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In-situ fluid-cell AFM has been used to investigate the corrosion mechanisms of TaZrO and BCN thin films as protective coatings for magnetic media. This technique allows for real-time, in-situ monitoring of corrosion with nanometer resolution. The technique proved valuable in revealing peculiarities that cannot be detected using conventional techniques. In contrast to the nitride films, the results point to defect-based diffusion type corrosion mechanism in the oxide films.

Surfactant coated FePt nanoparticles were characterized using Fourier transform infrared spectroscopy (FTIR). The FTIR spectra indicate that there is a conversion of the alkyl chain of the surfactant from the oleyl form ( cis -9-octadecenyl) to the elaidyl form ( trans -9-octadecenyl) during the synthesis of the FePt nanoparticles. This is revealed by the presence of several vibrational absorption bands in the region of the olefinic C H stretching modes. The appearance of infrared absorption bands due to olefinic C H stretching is due to the presence of Fe in the nanoparticles. The FTIR spectrum of platinum nanoparticles does not reveal the presence of olefinic C H modes. The concentration of Fe in the FePt nanoparticles influences the intensity of the olefinic C H stretching modes. The high intensity of these olefinic C H modes in nanoparticles with high Fe concentration indicates that Fe acts as a catalyst for cis to trans conversion and may lead to dehydrogentation of the alkyl chains.

The electrodeposition of Cu1-xPtx alloys by underpotential co- deposition of Cu with Pt is demonstrated using an H2SO4-CuSO4- PtCl42- electrolyte. The composition and structure of 1 micrometer thick alloy films grown at different potentials were examined by EDS, XRD and TEM. A thermodynamic rational for the alloying process is provided by a symmetrical regular solution model whereby underpotential co-deposition of Cu is ascribed to the negative enthalpy of mixing with Pt. The observed dependence of alloy composition on potential is in good agreement with equiatomic mixing enthalpy of -18 kJ/mol, obtained from calculations by Miedema et al. An EQCM was used to provide a time resolved assessment of the alloy formation process. Simultaneous measurement of the mass and current transients during potential steps enable the effects of submonolayer underpotential deposition of Cu onto a Pt rich surface to be observed and separated from the subsequent steady-state co-deposition of Cu with Pt.

Ordered self-assembled monolayers of FePt nanoparticles have been studied for the first time on fluorinated carbon thin film substrates. High resolution scanning electron microscopy of the resulting films showed homogenous hexagonally closed packed monolayers of FePt ordered over length scales of several millimeters. The annealing of self-assembled monolayers of FePt nanoparticles at 600 °C for 30 min showed significantly less sintering than on other types of substrates and the hexagonal ordering of the self-assembled monolayers was preserved during the annealing step. This is a significant step towards development of a viable patterned media for high density data storage.

Chemically modified patterns were used to achieve selective adsorption of magnetic FePt nanoparticles on substrates. In this work, thiol chemistry was used to create chemical patterns on silicon surfaces and gold patterned silicon surfaces. The adsorption of FePt nanoparticles on the silicon and gold patterned surface was studied using FTIR and HRSEM (high-resolution scanning electron microscopy). We have demonstrated in this work that chemical patterning can be used to achieve selective adsorption of magnetic nanoparticles on surfaces. Our results indicate that FePt nanoparticles coated with a 2 nm thick surfactant layer will adsorb when spin-coated onto gold surfaces modified with 11-mercapto-1-undecanol {HS(CH2)11OH, MDOL}. The adsorption of nanoparticles was confirmed by FTIR spectra and HRSEM. FTIR spectra revealed the presence of peaks at 3004 cm− 1 and 1709 cm− 1 on MDOL modified gold surfaces, which are indicative of the presence of the FePt nanoparticles on the surface. Adsorption of FePt nanoparticles was not observed on 1-octadecanethiol {CH3(CH2)17SH, ODT} modified gold surfaces.

The effect of surfactant coatings on the shapes and sizes of cobalt nanoparticles has been investigated. Cobalt nanoparticles were synthesized by thermal decomposition of a cobalt containing precursor in the presence of various surfactants. At room temperature the cobalt nanoparticles have a β-manganese structure also known as the e-cobalt structure. The shapes of the cobalt nanoparticles include: spherical, triangular, rod-like, and hexagonal. The shapes of cobalt nanoparticles depend on the type of the surfactant used in the synthesis and the temperature at which the cobalt precursor was added to the reaction mixture.

An approach to fabrication of a patterned magnetic recording medium for next generation data storage systems is presented. (Co/Pd)n magnetic multilayers are evaluated as candidates for patterned medium materials for their high and easily controllable magnetic anisotropy. The multilayer films deposited on a Ta seed layer enable high intergranular exchange coupling—an essential feature of a patterned magnetic recording medium. The quality of (Co/Pd)n superlattices was optimized via deposition conditions and monitored using low-angle x-ray diffraction. An estimated in-plane (hard-axis) magnetization saturation field in excess of 40 000 Oe was observed. Vertical (easy-axis) hysteresis loops for as-deposited continuous magnetic multilayers exhibited a low coercivity of 930 Oe, indicating highly uniform (magnetically) films with weak domain wall pinning. Ion-beam proximity lithography was used to pattern magnetic multilayers into 43 nm islands on a 135 nm pitch. Following patterning, easy-axis coercivity increased nearly 15-fold to 12.7 kOe.

