Nanofluidic networks based on surfactant membrane technology

We explore possibilities to construct nanoscale analytical devices based on lipid membrane technology. As a step toward this goal, we present nanotube-vesicle networks with fluidic control, where the nanotube segments reside at, or very close (<2 microm) to optically transparent surfaces. These nanofluidic systems allow controlled transport as well as LIF detection of single nanoparticles. In the weak-adhesion regime, immobilized vesicles can be approximated as perfect spheres with nanotubes attached at half the height of the vesicle in the axial (z) dimension. In the strong-adhesion regime (relative contact area, Sr* approximately 0.3), nanotubes can be adsorbed to the surface with a distance to the interior of the nanotubes defined by the membrane thickness of approximately 5 nm. Strong surface adsorption restricts nanotube self-organization, enabling networks of nanotubes with arbitrary geometries. We demonstrate LIF detection of single nanoparticles (30-nm-diameter fluorescent beads) inside single nanotubes. Transport of nanoparticles was induced by a surface tension differential applied across nanotubes using a hydrodynamic injection protocol. Controlled transport in nanotubes together with LIF detection enables construction of nanoscale fluidic devices with potential to operate with single molecules. This opens up possibilities to construct analytical platforms with characteristic length scales and volume orders of magnitudes smaller than employed in traditional microfluidic devices.     

Charge transport in cellular nanoparticle networks: meandering through nanoscale mazes

The transport of electrons through topologically complex two-dimensional Au nanoparticle networks has been investigated using a combination of low temperature (4.5 K) direct current I(V) measurements and numerical simulations. Intricate, spatially correlated nanostructured networks were formed via spin-casting. The topological complexity of the nanoparticle assemblies produces I(V) curves associated with nonlinearity exponents, zeta approximately 4.0. Simulations based on tunneling transport in sparse and inhomogeneous planar networks are used to elucidate the influence of topology on the value of zeta.     

Electrophoretic transport in surfactant nanotube networks wired on microfabricated substrates

Nanofluidic devices are rapidly emerging as tools uniquely suited to transport and interrogate single molecules. We present a simple method to rapidly obtain compact surfactant nanotube networks of controlled geometry and length. The nanotubes, 100-300 nm in diameter, are pulled from lipid vesicles using a micropipet technique, with multilamellar vesicles serving as reservoirs of surfactant material. In a second step, the nanotubes are wired around microfabricated SU-8 pillars. In contrast to unrestrained surfactant networks that minimize their surface free energy by minimizing nanotube path length, the technique presented here can produce nanotube networks of arbitrary geometries. For example, nanotubes can be mounted directly on support pillars, and long stretches of nanotubes can be arranged in zigzag patterns with turn angles of 180 degrees. The system is demonstrated to support electrophoretic transport of colloidal particles contained in the nanotubes down to the limit of single particles. We show that electrophoretic migration velocity is linearly dependent on the applied field strength and that a local narrowing of the nanotube diameter results from adhesion and bending around SU-8 pillars. The method presented here can aid in the fabrication of fully integrated and multiplexed nanofluidic devices that can operate with single molecules.     

Depth profile analysis of electrodeposited nanoscale multilayers by SNMS

As early as 10 years after the discovery of the giant magnetoresistance (GMR) the magnetic/non-magnetic multilayers found their first application in the read-out units of magnetic recording media, and the hard disk drives with GMR-based sensors since gained a dominating market share. In spite of the large number of works published on nanoscale multilayers, data on the depth profile of electrodeposited multilayer samples are very scarce. This work deals with the depth profile analysis of electrodeposited CoNiCu/Cu and Co/Cu multilayers films. Commercial Cu sheet and a Cr/Cu layer evaporated onto Si (1 1 1) surface were used as substrates with high and low roughness, respectively. The Secondary Neutral Mass Spectrometry (SNMS) depth profile analysis clearly revealed the layered structure of the samples. The resolution of the individual layers varied with the initial roughness of the substrate. The SNMS spectra showed that the oxygen incorporation into the layers is insignificant. When both Ni and Co are present in the magnetic layer, the composition of the samples is influenced by both the anomalous codeposition properties of the iron-group elements and the mass transport of the corresponding ions in the electrolyte. This observation draws the attention to the possible inhomogeneity of the magnetic layers in electrodeposited samples.     

