bluuebunny/crossref_metadata_2025_split huggingface dataset:
Interfacial Polymerization of Molecular Squares: Thin Microporous Membranes Featuring Size Selective Transport
Authors: O′Donnell Jodi L. , Keefe Melinda H. , Hupp Joseph T. 
Published: April 2011

ABSTRACTFlat porphyrin molecules have been linked at right angles, using metal atoms, to create square or open-ended box structures having minimum cavity widths of about 2.4 nm and nominal volumes of ca. 14 nm3. Chemically modified versions of the squares feature reactive hydroxyl groups at the top and bottom of each of the four walls of the box structure. These groups combine readily with acid chloride functionalized molecules to yield robust ester linkages. If the reactions are carried out at a liquid-liquid interface with squares in one layer and difunctional acid chloride linkers in the other, polymer formation occurs at the interface. As with other liquid-liquid interfacial polymerizations, the reaction is self-limiting because transport of reactants is inhibited by membrane formation. Polymer films prepared by this method have controllable thicknesses ranging from about 200 nm to 2 microns. The membranes display size-selective porosity with respect to molecules smaller than the intra-square cavity and blocking behavior with respect to larger molecules. Electrochemical and electrochemiluminescence methods are used to measure qualitative and quantitative sieving behavior by employing a conductive metal or ceramic electrode as an underlying platform. In these and related membranes, selective molecular transport is being engineered for applications such as chemical sensing, energy conversion, and chemical catalysis.
Direct Imaging of Nanoparticle Embedding into PS Films
Authors: Teichroeb J.H. , Forrest J.A. 
Published: April 2011

ABSTRACTNon-contact Atomic Force Microscopy (AFM) was used to study the embedding of 10 nm and 20 nm gold nano-particles into the surface of polystyrene films spin-coated onto silicon substrates. The rate of embedding was determined by measuring the apparent nanosphere height as a function of annealing time. This was accomplished by two different methods. In the first case, each image (after a specific annealing time) is acquired at a different spot on the sample surface. In this case a fairly large (∼40) number of particles were imaged in order to have acceptable statistics. A second method involved the use of a kinematic mounting hot stage that allowed the same spot on the sample to be imaged at each time. This allows the same final precision without the same necessity for imaging large numbers of particles. The results indicate that sub nm resolution is easily obtainable with either technique.
Potential Profile Surveyed Directly by Nanomanipulator with Probing Tip in Al/Poly(3-alkylthiophene)/Au Diodes
Authors: Kaneto K. , Nakagawa M. , Takashima W. 
Published: April 2011

ABSTRACTThe potential profiles along the channel of Al/Poly(3-hexylthiophene), PHT film/Au diode from Al to Au electrodes have been measured directly using nanomanipulator with potential probing tips. The steep potential cliff is observed at the interface of Al/PHT, indicating the existence of depletion layer with higher resistance than that of bulk region. For the forward bias, the resistance at the depletion layer decreased significantly and the potential gradient in the PHT bulk region is observed above the onset bias of 1 V. It is found that the contact resistance of PHT/Au is unexpectedly large in spite of the ohmic behavior and also for Al/PHT at forward bias. The effect of light on the depletion layer will be also mentioned. It is stressed that the contact resistances of PHT and metals are significantly important to improve the performance of organic electronics devices.
The Characterization of Copper-Doped Carbon Aerogels by Transport Properties Measurements
Authors: Fu R.W. , Yoshizawa N. , Hanzawa Y. , Kaneko K. , Santos A. P. , Dresselhaus M. S. , Dresselhaus G. , Satcher J. , Baumann T. 
Published: April 2011

