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Micro x-ray fluorescence (MXRF) is a microscopic analysis and imaging technique that is used to characterize the elements in a material non-destructively. Micro XRF instruments use an x-ray source to shine x-rays on a sample, and a detector to detect the characteristic x-rays given off. These fluorescent x-rays have very specific energies corresponding to specific electron energy transitions. Therefore, it is possible to detect and identify all of the elements present in a sample (typically above sodium) as well as measure their concentrations. This technique is widely used for the characterization of materials including polymer and metallic foams, powder samples, forensics applications, geological samples, works of art and nuclear fuels. Commercial MXRF instruments use a fused silica optic (mono or polycapillary) to focus the x-rays on the sample with no optic on the detector (Figure 1a).

High‐pressure laser chemical vapor deposition (HP‐LCVD) is a powerful tool for growing complex microstructures at rapid rates. Not only is it possible to deposit functionally graded materials, but new metastable phases, alloys, and composite materials may be realized. In this paper, the diversity of microstructures that may be obtained through HP‐LCVD is demonstrated, including the growth of metastable materials, e.g., diamond‐like carbon (DLC). For the first time, a pressure–temperature (P–T) phase diagram has been created for HP‐LCVD, identifying nine distinct material phases of carbon from ethene. Regions of high sp3 content are identified via Raman spectroscopy. The kinetics, rate limitations, and thermodynamics of the process are also characterized at hyperbaric pressures, creating a first‐ever process‐rate map—covering the entire useful pressure range for ethene. Thermodynamically enhanced growth is also documented for the first time, where the contribution of the heat of reaction is much greater than the incident laser power—demonstrating a quasi‐self‐sustaining reaction. Finally, sufficient information is provided to reconstruct specific fiber geometries, structures, and growth rates for potential industrial production of carbon fibers from the gas phase.