Growth Mechanism Of Thin Films Research Articles

Enhanced visible light response of ZnO porous thin film by post-annealing treatment

ZnO thin films were synthesized by a facile electrodeposition method in the aqueous solution. Porous ZnO thin films with wurtzite structure could be achieved by mean of annealing treatment. The growth mechanism of the porous ZnO thin film was discussed. The intensity of the E 2 mode in the ZnO thin film, which represents crystalline quality of the thin film increases with the increasing of annealing temperature. Optical properties indicate that annealing temperature has strong effect on the optical band gap value and defect concentrations. Both the green and yellow emissions corresponding to respective oxygen vacancies and oxygen interstitials can be identified. The results show that ZnO annealed at 400 °C exhibits a significant photocurrent density enhancement which is about 18 times larger than that of the as-deposited ZnO thin films. The mechanism of the enhanced photoresponse for the ZnO thin film has been discussed in detail.

Comprehensive Study of Growth Mechanism and Properties of Low Zn Content Cd1-xZnxS Thin Films by Chemical Bath

Cd1-xZnxS thin films have been studied extensively as window layers for solar cell applications. However, a mismatch between the Cd1-xZnxS and copper-indium-gallium-selenide absorber layers increases with Zn film concentration, which reduces the device efficiency. In this work, Cd1-xZnxS thin films with low Zn concentrations were analyzed. The effect of the addition of different molar Zn concentrations to the reaction mixture on the growth mechanism of Cd1-xZnxS thin films and the influence of these mechanisms on structural, optical and morphological properties of the films has been studied. Cd1-xZnxS thin films were synthesized by chemical bath deposition using an ammonia-free alkaline solution. Microstructural analysis by X-ray diffraction showed that all deposited films grew with hexagonal structure and crystallite sizes decreased as the Zn concentration in the film increased. Optical measurements indicated a high optical transmission between 75% and 90% for wavelengths above the absorption edge. Band gap value increased from 2.48 eV to 2.62 eV, and the refractive index values for Cd1-xZnxS thin films decreased as the Zn increased. These changes in films and properties are related to a modification in growth mechanism of the Cd1-xZnxS thin films, with the influence of Zn(OH)2 formation being more important as Zn in solution increases.

Investigate the growth mechanism of Cu2FeSnS4 thin films by sulfurization of metallic precursor

Cu2FeSnS4 (CFTS) thin films have been prepared on glass substrates by a process of sputtering metallic precursor with post-sulfurization. By means of various holding times, the growth mechanism of CFTS has been determined by X-ray diffraction and Raman patterns. Three steps have been involved, the binary-phases CuSx, FeSx and SnSx are synthesized in the preliminary stage, and afterwards, CuSx reacts with FeSx to generate ternary-compound CuFeS2. At last, the target product CFTS is obtained with the increasing holding time of sulfurization. All the thin films have smooth and closely packed surface, and longer holding time is in favor of the grain growth. The thickness of these thin films is around 1µm.

Effects of Sputtering Parameters on AlN Film Growth on Flexible Hastelloy Tapes by Two-Step Deposition Technique.

AlN thin films were deposited on flexible Hastelloy tapes and Si (100) substrate by middle-frequency magnetron sputtering. A layer of Y2O3 films was used as a buffer layer for the Hastelloy tapes. A two-step deposition technique was used to prepare the AlN films. The effects of deposition parameters such as sputtering power, N2/Ar flow rate and sputtering pressure on the microstructure of the AlN thin films were systematically investigated. The results show that the dependency of the full width at half maximum (FWHM) of AlN/Y2O3/Hastelloy on the sputtering parameters is similar to that of AlN/Si (100). The FWHM of the AlN (002) peak of the prepared AlN films decreases with increasing sputtering power. The FWHM decreases with the increase of the N2/Ar flow rate or sputtering pressure, and increases with the further increase of the N2/Ar flow rate or sputtering pressure. The FWHM of the AlN/Y2O3/Hastelloy prepared under optimized parameters is only 3.7° and its root mean square (RMS) roughness is 5.46 nm. Based on the experimental results, the growth mechanism of AlN thin films prepared by the two-step deposition process was explored. This work would assist us in understanding the AlN film’s growth mechanism of the two-step deposition process, preparing highly c-axis–oriented AlN films on flexible metal tapes and developing flexible surface acoustic wave (SAW) sensors from an application perspective.

