Oxide films up to 200 nm thick were grown at high temperatures on Ni substrates implantedwith 2x1016 Ce ions/cm2. The surface morphology, microstructure and microchemistry were examined by AFM and TEM/STEM techniques. It has been found that the oxide films are composed of three well defined sublayers, with essentially different microstructure and Ce concentration. The outer layer is composed of NiO and CeO2 nanocrystals with a size less than 5 nm. The same two phases are also present within the middle layer, although the NiO grains are much larger in comparison to nano-sized CeO2. In addition, Ce segregation along the NiO grain boundaries is detected in this layer. The inner layer is the thickest one and is composed of pure NiO grains. Oxide films having such a complex structure are characterized by a very low diffusion rate for both metal and oxygen ions. Oxygen isotope experiments revealed that the diffusion processes within the oxide film are controlled by the Ce-rich layers.

In the common applications of multilayer materials a strict separation of the single layers as well as very sharply defined interlayer interfaces are highly desired. On the otherhand there exists a large class of materials which consist of small particles dispersed in a matrix with mechanically different properties.

In this paper the theoretical concepts of producing this second class of materials via a multilayer deposition approach are presented. Although the focus is on the preparation ofsputter deposited immiscible metallic two component materials, the concepts presented arevalid for a greater variety of materials and deposition techniques.

The phase distribution as well as the roughness evolution of a material consisting of oneisland- and one layer forming component is quantitatively described by considerations about the minimization of the surface free energy of the whole system. On the atomistic level the formation of critical nuclei on an arbitrarily shaped surface is briefly discussed and a connection to the thermodynamic minimization of the surface free energy is made.

We report on the photoconductivity of thin films consisting of a porous nanocrystalline TiO2 matrix and quantum size PbS clusters adsorbed on the inner surfaces of theTiO2. The PbS clusters are typically a few nm in size and are not connected. Due to quantum confinement the bandgap of the clusters is widened to around 2 eV from the 0.41 eV value for PbS bulk. The clusters thus absorb in the visible spectrum. However, due to their spatial separation, photoconductance through the film requires carrier transfer through the TiO2 matrix. Our data show this to occur only for clusters <25 Å, for which the conduction band edge lies above the TiO2 conduction band edge. For larger clusters the band alignment at the TiO2/PbS interface appears to be unfavorable for carrier transfer; these clusters do not contributeto photoconduction.

In-plane and out-of-plane lattice parameters were measured in a series of coherent Fe-Cu multilayers using non-axial high resolution electron microscopy (HREM). The results indicate that the multilayers are tetragonally distorted with the magnitude of the distortion varying with the thickness of the Fe component. These distortions preclude an understanding of the multilayer structure in terms of conventional elasticity theory. The breakdown of epitaxy for thicker Fe layers was also investigated and it was found that the b.c.c. Fe grew with [110] parallel to [001] of the coherent f.c.c. multilayer.

Pd/Co multilayers are candidates as perpendicular magnetic recording media. A softmagnetic underlayer can both improve crystallographic orientation and reduce the magnetostatic energy of recorded domains. Pd/Co multilayers have been deposited onto silicon nitride by DC magnetron sputtering with and without CoZrNb (CZN) seed layers. Cross-sectional transmission electron microscopy shows that the CZN layer imposes a columnar grain structure on the multilayer film through epitaxy. Seeded multilayers have columnar 200Å grains that begin at the CZN interface and extend through the film thickness. In contrast, the grains in unseeded multilayers are not columnar. X-ray rocking curves on the (111) Pd/Co peak show that the CZN seed layer improves the (111) crystallographic texture of the multilayer film. We observe a correspondence between FWHM rocking curve widths in the CZN and the subsequently deposited multilayer. The CZN seeding produces changes in perpendicular hysteresis loops, which are attributed to an exchange interaction and a change in the multilayer amicrostructure due to seeding.

Reflection electron microscopy (REM) studies of Co electrodeposition on Pt(111) singlecrystal surfaces under potential control have revealed a heteroepitaxial and simultaneous multinuclear multilayer growth in a range from several up to some ten monolayer coverages at room temperature. This growth process has been dependent upon the crystallization overpotential during electrodeposition. REM observations have also suggested the formation of an ordered CoPt3 alloy at the interface between the Pt/Co ultrathin bilayers grown epitaxially on Pt(111) surfaces. Auger and photoelectron spectroscopy experiments on the Pt/Co/Pt(111) system have confirmed a limited interdiffusion or interfacial alloying below the Pt overlayer leading to an induced magnetic moment on the Pt atoms. The Pt/Co interface exhibits electronic interface states of mainly Pt-5d character. Cross-sectional transmission electron microscopy (TEM) observations have provided the first direct experimental evidence for composition modulation across successive layers in a Pt/Co nanometer-multilayered structure prepared by electrodeposition.

