Essential Macleod Program (EMP) simulated fabrication of high quality Zn:SnO2/Ag/Zn:SnO2 multilayer transparent conducting electrode on flexible substrates

In the quest of promising Indium free amorphous transparent conducting oxide (TCO), Zn-doped SnO₂/Ag/Zn-doped SnO₂ (OMO) multilayer films were prepared on flexible polyethylene terephthalate (PET) substrates by RF sputtering at room temperature (RT). Growth parameters were optimized by varying sputtering power and working pressure, to have high electrical conductivity and optical transmittance. Optimization of the thickness of each layer was done by Essential Macleod Program (EMP) simulation to get the higher transmission through OMO multilayer. The sheet resistance and transmittance of 3 at% Zn-doped SnO₂ thin film (30 nm) were 2.23 kΩ/□, (ρ ~ 8.92×10⁻³ Ω∙cm) and 81.3% (at λ ~ 550 nm), respectively. By using optimized thicknesses of Zn-doped SnO₂ (30 nm) and Ag (12 nm) and optimized growth condition Zn-doped SnO₂/Ag/Zn-doped SnO₂ multilayer thin films were deposited. The low sheet resistance of 7.2 Ω/□ and high optical transmittance of 85.1% in the 550 nm wavelength region was achieved with 72 nm multilayer film.     

Transparent and high infrared reflection film having sandwich structure of SiO2/Al:ZnO/SiO2

New transparent and high infrared reflection films having the sandwich structure of SiO₂/Al:ZnO(AZO)/SiO₂ were deposited on the soda-lime silicate glass at room temperature by radio frequency (R.F.) magnetron sputtering. The optical and electrical properties of SiO₂ (110 nm)/AZO (860 nm)/SiO₂ (110 nm) sandwich films were compared with those of single layer AZO (860 nm) films and double layer SiO₂ (110 nm)/AZO (860 nm) films. The results show that these sandwich films exhibit high transmittance of over 85% in the visible light range (380–760 nm), and low reflection rate of below 4.5% in the wavelength range of 350–525 nm, which is not shown in the conventional single layer AZO (860 nm) films and double layer SiO₂ (110 nm)/AZO (860 nm) films. Further these sandwich films display a low sheet resistance of 20 Ω/sq by sheet resistance formula and high infrared reflection rate of above 80% in the wavelength range of 15–25 μm. In addition, the infrared reflection property of these sandwich films is determined mainly by the AZO film. The outer SiO₂ film can diminish the interference coloring and increase transparency; the inner SiO₂ film improves the adhesion of the coating to the glass substrate and prevents Ca²⁺ and Na⁺ in the glass substrate from entering the AZO film.     

A study on the thermoelectric properties of ALD-grown aluminum-doped tin oxide with respect to nanostructure modulations

The thermoelectric properties of aluminum-doped tin oxide (ATO) thin films synthesized by thermal atomic layer deposition (ALD) were studied with respect to the aluminum concentration. The overall aluminum content in each layer was modulated by adjusting the relative number of tin oxide (SnO₂) and aluminum oxide (Al₂O₃) growth cycles, where a sequential process involving n cycles of SnO₂ growth followed by 1 cycle of Al₂O₃ deposition was performed (building up a super-cycle). The electrical conductivity (620 S/cm), free carrier concentration (1.23x10²¹ cm^-3), and power factor (0.49 mW/K²m) increase until their maximum values are reached when the Al content is approximately 1.50 at% of the cations, and decrease as more Al is added in. On the other hand, the Seebeck coefficient decreases monotonically as the Al content increases up to about 2.88 at%, and begins to increase with further Al doping. Here the thermoelectric efficiency is therefore determined primarily by the free carrier concentration, while the Seebeck coefficient appears to be influenced by the overall crystal structure.     

