Methylammonium‐Mediated Evolution of Mixed‐Organic‐Cation Perovskite Thin Films: A Dynamic Composition‐Tuning Process

Methylammonium‐mediated phase‐evolution behavior of FA_1−xMA_xPbI₃ mixed‐organic‐cation perovskite (MOCP) is studied. It is found that by simply enriching the MOCP precursor solutions with excess methylammonium cations, the MOCPs form via a dynamic composition‐tuning process that is key to obtaining MOCP thin films with superior properties. This simple chemical approach addresses several key challenges, such as control over phase purity, uniformity, grain size, composition, etc., associated with the solution‐growth of MOCP thin films with targeted compositions.     

Effect of biphase on dielectric properties of Bi-doped lead strontium titanate thin films

Pb_0.4Sr_0.6TiO₃ (PST) thin films doped with various concentration of Bi were prepared by a sol-gel method. The phase status, surface morphology and dielectric properties of these thin films were measured by X-ray diffraction (XRD), scanning electron microscopy (SEM) and impedance analyzer, respectively. Results showed that the thin films with the maximum dielectric constant and minimum dielectric loss were obtained for x=0.15. For x<0.15, only pure PST perovskite phase were in the thin films. For 0.2<x<0.4, the PST/Bi₂Ti₂O₇ biphase were obtained. The thin films with pure Bi₂Ti₂O₇ pyrochlore phase were obtained for x=0.67. The biphase thin films had high tunability and high figure of merit (FOM). The FOM of PST/Bi₂Ti₂O₇ biphase thin film was about 6 times higher than that thin films formed with pure perovskite phase or pure pyrochlore phase.     

SnOx thin films with tunable conductivity for fabrication of p–n homo‐junction

Tin oxide (SnO_x) has been widely used for the fabrication of transparent and flexible devices because of its excellent optical and electronic properties. In this work, we established a methodology for the synthesis of SnO_x thin films with p‐type and n‐type tunable conductivity by direct currecnt (DC) magnetron sputtering. The SnO_x thin films changed from p‐type to n‐type by increasing the relative oxygen partial pressure (ppO₂) from 4.8% to 18.5% and by varying the working pressure between 1.8 and 2.5 mTorr. The SnO_x thin films were annealed at 160°C, 180°C, and 200°C for 30 min to promote the formation of the desired crystalline structures. At the annealing temperature of 180°C in air ambient, the SnO_x thin films showed a tetragonal structure with Sn traces. Having found the optimal conditions, we deposited both types of SnO_x thin films with the same tetragonal structure and similar chemical stoichiometry. Also, the conditions to obtain thin films with the highest mobility values for p‐type (1.10 cm²/Vs) and n‐type (22.20 cm²/Vs) were used for fabricating the device. Finally, the implementation of a SnO_x‐based p–n diode was demonstrated using transparent SnO_x thin films developed in this work, illustrating their potential use in transparent electronics.     

Structural,compositional and hardness properties of hydrogenated amorphous carbon nitride thin films synthesized by dense plasma focus device

The hydrogenated amorphous carbon nitride (a‐CN_x:H) thin films were synthesized on the SS‐304 substrates using a dense plasma focus device. The a‐CN_x:H thin films were synthesized using CH₄/N₂ admixture gas and 20 focus deposition shots on substrates placed at different distances from the anode top. X‐ray photoelectron spectroscopy and Raman analysis confirmed different C–N bonding in the a‐CN_x:H thin films. A decrease in the N/C ratio as well as the sp³/sp² ratio with an increase in the substrate distance has been observed. The higher amount of C–N formation for the film synthesized at 10 cm is observed which decreases with increasing distance. The X‐ray photoelectron spectroscopy and Raman analysis affirmed the C ≡ N presence in all the thin films synthesized at different distances. The morphology of the synthesized a‐CN_x:H thin films showed nanoparticles and nanoparticle clusters formation at the surface. The hardness results showed comparatively lower hardness of the a‐CN_x:H thin films due to the presence of C ≡ N. The C–N formation with lower amount of C ≡ N and a higher N/C ratio as well as a higher sp³/sp² ratio for the films synthesized at 10 cm show reasonably higher hardness. Copyright © 2016 John Wiley & Sons, Ltd.     

