Adsorption and orientation kinetics of self‐assembled films of octadecyltrimethoxysilane on aluminium oxide surfaces

X‐ray photoelectron spectroscopy (XPS) and near‐edge x‐ray absorption fine structure (NEXAFS) spectroscopy have been used to study the time‐dependent adsorption and molecular orientation behaviour of octadecyltrimethoxysilane (ODTMS) on native aluminium oxide surfaces. By measuring the adsorption isotherm using XPS, we show that ODTMS molecules exhibit oscillatory adsorption. The oscillatory adsorption behaviour for ODTMS is analogous to that observed for its simpler short‐chain ‘cousin’—propyltrimethoxysilane (PTMS)—and suggests that the length of the functional alkyl chain on an organosilane does not have a significant influence upon the oscillatory adsorption mechanism. The oscillation in the ODTMS adsorption isotherm shows a maximum and a minimum in coverage at an adsorption time of ～30 and ～65 s, respectively, for a 0.75% ODTMS solution in a 90% ethanol–10% water mixture at pH 4. The time‐dependent orientation behaviour of the ODTMS molecules during adsorption was examined using angular‐dependent carbon K‐edge NEXAFS spectroscopy. We show that the alignment of the ODTMS film changes systematically with deposition time and appears to be correlated with coverage measurements obtained using XPS. In particular, by combining the XPS and NEXAFS results we demonstrate that the minimum ODTMS coverage corresponds to a film whose alignment appears to be predominantly randomized. Copyright © 2005 John Wiley & Sons, Ltd.     

Electrophilic Alkylations of Vinylsilanes: A Comparison of α‐ and β‐Silyl Effects

Kinetics of the reactions of benzhydrylium ions (Aryl₂CH⁺) with the vinylsilanes H₂C?C(CH₃)(SiR₃), H₂C?C(Ph)(SiR₃), and (E)‐PhCH?CHSiMe₃ have been measured photometrically in dichloromethane solution at 20 °C. All reactions follow second‐order kinetics, and the second‐order rate constants correlate linearly with the electrophilicity parameters E of the benzhydrylium ions, thus allowing us to include vinylsilanes in the benzhydrylium‐based nucleophilicity scale. The vinylsilane H₂C?C(CH₃)(SiMe₃), which is attacked by electrophiles at the CH₂ group, reacts one order of magnitude faster than propene, indicating that α‐silyl‐stabilization of the intermediate carbenium ion is significantly weaker than α‐methyl stabilization because H₂C?C(CH₃)₂ is 10³ times more reactive than propene. trans‐β‐(Trimethylsilyl)styrene, which is attacked by electrophiles at the silylated position, is even somewhat less reactive than styrene, showing that the hyperconjugative stabilization of the developing carbocation by the β‐silyl effect is not yet effective in the transition state. As a result, replacement of vinylic hydrogen atoms by SiMe₃ groups affect the nucleophilic reactivities of the corresponding C?C bonds only slightly, and vinylsilanes are significantly less nucleophilic than structurally related allylsilanes.     

Synthesis and characterization of methylcyclopentadienyl‐(η3‐allyl)platinum and its use as a metallo‐organic chemical vapour deposition precursor of platinum

This communication reports on rapid, efficient synthesis of the metal‐organic chemical vapor deposition (MOCVD) precursor (methylcyclopentadienyl)allylplatinum. The compound is shown to be an effective precursor for the deposition of platinum thin films giving deposits of high quality and purity, probably due to the nature of ligands which seems to be good leaving <?tw=99%>groups as confirmed by mass spectrometric path‐­way. Copyright © 1999 John Wiley & Sons, Ltd.     

