Hybrid Thin Films Research Articles

Corrosion-resistant organic-inorganic hybrid pretreatments obtained by UV-initiated process suitable for primer-less coating systems

A photo-initiated sol-gel process has been developed to deposit organic-inorganic hybrid (OIH) thin films on metal substrates for corrosion protection. Wet films of non-aqueous compositions containing specially designed organo-silane precursors and photo-latent catalysts –photo-acid generator (PAG) or photo-base generators (PBG)-, were exposed to ultraviolet (UV) radiation under ambient moisture environment leading to OIH films by sol-gel reactions. Synthesis and curing of organo-silanes were characterized using instrumental and gravimetrical techniques. Moreover, the corrosion resistance performance of OIH films based on two families of organo-silane precursors cured by PAG and PBG were compared with those obtained by the conventional aqueous sol-gel process. The effects of precursor and photocatalyst type, UV light intensity, cure conditions, and film thickness on anti-corrosion performance of OIH coatings were studied using various qualitative and quantitative techniques such as DC polarization, electrochemical impedance spectroscopy (EIS), and accelerated salt spray test. Results revealed that selected OIH pretreated samples showed corrosion current density as low as 1.2 nA/cm2, which is superior compared to conventional hexavalent chromium-based Cr (VI) pretreatments. The study demonstrates the feasibility of this sustainable photo-initiated sol-gel process for many applications, such as primer-less coating systems.

Novel prussian blue@Carbon-dots hybrid thin film: The impact of carbon-dots on material structure and electrochromic performance

Herewith, a series of Prussian blue@Carbon-dot (P@C-dot) hybrids were directly grown on FTO substrate by simple, one-step hydrothermal method in different dosage of aqueous dispersion of carbon dots. Being a new class of carbon allotropes, Carbon dot (C-dot) hybridized with Prussian blue (PB) will enhance the electroactivity of the hybrid film. It was found that the incorporation of C-dots influences the appearance color of the sample, the microstrucutre and electrochromic performance of the hybrids. Raman and XPS analysis revealed structural changes of the hybrid with different dosage of C-dots. The P@C-dot hybrid film exhibits a high-contrast electrochromism, fast response time and highly reversible nature compared to the sample without C-dots. This improved performance of P@C-dot hybrids can be attributed to the role of reinforced C-dots in facilitating electron transport and ionic motion in the hybrid film. Thus, the P@C-dot hybrid film provides a versatile and promising application towards the fabrication of smart windows.

High moisture-resistive MoOx/metal/graphite barrier films with excellent thermal dissipation for the encapsulation of organic electronics

We have developed very simple and cost-effective encapsulation method using thermal-deposited MoOx/metal hybrid thin film followed by graphite patch technology. The water vapor transmission rate of the optimized film reached 8.7 × 10−5 g/m2/day based on the calcium test, which is comparable to those of inorganic hybrid films prepared by plasma-enhanced chemical vapor deposition method. With this novel barrier film, the operation lifetime of the organic light-emitting diode (OLED) reached 1032 h operated at an initial luminance of 2000 cd/m2. Moreover, the heat dissipation coefficient of the encapsulation film with graphite patch is superior to metals, indicating that the encapsulation film has potential application in organic electronics including OLEDs in high-temperature environment.

Electrochemical Self-Assembly of CuSCN/4-Cyano-4’-(N’-methyl)Stilbazolium Hybrid Thin Films

Electrochemical self-assembly (ESA) of CuSCN/4-cyano-4’-(N’-methyl)stilbazolium (CNS+) hybrid thin films has been performed and analyzed in comparison with CuSCN/4-(N,N-dimethylamino)-4’-(N’-methyl)stilbazolium (DAS+) hybrid system. Due to the presence of strongly electron-withdrawing -CN group, CNS+ has a much higher dipole moment than DAS+ to exhibit stronger affinity to CuSCN. CNS+ therefore gave strong impact to the crystal growth of CuSCN with its smaller concentration than DAS+, such as changing crystal orientation, creating unique nanostructure and phase transition from β- to α-CuSCN. CNS+ has been found to obey the same mechanism as DAS+ for its loading into the film. The limit for diffusion limited loading was pushed up to its bulk concentration of 200 μmol dm-3, much higher than that for DAS+ (60 μmol dm-3). Also, the efficiency of dye uptake in the surface reaction limited loading was enhanced about 3 times due to the improved stability of CuSCN/CNS surface complex.

