The utility of ion-assisted deposition is investigated to explore the possibility of counteracting the deficiency of back-reflected current of Ar neutrals in the case of lighter elements such as Al. A range of energetically ion bombarded Fe∕Al multilayers sputtered with applied surface bias of 0, −200, or −400V were deposited onto Si(111) substrates in an argon atmosphere of 4mTorr using a computer controlled dc magnetron sputtering system. Grazing incidence reflectivity and rocking curve scans by synchrotron x rays of wavelength of 1.38Å were used to investigate the structures of the interfaces produced. Substantial evidence has been gathered to suggest the gradual suppression of interfacial mixing and reduction in interfacial roughness with increases of applied bias. The densification of the Al microstructure was noticeable and may be a consequence of resputtering attributable to the induced ion bombardment. The average interfacial roughnesses were calculated for the 0, −200, and −400V samples to be 7±0.5, 6±0.5, and 5±0.5Å respectfully demonstrating a 30% improvement in interface quality. Data from rocking curve scans point to improved long-range correlated roughness in energetically deposited samples. The computational code based on the recursive algorithm developed by Parratt [Phys. Rev. 95, 359 (1954)] was successful in the simulation of the specular reflectivity curves.

Multilayers of Co and Cu on Si(111) substrates have been produced by pulsed laser deposition at the second harmonic of a Nd:YAG laser (532 nm). The effect of varying the laser power on the film microstructure has been investigated using grazing incidence X-ray reflectivity measurements. Quantitative analysis of the reflectivity curves indicates that higher laser powers are associated with greater intermixing at the Co/Cu interfaces. Offset scans indicate that there is conformal roughness. The deposition process introduces some droplets into the layers, principally of Cu.

The interaction of Mn with the Cu(111) surface has been investigated using the normal incidence X-ray standing wave (NIXSW) method. Analysis of the NIXSW was complicated by the apparent large shift in position of many layers of the Cu atoms relative to their expected bulk positions indicated by a change in the coherent position. Quantitative analysis of the NIXSW shows that there are at least two but possibly many sites for each element in the altered layer. (C) 2004 Elsevier B.V. All rights reserved.

The growth of Mn films on Cu(111) has been investigated in the range of 0.5-4.5 monolayer equivalents using the normal-incidence x-ray standing-wave method. The films have been found to be incommensurate at all coverages as determined by the coherent fraction of the Mn in the substrate ((1) over bar 11) reflection. The (111) reflection gives a coherent position that increases with coverage, but a coherent fraction that decreases. At submonolayer exposure, the low coherent position reveals that the majority of the Mn atoms are at a z position near to, but slightly expanded from, the Cu(111) d spacing, but that 15%+/-5% of the Mn are at a z position of 0.57+/-0.18 of the substrate d spacing. Modeling of the trends in coherent position and fraction with Mn exposure eliminates the possibility of the overlayer being alpha-Mn, gamma-Mn (fcc), or delta-Mn (bcc). However, the trends are entirely consistent with the Mn overlayer being a Laves phase similar in structure to Zn2Mg.

The structure of annealed ultra-thin Fe films on Cu(111) has been investigated using normal incidence X-ray standing wave (NIXSW). Films of between 0.5 and 5.3 monolayer equivalence (MLE) have been deposited in situ and briefly annealed to 513 K. NIXSW measurements of the (111) and (1̄11) reflections using 2p3/2 photoemission show that the film is pseudomorphic up to 2 MLE, with near complete occupation of the fcc hollow sites. For this regime, the value of the (111) coherent position is equivalent to a film spacing relative to the lattice of 2.00±0.03 Å. For the 5.3 MLE film, there is a drastic reduction in the (1̄11) coherent fraction and shift in the (1̄11) coherent position that is consistent with the transformation of the entire film to a Kurjumov-Sachs oriented bcc(110) structure.

The technique of chemical-shift normal-incidence X-ray standing waves (CS-NIXSW) has been applied to a study of the interaction of SO2 with Cu(111), yielding quantitative information on the local adsorption geometry of adsorbed SO2 at low temperature and coadsorbed atomic sulfur with an SOx species, identified on the basis of near-edge X-ray absorption fine structure (NEXAFS) as SO3. Atomic sulfur appears to occupy a mixture of face-centred cubic and hexagonal close-packed hollow sites, while the SO3 species adsorbs with its C3v axis perpendicular to the surface atop a surface copper atom with the SO bonds out of plane such that the oxygen atoms are closer to the surface; there appears to be some local distortion of the outermost copper layers around this species. While SO2 is found to adsorb with its molecular plane essentially perpendicular to the surface, and the data are most readily interpreted in terms of a bridging geometry bonding through the oxygen atoms, there are marked inconsistencies between these results and those of an earlier surface extended XAFS (SEXAFS) investigation of this species on Cu(111), and alternative interpretations are discussed.

