A. Luches

Pulsed laser deposition of Co- and Fe-based amorphous magnetic films and multilayers

Abstract Magnetic films and multilayers were prepared by pulsed laser ablation of Co- and Fe-based amorphous magnetic ribbons with compositions Co 67 Cr 7 Fe 4 Si 8 B 14 and Fe 73.5 Nb 3 Cu 1 Si 13.5 B 9 , respectively. Targets were ablated in vacuum (∼10 −5 Pa) by KrF excimer laser pulses at fluences from 3 to 7 J/cm 2 . Films were deposited on oxidized silicon wafers, placed 80 mm apart from the target. From X-ray diffraction spectra it follows that all the films are amorphous, while Rutherford backscattering spectrometry analyses confirm that their composition is close to the respective target when they are deposited at the lower fluence. In the case of higher fluence, the concentrations of both Si and B in the films decrease. From ferromagnetic resonance studies it results that the effective magnetizations 4 πM eff and g -factors of the films are close to the values of the respective ribbon only in the case of Fe-dominating composition. Nanometric multilayers (4-nm magnetic alloy/6 nm Cu) ×5 were also deposited and electrically and magnetically characterized.

Characterization of TiAlN films deposited by reactive pulsed laser ablation

Abstract We have deposited TiAlN films by using the reactive laser ablation technique. TiAl targets were ablated in low-pressure N2 (0.1–10 Pa) atmosphere by 2×104 XeCl excimer laser pulses at the repetition rate of 10 Hz. The laser fluence at the target was set at 6 J/cm2, corresponding to a power density of 0.2 GW/cm2. The films were deposited on Si substrates at room temperature, placed at 40 mm from the target. Their characteristics were investigated by many different techniques. Scanning electron micrographs show that surfaces are plane without cracks or corrugations. From Rutherford backscattering spectra it results that the thickness vary from ∼100 nm for films deposited at 0.1–0.5 Pa to 50 nm for the film deposited at 10 Pa. The mean composition is close to TiAlN for the film deposited at 0.1 Pa and close to TiAlN2 for the film deposited at 0.5 Pa. X-Ray diffraction analysis points to an amorphous structure of the film deposited at the lowest pressure (0.1 Pa), while peaks of fcc TiN and hexagonal Ti3Al2N2 appear in the spectra of the films deposited at higher N2 pressures. The complex chemical bonding of the top surface layer of the films was studied by X-ray photoelectron spectroscopy.

Intermixing at interfaces of Fe/W multilayers

The interface reactions in (1 nm Fe/x nm W) and (2 nm Fe/x nm W) multilayers (x = 1, 2, 5 and 7) with 5 or 10 periods in as-deposited state and under KrF laser irradiation with fluences, F= 0.05-0.25 J cm -2 and 1 or 10 pulses were studied by X-ray diffraction (XRD), grazing incidence (GI) XRD, X-ray reflectivity, GI X-ray diffuse scattering and cross-section transmission electron microscopy (XTEM). Structurally coherent layers along the [110] direction with bcc symmetry were found in as-deposited and irradiated samples. This coherency is affected by the lateral waviness of the interfaces. The layered structure persists up to F = 0.25 J cm -2 and 10 pulses. Under the laser treatment, both the interface roughness and mixing increase with increasing deposited energy and promoted bcc W grain growth is observed.

Structure and in-depth concentrations in excimer laser irradiated Pb–Co codeposited films

Abstract Pb 100− x Co x , x =0, 9, 25, 32 and 36 at.% films composed of mutually immiscible metals were codeposited by two electron beam sources in UHV system at the SiO 2 /Si substrate temperature of 40°C. The samples were processed by XeCl excimer laser irradiation at the fluences F ≤0.2 J/cm 2 and number of pulses n =1, 10, 100 and 1000. The samples were analyzed by X-ray diffraction (XRD), Rutherford backscattering spectrometry (RBS), EDAX/SEM and by resistometry. In the films fcc Pb was found. Neither fcc nor hcp Co were detected. From RBS analyses it follows that in Pb–Co films Co segregates at the surface, even in the as-deposited state. This distribution of concentration remains almost unchanged after laser irradiation. The porosity of Pb–Co films was considerably suppressed by laser irradiation in the melting regime.

Pulsed laser deposition of Cd1−xMnxTe thin films

Abstract Cd 1− x Mn x Te films (0.5–0.6 μm) were deposited on sapphire and silicon substrates by XeCl laser ablation of targets with different Mn content ( x =0.05, 0.36 and 0.43). Energy dispersive spectroscopy and optical transmission measurements in the 200–3500 nm range were performed to evaluate the film composition and band-gap energy. The film stoichiometry resulted in quite good agreement with one of their relative targets. Scanning electron microscopy inspection showed that the surface morphology is good for films with low Mn concentration ( x =0.05), but it deteriorates with increasing Mn concentration. From photoluminescence spectroscopy only the peak at ∼2.0 eV, associated to the Mn 2+ 4 T 1 → 6 A 1 transition, was detected in samples with x ≥0.36.

Excimer laser-induced intermixing in irradiated Co/Ag nanometric bilayers and trilayers

Abstract Ag/Co bilayers and Co/Ag/Co trilayers were studied in order to extend our previous results on the excimer laser-induced grain boundary diffusion in Ag/Co layered structures, used in giant magnetoresistance devices. The e-beam deposited structures were processed by KrF excimer laser at the fluences F =0.1–0.25 J cm −2 with 1–1000 pulses. The temperature and depth of melting vs. time evolutions were computed for the first laser pulse. Samples were studied by X-ray reflectivity (XRR), X-ray diffraction (XRD), grazing incidence XRD, Rutherford backscattering spectrometry (RBS) and resistometry. The intermixing phenomena at the Ag/Co solid–solid, liquid–solid and liquid–liquid interfaces were quantitatively characterized. It was shown that in the immiscible Ag/Co combination of metals the interfaces could become sharper under laser processing, probably due to the back-diffusion effect.

The thermal stability of tungsten/silicon multilayered nanostructures

Abstract The influence of excimer laser processing on the thermal stability, especially on the surface roughness evolution of W1−xSix/Si multilayers (MLs), is studied. MLs with the compositions x=0 (W/Si) and x=0.33, 0.5 and 0.66 were evaporated by e-beam evaporation and co-evaporation onto Si substrates. The samples were irradiated by XeCl laser pulses at fluences F=0.075–0.6 J cm−2 and N=1 or 100 pulses. Then, they were studied by atomic force microscopy, thus completing previous X-ray scattering analyses. It was found that for x≥0.5 the clusters are formed at the MLs surface even in the as-deposited state. Sources of surface roughness are the laser melting itself, Si crystallization and shrinking of the volume connected with the formation of tungsten silicides.