Nanometer Gap Research Articles

Dilation of nanonatennas induced by an electromagnetic source

The illumination of plasmonic mesostructures produces high confinement of light in their vicinity. This confinement of light can be enhanced in the gap between the two metallic nanorods of a nanonantenna, in particular for the design of biosensors. The nanometric gap can be reduced if the elevation of temperature of the nanonantenna is sufficient, and therefore the fine tuning of the sensor requires the description of the photo-thermal induced dilation. The multiphysics problem associated to such photo-thermal and mechanical effects is modeled through a Finite Element Method (FEM). The problem consists in computing the electromagnetic field, the temperature and the induced dilation surface. This contribution consists in discussing the numerical efficiencies of a sequential, and a coupled approaches, especially in terms of adaptive meshing of the space of computation. The relationship between the field enhancement and the reduction of the gap is studied. Finally the validity of the 2D multiphysic model is discussed.

Electronic conduction and microstructure in polymer composites filled with carbonaceous particles

Physical and physico-chemical properties of polymer filled with carbon black (CB) particles, namely, the microstructure dependence of these properties, are not only interesting on their own but are particularly important for electronic applications as they can impose limits on the sensitivity of a device. With this purpose, we report on an experimental study of the structural and electrical properties of semi-crystalline ethylene-co-butyl acrylate polymer filled with conductive CB nano-particles. We found that the value of the direct current conductivity exhibits a jump of 12 orders of magnitude over a small change in CB concentration and is due to a percolation-like behavior. To assess the temperature evolution of supercolative samples, we present measurements of the conductivity as function of temperature. Above the glass transition temperature of the polymer, the CB network restricts the motions of the polymer chains. This behavior was ascribed to the change in CB mesostructure in the polymer matrix as probed by scanning electron microscopy and atomic force microscopy as well as to the difference in the thermal expansion between the two phases. In addition to the observed conductivity increase, the effect of adding CB particles in the polymer matrix is to increase the thermal stability as is probed by thermogravimetric analysis tests. The room temperature alternating current conductivity, studied over the frequency range from 100 Hz to 15 MHz, is interpreted as arising mainly from inter-aggregate polarization effects. By considering carefully the CB content of the alternating current conductivity, we found that our experimental data agree well with the Sheng’s model of fluctuation-induced tunnelling of charge carriers over nanometric gaps between adjacent CB aggregates. For studying the filler content dependence of the effective permittivity, several mixing laws and effective medium theories have been used. The observed discrepancies between our experimental data and these theoretical predictions may be occur partly because these analysis contain an inaccurate knowledge of the physicochemical properties of the carbonaceous phase, give a poor description of the interfaces in these complex heterostructures, or both. As part of the present investigation, present results are compared to transport properties of polystyrene-cobutyl acrylate latex and epoxy resin matrices filled with different loadings of multiwalled carbon nanotubes (MWCNT) and over wide temperature and frequency ranges. It is remarkable that the MWCNT’s anisotropy (length-to-diameter ratio close to 100) manifests itself in percolation-like behavior with lower threshold volume fraction and different mesostructure than that evidenced for CB filled samples.

Suspended SWNT electrode with nanosize gaps

Abstract We report a robust method to fabricate a single walled carbon nanotube (SWNT) electrode array with nanosize gaps. As a first step, several SWNTs are suspended between a pair of preformed gold electrodes utilizing dielectrophoresis (DEP) and turned into a rope configuration by capillary densification during drying process. Electrical breakdown is followed to make a gap in the SWNT rope and the dimension of the gap can be controlled by the bias sweep rate. When an electric voltage is applied to the SWNT rope, electrical joule heating increases the temperature, oxidizes the SWNT, and the rope eventually breaks at the midpoint. The SWNT electrodes are successfully fabricated with gaps in the range of 1–60 nm by controlling the bias sweep rate. As a demonstration in nanoscale electronics, the electrical resistance of fullerene (dimension of ∼1 nm) is measured by capturing it between the SWNT electrodes with one nanometer gap.

