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Ultrathin Films (ultrathin + film)
Selected AbstractsDendrimer Precursors for Nanomolar and Picomolar Real-Time Surface Plasmon Resonance/Potentiometric Chemical Nerve Agent Sensing Using Electrochemically Crosslinked Ultrathin Films,ADVANCED FUNCTIONAL MATERIALS, Issue 15 2006P. Taranekar Abstract Nanomolar detection and specific recognition of pinacolyl methylphosphonate (PMP), a hydrolysis product and an analog of a relatively persistent class of toxic nerve agents, has been achieved. In addition, picomolar sensitivity is observed with methylphosphonic acid (MPA), an end-hydrolysis product for all organophosphate-based nerve agents. This is achieved using a combined surface plasmon resonance (SPR) and potentiometry setup. A modified polyamidoamine (PAMAM) carbazole/Cu2+ dendrimer, which is electrochemically crosslinked on a self-assembled monolayer (SAM) modified Au,substrate, is used as an active sensing element for trapping the nerve-agent analogs. The ultrathin films have been used to study the anchoring of nerve agents via non-covalent interactions. The carbazole to amine ratio is optimized to ensure free primary amines are available to interact with the analyte and the Cu2+ ions present in the system, which further enhances the selectivity. The carbazole group on the periphery serves a dual purpose: crosslinking the dendrimers to form a conjugated network film, and generating the potentiometric response. The adsorption kinetics are monitored by using an in,situ SPR/potentiometric setup. This technique not only offers a real-time dual detection of highly toxic nerve-agent analogs, but also shows viability for future sensor-device applications. [source] Ultrathin Films of Single-Walled Carbon Nanotubes for Electronics and Sensors: A Review of Fundamental and Applied AspectsADVANCED MATERIALS, Issue 1 2009Qing Cao Abstract Ultrathin films of single-walled carbon nanotubes (SWNTs) represent an attractive, emerging class of material, with properties that can approach the exceptional electrical, mechanical, and optical characteristics of individual SWNTs, in a format that, unlike isolated tubes, is readily suitable for scalable integration into devices. These features suggest the potential for realistic applications as conducting or semiconducting layers in diverse types of electronic, optoelectronic and sensor systems. This article reviews recent advances in assembly techniques for forming such films, modeling and experimental work that reveals their collective properties, and engineering aspects of implementation in sensors and in electronic devices and circuits with various levels of complexity. A concluding discussion provides some perspectives on possibilities for future work in fundamental and applied aspects. [source] Reversibility of the Perovskite-to-Fluorite Phase Transformation in Lead-Based Thin and Ultrathin Films,ADVANCED MATERIALS, Issue 8 2008Geoff L. Brennecka As film thicknesses decrease below 50 nm, control of cation stoichiometry in Pb-based dielectrics becomes increasingly difficult, a problem that is exacerbated by interaction with technologically important Pt bottom electrodes. Post-crystallization annealing in a Pb-rich atmosphere is shown to be a general technique to reversibly convert low-permittivity Pb-deficient fluorite into ferroelectric high-permittivity stoichiometric perovskite with outstanding dielectric properties (see figure). [source] Layer-by-Layer Assembly of Reactive Ultrathin Films Mediated by Click-Type Reactions of Poly(2-Alkenyl Azlactone)s,ADVANCED MATERIALS, Issue 22 2007E. Buck Covalently crosslinked ultrathin films can be fabricated layer-by-layer by exploiting fast and efficient click-type reactions between polyamines and the ,spring-loaded' functionality of poly(2-alkenyl azlactone)s. The accessibility and reactivity of residual azlactone functionality in these ultrathin materials permits further functionalization post-fabrication, suggesting new approaches to the modification, passivation, or patterning of curved or topologically complex surfaces with chemical or biological functionality. [source] Fabrication of Ultrathin Films with Large Third-Order Nonlinear Optical PropertiesCHEMPHYSCHEM, Issue 3 2005Li Jiang Abstract An ultrathin composite film containing anionic Ag-His complexes (His: L -Histidine) and oppositely charged BH-PPV was fabricated by means of the electrostatic layer-by-layer self-assembly technique. UV/Vis spectra showed a continuous deposition process of Ag-His complexes and BH-PPV. The film structure was characterized by using small-angle X-ray diffraction, AFM, and SEM. The nonlinear optical properties of the ultrathin film were studied by using the Z -scan technique with a laser duration of 8 ns at a wavelength of 532 nm. The film sample exhibited a strong nonlinear saturated absorption, with an ,2value of ,3.9×10,5m,W,1and a self-defocusing effect with an n2value of ,4.78×10,12m2,W,1. [source] Ultrathin Films of Single-Walled Carbon Nanotubes for Electronics and Sensors: A Review of Fundamental and Applied AspectsADVANCED MATERIALS, Issue 1 2009Qing Cao Abstract Ultrathin films of single-walled carbon nanotubes (SWNTs) represent an attractive, emerging class of material, with properties that can approach the exceptional electrical, mechanical, and optical characteristics of individual SWNTs, in a format that, unlike isolated tubes, is readily suitable for scalable integration into devices. These features suggest the potential for realistic applications as conducting or semiconducting