Self-assembly of naphthalene diimides into cylindrical microstructures

We have designed two rod-shaped compounds each incorporating a naphthalene diimide core and two terminal carboxylic acids. Both molecules aggregate in aqueous solution and spontaneously organize into cylindrical microstructures on the surface of solid substrates. Presumably, hydrogen bonds between the carboxylic acid termini and hydrophobic contacts between the naphthalene diimide cores are mainly responsible for the formation of these supramolecular arrays. Indeed, extended stacks of molecules self-assemble with close contacts between their aromatic cores in single crystals grown from polar solvents.     

Ion‐beam synthesis of 3C‐SiC surface layers on silicon

The attempt to grow 3C‐SiC thin films on silicon substrates has become an area of significant scientific interest, largely as a consequence of the impressive electrical properties that this polytype displays. In this paper, we have utilized low‐energy (20 keV) high‐fluence carbon implantation and a subsequent annealing step to form layers of 3C‐SiC directly on a silicon surface, and have investigated the effect of implantation fluence on the resultant materials properties. The quality of the Si/SiC interface is shown to be highly fluence‐dependent, with the formation of voids decreasing significantly with increased fluence. The conversion of carbon into 3C‐SiC is found to be most efficient at near‐stoichiometric concentrations, while at higher implantation fluences clusters of excess carbon are discovered to form within the silicon and to diffuse to the surface of the grown 3C‐SiC layer upon annealing. Copyright © 2011 John Wiley & Sons, Ltd.     

Effect of pH on the control of molecular orientation in monolayer of bent-core liquid crystal materials by Langmuir–Blodgett method

Control of molecular orientation at the substrate surface is significant to understand the surface science. Langmuir films of bent-core liquid crystals having alkyl chains at both ends were deposited on silicon substrate. Studies were carried out on air–water interface by changing pH of the subphase. On compression, molecules were arranged in stacks at high pH where as uniform monolayer was formed at lower pH. Limiting area increased at low pH, which resulted in the formation of monolayer after attaining a sustainable surface pressure. Langmuir films were transferred to silicon substrate, and atomic force microscopy images showed appropriate height profiles.     

Oriented Two‐Dimensional Porous Organic Cage Crystals

The formation of two‐dimensional (2D) oriented porous organic cage crystals (consisting of imine‐based tetrahedral molecules) on various substrates (such as silicon wafers and glass) by solution‐processing is reported. Insight into the crystallinity, preferred orientation, and cage crystal growth was obtained by experimental and computational techniques. For the first time, structural defects in porous molecular materials were observed directly and the defect concentration could be correlated with crystal growth rate. These oriented crystals suggest potential for future applications, such as solution‐processable molecular crystalline 2D membranes for molecular separations.     

Surface orientation characterisation of rough mc‐silicon surfaces by confocal microscopy and EBSD

For many semiconductor and photovoltaic applications the quality of substrate surfaces is an important requirement for the development of new devices. Therefore, methods are needed to analyse the surface structure in detail. In the following a new method is described that allows a fast analysis of as‐cut or artificially modified and textured surfaces. It uses laser confocal microscopy images. Therefrom the orientation of small surface elements are detected and depicted in an orientation distribution function of surface normals. The method is applied to as‐sawn mc‐silicon surfaces. It will be shown that it is also possible to determine the grain orientation for grains near 〈111〉 crystal direction by this method. The combination of electron backscatter diffraction and orientation distribution function analysis enables the detailed investigation of surface elements of an anisotropic etched silicon wafer. Inhomogeneity of surface textures can easily and rapidly be visualised by this method. Copyright © 2012 John Wiley & Sons, Ltd.     

