Growth Behavior Of Films Research Articles

Role of template layers for heteroepitaxial growth of lanthanum oxide on GaN(0001) via atomic layer deposition

La2O3 has been reported as a good gate dielectric for GaN-based high electron mobility transistor and metal-oxide-semiconductor field effect transistor applications. In this study, atomic layer deposition (ALD) was selected as the deposition technique, and the growth behavior and structure of La2O3 films on GaN(0001) were investigated. Unlike La2O3 deposited by molecular beam epitaxy (MBE) at 450 °C that can form a two-dimensional film directly on GaN(0001), island growth mode was observed when a La2O3 film was deposited directly on GaN(0001) at 250 °C by ALD using tris(N,N′-diisopropylformamidinato)-lanthanum as the precursor and H2O as the coreactant. Only with the use of a template layer, a 2 nm-thick hexagonal La2O3 film deposited by MBE or a 3 nm-thick cubic Er2O3 film deposited by ALD, can a two-dimensional crystalline ALD-La2O3 thin film be formed on GaN(0001). Reflection high-energy electron diffraction, x-ray diffraction, and scanning transmission electron microscopy were conducted to verify the films’ crystalline nature and structure. The ALD-La2O3 film retains a cubic structure on ALD-Er2O3 templated-GaN(0001), while it transforms from the cubic phase to a mix of cubic and hexagonal phases on MBE-La2O3 templated-GaN(0001) when the film is thicker than 15 nm. The stabilization of a thin cubic La2O3 phase could be related to a difference in the surface energy and the ALD growth temperature.

Modulation of Growth Kinetics of Vacuum-Deposited CsPbBr3 Films for Efficient Light-Emitting Diodes.

Because of its excellent optical properties and good stability, all-inorganic halide perovskite CsPbX3 (X = I, Br, Cl) has been attracting interest for use in light-emitting diodes (LEDs). One challenge is improving the efficacy of the spatial confinement of excitons for higher luminescence efficiency. Here, we present a simple yet very effective strategy to form fine-grain-structured CsPbBr3 polycrystalline films prepared by thermal co-evaporation. The strategy involves controlling growth kinetics by adjusting the deposition rate, which, along with growth temperature, determines the nucleation rate and therefore the eventual grain structure. A correlation between deposition rate and average grain size was noted except for a very large deposition rate when there were large hillocks, which we attributed to the peculiar growth behavior of PbBr2 films. The growth conditions that produced a nanoscale grain structure and textured orientations without large hillocks also resulted in the highest luminescence efficiency as we anticipated. With the optimized CsPbBr3 light emitters, we demonstrate a green-light-emitting (at 524 nm) LED with a maximum current efficiency of 1.07 cd/A and an extremely narrow electroluminescence spectrum of 18 nm, a result that highlights the potential of vacuum-processed CsPbBr3 films for high-efficiency LEDs.

Semiconducting behavior and kinetics of passive film growth on AISI 321 stainless steel in sulfuric acid

AbstractIn the present study, the effects of aging and formation potential on the semiconducting behavior of AISI 321 stainless steel as well as the kinetics of the early stages of pitting are discussed. The donor and acceptor densities decrease with increasing formation potential. The steady-state passive film thickness and the coefficient of oxygen vacancies are estimated. The electrode polarization at higher anodic potentials causes the increase in the rate of pit initiation and slows down the growth rate of passive film. Also, the openness of the pits and their coalescence are highly promoted with the increase in the applied potential.

Gradient growth of fcc and bcc phase within FexNi1−x (50 < x < 75) films during direct-current wafer electroplating

In order to investigate the performance of Fe-Ni magnetic cores within embedded inductor in 3D package, a series of Fe-Ni films with compositions ranging from 15 wt% to 80 wt% iron were electrodeposited on 8-inch silicon wafer. The uniformity on brightness, phase structure and grain size of Fe-Ni magnetic films were investigated through SEM (scanning electron microscopy) and XRD (X-ray diffraction). A gradient growth behavior of fcc (face-centered cubic) and bcc (body-centered cubic) phase was revealed when Fe content ranges 50–75 wt% within Fe-Ni films, which can be attributed to the slightly faster growth rate of fcc phase. As also revealed in TEM (transmission electron microscope) observation, the fcc phase gradually spread over bcc phase region during the electroplating process, and formed an interface with a slight tilt angle to the substrate on the thickness direction. Several methods, such as increasing solution stirring, temperature or decreasing the current density, were proposed to restrain the gradient growth behavior of Fe-Ni film in wafer level.

