We studied the effects of the surface hydrogenation on the adsorption, penetration, and silicidation, i.e., the initial reaction processes of the transition-metal Ni and Ti adatoms on the Si surfaces by the first-principles theoretical calculations. We found for both Ni and Ti that the surface hydrogenation changes the most stable surface site and reduces the adsorption energy. In addition, it blocks the penetration, and thus prevents the silicidation. Furthermore, we newly propose its interesting effects from our results, i.e., impurity metal atoms existing in the Si subsurface are extracted onto the surface by the surface hydrogenation. Thereby, highly pure and atomically flat Si surfaces are expected to be obtained.

This work reports on the photoluminescence properties of self-organized fully strained Ge dots fabricated using two different growth techniques: gas source molecular beam epitaxy (GS-MBE) and solid source molecular beam epitaxy (SS-MBE). Variable temperature photoluminescence (PL) measurements were carried out on Si/(n)Ge/SiGe/Si structures (n varying from 1 to 7 monolayers) consisting in double layer structures (Ge(n)/Si1-xGex) deposited on (118) oriented Si substrates. The process used consists in realising in a first step a Si1-xGex template layer with a “self-patterned” morphology. Such patterning, based on periodic morphological modulation of the surface is used to confine and organise the Ge dots in a second deposition step. Similar series of experiments with various growth temperatures, Ge coverage levels and Si1-xGex concentrations (x) were done by both GS-MBE and SS- MBE. The PL from the 2D wetting layer in the case of n = 3 ML has been found to be more intense in GS-MBE thanks to the passivating role of the hydrogen atoms. The 2D to 3D growth transition is accompanied by the occurrence of a red-shifted broad PL band (L) attributed to the Ge dots. While broadened luminescence is obtained from dots directly deposited on the Si substrate, a narrower band is obtained from dots deposited on the template layer. Moreover the red-shift of the (L) band observed in the latter case is attributed to higher Ge concentration in the dots. On the other hand, there is no effect of the hydrogen on the formation of the islands which show similar optical and structural properties in both growth techniques. The main difference between GS-MBE and SS-MBE concerns a low energy shift in the PL of the SSMBE Ge dots we interpret as due to size, dispersion and Ge concentration or strain effects

Diffusivity of a strained heterostructure was theoretically investigated, and general diffusion equations with strain potential were deduced. There was an additional diffusivity by the strain potential gradient as well as by the concentration gradient. The strain-induced diffusivity was a function of concentration, and its temperature dependence was formulated. The activation energy of the strain-induced diffusivity was measured by high-resolution transmission electron microscopy. This result can be generally applied for the investigation of the diffusion in strained heterostructures.

Growth front scaling aspects are investigated for PPV-type oligomer thin films vapor- deposited onto silicon substrates at room temperature. For film thickness d~15-300 nm, commonly used in optoelectronic devices, correlation function measurement by atomic force microscopy yields roughness exponents in the range H=0.45±0.04, and an rms roughness amplitude which evolves with film thickness as a power law σ∝ dβ with β=0.28±0.05. The non-Gaussian height distribution and the measured scaling exponents (H and β) suggest a roughening mechanism close to that described by the Kardar-Parisi-Zhang scenario.

Numerical simulations have been performed for generic III-V MBE growth. The key aspects of the simulation include two deposited species one volatile and the second with high surface mobility. Simulations reproduce the experimentally observed adatom concentrations for GaAs and show that smooth surfaces are produced for films deposited with a substrate temperature in a crossover regime between kinetically limited and entropically roughened growth.