Micro-structure of ITO ceramics sintered at different temperatures and its effect on the properties of deposited ITO films

Structural characterizations of two ITO ceramics that were respectively sintered at 1560 °C and 1600 °C were focused on and the results indicate that the lower sintering temperature is good for ITO ceramics to have the triangle fine grains, larger elemental concentration gradients of indium and tin and more content of In₄Sn₃O₁₂ phase which displays the stronger grain orientation growth along the crystallographic direction of [0-11]. ITO films with 100 nm thickness deposited at 25 °C–230 °C were used to investigate the effect of micro-structure on the film properties. Grain orientation growth of In₄Sn₃O₁₂ phase is conductive to form ITO films of columnar structure. Otherwise, uniform micro-structure and higher solubility of SnO₂ in In₂O₃ main phase contribute to deposit ITO films of higher sheet resistance, less thickness uniformity and higher transmittance at 25 °C, smaller etching angle and lower etching rate at 230 °C.     

Sintering of nanocrystalline Ta2O5 and ZrO2 films compared to that of TiO2 films

Thin (d = 60 nm/140 nm) nanocrystalline Ta₂O₅ and ZrO₂ films were deposited onto SiO₂ flakes, using a liquid route synthesis. Their sintering behaviour was characterized and compared to that of the corresponding powders and the known equivalent TiO₂ film in terms of grain size, grain growth and layer porosity. The effect of the substrate was noticeable on crystallisation process but not on grain growth. The sintering behaviour was actually dictated by the initial size and the packing of the precipitated grains related to the synthesis of the film.     

Robust SiO2 gate dielectric thin films prepared through plasma-enhanced atomic layer deposition involving di-sopropylamino silane (DIPAS) and oxygen plasma: Application to amorphous oxide thin film transistors

DIPAS (di-isopropylamino silane, H₃Si[N(C₃H₇)₂]) and O₂ plasma were employed, using plasma-enhanced atomic layer deposition (PEALD), to deposit silicon oxide to function as the gate dielectric at low temperature, i.e., below 200 °C. The superior amorphous SiO₂ thin films were deposited through the self-limiting reactions of atomic layer deposition with a deposition rate of 0.135 nm/cycle between 125 and 200 °C. PEALD-based SiO₂ thin layer films were applied to amorphous oxide thin film transistors constructed from amorphous In-Ga-Zn-O (IGZO) oxide layers, which functioned as channel layers in the bottom-gated thin film transistor (TFT) structure, with the aim of fabricating transparent electronics. The SiO₂ gate dielectric exhibited the highest TFT performance through the fabrication of heavily doped n-type Si substrates, with a saturation mobility of 16.42 cm²/V·s, threshold voltage of 2.95 V and large on/off current ratio of 3.69 × 10⁸. Ultimately, the highly doped Si was combined with the ALD-based SiO₂ gate dielectric layers, leading to a saturation mobility of 16.42 cm²/V·s, threshold voltage of 2.95 V, S-slope of 0.1944, and on/off current ratio of 3.69 × 10⁸. Semi-transparent and transparent TFTs were fabricated and provided saturation mobilities of 22.18 and 24.29 cm²/V·s, threshold voltages of 4.18 and 2.17 V, S-slopes of 0.1944 and 0.1945, and on/off current ratios of 9.63 × 10⁸ and 1.03 × 10⁷, respectively.     

Fabrication of highly efficient TiO2/Ag/TiO2 multilayer transparent conducting electrode with N ion implantation for optoelectronic applications