Applications of the techniques of normal-incidence x-ray standing wave (NIXSW) and medium-energy ion scattering (MEIS) to the elucidation of the structure of an ultrathin metallic film, Co on Cu(lll), are reported. NIXSW and MEIS are shown to yield valuable and complementary information on the structure of such systems, yielding both the local stacking sequence and the global site distribution. For the thinnest films of nominally two layers, the first layer is of entirely fee registry with respect to the substrate, but in the outermost layer there is significant occupation of hcp local sites. For films up to 8 monolayers (ML) thick, the interlayer spacing of the Co layers is 0.058+/-0.006 Angstrom smaller than the Cu substrate (111) layer spacing. With increasing coverage, the coherent fraction of the ((1) over bar 11) NIXSW decreases rapidly, indicating that the film does not grow in a fee continuation beyond two layers. For films in this thickness range, hcp-type stacking dominates fee twinning by a ratio of 2:1. The variation of the ((1) over bar 11) NIXSW coherent fraction with thickness shows that the twinning occurs close to the Co/Cu interface. For thicker films of around 20 ML deposited at room temperature, medium-energy ion scattering measurements reveal a largely disordered structure. Upon annealing to 300 degreesC the 20-ML films order into a hcp structure.

Surface extended X-ray absorption fine structure (SEXAFS) has been used to probe the structure of ultrathin films of iron on Cu(111). With increasing film thickness, the interatomic separation falls from 2.57Å rapidly towards that of bulk iron (2.48Å). The degree of order and coordination in the films also fall over this region. These changes are consistent with a loss of face-centred cubic structure. However, the structure does not exhibit a clear body-centred cubic SEXAFS fingerprint until around eight layers.

The surface magnetism of as-cast and field annealed amorphous in ribbon form has been studied by spin-polarized secondary electron spectroscopy, by recording energy-resolved spin asymmetry hysteresis loops and by scanning electron microscopy with polarization analysis. Large lateral variations in surface magnetization have been detected, indicating that , in particular, and ferromagnetic melt-spun ribbons, in general, are not suitable as standard sources of polarized electrons. Deposition of an iron film onto the did not result in a more uniform surface but rather served to emphasize the substrate magnetic structure. Thus utilization of ferromagnetic melt-spun amorphous alloys as substrates for the growth of thin magnetic films should be undertaken with caution.

Synchrotron radiation based measurements of the soft x-ray photoemission spectrum of the valence band of Pd2MnSn, Co2MnSn, and Cu2MnAl are presented. The focus is on the Cooper minimum effect in Pd2MnSn and on the Mn 3p-3d resonance in all three. Heusler alloys are magnetic alloys with localized moments on the Mn atoms.

A novel technique for the deposition of thin films by pulsed laser deposition over large substrate areas has been modelled. It is shown that by rastering the ablation plume across the substrate as well as rotating the substrate, larger areas can be covered more uniformly than has been possible by previously reported methods. Calculations demonstrate that film thickness values with only a ±0.5% variation over substrates as large as 100mm in diameter could be produced by this method. These results compare favourably with other deposition techniques.

The polycrystalline Pt3Cr1−xMnx (x=0,…,1) materials are a model system for the investigation of magnetic ordering and verification of band calculation schemes. Five samples with stoichiometries x=0, 0.3, 0.5, 0.7 and 1 were produced and analysed using X-ray diffraction and SEM. Subsequently, photoemission measurements were carried out at the synchrotron radiation source at Daresbury. The photoemission measurements indicated that there is little hybridisation between the Mn and Cr 3d states.

To characterize the possible magnetic structures created on magnetic multilayers a model has been formulated and studied. The interlayer inhomogeneous structures found indicate either (i) a regular periodic, (ii) a quasiperiodic change in the magnetization or (iii) spatially chaotic glass states. The magnetic structures created depend mainly on the ratio of the magnetic anisotropy constant to the exchange constant. With the increase of this ratio the periodic structures first transform into the quasiperiodic and then into the chaotic glass states. The same tendency arises with the depolarization of the magnetic moments of the first layer deposited on the substrate.

