Quantitative analysis of mixed self-assembled monolayers using ToF-SIMS

The spacing of chemical functional groups on self-assembled monolayers (SAMs) plays an important role in controlling the density of biomolecules in biochips and biosensors. In this sense, a mixed SAM made of two different terminal groups is a useful organic surface since spacing can be easily controlled by changing a relative mole fraction in a mixture solution. In this study, an acetylene-OCH₂O(EG)₃(CH₂)₁₁S-S(CH₂)₁₁(EG)₃OCH₂O-propene (Eneyne) SAM and mixed SAMs made by a mixture of (S(CH₂)₁₁(EG)₃OCH₂O-acetylene)₂ (Diyne) and (S(CH₂)₁₁(EG)₃OCH₂O-propene)₂ (Diene) were produced on gold substrates and measured by using ToF-SIMS. The secondary ion yield ratio of [Au·S(CH₂)₁₁(EG)₃OCH₂O-acetylene]⁻ to [Au·S(CH₂)₁₁(EG)₃OCH₂O-propene]⁻ was measured for each mixed SAM and plotted as a function of the mole fraction of Diyne to Diene in a SAM solution. The ion yield ratio of a mixed SAM produced from a solution with a mole fraction of 0.5 (i.e., 1:1 mixture) was 0.3, which corresponded well to the ion yield ratio measured from an Eneyne SAM. A time-dependent experiment of Eneyne SAM formation and immersion experiment of Eneyne SAM into Diyne solution or into Diene solution were performed. The relative ion yield ratio of 0.3 was due to a different secondary ion formation and not due to the difference in the amount of adsorbates on the surface, nor to the different binding strengths onto the gold surface. Our study shows that a mixed SAM with well-controlled spacing can be produced and quantified by using the ToF-SIMS technique.     

Epitaxial growth of non-c-oriented ferroelectric SrBi2Ta2O9 thin films on Si(100) substrates

Epitaxial SrBi₂Ta₂O₉ (SBT) thin films with well-defined (116) orientation have been grown by pulsed laser deposition on Si(100) substrates covered with an yttria-stabilized ZrO₂ (YSZ) buffer layer and an epitaxial layer of electrically conductive SrRuO₃. Studies on the in-plane crystallographic relations between SrRuO₃ and YSZ revealed a rectangle-on-cube epitaxy with respect to the substrate. X-ray diffraction pole figure measurements revealed well-defined orientation relations, viz. SBT(116)SrRuO₃(110)YSZ(100)Si(100), SBT[110]SrRuO₃[001], and SrRuO₃[111]YSZ[110]Si[110].     

The Influence on NMR Parameters of Silicon Penta Coordination in Silatranes

¹H, ¹³C, ¹⁹F and ²⁹Si NMR chemical shifts and coupling constants for Si-substituted silatranes, XSi(OCH₂CH₂)₃N, and triethoxysilanes, XSi(OCH₂CH₃)₃, where X = H, CH₃, and F have been studied. Expansion of the coordination numbers of silicon and tin leads to similar changes in the NMR parameters.     

Control of surface properties of self-assembled monolayers by tuning the degree of molecular asymmetry

We have studied self-assembled monolayers (SAMs) of asymmetric dialkyldisulfide derivatives of the form CH₃-(CH₂)_11+m-S-S-(CH₂)₁₁-OH with m = −4, −3, 0, +2 and +4 on gold. Sub-nanoscale changes in the length of the CH₃-terminated alkylchain have been used to selectively protrude one particular end group in the resulting film. The alteration of the chain length in only two methylene units already results in changes of surface properties, which have been detected with local (chemical force microscopy) and macroscopic (contact angle) techniques. In particular, advancing contact angles can be adjusted between 40° and 80°. The adhesion between a hydrophobic tip and these SAMs in water is determined by the chemical nature of the protruding end group. Chemical force microscopy, X-ray photoelectron spectroscopy and infrared reflection absorption spectroscopy have shown that these SAMs are composed of mixed, well-packed CH₃- and OH-alkylthiolate branches. The surface composition ratio is close to 1:1 for all investigated SAMs.     