layers in diverse types of electronic, optoelectronic and sensor systems. This article reviews recent advances in assembly techniques for forming such films, modeling and experimental work that reveals their collective properties, and engineering aspects of implementation in sensors and in electronic devices and circuits with various levels of complexity. A concluding discussion provides some perspectives on possibilities for future work in fundamental and applied aspects. [source] Photoinitiated polymerization of styrene from self-assembled monolayers on gold.JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 19 2002Abstract Ultrathin films of polystyrene (PS) were grown from self-assembled monolayers by the "grafting-from" technique. The initiating system consisted of a dithiol azobisisobutyronitrile-type free-radical initiator that was activated by irradiation at 300 nm. The thickness of the PS films ranged from 7 to 190 nm and could be controlled by varying the reaction time or the monomer concentration. The films were characterized by ellipsometry and Fourier transform-reflection absorption infrared spectroscopy after Soxhlet extraction of residual physisorbed polymer. These films were unstable above 60 °C, and a water-jacketed Soxhlet extractor was designed to maintain solvent temperatures below 45 °C during extraction. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3284,3291, 2002 [source] Selective Deposition of Ultrathin Poly(p -xylene) Films on Dielectrics Versus Copper SurfacesCHEMICAL VAPOR DEPOSITION, Issue 5 2004J.J. Senkevich Ultrathin films of poly(p -xylylene) are selectively deposited on oxide surfaces but not on air exposed copper. The polymers are deposited under conditions favorable for forming highly conformal ultrathin films appropriate for ,pore sealing' the surface of ultra-low , dielectrics. Variable angle spectroscopic ellipsometry is used to measure the polymer deposit on SiO2, and shows the lack of deposition on air-exposed copper. X-ray photoelectron spectroscopic analysis of the copper samples shows deposition of adventitious carbon on the metal surface, and confirms that no polymer deposition occurs. [source] Enhanced performance by inserting ultrathin SiO2 layer in organic light-emitting devicesPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 3 2007Lianbin Niu Abstract Improved performance of organic light-emitting devices (OLEDs) has been obtained by insertion of an ultrathin film of silicon oxide (SiO2) at the interface of 8-hydroxyquinoline aluminum (Alq3) and N,N ,-bis(1-naphthyl)- N,N ,-diphenyl-1,1,-biphenyl-4,4,-diamine (NPB) layers. When a 1.0 nm SiO2 film was inserted, for an unoptimized indium,tin oxide (ITO)/NPB/SiO2/Alq3/Al device, the current efficiency was as high as 7.35 cd/A. Compared with conventional devices, a higher efficiency has been achieved. The mechanism of performance enhancement is discussed. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Fabrication of Ultrathin Films with Large Third-Order Nonlinear Optical PropertiesCHEMPHYSCHEM, Issue 3 2005Li Jiang Abstract An ultrathin composite film containing anionic Ag-His complexes (His: L -Histidine) and oppositely charged BH-PPV was fabricated by means of the electrostatic layer-by-layer self-assembly technique. UV/Vis spectra showed a continuous deposition process of Ag-His complexes and BH-PPV. The film structure was characterized by using small-angle X-ray diffraction, AFM, and SEM. The nonlinear optical properties of the ultrathin film were studied by using the Z -scan technique with a laser duration of 8 ns at a wavelength of 532 nm. The film sample exhibited a strong nonlinear saturated absorption, with an ,2value of ,3.9×10,5m,W,1and a self-defocusing effect with an n2value of ,4.78×10,12m2,W,1. [source] Controlling Photoactivity in Ultrathin Hematite Films for Solar Water-SplittingADVANCED FUNCTIONAL MATERIALS, Issue 7 2010Florian Le Formal Abstract A promising route to increase the performance of hematite (,-Fe2O3) photoelectrodes for solar hydrogen production through water-splitting is to use an extremely thin layer of this visible light absorber on a nanostructured scaffold. However, the typically poor performance of ultrathin (ca. 20,nm) films of hematite has been the limiting factor in implementing this approach. Here, the surprising effect of a substrate pretreatment using tetraethoxysilicate (TEOS) is reported; it results in drastic improvements in the photoperformance of 12.5,nm thick films of hematite. These films exhibit a water oxidation photocurrent onset potential at 1.1,V versus the reversible hydrogen electrode (vs. RHE) and a plateau current of 0.63,mA cm,2 at 1.5,V vs. RHE under standard illumination conditions, representing the highest reported performance for ultrathin hematite films. In contrast, almost no photoactivity is observed for the photoanode with the same amount of hematite on an untreated substrate. A detailed study of the effects of the TEOS treatment shows that a monolayer of SiOx is formed, which acts to change the hematite nucleation and growth mechanism, increases its crystallinity, reduces the concentration of carrier trapping states of the ultrathin films, and suggests its further application to quantum-dot and extremely-thin-absorber (ETA)-type solar cells. [source] Layer-by-Layer Hydrogen-Bonded Polymer Films: From Fundamentals to ApplicationsADVANCED MATERIALS, Issue 30 2009Eugenia Kharlampieva Abstract Recent years have seen increasing interest in the construction of nanoscopically layered materials involving aqueous-based sequential