A modified unbalanced magnetron sputtering technique was applied to the growth of multilayer Co/Cu films in order to systematically study the interface structure evolved under ion bombardment. X-ray reflectivity measurements revealed an interface smoothing effect in samples deposited under ∼200eV ion bombardment. A reduction in the Bragg peak intensity for samples with a greater number of bilayer repeats was also observed. This was attributed to roughening of the final surface in the thicker films.

The structure of PF3 adsorbed on Cu(111) at 110K has been determined using both near edge X-ray absorption fine structure (NEXAFS) and normal incidence X-ray standing wave (NIXSW) methods. Two X-ray reflection conditions were used, the (111) and (1̄11), to determine the atomic positions of the phosphorus and fluorine atoms by triangulation using NIXSW, whereas NEXAFS was used to determine the alignment of the molecule. PF3 adsorbs at atop sites with the fluorine atoms away from the surface and its C3 axis aligned along the surface normal. The Cu–P distance is 2.25±0.04Å, and the distance between the copper and the fluorine layers along the C3 axis is 3.05±0.04Å. The adsorbed molecule maintains its gas-phase geometry and undergoes either free rotation about the C3 axis, or is azimuthally orientated such that the projections of the P–F bonds on to the surface point towards the next nearest neighbour copper atoms. The NIXSW analysis for the fluorine photoemission data was carried out using a backward/forward asymmetry parameter to compensate for a breakdown in the dipole approximation for photoemission that occurs for fluorine 1s photoemission under the NIXSW conditions used here.

Ultraviolet-photoemission spectroscopy has been employed to investigate the valence-band electronic structures of the magnetic alloys Co2MnSn, Cu2MnAl, and Pd2MnSn. The valence band of Co2MnSn extends to approximately 5 eV below the Fermi level with a high density of states immediately below the Fermi edge. Cu2MnAl and Pd2MnSn have valence-band widths of 6 and 7 eV, respectively, with the highest density of states lying some 3 eV below the Fermi level in each case. Photoemission measurements in the region of the Mn 3p threshold indicate that Mn 3d character extends across the full width of the valence band for all three alloys. For Pd2MnSn, additional photoemission measurements in the region of the Pd 4d Cooper minimum confirm this conclusion. Modulations in photocurrent resulting from Mn 3p-to-3d resonances across the valence band of Co2MnSn are most intense towards the bottom of the band. This is discussed in terms of possible variations in initial-state hybridization. The experimental photoemission spectra are compared with calculated spectra derived from theoretical band structures. Although there are some differences in shape, the bandwidths of the calculated spectra agree very well with the experimental results.

Substrate ion fluxes from unbalanced magnetron sources are generally controlled by the use of additional magnetic fields. These methods are not always suitable for differentially controlling the ionic flux from multiple sources. We report here a simple method suitable for attaining such control that can be easily adapted to most unbalanced magnetron systems. The flux leakage from an unbalanced magnetron is controlled by the use of a mild steel keeper with a detachable mild steel annulus. The annulus redirects the unbalanced field lines through the keeper to the rear poles of the magnetron. The flux leakage is thus controlled by varying the thickness of the annulus. Ion saturation currents measured at the substrate, with and without a 0.9 mm thick mild steel annulus, were found to differ by a factor of approximately 3 at an argon partial pressure of 1 mTorr. Furthermore we demonstrate that the changes in ion current density are achieved without alteration to the magnetron operating parameters.

The interfacial structure of Co/Cu multilayers deposited under energetic particle bombardment is investigated using x-ray reflectivity. The energetic bombardment is varied by controlling the ion bombardment of the growing film. Specially modified unbalanced magnetron sources are used in collaboration with bias sputtering techniques in order to independently vary both the ion flux and average ion energy of the bombardment. Quantitative analysis of the specular reflected intensity reveals the existence of variations of the interface roughness in multilayers deposited with high applied negative biases of 200 V, such that the interfaces become smoother towards the free surface. A maximum smoothing effect is observed for films deposited with the highest available levels of ion flux. A static interface roughness is observed when applied biases of are applied.

The microstructure of Co/Cu multilayers deposited by low energy ion-assisted deposition was investigated. The samples studied were grown by unbalanced magnetron sputtering with and without an applied d.c. substrate bias of −50 V. Specular and off-specular X-ray reflectivity measurements were performed on the samples and revealed the presence of roughness at the interfaces that was partially correlated throughout the film. The effect of applying a −50 V bias was to suppress the correlation of the lower frequency roughness and to slightly reduce the bilayer period of the multilayer. The differences between the samples are discussed in terms of possible ion bombardment induced smoothing of the layers and densification of the microstructure.