Design and fabrication of g-C3N4 nanosheets decorated TiO2 hybrid sensor films for improved performance towards CO2 gas

The g-C3N4 decorated titanium dioxide (TiO2) porous nanospheres composites thin films were successfully synthesized via a spray pyrolysis technique. The structural, morphological and textural properties of the fabricated thin film sensors were analyzed through X-ray diffraction (XRD), electron microscopy (SEM and TEM), Raman and N2 adsorption-desorption analysis. The incorporation g-C3N4 in to TiO2 matrix was also confirmed through Energy dispersive spectra (EDS) and X-ray photoelectron microspore (XPS) analysis. Gas-sensing properties of the pure and g-C3N4/TiO2 hybrid thin film sensors were investigated towards H2S and CO2 gases with various ppm levels (0–1500). The results illustrates that 10 wt.% g-C3N4 decorated TiO2 composite film show outstanding sensing response (88%) and high stability (only loss 2.5% of its initial response value) towards CO2 gas at 1500 ppm (450 °C), which is comparatively high response towards H2S gas (67%) under same ppm level. The improved sensing response is due to the incorporated g-C3N4 could provide high conductivity, large surface area (108.5 m2/g) with porous nature (15.7 nm), which is consists of interconnection between g-C3N4 nanosheets and TiO2 spheres. The improved mechanism of the proposed sensor was also discussed in detail.

A novel electrochemical sensor based on double-walled carbon nanotubes and graphene hybrid thin film for arsenic(V) detection

In this work, we demonstrate the preparation of hybrid thin films based on double-walled carbon nanotubes and graphene for electrochemical sensing applications. The hybrid films were synthesized on polycrystalline copper foil by thermal chemical vapor deposition under low pressure. This carbonaceous hybrid film has exhibited high transparency with a transmittance of 94.3 %. The occurrence of this hybrid material on the electrode surface of screen-printed electrodes was found to increase electroactive surface area by 1.4 times, whereas electrochemical current was enhanced by 2.4 times. Such a highly transparent and conductive hybrid film was utilized as a transducing platform of enzymatic electrochemical arsenic(V) sensor. The as-prepared sensor shows the linear detection of arsenic(V) in the range from 1 to 10 ppb, with a limit of detection as low as 0.287 ppb. These findings provide a promising approach to develop new multifunctional electrochemical sensing systems for environmental monitoring and biomedical diagnostics.

Ion beam engineering in WO3-PEDOT: PSS hybrid nanocomposite thin films for gas sensing measurement at room temperature

This work focus upon influence of low energy ion beam irradiation on the physico-chemical, structural and optical properties of (Glass/WO3-PEDOT: PSS) hybrid thin films. The hybrid nanocomposites were synthesized by uniform dispersion of 1 wt% and 5 wt% WO3 nanoparticles in PEDOT: PSS conducting polymer solution. The hybrid films were irradiated with low energy Ar4+ (700 keV) beam at fluence 1 × 1015 ions.cm−2 and 1 × 1016 ions.cm−2 in IUAC, New Delhi, India. The particle size was determined to be 63 nm–33 nm (1 wt% hybrid film) and 62–61 nm (5 wt% hybrid film) using Scherer’s formula. The band gap for pristine and irradiated films of 1 wt% (2.34–2.18 eV) and 5 wt% (2.39–2.14 eV) were calculated from Tauc’s relation. FTIR and Raman spectroscopy analysis confirmed the formation of chemical bonds and carbonization of film at higher fluences. The change in properties of hybrid nanocomposite material by ion irradiation may be useful for sensing applications. The sensor response of pristine and irradiated hybrid composite films was studied from liquefied petroleum gas (LPG) at room temperature.

