Enhancing Laser Damage Resistance of Co²⁺:MgAl₂O₄ Crystal by Plasma Etching

Co2+:MgAl2O4 crystals are successfully used as passive Q-switches within the cavity of erbium glass lasers. Their limited resistance to laser radiation might also put constraints on the generated output peak power. Usually, polishing of optical substrates induces a contaminated Beilby layer and damages the subsurface layer, which leads to a considerably lower optical resistance of the obtained surface. Low-energy oxygen plasma etching using different depths of 50, 100, 250 and 400 nm was performed on polished crystals. The surface morphology by atomic force microscopy, transmission spectra, subsurface structure by transmission electron microscopy and the LIDT (R(1)-in-1) using 1540 nm nanosecond pulses were analyzed. It was demonstrated that plasma etching substantially increased the initial crystal surface LIDT. It also allowed the removal of the damaged subsurface layer and almost maintained the initial surface roughness. The presented results demonstrated the good potential of oxygen plasma etching for obtaining highly laser-damage-resistant Co2+:MgAl2O4 crystals for high-power laser applications

Structure Modification, Evolution, and Compositional Changes of Highly Conductive La:BaSnO3 Thin Films Annealed in Vacuum and Air Atmosphere

Perovskite-type La:BaSnO3 (LBSO) has been drawing considerable attention due to its high electron mobility and optical transparency. Its thin film electrical properties, however, remain inferior to those of single crystals. This work investigates the thermal post-treatment process of films deposited using the metalorganic chemical vapor deposition method to improve the electrical properties of different stoichiometry films, and demonstrates the modification of thin film’s structural properties using short and excessive annealing durations in vacuum conditions. Using vacuum post-treatment, we demonstrate the improvement of electrical properties in Ba-rich, near-stoichiometric, and Sn-rich samples with a maximum electron mobility of 116 cm2V−1s−1 at r.t. However, the improvement of electrical properties causes surface morphology and internal structural changes, which depend on thin film composition. At temperatures of 900 °C–1400 °C the volatile nature of LBSO constituting elements is described, which reveals possible deterioration mechanisms of thin LBSO air. At higher than 1200 °C, LBSO film’s decomposition rate increases exponentially. Thin film structure evolution and previously unreported decomposition is demonstrated by Ba and La diffusion to the substrate, and by evaporation of SnO-SnOx species

Structural control and electrical behavior of thermally reduced graphene oxide samples assisted with malonic acid and phosphorus pentoxide

We present a detailed study of the structural and electrical changes occurring in two graphene oxide (GO) samples during thermal reduction in the presence of malonic acid (MA) (5 and 10 wt%) and P2O5 additives. The morphology and de-oxidation efficiency of reduced GO (rGO) samples are characterized by Fourier transform infrared, X-ray photoelectron, energy-dispersive X-ray, Raman spectroscopies, transmission electron and scanning electron microscopies, X-ray diffraction (XRD), and electrical conductivity measurements. Results show that MA and P2O5 additives are responsible for the recovery of π-conjugation in rGO as the XRD pattern presents peaks corresponding to (002) graphitic-lattice planes, suggesting the formation of the sp2-like carbon structure. Raman spectra show disorders in graphene sheets. Elemental analysis shows that the proposed reduction method in the presence of additives also suggests the simultaneous insertion of phosphorus with a relatively high content (0.3–2.3 at%) in rGO. Electrical conductivity measurements show that higher amounts of additives used in the GO reduction more effectively improve electron mobility in rGO samples, as they possess the highest electrical conductivity. Moreover, the relatively high conductivity at low bulk density indicates that prepared rGO samples could be applied as metal-free and non-expensive carbon-based electrodes for supercapacitors and (bio)sensors

The crystalline structure of thin bismuth layers grown on silicon (111) substrates

Bismuth films with thicknesses between 6 and ∼30 nm were grown on Si (111) substrate by molecular beam epitaxy (MBE). Two main phases of bismuth — α-Bi and β-Bi — were identified from high-resolution X-ray diffraction (XRD) measurements. The crystal structure dependencies on the layer thicknesses of these films were analyzed. β-Bi layers were epitaxial and homogenous in lateral regions that are greater than 200 nm despite the layer thickness. Further, an increase in in-plane 2θ values showed the biaxial compressive strain. For comparison, α-Bi layers are misoriented in six in-plane directions and have β-Bi inserts in thicker layers. That leads to smaller (about 60 nm) lateral crystallites which are compressively strained in all three directions. Raman measurement confirmed the XRD results. The blue-sift of Raman signals compared with bulk Bi crystals occurs due to the phonon confinement effect, which is larger in the thinnest α-Bi layers due to higher compression