ABSTRACTCopper-doped carbon aerogels, which were prepared by sol-gel polymerization of a mixture of resorcinol, formaldehyde and copper ions, followed by supercritical drying with liquid CO2 and carbonization at different temperatures under a N2 atmosphere, were characterized by magnetic susceptibility and temperature-dependent conductivity measurements. The experimental results show that the magnetic susceptibilities (χ) of all the copper-doped carbon aerogels are larger than that of the blank carbon aerogel. The temperature-dependent magnetic susceptibilities of the copper-doped carbon aerogels are well fit to a Curie function in the low temperature region (below 45 K). According to the Curie constant obtained, the spin concentration (N) of the copper-doped carbon aerogels was calculated and the results show that the spin concentration of doped samples increases at first with an increase in the copper concentration used in doping, and then drops from the maximum in N and χ when the copper concentration is further increased above 0.1 wt%. Magnetic susceptibility results suggest that copper-doped carbon aerogels carbonized at 800 °C are more disordered than those carbonized at 1000 °C. The conductivity of these copper-doped carbon aerogels is apparently higher than that of the blank carbon aerogel, especially at low temperature (T < 45 K). The temperature-dependent resistivities of both the copper-doped and the blank carbon aerogels follow a linear functional form log ρ(T) ∼ (1/T)1/2 with two distinct regions below and above 45 K, indicating that the conduction of both the copper-doped and the blank carbon aerogels obey a tunneling and/or a hopping mechanism.
Experimental Studies and Physical Model of Efficient, Tunable Injection Using Tunnel-Transparent Dielectric Contacts on Polymer Light-Emitting Devices
Authors: Bakueva Ludmila , Musikhin Sergei , Sargent Edward H. , Shik Alexander 
Published: April 2011

ABSTRACTMost conducting polymers used for light-emitting devices have a small electron affinity, creating a high barrier for electron injection resulting in low injection efficiency. To improve injection characteristics, we fabricated and investigated multi-layer contacts with a tunneltransparent dielectric layer of nanometer thickness. Polymer layers were prepared by spin coating, and dielectric and metallic contact layers subsequently grown by vacuum deposition. Samples with such multi-layer cathodes demonstrated a current-voltage characteristic with negative differential resistance. At larger applied voltage, electroluminescence was observed with an efficiency larger than for a simple cathode of the same metal. We have developed a model to describe double injection through multi-layer contacts which explains these salient observed features. The increase in injection efficiency is caused by the voltage drop at the dielectric layer, shifting the metal Fermi level relative to the polymer molecular orbitals responsible for carrier transport. The negative differential resistance is explained by the strong dependence of dielectric tunnel transparency on voltage, a dependence which is qualitatively different for electrons and holes. Further flexibility in the functional characteristics of the injecting contacts is achieved through the use of an additional thin metallic layer playing the role of a base electrode, similar to hot-electron transistors with metallic base.
Chemical Structure of MEH-PPV/LiF/Al Interface
Authors: Feng X. D. , Grozea D. , Lu Z. H. 
Published: April 2011

ABSTRACTWe studied the poly [2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV)/LiF/Al interface by angle-dependent X-ray photoemission spectroscopy (XPS). The changes in the C1s, O 1s, Al 2p core level spectra, and the evolution of O to C and Li to F atomic ratios at different photoelectron take-off angles were carefully analyzed. A reduced oxygen concentration with a LiF layer at the interface suggests that LiF can help reduce the oxidation of Al. The interface was found rich in Li+ ions, some of which might be attached to MEH-PPV to form “N type” doping. The electron injection layer consists of Li+doped MEH-PPV, LiF, Al oxides, and metallic Al.
Electrochemical Polymerization of Conducting Polymer Coatings on Neural Prosthetic Devices: Nanomushrooms of Polypyrrole Using Block Copolymer Thin Films as Templates
Authors: Yang Junyan , Xiao Yinghong , Martin David C. 
Published: April 2011

ABSTRACTWe have demonstrated a method to rapidly and reliably fabricate arrays based on the self-assembled morphology of block copolymer ultra thin films. An ordered, nanoporous structure obtained from the block copolymer thin films is used a template for the subsequent electrodeposition of conducting polymer nanomushrooms of polypyrrole (PPy). The influence of current density, deposition charge and morphology of the templates and nanostructured conducting polymer coatings has been investigated. The electrical properties of the polymer coatings were studied.
A New Approach to Design Light Emitting Devices Using Electroactive Dyes
Authors: Pan Michael , Patra Amitava , Friend Christopher S. , Lin Tzu-Chau. , Cartwright Alexander N. , Prasad Paras. N. , Burzynski Ryszard 
Published: April 2011

