Thin Films In Aqueous Solution Research Articles

Doping of molecular semiconductors through proton-coupled electron transfer.

The chemical doping of molecular semiconductors is based on electron-transfer reactions between the semiconductor and dopant molecules; here, the redox potential of the dopant is key to control the Fermi level of the semiconductor1,2. The tunability and reproducibility of chemical doping are limited by the availability of dopant materials and the effects of impurities such as water. Here we focused on proton-coupled electron-transfer (PCET) reactions, which are widely used in biochemical processes3,4; their redox potentials depend on an easily handled parameter, that is, proton activity. We immersed p-type organic semiconductor thin films in aqueous solutions with PCET-based redox pairs and hydrophobic molecular ions. Synergistic reactions of PCET and ion intercalation resulted in efficient chemical doping of crystalline organic semiconductor thin films under ambient conditions. In accordance with the Nernst equation, the Fermi levels of the semiconductors were controlled reproducibly with a high degree of precision-a thermal energy of about 25 millielectronvolts at room temperature and over a few hundred millielectronvolts around the band edge. A reference-electrode-free, resistive pH sensor based on this method is also proposed. A connection between semiconductor doping and proton activity, a widely used parameter in chemical and biochemical processes, may help create a platform for ambient semiconductor processes and biomolecular electronics.

Electrodeposition of crystalline germanium thin films by the electrochemical liquid-liquid-solid method

The direct electrodeposition of crystalline germanium thin films in aqueous solutions at low temperatures represents a promising and cost-effective method for synthesising semiconductor materials. This study investigates the influence of the deposition potential and time on the characteristics of crystalline germanium thin films derived from germanium oxide precursors in aqueous solution through electrochemical liquid–liquid-solid (ec-LLS) process at low temperature. Additionally, it establishes a Ge/Cu Schottky junction by heterogeneous growth of germanium films on copper (Cu) metal via electrochemical liquid–liquid-solid–solid (ec-LLSS) process.X-ray diffraction (XRD) analysis revealed that an increase in the deposition potential to −1.7 V resulted in a shift in the crystal orientation of the germanium film from (220) to (111), while excessive deposition potential (>−2.0 V) led to a reduction in the crystallinity of the deposited samples. At a deposition temperature of 70 °C and a deposition potential of −1.8 V, the crystal cluster size and the crystal quality increased with the increasing deposition time. However, at −2.0 V, the crystallinity of the germanium film reached an optimal state after 30 min and then gradually declined with time.Charactersation techniques such as EDS, XPS and Raman spectroscopy indicated that the use of liquid electrode Ga(l) as a doping source during the electrodeposition process allowed for heterogeneous growth of Ga-doped p-type germanium films on a Cu substrate.The I-V characteristic curves demonstrated that the Ge/Cu Schottky junctions exhibited significant rectification characteristics, rendering them suitable for potential applications in solar cells.

Novel highly stable conductive polymer composite PEDOT:DBSA for bioelectronic applications

In this work, a novel conductive polymer composite consisting of poly(3,4-ethylenedioxythiophene) doped with dodecylbenzenesulfonic acid (PEDOT:DBSA) for bioelectronic applications was prepared and optimized. The novel PEDOT:DBSA composite possesses superior biocompatibility toward cell culture and electrical characteristics comparable to the widely used PEDOT:PSS. The cross-linking processes induced by the cross-linker glycidoxypropyltrimethoxysilane (GOPS), which was investigated in detail using Fourier transform Raman spectroscopy and XPS analysis, lead to the excellent long-term stability of PEDOT:DBSA thin films in aqueous solutions, even without treatment at high temperature. The electrical characteristics of PEDOT:DBSA thin films with respect to the level of cross-linking were studied in detail. The conductivity of thin films was significantly improved using sulfuric acid posttreatment. A model transistor device based on PEDOT:DBSA shows typical transistor behavior and suitable electrical properties comparable or superior to those of available conductive polymers in bioelectronics, such as PEDOT:PSS. Based on these properties, the newly developed material is well suited for bioelectronic applications that require long-term contact with living organisms, such as wearable or implantable bioelectronics.