A novel PANI@Carbon dot hybrid with enhanced electrochemical and electrochromic properties

A novel Polyaniline@carbon dot (PANI@C-dot) hybrid was synthesized through copolymerization of aniline in the presence of carbon dots (C-dots) suspension. The PANI@C-dot hybrid thin film exhibits higher optical contrast and faster switching speed compared to the pristine PANI. The enhanced electrochromic performance was presumably due to the synergistic effect between the PANI and C-dots, which improved the electron transport and ionic motion of the electrochromic layer. Thus, the PANI@C-dot hybrid opens a new avenue for developing of C-dots based electrochromic materials and uses in energy conversation and storage devices.

Elucidation of the Controversial Layer Growth Mechanism of Vapor Phase Polymerization in the Preparation of Conductive Poly(3,4‐ethylenedioxythiophene)‐SiO2 Hybrid Films

AbstractIn recent times, there have been debates to ascertain whether the growth mechanism in vapor phase polymerization is a top‐down or a bottom‐up process. The objective of the present study is to identify the formation mechanisms of the organic–inorganic hybrid film prepared in the gaseous phase on the basis of the practical importance of the hybridization of materials. To this end, poly(3,4‐ethylenedioxythiophene)‐SiO2 conductive hybrid films with different layered structures are successfully fabricated. The growth mechanism of the layered organic–inorganic conductive hybrid thin film is elucidated by investigating the variations in the morphological and chemical compositions of its surface. Additionally, a cross‐sectional analysis is performed using a scanning electron microscope‐energy dispersive X‐ray spectroscopy and X‐ray photoelectron spectroscopy. The results indicate a “bottom‐up” growth mechanism, wherein the oxidant diffused through the recently formed layer, generating novel layers; this ultimately leads to formation of the organic–inorganic conductive hybrid film. Moreover, the optoelectronic and mechanical properties of the hybrid conductive films are precisely controlled by adjusting the order of incorporation of monomers in the process and the duration of polymerization of each monomer. Thus, this study achieves the fabrication of a mechanically robust and optically enhanced conductive hybrid film.

A novel optical model of the experimental transmission spectra of nanocomposite PVC-PS hybrid thin films doped with silica nanoparticles

We propose a novel derived optical model fitted to the experimental transmittance of PVC-PS hybrid thin films doped with Silica nanoparticles. The films are synthesized using a simple dip-coating method. The model has successfully interpreted the experimental spectral behaviour of transmittance of amorphous semiconductors and dielectric thin films. Interestingly, our model reproduces the optical parameters of the investigated thin films in good agreement with those predicted by Tauc plot. The great advantage of the proposed model over other models lies in its ability to explain the correlations between the film thickness and the optical bandgap. Furthermore, we investigate the structural, physical, and optical properties of PVC-PS- SiO2 thin films, in relevance to the silica percentage content. XRD measurements show that the as-prepared polymeric thin films are amorphous. In addition, SEM micrographs indicate that silica nanoparticles are well dispersed on the surface of the PVC-PS thin films with an average diameter of 100–400 nm. The effect of annealing parameters is also investigated to optimize the projected water contact angle of PVC-PS- SiO2 thin films. At annealing temperature of 2000°C, films become hydrophobic. The transmittance T% of the PVC-PS thin films is found to be about 83% in the visible region. The T% enhances to 90% upon adding silica NPs into PVC-PS polymeric thin films. Obtaining coatings with high transmittance is of crucial importance for several optoelectronic and photonic applications.

Paper based organic–inorganic hybrid photodetector for visible light detection

Photodetectors based on organic–inorganic hybrid are promising which can combine the merits like function tunability of organic materials as well as broadband absorption, excitonic mechanisms and high carrier mobility of inorganic materials. Flexible thin film photodetectors based on inorganic WSe2 nanosheets and organic PANI by tuning composition are developed by simple, cost effective solution blending process. The fabricated hybrid thin films on filter paper substrate manifest visible light detection with high responsivity, fast photoswitching and high specific detectivity. In addition, the performance of hybrid film is retained even after 400 bending cycles. In case of WSe2-PANI hybrid films, the enhanced photoresponse is due to change in work function between PANI and WSe2 nanosheets, local electric fields are formed at WSe2-PANI interface thereby generating a greater number of photogenerated electrons. Compared with other hybrid-based photodetectors, this work advocates huge development in future applications in wearable electronics, security surveillance, high-performance optoelectronics, etc.

