CiteULike: Tag nano

Considering process variations during system-level power analysis

Saumya Chandra — 2007-10-23T04:29:36-00:00

(2006), pp. 342-345.

Variable liquid crystal pretilt angles by nanostructured surfaces

Fion Yeung — 2006-02-08T05:39:40-00:00

Applied Physics Letters, Vol. 88, No. 5. (2006)

Variable liquid crystal pretilt angles of any value from 0 to 90° can be obtained by using a nanostructured alignment layer. This layer is robust and reliable. The pretilt angles obtained are stable against high storage and operating temperatures, and have strong anchoring energies. ©2006 American Institute of Physics

Recent trends in the application of carbon nanotubes-polymer composite modified electrodes for biosensors: A review

U Yogeswaran — 2008-03-07T06:23:48-00:00

Anal. Lett., Vol. 41, No. 2. (2008), pp. 210-243.

Carbon Nanotubes (CNTs) with polymers are promising new sensing materials for biosensors, which have the characteristics of low weight of extraordinary mechanical, electrical, thermal, and multifunctional properties. The size scale, aspect ratio, and properties of CNTs provide advantages in a variety of sensor applications. The various processing methods for these nanocomposites are discussed in particular, CNT synthesis, purification of CNTs, pretreatment and functionalization of CNTs, different dispersion methods, and electropolymerization of the monomers. The advantages of these composite modified electrodes toward biosensors have also been presented in detail. Some key results from each article are summarized by relating the concept and mechanism behind each sensor, experimental conditions, and the behavior of the sensors at different conditions, etc. Copyright © Taylor & Francis Group, LLC.

Nanocomposite of functionalized multiwall carbon nanotubes with nafion, nano platinum, and nano gold biosensing film for simultaneous determination of ascorbic acid, epinephrine, and uric acid

Umasankar Yogeswaran — 2008-03-07T06:08:19-00:00

Analytical Biochemistry, Vol. 365, No. 1. (1 June 2007), pp. 122-131.

A unique bimetallic, nano platinum (Pt) with nano gold (Au) on nafion (NF) incorporated with functionalized multiwall carbon nanotubes (f-MWCNTs) composite film (f-MWCNTs-NF-PtAu) was developed by the potentiostatic method. The composite film exhibits promising efficient catalytic activity towards the oxidation of mixture of biochemical compounds and simultaneous measurement of ascorbate anion, epinephrine and urate anion in aqueous buffer solution (pH 6.75). Both, the cyclic voltammetry (CV) and differential pulse voltammetry (DPV) were used for the measurement of electroanalytical properties of neurotransmitters by means of composite film modified electrodes. Well-separated voltammetric peaks were obtained for ascorbate, epinephrine and urate anions with the peak separations of 0.222 and 0.131 V. The composite film can also be produced on gold and transparent semiconductor indium tin oxide electrodes for different kinds of studies such as electrochemical quartz crystal microbalance (EQCM), scanning electron microscopy (SEM), and atomic force microscopy (AFM). The incorporation of Pt and Au onto the f-MWCNTs-NF was revealed by the EQCM technique and the morphology of the film was studied using SEM, AFM and scanning electrochemical microscopy (SECM) techniques. Further, extensive studies were carried out using SECM for obtaining the surface current topographic images of composite film modified electrodes, and these indicated the presence of f-MWCNTs-NF-PtAu composite film on the electrode.

Materials scienceNanostructures in a new league

John Rehr — 2006-03-29T16:56:18-00:00

Nature, Vol. 440, No. 7084. (29 March 2006), pp. 618-619.

Ab initio determination of solid-state nanostructure

P Juhã¡s — 2006-03-29T16:56:18-00:00

Nature, Vol. 440, No. 7084., pp. 655-658.

Electronic properties of silicon nanoneedle structure obtained by RIE for nonvolatile memory applications

Sungwook Jung — 2005-12-06T21:25:40-00:00

Materials Science and Engineering: C, Vol. In Press, Corrected Proof

Nanotechnology is one of the newly rising technological fields and acquiring the research priorities in these days. Nanostructures found to have high optical gain, and found to be a key element in the nonvolatile memory devices. The major drawback in the formation of nanocrystalline silicon (nc-Si) is the lack of uniformity and low density. Uniform and packed needle like silicon surface with a size of 50 nm and with a depth of 300 nm was established in the present study using a reactive ion etching (RIE) system. SF6 and O2 gases were used for the reactive ion etching process. The ratio of gas flow rates during etching was optimized for the anisotropic etching of silicon to generate nanostructures. Surface morphology was investigated after etching using scanning electron microscope (SEM). The sample etched at an SF6 flow rate of 13 sccm was found to be smooth, but as the SF6 flow rate increases, we can see the formation of columnar microstructures. For a typical flow of SF6 with the flow rate of 22 sccm, we found the silicon surface covered by columnar structures with diameters ~ 50 nm and depth of about 300 nm. Radio Frequency (RF) power, etching time and oxygen flow rate were fixed to 100 W, 15 min and 12 sccm, respectively, during the experiment for all the samples. In order to observe the effect of RF power on the formation of nanoneedle silicon surface, experiments were carried out at different powers (60 W, 80 W and 100 W) and at a constant SF6 and oxygen flow rates of 22 sccm and 13 sccm. From this study, we formed a deep nanoneedle structured silicon surface at a power of 100 W. Photoluminescence (PL) and capacitance-voltage (C-V) characteristics were recorded on metal-oxide-semiconductor (MOS) capacitors with nanoneedle surface structure of silicon.