We have studied particle size distributions of FePt nanoparticles with analytical ultracentrifugation. The particles were made with the common polyol process by thermal decomposition of iron pentacarbonyl and reduction of platinum (II) acetylacetonate. The size distribution is found to be bimodal (dual) rather than a monomodal distribution as normally reported. The density values for these particles indicates that the smaller particles, ~7.4?nm diameter, have a density above 4?g?cm?3 while the larger particles, ~16?nm, have a density of ~3.2?g?cm?3 due to a higher Fe content in the lighter particles.

We have investigated the circumstances underlying recent reports of very large values of ballistic magnetoresistance (BMR) in nanocontacts between magnetic wires. We find that the geometries used are subject to artifacts due to motion of the wires that distort the nanocontact thereby changing its electrical resistance. Since these nanocontacts are often of atomic scale, reliable experiments would require stability on the atomic scale. No method for achieving such stability in macroscopic wires is apparent. We conclude that macroscopic magnetic wires cannot be used to establish the validity of the BMR effect.

This work presents a study of Ga+ ion implantation of polycrystalline hcp cobalt thin films and nanostructures. It is shown that Ga+ ion implantation leads to a substantial modification of magnetic properties including large coercivity increase and shearing of in-plane magnetization loops suggesting the introduction of domain wall pinning sites and the reduction of intergranular exchange coupling. Because ion implantation can be accompanied by substantial heat dissipation, it is discussed how the annealing effects can be minimized. Application of ion implantation to selectively tailor properties of magnetic nanostructures is demonstrated.

Magnetic force microscopy (MFM) is a widely used form of scanning probe microscopy (SPM) that is used for obtaining a magnetic image from a surface with nanoscale resolution. Currently, the resolution of MFM is limited to approximately 20 nm due to the long-range nature of magnetic interactions between the MFM probe's tip and the magnetic medium. This paper describes an optimal signal processing solution to the problem of achieving high resolution MFM with the goal of significantly exceeding the level at which MFM metrology currently performs, thus providing metrologists with a means of resolution increase that is believed will enable, for example, the rapid development of high-density magnetic recording media (>100 Gbit in−2). This is achieved by using focused-ion beam trimming of a conventional tip to create a probe tip of predictable magnetic characteristics and then, provided that the sample could be approximated as a thin-film, using knowledge of this tip's sensitivity field for performing a deconvolution on the measured signal to better estimate the magnetic state of the surface under study. Stated differently, as the MFM measured signal is modelled as the convolution of the magnetized surface and the tip's sensitivity field, we exploit knowledge of the tip's properties to increase the resolution of the MFM image. Details of the deconvolution approach as well as images resulting from this processing are the focus of this paper.

We have carried out an extensive search for credible evidence to support the existence of a ballistic magnetoresistance (BMR) effect in magnetic nanocontacts. We have investigated both thin-film and thin-wire geometries for both mechanically formed and electrodeposited nanocontacts. We find no systematic differences between mechanically formed and electrodeposited nanocontacts. The samples we have investigated include mechanical contacts between ferromagnetic wires, electrodeposited nanocontacts between ferromagnetic wires, ferromagnetic nanocontacts electrodeposited on Cu wires, nanocontacts electrodeposited between ferromagnetic films anchored on wafers, ferromagnetic nanocontacts electrodeposited on Cu films anchored on wafers, nanocontacts between two ferromagnetic films connected by a pinhole through an insulating film, and nanocontacts formed by focused ion-beam etching. In none of these samples did we find credible evidence for a BMR effect. However, we did find a number of artifacts due to magneto...

Spin-valve structures might be exposed to higher temperatures in future disk drive applications and might thus degrade faster than it does today if proper materials and methods are not used. In order to determine whether this degradation is due to interdiffusion between constituent layers or is dominated by other phenomena, the interdiffusion coefficients for all layers in the spin valve have to be determined. For diffusion driven degradation it would then be possible to predict lifetimes based on a maximum allowed reduction in ΔR/R where R is the resistivity. Here we report the initial results for a CoFe/Cu interface, common to many spin-valve structures. Interdiffusion in (111) textured polycrystalline CoFe/Cu multilayers has been measured and quantified by x-ray reflectometry. Bulk diffusion is dominant at temperatures above ∼540 °C and is described by an activation energy of Ea=2.41 eV and a prefactor of D0=2.92×10−8 m2/s. Below temperature of 540 °C grain boundary diffusion dominates and is character...