Growth mechanism of single-crystalline NiO thin films grown by metal organic chemical vapor deposition

Nickel oxide (NiO) thin films were grown by atmospheric-pressure metal organic chemical vapor deposition (APMOCVD). Growth was carried out using various growth parameters, including the growth temperature, the input precursor (O2/Ni) ratio, and the type of substrate material. Effects of the growth parameters on the structural and electrical properties of the films were investigated. X-ray diffraction analysis revealed that the crystal structure and quality were strongly affected by the growth temperature and the type of substrate material. At an optimized growth temperature, single-crystalline NiO films were grown on MgO(100) and MgO(111) substrates in a cube-on-cube orientation relationship, while on an Al2O3(001) substrate, the film was grown in the NiO[111] direction. The use of MgO substrates successfully suppressed the formation of twin defects, which have been frequently reported in the growth of NiO. The difference in the formation of the twin defects on MgO and Al2O3 substrates was discussed. It was observed that the resistivity dependence on crystal quality was affected by the choice of substrate material. The effects of the precursor ratio on the transmittance and resistivity of the films were also investigated. Improved transparency in the visible wavelength region and higher conductivity were found in films grown with higher O2/Ni ratios.

Ab initio modeling of zincblende AlN layer in Al-AlN-TiN multilayers

An unusual growth mechanism of metastable zincblende AlN thin film by diffusion of nitrogen atoms into Al lattice is established. Using first-principles density functional theory, we studied the possibility of thermodynamic stability of AlN as a zincblende phase due to epitaxial strains and interface effect, which fails to explain the formation of zincblende AlN. We then compared the formation energetics of rocksalt and zincblende AlN in fcc Al through direct diffusion of nitrogen atoms to Al octahedral and tetrahedral interstitials. The formation of a zincblende AlN thin film is determined to be a kinetically driven process, not a thermodynamically driven process.

Growth and structure of thermally evaporated Bi2Te3 thin films

The growth mechanism, microstructure, and crystal structure of the polycrystalline n-Bi2Te3 thin films with thicknesses d=15–350nm, prepared by thermal evaporation in vacuum onto glass substrates, were studied. Bismuth telluride with Te excess was used as the initial material for the thin film preparation. The thin film characterization was performed using X-ray diffraction, X-ray photoelectron spectroscopy, energy-dispersive X-ray spectroscopy, scan electron microscopy, and electron force microscopy. It was established that the chemical composition of the prepared films corresponded rather well to the starting material composition and the films did not contain any phases apart from Bi2Te3. It was shown that the grain size and the film roughness increased with increasing film thickness. The preferential growth direction changed from [00l] to [015] under increasing d. The X-ray photoelectron spectroscopy studies showed that the thickness of the oxidized surface layer did not exceed 1.5–2.0nm and practically did not change in the process of aging at room temperature, which is in agreement with the results reported earlier for single crystals. The obtained data show that using simple and inexpensive method of thermal evaporation in vacuum and appropriate technological parameters, one can grow n-Bi2Te3 thin films of a sufficiently high quality.

CoFe2/Al2O3/PMNPT multiferroic heterostructures by atomic layer deposition

Multiferroic materials and applications allow electric bias control of magnetism or magnetic bias control of polarization, enabling fast, compact, energy-efficient devices in RF/microwave communication systems such as filters, shifters, and antennas; electronics devices such as inductors and capacitors; and other magnetic material related applications including sensors and memories. In this manuscript, we utilize atomic layer deposition technology to grow magnetic CoFe metallic thin films onto PMNPT, with a ∼110 Oe electric field induced ferromagnetic resonance field shift in the CoFe/Al2O3/PMNPT multiferroic heterostructure. Our work demonstrates an atomic layer deposition fabricated multiferroic heterostructure with significant tunability and shows that the unique thin film growth mechanism will benefit integrated multiferroic application in near future.

