Grain Size Of Films Research Articles

Growth-Temperature Dependent Unpassivated Oxygen Bonds Determine the Gas Sensing Abilities of Chemical Vapor Deposition-Grown CuO Thin Films.

CuO is a multifunctional metal oxide excellent for chemiresistive gas sensors. In this work, we report CuO-based NO2 sensors fabricated via chemical vapor deposition (CVD). CVD allows great control on composition, stoichiometry, impurity, roughness, and grain size of films. This endows sensors with high selectivity, responsivity, sensitivity, and repeatability, low hysteresis, and quick recovery. All these are achieved without the need of expensive and unscalable nanostructures, or heterojunctions, with a technologically mature CVD. Films deposited at very low temperatures (≤350 °C) are sensitive but slow due to traps and small grains. Films deposited at high temperatures (≥550 °C) are not hysteretic but suffer from low sensitivity and slow response due to lack of surface states. Films deposited at optimum temperatures (350-450 °C) combine the best aspects of both regimes to yield NO2 sensors with a response of 300 % at 5 ppm, sensitivity limit of 300 ppb, hysteresis of <20%, repeatable performance, and recovery time of ∼1 min. The work demonstrates that CVD might be a more effective way to deposit oxide films for gas sensors.

Enhancement of metal-insulator transition performance of VO2 thin films by conventional furnace annealing

The vanadium dioxide (VO2) thin films fabricated by rapid thermal annealing (RTA) of vanadium thin films have high defect density and low phase transition magnitude. In this manuscript, VO2 thin films were fabricated by sputtering deposition and RTA process, then the VO2 thin films were annealed by the conventional furnace to improve metal-insulator transition performance. The effect of conventional furnace annealing (CFA) on content, grain size and phase transition property of VO2 thin films were studied. From the calculations of the VO2 grain size, the CFA method effectively increases the VO2 grain size. The valence and chemical composition of vanadium before and after annealing were studied by X-ray photoelectron spectroscopy. The results show that the content of V4+ in the film is significantly increased by CFA. After CFA on the basis of RTA, the transition magnitude of VO2 film increased from 90 to about 1600. It is feasible to prepare high-quality VO2 films with enhanced metal-insulator transition performance by CFA of VO2 films after RTA, which is beneficial to the application of VO2 thin films in optoelectronic devices.

Experimental and Ab Initio Investigation of the Physical Properties of PbS Thin Films Prepared by Chemical Bath Deposition (CBD)

In this work, high-quality PbS thin films were prepared by the chemical bath deposition (CBD) method for different molarities of sulfur precursors (1 M to 1.4 M) in a basic solution. The composition, morphology, and structural and optical properties of the PbS thin films were studied by means of scanning electron microscopy (SEM–EDS), X-ray diffraction (XRD), and UV–visible spectrophotometry (UV–Vis). The spectra obtained by XRD show that the PbS thin films crystallize in a NaCl structure with the grating parameter (a = 5.9202 A) and the (002) plane is a preferential orientation of the films. The optical band gap decreases from 1.5 to 1.23 eV as the grain size of the PbS thin films increases from 15 to 37 nm. The decrease in the band gap is due to quantum confinement effects promoted by the small Bohr radius of this material (18 nm). Our experimental results have been validated by theoretical calculations in the framework of the functional density theory (FDT) using the full potential linearized augmented plane wave (FP-LAPW) as implemented in the WIEN2K code. The value of the optical band gap found in PbS nanoparticles is suitable for solar cell applications.

Evaluation of correlation between fill factor and high mobility transparent conductive oxide film deposition temperature in the silicon heterojunction solar cells

We investigated the degradation factor of the conversion efficiency of the silicon heterojunction solar cells. In particular, we clarified the effect of the transparent conductive oxide film deposition conditions on the film quality and interface states, and the relationship between these factors and the conversion efficiency. Heat process causes a decrease in carrier mobility due to a decrease in the grain size of the TCO film, but has an effect of improving the TCO/a-Si:H(p) interface states. In particular, the silicon oxide layer between the TCO film and a-Si:H(p) increases the series resistance and moderates the band bending at the TCO/a-Si:H(p) interface, leading to FF degradation. Since In2O3:H film easily forms a silicon oxide layer at the TCO/a-Si:H(p) interface, the interface treatment is important factor in the cell manufacturing process.

