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Browsing by Author "Menoni, Carmen S., advisor"

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    A study of structural organizations in amorphous oxide thin films for low mechanical loss mirror coatings in interferometric gravitational wave detectors
    (Colorado State University. Libraries, 2021) Yang, Le, author; Menoni, Carmen S., advisor; Chung, Jean K., committee member; Szamel, Grzegorz, committee member; Bradley, Mark R., committee member
    Amorphous thin films prepared from vapor deposition are nonequilibrium solids with structures dependent on their physical parameters, such as composition, and method of preparation. The macroscopic properties of an amorphous material are fundamentally connected to the atomic configuration at the microscopic level. Two-level systems, conceptualized as two adjacent potential wells in the potential energy landscape, are due to intrinsic atomic disorder in amorphous materials. When coupled with an elastic field, the configuration change between the two wells creates a dissipation of mechanical energy that manifests itself as the mechanical loss angle. The mechanical loss of the thin films composing the high reflectivity mirror coating has become the dominant noise source limiting further performance improvements for the next generation gravitational wave detectors. The study presented here comprises investigations of key structural organizations that correlate with the room temperature mechanical loss in vapor-deposited amorphous oxide thin films. In theory, manipulations of substrate temperature or use of assist ion bombardment that transfers energy to the film surface are capable of introducing structural changes during the highly dynamic transition of sputtered particles from the vapor to the solids phase. Tuning the composition by doping or nanolayering is also effective at altering the atomic structure of the amorphous materials. Herein, we discuss in detail the findings from each work. In work on Ta2O5, the effects of low energy assist ion bombardment on the mechanical loss of amorphous thin films are presented. Bombarding ions of Ar+, Xe+, and O2+ of different energy and different dose are directed to the thin films' surface during growth. Negligible influence is found from the assist ion bombardment on the atomic structure and mechanical loss of the Ta2O5 thin films. Based on an analysis of surface diffusivity, it is suggested that the dominant deposition of Ta2O2 cluster might be responsible for the unaltered mechanical loss for Ta2O5 thin films. The parameter space explored within the experimental setup is not capable of affecting the atomic arrangements. It has been proposed that modifiers such as dopants and nanolayers incorporated into the Ta2O5 matrix alter the atomic network in a beneficial way. Two systems of SiO2/Ta2O5 and TiO2/Ta2O5 in both mixture and nanolaminate forms are investigated. For the nanolaminates, it is demonstrated that thermal treatment results in a morphological change that involves layer breakup and mixture formation at the interface in the TiO2/Ta2O5 nanolaminate. Similarly, a stable mixed phase is only formed in the TiO2/Ta2O5 mixture after annealing. The formation of a mixture is suggested to be the key to the lower mechanical loss of the TiO2/Ta2O5 in contrast to the SiO2/Ta2O5 system. The two-level systems are essentially modified when the system con- figures itself in a thermodynamically more stable state. Combined with results from the atomic modeling using molecular dynamics of TiO2/Ta2O5, it is then proposed that the medium-range order in these oxides is key to lowering the room temperature mechanical loss. A direct evaluation of the modifications at the medium-range order is obtained from work on amorphous GeO2 thin films. GeO2 with a maximized degree of medium-range order is investigated with elevated temperature deposition. It is demonstrated that the medium-range or- der of amorphous GeO2, characterized by GeO4 tetrahedra connected in rings of various sizes, evolves into a more ordered configuration at elevated temperatures. A systematic decrease in mechanical loss is associated with the increase in medium-range order for the GeO2 thin films. We conclusively show that an improved packing at medium range is linked to the low mechanical loss for the amorphous oxide thin films. Furthermore, engineering of GeO2 to achieve a high refractive index is carried out by the incorporation of TiO2. We identified the optimal cation concentration Ti/(Ge+Ti) around 44%, which provides both low mechanical loss and low absorption loss for the mixture to be used in the multilayer stack. The designed high reflector multilayer is calculated to have the Brownian thermal noise near the target for next-generation Advanced LIGO. In combination, the results described in this dissertation have identified key structural organizations that affect the room temperature mechanical loss of amorphous oxide thin films. The evolution in the connecting rings of metal-centered oxygen polyhedra in these thin films is essential to altering the medium-range order in the atomic network. Such modifications could be achieved with the formation of a thermodynamically more stable phase, elevated deposition temperature, or post-deposition thermal treatment. Future work to identify the microscopic origin of low-temperature mechanical loss is envisioned for a thorough understanding of the two-level systems present in the amorphous oxides.
