Characterization Of Thin Films Research Articles

Fabrication and Characterization of Dielectric ZnCr2O4 Nanopowders and Thin Films for Parallel-Plate Capacitor Applications.

We report here the successful shape-controlled synthesis of dielectric spinel-type ZnCr2O4 nanoparticles by using a simple sol-gel auto-combustion method followed by successive heat treatment steps of the resulting powders at temperatures from 500 to 900 °C and from 5 to 11 h, in air. A systematic study of the dependence of the morphology of the nanoparticles on the annealing time and temperature was performed by using field effect scanning electron microscopy (FE-SEM), powder X-ray diffraction (PXRD) and structure refinement by the Rietveld method, dynamic lattice analysis and broadband dielectric spectrometry, respectively. It was observed for the first time that when the aerobic post-synthesis heat treatment temperature increases progressively from 500 to 900 °C, the ZnCr2O4 nanoparticles: (i) increase in size from 10 to 350 nm and (ii) develop well-defined facets, changing their shape from shapeless to truncated octahedrons and eventually pseudo-octahedra. The samples were found to exhibit high dielectric constant values and low dielectric losses with the best dielectric performance characteristics displayed by the 350 nm pseudo-octahedral nanoparticles whose permittivity reaches a value of ε = 1500 and a dielectric loss tan δ = 5 × 10-4 at a frequency of 1 Hz. Nanoparticulate ZnCr2O4-based thin films with a thickness varying from 0.5 to 2 μm were fabricated by the drop-casting method and subsequently incorporated into planar capacitors whose dielectric performance was characterized. This study undoubtedly shows that the dielectric properties of nanostructured zinc chromite powders can be engineered by the rational control of their morphology upon the variation of the post-synthesis heat treatment process.

Optimizing CuFeS2 Chalcopyrite Thin Film Synthesis: A Comprehensive Three-Step Approach Using Ball-Milling, Thermal Evaporation, and Sulfurization Applied for Thermoelectric Generation

CuFeS2 (CFS) stands out as a promising narrow band-gap semiconductor for thermoelectric (TE) applications. However, its high lattice thermal conductivity is one of the factors hampering its potential for TE generation. A common strategy for tackling this problem is to produce this material in thin film form. Thus, this study aims to practically understand and optimize the synthesis of CFS 2D materials using a simple three-step approach of ball-milling, thermal evaporation, and sulfurization of the CuFe metallic precursors. The tools for thin film characterization employ X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Energy-Dispersive X-ray Spectroscopy (EDXS), and Hall-effect measurements. DFT phase diagrams are also used to understand the energy of formation of the secondary phases present in the film. Here, we highlight that the ball-milling mechanisms, allied with high vacuum and high energy density during evaporation, are essential for the interdiffusion of Cu and Fe during the evaporation process. The film presented a flower-like morphology and p-type semiconducting behavior. A proof-of-concept Thermoelectric Generator (TEG) was designed in an in-plane geometry, showing a power output per unit active area of 114 nW cm−2 (ΔT = 180 °C), comparable to other Cu-based materials, thus demonstrating the feasibility of this method of synthesis for TE applications.

Synthesis and characterization of doped-ZnO thin films over wide temperature range for applications as a transparent conducting material

Synthesis and characterization of doped-ZnO thin films over wide temperature range for applications as a transparent conducting material

Direct electrodeposition of CoFeNiMoW high entropy alloy thin films from aqueous medium

The direct electrodeposition of CoFeNiMoW high entropy alloy (HEA) thin films from aqueous medium is demonstrated. By employing a citrate-containing bath and varying the applied current density (ic), HEAs with different compositions are obtained. Specifically, the composition of the HEA thin film obtained at ic = 50 mA cm−2 is Co30Fe21Ni19Mo25W5. The physical characterization of the HEA thin films is performed by energy dispersive x-ray spectrometry (EDS), grazing incidence x-ray diffraction (GIXRD), and 57Fe Mössbauer spectroscopy. Results confirm the presence and composition of the multicomponent HEA thin films and highlight galvanostatic electrodeposition as a simple, versatile, and cost-effective technique to create these HEA thin films.

