Showing papers in "IEEE Transactions on Nanotechnology in 2010"

Single-Conductor Transmission-Line Model of Multiwall Carbon Nanotubes

Abstract: The equivalent single-conductor model of a multiwall carbon nanotube (MWCNT) interconnect is derived analytically from the rigorous formulation of the complex multiconductor transmission-line propagation equations. The expressions of the per-unit-length (p.u.l.) equivalent quantum capacitance and kinetic inductance are obtained in closed form. A new accurate approximated expression of the equivalent p.u.l. quantum capacitance is proposed. It is demonstrated, through analytical derivations and numerical calculations, that the new expression is valid for the most of MWCNT interconnect configurations, whereas a more simplified formula, obtained on the basis of qualitative considerations, produces high approximation errors. The proposed model is solved in both the frequency and time domains. Transient analyses are performed in order to predict the attenuation and time delay of a pulse signal transmitted along an MWCNT as a function of the tube length and number of shells. Simulation results are also compared with measured data available in literature.

A New Method for Robust Damping and Tracking Control of Scanning Probe Microscope Positioning Stages

Abstract: This paper demonstrates a simple second-order controller that eliminates scan-induced oscillation and provides integral tracking action. The controller can be retrofitted to any scanning probe microscope with position sensors by implementing a simple digital controller or operational amplifier circuit. The controller is demonstrated to improve the tracking bandwidth of an NT-MDT scanning probe microscope from 15 Hz (with an integral controller) to 490 Hz while simultaneously improving gain-margin from 2 to 7 dB. The penalty on sensor induced positioning noise is minimal. A unique benefit of the proposed control scheme is the performance and stability robustness with respect to variations in resonance frequency. This is demonstrated experimentally by a change in resonance frequency from 934 to 140 Hz. This change does not compromise stability or significantly degrade performance. For the scanning probe microscope considered in this paper, the noise is marginally increased from 0.30 to 0.39 nm rms. Open and closed-loop experimental images of a calibration standard are reported at speeds of 1, 10, and 31 lines per second (with a scanner resonance frequency of 290 Hz). Compared with traditional integral controllers, the proposed controller provides a bandwidth improvement of greater than 10 times. This allows faster imaging and less tracking lag at low speeds.

On-Chip Clocking for Nanomagnet Logic Devices

Abstract: We report local control of nanomagnets that can be arranged to perform computation in a cellular automata-like architecture. This letter represents the first demonstration of deterministically placed quantum-dot cellular automata (QCA) devices (of any implementation), where devices are controlled by on-chip local fields.

Reversible Logic-Based Concurrently Testable Latches for Molecular QCA

Abstract: Nanotechnologies, including molecular quantum dot cellular automata (QCA), are susceptible to high error rates. In this paper, we present the design of concurrently testable latches (D latch, T latch, JK latch, and SR latch), which are based on reversible conservative logic for molecular QCA. Conservative reversible circuits are a specific type of reversible circuits, in which there would be an equal number of 1's in the outputs as there would be on the inputs, in addition to one-to-one mapping. Thus, conservative logic is parity-preserving, i.e., the parity of the input vectors is equal to that of the output vectors. We analyzed the fault patterns in the conservative reversible Fredkin gate due to a single missing/additional cell defect in molecular QCA. We found that if there is a fault in the molecular QCA implementation of Fredkin gate, there is a parity mismatch between the inputs and the outputs, otherwise the inputs parity is the same as outputs parity. Any permanent or transient fault in molecular QCA can be concurrently detected if implemented with the conservative Fredkin gate. The design of QCA layouts and the verification of the latch designs using the QCADesigner and the HDLQ tool are presented.

