Nucleation Of Thin Films Research Articles

Nucleation and growth of Ag films on a quasicrystalline AlPdMn surface

Nucleation and growth of thin films of Ag on the fivefold surface of an ${\mathrm{Al}}_{72}{\mathrm{Pd}}_{19.5}{\mathrm{Mn}}_{8.5}$ icosahedral quasicrystal is studied with scanning-tunneling microscopy. For low coverages, flux-independent island nucleation is observed involving adatom capture at ``traps.'' With increasing coverage, islands start growing vertically, but then spread, and ultimately form hexagonal nanocrystals. These have fcc symmetry and pyramidlike multilayer stacking along the 〈111〉 direction. The constituent hexagonal islands have five different orientations, rotated by 2\ensuremath{\pi}/5, thus reflecting the symmetry of the substrate.

A molecular dynamics study of thin-film formation via molecular cluster beam deposition: effect of incident species

Molecular dynamics simulations are used to study thin-film nucleation and growth through the deposition of molecular cluster beams on diamond surfaces. A reactive, empirical bond-order hydrocarbon potential is used to calculate the forces on the atoms. Beams of ethylene (C 2H 4) molecular clusters, adamantane (C 10H 16) molecules, and fullerene (C 20) molecules are deposited on hydrogen terminated diamond (1 1 1) surfaces at room temperature. These three beams are chosen because of the different chemical bonding in the incident particles––van der Waals interactions in the case of the ethylene molecular clusters, pure sp 3 bonds in the case of the adamantane molecules, and covalent sp 2 bonds with distorted p-orbitals in the case of the fullerene molecules. All three beams are deposited on the surface along either the [ 1 ̄ 1 ̄ 2] direction or the [ 1 ̄ 1 0] direction at incident angles of 0°, 15°, 45° and 60° from the surface normal. Two deposition energies are considered: a total energy of 400 eV/cluster or molecule and a total energy where the momentum normal to the surface is equivalent to an energy of 400 eV/cluster or molecule. The C 20 is found to be the most efficient species at producing an amorphous thin film while the molecular cluster beam of ethylene is the least efficient. Despite the differences in the chemical bonding in the three incident species, the structures of the resultant thin films are predicted to be similar at these energies.

Molecular Dynamics Simulations of Nucleation and Crystallization Processes During Excimer-Laser Annealing of Amorphous Silicon on Glass

AbstractWe have investigated atomistic processes of nucleation and crystallization in excimer-laser annealed thin Si films on glass based on molecular-dynamics (MD) simulations using the Tersoff potential. MD cells composed of up to approximately 50000 Si atoms were heated to produce melted Si, and then melted Si was quenched under various supercooled conditions with or without a temperature gradient and the corresponding nucleation processes were visualized. Lateral growth of thin Si crystalline films was also simulated by embedding a crystalline nano-particle with various crystal surfaces in melted Si. It has been found that the crystal surfaces become predominantly {111} during the lateral growth processes.

Kinetics of Crystal Nucleation and Growth in Thin Films of Amorphous Te Alloys measured by Atomic Force Microscopy

ABSTRACTBoth the crystal nucleation rate and the crystal growth velocity of sputtered amorphous Ag0.055In0.065Sb0.59Te0.29 and Ge4Sb1Te5 thin films used for optical data storage were determined as a function of temperature. Crystals were directly observed using ex-situ atomic force microscopy, and their change in size after each anneal was measured. Between 140°C and 185°C, these materials exhibited similar crystal growth characteristics, but differed in their crystal nucleation characteristics. These observations provide an explanation for the different re-crystallization mechanisms observed upon laser-induced crystallization of amorphous marks.

Pit nucleation in compound semiconductor thin films

ABSTRACTPit nucleation has been observed in a variety of semiconductor thin films. We present a model in which pit nucleation is considered to arise from a near-equilibrium nucleation process in which the adatom concentration plays an important role. Although pits relieve elastic energy more efficiently than islands, pit nucleation is prevented if the adatom concentration is too high. Inhomogeneities in the adatom density on the surface due to three-dimensional islands enhance pit nucleation. Thermodynamic considerations predict several different growth regimes in which pits may nucleate at different stages of growth depending on the materials system and growth conditions. However kinetics must be taken into account to make direct comparisons to experimental observations. These comparisons show good agreement given the uncertainties in quantifying experimental parameters such as the surface energy.

