Two-step Deposition Method Research Articles

Radial growth of zinc oxide nanowire for piezoelectric nanogenerator application

Nano- and micro-self-biased sensors employed environmental harvested energy, which are provided by different methods, such as piezoelectric. Piezoelectric materials are capable of producing electrical energy from environmental mechanical force. In this paper, a radial layer of well-arrayed hexagonal zinc oxide nanowires is grown on carbon fiber substrate using a two-step Chemical deposition method of metal salt growth. The resulted morphology is examined using Field Emission Scanning Electron Microscopy (FESEM) micrographs and X-ray Diffraction (XRD) pattern which indicates the quality and the crystallization order of the samples. In addition, composition of the material is studied using a Fourier Transform Infrared (FTIR) spectroscopy method. The results show that zinc oxide nanowires are well managed in vertical direction on the cylindrical carbon fibers. The hexagonal nanowires are grown with a length from 206 to 286 nm (Nanometer) and the diameter from 75 to 103 nm. The results of FTIR spectroscopy and XRD also illustrate the wurtzite structure of zinc oxide. The synthesized nanowires are then applied in a flexible capacitive piezoelectric nanogenerator consisting of a thin Ag layer as the upper contact and a carbon substrate as the back contact which are separated by a PMMA dielectric film. The output current and voltage are measured by applying a random pulse mechanical force on the upper contact. A maximum voltage and current of 14 mV (millivolt) and 20 nA (nanoampere) are generated at the output of nanogenerator, respectively.

Enhanced Efficiency and Stability of Perovskite Solar Cells via Anti-Solvent Treatment in Two-Step Deposition Method.

The low-cost inorganic-organic lead halide perovskite materials become particularly promising for solar cells with high photovoltaic conversion efficiency. The uniform and pinhole-free perovskite films play an important role for high-performance solar cells. We demonstrate an antisolvent treatment by controlling the PbI2 morphology to enhance the perovskite conversion and photophysical properties, including high absorption, crystallinity, and rapid carrier transfer. The fabricated perovskite solar cells show tremendous PCE improvement to about 16.1% from 12% with less hysteresis, and retain over 90% initial PCE after 30 days in ambient and dark atmosphere. In prospect, this antisolvent treatment will be a feasible route to prepare high-quality perovskite films including favorite photophysical properties.

An Enzymatic Glucose Sensor Composed of Carbon-Coated Nano Tin Sulfide.

In this study, a biosensor, based on a glucose oxidase (GOx) immobilized, carbon-coated tin sulfide (SnS) assembled on a glass carbon electrode (GCE) was developed, and its direct electrochemistry was investigated. The carbon coated SnS (C-SnS) nanoparticle was prepared through a simple two-step process, using hydrothermal and chemical vapor deposition methods. The large reactive surface area and unique electrical potential of C-SnS could offer a favorable microenvironment for facilitating electron transfer between enzymes and the electrode surface. The structure and sensor ability of the proposed GOx/C-SnS electrode were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, UV–vis spectroscopy, Fourier transform infrared spectroscopy (FTIR), and cyclic voltammetry study (CV).

Controllable Synthesis of TiO2@Fe2O3 Core-Shell Nanotube Arrays with Double-Wall Coating as Superb Lithium-Ion Battery Anodes

Highlighted by the safe operation and stable performances, titanium oxides (TiO2) are deemed as promising candidates for next generation lithium-ion batteries (LIBs). However, the pervasively low capacity is casting shadow on desirable electrochemical behaviors and obscuring their practical applications. In this work, we reported a unique template-assisted and two-step atomic layer deposition (ALD) method to achieve TiO2@Fe2O3 core-shell nanotube arrays with hollow interior and double-wall coating. The as-prepared architecture combines both merits of the high specific capacity of Fe2O3 and structural stability of TiO2 backbone. Owing to the nanotubular structural advantages integrating facile strain relaxation as well as rapid ion and electron transport, the TiO2@Fe2O3 nanotube arrays with a high mass loading of Fe2O3 attained desirable capacity of ~520 mA h g−1, exhibiting both good rate capability under uprated current density of 10 A g−1 and especially enhanced cycle stability (~450 mA h g−1 after 600 cycles), outclassing most reported TiO2@metal oxide composites. The results not only provide a new avenue for hybrid core-shell nanotube formation, but also offer an insight for rational design of advanced electrode materials for LIBs.