Chemical Stability of Atomic Layer Deposited (ALD) Alumina Thin Films in Aqueous Solutions

Aluminum oxide (alumina) thin films deposited through atomic layer deposition (ALD) are of great interest in chemical barrier and corrosion protection applications. However, the stability of ALD alumina in aqueous solutions is still not fully understood. Due to its metastable amorphous phase, the hydration and degradation behavior of ALD alumina films behaves differently from its crystalline Al2O3 counterpart. A full understanding of why these films hydrate and/or dissolve requires the exploration of different deposition conditions and ion content in solutions used. This talk will discuss efforts to further elucidate the hydration and dissolution behavior of ALD alumina films. For this study, alumina thin films were ALD deposited onto silicon substrate at 150 °C using trimethylaluminum (TMA) and H2O. These films were then studied in Type 1 DI water, 2M NaCl, .5M NaCl, and .1M NaCl solutions at room temperature. Films were gently dried using a nitrogen gun and thickness was measured using a Cauchy ellipsometry model. After 15 days of immersion in Type 1 DI water, significant thickness growth is observed at twice (27 days) and 2.5 times (33 days) the normalized thickness. Similar hydration is not observed in salt-containing aqueous solutions nor upon exposure to air. We will discuss the possible effects of CO2 dissolution and carbonate formation as well as ionic species on the hydration and dissolution processes of these alumina films. Finally, we will show how a post-ALD plasma treatment to the film’s surface alters the hydration and dissolution behavior, improving stability in several aqueous conditions.

Photocatalytic Degradation of Methylene Blue under Visible Light Using TiO2 Thin Films Impregnated with Porphyrin and Anderson-Type Polyoxometalates (Cu and Zn)

In this work, tetra(4-carboxyphenyl)porphyrin (TCPP) and two Anderson-type polyoxomolybdates (containing Cu and Zn, respectively; CuPOM, ZnPOM) were synthesized and deposited on TiO2 thin films. The properties of the obtained materials were characterized through UV–vis spectroscopy, Fourier transform infrared spectroscopy (FT-IR), diffuse reflection spectroscopy, scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). The adsorption and photodegradation under the visible light irradiation of methylene blue (MB) were studied for TiO2, TCPP/TiO2, TCPP/CuPOM/TiO2 and TCPP/ZnPOM/TiO2 thin films in aqueous solution. The results of the diffuse reflectance showed two bands in the visible light spectrum for the TCPP/POM/TiO2 systems compared to unmodified TiO2 that does not show any bands in the same region of the spectrum. The TCPP/POM/TiO2 systems showed a higher removal of MB, with an adsorption rate near to 31% for the TCPP/CuPOM/TiO2 film compared to 9% adsorption on the TiO2 film. The kinetic results show that the pseudo-second order model was the best fitting model for the MB adsorption process onto fabricated materials. The photodegradation studies under visible light showed a better performance on TCPP/POM/TiO2 thin films, with an efficiency in the MB photodegradation of near 49% and 44% in aqueous solution for TCPP/CuPOM/TiO2 and TCPP/ZnPOM/TiO2, respectively. The reusability test indicated that the porphyrin films are moderately stable after the performed cycles.