Invoking stoichiometric protocols for chemical synthesis of CdSe thin films

An attempt is made to establish the procedure for regulating stoichiometry and hence the materials properties of the chemically deposited CdSe thin films. Reliance of the structural, morphological, optical and electrical properties on the stoichiometry was studied to support the established protocols. To upkeep the appealed modus operandi, growth mechanism of CdSe thin films is proposed. The compositional studies revealed stoichiometric adaptations harmonizing the synthesis protocols. Crystallography remained the same regardless of the variation in deposition conditions. The as-deposited CdSe thin films are polycrystalline in nature with the hexagonal (P63/mmc space group) crystal geometry. Globule shaped grains of nanosize are observed through the scanning electron microscopy. Morphological modifications coupled with the stoichiometric deviations established control over the bandgap and electrical transport characteristics. Thus, with the ambitions to set up the standards for regulating stoichiometry and consequently the physical properties, we communicate the synthesis and preliminary studies on the CdSe thin films through this paper.

Growth mechanism of GaAs1-xSbx ternary alloy thin film on MOCVD reactor using TMGa, TDMAAs and TDMASb

Metal Organic Chemical Vapor Deposition (MOCVD) is a method for growing a solid material (in the form of thin films, especially for semiconductor materials) using vapor phase metal organic sources. Studies on the growth mechanism of GaAs1-xSbx ternary alloy thin solid film in the range of miscibility-gap using metal organic sources trimethylgallium (TMGa), trisdimethylaminoarsenic (TDMAAs), and trisdimethylaminoantimony (TDMASb) on MOCVD reactor has been done to understand the physical and chemical processes involved. Knowledge of the processes that occur during alloy formation is very important to determine the couple of growth condition and growth parameters are appropriate for yield high quality GaAs1-xSbx alloy. The mechanism has been studied include decomposition of metal organic sources and chemical reactions that may occur, the incorporation of the alloy elements forming and the contaminants element that are formed in the gown thin film. In this paper presented the results of experimental data on the growth of GaAs1-xSbx alloy using Vertical-MOCVD reactor to demonstrate its potential in growing GaAs1-xSbx alloy in the range of its miscibility gap.

Promotion Effect of Electrodeposition Parameters on the Performances of MnO2 Thin Films Used As Photoelectrocatalysts for Water Oxidation