Signal degradation in spin-valve structures is today a concern for long-term stability of data storage devices. One of the possible degradation mechanisms of spin-valve structures in disk drive applications could be thermally activated diffusion between constituent layers. In order to predict and control performance degradation, the interdiffusion coefficients for all bilayers in the spin-valve structure will have to be determined. Here we report results from a Co90Fe10/Ru interface, common in many spin-valve structures. The diffusion in (0002) oriented polycrystalline Co90Fe10/Ru multilayers has been measured and quantified by x-ray reflectivity in the temperature range of 450–540 °C. The bulk diffusion in this case is described by an activation energy of Ea=4.95 eV and a prefactor of D0=6.43×10−9 m2/s. No grain boundary diffusion was detected in the large-grain structure dominated by high symmetry grain boundaries at the temperature interval in this study. For a spin-valve structure that contains Co90Fe...

Deposition of films with controlled gradients across the wafer in terms of both composition and thickness were used together with statistical experimental design methodologies to explore large parameter spaces relevant to the optimization of perpendicular magnetic recording media. With this approach, thickness and composition of the media and the interdependencies of these variables were efficiently investigated and correlated to the coercivity of the material and the squareness of the hysteresis loops. To determine dependencies and codependencies between additives to CoCr alloys on the magnetic properties, this method was used to study magnetic layers of CoCrPt, CoCrPtTa, CoCrPtTi, and CoCrTiTa. The best models associated with each alloy had the same terms for the three magnetic parameters measured (Hc, S, and θk,perp). Additions to the CoCr alloy introduced dependencies on the Cr and cross-term dependencies with Cr (i.e., CrTa, CrPt, or CrTi). In some cases, thickness became an important parameter and f...

Magnetic force microscopy measurements of perpendicular media with a CoCr-based hard layer and a CoFe soft underlayer has been made to investigate skew angle effects. The recorded tracks were produced using a focused ion beam made single pole head with a track width of approximately 400 nm and a gap thickness of approximately 1 μm at a 25 nm flying height. Magnetic force microscopy images of tracks recorded at write currents above and below the saturation value of approximately 100 mA turn were studied at different values of the linear density, 20–100 kfci, at zero skew angle as well as −15° and +15°. Calculated perpendicular recording fields versus the distance down the track, and across the track, near the trailing pole edge was performed using three-dimensional boundary element modeling and compared to the results from the microscopy data. Drawbacks and possible solutions to the skew angle problem for perpendicular recording are discussed.

Humidity influences the tribological performance of the head-disk interface in magnetic data storage devices. In this work a quartz crystal microbalance was used to measure the uptake of water on amorphous hydrogenated carbon (a-CHx) films at room temperature and pressures of water corresponding to relative humidities of ∼25%. These experiments have used a-CHx films of varying thickness with and without lubricant. The lubricants used included Fomblin Z-03, Z-disoc, and Z-tetraol deposited on the surfaces of a-CHx films of various thickness. The amount of water adsorbed on the unlubricated a-CHx films is roughly independent of a-CHx film thickness. The presence of the lubricant reduces the amount of adsorbed water; however, the amount of water adsorbed in the presence of a lubricant does not depend significantly on the type of lubricant. These observations imply that water is adsorbed on the surfaces of the lubricant or the a-CHx film rather than being absorbed in their bulk.

The long-term stability of a CoCrPt perpendicular storage media has been investigated by thermal aging at temperatures ranging from 95 to 280 °C during otherwise normal ambient conditions. The signal-to-noise ratio from magnetic force microscopy images has been extracted by the autocorrelation method and compared for the different aging conditions. During aging at elevated temperatures, the media stack undergoes some structural and crystallographic changes. It is found that the severity of the aging process is higher for low-density bit patterns due to the higher value of demagnetizing fields for large bits. A comparison to the thermal aging is done with a set of disks in which a deterioration of the magnetic bit pattern was induced by an external magnetic field. Two experiments, including fields with a single polarity as well as with a cycled polarity, mimic different magnetic situations for the disk. During the external field experiments, no structural or crystallographic changes occur in the media. The magnetic background noise of the disks is also analyzed. For aging in a magnetic field, it is found that below a certain threshold value, mostly low-density bit patterns are affected by the aging process. However, above the threshold value, both low and high-density bit patterns are affected.

The influence of Cu, Ag, and Au additives on the L10 ordering, texture, and grain size of FePt thin films has been examined. Lattice parameter data indicated that Au and Ag additives tended to segregate from FePt, but Cu alloyed with FePt. FePt films with Au or Ag additive showed 1–2 kOe higher coercivity values compared to a pure FePt film after annealing at 450 °C and above for 10 min. The addition of at least 20 vol. % Cu to FePt boosted average coercivity values and increased (001)/(002) x-ray peak intensity ratios, suggesting an accelerated L10 ordering process for annealing temperatures exceeding 350 °C. Decreasing the film thickness promoted (001) film texture in FePt+20% Cu films, but higher annealing temperatures were required to achieve large coercivity. Au and Ag limited the average grain size compared to a pure FePt film. Cu additive increased the average grain size and film roughness.