Annealing temperatures effect on the electrical and structural properties of nanocrystalline vanadium dioxide films prepared by Sol–Gel technique

Vanadium oxide (VO2) films glass substrate deposition was achieved at room temperature by the sol–gel method. The fabricated VO2 films were annealed for 1 h at 200, 250, and 300 °C in air. The annealing temperature’s effects on the electrical and structural properties of VO2 films were investigated by DC conductivity, dielectric, AC conductivity, and X-ray diffraction (XRD). XRD results of the annealed films reveal the presence of polycrystalline VO2 with a monoclinic structure. Using the Scherrer equation, an average grain size of VO2 films was estimated to be 2.1–10.8 nm. The density of annealed films was found to be 4.53–4.75 g/cm3. The DC-electrical conductivity reveals the semiconductor behavior of all samples. The activation energy of the prepared films was deduced as 0.22–0.38 eV. The DC conductivity for the VO2 films decreases at an annealed temperature higher than 200 °C, which may due to the increase in grain boundary scattering due to the increase in grain size. The dielectric measurements show that the dielectric loss and dielectric constant decline with the increasing frequency however of these parameters with the annealing temperature. Moreover, the increasing of the AC conductivity with the temperature and frequency is observed. These results suggest that the mobility of charge carriers was increased.

Tuning grain size, morphology, hardness and magnetic property of electrodeposited nickel with a single multifunctional additive

The room temperature electrodeposition of high purity, nanocrystalline Ni films prepared in the presence of poly-(2-ethyl-2-oxazoline) (PEOX) as a new multipurpose polymeric additive in Watts bath is presented. The grain size, morphology, hardness and magnetic property of the nickel films were simply tuned by adjusting the concentration of PEOX. Increasing PEOX concentration contributed to grain refinement down to 12.5 nm grain size and crystalline orientation towards (220) planes. The control over the crystalline grain size and the orientation by PEOX concentration allows the preparation of tailor made nickel layers with adjustable physical and chemical properties. The effect of PEOX on the structure is attributed to the high affinity of tertiary amide groups in PEOX for metal surfaces, whereas the incorporation of the macromolecular additive into the nickel layers was prevented. These findings are especially important in emerging applications where smooth, high purity nanocrystalline layers are required. PEOX as a multifunctional additive eliminates the need to use multiple electrolyte additives to obtain a set of desirable properties.

Effect of Annealing Temperature on Microstructure and Resistivity of TiC Thin Films

Titanium carbide (TiC) thin films were prepared by non-reactive simultaneous double magnetron sputtering. After deposition, all samples were annealed at different temperatures under high-vacuum conditions. This paper mainly discusses the influence of deposition methods and annealing temperatures on microstructure, surface topography, bonding states and electrical resistivity of TiC films. XRD (X-ray diffraction) results show that TiC thin films can still form crystals without annealing, and the crystallinity of thin films is improved after annealing. The estimated grain size of the TiC films varies from 8.5 nm to 14.7 nm with annealing temperature. It can be seen from SEM (scanning electron microscope) images that surfaces of the films are composed of irregular particles, and when the temperature reaches to 800 °C, the shape of the particles becomes spherical. Growth rate of film is about 30.8 nm/min. Oxygen-related peaks were observed in XPS (X-ray photoelectron spectroscopy) spectra, which is due to the absorption of oxygen atoms on the surface of the film when exposed to air. Raman spectra confirm the formation of TiC crystals and amorphous states of carbon. Resistivity of TiC films decreases monotonically from 666.73 to 86.01 μΩ·cm with the increase in annealing temperature. In brief, the TiC thin films prepared in this study show good crystallinity, thermal stability and low resistivity, which can meet the requirements of metal gate applications.

