Inhibition effect of self-assembled films formed by gold nanoparticles on iron surface

The self-assembled (SA) films formed by gold nanoparticles on iron surface had been proved to have inhibition effect for the substrate in 0.5 M H₂SO₄ solutions. The inhibition action was investigated using electrochemical impedance spectroscopy (EIS). The SA films formed by gold nanoparticles protected with sodium oleate had better corrosion protection to the iron substrate than only by sodium oleate. Scanning electron microscopy (SEM) was used to observe the imagines of the SA films. In addition, it was found that the gold nanoparticles could influence the nickel electroless plating films on the iron substrate. The structure and composition of the plating films were test by electron probe microanalyzer (EPMA). The mechanisms of the formation of the SA films and the nickel electroless plating reaction were also discussed.     

Integrity of functional self-assembled monolayers on hydrogen-terminated silicon-on-insulator wafers

Silicon-on-insulator (SOI) wafers are commonly used to design microelectronics, energy conversion, and sensing devices. Thin solid films on the surfaces of SOI wafers have been a subject of numerous studies. However, SOI wafers modified by self-assembled monolayers (SAMs) that can also be used as functional device platforms have been investigated to a much lesser extent. In the present work, tert-butoxycarbonyl (t-boc, (CH₃)₃-C-O-C(O)-)-protected 1-amino-10-undecene monolayers were covalently attached to a H-terminated SOI (1 0 0) surface. The modified wafers were characterized by X-ray photoelectron spectroscopy to confirm the stability of the SAM/Si interface and the integrity of the secondary amine in the SAM. The transmission electron microscopy investigation suggested that this t-boc-protected 1-amino-10-undecene SAM produces atomically flat interface with the 2 μm single crystalline silicon of the SOI wafer, that the SiO_x and both available Si/SiO_x interfaces are preserved, and that the organic monolayers are stable, with apparent thickness of 1.7 nm, which is consistent with the result of the density functional theory modeling of the molecular features within a SAM.     

Step-wise decomposition process of azobenzene self-assembled monolayers

The step-wise decomposition of 4-(12-(dodecyldithio)dodecyloxy)azobenzene (AzoC24) in self-assembled monolayer (SAMs) on Au(1 1 1) was observed by thermal desorption spectroscopy (TDS) and X-ray photoelectron spectroscopy (XPS) under the ultra-high vacuum (UHV) condition. This decomposition process only occurred after the formation of the SAM.The TD spectra clearly showed two steps of thermal decomposition of the azobenzene moiety. At approximately 450 K, fragments of m/e = 77 and 105 were clearly observed. These fragments were decomposed species obtained by the breakage of the C-N bonds of the azobenzene moiety. At about 490 K, other fragment of m/e = 93 assigned to the phenoxy ion was detected. In order to examine the decomposition process, we measured the S 2p and N 1s XPS of the SAM at various temperatures. The results suggest that diazonium moiety is the first to be decomposed and the remaining structure is desorbed together with breakage of C-O bond between the phenoxy moiety and alkyl chain with increasing temperature.     

Characterization of iron surface modified by 2-mercaptobenzothiazole self-assembled monolayers

A self-assembled monolayer of 2-mercaptobenzothiazole (MBT) adsorbed on the iron surface was prepared. The films were characterized by electrochemical impedance spectroscopy (EIS), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared reflection spectroscopy (FT-IR) and scanning electron microscopy (SEM). Besides, the microcalorimetry method was utilized to study the self-assembled process on iron surface and the adsorption mechanism was discussed from the power-time curve. The results indicated that MBT was able to form a film spontaneously on iron surface and the presence of it could protect iron from corrosion effectively. However, the assembling time and the concentration influence the protection efficiency. Quantum chemical calculations, according to which adsorption mechanism was discussed, could explain the experimental results to some extent.     