Fabrication of highly conductive and transparent TiO₂/Ag/TiO₂ (referred hereafter as TAT) multilayer films with nitrogen implantation is reported. In the present work, TAT films were fabricated with a total thickness of 100 nm by sputtering on glass substrates at room temperature. The as-deposited films were implanted with 40 keV N ions for different fluences (1×10¹⁴, 5×10¹⁴, 1×10¹⁵, 5×10¹⁵ and 1×10¹⁶ ions/cm²). The objective of this study was to investigate the effect of N⁺ implantation on the optical and electrical properties of TAT multilayer films. X-ray diffraction of TAT films shows an amorphous TiO₂ film with a crystalline peak assigned to Ag (111) diffraction plane. The surface morphology studied by atomic force microscopy (AFM) and field emission scanning electron microscope (FESEM) revealed smooth and uniform top layer of the sandwich structure. The surface roughness of pristine film was 1.7 nm which increases to 2.34 nm on implantation for 1×10¹⁴ ions/cm² fluence. Beyond this fluence, the roughness decreases. The oxide/metal/oxide structure exhibits an average transmittance ~80% for pristine and ~70% for the implanted film at fluence of 1×10¹⁶ ions/cm² in the visible region. The electrical resistivity of the pristine sample was obtained as 2.04×10⁻⁴ Ω cm which is minimized to 9.62×10⁻⁵ Ω cm at highest fluence. Sheet resistance of TAT films decreased from 20.4 to 9.62 Ω/□ with an increase in fluence. Electrical and optical parameters such as carrier concentration, carrier mobility, absorption coefficient, band gap, refractive index and extinction coefficient have been calculated for the pristine and implanted films to assess the performance of films. The TAT multilayer film with fluence of 1×10¹⁶ ions/cm² showed maximum Haacke figure of merit (FOM) of 5.7×10⁻³ Ω⁻¹. X-ray photoelectron spectroscopy (XPS) analysis of N 1s and Ti 2p spectra revealed that substitutional implantation of nitrogen into the TiO₂ lattice added new electronic states just above the valence band which is responsible for the narrowing of band gap resulting in the enhancement in electrical conductivity. This study reports that fabrication of multilayer transparent conducting electrode with nitrogen implantation that exhibits superior electrical and optical properties and hence can be an alternative to indium tin oxide (ITO) for futuristic TCE applications in optoelectronic devices.     

Fabrication and laser oscillation of Yb:Sc2O3 transparent ceramics from co-precipitated nano-powders

Ytterbium doped scandium oxide (Yb:Sc₂O₃) transparent ceramics were fabricated by a co-precipitation and vacuum sintering method. The characteristics of the precursor and the calcined powders were investigated by BET, XRD, and SEM. Ultra-fine and low agglomerated 5at%Yb:Sc₂O₃ powders with the average particle size about 65.4 nm were obtained after calcined at 1100 °C for 5 h. Using the synthesized powders as starting materials, 5at%Yb:Sc₂O₃ transparent ceramics with the in-line transmittance of 71.1% at 1100 nm and average grain size of 145 μm were fabricated by vacuum sintering at 1825 °C for 10 h. Quasi-CW laser oscillation of Yb:Sc₂O₃ ceramics was obtained at 1040.6 nm. A maximum output power as high as 2.44 W with a corresponding slope of 35% was achieved. Finally, the tunability of the ceramic was explored measuring a tuning range up to 55 nm.     

Controlled precipitation of lithium disilicate (Li2Si2O5) and lithium niobate (LiNbO3) or lithium tantalate (LiTaO3) in glass-ceramics

In the present study, the crystallization principles and phenomena of base glasses from the system of SiO₂-Li₂O-P₂O₅-Al₂O₃-K₂O-Nb₂O₅ or Ta₂O₅ were investigated. Annealing parameters such as temperature and time were varied. Annealing the base glasses 10 min at temperatures <850 °C for Nb₂O₅ or Ta₂O₅ containing samples lead to the crystallization of Li₂SiO₃. At higher annealing temperatures or longer annealing times, Li₂SiO₃ disappeared and Li₂Si₂O₅ was the main crystal phase in all glass-ceramics. After the dissolution of Li₂SiO₃, the minor crystal phases of LiNbO₃ or LiTaO₃ were precipitated. Increasing the annealing temperatures as well as the annealing times lead to higher bending strengths up to about 676 MPa and CR-values of up to 100. Increasing the contents of Nb₂O₅ or Ta₂O₅ lead to higher CR-values. The radiopacities increased up to 355% compared to aluminum.     

Low-temperature crystallization of tantalum pentoxide films under elevated pressure

Ta₂O₅ thin films deposited via a metal-organic decomposition method were crystallized via atmospheric pressure annealing and a high-pressure crystallization (HPC) process. Ta₂O₅ thin films started to become crystallized at 700 °C as subjected to atmospheric pressure annealing. When the HPC process was adopted and annealing at 16.5 MPa was performed, the crystallization temperature of Ta₂O₅ films was greatly dropped to as low as 350 °C. The developed HPC process considerably reduced the thermal budget and energy consumption during film processing. The crystallized Ta₂O₅ phase was found to be homogeneously distributed within the HPC-derived films. With annealing at 700 °C under atmospheric pressure, the silicon species diffused from the substrates into the Ta₂O₅ layers, thereby leading to reduced dielectric constants. The HPC process effectively suppressed the interdiffusion between the substrates and dielectric layers by lowering the required heating temperature, and also significantly increased the dielectric constants of Ta₂O₅ thin films. The HPC process was confirmed to effectively lower the crystallization temperature and improve the dielectric properties of Ta₂O₅ thin films.     