Interface structure and misfit relaxation in YBa2Cu3O7‐δ/PrBa2Cu3O7‐δ heterostructures on SrTiO3(001) substrates

Structural properties of YBa₂Cu₃O_7‐δ/PrBa₂Cu₃O_7‐δ heterointerfaces have been investigated by aberration‐corrected electron microscopy. Experimental evidence shows that c‐axis‐oriented YBa₂Cu₃O_7‐δ/PrBa₂Cu₃O_7‐δ heterostructures with atomically sharp interface epitaxially grow on SrTiO₃(001) substrates. In terms of the contrast analysis, no apparent interdiffusion between YBa₂Cu₃O_7‐δ and PrBa₂Cu₃O_7‐δ occurs at the interface. In addition, stand‐off misfit dislocations and planar faults appear within PrBa₂Cu₃O_7‐δ layer near the interface. Both misfit dislocations and interfacial dislocations resulting from the termination of planar faults contribute to misfit relaxation at the YBa₂Cu₃O_7‐δ/PrBa₂Cu₃O_7‐δ interface. The defect configuration of planar faults and stand‐off misfit dislocations is explored. Copyright © 2013 John Wiley & Sons, Ltd.     

Chemical and thermo‐responsive characterisation of surfaces formed by plasma polymerisation of N‐isopropyl acrylamide

Plasma polymerisation of N ‐isopropyl acrylamide (NIPAAm) presents an exciting route for the production of thermally responsive coatings on a wide variety of substrates for applications in tissue culture and microfluidics. One issue associated with the polymerisation of NIPAAm via plasma polymerisation is the limited volatility of the monomer and the subsequent requirement for monomer and reactor heating to create and maintain the vapour. It is already well established that power is critical in the balance between polymer functionality and coating stability in plasma polymers. However, little is known of how reactor and substrate temperatures may be used to influence the physico‐chemical characteristics of polymers produced from such low‐volatility monomers. In this paper, we examine the effects of a range of plasma deposition parameters on the functionality and stability of plasma‐polymerised NIPAAm surfaces. X‐ray photoelectron spectroscopy (XPS), near‐edge X‐ray absorption fine structure spectroscopy (NEXAFS), ellipsometry and contact angle goniometry have been used to examine coating chemistry, stability in aqueous environments, deposition rates and thermo‐responsive behaviour. Our results indicate that plasma polymerisation at low powers and low temperatures enhances the ability of plasma‐polymerised NIPAAm to display a wettability phase transition, but also contributes to instability of the coating to dissolution or delamination in water. Our spectroscopic measurements confirm that retention of the monomer structure is facilitated by low power and temperature deposition and reveal that conversion of the amide groups to amine and nitrile groups occurs during the polymerisation process, particularly at high discharge powers. Copyright © 2006 John Wiley & Sons, Ltd.     

XPS and AES characterization of hydrolysed γ‐mercaptopropyltrimethoxysilane deposited on Al,Zn and Al–43.4Zn–1.6Si alloy‐coated steel

In this paper Al, Zn and Al–43.4Zn–1.6Si (AlZn) alloy‐coated steel have been treated with the organofunctional silane γ‐mercaptopropyltrimethoxysilane (γ‐MPS). The influence of different metal substrates on the structure and composition of the silane films was investigated with XPS and AES. The films were obtained by dipping the substrates in the silane solution followed by a blow‐dry procedure in nitrogen gas. The results show that the surface concentration of the deposited silane is independent of the metal substrate and that the thickness of the silane film is non‐uniform. The AES measurements indicate that the silane film covers the entire substrate surface and XPS analysis of the silane‐treated substrate surfaces at different take‐off angles indicates that the γ‐MPS molecule is randomly orientated. Also, the results show that the silane is well hydrolysed under the solution conditions used. Finally, in the zinc‐containing silane‐metal systems, i.e. the silane‐treated AlZn and Zn substrates, the results indicate that the γ‐MPS molecules can bond to the substrate surfaces via the thiol group of the molecule. Copyright © 2004 John Wiley & Sons, Ltd.     

A theoretical and experimental study of the near edge X-ray absorption fine structure (NEXAFS) and X-ray photoelectron spectra (XPS) of nucleobases: Thymine and adenine

The core level electron excitation and ionization spectra of thymine and adenine have been investigated by photoabsorption and photoemission spectroscopy, and the results interpreted by means of ab initio calculations using the second-order algebraic–diagrammatic construction (ADC(2)) method for the polarization propagator and the fourth-order ADC method (ADC(4)) for the one-particle Green’s function. The photoabsorption spectra are dominated by transitions from core levels to unoccupied π states, but also show clear structures due to Rydberg transitions. The calculated spectra are in good agreement with the experimental results, and many of the observed structures are assigned.     