CH3NH3PbI3 films prepared by combining 1- and 2-step deposition: how crystal growth conditions affect properties

Perovskite solar cells continue to attract strong attention because of their unprecedented rate of power conversion efficiency increase. CH3NH3PbI3 (MAPbI3) is the most widely studied perovskite. Typically one-step (1-s) or two-step (2-s) deposition methods are used to prepare MAPbI3 films. Here, we investigate a new MAPbI3 film formation method that combines 1-s and 2-s deposition (termed 1 & 2-s) and uses systematic variation of the stoichiometric mole ratio (x) for the PbI2 + xMAI solutions employed. The PbI2 + xMAI solutions were used to deposit precursor films that were subsequently dipped in MAI solution as a second step to produce the final MAPbI3 films. The morphologies of the 1 & 2-s MAPbI3 films consisted of three crystal types: tree-like microcrystals (≫1 μm), cuboid meso-crystals (∼0.1-1 μm) and nanocrystals (∼50-80 nm). Each crystal type and their proportions were controlled by the value for x. The new 1 & 2-s deposition method produced MAPbI3 films with tuneable optoelectronic properties that were related to those for the conventional 1-s and 2-s films. However, the 1 & 2-s film properties were not simply a combination of those for the 1-s and 2-s films. The 1 & 2-s films showed enhanced light scattering and the photoluminescence spectra displayed a morphologically-dependent red-shift. The unique morphologies for the 1 & 2-s films also strongly influenced PbI2 conversion, power conversion efficiency, hysteresis and recombination. The trends for the performance parameters and hysteresis were compared for devices constructed using spiro-MeOTAD and P3HT and were similar. The 1 & 2-s method should apply to other perovskite formulations and the new insights concerning MAPbI3 crystal growth conditions, morphology and material properties established in this study should also be transferable.

The Influence of PbI<sub>2</sub> on Characteristic of Organic-Inorganic Hybrid Perovskite Thin Films

Organic-inorganic hybrid perovskite materials have attracted significant research efforts because of their outstanding properties. Meanwhile the crystallization of organic-inorganic hybrid perovskite materials can significantly influence the films quality. Here, we research the influence of the characteristics of PbI2 thin film on final perovskite films and the mechanisms of film formation based on the two-step sequential deposition method. We found that the characteristics of PbI2 thin film, such as the grain size, the grain shape, the surface roughness and the film densification, have significant effects on the final perovskite films due to different film crystallization process. According to the analysis on the characteristics of the perovskite films obtained from different PbI2precursor, we suggested that the formation of perovskite film begins from the PbI2 crystals expanding when they are converted to MAPbI3 perovskite by migration of MA+ cations from the grain boundaries.

Enhanced efficiency of planar perovskite solar cells via a two-step deposition using DMF as an additive to optimize the crystal growth behavior

We present a facile way towards the use of the polar solvent additive in the inter-diffusion two-step sequential deposition method for a high quality perovskite film.

Label-free and high-throughput biosensing of multiple tumor markers on a single light-addressable photoelectrochemical sensor

The sensitive and label-free detection of multiple biomarkers on a single electrode by photoelectrochemical (PEC) sensors based on light addressing strategies is very attractive for developing portable and high-throughput biosensing systems. The essential prerequisite of this proposal is the employment of uniform photovoltaic material modified electrodes with high conversion efficiency. Herein, a novel two-step constant potential deposition method for the rapid fabrication of bismuth sulfide film modified ITO electrodes (Bi2S3/ITO) was established. The produced Bi2S3/ITO, with excellent uniformity and high conversion efficiency in visible light ranges, was further modified with gold nanoparticles (AuNPs) and then divided into separated identical sensing zones by insulative paints. The adsorption-based immobilization of antibodies of three tumor markers, i.e., a-fetoprotein (AFP), carcinoembryonic antigen (CEA) and cancer antigen 19-9 (CA19-9), onto different sensing zones of the electrode and the further blocking with BSA established a label-free and light-addressable PEC sensor (LF-LAPECS), which can achieve the rapid and sensitive detection of these biomarkers with wide linear ranges, low detection limits and self-calibration ability. Moreover, the detection throughput can be conveniently improved by enlarging the size of the substrate electrode and increasing the number of separated sensing zones. The present work thus demonstrates the promising applications of PEC techniques for developing sensitive, time-saving, cost-effective and high-throughput biosensing methods.