Microelectromechanical accelerator of solids

A possibility of using electric field energy for accelerating solids to significant velocities (1–10 km/s) is considered. A microelectromechanical electrostatic energy converter is used as a capacitive linear actuator, where energy conversion is performed in nanometer gaps, which allows the specific energy density of ∼(3–10) J/m2 and more to be reached in a single act of energy conversion at clock frequencies of 1 MHz and more. Such parameters allow pumping of electric field energy up to 10–30 MJ with the 1 m2 area of the energy converter, with subsequent conversion of this energy to the kinetic energy of object motion. Specific features of the structure of the high-energy-intensity electrostatic energy converter and its operation at high clock frequencies in the regime of acceleration of a slider with a mass up to 10 kg are considered.

How Chain Plasmons Govern the Optical Response in Strongly Interacting Self-Assembled Metallic Clusters of Nanoparticles

Self-assembled clusters of metallic nanoparticles separated by nanometric gaps generate strong plasmonic modes that support both intense and localized near fields. These find use in many ultrasensitive chemical and biological sensing applications through surface enhanced Raman scattering (SERS). The inability to control at the nanoscale the structure of the clusters on which the optical response crucially depends, has led to the development of general descriptions to model the various morphologies fabricated. Here, we use rigorous electrodynamic calculations to study clusters formed by a hundred nanospheres that are separated by ∼1 nm distance, set by the dimensions of the macrocyclic molecular linker employed experimentally. Three-dimensional (3D) cluster structures of moderate compactness are of special interest since they resemble self-assembled clusters grown under typical diffusion-limited aggregation conditions. We find very good agreement between the simulated and measured far-field extinction spectra, supporting the equivalence of the assumed and experimental morphologies. From these results we argue that the main features of the optical response of two- and three-dimensional clusters can be understood in terms of the excitation of simple units composed of different length resonant chains. Notably, we observe a qualitative difference between short- and long-chain modes in both spectral response and spatial distribution: dimer and short-chain modes are observed in the periphery of the cluster at higher energies, whereas inside the structure longer chain excitation occurs at lower energies. We study in detail different configurations of isolated one-dimensional chains as prototypical building blocks for large clusters, showing that the optical response of the chains is robust to disorder. This study provides an intuitive understanding of the behavior of very complex aggregates and may be generalized to other types of aggregates and systems formed by large numbers of strongly interacting particles.

A Novel CMOS Device Capable of Measuring Near-Field Thermal Radiation

We report on the design, fabrication, and characterization of a micro plane-plane geometry CMOS device, which has a heat emitter and a heat receiver, capable of studying the near-field radiative heat transfer at a 550 nm gap. Under high vacuum conditions, the heat emitter is heated by supplying driving currents and heated again after removing the heat receiver. The heating power difference between the two kinds of heating experiments indicates the existence of a proximity effect in the heat transfer between the emitter and the receiver. Our experiments pave the way towards overcoming the construction difficulty of plane-plane geometry with a nanometer gap.

Efficient optical trapping using small arrays of plasmonic nanoblock pairs

We report that a small two-dimensional array of gold nanoblock pairs separated by a nanometric gap significantly improves the performance of optical trapping compared to a single nanoblock pair. The array of 4 × 4 pairs suppresses the Brownian motion of a trapped 1 μm diameter particle by a factor of six compared to the single pair. In addition, the array enables particle trapping for a longer period of time. These results are essential for biological applications where intense optical irradiation is a concern.

New Design Concepts for the Fabrication of Nanometric Gap Structures: Electrochemical Oxidation of OTS Mono‐ and Bilayer Structures

A reliable nanofabrication concept to engineer metallic nanometric gap structures and to incorporate silver nanoparticles within the gaps utilizing a combination of self-assembly strategies and electrochemical oxidation lithography is developed. The approach uses the differences in oxidation kinetics of n-octadecyltrichlorosilane (OTS) monolayer and bilayer structures. The processes are investigated in detail and form the basis for a new nanofabrication process.

Design of Microcantilever-Based Biosensor with Digital Feedback Control Circuit

This paper present the design of cantilever-based biosensors with new readout, which hold promises as fast and cheap “point of care” device as well as interesting research tools. The fabrication process and related issues of the cantilever based bio-sensor are discussed. Coventorware simulation is carried out to analyze the device behavior. A fully integrated control circuit has been designed to solve manufacturing challenge which will take care of positioning of the cantilever instead of creating nanometer gap between the electrodes. The control circuit will solve the manufacturing challenge faced by the readout methods where it is essential to maintain precise gap between the electrodes. The circuit can take care of variation obtained due to fabrication process and maintain the precise gap between the electrodes by electrostatic actuation. The control circuit consist of analog and digital modules. The reliability issues of the sensor are also discussed.