The development of alternative energy sources, especially green energy sources for traditional fossile fuels is a major challenge that humankind is currently facing. The conversion of solar energy into chemical fuels is a promising method. Inspired by photosynthesis taking place in the green plants, artificial photosynthesis was proposed. The targeted reaction is as follows: 2 H2O (l) → 2 H2 (g) + O2 (g) Theoretically, the half redox equation related to water oxidation, also called oxygen evolution reaction (OER), which is a key step for water splitting, needs a high potential bias, as a consequence of the very slow kinetics of this reaction. This latter could be improved by employing a catalyst in order to make it energetically less expensive. Catalysts based on metal oxides have shown bright prospects for this application [1]. As a consequence of the determination of the fine structure of photosystem II in charge of this redox process in plants, it was revealed that the oxygen evolving complex (OEC) was a Mn4CaO5 entity resembling strongly the one that can be found in manganese oxides. These latter attracted consequently a considerable attention of scientists over the last years as possible OER photoelectrocatalysts. After comparison with traditional catalysts based on precious metals, manganese oxides, and mainly MnO2, have the advantages of being abundant on Earth, and therefore inexpensive, and also environmentally friendly. In particular, many investigations reported in literature showed in a rather convincing manner that MnO2 is a promising candidate as OER photoelectrocatalysis. In a work published in 2011, T. F. Jaramillo et al. showed that birnessite-type MnO2 could be a good solar water splitting catalyst [2], whereas S.S. Stahl et al. found that the OER activity of manganese oxides depends on their crystalline structure [3]. D.G. Nocera and co-workers investigated the nucleation and growth mechanism of MnOx thin films electrodeposited in potentiostatic conditions using a potential value selected inside a narrow potential range [4]. Few studies were thus focused on large variations of the potential used during the electrodeposition of MnO2thin films in potentiostatic conditions, and on the corresponding performances of these films towards photoelectrocatalysis of water oxidation. In this work, manganese dioxide (MnO2) thin films with different morphologies were prepared by one-step potentiostatic deposition using an aqueous electrolyte containing MnSO4 and NaClO4 in a traditional three-electrode cell. Fluorine doped tin oxide (FTO) substrates were used as working electrodes, and a platinum grid and a K2SO4 saturated Hg/Hg2SO4 electrode (SSE) were used as counter- and reference electrodes, respectively. The same setup was used during the OER tests except that a 0.1 M KOH Hg/HgO reference electrode (MOE) and a 0.1 M NaOH electrolyte were used instead of SSE and NaClO4respectively. Our results show that the value of the electrodeposition potential has a strong influence on the morphology and crystallinity of resulting MnO2 thin films, as evidenced by SEM-FEG and XRD characterisations. The birnessite type crystalline structure was obtained only for films electrodeposited at potential values close to the peak potential related to MnO2 electrodeposition, whereas MnO2thin layers electrodeposited at potential values situated far beyond this peak potential value and before the foot of the anodic wall related to water oxidation were found to be amorphous, which clearly promoted their activity towards OER, by comparison with those of the birnessite variety. In the course of our investigations, chronoamperometry experiments were carried out for all the samples. They allowed us to find out that the stability of the electrocatalytic behaviour, as well as the adherence on the underlying substrate, were both better for amorphous films. Electrochemical impedance spectroscopy (EIS) experiments were also carried out to develop a better understanding of their electrochemical properties in the course of water oxidation experiments. Moreover, their semi-conductor behaviour was evidenced using water oxidation experiments in the presence of a solar simulator, and deeply investigated with the help of Incident Photon to electron Conversion Efficiency (IPCE), UV-visible spectrophotometry and Current Sensing Atomic Force Microscopy (CS-AFM).

Surface Morphology of Vapor-Deposited Chitosan: Evidence of Solid-State Dewetting during the Formation of Biopolymer Films.

Chitosan is a useful and versatile biopolymer with several industrial and biological applications. Whereas its physical and physicochemical bulk properties have been explored quite intensively in the past, there is a lack of studies regarding the morphology and growth mechanisms of thin films of this biopolymer. Of particular interest for applications in bionanotechnology are ultrathin films with thicknesses under 500 Å. Here, we present a study of thin chitosan films prepared in a dry process using physical vapor deposition and in situ ellipsometric monitoring. The prepared films were analyzed with atomic force microscopy in order to correlate surface morphology with evaporation parameters. We find that the surface morphology of our final thin films depends on both the optical thickness, i.e., measured with ellipsometry, and the deposition rate. Our work shows that ultrathin biopolymer films can undergo dewetting during film formation, even in the absence of solvents and thermal annealing.

Growth of single crystal, oriented SnO2nanocolumn arrays by aerosol chemical vapour deposition

A single-step, template-free aerosol chemical vapor deposition (ACVD) method is demonstrated to grow well-aligned SnO2 nanocolumn arrays. The ACVD system parameters, which control thin film morphologies, were systematically explored to gain a qualitative understanding of nanocolumn growth mechanisms. Key growth variables include feed rates, substrate temperature, and deposition time. System dynamics relating synthesis variables to aerosol characteristics and processes (collision and sintering) are elucidated. By adjusting system parameters, control of the aspect ratio, height, and crystal structure of columns is demonstrated. A self-catalyzed (SnO2 particles) vapor–solid (VS) growth mechanism, whereby a vapor–particle deposition regime results in the formation of nanocrystals that act as nucleation sites for the preferential formation and growth of nanocolumns, is proposed and supported. Density functional theory (DFT) calculations indicate that the preferential orientation of thin films is a function of the system redox conditions, further supporting the proposed VS growth mechanism. When taken together, these results provide quantitative insight into the growth mechanism(s) of SnO2 nanocolumn thin films via ACVD, which is critical for engineering these, and other, nanostructured films for direct incorporation into functional devices.