Self-assembling of cyano- and carboxyl-terminated monolayers using short-chain alkylsiloxane

A simple method was developed for the preparation of cyano- and carboxyl-terminated alkylsiloxane monolayers on the hydroxylated surface of the SiO₂/Si substrate through using adsorption and hydrolysis reaction of a short-chain 2-cyanoethyl triethoxysilane [(CH₃CH₂O)₃SiCH₂CH₂CN]. The contact angle and the X-ray photoelectron spectroscopy (XPS) measurements have proved that the cyano terminal group indeed formed on the substrate and was transformed into the carboxylic terminal group after hydrolysis. The ellipsometry shows the presence of an intact monolayer with thickness of around 0.7 nm before and during the hydrolysis reaction. The surface morphology was observed with atomic force microscopy (AFM) imaging. Those all indicate that uniform and ordered self-assembled monolayers (SAMs) were formed on the substrate.     

Computing surface dipoles and potentials of self-assembled monolayers from first principles

We discuss methodological aspects of first principles calculations of surface dipoles and potentials in general, and surface-adsorbed self-assembled monolayers in particular, using density functional theory with a slab/super-cell approach. We show that calculations involving asymmetric slabs may yield highly erroneous results for the surface dipole and demonstrated the efficacy of a simple dipole correction scheme. We explain the importance of the electrostatic dipole distribution, show how to compute it, and establish conditions for the equivalence of calculations for the dipole distribution and the electrostatic potential distribution.     

Protection of iron against corrosion by coverage with Au nanoparticles and n-hexylthiol mixed films

Through a one-step thermal reaction, Au nanoparticles were synthesized and self-assembled mixed films of Au nanoparticles and n-hexylthiol were prepared on iron surface. The size distribution and shape of Au nanoparticles were examined using transmission electron microscopy (TEM). Results of two electrochemical methods - electrochemical impedance spectroscopy (EIS) and polarization curves indicate that self-assembled mixed films can form on the iron surface and prevent it from corrosion effectively. Energy-dispersive X-ray spectroscopy (EDS) and scanning electron microscopy (SEM) measurements were applied to identify the formation of the mixed films on iron surface.     

A novel fullerene lipoic acid derivative: Synthesis and preparation of self-assembled monolayers on gold

Synthesis and preparation of self-assembled monolayers of a novel fullerene lipoic acid derivative on gold are reported. The presence of densely packed SAMs was confirmed by ellipsometry and cyclic voltammetry. The electrochemical response of the modified electrode in organic media exhibits the first two redox peaks characteristic of the extended π-electron system of fullerene. C₆₀ surface coverage (1.4 × 10⁻¹⁰ mol cm⁻²) has been electrochemically determined by the redox process of the adsorbed fullerene moiety and by reductive desorption of the SAM in strong alkaline solution. Electrochemical data indicate that all four sulphur atoms are involved in the self-assembly process, providing an increase of SAM stability in comparison to mono or di-thiolated appended molecules. Visualisation of discrete fullerene molecules by scanning tunnelling microscopy supplied further evidence for gold modification and molecular distribution on the surface. Mixed monolayers of hexanethiol and fullerene derivatives in a proportion of 1:2 have been also studied with the purpose of controlling the amount and distribution of fullerene units on the gold surface.     

Inhibition of iron corrosion in 0.5 M sulphuric acid by metal cations

Corrosion inhibitors are widely used in acid solutions during pickling and descaling. Mostly organic compounds containing N, O, and S groups are employed as inhibitors. In this study, the inhibition performance of metal cations such as Zn²⁺, Mn²⁺ and Ce⁴⁺ ions in the concentration range 1-10 × 10⁻³ M has been found out. The corrosion behaviour of iron in 0.5 M H₂SO₄ in the presence of metal cations is studied using polarization and impedance methods. It is found that the addition of these metal cations inhibits the corrosion markedly. The inhibition effect is in the following order Ce⁴⁺ ? Mn²⁺ > Zn²⁺.     

