Growth Mechanism Of Thin Films Research Articles

Qualitative analysis of growth mechanism of polycrystalline InAs thin films grown by molecular beam epitaxy

The mechanism of surfaces/interfaces and precise control of growth morphology is a key parameter for any specific device application. Herein, we report on a qualitative growth study of molecular beam epitaxy-grown polycrystalline InAs thin films on a lattice-mismatched Si(1 0 0) substrate using atomic force microscopy. The height-height correlation function (HHCF) and power spectral density function (PSDF) were employed to analyze the surface structures. Clear oscillatory behavior in the HHCF for sufficiently larger lateral distances suggests a mound-like morphology, which was confirmed by the existence of a characteristic frequency peak in the PSDF. The growth mechanism is described qualitatively by the Schwoebel barrier (roughening) effect coupled with the Mullins diffusion model (smoothing effect).

Method to reduce the formation of crystallites in ZnO nanorod thin-films grown via ultra-fast microwave heating

This paper discusses the nucleation and growth mechanisms of ZnO nanorod thin-films and larger sized crystallites that form within the solution and on surfaces during an ultra-fast microwave heating growth process. In particular, the work focusses on the elimination of crystallites as this is necessary to improve thin-film uniformity and to prevent electrical short circuits between electrodes in device applications. High microwave power during the early stages of ZnO deposition was found to be a key factor in the formation of unwanted crystallites on substrate surfaces. Once formed, the crystallites, grow at a much faster rate than the nanorods and quickly dominate the thin-film structure. A new two-step microwave heating method was developed that eliminates the onset of crystallite formation, allowing the deposition of large-area nanorod thin-films that are free from crystallites. A dissolution-recrystallization mechanism is proposed to explain why this procedure is successful and we demonstrate the importance of the work in the fabrication of low-cost memristor devices.

The effect of thickness on optical, structural and growth mechanism of ZnO thin film prepared by magnetron sputtering

In this contribution we discuss the structural, morphological and optical properties of ZnO thin films deposited on glass substrates by radio frequency magnetron sputtering technique. Our results indicate that an increase in deposition time leads to a change in the film growth mechanism. Three different growth regimes can be observed when the deposition time changes. Islands initially start to nucleate and grow into rough and highly stressed films. Increasing the surface population leads to island coalescence compatible with a planar architecture, where the stress is relieved, and the roughness is minimized. Longer still deposition times induce the growth of columnar structures. The increase in deposition time brings about a stress relaxation and grain growth together with a reduction of the texture coefficient, c-lattice contraction and an increase of band gap values.

Six complexing agents and their effects on optical, structural, morphological and photoluminescence properties of lead sulphide thin films prepared by chemical route

Lead sulphide (PbS) nanocrystalline thin films were deposited on silica glass substrate by chemical bath deposition method at a bath temperature of 70 °C from six different complexing agents. Different characterization techniques were employed to investigate the effect of applying various complexing agents on the growth mechanism and physical properties of PbS thin films. The XRD results revealed that all the deposited thin films shows a face centered cubic crystal structure however, the preferred orientations of the crystallites varied along the (111) and (200) planes with complexing agents. It was also observed that the complexing agents had a strong influence on the average crystalline size, microstrain and dislocation density of the PbS thin films. The EDX study confirmed that complexing agents had a noticeable effect on the stoichiometry of PbS thin films. The optical absorption spectroscopy study revealed that the optical band gap of the PbS thin films found in the range of 0.77–1.34 eV. The room temperature photoluminescence study verified that irrespective of complexing agents all the deposited thin films experienced emission at 761 nm. Raman studies showed a strong peak around 134 cm−1 irrespective of complexing agents.

Effect of Ascorbic Acid Additions on the Mechanism Underlying the Growth of Nanostructured PbSe Films via Hydrochemical Deposition

The effect of ascorbic acid additions on the growth mechanism of thin PbSe films produced by hydrochemical deposition has been studied by atomic force microscopy (AFM). A fractal analysis of AFM images of the lead selenide films has shown that their formation follows the “cluster–particle” aggregation mechanism. The fractal dimension assessed by the box-counting method is 2.26 at an average grain size of ~150 nm. From the transmission spectra of the films grown at deposition times from 20 to 120 min, we have evaluated their optical band gap, which has been shown to decrease from 0.595 to 0.53 eV with increasing deposition time. These values are attributable to the manifestation of quantum size effects in the grown PbSe films.