Picosecond time scale magnetization reversal dynamics in a 15nm thick Ni80Fe20 microstructure (10μm×2μm) is studied using time-resolved scanning Kerr microscopy. The time domain images reveal a striking change in the magnetization reversal mode, associated with the dramatic reduction in switching time when the magnetization vector is pulsed by a longitudinal switching field while a steady transverse biasing field is applied to the sample. According to the time domain imaging results, the abrupt change of the switching time is due to the change in the magnetization reversal mode; i.e., the nucleation dominant reversal process is replaced by domain wall motion if transverse biasing field is applied. Furthermore, magnetization oscillations subsequent to reversal are observed at two distinct resonance frequencies, which sensitively depend on the biasing field strength. The high frequency resonance at f=2 GHz is caused by damped precession of the magnetization vector, whereas another mode at f≈0.8 GHz is observed to arise from domain wall oscillation.

The evolution of surface structures of coevaporated and sputtered amorphous Zr65Al7.5Cu27.5 films with varying deposition conditions is investigated primarily with scanning tunneling microscopy (STM). While vapor deposited thin films reveal pronounced structure formation, depending on parameters, such as substrate temperature, film composition (variation of the Al versus the Cu content) and the angle of incidence, comparable sputtered films hardly show any structure formation. With the help of a numerical analysis of the STM data, surface diffusion, self–shadowing and energy transfer in the case of sputtering can be identified as the main structure forming mechanisms. Presuming these atomic processes, it is possible to model the main experimentally observed features of amorphous thin film growth by the use of stochastic continuum growth equations, which are numerically solved. Additionally, the connection to intrinsic stress formation during film growth is discussed.

We report on random laser emission in pulsed laser deposited nanocrystalline ZnO thin films. The deposition was done on silicon and glass substrates in ambient oxygen pressure ranging from 10 mTorr to 1 Torr at room temperature. The deposited films were characterized using XRD, RBS, PL and AFM. The films grown at pressures less than 300 mTorr are found to be preferentially oriented along (002) plane. Morphology of the films deposited at different background pressures showed that the films deposited at lower pressures are significantly smoother than those at higher back ground pressure. PL intensity depends on the stoichiometry of the films and hence on oxygen pressure. Laser action was observed on optically pumping the films with 355 nm radiation. At excitation intensity above threshold, very narrow peaks are observed in the emission spectrum. The dependence of the laser emission on the size of nanocrystallites at different pressures of the ambient gas is presented.

We have carried out a series of experiments aimed at producing arrays of mesas on both Si(001) and Si(111) which are free from atomic steps. These are of interest in CMOS technology and for quantum well structures. They also provide interesting substrates for fundamental surface science experiments. In previous work we have created atomically flat regions surrounded by ridges through an evaporation method. The present work ‘inverts’ the previous process by using a pattern of trenches to define the mesas and then depositing Si to grow the atomic steps off the edges. The mesas are created on Si wafers, which are ~1° from the (111) and (001) plane by lithography and reactive ion etching. Step-free mesas were formed on Si(111) but not yet on Si(001). Both the evaporation and this new growth technique rely on step flow to move the steps to the edges of the flat areas. Although the evaporation method is simpler, an advantage of the growth technique is that it can be carried out at lower temperature. The maximum size of mesa that can be made free of atomic steps depends on the combination of temperature and deposition rate. On very large step-free terraces nucleation of islands and concentric arrays of mono-atomic steps are observed; these correspond to the vacancy pits observed with the evaporation method.

We have investigated the decay of two-dimensional islands on the anisotropic Ag(110) surface using variable-temperature scanning tunneling microscopy. Contrary to predictions from traditional Ostwald ripening theory, a quasi-one-dimensional decay mode is observed at low temperatures (175-220 K). A surprisingly sharp transition to the quasi-two-dimensional decay mode is observed around 220 K. This transition is accompanied by a fast equilibration of the island shape. These findings have tentatively been rationalized within a simple model to identify the underlying rate limiting atomistic processes.

We theoretically address epitaxial growth on (001) crystalline surfaces symmetry, in the regime when pyramids are formed across the growing interface due to Schwoebel step-edge barriers. We develop a kinetic scaling theory that analytically explains numerous experiments and simulations suggesting that pyramid size grows, via coarsening, as a fourth root of the deposition time. Pyramid dynamics is elucidated in terms of pyramid edges that form a growing self-organized square lattice across the growing interface. The edge lattice of pyramids is disordered by topological defects that are characterized here as dislocations. We show that pyramid coarsening is mediated by climb-motion of the dislocations of the edge lattice.

