Most of the interest in the magnetic thin films or multdayers has been focused on ferromagnetic materials because of the inherent potential applicability. Very little attention has been given to the experimental study of the most fuadamentally important structures -from a physics point of view- the antiferromagnetic (AF') insulators. Also, proportionally little attention has been given to the growth characte ization of ionic materials. Using relatively primitive MBE techniques, we have grown el itaxial thin films of MnF2, FeF2, as well as superlattices of (FeF2)m(CoF2)n and (FeF2)m(ZnF2)n. In the FeF2/CoF2 superlattices we have deduced coherence lengths of up o ξ ≈ 2,200 Å from x-ray θ–2θ scans, for superlattice periods of 90≈ We will review some of our recent results in the characterization of the magnetic, structural and infrarod phonon properties, using high resolution x-ray diffraction, atomic force microscopy, AF resonance, infrared spectroscopy, capacitance, and dilation measurements.

The magnetic properties of epitaxial magnetic metal multilaycrs, superlatticcs and ultrathin films are of intense current interest because of the novel and potentially useful properties which these structures exhibit. MBE techniques permit the growth and in-situ characterization of such structures and the control of the growth axis of films and multilayers through epitaxial seed layers on semiconductor substrates. Techniques for controlling the growth axis of Co/Cu superlattices, for magnetoresistance studies, are described. In this and other other material systems it is necessary to combine the in situ probes of RHEED, LEED and X-ray photoelectron diffraction (XPD) with post-growth HRXTEM to understand and control the formation and nature of the interfaces in the structures.

The microstructure of BaTiO3 thin-films deposited on MgO by pulsed-laser ablation has been examined by both scanning and transmission electron microscopy. The films were epitactic as evidenced by electron diffraction studies. Preliminary capacitance measurements on these films have shown clear evidence for a ferroelectric phase transition at ∼110°C.

The epitactic growth of oxides on Si requires structural and chemical compatibility between the substrate and film. The growth of (Ba0.7,Sr0.3)TiO3 (BST) by pulsed laser deposition on HF-cleaned Si (001) and Si with a buffer layer of CaF2 was studied. The BST can form a low misfit interface with Si and CaF2 but chemical reactions between the BST and the Si prevented the epitactic growth on Si. An x-ray photoelectron spectroscopy (XPS) depth profile indicated that the BST had reacted to form a silicate and titanium silicide. The BST on CaF2 -Si(00l) substrate was partially epitactic and formed a 45° rotated orientation relationship such that the Si (110) is parallel to the BST (100).

Silicon films were grown on epitaxial (ZrO2)1-x(Y2O3). films on the Si substrate. The deposition of Si was carried out by conventional plasma-CVD of the mixture of SiH4, H2 and PH3 gases. The appropriate deposition conditions for the epitaxial growth of Si were examined. The crystallographic properties of the Si films were characterized by reflection high-energy electron diffraction (RHEED).

We have formed PbTIO thin films on SrTiO3 substrate (100) at low temperature of 350°C using an ArF excimer laser ablation technique. Until now, the PbTiO3 films have not been formed at the temperature lower than 500°C using other thin film techniques. The Important points In the present study are the laser excitation of the substrate during the film growth and the lattice matching between the film and the substrate. The film deposited on the SrTiO3 substrate, shows preferential orientation of the c-axis perpendicular to the substrate surface.

Heteroepitaxial multilayers of YBa2Cu3Ox/PrBa2Cu3Ox/YBa2Cu3Ox have been made by sputtering. Typical thicknesses of the individual layers are of the order of 50 nm. No degradation of the transition temperature and the critical current density due to the presence of the PrBa2Cu3Ox layer could be observed. By using High Resolution Transmission Electron Microscopy the atomic details of the interfaces and the defect structures have been studied. These films showed a perfectly stacked lattice just above the interface between film and substrate. The orientation of the c-axis perpendicular to the substrate was fairly perfect. The structural faults are mainly distributed in the middle and overlying layers. The dominant defects in our films seems to be stacking faults which give rise to nano-sized coherent anti-phase domains with the 1-2-3 structure.

