Stoichiometry Of Thin Films Research Articles

First Principles Study of Bismuth Vacancy Formation in (111)-Strained BiFeO3

Epitaxial strain is known to significantly influence the structural and functional properties of oxide thin films. However, its impact on point defect concentration has been less explored. Due to the challenges in experimentally measuring thin-film stoichiometry, computational studies become crucial. In this work, we use first-principles calculations based on density functional theory to investigate the formation and stability of Bi vacancies and Bi-O vacancy pairs in BiFeO3 (BFO) under (111) epitaxial strain. Our results demonstrate that compressive strain (−4%) decreases the formation enthalpy of Bi vacancies by 0.88 eV, whereas tensile strain (4%) increases it by 0.39 eV. Out-of-plane (OP) Bi-O vacancy pairs exhibit enhanced stability under both compressive and tensile strain, with formation enthalpy reductions of 1.49 eV and 1.05 eV, respectively. In contrast, in-plane (IP) vacancy pairs are stabilized under compressive strain but are insensitive to tensile strain. Finally, we discuss how these findings influence Bi stoichiometry during thin-film growth and the role of local strain fields in the formation of conducting domain walls.

Thin Film Stoichiometry and Defects Management for Low Threshold and Air Stable Near-Infrared Perovskite Laser.

While significant efforts have been devoted to optimize the thin-film stoichiometry and processing of perovskites for applications in photovoltaic and light-emitting diodes, there is a noticeable lack of emphasis on tailoring them for lasing applications. In this study, it is revealed that thin films engineered for efficient light-emitting diodes, with passivation of deep and shallow trap states and a tailored energetic landscape directing carriers toward low-energy emitting states, may not be optimal for light amplification systems. Instead, amplified spontaneous emission (ASE) is found to be sustained by shallow defects, driven by the positive correlation between the ASE threshold and the ratio of carrier injection rate in the emissive state to the recombination rate of excited carriers. This insight has informed the development of an optimized perovskite thin film and laser device exhibiting a low threshold (≈ 60 µJ cm-2) and stable ASE emission exceeding 21 hours in ambient conditions.

Quantitative Raman and x-ray photoelectron spectroscopy of mixed-phase indium selenide films

Indium selenide is a polymorphous material system that has attracted considerable attention due to the outstanding electronic, optical, ferroelectric, and antiferroelectric properties of its various crystalline phases; however, this polymorphism adds a layer of complexity to the analysis of Raman and x-ray photoelectron (XPS) data of these materials. In this report, a method of quantitative analysis of combined Raman and XPS data is developed to determine the stoichiometry of indium selenide thin films, as well as the phase fraction of β-In2Se3, γ-In2Se3, and κ-In2Se3 within the films. A 13:1 ratio of the indium to selenium sensitivity factors (σIn/σSe = 13) was found to yield the most accurate stoichiometry results. Further structural characterization of the κ-In2Se3 film was performed and points to its existence in these films as a distinct phase, rather than strained γ-In2Se3.

Substrate temperature dependent crystal structure and deep-ultraviolet photodetection of ZnGa2O4 thin films * *Project supported by This work was supported by the National Natural Science Foundation of China (No. 12074044), the Fund of State Key Laboratory of Information Photonics and Optical Communications (IPOC2021ZT05), and the Fundamental Research Funds for the Central Universities (BUPT, 2023ZCJH1).

Zinc gallate (ZnGa2O4) is a promising material for deep-ultraviolet (DUV) photodetectors, owing to its wide bandgap and high transparency. However, the effect of substrate temperature on the structural and optical properties of ZnGa2O4 thin films prepared by magnetron sputtering is not well understood. Here, we report a systematic study of the influence of substrate temperature on the crystal quality, stoichiometry, bandgap, and photodetection performance of ZnGa2O4 thin films deposited on sapphire substrates. We find that the films undergo a phase transition from amorphous to polycrystalline at 300 °C, and then to single crystalline at 500 °C, accompanied by an increase in the bandgap from 4.6 to 4.9 eV. We also fabricate metal-semiconductor–metal photodetectors based on the ZnGa2O4 thin films with Ti/Au electrodes, which exhibit excellent Ohmic contact and high light-to-dark current ratio. The photodetectors show remarkable and stable DUV response, with the highest performance achieved at a substrate temperature of 650 °C. Our results demonstrate the crucial role of substrate temperature in tailoring the crystal structure and DUV photodetection of ZnGa2O4 thin films, and provide a facile route for optimizing their performance.

