We have studied the reactions which occur in metal-metalloid multilayers made from elements which have binary eutectic phase diagrams. The metal mediates crystallization of the amorphous as-deposited metalloid by crystal nucleation inside the metal layer followed by rapid diffusion through the metal from amorphous to crystalline phases. The metalloid crystallization temperature is significantly reduced by this reaction. Systems showing this behavior are Al-Si, Ag-Si, Ag-Ge, Co-C, Ni-C and Fe-C. We believe, therefore, that it is a general phenomenon which we have now extended to the case of Ag-SiC.

The use of metallic multilayers for diffusion measurements is reviewed. Experiments on epitaxial Ag/Au multilayers show that microstructural evolution can affect the measurements, but that nonetheless accurate determinations of lattice interdiffusivity can be made down to exceptionally low temperatures. Experiments on amorphous Ni-Zr multilayers show that with diffusional symmetry there can significant diffusion-induced stresses. Analysis of the interdiffusion kinetics as influenced by stress permits the determination of a range of materials parameters, including the diffusivities of individual species and plastic flow behaviour.

The exothermic, solid state reaction of Al and Zr has been studied in thick AL/Zr multilayers using Differential Scanning Calorimetry and X-ray diffraction. The multilayersamples were magnetron sputter deposited into highly textured alternate layers of Al and Zr with nominal composition A13Zr. The samples used in this study were 47μm thick with a 427Å period. When samples were isochronally scanned from 25º to 725ºC, a large exotherm at ˜350ºC was followed by one or two smaller exotherms at ˜650ºC. The first exotherm is dominated by a diffusionbased reaction of Al and Zr that produces two phases in isochronal scans: amorphous AI-Zrand cubic A13Zr, and two additional phases in isothermal anneals: A12Zr and tetragonal AI3Zr. The exothermic heat from this multi-phase reaction is measured using isochronal scans and isothermal anneals, and the heat flow is analyzed using a l-D diffusion based model. An average activation energy and a diffusion constant are determined. In the isothermal scans, the total exothermic heat increases linearly with √ime, and layer thicknesses vary linearly with heat.

The exothermic, solid state reaction of Al and Zr has been studied in thick AL/Zr multilayers using Differential Scanning Calorimetry and X-ray diffraction. The multilayersamples were magnetron sputter deposited into highly textured alternate layers of Al and Zr with nominal composition A13Zr. The samples used in this study were 47μm thick with a 427Å period. When samples were isochronally scanned from 25º to 725ºC, a large exotherm at ˜350ºC was followed by one or two smaller exotherms at ˜650ºC. The first exotherm is dominated by a diffusionbased reaction of Al and Zr that produces two phases in isochronal scans: amorphous AI-Zrand cubic A13Zr, and two additional phases in isothermal anneals: A12Zr and tetragonal AI3Zr. The exothermic heat from this multi-phase reaction is measured using isochronal scans and isothermal anneals, and the heat flow is analyzed using a l-D diffusion based model. An average activation energy and a diffusion constant are determined. In the isothermal scans, the total exothermic heat increases linearly with √ime, and layer thicknesses vary linearly with heat.

We have investigated reactive phase formation in magnetron sputter-deposited Ni/Al multilayer thin films with a 3:1 molar ratio and periodicities ranging from 2.5-320 nm. In addition, we studied the transformation of a codeposited film of the same composition. We find that an amorphous phase has already formed during deposition, and that the extentof formation of this phase increases with decreasing periodicity. The first crystalline phase then nucleates from this amorphous phase upon annealing. The formation of the amorphous phase considerably reduces the driving force and explains why during subsequent reactions nucleation kinetics become important. We obtain Ni2Al9 as the first product phase during heat treatment in some cases before NiAl3 occurs. For films with modulation periods larger than 40 nm, formation of NiAI3 is a two stage process as reported earlier, with the first stage being due to nucleation and growth to coalescence of NiAl3 grains, and the second stage being the growth of NiA13 normal to the initial interface until the reactant phases are consumed.