The missing memristor found

Dmitri Strukov — 2008-04-30T19:31:59-00:00

Nature, Vol. 453, No. 7191., pp. 80-83.

Nano-crystallinite hydroxyapatite synthesized by neutralization with the assist of citric acid

Chengfeng Li — 2007-12-30T05:06:54-00:00

Materials Letters, Vol. 62, No. 6-7. (15 March 2008), pp. 932-934.

Bioactive hydroxyapatite (HA) powders with nano-crystallinity were prepared by an economic way, i.e. the neutralized route, during which a supersaturated suspension of lime chelated with citric acid was titrated by orthophosphoric acid diluted with deionized water or ethanol. The crystal behaviors of HA powders were characterized by X-ray diffraction and Fourier transform infrared spectra. It was found that uncalcined powders were amorphous calcium phosphate, while the crystallinity increased significantly after calcined at 800 [degree sign]C and their crystal sizes synthesized with aqueous and ethanol solutions were determined as 54.8 and 85.4 nm, respectively. The inhibition of crystal growth was attributed to the chelating reagent, resulting in the B-substituting CO32- ions to PO43- groups and causing a-axis shortened and c-axis lengthened in the crystal cell.

Water based simple synthesis of re-dispersible silver nano-particles

PK Khanna — 2007-06-22T17:21:21-00:00

Materials Letters, Vol. 61, No. 16. (June 2007), pp. 3366-3370.

Successful experiments with tri-sodium citrate as initial surfactant-cum-reducing agent followed by a secondary reducing agent i.e. sodium formaldehyde sulphoxylate (SFS) to silver nitrate were performed which established a clear large-scale method for the preparation of silver nano-powder of particle size of less than 50 nm. The citrate ions also create hydrophilic capping to in-situ generated zero-valent silver, thus leading to surfactant capped particles. Partial re-dispersion of such nano-powder in aqueous medium leads to colloidal silver which can be loaded in water friendly polymers such as polyvinyl alcohol (PVA) and polyvinyl pyrrolidone (PVP). UV-Visible absorption band at about 275 and 400 nm of colloidal silver in water can be retained even after loading in polymer. Transmission electron microscopy (TEM) of the colloidal solution showed a particle of the size < 30 nm. Particle size distribution by dynamic light scattering technique (DLS) showed that the particles are in the range of 10-40 nm. The elemental composition was studied by energy dispersive analysis of X-rays (EDS).

Controlling the rates of biochemical reactions and signaling networks by shape and volume changes

L Lizana — 2008-03-19T15:15:06-00:00

Proceedings of the National Academy of Sciences, Vol. 105, No. 11. (18 March 2008), pp. 4099-4104.

In biological systems, chemical activity takes place in micrometer- and nanometer-sized compartments that constantly change in shape and volume. These ever-changing cellular compartments embed chemical reactions, and we demonstrate that the rates of such incorporated reactions are directly affected by the ongoing shape reconfigurations. First, we show that the rate of product formation in an enzymatic reaction can be regulated by simple volume contractiondilation transitions. The results suggest that mitochondria may regulate the dynamics of interior reaction pathways (e.g., the Krebs cycle) by volume changes. We then show the effect of shape changes on reactions occurring in more complex and structured systems by using biomimetic networks composed of micrometer-sized compartments joined together by nanotubes. Chemical activity was measured by implementing an enzymatic reactiondiffusion system. During ongoing reactions, the network connectivity is changed suddenly (similar to the dynamic tube formations found inside Golgi stacks, for example), and the effect on the reaction is registered. We show that spatiotemporal properties of the reactiondiffusion system are extremely sensitive to sudden changes in network topology and that chemical reactions can be initiated, or boosted, in certain nodes as a function of connectivity. 10.1073/pnas.0709932105

Building programmable jigsaw puzzles with RNA.

A Chworos — 2004-12-20T03:27:54-00:00

Science, Vol. 306, No. 5704. (17 December 2004), pp. 2068-2072.

