Electronic structure of crystalline and amorphous silicon dioxide

Ligand-Driven and Full-Color-Tunable Fiber Source: Toward Next-Generation Clinic Fiber-Endoscope Tomography with Cellular Resolution

In many biomedical applications, broad full-color emission is important, especially for wavelengths below 450 nm, which are difficult to cover via supercontinuum generation. Single-crystalline-core sapphires with defect-driven emissions have potential roles in the development of next-generation broadband light sources because their defect centers demonstrate multiple emission bands with tailored ligand fields. However, the inability to realize high quantum yields with high crystallinity by conventional methods hinders the applicability of ultra-broadband emissions. Here, we present how an effective one-step fiber-drawing process, followed by a simple and controllable thermal treatment, enables a low-loss, full-color, and crystal fiber-based generation with substantial color variability. The broad spectrum extends from 330 nm, which is over 50 nm further into the UV region than that in previously reported results. The predicted submicrometer spatial resolutions demonstrate that the defect-ligand fields are potentially beneficial for achieving in vivo cellular tomography. It is also noteworthy that the efficiency of the milliwatt-level full-color generation, with an optical-to-optical efficiency of nearly 5%, is the highest among that of the existing active waveguide schemes. In addition, direct evidence from high-resolution transmission electron microscopy together with electron energy loss spectroscopy and crystal-field ligands reveals an excellent crystalline core, atomically defined core/cladding interfacial roughness, and significant enhancements in new laser-induced electronic defect levels. Our work suggests an inexpensive, facile, and highly scalable route toward achieving cellular-resolution tomographic imaging and represents an important step in the development of endoscope-compatible diagnostic devices.

Chemical bonding and electronic structures of microcline, orthoclase and the plagioclase series by X-ray photoelectron spectroscopy

A detailed analysis was undertaken of the X-ray photoelectron spectra obtained from microcline, orthoclase and several samples of plagioclase with varying Na/Ca ratio. Comparison of the spectra was made based on the chemical bonding and structural differences in the Al- and Si-coordination within each specimen. The spectra for Si 2p and Al 2p vary with the change in symmetry between microcline and orthoclase, while in plagioclase an increase in Al-O-Si linkages results in a small but observable decrease in binding energy. The overall shapes of the O 1s peaks observed in all spectra are similar and show shifts similar to those observed for Si 2p and Al 2p. The lower-VB spectra for microcline and orthoclase are similar intermediate between α-SiO2 and α-Al2O3 in terms of binding energies. In the plagioclase series increasing coupled substitution of Na and Si for Ca and Al results in a change of the overall shape of the spectra, showing a distinct broadening associated with the presence of two separate but overlapping bands similar to the 21 eV band observed for quartz and the 23 eV band observed for corundum. The bonding character for microcline and orthoclase is more covalent than that of α-Al2O3, but less than that of α-SiO2. In contrast, the plagioclase samples show two distinct bonding characters that are comparable with those of α-SiO2 and α-Al2O3.

Light scattering of ultrafine silica particles by VUV synchrotron radiation

Vacuum ultraviolet (VUV) light scattering from ultrafine silica particles is studied with an aerosol instrument recently established at the Advanced Light Source (ALS) in Berkeley. Silica particles, size-selected by a differential mobility analyzer, are introduced into vacuum through a set of aerodynamic lenses to form a particle beam. The scattered photons from the crossing area of the VUV synchrotron beam and particle beam are detected with a rotatable VUV photon detector. The angular distributions of scattered photons (ADSP) originating from 70, 100, 200 nm diameter silica particles are measured with 145.9 and 118.1 nm synchrotron radiation. These angular distributions show strong forward scattering. The measured ADSPs are consistent with simulation of Mie scattering. The refractive indices of silica particles, 2.6 + 1.1i and 1.6 + 0.0001i for 118.1 and 145.9 nm, respectively, are obtained by fitting the measured ADSPs; the least average percentage deviations are 18% and 6%, respectively. The scattered fluxes at widely different wavelengths (visible versus VUV) also exhibit clear size sensitivity. Under comparable experimental conditions of photon fluxes and detection efficiencies, limits of particle size detection of 70 and 250 nm are obtained, respectively, when using 118.1 and 532 nm illumination. As anticipated, VUV scattering is a more sensitive probe for ultrafine particles, which will find application in detection of these ubiquitous species beyond the confines of a laboratory.