The metal-oxide interface is a crucial zone in the fundamental understanding of oxide growth and growth instabilities. However, obtaining fundamental information on this buried interface has proven extremely difficult using modern surface and interfacial characterization methods. Using copper oxide growth over copper metal, examined between RT and 250°C, as a model system, we have delineated the fundamental physical chemical processes that determine the oxide growth and instabilities at the metal-oxide interface. Application of controlled thermal growth studies in combination with linear sweep voltammetry (LSV) has allowed experimental access to the metal-oxide interface with surprising characterization capabilities. The methodologies involved and the physical chemical phenomena will be discussed in context of the application of modern surface characterization methods including pulsed field desorption mass spectrometry, XPS combined with depth profiling and angular resolved methods. The evolution and alteration of the precursor oxide that develops at low temperatures <75°C will be explained on the basis of previously observed metal oxide interfacial phenomena involving coupled bulk and surface reactions. The nature of the interfacial zone will be discussed with electron transfer and oxygen absorption models that are applicable to oxide growth and instabilities in general.

We have investigated InAsSb nanostructures formed on GaAs during MOCVD. The transition thickness from 2D growth to 3D growth is reduced by the addition of TMSb/Sb4. This is consistent with both an increase in the adatom diffusion length and a reduction in the epilayer/vapor surface energy attributed TMSb/Sb4.

Near-square islands form during sub-monolayer homoepitaxial growth on metal (100) surfaces. Diffusion of these islands after deposition leads to collision of island pairs, typically corner-to-corner creating dumbbell-shaped clusters. Subsequent coalescence (or sintering) recovers a near-square equilibrium shape. This process is mediated by periphery diffusion (PD) and its study can provide detailed insight into the underlying dynamic processes and energetics. Atomistic modeling reveals that the size scaling of the characteristic relaxation time, τ, depends on the detailed energy barriers of various hopping processes that contribute to PD. Simulations without an extra kink or corner rounding barrier for PD reveals τ ∼ L4, while behavior approaching τ ∼ L3 is observed with a significant extra kink rounding barrier for PD. The latter is consistent with experimental observations for Ag/Ag(100) at 300 K.

Self-organized Ag nanodots were deposited on Si(100) by a pulsed laser deposition method. A compact apparatus was specially developed for this purpose with Nd:YAG-laser. Factors dominating size and morphology of the nanodots were examined by systematically varying species and pressure of the gas in the deposition chamber, deposition time, and the target –substrate distance (TSD). Pulse frequency (10Hz), pulse width (8ns) and laser wavelength (266nm) were kept constant. The dot size increased with pressure in the range between 0.005Pa to 1Pa, in Ar gas. At pressures as high as 100Pa, dot size decreased again with slightly different morphology. Increasing deposition time from 3, 5, to 10min brought about an increase in the average dot size from 5±2.1nm, 9±2.4nm, 10±3.0nm, respectively, under the constant Ar pressure, 100Pa. It is particularly to be noted that decreasing TSD from 100mm to 50mm brought about an increase in the dot size from 5±2.1nm to 9±3.3nm at Ar pressure, 100Pa, and deposition time, 3min. We discuss factors making self-organized Ag nanodots, and proposed key values to evaluate homogenize of dots assembly.

Arrays of step-free regions on the surface of silicon have been created either by evaporating atoms from craters[1] or by depositing atoms on mesas[2]. In most cases the maximum extent of the step-free regions is limited by the occurrence of circular pits or islands in the crater or mesa structures. We model the process of step clearing and nucleation of these pits and islands by approximating the initial surface by an array of circular steps whose movement is mediated by adatoms. BCF (Burton-Cabrera-Frank) theory[3] is used to incorporate the effects of surface diffusion, evaporation and the deposition of atoms on the surface. We include the effects of step curvature and step interactions. If the step spacing is large enough, we find that the innermost step moves outwards to create a step-free region; otherwise it moves inward and leads to large scale smoothening of the surface. Pit or island nucleation in the center of the craters or mesas is also included in the model by using classical nucleation theory. We investigate the effect of deposition flux and temperature on the formation of step-free surfaces and compare the results to reported experiments on silicon and to some of our recent work on sapphire.