Electrical properties of La0.6Ca0.4MnO3–Bi3.4Nd0.6Ti3O12 thin films derived by a sol–gel process

Magnetoelectric (ME) xLa_0.6Ca_0.4MnO₃–(1 ? x)Bi_3.4Nd_0.6Ti₃O₁₂ (LCMO–BNT) composite thin films have been prepared by a sol–gel process and spin-coating technique. The effects of LCMO content on the microstructure, leakage current density, ferroelectric properties, fatigue endurance and ME voltage coefficient of LCMO–BNT thin films derived by sol–gel method were studied. It was found that the composite thin films have better fatigue endurance properties and lower leakage current densities compared with pure BNT thin films, as well as large ME voltage coefficients.     

Photocatalytic Activity and Characterization of the Sol-Gel Derived Pb-Doped TiO2 Thin Films

Photocatalytically active Pb-doped TiO₂ thin films were prepared on a soda-lime glass substrate by sol-gel dip-coating technique using TiO₂ sols containing lead(II) nitrate. The thin films were characterized by X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), UV-VIS spectroscopy and X-ray diffraction (XRD). A shift of the UV-VIS absorption towards longer wavelengths was observed, which indicated a decrease in the band-gap of TiO₂ upon Pb doping. XRD results showed both pure and Pb-doped TiO₂ thin films were polycrystalline, anatase type, and oriented predominantly to the (101) plane. A slight shift in the d-spacing for the Pb-doped film indicated the incorporation of Pb into the TiO₂ lattice to form Pb _x Ti_1–x O₂ solid solution. AFM results showed Pb-doped TiO₂ thin films were composed of larger TiO₂ particles and had rougher surface, compared with un-doped TiO₂ thin films. XPS results showed that except for the enrichment of Pb near the surface, Pb exists in the forms of Pb _x Ti_1–x O₂ and PbO. Dimethyl-2,2-dichlorovinyl phosphate (DDVP) was efficiently degraded in the presence of the Pb-doped TiO₂ thin films by exposing the insecticide solution to sunlight. The mechanism of photocatalytic activity enhancement of the Pb-doped TiO₂ thin films was discussed.     

Direct measurement of the nitrogen content by XPS in self‐passivated TaNx thin films

The nitrogen content in tantalum nitride (TaN_x) thin films, where x indicates that TaN_x is not generally stoechiometric, can be measured directly by XPS. This is the purpose of the present study. However, the XPS spectra of TaN_x present electron energy loss spectroscopy (EELS) peaks that lead to a complex peak fitting, particularly for self‐passivated thin films. A complete peak fitting procedure based upon Tougaard's background, the Doniach‐Sunjic Function and EELS peaks, is presented. It is applied to two self‐passivated TaN_x thin films elaborated by reactive sputtering and presenting a different nitrogen content. The physical properties of these surfaces are interpreted in terms of Ta 4f_7/2 chemical states directly dependent on the nitrogen content. The main results are discussed and improvements are proposed to the method. Copyright © 2008 John Wiley & Sons, Ltd.     

Fabrication and properties of xBiFeO3-(1 − x)Bi4Ti3O12 system by sol–gel process

The thin films of mixture of xBiFeO₃-(1 − x)Bi₄Ti₃O₁₂ (x = 0.4, 0.5, and 0.6) system were prepared by a sol–gel process. The thicknesses of the thin films were 540, 500, and 570 nm, respectively. The crystal structure of all thin films annealed at 650 °C was analyzed by X-ray diffraction. It was found that the thin films at x = 0.4 and 0.5 mainly consisted of a Bi₄Ti₃O₁₂ phase while Bi₅Ti₃FeO₁₅ was the major phase of the thin film at x = 0.6. The thin film (x = 0.6) showed better ferroelectric properties in remnant polarization and polarization fatigue than those observed in the thin films (x = 0.4 and 0.5). The values of remnant polarization 2P _r and coercive field 2E c of the thin film at x = 0.6 were 36 μC/cm² and 192 kV/cm at an applied electric field of 260 kV/cm, respectively. There was almost no polarization fatigue up to 10¹⁰ switching cycles. Also weak ferromagnetism was observed in the thin film at x = 0.6.     