INFLUENCE OF ANNEALING TEMPERATURE ON ZINC OXYSULPHIDE THIN FILMS PROPERTIES DEPOSITED BY THERMAL SPRAY TECHNIQUE

This article studies the effects of annealing temperatures on the stoichiometry, structure, and optical characteristics of Zinc Oxysulphide thin films deposited on glass substrates using the thermal spray method. The annealing was done in the air under a temperature of 150 ºC, 250 ºC and 350 ºC. Field Emission Scanning Electron Microscopy (FESEM), X-ray diffractometry (XRD), and a UV-Vis Spectrophotometer were utilized to examine the thin films' morphological, structure, and optical characteristics as grown and annealed samples. It has been observed that the film thickness decreases as the annealing temperature increases. The XRD pattern demonstrates that as-prepared and annealed samples at 250C, and 350C are amorphous, while film annealed at 150 C is crystalline with the hexagonal phase and orientated along (110) plane. FESEM image of the as-prepared Zinc Oxysulphide thin films shows flower-like sheet nanostructures. However, for the annealed samples, the FESEM images show cone-like with a combination of sheets and aggregate nanoparticles. EDX analysis reveals the presence of Zn, O as well as sulfur. The transmittance of the film decreases from 63% to 37% and the band gap energy reduces slightly from 3.99 to 3.92 eV as the annealing temperature increase.

Bioglass and Vitamin D3 Coatings for Titanium Implants: Osseointegration and Corrosion Protection.

The use of MAPLE synthesized thin films based on BG and VD3 for improving the osseointegration and corrosion protection of Ti-like implant surfaces is reported. The distribution of chemical elements and functional groups was shown by FTIR spectrometry; the stoichiometry and chemical functional integrity of thin films after MAPLE deposition was preserved, optimal results being revealed especially for the BG+VD3_025 samples. The morphology and topography were examined by SEM and AFM, and revealed surfaces with many irregularities, favoring a good adhesion of cells. The thin films' cytotoxicity and biocompatibility were evaluated in vitro at the morphological, biochemical, and molecular level. Following incubation with HDF cells, BG57+VD3_ 025 thin films showed the best degree of biocompatibility, as illustrated by the viability assay values. According to the LDH investigation, all tested samples had higher values compared to the unstimulated cells. The evaluation of cell morphology was performed by fluorescence microscopy following cultivation of HDF cells on the obtained thin films. The cultivation of HDF's on the thin films did not induce major cellular changes. Cells cultured on the BG57+VD3_025 sample had similar morphology to that of unstimulated control cells. The inflammatory profile of human cells cultured on thin films obtained by MAPLE was analyzed by the ELISA technique. It was observed that the thin films did not change the pro- and anti-inflammatory profile of the HDF cells, the IL-6 and IL-10 levels being similar to those of the control sample. The wettability of the MAPLE thin films was investigated by the sessile drop method. A contact angle of 54.65° was measured for the sample coated with BG57+VD3_025. Electrochemical impedance spectroscopy gave a valuable insight into the electrochemical reactions occurring on the surface.

Deposition of stoichiometry – tailored amorphous Cu-S thin films by MOCVD technique

ABSTRACT Deposition technique and associated deposition parameters play significant roles in determining the stoichiometry of thin films, and consequently, their properties. Herein, Cu-S thin films were deposited on a sodalime glass substrate via metal organic chemical vapour deposition (MOCVD) at temperatures between 350 and 450°C using a single solid source precursor. The deposited Cu-S films were characterized using Rutherford backscattering spectroscopy (RBS), X-ray diffraction (XRD), scanning electron microscopy (SEM), UV–visible spectrophotometry, and four-point probe technique. RBS characterization revealed that the films are non-stoichiometry while thickness increased from 480 to 655 nm as deposition temperature increased. SEM revealed micrographs that are temperature-dependent. A direct band gap value between 2.75 and 3.80 eV was obtained as the deposition temperature increased. Electrical characterization showed ohmic characteristics in which, resistivity decreased from 18.50 × 10−3 Ωcm to 8.20 × 10−3 Ωcm as deposition temperature increased.