Fast fitting of reflectivity data of growing thin films using neural networks.

X-ray reflectivity (XRR) is a powerful and popular scattering technique that can give valuable insight into the growth behavior of thin films. This study shows how a simple artificial neural network model can be used to determine the thickness, roughness and density of thin films of different organic semiconductors [diindenoperylene, copper(II) phthalocyanine and α-sexithiophene] on silica from their XRR data with millisecond computation time and with minimal user input or a priori knowledge. For a large experimental data set of 372 XRR curves, it is shown that a simple fully connected model can provide good results with a mean absolute percentage error of 8-18% when compared with the results obtained by a genetic least mean squares fit using the classical Parratt formalism. Furthermore, current drawbacks and prospects for improvement are discussed.

High Temperature Grain Growth Behavior of Aerosol Deposited BaTiO3 Film on (100), (110) Oriented SrTiO3 Single Crystal

Single crystals, which have complexed composition, are fabricated by solid state grain growth. However, it is hard to achieve stable properties in a single crystal due to trapped pores. Aerosol deposition (AD) is suitable for fabrication of single crystals with stable properties because this process can make a high density coating layer. Because of their unique features (nano sized grains, stress inner site), it is hard to fabricate single crystals, and so studies of grain growth behavior of AD film are essential. In this study, a BaTiO3 coating layer with ~ 9 μm thickness is fabricated using an aerosol deposition method on (100) and (110) cut SrTiO3 single crystal substrates, which are adopted as seeds for grain growth. Each specimen is heat-treated at various conditions (900, 1,100, and 1,300 °C for 5 h). BaTiO3 layer shows different growth behavior and X-ray diffraction depending on cutting direction of SrTiO3 seed. Rectangular pillars at SrTiO3 (100) and laminating thin plates at SrTiO3 (110), respectively, are observed.

A simple way to investigate the temperature of film growth surface during sputtering process

During the sputtering-deposition process, the temperature of film growth surface is more important than that of the substrate, which could seriously influence the film growth behavior. While, it is difficult to measure the temperature of film growth surface, because of the low space resolution of traditional temperature measurement systems. In this paper, the temperature of TiO2 film growth surface and substrate were monitored by the home-made NiCr/NiSi film thermocouple and standard NiCr/NiSi K type wire thermocouple. With the same sputtering parameters, the temperature of TiO2 film growth surface could reach [Formula: see text]C. While, the temperature of substrate was only about [Formula: see text]C. Finally, combining the temperature of film growth surface in sputtering-deposition process, the film growth behavior can be investigated and controlled in future.

Growth Behavior of SiO2 Films on Polyimide Substrates after Ion-Beam Treatment

This study investigated the effects on physical and chemical properties of a polyimide (PI) substrate of the exposure time and the flow rates of argon and oxygen for ion-beam treatment. The surface roughness, morphology, and chemical bonding states of the PI surface were analyzed, and the change in hydrophilicity of PI after ion-beam treatment was investigated. The contact angle of PI decreased after ion-beam treatment, which is considered to be due to increases the in surface roughness and the proportion of hydrophilic bonds such as C-O. Particularly, ion-beam treatment with argon and oxygen flow rates of 25 and 25 sccm, respectively, decreased the contact angle from 61.6° to 32.9° and increased the proportion of C-O bonds from 3.5% to 15.7%. Finally, the thin SiO2 layer which was deposited on ion-beam treated PI showed a smoother and flatter morphology than that on pristine PI due to the increase in the hydrophilicity of the PI substrate.

Al2O3 Thin Films Prepared by a Combined Thermal‐Plasma Atomic Layer Deposition Process at Low Temperature for Encapsulation Applications

In this article, a combined H2O thermal atomic layer deposition of Al2O3 with in situ N2 plasma treatment process at 90 °C for encapsulation applications is reported. The effect of process parameters on the growth behavior and properties of Al2O3 thin films, such as elemental composition, residual stress, moisture permeation barrier ability, density, and roughness, is investigated. Optimization of plasma exposure time gives films with a low impurity (≈3.8 at% for hydrogen, ≈0.17 at% for carbon, and ≈0.51 at% for nitrogen), a high mass density (≈3.1 g cm−3), and a low tensile residual stress (≈160 MPa). A water vapor transmission rate of 2.9 × 10−3 g m−2 day−1 is obtained for polyethylene naphthalate substrates coated with 4‐nm‐thick Al2O3 films.

