Effect Of Pulsed Laser Annealing Research Articles

Pulsed laser annealed rare earth doped TiO2 thin films for luminescence and sensing applications

Many research activities target functional luminescent materials based on metal oxides activated with trivalent rare earth ions. Specific applications necessitate optimization of material preparation, annealing and excitation-detection techniques. Hereby we utilized pulsed laser deposition to obtain thin (150 nm) TiO2 films containing 1at% of samarium (Sm) or neodymium (Nd) impurity ions. The effect of pulsed laser annealing (ArF excimer laser, wavelength 193 nm, pulse duration 20 ns) on their structural and luminescent properties was investigated. It was found that, compared to conventional thermal annealing at 700 °C, proper laser annealing (fluence 50 mJ/cm2, 5–15 shots) induced much better crystallization (nearly phase-pure anatase) along with respective improvement of host-sensitized trivalent rare earth fluorescence. The outcome significantly depends on the applied fluence and number of laser shots. Effects of under- and overannealing were witnessed (poor or mixed phase crystallization, weak luminescence and melting/dewetting of the film). A strong luminescence from optimally annealed samples was detected under excitation of 365 nm light emitting diode, which is favorable for potential applications of such thin films. As an example, trace oxygen sensing is demonstrated with the laser annealed TiO2:Sm film.

Pulsed laser modification of layered B-C and mixed BCx films on sapphire substrate

The effect of pulsed laser annealing (PLA, i.e., action of nanosecond laser pulses in air atmosphere) on surface morphology, structure, chemical state, and electrical properties of thin films consisting of boron and carbon atoms was studied. The nanolayered В/С and mixed ВСx~3 thin film precursors (with a thickness ~110–140 nm) were created on sapphire substrates by using the pulsed laser deposition. Scanning electron microscopy and Raman scattering measurements indicate that the process of stratification of the multilayer B/C films dominated during PLA of the films. The outer layers were removed, and closer to the substrate, the B and C layers were preserved, and they were not mixed. For the mixed ВСх films deposited at elevated temperatures, the PLA treatment enhances ordering of initially amorphous film structure. At the stage of melting of these films, oxygen (from surrounded air) penetrated inside the top layer of the film leading to the formation of a multiphase structure from g-BCx and B-doped GO/rGO after solidification. Studies of the chemical state of elements in the irradiated film have shown that О atoms, which penetrated the under-surface layers of the film, facilitated the formation of new chemical bonds in the B–C–O system. The concentration of O atoms in the depth of the film could reach 8%. The preferential oxidation of boron in a homogeneous mixture of B–C–O atoms indicated that intercalation of carbon matrix could be due to the incorporation of not only O atoms, but also B–O molecules. The laser irradiated ВСх films have a relatively low resistivity (~1.6 mΩ·cm) and semi-metallic dependence on temperature in the range 4.2–300 К. The spatial distribution of conductivity zones after PLA has an irregular structure, and its pattern looks like sand dunes, indicating that the PLA treatment leads to mixing zones of high with those of lower conductivity. The contact-tip resistivity inside the areas of high conductivity of the ВСx/Al2O3 samples may be significantly lower than that of pure graphite.

Influence of pulsed laser annealing on the optical properties of ZnO nanorods

AbstractThe effect of pulsed laser annealing (PLA) on the photoluminescence (PL) properties of ZnO nanorods was investigated. As the fluence of pulsed laser increases, the UV PL in ZnO nanorods shows a general increasing trend, except at a range of fluences from 10 to 70 mJ/cm2. It is found that the treatment with the PLA at the fluence of 70 mJ/cm2 leads to a larger improvement of crystalline properties than that with rapid thermal annealing (RTA). The relationship between PL intensity and fluence of pulsed lasers can be well explained by a combination of the deterioration in surface crystallinity and the increased donor densities after PLA.

Pulsed laser annealing of self-organized InAs/GaAs quantum dots

The effect of pulsed laser annealing (PLA), using an excimer laser, on the luminescence efficiency of self-organized InAs/GaAs and In0.4Ga0.6As/GaAs quantum dots has been investigated. It is found that such annealing can enhance both the peak and integrated photoluminescence (PL) efficiency of the dots, up to a factor of 5–10 compared to as-grown samples, without any spectral shift of the luminescence spectrum. The improved luminescence is attributed to the annealing of nonradiative point and extended defects in and around the dots.

Pulsed laser annealing for high-efficiency thin film electroluminescent devices

Thin film electroluminescent (TFEL) structures composed of ZnS:Mn (phosphor) and Y2O3 (insulator) films were annealed using pulsed (∼20 ns) KrF laser irradiations under an environment of 150 psi (∼10.34 bars) of argon. The crystallinity of both layers was studied via x-ray diffraction analysis. Their degree of lattice misfit and the integrated diffraction line intensities were examined to assess the thermal effects of pulsed laser annealing. In agreement with a thermal model of the laser–matter interaction and previous results, we suggest that the pulsed laser annealing technique improves the luminescent efficiencies of thin film electroluminescent phosphors by generating an in-depth solid-state phase transition. We report that the laser processed TFEL structure exhibits better display performance than equivalent devices thermally annealed at a temperature of 450 °C as demonstrated by sharper turn-on response and also an increase in brightness by a factor greater than four times. We attribute these performance improvements to a smaller lattice misfit value, which has been previously correlated to interface states density.

Fast annealing of II-VI compounds by pulsed laser irradiation

The effects of pulsed laser annealing of CdTe (containing small quantities of Zn or Hg) are described for single crystals and thin film samples. The influence of laser power, wavelength, number of applied pulses, and homogenization on the morphological changes and some physical parameters are investigated with the help of scanning electron microscopy (SEM), x-ray diffraction (XRD), UV/VIS absorption spectrophotometry and (photo)electrochemical characterization. Melting of the sample surface was observed in most cases at the laser pulse energies used; the surface modifications as seen by SEM depended in a characteristic way on laser wavelength and photon density. Use of homogenized beams led to a restructuring of the surface, entailing in-depth melting with the formation of holes and spongy structures, in particular upon multi-pulse irradiation at lambda =532 nm. In general, surface melting promoted the healing of cracks which were sometimes formed by laser-induced thermal shock in the crystal plates (such cracks were not found in the thin films). Surface melting and material loss by evaporation is accompanied by some amorphization and maybe caused by a change in doping profile and/or stoichiometry near the surface.

Laser annealing of radiation damage in Be-implanted InSb single crystals

Ion backscattering and channeling of proton and helium beams have been used to study the effect of pulsed laser annealing of the radiation damage in ion-implanted InSb single crystals. The single crystals were implanted at room temperature with Be ions with a dose of 1 × 1016 ions/cm2 at energies of 100 and 200 keV. Although the laser annealing resulted in a significant decrease in the lattice disorder of the near-surface damaged region, a higher dechanneling rate at greater depths indicated that the structure could not be fully restored. However, in comparison with isochronal thermal annealing the application of pulsed laser beams rendered roughly the same single-crystal properties at energy densities above the melting point.