Photocatalytic activities of SnS thin films deposited at room temperature

Tin monosulfide (SnS) thin films were deposited on glass substrates at room temperature utilising a simple, inexpensive, and modified chemical approach known as Successive Layer Adsorption and Reaction (SLAR). The properties of the films were thoroughly studied using an XRD, SEM, EDAX, and UV-VIS spectrophotometer. It was possible to deposite smooth, homogeneous, and uniform thin films with pollycrystalline nature, orthorombic structure, and UV-VIS absorption. Under visible light irradiation, SnS thin films demonstrated high photocatalytic degradation of Methylene Blue. It showed effective degradation of a common textile dye available in the marker as well. Dye degradation was found to be of first order, following the Langmuir-Hinshelwood mechanism. Theoretical band structure calculations suggested that the relative positions of the highest valence band and lowest conduction band were 1.605 eV and -0.085 eV, respectively. The photocatalyst's reusability, the involvement of the hydroxyl radical in photodegradation, and the variation in photocatalytic performance of SnS thin films with dye solution pH and initial dye concentration were all examined. Changes in the cationic precursor's molarity caused changes in the thin film's crystallinity, stoichiometry, and bandgap. Non-stoichiometric films demonstrated higher photocatalytic activity.

Self-limiting stoichiometry in SnSe thin films.

Unique functionalities can arise when 2D materials are scaled down near the monolayer limit. However, in 2D materials with strong van der Waals bonds between layers, such as SnSe, maintaining stoichiometry while limiting vertical growth is difficult. Here, we describe how self-limiting stoichiometry can promote the growth of SnSe thin films deposited by molecular beam epitaxy. The Pnma phase of SnSe was stabilized over a broad range of Sn : Se flux ratios from 1 : 1 to 1 : 5. Changing the flux ratio does not affect the film stoichiometry, but influences the predominant crystallographic orientation. ReaxFF molecular dynamics (MD) simulation demonstrates that, while a mixture of Sn/Se stoichiometries forms initially, SnSe stabilizes as the cluster size evolves. The MD results further show that the excess selenium coalesces into Se clusters that weakly interact with the surface of the SnSe particles, leading to the limited stoichiometric change. Raman spectroscopy corroborates this model showing the initial formation of SnSe2 transitioning into SnSe as experimental film growth progresses. Transmission electron microscopy measurements taken on films deposited with growth rates above 0.25 Å s-1 show a thin layer of SnSe2 that disrupts the crystallographic orientation of the SnSe films. Therefore, using the conditions for self-limiting SnSe growth while avoiding the formation of SnSe2 was found to increase the lateral scale of the SnSe layers. Overall, self-limiting stoichiometry provides a promising avenue for maintaining growth of large lateral-scale SnSe for device fabrication.

Effect of precursor concentration on stoichiometry and optical properties of spray pyrolyzed nanostructured NiO thin films

In this study, spray pyrolysis was used to produce nanostructured NiO thin films from high purity nickel acetate (Ni(CH3COO)2.3H2O) precursors on pre-heated ultrasonically cleaned soda-lime glass substrates. The metallic constituent concentrations in the films were varied, and the precursors were produced in distilled water at various molarities ranging from 0.1 to 0.4 M. In the study, the field-emission scanning electron microscope (FESEM) results strongly confirmed adherence of the films to the glass substrate at 350 °C. The presence of Ni and O in the samples was confirmed using Rutherford backscattering spectroscopy (RBS), X-ray diffractometry (XRD) and energy dispersive X-ray spectroscopy (EDX). For the 0.1 M NiO thin films, the thickness was approximately 43 nm, and for the 0.2 M, 0.3 M, and 0.4 M films, the thickness was 46 nm, 47 nm, and 49 nm, respectively. The XRD findings were supported by the increased Raman intensity peaks with increased precursor concentration, which confirmed the films' improved crystallinity. For the same number of passes of films deposition, as the molar concentration increases, the films thickness increases. The amount of nickel in NiO thin films increases as the molarity increases, but the amount of oxygen in NiO thin films decreases as the molarity increases. It was discovered that as molarity increases, the optical transmittance decreases and the optical band gap narrows. The qualities of NiO discovered in this study suggest the films’ potentials for usage as window layer and buffer material in thin film solar cells.