Multi-scale modeling of gas-phase reactions in metal-organic chemical vapor deposition growth of WSe2

We present a multi-scale computational approach to model the gas-phase chemical kinetics for Metal-Organic Chemical Vapor Deposition (MOCVD) of WSe2 using W(CO)6 and H2Se as gas-phase precursors. This framework combines Quantum Mechanical (QM) methods based on Density Functional Theory (DFT), ReaxFF-based reactive molecular dynamics, and Computational Fluid Dynamics (CFD) to efficiently model the gas-phase physiochemical processes leading to WSe2 growth in a cold-wall horizontal MOCVD chamber. A detailed gas-phase chemical kinetic reaction model is developed to describe all major chemical reaction pathways from the precursors W(CO)6 and H2Se to the most thermodynamically stable molecules, with quantified kinetic rate constants. First QM calculations are performed to suggest key reaction types and to provide the necessary training set to determine ReaxFF reactive force-field parameters for the W/H/C/O/Se system. Using the developed force field, ReaxFF simulations are performed to identify all major chemical reaction pathways and determine their associated activation energies. Other kinetic parameters, together with the thermal and transport properties of all species involved, are estimated using well-established theories or correlations. This chemical kinetic model with thermal and transport parameters is then integrated into a reacting flow solver for full-scale CFD simulations of the MOCVD chamber under realistic operating conditions, to demonstrate its capabilities in predicting the major processes in the gas phase and qualitatively estimating thin film growth behavior. The predicted gas-phase concentrations of tungsten chalcogenides at the growth substrate correlate well with experimental measurements of average film thickness across the substrate, which suggests that crystal growth may result from surface deposition reactions of these species. This computational framework for the gas-phase chemical kinetics in MOCVD (prior to surface deposition and subsequent crystal growth) can thus test experimental MOCVD conditions, generate insights into more effective growth protocols, shed light on the significance of reactor geometry, and improve the reproducibility of MOCVD results across different experimental growth chambers. The computational framework is also transferable to other CVD chemistries.

Electrochemical behavior of CoCrMo alloy for dental applications in acidic artificial saliva containing albumin

The electrochemical properties of CoCrMo alloy immersed in different artificial saliva with or without Ca2+ and albumin were studied by open circuit potential (OCP), electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PP), and meanwhile the microstructures features, phase identification and chemical composition of the alloy were analyzed by SEM, EDS, XRD and RA-IR to further understand the electrochemical behavior of the alloy. The results indicated that the self-passivation behavior of the alloy occurred universally and was obviously distinct with each other in different acidic artificial saliva. No phase transformation was observed and the oxide layer and corrosion products exhibited amorphous nature. There was an obvious complexation of the adsorbed albumin with the alloy, and the adsorption capacity of albumin increased with the prolongation of immersion time. The adsorbed albumin presenting black stripped spots had a certain inhibition to the formation of passivation film, and Ca2+ in saliva promoted the further adsorption of albumin as an intermediate bridge, going against the improvement of the corrosion resistance of passivation film/alloy system. In addition, the passivation state of the alloy surface was changed by different methods to investigate the adsorption behavior of albumin and its influence on the further passivation behavior in depth. Hitherto, we tried to propose a model to explain the dynamic adsorption process of albumin and its influencing mechanism on the growth behavior of passivation film.

Growth behavior, work function, and band gap tuning of nanocrystalline LiMn2O4 thin films

We report on the effect of growth (TS) and annealing (Ta) temperatures on structural, morphological, work function mapping, and bandgap properties of nanocrystalline LiMn2O4 thin films grown by the radio frequency sputtering technique. Phase formation in the target material and thin films is confirmed from the presence of all the allowed Raman active modes (A1g + Eg + 3F2g) corresponding to the spinel LiMn2O4 structure. With increasing TS and Ta, the grain size of LiMn2O4 thin films increases exponentially and the activation energy associated with the thermally activated grain growth is observed to be 0.22 eV. The average work function of the LiMn2O4 nanocrystalline thin film grown on stainless steel at 573 K is found to be 5.63 eV. Upon increasing TS and Ta from RT to 973 K, the bandgap increases linearly from 0.58 eV to 1.05 eV and then decreases to 0.89 eV when Ta is 1073 K. The bandgap of LiMn2O4 thin films can be tuned by changing the grain size and the amount of defects present in the films.