Traveling-Wave Metal/Insulator/Metal Diodes for Improved Infrared Bandwidth and Efficiency of Antenna-Coupled Rectifiers

Abstract: We evaluate a technique to improve the performance of antenna-coupled diode rectifiers working in the IR. Efficient operation of conventional, lumped-element rectifiers is limited to the low terahertz. By using femtosecond-fast MIM diodes in a traveling-wave (TW) configuration, we obtain a distributed rectifier with improved bandwidth. This design gives higher detection efficiency due to a good match between the antenna impedance and the geometry-controlled impedance of the TW structure. We have developed a method for calculating the responsivity of the antenna-coupled TW detector. Three TW devices, made from different materials, are simulated to obtain their impedance and responsivity at 1.5, 3, 5, and 10 μm wavelengths. The characteristic impedance of a 100-nm-wide TW is in the range of 50 Ω and has a small variation with frequency. A peak responsivity of 0.086 A/W is obtained for the Nb-Nb2 O5 -Nb TW diode at 3-μm wavelength. This corresponds to a quantum efficiency of 3.6% and is a significant improvement over the antenna-coupled lumped-element diode rectifiers. For IR imaging, this results in a normalized detectivity of 4 × 106 Jones at 3 μm. We have identified several ways for improving the detectivity of the TW detector. Possible methods include decreasing the diode resistance, reducing the noise, and increasing the effective antenna area.

Nanopore Sequencing: Electrical Measurements of the Code of Life

Abstract: Sequencing a single molecule of deoxyribonucleic acid (DNA) using a nanopore is a revolutionary concept because it combines the potential for long read lengths (>5 kbp) with high speed (1 bp/10 ns), while obviating the need for costly amplification procedures due to the exquisite single molecule sensitivity. The prospects for implementing this concept seem bright. The cost savings from the removal of required reagents, coupled with the speed of nanopore sequencing places the $1000 genome within grasp. However, challenges remain: high fidelity reads demand stringent control over both the molecular configuration in the pore and the translocation kinetics. The molecular configuration determines how the ions passing through the pore come into contact with the nucleotides, while the translocation kinetics affect the time interval in which the same nucleotides are held in the constriction as the data is acquired. Proteins like ?-hemolysin and its mutants offer exquisitely precise self-assembled nanopores and have demonstrated the facility for discriminating individual nucleotides, but it is currently difficult to design protein structure ab initio, which frustrates tailoring a pore for sequencing genomic DNA. Nanopores in solid-state membranes have been proposed as an alternative because of the flexibility in fabrication and ease of integration into a sequencing platform. Preliminary results have shown that with careful control of the dimensions of the pore and the shape of the electric field, control of DNA translocation through the pore is possible. Furthermore, discrimination between different base pairs of DNA may be feasible. Thus, a nanopore promises inexpensive, reliable, high-throughput sequencing, which could thrust genomic science into personal medicine.

Enhanced Electromagnetic Interference Shielding Through the Use of Functionalized Carbon-Nanotube-Reactive Polymer Composites

Abstract: We report on a new principle yielding enhanced electromagnetic shielding, using as an example a composite comprised of carbon nanotubes (CNTs) integrated with a reactive ethylene terpolymer (RET). Such composites were synthesized through the chemical reaction of the functional groups on the CNT with the epoxy linkage of the RET polymer. The main advantages of these composites include good dispersion with low electrical percolation volume fractions (~0.1 volume%), yielding outstanding microwave shielding efficiency for electromagnetic interference applications. The shielding effectiveness was characterized for both single-walled and multiwalled CNT-based composites and was much enhanced in the former. The specific roles of absorption and reflection in determining the total shielding, as a function of the nanotube filling fraction, is also discussed.

Continuum Models Incorporating Surface Energy for Static and Dynamic Response of Nanoscale Beams

Abstract: Nanoscale beams are commonly found in nanomechanical and nanoelectromechanical systems (NEMS) and other nanotechnology-based devices. Surface energy has a significant effect on nanoscale structures and is associated with their size-dependent behavior. In this paper, a general mechanistic model based on the Gurtin-Murdoch continuum theory accounting for surface energy effects is presented to analyze thick and thin nanoscale beams with an arbitrary cross section. The main contributions of this paper are a set of closed-form analytical solutions for the static response of thin and thick beams under different loading (point and uniformly distributed) and boundary conditions (simply-supported, cantilevered, and clamped ends), as well as the solution of the free vibration characteristics of such beams. Selected numerical results are presented for aluminum and silicon beams to demonstrate their salient response features. It is shown that classical beam theory is not accurate in situations where the surface residual stress and/or surface elastic constants are relatively large. An intrinsic length scale for beams is identified that depends on beam surface properties and cross-sectional shape. The present work provides a convenient set of analytical tools for researchers working on NEMS design and fabrication to understand the static and dynamic behavior of nanoscale beams including their size-dependent behavior and the effects of common boundary conditions.