assembly of polymers on solid substrates. In the booming research area of layer-by-layer (LbL) assembly of oppositely charged polymers, self-assembly driven by hydrogen bond formation emerges as a powerful technique. Hydrogen-bonded (HB) LbL materials open new opportunities for LbL films, which are more difficult to produce than their electrostatically assembled counterparts. Specifically, the new properties associated with HB assembly include: 1) the ease of producing films responsive to environmental pH at mild pH values, 2) numerous possibilities for converting HB films into single- or two-component ultrathin hydrogel materials, and 3) the inclusion of polymers with low glass transition temperatures (e.g., poly(ethylene oxide)) within ultrathin films. These properties can lead to new applications for HB LbL films, such as pH- and/or temperature-responsive drug delivery systems, materials with tunable mechanical properties, release films dissolvable under physiological conditions, and proton-exchange membranes for fuel cells. In this report, we discuss the recent developments in the synthesis of LbL materials based on HB assembly, the study of their structure,property relationships, and the prospective applications of HB LbL constructs in biotechnology and biomedicine. [source] Layer-by-Layer Assembly of Reactive Ultrathin Films Mediated by Click-Type Reactions of Poly(2-Alkenyl Azlactone)s,ADVANCED MATERIALS, Issue 22 2007E. Buck Covalently crosslinked ultrathin films can be fabricated layer-by-layer by exploiting fast and efficient click-type reactions between polyamines and the ,spring-loaded' functionality of poly(2-alkenyl azlactone)s. The accessibility and reactivity of residual azlactone functionality in these ultrathin materials permits further functionalization post-fabrication, suggesting new approaches to the modification, passivation, or patterning of curved or topologically complex surfaces with chemical or biological functionality. [source] Synthesis of Polymer Brushes Using Atom Transfer Radical PolymerizationMACROMOLECULAR RAPID COMMUNICATIONS, Issue 18 2003Jeffrey Pyun Abstract Atom transfer radical polymerization (ATRP) is a robust method for the preparation of well-defined (co)polymers. This process has also enabled the preparation of a wide range of polymer brushes where (co)polymers are covalently attached to either curved or flat surfaces. In this review, the general methodology for the synthesis of polymer brushes from flat surfaces, polymers and colloids is summarized focusing on reports using ATRP. Additionally, the morphology of ultrathin films from polymer brushes is discussed using atomic force microscopy (AFM) and other techniques to confirm the formation of nanoscale structure and organization. Formation of polymer brushes by ATRP. [source] Fabrication of free-standing ultrathin films of porous metal-organic frameworks by liquid-phase epitaxy and subsequent delaminationPHYSICA STATUS SOLIDI - RAPID RESEARCH LETTERS, Issue 8-9 2010Masih Darbandi Abstract In this work we describe an approach to fabricate MOF (metal-organic framework) platelets with predefined shapes and well-defined thicknesses. The process is based on growing thin, highly oriented and ordered MOF films by selective liquid-phase epitaxy on prestructured organic substrates. In a second step, the MOF platelets are delaminated employing a lift-off process. The freestanding MOF platelets were characterized with TEM and SEM, which showed no evidence of fracture or deformation of the delaminated shapes. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Nanoscale Structural and Electronic Properties of Ultrathin Blends of Two Polyaromatic Molecules: A Kelvin Probe Force Microscopy InvestigationCHEMPHYSCHEM, Issue 4 2006Vincenzo Palermo Dr. Abstract We describe a Kelvin Probe Force Microscopy (KPFM) study on the morphological and electronic properties of complex mono and bi-molecular ultrathin films self-assembled on mica. These architectures are made up from an electron-donor (D), a synthetic all-benzenoid polycyclic aromatic hydrocarbon, and an electron-acceptor (A), perylene-bis-dicarboximide. The former molecule self-assembles into fibers in single component films, while the latter molecule forms discontinuous layers. Taking advantage of the different solubility and self-organizing properties of the A and D molecules, multicomponent ultrathin films characterized by nanoscale phase segregated fibers of D embedded in a discontinuous layer of A are formed. The direct estimation of the surface potential, and consequently the local workfunction from KPFM images allow a comparison of the local electronic properties of the blend with those of the monocomponent films. A change in the average workfunction values of the A and D nanostructures in the blend occurs which is primarily caused by the intimate contact between the two components and the molecular order within the nanostructure self-assembled at the surface. Additional roles can be ascribed to the molecular packing density, to the presence of defects in the film, to the different conformation of the aliphatic peripheral chains that might cover the conjugated core and to the long-range nature of the electrostatic interactions employed to map the surface by KPFM limiting the spatial and potential resolution. The local workfunction studies of heterojunctions can be of help to tune the electronic properties of active multicomponent films, which is crucial for the fabrication of efficient organic electronic devices as solar cells. [source] | |||||||||||||||||||||||||