Ni/Ti multilayers were prepared by argon sputtering. We observe changes of latticeparameter, strain, grain size and texture depending on the single layer thickness and thepressure of the sputter gas. Moreover the quality of the layers can be improved by including impurities during the growth of the Ni and the Ti layers. Generally the results show that such additions lead to more planar layers and to structural changes within the individual layers. Although we observe hexagonal Titanium in the as-deposited films, some of the specimens which were prepared for TEM observation reveal an fcc-Ti structure.The chemical composition of the layers has been investigated in a field emission microscope using a probe diameter of nmmC. omposition profiles were determined by evaluating EELS spectra taken at each point in an automated scan, In this way it was possible to determine residual concentrations of Ni in Ti layers lower than 0.5%. In the samples studied the interface width appears to be of the order of 4-5nm and the concentration profiles of Ni—Ti interfaces appear to be different from those of the Ti—Ni interfaces.

A novel in situ transmission electron microscopy technique for the observation of reaction processes in multilayered materials is reported. The technique involves constantheating rate experiments of multilayered materials in image and diffraction modes. Because the fine scale microstructure of multilayered materials is typically a small fraction of the TEM specimen thickness, realistic comparison of the microstructural evolution with that of similarly processed thick foil samples is possible. Such experiments, when well designed, can provide rapid characterization of phase transformations and stability of nano-structured materials. The results of these experiments can be recorded in both video and micrograph format. The results and limitations of this technique will be shown for the Al/Zr and A1/Monel multilayered systems.

High-resolution transmission electron microscopy has been used to investigate the structure and growth behavior of three separate multilayer systems composed of spin-glass alloys(AuFe.03,CuMn.15, and AgMn.09) alternating with amorphous silicon. Each of the three systems was fabricated with two different sample configurations. The first consisted of bilayers with 3 nm spinglass alloy and 7 nm amorphous siliconlayers. The second consisted of 7 nm spin-glass alloy and 7 nm amorphous silicon layers. HRTEM images of ion-milled cross-sectioned samples revealed variations in the degree of crystallinity of the spin-glass material. Variations in the amount and symmetry of interlayer formation were also observed. Systematic studies of such variations should help to explain differences in their measured spin-glass properties.

Multilayer foils of Cu-304 stainless steel (304SS) with equal layer thicknesses in the range t=5.0-500 Å and total thicknesses 10-20 μm have been synthesized using magnetron sputtering at ambient substrate temperature. The x-ray diffraction data of as-deposited films show two structural regimes: small thickness (t=5-10 Å) which is characterized by epitaxial FCC growth of 304SS on copper, and large thickness (t=13.5-500 Å) which shows epitaxial FCC 304SS growth near the interface and BCC 304SS growth away from the interface. FCC structured films show very small magnetic moments at room temperature similar to bulk 304SS stable FCC phase. However, a strong magnetic moment is observed for thicker samples due to ferromagnetic metastable 304SS BCC phase. Two opposing transformations occur in the 304 layers as the samples are heated. The first transformation is from the metastable BCC 304SS to the stable FCC phase. This transformation produces a strong drop in magnetic moment and is clearly visible in the large period multilayers which contain high volume fractions of BCC 304SS. The second transformation is from the original FCC phase to a new stable BCC phase in the 304SS near the copper-304SS interfaces.The transformation is produced by diffusion of nickel from the 304SS into the surroundingcopper and the chemical destabilization of the FCC phase which starts near 400 ºC.This transformation produces a sharp increase in magnetic moment. The magnetic signal drops to zero near 675 ºC which is the Curie temperature of ferromagnetic BCC Fe.75 Cr25..

The structure of magnetron-sputtered Ni80Co20/Cu multilayershas been investigated by low and high-angle X-ray diffractometry. Low-angle x-ray reflectivity data reveal well-defined compositional modulation along the film growth direction for a wide Cii thickness range of 5-40 Å. The data analysis, based on anl optical model, shows that interfacial mixing is limited to ∼3-4 Å As the number of bilayers increased from 8 to 100, the interface roughness increased by a factor of 3. Better layered structures were found for relatively thick Cu layers (tCu>10Å). The high-angle diffraction data were analyzed using a trapezoidal model. The results indicate that the films have a polycrystalline structure with a preferred (111)orientation with coherent interfaces of ∼ 100-240 Ådepending on the Cu layer thickness. The relatively large expansion of (111) spacings in NiCo alloy layers gives rise to the lower atomic ordering in NiCo/Cu multilayers.

We calibrated secondary ion mass spectrometry (SIMS) depth profiles of a-SiNx:H/a-Si:H and a-SiOx:H/a-Si:H multilayer samples by comparing them to high-spatial-resolution SIMS maps of cross sections through the layers. Both profiles and images were acquired with a focused scanning 45 keV Ga+ ion microprobe. During depth profiling an area gating technique was used to improve depth resolution. At the beginning of the profile the resolution was 8 nm. By cutting the multilayer films at a small angle through the layers, we obtained SIMS images of cross sections through thesemultilayer samples. The resolution along the expanded direction is about 10 nm. By comparing the depth profiles and the cross section images, we determined the ionbeam-induced atomic mixing in the samples, as a function of depth and the sputtering yield for each layer.

