Stages Of Thin Film Growth Research Articles

Amorphous-to-crystalline transition during the early stages of thin film growth of Cr on SiO2

The growth of sputter-deposited Cr thin films on amorphous SiO2 during the early stages was studied using transmission electron microscopy. Amorphous three-dimensional islands were first formed, and then they grew with continuously increasing density and slowly increasing size as the deposition proceeded. When these islands began to coalesce at a nominal film thickness of 2.3–3.0 nm, they abruptly crystallized into randomly oriented crystalline nuclei. The depth profile analysis by x-ray photoelectron spectroscopy indicates the existence of interfacial Cr–O interactions. After excluding the possibilities of kinetic limitation and interfacial mixing, a thermodynamic model was employed to explain the size-dependent amorphous-to-crystalline transition. Our results suggest that the interfacial-interaction-induced strain relaxation at island/substrate interfaces might result in the thermodynamic stabilization of substrate-supported amorphous islands below a critical size.

Reflection high-energy electron loss spectroscopy (RHEELS): a new approach in the investigation of epitaxial thin film growth by reflection high-energy electron diffraction (RHEED)

Reflection high-energy electron diffraction (RHEED) is attractive as a technique for structural surface determination. The RHEED facility was equipped with a novel energy analyser permitting to measure energy loss spectra of diffracted high-energy electrons (RHEELS). The combination of RHEED and RHEELS is especially useful in the early stages of thin film growth when the intensity of the diffraction pattern is too low. The use of RHEED and RHEELS is demonstrated by the examples of the heteroepitaxial growth of ultrathin Pd layers on (0 0 0 1) alumina single-crystalline and natural (1 1 0) tin dioxide (cassiterite) substrate surfaces. The particle structure and epitaxial orientation was controlled by RHEED. It was shown that Pd formed three-dimensional clusters with the Pd (1 1 1) plane parallel to the substrate surface. Two different growth modes of Pd overlayers were found according to the nature of the substrate surface. The Pd surface plasmon peaks were found at rather low energy of 5 eV. It is probably a consequence of the very small size of Pd particles.

Structure of phthalocyanine overlayers on the [formula omitted] surfaces of InSb and InAs

The structure of free-base phthalocyanine (H 2Pc) and copper phthalocyanine (CuPc) overlayers deposited on the indium-terminated InSb(1 0 0) and InAs(1 0 0) (4×2)/c(8×2) reconstructed surfaces have been studied by low-energy electron diffraction and van der Waals (vdW) intermolecular interaction energy calculations. The diffraction pattern for H 2Pc grown on InSb(1 0 0) is a superposition of a (3×3) and (√10×√10) R±18.4° structure, whilst no ordered structure is formed when H 2Pc is grown on InAs(1 0 0). In contrast, CuPc films exhibit a (3×3) structure on InSb(1 0 0) and a (√10×√10) R±18.4° structure on InAs(1 0 0). These differences can be rationalised by the vdW intermolecular interaction energy calculations of the quadratic unit cells of H 2Pc and CuPc. The results show that the lattice structure during the initial stages of thin film growth is influenced strongly by the intermolecular interaction energy of their unit cells.

Study on the early stage of thin film growth in pulsed beam deposition by kinetic Monte Carlo simulation

In this study a pulse beam (PB) deposition model based on a square lattice is proposed and is used to simulate the process of thin film growth with the kinetic Monte Carlo method. The influence of frequency and duration of pulse on the nucleation, aggregation, and morphology of thin film growth in the early stage is investigated and discussed. The simulation results show that the morphology, island-size distribution, and dynamics behavior of island growth in PB deposition are different from that in DC deposition when their average deposition rates are same. With the increase of transient deposition rate during the pulse activation, the island-size distribution and morphology lose the characteristics of the i=1 model. Due to the high transient deposition rate during the pulse activation, PB deposition promotes nucleation and suppresses the growth of islands and increases the island density. The atomistic mechanism of thin film growth in pulse beam deposition is also discussed.