The influence of Au-nanoparticles presence in PDMS on microstructures creation by ion beam lithography

3D microstructures in pure poly(dimethylsiloxane) (PDMS) and PDMS with embedded Au nanoparticles were prepared by ion beam lithography without any further etching. Two mega-electron volts helium and 10 MeV oxygen ions were used for ion microstructuring. Parallel lines of 1 mm in length and 10 μm in thickness were fabricated for investigation of the effect of the nanoparticles presence in the polymer on the surface morphology of the created microstructures. The created microstructures were checked by optical microscope. Infrared (IR) spectrometry was used to study the effect of the ions type and fluence on the chemical changes of the material. Atomic force microscopy was used for the fine detail study as well as for checking the microstructure quality. Analysis revealed an increased radiation resistance of the nanocomposite compared to the pure PDMS. Shrinkage is proportional to the fluence, but the maximum value for both materials is limited by saturation. 3D microstructure in modified PDMS obtained at the same irradiation condition as pure PDMS is characterized by its smaller height. Obtaining the microstructure in nanocomposite of the same height as in pure PDMS by increasing the fluence can be impossible due to saturation of shrinkage and/or radiation-induced heating of the material.     

Laser‐induced periodic surface structure on a polymer surface: The effect of a prerubbing treatment on the surface structure

The influence of the mechanical rubbing of a polyimide (PI) film on the laser‐induced periodic structure (LIPS) was demonstrated. The periodicity and amplitude of LIPS were greater when the rubbing direction was parallel to the laser polarization direction. The amplitude became small and the periodicity of LIPS did not show an obvious change when the rubbing direction was perpendicular to the laser polarization direction. The effect of the rubbing pretreatment on LIPS was explained on the basis of the wave‐guide effect of rubbing‐induced microgrooves on LIPS formation. The orientation of PI chains induced by mechanical rubbing was relaxed after laser irradiation, and a new orientation of PI chains was formed during the LIPS formation. When the rubbing direction was perpendicular to the laser polarization direction, the orientation of PI chains remained in the rubbing direction. The laser‐irradiated, perpendicularly rubbed PI surface could be used to verify the effects of surface morphologies and intermolecular interactions on liquid‐crystal alignment. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1273–1280, 2003     

Polarization dependent fragmentation of ions produced by laser desorption from nanopost arrays

Tailored silicon nanopost arrays (NAPA) enable controlled and resonant ion production in laser desorption ionization experiments and have been termed nanophotonic ion sources (Walker et al., J. Phys. Chem. C, 2010, 114, 4835-4840). As the post dimensions are comparable to or smaller than the laser wavelength, near-field effects and localized electromagnetic fields are present in their vicinity. In this contribution, we explore the desorption and ionization mechanism by studying how surface derivatization affects ion yields and fragmentation. We demonstrate that by increasing the laser fluence on derivatized NAPA with less polar surfaces that have decreased interaction energy between the structured silicon substrate and the adsorbate, the spectrum changes from exhibiting primarily molecular ions to showing a growing variety and abundance of fragments. The polarization angle of the laser beam had been shown to dramatically affect the ion yields of adsorbates. For the first time, we report that by rotating the plane of polarization of the desorption laser, the internal energy of the adsorbate can also be modulated resulting in polarization dependent fragmentation. This polarization effect also resulted in selective fragmentation of vitamin B(12). To explore the internal energy of NAPA generated ions, the effect of the post aspect ratios on the laser desorption thresholds and on the internal energy of a preformed ion was studied. Elevated surface temperatures and enhanced near fields in the vicinity of high aspect ratio posts are thought to contribute to desorption and ionization from NAPA. Comparison of the fluence dependence of the internal energies of ions produced from nanoporous silicon and NAPA substrates indicates that surface restructuring or transient melting by the desorption laser is a prerequisite for the former but not for the latter.     

