Undoped Thin Films Research Articles

Cu-Doped and Un-Doped WO3 Photochromic Thin Films

In this work, 0%, 0.5%, 1%, and 2% Cu-doped WO3 nanoparticles were synthesized via a polyol method. The as-synthesized materials were characterized by x-ray diffraction, scanning electron microscopy (SEM), electron paramagnetic resonance (EPR), x-ray photoelectron spectroscopy (XPS), and UV-Vis photochromic activity. A bond valence model was adopted to explain the relationship between the lattice parameter and Cu percentage. Additionally, two films (1% Cu-doped and un-doped samples) obtained by dip-coating from a well-dispersed suspension were optically investigated using ex situ and in situ UV-Vis spectrometry; coloring/bleaching kinetics were thoroughly studied. The Cu-doped WO3 film was found to have a high-quality bleaching mechanism (five times as fas as the un-doped WO3 film). Finally, the high bleaching performance of the doped films was confirmed by successive cycling, showing that the as-prepared compounds are of great interest for smart window applications, for example.

Multilevel Absorbers via the Integration of Undoped and Tungsten-Doped Multilayered Vanadium Dioxide Thin Films.

Reconfigurable light absorbers have attracted much attention by providing additional optical responses and expanding the number of degrees of freedom in security applications. Fabry-Pèrot absorbers based on phase change materials with tunable properties can be implemented over large scales without the need for additional steps such as lithography, while exhibiting reconfigurable optical responses. However, a fundamental limitation of widely used phase change materials such as vanadium dioxide and germanium-antimony-tellurium-based chalcogenide glasses is that they have only two distinct phases; therefore, only two different states of optical properties are available. Here, we experimentally demonstrate active multilevel absorbers that are tuned by controlling the external temperature. This is produced by creating large-scale lithography-free multilayer structures with both undoped and tungsten-doped solution-processed monoclinic-phase vanadium dioxide thin films. The doping of vanadium dioxide with tungsten allows for the modulation of the phase-transition temperature, which results in an extra degree of freedom and therefore an additional step for the tunable properties. The proposed multilevel absorber is designed and characterized both numerically and experimentally. Such large-scale multilevel tunable absorbers realized with nanoparticle-based solution fabrication techniques are expected to open the way for advanced thermo-optical cryptographic devices based on tunable reflective coloration and near-infrared absorption.

High-sensitivity room temperature p-doped and undoped GaN thin film resistive gas sensor

The behaviour and performance of p-doped GaN and undoped GaN thin film in the presence of methanol gas were studied. GaN thin films were grown using metal organic chemical vapour deposition (MOCVD), which were then fabricated into resistive sensors. Gas-sensing characterisation with the in-house gas chamber demonstrates that the resistive sensors based on undoped and p-doped GaN exhibit high sensitivity and fast response to methanol vapour in less than a minute, as well as excellent stability in room temperature operations. Without high temperature measurements, both undoped and p-doped GaN resistive sensors exhibit significant resistance variation and response over time when exposed to methanol, albeit with distinct properties. Here we demonstrate the comparison between the two and their sensing capabilities of both p-doped GaN and undoped GaN thin film resistive sensors.

Optical and Electrochromic Analysis of (Al-B) Co-Doped and Un-Doped V2o5 Thin Films

Optical and Electrochromic Analysis of (Al-B) Co-Doped and Un-Doped V2o5 Thin Films

Thin films composed of Zr-doped In2O3 grains rich in fracture surfaces and cracks for photoelectrochemical water oxidation

Zr-doped In2O3 thin films composed of grains with abundant fracture surfaces and cracks prepared by a two-step method show significantly improved PEC water oxidation performance in comparison with the undoped In2O3 thin films.