We report fundamental changes in island nucleation dynamics as the kinetic energy of the constituent particles used for film grown is increased. A hyperthermal energy ion beam-line with precise control over ion kinetic energy was used to grow copper islands on a Cu(100) substrate. Dramatic increases in island densities were observed with increasing kinetic energy from thermal energies to 150 eV. We find that sputter erosion and the formation of adatom-vacancy pairs contribute to this increase. In addition, variations in flux and temperature suggest that the mean-field scaling exponent is sensitive to atomistic mechanisms activated by the ion beam.

Spontaneous lateral composition modulation during semiconductor thin film growth offers a particularly versatile and cost-effective approach to manufacture nanoscale devices. Recent experimental and theoretical studies have revealed that regular lateral composition modulation can be achieved via MBE growth of the so-called short-period superlattices and can be optimized via appropriate control of the global strain, substrate surface, and processing conditions. To characterize this phenomenon, we used synchrotron x-ray scattering to identify the interfacial morphology and laterally modulated composition profile of nearly strain-balanced InAs/AlAs short-period superlattices. Our results were compared with a theoretical model. It is shown that the lateral composition modulation is predominately caused by a vertically correlated morphlogical undulation of the superlattice layers.

Smoothing effect by large gas cluster ion irradiation was studied. Ar cluster ion beams were irradiated on rough Si surface with various ion dosage. 100×100μm2 AFM image was measured for each surface. These AFM images were treated with fast Fourier transform in order to examine the change of surface morphologies with cluster ion irradiation. Power spectra analysis showed that the intensity at each wave number (the inverse number of wavelength) exponentially decreases with ion dose. The relationship between smoothing rate and wave number was derived. The surface smoothing process was modeled with the use of this wave number dependence on decreasing rate. The calculated and the experimental surface profiles are in good agreements. With this model, roughness of cluster-irradiated surface can be calculated from initial surface images.

The optical and mechanical properties of TiO2 film prepared by ion-assisted e-beam evaporation have been examined in this research. Spectroscopic ellipsometry analysis revealed an inhomogeneous behavior in both optical property and growth structure, vertically from substrate to the top surface of the film. This phenomenon was further confirmed with the electron microscopic analyses. The effects of deposition rate, chamber pressure, anode voltage and current on the stress of TiO2 films were also investigated and reported. Further study showed that a structural homogeneous film could be obtained through TiO2-SiO2 co-evaporation.

We developed a chemical-vapor deposition (CVD) apparatus with a 0.5×240 mm2 slit-type nozzle that scans at an area of 240×315 mm2 in the atmosphere. This apparatus forms uniform oxide crystals on substrates through the decomposition process of precursors emitted from the nozzle. In this study, ZnO whiskers were synthesized on a single-crystalline 8-inch wafer of (100)-oriented silicon using this apparatus. Morphological and crystallographic properties of the samples were evaluated using scanning electron microscopy and X-ray diffractometry.

We report crack formation in alumina films grown on Si(100), caused by annealing in a controlled oxidizing ambient. The films were grown in a low-pressure CVD reactor, using aluminium acetylacetonate as precursor. High purity argon and nitrous oxide were employed as carrier and oxidizing gas, respectively. The films were characterized by optical microscopy and SEM/EDAX. The proportion and chemical nature of the heteroatoms, namely C and H, incorporated into the films from the precursor, were characterized by XPS, and FTIR. As-deposited films do not exhibit any cracks, while post-deposition annealing results in cracks. Apart from the delamination of the films, annealing in nitrous oxide ambient leads to an unusual crack geometry, which we term the “railway-track”. These twin cracks are very straight and run parallel to each other for as much as several millimeters. Often, two such linear tracks meet at exactly 90°. Between some of these tracks lie bullet-like structures with very sharp tips, oriented in a specific direction. As cracks are generally activated by residual stress, both thermal and intrinsic, the origins of the stresses that generate these linear cracks are discussed. The redistribution of stress, arising from the removal of C and H during annealing, will also be discussed. An attempt has been made to correlate the formation of cracks with the crystal structure of the film.