Nucleation and initial growth of platinum islands by plasma sputter deposition

The nucleation and islands growth of platinum have been followed from an early stage through to complete substrate coverage. Thus, this study of initial stages of thin film growth has allowed to improve the understanding of growth mechanisms and to control the final nanomaterials structure. In the presented deposition method, the metal atom source is a negatively biased metal wire submitted to the bombardment of ions created in HF plasma. The originality of this plasma sputtering technique is that in addition to the metal atom flux, the substrate surface is submitted to a high flux of low energy ions, inducing a high atomic surface mobility and modifying the growth mode with respect to conventional deposition techniques (magnetron sputtering or evaporation). Platinum deposits have been investigated by ex situ characterisation techniques: grazing incidence-small angle X-ray scattering (GISAXS) and X-ray diffraction (GIXD) in conjunction with transmission electron microscopy (TEM). Using morphological parameters as coverage rate, islands number density and islands size, different mechanisms (scale laws, islands mobility, coalescence, etc.) governing the growth are described vs. Ar ion and Pt atom energies and fluxes.

Nanostructure initiation during the early stages of thin film growth

It is shown how the combination of atomic deposition and nonlinear diffusion may lead, below a critical temperature, to the growth of nonuniform layers on a substrate. The dynamics of such a system is of the Cahn–Hilliard type, supplemented by reaction terms representing adsorption–desorption processes. The instability of uniform layers leads to the formation of nanostructures which correspond to regular spatial variations of substrate coverage. Patterns wavelengths and symmetries are selected by the dynamics and not by variational arguments. For increasing coverage, one should observe a succession of structures going from hexagonal arrays of high coverage dots, to stripes and finally to hexagonal arrays of low coverage dots. At low deposition rates instability may occur for certain time intervals only, and induce transient structures which may provide templates for further structure development.

Atomistic processes and the strain distribution in the early stages of thin film growth

Structural relaxations in small Co islands on the Cu(001) surface are investigated performing atomistic calculations. We demonstrate that the strain relief at the metal interface in the early stages of heteroepitaxy is more complicated than suggested by simple considerations based on the small mismatch between the Co and Cu bulk metals. We found that the strain distribution in the surface region near the islands varies strongly on an atomic scale. The effect of strain on the shape of the Co islands is revealed. Diffusion on the top of strained islands and edge diffusion are considered.

“Magic” Nanostructures During the Early Stage of Thin Film Growth

ABSTRACTThe behaviors of thin indium films in the early stage of growth are studied in situ by a novel ultra-sensitive thin film scanning calorimetry technique. The films consist of ensembles of self-assembled indium nanostructures whose melting temperatures are strongly influenced by size. We experimentally determine the relationship between a nanostructure's radius and its melting point by combining the measured caloric results with nanostructure size distributions obtained from TEM. The results show a linear melting point depression. Moreover, by looking at the fine structures of these caloric curves, we found the discrete nature of nanostructures during the early stage of thin film growth. The measured heat capacity values show several local maxima at certain temperatures. This suggests that preferred energy states exist among these supported nanostructures on amorphous surfaces. These local maxima are related to each other by increments of one monolayer of indium atoms. These findings could be extended from the magic numbers observed previously in cluster beams studies.

EFFECT OF LOW-ENERGY DEPOSITION PARTICLES ON INITIAL STAGE OF THIN FILM

The effect of low-energy deposition particles on the initial stage of thin film growth is studied by Monte Carlo simulation in this paper. The energy range of deposition particles is from 0 to 0.7eV. Three processes are considered: atom deposition, adatom diffusion and re evaporation. The effect of nearest adatoms and next near adatoms is also considered. The results show that the low-energy ion irradiation strongly affects the island film growth process at low temperature. Morphologies and size distributions of islands have significantly changed with the increase of incident ion energy.