Growth of TiO<sub>2</sub> Thin Films by Atomic Layer Deposition (ALD)

Ceramic oxide thin films are an important material, with applications in many areas of science and technology. Titanium oxide (TiO2) is also a well-known and important material for applications such as gas sensors [1], photocatalysis materials [3], and electrochemicals [1], due to its self-cleaning [2], good corrosion resistance and biocompatibility. Atomic Layer Deposition (ALD) is a nanotechnology tool that is used for the deposition of nanostructured thin films. The unique advantage of ALD is the self-limiting film growth mechanism, which offers attractive properties, simple and accurate film thickness control, sharp interfaces, uniformity over large areas, excellent conformality, good reproducibility, a multilayer processing capability, and high quality films at low temperatures [3, 4]. TiO2 thin films were grown using TTIP (Titanium isopropoxide) ALD on silicon wafers, glass slides, and stainless steel plates in order to study the effect of substrates on the growth of TiO2. In order to achieve the desired advantages of using TTIP, a series of experiments were performed to study the growth mechanism of TiO2 thin films using TTIP and H2O by ALD.

Growth mechanism of Ge-doped CZTSSe thin film by sputtering method and solar cells.

Ge-doped CZTSSe thin films were obtained by covering a thin Ge layer on CZTS precursors, followed by a selenization process. The effect of the Ge layer thickness on the morphologies and structural properties of Ge-doped CZTSSe thin films were studied. It was found that Ge doping could promote grain growth to form a compact thin film. The lattice shrank in the top-half of the film due to the smaller atomic radius of Ge, leading to the formation of tensile stress. According to thermodynamic analysis, Sn was easier to be selenized than Ge. Thus, Ge preferred to remain on the surface and increased the surface roughness when the Ge layer was thin. CZTSe was easier to form than Ge-doped CZTSe, which caused difficulty in Ge doping. These results offered a theoretical and experimental guide for preparing Ge-doped CZTSSe thin films for the potential applications in low-cost solar cells. With a 10 nm Ge layer on the top of the precursor, the conversion efficiency of the solar cell improved to 5.38% with an open-circuit voltage of 403 mV, a short-circuit current density of 28.51 mA cm-2 and a fill factor of 46.83% after Ge doping.

Precise Control of Metal Oxide Thin Films Deposition in Magnetron Sputtering Plasmas for High Performance Sensing Devices Fabrication

Magnetron sputtering deposition is a widely used technique to deposit thin film precisely at nanoscale level. During the deposition of metal oxide thin films, reactive oxygen gas is introduced into the deposition chamber. Pure metal and metal oxide materials can be used as sputter target, although the simplest way is by using a pure metal target. In such reactive process, the effect of target poisoning significantly influence the deposition process and the growth mechanisms of metal oxide thin films became very complex. In general, external parameters such as discharge power, working pressure, reactive gases ratio and substrate temperature are used to optimize the properties of deposited thin films. Then, ex-situ analyses such as scanning electron microscope and X-ray diffraction analysis are performed to obtain the optimized parameter. Sample depositions and ex-situ analyses consume time to achieve the goal through try and error. In this article, in-situ plasma diagnostics are reviewed focusing on an optical emission spectroscopy to precisely control and investigate the sputter target poisoning effect during the deposition of metal oxide thin films. The emission of atomic lines from several metal and oxygen atoms were used to discuss the deposition mechanisms and their correlation with the deposited thin films was observed. Finally, the deposited metal oxide thin films were proposed and tested for several applications such as gas sensor and frequency selective surface glass.