ABSTRACTOrganic electroluminescence (EL) single layer devices using electroactive dyes incorporated in poly-vinylcarbazole (PVK) were fabricated. The molecular structures of the two-photon dyes are the generic D-π-A;, D-π-D, and A-π-A;, structural motif, composed of a diphenylamine donor (D), a distyrylfluorene π-bridge, and an oxadiazole acceptor (A). A single layer type of EL device of ITO/PVK:DYE/Ca/Al was fabricated. The light emission peak and the threshold of the electroluminescence emission depend on the structure and concentration of the dye. The EL intensity increases with the dye concentration and it was found that as the voltage is increased the brightness increases and reaches a value 498 cd/m2 at an applied voltage of 25 V for the D-π-A; dye. We present a physical explanation of this observed behavior and show that this has significant impact on the design of light emitting devices using these organic dyes.
Temperature Dependence of the Electrical Resistivity of Polymerized C60 Thin Films
Authors: Govinthasamy R. , Rhee J. H. , Sharma S. C 
Published: April 2011

ABSTRACTHighly conducting thin films of C60 were deposited by thermal evaporation in high vacuum on single crystal silicon substrates. The microstructure of the films was characterized by using Atomic Force Microscopy, and laser Raman spectroscopy. The films were polymerized by uv irradiation. The dc electrical resistivities of the as-deposited and uv-polymerized films were measured as functions of temperature between 295 and 17K by the four-probe technique. We present results on the effects of uv-irradiation on the surface microstructure and the temperature dependence of the electrical resistivity of these films.
Raman Spectroscopy Measurements of Interface Effects in C60/Copper-Oxide/Copper
Authors: Li Y. , Rhee J. H. , Singh D. , Sharma S. C 
Published: April 2011

ABSTRACTWe have investigated interface effects in C60/Cu-oxide/Cu structures. C60 thin films were grown under high vacuum by thermal evaporation and the well-known “pentagonal pinch mode” of C60, Ag(2) band was examined by Raman spectroscopy. We observe Raman-active bands centered at 1420, 1448, 1455, and 1465 cm−1 in C60/Cu-oxide/Cu samples with a thin (∼40 nm) C60 overlayer. The 1420, 1448, and 1455 cm−1 Raman bands are not observed in the spectra of pristine C60 powder, copper-oxide substrate, and C60/Cu-oxide/Cu samples with thick (∼1.3 μm) C60 overlayer. We associate these new Raman-active bands with C60/copper-oxide interface.
Gate Bias Modulated Current Flow Analysis at Organic Semiconductor / Metal Interface for Developing High Performance Organic Fet
Authors: Yoshida Manabu , Uemura Sei , Hoshino Satoshi , Kodzasa Takehito , Kamata Toshihide 
Published: April 2011

ABSTRACTWe have developed a current flow analysis system for Field Effect Transistors (FET) using a conductive cantilever of a probe microscope. Using this analysis system, nanoscale current images were observed on a pentacene active layer grown on a bottom electrode in ordinary FETs. When gold (Au) was employed as a bottom electrode, we found the special region around the electrode edge. The current flow hardly occurred in this region. On the other hand, using a conductive polymer (PEDOT) bottom electrode, such a region was not observed. From the detailed observation around the electrode edge, we concluded that the special region would be caused by diffusion of Au particles that evoked heterogeneous pentacene growth, and then the heterogeneity worked as a contact resistance.
Fluctuation Microscopy Studies Of Aluminum Oxides Exposed To CL Ions
Authors: Chen Xidong , Sullivan John , Barbour Charles , Johnson Craig , Zhou Guangwen , Yang Judith 
Published: April 2011

ABSTRACTFluctuation electron microscopy studies have been performed on several aluminum oxides exposed to different electrochemical conditions. Little is known about amorphous aluminum oxide structures and their relationship with their passivation behaviors. Corrosion studies have shown that exposure of aluminum oxide films to Cl ions in solution reduces the oxide's passivity, and this results in the onset of pitting corrosion. The physical changes that occur in the oxide as a result of Cl exposure have not been previously identified due to the difficulty in investigating the structure of this amorphous material. Fluctuation microscopy is a new electron microscopy technique that is able to detect the presence of medium range order structures in amorphous systems. In this paper, we will report fluctuation microscopy results on amorphous aluminum oxides that have been exposed to Cl ions in solution and compare them with oxides that have seen no electrolyte exposure or that have been exposed to electrolytes that do not contain Cl-,such as SO42- containing electrolytes. We will also compare the Cl-exposed oxides with oxides that have been implanted with Cl ions. The differences in pitting behaviors for these oxidesare consistent with our previous speculation on the effect of medium range order on the passivation behavior of aluminum oxides grown using ozone.
High-resolution thermoreflectance microscopy
Authors: Thorne S.A. , Ippolito S.B. , Ünlü M.S. , Goldberg B.B. 
Published: April 2011

