Browsing by Author "Rocca, Jorge J., committee member"
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Item Open Access 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 memberThe 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.Item Open Access Investigation of laser cooling and trapping of atomic silicon: towards the development of a deterministic single ion source(Colorado State University. Libraries, 2023) Ronald, Samuel R., author; Lee, Siu Au, advisor; Fairbank, William M., Jr., advisor; Rocca, Jorge J., committee member; Marconi, Mario C., committee memberThe laser cooling and magneto-optical trapping of silicon atoms were investigated experimentally. These are the first steps towards the development of a deterministic single ion source suitable for single ion implantation of a Kane quantum computer. We identified the 3s23p2 3P2 → 3s3p3 3Do3 transition at 221.74nm as a cycling transition suitable for laser cooling. We also identified the 3s23p2 1D2 → 3s3p3 3Do3 at 256.26nm as a repump transition coupling a lower metastable state with the upper cooling state. Two deep ultraviolet (DUV) laser systems were implemented to provide the cooling and repump laser light. Both systems utilized two stage second harmonic generation to quadruple the frequency of a fundamental laser to produce the DUV light. The cooling laser system utilized frequency quadrupling of a tunable cw Ti:Sapphire ring laser to produce up to 90mW at 221.74nm. The repump laser system utilized frequency quadrupling of an external cavity diode laser to produce up to 35mW at 256.26nm. A silicon atomic beam source operating at 1400°C was developed that produced a beam of free silicon atoms for laser studies. The atomic beam characteristics were analyzed, and the velocity distribution was manipulated via laser cooling. Careful spectroscopic studies were performed on the cooling and repump transitions. Frequency references for the DUV lasers were investigated in Te2 and I2 with Doppler free saturated absorption spectroscopy, using the first doubling stage output of the cooling and repump laser, respectively. Specific hyperfine components of the molecular transitions in Te2 and I2, suitable for frequency references, were identified and measured. Locking of the cooling laser on the Te2 reference was demonstrated. A magneto-optic trap (MOT) was implemented in the silicon atomic beam. A CCD optical system to image the fluorescence from atoms in the MOT was developed and achieved single atom ii detection capability. MOT trapping of silicon atoms was attempted. The low flux of atoms in the MOT velocity capture range precluded any observation of trapped atoms. A Zeeman slower, based on a novel design utilizing a variable pitch helical solenoid, was designed, simulated, and constructed to improve the flux of slow atoms. No magneto-optic trap was observed due to insufficient laser power for simultaneous Zeeman slowing and magneto-optic trapping. Investigations were performed for one dimensional laser cooling, via a Zeeman slower, along the atomic beam motion direction. Atomic beam velocity distribution profiles were observed to be modified when the Zeeman slower was on. The parameter space of Zeeman slower currents, laser power and detuning, was explored. A simulation of the atom motion over the 1m long flight path under the influence of the Zeeman slower was carried out and found to agree with the observed results.Item Open Access 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 memberMicroscopes 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.