Preparation of superhydrophobic films on titanium as effective corrosion barriers

Stable superhydrophobic films were prepared on the electrochemical oxidized titania/titanium substrate by a simple immersion technique into a methanol solution of hydrolyzed 1H,1H,2H,2H-perfluorooctyltriethoxysilane [CF₃(CF₂)₅(CH₂)₂Si(OCH₂CH₃)₃, PTES] for 1 h at room temperature followed by a short annealing at 140 °C in air for 1 h. The surface morphologies and chemical composition of the film were characterized by means of water contact angle (CA), field emission scanning electron microscopy (FESEM), atomic force microscope (AFM) and X-ray photoelectron spectroscopy (XPS). The water contact angle on the surface of this film was measured to be as high as 160°. SEM images showed that the resulting surfaces exhibited special hierarchical structure. The special hierarchical structure along with the low surface energy leads to the high surface superhydrophobicity. The corrosion resistance ability and durance property of the superhydrophobic film in 3.5 wt.% NaCl solution was evaluated by the electrochemical impedance spectroscopy (EIS). The anticorrosion properties of the superhydrophobic film are compared to those of unmodified pure titanium and titania/titanium substrates. The results showed that the superhydrophobic film provides an effective corrosion resistant coating for the titanium metal even with immersion periods up to 90 d in the 3.5 wt.% NaCl solution, pointing to promising future applications.     

紫外激光作用下四甲基硅的MPI和硅原子的(2+1)电离

本文报道了在390～371nm内利用平行板电极装置和飞行时间质谱仪相结合的方法对四甲基硅进行MPI光谱及TOF质谱研究的实验结果,并据此讨论了该分子可能的MPI机理。     

Hydroxyl end groups influence in vibrational and transport properties in polymer/monomer solutions: the PEO/EG case

A study has been made of vibrational properties in ethylene glycol (EG; H(OCH₂CH₂)OH) and EG monomethyl ether (EGmE; CH₃(OCH₂CH₂)OH) in solution together with poly(ethylene oxide) (PEO; H(OCH₂CH₂)_n,OH) at different concentrations, performed by Fourier transform infrared absorbance (FT-IR) spectroscopy. The results ae compared with previous viscometry and photon correlation spectroscopy (PCS) studies, using EG dimethyl ether (EGdE; CH₃(OCH₂CH₂)OCH₃) as solvent as well. These homologous systems differ from each other in the number of OH end groups, in particular two for EG, one for EgmE and zero for EGdE. Combining analysis of the vibrational and transport properties of EG, EGmE and EGdE in solution with PEO over a wide range of concentration made it possible to check the quality (good theta or poor) of these three different solvents and the role played by the hydrogen bond in the various solute-solvent interaction mechanisms, resulting in the well known de Gennes scaling law.     

Chemisorption and decomposition reactions of oxygen-containing organic molecules on clean Pd surfaces studied by UV photoemission

We have used uv photoeinission (primarily at a photon energy hv = 40.8 eV) to study chemisorption and decomposition reactions of small oxygen-containing organic molecules on clean polycrystalline Pd surfaces at 120 and 300 K. These molecules include methanol (CH₃OH), dimethyl ether (CH₃OCH₃) formaldehyde (H₂CO), acetaldehyde [H(CH₃)CO], and acetone [(CH₃)₂CO]. Chemisorption bonding of these molecules to the Pd surface occurs primarily through the lone-pair orbitais associated with the oxygen atoms, as evidenced by chemical bonding shifts of these orbitais toward larger electron binding energy relative to the other adsorbate valence orbitals. At 300 K all the molecules studied decompose on the surface, resulting in chemisorbed CO. Since chemisorbed (as well as condensed) phases of some of these molecules (CH₃OH and H(CH₃)CO) are observed at low temperature, the decomposition to CO is a thermally-activated reaction. The observed orbital shifts associated with chemisorption bonding are used to make rough estimates of interaction strengths and chemisorption bond energies (within the framework of Mulliken's theory of electron donor-acceptor complexes as applied to chemisorption by Grimley). The resulting heats of chemisorption are consistent with the observed surface reactions.     