Nanopatterned surface with adjustable area coverage and feature size fabricated by photocatalysis

We report an effective approach to fabricate nanopatterns of alkylsilane self-assembly monolayers (SAMs) with desirable coverage and feature size by gradient photocatalysis in TiO₂ aqueous suspension. Growth and photocatalytic degradation of octadecyltrichlorosilane (OTS) were combined to fabricate adjustable monolayered nanopatterns on mica sheet in this work. Systematic atomic force microscopy (AFM) analysis showed that OTS-SAMs that have similar area coverage with different feature sizes and similar feature size with different area coverages can be fabricated by this approach. Contact angle measurement was applied to confirm the gradually varied nanopatterns contributed to the gradient of UV light illumination. Since this approach is feasible for various organic SAMs and substrates, a versatile method was presented to prepare tunable nanopatterns with desirable area coverage and feature size in many applications, such as molecular and biomolecular recognition, sensor and electrode modification.     

An electrochemical study for corrosion inhibition of iron by some organic phosphonium chloride derivatives in acid media

The inhibiting action of (chloromethyl) triphenyl phosphonium chloride (CTP), tetraphenyl phosphonum chloride (TP), triphenyl phosphine oxide (TPO), triphenyl (phenylmethyl) phosphonium chloride (TPM) and triphenyl phosphine (TPP) on the corrosion of iron in 1 M HCl solution was studied using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). Experimental results revealed that CTP, TP, TPO, and TPM act as inhibitors for iron in acid environments, while TPP is an accelerator. These compounds are mixed-type inhibitors and the inhibition efficiency increased with increasing concentrations. Equivalent circuits of the investigated systems are suggested.     

Au(111)上烷烃硫醇SAMs表面应力的理论研究

应用已建立的关于金属表面吸附层中表面应力的统计热力学理论 ,计算了Au(111)上烷烃硫醇SAMs的表面应力及其与烷烃硫醇链长、吸附覆盖度的定量关系 .计算结果与实验相符 ,较好地解释了Berger等人的实验结果 ,特别是解决了在表面应力符号性质上理论与实验的矛盾 .在表面吸附层应力的多种物理起源中 ,通过底物的分子间作用力有着决定性的贡献 ,揭示了分子的吸附能间接地起着重要作用 .这与阴离子化学吸附体系Cl-/Au(111)的有关研究结果相同 .     

Substrate effects on photophysical properties of fluorescent self‐assembled monolayers (SAMs)

Substrate materials play an important role to modulate the photophysical properties of fluorescent self‐assembled monolayers (SAMs) constructed on them. The substrate–fluorophore interactions in fluorescent SAMs can affect their fluorescence intensity. Hence, it is important to take into account such alteration of fluorescence properties and study the underlying mechanisms. In this brief overview, substrate effects on fluorescence properties of chemisorbed or physisorbed fluorescent SAMs on two‐dimensional (chips) and three‐dimensional (nanoparticles) surfaces are highlighted. Examples of fluorescence quenching and enhancement on various substrate materials by different factors are discussed and analyzed. Additionally, some strategies to limit metallic substrate–fluorophore interactions are discussed briefly. Copyright © 2016 John Wiley & Sons, Ltd.     

Construction of self-assembled monolayer terminated with N-heterocyclic carbene-rhodium(I) complex moiety

Functionalization of self-assembled monolayer (SAM) of alkanethiolate with metal containing unit is one of the versatile methods to obtain functional surfaces such as heterogeneous catalysts. However, organic molecules that strongly bind to transition metals at SAM terminal are limited. Recently N-heterocyclic carbenes (NHCs) such as cyclic diaminocarbenes have emerged as strongly σ-donating ligands forming a robust bond with broad spectrum of transition metals. In the present study, for the purpose of establishment of a new robust basement for heterogeneous metal catalysts, a SAM of the alkanethiolate terminated with NHC-rhodium(I) complex moiety was prepared by utilizing a newly designed disulfide molecule bearing NHC-metal complex terminals. X-ray photoelectron spectroscopy (XPS) analysis and angle resolved XPS measurement revealed successful formation of the Rh-complex-terminated SAM on a gold substrate. Infrared reflection absorption spectroscopy (IRRAS) analysis suggested that the linker methylene chains connecting the rhodium complex moiety and the gold surface are in a loosely packed structure. This unique chemical species, NHC, would be a promising candidate as a basement for the construction of functional surface.     