Hybrid Nanoparticle Layers Toward Enhanced Luminescence of Phosphor Plates for White LEDs.

MgF2 porous nanoparticle-silica hybrid coating layers were utilized to enhance luminescence efficiency of phosphor plates for white light-emitting diodes (wLEDs). Silica and chemically synthesized porous MgF2 nanoparticles were sequentially deposited by spin coating on the phosphor plate with phosphor-in-glass (PiG) configuration. Microscopic investigation the hybrid film suggested intermixing of silica and porous MgF2 nanoparticles. Numerical estimation based on transfer matrix method expected a significant reduction in reflectance and enhancement of transmission spectra by the hybrid coating. In accordance, the photoluminescence intensity of phosphor plates showed a drastic improvement and quantum yield were enhanced from 30% (for bare PiG plate) to 45% (for hybrid-layer-coated PiG plate). When assembled with blue LEDs, hybrid nanoparticle coating on the PiG phosphor plates improved luminescence efficacy from 40 to 49 lm/W without deterioration of chromaticity during operation. In addition, mechanical durability of the hybrid thin film was confirmed by an abrasion test. Conformal coating of matching layer consisting of porous MgF2 nanoparticles and silica can provide an efficient route to highly luminescent white LEDs with mechanical stability.

Concerted Photoluminescence of Electrochemically Self-Assembled CuSCN / Stilbazolium Dye Hybrid Thin Films

Whether they are inorganic or organic, the key words for creation of new functional materials should be (1) solution, (2) low temperature, and (3) rare-element-free for sustainable development. As a leading example, we explore electrochemical self-assembly (ESA) of inorganic / organic hybrid thin films. In addition to the interests to study evolution of unique hybrid structures, concerted new functionalities are anticipated due to intimate interaction between the inorganic and organic constituents. Herein, we report ESA of CuSCN / 4-(N,N-dimethylamino)-4’-(N’-methyl)stilbazolium (DAS) hybrid thin films and its concerted photoluminescence (PL) behavior [1]. Hybrid thin films of crystalline CuSCN/DAS in three distinctively different nanostructures were obtained by ESA from a single pot containing all the chemical ingredients. Adsorption of DAS during the electrochemical precipitation of CuSCN result in significant change of film morphology, crystal structure and its orientation, as DAS “occluded” into crystal grains of β-CuSCN, DAS phase separated nano-“haircomb” shape β-CuSCN, and DAS phase-separated in nano-“scale” shape α-CuSCN, by simply increasing DAST concentration in the bath [2]. Their optical properties for UV-vis-NIR absorption, photoluminescence (PL), and PL excitation (PLE) spectra were examined between 77 and 298 K, in comparison with solution and solid powder of DAS tosylate (DAST). While all the fluorescent dyes we previously found to hybridize with CuSCN underwent quenching due to hole injection from dye excited state to the valence band of CuSCN, DAS presented the first and only example to exhibit PL when combined with CuSCN [3]. DAST exhibited a strong exciton-phonon coupling to weaken, broaden, and red shift PL at room temperature, so that it inversely is strongly enhanced, sharpened, and blue-shifted at 77 K. However, the PL of the same dye in the hybrid thin film shows a slight red shift and not much intensified. Dielectric environment as well as ordered alignment of DAS greatly stabilize exciton against thermalization loss by suppressing twisted intramolecular charge transfer (TICT) and exciton-phonon coupling. The smallest temperature dependence, thus to be interpreted as the strongest exciton stabilization, was found for the “haircomb” β-CuSCN/DAS hybrid. The PLE spectra of the “scale” α-CuSCN/DAS hybrid show a prominent sharp peak at 380 nm and another double-peak between 400 and 450 nm by cooling temperature. The former corresponds to the band-edge absorption of CuSCN, while the latter being similar to the LMCT absorption of [Cu(SCN)]+ complex. It has been confirmed that those peaks in PLE spectra indicate the contribution of CuSCN thin film without DAS for the generation of PL. These contributions of the light absorption by CuSCN to the PL from DAS clearly indicate energy transfer from CuSCN to DAS as a concerted PL mechanism. Concerted PL by energy transfer from CuSCN to DAS has also been found to occur efficiently, especially for the “scale” α-CuSCN/DAS with the largest contact area due to interpenetrating hybrid nanostructure in the smallest domain size. Those hybrid thin film having the concerted PL mechanism (Fig. 1) can possibly make these materials useful as LEDs.[1] K. Uda et al., ACS Omega, 2019, 4 (2), 4056-4062.[2] Y. Tsuda et al., Chem., 2017, 148, 845-854.[3] K. Uda et al., ECS Trans., 2019, 88, 323-333. Figure 1