Stress and microstructure evolution during initial growth of Pt on amorphous substrates

An understanding of the relationship between stress and the corresponding microstructure at various stages of thin film growth might allow prediction and control of both microstructure and film stress during thin film deposition. In the present study, a combination of in situ curvature measurement and ex situ microstructural characterization was used to make correlations between stress and microstructure for the growth of Pt on SiO2. Plan view transmission electron micrographs of Pt films with average thicknesses ranging from 3 to 35 Å show the evolution of microstructure from isolated islands to a coalesced film, in agreement with models for stress behavior during the early stages of film growth. Quantitative measurements of grain size, island size, and areal fraction covered are extracted from these micrographs and, in conjunction with an island coalescence model, used to calculate the magnitude of the tensile stresses generated during coalescence. The predicted curvature is shown to compare favorably with the measured stresses.

Discrete periodic melting point observations for nanostructure ensembles

We report a study of the thermodynamic properties of indium clusters on a SiN (x) surface during the early stages of thin film growth using a sensitive nanocalorimetry technique. The measurements reveal the presence of abnormal discontinuities in the heat of melting below 100 degrees C. These discontinuities, for which temperature separation corresponds to a spatial periodicity equal to the thickness of an indium monolayer, are found to be related to the atomic "magic numbers," i.e., the number of atoms necessary to form a complete shell of atoms at particle surface.

Influence of microstructure of substrate surface on early stage of thin film growth

The early stage of thin film growing is studied by a Monte Carlo simulation (MCS). We focus on the effect of the microstructure of the substrate surface (lattice structure and surface defect) at different substrate temperature. The results illustrate that the surface microstructure affects strongly the film morphology with increasing substrate temperature. With increasing temperature, the growth of island film goes through fractal, dendritic and compact growth processes. At high temperature, the island geometry shape resembles the substrate lattice structure. There is a temperature region in which the island film transforms from fractal-to-compact growth, 310–400 K for triangular lattice substrate and about 250–390 K for square lattice substrate. A surface factor is introduced to represent the effect of a non-ideal surface, changing this factor, different island morphologies can be obtained at the same temperature.

Simulation of fractal growth of thin films at low temperature

Fractal growth of thin films at low temperature (50–175 K) is simulated by Monte Carlo method. It is shown that the thin film growth is quite different from the diffusion-limited aggregation (DLA) model when the coverage is larger than 0.1 ML. The average branch width of clusters increases with increasing temperature and it usually larger than the branch width (1.9 atom) in the classic DLA model. The average fractal dimension of clusters increases also with increasing coverage while the fractal dimension of DLA model remains constant. This difference comes from the weak screening effect during the late stage of thin film growth. The relationship between the saturation island number ns and deposition interval Δt is described in a power law: ns ∝ Δtγ, where γ = −0.332 is very close to the theoretical value -1/3 of rate equations from nucleation theory.

A Model for Calculating Substrate Curvature During Coalescence of PT Islands on an Amorphous Substrate

AbstractPrevious work using in-situ curvature measurement has shown a correlation between stress and microstructure during the early stages of thin film growth. The model presented here can be used to predict the curvature change of the substrate during part of this growth process. Curvature, and thus film stress, is measured in-situ during growth of sputter-deposited Pt on amorphous substrates. The average film stress is observed to be slightly compressive initially, followed by a change towards a tensile maximum, after which the stress becomes compressive again. Plan view TEM micrographs of Pt films of thicknesses up to 35 Å show the evolution of microstructure from isolated islands to a coalesced film. This evidence suggests that the tensile regime is due to island coalescence. The model calculates the curvature induced in a substrate during the tensile excursion associated with island coalescence, where discontinuous islands are modeled as a series of cracks in an otherwise continuous film. Quantitative measurements of island size and areal fraction covered are extracted from the TEM micrographs and used to predict the curvature during coalescence. The predicted stresses are shown to compare favorably with the measured stresses.