Visible-laser desorption/ionization on gold nanostructures

In this report, we describe the visible-laser desorption/ionization of biomolecules deposited on gold-coated porous silicon and gold nanorod arrays. The porous silicon made by electrochemical etching was coated with gold using argon ion sputtering. The gold nanorod arrays were fabricated by electrodepositing gold onto a porous alumina template, and the subsequent partial removal of the alumina template. A frequency-doubled/tripled Nd : YAG laser was used to irradiate the gold nanostructured substrate, and the desorbed molecular ions were mass-analyzed by a time-of-flight mass spectrometer. The desorption/ionization of biomolecules for both substrates was favored by the use of the 532-nm visible-laser, which is in the range of the localized surface plasmon resonance of the gold nanostructure. The present technique offers a potential analytical method for low-molecular-weight analytes that are rather difficult to handle in the conventional matrix-assisted laser desorption/ionization (MALDI) mass spectrometry.     

Area-selective formation of macropore array by anisotropic electrochemical etching on an n-Si(100) surface in aqueous HF solution

A photoassisted anodization process to fabricate arrays of uniform and straight macropores at selected areas of a Si wafer surface was developed. The front- and backside surfaces of n-type Si(100) wafers were coated with a thin Si(3)N(4) layer, and the frontside layer was micro-patterned using photolithography and reactive ion etching to form an array of microscopic openings at selected areas. The inverted pyramid-shape micropits were formed at these openings by anisotropic etching using aqueous KOH solution; these pits act as the initiation sites for the anodization to form macropores. The electrochemical etching was carried out in aqueous HF solution under illumination from the backside of the wafer, on which Au/Cr electric contact was formed following removal of the Si(3)N(4) layer. To improve the uniformity of the formation condition of the macropores at the selected area, holes were area-selectively generated by controlling the illumination condition during the anodization. For this, micropatterns were formed on the Au/Cr layer at the backside surface, which were aligned to those at the frontside surface. The parameters, such as HF concentration, current density, and wafer thickness, i.e., hole diffusion length, were optimized, and the arrays of uniform and high-aspect-ratio macropores were formed at the selected area of the domain at the silicon surface.     

Ruthenium porphyrin functionalized single-walled carbon nanotube arrays--a step toward light harvesting antenna and multibit information storage

Ruthenium porphyrin functionalized single-walled carbon nanotube arrays have been prepared using coordination of the axial position of the metal ion onto 4-aminopyridine preassembled single-walled carbon nanotubes directly anchored to a silicon(100) surface (SWCNTs-Si). The formation of these ruthenium porphyrin functionalized single-walled carbon nanotube array electrodes (RuTPP-SWCNTs-Si) has been monitored using infrared spectroscopy (IR), differential pulse voltammetry (DPV), atomic force microscopy (AFM), laser desorption time-of-flight mass spectroscopy (LDI-TOF-MS), UV-vis spectroscopy, fluorescence spectroscopy, and cyclic voltammetry. Electrochemical results show two successive one-electron reversible redox waves. The surface concentration of the ruthenium porphyrin molecules is 3.44 x 10 (-8) mol cm (-2). Optical results indicate that the immobilization of ruthenium porphyrin enhances the light absorption of SWCNTs-Si surfaces in the visible light region. Moreover mixed assembly of ferrocene/porphyrin onto carbon nanotube arrays has been achieved by altering the ratio of two redox-active species in the deposition solution. These results suggest the ruthenium porphyrin modified electrodes are excellent candidates for molecular memory devices and light harvesting antennae.     

Laser treatment of A286 superalloy: corrosion resistance of the treated surface

Laser controlled melting of metal surface provides a local treatment with improved surface properties such as corrosion resistance. In the present study, laser surface treatment of iron base superalloy (A286) is carried out. The corrosion resistance of the laser‐treated surface is examined through potentiodynamic tests using 0.5 N NaCl solution. The microstructural and morphological changes in the laser‐treated layer are investigated incorporating scanning electron microscopy (SEM), X‐ray diffraction (XRD) and energy dispersive spectroscopy. The residual stress formed at the laser‐treated surface is measured using the XRD technique. It is found that laser treatment enhances corrosion resistance of A286 superalloy surface, which is attributed to the formation of fine grains and dense layer at the treated surface. Although locally scattered few corrosion induced microcracks are observed at the treated surface, they are not extended to form large cracks or crack network at the surface. Copyright © 2012 John Wiley & Sons, Ltd.     