Enhancement of the power conversion efficiency for inverted polymer solar cells due to an embedded CuxO interlayer formed by using Cu(I) acetate and Cu(II) acetate

Structural, optical, and photovoltaic properties of copper-oxide (Cu_xO) thin films formed by using a sol–gel method were investigated. X-ray diffraction patterns showed that the Cu_xO films prepared utilizing Cu(I) acetate or Cu(II) acetate and annealed under ambient atmosphere at various temperatures were polycrystalline with two phases, Cu₂O and Cu₆₄O. Transmittance spectra showed that the energy band gaps of the Cu_xO thin films formed by using Cu(II) acetate were smaller than those formed by using Cu(I) acetate. Current–voltage results showed that the power conversion efficiencies of the inverted polymer solar cells utilizing the Cu_xO interlayer formed by using Cu(II) acetate were better than those utilizing the Cu_xO interlayer formed by using Cu(I) acetate due to the multiple band gaps of the Cu(II) acetate.     

Study of dielectric characteristics of graded Ba<Subscript>1−x</Subscript>Ca<Subscript>x</Subscript>Zr<Subscript>0.05</Subscript>Ti<Subscript>0.95</Subscript>O<Subscript>3</Subscript> thin films grown by a sol-gel process

The compositionally graded Ba_1−xCa_xZr_0.05Ti_0.95O₃ (x = 0, 0.05, 0.10) (BCZT) thin films with compositional gradient from BaZr_0.05Ti_0.95O₃ to Ba_0.90Ca_0.10Zr_0.05Ti_0.95O₃ were deposited on Pt/Ti/SiO₂/Si substrates by sol-gel processing. The crystal structure of the thin films was determined by X-ray diffraction. Field emission scanning electron microscopy (FESEM) was used to examine crystallite size and morphology of compositionally graded thin films. The dielectric properties of compositionally graded thin films were characterized by measuring the dielectric constant and dielectric loss as a function of temperature, applied electric field and frequency. As a result, compositionally graded thin films with weak temperature dependence were realized. Dielectric constant peaks, common to a ferroelectric transition, were not observed in the temperature range from 298 to 413 K. The compositionally graded BCZT thin films with weak temperature dependence of tunability could be attractive materials for frequency and phase agile tunable microwave components such as tunable filters, tunable oscillators, and phase shifters for application in phased array antennas.     

XPS Analysis of Lead Zirconate Titanate Thin Films Prepared Via a Sol-Gel Process

The crystalline phase and composition of sol-gel-derived lead zirconate titanate (PbZr _x Ti_{1 – x} O₃, PZT) thin films were determined by an X-ray photoelectron spectroscopic (XPS) data processing technique. As a result, it was proved that existence of the surface layer with several tens nm in thickness, of which the crystalline phase and composition were different from those of the inside of the thin films, was found. The newly developed XPS analytical technique is much applicable for the characterization of PZT thin film surface.     

Structure and magnetic properties of La0.67Sr0.33MnO3 thin films prepared by sol–gel method

La_1?xSr_xMnO₃ (x = 0.33) (LSMO) thin films have been fabricated successfully by sol–gel method on two different types of substrates, Si (111) and SrTiO₃ (STO) (001). Microstructure and magnetic properties of LSMO thin films have been investigated. The X-ray diffraction studies of the films confirm the pure phase of the LSMO thin films. In contrast with LSMO thin films on Si substrate, the performances of LSMO on STO substrate are superior both from structural and magnetic properties. For the samples deposited on STO substrate, highly preferred orientation as well as less strain and grain defects was found; in other aspect, the magnetization, the residual and saturation moment value, tended greater while a decreased coercive field required merely (saturation moment value was about five times and coercive field was only about 13 % of those on Si substrate). The Curie temperature of LSMO thin films on Si and STO substrates is estimated to be about 349.7 and 359 K, respectively.     

