Showing papers in "IEEE Transactions on Nanotechnology in 2006"

Quantitative theory of nanowire and nanotube antenna performance

Abstract: We present quantitative predictions of the performance of nanotubes and nanowires as antennas, including the radiation resistance, the input reactance and resistance, and antenna efficiency, as a function of frequency and nanotube length. Particular attention is paid to the quantum capacitance and kinetic inductance. We develop models for both far-field antenna patterns as well as near-field antenna-to-antenna coupling. In so doing, we also develop a circuit model for a transmission line made of two parallel nanotubes, which has applications for nanointerconnect technology. Finally, we derive an analog of Hallen's integral equation appropriate for single-walled carbon nanotube antennas

A Low-Power Nonvolatile Switching Element Based on Copper-Tungsten Oxide Solid Electrolyte

Abstract: We describe the materials aspects and electrical characteristics of W-(Cu/WO3)-Cu switching elements. These materials are compatible with back-end-of-line processing in CMOS integrated circuits where both tungsten and copper already play a significant role. Devices based on Cu/WO3 solid electrolytes formed by photodiffusion of copper into tungsten oxide switch via the electrochemical formation of a conducting filament within the high resistance electrolyte film. They are able to switch reversibly between widely spaced nonvolatile resistance states at low voltage ( 125 degC). This difference in behavior was attributed to the observation that the copper tends to oxidize in the plasma-grown oxide whereas the copper in the deposited oxide exists in an unbound state and is, therefore, more able to participate in the switching process

Natural convective heat transfer of suspensions of titanium dioxide nanoparticles (nanofluids)

Abstract: This paper reports an experimental study on the natural convective heat transfer of nanofluids, an area in which little work has been carried out in the past. Aqueous-based titanium-dioxide nanofluids of various concentrations are formulated by using the two-step method and a high shear homogenizer is used to break large aggregates. Instead of the use of dispersant and/or surfactant, the electrostatic repulsion mechanism is adopted to stabilize nanoparticles. The resulting nanofluids are found to be very stable, although the actual measured particle size is much larger than the primary nanoparticle size. The stable nanofluids are then used for both the transient and steady-state heat transfer experiments under natural convection conditions. The results show that the presence of nanoparticles systematically decreases the natural convective heat transfer coefficient under the conditions of this study, which is an observation that contrasts with the previous expectation. Discussion of the results suggests that changes in the nanofluids' thermal conductivity and viscosity could not explain the observed decrease in the heat transfer coefficient, and particle-surface interactions may play an important role.

Understanding the Impact of Inductance in Carbon Nanotube Bundles for VLSI Interconnect Using Scalable Modeling Techniques

Abstract: In this paper, we develop accurate and scalable models for the magnetic inductance in bundles of single-walled carbon nanotubes, which have been proposed as a means to alleviate the increasingly critical resistance problems associated with traditional copper interconnect in very large scale integration (VLSI) applications. The models consider the density and statistical distribution of both metallic and semiconducting nanotubes within the bundle. We evaluate the speed, accuracy, and scalability of our magnetic inductance modeling techniques and previously proposed inductance models. The inductance model with the best performance evaluates the magnetic inductance of nanotube bundles with excellent accuracy when compared to modeling each nanotube individually and provides orders of magnitude improvement in CPU time as the bundle size increases. Leveraging the magnetic inductance modeling techniques, we determine the relative impact of magnetic and kinetic inductance. Based on our results, the relative value of magnetic and kinetic inductance on single-walled carbon nanotube (SWCNT) bundles is highly dependent on the bundle geometry and the per unit length kinetic inductance

Terabit-per-square-inch data storage using phase-change media and scanning electrical nanoprobes

Abstract: A theoretical study of the write, read, and erase processes in electrical scanning probe storage on phase-change media is presented. Electrical, thermal, and phase-transformation mechanisms are considered to produce a physically realistic description of this new approach to ultrahigh-density data storage. Models developed are applied to the design of a suitable storage layer stack with the necessary electrical, thermal, and tribological properties to support recorded bits of nanometric scale. The detailed structure of nanoscale crystalline and amorphous bits is also predicted. For an optimized trilayer stack comprising Ge/sub 2/Sb/sub 2/Te/sub 5/ sandwiched by amorphous or diamond-like carbon layers, crystalline bits were roughly trapezoidal in shape while amorphous bits were semi-ellipsoidal. In both cases, the energy required to write individual bits was very low (of the order of a few hundred picoJoules). Amorphous marks could be directly overwritten (erased), but crystalline bits could not. Readout performance was investigated by calculating the readout current as the tip scanned over isolated bits and bit patterns of increasing density. The highest readout contrast was generated by isolated crystalline bits in an amorphous matrix, but the narrowest readout pulses arose from isolated amorphous marks in a crystalline background. To assess the ultimate density capability of electrical probe recording the role of write-induced intersymbol interference and the thermodynamic stability of nanoscale marks were also studied.