A light detection cell to be used in a micro analysis system for ammonia

This paper describes the design, realization and characterization of a micromachined light detection cell. This light detection cell is designed to meet the specifications needed for a micro total analysis system in which ammonia is converted to indophenol blue. The concentration of indophenol blue is measured in a light detection cell. The light detection cell was created using KOH/IPA etching of silicon. The KOH/IPA etchant was a 31 wt.% potassium hydroxide (KOH) solution with 250 ml isopropyl alcohol (IPA) per 1000 ml H(2)O added to it. The temperature of the solution was 50 degrees C. Etching with KOH/IPA results in 45 degrees sidewalls ({110} planes) which can be used for the in- and outcoupling of the light. The internal volume of the realized light detection cell is smaller than 1 mul, enabling measurements on samples in the order of only 1 mul. Measurements were performed on indophenol blue samples in the range of 0.02 to 50 muM. In this range the measurements showed good reproducibility.     

Formation of supramolecular nanobelt arrays consisting of cobalt(II) "picket-fence" porphyrin on Au surfaces

Adlayers of cobalt(II) 5,10,15,20-tetrakis(alpha,alpha,alpha,alpha-2-pivalamidophenyl)porphyrin (CoTpivPP) were prepared by immersing either Au(111) or Au(100) substrate in a benzene solution containing CoTpivPP molecules, and they were investigated in 0.1 M HClO4 and 0.1 M H2SO4 by cyclic voltammetry and in situ scanning tunneling microscopy (STM). The adlayer structure and electrochemical properties of CoTpivPP are compared to those of 5,10,15,20-tetraphenyl-21H,23H-porphine cobalt(II) (CoTPP). Characteristic nanobelt arrays consisting of CoTpivPP molecules were produced on both Au(111) and Au(100) surfaces. The stability of the nanobelt arrays was controlled by manipulating the electrode potential. On the other hand, the formation of nanobelt arrays consisting of O2-adducted CoTpivPP molecules depended upon the crystallographic orientation of Au. The state of O2 trapped in the cavity of CoTpivPP was distinctly observed in STM images as a bright spot in the nanobelt array formed on reconstructed Au(100)-(hex) surface, but not on Au(111) surface. This result suggests that the arrangement of underlying Au atoms plays an important role in the formation of nanobelt arrays with the sixth ligand coordination.     

Large-scale CdX (X=S, Se) microtube arrays on glass substrate: transformation of CdOHCl microrod arrays by a simple template-sacrificing solution method

Large-scale arrayed CdX (X=S, Se) microtubes have been successfully prepared on glass substrate by a simple solution route. In this process, cadmium hydroxyl chloride (CdOHCl) microrod arrays, which could be directly grown on glass surface in solution of CdCl₂ and methenamine, were used not only as a source of cadmium but also as a new reactive template to fabricate these highly ordered cadmium chalcogenide tube arrays, and the orientation of CdOHCl microrods on glass substrate could be easily achieved by pretreating the glass surface with appropriate concentration of NaOH aqueous solution. The transformation from arrayed CdOHCl rods to CdS and CdSe microtube arrays were conducted in thioacetamide and Na₂SeSO₃ solution, respectively. The conversion was convenient, and no CdOHCl crystallites were detected in the final products measured by X-ray powder diffraction. The hexagonal prismatic morphology and orientation of CdOHCl rods were perfectly maintained in the as-prepared cadmium chalcogenide films according to scanning electron microscopy. Transmission electron microscopy was used to further characterize these microtube structures. The effect of NaOH pretreatment on CdOHCl orientation and the formation of tubular structures were also discussed.     