From transparent to black amorphous zinc oxide thin films through oxygen deficiency control

Despite the fact that zinc oxide is a well-known transparent oxide, several recent studies on “black” ZnO have renewed its potential for photocatalytic applications. We report on the control of oxygen deficiency in ZnO thin films grown at 300 °C on c-cut sapphire single-crystal substrates by pulsed electron beam deposition (PED) through a slight variation of argon pressure in PED. At a pressure of 2 × 10−2 mbar transparent, stoichiometric (ZnO) and crystalline films are obtained, while at 9 × 10−3 mbar black, oxygen-deficient (ZnO0.85) and amorphous films result. Stoichiometry, structural, and optoelectronic properties of transparent and black ZnO thin films were comparatively analyzed as a function of oxygen deficiency. Black ZnO thin films exhibit enhanced absorption in the visible and near-infrared due to oxygen deficiency, thus extending the range of applications of zinc oxide thin films from transparent electronics to solar absorbers and photocatalysis.

Relative effects of pulsed laser deposition parameters on the stoichiometry of thin films

Pulsed laser deposition has a reputation for maintaining the stoichiometry of the ablation target in the deposited film. Exceptions to this "rule" occur, however, for materials, such as multiferroic BixDy(1-x)FeO3 (BDFO), that contain elements with large differences in volatility, like Bi and Fe. The relative effect of various pulsed laser deposition processes on the resulting stoichiometry of BDFO films as a function of time (or number of laser pulses) has been examined using an interactive spreadsheet, as well as experimentally. The adjustable parameters within the spreadsheet include target composition, target element ablation yield, ablation plume spread, background gas pressure, ablated target atom kinetic energy, and ablated element sticking coefficient on the substrate. Examples of how the calculated film composition might evolve are given, along with experimental results showing how the deposition parameters individually affect BDFO film stoichiometry. Finally, the calculated relative contributions of the various deposition processes, in terms of how much they affect the deposited film stoichiometry, are compared.

MOCVD growth and band offsets of κ-phase Ga2O3 on c-plane sapphire, GaN- and AlN-on-sapphire, and (100) YSZ substrates

Epitaxial growth of κ-phase Ga2O3 thin films is investigated on c-plane sapphire, GaN- and AlN-on-sapphire, and (100) oriented yttria stabilized zirconia (YSZ) substrates via metalorganic chemical vapor deposition. The structural and surface morphological properties are investigated by comprehensive material characterization. Phase pure κ-Ga2O3 films are successfully grown on GaN-, AlN-on-sapphire, and YSZ substrates through a systematical tuning of growth parameters including the precursor molar flow rates, chamber pressure, and growth temperature, whereas the growth on c-sapphire substrates leads to a mixture of β- and κ-polymorphs of Ga2O3 under the investigated growth conditions. The influence of the crystalline structure, surface morphology, and roughness of κ-Ga2O3 films grown on different substrates are investigated as a function of precursor flow rate. High-resolution scanning transmission electron microscopy imaging of κ-Ga2O3 films reveals abrupt interfaces between the epitaxial film and the sapphire, GaN, and YSZ substrates. The growth of single crystal orthorhombic κ-Ga2O3 films is confirmed by analyzing the scanning transmission electron microscopy nanodiffraction pattern. The chemical composition, surface stoichiometry, and bandgap energies of κ-Ga2O3 thin films grown on different substrates are studied by high-resolution x-ray photoelectron spectroscopy (XPS) measurements. The type-II (staggered) band alignments at three interfaces between κ-Ga2O3 and c-sapphire, AlN, and YSZ substrates are determined by XPS, with an exception of κ-Ga2O3/GaN interface, which shows type-I (straddling) band alignment.

