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ABSTRACT: Contact electrochemical transfer of silver from a metal-film stamp (parallel process) or a metal-coated scanning probe (serial process) is demonstrated to allow site-selective metallization of monolayer template patterns of any desired shape and size created by constructive nanolithography. The precise nanoscale control of metal delivery to predefined surface sites, achieved as a result of the selective affinity of the monolayer template for electrochemically generated metal ions, provides a versatile synthetic tool en route to the bottom-up assembly of electric nanocircuits. These findings offer direct experimental support to the view that, in electrochemical metal deposition, charge is carried across the electrode-solution interface by ion migration to the electrode rather than by electron transfer to hydrated ions in solution.
Beilstein Journal of Nanotechnology 01/2012; 3:134-43. · 0.79 Impact Factor
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ABSTRACT: Experimental evidence is presented, demonstrating the feasibility of a surface-patterning strategy that allows stepwise electrochemical generation and subsequent in situ metallization of patterns of carboxylic acid functions on the outer surfaces of highly ordered OTS monolayers assembled on silicon or on a flexible polymeric substrate. The patterning process can be implemented serially with scanning probes, which is shown to allow nanoscale patterning, or in a parallel stamping configuration here demonstrated on micrometric length scales with granular metal film stamps sandwiched between two monolayer-coated substrates. The metal film, consisting of silver deposited by evaporation through a patterned contact mask on the surface of one of the organic monolayers, functions as both a cathode in the printing of the monolayer patterns and an anodic source of metal in their subsequent metallization. An ultrathin water layer adsorbed on the metal grains by capillary condensation from a humid atmosphere plays the double role of electrolyte and a source of oxidizing species in the pattern printing process. It is shown that control over both the direction of pattern printing and metal transfer to one of the two monolayer surfaces can be accomplished by simple switching of the polarity of the applied voltage bias. Thus, the patterned metal film functions as a consumable "floating" stamp capable of two-way (forward-backward) electrochemical transfer of both information and matter between the contacting monolayer surfaces involved in the process. This rather unusual electrochemical behavior, resembling the electrochemical switching in nanoionic devices based on the transport of ions in solid ionic-electronic conductors, is derived from the nanoscale thickness of the water layer acting as an electrolyte and the bipolar (cathodic-anodic) nature of the water-coated metal grains in the metal film. The floating stamp concept introduced in this report paves the way to a series of unprecedented capabilities in surface patterning, which are particularly relevant to nanofabrication by chemical means and the engineering of a new class of molecular nanoionic systems.
Langmuir 06/2011; 27(13):8562-75. · 4.19 Impact Factor
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Beilstein Journal of Nanotechnology 01/2011; 2:824-5. · 0.79 Impact Factor
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ABSTRACT: Monolayer self-assembly (MSA) was discovered owing to the spectacular liquid repellency (lyophobicity) characteristic of typical self-assembling monolayers of long tail amphiphiles, which facilitates a straightforward visualization of the MSA process without the need of any sophisticated analytical equipment. It is this remarkable property that allows precise control of the self-assembly of discrete, well-defined monolayers, and it was the alternation of lyophobicity and lyophilicity (liquid affinity) in a system of monolayer-forming bifunctional organosilanes that allowed the extension of the principle of MSA to the layer-by-layer self-assembly of planed multilayers. On this basis, the possibility of generating at will patterned monolayer surfaces with lyophobic and lyophilic regions paves the way to the engineering of molecular templates for site-defined deposition of materials on a surface via either precise MSA or wetting-driven self-assembly (WDSA), namely, the selective retention of a liquid repelled by the lyophobic regions of the pattern on its lyophilic sites. Highly ordered organosilane monolayer and thicker layer-by-layer assembled structures are shown to be ideally suited for this purpose. Examples are given of novel WDSA and MSA processes, such as guided deposition by WDSA on lyophobic-lyophilic monolayer and bilayer template patterns at elevated temperatures, from melts and solutions that solidify upon cooling to the ambient temperature, and the possible extension of constructive nanolithography to thicker layer-by-layer assembled films, which paves the way to three-dimensional (3D) template patterns made of readily available monofunctional n-alkyl silanes only. It is further shown how WDSA may contribute to MSA on nanoscale template features as well as how combined MSA and WDSA modes of surface assembly may lead to composite surface architectures exhibiting rather surprising new properties. Finally, a critical evaluation is offered of the scope, advantages, and limitations of MSA and WDSA in the bottom-up fabrication of surface structures on variable length scales from nano to macro.