Self-limiting behavior of the grain growth in lead zirconate titanate thin films

During the lateral grain-growth process in lead zirconate titanate (PZT) thin films by selectively nucleated lateral crystallization using PZT seed, it was found that the lateral growth was saturated with the annealing temperature. The saturation of lateral growth was analyzed by the interface energy, which appeared during the crystallization process. The factors affecting the saturation of lateral growth were found to be the interface energy between the perovskite phase and the pyrochlore phase, and the one between the PZT thin film and the bottom Pt electrode. When the ion damage was introduced to the growth-saturated PZT thin films, further lateral growth was observed. Pt bottom electrode thickness was changed to control the interface energy between the PZT thin film and the Pt bottom electrode. PZT grain size increased according to the Pt thickness, because the lattice parameter of Pt films increased with the thickness of the Pt films. The incubation time for nucleation in the PZT thin films increased with the amount of the ion damage on the Pt films.

Hole nucleation in thin diblock copolymer films.

This paper reports an experimental study of a homogeneous nucleation process in the direct space, using an atomic-force microscope. Nucleated patterns are holes in a thin diblock copolymer film. The formation of nuclei from the metastable majority phase is followed either by the dissolution or by the growth of the hole. It is also preceded by the unexpected presence of a bump at the free surface. From the study of the nucleus surface topography at different stages of the evolution, we infer a description of the nucleation mechanism at a molecular level. It involves the existence of ordered metastable states characterized by the presence of compressed internal layers, the formation of pores in the center of the film, and the existence of interfacial flows across these pores. The presence of compressed internal layers was directly demonstrated using Neutron Reflectivity experiments, Our scheme is also consistent with all existing experimental data. After hole nucleation, we identify two distinct growth regimes: the first one is individual and the second one is interactive.

Preparation and Aging Behavior of Chemical‐Solution‐Deposited (Pb(Mg1/3Nb2/3)O3)1‐x–(PbTiO3)x Thin Films without Seeding Layers

The aging behavior of the solid‐solution series (Pb(Mg1/3Nb2/3)O3)1−x–(PbTiO3)x (PMN1−x−PTx) prepared by chemical‐solution deposition without seeding layers was investigated. A strong influence of the rapid thermal annealing step on the film density was determined. The best nucleation and density of the thin films occurred when each deposited layer was separately pyrolyzed and crystallized. The thin‐film microstructure was investigated using scanning electron microscopy. Conventional capacitance‐voltage and hysteresis measurements were performed. For the first time, investigations on the fatigue performance and the leakage current for alternating‐current and direct‐current voltage were executed, which are important for the reliability in device applications.

Molecular dynamics simulation of thin film nucleation through molecular cluster beam deposition: Effect of incident angle

Deposition of organic cluster beams on solid substrates leads to the creation of thin films through rapid chemical reactions, which makes the process suitable for study by molecular dynamics (MD) simulations. In this work, angular effects of molecular organic beam deposition are studied extensively through classical MD simulations. The reactive empirical bond potential parameterized by Brenner is used. The specific system that is examined consists of an ethylene molecular cluster beam that is deposited on a hydrogen-terminated diamond (1 1 1) substrate at room temperature. The beam impacts the substrate along two crystallographic orientations at incident angles of 0°, 15°, 45° and 60° from the surface normal. Two sets of conditions are considered: one where the total incident energy is constant and one where the momentum normal to the surface is constant. The results are seen to depend on the total energy and incident angle and to be independent of crystallographic orientation.

Nucleation in polycrystalline thin films using a preconditioned finite element method

The dynamic response of a 80 nm×400 nm×25 nm Co film with and without polycrystalline grains is calculated. The numerical method combines a finite element scheme for space discretization with a preconditioned backward differentiation method for the time integration of the Landau–Lifshitz–Gilbert equation. The use of proper preconditioning techniques for the backward differentiation formulas increases its efficiency by a factor of 40. The speed up factor compared to the Adams method is more than three orders of magnitude. In the polycrystalline thin film the nucleation of reversed domains occurs throughout the sample at grain boundaries and sharp edges. For the single crystalline film reversal starts at particle ends. Surface roughness does not significantly change the reversal mode but reduces the switching time by 40%.

Influence of heterogeneous surface morphology on analytical signal formation in total reflection x‐ray fluorescence analysis

AbstractThe fundamentals of the influence of heterogeneous surface morphology on the analytical signal formation in total reflection x‐ray fluorescence (TXRF) analysis were developed. The dependence of x‐ray fluorescence line intensity on mechanisms of new phase nucleation and growth on a foreign low‐density substrate (reflector) was considered theoretically. The approaches were tested during the study of surfaces of disc glass–ceramic carbon electrodes electrochemically modified by metal deposition and co‐deposition from aqueous solutions. It was shown that TXRF could be effectively applied for the identification of nucleation and growth mechanisms of metal and alloy thin films. Copyright © 2002 John Wiley & Sons, Ltd.