Synthesis and Structural Characterization of β‐Ketoiminate‐Stabilized Gallium Hydrides for Chemical Vapor Deposition Applications

Bis‐β‐ketoimine ligands of the form [(CH₂)_n{N(H)C(Me)?CHC(Me)?O}₂] (LⁿH₂, n=2, 3 and 4) were employed in the formation of a range of gallium complexes [Ga(Lⁿ)X] (X=Cl, Me, H), which were characterised by NMR spectroscopy, mass spectrometry and single‐crystal X‐ray diffraction analysis. The β‐ketoimine ligands have also been used for the stabilisation of rare gallium hydride species [Ga(Lⁿ)H] (n=2 ( 7 ); n=3 ( 8 )), which have been structurally characterised for the first time, confirming the formation of five‐coordinate, monomeric species. The stability of these hydrides has been probed through thermal analysis, revealing stability at temperatures in excess of 200 °C. The efficacy of all the gallium β‐ketoiminate complexes as molecular precursors for the deposition of gallium oxide thin films by chemical vapour deposition (CVD) has been investigated through thermogravimetric analysis and deposition studies, with the best results being found for a bimetallic gallium methyl complex [L³{GaMe₂}₂] ( 5 ) and the hydride [Ga(L³)H] ( 8 ). The resulting films ( F5 and F8 , respectively) were amorphous as‐deposited and thus were characterised primarily by XPS, EDXA and SEM techniques, which showed the formation of stoichiometric ( F5 ) and oxygen‐deficient ( F8 ) Ga₂O₃ thin films.     

C K‐edge NEXAFS study of fluorocarbon formation on carbon anodes in molten NaF–AlF3–CaF2

Operational instability from processes occurring at the anode during the production of aluminum in the commercial Hall‐Héroult process may lead to an increase in undesirable fluorocarbon emissions, higher energy use, and shorter plant life. One contribution to this instability may be the possible formation of a fluorocarbon film at the electrode interface. Here, the surface composition of graphite anodes after electrolysis in molten NaF–AlF₃–CaF₂ at 990 °C is investigated for evidence of fluorocarbon formation using C K‐edge near edge X‐ray absorption fine structure. Fluorocarbon is identified on an anode surface after prolonged anode effect (very high overpotential with increased cell resistance) and also on an anode surface after normal electrolysis without anode effect. This provides evidence that fluorocarbon formation may occur prior to anode effect lowering the surface tension of the anode and therefore resulting in dewetting to contribute to the onset of the anode effect. Confirmation that such compounds form furthers our understanding of electrochemical reactions of graphite with fluoride and of the fundamental processes that occur in an aluminum smelter cell. Copyright © 2013 John Wiley & Sons, Ltd.     

Enhanced Performance of Benzothieno[3,2‐b]thiophene (BTT)‐Based Bottom‐Contact Thin‐Film Transistors

Three new benzothieno[3,2‐b]thiophene ( BTT ; 1 ) derivatives, which were end‐functionalized with phenyl ( BTT‐P ; 2 ), benzothiophenyl ( BTT‐BT ; 3 ), and benzothieno[3,2‐b]thiophenyl groups ( BBTT ; 4 ; dimer of 1 ), were synthesized and characterized in organic thin‐film transistors (OTFTs). A new and improved synthetic method for BTT s was developed, which enabled the efficient realization of new BTT ‐based semiconductors. The crystal structure of BBTT was determined by single‐crystal X‐ray diffraction. Within this family, BBTT , which had the largest conjugation of the BTT derivatives in this study, exhibited the highest p‐channel characteristic, with a carrier mobility as high as 0.22 cm² V^?1 s^?1 and a current on/off ratio of 1×10⁷, as well as good ambient stability for bottom‐contact/bottom‐gate OTFT devices. The device characteristics were correlated with the film morphologies and microstructures of the corresponding compounds.     

