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Zinc, silicon, and steel superhydrophobic surfaces were prepared by a simple solution-immersion technique. In the case of zinc, the method consists of dipping of the substrate in a prehydrolyzed methanol solution of 1H,1H,2H,2H-(perfluorooctyl)trichlorosilane [CF(3)(CF(2))(5)(CH(2))(2)SiCl(3), PFTS] for 24 h at 50 degrees C. Micron-sized spheres (1.7-2 microm in diameter) were formed on the zinc substrate at 50 degrees C, while a featureless coating was obtained when the solution-immersion process was conducted at room temperature. When the reaction was performed at room temperature, the formation of superhydrophobic coatings took several days (up to 5 days). In contrast, immersion of silicon or steel substrates in the PFTS/methanol solution led to the formation of hydrophobic interfaces even for a prolonged immersion period at 50 degrees C. The formation of superhydrophobic surfaces on silicon and steel surfaces was only possible if a zinc foil was added in the PFTS/methanol solution containing the silicon or steel substrate. X-ray photoelectron spectroscopy analysis was used to characterize the resulting surfaces and to underline a plausible reaction mechanism.
ACS Appl Mater Interfaces 2009 Sep
PMID:Preparation of superhydrophobic coatings on zinc, silicon, and steel by a solution-immersion technique. 2035 37

Patterned sol-gel-derived lead zirconate titanate (PZT) thin films with lateral resolutions down to 100 nm on silicon are reported. Both an imprint and a transfer-molding method were employed. The formed patterns after annealing were characterized with scanning electron microscopy, atomic force microscopy, and X-ray diffraction. Despite the small dimensions and flexibility of the poly(dimethylsiloxane) (PDMS) stamps used for patterning, the quality of replication was found to be good. The influence of the surface energies of the substrate, PDMS mold, and precursor solution on the quality of pattern replication is discussed. The colloidal structure of the PZT sol-gels from which the patterns were made was studied with small-angle X-ray scattering. The sols were found to be chemically homogeneous down to a length scale of approximately 2 nm and higher, which is sufficient for pattern replication on approximately 100 nm scale.
ACS Appl Mater Interfaces 2009 Oct
PMID:Patterning lead zirconate titanate nanostructures at sub-200-nm resolution by soft confocal imprint lithography and nanotransfer molding. 2035 59

Self-assembled patterned multilayers may be fabricated using DNA monolayers and the orchestrated reactions of DNA-modifying enzymes. To demonstrate this approach, DNA monolayers were formed on silicon and cleaved quantitatively with a restriction enzyme. Subsequently, fluorescently labeled nucleotides were covalently incorporated to the cleaved DNA. Nucleotide addition was shown to be highly selective according to the sequence at the cleavage site, and no nonspecific adsorption to the surface was observed. The dual action of the DNA-modifying enzymes was quantitative and could be utilized in the fabrication of multilayered structures. Other DNA-modifying enzymes can be exploited in this manner to enrich the repertoire of self-assembly supramolecular structure fabrication.
ACS Appl Mater Interfaces 2009 Oct
PMID:Three-dimensional surface patterning by DNA-modifying enzymes. 2035 68

The adsorption of asphaltenes onto flat silica surfaces modified with self-assembled monolayers (SAMs) of alkyltrichlorosilanes of varying thickness due to a variable number of carbon atoms (N(C)) has been studied by means of contact angle measurements, spectroscopic ellipsometry, and near-edge X-ray absorption fine structure spectroscopy. The extent of asphaltene adsorption was found to depend primarily on the ability of the SAM layer to shield the underlying silicon substrate from interacting with the asphaltenes present in solution. Specifically, asphaltene adsorption decreased with an increase in N(C) and/or an increase in SAM grafting density, sigma(SAM), (i.e., number of SAM molecules per unit area). The effect of the solvent quality on the extent of asphaltene adsorption was gauged by adsorbing asphaltenes from toluene, 1-methylnaphthalene, tetralin, decalin, and toluene-heptanes mixtures. The extent of asphaltene adsorption was found to increase proportionally with a decrease in the Hildebrand solubility parameter of the solvent.
ACS Appl Mater Interfaces 2009 Jun
PMID:Asphaltene adsorption onto self-assembled monolayers of alkyltrichlorosilanes of varying chain length. 2035 32

