Growth Mechanism Of Films Research Articles

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.

Highly conformal carbon-doped SiCN films by plasma-enhanced chemical vapor deposition with enhanced barrier properties

A plasma-enhanced chemical vapor deposition (PECVD) was developed for the growth of highly conformal carbon-doped silicon nitride (SiCN) films with enhanced barrier properties drawing on tunable carbon contents, k-values, and wet etch rates (WER). Trisilylamine (TSA) was used as the main precursor and hexane was used as a hydrocarbon-containing additive precursor for carbon doping. At low deposition temperatures ≤ 400 °C, we show that this PECVD process leads to the formation of SiCN films with good conformality of approximately 91% over high aspect ratio trench nanostructures (4.2:1) with a growth rate of ~2.5 (Å/cycle). In particular, the role of TSA and hexane precursors on the film growth mechanism and the k-values, and WER in the composite structures has been explored. The precursors were introduced pulse-wise into the reaction chamber while plasma was excited. The WER of the film was evaluated in a buffered hydrofluoric acid etchant. The k-value and carbon concentration varied depending on the TSA/hexane supply time in the ranges of 7–4.5 and around 6–40%, respectively. Analysis showed that the hexane precursor improved the WER of deposited SiCN films by more than a factor of 100 compared to when only TSA was used. The SiCN film with a thickness of 5.0 nm exhibited excellent prevention of moisture diffusion into the device. Furthermore, the step coverage was improved to equivalent conformality of the plasma-enhanced atomic layer deposition (PEALD) by modifying the supply method of the Si and carbon precursors and the moisture barrier property was secured with thicknesses of <10 nm. In particular, the Si and carbon precursors are biased to maximize the process margin and control the film characteristics, where tuning can be easily implemented.

Effect of Substrates on Structural Properties of Pure Anatase Phase Titanium Dioxide Thin Films Prepared By Mist Chemical Vapor Deposition

Titanium dioxide (TiO2) thin film has attracted considerable interest as one of promising sensing materials applying for various thin-film gas sensors because of its outstanding sensing properties, chemical stability and electrical properties, etc. [1]. Among the three phases of TiO2 films, anatase phase TiO2 has better sensitivity to H2 and volatile organic compound gases than rutile phase TiO2 [2,3]. However, there were still issues on synthesizing the stable pure anatase phase TiO2 using different methods. Compared with other reported methods, the mist chemical vapor deposition (mist CVD) [4] is an alternative method to synthesize TiO2 thin films, by which the growth of oxide thin film can be precisely controlled according to our previously research [5]. In order to investigate the effect of substrates on structural properties of TiO2 films fabricated by mist CVD method, four kinds of substrates were selected for comparison: glass, quartz glass, gallium doped zinc oxide (GZO) film and p-type silicon. During the mist CVD process, a solution of mixed precursors was prepared by dissolving titanium tetraisopropanolate in ethanol. The mist droplets were generated from the solution by ultrasonic transducer and transferred to the reaction chamber by compressed air. The substrates were set in the reaction chamber, which was heated and kept at 400 ˚C during the deposition. The structural properties of TiO2 thin films were investigated by X-ray diffraction (XRD), Raman spectroscopy and scanning electron microscope, atomic force microscope. The optical properties of TiO2 thin films were investigated by transmittance spectroscopy. According to the morphological analysis, TiO2 films with uniform surface were observed on the different substrates. Examining the XRD patterns of TiO2 films, the following diffraction peaks (101), (004), (200), (211), (201), (204) and (215) were observed, which corresponded to the diffraction peaks of anatase phase TiO2. However, it was found that the intensity of dominated (101) peak increased with the order of TiO2 films on quartz glass, GZO, silicon and glass. The results of TiO2 films by Raman spectroscopy measurement were also agreed with that of XRD measurement. In summary, the pure anatase phase TiO2 thin films could be synthesized by mist CVD method. The obtained anatase phase TiO2 films have high potential to be applied to thin film gas sensors, photocatalyst and dye-sensitized solar cells. The growth mechanism of TiO2 films on the different substrates will be revealed in the paper. References M. V. Baryshnikova, L. A. Filatov, A.S. Petrov, and S. E. Alexandrov, Chemical Vapor Deposition, 21, 327-333 (2015).M. Epifani, A. Helwig, J. Arbiol, R. Díaz, L. Francioso, P. Siciliano, G. Mueller, and J. R. Morante, Sensors and Actuators B, 130, 599-608 (2008).E. Sennik, N. Kilinc, Z. and Z. Ozturk, Journal of Alloys and Compounds, 616, 89-96 (2014).T. Kawaharamura, K. Mori, H. Orita, T. Shirahata, S. Fujita, and T. Hirao, Japanese Journal of Applied Physics, 52, 035501 (2013).X. Li, C. Li, T. Kawaharamura, D. Wang, N. Nitta, M. Furuta, H. Furuta, and A. Hatta, Transactions of the Materials Research Society of Japan, 39[2], 161-164 (2014).