Piperidin-1-yl-phosphonic acid and (4-phosphono-piperazin-1-yl) phosphonic acid: A new class of iron corrosion inhibitors in sodium chloride 3% media

The inhibiting effect of the piperidin-1-yl-phosphonic acid (PPA) and (4-phosphono-piperazin-1-yl) phosphonic acid (PPPA) on the behavior of iron in 3% NaCl media has been examined by electrochemical and gravimetric measurements. Potentiodynamic polarization studies clearly reveal the fact that the addition of increasing concentrations of phosphonic acids moves the corrosion potential towards negative values and reduces the corrosion rate. In uninhibited and inhibited solutions, the increasing of temperature reduces the inhibition efficiency. Changes in impedance parameters (R_t and C_dl) are indicative of adsorption of PPA and PPPA on the metal surface leading to the formation of protective films. Gravimetric measurements reveal that the presence of PPA and PPPA increases the inhibition efficiency by decreasing the corrosion rate. The results obtained by corrosion weight loss tests reveal that adsorption of compounds tested on the ARMCO iron surface obeys to Langmuir adsorption isotherm.     

Electrochemical and SERS spectroscopic investigations of 4-methyl-4H-1,2,4-triazole-3-thiol monolayers self-assembled on copper surface

Electrochemically anticorrosive behaviors of 4-methyl-4H-1,2,4-triazole-3-thiol (4-MTTL) monolayers self-assembled on copper surface have been investigated by electrochemical impedance spectroscopy (EIS), electrochemical polarization measurement and surface-enhanced Raman scattering (SERS) spectroscopy. The EIS mechanism of the copper surface adsorbed with 4-MTTL monolayers was fitted with the mode of R(QR)(QR)(CR). The electrochemical polarization experimental results indicated the high inhibitive efficiency of about 81.1%. Potential dependent SERS result suggests that 4-MTTL molecule was anchored at the copper surface via S⁶ and N² atoms with a tilted orientation, which resulting in a strong interaction between the 4-MTTL molecule and copper surface. The molecule tended to experience a transition state of the adsorption at the copper surface via S⁶ atom only as the potential applied at −0.5 V vs. SCE.     

Failure of thin films: Optical shearography versus electrochemical impedance spectroscopy

In the present work, the temperature versus thermal deformation (strain) with respect to time, of different coating films, was studied by a non-destructive technique (NDT) known as shearography. An organic coating, i.e., ACE Premium Enamel, on a metallic alloy, i.e., a carbon steel, was investigated at a temperature range simulating the severe weather temperatures in Kuwait, especially between the daylight and the nighttime temperatures, 20-60 °C. The investigation focused on determining the in-plane displacement of the coating, which amounts to the thermal deformation (strain) with respect to the applied temperature range. Furthermore, the investigation focused on determining the thermal expansion coefficients of coatings, the slope of the plot of the thermal deformation (strain) versus the applied temperature range. In other words, one could determine, from the decreasing value of the thermal expansion coefficients of coatings, a critical (steady state) value of the thermal expansion coefficients of coatings, in which the integrity of the coatings can be assessed with respect to time. In fact, determination of the critical (steady state) value of the thermal expansion coefficients of coatings could be accomplished independent of parameters, i.e., ultraviolet (UV) exposure, humidity, and exposure to chemical species, which normally are considered in conventional methods of assessing the integrity of coatings. Furthermore, results of shearography indicate that the technique is a very useful NDT method not only to determine the critical value of the thermal expansion coefficients of different coatings but also to be used as a 2D-microscope for monitoring the deformation of the coatings in real time at a submicroscopic scale. Also, the obtained data of the shearography technique were compared with data obtained by electrochemical impedance spectroscopy (EIS) in an aqueous solution of 3% NaCl.     