One challenge in supramolecular chemistry is the design of versatile, self-assembling building blocks to attain total control of arrangement of matter at a molecular level. We have achieved reliable prediction and design of the three-dimensional structure of artificial RNA building blocks to generate molecular jigsaw puzzle units called tectosquares. They can be programmed with control over their geometry, topology, directionality, and addressability to algorithmically self-assemble into a variety of complex nanoscopic fabrics with predefined periodic and aperiodic patterns and finite dimensions. This work emphasizes the modular and hierarchical characteristics of RNA by showing that small RNA structural motifs can code the precise topology of large molecular architectures. It demonstrates that fully addressable materials based on RNA can be synthesized and provides insights into self-assembly processes involving large populations of RNA molecules.

Translation of DNA signals into polymer assembly instructions.

S Liao — 2004-12-20T03:27:24-00:00

Science, Vol. 306, No. 5704. (17 December 2004), pp. 2072-2074.

We developed a DNA nanomechanical device that enables the positional synthesis of products whose sequences are determined by the state of the device. This machine emulates the translational capabilities of the ribosome. The device has been prototyped to make specific DNA sequences. The state of the device is established by the addition of DNA set strands. There is no transcriptional relationship between the set strands and the product strands. The device has potential applications that include designer polymer synthesis, encryption of information, and use as a variable-input device for DNA-based computation.

A reversible synthetic rotary molecular motor.

JV Hernández — 2004-12-01T17:10:57-00:00

Science, Vol. 306, No. 5701. (26 November 2004), pp. 1532-1537.

The circumrotation of a submolecular fragment in either direction in a synthetic molecular structure is described. The movement of a small ring around a larger one occurs through positional displacements arising from biased Brownian motion that are kinetically captured and then directionally released. The sense of rotation is governed solely by the order in which a series of orthogonal chemical transformations is performed. The minimalist nature of the [2]catenane flashing ratchet design permits certain mechanistic comparisons with the Smoluchowski-Feynman ratchet and pawl. Even when no work has to be done against an opposing force and no net energy is used to power the motion, a finite conversion of energy is intrinsically required for the molecular motor to undergo directional rotation. Nondirectional rotation has no such requirement.

Growth mechanisms of one-dimensional zinc oxide hierarchical structures

Yang — 2006-10-30T22:09:23-00:00

Nanotechnology, Vol. 17, No. 22. (28 November 2006), pp. 5556-5560.

Intersubband Raman laser from GaInAs/AlInAs double quantum wells

Maxi Scheinert — 2007-10-01T15:24:25-00:00

Applied Physics Letters, Vol. 91, No. 13. (2007)

We demonstrate optically pumped GaInAs/AlInAs based intersubband lasers operating at a wavelength of ~5.5 µm applying a simple three-level design. Using a subnanosecond long pulsed excitation laser tunable over the linewidth of the transition from the first level to the third level E13, Raman shift in the lasing spectra was observed. Lasing output power of ~14 W and an internal conversion efficiency between pump and intersubband laser of ~1.3% at 70 K is observed. ©2007 American Institute of Physics

Controlling Nonequilibrium Phonon Populations in Single-Walled Carbon Nanotubes

M Steiner — 2007-12-19T12:34:51-00:00

Nano Lett., Vol. 7, No. 8. (8 August 2007), pp. 2239-2242.

Abstract: We studied spatially isolated single-walled carbon nanotubes (SWNTs) immobilized in a quasi-planar optical /2-microresonator using confocal microscopy and spectroscopy. The modified photonic mode density within the resonator is used to selectively enhance or inhibit different Raman transitions of SWNTs. Experimental spectra are presented that exhibit single Raman bands only. Calculations of the relative change in the Raman scattering cross sections underline the potential of our microresonator for the optical control of nonequilibrium phonon populations in SWNT.

High-harmonic generation by resonant plasmon field enhancement

Seungchul Kim — 2008-06-06T03:01:26-00:00

Nature, Vol. 453, No. 7196., pp. 757-760.

High-harmonic generation by focusing a femtosecond laser onto a gas is a well-known method of producing coherent extreme-ultraviolet (EUV) light. This nonlinear conversion process requires high pulse intensities, greater than 10^13 W cm-2, which are not directly attainable using only the output power of a femtosecond oscillator. Chirped-pulse amplification enables the pulse intensity to exceed this threshold by incorporating several regenerative and/or multi-pass amplifier cavities in tandem. Intracavity pulse amplification (designed not to reduce the pulse repetition rate) also requires a long cavity. Here we demonstrate a method of high-harmonic generation that requires no extra cavities. This is achieved by exploiting the local field enhancement induced by resonant plasmons within a metallic nanostructure consisting of bow-tie-shaped gold elements on a sapphire substrate. In our experiment, the output beam emitted from a modest femtosecond oscillator (100-kW peak power, 1.3-nJ pulse energy and 10-fs pulse duration) is directly focused onto the nanostructure with a pulse intensity of only 10^11 W cm-2. The enhancement factor exceeds 20 dB, which is sufficient to produce EUV wavelengths down to 47 nm by injection with an argon gas jet. The method could form the basis for constructing laptop-sized EUV light sources for advanced lithography and high-resolution imaging applications.

Compiling the ethical, legal and social implications of nanotechnology.