Metal mediated crystallization of an amorphous phase has been found in many systems, in which eutectic phase diagrams are formed. It is interesting to know if an amorphous phase containing two elements, which can form compound, can react and form a crystalline compound at a low temperature in contact with metals. In this paper we studied the Ag/Sil−xCx system by transmission electron microscopy(TEM). It was foundthat amorphous silicon carbide was crystallized into cubic SiC at about 800°C in areas containing Ag. The silver diffused and segregated into the a-SiC phase upon annealing. The silver grains in the original deposited layer as well as those segregated act as nucleation sites for the crystallization of β-SiC. A nucleation temperature as low as 800°C was observed.

Reactions between Fe and amorphous carbon (a-C) below 600ºC have been investigated. In situ annealing in a transmission electron microscopy (TEM) was performed on a-C/Fe/a-C trilayer films deposited by DC sputtering. As-deposited films showed a well defined tri-layered structure and an average Fe grain size of about 50Å. Cementite (Fe3C) grains appeared in the Fe layer by annealing around 300ºC. As the annealing temperature was raised, the number and size of the cementite grains increased. When the annealing temperature reached 500ºC, the Fe layer completely turned into cementite with an average grain size of 1000Å. At this point the film still kept a well defined tri-layered structure even though some parts of the cementitelayer agglomerated. Above 500ºC, the cementite layer started to “move” into the a-C leaving graphite behind. Graphite formed in this process is strongly textured with the (0002) graphite basal planes parallel to the surface of the moving cementite. This process is concluded to be carbide mediated crystallization of a-C, similar to silicide mediated crystallization of silicon in Ni-Si and Pd-Si systems.

We have made new ternary compounds in the copper tungsten selenium system using multilayer thin films as reactants. The compounds appear to be unstable above temperatures near 1000ºC with respect to binary compounds, which helps to explain the difficulty in making these compounds by conventional methods.

What happens as the interface of the initial virgin couple of materials at the very beginning of reactive diffusion?-composition changes, vacancy fluxes, stress generation, nucleation of intermediate phases and movement of newly born interphase interfaces. All these processes are closely interrelated and lead to formation and growth of certain phases andto suppression of others. We present the review of phase competition theory taking into account some of aforementioned factors and application of this theory to the description of solid state amorphizing reactions.

Nontraditional methods of producing the amorphous metallic alloys based on the solid state arnorphizing reactions have been developed during the last decade - amorphizing by diffusion, by ball milling, spontaneous vitrification and others. The main problem here from the theoretical point of view is to explain why doesthe metastable amorphous phase appears instead of stable intermediate phases with corresponding composition.

Diffusion couples combining a h.c.p. Zr90Al10 supersaturated solid solution with a fc.c. Cu64Ni36 solid solution were annealed at 410°C for different times. The reaction at the interface was investigated by transmission electron microscopy (TEM) and energy dispersive x-ray spectroscopy (EDAX). Cross sectional TEM images and electron diffraction patterns reveal the formation of a non-crystalline layer at the interface between the two solid solutions which grows to a maximum thickness of more than 0.3 μm. Using EDAX, the concentration profiles across the layerswere determined. The glassy layer consists of a Zr-Ni-Al alloy with a small amount of Cu.The concentration profiles reveal that two non-crystalline phases coexist in the diffusion couple. One phase is Ni-rich and the other is Zr-rich. A small gradient of the Ni concentration in the Ni-rich amorphous phase and a steeper gradient in the Zr-rich non crystalline phase indicate that the Ni diffusion constant in the Ni-rich phase is larger than the Ni diffusion constant in the Zr-rich phase. In the late stage of the reaction, the growth of a nanocrystalline layer with an average concentration of Cu 90Nij 0 is observed on the Cu-Ni side of the diffusion couple. Crystallization starts at the Zr-Al side of the diffusion couple.