Atomic layer deposition of copper thin film and feasibility of deposition on inner walls of waveguides

Copper thin films were deposited by plasma-enhanced atomic layer deposition at low temperature, using copper(I)-N,N′-di-sec-butylacetamidinate as a precursor and hydrogen as a reductive gas. The influence of temperature, plasma power, mode of plasma, and pulse time, on the deposition rate of copper thin film, the purity of the film and the step coverage were studied. The feasibility of copper film deposition on the inner wall of a carbon fibre reinforced plastic waveguide with high aspect ratio was also studied. The morphology and composition of the thin film were studied by atomic force microscopy and x-ray photoelectron spectroscopy, respectively. The square resistance of the thin film was also tested by a four-probe technique. On the basis of on-line diagnosis, a growth mechanism of copper thin film was put forward, and it was considered that surface functional group played an important role in the process of nucleation and in determining the properties of thin films. A high density of plasma and high free-radical content were helpful for the deposition of copper thin films.

High cubic phase purity and growth mechanism of cubic InN thin-films by Migration Enhanced Epitaxy

Metastable cubic InN is a promising semiconductor for developing optoelectronic, photovoltaic and electronic devices. The suitable application of the material requires a high crystalline quality and a high cubic phase purity. For this reason, it is important to identify the growth mechanism of both the cubic phase and the structural defects, as well as to quantify the cubic phase purity. In this work, we determine and quantify the cubic phase purity in c-InN samples grown by Migration Enhance Epitaxy (MEE) using Raman spectroscopy. We found, the LO and TO phonon modes attributed to the cubic phase of InN at 589 and 462cm-1, respectively. The hexagonal phase inclusions were also identified with the E2 mode observed at 488cm-1. The quantification of the cubic phase purity was performed employing a model that takes into account the intensities of the LO and E2 modes of the Raman spectra in a depth profile. The highest cubic phase purity obtained was 93.7% for a sample grown at 510°C. We also analyzed the growth mechanism of c-InN by transmission electron microscopy (TEM), finding the cubic phase, the characteristic planar defects and a small hexagonal inclusion (h-InN). The characteristic planar defects in the samples are the stacking faults (SF). We quantified the SF density using the cross section TEM images. The lowest density was 3.27×105cm-1 for the sample grown at 510°C. Additionally, the high cubic phase purity in the c-InN samples was identified in a phase map obtained by Precession Electron Diffraction.

Growth dynamics of copper thin film deposited by soft-landing of size selected nanoclusters

We investigate surface kinetic roughening of copper films grown on Si(1 0 0) substrates at room temperature by means of atomic force microscopy study. Films were deposited at various durations by soft landing of size selected (~3 nm) nanoclusters using a state of the art nanocluster deposition system. The film growth exhibits two growth regimes with a crossover time of 40 min. In the first regime, surface morphologies show bimodal distribution and surface roughness shows a linear increase with growth exponent β = 0.14 ± 0.02. In the second regime, the height distribution becomes Gaussian and surface roughness shows a steep rise with high β value 0.83 ± 0.45. On the other hand, the roughness exponent α ranges from 0.68 ± 0.03 to 0.84 ± 0.01 for low to high deposition regimes. Estimated scaling exponent suggests the diffusion of clusters on substrate surface and shadowing effect play dominant role in growth mechanism of the nanostructured thin film.