Rapid biaxial texture development during nucleation of MgO thin films during ion beam-assisted deposition

We propose a mechanism for the nucleation of highly aligned biaxially textured MgO on amorphous Si3N4 during ion beam-assisted deposition. Using transmission electron microscopy, reflection high-energy electron diffraction, energy dispersive x-ray analysis, and ellipsometery, we have observed that highly aligned biaxially textured grains emerge from a “diffraction-amorphous” film when the film thickens from 3.5 to 4.5 nm. Transmission electron microscopy dark-field images also show the onset of rapid grain growth during this same film thickness interval. These results suggest biaxial texturing through aligned solid phase crystallization.

Initial Stage of Amorphous Si and Si0.7Ge0.3 Deposition on SiO2 by Low-Pressure Chemical Vapor Deposition

The initial stage of amorphous Si and deposition on by low-pressure chemical vapor deposition was investigated in the temperature range from 375 to 450°C. Both amorphous Si and layers with a nominal thickness of about 5 nm did not form a continuous layer. Rather, the layers grew by island formation. The results also show that the surface roughness of amorphous Si and films increases with decreasing temperature at a similar nominal film thickness. The formation of islands and the dependence of the surface roughness of amorphous Si and films on deposition temperature are explained on the basis of the nucleation and growth behavior of thin films with respect to the thermodynamic driving force of nucleation and the mechanism of adatom attachment. © 2002 The Electrochemical Society. All rights reserved.

Thin-film nucleation through molecular cluster beam deposition: Comparison of tight-binding and many-body empirical potential molecular dynamics simulations

Molecular dynamics simulations are performed to investigate the chemical products of molecular ethylene-cluster beam deposition on diamond substrates at room temperature. The substrates are hydrogen-terminated diamond (111) surfaces of varying sizes. The computational approach is molecular dynamics simulations with two different methods for determining the forces on the atoms: an empirical reactive empirical bond-order hydrocarbon potential and an order-N nonorthogonal tight-binding method. The results of these two approaches to thin-film nucleation through ethylene-cluster beam deposition are compared and contrasted. The results are used to determine the similarities, differences, advantages, and limitations of these two approaches.

Nucleation and growth of thin (Ba,Sr)TiO3 films in a MOCVD reactor

ABSTRACT(BaxSr1-x)TiO3 thin films were deposited on Pt electrodes in a planetary multi-wafer MOCVD reactor combined with a liquid delivery system. The nucleation behavior and the size of the stable nuclei were investigated by different SPM techniques and by XPS. Characteristic differences were observed between deposition temperatures of 565°C and 655°C, i.e. a homogeneous nucleation of small BST grains on the larger Pt grains (100 − 200 nm in-plane size) at low temperatures and a dominating nucleation at the grain boundaries at high temperatures. Further film growth was investigated for nominal film thickness between 5 and 100 nm and details of the grain structure are revealed by HRTEM, e.g., randomly oriented grains (typical in-plane size 10–20nm) with a high density of twins at 565°C and (100)-oriented defect free grains of slightly increased size at 655°C. As the electrical properties like permittivity and also leakage current depend on film thickness the final discussions of the electrical properties are based on thickness series and evaluated within the phenomenological dead layer model.

Setup for in situ X-ray diffraction studies of thin film growth by magnetron sputtering

A novel method is described for the in situ-investigation of nucleation and growth of thin films during magnetron sputtering. Energy dispersive X-ray diffraction with synchrotron light is used for the structural analysis during film growth. An in situ-magnetron sputtering chamber was constructed and installed at a synchrotron radiation beam line with a bending magnet. The white synchrotron light (1–70 keV) passes the sputtering chamber through Kapton windows and hits one of the substrates on a four-fold sample holder. The diffracted beam, observed under a fixed diffraction angle between 3° and 10°, is energy analyzed by a high purity Ge-detector. The in situ-EDXRD setup is demonstrated for the growth of tin-doped indium oxide (ITO) films prepared by reactive magnetron sputtering from a metallic target.