Impact of indium ions on some properties of TiO2 thin films for sensor applications

Indium doped Titanium dioxide (TiO2: In) thin layers were deposited on glass substrates by the spray pyrolysis deposition with the substrate temperature 450 °C. The structural and the optical properties studies were investigated for the films deposited with various atomic doping indium percentage (0, 1, 3, 5 and 7 at.%). The results of X-ray diffraction (XRD) was shown the presence of anatase peak with a strong orientation along (101) plane. The crystallite size was found to be between 7.09 and 14.43 nm. Raman spectroscopy of undoped and doped TiO2 thin films were confirmed the presence of single phase of anatase TiO2. The optical properties were determined using absorbance and transmittance results in the range of wavelength between 300 and 800 nm. The calculated optical band gap varied between 3.08 and 3.25 eV. The Hall measurement displayed an increase of conductivity 1.04 to 5.03 Ω−1.cm−1 and the electron mobility from 11.33 to 35.70 cm2/V.s in front of the decrease of the resistivity from 9.56 × 10−1 to 1.98 × 10−1 Ω.cm for the variation of atomic doping from 0% to 7%. The best obtained properties of undoped and doped TiO2 make our sprayed thin films suitable to be as sensitive layer for optoelectronic applications among these, a gas sensor application.

Effect of fluorine doping on the structural and gas sensing property of V2O5 thin films

Pristine and fluorine doped vanadium pentoxide (V2O5) thin films are prepared by spray pyrolysis technique at different molar, dopant concentrations at a substrate temperature of 450 ˚C. The structural, optical, morphological, electrical and ethanol sensor studies are then carried out for these films. The band gap of the prepared host film at 0.03 M concentration has a lowest value of 2.43 eV and the 3 % of F doped V2O5 thin film has a lowest value of 2.39 eV. Morphological studies reveal that the film prepared at 0.03 M and 3 % doped films have good crystallinity. The electrical studies like I-V and Hall measurement on the host film has a conductivity of 245 Ω−1 m−1 and the carrier concentration of 4.74 × 1018 cm−3 where as for the doped film they are 253 Ω−1 m−1 and 7.25 × 1018 cm−3 respectively. Ethanol sensing property of these doped and un-doped V2O5 thin films are then studied. It is observed that F doped V2O5 thin films have higher sensitivity compared to the pure V2O5 thin films.

Enhanced visible photocatalytic performance of un-doped TiO2 nanoparticles thin films through modifying the substrate surface roughness

Titanium oxide (TiO2) has been widely utilized for application in environmental pollution due to its unique properties. However, large bandgap (3.2 eV) and low surface area of bulk TiO2 are the main properties that limit its photocatalytic applications. In this work, a thin layer of TiO2 (<200 nm) nanoparticles (NPs) on mechanically roughened glass substrates is deposited by a simple sol-gel method followed by a dip-coating process along with fast heating and sintering. The effect of substrate surface roughness on the morphology, hydrophilicity, and optical properties which results in a more electron-hole generation and consequently improved photocatalytic activity was investigated by different characterization techniques. The TiO2 layer on the roughest substrate (RMS = 76.90 nm) showed the smallest average NP size (3 nm) with the highest surface roughness (RMS = 121.00 nm) and hydrophilicity (74.5%) as well as strong optical absorption. This sample photodegraded the pollutant with an efficiency of 85% at a rate of 0.0054 min−1 under the illumination of the vis-light emitting diode (LED)-based source (440 and 590 nm). Therefore, an enhanced photocatalytic activity accompanied by recyclability was achieved by modifying the substrate surface roughness and thermal treatment in the process of synthesis. Conclusively, intrinsic defects and grain boundaries appear which behave as active areas for charge transfer in the photocatalytic process under visible irradiation. This research may provide an insight into the fabrication of highly efficient photocatalysts based on commonly used wide band gap materials to work in the absence of UV light.