Self‐Standing Membranes Consisting of Inherently Chiral Electroactive Oligomers: Electrosynthesis, Characterization and Preliminary Tests in Potentiometric Setups

AbstractSelf‐standing chiral electroactive synthetic membranes are presented, prepared by oxidative electro‐oligomerization of a thiophene‐based “inherently chiral” electroactive monomer on indium tin oxide (ITO) or fluorine‐doped tin oxide (FTO) electrodes, followed by detachment of the electrodeposited thin films in aqueous solution. The membranes, possibly mesoporous, consist of a mixture of open and cyclic “inherently chiral” oligomers, that is, in which both chirality and electroactivity originate from the same source, and this is the main conjugated backbone featuring a tailored torsion. Such a combination can afford outstanding chirality manifestations. The electrosynthesis conditions significantly modulate the oligomer distribution. Racemate films are compared to enantiopure ones. Circular dichroism confirms that (R)‐ or (S)‐ enantiopure films are obtained, starting from the corresponding (R)‐ or (S)‐ enantiopure monomers. Reliable transmembrane potential readings are obtained in preliminary tests in ion‐selective electrode (ISE)‐like setups, consistent with those predicted considering the membrane features, offering a first step towards extension of the protocol to chiral experiments.

Tuning the c-Axis Orientation of Calcium Phosphate Hybrid Thin Films Using Polymer Templates

The orientation of the c-axis in octacalcium phosphate (OCP) nanocrystals that were incorporated into hybrid thin films was successfully tuned using poly(vinyl alcohol) (PVA) thin-film templates of varying thicknesses. This approach was inspired by biomineralization. Thicker PVA templates enhanced the c-axis orientation of the OCP crystals perpendicular to the substrate. Using this approach with a 900 nm thick PVA template, OCP/PVA hybrid thin films (1.8 μm thick) with a c-axis orientation perpendicular to the substrate were formed. Hydroxyapatite (HAP) hybrid thin films that also exhibited a perpendicular c-axis orientation were obtained through the topotactic transformation of the OCP/PVA hybrid thin films in aqueous solution. The thickness change of the polymer templates had a significant effect on the structure of the OCP nanocrystals in the hybrid thin films. The structural control of the OCP hybrid thin films that were formed through the biomineralization-inspired approach allowed the formation of HAP hybrid thin films with controlled structures.

Shedding Light on the Dark Corners of Metal-Organic Framework Thin Films: Growth and Structural Stability of ZIF-8 Layers Probed by Optical Waveguide Spectroscopy.

Metal-organic framework (MOF) thin films are promising materials for multiple technological applications, such as chemical sensing. However, one potential limitation for their widespread use in different settings is their stability in aqueous environments. In the case of ZIF-8 (zeolitic imidazolate framework) thin films, their stability in aqueous media is currently a matter of debate. Here, we show that optical waveguide spectroscopy (OWS), in combination with surface plasmon resonance (SPR) spectroscopy, offers a convenient way for answering intriguing questions related to the stability of MOF thin films in aqueous solutions and, eventually provide a tool for assessing changes in MOF layers under different environmental conditions. Our experiments relied on the use of ZIF-8 thin films grown on surface-modified gold substrates, as optical waveguides. We have found a linear thickness increase after each growing cycle and observed that the growing characteristics are strongly influenced by the nature of the primer layer. One of our findings is that substrate surface modification with a 3-mercapto-1-propanesulfonate (MPSA) primer layer is critical to achieve ZIF-8 layers that can effectively act as optical waveguides. We observed that ZIF-8 films are structurally stable upon exposure to pure water and 50 mM NaCl solutions but they exhibit a slight swelling and an increase in porosity probably due to the permeation of the solvent in the intergrain mesoporous cavities. However, OWS revealed that exposure of ZIF-8 thin films to phosphate-buffered saline solutions (pH 8) promotes significant film degradation. This poses an important question as to the prospective use of ZIF-8 materials in biologically relevant applications. In addition, it was demonstrated that postsynthetic polyelectrolyte modification of ZIF-8 films has no detrimental effects on the structural stability of the films.