Plasmonic coupled nanotorch structures leading to uniform surface enhanced Raman scattering detection

Nanocrescent-like structures have become important surface enhanced Raman scattering structures because instead of relying on a few nanometer gap inter-particle plasmonic coupling to achieve local field enhancement, intra-particle plasmonic coupling between the cavity modes and the tip edges are utilized to achieve high local field enhancement at the tips. Our fabrication approach creates 'nanotorch' structures with controllable cavity rim opening and deterministic orientation to yield uniform Raman measurements, consisting of three-dimensional upright-oriented nanocrescent structures resting on nanopillars. Each structure serves as a single SERS substrate. We demonstrate that a nanotorch with a smaller rim opening results in a higher enhancement factor compare to one with a larger opening. More importantly, the uniformity of all the analysed Raman modes of adsorbed benzenethiol is better than 80% due to the consistent, upright orientation of each single nanotorch SERS substrate, paving the way for practical implementation of SERS detection.

Studies on confined crystallization behavior of nanobiocomposites consisting of acetylated bacterial cellulose and poly (lactic acid)

This article deals with the confined crystallization behavior of nanobiocomposites consisting of acetylated bacterial cellulose (BC) and poly(lactic acid) (PLA). PLA/acetylated BC nanobiocomposites were prepared by compressed molding. Nonisothermal crystallization, melting behavior and isothermal crystallization kinetics within confined spaces were investigated by differential scanning calorimetry (DSC). The results indicated that acetylated BC was favorable to the crystallization of PLA at higher temperatures. On one hand, due to better compatibility between acetylated BC and PLA, crystal nucleation and growth of PLA took place while crystallization process of PLA was restricted. Acetylated BC had an effect of heterogeneous nucleation on PLA crystallization. On the other hand, crystal growth of PLA molecular chain was confined within the nanometer gaps between the microfibrils of acetylated BC. The interaction between microfibrils of acetylated BC and PLA also had an effect on the crystal growth of PLA, which resulted in the growth of confined crystallization. As the time course of acetylation became longer and longer, the compatibility of acetylated BC and PLA was enhanced and the crystallization of PLA became more difficult. This result was in accordance with the observation of polarized optical microscope (POM) pictures. Activation energy of crystallization and free energy surface of PLA were reduced in PLA and acetylated BC composites.

Verification of evanescent coupling from subwavelength grating pairs

Near-field evanescent wave coupling of various subwavelength grating pairs, using a 1.55 μm infrared semiconductor laser has been demonstrated for use as an optical MEMS sensor. Subwavelength grating pairs were fabricated on both glass and silicon substrates. When coupled together the effective grating period is not subwavelength and can exhibit several diffraction orders. The 1.55 μm infrared source was incident on the coupled pairs and the first-order output intensity was recorded and compared with the output intensity from simulated results. This demonstrated evanescent wave coupling concept can be applied to MEMS systems with nanometer gap separations (e.g., pressure sensors, biosensors, and accelerometers) to allow for subnanometer displacement detection.

Real-Space Investigation of Electrical Double Layers. Potential Gradient Measurement with a Nanometer Potential Probe

We report measurement of the potential gradient in a nanometer gap between a Au(111) electrode and a gold tip immersed in a NaClO4 solution. A miniaturized potential probe, constructed with a gold ...

A New Method for Measuring Normal Forces with Accurate Gap Control Using a Microfabricated Quartz Resonator for Lubrication at Nanometer Gaps

A new method using a microfabricated quartz double-ended tuning fork (DETF) resonator is presented for simultaneously measuring normal and lateral forces with accurate gap control. The quartz resonator provides high force sensitivity due to its smaller device size. An optical fiber probe for lateral force detection was combined with the resonator by adding a support frame, thereby for increasing lateral rigidity. The normal and lateral forces exerted by a lubricant in nanometer-sliding gaps were simultaneously measured using the quartz DETF resonator with the optical fiber probe. This method is useful for clarifying the tribological properties in small sliding gaps for micro/nano-mechanical devices such as the head–disk interface of hard disk drives.