Structures and enhanced electrocaloric effect in Fe-doped (Ba0.904Ca0.096)(Zr0.136Ti0.864)O3 thin films

In this study, the electrocaloric (EC) effect was enhanced at room temperature for (Ba0.904Ca0.096)(Zr0.136Ti0.864−xFex)O3 (BZT-0.32BCT-xFe 0 ≤ x ≤ 0.015) thin films prepared on Pt/Ti/SiO2/(100)Si substrates. The existence of an orthorhombic phase in the Fe-doped thin films at room temperature was confirmed by X-ray diffraction and Raman spectra. Tetragonal, orthorhombic, and rhombohedral phases coexist in all the investigated Fe-doped thin films. The relative content of the orthorhombic phase is most prominent at x = 0.0075. The BZT-0.32BCT-xFe thin film exhibits excellent properties with a giant EC effect (ΔT = 22.99 K, E = 1050 kV/cm, and T = 307 K) at x = 0.0075 compared to the undoped thin film, stemming from multiphase coexistence and a larger orthorhombic phase. The results of this study are useful for developing lead-free electrocaloric materials with superior properties.

Unraveling the Surface Reactivity of Pristine and Ti-Doped Hematite with Water.

Water adsorption and dissociation on undoped and Ti-doped hematite thin films were investigated using near-ambient pressure photoemission and DFT calculations. A fine understanding of doping effects is of prime importance in the framework of photoanode efficiency in aqueous conditions. By comparison to pure Fe2O3 surface, the Ti(2%)-Fe2O3 surface shows a lower hydroxylation level. We demonstrate that titanium induces wide structural modifications of the surface, preventing it from reaching full hydroxylation.

Thin-film chemical expansion of ceria based solid solutions: laser vibrometry study

Abstract The chemical expansion of Pr0.1Ce0.9O2–δ (PCO) and CeO2–δ thin films is investigated in the temperature range between 600 °C and 800 °C by laser Doppler vibrometry (LDV). It enables non-contact determination of nanometer scale changes in film thickness at high temperatures. The present study is the first systematic and detailed investigation of chemical expansion of doped and undoped ceria thin films at temperatures above 650 °C. The thin films were deposited on yttria stabilized zirconia substrates (YSZ), operated as an electrochemical oxygen pump, to periodically adjust the oxygen activity in the films, leading to reversible expansion and contraction of the film. This further leads to stresses in the underlying YSZ substrates, accompanied by bending of the overall devices. Film thickness changes and sample bending are found to reach up to 10 and several hundred nanometers, respectively, at excitation frequencies from 0.1 to 10 Hz and applied voltages from 0–0.75 V for PCO and 0–1 V for ceria. At low frequencies, equilibrium conditions are approached. As a consequence maximum thin-film expansion of PCO is expected due to full reduction of the Pr ions. The lower detection limit for displacements is found to be in the subnanometer range. At 800 °C and an excitation frequency of 1 Hz, the LDV shows a remarkable resolution of 0.3 nm which allows, for example, the characterization of materials with small levels of expansion, such as undoped ceria at high oxygen partial pressure. As the correlation between film expansion and sample bending is obtained through this study, a dimensional change of a free body consisting of the same material can be calculated using the high resolution characteristics of this system. A minimum detectable dimensional change of 5 pm is estimated even under challenging high-temperature conditions at 800 °C opening up opportunities to investigate electro-chemo-mechanical phenomena heretofore impossible to investigate. The expansion data are correlated with previous results on the oxygen nonstoichiometry of PCO thin films, and a defect model for bulk ceria solid solutions is adopted to calculate the cation and anion radii changes in the constrained films during chemical expansion. The constrained films exhibit anisotropic volume expansion with displacements perpendicular to the substrate plane nearly double that of bulk samples. The PCO films used here generate high total displacements of several 100 nm’s with high reproducibility. Consequently, PCO films are identified to be a potential core component of high-temperature actuators. They benefit not only from high displacements at temperatures where most piezoelectric materials no longer operate while exhibiting, low voltage operation and low energy consumption.