Three new crystalline NbSe2/TiSe2 superlattice compounds with 43.472±0.005A, 80.66±0.03A and 117.9±0.1Å unit cells in thec direction were prepared through controlled crystallization of Ti/Se/Nb/Se superlattice reactants with different compositional layer thicknesses. Theta-theta and rocking curve data were collected using a theta-theta diffractometer to study the evolution of the initially layered reactants into the crystalline superlattices as a function of temperature. Low angle diffraction data demonstrates that the initial layered reactant contracts in the c-axis direction upon initial annealing and suggests that the interfaces become smoother during this initial interdiffusion. High angle rocking curve diffraction data shows the development of caxis oriented NbSe2fTiSe2 crystal growth perpendicular to the substrate surface. Theta-theta scans show a gradual decrease of the (001) diffraction linewidths of the growing compound as a function of annealing time and temperature indicating an increase in the c-axis domain size. High quality caxis oriented TiSe2/NbSe2 crystalline superlattices result from annealing at the relatively low temperature of 500ºC. The rational synthesis of intergrowth compounds from superlattice reactants as described herein will permit the tailoring of physical properties as a function of compositional layer thicknesses and nativeproperties of the parent compounds.

A new process has been developed to deposit acrylate thin films at speeds of 1500 ft/minute or higher. These films range in thickness from a few hundred Angstroms to a fewmicrons and are uniform in thickness to within 5%. They can vary in refractive index from 1.35 to 1.60 and have mechanical properties from very hard and abrasion resistantto very soft and flexible.

The acrylate deposition process was originally developed for multilayer acrylate/aluminum capacitors where over 10,000 layer structures were produced[l]. The process is compatible with other vapor deposition processes such as sputtering, evaporation, and CVD. Both processes can take place at the same time in the same vacuum chamber toproduce various multilayer structures.

This paper will discuss some of the features of this process and the associated equipment. It will present examples of the wide range of acrylate/acrylate, acrylate/metal, and acrylate/inorganic material structures that can be made. It will discuss various applications for these structures.

PLD of uniform thin films on 4”-wafers has been realized by the integration of a PLD-source into a commercial MBE-system. Thickness homogeneity over the total substrate area is obtained by precise spatial control of the plasma plumes excited simultaneously at 4 adjacent target locations. Computer controlled motion of a cylindrical target with respect to the stationary focal spots of the laser beams, has to provide (a) a suitable deflection of the plume axis and (b) a uniform target erosion. Process control was investigated by computer simulations. The efficiency of the developed technique for large area coating is illustrated by the preparation of DLC thin film specimens and their ellipsometric characterization

High-quality thin-film superlattices of permalloy (NiFe) and silver (Ag) have been grown by pulsed laser deposition (PLD) for the first time. The alternating metallic layers weregrown from individual NiFe and Ag targets utilizing an automated multi-target holder coupled to a conventional PLD system. The targets were ablated at a base pressure of 4×10−7 Torr and the material deposited on room-temperature (100) silicon and on fused silica substrates. The films were characterized by X-ray diffraction (XRD), magnetic field-dependent resistivity, and ferromagnetic resonance (FMR). XRD was used to confirm uniform bilayer thicknesses. The magnetic field-dependent resistance measurements indicated the presence of magnetoresistance in the deposited films. An as-deposited film with a bilayer thickness of 75 Å demonstrated a roomtemperature magnetoresistive effect of 0.15 %. FMR has been used to determine the relationship between NiFe magnetism and the observed magnetoresistance.

Multilayered structures with small periods were fabricated using RF-magnetron sputtering device. The conditions of deposition and small changes in the plasma during all deposition period was investigated by optical emission spectroscopy. We studied influence of different parameters (pressure, power, sputtered material) to emission lines corresponding to the working gas Ar and W or Si. Structure and properties of multilayers were estimated, using transmission electron microscopy (TEM) and small-angle x-ray (1.54 Å) scattering techniques. The results was compared with emission line intensities of Ar, W and Si and self-bias data written for each layer with computer during multilayer fabrication. Wediscuss X-ray reflection properties of multilayers fabricated under our conditions and correlation of emission spectroscopy analysis data with another parameters of plasma (self-bias).

Epitaxial thin film multilayers are limited by the need for both lattice and thermal expansion matching. Recently, a new deposition technique, known as van der Waals epitaxy, has been developed to overcome these limitations. Van der Waals Epitaxy (VDWE)promises the ability to deposit multilayers based on the property of interest without being limited by lattice and thermal expansion mismatch. The crystallographic two dimensional metal chalcogenides are characterized by strong covalent bonding within a layer and weak van der Waals bonds between layers. By combining the layered nature of the metal chalcogenides with other layered materials as well as crystallographic 3D materials, oriented single crystal layers can be deposited, resulting in novel structures with atomically abrupt interfaces. However, even with the weak van der Waals bond, substrate/film interactions play a large role in the final structure.