Efficient green-emitting perovskite light-emitting diodes using a conjugated polyelectrolyte additive

Charge carrier confinement and defect passivation are the main research struggle for the development of efficient perovskite light-emitting diodes (PeLEDs). In this study, we report a green-emitting PeLED by adding an anionic conjugated polyelectrolyte containing tetraethylammonium counter ions (MPS2-TEA) into formamidinium lead tribromide quasi-2D perovskites. X-ray diffraction shows that perovskite films with MPS2-TEA are more randomly oriented compared to the films without MPS2-TEA. Interestingly, the incorporation of MPS2-TEA reduces the roughness of surfaces and grain sizes of the perovskite films. The increases in photoluminescence intensity (by three times) and lifetime (18.11 vs. 9.81 ns) of perovskite films with MPS2-TEA compared to those of the pristine films suggest improved radiative recombination by intermixing perovskite with MPS2-TEA. Defect density in perovskite films with MPS2-TEA is significantly suppressed owing to defect passivation at the grain boundaries by MPS2-TEA. The PeLED with MPS2-TEA shows a significantly improved external quantum efficiency of up to 15.47%, the current efficiency of 69.02 cd/A, and maximum luminance of 12,252 cd/m2, compared to a device without MPS2-TEA.

Small grains as recombination hot spots in perovskite solar cells

Summary Non-radiative recombination in the perovskite bulk and at its interfaces prohibits the photovoltaic performance from reaching the Shockley-Queisser limit. While interfacial recombination has been widely discussed and demonstrated, bulk recombination and especially the influence of grain boundaries remain under debate. Most studies explore the role of grain boundaries on perovskite films rather than devices, making it difficult to link the film properties with those of the devices. Here, we systematically investigate the effects of grain boundaries on the performance of perovskite solar cells by two different methods. By combining experimental characterization with theoretical device simulations, we find that the recombination at grain boundaries is diffusion limited and hence is inversely proportional to the grain area to the power of 3/2. Consequently, the prevalence of small grains—which act as recombination hot spots—across the perovskite active layer dictates the photovoltaic performance of the perovskite solar cells.

Controlling the Microstructure and Porosity of Perovskite Films by Additive Engineering

In this work, a facile, versatile approach to control the grain size and layer porosity of perovskite films is introduced. By gradually tuning the amount of additive (hypophosphorous acid, HPA) in the methylammonium lead triiodide (MAPbI3) perovskite precursor solution, the perovskite grain size can be enhanced by over one order of magnitude regardless of the choice of the underlying layer or substrate. A further increase in the HPA amount results in the formation of a porous perovskite layer with large grains. When incorporated in perovskite solar cells with an inverted architecture, the increase in grain size results in devices with a far higher open-circuit voltage (up to 1.16 V), corresponding to a power conversion efficiency of 20.1%. This work shows that HPA is superior to many other additives in its ability to tune the film microstructure and further demonstrates that unlike other additives, it can also be used to form high-quality porous perovskite films of great interest for application in light-emitting diodes.

ELECTRODEPOSITION OF SILVER THIN FILMS ON A GOLD SUBSTRATE IN THE PRESENCE OF OCIMUM GRATISSIMUM (Og) AND VERNONIA AMYGDALINA (Va) PLANT LEAF EXTRACTS.

Electrodeposition an advanced thin film deposition method originally used for decorative purposes and now widely used in industrial applications such as electronics, phonics, magnetic recording and protective coatings, has also been used for the production of size and structure-controlled nanoparticles. In this research, the electrodeposition of silver (Ag) films on gold (Au) substrates with two plant (Ocimum gratissimum (Og) and Vernonia amygdalina (Va) leaf extracts as additives was explored . The effect of these leaf extracts immediately after addition and after a prolonged exposure in the electrolyte on the silver deposits was studied using cyclic voltammetry (CV), chronoamperometry (CA) and linear sweep voltammetry (LSV). Silver thin films were electrodeposited on gold film from an electrolyte of 5 mM AgNO3 and later 5 mM AgNO3 +0.1 M KNO3 for 10 minutes, using a double potential step protocol and potentials -0.15 V and -0.3 V with and without the plant leaf extracts. As silver was grown on the gold substrate, silver nanoparticles were also discovered to have been formed in the electrolyte. Though the deposition potential in the presence of the plant leaf extracts affected the kinetics of the silver deposition on the gold substrate, it only slightly affected the silver film thickness on the gold. CV graphs with the plant leaf extracts show lower current densities indicating a slowing down of the deposition/dissolution rates of silver probably due to the adsorption of the leaf extracts on the surface of the growing silver films which may have affected the transport of silver ions (Ag+) towards the electrode and impacted on the silver deposition/dissolution kinetics. The deposited silver film thickness was 7 nm to 8 nm with the Og leaf extract and 1.5 nm to 2 nm with the Va leaf extract. Atomic Force microscope (AFM) was used for viewing the silver films and the mean grain sizes of the Og silver films was calculated to be . This was larger than those of the Va silver films calculated to be While the Va silver films surface roughness was higher at 10.6 , that of the Og silver film was 9.3.

