parasitic leakage resistance were studied. Turn-on voltages with magnitudes under 15 V that further decreased as a function of increasing temperature for the two-terminal device were reported. Gating at temperatures of 150 °C and 300 °C was shown for the four-terminal device, and corresponding transconductance and cutoff frequency values were computed

Suspended Nanoscale Field Emitter Devices for High-Temperature Operation

In this work, we demonstrate suspended two- and four-terminal field emission devices for high-temperature operation. The planar structures were fabricated with tungsten on a 200-nm silicon nitride membrane. The insulator in the vicinity of the terminals was removed to minimize undesirable Frenkel–Poole emission and increase the resistance of leakage current pathways. The effects of temperatures up to 450 °C on Fowler–Nordheim emission characteristics and parasitic leakage resistance were studied. Turn-on voltages with magnitudes under 15 V that further decreased as a function of increasing temperature for the two-terminal device were reported. Gating at temperatures of 150 °C and 300 °C was shown for the four-terminal device, and corresponding transconductance and cutoff frequency values were computed

In situ interface engineering for probing the limit of quantum dot photovoltaic devices.

Quantum dot (QD) photovoltaic devices are attractive for their low-cost synthesis, tunable band gap and potentially high power conversion efficiency (PCE). However, the experimentally achieved efficiency to date remains far from ideal. Here, we report an in-situ fabrication and investigation of single TiO2-nanowire/CdSe-QD heterojunction solar cell (QDHSC) using a custom-designed photoelectric transmission electron microscope (TEM) holder. A mobile counter electrode is used to precisely tune the interface area for in situ photoelectrical measurements, which reveals a strong interface area dependent PCE. Theoretical simulations show that the simplified single nanowire solar cell structure can minimize the interface area and associated charge scattering to enable an efficient charge collection. Additionally, the optical antenna effect of nanowire-based QDHSCs can further enhance the absorption and boost the PCE. This study establishes a robust 'nanolab' platform in a TEM for in situ photoelectrical studies and provides valuable insight into the interfacial effects in nanoscale solar cells

Ultra-thin boron nitride films by pulsed laser deposition: Plasma diagnostics, synthesis, and device transport

This work describes, for the first time, a pulsed laser deposition (PLD) technique for growth of large area, stoichiometric ultra-thin hexagonal and amorphous boron nitride for next generation 2D material electronics. The growth of boron nitride, in this case, is driven by the high kinetic energies and chemical reactivities of the condensing species formed from physical vapor deposition (PVD) processes, which can facilitate growth over large areas and at reduced substrate temperatures. The use of optical emission spectroscopy during plasma growth provides insight into chemistry, kinetic energies, time of flight data, and spatial distributions within a PVD plasma plume ablated from a boron nitride (BN) target by a KrF laser at different pressures of nitrogen gas. Time resolved spectroscopy and wavelength specific imaging were used to identify and track atomic neutral and ionized species including B +, B*, N+, N*, and molecular species including N2*, N2+, and BN. Formation and decay of these species formed both from ablation of the target and from interactions with the background gas were investigated and provided insights into fundamental growth mechanisms of continuous, amorphous boron nitride thin films. By selectively choosing substrates that can facilitate epitaxial hexagonal growth, synthesis of ultra-thin, few-layer hexagonal boron nitride ( h-BN) was possible using the PLD technique. This process permits growth of thin, polycrystalline h-BN at 700°C, a much lower temperature than that required by traditional growth methods, most typically chemical vapor deposition (CVD). Analysis of the as-deposited films reveals epitaxial-like growth on the nearly lattice matched HOPG substrate, resulting in a nanocrystalline h-BN film with grain sizes of approximately 5 nm, and amorphous BN (a-BN) on the non-lattice matched sapphire substrates, both with film thicknesses of 1.5–2 nm. Stoichiometric films with boron-to-nitrogen ratios of unity were achieved by adjusting the background pressure within the deposition chamber and the distance between the target and substrate. Conductive atomic force microscopy (C-AFM) measurements of electron tunneling behavior depict a uniform The reduction in deposition temperature and formation of stoichiometric, large-area h-BN films by PLD provides a process that is easily scaled-up for two-dimensional dielectric material synthesis and also presents a possibility to produce very thin and uniform a-BN. Little is known as to how the degree of crystallinity, surface roughness, and other properties of the Graphene device performance including electron and hole mobility, as well as Dirac point, were substantially influenced by the presence of the dielectric material. In few-layer graphene films transferred to traditional h-BNSiO2 substrates, as well as SiO2 substrates coated with 5 nm a-BN, the transport properties in graphene were significantly suppressed in comparison to the annealed nanocrystalline h-BN, presumably due to increased scattering events. The weak van der Waals terminated h-BN films suppressed these scattering events from the presence of high energy surface optical phonon modes and lack of Coulombic scattering. A two-fold improvement in average hole mobility and a Dirac point shift from \u3e 60V to approximately 3.5V indicate that the influence of hexagonal crystallinity in the channel material is vital for high performance graphene devices. Thermal conductivity measurements of as-deposited a-BN and annealed h-BN were made possible by a nanofabricated freestanding bridge configuration, where the enhanced surface diffusion allowed for 100 nm h-BN grain formation at 600°C. Infrared microscopy and a one-dimensional heat transport model were used to measure both structural configurations of a-BN and h-BN to have inplane thermal conductivities of 5 W m−1 K−1 and 65 W m−1 K−1, respectively. In this study, the amorphous boron nitride was investigated as a means to enhance thermal conductance at dielectric/metal interfaces. Due to the atomic-scale roughness, covalently terminated bonding, as well as the high Debye temperature of BN, engineering a high contact thermal conductance is possible using different deposition techniques as a function of metal Debye temperatures. A high thermal conductance of 130 MW m−2 K−1 was measured on an a-BN/aluminum metal interface when the Al was prepared under the proper DC conditions, with a reduction in almost 50% when prepared in sub-optimum conditions using high power impulse magnetron sputtering (HIPIMS). (Abstract shortened by ProQuest.

Nanodiamonds for Field Emission: State of the Art

The aim of this review is to highlight the recent advances and the main remaining challenges related to the issue of electron field emission (FE) from nanodiamonds. The roadmap for FE vacuum microelectronic devices envisages that nanodiamonds could become very important in a short time. The intrinsic properties of the nanodiamond materials indeed meet many of the requirements of cutting-edge technologies and further benefits can be obtained by tailored improvements of processing methodologies. The current strategies used to modulate the morphological and structural features of diamond to produce highly performing emitting systems are reported and discussed. The focus is on the current understanding of the FE process from nanodiamond-based materials and on the major concepts used to improve their performance. A short survey of non-conventional microsized cold cathodes based on nanodiamonds is also reported

Nanocomposites of Carbon Nanotubes and Semiconductor Nanocrystals as Advanced Functional Material with Novel Optoelectronic Properties

Semiconductor nanoparticles of very small size, or quantum dots, exhibit fascinating physical properties, completely different from their bulk varieties, mostly because of the quantum confinement effect. Due to their modified band structure, they particularly show attractive optoelectronic characteristics. Carbon nanotubes are a class of nanomaterials, which also possess wonderful optoelectronic properties and can revolutionize modern semiconductor technology to a great extent. Carbon nanotube field-effect transistors (CNTFETs) can replace standard MOSFETs in an array of devices and can function in a more effective way. When these two optoelectronic components combine together in nanocomposites, one may get advanced optoelectronic devices for widespread application in sensors, solar cells, energy storage devices, light-emitting diodes, electrocatalysts, etc