Photocatalytic degradation of methylene blue by the Anderson-type polyoxomolybdates/TiO2 thin films

In the herein work, two Anderson-type polyoxomolybdates (containing Cu and Zn, respectively) were synthesized and deposited on TiO2 thin films. The properties of the films were studied through measurements of inductively coupled plasma optical emission spectrometry (ICP), Fourier transform infrared spectroscopy (FT-IR) and absorption diffuse reflectance.The photodegradation of methylene blue (MB) was studied under UV-irradiated on TiO2 and polyoxomolybdates/TiO2 thin films in aqueous solution. Langmuir–Hinshelwood model was used to obtain kinetic information of the photocatalytic process. Results showed that the polyoxomolybdates/TiO2 photocatalytic activity is improved with respect to the TiO2 pure. The highlighted result was reached when copper polyoxomolybdates/TiO2 film was employed and the efficiency in the MB photodegradation improved from 18.8% to 40%. Furthermore, DFT and TD-DFT quantum mechanics calculations were used to characterize the geometry and electronic structure of the compounds and to give a rational explanation to the measured photocatalytic activity.

Aqueous-Solution-Processed Cu2ZnSn(S,Se)4 Thin-Film Solar Cells via an Improved Successive Ion-Layer-Adsorption-Reaction Sequence.

A facile improved successive ionic-layer adsorption and reaction (SILAR) sequence is described for the fabrication of Cu2ZnSn(S,Se)4 (CZTSSe) thin-film solar cells (TFSCs) via the selenization of a precursor film. The precursor films were fabricated using a modified SILAR sequence to overcome compositional inhomogeneity due to different adsorptivities of the cations (Cu+, Sn4+, and Zn2+) in a single cationic bath. Rapid thermal annealing of the precursor films under S and Se vapor atmospheres led to the formation of carbon-free Cu2ZnSnS4 (CZTS) and CZTSSe absorber layers, respectively, with single large-grained layers. The best devices based on CZTS and CZTSSe absorber layers showed total area (∼0.30 cm2) power conversion efficiencies (PCEs) of 1.96 and 3.74%, respectively, which are notably the first-demonstrated efficiencies using a modified SILAR sequence. Detailed diode analyses of these solar cells revealed that a high shunt conductance (Gsh), reverse saturation current density (Jo), and ideality factor (nd) significantly affected the PCE, open-circuit voltage (Voc), and fill factor (FF), whereas the short-circuit current density (Jsc) was dominated by the series resistance (Rs) and Gsh. However, the diode analyses combined with the compositional and interface microstructural analyses shed light on further improvements to the device efficiency. The facile layer-by-layer growth of the kesterite CZTS-based thin films in aqueous solution provides a great promise as an environmentally benign pathway to fabricate a variety of multielement-component compounds with high compositional homogeneities.

Influence of Gas Adsorption on the Luminous Properties of Layered Double Hydroxide/Anionic Fluorescein Dye Hybrid Thin Solid Films

Abstract Layered double hydroxide (LDH)/anionic fluorescein dye (AFD)/1-butanesulfonate (C4S) hybrid thin solid films prepared by immersing LDH thin films in aqueous solutions of AFD and C4S were investigated as sensing materials for relative humidity (RH) and/or various organic vapors. The basal spacing, i.e., the d003 value, of the LDH/AFD/C4S hybrid films under wet conditions became larger than that under dry conditions when water was adsorbed into the interlayer space. The intensity of photoluminescence (PL) from the AFD incorporated into the hybrid also increased upon water adsorption. This PL intensity exhibited a maximum value at 10% RH and was constant when the RH exceeded 20%. This behavior is explained by an increase in the population of dianionic AFD caused by water adsorption. The PL intensity of the LDH/AFD/C4S hybrid thin solid films also increased in the presence of alcohol vapor and became larger than under wet conditions. Moreover, the PL intensity also depended on the species of alcohol. Specifically, the PL intensity decreased in the presence of nonpolar organic solvent vapors. Therefore, the present hybrid materials can be used as a sensor for relative humidity and polar organic solvent vapors.