Co1−xCrx/Pt multilayers have been deposited by magnetron sputtering onto different seed layers with simultaneous gradients in both Co1−xCrx thickness and composition x. These gradients make it possible to perform magnetic and structural measurements for different thicknesses and compositions on one single wafer. Hence, the depositions are not sensitive to variations in background conditions such as temperature, pressure, or contaminants that could otherwise vary between runs. The study concluded that the maximum for the coercivity of the multilayers is, in this case, dependent on the microstructure, namely the degree of c-axis orientation in the films. Specifically, the coercivity maximum coincides with the maximum of the x-ray diffraction peak full-width at-half-maximum for the two separate cases shown.

A set of seed and underlayers for thin film perpendicular recording media has been optimized using a technique involving simultaneous thickness and composition gradients on a single test wafer. Magnetron sputtering under ultrahigh vacuum conditions in Ar gas was used for the deposition of the layers. The structure being optimized consisted of a Ta seed layer, RuxCo1−x, Co63Cr37 underlayers, and a Co68Cr18Pt8B6 hard magnetic layer. One of the layers in the stack on a wafer has been deposited so that both a thickness variation and composition variation occurred. The method allows cross terms between thickness and the individual compositional terms to be investigated. Coercivity and squareness of the samples was measured by magneto-optical Kerr rotation. The results showed that for the range of thickness under investigation, the highest coercivity and squareness does not occur for the same set of conditions. Maximum squareness is reached without a radio frequency (rf) bias, while the coercivity increases fur...

The influence of buffer layer characteristics on the structural and magnetic properties of CoCrPt perpendicular media has been investigated. Thin (∼10–15 nm) buffer layers consisting of Ta/Ru, Ta/Hf, or amorphous (CoCrPt)Ta 25 produced media layers having high perpendicular coercivity of nearly 3 kOe, but the coercivity was only 1.7 kOe when using a Ta/Ti buffer. X-ray diffraction rocking curves showed the highest degree of (0 0 0 2) texture for the Ta/Ru buffer. In-plane diffraction indicated that the Ta/Ru buffer also had the smallest lattice mismatch (5.6%) with the CoCrPt. Cross-sectional transmission electron microscopy showed that the Ta/Ru buffer promoted local epitaxy with the media layer. Amorphous transition regions were observed at the interfaces between the media and the Ta/Hf and Ta/Ti buffer layers. Some small CoCrPt grains were observed at the interface with the amorphous CoCrPtTa buffer.

Signal-to-noise ratio (SNR) from a limited bit sequence has been extracted from magnetic force microscopy (MFM) images by two different methods and compared. The autocorrelation SNR properties extracted from the MFM image data are in better agreement with spinstand data than “normal” Fourier extracted SNR values. Transition noise data were also extracted and analyzed, “Squeezing” of the noise was measured as the periodicity of the recorded bit pattern became smaller than 250 nm and subsequently a relaxation at ∼200 nm occurred. MFM analysis based SNR data for two media types (CoCrPtTa alloy and CoB/Pd multilayer based) are compared. Ni45Fe55 alloy was used for the soft underlayer material.

The magnetic properties of Ni particles with well-defined geometry, prepared by electron lithography from epitaxial Ni(001) films of thickness 50 and 60 nm were studied. The particles were circles with diameters 0.6 m and rectangles with sides 0.9 m and 0.3 m, that were positioned in square and rectangular lattices, having lattice constants about twice the particle dimensions. Reference samples and particles with the lattices oriented along the [100] and [110] directions were prepared. Hysteresis curves were obtained for particles and reference samples, in the field range 2T at temperatures between 50 and 300 K. The particles were further imaged by magnetic force microscopy. The coercivities of the particles are about the same as that of the reference samples, being of the order of 10 mT at room temperature and increasing with decreasing temperature. This may be explained by the temperature dependence of the magnetic anisotropy of the Ni film, estimated to K1=-12.5, -12.8 and -87.6 kJ m-3 at 295, 250 and 50 K, respectively. Whereas the hysteresis curves of the particles are governed by the intrinsic properties of the starting film in low fields, the decreased lateral size influences the behaviour in higher fields as demagnetization effects and features characteristic for annihilation and nucleation of domain walls. One of the samples, rectangles with the long axis alone the [110] direction, has a significantly higher remanence and coercivity than the others. The magnetic images show that the demagnetized state of this sample comprises both single-domain and multidomain particles. Corresponding images showed only multidomain particles in all other samples. Thus it was concluded that the actual size (0.9 m0.3 m50 nm) is close to the critical size for single domains in Ni

Measurements are presented of sub-ns magnetization reversal processes of perpendicularly magnetized (CoCr/Pt) multilayers, using real-time Kerr microscopy with a 10 ps temporal resolution. The multilayers are placed in contact with a ring-type recording head, which is used as a sub-ns risetime magnetic field source (Δ t =0.8 ns). By scanning the laser beam across the gap the influence of the field angle on the reversal process is studied.

