We report on recent studies of small platinum clusters supported on highly-oriented pyrolytic graphite, using a scanning tunneling microscope (STM). The clusters are generated by vapor deposition of single atoms with subsequent diffusion and growth processes occurring on large, flat and ordered substrates. Single adatoms, small clusters and larger islands are imaged with atomic resolution and their atomic structures are determined by direct observation. We find different isomeric structures for clusters of one size. Taking the substrate lattice as reference we determine bond lengths and angles for the clusters. We investigate the effect of the substrate on the adsorbed particles.

Epitaxial TiO2 films have been successfully grown on sapphire substrate at temperatures from 400 to 800°C by thermally decomposing titanium isopropoxide in the presence of O2 in a cold wall low pressure MOCVD system. Rutile film was grown on sapphire (1120) at 800°C with (101) being the growth plane and 〈010〉 being parallel to sapphire 〈0001〉. Anatase film was grown on sapphire (0001) at 400°C with (112) being the growth plane and 〈112〉 being parallel to sapphire 〈1100〉. The film structure as a function of substrate surface orientation and growth temperature is discussed in detail.

Epitaxial films of a variety of magnetic transition metal difluoride films have been grown by molecular beam epitaxy techniques. The structural quality of these films have been characterized using X-ray double crystal rocking curve analysis. The observed rocking curve linewidths were compared to their intrinsic values as calculated by dynamical diffraction theory. The degree of crystalline perfection as judge by the rocking curves have been correlated with the amount of lattice mismatch between the various epitaxial films and substrates. In the well lattice match case (Δa/a < 0.2%) of epitaxial films of FeF2 and CoF2 grown on (001) ZnF2 substrates, the rocking curve line widths approached their intrinsic limit indicative of extremely high quality material. This work represents some of the best epitaxial magnetic insulating films grown to date.

Conventional heteroepitaxial thin film growth may result in a film whose epitaxial orientation is metastable. One method of probing the relative energies of various film orientations is epitaxial grain growth. Epitaxial grain growth selects the orientation having lowest total free energy, including the free energy of both the film-substrate interface and the free surface of the film. Experimental examples of epitaxial grain growth in metal films on insulating substrates will be discussed.

In this paper we propose a new method for the synthesis of Si1−xGex strained-layer alloys using high-dose ion implantation of 74Ge at 200 keV into a preamorphized <001> Si wafer followed by solid phase epitaxy (SPE). Cross-sectional TEM was performed on samples at various stages of regrowth which revealed the evolution of the amorphous/crystalline interface and the development of strain relieving defects during SPE. We report that stacking faults are kinetically favored during SPE of Si1−xGex but are energetically feasible only above a critical strain energy. We propose a model that is based on the well known Matthews and Blakeslee approach which predicts the onset of stacking faults during SPE of high-dose ion implant-synthesized Si1−xGex/Si.

Using the embedded atom method we atomistically model the compensation of the misfit induced stresses in a “cube on cube” oriented Ag/Ni bicrystal with (011) interface plane, in which zones of maximum misfit (misfit dislocations) run along the [100] and the [011] directions.

The ideal interface corresponds to an abrupt transition between Ag and Ni. The interfacial enthalpy is found to be lowered by the introduction of vacancies on the Ni side (equivalently, vacancies are trapped on the Ni side of the boundary). Pursuing this perspective, we find that the interfacial enthalpy is lowered considerably by the removal of a complete line of Ni atoms along the [011] direction from the Ni side of the boundary. The minimum energy configuration consists of a Ni layer whose atomic density is reduced by 16% sandwiched between the ordinary Ni and Ag lattices.

The energy interphase boundaries can be described as a function of the lattice matching at the interface between two adjacent crystals, the chemical interaction and the interfacial entropy of the boundaries. Geometric models relating the energy of interphase boundaries (metal/metal and metal/non-metal) to their atomic structure can be based on the static distortion wave concept. This approach constitutes the physical basis for the lock-in model and the planar CSL-model proposed previously to describe the low energy configurations of such interfaces.