Random surface roughness very often can occur during the growth or etching of films under non-equilibrium conditions. Several competing mechanisms such as noise, surface diffusion, and shadowing all play a role in the evolution of surface roughness. However, recent results obtained in many growth and etching processes exhibit an unusual tendency: the morphology is very rough where it is expected to be smooth and vice versa. The origin, we believe, is due to the fact that during the deposition and etching processes the atoms very often do not stick to the surface upon their first strikes. Atoms actually bounce around before all settle on surface sites. This non-unity sticking probability can lead to a very rough surface during etching and a very smooth surface during sputter or chemical vapor deposition that cannot be explained by the conventional mechanisms.

In this study we investigate the nucleation and growth mechanisms of tungsten films processed by focused ion beam (FIB) induced chemical vapor deposition. For our investigation we use a 50 keV Ga+ ion beam focused on the substrate target and tungsten hexacarbonyl (W(CO)6) as precursor gas. Mediated by the substrate the energy of the impinging ions leads to the decomposition of the tungsten hexacarbonyl molecules adsorbed on the substrate into volatile parts and nonvolatile residues forming a metal deposit. Time resolved FIB secondary electron microscope imaging in combination with atomic force microscopy reveal first the formation of isolated nuclei and further their coalescence finally resulting in the formation of a contiguous metal layer. Despite the local impacts of the ion beam within the irradiated area of the substrate the localization of the nucleation spots is neither correlated to the spot centers nor to the scan path of the ion beam. After formation, the nanoscale tungsten nuclei preserve their positions and typical shapes during further deposition. Only after merging the nuclei to a contiguous tungsten layer, a further regime of growth sets on which is characterized by deposition of tungsten on a tungsten surface. In this regime the deposition process is determined by the total ion dose and the average current density the samples are subjected to. In this regime, deposition yields up to 3.5 atoms per incident gallium ion are achieved. The contiguous layer quality is determined by Auger electron analysis. The measured growth data were interpreted by adopting the analytic Ruedenauer Steiger approach mainly incorporating ion current density, precursor gas transformation rate, and ion induced sputtering. As a result, the critical ion current density, where ion sputtering exceeds deposition, was identified by the model. Because the model shows excellent agreement with the measurement it should be suitable for further survey concerning focused ion beam process development.

Chemical-vapor-deposition of titanium tetra-isopropoxide (TTIP) under the atmosphere at low temperature has been conducted. The structure of the obtained films was assessed using Fourier transform infrared spectroscopy, X-ray diffractometry and Raman spectroscopy. These analyses indicated that amorphous TiOxHy films were obtained at gas temperatures in the range of 150–300 °C, and crystalline anatase-TiO2 film was formed at 350 °C. This distinction is accounted for by plausible chemical reactions as follows; the hydroxyl reaction of TTIP below 350 °C promotes the formation of the amorphous TiOxHy. As the temperature goes up to 350 °C, dehydrogenation of the TiOxHy films promotes to form crystalline TiO2. Also the obtained amorphous films were annealed for 10 min under the atmosphere in assessing the transformation proceeding in the solid state. The structural change is shown at 350 °C, indicating that the crystalline phase would be formed via dehydrogenation and polymerization on the surface of the amorphous phase under the atmosphere. The crystal size of the annealed films was evaluated in assessment for the transformation.

The mechanisms of the misfit strain relaxation in heteroepitaxial islands are investigated in two-dimensional molecular dynamics simulations. Stress distributions are analyzed for coherent and dislocated islands. Thermally-activated nucleation of misfit dislocations upon annealing at an elevated temperature and their motion from the edges of the islands towards the positions corresponding to the maximum strain relief is observed and related to the corresponding decrease of the total strain energy of the system. Differences between the predictions of the energy balance and force balance criteria for the appearance of misfit dislocations is discussed. Simulations of an island located at different distances form the edge of a mesa indicate that the energy of the system decreases sharply as the island position shifts toward the edge. These results suggest that there may be a region near the edge of a mesa where nucleation and growth of ordered arrays of islands is favored.