The characteristics of exchange-biased soft underlayers (SULs) were investigated using magnetic force microscopy and spin stand measurements with a single-pole (focused ion-beam trimmed gap) writer and magnetoresistive head. The SUL high-moment materials (FeCoB, FeAlN) were exchange biased by using IrMn. Spin stand data on perpendicular media (CoCrPtB) with an exchange-biased FeCoB SUL also showed a low integrated dc erase noise level, demonstrating its potential for use in double-layered perpendicular media.

The formation of Al/Si/p-4H SiC ohmic contacts at temperatures as low as 750 degreesC is reported in this paper. The dependence of electrical properties and contact morphology have been investigate ...

MgO{1 1 1} and {1 0 0} crystals are widely used as substrates for thin film growth, in many different areas of research such as superconductors, and other oxide, metal and nitride films, multilayers and superlattices. Since the quality of the thin film can be strongly dependent on that of the substrate, the optimal film properties will only be fully conceived if the substrate is well characterized in advance. The goal of this work was to create a characterization method which was inexpensive, fast, efficient, and of course nondestructive, for assessing imperfect metal-oxide substrates. X-ray diffraction (XRD) was chosen because of its low cost, simplicity, nondestructiveness, and the fact that we have access to many different parameters using the same instrument. The miscut of the MgO crystals studied herein were characterized with a high resolution of 0.01°. The number of domains, their distribution and their size were characterized by ω–φ maps and topography measurements. In this case, atomic force microscopy (AFM) was found to be more appropriate for assessing roughness than X-ray reflectivity measurements.

Thick GaN films grown by hydride vapour phase epitaxy have been investigated by cathodoluminecsence, X-ray diffraction, and photoluminescence. Cross-sectional studies of thick GaN layers grown on sapphire without buffers reveal three zones: a highly disordered interface region; a columnar defective region and a good quality main region of the layer. The influence of the highly doped columnar region on the surface morphology and crystal structure of the layers has been studied. We show that the columnar region influences the material quality more strongly in thinner films. Thicker layers exhibit improved morphology with lower surface pit density and better crystal quality shown in photoluminescence and X-ray diffraction spectra. The relationship between the near-interface columnar structures and surface pits is revealed. A strong effect of the growth rate on the structure of thick layers is found. The results suggest that GaN layers with optimum crystalline quality may be obtained by varying the growth rate during growth.

Highly textured epitaxial metallizations will be required for the next generation of devices with the main driving force being a reduction in electromigration. Herein a model system of 190 nm of Al on a 140 nm layer of W grown on MgO 〈00l〉 substrates was studied. The W layer was 〈00l〉 oriented and rotated 45° with respect to the MgO substrate to minimize the misfit; the remaining strain was accommodated by dislocations, evident in transmission electron microscopy images. From high-resolution x-ray diffraction (XRD) measurements, the out-of-plane lattice parameter was determined to be 3.175 A, and the in-plane parameter was 3.153 A, i.e., the W film sustained a strain resulting in a tetragonal distortion of the lattice. XRD pole figures showed that the Al had four fold symmetry and two dominant orientations, 〈016〉 and 〈3 9 11〉, which were twinned with multiple placements on the epitaxial W layer. The driving force for the tilted 〈001〉 and 〈011〉 orientations of Al on W is due to strain minimization through ...

Studies of epitaxial growth of Mo thin films on MgO(001) substrates by ultrahigh Vacuum (UHV) d.c. magnetron sputter deposition have shown independently by in situ low energy electron diffraction ( ...

We report a comparative study of the crystalline quality of thick GaN layers grown by hydride vapour phase epitaxy, using a nitridation and a GaCl pretreatment of the sapphire as well as a reactive sputtered AlN buffer and metalorganic chemical vapour deposition grown GaN ‘template’ layers. The structure quality was investigated using X-ray diffraction measurement and cathodoluminescence spectroscopy and imaging of cross-section of the films. The morphology of the layers was revealed by optical and atomic force microscopy. A distinct reduction of both the columnar near-interface region and the domain formation were observed in layers grown on AlN and GaN ‘template’ buffers resulting in improved bulk quality and significant smoother film surfaces.

The mechanisms behind the formation of smooth 〈111〉 oriented single domain epitaxial Ni films grown on MgO(111) substrates by ultra-high vacuum dc magnetron sputtering were studied using time-resolved in-situ reflection high energy electron diffraction (RHEED) measurements. The results show that whether a single- or a two-domain 〈111〉 oriented film forms is decided already during the deposition of the first two or three monolayers of Ni, and that the Ni appears to nucleate as strained islands during this initial growth. This implies that an interaction between the atoms in the second Ni layer and the second and third atomic layers of the substrate must exist, making the Ni atoms always choose the same stacking sequence at a growth temperature of 300°C. Prior to growth, the MgO(111) surface is smooth, non-faceted and without reconstructions.