Nanostructural properties of zinc oxide thin films grown on non‐planar substrates

The crystallographic structure of zinc oxide thin films grown on optical fibres using single source chemical vapour deposition (SSCVD) was analysed using near edge X‐ray absorption fine structure (NEXAFS). Zinc diethyl carbamate was used as a precursor for the growth of highly conformal films in a one‐step deposition process without substrate rotation and at substrate temperatures of 400–575 °C. It was found that the growth temperatures greatly affected the crystallographic structure of the film with no preferred crystallographic orientation and negligible crystallinity at low temperatures and very high crystallinity with pure c‐axis orientation at high temperatures. Cross‐sectional analysis of the films by scanning electron microscopy (SEM) showed the presence of a film at all points around the fibre. These films generally consisted of densely packed columns that bore a strong resemblance to c‐axis‐oriented films grown on planar substrates. Copyright © 2005 John Wiley & Sons, Ltd.     

Free‐Standing Gold‐Nanoparticle Monolayer Film Fabricated by Protein Self‐Assembly of α‐Synuclein

Free‐standing nanoparticle films are of great importance for developing future nano‐electronic devices. We introduce a protein‐based fabrication strategy of free‐standing nanoparticle monolayer films. α‐Synuclein, an amyloidogenic protein, was utilized to yield a tightly packed gold‐nanoparticle monolayer film interconnected by protein β‐sheet interactions. Owing to the stable protein–protein interaction, the film was successfully expanded to a 4‐inch diameter sheet, which has not been achieved with any other free‐standing nanoparticle monolayers. The film was flexible in solution, so it formed a conformal contact, surrounding even microspheres. Additionally, the monolayer film was readily patterned at micrometer‐scale and thus unprecedented double‐component nanoparticle films were fabricated. Therefore, the free‐floating gold‐nanoparticle monolayer sheets with these properties could make the film useful for the development of bio‐integrated nano‐devices and high‐performance sensors.     

Asymmetric Conjugate Addition of Grignard Reagents to 3‐Silyl Unsaturated Esters for the Facile Preparation of Enantioenriched β‐Silylcarbonyl Compounds and Allylic Silanes

A highly enantioselective conjugate addition of Grignard reagents to 3‐silyl unsaturated esters to deliver synthetically useful chiral β‐silylcarbonyl compounds was developed. The synthetic value of this methodology was further illustrated by the synthesis of enantioenriched β‐hydroxyl esters and the facile access granted to various α‐chiral allylic silanes. A plethora of diastereoselective transformations of β‐silylenolates were also investigated and afforded manifold organosilanes that contained contiguous stereogenic centers with excellent enantioselectivity.     

Growth and SIMS study of d.c.‐sputtered indium oxide films on silicon

Indium oxide thin films were grown onto Si and quartz substrates by d.c. reactive sputtering of elemental indium. X‐ray diffraction and transmission electron microscopy studies confirmed the single‐phase and polycrystalline nature of the films. Secondary ion mass spectrometry investigations of In₂O₃/Si structures showed the formation of an inhomogeneous interface region ～20 nm thick between In₂O₃ and Si. The overall feature of the interface remained the same under annealing in an oxygen atmosphere, but annealing in an argon atmosphere drastically altered the nature of the interface. The observations indicate that interface formation and stability depend critically on the availability of oxygen. Copyright © 2005 John Wiley & Sons, Ltd.     

Flexible triboelectric generator and pressure sensor based on poly[(R)‐3‐hydroxybutyric acid] biopolymer

The utilization of poly[(R)‐3‐hydroxybutyric acid] (PHB) biopolymer for a device that uses charging process in friction to convert mechanical energy into electric power is reported. The triboelectric generator (TEG) is fabricated by stacking a drop cast PHB film between indium tin oxide coated poly(ethylene terephthalate) (PET) and PET sheet. The charge transfer takes place through an established general rule according to which the material with higher dielectric constant becomes positively charged. Furthermore, the utilization of such TEG as pressure sensor is illustrated. TEGs have the potential of harvesting energy from touch screen, mechanical vibration, and more, with great applications in self‐powered sensors for heat and environmental monitoring and even large‐scale applications. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 859–863     