Research implementing different dopants (M = Al, Sn, and Eu) on the properties of Schottky diodes with structure TCO/CdS/C and TCO/CdS:M/C

A metal-semiconductor interface is an integral part of numerous electronic devices such as Schottky barrier diodes, photodetectors, photovoltaic detectors, photoelectric converters for UV radiation, among others. On the other hand, semiconductor thin films of cadmium sulfide have been applied to several electronic devices. This study presents the synthesis of semiconductor thin films of pure cadmium sulfide and those doped with Al, Sn, and Eu by a chemical bath deposition technique. XRD, SEM, EDS, XPS, UV-Vis spectroscopy, I-V, and photocurrent measurement analyzed these semiconductor thin films. Afterwards, the doped and undoped CdS thin films were applied to the manufacture of Schottky diodes. The doped CdS thin films reveals differences in the size of the crystallites, which decreased by 5.7%, 11.5%, and 60.1% after doping with aluminum, tin, and europium, respectively. The CdS thin films show morphological differences, decreasing grain size by 5.3% in the case of tin doping and increasing by 21.9% with aluminum and 32.6% after being doped with europium. Additionally, the energy bandgap of the doped CdS thin films show a blue shift, except when doped with Eu, which shows a red shift. This enables the design of window layers by choosing the suitable dopant of CdS. The effect of the CdS doping on the electrical photoresponse of the Schottky diodes was also analyzed. Due to the incorporation of dopants, the photoresponse of the aluminum-doped CdS Schottky diodes improved by 176% compared to its undoped counterpart and by up to 493% with other reports in the literature. The Schottky diodes manufactured in this work show variation in height of the potential barrier, increasing by 6% in the case of aluminum doping and decreasing by 5% and 25% after being doped with europium and tin respectively. These results demonstrated the beneficial impact of dopants on the characteristics of the CdS-based Schottky diodes and elaborated photodiodes, exhibiting an impressive enhancement in their photoresponse, in the potential barrier reached for photosensitivity and in the energy band gap value. Overall, our extensive study reveals that there is great potential in the design of affordable multifunctional optoelectronic devices.

Influence of manganese rate on structural, optical and electrochemical properties of CeO2 thin films deposited by spray pyrolysis: Supercapacitor applications

The present work aimed to investigate the electrochemical properties of ITO substrates in propylene carbonate (PC) with 0.5 mol/L lithium perchlorate (LiClO4) medium in the presence of elaborated thin films of cerium dioxide pure and doped with manganese at varying percentages. Ce1–xMnxO2 (x = 0 wt%, 2 wt%, 4 wt% and 6 wt%) were successfully deposited by the spray pyrolysis (SP) technique on the glass substrate and ITO at 450 °C. The effects of manganese (Mn) doped thin films Ce1–xMnxO2 were studied and investigated by using different analyses namely X-ray diffraction (XRD) analysis, Raman spectroscopy method, UV–Vis spectrophotometer technique, atomic force microscopy (AFM) analysis and electrochemical properties. XRD data obtained present a polycrystalline with a face-centred cubic structure of fluorite type. Raman results of undoped and Mn doped thin films show two peaks at 465 and 600 cm−1, due to the formation of extrinsic oxygen vacancies by the incorporation of Mn into Ce1–xMnxO2 matrix. Energy dispersive spectroscopy (EDS) data show the presence of Ce, O, and Mn elements in the elaborated films. The AFM results reveal that the surface roughness decreases with increasing Mn rate. Further, band gap energy of thin films decreases with increasing in Mn rate due to the formation of defect state between valence and conduction band. The storage capacity of the elaborated Ce1–xMnxO2/ITO/PC + LiClO4 electrode reaches a maximum of 1.997 mF in the presence of 6 wt% of Mn.