Molecular energy dissipation in nanoscale networks of Dentin Matrix Protein 1 is strongly dependent on ion valence

The fracture resistance of biomineralized tissues such as bone, dentin, and abalone is greatly enhanced through the nanoscale interactions of stiff inorganic mineral components with soft organic adhesive components. A proper understanding of the interactions that occur within the organic component, and between the organic and inorganic components, is therefore critical for a complete understanding of the mechanics of these tissues. In this paper, we use Atomic Force Microscope (AFM) force spectroscopy and dynamic force spectroscopy to explore the effect of ionic interactions within a nanoscale system consisting of networks of Dentin Matrix Protein 1 (DMP1) (a component of both bone and dentin organic matrix), a mica surface, and an AFM tip. We find that DMP1 is capable of dissipating large amounts of energy through an ion-mediated mechanism, and that the effectiveness increases with increasing ion valence.     

Chemical reduction of an unbuffered nitrate solution using catalyzed and uncatalyzed nanoscale iron particles

Uncatalyzed and catalyzed nanoscale Fe(0) systems were employed for the denitrification of unbuffered 40 mgN L(-1) nitrate solutions at initial neutral pH. Compared to microscale Fe(0) (<100 mesh), the efficiency and rate of nitrate removal using uncatalyzed and catalyzed nano-Fe(0) were highly promoted, in which the maximum promoted rate was obtained using copper-catalyzed nano-Fe(0) (nano-Cu/Fe). Nitrate first-order degradation rate constants (k(obs)) decreased significantly (>70%) with aged nano-Fe(0) and aged nano-Cu/Fe, and were recovered with NaBH(4) as reductants at levels of about 85 and 75%, respectively. Activation energies (E(a)) of nitrate reduction over the temperature range of 10-60 degrees C were 42.5 kJ mol(-1) for microscale Fe(0), 25.8 kJ mol(-1) for nano-Fe(0) and 16.8 kJ mol(-1) for nano-Cu/Fe. Unlike microscale Fe(0), the kinetics of denitrification by nano-Fe(0) and nano-Cu/Fe began to show characteristics of mass transport in addition to chemical reaction control. Ammonium was the predominant end product in all the systems. However, as for nitrite, 40% of the degraded nitrate persisted in the nano-Cu/Fe system. Thus, relative to nano-Cu/Fe, nano-Fe(0) is a potential reductant for denitrification of groundwater as far as toxic nitrite generation is concern.     

Nonlinear flow analysis in pipe networks

Pipe networks are computed in an analogous mannner to frameworks in structural mechanics loaded only by moments. The mesh method (force method) is applied. Due to the boundary layer effects in special pipe members, the flow problem is in general nonlinear. Therefore, the Newton-Raphson iteration procedure is used to solve the nonlinear system of equations. Using the computed flow rates in the TREE structure (determined by graph theory) as initial values, the iteration procedure converges rapidly to a user specified tolerance value. The loss coefficients of pressure for different pipe members (TUBE, VALVE, BOW, TEE, PUMP, KNEE, ±CONTR, ±DIFSR) need only be given in diagrams. These diagrams are used in digitalized form. In the back-substitution phase with known flow rates in all members, the pressure at the joints is computed. The main advantages of the analysis as outlined are that no initial values for the member flow rates need be known, the iteration procedure converges rapidly, and within each iteration step only small systems of linear equations need to be solved. Due to the fact that the loss coefficients of pressure need only be given in diagrams, arbitrary nonlinear networks can be analysed by the unchanged program system. A flow rate assumption may be specified in the input for a member of a mesh. The pressures at the joints are defined as unknowns (displacement method) in References 7, 8 and 10. The flow rates in the members are defined as unknowns (force method) in Reference 9. The nonlinear system of equations is always solved by the Newton-Raphson procedure. In Reference 10 a strategy is presented to take into account different pipe members, but in a different way from that outlined in this paper. The members BOW, TEE, KNEE, CONTR, DIFSR are not examined in Reference 10.     