Modelling of Diffusion-Limited Growth in the Electrodeposition of Porous ZnO

Electrodes of ZnO sensitized with appropriate dyes are very suitable as photoanodes in dye-sensitized solar cells (DSSCs).1 They are of particular advantage relative to established photoanodes based on nanoparticulate TiO2 since they- can be processed at low temperature and- provide higher electron mobility.Processing at low temperature is beneficial in itself because it leads to lower energy consumption during preparation and, hence, helps to reach payback times. Further, it allows using plastic foils as substrates and, thereby, further improves the energy balance and allows constructing lightweight and mechanically flexible solar cells. The higher electron mobility in ZnO helps to reduce the transport resistance in films which becomes important to suppress recombination in DSSCs using reversible redox shuttles to achieve higher photovoltage and, hence, higher efficiency.The electrodeposition of porous ZnO was optimized1 by addition of structure-directing agents (SDAs) in a reaction sequenceO2 + 2 H2O + 4 e- → 4 OH- (1)Zn2+ + 2 OH- → [Zn(OH)2] → ZnO + H2O (2)in which the growth rate of porous ZnO is limited by the diffusion of O2. Optimization of porosity and pore radius of ZnO essential for its application in dye-sensitized solar cells in order to enhance the cell performance can be obtained by proper choice of SDAs. Larger pores, e.g., showed a significantly decreased impedance of mass transport leading to an increased photocurrent in DSSCs. Successful application of these new ZnO films in dye-sensitized solar cells confirmed improved pathways for large complex ions as redox shuttles through the ZnO pore structure.2 Further optimization of film growth requires appropriate modelling. Simulations and experiments are presented for electrodeposition on microstructured electrode arrays (MEAs), namely, parallel band electrodes as model for planar substrates. Microelectrodes are very attractive in electrochemical applications because of easily reached high current densities and fast establishment of a steady state. In the present case of band arrays, however, the overlap of diffusion layers of adjacent electrodes has to be considered and leads to a reduced mass flux to each individual electrode band in comparison to a single electrode. A lower current density and, hence, lower rate of electrodeposition is observed. Three consecutive steps in the build-up of diffusion profiles have been established in the literature: at the beginning, each electrode band can be treated separately, then the overlap has to be considered and finally the diffusion profile can be described as planar, well comparable to a macroscopic electrode. Simulations were performed considering the detailed distribution of concentration changes in the electrolyte and also including all changes brought forward by the deposition of material (see Figure) and, hence, changes of the electrode geometry.3 The simulated current densities and the simulated shape of electrodeposited films compared very well to experimentally observed values, proving the validity of the chosen approach. 1. T. Yoshida, J. B. Zhang, D. Komatsu, S. Sawatani, H. Minoura, T. Pauporte, D. Lincot, T. Oekermann, D. Schlettwein, H. Tada, D. Wöhrle, K. Funabiki, M. Matsui, H. Miura, H. Yanagi, "Electrodeposition of Inorganic/Organic Hybrid Thin Films", Adv. Funct. Mat. (2009) 19, 17-43.2. T. H. Q. Nguyen, R. Ruess, D. Schlettwein, "Adjusting Porosity and Pore Radius of Electrodeposited ZnO Photoanodes", J. Electrochem. Soc. (2019) 166, B3040-B3046.3. C. Lupó, D. Schlettwein, "Modeling of Dendrite Formation as a Consequence of Diffusion-Limited Electrodeposition", J. Electrochem. Soc. (2019) 166, D3182-D3189.Figure: Simultaneously obtained modelling results of interdependent electrodeposition of porous ZnO (in grey) and concentration changes of O2 in the electrolyte (red for high, blue for low concentrations) after 100 s of electrodeposition under diffusion limitation. Figure 1