Infrared and Optical Properties of Carbon Nanotube Dipole Antennas

Abstract: The characteristics of armchair carbon nanotube dipole antennas are investigated in the infrared and optical regime. The analysis is based on a classical electromagnetic Halleacuten's-type integral equation, and an axial quantum mechanical conductance function for the tube. It is found that, within a certain frequency span in the GHz-THz range, finite-length carbon nanotube dipoles resonate at approximately integer multiples of one-half of a plasma wavelength. Outside of this range, current resonances are strongly damped. In the optical regime, antenna properties are strongly modulated by interband transitions. General antenna characteristics of finite-length carbon nanotube dipoles are presented, such as input impedance, current profile, gain, and efficiency, and radiation patterns are discussed

Chemical sensing with ZnO nanowire field-effect transistor

Abstract: Zinc oxide nanowires are configured as n-channel FETs. These transistors are implemented as chemical sensors for detection of various chemical gases. It is observed that the nanowire conductance is reduced when it is exposed to oxygen, nitrogen dioxide, ammonia gases at room temperature. Its ammonia sensing behavior is observed to switch from oxidizing to reducing when temperature is increased to 500 K. This effect is mainly attributed to the temperature dependent Fermi level shift. In addition, carbon monoxide is found to increase the nanowire conductance in the presence of oxygen. Furthermore, the detection sensitivity dependence on the nanowire radius is presented

Investigation of the TiN Gate Electrode With Tunable Work Function and Its Application for FinFET Fabrication

Abstract: The titanium nitride (TiN) gate electrode with a tunable work function has successfully been deposited on the sidewalls of upstanding Si-fin channels of FinFETs by using a conventional reactive sputtering. It was found that the work function of the TiN (phiTiN) slightly decreases with increasing nitrogen (N2) gas flow ratio, RN=N2/(Ar+N2) in the sputtering, from 17% to 100%. The experimental threshold voltage (Vth) dependence on the RN shows that the more RN offers the lower Vth for the TiN gate n-channel FinFETs. The composition analysis of the TiN films with different RN showed that the more amount of nitrogen is introduced into the TiN films with increasing RN, which suggests that the lowering of phi TiN with increasing RN should be related to the increase in nitrogen concentration in the TiN film. The desirable Vth shift from -0.22 to 0.22 V was experimentally confirmed by fabricating n+ poly-Si and TiN gate n-channel multi-FinFETs without a channel doping. The developed simple technique for the conformal TiN deposition on the sidewalls of Si-fin channels is very attractive to the TiN gate FinFET fabrication

A closed-form analytical model for single nanoshells

Abstract: In this paper, we develop an accurate analytical closed-form model for the frequency resonance and scattering characteristics of single nanoshells. Nanoshells, dielectric spheres that are coated with noble metal, possess excellent tunability of their resonance frequency as a function of the relative sizes of the core and the thickness of the shell. Consequently, nanoshells offer much improved sensitivity, specificity, and cost-effectiveness in their applications. Simulation results show that our new closed-form model matches very closely with the exact solution for typical nanoshell configurations used in near-infrared applications.

RLC Ladder Model for Scattering in Single Metallic Nanoparticles

Abstract: In this paper, we present a new modeling technique for plasmon-based metallic nanoparticles under the influence of an electromagnetic field. The model approximates the coefficients of the admittance rational function. The proposed model utilizes spherical wave functions to describe the field and it provides an equivalent ladder-form RLC realization. Simulation results show that our model matches very closely with the exact solution. Our newly developed model can be used as a basic building block to develop an equivalent circuit model for metallic nanoparticle-based plasmonic waveguides

In situ measurement of Young's modulus of carbon nanotubes inside a TEM through a hybrid nanorobotic manipulation system