Growth Mechanism of ZnO Thin Films Grown by Spray Pyrolysis Using Diethylzinc Solution

Non‐doped ZnO thin films are deposited on glass by spray pyrolysis using Diethylzinc diluted with diisopropyl ether. The droplet impacts are observed and the structural properties of films are studied as deposition temperature dependence. The shape of a droplet impacts changes from a hemisphere to a flat plane with increasing the deposition temperature. The images of cross sectional transmittance electron microscopy show granular non‐crystalline for RT (room temperature) sample and columnar polycrystalline for 150 °C sample as shown on the right‐side. The growth mechanism of ZnO thin films is discussed by considering the relationship between the shape of droplet impacts and the morphology of the deposited films. Also, the presence of the crystal formed by precursor is suggested for the films deposited at lower temperature.

Morphology improvements in CdSe thin films: A realization through mechanical agitation and incubation period

Albeit neglected, the subsidiary deposition parameters of mechanical agitation and incubation period affect the growth mechanism and quality of thin films. Therefore, the secondary parameters of mechanical agitation and incubation period were studied systematically for cadmium selenide thin films. As-grown CdSe thin films revealed independence of crystal structure on the secondary growth parameters. A detailed study on surface morphology leads to an observation of globular crystallites formation. The observed microstructural details were supported by atomic force microscopy. Advanced techniques based on Sobel transformation, angular spectrum, and electrostatic force microscopy were also employed in assessing the surface topographic details. The as-deposited CdSe thin films showed semiconductor nature with a direct bandgap of ≈1.75 eV. The d.c. electrical conductivity ≈10−6 (Ω cm)−1 was observed. Changes in the electrical conduction and bandgap were attributed to the topographical amendments.

Ex-situ atomic force microscopy on the growth mode of SrRuO3 epitaxial thin film

The functional properties of devices based on perovskite oxides depend strongly on the growth modes that dramatically affect surface morphology and microstructure of the hetero-structured thin films. To achieve atomically flat surface morphology, which is usually a necessity for the high quality devices, understanding of the growth mechanism of heteroepitaxial thin film is indispensable. In this study, we explore heteroepitaxial growth kinetics of the SrRuO3 using intermittent growth scheme of pulsed laser epitaxy and ex-situ atomic force microscopy. Two significant variations in surface roughness during deposition of the first unit cell layer were observed from atomic force microscopy indicating the possible formation of the half unit cell of the SrRuO3 before the complete formation of the first unit cell. In addition, layer-by-layer growth mode dominated during the first two unit cell layer deposition of the SrRuO3 thin film. Our observation provides underlying growth mechanism of the heteroepitaxial SrRuO3 thin film on the SrTiO3 substrate during the initial growth of the thin film.

The growth mechanism of VO2 multilayer thin films with high thermochromic performance prepared by RTA in air

In this paper, the multilayer thin films with SiNx/NiCr/NiCrOx/VO2/NiCrOx/NiCr/SiNx structure were prepared by reactive magnetron sputtering at room temperature and subsequently rapid thermal annealing (RTA) in air. The effects of annealing temperature on the microstructure and thermocheromic performance of the VO2 multilayer thin films were systemacially investigated by UV–Vis-NIR, XRD, SEM, XPS and TEM. The results showed that the crystalline VO2 multilayer thin films can be obtained as the temperature rose from room temperature to 301 °C within 6 s, and the high thermochromic performance with solar modulation (∆Tsol) of 17.2%, luminous transmittance (Tlum) of 26.9% and phase transition temperature (Tc) of 60 °C can be acquired as the temperature rose from room temperature to 571 °C within 10 s, which indicates the VO2 multilayer thin films show the good antioxidation. Based on growth mechanism of VO2 multilayer thin films, it can be found that the atomic diffusion may form crystal nucleation and induce the rapid crystallization of VO2 thin film at low temperature, the drastic diffusion reaction results in the degeneration of crystallinity and performance of VO2 film with increasing temperature. Finally, the unbalance of interfacial stress lead to the rupture of the films, and the VO2 was completely oxidized into V2O5. The exploration of the growth mechanism provides the basis for the optimization of the film structure and annealing parameters, so as to promote the practical application of VO2 multilayer thin films with high thermochromic performance.