Explosive crystallization, a self-sustaining transformation of an amorphous phase to a crystalline phase mediated by a thin liquid layer, exhibits three distinct kinetic and morphological regimes in germanium. Dynamics of these growth processes and the resulting morphologies have been examined in detail. Steady-state crystallization velocities were measured as a function of heat loss into the substrate. Dark field optical microscopy, tapping mode atomic force microscopy, transmission electron microscopy, and x-ray diffraction were used to examine the crystallized films. Analyses of the experimental results provide evidence for two distinct processes governing explosive crystallization in limits of high substrate temperature (low heat loss) and low substrate temperature (high heat loss). The low temperature growth mode produces a “scalloped” structure with propagation velocities that monotonically increase with temperature. At high substrate temperatures, the velocity is independent of temperature and a “columnar” pattern with preferred texture is formed.

Lateral integration of optoelectronic devices comprising strained multiple quantum well (MQW) structures can most successfully be accomplished by selective area epitaxy using metal organic molecular beam epitaxy (MOMBE). We optimized the growth parameters with respect to a planar butt coupling and sharp, flat MQW interfaces in an integrated MQW laser / MQW modulator structure. Defect generation in metal organic vapor phase epitaxy (MOVPE) overgrown cladding layers is analyzed and shown to contain information about the quality of the buried butt coupling. A ridge waveguide structure has successfully been fabricated from an optimized integrated laser / modulator structure.

The Ge adsorption and diffusion processes on the monohydride terminated Si(001) surface are investigated by using first-principles total-energy calculations and kinetic Monte Carlo simulations. We find that the adsorbed Ge atoms tend to exchange sites with substrate Si dimer atoms. The site exchange plays an important role, which provides the most stable geometry and the easiest diffusion pathway. The Ge adatom migrates in the subsurface region instead of on the surface. The temporal variation in the adsorption geometry during diffusion is found. The Si atoms can become the surface diffusion species instead of the Ge atoms, as a result of the site exchange.

Polycrystalline silicon is an important technological material in microelectronics, and more recently in microelectromechanical systems (MEMS). For MEMS applications polysilicon films with residual tensile stress are often used, requiring film growth in the transition zone from 550-600°C. In this study polysilicon films were grown in a hot walled LPCVD reactor at 590°C to a thickness of 450 nm. The tensile as-deposited stress in the wafers was found to decrease with distance from the reactor front and served as a marker for the changing microstructure and surface roughness of the film as measured by Transmission Electron Microscopy (TEM) and Atomic Force Microscopy (AFM). It was found that the surface contained a high density (≍30 /µm2) of grains that protruded 30 nm above the mean film surface. The size and volume of these grains increased linearly with decreasing stress until the surface saturated and became uniformly rough. The nature of these surface grains, their spatial characteristics, and their annealing behavior is discussed.

We have investigated the growth of 3 ML (mono-layer) of Ag on Cu(111) for substrate temperatures from 170 through 640 K by using time of flight-impact collision ion scattering spectroscopy (TOF -ICISS). Two different types of epitaxial growth exist: Ag [112]//Cu[112](type-n) and Ag [112]//Cu[112] (type-r).The growth modes of the Ag thin films on Cu(111) surfaces depend strongly on the temperature during deposition with the Ag(111) planes having a preferred orientation of either type-n growth mode or type-r growth mode as a function of theCu substrate temperature. The experimental results concerning Ag/Cu(111) show many similarities to those in the previous study of Au/Ni(111). This would suggest that an observed oscillation in the growth mode, dependent on the substrate temperature during deposition may a general phenomenon on solid surfaces, in cases of large misfit since it has now been seen for both Au/Ni(111) and Ag/Cu(111) systems.