J Lopez — 2005-03-28T19:08:37-00:00

Health Law Rev, Vol. 12, No. 3. (2004), pp. 24-27.

This paper maintains that although there is much interest at the moment in exploring the Ethical, Legal and Social Implications (ELSI) of nanotechnology, the ability to do so in a critical and reflective way, in part, depends on how nanotechnology's future is envisioned. It is argued that, at present, this vision is articulated through the novum, a narrative device borrowed from the science fiction (SF) genre. The paper concludes by arguing that the widely shared narratives about nanotechnology's future, structured by the novum, not only limit the types of ELSI questions that can be addressed but also lead to a polarized debate. It is also suggested that the device of the novum also obscures the heterogeneous nature of nanotechnology itself.

Simultaneous visualization of dry spots and bubbles for pool boiling of R-113 on a horizontal heater

Heung Chung — 2007-02-19T18:25:42-00:00

International Journal of Heat and Mass Transfer, Vol. 46, No. 12. (June 2003), pp. 2239-2251.

A new experimental attempt was made to simultaneously observe the dynamic behaviors of bubbles and dry spots in the vicinity of boiling surface. Also, the two-dimensional bubble structures were obtained separately. From the visualization results, the formation of bubbles and dry spots occurs simultaneously. At critical heat flux (CHF), the surface rewetting is repeated by the local nucleate boiling around the large vapor film. At just after CHF, nucleate boiling at the locally wetted region is extinguished, resulting in the dryout of the whole heater surface. Therefore, we conclude that CHF is initiated from the locally limited nucleate boiling activity rather than any hydrodynamic instability.

Preparation of Unique TiO2 Nano-particle Photocatalysts by a Multi-gelation Method for Control of the Physicochemical Parameters and Reactivity

Bernaurdshaw Neppolian — 2005-10-21T14:39:32-00:00

Catalysis Letters, Vol. 105, No. 1-2. (November 2005), pp. 111-117.

Effect of Niobium on the Structure and Photoactivity of Anatase (TiO2) Nanoparticles

Masanori Hirano — 2006-02-12T17:11:00-00:00

Journal of Nanoscience and Nanotechnology, Vol. 6, No. 3. (March 2006), pp. 762-770.

Effect of metal powder packing on the conductivity of nanometal ink.

NS Kim — 2007-12-12T18:33:15-00:00

J Nanosci Nanotechnol, Vol. 7, No. 11. (November 2007), pp. 3902-3905.

The power of nanotechnology is realized in its application in numerous areas. One such area is undoubtedly the use of metallic nanoparticles as a direct write application. An effort in this area has resulted in a conductive ink whose conductivity approaches 60-70% that of the bulk copper. Such an ink has been developed by reducing silver, gold, and copper nano-sized powders by a wet method and followed by a heat treatment at less than 400 degrees C. The conductivity of the resulting ink product was found to be very much affected by how various sizes of metal powders are packed when particles were dried and packed on various substrates. The effect of packing and various kinds of metal powders on the eventual conductivity of the final product of the ink has been described and discussed in this paper.

Jumping Nanodroplets

A Habenicht — 2005-09-23T08:37:32-00:00

Science, Vol. 309, No. 5743. (23 September 2005), pp. 2043-2045.

Flat gold nanostructures on inert substrates like glass or graphite were illuminated by single intensive laser pulses with fluences above the gold melting threshold. The liquid structures produced in this way are far from their equilibrium shape, and a dewetting process sets in. On a time scale of a few nanoseconds, the liquid contracted toward a sphere. During this contraction, the center of mass moved upward, which could lead to detachment of droplets from the surface due to inertia. The resulting velocities were on the order of 10 meters per second for droplets with radii in the range of 100 nanometers.

Value-free nanotech?

2005-09-23T08:02:34-00:00

Nature, Vol. 437, No. 7058. (2005), pp. 451-452.

Thermal Expansion and Diffusion Coefficients of Carbon Nanotube-Polymer Composites

C Wei — 2007-05-09T14:55:44-00:00

Nano Lett., Vol. 2, No. 6. (12 June 2002), pp. 647-650.

Abstract: Classical molecular dynamics (MD) simulations employing Brenner potential for intra-nanotube interactions and van der Waals forces for polymer-nanotube interface are used to investigate the thermal expansion and diffusion characteristics of carbon nanotube-polyethylene composites. Additions of carbon nanotubes to a polymer matrix are found to increase the glass transition temperature Tg, and thermal expansion and diffusion coefficients in the composite above Tg. These findings could have implications in CNT composite processing, coating and painting applications.

Organization of Polymers onto Carbon Nanotubes: A Route to Nanoscale Assembly

R Czerw — 2007-05-18T11:05:57-00:00

Nano Lett., Vol. 1, No. 8. (8 August 2001), pp. 423-427.