Design and Implementation of Functional Nanoelectronic Interfaces With Biomolecules, Cells, and Tissue Using Nanowire Device Arrays

Abstract: Nanowire FETs (NWFETs) are promising building blocks for nanoscale bioelectronic interfaces with cells and tissue since they are known to exhibit exquisite sensitivity in the context of chemical and biological detection, and have the potential to form strongly coupled interfaces with cell membranes. We present a general scheme that can be used to assemble NWs with rationally designed composition and geometry on either planar inorganic or biocompatible flexible plastic surfaces. We demonstrate that these devices can be used to measure signals from neurons, cardiomyocytes, and heart tissue. Reported signals are in millivolts range, which are equal to or substantially greater than those recorded with either planar FETs or multielectrode arrays, and demonstrate one unique advantage of NW-based devices. Basic studies showing the effect of device sensitivity and cell/substrate junction quality on signal magnitude are presented. Finally, our demonstrated ability to design high-density arrays of NWFETs enables us to map signal at the subcellular level, a functionality not enabled by conventional microfabricated devices. These advances could have broad applications in high-throughput drug assays, fundamental biophysical studies of cellular function, and development of powerful prosthetics.

An Optimized Majority Logic Synthesis Methodology for Quantum-Dot Cellular Automata

Abstract: Quantum-dot cellular automata (QCA) has been widely considered as a replacement candidate for complementary metal-oxide semiconductor (CMOS). The fundamental logic device in QCA is the majority gate. In this paper, we propose an efficient methodology for majority logic synthesis of arbitrary Boolean functions. We prove that our method provides a minimal majority expression and an optimal QCA layout for any given three-variable Boolean function. In order to obtain high-quality decomposed Boolean networks, we introduce a new decomposition scheme that can decompose all Boolean networks efficiently. Furthermore, our method removes all the redundancies that are produced in the process of converting a decomposed network into a majority network. In existing methods, however, these redundancies are not considered. We have built a majority logic synthesis tool based on our method and several existing logic synthesis tools. Experiments with 40 multiple-output benchmarks indicate that, compared to existing methods, 37 benchmarks are optimized by our method, up to 31.6%, 78.2%, 75.5%, and 83.3% reduction in level count, gate count, gate input count, and inverter count, respectively, is possible with the average being 4.7%, 14.5%, 13.3%, and 26.4%, respectively. We have also implemented the QCA layouts of 10 benchmarks by using our method. Results indicate that, compared to existing methods, up to 33.3%, 76.7%, and 75.5% reduction in delay, cell count, and area, respectively, is possible with the average being 8.1%, 28.9%, and 29.0%, respectively.

Design of a CNTFET-Based SRAM Cell by Dual-Chirality Selection

Abstract: This paper proposes a new design of a highly stable and low-power static RAM (SRAM) cell using carbon nanotube FETs (CNTFETs) that utilizes different threshold voltages for best performance. In a CNT, the threshold voltage can be adjusted by controlling the chirality vector (i.e., the diameter). In the proposed six-transistor SRAM cell design, while all CNTFETs of the same type have the same chirality, n-type and p-type transistors have different chiralities, i.e., a dual-diameter design of SRAM cell. As figures of merit, stability, power dissipation, and write time are considered when selecting the chirality for the best overall performance. A new metric, denoted as ?SPR,? is proposed to capture these figures of merit. This metric shows that a CNTFET-based SRAM cell provides an ?SPR? that is four times higher than for its CMOS counterpart that has the same configuration, thus attaining superior performance. Finally, the sensitivity of the CNTFET SRAM design to process variations is assessed and compared with its CMOS design counterpart. Extensive simulations have been performed to investigate the distribution of the power and delay of the CNTFET-based SRAM cell due to variations in the diameter, supply voltage, and temperature of the CNTFETs. The CNTFET-based SRAM cell demonstrates that it tolerates the process, power supply voltage, and temperature variations significantly better than its CMOS counterpart.