Microstructure analysis of sol‐gel‐derived nanocrystalline ITO thin films

The technique for ITO (Tin‐doped indium oxide) thin films by sol‐gel process is presented in this paper. After annealing at 500° for 15 min, ITO gel films get transformed into nanocrystallined indium tin oxide films. We studied the microstructure of ITO thin film which is closely related to optical and electrical properties. The microstructure of ITO thin film can be observed through high‐resolution transmission electronic spectroscopy (HRTEM) and the Fast Fourier Transform (FFT) technique. The film is nanocrystallite with grain sizes about 20 nm. Also, the surface chemical components were studied by XPS spectra. The transmission and the resistivity of ITO films is 97.0% and 3.5 × 10^?3 Ω?cm, respectively. Copyright © 2010 John Wiley & Sons, Ltd.     

The oscillatory adsorption of self‐assembled organosilane films on aluminium oxide surfaces

The time‐dependent oscillatory growth mechanism of organosilane film self‐assembly on aluminium oxide has been investigated using X‐ray photoelectron spectroscopy. While this unusual oscillatory process has been reported for the trifunctional silane, propyltrimethoxysilane, we report here, for the first time, that this oscillatory behaviour is also present during the self‐assembly of the difunctional silane propylmethyldimethoxysilane. The presence of multiple oscillations in this growth mechanism is also first reported for propyltrimethoxysilane and propylmethyldimethoxysilane as a function of exposure time. Multiple oscillations indicate that the 3‐component model that is used to describe and fit a single coverage oscillation must be reconsidered and contain additional components to account for the multiple oscillations seen experimentally. The absence of such oscillatory behaviour in the growth of the monofunctional organosilane propyldimethylmethoxysilane, which in fact follows a Langmuir‐type growth mechanism, indicates that this measurable oscillatory behaviour is because of the ability of multifunctional silanes to oligomerise both on the substrate and in solution.     

Naphthodithiophene‐Diketopyrrolopyrrole‐Based donor–Acceptor alternating π‐Conjugated polymers for Organic thin‐Film transistors

Novel naphtho[1,2‐b:5,6‐b′]dithiophene (NDT) and diketopyrrolopyrrole (DPP)‐containing donor‐acceptor conjugated polymers (PNDTDPPs) with different branched side chains were synthesized via Pd(0)‐catalyzed Stille coupling reaction. Octyldodecyl (OD) and dodecylhexadecyl (DH) groups were tethered to the DPP units as the side chains. The soluble fraction of PNDTDPP‐OD polymer in chloroform has much lower molecular weight than that of PNDTDPP‐DH polymer. PNDTDPP‐DH polymer bearing relatively longer DH side chains exhibited much better charge‐transport behavior than PNDTDPP‐OD polymer with shorter OD side chains. The thermally annealed PNDTDPP‐DH polymer thin films exhibited an outstanding charge carrier mobility of ～1.32 cm² V^?1 s^?1 (I_on/I_off ～ 10⁸) measured under ambient conditions, which is almost six times higher than that of thermally annealed PNDTDPP‐OD polymer thin films. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 5280–5290     

Ultrahigh Energy Density Realized by a Single‐Layer β‐Co(OH)2 All‐Solid‐State Asymmetric Supercapacitor

A conceptually new all‐solid‐state asymmetric supercapacitor based on atomically thin sheets is presented which offers the opportunity to optimize supercapacitor properties on an atomic level. As a prototype, β‐Co(OH)₂ single layers with five‐atoms layer thickness were synthesized through an oriented‐attachment strategy. The increased density‐of‐states and 100 % exposed hydrogen atoms endow the β‐Co(OH)₂ single‐layers‐based electrode with a large capacitance of 2028 F g^?1. The corresponding all‐solid‐state asymmetric supercapacitor achieves a high cell voltage of 1.8 V and an exceptional energy density of 98.9 Wh kg^?1 at an ultrahigh power density of 17 981 W kg^?1. Also, this integrated nanodevice exhibits excellent cyclability with 93.2 % capacitance retention after 10 000 cycles, holding great promise for constructing high‐energy storage nanodevices.