Au@Pd/TiO2 with atomically dispersed Pd as highly active catalyst for solvent-free aerobic oxidation of benzyl alcohol

In this study, bimetallic Au@Pd/TiO2 catalysts with an Au loading amount of 0.94wt.% and Pd loading amounts varying from 0.017 to 0.13wt.% were prepared using a two-step photocatalytic deposition method, and the solvent-free aerobic oxidation of benzyl alcohol was investigated on the catalysts. For comparison, monometallic Pd/TiO2 with a Pd loading amount of 0.048wt.% (denoted as Pd(0.048)/TiO2) and Au/TiO2 with a Au loading amount of 0.94wt.% were also prepared. The catalysts were characterized using X-ray diffraction, transmission electron microscope, UV–Vis diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy, infrared spectroscopy of CO adsorption, and energy dispersive spectroscopy. Characterization results suggested that in the bimetallic catalysts Pd atoms were preferentially deposited on exposed Au surface and core-shell structured Au@Pd particles with atomically dispersed Pd as the shell were formed. Additionally, monomeric and paired Pd sites were dominated in bimetallic catalysts with Pd contents below 0.066wt.%, and increasing Pd deposition amount led to gradual development of Pd ensembles. For the solvent-free aerobic oxidation of benzyl alcohol, Au/TiO2 had negligible catalytic activity, while Pd(0.048)/TiO2 exhibited marked conversion of benzyl alcohol. As for bimetallic catalysts, the conversion of benzyl alcohol increased with the increase of Pd deposition amount from 0.017 to 0.049wt.%, whereas kept constant when Pd deposition amount was further increased to 0.13wt.%. Accordingly, Au@Pd(0.049)/TiO2 had a highest turnover frequency value of 21961h−1 for the oxidation of benzyl alcohol among the test bimetallic catalysts.

Applied bias photon-to-current conversion efficiency of ZnO enhanced by hybridization with reduced graphene oxide

The role of reduced graphene oxide (rGO) in the enhancement of photo-conversion efficiency of ZnO films for photoelectrochemical (PEC) water-splitting applications was analyzed. ZnO and rGO-hybridized ZnO (rGO/ZnO) films were prepared via a two-step electrochemical deposition method followed by annealing at 300°C under argon gas flow. The physical, optical and electrochemical properties of the films were characterized to identify the effect of rGO-hybridization on the applied bias photon-to-current efficiency (ABPE) of ZnO. Scanning electron microscopy and X-ray diffraction indicated the formation of vertically-aligned, wurtzite-phase ZnO nanorods. Diffuse-reflectance UV–visible spectroscopy indicated that rGO-hybridization was able to increase the light absorption range of the rGO/ZnO film. UPS analysis showed that hybridization with rGO increased the band gap of ZnO (3.56eV) to 3.63eV for rGO/ZnO sample, which may be attributed to the Burstein–Moss effect. Photoluminescence (PL) spectra disclosed that rGO-hybridization suppressed electron-hole recombination due to crystal defects. Linear sweep voltammetry of the prepared thin films showed photocurrent density of 1.0 and 1.8mA/cm2 for ZnO and rGO/ZnO at +0.7V, which corresponded to an ABPE of 0.55% and 0.95%, respectively. Thus, this report highlighted the multi-faceted role of rGO-hybridization in the enhancement of ZnO photo-conversion efficiency.

Growing and Etching MoS₂ on Carbon Nanotube Film for Enhanced Electrochemical Performance.

In this work we directly synthesized molybdenum disulfide (MoS2) nanosheets on carbon nanotube film (MoS2@CNT) via a two-step chemical vapor deposition method (CVD). By etching the obtained MoS2@CNT into 10% wt HNO3, the morphology of MoS2 decorated on CNT bundles was modulated, resulting in more catalytic active MoS2 edges being exposed for significantly enhanced electrochemical performance. Our results revealed that an 8 h acid etching sample exhibited the best performance for the oxygen evolution reaction, i.e., the current density reached 10 mA/cm2 under 375 mV over-potential, and the tafel slope was as low as 94 mV/dec. The enhanced behavior was mainly originated from the more catalytic sites in MoS2 induced by the acid etching treatment and the higher conductivity from the supporting CNT films. Our study provides a new route to produce two-dimensional layers on CNT films with tunable morphology, and thus may open a window for exploring its promising applications in the fields of catalytic-, electronic-, and electrochemical-related fields.