Effect of substrate temperature on microstructure and optical properties of nanocrystalline alumina thin films

Aluminum oxide (Al₂O₃) thin films were deposited on silicon (100) and quartz substrates by pulsed laser deposition (PLD) at an optimized oxygen partial pressure of 3.0×10^?3 mbar in the substrate temperatures range 300–973 K. The films were characterized by X-ray diffraction, transmission electron microscopy, atomic force microscopy, spectroscopic ellipsometry, UV–visible spectroscopy and nanoindentation. The X-ray diffraction studies showed that the films deposited at low substrate temperatures (300–673 K) were amorphous Al₂O₃, whereas those deposited at higher temperatures (≥773 K) were polycrystalline cubic γ-Al₂O₃. The transmission electron microscopy studies of the film prepared at 673 K, showed diffuse ring pattern indicating the amorphous nature of Al₂O₃. The surface morphology of the films was examined by atomic force microscopy showing dense and uniform nanostructures with increased surface roughness from 0.3 to 2.3 nm with increasing substrate temperature. The optical studies were carried out by ellipsometry in the energy range 1.5–5.5 eV and revealed that the refractive index increased from 1.69 to 1.75 (λ=632.8 nm) with increasing substrate temperature. The UV–visible spectroscopy analysis indicated higher transmittance (>80%) for all the films. Nanoindentation studies revealed the hardness values of 20.8 and 24.7 GPa for the films prepared at 300 K and 973 K respectively.     

Preparation of antireflective SiO2 nanometric films

Antireflective nanometric SiO₂ films were formed on glass substrates by dip coating from a colloidal SiO₂ sol having an average particle size of 9 nm. Withdrawal speed of dip coating was varied between 100 and 200 mm/min with 25 mm increments, and baking temperature of the films was altered between 300 and 550 °C with 50 °C increments. Obtained SiO₂ films were in 80–200 nm thickness range. Film thickness was seen to increase with increasing withdrawal speed and to decrease with increasing baking temperature. A maximum light transmittance of 95% was obtained with 4.5% points increase, from the films which were withdrawn at 100 mm/min and baked at 450 or 500 °C. It was seen from SEM observations that the films exhibited full coverage on glass surface and contained no voids or cracks. Size of SiO₂ particles in the film was seen in the AFM analyses to increase with baking temperature. Sintering of SiO₂ particles appeared to accelerate at temperatures over 450 °C.     

Dielectric properties and bright red emission of Y3+/Eu3+-codoped ZrO2 thin films prepared by chemical solution deposition

We report on an effective combination of good dielectric properties with bright red emission in Y³⁺/Eu³⁺-codoped ZrO₂ thin films. The thin films were deposited on fused silica and Pt/TiO₂/SiO₂/Si substrates using a chemical solution deposition method. The crystal structure, surface morphology, electrical and optical properties of the thin films were investigated in terms of annealing temperature, and Y³⁺/Eu³⁺ doping content. The 5%Eu₂O₃–3%Y₂O₃–92%ZrO₂ thin film with 400 nm thickness annealed at 700 °C exhibits optimal photoluminescent properties and excellent electrical properties. Under excitation by 396 nm light, the thin film on fused silica substrate shows bright red emission bands centered at 593 nm and 609 nm, which can be attributed to the transitions of Eu³⁺ ions. Dielectric constant and dissipation factor of the thin films at 1 kHz are 30 and 0.01, respectively, and the capacitance density is about 65.5 nf/cm² when the bias electric field is less than 500 kV/cm. The thin films also exhibit a low leakage current density and a high optical transmittance with a large band gap.     