XANES and XPS characterization of hard amorphous CSixNy thin films grown by RF nitrogen plasma assisted pulsed laser deposition

Amorphous carbon silicon nitride thin films were grown on (100) oriented silicon substrates by pulsed laser deposition (PLD) assisted by an RF nitrogen plasma source. Up to about 30 at. % nitrogen and up to 20 at. % silicon were found in the hard amorphous thin films by XPS in dependence on the composition of the mixed graphite / Si₃N₄ PLD target. The universal nanohardness was measured to be at maximum load force of 0.1 mN up to 23 GPa for thin CSi_xN_y films with reference value of 14 GPa for single crystalline silicon. X-ray photoelectron spectroscopy (XPS) of CSi_xN_y film surfaces showed a clear correlation of binding energy and intensity of fitted features of N 1s, C 1s, and Si 2p peaks to the composition of the graphite / Si₃N₄ target and to nitrogen flow through the plasma source, indicating soft changes of binding structure of the thin films due to variation of PLD parameters. Auger electron spectroscopy (AES) of Si KL₂₃L₂₃;¹D Auger transition gave a detailed view of bonding structure of Si in the CSi_xN_y films. The intensity of π* and σ* resonances at the carbon K-edge X-ray absorption near-edge structure (XANES) of the CSi_xN_y films measured at BESSY I corresponded to the nanohardness of the CSi_xN_y films, thus giving insight into chemical binding structure of superhard amorphous materials.     

The Influence of Dopant Concentration on Optical-Electrical Features of Quantum Dot-Sensitized Solar Cell

In this study, TiO₂/CdS/Cd_xCu_1−xSe, TiO₂/CdS/Cd_xMn_1−xSe, and TiO₂/CdS/Cd_xAg_2−2xSe thin films were synthesized by chemical bath deposition for the fabrication of photoanode in quantum-dot-sensitized solar cells. As a result, the structural properties of the thin films have been studied by X-ray diffraction, which confirmed the zinc Blende structure in the samples. The optical films were researched by their experimental absorption spectra with different doping concentrations. Those results were combined with the Tauc correlation to estimate the absorption density, the band gap energy, valence band and conduction band positions, steepness parameter, and electron–phonon interaction. Furthermore, the electrical features, electrochemical impedance spectrum and photocurrent density curves were carried out. The result was used to explain the enhancing performance efficiency.     

Lithium electrochromism of atmospheric pressure plasma jet-synthesized NiO x C y thin films

Reversible lithium intercalation and deintercalation behavior of atmospheric pressure plasma jet (APPJ)-synthesized organonickel oxide (NiO _x C _y ) thin films under various substrate distances is testified in an electrolyte (1?M LiClO₄–propylene carbonate solution) at low driving voltages from ?0.5 to 1.5?V. Fast responses of 2?s bleaching at ?0.5?V and 6?s coloration at +1.5?V are accomplished for the nano-porous NiO _x C _y thin films. This study reveals that a rapid synthesis of electrochromic NiO _x C _y thin films in a single process via APPJ by 21?s is investigated. This study presents a noteworthy electrochromic performance in a light modulation with up to 43% of transmittance variation and a coloration efficiency of 36.3?cm²/C at a wavelength of 830?nm after 200?cycles of cyclic voltammetry measurements.     

XPS/EXAFS study of cycleability improved LiMn2O4 thin film cathodes prepared by solution deposition

The influence of Sn substitution in LiMn₂O₄ thin films as a cathode has been studied via solution deposition to improve the electrochemical performance of thin film lithium batteries. LiSn_0.025Mn_1.95O₄ thin films showed the most promising performance, i.e. a high capacity retention of 77% at 10 C after the 500th cycle, due to the increased average Mn valence state. The thin films of LiSn_x/2Mn_2?xO₄ (x ? 0.10) showed significant precipitation of SnO₂ and SnO after the cycling evaluation.     