Porous/dense ZnO bilayer films grown by thermal oxidation of ZnS film with gallium

Porous/dense ZnO bilayer films were grown by thermal oxidation of ZnS films deposited with gallium in air. The microstructures and photoluminescent properties of the as-grown ZnO bilayer films were investigated by XRD, SEM, HRTEM, XPS and PL. It was found that Ga doping contributed to the growth of ZnO dense layer, which covers the ZnO porous layer formed due to the evaporation of sulfur oxides. The diffusion-limited Ga gradient distribution along the thickness of ZnO films was observed. The remained Ga on the surface region led to the formation of ZnGa2O4 layer covering the ZnO film. The growth mechanism and morphology of the ZnO film covered by ZnGa2O4 grown by physical vapor deposition of metal gallium are quite different from that of the ZnO film covering ZnGa2O4 grown by manual application of molten gallium. Meanwhile, the formation of ZnGa2O4 was prohibited by altering Ga deposition distance. Higher Ga doping decreased the concentration of oxygen vacancy, which reduced the visible emission from ZnO film in combination with existence of ZnGa2O4 layer.

Review on modeling of the anode solid electrolyte interphase (SEI) for lithium-ion batteries

A passivation layer called the solid electrolyte interphase (SEI) is formed on electrode surfaces from decomposition products of electrolytes. The SEI allows Li+ transport and blocks electrons in order to prevent further electrolyte decomposition and ensure continued electrochemical reactions. The formation and growth mechanism of the nanometer thick SEI films are yet to be completely understood owing to their complex structure and lack of reliable in situ experimental techniques. Significant advances in computational methods have made it possible to predictively model the fundamentals of SEI. This review aims to give an overview of state-of-the-art modeling progress in the investigation of SEI films on the anodes, ranging from electronic structure calculations to mesoscale modeling, covering the thermodynamics and kinetics of electrolyte reduction reactions, SEI formation, modification through electrolyte design, correlation of SEI properties with battery performance, and the artificial SEI design. Multi-scale simulations have been summarized and compared with each other as well as with experiments. Computational details of the fundamental properties of SEI, such as electron tunneling, Li-ion transport, chemical/mechanical stability of the bulk SEI and electrode/(SEI/) electrolyte interfaces have been discussed. This review shows the potential of computational approaches in the deconvolution of SEI properties and design of artificial SEI. We believe that computational modeling can be integrated with experiments to complement each other and lead to a better understanding of the complex SEI for the development of a highly efficient battery in the future.

From Nanostructural Evolution to Dynamic Interplay ofConstituents: Perspectives for Perovskite Solar Cells.

Moving away from the high-performance achievements in organometal halide perovskite (OHP)-based optoelectronic and photovoltaic devices, intriguing features have been reported in that photocarriers and mobile ionic species within OHPs interact with light, electric fields, or a combination of both, which induces both spatial and temporal changes of optoelectronic properties in OHPs. Since it is revealed that the transport of photocarriers and the migration of ionic species are affected not only by each other but also by the inhomogeneous character, which is a consequence of the route selected to deposit OHPs, understanding the nanostructural evolution during OHP deposition, in terms of the resultant structural defects, electronic traps, and nanoscopic charge behaviors, will be valuable. Investigation of the film-growth mechanisms and strategies adopted to realize OHP films with less-defective large grains is of central importance, considering that single-crystalline OHPs have exhibited the most beneficial properties, including carrier lifetimes. Critical factors governing the behavior of photocarriers, mobile ionic species, and nanoscale optoelectronic properties resulting from either or all of them are further summarized, which may potentially limit or broaden the optoelectronic and photovoltaic applications of OHPs. Through inspection of the recent advances, a comprehensive picture and future perspective of OHPs are provided.

Effects of growth rate on structural property and adatom migration behaviors for growth of GaInNAs/GaAs (001) by molecular beam epitaxy

We have investigated the structural properties and the growth mode of GaInNAs films prepared at different growth rates (Rg) by molecular beam epitaxy. The crystalline structure is studied by high resolution X-ray diffraction, and the evolution of GaInNAs film surface morphologies is studied by atomic force microscopy. It is found that both the crystallinity and the surface roughness are improved by increasing Rg, and the change in the growth mode is attributed to the adatom migration behaviors particularly for In atoms, which is verified by elemental analysis. In addition, we have presented some theoretical calculation results related to the N adsorption energy to show the unique N migration behavior, which is instructive to interpret the growth mechanism of GaInNAs films.