Abstract: A hybrid nanorobotic manipulation system inside a scanning electron microscope (SEM) and a transmission electron microscope (TEM) is presented. The SEM manipulators have been constructed with 8 degrees of freedom (DOFs) with three units for effective TEM sample preparation. The TEM manipulator consists of a 3-DOF manipulator actuated with four multilayer piezoelectric actuators and a 3-DOF passively driven sample stage. High resolution and transmission image of TEM is readily used for measurement and evaluation of samples. The stage is premanipulated by the SEM manipulator for sample preparations inside the SEM. This methodology is called the hybrid nanorobotic manipulation so as to differentiate it from those with only an exchangeable specimen holder. To show the effectiveness of the system, the Young's modulus of a carbon nanotube (CNT) was measured to be 1.23 TPa inside a TEM after being premanipulated inside the SEM. With this system, we can measure the inner diameter of a CNT and improve the accuracy in measuring the Young's modulus of a CNT.

High-frequency performance projections for ballistic carbon-nanotube transistors

Abstract: A quasi-static approach is combined with a theory of ballistic nanotransistors to assess the high-frequency performance potential of carbon-nanotube field-effect transistors. A simple equivalent circuit, which applies in the ballistic limit of operation, is developed for the intrinsic device, and then employed to determine the behavior of the unity-current-gain frequency (f/sub T/) with gate voltage. The circuit is shown to reduce to the expected forms in the so-called "MOS" and "bipolar" limits. The f/sub T/ is shown to approach a maximum value of v/sub F//2/spl pi/L/spl ap/130 GHz/L (/spl mu/m) at high gate voltage, where v/sub F/ is the nanotube's Fermi velocity and L is the channel length, and to fall at low gate voltage due to the presence of source and drain electrostatic capacitances. The impact of the gate electrostatic capacitance on the f/sub T/ is also discussed. Numerical simulations on a "MOSFET-like" or "bulk-switched" carbon-nanotube transistor are shown to support the conclusions.

Memory effect of a polymer thin-film transistor with self-assembled gold nanoparticles in the gate dielectric

Abstract: A self-assembled film of gold nanoparticles is integrated into the gate dielectric of an organic thin-film transistor to produce memory effects. The transistor is fabricated on a heavily doped n-type silicon (n+-Si) substrate with a thermally grown oxide layer of 100 nm thick. n+-Si serves as the gate electrode while the oxide layer functions as the gate dielectric. Gold nanoparticles as the floating gate for charge storage are deposited on the gate oxide by electrostatic layer-by-layer self-assembly method. A self-assembled multilayer of polyelectrolytes, together with a thin spin-coated poly(4-vinyl phenol) layer, covers the gold nanoparticles and separates them from the poly(3-hexyl thiophene) channel. Gold nanoparticles are charged or discharged with different gate bias so that the channel conductance is modulated. The memory transistor has an on/off ratio over 1500 and data retention time of about 200 s. The low-temperature solution-based process is especially suitable for plastic-based circuits. Therefore, the results of this study could accelerate achievement of cheap and flexible organic nonvolatile memories

Integrating nanowires with substrates using directed assembly and nanoscale soldering

Abstract: This paper describes a new methodology for integrating nanowires with micropatterned substrates using directed assembly and nanoscale soldering. Nanowires containing ferromagnetic nickel segments were fabricated by electrodeposition in nanoporous membranes. The nanowires were released by dissolution of the membrane and subsequently aligned relative to micropatterned substrates using magnetic field-directed assembly. After assembly, the wires were permanently bonded to the substrates using solder reflow to form low-resistance electrical contacts. This is the first demonstration of the use of nanoscale solder reflow to form low-resistance electrical interconnects between nanowires and substrates, and we demonstrated the utility of the strategy by fabricating a nanowire-based functional analog integrator.