Tunable structural, morphological and optical properties of undoped, Mn, Ni and Ag-doped CuInS2 thin films prepared by AACVD

The preparation of high-quality copper indium sulphide, CuInS2 photo-absorber material with tunable properties for efficient, low-cost, thin film solar cells using scalable methods remains a challenge. In order to address this, high quality off-stoichiometric undoped and Mn, Ni and Ag-doped CuInS2 (CIS) thin films have been deposited onto glass substrates by aerosol-assisted chemical vapour deposition (AACVD) using metal diethyldithiocarbamate precursors at temperatures of 350, 400 and 450 °C. Data from powder X-ray diffraction (p-XRD), Raman spectroscopy and scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) suggest a correlation of morphology and composition of tetragonal phase (chalcopyrite and copper-gold-type) sulphur-deficient microcrystalline CIS thin films. For undoped thin films, near-infrared optical absorption and emission with tunable band gap between 1.32 and 1.42 eV are likely associated with donor-acceptor pairs involving deep or shallow electronic states such as sulphur vacancies (VS••), indium-copper anti-sites (InCu••) and indium interstitials (Ini•••) as donors and copper vacancies (VCu′) as acceptors. Whilst Mn-doped thin films exhibit minimal tunable properties, Ni and Ag-doped films exhibit tunable morphology, composition and near-infrared absorption for small dopant content. Though further studies are required to explore the defect chemistry, these results show the utility of AACVD in tuning structural, morphological and optical properties of undoped, Mn, Ni and Ag-doped CIS thin films.

Undoped and Tl‐Doped Cs3Cu2I5 Thin Films as Potential X‐ray Scintillators

0D halide perovskite Cs3Cu2I5‐based nanocrystals and bulk crystals are proven to be sensitive and efficient scintillators for X‐ray and γ‐ray detection. Herein, undoped and Tl‐doped Cs3Cu2I5 microcrystalline films are synthesized by a thermal evaporation method. Both films crystallize into a Pnma space group of orthorhombic crystal lattice with preferred (004) growth orientation. The undoped Cs3Cu2I5 thin film shows a sole emission peaking at 440 nm associated with the self‐trapped exciton emission. Doping of Tl+ ions introduces another emission that peaks at 520 nm. The scintillation efficiency of both undoped and Tl‐doped Cs3Cu2I5 thin films is about one‐third of that of CsI:Tl thin film with the same size and thickness. Within the first 5 s after X‐ray cutoff, afterglow signals of both the undoped and Tl‐doped Cs3Cu2I5 thin films are over one order of magnitude lower than that of CsI:Tl thin film.

Investigation of Physical and electrochemical properties of Ni doped CeO2 Thin films: DFT calculation

Undoped and Ni-doped thin films of cerium dioxide have been deposited by spray pyrolysis technique on the glass substrate at the optimized temperature (450 ± 5) °C. Thin films Ce1-xNixO2 doped by different concentrations of Ni was characterized by X-ray diffraction. Raman analysis showed a peak at 461 ± 1 cm−1 position for the undoped film, which corresponds to the active mode (F2g mode) of the cubic fluorite structure. SEM images showed that the particles have a uniform spherical shape. EDS data have confirmed all elements (Ce, Ni and O) existence. Optical properties of samples show a decrease in band gap energy with increasing the nickel rate. Cyclic voltammetry indicates that the storage capacity of samples increases as the Ni rate increases. The EIS of CeO2/ITO electrodes displays a small semicircular at high frequency. The theoretical results obtained using WIEN2k match well with the experimental ones.

Physical Properties of Nanostructured Fe2O3 Thin films - Effect of Cobalt Doping Deposited by CSP