The plane form is the equilibrium one for surfaces of condensed matter. Deviations can be caused usually by crystal structure. Herein we will describe an effect of surface instability due to self- diffusion processes of atoms and molecules in the near surface electric field.

Self-diffusion processes (as it was shown by Mullins) cause relaxation of any deviation (protuberance) from the plane form due to the increased concentration of surface atoms and its consequent smoothing. This process we studied for the case when there is an electric field near the surface. The near surface electric field can be due to either the location of material in an external (homogeneous or inhomogeneous) electrical field or self-charges on the surface. There is an increasing of electric field intensity near protuberances both in external and self-formed electrical fields: the higher is the curvature of surface the stronger is the intensity of the near surface electrical field. Consequently two competing processes occur during surface molecules mass transfer: both the self- diffusion smoothing of surface molecule concentration and drawing of molecules in the strong electric field regions. Depending on the initial shape of the protuberance either relaxation or instability occurs. There is a critical wavelength λ0=RskBT/2Uz, which shows that shorter wavelength deviations decrease their amplitudes and longer wavelength deviations grow in amplitude by time. Here Rs is characteristic of the material, T is temperature, and Uz is the interaction energy of surface molecules with the electric field. Since there are random variations of any surface from the plane form, being placed in an electric field these surfaces will be unstable depending on the intensity of electric field and properties of material.

The ability to grow single-crystalline Al and Cu films is of significance for several areas of materials research, such as the resistivity size effect in thin metal films, electromigration failure of interconnects, and magneto-resistance studies. Here, we explore the microstructure and resistivity of thin Al and Cu films grown on CaF2/Si(111). A three-step technique of CaF2 growth is described that permits deposition under imperfect vacuum conditions and promotes smoothness of subsequent thin metal films. Reflection high-energy electron diffraction shows that epitaxial Al(111) is obtained directly on CaF2, while epitaxial Cu(111) is obtained only by growing on a 1 nm thick Al seed layer pre-deposited on CaF2. Transmission electron microscopy reveals that 75 nm thick Al films have 150 nm wide sub-grains misoriented by less than 1 degree. For 75 nm thick Cu, the grains are only 30 nm wide and are misoriented by as much as 10 degrees. Room temperature resistivity measurements of the 10-300 nm thick Al films agree with the Fuchs-Sondheimer model in which conduction electrons scatter totally diffusely at the film interfaces. For 50-1000 nm thick Cu films, the resistivity size effect is substantially greater than the prediction of this model, which may be explained in terms of grain boundary scattering.

We develop a new approach to the modeling of thin film growth. Our model treats the adatom density on the surface of the film as an explict unknown. This approach (1) clarifies the role of the “uphill current” associated with the Schwoebel barrier; (2) facilitates simple, physically natural coupling to the mechanism of deposition; and (3) permits discussion of multispecies effects. Our implementation focuses on spiral mode growth of YBCO thin films, with MOCVD (Metallorganic chemical vapor deposition) as the deposition mechanism.

Atomic-scale calculations were performed for the first time to investigate mechanical properties of amorphous carbon films grown by a realistic simulation of ion-beam deposition. The simulated films have a thickness of a few nanometers and reproduce the main structural features of real films, with the bulk content of sp3 bonded atoms varying from 35 to 95%, depending on the ion energy (E = 20-80 eV). Employing empirical interatomic potentials for carbon, the average bulk stresses as well as the atomic-level stress distributions were calculated and analysed. The bulk stresses were found to depend not only on the ion energy, but also on the film quality, in particular, on such structural inhomogeneities as local fluctuations of the sp3 fraction with the depth. The local variation of the bulk stress from the average value considerably increases as the local content of sp2 bonded atoms increases. Elastic constants of amorphous carbon films were also computed using the method of inner elastic constants, which allows for the stress dependence of elastic constants to be analysed. The variation of Young's modulus as a function of the lateral bulk stress in an amorphous film is demonstrated.