Mass spectroscopy and ablation characteristics of nylon 6.6 in the ultraviolet

We report on the mass spectroscopic and the laser ablative characteristics of nylon 6.6 [-NH-(CH₂)₆-NH-CO-(-CH₂)₄-CO-] at 193 and 248 nm, using the ArF and KrF excimer lasers. The characteristic parameters of the laser ablative process, such as etch rate at different fluences, the threshold fluence, and the absorption coefficient for both wavelengths were determined. Even at low laser energy, there was a complete breaking of the polymeric chain bonds. The following photofragments were observed at 248 nm: H, H₂, C, CH, CH₂, N, NH, O, OH, H₂O, C₂H, C₂H₂, CN, C₂H₃, HCN, N₂, CO, C₂H₄, COH, C₂H₅, N₂H, NO, C₂H₆, H₂CO, N₂H₂, C₂, CH₂NH, O₂, C₃H₃, C₃H₄, C₃H₅, C₃H₆, CNO, HCNO, and H₂CNO. At 193 nm no photofragments were observed for m/e larger than 30 amu. The photofragments with two carbon atoms have a relatively higher probability to be dissociated from the parent monomer, than heavier photofragments with four carbon atoms. The mass spectroscopic studies and the absorption spectrum of nylon 6.6 in the ultraviolet, suggest photochemical bond-breaking at 248 and 193 nm. The monomer dissociates into fragments with the predominant mass at 28 amu for both laser wavelengths. Therefore the amide group is mainly involved in the photodissociation process of nylon 6.6 in the ultraviolet. The experimental results suggest that the photochemical dissociation of the polymeric chain is the dominant mechanism of the laser ablation of nylon 6.6 at 193 and 248 nm.     

A comprehensive study of (CH3)2CHOC(S)SC(O)OCH3 using matrix isolation technique,X‐ray analysis,spectroscopic studies and theoretical calculations

Potassium isopropyl xanthate, (CH₃)₂CHOC(S)SK, reacts with methyl chloroformiate ClC(O)OCH₃ to yield (methoxycarbonyl) (2‐propoxythiocarbonyl) sulfide, (CH₃)₂CHOC(S)SC(O)OCH₃. This novel xanthogen formate was characterized by ¹H and ¹³C{¹H} NMR spectroscopy, mass spectrometry and IR and Raman spectroscopy. The structure of a single crystal of (CH₃)₂CHOC(S)SC(O)OCH₃ was determined by X‐ray diffraction analysis at 173 K. The conformational properties have been studied by liquid IR and Raman spectroscopy, matrix isolation spectroscopy together with photochemical studies and quantum chemical calculations (HF and B3LYP methods with the 6‐31+G* basis set). The analysis of the IR spectrum of liquid (CH₃)₂CHOC(S)SC(O)OCH₃ suggests the presence of two conformers in equilibrium at room temperature. However, in the photochemical matrix study, an equilibrium of three conformers was detected. These forms were further characterized by theoretical calculations. Different photolysis products, such as CH₃OC(O)SCH(CH₃)₂, OCS, CO, CO₂ and CS₂, were identified by matrix spectroscopy. The IR absorptions of CH₃OC(O)SCH(CH₃)₂, for which literature data are scarce, were analysed in the light of the results of appropriate theoretical calculations. Copyright © 2009 John Wiley & Sons, Ltd.     