Langmuir 10/2009; 25(24):13984-4001. · 4.19 Impact Factor
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ABSTRACT: Contact electrochemical replication (CER) is a novel pattern replication methodology advanced in this laboratory that offers the unprecedented capability of direct one-step reproduction of monolayer surface patterns consisting of hydrophilic domains surrounded by a hydrophobic monolayer background (hydrophilic @ hydrophobic monolayer patterns), regardless of how the initial "master" pattern was created. CER is based on the direct electrochemical transfer of information, through aqueous electrolyte bridges acting as an information transfer medium, between two organosilane monolayers self-assembled on smooth silicon wafer surfaces. Upon the application of an appropriate voltage bias between a patterned monolayer/silicon specimen playing the role of "stamp" and a monolayer/silicon specimen playing the role of "target", the hydrophilic features of the stamp are copied onto the hydrophobic surface of the target. It is shown that this electrochemical printing process may be implemented under a variety of experimental configurations conducive to the formation of nanometric electrolyte bridges between stamp and target; however, using plain liquid water for this purpose is, in general, not satisfactory because of the high surface tension, volatility, and incompressibility of water. High-fidelity replication of monolayer patterns with variable size of hydrophilic features was achieved by replacing water with a sponge-like hydrogel that is nonvolatile, compressible, and binds specifically to the hydrophilic features of such patterns. Since any copy resulting from the CER process can equally perform as stamp in a subsequent CER step, this methodology offers the rather unique option of multiple parallel reproduction of an initially fabricated master pattern.
ACS Nano 01/2009; 2(12):2554-68. · 10.77 Impact Factor
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ABSTRACT: Experimental evidence derived from a comprehensive study of a self-assembled organosilane multilayer film system undergoing a process of postassembly chemical modification that affects interlayer-located polar groups of the constituent molecules while preserving its overall molecular architecture allows a quantitative evaluation of both the degree of intralayer polymerization and that of interlayer covalent bonding of the silane headgroups in a highly ordered layer assembly of this type. The investigated system consists of a layer-by-layer assembled multilayer of a bifunctional n-alkyl silane with terminal alcohol group that is in situ converted, via a wet chemical oxidation process conducted on the entire multilayer, to the corresponding carboxylic acid function. A combined chemical-structural analysis of data furnished by four different techniques, Fourier transform infrared spectroscopy (FTIR), synchrotron X-ray scattering, X-ray photoelectron spectroscopy (XPS), and contact angle measurements, demonstrates that the highly ordered 3D molecular arrangement of the initial alcohol-silane multilayer stack is well preserved upon virtually quantitative conversion of the alcohol to carboxylic acid and the concomitant irreversible cleavage of interlayer covalent bonds. Thus, the correlation of quantitative chemical and structural data obtained from such unreacted and fully reacted film samples offers an unprecedented experimental framework within which it becomes possible to differentiate between intralayer and interlayer covalent bonding. In addition, the use of a sufficiently thick multilayer effectively eliminates the interfering contributions of the underlying silicon oxide substrate to both the X-ray scattering and XPS data. The present findings contribute a firm experimental basis to the elucidation of the self-assembly mechanism, the molecular organization, and the modes and dynamics of intra- and interlayer bonding prevailing in highly ordered organosilane films; with further implications for the rational exploitation of some of the unique options such supramolecular surface entities can offer in the advancement of a chemical nanofabrication methodology.
ACS Nano 04/2008; 2(3):579-99. · 10.77 Impact Factor
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ABSTRACT: Wetting driven self-assembly (WDSA) of appropriate materials in their liquid state on organic monolayer nanopatterns consisting of wettable (lyophilic) surface features surrounded by a nonwettable (lyophobic) monolayer background is shown to provide the basis of a versatile new approach to template-guided fabrication of metal nanopatterns. Monolayer nanopatterns with planned distributions of lyophilic/lyophobic surface regions are conveniently generated by constructive nanolithography upon local electrochemical oxidation of the top -CH3 groups of a highly ordered OTS (n-octadecyltrichlorosilane) monolayer self-assembled on silicon to -COOH (Adv. Mater. 2000, 12, 725-731). Retraction of such a patterned monolayer from a liquid that does not wet its nonpolar -CH3 surface (lyophobic) results in selective, site-defined immobilization of nanosized volumes of the liquid on the locally generated polar -COOH groups (lyophilic). Examples are given of WDSA of organic materials that offer further options for post-assembly chemical processing, such as nonvolatile low-melting olefins, acids, or thiols, the former being in situ reacted to generate polar functions like -COOH or -SH. Loading surface patterns created in this manner with silver or gold ions followed by further chemical processing results in elemental metal nanoparticles generated within the ion-binding organic material, which thus functions as a guiding template for planned metal deposition at predefined surface sites. WDSA is particularly versatile, as any nonvolatile material with appropriate melting temperature and surface wetting characteristics or solubility in a liquid displaying such properties may in principle be utilized to fabricate potentially useful surface nanostructures.