Ag/Ni multilayers have been grown by ultra high vacuum d.c. magnetron sputtering onto oxidized Si(001) substrates held at room temperature. Films were grown in both Ar and Kr discharges at different sputtering pressures p. The effects of the different discharge pressures and post-deposition annealing were investigated. The structure evolution was studied using atomic force microscopy (AFM), X-ray diffraction (XRD) and transmission electron microscopy (TEM). XRD pole figure analysis show that all films exhibit a pronounced 〉111〈 fiber texture. Sputtering using low pressures resulted in a reduction of the surface roughness, compared to films grown at higher pressures, and films with rms roughness values as low as 1–2 nm were obtained. XRD analysis show that also the definition of the layer interfaces and the crystallinity of the films improved when the pressure was lowered and when using Ar instead of Kr. The increase in surface roughness with discharge pressure is explained by a reduced adatom mobility on the growing film surface at higher pressures and a wider range of incidence angles of the adatoms when arriving at the surface due to gas scattering. The improved crystalline quality when using Ar instead of Kr is explained using similar arguments. Short post-deposition annealing at 280°C resulted in improved layer definitions as well as improved intralayer order whereas prolonged annealing or annealing at 390°C resulted in agglomeration of Ag precipitates and loss of the compositional modulation. A qualitative model based on the immiscibility of the Ag-Ni system and different diffusivities of Ag and Ni, is proposed.

The use of video recording of reflection high energy electron diffraction (RHEED) patterns for assessing the dynamic evolution of the surface morphology and crystallinity during growth was evaluated. As an example, Mo/V(001) superlattices with varying layer thickness (with periods Λ of 2.5 to 8.9 nm and a constant Mo:V ratio of 1:1) were examined. During the deposition, changes from two- to three-dimensional growth were observed in situ. From prior transmission electron microscopy (TEM) and X-ray diffraction (XRD) studies, it is known that this transition is associated with a critical thickness and concurrent roughening of the V layer. Video recording and subsequent image and data processing allowed the surface morphology to be continuously followed during growth. Post-growth analyses of the recorded data provided the evolution of surface lattice parameters and short range [1–2 monolayer (ML)] surface roughnesses with a time resolution of 200–400 ms (0.02–0.04 nm thickness resolution). During growth of Mo, a smoothening effect could be observed while the growth of V evidently increased the surface roughness from 1 to 2 ML. Furthermore, the onset of coherency strain relaxation of the topmost growing layers was observed to occur at 2.0–2.5 nm layer thicknesses for both materials, which is in qualitative agreement with theoretical predictions.

The growth of Ni films by d.c. magnetron sputtering onto MgO (100) substrates was investigated with the aim of producing epitaxial smooth Ni layers for magnetic multilayer applications. Growth temperatures ranging from 20 to 700°C for 200 nm thick Ni films were examined. At a reduced temperature, 20°C, a complex texture dominated by 〈022〉 orientated grains co-existing with 〈141〉 and traces of 〈002〉 texture was obtained. However, at 100–200°C, smooth, single-crystal layers with a complete 〈200〉 texture were obtained, as demonstrated by analyses of {200}, {2 2 0} and {111} X-ray diffraction pole figures. All higher deposition temperatures produced a 〈751〉 texture that was fourfold degenerate and twinned that gradually became better defined at higher temperatures. This change in texture also marked a transition to a faceted surface, as shown by atomic force microscopy (AFM). The increase in deposition temperature between samples allows the initially nucleated Ni islands to rearrange to the 〈002〉 texture. However, at even higher temperatures, the mobility of the Ni atoms is higher, and thus, the Ni can rearrange further and grow with a 〈751〉 texture. This texture accommodates both the strong Ni metal–metal bonds, as well as placing each interfacial Ni atom in such a position that a minimal mismatch between the two crystal lattices occurs. Thus, the (751) plane Ni atoms can be said to form a c(3×1) surface lattice on the MgO surface. The surface feature size, extracted from the measurements of the power spectral density, and surface roughness both showed increased values by an order of magnitude as the crystallographic orientation changed from being single 〈002〉 to multiple 〈751〉 domained.