We report epitaxial growth of the simple cubic perovskites Ba1-xKxBiO3 and Ba1-xRbxBiO3 on Ba3LaNb3O12, LiBaF3, BaF2, and Al2O3. Films with excellent crystallinity are obtained on the perovskite substrates, LiBaF3, and Ba3LaNb3O12. (1 1 1) or (1 1 0) films can be obtained on {1 1 1} BaF2, depending on the nucleation temperature. Non-epitaxial superconducting films have been grown on Si and on GaAs. At the low growth temperatures used (200–450°C), reactions with the substrates do not pose problems. The choice of substrate not only determines the microstructure of the film, but also plays a role in allowing the film to change its oxygen stoichiometry. Stoichiometry shifting is a pervasive necessity for the synthesis of high Tc thin films.

TiO2 thin films were grown epitaxially on (1120) sapphire (α-Al2O3) at 800 °C by the MOCVD method. The TiO2 films and TiO2/Al2O3 interfaces were characterized by TEM and HREM. The observations indicate that the TiO2 films are single crystalline and have the rutile structure. A majority of the films has the epitaxial orientation relationship between the TiO2 rutile films (R) and the α-Al2O3 substrates (S): (101)[010]R||(1120)[0001]S, while the epitaxial relationship of (100)[010]R||(1120)[0001]s has also been observed for one film. HREM studies show that the (100) film was grown on an off-cut substrate, vicinal to (1120). Detailed atomic structures of the interfaces will be presented and discussed in terms of the growth mechanism and misfit dislocation structure.

Perovskite KNbO3 thin films were epitaxially grown on (001) MgO by sequential deposition of ultrathin layer (<10Å) single component (KOx and NbOy) species. By engineering the first overlayer species from NbOy to KOx, on (001) MgO, a 45° in-plane rotation of the epitaxial KNbO3 films was observed. This 45° rotation is a result of minimization of the electrostatic energy within the KNbO3/MgO interface. Transmission electron microscopy was employed to characterize these epitaxial KNbO3 films.

Growths of single crystal NiSi2 on Si(lll), (100) and (110) are described. The atomic structures at these interfaces have also been studied and found to influence the observed Schottky barrier height significantly.

The growth of Al on (111) Si single crystal substrates by various techniques usually leads to films with (111) texture, sometimes with a small (100) component. Using X-ray diffraction and electron microscopy, the present study shows that the (100) texture component can be enhanced to the point of forming an oriented (100) continuous tricrystal structure. The formation of this texture is shown to be related the presence of Cu. It is concluded that an understanding of heteroepitaxy must take into account the effect of chemistry in addition to the crystallographic criteria of lattice matching.

Using molecular beam epitaxy (MBE), we have grown high quality, low stress, single crystal Al on Si( 111) and CaF2(111). X-ray diffraction was used to characterize the crystalline quality, stress, and epitaxial relations of the films. AI(lll) was grown at a substrate temperature as low as 25°C on as-deposited CaF2(111) and Si(111) cleaned by either wet etching or high temperature annealing. Aluminum Film stresses, derived from deformation of the Al atomic planes, are compressive when the films are grown at low temperatures. The stress becomes tensile and increases as the growth temperature increases. Consequently, films of low stress can be achieved by choosing the appropriate growth temperature. Epitaxial relations are dependent on the growth temperature and Si substrate preparation methods. Aluminum films with crystalline orientations identical to the substrates (A type), rotated 180° about the surface normal of the substrates (B type), and mixed A and B types have been observed.

Nb/MgO/Nb/Al2O3 multilayer stacks were prepared by MBE growth of Nb and MgO films on a (0112)A1203 sapphire substrate. Sequential deposition of Nb followed by MgO on the sapphire substrate resulted in three different interfaces: one between Nb deposited on sapphire as the substrate (the Nb1/Al2O3 interface), one between MgO deposited on Nb as the substrate (the MgO/Nb1 interface), and finally one between Nb deposited on MgO as the substrate (the Nb2/MgO interface). Cross-sectional TEM specimens from the multilayer were prepared and the various interfaces were investigated by high resolution electron microscopy (HREM). Orientation relationships between Nb1 and Al2O3 and also between MgO and Nb1 were determined and misfit dislocations, steps and facets at the Nb1/Al2O3 and MgO/Nb1 interfaces were analyzed. The HREM observations showed that an intterfacial phase forms at the Nb1/Al2O3 interface by a solid state reaction under electron beam irradiation.