Abstract: Atomic scale imaging using scanning tunneling microscopy has been used to investigate the morphology and structure of high molecular weight polymers attached to carbon nanotubes. A surprising degree of regularity is observed in the attached polymers, suggesting a "nanotube-driven" crystallization process is present. The symmetries of this crystalline state of the polymer are directly determined by the underlying nanotube's chirality. Tunneling spectroscopy further demonstrates that the crystallization of the polymer onto the nanotube results in modifications to the nanotube's electronic structure, as would be expected from a strong polymer-tube interaction. The assembly of nanoscale organics into objects with such perfect order clearly foreshadows the construction of large-scale nanoarchitectures with order over many lengths scales.

Chains of semiconductor nanoparticles templated on DNA

Wendy Dittmer — 2007-09-04T12:11:57-00:00

Applied Physics Letters, Vol. 85, No. 4. (2004), pp. 633-635.

Towards the construction of DNA templated nanowires for self-assembled nanodevices, nanocrystals of the p-type semiconductor CuS were grown selectively and densely on DNA both in solution and stretched on a surface. Atomic force microscopy and transmission electron microscopy measurements display chains of CuS nanoparticles up to 10 nm diameter separated by less than 40 nm. By increasing the number of nucleation sites through the use of bundles of DNA, highly dense coverage of the DNA with nanocrystals is observed. ©2004 American Institute of Physics

Nanoscale lateral epitaxial overgrowth of GaN on Si (111)

KY Zang — 2007-08-28T16:33:23-00:00

Applied Physics Letters, Vol. 87, No. 19. (2005)

We demonstrate that GaN can selectively grow by metalorganic chemical vapor deposition into the pores and laterally over the nanoscale patterned SiO2 mask on a template of GaN/AlN/Si. The nanoporous SiO2 on GaN surface with pore diameter of approximately 65 nm and pore spacing of 110 nm was created by inductively coupled plasma etching using anodic aluminum oxide template as a mask. Cross-section transmission electron microscopy shows that the threading-dislocation density was largely reduced in this nanoepitaxial lateral overgrowth region. Dislocations parallel to the interface are the dominant type of dislocations in the overgrown layer of GaN. A large number of the threading dislocations were filtered by the nanoscale mask, which leads to the dramatic reduction of the threading dislocations during the growth within the nano-openings. More importantly, due to the nanoscale size of the mask area, the very fast coalescence and subsequent lateral overgrowth of GaN force the threading dislocations to bend to the basal plane within the first 50 nm of the film thickness. The structure of overgrown GaN is a truncated hexagonal pyramid which is covered with six 101 side facets and (0001) top surface depending on the growth conditions. ©2005 American Institute of Physics

Nanoheteroepitaxy of GaN on a nanopore array of Si(111) surface

KY Zang — 2007-08-28T15:29:56-00:00

Thin Solid Films, Vol. 515, No. 10. (26 March 2007), pp. 4505-4508.

Nanoheteroepitaxial (NHE) growth of GaN using AlN/AlGaN as a graded buffer layer by metalorganic chemical vapor deposition has been demonstrated on the nanoporous patterned Si(111) substrates. The nanopore array on Si(111) has been fabricated by using anodized aluminum oxide membrane as an induced couple plasma dry etching mask. The reduction of the threading dislocation density and relaxation of the tensile stress in NHE GaN are revealed by transmission electron microscopy (TEM), micro-Raman spectrum and photoluminescence spectrum, respectively. Cross-sectional TEM analysis shows that dislocations nucleated at the interface are forced to bend into (0001) basal plane. Red shift in the E2 (TO) phonon peak of micro-Raman spectrum indicates the relaxation of tensile stress in the nanoheteroepitaxial lateral overgrowth of GaN. A single step ELO without mask on nanopatterned Si(111) substrates is a simple and promising way for the improvement of the quality of GaN on Si substrates.

Synthesis and optical properties of In-doped GaN nanocrystals

SV Bhat — 2007-08-28T16:16:25-00:00

Solid State Communications, Vol. 141, No. 6. (February 2007), pp. 325-328.

Indium-doped GaN nanocrystals with 5% and 10% In have been prepared by a low temperature solvothermal method using hexamethyldisilazane as the nitriding reagent. The nanocrystals show Raman bands at lower frequencies compared to GaN. Photoluminescence spectra of the In-doped GaN nanocrystals exhibit an increase in the FWHM with the decrease in the PL band energy, the band energy itself decreasing with increase in the In content.

Time-Resolved Shadowgraphs of Material Ejection in Intense Femtosecond Laser Ablation of Aluminum

Nan Zhang — 2008-05-03T23:46:49-00:00

Physical Review Letters, Vol. 99, No. 16. (2007)

The dynamic process of intense 50 fs laser ablation of aluminum is investigated by ultrafast time-resolved microscopy. A stripe pattern preceding phase explosion is clearly seen in the shadowgraph of 1 ns time delay. Intermittent material ejections are observed within the ejected plume after 2.5 and 7 ns time delay, respectively, which may be attributed to the material response to the generation of an extremely strong thermoelastic wave. Similar processes are also recorded in the ablation of silicon and glass samples, except for the glass samples, the intermittent material ejections are not found.