Epitaxial Ni films were deposited on (0 0 1)MgO by DC magnetron sputtering under ultra-high vacuum conditions for studies involving magnetic-multilayer applications. The deposition temperatures of the Ni films studied in this work were 100 and 400°C. Examination by transmission electron microscopy (TEM) and electron diffraction revealed that the film deposited at the lower temperature was predominately Ni[0 0 1]‖MgO[0 0 1] and Ni(0 1 0)‖MgO(0 1 0) oriented and smooth, as expected. However, the higher temperature films were predominately of the Ni [7 5 1 ] ‖MgO[0 0 1] and Ni ( 1 1 2 ) ‖MgO(1 0 0) orientation and facetted. The [7 5 1 ] orientation has been confirmed by X-ray diffraction, where this orientation was observed to be four-fold degenerate. For each of these four orientations there also existed a twin orientation, reflected about the MgO(1 0 0) planes, giving eight possible orientations for the Ni crystallites on MgO. This [7 5 1 ] epitaxial relationship was studied by dark-field TEM and electron diffraction. Because these films were polycrystalline and hence produced many diffraction spots from both the Ni and MgO with similar lattice spacings, electron diffraction patterns of the films were indexed using an electron diffraction image processing (EDIP) technique. In this technique, the polycrystalline electron diffraction pattern was converted into a graph, with the x -axis displaying lattice spacings and the y -axis, integrated intensity.

The formation of low resistivity Pd-based ohmic contacts to p-type 4H-SiC below 750/spl deg/C are reported herein. The electrical properties of the contacts were examined using I-V measurements and the transmission-line model (TLM) technique. Contact resistivity as a function of annealing was investigated over the temperature range of 600/spl deg/C-700/spl deg/C. The lowest contact resistivity (5.5/spl times/10/sup -5/ /spl Omega/cm/sup 2/) was obtained after annealing at 700/spl deg/C for 5 min. Atomic force microscopy of the as-deposited Pd layer showed a root-mean-square roughness of /spl sim/8 nm, while after annealing at 700/spl deg/C, agglomeration occurred, increasing the roughness to 111 nm. Auger electron spectroscopy depth profiles revealed that with annealing, interdiffusion had resulted in the formation of Pd-rich silicides. However, X-ray diffraction and Rutherford backscattering showed that the majority of the film was still (unreacted) Pd. The thermal stability and reliability of the Pd contacts were examined by aging and temperature dependence electrical tests. The contacts annealed at 700/spl deg/C were stable at prolonged heating at a constant temperature of 500/spl deg/C and they showed thermal stability in air at operating temperatures up to 450/spl deg/C. This stability was not found for contacts formed at lower temperatures of 600/spl deg/C or 650/spl deg/C.

Ni films were deposited by using ultra high vacuum DC magnetron sputtering onto MgO(1 1 1) substrates kept at temperatures between 20°C and 600°C. The structure and the surface morphology of the 100 nm thick films were analyzed using X-ray diffraction (XRD), atomic force microscopy and Auger electron spectroscopy. XRD analysis shows that all Ni films have a strong 〈1 1 1〉 oriented texture with high out-of-plane as well as high in-plane orientations with an increased crystalline quality with temperature. At 300°C the Ni 1 1 1 rocking curve width is ∼0.25°, showing a high crystalline quality for a heteroepitaxial metal film. Pole-figure analysis shows that the films are built up of two domains for temperatures ⩽200°C and at 600°C, while at 300 and 400°C only a single domain is formed. The root mean square surface roughness of the films increases with temperature with a local maximum between 150 and 200°C and a local minimum at 300°C, corresponding to the transition from two domains to one. The mechanism behind the high in-plane orientation, despite the large lattice misfit between Ni and MgO, based on super cell matching is discussed. Possible mechanisms for the transition from two domains to one are also discussed.

The crystal structure and surface morphology of hydride vapour phase epitaxy grown thick (12-105 μm) GaN layers have been investigated as a function of growth rate using several structure sensitive techniques like atomic force microscopy (AFM), x-ray diffraction (XRD) in ω-2Θ and ω-rocking curve measurements as well as low temperature photoluminescence (PL). PL and XRD measurements reveal rather narrow lines: full width at half maximum (FWHM) values of the strongest donor-bound exciton line are in the range from 6.0 to1.8 meV and ω-2Θ FWHM values are between 80 and 23 arcsec indicating good structural quality of the films. The ω-rocking curves show a single peak for the thinnest films with a FWIM of 250 arcsec and multiple peaks with FWHIM of about 250-350 arcsec in thicker films indicating the formation of several high-quality domains when increasing either thickness or growth rate. Optical microscopy and AFM images reveal a domain type of morphology and also show an appearance of spiral hillocks in layers grown at growth rates exceeding a critical value. We interpret these results as dominating 2D multilayer growth at low growth rates, and competing 2D multilayer and spiral growth mechanisms at high growth rates.

Structural and magnetic properties of Fe/V(0 0 1) superlattices consisting of 3 monolayers Fe separated by V interlayers of thickness in the range 8–17 monolayers have been investigated. RHEED and X-ray diffraction investigations show that the samples are grown with well-defined interfaces and with an out-of-plane crystal coherence length of the order of the film thickness, and an in-plane coherence length of about 500 A. For V thicknesses exceeding 16 monolayers, a transition from 2D to 3D growth was observed. The magnetisation measurements show that the magnetisation is aligned in the film plane and possesses an in-plane isotropic behaviour. Antiferromagnetic coupling between the Fe layers was observed for a vanadium thickness in the region, 13–14 monolayers, with a corresponding giant magnetoresistance effect reaching 7% at 10 K.