Preparation and characterization of Cu2ZnSnS4 thin films with various compositions deposited by a dual thermal evaporation technique

Cu2ZnSnS4 (CZTS) thin films were deposited successfully with four different compositions, namely, Cu-rich, Sn-rich, Zn-rich and near-stoichiometric CZTS, by a dual thermal evaporation technique to investigate the effect of stoichiometry on the physical properties of the deposited films. The thin films were characterized by energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction, Raman spectroscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM), and UV–VIS–NIR spectroscopy in the as-deposited state and after annealing in nitrogen at 350 °C for 30 min. It was found that the stoichiometry of the film played a critical role in the physical properties and stability after annealing. Increasing the amount of each element compared to that of the others impacted the colour, preferred orientation, grain size, microstrain, dislocation density, surface morphology, transmittance, reflectance, absorbance and band gap of the thin films. A (112) preferred orientation was obtained, and this orientation became more pronounced after the annealing of all films. The stoichiometry of the films changed after annealing due to re-evaporation of the sulfur, and the Cu-rich film was the most stable of the films studied herein. The estimated band gap (Eg) for the as-deposited films varied between 1.53 eV and 2.3 eV and were reduced to 1.1 eV for the Cu-rich film after annealing.

Synthesis and optical analysis of nanostructured F-doped ZnO thin films by spray pyrolysis: Transparent electrode for photocatalytic applications

In this paper, spray pyrolysis as a valuable cost-effective deposition technique was used to obtain nanostructured thin films of ZnO and ZnO: F on soda-lime glass substrates at 400 °C. The crystal structure and surface morphology of the as-deposited thin films have been characterized by the X-ray diffraction (XRD) technique and high-resolution atomic force microscope (AFM). XRD patterns indicated the wurtzite hexagonal structure of the deposited films with mean grain size in nanoscale. AFM and XRD confirmed that the mean grain size of ZnO film was increased with the F doping level. The optical parameters like refractive index, absorption coefficient, and optical bandgap have been obtained through Swanepoel's model depending on the transmission spectra of the deposited films. The direct optical band gap of ZnO film was slightly decreased with the F doping level. The single oscillator model was applied to determine the dispersion parameters of the films under study. The photocatalytic activity of the ZnO and ZnO: F thin films for the phenol photodegradation under UV-irradiation also has been evaluated to purify water from phenol as colorless organic waste. 3%F doped ZnO film has the highest constant rate of phenol photodegradation with high stability in reusing and recycling, confirming the high efficiency of F doped ZnO films as environmentally friendly photocatalysts for the removal of phenol from water.

Cuprous iodide dose dependent passivation of MAPbI3 perovskite solar cells

MAPbI3 has been considered as a candidate for the active layer of perovskite solar cells in recent years. We proposed a device model to investigate the contribution of cuprous iodide (CuI) to MAPbI3 perovskite thin films to power conversion efficiency (PCE) and demonstrated that the dosage of CuI affects the grain size of thin films and the PCE. Through the results of the SEM analysis, we found that the grain boundaries of MAPbI3 perovskite films decreased with increases in the dosage of CuI and the grain size increased significantly from 164 nm ± 49 nm–299 nm ± 127 nm. In addition, the results of the PL measurement showed that the PL intensity decreased after addition of CuI to the MAPbI3 perovskite thin films, suggesting a reduction in the charge recombination. The XRD patterns indicated that the addition of CuI did not influence the main structure of the MAPbI3 perovskite. Interestingly, CuI plays a key role in the passivation of defects in MAPbI3 perovskite thin films, which can reduce non-radiative recombination and increase the fill factor and open-circuit voltage of the device. In this study, we adjusted the grain size and passivated the MAPbI3 thin film by controlling the dosage of CuI. We also increased the power conversion efficiency from 10% to 13%. This type of perovskite solar cell provided a simple, low cost preparation process for practical applications.