Water-Soluble Epitaxial NaCl Thin Film for Fabrication of Flexible Devices

We studied growth mechanisms of water-soluble NaCl thin films on single crystal substrates. Epitaxial growth of NaCl(100) on Si(100) and domain-matched growth of NaCl(111) on c-sapphire were obtained at thicknesses below 100 nm even at room temperature from low lattice mismatches in both cases. NaCl thin film, which demonstrates high solubility selectivity for water, was successfully applied as a water-soluble sacrificial layer for fabrication of several functional materials, such as WO3 nano-helix and Sn doped In2O3 nano-branches.

Structural evolution and growth mechanisms of RF-magnetron sputter-deposited hydroxyapatite thin films on the basis of unified principles

The structural features of RF-magnetron sputter-deposited hydroxyapatite (HA) coatings are investigated in order to reveal the effect of the working gas composition and the sample position of the substrate relative to the target erosion zone. The film properties were observed to change as a result of bombardment with energetic ions. XRD analysis of the coated substrates indicates that with the increase of the ion-to-atom ratio, the fiber texture changes from a mixed (112¯2)+(0002)over (0002) orientation, finally reaching a (303¯0) out-of-plane orientation at high ion-to-atom ratios. TEM reveals that the microstructure of the HA coating consists of columnar grains and differs with the coating texture. The contribution of Ji/Ja to the development of microstructure and texture of the HA coating is schematically represented and discussed. The obtained results may contribute substantially to the progress of research into the development of HA coatings with tailored properties, and these coatings may be applied on the surfaces of metal implants used in bone surgery.

Scaling behavior and morphology evolution of CH3NH3PbI3 perovskite thin films grown by thermal evaporation

The growth dynamics of CH3NH3PbI3 (MAPbI3) perovskite thin films, deposited by thermal evaporation, has been investigated by atomic force microscope and height–height correlation function analysis. The unstable scaling behavior of initial perovskite films exhibiting the growth of islands, resulting in rougher film formation has been observed. After the formation of continuous film, the roughening has been characterized by analyzing the scaling exponent α ~ 0.70, growth exponent β = 0.79 ± 0.057, 1/z = 0.78 ± 0.038, and 2D fast Fourier transform. Anomalous scaling behavior of the MAPbI3 thin films and the formation of the rapid surface roughening are discovered. It is demonstrated that step-edge barrier induced mound growth may play the dominate role in the growth mechanism of MAPbI3 thin films on Si substrates. Further, the growth behavior of MAPbI3 film on ITO substrates is investigated as a comparison, and it reveals that the growth of MAPbI3 thin films is largely affected by the initial substrates underneath the growing films.

Computational Design and Sensitivity Analysis of Non-Aqueous Lithium O2 Batteries

In this study, a gradient-based optimization algorithm is used for the computational design and optimization of a non-aqueous lithium-O2 battery. The sensitivity analysis and numerical optimization capabilities are appended to the multiscale framework previously developed at LRCS for the discharge behavior of this type of batteries. The transport of oxygen in the porous cathode is modeled using Fick’s law at the continuum scale, by assuming isothermal conditions. A micro-scale model predicting the discharge product morphology is coupled to the continuum one. The final discharge product is assumed to form, through both the surface limited thin film growth mechanism and the solution phase reaction mechanism. The cathode microstructure in the model is based on experimentally measured PSD (pore size distribution). A detailed reaction mechanism considering the microstructural properties of the cathode, the surface limited reaction, surface thin film growth and solution phase reaction is used. The sensitivity analysis for the Lithium-O2 cell is performed using the finite difference approach. Sensitivity derivatives are used to identify the variables that have the most significant impact on design performance of the battery. This information is helpful prior to an optimization study as it can be used to remove design parameters that do not strongly influence. Design variables investigated are the O2diffusion coefficient, the cathode porosity, temperature, separator porosity and the cathode thickness. The cell performance is optimized and improved using a quasi-Newton algorithm. In the quasi-Newton algorithm, sensitivity derivatives are utilized in determining a search direction that maximizes a cost function representing the cell capacity. This work provides a comprehensive receipt on the implementation of efficient algorithms devoted to the predictions of optimized cell designs. Design guidelines arising from the computational results are discussed from an engineering perspective.