Electrochemical Self-Assembly of CuSCN/4-Cyano-4’-(N’-Methyl)Stilbazolium Hybrid Thin Films

Electrochemically self-assembled (ESA) CuSCN/4-(N,N-dimethylamino)-4’-(N’-methyl)stilbazolium (DAS) hybrid thin film was found to exhibit concerted photoluminescent (PL) property based on energy transfer from CuSCN to DAS [1]. The amount of co-precipitated DAS (P DAS) during ESA linearly increased on increasing DAS concentration (C DAS) in the bath but changes its slope due to switching of dye loading mechanism from diffusion limited to surface reaction limited [2]. The full analysis revealed the switching border to be dependent on the ratio between the concentration of CuSCN precursor complex, [Cu(SCN)]+ (C comp), and C DAS as C comp/C DAS = ca. 31 [3]. When the dye loading operates as surface reaction limited, phase separation of CuSCN and DAS in nano-scale occurs to exhibit efficient PL. Thus, finding an alternative chromophore with higher or lower affinity with CuSCN than DAS should result in shifting of the switching border with smaller or larger C comp/C dye than the above indicated value for DAS. In this study, we employed 4-cyano-4’-(N’-methyl)stilbazolium (CNS) for ESA with CuSCN. CNS has a strong dipole moment due to the presence of strongly electron withdrawing cyano group and thus is expected to exhibit a higher affinity to CuSCN than DAS.CuSCN/CNS hybrid thin films were obtained by cathodic electrolysis with various C CNS while fixing C comp = 2.5 mM. P CNS linearly increased upon increase of C CNS and changes its slope at around 200 μM, far larger than the switching point observed for DAS (around 60 μM). The steep slope for the low C CNS range should be determined by the diffusion of CNS to yield its diffusion coefficient D CNS = 1.49×10-6 cm2 s-1, slightly larger than that found for DAS (D DAS = 1.25×10-6 cm2 s-1). On the other hand, about 3 times larger P CNS for given dye concentrations and steeper slope of surface reaction limited regime for CNS than those found for DAS indicate higher adsorption stability of CNS than DAS to CuSCN surface. Soaking the CuSCN/CNS hybrid thin films electrodeposited at C CNS = 60 and 800 μM to represent the dye loading as diffusion and surface reaction limited, respetively, into dimethylacetamide resulted in partial and total extraction of CNS to reveal entrapment and phase-separation of CNS, just like the case of CuSCN/DAS. The maximum P CNS appears to be saturated when C CNS > 800 μM for CNS aggregate to occupy close to 30% of the total film volume.The present results already nicely support the validity of the switching of ESA mechanism, being common for both DAS and CNS. Smaller C comp/C CNS for the switching border and larger stability constant for surface complex formation are expected for CNS than DAS from full analysis.[1] K. Uda et al., ACS Omega, 4, 4056-4062 (2019).[2] Y. Tsuda et al., Monatsh. Chem., 148, 845 (2017).[3] Y. Tsuda et al., J. Electrochem. Soc., 166, B3096-B3102 (2019). Figure 1

Mechanistic Studies for Electrochemical Self-Assembly of CuSCN/Stilbazolium Dye Hybrid Thin Films