Homogeneity- and Stoichiometry-Induced Electrical and Optical Properties of Cu-Se Thin Films by RF Sputtering Power.

P-type Cu-Se thin films were deposited on glass substrates at room temperature using radio frequency magnetron sputtering by a single multi-component CuSe2 target. When using a multi-component target, the impact of the sputtering power on the homogeneity and stoichiometry within the thin films should be investigated in the depth direction to demonstrate a secondary effect on the electrical and optical properties of the thin films. Systematic characterization of the Cu-Se thin films, including the morphology, microstructure, chemical composition, and depth-directional chemical bonding state and defect structure of the thin films, revealed that the sputtering power played an important role in the homogeneity and stoichiometry of the thin films. At very low and very high sputtering power levels, the Cu-Se thin films exhibited more deviations from stoichiometry, while an optimized sputtering power resulted in more homogenous thin films with improved stoichiometry across the entire thin film thickness in the X-ray photoelectron spectroscopy depth profile, despite showing Se deficiency at all depths. A rapid decrease in carrier concentration, indicating a reduction in the net effect of total defects, was obtained at the optimized sputtering power with less deviation from stoichiometry in the Cu-Se thin films and the closest stoichiometric ratio at an intermediate depth.

Effect of Annealing on Gas Detecting Property of BFO Thin Films

The thin films of pure BFO have been developed using spray pyrolysis technique. The characterization of thin films is carried out before and after annealing. The outcomes obtained from XRD showed the polycrystalline rhombohedral crystal structure and an improvement in the crystallinity with annealing. The results from FESEM showed reduction of particle size with annealing. The results of AFM reveal the enhancement in the surface roughness with annealing. The gas sensing studies carried out for the developed thin films showed a good sensitivity to ethanol and it was found that the operating temperature reduced from 250 °C to 150 °C with annealing.

Investigation of Frequency and Temperature Dependent Electrical and Structural Characterization of PVC-PMMA Thin Films with Salicylic Acid Doping

Investigation of Frequency and Temperature Dependent Electrical and Structural Characterization of PVC-PMMA Thin Films with Salicylic Acid Doping

Atomic layer deposition and characterization of Bi1Se1 thin films

Atomic layer deposition and characterization of Bi1Se1 thin films

Structural and electrical characterization of Cd-doped ZnO thin films produced on p-type Si substrate by SILAR technique

Structural and electrical characterization of Cd-doped ZnO thin films produced on p-type Si substrate by SILAR technique

2% Transmitted Electrochromic Films by Hydrogen Adsorption

Hydrogen adsorption in WO3 thin films is known to cause the change of color of the films. Due to its high sensitivity, chemical stability as well as biocompatibility, the WO3 offers itself as an efficient hydrogen sensor, especially for detection of hydrogen in humid environments. In this paper we report the preparation and characterization of WO3 electrochoromic thin films prepared on ITO substrates by thermal evaporation synthesis. These films show significant decreases in transparency from over 92% to as low as 2% at an applied bias of −0.7 V. Structure as well as the effect of annealing temperature on the structure and properties of the films are also studied. The changes of optical band gap and the role of hydrogen in coloration process are also discussed.

Fabrication and optical characterization of zinc telluride thin films using electrodeposition technique

A well adherent thin film of Zinc Telluride (ZnTe) has been deposited on Flourine doped Tin oxide glass substrates from acidic baths containing Zinc heptahydrate and Tellurium dioxide. Films of different thicknesses with their molar concentrations were obtained. A mini Schimadzu UV-VIS Spectrophotometer was used to determine the optical absorbance of the films over the wavelength range of 300-900nm at room temperature. There is a decrease in absorbance as the molar concentrations of the precursors increases; while transmittance and energy band gap shown an increase. The band gap values obtained varied between 2.10eV and 2.7eV, for as deposited films. Also, photoelectrochemical cell (PEC) measurement reveals that ZnTe thin films exhibit p-type conductivity.