Plasmonic Metamaterial Cloaking at Optical Frequencies

Abstract: In this paper, we present the design of cylindrical and spherical electromagnetic cloaks working at visible frequencies. The cloak design is based on the employment of layered structures consisting of alternating plasmonic and nonplasmonic materials, and exhibiting the collective behavior of an effective epsilon-near-zero material at optical frequencies. The design of a cylindrical cloak to hide cylindrical objects is first presented. Two alternative layouts are proposed, and both magnetic and nonmagnetic objects are considered. Then, the design of spherical cloaks is also presented. The full-wave simulations presented throughout the paper confirm the validity of the proposed setup, and show how this technique can be used to reduce the observability of cylindrical and spherical objects. The effect of the losses is also considered.

Strain-Dependent Resistance of PDMS and Carbon Nanotubes Composite Microstructures

Abstract: We report the development of a micropatterned nanocomposite composed of elastomer poly(dimethylsiloxane) (PDMS) and multiwalled carbon nanotubes, and its resistive response to large mechanical deformations. Microstructures of nanocomposite were embedded into unfilled PDMS to work as a strain sensor and devices were fabricated with simplicity through microcontact printing and screen-printing approaches. When subject to large tensile strains (>45%), nanocomposite sensors revealed significant change in electrical resistance. Also, cyclic loadings of sample yielded repeatable resistive responses. An interesting observation of hysteresis effect was confirmed with multiple tests and possible underlying mechanisms were discussed. As a flexible and biocompatible elastomer, the micropatterned nanocomposite could prove useful in sensing biomechanical strains and other various applications.

Numerically Efficient Modeling of CNT Transistors With Ballistic and Nonballistic Effects for Circuit Simulation

Abstract: This paper presents an efficient carbon nanotube (CNT) transistor modeling technique that is based on cubic spline approximation of the nonequilibrium mobile charge density. The approximation facilitates the solution of the self-consistent voltage equation in a CNT so that calculation of the CNT drain-source current is accelerated by at least two orders of magnitude. A salient feature of the proposed technique is its ability to incorporate both ballistic and nonballistic transport effects without a significant computational cost. The proposed models have been extensively validated against reported CNT ballistic and nonballistic transport theories and experimental results.

Integration of Carbon Nanotubes to C-MEMS for On-chip Supercapacitors

Abstract: Carbon nanotubes (CNTs)/carbon microelectromechanical systems (C-MEMS) composites were fabricated as electrode materials for on-chip supercapacitors. By using photolithography and pyrolysis process, 3-D C-MEMS architectures were prepared. The iron catalyst particles were conformally coated on the C-MEMS by electrostatic spray deposition (ESD) and CNTs were synthesized on the surfaces of C-MEMS by catalytic CVD method. The CNT/C-MEMS composites exhibited higher specific capacitance than C-MEMS. Furthermore, the composites with more homogeneous CNTs showed better capacitance. After treatment of oxygen plasma, the specific capacitance of the composite increased due to the contribution of oxygen functional groups.

Modeling SWCNT Bandgap and Effective Mass Variation Using a Monte Carlo Approach

Abstract: Synthesizing single-walled carbon nanotubes (SWCNTs) with accurate structural control has been widely acknowledged as an exceedingly complex task culminating in the realization of CNT devices with uncertain electronic behavior. In this paper, we apply a statistical approach in predicting the SWCNT bandgap and effective mass variation for typical uncertainties associated with the geometrical structure. This is first carried out by proposing a simulation-efficient analytical model that evaluates the bandgap (Eg) of an isolated SWCNT with a specified diameter (d) and chirality (?). Similarly, we develop an SWCNT effective mass model, which is applicable to CNTs of any chirality and diameters >1 nm. A Monte Carlo method is later adopted to simulate the bandgap and effective mass variation for a selection of structural parameter distributions. As a result, we establish analytical expressions that separately specify the bandgap and effective mass variability (Eg?, m? *) with respect to the CNT mean diameter (d?) and standard deviation (d?). These expressions offer insight from a theoretical perspective on the optimization of diameter-related process parameters with the aim of suppressing bandgap and effective mass variation.

A Novel Nanometeric Plasmonic Refractive Index Sensor

Abstract: A novel surface plasmon-polariton (SPP) refractive index sensor based on the coupling of a split waveguide mode with a cavity mode in the metal is proposed and studied in this paper. Both analytic and simulated results show that the resonant wavelength of the sensor has a linear relationship with the refractive index of materials under sensing. Based on the relationship, the refractive index of the material can be obtained from the detection of the resonant wavelength. The resolution of refractive index of the nanometeric sensor can reach as high as 10-6, given the wavelength resolution of 0.01 nm. It can be applied to high-resolution biosensor.