Investigation of AlN thin film growth on MgO(111) substrates using low temperature helicon sputtering system

An aluminum nitride (AlN) thin film has been grown on annealed magnesium oxide (MgO) (111)-plane substrate using low temperature helicon sputtering system. Both AlN films on as-received and annealed MgO(111) substrate are single crystalline with AlN[0001] || MgO[111]. X-ray rocking curve shows that AlN film on annealed MgO exhibits superior crystalline quality, which means more suitable for AlN crystal growth. Two different growths were found for the deposition of AlN on annealed MgO. It is believed that the partially recovered substrate surface caused by annealing process provides atomic smooth surface terraces with small lattice mismatch for AlN crystal to grow in 2D mode, enhance grain size, and thus reduce the dislocation density. This is the first time demonstrated for the growth mechanism of single crystal AlN thin film prepared on MgO(111) by sputtering system.

Regulated magnetic domains and high-frequency property in magnetic materials with columnar structure

The regulation of magnetic domains and high-frequency property in Fe20Ni80 thin films sputtered on anodic aluminum oxide (AAO) substrates with different apertures and a Si substrate were investigated. The obvious stripe domain structure was observed in FeNi thin film sputtered on AAO (pore in diameter d ~ 20 nm) substrate. The distinct cross-sectional columnar structures prepared on three different substrates and measured by scanning electron microscope were shown, which arose from different growth mechanisms on various kinds of substrates. The structure of AAO substrate could modulate the growth mechanism of thin films and the appearance of stripe domains structure. In addition, the resonant frequency was enhanced in FeNi thin film prepared on AAO (d ~ 20 nm) substrate.

Strain study of gold nanomaterials as HR-TEM calibration standard

This work presents the use of high resolution electron microscopy (HREM) and geometric phase analysis (GPA) to measure the interplanar spacing and strain distribution of three gold nanomaterials, respectively. The results showed that the {111} strain was smaller than the {002} strain for any kind of gold materials at the condition of same measuring method. The 0.65% of {111} strain in gold film measured by HREM (0.26% measured by GPA) was smaller than the {111} strains in two gold particles. The presence of lattice strain was interpreted according to the growth mechanism of metallic thin film. It is deduced that the {111} interplanar spacing of the gold thin film is suitable for high magnification calibration of transmission electron microscopy (TEM) and the gold film is potential to be a new calibration standard of TEM.

Growth of Cu2ZnSnS4 absorber layer on flexible metallic substrates for thin film solar cell applications

In this work, Cu2ZnSnS4 (CZTS) absorber layers were fabricated using a two-stage process. Sequentially deposited Cu–Zn–Sn thin film layers on metallic foils were annealed in an Ar+S2(g) atmosphere. We aimed to investigate the role of flexible titanium and molybdenum foil substrates in the growth mechanism of CZTS thin films. The Raman spectra and X-ray photoelectron spectroscopy analyses of the sulfurized thin films revealed that, except for the presence of Sn-based secondary phases, nearly pure CZTS thin films were obtained. Additionally, the intense and sharp X-ray diffraction peak from the (112) plane provided evidence of good crystallinity. Electron dispersive spectroscopy analysis indicated sufficient sulfur content but poor Zn atomic weight percentage in the films. Absorption and band-gap energy analyses were carried out to confirm the suitability of CZTS thin films as the absorber layer in solar cell applications. Hall effect measurements showed the p-type semiconductor behavior of the CZTS samples. Moreover, the back contact behavior of these metallic flexible substrates was investigated and compared. We detected formation of cracks in the CZTS layer on the molybdenum foils, which indicates the incompatibility of molybdenum's thermal expansion coefficient with the CZTS structure. We demonstrated the application of the magnetron sputtering technique for the fabrication of CZTS thin films on titanium foils having lightweight, flexible properties and suitable for roll-to-roll manufacturing for high throughput fabrication. Titanium foils are also cost competitive compared to molybdenum foils.