Mihaela E. Koleva

Sr-ferrite thin films grown on sapphire by pulsed laser deposition

High-quality epitaxial strontium-hexaferrite (SrFe12O19) thin films were grown by pulsed laser deposition (PLD) on c-cut sapphire using KrF∗ excimer laser at a fluency of 2 J/cm2 and substrate temperature of 800°C in 100 mTorr oxygen environment. The X-ray diffraction (XRD) and morphology analyzes showed films with excellent crystalline structure and flat surface. The thickness was found to influence considerably the surface morphology and magnetic properties of the as-deposited films. The highest orientation and the best morphology with smooth surface and fine grain structure was obtained for the film having a thickness of 750 nm. The highest coercive force of 1453 Oe was measured for this film in perpendicular to the plane direction.

Pulsed laser deposition of Mn-Zn ferrite thin films

Mn-Zn ferrite thin films were deposited on sapphire substrates by pulsed laser deposition from sintered Mn1 − xZnxFe2O4 ceramic targets. A full stoichiometric transfer from targets to substrates was achieved. Magnetic inplane measurements in two perpendicular directions were carried out and the macromagnetic properties of films were determined. The hysteresis loops obtained are rectangular and the values of the coercive force, the saturation, and the remanent magnetization are comparable to the same parameters of the bulk Mn-Zn ferrite. The films were characterized using a vibrating sample magnetometer (VSM), a scanning electron microscope (SEM) and by X-ray photoelectron spectroscopy (XPS).

Growth and characterization of pulsed laser-deposited Mn–Zn ferrite thin films ☆

Abstract The magnetic behavior of Mn–Zn ferrite thin films deposited on silicon and sapphire substrates with and without a buffer layer of MgO was studied. The films were grown in a vacuum chamber using a KrF ∗ excimer laser. The magnetic and structural properties of the films deposited were examined. The magnetic behaviour of the film deposited on Si with a buffer layer of MgO was studied comparatively to that deposited on other substrates, using Kerr effect. The large coercive force obtained is related to the microstructure, which was investigated by AFM. The films were smooth and homogeneous. XRD-analyses revealed the formation of Mn–Zn ferrite phase.

Fabrication of ZnO nanostructures by PLD

Different types of ZnO nanostructures were fabricated on metal (Au or Ag) coated silicon substrates by applying the pulsed laser deposition (PLD) method. The samples were prepared at substrate temperatures in the range of 300 – 650 °C, oxygen pressure of 5 Pa, and laser fluence ≤ 1 J.cm-2– process parameters usually used for thin-film deposition. The metal layer is essential for the preparation of nanostructures. The nanostructures grown at different substrate temperatures showed obvious morphological differences. The substrate temperature increase led to changes in the morphology of the nanostructures from nanowhiskers to nanowalls when a thin Au layer was used. It was also observed that the type and thickness of the metal layer affect the morphology of the nanostructure.

PLD fabrication of ZnO nanostructures on metal-coated substrates

In this work, ZnO nanostructures were fabricated on metal (a metal alloy containing Fe, Cr, Mn and Ni) coated silicon substrates by applying pulsed laser deposition. The samples were prepared at substrate temperatures in the range of 550 – 650 °C, oxygen pressure of 5 Pa, and laser fluence ≤ 1 J cm−2 i.e., process parameters usually used for thin-film deposition. We found that the metal layers role is substantial in the preparation of nanostructures, the morphology of the catalyst layer determines the growth of the ZnO nanowalls and the increase of the process temperature leads to nanorods formation on the nanowalls.

Ag/ZnO nanocomposites prepared by laser methods

The composite nanostructures of double layer, multilayer and mosaic Ag/ZnO containing nano-sized particles have been produced by laser deposition and annealing procedures. The samples are investigated and the results indicated that laser annealing of Ag or Ag/ZnO layer is a feasible method to tune the optical properties of the nanostructures. Their morphology and optical absorption were investigated as a function of annealing regime and preparation procedure, leading to different silver arrangement. All annealed samples showed surface plasmon resonance (SPR) properties. The red shifted SPR was observed with the increase of the number of layers and is associated with the reduction of the interparticle distance. The absorption minimum of a mosaic samples broadens towards the longer wavelengths with reducing the thickness, due to the broader NPs size distribution. A ZnO excitonic feature visible in the spectra of double layer and multilayer structures disappear in the spectrum of a mosaic sample. The X-ray photoelectron spectroscopy was used to study the composition and chemical state of the double layer Ag/ZnO nanocomposites on the surface and in depth. The binding energy of Ag3d5/2 shifts to the lower values compared to the pure metallic Ag due to the interaction between Ag and ZnO.

Preparation of metal nanorods substrates for SERS application

Pulsed laser deposition was used together with a glancing angle deposition technique in order to produce suitable metal substrates for surface enhanced Raman scattering (SERS) applications. The surface morphology, crystallinity, optical properties, and enhancement factor of these substrates were investigated. Rodamine-6G was used as a SERS active molecule pumped at 785 nm. The Au nanorods with average lengths of 50 – 70 nm having diameter in the range of 10 – 20 nm exhibited a SERS enhancement factor of 105. The as-prepared metal substrates were found to meet the criteria of a sensitive, uniform, and easily produced SERS substrate.

Modification of pulsed laser deposited yttrium iron garnet thin films by post-deposition annealing procedures

Yttrium iron garnet (YIG) thin films were grown on (0001) sapphire substrates using pulsed laser deposition (PLD) technique with a XeCl excimer laser. The as-deposited films were amorphous and diamagnetic. Two kind of annealing procedures were carried out to modify the properties of garnet films. The structural, morphological, and magnetic behavior of YIG films treated by laser-magnetic field or annealed at temperature close to the melting point for 24 h were studied and compared. Polycrystalline films with flat surface, small grain size, and low droplet contamination were produced. The films exhibit soft magnetic properties, where easy axis of magnetization lies in the film plane. The high values of perpendicular magnetic anisotropy were registered.

Nd-doped KGW crystalline waveguides fabricated by pulsed laser deposition

The KGW thin films doped with Nd were prepared by pulsed laser deposition (PLD) on MgO, YAG and YAP substrates at substrate temperatures (Ts) varied from 400 degree(s)C to 800 degree(s)C in oxygen ambient atmosphere. The influence of the Ts and type of substrate on the film properties including the structure, luminescence and refractive index was studied. The best crystalline structure and strongest fluorescence signal was achieved at higher Ts on YAG substrate.

Influence of substrate orientation on the characteristics of Sr-ferrite thin films obtained by pulsed laser deposition

We investigated the effect of substrate orientation and film thickness on the microstructure and magnetic properties of Sr- ferrite films grown on (0001) and 1102) sapphire substrates by pulsed laser deposition (PLD). The films grown on (1102) sapphire displayed a presence of various magnetic phases, including SrFe12O19 Fe2O3 and Fe3O4. The single hexaferrite phase was obtained in GIXRD at 1 degree and 5 degree for the thicker film. The structure measurements showed that all films on (0001) sapphire were single-phase c- axis oriented hexaferrites. The highest in-plane coercive force of 2.5 kOe was detected for the thicker film grown on (1102) sapphire. These films exhibit the highest in-plane squareness. The saturation magnetization of the films on (0001) sapphire rose when the film thickness was reduced.