Silver nanoparticles (Ag NPs) were chemically deposited on silicon nanowires (SiNWs), prepared using the vapor-liquid-solid (VLS) growth mechanism, using an in situ electroless metal deposition technique. The resulting SiNWs/Ag NPs composite interfaces showed large Raman scattering enhancement for rhodamine 6G (R6G) with a detection limit of 10(-14) M and an enhancement factor of 2.3 x 10(8). This large enhancement factor was attributed to the presence of "hot" spots on the SiNWs/Ag NPs substrate.
ACS Appl Mater Interfaces 2009 Jul
PMID:Silicon nanowires coated with silver nanostructures as ultrasensitive interfaces for surface-enhanced Raman spectroscopy. 2035 41

Diamond films with grain sizes in the range of 5-1000 nm and grain boundaries containing nondiamond carbon are deposited on a silicon substrate by varying the deposition parameters. The overall morphologies of the as-deposited diamond-nondiamond composite films are examined by scanning electron microscopy and atomic force microscopy, which show a decrease in the surface roughness with a decrease in the diamond grain size. Although the Raman spectra show predominately nondiamond carbon features in the diamond films with smaller grain sizes, glancing-angle X-ray diffraction spectra show the absence of graphitic carbon features and the presence of very small amorphous carbon diffraction features. The CH4 percentage (%) in Ar and H2 plasma during deposition plays a crucial role in the formation of diamond films with different grain sizes and nondiamond carbon contents, which, in turn, determines the field-emission behavior of the corresponding diamond films. The smaller the grain size of the diamond, the lower is the turn-on field for electron emission. A lower turn-on field is obtained from the diamond films deposited with 2-5% CH4 than from the films deposited with either 1% or 7.5% CH4 in the Ar medium. A current density greater than 1 mA/cm2 (at 50 V/microm) is obtained from diamond films deposited with a higher percentage of CH4. A model is suggested for the field-emission mechanism from the diamond-nondiamond composite films with different diamond grain sizes and nondiamond contents.
ACS Appl Mater Interfaces 2009 Jul
PMID:Grain-size-dependent diamond-nondiamond composite films: characterization and field-emission properties. 2035 47

The effect of incorporating an organic linking group, 1,6-bis(trimethoxysilyl)hexane (BTMSH), into the underlying silica structure of a styrene cross-linked silica aerogel is examined. Vinyltrimethoxysilane (VTMS) is used to provide a reactive site on the silica backbone for styrene polymerization. Replacement of up to 88 mol % of the silicon from tetramethoxyorthosilicate with silicon derived from BTMSH and VTMS during the making of silica gels improves the elastic behavior in some formulations of the cross-linked aerogels, as evidenced by measurement of the recovered length after compression of samples to 25% strain. This is especially true for some higher density formulations, which recover nearly 100% of their length after compression to 25% strain twice. The compressive modulus of the more elastic monoliths ranged from 0.2 to 3 MPa. Although some of these monoliths had greatly reduced surface areas, changing the solvent used to produce the gels from methanol to ethanol increased the surface area in one instance from 6 to 220 m(2)/g with little affect on the modulus, elastic recovery, porosity, or density.
ACS Appl Mater Interfaces 2009 Mar
PMID:Tailoring elastic properties of silica aerogels cross-linked with polystyrene. 2035 84