Development of Infrared Detectors Using Single Carbon-Nanotube-Based Field-Effect Transistors

Abstract: Carbon nanotube is a promising material to fabricate high-performance nanoscale-optoelectronic devices owing to its unique 1-D structure. In particular, different types of carbon-nanotube-infrared detectors have been developed. However, most previous reported carbon-nanotube-IR detectors showed poor device characteristics due to limited understanding of their working principles. In this paper, three types of IR detectors were fabricated using carbon-nanotube field effect transistors (CNTFETs) to investigate their performance: 1) symmetric Au-CNT-Au CNTFET IR detector; 2) symmetric Ag-CNT-Ag CNTFET IR detector; and 3) asymmetric Ag-CNT-Au CNTFET IR detector. The theoretical analyses and experimental results have shown that the IR detector using an individual single-wall carbon nanotube (SWCNT), with asymmetric Ag-CNT-Au CNTFET structure, can suppress dark current and increase photocurrent by electrostatic doping. As a result, an open-circuit voltage of 0.45 V under IR illumination was generated, which is the highest value reported to date for an individual SWCNT-based photodetector. The results reported in this paper have demonstrated that the CNTFET can be used to develop high-performance IR sensors.

Characterization and Functionalization of Biogenic Gold Nanoparticles for Biosensing Enhancement

Abstract: The unique tunable physicochemical properties of gold nanoparticles (AuNPs). In addition to their excellent biological compatibility, conducting properties, and high surface-to-volume ratio make them ideal candidates for electronic signal transduction of biological recognition events in biosensing platforms. Commonly, AuNPs are synthesized by chemical reduction of HAuCl4 and the introduction of a protective agent (stabilizer). In recent years, alternative biosynthetic approaches have been explored using microorganisms as bionanofactories to produce metal nanoparticles. AuNP biosynthesis procedures include the use of fungi and bacteria strains. In this study, the alkalothermophilic actinomycetes Thermomonospora curvata, Thermomonospora fusca, and Thermomonospora chromogena were used for the extracellular biosynthesis of AuNP. Optimal growth and biosynthesis conditions were established for each microorganism. The average AuNP size obtained was in the range of 30-60 nm. The AuNP were characterized using UV-Vis spectra, transmission electron microscopy images, and particle-size distribution. The obtained particles were monodisperse and water soluble. In order to improve stability, glutaraldehyde was used to functionalize the AuNP after synthesis. The green-chemistry AuNP obtained in this study can potentially be used to enhance biosensing applications: as transducers or electroactive labels, especially in nanoparticle-based electrochemical DNA detection systems.

Self-Adaptive Write Circuit for Low-Power and Variation-Tolerant Memristors

Abstract: Memristive devices such as memristors that have been intensively studied for their possibilities as a strong candidate for future memories are known to have two problems. First, they need a large current in write operation, and second their process-V -temperature (PVT) variations are large compared with the conventional DRAM and FLASH memories. Moreover, the large writing current can be magnified with PVT variations. In this letter, a new write circuit is proposed to prevent unnecessary power loss by using a self-adjusting circuit for properly sizing the writing pulsewidth, thereby minimizing power consumption. The simulation results show that self-adjusting the pulsewidth can save power by 76% on average, compared to the conventional write circuit with a fixed pulsewidth.

Electronic Properties of Nitrogen-Atom-Adsorbed Graphene Nanoribbons With Armchair Edges

Abstract: Calculation of electronic structures has been performed for graphene nanoribbons with eight-armchair edges containing nitrogen or boron substitutional impurity by using ab initio density functional theory. It is found that the electronic structures of the doped graphene nanoribbon are different from those of doped carbon nanotubes. The impurity levels are autoionized, so that the relevant charge carriers occupy the conduction or valence bands. The donor and acceptor levels are derived mainly from the lowest unoccupied orbital and highest occupied orbital of pristine graphene nanoribbon, respectively. N introduces an impurity level above the donor level, while an impurity level introduced by B is below the acceptor level. The doped graphene nanoribbons with armchair edges are inactive compared to the doped carbon nanotubes around the impurity site, which may indicate that the doped graphene nanoribbons with armchair edges could be more stable than the doped carbon nanotubes at the ambient.