Microrheology with modulated optical nanoprobes (MOONs)

Caleb Behrend — 2007-07-26T18:15:07-00:00

Journal of Magnetism and Magnetic Materials, Vol. 293, No. 1. (May 2005), pp. 663-670.

Metal-capping of one hemisphere of a nano or microparticle breaks the particle's optical symmetry, allowing its orientation to be tracked using fluorescence and reflection. Tracking orientation and rotation allows the torques acting on the particles be inferred. In addition to serving as rotational nanoviscometers these probes report on local Brownian, magnetic and biomechanical torques.

Nanoparticle Assembly at Fluid Interfaces: Structure and Dynamics

Y Lin — 2008-04-29T22:19:44-00:00

Langmuir, Vol. 21, No. 1. (4 January 2005), pp. 191-194.

Abstract: The self-assembly of nanoparticles at fluid interfaces, driven by the reduction in interfacial energy, was investigated. With spherical, tri-n-octyl-phosphine-oxide covered cadium selenide (CdSe) nanoparticles (1-8 nm), thermal fluctuations compete with the interfacial segregation giving rise to a size-dependent self-assembly of the particles. The structure of the nanoparticle assembly was studied using electron microscopy, atomic force microscopy, and X-ray scattering in situ, which indicate that the particles form a densely packed monolayer. The energetics of the adsorption of nanoparticles onto the interface was revealed by time-dependent fluorescence studies on a mixture of two different sized nanoparticles at the interface. The dynamics of the nanoparticles at the fluid interface, probed using fluorescence photobleaching methods, suggests a liquid-like behavior. The results have implications in the design of hierarchical self-assemblies of nanoparticles for the one-step fabrication of devices on multiple length scales.

Polymer Chain Swelling Induced by Dispersed Nanoparticles

Anish Tuteja — 2008-03-17T22:54:34-00:00

Physical Review Letters, Vol. 100, No. 7. (2008)

The dimensions of individual deuterated polystyrene (d-PS) chains in a well-dispersed mixture of protonated polystyrene and chemically identical nanoparticles was determined by neutron scattering. A 10%–20% increase in the radius of gyration of d-PS was found when the nanoparticles are homogeneously dispersed in the polymer, an effect that occurs only when the radius of gyration of the polymer is larger than the nanoparticle radius. These results are reconciled with the existing literature.

Soft Nanopolyhedra as a Route to Multivalent Nanoparticles

Jiunn Roan — 2008-05-05T15:43:40-00:00

Physical Review Letters, Vol. 96, No. 24. (2006)

Computer simulations show that end-grafted immiscible homopolymers can confer multivalence to nanoparticles, resulting in soft nanopolyhedra with structures identical to those found in small clusters of colloidal microspheres. Unprecedented structure tunability is demonstrated by several structure transition sequences, including a reentrant transition, induced by varying composition, polymer lengths, or grafting patterns. These results suggest a new method for fabricating nanoparticles with precisely controlled numbers and locations of functional sites (i.e., multivalent nanoparticles).

Hard-X-Ray Lensless Imaging of Extended Objects

JM Rodenburg — 2008-03-19T17:07:12-00:00

Physical Review Letters, Vol. 98, No. 3. (2007)

We demonstrate a hard-x-ray microscope that does not use a lens and is not limited to a small field of view or an object of finite size. The method does not suffer any of the physical constraints, convergence problems, or defocus ambiguities that often arise in conventional phase-retrieval diffractive imaging techniques. Calculation times are about a thousand times shorter than in current iterative algorithms. We need no a priori knowledge about the object, which can be a transmission function with both modulus and phase components. The technique has revolutionary implications for x-ray imaging of all classes of specimen.

Two-Dimensional Dynamics of Metal Nanoparticles on the Surface of Thin Polymer Films Studied with Coherent X Rays

S Streit — 2008-03-19T17:03:19-00:00

Physical Review Letters, Vol. 98, No. 4. (2007)

X-ray photon-correlation spectroscopy is used to measure the dynamic structure factor f(q,) of gold particles moving on the surface of thin polymer films. Above the glass transition of the polymer the peculiar form f(q,)~exp[-()] is found with 0.7<<1.5, depending on sample age and temperature. The relaxation rates scale linearly with q, excluding a simple Brownian diffusive motion. This type of behavior, already observed in aging bulk soft matter systems, is explained by a power law distribution of particle velocities due to ballistic motion.