Chemical Vapor Transport Deposition of Stable Cubic CsPbI3 Optical Films on the Porous Alumina Substrate

ABSTRACTCesium lead iodide perovskite (CsPbI3) with excellent optical and electrical properties have attracted numerous academic attentions. Specifically, the black cubic phase CsPbI3 with a direct band gap of 1.74 eV has been most appropriate materials for various optoelectronic applications, especially for photovoltaic (PV), Light-Emitting Diodes (LED) and photodetector applications1. However, the preferred cubic phase of bulk CsPbI3 (α-CsPbI3) is usually only stable at high temperatures and it will undergo an immediate phase transformation to orthorhombic phase (δ-CsPbI3) after fabrication at room temperature. In this work, we have discovered a convenient CVD method to investigate the growth behavior of the cubic α-CsPbI3 film on the porous alumina substrate. The lead iodide and cesium iodide were used as the precursors for the deposition of CsPbI3. The porous alumina with high surface area and large pore volume was used as growth substrate. It was shown that the porous alumina promoted the growth of CsPbI3 film by absorbing the precursor and increasing the nucleation density. The prepared CsPbI3 film emitted strong and stable red light under ultraviolet light excitation at room temperature and ambient atmosphere. The lead iodide was absorbed on the surface of the porous alumina firstly then reacted with cesiumiodide to form the CsPbI3. The successful preparation of the CsPbI3 by the direct CVD method paves the way for its large scale growth and application in optoelectronic devices.

Scalable Deposition Methods for Large‐area Production of Perovskite Thin Films

The recent steady improvements in the performance of the nascent hybrid perovskite photovoltaic (PV) devices have led to power conversion efficiencies that rival the best‐performing established PV technologies. However, to scale these laboratory demonstrations to PV module‐scale production will require development of scalable deposition methods for perovskite thin films. Every record result for perovskite PVs so far was achieved via spin coating, a technique that is popular in research laboratories for thin‐film coating over relatively small device areas, but not considered to be a method that could be used to scale up the manufacturing of perovskite PVs. Significantly larger thin‐film areas are needed for future commercial PV products. Hence, some researchers have focused their efforts on perovskite deposition techniques that can be considered as scalable for mass production and have achieved notable results even on large areas. Here, we present an overview of the solution‐based and vapor‐based deposition processes; we explain their influence on the molecular crystal growth behavior of perovskite thin films and discuss the morphology as well as other material quality characteristics. By presenting a comprehensive comparison of the deposition techniques and the corresponding performance parameters for different device sizes, we intent to guide the growing research community through the methods that might enable mass production of perovskite solar products.

Hydrogen-bonded thin films of cellulose ethers and poly(acrylic acid)

Etherification of cellulose can get a series of water soluble derivatives, which can form hydrogen-bonded polymer complex with poly(acrylic acid) (PAA). Three cellulose ethers hydroxyethyl cellulose (HEC), hydroxypropyl cellulose (HPC) and methyl cellulose (MC) are LbL assembled with PAA to fabricate thin films. The hydrogen bonding of the films is characterized with FT-IR. The film growth behaviors are monitored by a quartz crystal microbalance (QCM) and a spectroscopic interferometer, which shows a different growth rate for different system and a strong dependence on pH values. The stability of the films can be increased by heat treatment. Once the cross-linked structure is formed, and the dissolution of film can be prevented even in the high pH value. In addition, the films show good water adsorption ability from environment. Owing to pH responsive behavior and good water adsorption, CE/PAA films can be explored for various applications, especially for biomedical application.

A high growth rate atomic layer deposition process for nickel oxide film preparation using a combination of nickel(II) diketonate–diamine and ozone

In this study, we described an atomic layer deposition (ALD) process for the preparation of nanoscale nickel oxide (NiO) films with high growth rate by using a combination of nickel(II) diketonate–diamine (Ni(acac)2(TMEDA), TMEDA = N,N,N′,N′-tetramethyl-ethylenediamine) and ozone (O3). Typical self-limiting film growth behavior was observed between 200 and 275 °C, and growth saturation with respect to both precursor pulse time was verified. The chemical composition, crystalline phase, and surface morphology of the films were studied using X-ray photoelectron spectroscopy, X-ray diffraction, and atomic force microscopy. All the results confirmed that the ALD process occurred with high growth rate of approximately 2.0 Å/cycle and resulted in high-quality, smooth films.