In the present study we report the first results pertaining to the heteroepitaxial growth of Ti films on 6H-SiC (0001). The Ti epitaxial films of typically 400–1000 Å thickness have been deposited at room temperature in ultra-high vacuum (< 10−9 torr) using both thermal and electron beam evaporation sources. In-vacuo techniques of low energy electron diffraction (LEED) and x-ray photoelectron spectroscopy (XPS) have been used to monitor the surface structure and interface chemistry during growth. An unreconstructed (1×1) ordered LEED pattern corresponding to that of the SiC (0001) surface was observed for all Ti coverages. Epitaxial growth of Ti has been confirmed from cross-sectional TEM diffraction patterns and images, which indicate the presence of threading dislocations to relieve a 4% lattice mismatch strain. Rutherford backscattering (RBS) with channeling of 2 MeV He+ ions gave X = 0.71 for Ti deposited at room temperature. Current-voltage measurement for both un-annealed and annealed Ti contacts displayed rectifying characteristics with low leakage currents (≈, 6 nA at −10V) and low ideality factors (1.02–1.08).

Two heterophase interfaces formed in the joining of α-SiC were investigated using high-resolution electron microscopy coupled with a multi-slice structural image simulation. A reaction product TiC was formed epitaxially on the basal plane of α-SiC single crystal when SiC was brazed with a Ag-Cu alloy containing small amount of Ti. A coherent interface with Si-C and Ti-C bonding was found between the SIC(0001) and TiC(111). Al4C3 was grown also epitaxially on the basal plane of SiC when it was brazed with AL. A semicoherent interface including interfacial dislocations and intermediate' transition phase was observed between the SIC(0001) and Al4C3(0001). It was estimated that the carbon atom sublattice was maintained through those crystals.

When preparing single-crystal films of CaF2 on (111) oriented silicon by molecular beam epitaxy (MBE), we found that these dielectric films grew into either A or B type depending on the substrate temperature during growth. A-type films follow the same orientation as that of the substrate silicon, while B-type films rotate 180° about the surface normal with respect to the substrates.

X-ray diffraction (XRD) confirms the single crystallinity and identifies the epitaxial relationships between the film and the substrate. Epitaxial CaF2 films were obtained at growth temperatures ranging from 200°C to 800°C. Employing the asymmetric x-ray diffraction of atomic planes inclined to the sample surface, we found that A-type CaF2 grows at lower substrate temperatures, while B-type films dominate at higher temperatures.

Effects of substrate materials and their properties on photoassisted MOVPE of ZnSe using DMZn and DMSe as reactants have been investigated. For GaAs substrates, the presence of a thin predeposited ZnSe buffer layer and its quality greatly affect the subsequent film growth. However, for InP substrates, no essential effect of the buffer layer has been observed. Furthermore, in both substrates, the conduction type makes no significant difference to the results of photoassisted MOVPE. These results can be interpreted by a proposed growth model in which photoinduced excess holes In the ZnSe layer contribute to the film growth.

Artificial epitaxy (or graphoepitaxy) is considered as an alternative to classic (“atomic”) heteroepitaxy, being especially suitable for the preparation of single-crystalline films of some materials on strongly-dissimilar substrates.

The epitaxial structural development and surface reactions of barium metal with silicon have been studied as a function of surface coverage. BaSi2 is orthorhombic, and grows epitaxially on Si(001) and Si(111) for surface coverages greater than 1 monolayer (ML). From 0 to 1 ML a series of ordered surface structures develops that suggests a cubic Ba-Si compound. Reflection high energy electron diffraction (RHEED), Auger and x-ray photoelectron spectroscopy (XPS) data have been obtained in this thin film regime that support a chemical reaction and compound formation between barium and silicon for all barium coverages. In bulk form, at high pressures, BaSi2 can be stabilized into the cubic SrSi2 structure. We suggest that epitaxial strain at the silicon surface provides a mechanism for stabilizing the low-coverage precursors of the orthorhombic BaSi2.