Fractal Substructure of a Nanopowder

Thomas Schwager — 2008-06-05T20:43:08-00:00

Physical Review Letters, Vol. 100, No. 21. (2008)

The structural evolution of a nanopowder by repeated dispersion and settling can lead to characteristic fractal substructures. This is shown by numerical simulations of a two-dimensional model agglomerate of adhesive rigid particles. The agglomerate is cut into fragments of a characteristic size , which then are settling under gravity. Repeating this procedure converges to a loosely packed structure, the properties of which are investigated: (a) The final packing density is independent of the initialization, (b) the short-range correlation function is independent of the fragment size, (c) the structure is fractal up to the fragmentation scale with a fractal dimension close to 1.7, and (d) the relaxation time increases linearly with .

Effect of water-wall interaction potential on the properties of nanoconfined water

Pradeep Kumar — 2008-06-11T20:12:46-00:00

Physical Review E (Statistical, Nonlinear, and Soft Matter Physics), Vol. 75, No. 1. (2007)

Much of the understanding of bulk liquids has progressed through study of the limiting case in which molecules interact via purely repulsive forces, such as a hard-core or “repulsive ramp” potential. In the same spirit, we report progress on the understanding of confined water by examining the behavior of waterlike molecules interacting with planar walls via purely repulsive forces and compare our results with those obtained for Lennard-Jones (LJ) interactions between the molecules and the walls. Specifically, we perform molecular dynamics simulations of 512 waterlike molecules interacting via the TIP5P potential and confined between two smooth planar walls that are separated by 1.1 nm. At this separation, there are either two or three molecular layers of water, depending on density. We study two different forms of repulsive confinement, when the water-wall interaction potential is either (i) 1/r9 or (ii) a WCA-like repulsive potential. We find that the thermodynamic, dynamic, and structural properties of the liquid in purely repulsive confinements qualitatively match those for a system with a pure LJ attraction to the wall. In previous studies that include attractions, freezing into monolayer or trilayer ice was seen for this wall separation. Using the same separation as these previous studies, we find that the crystal state is not stable with 1/r9 repulsive walls but is stable with WCA-like repulsive confinement. However, by carefully adjusting the separation of the plates with 1/r9 repulsive interactions so that the effective space available to the molecules is the same as that for LJ confinement, we find that the same crystal phases are stable. This result emphasizes the importance of comparing systems only using the same effective confinement, which may differ from the geometric separation of the confining surfaces.

Superstability of Surface Nanobubbles

Bram Borkent — 2008-05-04T16:08:51-00:00

Physical Review Letters, Vol. 98, No. 20. (2007)

Shock wave induced cavitation experiments and atomic force microscopy measurements of flat polyamide and hydrophobized silicon surfaces immersed in water are performed. It is shown that surface nanobubbles, present on these surfaces, do not act as nucleation sites for cavitation bubbles, in contrast to the expectation. This implies that surface nanobubbles are not just stable under ambient conditions but also under enormous reduction of the liquid pressure down to -6 MPa. We denote this feature as superstability.

From Micro- to Nanofabrication with Soft Materials

Stephen Quake — 2007-09-27T08:45:33-00:00

Science, Vol. 290, No. 5496. (24 November 2000), pp. 1536-1540.

10.1126/science.290.5496.1536

Imaging Surface Topography using Lloyd's Mirror in Photoemission Electron Microscopy

DE Jesson — 2008-05-03T18:26:53-00:00

Physical Review Letters, Vol. 99, No. 1. (2007)

We use Lloyd's mirror to modulate electron photoemission in photoemission electron microscopy. This results in the projection of Lloyd's fringes on to three-dimensional (3D) surface objects. An iterative reconstruction method is used to correct for distortions in the fringe pattern due to the cathode immersion lens, thereby providing a quantitative interpretation of surface shape. It is therefore possible to extract 3D height information directly from a two-dimensional, plan-view image. The technique is of sufficient intensity and contrast to study real-time changes in surface topography and we apply the method to study unusual contact-line dynamics during the reactive wetting of metal droplets.

High-performance liquid chromatography analysis of nanomole levels of glutathione, glutathione disulfide, and related thiols and disulfides.

DJ Reed — 2005-02-27T21:31:40-00:00

Anal Biochem, Vol. 106, No. 1. (15 July 1980), pp. 55-62.

GLOBAL VOICES OF SCIENCE: Ascent of Nanoscience in China

Chunli Bai — 2008-04-27T23:30:22-00:00

Science, Vol. 309, No. 5731. (1 July 2005), pp. 61-63.

10.1126/science.1115172

Staphylococcus aureus adhesion to titanium oxide surfaces coated with non-functionalized and peptide-functionalized poly(L-lysine)-grafted-poly(ethylene glycol) copolymers.

LG Harris — 2008-02-18T16:31:41-00:00

Biomaterials, Vol. 25, No. 18. (August 2004), pp. 4135-4148.