In this research, we have focused on the morphological evolution of a model metal film / silicon substrate system. When aluminum (Al) is physical vapor deposited on (100) oriented single crystal silicon (Si) at 280 °C it grows heteroepitaxially. Crystallographically, the resulting films are a Potts model system with degeneracy two; their topology simulates a polycrystalline grain structure, with the two types of grains enveloping each other in a convoluted, maze-like arrangement. The morphological evolution of the films during annealing was determined via a combination of transmission electron microscopy (TEM) and atomic force microscopy (AFM). Films with thickness' of 100 to 500 nm were annealed in-situ in the TEM from 250 °C to 550 °C, and characterized using a (220) two-beam condition from one of the grain orientations. This yields predominantly white on black images, which are amenable to quantitative image processing techniques. As anticipated, the grain size increased linearly during the first annealing cycle. Also so-called sub-grain boundaries were observed. These low angle boundaries originate during film deposition when arrays of dislocations are introduced in the areas where coalescing islands of the same orientation meet. After cooling and reheating the sub-grain boundaries disappear. This happens because upon cooling, misfit dislocations were introduced into the films to relieve the thermal misfit strain, resulting in a dense array of dislocations at the film / substrate interface. These thermal misfit dislocations interact strongly with pre-existing sub-grain dislocations; this, in effect, heals the microstructure.

Thin films of VO2(B), a metastable polymorph of vanadium dioxide, have been grown on glass by low-pressure metalorganic chemical vapor deposition (MOCVD). The films grown for 90 minutes have atypical microstructure, comprising micrometer-sized, island-like entities made up of numerous small, single-crystalline platelets (≅1 μm) emerging orthogonally from larger ones at the center. Microstructure evolution as a function of deposition time has been examined by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The metastable VO2(B) transforms to the stable rutile (R) phase at 550°C in inert ambient, which on cooling convert reversibly to M phase. Electron microscopy shows that annealing leads to the disintegration of the VO2(B) platelets into small crystallites of the rutile phase VO2(R), although the platelet morphology is retained. The magnitude of the jump in resistance at the semiconductor-to-metal, VO2(M)→VO2(R) phase transition depends on the arrangement of polycrystalline platelets in the films.

The evolution from straight-sided wrinkles to both worm-like and varicose structures has been investigated mainly by atomic force microscopy. The elastic energy variation related to the formation of these two buckling structures has been computed and discussed. It is shown that both transitions are energetically favourable above a longitudinal (along the initial wrinkle axis) critical stress of few GPa in compression, that is of the order of the internal compressive stresses present in the thin films.

Transmission electron microcopy (TEM) in both the parallel illumination and scanning probe mode revealed atomically ordered entities within a 5 to 250 nm range in a IV-VI and a II-VI compound semiconductor quantum dot (QD) system. While the II-VI system was a nominal [001] CdSe/(Mn0.1Zn0.9)Se multilayer structure with the QDs embedded, the IV-VI system nominally consisted of [111] PbSe islands. The comparison of photoluminescence (PL) spectra from the CdSe/(Mn0.1Zn0.9)Se structure with those of a reference structure, that was grown to the same nominal specification under otherwise identical conditions except that no Mn was incorporated into the cladding layers, revealed for the former sample two peaks at approximately 2 and 2.1 eV. We tentatively attribute these two PL peaks to two groups of atomically ordered entities.

The growth front roughness of Ta2O5 amorphous films grown by pulsed plasma d.c. reactive sputtering has been investigated using atomic force microscopy. Film deposition during reactive sputter deposition is explained based on dynamic scaling hypothesis in which both time and space scaling are considered simultaneously. The interface width w increases as a power law with deposition time t, w ∼ tβ, with β = 0.45 ± 0.03. The lateral correlation length ξ grows as ξ ∼ t1/z, with 1/z = 0.61 ± 0.07. The roughness exponent extracted from the slope of height-height correlation analysis is α = 0.79 ± 0.04. The results are similar to that obtained by sputtering of elemental materials, and do not fit to any of the presently known growth models. Monte Carlo simulations were carried out based on a recently developed re-emission model, where incident flux distribution, shadowing, sticking coefficient, and surface diffusion mechanisms were accounted for in the deposition process. An important finding is that sticking coefficient must be less than unity to obtain the observed β value (∼0.45).