Fractal Analysis of Island Structures of Al Thin Films

Micro-island-structures with a diameter in a sub-micron range obtained in the initial stage of thin film growth are interesting to modify surface morphology or to vary surface area of micro devices. In such applications, the size and similarity of islands are thought to be important. In this study, Al micro islands on the Ti underlayer surface obtained by magnetron sputtering have been estimated by a fractal analysis method to estimate their statistical similarity by using an atomic force microscopy (AFM) as a function of Al amount deposited. In relation to this. surface characteristic factors such as average roughness, average diameter, bearing ratio have been estimated by using surface topology data obtained by AFM. The results show that the fractal dimension varies from about 2 to 3 as a deposited Al amount increased, showing the growth mode changed from two-dimensional to three-dimensional. An island structure with a similar topographical shape was obtained at a range of At amounts, yielding fractal dimensions of about 1.9 to 2.2.

Simulation of the early stages of thin film growth

To gain a better understanding of the silicon oxidation process, we perform numerical simulation of thermal thin-film growth. It is shown that the oxidation rate in the early stages of growth is governed by two processes: the rapid initial formation of the oxidation front and its subsequent diffusion. The resulting oxidation rate provides a rather good description of the experimental data with the minimum number of variable parameters, suggesting that the effect of external parameters (such as temperature and pressure) can be explained in terms of scaling concepts. The results of the simulation are also in agreement with the fitting of experimental data to a power law (where is the measured film thickness and t the oxidation time) predicted by a simple model for thin film growth.

Polymerization via Cluster−Solid Surface Impacts: Molecular Dynamics Simulations

Molecular dynamics simulations of collisions between simple organic molecular clusters and a nonrigid, hydrogen-terminated diamond (111) surface have been performed to study the chemical reactions that occur within the clusters and between the cluster and the surface as a result of impact. A second-generation version of the reactive empirical bond order potential for hydrocarbons developed by Brenner, which has been modified to include long-range van der Waals interactions, is used in the simulations. The velocities considered are in the hyperthermal region and are comparable to those that result in shock-induced chemistry in energetic materials and that occur between particles and solid surfaces in interstellar space. The outcome of the scattering event is monitored as the reactivity of the molecular cluster is varied, and the dependence of the chemistry on the incident cluster velocity and the position of the reacting molecules within the cluster is examined. We find that polymerization reactions occur when the incident cluster velocity corresponds to an external kinetic energy that is within 3 eV/molecule of the binding energy of an individual cluster molecule. Following impact, some of the chemical products chemisorb to the surface in the initial stages of thin film growth, but the exact nature of the thin film is not clear.

Initial Stages of Thin Film Growth in the Presence of Island-Edge Barriers

A model of submonolayer thin film growth is studied, where the attachment of atoms to island edges is hindered by an energy barrier. A novel behavior of the density of islands, N_s, is predicted as a function of flux F and temperature T. For example, N_s scales as F^X with X=2i^*/(i^*+3), where i^* is the critical island size, in contrast with the standard result X=i^*/(i^*+2). The theory is applicable to surfactant mediated growth and chemical vapor deposition. It explains recent experiments, which are inconsistent with the standard theory.

Modelling of the particle size distribution function in the nucleation and early stages of thin film growth

The nucleation and early stages of thin film growth on solid surfaces has been modelled through the rate equation approach at submonolayer coverages. The formation of stable clusters implies adsorption, nucleation and growth processes to occur at the substrate surface. The closure of the system of differential equations is achieved using the growth law of the nucleus. The kinetics, solved numerically, gives the time dependence of the surface coverages of free-monomers, unstable and stable clusters. The particle size distribution function is eventually obtained by the nucleation kinetics through the microscopic growth law of the islands. Preliminary results, at room temperature, are reported for the cases of two dimensional stable dimers and trimers in the total condensation regime. At a given value of the maximum surface coverage the effect of the monomer flux at the substrate surface, on the particle size distribution function, has been also studied. Experimental data on the Pt deposition at the Al 2O 3 NiAl(110) substrate have been analyzed according to the model and the activation energy for monomers diffusion at the oxide surface estimated on the basis of scaling laws.

Modeling of the 2-D Particle Size Distribution Function in the Early Stage of Thin Film Growth

Modeling of the 2-D Particle Size Distribution Function in the Early Stage of Thin Film Growth