Nano Letters 07/2007; 7(6):1770-8. · 13.20 Impact Factor
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ABSTRACT: Charge accumulation in an organosilane monolayer self-assembled on silicon is studied using electron-spectroscopy-based chemically resolved electrical measurements (CREM). By resolving the net electrical response of the organic layer, a significant capability of holding extra charge is indicated. Quantum size effects at a molecularly thin layer and the role of competing discharge mechanisms, including defect-assisted leakage currents, are discussed.
Nano Letters 12/2006; 6(11):2462-6. · 13.20 Impact Factor
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ABSTRACT: We demonstrate a hierarchical self-assembly approach to the fabrication of planned nanostructures of colloidal gold particles on silicon, comprising the initial assembly of a molecular template pattern with terminal amino functionality, which then guides the surface assembly and site specific anchoring of gold nanoparticles from a colloidal solution. Well defined amino-terminated templates are obtained via a chemical functionalization process whereby highly ordered bilayer nanopatterns produced by constructive nanolithography (Maoz, R.; Frydman, E.; Cohen, S. R.; Sagiv, J. Adv. Mater. 2000, 12, 725−731) are in-situ modified to generate the top amine functions. This novel approach offers promising performance in terms of the precision, reproducibility, and structural robustness needed for the advancement of a reliable bottom-up nanofabrication methodology.
04/2004;
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ABSTRACT: Micrometer-scale patterns consisting of water-wetted hydrophilic features on the surface of a rigid metallic object (stamp) are successfully transferred to the hydrophobic surface of a highly ordered organosilane monolayer self-assembled on silicon upon the application of an appropriate voltage bias between the stamp and the silicon wafer substrate while the two are pressed against one another. The monolayer imprint is the result of a water bridge-mediated electrochemical oxidation process selectively converting surface exposed −CH3 groups of the monolayer to −COOH. This novel electrochemical printing process, analogous to the monolayer pattern inscription with a conductive scanning probe tip underlying constructive nanolithography (Maoz, R.; Cohen, S. R.; Sagiv, J. Adv. Mater. 1999, 11, 55−61. Maoz, R.; Frydman, E.; Cohen, S. R.; Sagiv, J. Adv. Mater. 2000, 12, 424−429. Maoz, R.; Frydman, E.; Cohen, S. R.; Sagiv, J. Adv. Mater. 2000, 12, 725−731.), paves the way to the possible advancement of a “bottom-up” nano−micro fabrication methodology applicable within the entire nanometer−millimeter dimension range.
05/2003;
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ABSTRACT: Planned nanopatterns of [Au55(Ph2PC6H4SO3Na)12Cl6] clusters are generated on smooth silicon surfaces using a “bottom-up” fabrication methodology based on the selective self-assembly of the gold clusters on purpose-designed organic template patterns themselves fabricated via a hierarchical layer-by-layer self-assembly strategy. The patterns are laterally defined by constructive nanolithography, a novel surface patterning process utilizing conductive AFM tips as nanoelectrochemical “pens”, with which nanoscale chemical information is inscribed in a nondestructive manner (in the form of a localized chemical transformation) on the top surface of a highly ordered organosilane monolayer self-assembled on silicon. Development of the initial tip-imprinted information is achieved via further self-assembly and chemical derivatization steps. This generic all-chemical approach offers attractive options for the advancement of nanofabrication capabilities that might have real impact on future technologies.
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Advanced Materials 02/1999; 11(1):55 - 61. · 13.88 Impact Factor
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Advanced Materials 01/1999; 10(8):580 - 584. · 13.88 Impact Factor
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ABSTRACT: We demonstrate a new approach to the study and application of microwave-induced chemical reactions, using a purpose-designed molecular film as a discrete ultrathin antenna that can utilize absorbed electromagnetic energy to directly drive a specific chemical transformation. Exposure of such a bilayer “antenna” self-assembled on silicon to common microwave radiation in a domestic oven is shown to reproducibly generate a depleted top monolayer structure with molecular-size vacancies that can incorporate and control the further surface manipulation of various gap-fitting guest species. The nonthermal nature of this process is unequivocally demonstrated, as the irradiated bilayer cannot store heat, while conventional heating causes its irreversible structural deterioration, before an equivalent thermally activated transformation could occur. These findings shed new light on the much disputed issue of nonthermal microwave effects, suggesting, beyond obvious implications for basic research in this area, that microwave radiation could be rationally utilized to achieve specific (nondestructive) transformations in properly designed supramolecular systems and could be utilized particularly as an attractive new synthetic tool in molecular surface engineering.
