Comparative Characterization Of Molybdenum Oxide Thin Films Grown On Various Substrates Using Temporally Different Pulsed Laser Deposition Techniques

Pulsed Laser Deposition (PLD) technique, with its vast tunability in terms of thin film fabrication has been the center of this study. By changing the temporal component of the laser source used for deposition into the femtosecond (fs) regime, interesting structural, morphological changes can be achieved which may prove to be beneficial for photocatalytic applications. In particular, molybdenum oxide thin films, which are the less well-studied and potentially newer candidates for photocatalysis applications have been chosen for investigation. Hence, a detailed characterization study of molybdenum oxide thin films synthesized using femtosecond-based (f-PLD) and nanosecond-based (n-PLD) techniques, was carried out in terms of their structural, morphological, surface chemical/ electronic states and vibrational properties using X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy and Raman spectroscopy. The f-PLD technique was found to produce more favorable molybdenum oxide thin films deposited on glass for surface-related applications, in terms of having a higher surface to volume ratio, than the n-PLD technique. A related simultaneous study of substrate-based effect on the thin films produced using n-PLD system, also revealed both variation among the morphological, structural, and electronic (in terms of Mo oxidation state) properties depending upon the nature of the substrate used to synthesize the molybdenum oxide thin films. Special cases of thin films on epitaxial substrates (Si, sapphire) have been characterized to determine the parameters necessary for fabricating highly-textured thin films with large surface-area to volume ratio, which is key to efficient photo-catalysts.

The preparation and characterization of thin film oxides and chalcogenides by pulsed laser deposition (PLD) is presented. An overview of fundamental PLD concepts are presented and are followed by a description implementation and development of the PLD systems at OSU. We present the results of thin film growth of high electron mobility In2O3:W in which we have prepared films exhibiting □ > 100 cm2/Vs on vitreous SiO2 substrates. The growth of Cu3TaQ 4 (Q = S, Se) films is outlined as a two step process consisting of PLD of ceramic targets followed by ex-situ annealing in chalcogenide vapor. Also, BiCuOSe thin films have been prepared in-situ and exhibit a high hole mobility up to 4 cm2/Vs. A discussion of their electronic structure is presented which explains the nature of the low band gap energy on the basis of deep Bi 6p level at the conduction band minimum. Finally, the results of BaBiO3 thin film preparation are presented in which both polycrystalline and highly (00l) oriented samples were grown.

Pulsed laser deposition (PLD) is a promising technique for creating inexpensive, nanostructured thin films which may lead to structures suitable for photocatalysis. During this study, multiple tungsten oxide thin films were prepared using two types of PLD techniques. The first method was conducted at US Photonics, Springfield, MO, using a femtosecond laser while the second method relied on use of an excimer (nanosecond) laser located at Missouri State University. Films were first deposited on glass using both methods at room temperature. Further study was conducted on thin films deposited on sapphire and silicon deposited at room temperatures and at elevated temperatures. In addition to using two types of PLD, an investigation of the properties of tungsten oxide thin films incorporated with alkali metals was conducted. This was achieved by preparing a target using tungsten oxide with small amounts of sodium nitrate (NaNO3). The addition of alkali metals has been known to change the structure as well as the electrical, chemical, and physical properties of the bulk material. After deposition, the thin films were annealed at 450°C up to 30 hours in air. Characterization of the films’ structure and morphology were made using scanning electron microscopy (SEM), x-ray diffraction (XRD), Raman spectroscopy, and x-ray photoelectron spectroscopy (XPS) both before and after annealing. Characterization of the films allowed me to determine which method of PLD as well as which substrate (glass, silicon, or sapphire) is more suitable for growing thin films suitable for photocatalysis applications.

The objective of this work is to prepare Molybdenum thin films to be used as efficient back contact materials and utilize characterization techniques for the investigation of the growth as well the physical properties of Mo thin films deposited through DC-plasma magnetron sputtering on soda lime glass substrate. The effects of process parameters, such as Ar pressure, deposition power and substrate temperature, on the properties of the deposited films have been studied. These process parameters were optimized to get high conductivity Mo thin films to be used in CIGS based thin films solar cells as a back contact.