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    ItemOpen Access
    Characterization of scandium oxide thin films for use in interference coatings for high-power lasers operating in the near-infrared
    (Colorado State University. Libraries, 2010) Krous, Erik M., author; Menoni, Carmen S., advisor; Marconi, Mario C., committee member; Williams, John D., committee member
    The work presented in this thesis aims to investigate scandium oxide (scandia), deposited using dual ion beam sputtering, as a high-index material for interference coatings to be implemented in high-power lasers. Ion beam sputtered scandia coatings have the potential to allow for the power scaling of high-power lasers operating in the near-infrared. Ion beam sputtering is the technique currently used by many commercial companies to produce low-loss, high-damage-threshold coatings required by lasers operating with high fluences. The development of scandia, and other thin film materials, requires the reduction of defects in the material through modification of growth processes and post deposition treatment. Material defects give rise to absorption of laser light and laser induced damage initiation sites. The growth parameter investigated in this work is the oxygen partial pressure in the deposition chamber during the reactive sputtering process of a metal Sc target to form Sc2O3. The film properties are sensitive to the oxygen partial pressure. At 2 μTorr oxygen partial pressure, the films are metallic and highly absorbing with an absorption, at λ = 1.064 μm, of > 104 ppm. The absorption decreases to 10 ppm at 5 μTorr oxygen partial pressure and at 38 μTorr, the absorption reaches a value of 35 ppm. This, along with the increase in absorption near the optical band edge, suggests an increase in shallow-type defect concentrations for increasing oxygen partial pressures. The observed defects contain unpaired electrons, as assessed by electron paramagnetic measurements, that have a paramagnetic absorption signal with principle g-values [gxx, gyy, gzz] = [2.018, 2.019, 2.058]. Generally, the concentration of the paramagnetic species increased with increasing oxygen partial pressure. These spin defects are possibly O2̅ interstitials in the deposited films. These defects contribute to an approximately 40% increase in the film stress observed in x-ray diffraction measurements and measurements of stress-induced fused silica substrate curvature.
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    Extreme ultraviolet laser ionization mass spectrometry: probing materials at the micro and nano scales
    (Colorado State University. Libraries, 2023) Rush, Lydia Alexandra, author; Menoni, Carmen S., advisor; Duffin, Andrew M., advisor; Farmer, Delphine K., committee member; Marconi, Mario C., committee member; Rocca, Jorge J., committee member
    The focus of this dissertation is the use of 50 to 10 nanometer wavelength extreme ultraviolet (EUV) laser light as a next generation probe for mass spectrometry analyses at the micro (>100 nanometers) and nano (≤100 nanometer) spatial scales. While the unique properties of EUV light have revolutionized the semiconductor industry through nanoscale lithography fabrication, the use of EUV lasers with analytical instruments, like mass spectrometers, for high spatial resolution chemical analyses is a relatively untapped area. This unexplored territory is owed partly to only recently bringing EUV lasers to an accessible "bench-top" scale. Herein I show how EUV laser ionization can be used with different types of mass spectrometers as a new route for interrogating nuclear and geologic materials with micro and nano scale lateral spatial resolution. I focus on the application of a compact capillary discharge EUV laser operating at a wavelength of 46.9 nanometers connected to a time-of-flight (TOF) mass spectrometer, called the EUV TOF. I also show for the first time how the 46.9 nm EUV laser ionization source can be connected to a commercial magnetic sector mass spectrometer, called the EUV magnetic sector. Specifically, I demonstrate that the EUV TOF instrument can measure the 235U/238U isotope ratio in 100 nm sized pixels in a heterogeneous uranium fuel pellet that was made by blending different feedstocks together. The results show that the EUV TOF maps similar micrometer sized areas of 235U/238U heterogeneity as nanoscale secondary ionization mass spectrometry (NanoSIMS), indicating that EUV laser ionization can be used to accurately probe complex nuclear materials within the scope of the study. I also show that the EUV TOF can be used to measure 206Pb/238U and 232Th/238U isotope ratios at the 8 µm scale in select geologic matrices of silicates, zircons, monazites, and iron manganese within error (±2σ) using a single non-matrix matched calibration standard. However, the precision on the ratio measurements was low for useful geologic applications, ranging between 1-10% at elemental concentrations exceeding hundreds of ppm because of the limitations of using a TOF for isotope ratio measurements. To this end, I show the current development of the new EUV magnetic sector instrument that uses the EUV laser ionization source with a commercial double-focusing sector-field multi-collector mass spectrometer with the aim of achieving more precise (<1%) and sensitive (≤ppm) isotope ratio measurements at high spatial scales (<10 µm down to the nanoscale). The EUV magnetic sector is being developed to probe more complex isotopic systems in nuclear and geologic materials that was not possible with the TOF mass spectrometer. The work here shows that the 46.9 nm wavelength EUV laser ionization source can be interfaced with Thermo Fisher's commercial sector-field multi-collector mass spectrometer called the Neptune by removing its inductively coupled plasma (ICP) region. The Neptune's ion optics, electric sector, and magnetic sector were modified for acceptance of the pulsed EUV-generated ions. These modifications resulted in ions from ≤2 µm diameter craters created by EUV laser ablation and ionization being successfully focused, separated by mass, and detected using the Neptune's electron multipliers. However, further system upgrades to the Neptune's detectors are needed for accurate isotope ratio measurements at high spatial scales because the 10 to 30 nanosecond wide EUV-generated ion pulses are on the order of the electron multipliers' dead time. With proper detectors, the EUV magnetic sector's accuracy, precision, sensitivity, efficiency, and spatial resolution can be measured in future experiments. The demonstration of the EUV magnetic sector instrument here represents the first time that an EUV laser ionization source has been used with a sector-field mass spectrometer, paving the way for future high spatial resolution isotope ratio analyses.