09/1998;
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ABSTRACT: The damage caused to amphiphilic n-alkane monolayers under XPS measurement conditions was assessed in a combined XPS-FTIR study supplemented by additional AFM imaging and contact angle measurements. Nine different self-assembled monolayer/substrate systems were examined, comprising a long chain silane (C18, OTS), a short chain silane (C1, MTS), a functional (COOH-terminated) long chain silane (C18, NTSox), a long chain carboxylic acid (C20, AA), and four different solid substrates (silicon, quartz, glass, and ZnSe). Significant differences were observed in the behavior of the various examined monolayer systems under identical X-ray irradiation conditions. These are interpreted in terms of effects associated with the specific mode of layer-to-surface and intralayer coupling, the size of the monolayer hydrocarbon core, and the presence of radiation-sensitive functional groups in the layer. All these factors and their influence on the degradation path followed by a particular monolayer upon exposure to the X-rays were found to be interrelated, giving rise to a variety of possible damage patterns, including an unexpected overall stabilization effect initiated by the preferential rapid loss of a labile top functional group (NTSox). XPS is shown to be insufficient as a tool for the evaluation of the radiation-induced damage in such ultrathin films, because of its insensitivity to loss of hydrogen and to structural transformations that occur without a net loss of carbon from the surface. Independent methods of surface analysis (mainly FTIR), applied in conjunction with XPS, provide a more comprehensive picture of the induced damage, thus permitting a realistic interpretation of the XPS experimental data as well as the design of improved data acquisition procedures. This could also assist in the tailoring of monolayers with predetermined degradability, for specific purposes. Finally, results of combined AFM-XPS-FTIR-contact angle measurements suggest the possible formation of a “diamond-like” surface film upon extensive X-ray irradiation of an OTS/Si monolayer.
09/1997;
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ABSTRACT: MOLECULAR films with predetermined layered structures can be engineered by using techniques such as the Langmuir–Blodgett method1,2 and self-assembly1,3–9 to deposit discrete monolayers sequentially on a substrate. Such films might have a variety of uses—as smart surface coatings, nonlinear optical materials and in tribology, for example. Here we report the replicative growth of a molecular film of self-assembling silane bilayers with hydrogen-interlayer polar regions into which further identical bilayers can be intercalated. The intercalation step is triggered by a chemical treatment and so can be carried out controllably, allowing duplication in one step of an entire multilayer structure. In this way, we can achieve the stepwise exponential growth of a multilayer film with a predictable number of stacked bilayers.
11/1996; 384(6605):150-153.
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ABSTRACT: Two‐photon ionization has been used to probe NO scattered from two different long chain organic amphiphiles. Rotational and state‐resolved translational distributions were obtained. The results show that there is a large difference in the dynamics of scattering from an unsubstituted aliphatic chain as compared to a monolayer in which the exposed end has been perfluorinated. NO scattered from the latter is more energetic both rotationally, and translationally. This effect becomes particularly noticeable as the incident energy of the NO is raised. The results can be explained by a mechanism which ignores the weak NO–surface potential and treats only the differences in rigidity and phonon modes in the two monolayers.
The Journal of Chemical Physics 02/1988; 88(4):2757-2763. · 3.33 Impact Factor
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ABSTRACT: Hydrogen-bonded multilayer stacks of laterally interconnected long-chain silanes are a new class of synthetic self-assembling thin film organizates endowed with a somewhat unusual combination of structural and dynamic characteristics. In this paper we present experimental results obtained from a combined Fourier transform infra-red (FTIR) spectroscopic and X-ray scattering study, on the basis of which it is possible to derive a rather detailed picture of some of the main features of the microstructure of these novel multilayer films and their monolayer precursors. The films are shown to be composed of discrete monolayers, coupled to each other in a flexible, non-epitaxial manner, via interlayer multiple hydrogen bonds. The hydrocarbon tails assume a perpendicular average orientation on the layer planes and form a ‘rotator phase’-like hexagonal lattice with a lateral packing density of ca. 21 Å2 per molecule and a positional coherence length of ca.70 Å. Extensive lateral coupling of the silane head groups appears to be responsible for the high structural robustness and defect self-healing capability of these films, while the interlayer hydrogen bonding accounts for the facile post-assembly intercalation of various polar guest species into their vertically expandable interlayer polar regions. As the SiO bond is too short to permit extensive intralayer polymerization under the steric constraints imposed by the compact packing of the perpendicularly oriented hydrocarbon tails, the observed high interconnectivity of the silane head groups is rationalized in terms of a dynamic equilibrium model involving continuous redistribution of the SiO bonds within a two-dimensional network of oligomeric siloxane and silanol species. This model of dynamic equilibriation of siloxane linkages can also help to explain other intriguing properties of such silane monolayers.
Supramolecular Science.