Biased AC electro-osmosis for on-chip bioparticle processing

Abstract: Real-time detection of bioparticles is of great importance in deterring infectious diseases and bioterrorism. For bioparticle solutions with concentrations at an infectious level, culturing is typically used to increase the particle concentration to a detectable level, which is time consuming and often unfeasible under field conditions. Therefore, a real-time particle concentration technique is in demand to bridge the gap between the detectable level and infectious level of bacterial solutions. This paper describes a novel electrokinetic method that can potentially concentrate particles in real time. By studying surface flows on planar electrode pairs, two distinct ac electro-osmosis (ACEO) flows have been identified which are due, respectively, to capacitive and Faradaic charging of electrode double layers. Biased ACEO, combining dc bias with ac signals, breaks the symmetry of electrode charging, leading to asymmetric surface flows and a variety of directed surface flows that can concentrate, manipulate, and transport particles. Surface flows of opposite directions on planar electrodes produce stagnation lines that function as long-range particle traps and lead to net flows for micropumping. The device fabrication and operation are simple and compatible with integrated circuit technology

Threshold error penalty for fault-tolerant quantum computation with nearest neighbor communication

Abstract: The error threshold for fault-tolerant quantum computation with concatenated encoding of qubits is penalized by internal communication overhead. Many quantum computation proposals rely on nearest neighbor communication, which requires excess gate operations. For a qubit stripe with a width of L+1 physical qubits implementing L levels of concatenation, we find that the error threshold of 2.1/spl times/10/sup -5/ without any communication burden is reduced to 1.2/spl times/10/sup -7/ when gate errors are the dominant source of error. This /spl sim/175/spl times/ penalty in error threshold translates to an /spl sim/13/spl times/ penalty in the amplitude and timing of gate operation control pulses.

Augmented reality user interface for an atomic force microscope-based nanorobotic system

Abstract: A real-time augmented reality (AR) user interface for nanoscale interaction and manipulation applications using an atomic force microscope (AFM) is presented. Nanoscale three-dimensional (3-D) topography and force information sensed by an AFM probe are fed back to a user through a simulated AR system. The sample surface is modeled with a B-spline-based geometry model, upon which a collision detection algorithm determines whether and how the spherical AFM tip penetrates the surface. Based on these results, the induced surface deformations are simulated using continuum micro/nanoforce and Maugis-Dugdale elastic contact mechanics models, and 3-D decoupled force feedback information is obtained in real time. The simulated information is then blended in real time with the force measurements of the AFM in an AR human machine interface, comprising a computer graphics environment and a haptic interface. Accuracy, usability, and reliability of the proposed AR user interface is tested by experiments for three tasks: positioning the AFM probe tip close to a surface, just in contact with a surface, or below a surface by elastically indenting. Results of these tests showed the performance of the proposed user interface. This user interface would be critical for many nanorobotic applications in biotechnology, nanodevice prototyping, and nanotechnology education

A Novel Reference Scheme for Reading Passive Resistive Crossbar Memories

Abstract: A great effort today is concentrated on the development of resistive hysteretic materials and their related memory architecture. Resistive memories have a promising future to replace all current memory technologies to present an all-in-one memory solution. Passive resistive memories are of a special importance, since they can be scaled into the nanometer range without losing their functionality. This work is concerned with a novel scheme for generating reference voltages for the read operation. The scheme can be used with any passive crossbar based memory, regardless of the materials used for the implementation of the memory elements

Noise-Enhanced Detection of Subthreshold Signals With Carbon Nanotubes

Abstract: Electrical noise can help pulse-train signal detection at the nanolevel. Experiments on a single-walled carbon nanotube transistor confirmed that a threshold exhibited stochastic resonance (SR) for finite-variance and infinite-variance noise: small amounts of noise enhanced the nanotube detector's performance. The experiments used a carbon nanotube field-effect transistor to detect noisy subthreshold electrical signals. Two new SR hypothesis tests in the Appendix also confirmed the SR effect in the nanotube transistor. Three measures of detector performance showed the SR effect: Shannon's mutual information, the normalized correlation measure, and an inverted bit error rate compared the input and output discrete-time random sequences. The nanotube detector had a threshold-like input-output characteristic in its gate effect. It produced little current for subthreshold digital input voltages that fed the transistor's gate. Three types of synchronized white noise corrupted the subthreshold Bernoulli sequences that fed the detector. The Gaussian, the uniform, and the impulsive Cauchy noise combined with the random input voltage sequences to help the detector produce random output current sequences. The experiments observed the SR effect by measuring how well an output sequence matched its input sequence. Shannon's mutual information used histograms to estimate the probability densities and computed the entropies. The correlation measure was a scalar inner product of the input and output sequences. The inverted bit error rate computed how often the bits matched between the input and output sequences. The observed nanotube SR effect was robust: it persisted even when infinite-variance Cauchy noise corrupted the signal stream. Such noise-enhanced signal processing at the nanolevel promises applications to signal detection in wideband communication systems and biological and artificial neural networks