Growth Behavior of Au Films on SiO2Film and Direct Transfer for Smoothing Au Surfaces

Direct transfer of Au films deposited on smooth SiO2film with RMS (root mean square) surface roughness of 0.24 nm was investigated with the aim of generating smooth Au surfaces. Deposited Au films with different thicknesses were transferred to rough Au surfaces on target substrates at room temperature with a contact pressure of 50 MPa. Observation of the growth behavior of the deposited films revealed that they formed a continuous structure when their nominal film thickness was around 15 nm or above. The transfer of continuous Au films with a thickness of 20, 51, or 102 nm reduced the RMS roughness of the rough Au surfaces from 1.6 nm to 0.4 nm. In contrast, the transfer of Au films with a thickness less than 5 nm increased their surface roughness. This direct transfer technique should thus be useful for low temperature bonding.

Batch processing of aluminum nitride by atomic layer deposition from AlCl3 and NH3

Batch processing of aluminum nitride (AlN) by thermal atomic layer deposition (ALD) was studied at high temperatures of 500–550 °C using aluminum chloride (AlCl3) and ammonia (NH3) as metal and nitrogen precursors. The growth behavior, chemical composition, morphology, crystallinity, and residual stress of the AlN films were characterized by ellipsometry, x-ray photoelectron spectroscopy, atomic force microscopy, scanning electron microscopy, x-ray diffraction, and the wafer curvature method, respectively. The deposited AlN films at 525 °C had a good batch thickness uniformity of 2.6%, a low surface roughness of ∼1 nm, a low Cl impurity level of ∼1.2%, and a hexagonal polycrystalline structure with a preferential (002) orientation. An obvious dependence between film properties and deposition temperature was found. The evaluation in deposition temperature from 500 to 550 °C resulted in an increase of the growth-per-cycle, refractive index, and tensile stress as well as a decrease of Cl and O impurity levels in the AlN films. Based on these findings, the authors concluded that high quality polycrystalline AlN films with a preferential (002) orientation can be grown with ALD in a large batch reactor at high temperatures (500–550 °C).

A novel growth strategy of TiO2 anodic films using surface residual stress as driving force

The relationship between residual stress and growth behavior of anodic titanium oxide films (TiO2) was investigated in terms of defect chemistry and the nanocrystalline materials thermodynamic. The results showed that the surface residual stress can be controlled by acting on the duration of the surface mechanical attrition treatment (SMAT). When samples are processed by grinding for 30 min, the residual stress value reaches a maximum of 73.13 MPa, approximately 7.2 times higher than the one obtained with untreated sample. Under these conditions, the thickness of the anodic film was abound 1200 nm, three times that of the TA2 anodic film. Furthermore, the results of electrochemical tests showed that following the surface mechanical attrition treatment, the anodic film show lower density vacancies, higher resistance to the diffusion of Cl−, higher density, and an improved corrosion resistance when compared to TA2. Generally speaking, the growth behavior of the anodic film can be improved by identifying the suitable residual stress.

In-plane rotation and transition from rectification to bipolar resistive switching in ZnO/SrTiO3:Nb heterojunctions by substrate pretreatment.

The growth behavior and electrical transport properties of ZnO films was found to be strongly dependent on the deionized water soaking treatment of 0.7 wt% (111) SrTiO3:Nb substrates. Comparing the ZnO films on soaked SrTiO3:Nb substrates with those on unsoaked ones, the out-of-plane orientation of ZnO films are both along the c-axis, while there is an in-plane rotation of ZnO thin films. According to the variable frequency capacitance–voltage measurements, a much higher interface state density is found in the ZnO/soaked-SrTiO3:Nb heterojunction than that in the ZnO/unsoaked-SrTiO3:Nb heterojunction. Moreover, a rectification and bipolar resistive switching effect were observed in the ZnO/unsoaked-SrTiO3:Nb and ZnO/soaked-SrTiO3:Nb heterojunctions, respectively. The transition from rectification to a bipolar resistive switching effect can be ascribed to an increase of oxygen vacancies, the migration of which plays an important part in the resistive switching.