卟啉铜接枝SiO2有机-无机复合材料及强的非线性折射率

通过卟啉配合物Meso-四(4-羧基苯基)卟啉铜(简称Cu(Ⅱ)-TCPP)中的羧基与γ-氨基丙基三乙氧基硅烷(NH₂(CH₂)₃Si(OC₂H₅)₃,KH550)中的氨基的相互化学作用,成功地把卟啉配合物接枝到KH550中,随着KH550中乙氧基的水解与聚合反应的进行,卟啉铜连接到固体介质中,从而大幅度提高了卟啉在无机固体介质中的掺杂浓度. 将反应产物与γ-(2,3-环氧丙氧基)丙基三甲氧基硅烷(CH₂CHCH₂O(CH₂)₃Si(OCH₃)₃,KH560) 相杂化,形成物化性能良好、连接卟啉的有机-无机复合材料. 用红外光谱表征了Cu(Ⅱ)-TCPP与KH550的化学反应产物,用紫外—可见吸收光谱研究Cu(Ⅱ)-TCPP的分子状态. 应用Z扫描技术研究不同Cu(Ⅱ)-TCPP掺杂浓度的复合材料的非线性光学性质,其三介非线性折射率n₂达-1.1161×10^-16 m²/W. 关键词： 非线性折射率 有机-无机复合材料 接枝 Meso-四(4-羧基苯基)卟啉铜     

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.     

Direct synthesis and characterization of highly ordered functional mesoporous silica thin films with high amino-groups content

A series of continuous, crack-free, highly ordered amino-functionalized mesoporous silica thin films have been directly synthesized by co-condensation of tetraethoxysilane (TEOS) and 3-aminopropyltriethoxysilane (APTES) in the presence of cationic CH₃(CH₂)₁₅N⁺(CH₃)₃Br⁻ (CTAB), nonionic C₁₆H₃₃(OCH₂CH₂)₁₀OH (Brij-56) or triblock copolymer H(OCH₂CH₂)₂₀(OCH(CH₃)CH₂)₇₀(OCH₂CH₂)₂₀)OH (P123) surfactant species under acidic conditions by sol-gel dip-coating. The molar ration of APTES/(TEOS + APTES) in the starting sol attains a value of 0.4. The effect of the sol aging on the mesostructure of thin films is systematically studied, and the optimal sol aging time is obtained for different surfactant systems. The amino-functionalized mesoporous silica thin films exhibit long-range ordering of 2D hexagonal (p6mm) and 3D cubic (Fm3m) pore arrays of size range from 2.2 to 8.3 nm following surfactants extraction as demonstrated by XRD, TEM and physical adsorption techniques. Based on BET surface area and weight loss, the surface coverage of amino-groups for thin films prepared using different surfactants is calculated to be 3.2 and above amino-groups per nm², which is very useful and promising for incorporating inorganic ions and biomolecules into these mesoporous silica materials.     

Influence of boron concentration on growth characteristic and electro-catalytic performance of boron-doped diamond electrodes prepared by direct current plasma chemical vapor deposition

A series of boron-doped diamond (BDD) electrodes were prepared by direct current plasma chemical vapor deposition (DC-PCVD) with different compositions of CH₄/H₂/B(OCH₃)₃ gas mixture. A maximum growth rate of 0.65 mg cm⁻² h⁻¹ was obtained with CH₄/H₂/B(OCH₃)₃ radio of 4/190/10 and this growth condition was also a turning point for discharge plasma stability which arose from the addition of B(OCH₃)₃ that changed electron energy distribution and influenced the plasma reaction. The surface coating structure and electro-catalytic performance of the BDD electrodes were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, Hall test, and electrochemical measurement and electro-catalytic oxidation in phenol solution. It is suggested that the boron doping level and the thermal stress in the films are the main factors affecting the electro-catalytic characteristics of the electrodes. Low boron doping level with CH₄/H₂/B(OCH₃)₃ ratio of 4/199/1 decreased the films electrical conductivity and its electro-catalytic activity. When the carrier concentration in the films reached around 10²⁰ cm⁻³ with CH₄/H₂/B(OCH₃)₃ ratio over a range of 4/195/5-4/185/15, the thermal stress in the films was the key reason that influenced the electro-catalytic activity of the electrodes for its effect on diamond lattice expansion. Therefore, the BDD electrode with modest CH₄/H₂/B(OCH₃)₃ ratio of 4/190/10 possessed the best phenol removal efficiency.     