Electrolyte-Insulator-Semiconductor (EIS) Device with Hafnium Dioxide (HfO2) for pH Detecting

In this work Electrolyte-Insulator-Semiconductor (EIS) device has been developed for pH measurements. This device operates as a Metal-Oxide-Semiconductor capacitor but instead of having the metal contact electrode, an electrolyte solution and a reference electrode are used to apply voltage. As dielectric material and sensitive membrane was chosen hafnium dioxide (HfO2). This film was obtained by RF sputtering, and was structurally characterized by Raman and Ellipsometry. The structural characterization of HfO2 thin film shows the presence of tetragonal phase, physical thickness of 50 nm and refractive index of 1.89, close to stochiometric of 1.91. Was developed MOS capacitors to make the electrical characterization of HfO2 thin films in order to determine the thin film properties, defined by high dielectric constant value (high-k), lower charge density (Q0/q) and flat-band voltage (VFB) around -0.9V. The electrical characterization done by Capacitance x Voltage (CxV) curves revealed high dielectric constant, VFB of 0.02V and Q0/q in the order of -10+12/cm2. The Current x Voltage (IxV) curve shows that the current through the dielectric is approximately 1x10-9A. With dielectric characterized it was possible to develop the EIS device. From electrical characterization it was possible to test the integrity of the electrodes and determined the sensitivity of the device. For electrical measurement of EIS was used Normalized Capacitance x Voltage curve (CxV curve) using different pH (3, 4, 5, 7, 9, 10 and 12) solutions. From the flat band voltage (VFB) of the Normalized CxV curves was possible to determine the sensitivity of the device of 78mV/pH. This result is greater than the Nernst level and greater than results found in the literature.

Nano-Bio Interface Engineering Using Cyclovoltammetry and Design of Nanostructured Lanthanide Oxysulfide Thin Films