Improvement of corrosion resistance of AA6061 alloy by tapioca starch in seawater

This study examines the use of tapioca starch for improvement of corrosion resistance of AA6061 alloy in seawater. Gravimetric, potentiodynamic polarization, linear polarization resistance and electrochemical impedance measurements were employed to study the corrosion behavior of AA6061 alloy in seawater. The electrochemical measurements for AA6061 alloy in seawater showed that the presence of tapioca starch significantly decreases the corrosion rates, corrosion current densities (i_corr), and double layer capacitance (C_dl), simultaneously increases the values of polarization resistance (R_p). The inhibition efficiencies increase with increasing of tapioca starch concentration. The Langmuir adsorption isotherm fits well with the experimental data. The nature of adsorption of tapioca starch on the metal surface has also been examined. The analysis of SEM and EDS confirmed the formation of precipitates of tapioca starch on the metal surface, which reduced the overall corrosion reaction.     

Inhibition of copper corrosion by bis-(1,1′-benzotriazoly)-α,ω-diamide compounds in aerated sulfuric acid solution

Three kinds of novel corrosion inhibitors, bis-(1,1′-benzotriazoly)-α,ω-succinyldiamide (BSU), bis-(1,1′-benzotriazoly)-α,ω-adipoyldiamide (BAD), and bis-(1,1′-benzotriazoly)-α,ω-azelayldiamide (BAZ) were synthesized and certified by IR and ¹H NMR. Their corrosion inhibition effects for copper in 0.5 M H₂SO₄ were evaluated by weight-loss method. It shows that among the three compounds, only BSU behaves better compared with BTA. The inhibition efficiency (IE) increased with increasing BSU concentration to 85.2% at the 5 × 10⁻⁴ M level. Polarization studies showed that BSU suppressed both anodic and cathodic corrosion reactions. The minimum energy conformation of these compounds was obtained by MM2 force field program. The two benzotriazoly moieties in BSU molecule are more parallel than in other compounds. This is benefit to increase the inhibition effects of BSU.     

Improved aging performance of vapor phase deposited hydrophobic self-assembled monolayers

A hydrophobic self-assembled monolayer (SAM) of fluoro-octyl-trichloro-silane (FOTS) was deposited on silicon using a vapor phase technique. The aging of the hydrophobic layer was examined using water contact angle measurements. It has been found that while such monolayer films suffer from a loss of hydrophobicity with time, pre-immersion nitrogen annealing can significantly improve the aging characteristics of these monolayers. The effect of nitrogen annealing on the improved aging properties of SAM coatings has been investigated by atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). The hydrolytic stability and the effect of nitrogen annealing were studied by morphological evolution during immersion. A spontaneous formation of silane mounds on the surface of the monolayers was found by AFM. These mounds have been irreversibly transformed from initially uniform hydrophobic surface layers. It is highly probable that the compliance of these mounds can reasonably allow hydrophilic sites to be located around the mounds. Interestingly, the density of these mounds formation is very less on the annealed samples. XPS reveals a higher level of coverage by the N₂-annealed film due to agglomeration. A relative abundance of CF₃ and CF₂ moieties in the annealed film may explain the enhancement of the hydrophobicity as revealed by higher level of water contact angle. This hydrophobicity was found to be significantly stable in water. This novel finding explains the improved hydrophobic stability of FOTS monolayers as primarily a morpho-chemical effect that originates from the densification of the monolayers upon annealing.