Laser-irradiation-induced surface graft polymerization method

A laser-induced surface graft polymerization method is reported in which surface radicals generated upon laser irradiation initiated radical polymerization. The radical concentrations generated upon excimer laser irradiation under vacuum on poly-(ethylene terephthalate) film surfaces were measured using a radical scavenger, 1,1-diphenyl-2-picrylhydrazyl. The density of surface radicals increased with laser fluence at low fluences but decreased at high fluences. Upon laser irradiation and subsequent treatment with gaseous N,N-dimethylacrylamide, surface graft polymerization occurred. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 747–750, 1997     

General bottom-up construction of spherical particles by pulsed laser irradiation of colloidal nanoparticles: a case study on CuO

The development of a general method to fabricate spherical semiconductor and metal particles advances their promising electrical, optical, magnetic, plasmonic, thermoelectric, and optoelectric applications. Herein, by using CuO as an example, we systematically demonstrate a general bottom-up laser processing technique for the synthesis of submicrometer semiconductor and metal colloidal spheres, in which the unique selective pulsed heating assures the formation of spherical particles. Importantly, we can easily control the size and phase of resultant colloidal spheres by simply tuning the input laser fluence. The heating-melting-fusion mechanism is proposed to be responsible for the size evolution of the spherical particles. We have systematically investigated the influence of experimental parameters, including laser fluence, laser wavelength, laser irradiation time, dispersing liquid, and starting material concentration on the formation of colloidal spheres. We believe that this facile laser irradiation approach represents a major step not only for the fabrication of colloidal spheres but also in the practical application of laser processing for micro- and nanomaterial synthesis.     

Laser embedding of TiC particles into the surface of phosphor bronze‐bearing material

A carbon film containing 5% TiC particles is formed on a pre‐prepared bronze surface prior to laser treatment. The carbon film provides increased absorption of the incident laser beam and hosts TiC particles with a uniform distribution at the workpiece surface. Optical and scanning electron microscopy are used to examine the metallurgical and morphological changes in the laser treated layer. Micro‐hardness of the laser‐treated surface is measured, and the residual stress formed in the surface vicinity is measured using the X‐ray diffraction technique. It was found that a dense layer with fine grains was formed in the laser‐treated layer. The micro‐hardness of the laser‐treated surface increases almost three times compared with the base material hardness. The presence of a dense layer and the formation of Cu₃N in the surface region contribute to the hardness enhancement at the surface. Copyright © 2012 John Wiley & Sons, Ltd.     

InSb纳米线阵列的可控制备与光谱表征

采用脉冲电沉积结合阳极氧化铝模板技术制备了不同生长方向的闪锌矿型InSb纳米线阵列. 结果表明, 控制电解液中十二烷基硫酸钠(SDS)的浓度, 可使纳米线的择优生长方向从[400]向[220]方向转变. 利用X射线衍射仪、 场发射扫描电子显微镜、 高分辨透射电子显微镜对所制备纳米线的相组成和微结构进行了表征. 激光拉曼光谱结果表明, 不同生长方向的InSb纳米线阵列的拉曼光谱有明显差异. 与体材料相比, InSb纳米线阵列的红外吸收声子散射峰发生强烈红移, 其吸收带边发生了明显蓝移.     

Prediction of Thermal Damage upon Ultrafast Laser Ablation of Metals

Ultrafast lasers micromachining results depend on both the processing parameters and the material properties. The obtained thermal effects are negligible if a good combination of processing parameters is chosen. However, optimizing the processing parameters leading to the required surface quality on a given material can be quite complex and time consuming. We developed a semi-empirical model to estimate the heat accumulation on a surface as a function of the laser fluence, scanning speed and repetition rate. The simulation results were correlated with experimental ones on different materials, and compared with the transient temperature distributions calculated using an analytical solution to the heat transfer equation. The predictions of the proposed model allow evaluating the heat distribution on the surface, as well as optimizing the ultrafast laser micromachining strategy, yielding negligible thermal damage.