Self-assembly of human plasma fibrinogens on binary organosilane monolayers with micro domains

The adsorption behavior and self-assembly of human plasma fibrinogen (HPF) on binary methyl- and amino-terminated self-assembled monolayers (SAMs) were investigated by atomic force microscopy (AFM). The binary SAMs were fabricated through self-assembly mechanism of organosilane molecules. The height of domains is the domain height is 0.8 ± 0.2 nm from the AFM topographic image. It corresponds to the domain height is 0.8 ± 0.2 nm from the AFM topographic image. It corresponds to the difference between the length of the alkyl chain of octadecyltrichlorosilane (OTS) and that of n-(6-aminohexyl)aminopropyltrimethoxysilane (AHAPS). The fibrinogen solution used ultrapure water as the solvent and its pH was adjusted at 3 and 10. From the AFM results at pH 3, HPF only formed network structures on the OTS domains of the binary SAM at early immersion times, and then the network structures expanded and connected between OTS domains through the AHAPS surface at long immersion times. In this case, a few HPFs are discretely adsorbed on the AHAPS surface. However, HPF is uniformly adsorbed on the binary SAM under the other conditions of pH.     

Molecular simulation studies of self-assembled monolayers of alkanethiols on Au(111)

A review is presented of this group's recent molecular simulation studies of self-assembled monolayers (SAMs) of alkanethiols on Au(111) surfaces. SAMs are very useful for the systematic alteration of the chemical and structural properties of a surface by varying chain length, tail group and composition. The scientific and technological importance of SAMs cannot be overestimated. The present work has been centred on studies of atomic scale surface properties of SAMs. First, configurational-bias Monte Carlo simulations were performed in both semigrand canonical and canonical ensembles to investigate the preferential adsorption and phase behaviour of mixed SAMs on Au(111) surfaces. Second, a novel hybrid molecular simulation technique was developed to simulate atomic force microscopy (AFM) over experimental timescales. The method combines a dynamic element model for the tip-cantilever system in AFM and a molecular dynamics relaxation approach for the sample. The hybrid simulation technique was applied to investigate atomic scale friction and adhesion properties of SAMs as a function of chain length. Third, dual-control-volume grand canonical molecular dynamics (DCV-GCMD) simulations were performed of transport diffusion of liquid water and methanol through a slit pore with both inner walls consisting of Au(111) surfaces covered by SAMs under a chemical potential gradient. Surface hydrophobicity was adjusted by varying the terminal group of CH₃ (hydrophobic) or OH (hydrophilic) of the SAMs. Finally, ab initio quantum chemical calculations were performed on both clusters and periodic systems of methylthiols on Au(111) surfaces. Based on the ab initio results, an accurate force field capable of predicting c(4×2) superlattice structures over a wide range of temepratures for alkanethiols on Au(111) was developed. The extension of current work is discussed briefly.     

Synthesis of C-N and Si-C films by pulsed laser ablation with frozen N2 and CH4 targets

The possibilities of pulsed laser single ablation (PLSA) from the frozen target materials, such as inert gases (Ar, Kr, Xe), N₂ and CH₄, using KrF excimer and YAG(SHG) lasers have been investigated. The single ablations were realized by the pulsed YAG(SHG) laser in a relatively short time, but the KrF excimer laser was unsuccessful. As an example of the application of pulsed laser co-ablation (PLCA) of the frozen target, polycrystalline hexagonal SiC films were formed without any post-thermal annealing by using frozen CH₄ on Si targets. The films, however, contain splashing Si particles. On the other hand, the PLSA method, using a mixture of frozen N₂ and CH₄ targets, enabled the formation of amorphous C-N films without splashing particles.     