The interfacial structure in epitaxial Mo/W(001) superlattices, grown by magnetron sputtering on MgO(001) substrates has been studied. The films were grown in Ar and Kr discharges at a substrate temperature of 700 °C, and the as-deposited samples were analyzed by x-ray diffraction and found to be epitaxial with no high-angle grain boundaries. The degree of interfacial intermixing, caused by fluxes of different energetic species impinging on the growth surface, was estimated using a combination of Monte Carlo binary collision computer codes and a gas scattering computational model. In the Ar discharge case, large asymmetries in the Mo/W and W/Mo interfaces were found, with the W/Mo interface being more than a factor of 2 broader than the Mo/W interface. Simulations of x-ray reflectivity curves using the calculated interface profiles as input parameters without any additional fitting parameters agreed very well with measured data. The overall good fit between the calculated and measured reflectivity curves ...

Structural, magnetic, and magnetotransport properties of Fe/V (110) superlattices have been investigated. Using Al2O3 ( ) substrates and Mo or MoxV1-x allay seed layers, the superlattices could be grown with a large in- and out-of-plane cr

A series of Fe V multilayers was grown on polished MgO (001) substrates by dual-target magnetron sputtering. The structural quality of the samples was investigated by reflection high energy electron diffraction, low- and high-angle X-ray diffraction, reciprocal space mapping, polar scans, cross-sectional transmission electron microscopy and resistivity measurements. The results show that epitaxial Fe V (001) superlattices with high crystallographic and interface quality can only be grown in a narrow substrate temperature region, 300–330 °C. The average interface roughness was estimated to be as low as ± 1 A .

A near-equiatomic FePt face-centered-cubic alloy has been grown by electrodeposition onto Cu(001). Annealing at 450°C results in the onset of a A1 fcc to L10 face-centered-tetragonal phase transformation with a dominant FePt(001)⟨100⟩‖Cu(001)⟨100⟩ recrystallization texture, possibly driven by the reduced ordering temperature in an FePtCu intermixed interface region. Further annealing at 650°C leads to a more complete transformation, and magnetic measurements indicate that high perpendicular coercivities, of up to 10kOe, are accessible through the recrystallization reaction. The magnetic and structural properties reported in this work may allow electrodeposited FePt to play a leading role in future ultrahigh-density patterned perpendicular magnetic media.

Differential scanning calorimetry, in conjunction with x-ray and electron diffraction, is used to investigate the A1 to L10 ordering transformation in binary FePt films with compositions in the range of 47.5 to 55 at. % Fe, and in ternary alloys of FePt with Cu, Co, Ag, and Au. The lowest kinetic ordering temperatures, in the range of 355–375 °C, are found for Fe-rich binary FePt alloys, namely, Fe53Pt47 and Fe55Pt45, and for ternary FePt-Cu alloys that have the same amount of Pt as these binary alloys, namely, Fe50Cu3Pt47 and Fe50Cu5Pt45. Ternary additions of Co (28 at. %), Ag (11 at. %), and Au (7 and 12 at. %) increase the kinetic ordering temperature when compared to the equiatomic, binary FePt alloy. The activation energies of ordering lie between 1.6 and 1.9 eV, except for the Fe47Pt46Au7 alloy, for which the activation energy is 2.2 eV. The transformation enthalpies are in the range of −6.3 to −13.2 kJ/g atom. The Curie temperatures for the binary FePt alloys increase from 379 to 456 °C in the comp...

The magnetic properties of a 48 nm thick Fe50Pt50 film and submicron size elements made of the film were investigated. The initial film was grown by DC magnetron sputtering and post-annealed during 30 min at 300°C. Arrays of circular dots with diameters d = 200, 300 and 550 nm and a reference sample (diameter 1.7mm) were made of the film by electron lithography and Ar ion milling. After structural analysis by X-ray diffraction (XRD) and characterization by magnetization measurements and magnetic force microscopy, all samples were further annealed during 30min at 600°C. The XRD scans show that this led to an improvement of the crystalline quality in all samples, to a degree depending on the size of the dots. Both the structural and magnetic measurements imply that after the second heat treatment all samples have the easy magnetocrystalline direction (c-axis) mainly in the plane of the film, while the initial structures were characterized by a random distribution of c-axes.

We have studied the behavior of electrodeposited Ni and Fe nanocontacts in magnetic fields and the changes in resistivity (ΔR) that occur. Metallic particles suspended in plating solution, created and collected from the electroplating bath of a nanocontact that later exhibited high values of ΔR/R, have been transferred to a second set of electrodes, in which similar high values of ΔR/R were measured without any plating process being performed. We attribute this effect to a mechanical reorientation of magnetic nanoparticles at the junction between the electrodes as the field is close to zero, and relate this work to present work with ballistic magnetoresistance in nanocontacts. We also show that Fe whiskers brought in close contact can produce this effect as well.