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    Progress in coherent lithography using table-top extreme ultraviolet lasers
    (Colorado State University. Libraries, 2016) Li, Wei, author; Marconi, Mario C., advisor; Menoni, Carmen S., advisor; Wu, Mingzhong, committee member; Krapf, Diego, committee member
    Nanotechnology has drawn a wide variety of attention as interesting phenomena occurs when the dimension of the structures is in the nanometer scale. The particular characteristics of nanoscale structures had enabled new applications in different fields in science and technology. Our capability to fabricate these nanostructures routinely for sure will impact the advancement of nanoscience. Apart from the high volume manufacturing in semiconductor industry, a small-scale but reliable nanofabrication tool can dramatically help the research in the field of nanotechnology. This dissertation describes alternative extreme ultraviolet (EUV) lithography techniques which combine table-top EUV laser and various cost-effective imaging strategies. For each technique, numerical simulations, system design, experiment result and its analysis will be presented. In chapter II, a brief review of the main characteristics of table-top EUV lasers will be addressed concentrating on its high power and large coherence radius that enable the lithography application described herein. The development of a Talbot EUV lithography system which is capable of printing 50nm half pitch nanopatterns will be illustrated in chapter III. A detailed discussion of its resolution limit will be presented followed by the development of X-Y-Z positioning stage, the fabrication protocol for diffractive EUV mask, and the pattern transfer using self- developed ion beam etching, and the dose control unit. In addition, this dissertation demonstrated the capability to fabricate functional periodic nanostructures using Talbot EUV lithography. After that, resolution enhancement techniques like multiple exposure, displacement Talbot EUV lithography, fractional Talbot EUV lithography, and Talbot lithography using 18.9nm amplified spontaneous emission laser will be demonstrated. Chapter IV will describe a hybrid EUV lithography which combines the Talbot imaging and interference lithography rendering a high resolution interference pattern whose lattice is modified by a custom designed Talbot mask. In other words, this method enables filling the arbitrary Talbot cell with ultra-fine interference nanofeatures. Detailed optics modeling, system design and experiment results using He-Ne laser and table top EUV laser are included. The last part of chapter IV will analyze its exclusive advantages over traditional Talbot or interference lithography.
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    Single-shot flash imaging using a compact soft x-ray microscope
    (Colorado State University. Libraries, 2012) Carbajo, Sergio, author; Menoni, Carmen S., advisor; Rocca, Jorge J., committee member; Marconi, Mario C., committee member; Krapf, Diego, committee member; Van Orden, Alan K., committee member
    Microscopes extend the ability of our eyes to see objects at micro- and nanoscales. There are applications, however, for which a static image is not sufficient, and thus require information on the dynamics before a process can be understood and controlled. Therefore, the visualization of nanoscale dynamics in real-space can significantly contribute to the understanding of nanoscale processes and to accelerate the development of new nanodevices. Today, there is a need for practical microscopes capable of delivering nanometer spatial resolution and ultrafast temporal resolution in order to readily visualize any arbitrary nanoscale phenomenon. Conventional visible light microscopes can visualize ultrafast dynamics but are inherently limited in spatial resolution to about 200 nm. Alternatively, transmission electron microscopes can routinely provide atomic spatial resolutions of static samples. Probing dynamics is possible using stroboscopic schemes with nanosecond temporal resolution or scanning methods which can obtain femtosecond temporal resolution at the expense of hours-long image acquisition times. Soft x-rays (SXR) microscopes provide the ability to resolve at the nanoscale and at the same time image dynamics with nanosecond to picosecond time resolution. Pioneering work has been carried out using synchrotron illumination that has allowed to study repetitive phenomena in magnetic materials. There are however processes that are statistically reproducible but individually non-recurring that require SXR flash illumination to capture their dynamics. SXR flash imaging requires a large number of photons per pulse to illuminate the sample (about 10E12 photons per pulse). There are two types of SXR sources presently available which offer such high peak brightness: free electron lasers (FEL) and table-top SXR lasers. FELs have been used to probe dynamics using holographic and diffractive imaging configurations. This thesis describes the first demonstration of real-space flash imaging using a compact SXR laser operating at a wavelength of 46.9 nm. A sequence of flash images obtained with the full-field SXR microscope with a spatial resolution of 50 nm and temporal resolution of 1.5 ns captured the interaction dynamics of a rapidly oscillating magnetic tip in close proximity to a magnetized surface. The interaction of the tip and the stray magnetic fields led to changes in the amplitude of the tip oscillation as small as 30 nm. Modeling of the interaction assuming an undamped perturbed harmonic oscillator corroborate the experimental results. The use of compact plasma-based SXR lasers operating at wavelengths down to 10.9 nm will allow to capture flash images and render animations of picosecond phenomena with a few nanometers accuracy on a table-top.