Enhancement of the light-harvesting efficiency in poly(3-hexylthiophene)/fullerene derivative (P3HT/PCBM) bulk heterojunction solar cells has been demonstrated by the introduction of near-infrared phthalocyanine molecules as the third component at the P3HT/PCBM interface. The introduction of silicon phthalocyanine derivative (SiPc) increased the short-circuit current density and hence improved the overall power conversion efficiency by 20%, compared to the P3HT/PCBM control device. For P3HT/PCBM/SiPc devices, two distinct external quantum efficiency (EQE) peaks were observed at wavelengths for the absorption bands of SiPc as well as P3HT before and after thermal annealing, suggesting that SiPc molecules are located at the P3HT/PCBM interface because of crystallization of the P3HT and PCBM domains. Furthermore, the EQE for the device increased even at wavelengths for the absorption band of P3HT by the introduction of SiPc molecules. This indicates that P3HT excitons can be dissociated into charge carriers more efficiently in the presence of SiPc molecules at the P3HT/PCBM interface by energy transfer from P3HT to SiPc molecules. These findings suggest that there are two origins for the increase in the photocurrent by the introduction of SiPc; SiPc molecules serve not only as a light-harvesting photosensitizer but also as an energy funnel for P3HT excitons at the P3HT/PCBM interface.
ACS Appl Mater Interfaces 2009 Apr
PMID:Improvement of the light-harvesting efficiency in polymer/fullerene bulk heterojunction solar cells by interfacial dye modification. 2035 5

In this work, we introduce a maskless, resist-free rapid prototyping method to fabricate three-dimensional structures using electron beam induced deposition (EBID) of amorphous carbon (aC) from a residual hydrocarbon precursor in combination with metal-assisted chemical etching (MaCE) of silicon. We demonstrate that EBID-made patterned aC coating, with thickness of even a few nanometers, acts as a negative "mask" for the etching process and is sufficient for localized termination of the MaCE of silicon. Optimal aC deposition settings and gold film thickness for fabrication of high-aspect-ratio nanoscale 3D silicon structures are determined. The speed necessary for optimal aC feature deposition is found to be comparable to the writing speed of standard Electron Beam Lithography and the MaCE etching rate is found to be comparable to standard deep reactive ion etching (DRIE) rate.
ACS Appl Mater Interfaces 2010 Apr
PMID:Maskless and resist-free rapid prototyping of three-dimensional structures through electron beam induced deposition (EBID) of carbon in combination with metal-assisted chemical etching (MaCE) of silicon. 2035 53

Structured silicon surfaces, possessing hierarchical porous characteristics consisting of micrometer-sized cavities superimposed upon a network of nanometer-sized pillars or wires, have been fabricated by a plasma-etching process. These surfaces have superoleophobic properties, after being coated with fluorinated organic trichlorosilanes, on intrinsically oleophilic surfaces. By comparison with flat silicon surfaces, which are oleophilic, it has been demonstrated that a combination of low surface energy and the structured features of the plasma-etched surface is essential to prevent oil from penetrating the surface cavities and thus induce the observed macroscopic superoleophobic phenomena with very low contact-angle hysteresis and low roll-off angles. The structured silicon surfaces were coated with cellulose nanocrystals using the polyelectrolyte multilayer technique. The cellulose surfaces prepared in this way were then coated with a monolayer of fluorinated trichlorosilanes. These porous cellulose films displayed highly nonwetting properties against a number of liquids with low surface tension, including alkanes such as hexadecane and decane. The wettability and chemical composition of the cellulose/silicon surfaces were characterized with contact-angle goniometry and X-ray photoelectron spectroscopy, respectively. The nano/microtexture features of the cellulose/silicon surfaces were also studied with field-emission scanning electron microscopy. The highly oleophobic structured cellulose surfaces are very interesting model surfaces for the development of biomimetic self-cleaning surfaces in a vast array of products, including green constructions, packaging materials, protection against environmental fouling, sports, and outdoor clothing, and microfluidic systems.
ACS Appl Mater Interfaces 2009 Nov
PMID:Design of highly oleophobic cellulose surfaces from structured silicon templates. 2035 13


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