Electronic properties of CaF2 bulk and interfaces

Abstract

The electronic band structures of ultra-wide gap CaF2 are investigated with both the hybrid functional and the efficient generalized gradient approximation (GGA) + U scheme. The hybrid functional scheme is in excellent agreement with experiments, while introducing an on-site Coulomb interaction to F-2p orbitals also accurately reproduces the experimental bandgap and greatly improves the previous theoretical results using advanced electronic structure schemes. We also apply the GGA + U method to study CaF2/Si and metal/CaF2 interfaces. The CaF2/Si insulating interfaces with a clear bandgap are built based on the electron counting rule. Our supercell calculations of the CaF2/Si interfaces show a type-II band alignment and the valence band offset follows a descending trend from (001) to (111) then to (110). The calculation convergence of GGA + U is further tested with the metallic contacts. The metal/CaF2 interfaces are observed to be weakly pinned and different orientations of CaF2 sharing a similar pinning factor S up to ∼0.9, owing to the highly ionic nature of CaF2. The GGA + U approach is proven to be a useful tool in studying such fluoride interfaces and contacts.

Photoluminescent Microbit Inscripion inside Dielectric Crystals by Ultrashort Laser Pulses for Archival Applications

“…Specifically, the PL microbits inside the CaF2 slab exhibit the corresponding energy-dependent microbit dimensions above the inscription threshold value 3 nJ at the exposure of 10 7--10 9 pulses/microbit. Similarly, the PL microbits were inscribed inside the LiF slab in the same energy range, while the threshold energy appears considerably higher ( 5 nJ, Figure 2b, left side) at the exposure of 10 7--10 9 pulses/microbit, reflecting the higher bandgap energy of 13.0-14.2 eV in LiF [17,18], comparing to CaF2 -11.5-11.8 eV [19,20]. Finally, in the diamond plate the PL microbits were inscribed as a function of laser pulse energy, demonstrating their increasing dimensions at the exposure of 10 7--10 9 pulses/microbit (Figure 2c, left side).…”

Photonic crystal nanostructure as a photodetector for NaCl solution monitoring: theoretical approach

“…Calcium uoride (CaF 2 ) is a good insulator with an ultra-wide bandgap, a relatively high dielectric constant, a low absorption coefficient, and a wide range of transmission wavelengths (130 nm to 10 mm). 35,36 Moreover, it has good stability, a high melting point, insoluble material, exceptional hardness, and inertness. CaF 2 is a raw material used in the production of optical glasses, anti-reection coatings, excimer lasers, beam splitters, agriculture fertilizers, and dental preparations.…”

Characterization of Calcium Fluoride Prepared by Chemical Precipitation Method

“…Then, there will be two energy levels resulting from crystalline defects (Eg = 2.9 eV) and (Eg = 3.1 eV). CaF2 has a wide energy gap (12.1 eV) whose value in references ranges from (11.6 -12.1 eV) [19], but due to the exposure of calcium fluoride to X-ray, defects are produced in the crystal lattice. These defects are limited to the negative sub-lattice, while the charge is much less than the energy needed to excite the positive charge [20].…”