We have found electrochemical self-assembly (ESA) of inorganic / organic hybrid thin films in which the inorganic is CuSCN, known as a wide bandgap p-type semiconductor, whereas the organic is 4-N,N-dimethylamino-4’-N’-methylstilbazolium chromophore (abbreviated as DAS) as its salt with tosylate (DAST) known to exhibit second-order nonlinear optical property for terahertz emitters. DAS is also known to yield a layered inorganic-organic hybrid crystal in a (DAS)(Cu5I6) composition [1]. Strong dipole-dipole interaction of the DAS chromophores aligned between the CuI layers results in a spontaneous photocarrier generation and ambipolar transport in a single absorber solar cell. Thus, CuSCN/DAS hybrid thin films can be attractive alternatives for such opto-electrical applications, when ordered arrangement of DAS chromophore is achieved during ESA.In our previous study, switching of dye loading mechanism has been suggested, depending on DAS concentration (C DAS) in the bath [2]. In low C DAS, the loading is limited by diffusion so that DAS is entrapped within CuSCN crystal grains, while surface reaction of hybridization begins to limit the dye loading in high C DAS, resulting in formation of unique nanostructures as well as phase separation of inorganic and organic domains.In this study, electrochemical analysis by employing rotating disk electrode (RDE) has been performed to verify the mechanism of ESA and also to explore the limit of DAS loading. Electrodeposition of CuSCN undergoes as limited by transport of 1 : 1 complex between Cu2+ and SCN- ions, namely [Cu(SCN)]+ species, near 100% Faradic efficiency with marginal influence by the presence of DAS. Thus, the rate of CuSCN precipitation, P CuSCN, is always proportional to the concentration of the complex (C comp), and also to ω 1/2 (ω = angular speed of rotation of RDE) therefore P CuSCN can be expressed Eq. (1) from Levich equation. P CuSCN = J/F = 0.62×C comp×D comp 2/3×ν -1/6×ω 1/2 ··· (1)On the other hand, the rate of DAS precipitation, P DAS, should also be proportional to ω 1/2 under the regime of diffusion limited loading with a given C DAS, and is independent of CuSCN formation rate. P DAS = 0.62×C DAS×D DAS 2/3×ν -1/6×ω 1/2 ··· (2)Plots of P DAS against C comp for variation of C DAS were examined, and indeed such a trend as predicted from the above-mentioned model was found (Fig. 1). In the high C comp range, P DAS is independent of C comp and appears proportional to C DAS, because of the diffusion limited loading mechanism. When C comp goes below certain concentration, P DAS changes proportionally to C comp, while its slope also increase as dependent on C DAS. The relationship between the switching C comp and C DAS yields C DAS / C comp = 1/31 as the border for the switching of the mechanism [3], whereas the dependence of the slope on C DAS in the low C comp range should reveal the stoichiometry of surface complex between CuSCN and DAS. When the rate surface complex formation, P DAS become proportional to the P CuSCN, assuming n of DAS complexes with single CuSCN site yields the equilibrium as the right and the surface is expected to be always equilibrated such equation, P CuSCN + nC DAS ⇄ P DAS ··· (3)Stability constant K should be expressed like Eq. (4), K = P DAS/P CuSCN × C DAS n ··· (4)Eq. (4) can be re-written by inserting Eq. (1), P DAS/C comp= 0.62×D comp 2/3×ν -1/6×ω 1/2 ×K×CDAS n ··· (5)Plotted slope of Fig. 1 in the low C comp range (P DAS/C comp) against C DAS and did fitting with n as variable and then resulted n = 0.6. It means approximately one DAS coordinating two CuSCNs and stability constant K can be calculated as 6.78×102 mol−0.5 cm2.5.[1] Elena Cariati et al., Adv. Mater., 13, 1665-1668 (2001).[2] Yuki Tsuda et al., Monatshefte für Chemie, 148, 845-854 (2017).[3] Yuki Tsuda et al., J. Electrochem. Soc. 166(9) B3096-B3102 (2019). Figure 1

Molecular layer deposition of indicone and organic-inorganic hybrid thin films as flexible transparent conductor

Indicone films consisting of indium and organic aromatic linker are grown by molecular layer deposition (MLD) using diethyl[1,1,1-trimethyl-N-(trimethylsilyl)-silanaminato]-indium (INCA-1) as the indium precursor and hydroquinone (HQ) as the organic precursor. A constant growth rate typical for MLD is exhibited at temperature between 100 and 250 °C. The structure and the properties of the deposited thin films are analyzed using various experimental and theoretical techniques such as Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and density functional theory (DFT) calculations. Indicone films show time-dependent change upon exposure to ambient air, which is explained by adsorption of H2O. Furthermore, transparent and conducting organic-inorganic hybrid thin films are grown by applying supercycles of atomic layer deposition (ALD) of indium oxide and MLD of indicone. Structural, optical and electrical properties of the hybrid thin films can be adjusted according to the supercycle ratio. Especially, the hybrid film with 99:1 cycle ratio of indium oxide:indicone shows minimal change of electrical resistivity even after repeated bending over 100,000 cycles. Currently developed indicone-based hybrid thin films may have applications for flexible transparent conducting material.