We report on the results of molecular dynamics simulations of thin unsupported fcc films ranging in thickness from 20 layers to a monolayer. The films were oriented with either (001) or (111) free surface normals. The atomic interactions were modelled using a standard Lennard-Jones potential and a short range analytic form of the embedded atom potential. The elastic moduli of the films were determined by measuring their response to very low levels of applied stress.

We find that the embedded atom and Lennard-Jones results are in relative agreement for (001) films and qualitative disagreement for (111) oriented films. We relate these differences to the nature of the interatomic potential and the thermodynamic instability of the (001) surface.

Ag/Cr metallic superlattices with bilayer thickness in the range of 17–136Å were prepared by metal-MBE method. X-ray diffraction measurements indicated that the thickness fluctuations of each layer were rather small. The lattice matching at the interface between Ag(100) and Cr(100) is almost perfect. But, the interplanar spacings of Ag(100) and Cr(100) changed as a function of bilayer thickness. Surface wave velocities have been measured using Brillouin spectroscopy. In contrast to Au/Cr superlattices which show a hardening, a plot of surface wave velocities as a function of the bilayer thickness in Ag/Cr superlattices showed a distinct dip.

Ag/Co metallic superlattices were grown onto Ag buffer layers pre-deposited on sapphire or MgO substrates by ultrahigh vacuum alternate deposition technique. In-situ RHEED observations during superlattice growth and ex-situ XRD measurements revealed that structures of the superlattices were strongly affected by the condition of Ag buffer layer preparation. In case where the Ag buffer layers were single crystals with smooth (111) surfaces, Co layers were epitaxially grown on the buffer layers even in the presence of large lattice mismatch, and whole the superlattices were grown with an epitaxial relation. Interface smoothness was strongly related to the growth temperature. Spotty RHEED patterns of Co layers for a low growth temperature indicated that the Co layers had an FCC structure. Post-annealing of the samples, in some cases, destroyed a superlattice structure completely. From relations between magnetic anisotropy and Co-layer thickness obtained with VSM measurements, it was found that Ag/Co superlattice exhibited in-plane magnetic anisotropy down to a Co thickness of 4A and that the anisotropy was correlated with roughness of the interfaces.

The interfacial structure of Pt/Nb and Pt/Ni sputtered multilayer films was studied using x-ray diffraction in symmetric, asymmetric, and grazing incidence modes. The grazing incidence and asymmetric diffraction were used to distinguish alloying effects on the lattice spacing from strain in the films. This strain was shown to be consistent with semi-coherent interfaces in the Pt/Ni but not in the Pt/Nb in which another strain generating mechanism dominates.

We have investigated structural and elastic properties of Hf/Zr multilayer thin films by x-ray diffraction and transient piezoreflectance measurements. Similar structural and elastic behaviors have been observed in two series of samples grown at different deposition rates (1 – 10Å/sec). Our measurements suggest different (˜ 10%) effective elastic constants between multilayers with coherent and incoherent interfaces.

Structural characterization and strain measurements were conducted on Mo/Ni multilayers, with bilayer periods between 10 Å and 200 Å, utilizing symmetric, asymmetrin, and grazing incidence x-ray diffraction techniques. The structural difference between the 15 Å and 20 Å modulation wavelength samples, evident in the symmetric high angle diffraction spectra, is attributed to the absence of crystalline registry in the early stages of sputter deposition, yielding crystalline order only when the bilayer deposition thickness exceeded 15 Å. The dominant mechanism for the observed modulation wavelength dependent strain behavior, both in the growth direction and in the plane of the film, is consistent with a coherency strain model. The orientation relationship predicted for the Mo/Ni system, based on their atomic radii ratio is the Nishiyama-Wasserman relationship, (110)BCC//(111)FCCand[001]BCC//[101]FCC. This relationship would provide the source for the observed coherency strain.

The direct measurement of the composition variations in transition metal multilayers has been carried out using the atom-probe and the position sensitive atom-probe (POSAP). The atom-probe and POSAP do not have sufficient resolution to determine the crystal structure and this complementary information has been obtained using high resolution electron microscopy.