A NEW APPROACH TO PREPARE POLYCRYSTALLINE PbTe–TeO THIN FILM, AND ITS OPTICAL, STRUCTURAL, SURFACE AND ELECTRICAL CHARACTERIZATION

In this study, PbTe thin film was produced on glass substrates, via chemical bath deposition (CBD) method, with 3-h deposition time at 50∘C. The produced thin film had polycrystalline structure; TeO2, PbTe, PbTe3 and Te2O5 crystals that were characterized by X-ray diffraction (XRD) had tetragonal, cubic, tetragonal and monoclinic crystal structures, respectively. Reflectivity ([Formula: see text]; in %), optical transmission ([Formula: see text]; in %), optical bandgap ([Formula: see text], absorption, dielectric constant ([Formula: see text], extinction coefficient ([Formula: see text] and refractive index ([Formula: see text] of polycrystalline PbTe thin film obtained using UV–Vis spectrophotometer were 29.87%, 19.41%, 3.30[Formula: see text]eV, 0.6, 3.72, 0.05 and 4.08, respectively. Grain sizes of polycrystalline PbTe thin film varied between 8.79[Formula: see text]nm and 52.55[Formula: see text]nm. Optical and electrical conductivities of the crystals according to photon energy were calculated using optical parameters, whereas their surface morphology was characterized by scanning electron microscopy (SEM). The thickness of polycrystalline PbTe thin film was measured by atomic force microscopy (AFM), and found to be 900[Formula: see text]nm.

Effect of annealing hold time on thickness and optical properties of barium titanate solar cell material

The development of perovskite-based solar cells has recently attracted the attention of many researchers because the efficiency value increases rapidly in a short span of time. Third generation solar cells have the potential to achieve Shockley-Queisser Limit of 31% for single energy bandgap solar cells. Besides that, this solar cell technology is economically very promising because the manufacturing costs are cheaper. The main drawback of this solar cell is its low stability (lifetime), which is caused by degradation over its lifetime. In addition, most of the high efficiency perovskite-based solar cells still use lead (Pb), so they are not environmentally friendly. Another alternative perovskite material is required. One promising material is Barium Titanate (BaTiO3). As a material for solar cells, not much research has been done. BaTiO3 film has been successfully made, which is then given annealing treatment at temperature of 500 °C, with annealing time of 30 minutes, 60 minutes, 90 minutes, and 120 minutes. In general, increasing the annealing time increases absorbance, decreases film thickness, decreases energy bandgap, and tends to reduce grain size of film. Energy bandgap tends to decrease with the increasing grain size. The grain size of film decreases with the decreasing thickness. More in-depth characterization and analysis are needed, especially those related to microstructure analysis.

On the multiplying factor for the estimation of the average grain size in thin films

The lineal-intercept method is commonly used to estimate the average grain size, where the ‘Mendelson’ multiplying factor (1.60) that is typically used explicitly assumes tetrakaidecahedral grains. While this is appropriate for bulk equiaxed microstructures, grains in thin films where the grain size exceeds the film thickness, are closer to prismatic polyhedrons in shape. Thus, assuming log-normal distribution of hexagonal-prism-shaped grains, a new multiplying factor of 1.20 is derived which relates the average grain size and measured intercept size. This model is successfully validated using experimental measurements of three different coarse-grained thin films of halide perovskites used in solar cells.

Insertion of Dielectric Interlayer: A New Approach to Enhance Energy Storage in HfₓZr1-xO₂ Capacitors