From unstable CsSnI3 to air-stable Cs2SnI6: A lead-free perovskite solar cell light absorber with bandgap of 1.48 eV and high absorption coefficient

All-inorganic and lead-free cesium tin halides (CsSnX3, X=Cl, Br, I) are highly desirable for substituting the organolead halide perovskite solar cells. However, the poor stability of CsSnX3 perovskites has so far prevented the fabrication of devices that can withstand sustained operation under normal conditions. In this paper, a two-step sequential deposition method is developed to grow high-quality B-γ-CsSnI3 thin films and their unique phase change in atmosphere is explored in detail. We find the spontaneous oxidative conversion from unstable B-γ-CsSnI3 to air-stable Cs2SnI6 in air. Allowing the phase conversion of the CsSnI3 film to evolve in ambient air it gives the semiconducting perovskite Cs2SnI6 with a bandgap of 1.48eV and high absorption coefficient (over 105cm−1 from 1.7eV). More importantly, the Cs2SnI6 film, for the first time, is adopted as a light absorber layer for a lead-free perovskite solar cell and a preliminary estimate of the power conversion efficiency (PCE) about 1% with open-circuit voltage of 0.51V and short-circuit current of 5.41mA/cm2 is realized by optimizing the perovskite absorber thickness. According to the bandgap and the Shockley-Queisser limit, such inorganic perovskite solar cell with higher efficiency and pronounced stability can be expected by material quality improvement and device engineering.

Ambient Engineering for High-Performance Organic-Inorganic Perovskite Hybrid Solar Cells.

Considering the evaporation of solvents during fabrication of perovskite films, the organic ambience will present a significant influence on the morphologies and properties of perovskite films. To clarify this issue, various ambiences of N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), and chlorobenzene (CBZ) are introduced during fabrication of perovskite films by two-step sequential deposition method. The results reveal that an ambient CBZ atmosphere is favorable to control the nucleation and growth of CH3NH3PbI3 grains while the others present a negative effect. The statistical results show that the average efficiencies of perovskite solar cells processed in an ambient CBZ atmosphere can be significantly improved by a relatively average value of 35%, compared with those processed under air. The efficiency of the best perovskite solar cells can be improved from 10.65% to 14.55% by introducing this ambience engineering technology. The CH3NH3PbI3 film with large-size grains produced in an ambient CBZ atmosphere can effectively reduce the density of grain boundaries, and then the recombination centers for photoinduced carriers. Therefore, a higher short-circuit current density is achieved, which makes main contribution to the improvement in efficiency. These results provide vital progress toward understanding the role of ambience in the realization of highly efficient perovskite solar cells.

Platinum nanoparticles decorated dendrite-like gold nanostructure on glassy carbon electrodes for enhancing electrocatalysis performance to glucose oxidation

Platinum nanoparticles decorated dendrite-like gold nanostructure, bimetal composite materials on glassy carbon electrode (Pt/DGNs/GC) for enhancing electrocatalysis to glucose oxidation was designed and successfully fabricated by a facile two-step deposition method without any templates, surfactants, or stabilizers. Dendrite-like gold nanostructure was firstly deposited on the GC electrode via the potentiostatic method, and then platinum nanoparticles were decorated on the surface of gold substrate through chemical reduction deposition. X-ray diffraction (XRD), field-emission scanning electron microscope (FE-SEM), energy-dispersive X-ray spectroscopy (EDS) were applied to characterize the evolution of morphology and structure of the as-prepared Pt/DGNs/GC. Based on electrochemical measurements such as cyclic voltammetry, linear voltammetry and chronoamperometry, Pt/DGNs/GC exhibited significantly enhanced electrocatalytic performance to glucose oxidation compared those of pure dendrite-like Au nanoparticles in our previous report. Controlling chemical reduction deposition time, the amount of platinum nanoparticles on Au surface could be regulated, which further tuned electrocatalytic properties toward glucose oxidation. The dendrite-like gold surface partially covered by platinum nanoparticles dramatically enhanced the electrocatalytic performance for the oxidation of glucose because of excellent synergetic effects between gold and platinum species and the increased electrochemical active area from Pt nanoparticles loading. The non-enzymatic glucose biosensor based on Pt/DGNs/GC showed a rapid respond time (within 2s), wide linear range (from 0.1mM to 14mM), low detection limit (0.01mM), supernal sensitivity (275.44μAcm−2mM−1, R=0.993), satisfactory reproducibility and good stability for glucose sensing. It was demonstrated that Pt/DGNs/GC could work as promising candidate for factual non-enzymatic glucose detection.

A Three-Step Method for the Deposition of Large Cuboids of Organic-Inorganic Perovskite and Application in Solar Cells.

A three-step method for the deposition of CH3 NH3 PbI3 perovskite films with a high crystalline structure and large cuboid overlayer morphology is reported. The method includes PbI2 deposition, which is followed by dipping into a solution of C4 H9 NH3 I (BAI) and (BA)2 PbI4 perovskite formation. In the final step, the poorly thermodynamically stable (BA)2 PbI4 phase converts into the more stable CH3 NH3 PbI3 perovskite by dipping into a solution of CH3 NH3 I. The final product is characterized by XRD, SEM, UV/Vis, and photoluminescence analysis methods. The experimental results indicate that the prepared perovskite has cuboids with high crystallinity and large sizes (up to 1 μm), as confirmed by XRD and SEM data. Photovoltaic investigations show that the three-step method results in higher solar cell efficiency (15 % enhancement in efficiency) with a better reproducibility than the conventional two-step deposition method.