Excitons in nanoscale systems

Nanoscale systems are forecast to be a means of integrating desirable attributes of molecular and bulk regimes into easily processed materials. Notable examples include plastic light-emitting devices and organic solar cells, the operation of which hinge on the formation of electronic excited states, excitons, in complex nanostructured materials. The spectroscopy of nanoscale materials reveals details of their collective excited states, characterized by atoms or molecules working together to capture and redistribute excitation. What is special about excitons in nanometre-sized materials? Here we present a cross-disciplinary review of the essential characteristics of excitons in nanoscience. Topics covered include confinement effects, localization versus delocalization, exciton binding energy, exchange interactions and exciton fine structure, exciton-vibration coupling and dynamics of excitons. Important examples are presented in a commentary that overviews the present understanding of excitons in quantum dots, conjugated polymers, carbon nanotubes and photosynthetic light-harvesting antenna complexes.     

Molecular analysis of blood with micro-/nanoscale field-effect-transistor biosensors

Rapid and accurate molecular blood analysis is essential for disease diagnosis and management. Field-effect transistor (FET) biosensors are a type of device that promise to advance blood point-of-care testing by offering desirable characteristics such as portability, high sensitivity, brief detection time, low manufacturing cost, multiplexing, and label-free detection. By controlling device parameters, desired FET biosensor performance is obtained. This review focuses on the effects of sensing environment, micro-/nanoscale device structure, operation mode, and surface functionalization on device performance and long-term stability.     

Inlaying nanoscale surface recess patterns with nanoscale objects

A simple and versatile approach to constructing patterns on a solid surface using nanoscale objects is demonstrated. The approach is essentially an inlaying process, in which recess patterns fabricated on a surface are selectively filled with nanoscale objects. The objects are anchored firmly on the surface due to the spatial confinement provided by the recess structures. Protein molecules and inorganic nanoparticles are used in this demonstration. Cyclic voltammetry is used to detect electron transfer signals from patterns of protein molecules. The approach suggests a potentially fast, high-throughput and versatile technique for constructing architectural structures on a solid surface using nanoscale objects.     

一维硅锗纳米复合材料的制备及在场效应晶体管中的应用

一维硅锗纳米复合材料，主要包括硅锗纳米线异质结与纳米管，具有优异的电学、光学等性能，易与现代以硅为基础的微电子工业相兼容，所以在纳米器件等领域得到了广泛重视。总结了一维硅锗纳米复合材料的研究现状和相关的制备方法，重点评述了在纳米场效应晶体管中的应用，并对其研究前景做了展望。     

Self-assembled nanoscale ferroelectrics

Multifunctional ferroelectric materials offer a wide range of useful properties, from switchable polarization that can be applied in memory devices to piezoelectric and pyroelectric properties used in actuators, transducers and thermal sensors. At the nanometer scale, however, material properties are expected to be different from those in bulk. Fundamental problems such as the super-paraelectric limit, the influence of the free surface, and of interfacial and bulk defects on ferroelectric switching, etc., arise when scaling down ferroelectrics to nanometer sizes. In order to study these size effects, fabrication methods of high quality nanoscale ferroelectric crystals have to be developed. The present paper briefly reviews self-patterning and self-assembly fabrication methods, including chemical routes, morphological instability of ultrathin films, microemulsion, and self-assembly lift-off, employed up to the date to fabricate ferroelectric structures with lateral sizes in the range of few tens of nanometers.     

Vibration analysis of parabolic shear-deformable piezoelectrically actuated nanoscale beams incorporating thermal effects

Thermoelectric-mechanical vibration behavior of functionally graded piezoelectric (FGP) nanobeams is first investigated in this article, based on the nonlocal theory and third-order parabolic beam theory by presenting a Navier-type solution. Electro-thermo-mechanical properties of a nanobeam are supposed to change continuously throughout the thickness based on the power-law model. To capture the small-size effects, Eringen's nonlocal elasticity theory is adopted. Using Hamilton's principle, the nonlocal governing equations for the third-order, shear deformable, piezoelectric, FG nanobeams are obtained and they are solved applying an analytical solution. By presenting some numerical results, it is demonstrated that the suggested model presents accurate frequency results of FGP nanobeams. The influences of several parameters, including external electric voltage, power-law exponent, nonlocal parameter, and mode number on the natural frequencies of the size-dependent FGP nanobeams are discussed in detail. The results should be relevant to the design and application of the piezoelectric nanodevices.