Enhanced electrical and optical properties based on stress reduced graded structure of Al-doped ZnO thin films

Graded structures of aluminum-doped zinc oxide (AZO) multilayered thin film were prepared on quartz glass substrate by sol-gel process, and then sequentially annealed by raped thermal annealing(RTA) and UV laser annealing technologies for transparent conducting oxide (TCO) applications. Different Al mol% (0, 0.17, 0.33,0.5, 0.66, 0.83, 1) doped ZnO graded structures of multilayer thin films were prepared to optimize the lattice parameter to reduce stress, and then the annealing processes were sequentially performed. Introducing graded multilayered thin films, reduced the stress between the layers. The AZO graded structures of multilayer thin films were annealed by RTA followed by a 350 nm nanosecond pulsed UV laser annealing method. The graded structures of multilayered AZO thin films were investigated and analyzed by X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM), four-point probe, and UV–vis spectrophotometer, respectively. These results show that multilayered graded thin films were well grown with decreased stress, and well crystallized along the c-axis. The optical transmittance of the films is around 94.8% at 400–800 nm wavelength, and the energy band-gap is around 3.27 eV, respectively. The sheet resistance value of 13.2 kΩ/sq shows a 30% improvement.     

Dielectric and optical properties of electroceramic PBZNZT thin films prepared by pulsed laser deposition process

The 0.6[0.94Pb(Zn_1/3Nb_2/3)O₃ + 0.06BaTiO₃] + 0.4[0.48(PbZrO₃) + 0.52(PbTiO₃)], PBZNZT, thin films were synthesized by pulsed laser deposition (PLD) process. The PBZNZT films possess higher insulating characteristics than the PZT (or PLZT) series materials due to the suppressed formation of defects, therefore, thin-film forms of these materials are expected to exhibit superior ferroelectric properties as compared with the PZT (or PLZT)-series thin films. Moreover, the Ba(Mg_1/3Ta_2/3)O₃ thin film of perovskite structure was used as buffer layer to reduce the substrate temperature necessary for growing the perovskite phase PBZNZT thin films. The PBZNZT thin films of good ferroelectric and dielectric properties (remanent polarization P_r = 26.0 μC/cm², coercive field E_c = 399 kV/cm, dielectric constant K = 737) were achieved by PLD at 400 °C. Such a low substrate temperature technique makes this process compatible with silicon device process. Moreover, thus obtained PBZNZT thin films also possess good optical properties (about 75% transmittance at 800 nm). These results imply that PBZNZT thin films have potential in photonic device applications.     

Hybrid multilayer thin-film fabrication by atmospheric deposition process for enhancing the barrier performance

In this paper, a multilayer barrier thin film, based on polyvinylidene difluoride (PVDF)–silicon dioxide (SiO₂), has been fabricated on a PET substrate through a novel method of joint fabrication techniques. The inorganic SiO₂ thin film was deposited using a roll-to-roll atmospheric atomic layer deposition system (R2R-AALD), while the organic PVDF layer was deposited on the surface of SiO₂ through the electrohydrodynamic atomization (EHDA) technique. The multilayer barrier thin films exhibited very good surface morphology, chemical composition, and optical properties. The obtained values for arithmetic surface roughness and water contact angle of the as-developed multilayer barrier thin film were 3.88 nm and 125°, respectively. The total thickness of the multilayer barrier thin film was 520 nm with a high optical transmittance value (85–90%). The water vapor transmission rate (WVTR) of the barrier thin film was ~?0.9?×?10^?2 g m^?2 day^?1. This combination of dual fabrication techniques (R2R-AALD and EHDA) for the development of multilayer barrier thin films is promising for gas barrier applications.     

Effect of heterojunction on photocatalytic properties of multilayered ZnO-based thin films