Growth Mechanism of Copper Oxide Fabricaticated by Potentiostatic Electrodeposition Method

This experiment is about fabrication of n-type Cu2O thin film on fluorine doped thin oxide (FTO) glass by using copper acetate based solution through potentiostaticelectrodeposition. A range of deposition time was carried out from 20 to 40 minutes and the results were obtained. The other parameters such as potential deposition, bath temperature and pH value of solution were kept constant for-0.125Vvs Ag/AgCl, 60 °C and pH 6.3, respectively. It was found that the optimum deposition time for growth mechanism of n-type Cu2O thin film was 30 minutes. Structural, morphologicaland optical properties were characterized by using X-ray diffraction (XRD), Field Emission Scanning Electron Microscope (FE-SEM), and Ultraviolet and visible Absorption Spectroscopy (UV-Vis), respectively. The successfully fabrication of n-Cu2O was confirmed using PEC measurement result.

Growth behavior of Bi2Te3and Sb2Te3thin films on graphene substrate grown by plasma-enhanced chemical vapor deposition

A comparative study of the substrate effect on the growth mechanism of chalcogenide Bi2Te3 and Sb2Te3 thin films was carried out. Obvious microstructural discrepancy in both the as-deposited Bi2Te3 and Sb2Te3 thin films was observed when grown on graphene or SiO2/Si substrate. Bi2Te3 and Sb2Te3 thin films deposited on the graphene substrate were observed to be grown epitaxially along c-axis and show very smooth surface compared to that on SiO2/Si substrate. Based on the experimental results of this study, the initial adsorption sites on graphene substrate during deposition process, which had been discussed theoretically, could be demonstrated empirically.

Growth mechanism of Co thin films formed by plasma-enhanced atomic layer deposition using NH3 as plasma reactant

We investigated reaction mechanisms for the formation of Co thin films by plasma-enhanced atomic layer deposition (PE-ALD) using NH3 plasma as a counter-reactant. To investigate surface reactions during the PE-ALD Co, the process was divided into two half-reactions and these reactions were monitored using ex situ X-ray photoelectron spectroscopy (XPS) and an in situ residual gas analyzer (RGA). The cobaltocene (bis(cyclopentadienyl)-cobalt(II), CoCp2) precursor reacts with the N-terminated surface formed by NH3 plasma exposure, resulting in the formation of Co–Co bonds and the release of the Cp ligand and an N-containing byproduct. The NH3 plasma species adsorb to Co–Cp sites and promote dissociation of Cp. Therefore, N atoms on the surface are a key medium for the deposition of Co thin films during sequential adsorption and desorption reactions between CoCp2 and the surface. This result provides an insight into complicated chemical reactions involving PE-ALD and can be extended to other PE-ALD processes.

Polarity in GaN and ZnO: Theory, measurement, growth, and devices

The polar nature of the wurtzite crystalline structure of GaN and ZnO results in the existence of a spontaneous electric polarization within these materials and their associated alloys (Ga,Al,In)N and (Zn,Mg,Cd)O. The polarity has also important consequences on the stability of the different crystallographic surfaces, and this becomes especially important when considering epitaxial growth. Furthermore, the internal polarization fields may adversely affect the properties of optoelectronic devices but is also used as a potential advantage for advanced electronic devices. In this article, polarity-related issues in GaN and ZnO are reviewed, going from theoretical considerations to electronic and optoelectronic devices, through thin film, and nanostructure growth. The necessary theoretical background is first introduced and the stability of the cation and anion polarity surfaces is discussed. For assessing the polarity, one has to make use of specific characterization methods, which are described in detail. Subsequently, the nucleation and growth mechanisms of thin films and nanostructures, including nanowires, are presented, reviewing the specific growth conditions that allow controlling the polarity of such objects. Eventually, the demonstrated and/or expected effects of polarity on the properties and performances of optoelectronic and electronic devices are reported. The present review is intended to yield an in-depth view of some of the hot topics related to polarity in GaN and ZnO, a fast growing subject over the last decade.