H.V. Snelling

Blast-wave studies of excimer laser ablation of ZnS

Abstract Dye-laser imaging has been used to study the blast-wave created during KrF laser ablation of ZnS in a gaseous environment allowing the temporal and spatial development of the shock wave and contact surface to be visualised. The data suggest that, over short time-scales, a transverse pressure gradient exists across the ablation site and this may contribute to the observed spatially non-uniform ablation rates.

XeCl laser deposition of liquid crystals: results and mechanisms

Abstract Films of 4-cyano-4′-pentylbiphenyl (5CB) and E7 liquid crystals have been produced by 308 nm XeCl laser deposition. Film properties were investigated using visible–UV and IR absorption spectroscopy, optical microscopy, high-performance liquid chromatography and matrix-assisted laser desorption ionization–mass spectroscopy. For fluences in the range ≈30–100 mJ cm−2 the deposited layers are found to have properties closely similar to the parent material with no appreciable decomposition being detectable. Modelling of the interaction suggests that ablation could occur through explosive superheating, producing stoichiometric removal of the multicomponent liquid-crystal system.

Pulsed laser deposition – an alternative route to the growth of magnetic thin films

Abstract A variety of magnetic materials that have potential for sensor and microactuator applications have been grown by pulsed laser deposition (PLD). Studies have been carried out to assess the influence of parameters such as the incident laser fluence (J cm −2 ) on the magnetic and magnetoelastic responses of these films. Magnetic characterisation and magnetostriction measurements were made by vibrating sample magnetometry (VSM) and capacitance dilatometry respectively. No obvious trend was shown, in all the magnetic systems studied, between fluence and magnetic properties such as magnetisation or coercivity. Room temperature in-plane magnetostrictions of ∼800 ppm have been measured from thin films (∼200 nm) of the rare earth intermetallic compound Terfenol-D (Tb 0.3 Dy 0.7 Fe 1.95 ). The potential of post production laser processing has been evaluated on the Fe–Zr alloy system and the results point to the ability to tailor the magnetic response of a film for a specific application.

Magnetic And Magnetoelastic Properties Of Thin Films By Pulsed Laser Deposition.

Pulsed laser deposition (PLD) has been used to fabricate thin films (Fe, Fe/sub 0.9/Zr/sub 0.1/, TbFe/sub 2/, DyFe/sub 2/ and Tb/sub 0.3/Dy/sub 0.7/Fe/sub 1.95/) from a variety of magnetic materials that have potential for sensor and microactuator applications. The magnetic and magnetoelastic responses of these films have been studied to assess the influence of growth parameters such as incident laser fluence (Jcm/sup -2/) on such behaviour. Magnetic characterisation and magnetostriction measurements were made by VSM and capacitance dilatometry respectively. In all the magnetic systems studied, no obvious trend was shown between fluence and magnetisation or coercivity. Room temperature in-plane magnetostrictions of /spl sim/800 ppm have been measured from thin films (/spl sim/200 nm) of the Terfenol-D composition (Tb/sub 0.3/Dy/sub 0.7/Fe/sub 1.95/) Laser post production processing has been evaluated on the Fe-Zr alloy system and the results point to the ability to tailor the magnetic response of a film for a specific application.

A comparative study of rare earth–iron thin films prepared by TEA CO2 and excimer laser ablation deposition

Thin rare earth–iron magnetic films have been deposited by pulsed laser ablation deposition utilising TEA CO2 and excimer laser sources. The effect of stationary and rotating targets on the film composition has been studied. It has been found that using a wide range of fluences (19–66 J cm−2) and a rotating target, the TEA CO2 laser system produces terbium deficient films. There is also a concomitant non-stoichiometric track left on the target. The composition of films produced by ArF laser ablation of rotating TbFe2 targets over a fluence range of 0.2–0.8 J cm−2 is strongly fluence dependent. By keeping the target stationary, the film composition becomes largely fluence independent and stoichiometric deposition occurs. Data are presented to support mechanisms that may explain these observations; it is hypothesised that phase separation during the melt/resolidification cycle and possible resputtering of deposited material is responsible.

Glass micromachining using the VUV F2 laser

Theoretical and experimental studies of the surface quality in 157 nm F2 laser-ablated glasses are reported. Limitations set by statistical fluctuations in the multi- mode beam and by stationary beam non-uniformity are explored together with materials issues such as laser-induced surface cracking. Experimental work on ablating polymethyl methacrylate, used as a low threshold medium for recording of the VUV beam, and soda lime glass are described. Use is made of the probe beam deflection technique to determine ablation thresholds, and a variety of methods adopted for characterizing and assessing the quality of ablated surfaces e.g. scanning-electron microscopy, mechanical and optical interference profiling and atomic force microscopy. Preliminary roughness measurements are compared with theoretical expectations and the implication for glass micromachining with the F2 laser discussed.

Thin magnetoelastic films prepared by pulsed TEA CO2 LAD

Abstract Thin magnetic films ∼100 nm thick and 10 mm diameter have been deposited using a pulsed CO 2 laser from targets of reflowed Metglas ® 2605 SC ribbon. These films are found to have coercivities of H c ≈ 9 Oe in the plane of the film and H c ≈ 171 Oe perpendicular to the plane. X-ray diffraction has shown there to be some α-Fe present in the films.

High current photoelectric effects with VUV F2 laser irradiated metals

We report investigations of photoemission from a bulk Ni target using an ∼10 ns pulse duration, 157 nm F 2 laser source. Photoelectric response may provide information relevant for understanding the basic laser-solid interaction mechanisms and also has potential practical applications. One example of this is the development of a simple, solar-blind F 2 laser detector based on photoemission, which allows fast time response measurement of the laser pulse shape. It has also been demonstrated that with a suitably designed diode, current pulses of several amperes can be generated from Ni using the F 2 laser at very low cathode fluence (<1 mJ cm -2 on the cathode) where surface heating is negligible.

Liquid crystal films grown by pulsed laser deposition

Abstract The deposition of 5CB (4-cyano-41-pentylbiphenyl) liquid crystal films using different laser wavelengths (193 nm (ArF), 308 nm (XeCl) and 10.6 μm (CO 2 )) over a range of fluences (up to 3 J cm −2 ) has been investigated. Optical microscopy, visible–UV and infrared absorption spectroscopy have been employed to analyse the properties of the deposited material. Films with optical properties similar to those of the starting material and with no detectable degradation are obtained by using the XeCl laser, whereas ArF and CO 2 lasers produce severe and partial decomposition of the deposited material respectively. The results are discussed in terms of differences in the laser–liquid crystal interaction process for the wavelengths involved.

TEA CO2 laser ablation deposition and subsequent heat treatment of Fe and Zr thin film systems

TEA carbon-dioxide laser ablation deposition of iron and zirconium elemental layers has been investigated for the production of the FeZr magnetic system. Measurement of the individual deposition rates has allowed the production of bilayers on borosilicate glass substrates. The magnetic response and structure of these films has been measured using a vibrating sample magnetometer (VSM) and x-ray diffraction (XRD) respectively. Using a numerical heat flow model, the temperature profile within the layered system under laser irradiation has been calculated. Films heat treated in this way have shown significant changes in their magnetic behavior.