In the present study, the effects of the heterojunctions on the optical and structural characteristics and the resulting photocatalytic properties of multilayered ZnO-based thin films were investigated. The junctions were composed of semiconducting ZnO nano-porous films coated on the In₂O₃ and SnO₂ counterpart layers. The multilayered ZnO films based on the triple-layered Ag-doped indium oxide (AIO)/tin oxide (TO)/zinc oxide (ZnO), indium oxide (IO)/Ag-doped tin oxide (ATO)/zinc oxide (ZnO), indium oxide (IO)/tin oxide (TO)/zinc oxide (ZnO) and tin oxide (TO)/indium oxide (IO)/zinc oxide (ZnO) have been fabricated by subsequent sol–gel dip coating. Their structural and optical properties combined with photocatalytic characteristics were examined toward degradation of Solantine Brown BRL (C.I. Direct Brown), an azo dye using in Iran textile industries as organic model under UV light irradiation. Effects of operational parameters such as initial concentration of azo dye, irradiation time, solution pH, absence and presence of Ag doping and consequent of sublayers on the photodegradation efficiencies of ZnO nultilayered thin films were also investigated and optimum conditions were established. It was found that the photocatalytic degradation of azo dye on the composite films followed pseudo-first order kinetics. Photocatalytic activity of AIO/TO/ZnO interface composite film was higher compared with other films and the following order was observed for films activities: AIO/TO/ZnO > IO/TO/ZnO > ATO/IO/ZnO > TO/IO/ZnO. Differences in the film efficiencies can be attributed to differences in crystallinity, interfacial lattice mismatch, and surface morphology. Besides, the presence of Ag doping between layers that may act as trap for electrons generated in the ZnO over layer thus preventing electron–hole recombination.     

Interfacial electronic band alignment of Ta2O5/hydrogen-terminated diamond heterojunction determined by X-ray photoelectron spectroscopy

Ta₂O₅ films have been deposited on hydrogen-terminated diamond (H-diamond) by a radio-frequency sputter-deposition technique at room temperature. Electronic band structure of Ta₂O₅/H-diamond heterojunction has been investigated by X-ray photoelectron spectroscopy. Based on the binding energies of core-levels and valence band maximum values, valence band offset has been found to be 1.5 ± 0.2 eV for the Ta₂O₅/H-diamond heterointerface. It shows a type-II band configuration with conduction band offset of 2.4 ± 0.2 eV. The large ΔE_V value makes the Ta₂O₅/H-diamond heterojunction probably suitable for the application of high power and high frequency field effect transistors.     

Photophysical properties and photoelectrochemical performances of sol-gel derived copper stannate (CuSnO3) amorphous semiconductor for solar water splitting application

Copper tin oxide, CuSnO₃ (CSO), is an amorphous oxide semiconductor with a band-gap of 2.0–2.5 eV, and it is an attractive material for diverse applications such as transparent conducting oxides, transistors, and optoelectronic devices. In this study, we fabricated CSO thin films on fluorine-doped tin oxide (FTO)/glass substrates using a facile sol-gel process, and their optical properties, band structure and photoelectrochemical (PEC) properties were investigated using UV–Vis spectroscopy, photocurrent-density-potential (J-V) curves, electrochemical impedance spectroscopy, and Mott-Schottky analysis. The CSO film synthesized at 500 °C had an amorphous phase and a band gap of ~ 2.3 eV with n-type behavior, while the films synthesized at 550 °C and 600 °C had a phase mixture (SnO₂ + CuO). We identified for the first time that the CSO film could be applied to photoelectrodes for photoelectrochemical water-splitting systems. Importantly, when combining the CSO with nanostructured WO₃ film, i.e., the bilayer heterojunction of the a-CSO/WO₃ showed enhanced PEC performances (cathodic shift of onset potential, increase of photocurrent generation and O₂ evolution) compared to the pristine WO₃ film.     

Control of refractive index by annealing to achieve high figure of merit for TiO2/Ag/TiO2 multilayer films

We modified the refractive index (n) of TiO₂ by annealing at various temperatures to obtain a high figure of merit (FOM) for TiO₂/Ag/TiO₂ (45 nm/17 nm/45 nm) multilayer films deposited on glass substrates. Unlike the as-deposited and 300 °C-annealed TiO₂ films, the 600 °C-annealed sample was crystallized in the anatase phase. The as-deposited TiO₂/Ag/as-deposited TiO₂ multilayer film exhibited a transmittance of 94.6% at 550 nm, whereas that of the as-deposited TiO₂/Ag/600 °C-annealed TiO₂ (lower) multilayer film was 96.6%. At 550 nm, n increased from 2.293 to 2.336 with increasing temperature. The carrier concentration, mobility, and sheet resistance varied with increasing annealing temperature. The samples exhibited smooth surfaces with a root-mean-square roughness of 0.37–1.09 nm. The 600 °C-annealed multilayer yielded the highest Haacke's FOM of 193.9×10⁻³ Ω⁻¹.