Generation of Surface Plasmon Polariton Using Plasmonic Resonant Cavity Based on Microdisk Laser

We study the generation of surface plasmon polariton and its extraction efficiency from a microdisk-based plasmonic source to a metal-insulator-metal (MIM) waveguide. The field distribution is no longer a whispering gallery mode commonly found in microdisk lasers but hybridized with surface plasmon polariton. We observe the steady-state intensity of the surface plasmon polariton mode inside the plasmonic microdisk structure at 1.47- μm wavelength. This field intensity is extracted efficiently to a MIM plasmonic waveguide through a nanometer gap. The extraction efficiency reaches 60%.

Gas sensing of colloidal polyaniline in a chemoresistor consisting of nanometer electrodes

Abstract The high conductivity of colloid-conducting polymers is explained by the networking structures and the hopping mechanisms of the metallic particles [1] , [2] , [4] . To observe how the metallic region and the networking structures differ in sensing NH3 gas, E-beam lithography and electromigration were used to make chemoresistors with nanometer-gap electrodes. Colloid Pani was coated on a nanometer gap as a reaction matrix for the gas. The I–V curves were measured in a vacuum and the NH3 gas was nonlinear. In sensors with a gap of less than 10 nm, there was a two- or threefold increase in the conductivity, and the work function decreased from 600 meV in a vacuum to 250 meV in NH3 gas. In contrast, the conductivity of sensors with gaps of 200 and 500 nm decreased to 1/1000 in the NH3 gas environment. The decrease of the conductivity can be explained by electron–hole annihilation, which appears to occur on the surface of the secondary particles. With comb-type electrodes, the operating voltage can be decreased by three orders of magnitude. In electrodes with 200 and 500 nm gaps, the I–V has a step-type response to NH3 gas.

Phase of the electric field localized at surface-immobilized gold nanospheres determined by second-harmonic interferometry

Gold nanospheres immobilized above a gold surface, with a nanometer gap between, comprise a promising plasmonic system. Although many works have studied the magnitude of the enhanced electric fields that are localized at the plasmonic nanostructure, little is known about their phase. To probe the phase of the electric field localized adjacent to the plasmonic nanostructure, we undertook interferometry for second-harmonic (SH) light from hemicyanine monolayers on the surface-immobilized gold nanospheres (SIGNs), and from a hemicyanine monolayer in the nanogap. The SH phase from the hemicyanine monolayer on the SIGNs was found to be almost opposite to that from the hemicyanine monolayer in the nanogap. This result is supported by a theoretical calculation of the localized electric fields based on higher order multipoles.

Direct Measurement of Electron Transfer Distance Decay Constants of Single Redox Proteins by Electrochemical Tunneling Spectroscopy

We present a method to measure directly and at the single-molecule level the distance decay constant that characterizes the rate of electron transfer (ET) in redox proteins. Using an electrochemical tunneling microscope under bipotentiostatic control, we obtained current−distance spectroscopic recordings of individual redox proteins confined within a nanometric tunneling gap at a well-defined molecular orientation. The tunneling current decays exponentially, and the corresponding decay constant (β) strongly supports a two-step tunneling ET mechanism. Statistical analysis of decay constant measurements reveals differences between the reduced and oxidized states that may be relevant to the control of ET rates in enzymes and biological electron transport chains.

Control of near-field radiative heat transfer via surface phonon–polariton coupling in thin films

The possibility of controlling near-field radiative heat transfer with the use of silicon carbide thin films supporting surface phonon–polaritons in the infrared spectrum is explored. For this purpose, the local density of electromagnetic states is calculated and analyzed within the nanometric gap formed between two SiC films as well as the radiative heat flux exchanged between the thin layers.

A water-soluble carbon nanotube network conjugated by nanoparticles with defined nanometre gaps

Cage-shaped proteins with an affinity for carbonaceous materials were constructed and used to assemble a nanostructure in which single-walled carbon nanotubes are surrounded by cobalt oxide nanoparticles with nanometre gaps. By changing the size of proteins and materials incorporated inside the cavity, similar structures with distinctively different properties can be fabricated.