Synthesis of Cu-Modified Nickel Oxide Nanocrystals and Their Applications as Hole-Injection layers for Quantum-Dot Light-Emitting Diodes

Solution-processed NiO_x thin films have been applied as hole-injection layers (HILs) in quantum-dot light-emitting diodes (QLEDs). The commonly used NiO_x HILs are prepared by the precursor-based route, which requires high annealing temperatures of over 275 °C to in situ convert the precursors into oxide films. Such high processing temperatures of NiO_x HILs hinder their applications in flexible devices. Herein, we report a low-temperature approach based on Cu-modified NiO_x (NiO_x-Cu) nanocrystals to prepare HILs. A simple post-synthetic surface-modification step, which anchors the copper agents onto the surfaces of oxide nanocrystals, is developed to improve the electrical conductivity of the low-temperature-processed (135 °C) oxide-nanocrystal thin films. In consequence, QLEDs based on the NiO_x-Cu HILs exhibit an external quantum efficiency of 17.5 % and a T₉₅ operational lifetime of ∼2,800 h at an initial brightness of 1,000 cd m⁻², meeting the commercialization requirements for display applications. The results shed light on the potential of using NiO_x-Cu HILs for realizing high-performance flexible QLEDs.     

Deposition of copper‐doped iron sulfide (CuxFe1−xS) thin films using aerosol‐assisted chemical vapor deposition technique

Copper‐doped iron sulfide (Cu_xFe_1?xS, x = 0.010–0.180) thin films were deposited using a single‐source precursor, Cu(LH)₂Cl₂ (LH = monoacetylferrocene thiosemicarbazone), by aerosol‐assisted chemical vapor deposition technique. The Cu‐doped FeS thin films were deposited at different substrate temperatures, i.e. 250, 300, 350, 400 and 450 °C. The deposited thin films were characterized by X‐ray diffraction (XRD) patterns, Raman spectra, scanning electron microscopy, energy dispersive X‐ray analysis (EDX) and atomic force microscopy. XRD studies of Cu‐doped FeS thin films at all the temperatures revealed formation of single‐phase FeS structure. With increasing substrate temperature from 250 to 450 °C, there was change in morphology from wafer‐like to cylindrical plate‐like. EDX analysis showed that the doping percentage of copper increased as the substrate temperature increased from 250 to 450 °C. Raman data supports the doping of copper in FeS films. Copyright © 2010 John Wiley & Sons, Ltd.     

The effect of nitrogen on the cycling performance in thin-film Si1−xNx anode

The effects of nitrogen on the electrochemical properties of silicon-nitrogen (Si_1−xN_x) thin films were examined in terms of their initial capacities and cycling properties. In particular, Si_0.76N_0.24 thin films showed negligible initial capacity but an abrupt capacity increase to ∼2300 mA h/g after ∼650 cycles. The capacity of pure Si thin films was deteriorated to ∼20% of the initial level after 200 cycles between 0.02 and 1.2 V at 0.5 C (1 C=4200 mA/g), whereas the Si_0.76N_0.24 thin films exhibited excellent cycle-life performance after ∼650 cycles. In addition, the Si_0.76N_0.24 thin films at 50 °C showed an abrupt capacity increase at an earlier stage of only ∼30 cycles. The abnormal electrochemical behaviors in the Si_0.76N_0.24 thin films were demonstrated to be correlated with the formation of Li₃N and Si₃N₄.     

Nitrogen-doped TiO2 from TiN and its visible light photoelectrochemical properties

Homogeneous titanium nitride (TiN) thin film was produced by simple electrophoreic deposition process on Ti substrate in an aqueous suspension of nanosized TiN powder. Nitrogen-doped titanium dioxide (TiO_2−xN_x) was synthesized by oxidative annealing the resulted TiN thin film in air. Photoelectrochemical measurements demonstrated visible light photoresponse for the electrode of annealed electrophoreic deposited TiN samples. It is found that the synthesized TiO_2−xN_x electrode showed higher photo potential under white and visible light illumination than the pure TiO₂ electrode. The photocurrent under visible light illumination was also observed, which increased with the increase of deposition time of TiN thin films.