Processing dependent behavior of soft imprint lithography on the 1-10-nm scale

Abstract: This paper examines aspects of a soft nanoimprint lithography technique for operation at resolutions that approach the 1-nm regime. Systematic studies using polymer molds made with single walled carbon nanotubes (diameters between 0.5 and 5 nm) and high-resolution electron beam patterned layers of hydrogen silsesquioxane (line widths and heights /spl sim/10 and 20 nm, respectively) as templates reveal a dependence of the resolution limits on the polymer processing conditions. In particular, using a single choice of polymers for the molds and the molded materials, imprint results show that the conditions for spin casting and curing the polymers determine, to a large degree, the resolution and replication fidelity that can be achieved. Optimized procedures enable imprinted polymer surfaces that have a root mean squared surface roughness of /spl sim/0.26 nm or lower and a resolution as high as /spl sim/1 nm. These characteristics are significantly better than previous results obtained using these same polymers with unoptimized conditions. A diversity of molded polymers, including Bisphenol-F epoxy resin, polyacrylic acid, and polyurethane, show similar high-fidelity imprinting capabilities. Different procedures enable accurate relief replication for features with modest aspect ratios and dimensions of /spl sim/10 nm. The results indicate that choice of processing conditions is, in addition to materials selections, extremely important in achieving high-fidelity soft nanoimprint lithography in the 1-10-nm regime.

Electronic and Structural Properties of Oxygen-Doped BN Nanotubes

Abstract: The structural and electronic properties of oxygen substitutional doping in a (10,0) BN nanotube were obtained using ab initio calculation based on the density functional theory. For the oxygen replacing a boron atom in the tube (OB), the structure is locally deformed. In the case of nitrogen substitution (ON), however, the tube structure remains practically the same with negligible deformation observed around the oxygen atom. The electronic band structure for OB nanotubes is modified by the appearance of three strongly localized states, two of then as gap states. In the case of ON nanotubes the Fermi level is shifted into the conduction band inducing a metallic character to the doped tube. The analysis of the formation energies shows that the ON substitution is more favorable, particularly in the case of a boron-rich environment

Proximal Probes Based Nanorobotic Drawing of Polymer Micro/Nanofibers

Abstract: This paper proposes a nanorobotic fiber fabrication method which uses proximal probes to draw polymer fibers down to few hundred nanometers in diameter and several hundred micrometers in length. Using proximal probes such as Atomic Force Microscope (AFM) and Scanning Tunneling Microscope (STM) or glass micropipettes, liquid polymers dissolved in a solvent are drawn. During drawing, the solvent evaporates in real-time which solidifies the fiber. Controlling the drawn fibers trajectory and solidification in three-dimensions (3-D), suspended fibers, fiber cantilevers, custom 3-D fibers, and fiber networks, are proposed to be fabricated. Poly(methyl methacrylate) (PMMA) polymer dissolved in chlorobenzene is used to form a variety of suspended polymer fibers with diameters from few microns to 200nm. Fabrication of crossed and linear networks of fibers is also demonstrated. Viscoelastic modeling of polymer fiber drawing is realized using a finite element method to test the significance of the drawing speed and velocity profile on the extensional behavior of the drawn fiber. Since the mechanical properties of the drawn micro/nanofibers could vary from the bulk polymer material significantly, mechanical characterization of suspended fibers using an AFM and a Nanoindenter setup is proposed. Extending this technique to a variety of nonconductive and electroactive polymer fibers, many novel applications in micro/nanoscale sensors, actuators, fibrillar structures, and optical and electronic devices would become possible

A Study of Quantum Transport in End-of-Roadmap DG-MOSFETs Using a Fully Self-Consistent Wigner Monte Carlo Approach

Abstract: We present results of ultrascaled double-gate MOSFET operation and performance obtained from a new self-consistent particle-based quantum Monte Carlo (MC) approach. The simulation of quantum transport along the source-drain direction is based on the Wigner transport equation and the mode-space approximation of multi subband description. An improved method for correctly reproducing the Wigner function in the phase space by means of pseudo-particles is proposed. Our approach includes scattering effects for a two-dimensional (2-D) electron gas via standard MC algorithm. Detailed comparisons with both ballistic nonequilibrium Green's function and semiclassical multi subband Monte Carlo approaches show the ability of this Wigner transport model to incorporate correctly quantum effect into particle ensemble Monte Carlo simulation together with accurate description of scattering. This study of 6-nm-long MOSFET emphasizes the prevalent contribution of source-drain tunneling in subthreshold regime and the significant effect of quantum reflections in on-state. The influence of scattering in both the source access region and the gated part of the channel appears to be of prime importance for the correct evaluation of the on-state current, even for such small device in which the fraction of ballistic electrons is high