Optical performance of W/B4C multilayer mirror in the soft x-ray region

W/B4C x-ray multilayers (MLs) with 300 layer pairs and a period in the range of d = 2–1.6 nm are fabricated and investigated for the x-ray optical element in the soft x-ray regime. The structural analyses of the MLs are carried out by using hard x-ray reflectivity (HXR) measurements at 8.047 keV. Well-defined successive higher order Bragg peaks (up to 3rd order) in HXR data collected up to glancing incidence angles of ∼9° reveal a good quality of the periodic structure. The ML mirrors have an average interface width of ∼0.35 nm and have a compressive residual stress of ∼0.183 GPa and 0. 827 GPa for d = 1.62 nm and d = 1.98 nm, respectively. MLs maintain structural stability over a long time, with a slight increase in interface widths of the W layers by 0.1 nm due to self-diffusion. Soft x-ray reflectivity (SXR) performances are evaluated in the energy range of 650 to 1500 eV. At energy ∼ 1489 eV, measured reflectivities (energy resolution, ΔE) are ∼ 10% (19 eV) and 4.5% (13 eV) at glancing incident angles of 12.07° and 15° for MLs having periods of 1.98 nm and 1.62 nm, respectively. The optical performance from 1600 eV to 4500 eV is theoretically analysed by considering the measured structural parameters. The structure-stress-optical performance is correlated on the basis of the mechanism of film growth. The implications of W/B4C MLs are discussed, particularly with respect to the development of ML optics with high spectral selectivity and reflectance for soft x-ray instruments.

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.

Mg-doped ZnO films prepared by chemical bath deposition

A simple, low-temperature route for the chemical bath deposition of Mg-doped ZnO films, based on low-cost, abundant and non-toxic materials was developed. The film growth mechanism, the resulting morphology and texture were investigated in detail by scanning electron microscopy and X-ray diffraction measurements. It was found that substantial film growth is only possible in a narrow solution pH window due to the Zn(OH)2 supersaturation as driving force for the film deposition. Different amounts of Mg in the solution cause distinct (0001), (10 bar{1} 0) or (10 bar{1} 1) ZnO crystal textures. Speciation modelling helped to understand the solution chemistry and explain the occurrence of different textures by face-selective adsorption of Mg species onto specific ZnO faces. The amount of incorporated Mg into the ZnO lattice, determined by inductively coupled plasma atomic emission spectroscopy, was limited to 2.1 mol%. Optical band gaps, calculated from transmittance spectra, showed an increase with higher amounts of incorporated Mg and ranged between 3.41 and 3.55 eV.

Surface Dynamics Transition of Vacuum Vapor Deposited CH3NH3PbI3 Perovskite Thin Films

The growth dynamics of CH3NH3PbI3 perovskite thin films on ITO covered glass substrate were investigated. The evolution of the film could be divided into two stages. A mound-like surface was obvious at the first stage. Stable dynamic scaling was observed for thicker films at the second stage. Through analyzing the scaling exponent, growth exponent β, and 2D fast Fourier transform, it is concluded that, at the second stage, the growth mechanism of mound formation does not play a major role, and the film growth mechanism can be described by Mullins diffusion equation.

The Mechanism of Growth of GaN Films by the HVPE Method on SiC Synthesized by the Substitution of Atoms on Porous Si Substrates

The mechanisms of nucleation and growth of GaN films on porous silicon substrates with a buffer layer of silicon carbide grown by new method of substitution of atoms directly in the subsurface layer of the Si substrate were studied. P-type Si(111) plates with a deposited system of periodic mesopores of a diameter of 17 nm and a depth of 1.5 μm were used as the substrates for growth of SiC buffer layer. The buffer AlN layers of a thickness of the order of 500 nm followed by GaN layers of a thickness of the order of 5 μm were deposited by the HVPE method on SiC/Si substrates prepared in different ways. SEM micrographs, Raman and photoluminescence spectra of these samples are given. The influence of the Si substrate preparation method and the conditions of the SiC layer synthesis on the growth mechanisms of both AlN and GaN films has been experimentally revealed. The formation of two types of V-defects during the growth of GaN was observed. A theoretical model for the formation of defects of the first and second types is developed.

Growth from Solution, Structure, and Optical Properties of Single-Crystal para-Quaterphenyl Films

Samples of single-crystal para-quaterphenyl films up to 8 mm long and 50 μm thick have been obtained for the first time by the solvent‒antisolvent growth method. The films have been grown both on the liquid–air interface and in the solution bulk. The morphology, surface quality, and thickness of crystal films have been investigated by the optical, laser confocal, and atomic force microscopies. The structure of the para-quaterphenyl single crystal at room temperature has been refined by X-ray diffraction analysis. The formation and growth mechanisms of crystal films on the liquid–air interface have been discussed. The opticalabsorption and photoluminescence spectra of the solutions and crystal samples have been investigated.