The high resolution capability of the JEOL JSM-890 In Lens Field Emission Scanning Electron Microscope (ILFESEM) is used for the routine determination of both film thicknesses and surface morphologies from a single sample. This single sample approach is possible because of the 0.7 nm resolution of the instrument, and the simple sample preparation. In many cases, the desired information can be obtained from a simple cleave of the sample.

Multilayers are used in x-ray optics as mirrors.1 They usually consist of a stack of bi-layers of two different materials. For x-ray optics, the thickness of the bi-layer, or the d-spacing of the multilayer, ranges from 2 nm to 20 nm. Since x-ray multilayers are usually made by evaporation or sputtering technique, most of materials in multilayers are amorphous or polycrystalline.

Structural properties of molecular beam epitaxy-grown Bi2Sr2Cu1Oy'Bi2Sr2Ca1Cu2Oy multilayers have been studied by x-ray diffraction. A one-dimensional kinematic x-ray diffraction model has been used to describe the structural quality of the multilayers. Interface roughness, stacking defects and unit cell disorder are obtained by an iterative fitting of the calculated diffraction profile to the experimental spectra. The type and amount of disorder in the films was qualitatively determined. Results demonstrate that structural imperfections are present in the multilayers and have to be considered when transport properties are studied.

Magnetoresistance (MR) studies on non-coupled type multilayers are briefly surveyed. As a possible method to enhance MR effect, measurements with current in outof–plane directions are described. Non–coupled type multilayers were prepared on microstructured substrates with V–shaped grooves to measure the MR in a new geometry, with current at–an–angle–to–the–plane, and actually an enhanced MR ratio was observed.

Recently, the oscillation of the magneto-optical effect with respect to the ferromagnetic layer thickness was observed for bcc-Fe(001) ultrathin films. The oscillation periods have been explained by the theory concerning the formation of quantum well states in the ferromagnetic layer. In this paper, a physical picture how the electron confinement produces the quantum size effect of the magneto-optical responses is introduced, and experimental results on the magnetooptical effects of the bcc-Fe films of different orientations are presented. The (001) oriented films show clear oscillation. On the other hand, the (110) oriented films does not show any oscillation. The reason is discussed from the band structure and growth modes.

We investigate hyperfine field (Hhf) distributions and electronic structures in magnetic Fe5/Co5 and Fe5/Ni5 multilayer systems using the standard Green function KKR band structure calculation. For the Fe5/Ni5 system the Hhf at the interfacial Fe site is about 10kG smaller than that at the interior Fe site, however, system the Hhf are almost constant in Fe layer for the Fe5/Co5. At the interfacial Ni site the Hhf is almost twice as large as at the interior Ni site or in bulk fcc Ni. Valence contributions to the hyperfine fields (Hv) play important roles for the Hhf distributions. We discuss the relations between core contribution and local spin moment and between valence contribution and total moment within the 1st and 2nd nearest neighbor shells.

We report the formation of the CsCI FeSi phase in Fe/FeSi multilayers with constant Fe thickness and varying FeSi layer thickness. The crystallographic and magnetic properties of this metastable FeSi phase are determined in thick (62 nm) epitaxial silicide layers with ion channeling, X-ray diffraction and Mossbauer spectroscopy measurements which clearly show that the CsCl phase becomes increasingly magnetic upon cooling down to 4.2 K. These results indicate that the transition from antiferromagnetic to ferromagnetic coupling observed at low temperatures in such multilayers is controlled by a magnetic phase transition in the FeSi spacer layer.

We report the growth and characterization of amorphous Si (a-Si)/SiO2 superlattices on (100) Si. The a-Si layers (thickness varying from 1 to 10 nm) were vacuum-deposited at room temperature by molecular beam epitaxy while the SiO2 layers (1 nm) were grown by an ex-situ UV-ozone treatment. This procedure was repeated six times to produce periodic multilayer structures. The chemical modulation of these structures was confirmed by transmission electron microscopy and depth profiling using Auger electron spectroscopy. X-ray specular reflectivity showed that the structures have a well defined periodicity. The a-Si layers have a density approaching (>95 %) that of c-Si and an interfacial roughness that increases with the a-Si layer thickness. The Raman spectrum from the Si layers of all samples shows broad peaks near 150, 310 and 470 cm−1 that are typical of a-Si. On annealing at high temperatures, the three Raman bands decrease in intensity, while the 470 cm−1 band also shifts to higher frequency and becomes narrower. After annealing for 30 s at 1100 °C, the a-Si bands are weak and the 470 cm−1 band is merging with the c-Si 520 cm−1 line, indicating that partial re-crystallization of the Si layers has occurred. The room temperature light emission properties of these nanostructures in the green to red wavelength region is reported. The luminescence shifts to longer wavelength with increasing a-Si layer thickness, consistent with a quantum confinement mechanism.