ABSTRACTWe present very high-resolution thermal microscopy using the technique of thermoreflectance, a non-contact measurement of the temperature in and around active semiconductor devices. By measuring the local change in reflectivity and comparing to the optical index versus temperature for the interface materials, thermoreflectance can determine the local temperature distribution. Thermoreflectance allows us to work at wavelengths much smaller than those used in typical blackbody imaging, and thus the spatial resolution is significantly improved over that of traditional thermal microscopy. In our experimental setup, we have a confocal scanning optical microscope with a tunable laser, where reflected light is detected by a silicon photodiode in a heterodyne scheme. The sample consists of a 600 nm wide poly-silicon wire embedded in silicon dioxide on top of a silicon substrate. Varying the amount and temporal shape of the current through the poly-silicon wire, we generate a controlled thermal profile to test the imaging capability. Our preliminary results indicate sub-micron thermal resolution.
Spatially Resolved Characterization of Electromigration-Induced Plastic Deformation in al (0.5WT% CU) Interconnect
Authors: Barabash R.I. , Ice G.E. , Tamura N. , Patel J.R. , Valek B.C. , Bravman J. C. , Spolenak R. 
Published: April 2011

ABSTRACTElectromigration during accelerated testing can induce early stage plastic deformation in Al interconnect lines as recently revealed by the white beam scanning X-ray microdiffraction. In the present paper, we provide a first quantitative analysis of the dislocation structure generated in individual micron-sized Al grains during anin-situelectromigration experiment. Laue reflections from individual interconnect grains show pronounced streaking after electric current flow. We demonstrate that the evolution of the dislocation structure during electromigration is highly inhomogeneous and results in the formation of unpaired randomly distributed dislocations as well as geometrically necessary dislocation boundaries. Approximately half of all unpaired dislocations are grouped within the walls. The misorientation created by each boundary and density of unpaired individual dislocations is determined.
Synthesis, Characterization and the gas phase catalytic activity of metal doped nanoporous carbon
Authors: Ayyappan Ponnaiyan , Foley Henry C. 
Published: April 2011

ABSTRACTMetal doped nanoporous carbon(NPC) materials, based on polyfurfuryl alcohol and polyethylene glycol were synthesized using new method. The characterization were carried out using acid-base titration, PXRD, TEM, diffused reflectance FTIR, SEM and mass spectrometer. Their gas phase catalytic activities were checked by passing CO and H2 through the catalysts. Carbondioxide and methane were the evolved gases when CO was passed through the catalyst, whereas carbonmonoxide and methane are the resultant gases when H2 was taken up by the catalyst.
Characterisation of Nanocrystals by Scanning Capacitance Force Microscopy
Authors: Tallarida Grazia , Spiga Sabina , Fanciulli Marco 
Published: April 2011

ABSTRACTScanning capacitance force microscopy is used to localise Sn nanometer sized structures embedded in a silicon oxide thin film. The capacitance variation occurring between probe and sample in presence of a metallic cluster modifies the oscillation amplitude of the AFM probe at twice the frequency of the applied voltage. The extreme localisation of the interaction due to the small geometries involved allows a lateral resolution of few nm. Issues related to the contrast mechanism are discussed with the support 2D finite element calculation of the electric field distribution between probe and sample.
Yellow Luminescence Imaging Of Epitaxial Lateral Overgrown GaN Using Ionoluminescence
Authors: Teo E. J. , Bettiol A. A. , Osipowicz T. , Hao M.S. , Chua S.J. , Liu Y. Y. 
Published: April 2011

ABSTRACTLuminescence imaging techniques such as Photoluminescence (PL) and Cathodoluminescence (CL) have been extensively used to characterize the optical properties of GaN. However, analysis using these techniques is limited to near surface regions and may not represent bulk material properties. This restricts the understanding of the defect-related yellow luminescence in GaN, which tends to originate at the interface region. In this work, we propose the use of MeV protons to probe several microns into a Epitaxial Lateral Overgrown GaN layer. Monte Carlo simulations of the ionization profile show that MeV ions have a much higher penetration depth than the keV electrons used in CL. The well-defined electronic energy loss peak or ‘Bragg peak’ at the end of range for MeV ions enables us to perform depth resolved imaging of the yellow luminescence distribution. Another advantage of using a MeV ion beam over keV electrons is the relatively small lateral spreading of ions in a material, making it a more suitable technique for providing high-resolution images of any buried defects in GaN.
Optical gain and stimulated emission in silicon nanocrystals
Authors: Dal Negro L. , Cazzanelli M. , Gaburro Z. , Bettotti P. , Pavesi L. , Pacifici D. , Franzò G. , Priolo F. , Iacona F. 
Published: April 2011