Effect of Additives on the Microstructure of Electroplated Tin Films

Electroplated tin films are important for several technologies such as microelectronics, Li-ion batteries, and corrosion-resistant coatings. In this paper, we demonstrate that the microstructure of tin films can be precisely controlled by addition of certain combinations of organic additives to a methanesulfonic acid based electroplating bath. Tin films are deposited on a copper substrate by varying the concentrations of two such additives, namely, hydroquinone and gelatin. The plating process is characterized by linear sweep voltammetry and insights into the resulting microstructure are obtained using imaging by scanning electron microscopy. It is found that the addition of hydroquinone alone results in non-uniform tin films having significant dendrites and does not affect the hydrogen gas evolution during electroplating. The addition of gelatin alone is found to suppress the evolution of hydrogen gas and affects the film nucleation process that controls its grain morphology, but also creates pinholes in the film and sludge in the bath. A combination of the two additives, however, yields a highly uniform grain structure with little to no dendrite formation and a delayed onset of hydrogen gas evolution, which is highly desirable during the electroplating process. Experiments are carried out that show that the mechanism of tin film nucleation and growth during electroplating is altered in the presence of the additives, where gelatin suppresses the tin nucleation rate (thereby controlling the grain size) as well as the formation of large dendrites; while hydroquinone, acting as an antioxidant, prevents pinholes, creates a uniform film, and avoids sludge formation in the presence of gelatin. This work demonstrates a path to control electroplated tin microstructures by varying bath chemistries and process parameters which will prove highly useful to industry.

Au-nanoparticle-embedded cross-linked gelatin films synthesized on aqueous solution in contact with dielectric barrier discharge

A wine-red free-standing thin film has been formed by irradiating dielectric barrier discharge plasma on an aqueous solution containing HAuCl4 and gelatin. The film has a fibrous structure with an inhomogeneous thickness profile and is composed of cross-linked gelatin, as confirmed by optical microscopy and infrared absorption spectroscopy. The film has embedded Au nanoparticles (GNPs), as confirmed by transmission electron microscopy. In the region with a relatively small film thickness, the number density of GNPs is relatively low, and the sizes of GNPs range from 5.3 to 34.3 nm. In the region with a relatively large film thickness, on the other hand, GNPs are highly accumulated, and the sizes of GNPs range from 10.0 to 26.7 nm. The aqueous solution remains transparent even after the film growth process, which indicates that the plasma-induced processes involving GNP formation and film growth are confined near the surface of the aqueous solution. A possible film growth mechanism is discussed on the basis of the experimental results of this study.

Measurements and modeling of the impact of radical recombination on silicon nitride growth in microwave plasma assisted atomic layer deposition

High material quality silicon nitride thin film deposition by plasma enhanced atomic layer deposition (PEALD) is necessary for many advanced semiconductor device and memory fabrication applications. Understanding film growth mechanism is quite important not only for the device production control but also device performance due to the strong correlation of film growth speed and film chemical property. Nevertheless, predicting film deposition rates, let alone film quality, is difficult as quantitative surface reaction mechanisms are still not well known and the species fluxes that play the central role in film growth are not easy to measure. In this paper, the authors describe how a plasma reactor model for the nitridation step required in PEALD of silicon nitride can be combined with a phenomenological site balance model to predict film growth rate variation with some key process parameters. The relative insensitivity of growth rates to plasma power are explained by competing destruction and regeneration mechanisms for NH3, an important nitrogen source in Si3N4 growth. The model also helps to reveal why H2 can be important.

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.

Engineering plasmonic nanostructured surfaces by pulsed laser deposition

The synthesis and the optical response of gold nanoparticles (NPs) and thin nanostructured films grown by pulsed laser deposition (PLD) are here studied. Different PLD process parameters – including background gas pressure and the number of laser shots as well as post-deposition annealing treatments – have been varied to control the growth of Au NPs and films, thus tuning the surface plasmon characteristics. The mechanisms of NPs and film growth have been explored performing a morphological characterization by Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM), and the correlation with the optical behavior is investigated. We show that the size distribution and the morphology of the as deposited Au NPs depend on growth mechanisms which are controlled by tuning the deposition process, while the optical behavior is strongly affected by the average size and surface density of NPs or by the length of percolated Au domains. Furthermore, nucleation in gas phase has been reported at high (1000 Pa Ar) background pressures, enabling independent control of NP size and coverage, contrary to surface driven NP growth by diffusion and aggregation on substrate.