Doping effect on SILAR synthesized crystalline nanostructured Cu-doped ZnO thin films grown on indium tin oxide (ITO) coated glass substrates and its characterization

In the present study, a novel chemical route is used to synthesize the undoped and Cu-doped ZnO thin films in aqueous solution by successive ionic layer adsorption and reaction (SILAR) method. The synthesized thin films are characterized by x-ray diffractometer (XRD), field emission scanning electron microscopy (FE-SEM), energy dispersive x-ray analysis (EDAX), contact angle goniometer and UV–Vis spectroscopic techniques. XRD study shows that the prepared films are polycrystalline in nature with hexagonal crystal structure. The change in morphology for different doping is observed in the studies of FE-SEM. EDAX spectrum shows that the thin films consist of zinc, copper and oxygen elements. Contact angle goniometer is used to measure the contact angle between a liquid and a solid interface and after detection, the nature of the films is initiated from hydrophobic to hydrophilic. The optical band gap energy for direct allowed transition ranging between 1.60–2.91 eV is observed.

Electrodeposition of Sm-Fe Thin Film in Aqueous Solution under a High Magnetic Field

Electrodeposition of Sm-Fe Thin Film in Aqueous Solution under a High Magnetic Field

Formation of hydrated layers in PMMA thin films in aqueous solution

Neutron reflectometry (NR) measurements have been made on thin (70–150Å) poly(methylmethacrylate) (PMMA) films on Si/SiOx substrates in aqueous conditions, and compared with parameters measured using ellipsometry and X-Ray reflectometry (XRR) on dry films. All techniques show that the thin films prepared using spin-coating techniques were uniform and had low roughness at both the silicon and subphase interfaces, and similar surface energetics to thicker PMMA films. In aqueous solution, NR measurements at 25°C showed that PMMA forms a partially hydrated layer at the SiOx interface 10Å under the film, while the bulk film remains intact and contains around 4% water. Both the PMMA film layer and the sublayer showed minimal swelling over a period of 24h. At 50°C, PMMA films in aqueous solution roughen and swell, without loss of PMMA material at the surface. After cooling back to 25°C, swelling and roughening increases further, with loss of material from the PMMA layer.

Photoelectrochemical stability improvement of cuprous oxide (Cu2O) thin films in aqueous solution

The photoelectrochemical (PEC) stability of cuprous oxide (Cu2O) is improved by using the p-type Cu2O films containing metallic copper inclusions, which are electrodeposited by controlling the concentration of sodium dodecyl sulfate in the plating solutions. The deposited Cu2O films change from n-type to p-type semiconductor with the increase of sodium dodecyl sulfate concentration to 1.70 mM. The PEC stabilities of p-type Cu2O films reach 99.23% without bias and 86.34% with bias, which are significantly higher than the n-type Cu2O films or the pure p-type Cu2O without copper inclusions. The crystal structure, morphology, and composition of the Cu2O films are characterized, and the effect of Cu inclusions on the PEC stability is interpreted through the energy band diagrams. Copyright © 2015 John Wiley & Sons, Ltd.

Synthesis and Characterization of Polysulfone Hydrogels

Polysulfone (PSF) membranes are frequently used in ultrafiltration, due totheirchemical and structural stability and mechanical robustness. Despite these advantages, successful utilization of this membrane technology has been greatly limited by the susceptibility of these membranes to fouling, due totheirhydrophobic nature. Here we report on the synthesis and characterisation of hydrophilic PSF membrane materials prepared by incorporation of polyvinyl alcohol, through chemical crosslinking to produce mechanically and chemically stable PSF hydrogels. The hydrogel composition was controlled at three different ratios to evaluate the effect of the PSF contributioni.e.25:75, 50:50 and 75:25. PSF hydrogels were characterized using high resolution scanningelectronmicroscopy (HR-SEM), cyclicvoltammetry (CV), and drop shape analysis techniques. The polysulfone hydrogels formed showed a decrease in contact angle by 50% for all hydrogels regardless of their polysulfone contribution, confirming an improvement in hydrophilic nature. The electron diffusion and ionic transport properties of thehydrogels as immobilised thin films in aqueous solutions,wereevaluated using cyclic voltammetry.