Hybrid PEDOT:PSS to obtain high-performance Ag NW-based flexible transparent electrodes for transparent heaters

Silver nanowire (Ag NW) networks are remarkable components that may be able to replace indium tin oxide (ITO) as transparent electrodes. In this paper, the Ag NW based flexible transparent electrodes are prepared via PEDOT:PSS sol–gel transition without vacuum process, provides very high figure of merit by minimizing junction resistance, and also exhibit excellent mechanical robustness against bending. The sheet resistance of the flexible Ag NW-based films reduces from 1000 to 9.4 Ω/sq. at transmittance of ~ 90%. The conduction mechanism involves Ag NWs to PEDOT:PSS carrier injection prior to the formation of a continuous metal conduction pathway. Calculations of figure of merit display a large value of 340, which is superior to that obtained from the flexible ITO, carbon nanotube, graphene, copper nanowire, and other silver nanowire and hybrid thin films. Meanwhile, the sheet resistance does not show great change after tape test due to the effect of PEDOT:PSS. Finally, the successful implementation of the prepared Ag NWs-based transparent electrodes into a flexible transparent heater is demonstrated, verifying the applicability of the electrodes. It is believed that our study is the key step toward realizing the practical use of NW flexible transparent electrodes in various flexible electronic devices.

Solution-Processed Flexible Gas Barrier Films for Organic Field-Effect Transistors

The solution-processed gas barrier film was fabricated and used for organic field-effect transistors (OFETs). Organic-inorganic hybrid sol-gel materials and cyclic transparent optical polymer (CYTOP) were used as the bottom and top layers of the barrier films, respectively, to effectively protect against gas permeation through the barrier films. The organic-inorganic hybrid material includes sol-gel precursors and amphiphilic polymers. The conventional sol-gel precursors form siloxane bonds by sol-gel reaction and form densely-packed rigid part in thin films. The alkoxysilane-functionalized amphiphilic polymer in the sol-gel precursor solutions has two hydrophobic segments and a hydrophilic segment. The amphiphilic polymer with reactive alkoxysilane groups at both ends of the hydrophobic segments can be involved in the sol-gel reaction, and they can act as surfactants to surround the conventional precursors stabilizing the nanoparticles formed by the hydrolytic condensation reaction of precursors. The amphiphilic polymer also provides flexibility for hybrid sol-gel thin films. CYTOP was used to introduce hydrophobicity on top of the organic-inorganic hybrid thin films. The barrier films containing the organic-inorganic hybrid and hydrophobic CYTOP layers were applied to OFETs and exhibited notable gas barrier properties, high transparency, and flexibility. The encapsulated OFETs with 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-pentacene) as an organic semiconductor showed a slight decrease in hole mobility from 0.13 to 0.11 cm2 V-1 s-1, while the OFETs without barrier films showed a mobility decrease from 0.11 to 0.03 cm2 V-1 s-1.

Plasmonic and non-plasmonic contributions on photocatalytic activity of Au-TiO2 thin film under mixed UV–visible light

A highly photocatalytic Au-TiO2 hybrid thin film was prepared by the photocatalytic deposition of Au nanoparticles (NPs) on reactive sputtered TiO2 thin film. By altering the ratio of the visible (Vis) and ultra-violet (UV) light (Vis/UV), we investigated plasmonic and non-plasmonic contributions of Au NPs to the overall photocatalytic activity. While, a gradual increase of Vis/UV (≤0.24/1) led to a steady enhancement of the photocatalytic performance of Au-TiO2 hybrid structures, further increase in Vis/UV (≥0.30/1) did not foster the enhancement further. At high Vis/UV, plasmon excited electrons seem to start promoting electron-hole recombination in TiO2, which significantly reduces the photocatalytic performance.