Electrodeposition of three dimensional-porous Ni/Ni(OH)2 hierarchical nano composite via etching the Ni/Zn/Ni(OH)2 precursor as a high performance pseudocapacitor

We have electrochemically synthesized 3D-porous micro-nano Ni/Ni(OH)2 hierarchical nanocomposites with improved supercapacitive performance. Firstly, the 3D-porous micro-nano Ni/Zn hierarchical nanoplatelets were constructed in a two-step gas bubble dynamic template deposition method as a scaffold with the open porous structure and extra high surface area for the subsequent electrodeposition of Ni(OH)2 nanostructures. Then the zinc were removed from the prepared 3D Ni/Zn/Ni(OH)2 nanocomposite via performing an etching process. The resulted 3D-porous micro-nano Ni/Ni(OH)2 hierarchical nanocomposites showed a high areal capacitance of 2.18Fcm−2 (2400Fg−1) at the current density of 1.12mAcm−2 (1.25Ag−1) which is so higher than the measured amount for the prepared 3D-Ni/Ni(OH)2 nanocomposites by directly deposition of nickel hydroxide on the synthesized 3D nickel foam. In addition, the prepared nanocomposite films exhibit the great cycling stability. The capacitance retention was about 100.012% after performing 1000 charge–discharge cycles, and decreases only about 1.3% after the 2000th cycle.

Effect of annealing process in tuning of defects in ZnO nanorods and their application in UV photodetectors

ZnO nanorod (NR) arrays were grown by a simple two-step chemical bath deposition method. The as-deposited NRs were then annealed at different temperatures (300, 400 and 500°C) for two time durations (1 and 5h). The NRs were studied by scanning electron microscopy, photoluminescence spectroscopy, X-ray diffraction and two-point electrical test. Finally, ultraviolet (UV) detection properties of samples as an active layer in UV photodetector devices were evaluated. The structural results showed that the sample annealed at 400°C had the best crystallinity. Furthermore, it was seen that the optical transparency and band gap of NRs increased with increase of the annealing temperature up to 400°C and then decreased at 500°C. The electrical resistance decreases with increment of the annealing temperature due to intensive desorption of oxygen molecules from the surface of ZnO NRs. The UV detection results proved a meaningful relevance of UV detection properties with the density of defects and quantity of oxygen molecules absorbed on the surface. ZnO NRs annealed at 300°C for 1h had the highest photosensitivity of ∼300 and photoresponsivity of 2.067A/W which make it suitable for the practical applications.

Observation of Strong Interlayer Coupling in MoS2/WS2 Heterostructures.

Epitaxial growth of A-A and A-B stacking MoS2 on WS2 via a two-step chemical vapor deposition method is reported. These epitaxial heterostructures show an atomic clean interface and a strong interlayer coupling, as evidenced by systematic characterization. Low-frequency Raman breathing and shear modes are observed in commensurate stacking bilayers for the first time; these can serve as persuasive fingerprints for interfacial quality and stacking configurations.

High-efficiency perovskite solar cells based on anatase TiO2 nanotube arrays

Perovskite solar cells (PSCs) based on one-dimensional anatase TiO2 nanotube arrays were prepared by using a two-step deposition method to fill the arrays of TiO2 nanotubes in different lengths with perovskite. The photovoltaic performance of PSCs was found to be significantly dependent on the length of the TiO2 nanotubes, and the power conversion efficiency decreased as the length of the TiO2 nanotubes increased from ~0.40μm to ~0.65 and then to ~0.93μm. The PSC fabricated with ~0.40μm-long anatase TiO2 nanotube arrays yielded a power conversion efficiency of 11.3% and a fill factor of 0.68 under illumination of 100mW/cm2 AM 1.5G simulated sunlight, which is significantly higher than previously reported solar cells based on 1-D TiO2 nanostructures. Incident photon-to-current efficiency and electrochemical impedance spectroscopy measurements indicated that longer TiO2 nanotubes led to higher recombination losses of charge carriers, possibly due to poor filling of the nanotube arrays with perovskite.

Two-Step Deposition Method of Nanostructured ZnO Thin Films with Various Precursor Concentrations: The High Crystal Quality Enhances the Final Properties

Two-Step Deposition Method of Nanostructured ZnO Thin Films with Various Precursor Concentrations: The High Crystal Quality Enhances the Final Properties