ABSTRACTTime-resolved luminescence measurements on silicon nanocrystal waveguides have revealed a fast recombination dynamics, related to population inversion which leads to net optical gain. The waveguide samples were obtained by thermal annealing of plasma enhanced chemical vapour deposited thin layers of silicon rich oxide Variable stripe length measurements performed on the fast emission signal have shown an exponential growth of the amplified spontaneous emission, with net gain values of about 10 cm-1. Both the fast component intensity and its temporal width revealed threshold behaviour as a function of the incident pump intensity. A modelling of the decay dynamics is suggested within an effective four level rate equation treatment including the delicate interplay among stimulated emission and Auger recombinations.
AFM-based Electrical Characterization of Nano-structures
Authors: Biswas Sujit K. , Schujman Sandra B. , Vajtai Robert , Wei Bingqing , Parker Allen , Schowalter Leo J. , Ajayan Pulickel M. 
Published: April 2011

ABSTRACTCarbon nanotubes have the potential of being used as interconnects and active semiconducting material in future electronic circuits. It is necessary to study such nano-scale circuits with probes that can make measurements with molecular precision. We describe results using two nanoprobe techniques, namely scanning surface potential microscopy (SSPM), and conductive tip atomic force microscopy (CT-AFM), in the investigation of electrical properties of nanotube circuits. Vertical arrays of multi-walled nanotubes, grown in a porous alumina template with a metal back contact were analyzed. Current mapping confirmed that the nanotubes were electrically connected to the back contact. Isolated single-walled nanotube bundles deposited on an oxidized silicon wafer, and contacted electrically through chromium electrodes were also studied. Contact potential differences between the metal and nanotubes, and the current in some connected nanotubes were measured. Measurements of contact potential with different metals, and the nature of microscopic transport is crucial. Contact potential measurements can also provide fast and reliable characterization of junctions between metallic and semiconducting nanotubes and metals electrodes.
Fabrication of isolated ferroelectric nanostructures
Authors: Bhattacharyya S. , Chattopadhyay Soma , Alexe M. 
Published: April 2011

ABSTRACTIn this report, we explore the possibilities of the fabrication and characterization of ferroelectric nano-structures by various methods. Techniques include the self-assembly route and direct electron beam lithography. The chemical self-assembly route, which adopted the microemulsionmediated synthesis, appeared to be very encouraging for producing very small monodispersed nano particles and powders, with sizes of 10–60 nm. The possibility to form a two dimensional arrangement of these micro droplets was explored with a suitable choice of the substrate material, and the method of coating. For the patterns prepared by the e-beam technique, a strong coupling between two closely spaced nano elements was observed, the spacing between them was found to be the key factor in tailoring their interaction, i.e., whether they would arrange themselves in rod-like pattern or a two dimensional array of isolated squares or circles.
In-situ preparation of polymer-coated zirconia nanoparticles by decomposition of zirconium-tert-butoxide
Authors: Schallehn Michael , Lorenzen Volker , Seydel Johannes , Hahn Horst 
Published: April 2011

ABSTRACTNanocrystalline zirconia particles coated with polymers have been prepared by a two step Chemical Vapor Synthesis process using a hot wall reactor to synthesize the nanocrystalline ceramic core and a subsequent RF plasma reactor for the polymer coating. The polymer coating is built up of organic byproducts of the pyrolysis of the zirconia precursor. By using continuous and pulsed plasma deposition and variation of the plasma parameters, such as RF power, period and duty-cycle, the structure and thickness of the polymer coating can be influenced. Typical particle radii are in the range of 3 to 4 nm with radii of the ceramic core in the range of 2 nm and a coating thickness in the range of 1 to 2 nm. The powders have been characterized by FT-IR, XRD, BET and HRTEM. Consequences for the dispersibility are reported.