Experimental Demonstration of Fanout for Nanomagnetic Logic

Abstract: Nanomagnet logic (NML) shows great promise as an alternative to conventional digital architectures. We present the first experimental demonstration of fanout using magnetizations of nanomagnets in the NML scheme. Specifically, we show magnetic force microscopy images of functioning fanout circuits.

Plasmonics for Laser Beam Shaping

Abstract: This paper reviews our recent work on laser beam shaping using plasmonics. We demonstrated that by integrating properly designed plasmonic structures onto the facet of semiconductor lasers, their divergence angle can be dramatically reduced by more than one orders of magnitude, down to a few degrees. A plasmonic collimator consisting of a slit aperture and an adjacent 1-D grating can collimate laser light in the laser polarization direction; a collimator consisting of a rectangular aperture and a concentric ring grating can reduce the beam divergence both perpendicular and parallel to the laser polarization direction, thus achieving collimation in the plane perpendicular to the laser beam. The devices integrated with plasmonic collimators preserve good room-temperature performance with output power comparable to that of the original unpatterned lasers. A collimator design for one wavelength can be scaled to adapt to other wavelengths ranging from the visible to the far-IR regimes. Plasmonic collimation offers a compact and integrated solution to the problem of laser beam collimation and may have a large impact on applications such as free-space optical communication, pointing, and light detection and ranging. This paper opens up major opportunities in wavefront engineering using plasmonic structures.

Ultralow Voltage Nanoelectronics Powered Directly, and Solely, From a Tree

Abstract: Complex patterns of electrical potential differences exist across the structure of a tree. We have characterized these voltages, and measured values ranging from a few millivolts to a few hundred millivolts for Bigleaf maple trees. These potential differences provide a unique opportunity to power nanoelectronic circuits directly from a tree. We have designed, constructed, and successfully tested two ICs, powered solely through a connection to Bigleaf maple trees. The first circuit, built in a 130-nm technology, creates a stable 1.1 V supply from input voltages as low as 20 mV, and can be deployed to generate a usable voltage level for standard circuits. The second circuit, fabricated in 90-nm technology is a timer, operating at 0.045 Hz and can be used for time keeping in stand-alone sensor network nodes. The boost circuit and timer consume 10 and 2.5 nW of power during operation, respectively.

Parallel Recording of Single Ion Channels: A Heterogeneous System Approach

Abstract: The convergence of integrated electronic devices with nanotechnology structures on heterogeneous systems presents promising opportunities for the development of new classes of rapid, sensitive, and reliable sensors. The main advantage of embedding microelectronic readout structures with sensing elements is twofold. On the one hand, the SNR is increased as a result of scaling. On the other, readout miniaturization allows organization of sensors into arrays. The latter point will improve sensing accuracy by using statistical methods. However, accurate interface design is required to establish efficient communication between ionic-based and electronic-based signals. This paper shows a first example of a concurrent readout system with single-ion channel resolution, using a compact and scalable architecture. An array of biological nanosensors is organized on different layers stacked together in a mixed structure: fluidics, printed circuit board, and microelectronic readout. More specifically, an array of microholes machined into a polyoxymethylene homopolymer (POMH or Delrin) device coupled with ultralow noise sigma-delta converters current amplifiers, is used to form bilayer membranes within which ion channels are embedded. It is shown how formation of multiple artificial bilayer lipid membranes (BLMs) is automatically monitored by the interface. The system is used to detect current signals in the pA range, from noncovalent binding between single, BLM-embedded ?-hemolysin pores and s-cyclodextrin molecules. The current signals are concurrently processed by the readout structure.

Size-Dependent Infiltration and Optical Detection of Nucleic Acids in Nanoscale Pores

Abstract: Experiments and complimentary simulations are presented to demonstrate the size-dependent infiltration and detection of variable length nucleic acids in porous silicon with controllable pore diameters in the range of 15-60 nm. The pore diameter must be tuned according to target molecule size in order to most effectively balance sensitivity and size-exclusion. A quantitative relationship between pore size (15-60 nm), nucleic acid length (up to ~ 5.3 nm), and sensor response is presented with smaller molecules detected more sensitively in smaller pores as long as the pore diameter is sufficient to enable molecular infiltration and binding in the pores. The density of probe molecules on the pore walls and subsequent hybridization efficiency for target molecule binding are also reported and are shown to depend strongly on the method of infiltration as well as the target molecule size.