Application of Parametric Modeling in Atomic Layer Deposition

Atomic Layer Deposition (ALD) is sequential and conformal process that provides precise thickness control due to its self-limiting nature even in high aspect ratio structures. The exponential growth in the use of ALD is due the availability of hundreds of precursor chemistries for diverse technological applications beyond just semiconductors and microelectronics. However, one of recurring challenges is the problem of results disparity, and errors that underline the causes of disparity, primarily may be due to lack of consistency in process optimization and reproducibility. In this research, a Design of Experiment (DoE) approach is adopted for parametric optimization for synthesis of Al2O3 thin films using ALD. The objective of this work is to adopt DoE for reproducible ALD synthesis processes within statistical reliability.Briefly, the precursors used for Al2O3 ALD (Ultratech Veeco Thermal ALD) were Trimethylaluminum (TMA) and H2O with Ozone. The effect of four parameters, namely pulse duration of TMA and water, number of cycles, and temperature were evaluated for the response parameter of Al2O3 thickness on Si with 300 nm of SiO2. E-Chip DoE software was chosen for data modeling. E-Chip considers multivariate analysis to provide the parametric relationship for Analysis of Variances (ANOVA) and predictive surface response analysis, thus eliminating the need for extensive process optimization experiments that are required for full factorial design. Initially, screening experiments were conducted to determine the levels of input parameters. The pulse duration for TMA and H2O were 0.01-0.02 sec, the number of cycles were varied between 50 and 100, the temperature range was 100-200 0C. For each sample, five thickness and roughness readings were measured on an ex-situ ellipsometer and Atomic Force Microscope (AFM). The stoichiometry of Al2O3 thin films were evaluated using XPS.The data analysis reveals that the influential parameters are number of cycles, pulse duration, and temperature in the order of their significance. The direct relationship between number of cycles and Al2O3 thickness infers that flux available is effectively used for layer growth. The consistency of layer thickness is related not just to the conformality but also to the adsorption of reactive species effectively. Uneven pulse duration also contributes to the linear growth of layer thickness, which supports the effectiveness of reactive species saturation and purging of un-reactive elements. The temperature variation was also an influential parameter as it affected the vapor pressure for TMA and H2O. This mechanistic model based on DoE is a suitable tool to predict the ALD’s growth per cycle, which can further help in understanding of any chemisorption with substrate treatment or variation in film roughness characteristics. Study of other DoE parameters such as type of substrate, substrate functionalization, reactor size in relation to the size of substrate, and purge duration are ongoing. Figure 1 describes the ANOVA chart estimates and surface response graphs, which identifies the bounded parametric region along with the ability to predict the influence of change in parameters based on developed mechanistic model. Figure 1

Effect of swift heavy ion irradiation on the resistive random access memory performance of sputter deposited zinc rich zinc oxide thin films

Resistive Random-Access Memory (RRAM) devices are synthesized by sandwiching (i) ZnO thin film and (ii) Zn-rich ZnO thin film between top and bottom conducting electrodes consisting of Au thin layer and ITO substrate respectively. DC Sputtering was used to create the metal contact at the top of the device, while simultaneous RF and DC magnetron sputtering was used to form the ZnO and metal-rich oxide layer-based devices. The RRAM device was irradiated with 100 MeV Ag at a fluence of 1013 ions/cm2. The I-V characteristics of pristine and irradiated Au/ZnO/ITO and Au/Zn rich ZnO/ITO were measured using a semiconductor device analyser B1500. The thickness, stoichiometry, and crystallinity of zinc oxide thin films were determined using Rutherford Back Scattering, X-ray diffraction and Raman Spectroscopy. The present work shows that the performance of RRAM devices both in the ZnO and Zn rich ZnO significantly improves by ion irradiation.

Molecular dynamics, transport property, and surface stoichiometry of plasma polymerized cyclohexane thin films

The properties of cyclohexane (CHex) and plasma polymerized cyclohexane (PPCHex) thin films are studied, and the results are compared with those obtained using a computing model (under the density functional theory framework). Quantum chemical calculations are performed to calculate their molecular electrostatic potential (MEP), highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) gaps, thermodynamic stability, chemical reactivity, and vibrational properties. The HOMO–LUMO energy gap sharply decreased in the case of the PPCHex thin film compared to that of CHex. Gibbs free energy shows a similar phenomenon where the enthalpy of PPCHex (formation) is almost six times higher than that of CHex. The computed FTIR spectra indicate good agreement with the experimental results. RMS roughness shows a smooth surface, and it is compared with the FESEM image. Moreover, the dielectric constant and electrical conductivity of the PPCHex thin films are also studied.