Real-time spectroscopic ellipsometry studies of the nucleation and grain growth processes in microcrystalline silicon thin films

Real-time spectroscopic ellipsometry (SE) has been applied to investigate the nucleation and grain growth processes in microcrystalline silicon $(\ensuremath{\mu}c\ensuremath{-}\mathrm{S}\mathrm{i}:\mathrm{H})$ thin films deposited by a conventional plasma-enhanced chemical vapor deposition using hydrogen dilution of silane source gas. Real-time SE results revealed the $\ensuremath{\mu}c\ensuremath{-}\mathrm{S}\mathrm{i}:\mathrm{H}$ nucleation from hydrogenated amorphous silicon $(a\ensuremath{-}\mathrm{S}\mathrm{i}:\mathrm{H})$ phase, followed by the coalescence of isolated $\ensuremath{\mu}c\ensuremath{-}\mathrm{S}\mathrm{i}:\mathrm{H}$ grains exposed on growing surfaces. In the $\ensuremath{\mu}c\ensuremath{-}\mathrm{S}\mathrm{i}:\mathrm{H}$ grain growth process, the $\ensuremath{\mu}c\ensuremath{-}\mathrm{S}\mathrm{i}:\mathrm{H}$ shows an enhanced surface roughening. The onset of the $\ensuremath{\mu}c\ensuremath{-}\mathrm{S}\mathrm{i}:\mathrm{H}$ grain growth and the coalescence of $\ensuremath{\mu}c\ensuremath{-}\mathrm{S}\mathrm{i}:\mathrm{H}$ grains were readily characterized by monitoring surface roughness evolution. We found that a $\ensuremath{\mu}c\ensuremath{-}\mathrm{S}\mathrm{i}:\mathrm{H}$ nuclei density increases significantly as the hydrogen dilution ratio $R=([{\mathrm{H}}_{2}]/[{\mathrm{SiH}}_{4}])$ increases. In contrast, a film thickness at which most of the surface is covered with the $\ensuremath{\mu}c\ensuremath{-}\mathrm{S}\mathrm{i}:\mathrm{H},$ gradually reduces with increasing R. The real-time SE results described above showed remarkable agreement with those estimated by transmission electron microscopy and atomic force microscopy. For the $a\ensuremath{-}\mathrm{S}\mathrm{i}:\mathrm{H}/\ensuremath{\mu}c\ensuremath{-}\mathrm{S}\mathrm{i}:\mathrm{H}$ mixed-phase surface formed during the phase transition, however, the SE results showed relatively large errors in the analyses. Such difficulties in the real-time SE analysis for the $\ensuremath{\mu}c\ensuremath{-}\mathrm{S}\mathrm{i}:\mathrm{H}$ thin film are discussed.

SIMULATION OF THE INITIAL GROWTH OF METAL THIN FILMS AT HIGH TEMPERATURE

The atomic processes of nucleation and initial growth of thin films on metal surfaces are simulated by Monte Carlo method,using realistic growth model-Fe on Fe (001) surface and physical parameters.By taking into account the physical processes involved in film growth,such as deposition,diffusion,nucleation,growth,evaporation,edge diffusion and coalescence,the morphology and quantitative characteristies of thin film growth are obtained.The details of thin film growth at high substrate temperatures,such as the change of island density and growth rate with temperature and coverage,are obtained by making statistical counting during the growth processes,which are difficult to access directly in real experiments.

Dislocation Nucleation and Propagation During Deposition of Cubic Metal Thin Films

ABSTRACTIn this paper we present three-dimensional molecular dynamics simulations of dislocation nucleation and propagation during thin film deposition. Aiming to identify mechanisms of dislocation nucleation in polycrystalline thin films, we choose the film material to be the same as the substrate – which is stressed. Tungsten and aluminum are taken as representatives of BCC and FCC metals, respectively, in the molecular dynamics simulations. Our studies show that both glissile and sessile dislocations are nucleated during the deposition, and surface steps are preferential nucleation sites of dislocations. Further, the results indicate that dislocations nucleated on slip systems with large Schmid factors more likely survive and propagate into the film. When a glissile dislocation is nucleated, it propagates much faster horizontally than vertically into the film. The mechanisms and criteria of dislocation nucleation are essential to the implementation of the atomistic simulator ADEPT.

Comparison of growth of hydrocarbon thin films by molecular-beam and cluster-beam deposition: atomistic simulations

Molecular dynamics simulations have been performed to study the difference in the growth of polyethylene thin films via neutral ethylene molecular-beam and cluster-beam depositions. The collisions occurred at incident energies of 25 and 50 eV/molecule on a hydrogen-terminated diamond (111) surface. A many-body empirical bond order potential for hydrocarbons was used to model the interatomic interactions in the system that allowed for bonds to be broken and formed over the course of the simulations. In contrast to the expectations that the cluster beam would provide significantly enhanced thin-film nucleation, the results indicate few differences in thin-film adhesion that occurs as a result of the deposition. The role of substrate temperature on thin-film nucleation is also investigated and found to be negligible over a 1200° range. Finally, structural relaxation of thin-film fragments is investigated through energy minimization with AM1. The structures of the fragments are found to change slightly from the relaxed structures predicted in the molecular dynamics simulations.