Nanoparticles (NPs) in which magnetic and optical properties coexist have been intensively explored for diverse biomedical applications including diagnostic, in vivo imaging and therapy. Gadolinium oxysulfide (Gd2O2S) NPs are promising candidates for biotechnologies as they have been used as MRI contrast agent or X-ray absorbing materials. When doped with cerium, they gain an additional functionality as visible light absorber due to the decrease in the material bandgap from 4.7 eV non-doped to 2.5 eV with 5% of Ce. Further biomedical applications may be envisioned thanks to the combined antioxidant properties of cerium and the magnetic properties of gadolinium.Understanding the molecular-level interactions between organisms and nanoparticles to guide and enable the design of novel materials that are less toxic remains a challenge. In order to understand these interactions at the nanoscale, we studied the change in the physico-chemical properties of (Gd,Ce) oxysulfide NPs when they are immersed in a biological medium. In biological medium, pristine nanomaterials transform and acquire a corona of biomolecules, such as proteins, which can modify their identity. This is known as the nano-bio interface. A better understanding of how nanoparticles interaction with a biological system affect their properties is critical to the future development of multifunctional NPs.Our recent work provides us with a privileged access to composition-controlled nanoplates with a narrow size distribution for a large range of Ln. In particular, we mastered the preparation of mixed-lanthanide nanoplates with tunable band gap and magnetic properties while providing an in-depth understanding of their structural and surface features. The challenge addressed here is to prepare and characterize ligand-free nanostructured thin films made from the NPs suspension. Compared to studies realized in solution, thin films allow to reach the surface of the nanoparticles without any interaction from the ligands. Moreover, it allows spectroscopic and electrochemical methods to be used for the monitoring of the NPs intrinsic properties.The design and development of nanostructured thin films started with the colloidal synthesis of (Gd,Ce) oxysulfide NPs which provides a phase-pure powder. The nanoparticles were then dispersed into an optimized mix of solvents in order to get a stable colloidal suspension. Dip coating is an easy method to deposit matter on a substrate while having a fine control of the thickness and homogeneity. This process was optimized to obtain homogenous films with a withdrawal speed of 2 mm/s under low relative humidity. Thin films of optical quality with a thickness from 40 nm to 150 nm were obtained using single-layer and multilayer deposition on various substrates including silicon, FTO and kapton (Figure A). In situ UV and IR Spectroscopic Ellipsometry were used to monitor the variations of thickness and optical constants, together with the chemical species present at the surface, upon heating the films in different conditions. This study allowed to finely tune the thermal treatment in order to get rid of the stabilizing ligands while preserving the integrity of the nanoplates, as confirmed by Transmission Electron Microscopy (Figure B shows the scraped film). As a result, we have access to the bare surface of the NPs, which was hardly possible in solution. The change in the band gap of the material was monitored through UV-Variable Angle Spectroscopic Ellipsometry. This non-invasive technique is the gold-standard for the characterization of optical quality thin films and gives refractive index of the material (Figure C shows the Tauc plot with the linear fit giving the band gap of the material).The film can be immersed into a biological medium where proteins are expected to bind to the surface of the NP and significantly change their reactivity and mobility. Cyclovoltammetry helped us to probe the access to the NPs and monitor the position of the conduction band. We used redox probes of different standard potentials as electrolytes (Figure D). Electron exchange with the semiconductor electrode is supposed to occur through the conduction band as the valence band is too far in energy. For a redox couple with a standard potential negative to the conduction band edge, when the applied potential equals E0 redox, the semiconductor is accumulating electrons at its surface in a so-called space charge layer. Under these conditions, whether a positive or negative bias is applied (compared to E0 redox), the SC is maintained in an accumulation mode. This was very helpful to check whereas the electronical properties of the material changed upon exposition to biological medium. This could lead to a better understanding and prediction of the chemical interactions at the interface with biomolecular systems. Figure 1

Increasing the Accuracy of the Characterization of a Thin Semiconductor or Dielectric Film on a Substrate from Only One Quasi-Normal Incidence UV/Vis/NIR Reflectance Spectrum of the Sample.

OEMT is an existing optimizing envelope method for thin-film characterization that uses only one transmittance spectrum, T(λ), of the film deposited on the substrate. OEMT computes the optimized values of the average thickness, d¯, and the thickness non-uniformity, Δd, employing variables for the external smoothing of T(λ), the slit width correction, and the optimized wavelength intervals for the computation of d¯ and Δd, and taking into account both the finite size and absorption of the substrate. Our group had achieved record low relative errors, <0.1%, in d¯ of thin semiconductor films via OEMT, whereas the high accuracy of d¯ and Δd allow for the accurate computation of the complex refractive index, N˙(λ), of the film. In this paper is a proposed envelope method, named OEMR, for the characterization of thin dielectric or semiconductor films using only one quasi-normal incidence UV/Vis/NIR reflectance spectrum, R(λ), of the film on the substrate. The features of OEMR are similar to the described above features of OEMT. OEMR and several popular dispersion models are employed for the characterization of two a-Si films, only from R(λ), with computed d¯ = 674.3 nm and Δd = 11.5 nm for the thinner film. It is demonstrated that the most accurate characterizations of these films over the measured spectrum are based on OEMR.