Effective target arrangement for detecting the properties of Ni doped diamond-like carbon by pulsed laser deposition

In the current study, diamond-like carbon (DLC) was synthesized by pulsed laser deposition (PLD) in a vacuum at room temperature, focusing on Ni-dopant concentration and arrangement of Ni strips in both parallel and transverse positions. The morphology and structural properties of Ni-DLC films were analyzed by Raman spectroscopy, atomic force microscopy (AFM) analysis, cross-section analysis, energy-dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), contact angle (CA), and nanoindentation test. AFM images exhibit the new shapes of Ni-DLC thin films, named conic and nano-mushroom particles. The Raman spectra of Ni-DLC films show that the calculated intensities D-line to G-line ratio experiences a decrease with increasing Ni dopants in the transverse arrangement while the parallel arrangement represents a different trend. The stoichiometry of Ni-DLC thin films has been reported from the cross-section of thin films. It is also observed from the measured CA that the hydrophilic properties of Ni-DLCs increase in the transverse arrangement. Low nickel content in diamond-like carbon matrix exhibited the dominance of diamond phase and good mechanical properties have been found.

Titanium Nitride based multi-functional thin films

The aim of the present work is to demonstrate that the applications of TiN thin films can be expanded well beyond the traditional domains. For example, although TiN is known to exist in several sub-stoichiometric forms their properties have not been exploited fully. Using a patented sputtering process technology, we show that the Ti2N phase is semiconducting, possesses a band gap of the order of 3.5eV and a hardness in the region of 5-7 GPa. Thisimplies that Ti2N thin films can be candidates for light emitting diode applications. In some cases, reflectivity <2% in the visible region was also achieved which is useful for optical shielding applications. The nitrogen stoichiometry and thickness of TiN thin films can be tuned to achieve colours from blue to brown to golden yellow for decorative coating applications. TiN thin films can be a cost-effective replacement for Au since they also display a surface plasmon resonance at the same wavelength. The conductivity of TiN is sufficiently high to replace gold as an electrode material in electronic devices such as diodes. The properties of TiN-Si3N4 and TiN-Polyaniline composite thin films are also reported. The current work, thus, demonstrates the multi-functionality of TiN as an optical, opto-electronic and electronic material.

Atomic layer annealing for modulation of the work function of TiN metal gate for n-type MOS devices

Tailoring the work function of metal gates at a low temperature is critical to the electronic performance of advanced nanoscale MOSFET devices. In this paper, the work function of TiN thin films is effectively altered by the atomic layer annealing (ALA) technique, i.e. the layer-by-layer, in-situ argon plasma treatment incorporated into each atomic layer deposition cycle. The density, stoichiometry, and crystallinity of TiN thin films can be significantly improved by the ALA treatment at a low temperature of only 300℃, which leads to a wide tunability of the work function from 4.52 to 4.03 eV of the TiN metal gate. The sufficiently low work function of 4.03 eV is highly favorable to the low power consumption in n-type MOSFETs. The result indicates that the ALA technique is an advantageous approach to modulating the physical and material properties of metal gates in nanoscale MOS devices by precise energy transfer with atomic-scale accuracy.

Growth and characterization of crystalline Bi2Se3 thin films on flexible metal foils by magnetron sputtering system

We report the large area thin film deposition of Bi2Se3 on flexible thin molybdenum (Mo) and titanium (Ti) metal foils using magnetron sputtering technique at temperature of 400 °C. The crystallinity of post-selenized thin film was investigated using x-ray diffraction and high intense peaks of Bi2Se3 (0006) along other planes was obtained which showed the preferred orientation along c-axis on these polycrystalline substrates. Raman spectroscopy showed three main characteristic Raman peaks i.e. A11g, E2g, and A21g which revealed the formation of pure hexagonal phase of the Bi2Se3. Field emission scanning electron microscopy studied showed hexagonal nanoflakes shape Bi2Se3 films with large granular sizes ranging from 200 to 450 nm and stoichiometry of Bi2Se3 thin film was confirmed by energy dispersive x-ray analysis. The growth of crystalline hexagonal phase of Bi2Se3 thin films on large area polycrystalline low cost flexible metal foils using magnetron sputtering system pave the way for futuristics flexible energy devices.