Teleoperated 3-D Force Feedback From the Nanoscale With an Atomic Force Microscope

Abstract: In this study, 3-D experimental teleoperated force feedback during contact with nanoscale surfaces is demonstrated using an atomic force microscope (AFM) on the slave side and a haptic device on the master side. To achieve 3-D force feedback, coupling between one of the horizontal forces and the vertical force is a crucial bottleneck. To solve this coupling issue, a novel force decoupling algorithm is proposed. This algorithm uses local surface slopes, an empirical friction force model, and the haptic device motion angle projected onto the surface to estimate the friction value during experiments. With this estimation, it is possible to decouple the three orthogonal forces acting on the tip of the AFM cantilever. Moreover, using an adaptive observer, parameters of the friction model can be changed online, removing the necessity to calibrate the friction model initially. Finally, a modified passivity-based bilateral control is used to reflect the scaled nanoscale forces to the master side and the operator. The performance of the system is demonstrated on experimental results for flat and non-flat, and hard and soft surfaces.

Pd/Au/SiC Nanostructured Diodes for Nanoelectronics: Room Temperature Electrical Properties

Abstract: Pd/Au/SiC nanostructured Schottky diodes were fabricated embedding Au nanoparticles (NPs) at the metal-semiconductor interface of macroscopic Pd/SiC contacts. The Au NPs mean size was varied controlling the temperature and time of opportune annealing processes. The electrical characteristics of the nanostructured diodes were studied as a function of the NPs mean size. In particular, using the standard theory of thermoionic emission, we obtained the effective Schottky barrier height (SBH) and the effective ideality factor observing their dependence on the annealing time and temperature being the signature of their dependence on the mean NP size. Furthermore, plotting the effective SBH as a function of the effective ideality factor we observe a linear correlation, indicating that the Au NPs act as lateral inhomogeneities in the Schottky diodes according to the Tung's model. Therefore, we can control the size, fraction of covered area, and surface density of such intentionally introduced inhomogeneities. The application of the Tung's model for the electronic transport in inhomogeneous Schottky contacts allow us to obtain, in particular, the homogeneous SBH. These nanostructured diodes are proposed as possible components of integrated complex nanoelectronic devices.

Ion-Channel Biosensors—Part I: Construction, Operation, and Clinical Studies

Abstract: This paper deals with the construction and operation of a novel biosensor that exploits the molecular switching mechanisms of biological ion channels. The biosensor comprises gramicidin A channels embedded in a synthetic tethered lipid bilayer. It provides a highly sensitive and rapid detection method for a wide variety of analytes. In this paper, we outline the fabrication and principle of operation of the ion-channel switch (ICS) biosensor. The results of a clinical study, in which the ion-channel biosensor is used to detect influenza A in untreated clinical samples, is presented to demonstrate the utility of the technology. Fabrication of biochip arrays using silicon chips decorated with ?ink jet? printing is discussed. We also describe how such biochip arrays can be used for multianalyte sensing. Finally, reproducibility/stability issues of the biosensor are addressed.

Toward Cheap Disposable Sensing Devices for Biological Assays

Abstract: There is a significant demand for small, portable, and inexpensive analytical devices, which can be used in a wide range of sensing applications (e.g., food monitoring, detection of chemical, biological poisoning agents, environmental monitoring, medical diagnostics, military defense, etc.). Sensors based on organic semiconducting polymers, which are suitable for large-area, low-cost, flexible, and eventually single-use throwaway electronics, provide a unique opportunity in that sense. We report on low-operating voltage organic field-effect transistor devices, which can be used as sensors in electrolytes and liquid media, using a biofunctionalized, biocompatible, regioregular poly(3-hexylthiophene) semiconducting layer. Measurements in electrolytes and complex media relevant for cell analysis have shown that the devices can be directly used as ion-sensitive transducers and are suitable for in vitro biosensing applications. With the demonstration of biocompatible semiconducting polymeric devices, we have overcome a substantial hurdle for the realization of low-cost and mass-produced sensors, opening new possibilities of biological sensing using organic devices.