Implanted biomaterials are coated immediately with host plasma constituents, including extracellular matrix (ECM); this reaction may be undesirable in some cases. Poly(L-lysine)-grafted-poly(ethylene glycol) (PLL-g-PEG) has been shown to spontaneously adsorb from aqueous solution onto metal oxide surfaces, effectively reducing the degree of non-specific adsorption of blood and ECM proteins, and decreasing the adhesion of fibroblastic and osteoblastic cells to the coated surfaces. Cell adhesion through specific peptide-integrin receptors could be restored on surfaces coated with PLL-g-PEG functionalized with peptides of the RGD (Arg-Asp-Gly) type. To date, no study has examined the effect of surface modifications by PLL-g-PEG-based polymers on bacterial adhesion. The ability of Staphylococcus aureus to adhere to the ECM and plasma proteins deposited on biomaterials is a significant factor in the pathogenesis of medical-device-related infections. This study describes methods for visualizing and quantifying the adhesion of S. aureus to smooth and rough (chemically etched) titanium surfaces without and with monomolecular coatings of PLL-g-PEG, PLL-g-PEG/PEG-RGD and PLL-g-PEG/PEG-RDG. The different surfaces were exposed to S. aureus cultures for 1-24h and bacteria surface density was evaluated using scanning electron microscopy and fluorescence microscopy. Coating titanium surfaces with any of the three types of copolymers significantly decreased the adhesion of S. aureus to the surfaces by 89-93% for PLL-g-PEG, and 69% for PLL-g-PEG/PEG-RGD. Therefore, surfaces coated with PLL-g-PEG/PEG-RGD have the ability to attach cells such as fibroblasts and osteoblasts while showing reduced S. aureus adhesion, resulting in a selective biointeraction pattern that may be useful for applications in the area of osteosynthesis, orthopaedic and dental implantology.

Tracking in molecular bioimaging

E Meijering — 2006-06-28T08:59:37-00:00

Signal Processing Magazine, IEEE, Vol. 23, No. 3. (2006), pp. 46-53.

This paper aims to simulate the application of more advanced computer vision techniques to tracking in biological molecular imaging by surveying the literature and sketching the current state of affairs in the field for a signal and image processing audience. After describing the basic principles of visualizing molecular dynamics in living cells and giving some examples of biological molecular dynamics studies, the paper summarizes the problems and limitations intrinsic to imaging at this scale. The paper then discusses the main ingredients of the commonly used tracking paradigm and subsequently reconsider its competence by comparing it to certain aspects of visual motion perception in human beings, keeping in mind the complexity and variability of biological image data. Finally, it summarizes the main points of attention for future research and the challenges that lie ahead.

Spin Dependent Transport in Magnetic Nanostructures (Advances in Condensed Matter Science)

Sadamichi Maekawa — 2006-05-03T07:28:46-00:00

(11 July 2002)

<P>Since the discovery of giant magnetoresistance (GMR) in 1988, spin-dependent transport phenomena in magnetic nanostructures have received much attention both from the academic and a technological points of view. Ferromagnetic tunnel junctions, made of ferromagnetic metal electrodes and a very thin insulating barrier between them, also also hold a great deal of current interest. Spin Dependent Transport in Magnetic Nanostructures, edited by two of the world's leading authorities, introduces and explains the basics physics and applications of a variety of spin-dependent transport phenomena in magnetic nanostructures, with particular emphasis on magnetic multilayers and magnetic tunnel junctions. </P>

Edges and interactions for graphene in quantum Hall states

HA Fertig — 2007-12-28T07:52:11-00:00

Solid State Communications, Vol. 143, No. 1-2. (July 2007), pp. 86-91.

We study the electronic structure near a graphene edge in a strong perpendicular magnetic field. In high Landau levels these edge states are similar in structure to those of standard two-dimensional electron gas systems (s-2DEG's). The lowest Landau supports half as many edge states as those of higher Landau levels, leading to a quantization of the Hall conductance that is shifted relative to s-2DEG's. The presence of both hole-like and electron-like edge states is shown to lead to the existence of a domain wall at the edge of an undoped graphene armchair edge when one considers the effect of quantum Hall ferromagnetism. The domain wall supports both collective and charged gapless excitations whose consequences for tunnelling experiments are discussed.

Renormalization of graphene bands by many-body interactions

Aaron Bostwick — 2007-12-28T07:52:12-00:00

Solid State Communications, Vol. 143, No. 1-2. (July 2007), pp. 63-71.

We have determined the electronic bandstructure of clean and potassium-doped single layer graphene, and fitted the graphene [pi] bands to a first- and third-nearest-neighbor tight binding model. We characterized the quasiparticle dynamics using angle resolved photoemission spectroscopy. The dynamics reflect the decay of quasiparticles (holes) into collective excitations, namely plasmons, phonons, and electron-hole pairs. Electron-hole pair decay is found to be a minimum at the Dirac energy while electron-plasmon scattering is maximum around the same energy. Taking the topology of the bands around the Dirac energy for n-doped graphene into account, we show that these results follow from kinematic constraints imposed by graphene's gapless energy spectrum around the Dirac energy. We also show that the electron-phonon scattering in lightly doped graphene is around 6 times larger than the predictions of published calculations.