Magneto-plasmonic nanoparticles generated by laser ablation of layered Fe/Au and Fe/Au/Fe composite films for SERS application

Magneto-plasmonic nanoparticles were fabricated using a 1064 nm picosecond-pulsed laser for ablation of Fe/Au and Fe/Au/Fe composite thin films in acetone. Nanoparticles were characterized by electron microscopy, ultraviolet-visible (UV-VIS) absorption, and Raman spectroscopy. Hybrid nanoparticles were arranged on an aluminum substrate by a magnetic field for application in surface-enhanced Raman spectroscopy (SERS). Transmission electron microscopy and energy dispersive spectroscopy analysis revealed the spherical core-shell (Au-Fe) structure of nanoparticles. Raman spectroscopy of bare magneto-plasmonic nanoparticles confirmed the presence of magnetite (Fe3O4) without any impurities from maghemite or hematite. In addition, resonantly enhanced carbon-based bands were detected in Raman spectra. Plasmonic properties of hybrid nanoparticles were probed by SERS using the adsorbed biomolecule adenine. Based on analysis of experimental spectra and density functional theory modeling, the difference in SERS spectra of adsorbed adenine on laser-ablated Au and magneto-plasmonic nanoparticles was explained by the binding of adenine to the Fe3O4 structure at hybrid nanoparticles. The hybrid nanoparticles are free from organic stabilizers, and because of the biocompatibility of the magnetic shell and SERS activity of the plasmonic gold core, they can be widely applied in the construction of biosensors and biomedicine applications

Functionalized protein nanotubes based on the bacteriophage vb_klem-rak2 tail sheath protein

We report on the construction of functionalized nanotubes based on tail sheath protein 041 from vB_KleM-RaK2 bacteriophage. The truncated 041 protein (041∆200) was fused with fluorescent proteins GFP and mCherry or amidohydrolase YqfB. The generated chimeric proteins were successfully synthesized in E. coli BL21 (DE3) cells and self-assembled into tubular structures. We detected the fluorescence of the structures, which was confirmed by stimulated emission depletion microscopy. When 041∆200GFP and 041∆200mCherry were coexpressed in E. coli BL21 (DE3) cells, the formed nanotubes generated Förster resonance energy transfer, indicating that both fluorescent proteins assemble into a single nanotube. Chimeric 041∆200YqfB nanotubes possessed an enzymatic activity, which was confirmed by hydrolysis of N4-acetyl-2′-deoxycytidine. The enzymatic properties of 041∆200YqfB were similar to those of a free wild-type YqfB. Hence, we conclude that 041-based chimeric nanotubes have the potential for the development of delivery vehicles and targeted imaging and are applicable as scaffolds for biocatalysts

Bismuth Quantum Dots in Annealed GaAsBi/AlAs Quantum Wells

Abstract Formation of bismuth nanocrystals in GaAsBi layers grown by molecular beam epitaxy at 330 °C substrate temperature and post-growth annealed at 750 °C is reported. Superlattices containing alternating 10 nm-thick GaAsBi and AlAs layers were grown on semi-insulating GaAs substrate. AlAs layers have served as diffusion barriers for Bi atoms, and the size of the nanoclusters which nucleated after sample annealing was correlating with the thickness of the bismide layers. Energy-dispersive spectroscopy and Raman scattering measurements have evidenced that the nanoparticles predominantly constituted from Bi atoms. Strong photoluminescence signal with photon wavelengths ranging from 1.3 to 1.7 μm was observed after annealing; its amplitude was scaling-up with the increased number of the GaAsBi layers. The observed photoluminescence band can be due to emission from Bi nanocrystals. The carried out theoretical estimates support the assumption. They show that due to the quantum size effect, the Bi nanoparticles experience a transition to the direct-bandgap semiconducting state

Pantoea Bacteriophage vB_PagS_AAS23: A Singleton of the Genus Sauletekiovirus

A cold-adapted siphovirus, vB_PagS_AAS23 (AAS23) was isolated in Lithuania using the Pantoea agglomerans strain AUR for the phage propagation. The double-stranded DNA genome of AAS23 (51,170 bp) contains 92 probable protein encoding genes, and no genes for tRNA. A comparative sequence analysis revealed that 25 of all AAS23 open reading frames (ORFs) code for unique proteins that have no reliable identity to database entries. Based on the phylogenetic analysis, AAS23 has no close relationship to other viruses publicly available to date and represents a single species of the genus Sauletekiovirus within the family Drexlerviridae. The phage is able to form plaques in bacterial lawns even at 4 °C and demonstrates a depolymerase activity. Thus, the data presented in this study not only provides the information on Pantoea-infecting bacteriophages, but also offers novel insights into the diversity of cold-adapted viruses and their potential to be used as biocontrol agents