Undoped Fe2O3 and Fe2O3: Co thin films with thickness 350 ± 25 nm deposited by chemical spray pyrolysis CSP method at temperature of 450°C. The results of X-ray measurements analysis revealed a polycrystalline pattern for all samples oriented along (110) plane. The films crystallites were oriented along (110) plane. The Grain size for Undoped showed an increase from 12.47 nm to 14.42 nm upon Cobalt doping, whilst dislocation density (δ) for Undoped showed an decreased from 64.30 to 48.09 upon Cobalt doping, whilst strain (ε) decreased for Undoped showed an decreased from 27.96 to 24.03 upon Cobalt doping. Atomic force microscopy (AFM) tests showed nano particles and a decrease in surface roughness. The root mean square roughness (Rrms) decrease from 6.36 nm to 7.61 nm by increasing the for Undoped Fe2O3 to Fe2O3:2% Co. Transmittance values of undoped Fe2O3 and Cobalt doped films reaches 80% to 90% in Vis- NIR regions. Optical measurements illustrate an increase in the Refractive Index, absorption coefficient and extinction coefficient with increasing Cobalt content in comparison to undoped Fe2O3 thin films.

Comprehensive review of the morphological, linear and nonlinear optical characterization of spin-coated NiO thin films for optoelectronic applications

In the last few years, Nickel Oxide (NiO) started to be regarded as one of the most auspicious oxides that have been elaborated through several methods to eventually be used in optoelectronic applications, owing to its intriguing properties namely chemical stability, magnetic, optical and electrical as well as its wide-band-gap that ranges between 3.25 and 4.0 eV. We will initiate this review by providing an exhaustive description of the spin-coating method which is classified among the leading techniques to deposit an extensive variety of materials in thin film form. Then we will examine the structural, morphological, linear and nonlinear optical characteristics of the doped and undoped NiO thin films prepared by this technique. The improvement in quality and deposition efficiency of thin films is extremely crucial and it can be attained by optimizing the elaboration parameters of the spin-coating technique.

Large remanent polarization in Ta-doped HfO2 thin films by reactive sputtering

Ta-doped HfO2 thin films grown on Pt/Ti/SiO2/Si by reactive sputtering possess strong ferroelectric properties, as detected by corresponding polarization vs electric field measurement and mesoscopic piezoresponse force microscopy. Capacitance/current-electric field curves are used to reveal the substances with ferroelectric properties in the thin films. The ferroelectricity of Ta-doped HfO2 is influenced by Ta contents. The remanent polarization Pr can reach ∼53 μC/cm2 by optimizing the Ta percentage. X-ray diffraction and Raman scattering analyses indicate only the presence of monoclinic phase peaks in undoped HfO2 thin films, while Ta doping promotes the formation of the ferroelectric phase (orthorhombic Pca21). X-ray photoelectron spectroscopy demonstrates that the incorporation of Ta5+ within the HfO2 lattice boosts the ferroelectric properties. A polydomain structure is observed on the bare surface of 16% Ta-doped HfO2. Moreover, the switching behavior of the domain is explored by applying an external voltage, demonstrating the potential for storage device applications.

A systematic investigation on structural and optical properties of sol–gel spin coating fabricated CdS nanocrystalline thin films: effect of Ni doping

In the present work, we have successfully fabricated undoped and Ni-doped nanocrystalline CdS thin film on an ultrasonically cleaned glass substrate employing the sol–gel spin coating technique. The structural and spectroscopic properties of the films were investigated using XRD spectra, UV–Vis spectroscopy and photoluminescence spectra, respectively. The X-ray diffraction spectra revealed the polycrystalline nature of films with cubic structure and (111) as preferred orientation. The average crystallite size evaluated by the Debye–Scherrer formula lying in the range of 6–12 nm for the deposited films. According to UV–VIS Spectroscopy, the average transmittance of films in the visible region varies between 70–90%. The optical band gap of CdS thin film was evaluated from absorption spectra. The bandgap of the deposited films is in the range of 2.48–2.70 eV which is higher than that of bulk CdS (2.42 eV). This verifies the blue shifting in band edge of CdS nanocrystalline thin films due to the quantum confinement effect. Photoluminescence spectra of the thin film showed that the fundamental band edge emission peak centred at 485 nm also called blue band emission. It is observed that the low temperature resistivity of the films was in the range of 107–103 Ω cm and also found to decrease with increasing Ni concentration, as a result from dc two probe measurements.