The aim of this work is to show that material processing by laser-based technologies can lead to the growth of multifunctional thin films with potential in a large area of applications. The synthesis of Hf, Ta, Si, and Al metal oxides described here relies on the use of pulsed laser deposition (PLD), or radiofrequency (RF) assisted PLD. The morphology and structure of the as-grown thin films are investigated by atomic force microscopy, X-ray diffraction, and transmission electron microscopy, whilst the optical properties are determined by spectroellipsometry. The dielectric behaviour of the deposited layers is investigated by electrical measurements.

In order to fabricate layered electrochromic devices capable of reversibly changing color in response to applied voltage, pulsed laser deposition was used to deposit thin films of tungsten oxide on fluorine doped tin oxide substrates.The thin films were deposited at room temperature in an O2 atmosphere of the order of 10−1 mbar on FTO/glass substrates using a KrF pulsed laser source. XRD analysis confirmed the resulting films to be amorphous and UV-Vis spectroscopy confirmed transparency. Raman shift confirms non-crystalline WO3 presence. Electrochromic devices were connected to a cyclic voltammetry system to regulate voltage sweeps, investigate charge transport, response time and reversibility of color/bleached states. Scanning electron microscopy was performed on the films post device operation to examine the surface topography and composition. Raman spectroscopy and XRD was performed post device films to investigate any changes in the films. Li+ ion conducting glasses of composition xLi2SO4 - (1-x)[0.50Li2O-0.5(2NH4H2PO2)) were characterized using resistivity measurements and neutron diffraction experiments to evaluate them as suitable substitutes for the electrolyte in the electrochromic devices. Formation of crystallites above 400°C has been observed which is understood to hamper Li+ ion mobility, resulting in reduced performance of the electrolyte. The acid based electrochromic devices have exhibited superior reversibility.

A KrF excimer laser is used to ablate a pure MnO target to grow manganese oxide thin films on Si (111) substrates. The effect of oxygen pressure and substrate t emperature on the various film properties were investigated. Grazing incidence X -ray diffraction (GIXRD) is employed to determine the crystalline structure, whe reas Atomic Force Microscopy (AFM) is used to determine the surface roughness. C hemical bonding and the elemental composition were studied using Fourier Transfo rm Infrared Spectroscopy (FTIR) and Rutherford Backscattering Spectroscopy (RBS) . Two manganese oxide phases were obtained, namely Manganesetrioxide (Mn2O3) and M anganesetetraoxide (Mn3O4). GIXRD analysis indicates that the increase in substr ate temperature at a constant oxygen pressure leads to a change in the phase com position from Manganesetrioxide (Mn2O3) to Manganesetetraoxide (Mn3O4). FTIR stu dies support this result. The FWHM measurements reveal that the films become mor e crystalline at higher temperatures. Moreover, AFM measurements show that the f ilm roughness increases with the increase in temperature due to the fact that su rface atoms mobility is enhanced at higher temperatures. At constant temperature ; however, it was shown by both GIXRD and FTIR that varying the oxygen pressure does not affect the composition and crystallinity of the films. On the other han d, it has a considerable effect on the atomic ration of oxygen-to manganese obta ined by RBS.

Two-dimensional materials, or materials that are only one atomic layer thick, have seen much research in recent years because of their interesting electrical properties. The first of these materials, graphene, was found to have incredible electrical properties but lacked a bandgap in intrinsic films. Without a bandgap, graphene cannot create transistors that can be shut off. Molybdenum disulfide, however, is a two-dimensional semiconductor with a large bandgap. The main issue of molybdenum disulfide is that synthesized films are a much lower quality than their exfoliated counterparts. For molybdenum disulfide to be able to be used practically, a method of synthesis must be found that can reliably create quality large area monolayer films. In this thesis, three methods of molybdenum disulfide film synthesis are presented. Methods implemented used a tube furnace as a chemical vapor deposition system to evaporate source materials to synthesize thin films of molybdenum disulfide. An exploration into the different synthesis parameters shows optimal conditions for these specific methods. Then a discussion of these different methods is presented by judging films grown by using these methods on relevant criteria. This work shows methods to synthesize large area, polycrystalline, small grain, multilayer films, both intrinsic and doped, and to synthesize small area, single crystal and polycrystalline, monolayer films of molybdenum disulfide.