In this letter, we demonstrate an effective way to enrich the performance of HfxZr1–x O2 (HZO) energy storage capacitors (ESCs) by inserting Al2O3 dielectric interlayer (DIL) in the middle of HZO in TiN/HZO/TiN structure. The impact of DIL (1 A, 5 A and 10 A) is investigated in three different HZO compositions [1:1, 1:2 and 1:3]. Irrespective of HZO composition, insertion of DIL at critical thickness enhances the energy storage density (ESD) and efficiency of the ESCs. Grazing incident X-ray diffractometer (GIXRD) analysis reveals that Al2O3 DIL controls the grain size of the HZO films resulting in lower energy dissipation by controlling the linearity of the hysteresis loop. At 4.5 MV/cm, the best ESD ~55 J/cm3 with ~68% efficiency is achieved for HZO [1:2] capacitors at a critical Al2O3 thickness of 1 A which is ~35% and ~55% enhanced as compared to that without DIL [~41 J/cm3, ~44%]. The best efficiency of ~88% is achieved [ESD ~26 J/cm3] for HZO [1:3] capacitors at a critical DIL thickness of 10 A. The HZO [1:2] ESC with 1 A DIL displays robust thermal stability in 25 °C to 200 °C temperature range. Moreover, the aforesaid ESCs demonstrate excellent electrical stability even after 109 times of electric field cycling. Highest ESD of ~70 J/cm3 at ~50% efficiency is achieved for the same ESC when operated at 6.0 MV/cm. The results obtained herein provide a new strategy to achieve high performance ESCs and can be of significant scientific importance.

Micro and Nano-Crystalline Diamond Coatings of Co-cemented Tungsten Carbide Tools with Their Characterization

In this study, a bias-enhanced hot filament CVD system with methane and hydrogen as reactant gasses was used to deposit microcrystalline diamond (MCD) and nanocrystalline diamond (NCD) films on Co-cemented tungsten carbide substrates. They were then characterized using FE-SEM, Optical microscopy, XRD, and Raman Spectroscopy. Nanocrystalline diamond coating displays wide carbon peaks near 1350 cm−1 and 1580 cm−1 in Raman Spectroscopy, which correspond to D band and G band of carbon, and a sharp band increase near 1140 cm−1 because of the presence of trans-polyacetylene, confirming the sample as a nanocrystalline diamond. Similarly, the microcrystalline diamond phase was observed at 1350 cm−1 as broadened carbon peaks. The average grain size of the homogenous diamond film was roughly less than 90 nm, several tens of nanometres. The average indentation depths were 45 nm and 63 nm of MCD and NCD coatings and their average hardness values were found 80GPa and 50GPa, respectively. The morphology of the samples was observed using AFM, the average root mean square roughness of the MCD sample in the scanned area was found to be 354.11 nm and of the NCD sample was found to be 142.71 nm this indicates that the nanocrystalline diamond-coated WC was much smoother and had a smaller grain size than microcrystalline diamond coated ones. The values of the coefficient of friction vary from 0.38 to 0.42 for MCD coated sample. In contrast, for the NCD samples, the variations in the coefficient of friction were 0.30–0.36. A low coefficient of friction was observed in NCD as compared to MCD due to the presence of the graphite carbon phase.

Influence of the deposition temperature on the optical and electrical properties of TiN film by spectroscopic ellipsometry

Abstract Low emission (Low-e) films are widely used in modern architectural glass. In this presentation, spectroscopic ellipsometry (SE) between 1.12 and 2.75 eV (wavelength range: 450–1100 nm) was used to investigate the temperature dependence of dielectric function of TiN films. A Drude-3Lorentz dispersion model was selected and the results show both the real part e 1 and the imaginary part e 2 increase with the deposition temperature increasing. The structure and performance of the obtained TiN samples were characterized by X-ray diffraction, Raman, scanning electron microscope, UV/Visible (UV/VIS) spectrophotometer and Hall measurements. Combining the measured results, it is found that with the deposition temperature increasing, the grain size of TiN film changed from 15.4 nm to 17.4 nm and the surface becomes rougher. The concentrations of titanium and nitrogen vacancies decrease with increasing deposition temperature. A combined Drude-3Lorentz model was used to analyze the dielectric and optical properties of the obtained TiN films. It is found that TiN samples exhibit typical Drude-Lorentz like behavior in the visible and near-infrared (NIR) regions. The results were verified by Hall measurements and UV/VIS measurements. With the deposition temperature increasing, the reflectivity increased in the NIR region and a peak reflectivity of about 93% can be obtained at the wavelength of 1000 nm. With the deposition increasing, the infrared emissivity decreased. The infrared emissivities of the TiN film deposited at 673 K are 0.26 and 0.08 at wavelength of 2.5 μm and 25 μm, respectively, which shows TiN may be a good candidate for low-e film.