13C-NMR Study of Some Substituted 9-Acridanone Derivatives

¹³C-NMR spectra of several 9-acridanones with different substituents both on the ring (R₁ = CH₃, OCH₃, NH₂, N(CH₃)₂, NO₂) and at the nitrogen atom (R₂ = H, CH₃ C₂H₅, CH₂-C₆H₅, C[tbnd]C-CH₃, (CH₂)₂N(C₂H₂)₂, CH=C=CH₂) have been recorded. The C-NMR chemical shifts are discussed as a function of the nature of the substituent, the importance of peri steric interactions and the electronic structure of the acridanone ring. There is a good linear relationship between the total electronic density and the chemical shifts.     

氯化聚乙烯辐射效应的NMR研究

用¹H NMR,¹³C NMR谱,二维谱,FT-IR等方法研究了氯化聚乙烯（CPE）在室温下限量空气中经⁶⁰Co γ射线辐照后的辐照效应. 结果表明CPE在辐照过程中以发生裂解反应为主,在裂解反应过程中伴随着HCl脱出,HCl的脱出量随着辐照剂量的增加而增加. 辐照后CPE样品的大分子结构发生相应变化,序列结构为CH₂CHClCHClCH₂CHCl,CH₂CH₂CHClCH₂CH₂,CHClCH₂CHClCH₂CH₂,CHClCH₂CHClCH₂CHCl的单元数量减少,但没有形成新的序列结构类型,T₁ 和T₂值给出了有关辐照前后分子运动变化的信息.     

Electrochemical properties and radical anions of carbocycle‐fluorinated quinoxalines and their substituted derivatives

Electrochemical reduction (ECR) and oxidation (ECO) of 5,6,7,8‐tetrafluoroquinoxaline ( 1 ) and its derivatives bearing various substituents R (7‐H ( 2 ), 7,8‐H₂ (3 ), 6‐CF₃ ( 4 ), 6‐Cl ( 5 ), 5,7‐Cl₂ ( 6 ), 5‐NH₂ ( 7 ), 6‐OCH₃ ( 8 ), 6,7‐(OCH₃)₂ ( 9 ), 6,7,8‐(OCH₃)₃ ( 10 ), 5,6,7,8‐(OCH₃)₄ ( 11 ), 6‐OCH₃,7‐N(CH₃)₂ ( 12 ), 6‐N(CH₃)₂ ( 13 ), 6,7‐(N(CH₃)₂)₂ ( 14 ), 5,6,7‐(N(CH₃)₂)₃ ( 15 ), and 7,8‐cyclo‐(=CF‐CF = CF‐CF=) ( 16 )) in the carbocycle have been studied by cyclic voltammetry in MeCN. For 1 – 4 and 7 – 15 , the first reduction peaks have been found to be 1‐electron and reversible, thus corresponding to the formation of their radical anions (RAs), which are long lived at 295 K except those of 4 – 6 and 15 , 16 . Irreversible hydrodechlorination has been observed for 5 and 6 at the first step of their ECR confirmed by EPR detection of corresponding RAs of 2 and 5,7‐H₂ derivative of 1 ( 17 ) at the next steps. Electrochemically generated RAs of 1 – 3 , 7 – 14 , and 17 have been characterized in MeCN by EPR spectroscopy together with DFT calculations at the (U)B3LYP/6‐31 + G(d) level of theory using PCM to describe the solvent. A noticeable alternation of spin density on the –NCCN– moiety of quinoxaline has been observed for all RAs possessing R‐substitution asymmetry. The comparative electron‐accepting ability of 1 – 15 has been analyzed in terms of their experimental reduction peak potentials and the (U)B3LYP/6‐31 + G(d)‐calculated gas‐phase first adiabatic electron affinities (EAs). The differences in electron transfer solvation energies for 1 – 15 have been evaluated on the basis of ECR peaks' potentials and calculated gas‐phase EAs. The ECO of 1 – 5 and 7 – 14 has been found to be irreversible.