Fabrication and characterization of lead selenide thin film as X-ray sensors, photovoltaic devices and microwave resonators

Fabrication and characterization of lead selenide thin film as X-ray sensors, photovoltaic devices and microwave resonators

Structural and optical characterization of thin AlInN films on c-plane GaN substrates

The structure and optical characteristics of thin (∼30 nm) wurtzite AlInN films grown pseudomorphic on free-standing, c-plane GaN substrates are presented. The Al1−xInxN layers are grown by metalorganic chemical vapor deposition, resulting in films with varying In content from x = 0.142 to 0.225. They are measured using atomic force microscopy, x-ray diffraction, reciprocal space mapping, and spectroscopic ellipsometry (SE). The pseudomorphic AlInN layers provide a set where optical properties can be determined without additional variability caused by lattice relaxation, a crucial need for designing devices. They have smooth surfaces (rms &amp;lt; 0.29 nm) with minimum pit areas when the In content is near lattice-matched to GaN. As expected, SE shows that the refractive index increases and the bandgap energy decreases with increased In-content. Plots of bandgap energy vs In content are fitted with a single bowing parameter of 3.19 eV when using bandgap energies for AlN and InN pseudomorphic to GaN, which is lower than previous measurements and closer to theoretical predictions.

Synthesis and characterization of thin films of P3HT − G/MoS2 nanocomposites in photodetectors applications

Synthesis and characterization of thin films of P3HT − G/MoS2 nanocomposites in photodetectors applications

Preparation and Structural Characterization of Thin Films of CuInS2 by Sintering Colloidally Synthesized Nanoparticles at Moderate Temperature

Copper indium disulfide nanoparticles continue attracting attention as absorber material in light harvesting devices. The preparation of thin films by deposition of this material from colloidal solution remains challenging. Typically, colloidal semiconductor nanoparticles are surrounded by long organic ligand molecules which are required to stabilize the particles during synthesis. A common way to obtain conductive thin films is the development of ligand exchange procedures that need to be applied prior to film deposition. However, in the case of copper indium disulfide nanoparticles, appropriate procedures are still missing. Therefore, an alternative approach is investigated herein. Colloidal copper indium disulfide nanoparticles are synthesized and deposited on substrates. Instead of applying a ligand exchange procedure, thermal removal of the ligands and sintering of the inorganic film are explored. Results on the preparation of the nanoparticle films, their structural investigation, and conductivity measurements are reported.

Preparation and Characterization of Zn-doped CuAlO2 Thin Films

In this paper, the CuAl1-xZnxO2 (x=0, 0.03, 0.05, 0.07, 0.1) targets have been obtained by the solid phase reaction method using analytically pure Cu2O, Al2O3, and ZnO powders as experimental raw materials, and CuAl1-xZnxO2 thin films have been prepared on quartz glass substrates by magnetron sputtering. The characteristics of CuAl1-xZnxO2 thin films have been studied systematically. The results showed that Zn doping makes the (101) and (104) diffraction peaks of CuAlO2 shift. EDS results confirmed that Zn atoms replaced Al atoms. The average transmittance could reach 57.7% at 3%, and the band gap increased as the Zn doping concentration increased and could reach 3.83 eV at 10%.

Near room temperature tunability of thermochromic VO2 thin films prepared via thermal oxidation method, influence of CO2:N2 gas flux ratios

In this study, we have investigated the thermochromic characterizations of VO2 thin films synthesized by the thermal oxidation method. The oxidation process of a DC sputtered metallic vanadium layer on glass substrates, at 450 °C for 1 h, was carried out in the presence of CO2:N2 gases with different flux ratios of 30:70, 40:60, 50:50, 60:40, and 70:30, respectively. Using CO2, as the oxidizing gas, provides an easy control route for obtaining the VO2 phase among various vanadium oxide phases. The layers were characterized by FESEM, XRD & Raman spectra, sheet resistance vs. temperature (20–120 °C), and UV–Vis–NIR spectra at 25 and 90 °C. The XRD and Raman spectra confirmed all prepared layers have a VO2 polycrystalline structure in monoclinic phase. We found among the studied samples CN30-70 and CN50-50 having desirable optical characteristics of peak visible transmittance of about 55%, with low transition temperatures (Tcr) of ∼42 and 31 °C, and also relatively high amounts of ΔT1700nm, ΔTsol and Tlum,av are good candidates for thermochromic smart windows, both from optical properties and economical fabrication method points of view.