Photoelectrochemical performance of gallium-doped AgInS 2 photoelectrodes prepared by electrodeposition process

Gallium-doped silver–indium–sulfide (Ga-doped AgInS 2) samples were deposited onto fluorine-doped-tin-oxide (FTO) glass substrates using a one-step electrodeposition method. The effect of the [Ga]/[In] molar ratio in the solution bath on the structure, morphology, and photoelectrochemical (PEC) properties of samples is reported. X-ray diffraction (XRD) patterns of samples reveal that the peaks of samples shifted to higher angles with increasing [Ga]/[In] ratio in the solution bath. The thickness, direct band gap, and indirect band gap of the samples were in the ranges of 643–580 nm, 1.84 eV–1.93 eV, and 1.42–1.59 eV, respectively. The flat-band potentials of the films were in the range from –0.76 to –0.99 V vs. a normal hydrogen electrode (NHE), as obtained using Mott–Schottky plots and open-circuit potential (OCP) measurements of samples. The maximum photoenhancement current density (10.37±0.13 mA cm −2) was obtained for Ga-doped AgInS 2 films with a precursor ratio of [Ga]/[In]=0.03 at an applied bias of +1.0 V vs. Ag/AgCl electrode in K 2SO 3 (0.25 M) and Na 2S (0.35 M) aqueous solution. Results show that high-quality Ga-doped AgInS 2 thin films can be deposited on FTO glass using one-step electrodeposition for PEC applications. Stability test of the AgInS 2 thin films in aqueous solution is also reported in this study.

Room-Temperature Electrochemical Reduction of Epitaxial Magnetite Films to Epitaxial Iron Films

The electrochemical reduction of oxides to metals has been studied for decades. Earlier work produced polycrystalline bulk metals. Here, we report that pre-electrodeposited epitaxial face-centered cubic magnetite thin films can be electrochemically reduced to epitaxial body-centered cubic iron thin films in aqueous solution on single-crystalline gold substrates at room temperature. This technique opens new possibilities to produce special epitaxial metal/metal oxide heterojunctions and a wide range of epitaxial metallic alloy films from the corresponding mixed metal oxides.

Electrochromic response and electrochemiluminescence of CdS nanocrystals thin film in aqueous solution

The enhanced visible absorbance related to electrochromic response (ECR) of CdS nanocrystals (NCs) thin film in aqueous solution was firstly investigated to elucidate the detailed electrochemiluminescence (ECL) mechanism of semiconductor NCs/H 2O 2 system. The recovery efficiency of ECR was found as the key factor to affect the intensity of ECL. This preliminary study between ECR and ECL of semiconductor NCs in aqueous solution can provide the profound guidance to fabricate enhanced “signal-off” kind ECL sensors to widen its application in analytical field.

Growth and characterization of thin ZnO films deposited on glass substrates by electrodeposition technique

Electrodeposition technique was used in order to produce nanometric zinc oxide films on glass insulating substrates. The effect of electrolyte concentration and applied current density on the formation and growth of electrodeposited Zn thin films in aqueous solutions of ZnSO 4 were studied. After a thermal oxidation, a characterization of the structural morphology of the films deposited was carried out by optical microscopy (OM), atomic force microscopy (AFM), scanning electron microscopy (SEM) and by grazing incidence X-rays diffraction (GIXD). These characterization techniques show that the grains size of the films after oxidation at temperature 450 °C is between 5 and 15 nm, as well as the structure is polycrystalline nature with several orientations. UV/vis spectrophotometry confirms that it is possible to obtain transparent good ZnO films with an average transmittance of approximately 80% within the visible wavelength region, as well as the optical gap of obtained ZnO films is 3.17 eV.