To study the substrate/film interaction occurring during van der Waals Epitaxy growth on 3D surfaces, the metal chalcogenide GaSe has been systematically deposited on GaAs(1 11) substrates. To develop an understanding of the interaction of the substratewith the growing film, growth of GaSe on both atomically rough and smooth substrates was studied. Comparison of the information developed through RHEED, TEM and AFM have been used to understand the basic nucleation and growth process as well as the observation and formation of film defects.

High-resolution TEM, RBS-channeling and x-ray-diffraction techniques have been used to characterize multilayered structures formed by the high-dose co-implantation of vanadium and oxygen into single crystals of cx-A1203. Thin, two-dimensional multilayered structures have been formed by implanting c -axis and a -axis-oriented single crystals of A1203 at room temperature with vanadium (1017 ions/cm2 at 300 keV) and oxygen (2 × 1017 ions/cm 2, 120 keV) followed by a rapid anneal at 1000ºC. Cross-sectional TEM studies showed thatthis process produced a buried layer of V2O3 located about 120 nm below the A12O3 surface. X-raydiffraction investigations revealed that this layer is epitaxially oriented in three dimensions with respect to the host A12O3 lattice. The orientational relationship was subsequently confirmed by RBS/ channeling techniques. V2O3 exhibits a first-order phase transition at about 155 K that is accompanied by striking changes in its electrical and opticalproperties, and this phase transition was observed through in-situ TEM cooling studies ofcross-sectional samples.

Aluminum and copper nanolaminates have been fabricated at Jet Process Corporation using the novel, proprietary Jet Vapor DepositionTM (JVD)TM process. Laminates with a total thickness of 10 μm were made by depositing alternating layers ofapproximately equal thicknesses of copper and aluminum onto preheated silicon wafers at asubstrate temperature of ∼140 °C. The layer thicknesses were systematicallyvaried between 20 nm and 1 μm. The microstructure and properties of the laminates were investigated using transmission electron microscopy (TEM), scanning electron microscopy (SEM), and nanoindentation methods. TEM has shown that the laminates have a strong {111} texture. The hardness results show that above a critical layer thickness of approximately 50 nm, the yield strength of the composites varies inversely with thelayer thickness, while the strength of nanolaminates with layer thicknesses smaller than the critical thickness is better explained by the Koehler model. An alternative model recently proposed by Embury and Hirth fits the data equally well.

Electrodeposition is unique among thin film deposition techniques, since the current following a potential step from open circuit to a given overpotential (i.e., driving force) provides a real-time, in situ probe of the deposition process. We have used current-time transients to determine the kinetics and dimensionality of growth, and to calculatethe composition profiles of electrodeposited superlattices in the Pb-TI-O system. The transients are indicative of 2D growth, and the height of the 2D monolayer depends on the orientation of the film. A [100] oriented film has a step height of 0.13 nm and a [210] oriented film has a step height of 0.18 nm. These heights correspond to the (400) and (220) d-spacings, respectively. Using a Cottrell analysis, we were able to both calculate and tailor the composition profile in these superlattices. Superlattices grown by pulsing between 70 and 150 mV have square profiles, while those grown by pulsing between 70 and 230 mV have graded profiles.

Metastable face—centered cubic (fcc) Co was grown epitaxially on (111)Si with an intermediate Cu layer in an ultrahigh vacuum chamber at room temperature. The metastable fcc—Co was grown to extend to a thickness of 30 nm. Polycrystalline and epitaxial hexagonal close—packed (hcp) Co was grown on (111)Si without and with 3 nm or thicker intermediate Cu layer, respectively. The key to the successful growth of fcc—Co is to deposit Co directly onto a thin (2 nm or thinner) interface compound (—Cu, which is of hcp structure and consisting of 11.2 to 14.0 at.% Si. The growth of the metastable phase is attributed to the attainment of an appropriate electron/atomratio at the interface to favor the formation of the fcc—Co.