Noise in Silicon Nanowires

Abstract: The current-voltage and noise characteristics of bridging silicon wires have been measured at room temperature. From the linear current-voltage characteristics the bulk and contact resistance contributions are extracted and modeled. The excess noise observed at low frequencies is interpreted in terms of bulk and contact noise contributions, with the former comparable, in terms of Hooge parameter values, to the low noise levels observed in high-quality silicon devices. The contact noise is significant in some devices and is attributed to the impinging end of the bridging nanowires

Nanometer scale electrode separation (nanogap) using electromigration at room temperature

Abstract: Pairs of electrodes with nanometer separation (nanogap) are achieved through an electromigration-induced break-junction (EIBJ) technique at room temperature. Lithographically defined gold (Au) wires are formed by e-beam evaporation over oxide-coated silicon substrates silanized with (3-Mercaptopropyl)trimethoxysilane (MPTMS) and then subjected to electromigration at room temperature to create a nanometer scale gap between the two newly formed Au electrodes. The MPTMS is an efficient adhesive monolayer between SiO/sub 2/ and Au. Although the Au wires are initially 2 /spl mu/m wide, gaps with length /spl sim/1 nm and width /spl sim/5 nm are observed after breaking and imaging through a field effect scanning electron microscope. This technique eliminates the presence of any residual metal interlink in the adhesion layer (chromium or titanium for Au deposition over SiO/sub 2/) after breaking the gold wire, and it is much easier to implement than the commonly used low-temperature EIBJ technique which needs to be executed at 4.2 K. Metal-molecule-metal structures with symmetrical metal-molecule contacts at both ends of the molecule are fabricated by forming a self-assembled monolayer of -dithiol molecules between the EIBJ-created Au electrodes with nanometer separation. Electrical conduction through single molecules of 1,4-Benzenedimethanethiol (XYL) is tested using the Au/XYL/Au structure with chemisorbed gold-sulfur coupling at both contacts.

Adaptable End Effector for Atomic Force Microscopy Based Nanomanipulation

Abstract: Nanomanipulation using the atomic force microscope (AFM) has been extensively investigated for many years. But the efficiency and accuracy of AFM-based nanomanipulation are still major issues due to the nonlinearities and uncertainties in nanomanipulation operations. The deformation of the cantilever caused by manipulation force is one of the most major nonlinearities and uncertainties. It causes difficulties in accurately controlling the tip position, and results in missing the position of the object. The softness of the conventional cantilevers also causes the failure of manipulation of sticky nano-objects because the tip can easily slip over the nano-objects. In this paper, an active atomic force microscopy probe is used as an adaptable end effector to solve these problems by actively controlling the cantilever's flexibility or rigidity during nanomanipulation. A control voltage is applied to the piezo layer of the adaptable end effector to exert a reverse bending moment on the cantilever to balance the bending moment caused by the interaction force during manipulation. Thus, the adaptable end effector is controlled to maintain straight shape during manipulation. A detailed model of the adaptable end effector is presented in the paper. Control of the adaptable end effector employing an optimal LQR control law is derived and implemented. The experimental results verify the validity of the model and effectiveness of the controller. The nanomanipulation results also prove the increased efficiency of AFM-based nanomanipulation using the adaptable end effector

DNA-templated copper nanowire fabrication by a two-step process involving electroless metallization

Abstract: Here, we report a new fabrication method of DNA-templated copper nanowires. The copper nanowires were fabricated via two-step reactions. First, Pd(II) ions were electrostatically adsorbed onto negatively charged DNA molecules immobilized on the substrate surfaces and reduced chemically. As a result, palladium nanowires with a diameter of approximately 6 nm were obtained. Second, the palladium nanowires were dipped into a copper electroless plating bath. Electroless deposition of copper proceeded specifically on the palladium nanowires. The diameters of the copper nanowires were controlled by the plating time

Analysis of the Frequency Response of Carbon Nanotube Transistors

Abstract: The characterizations of carbon nanotube transistors at high frequencies have so far been hindered by large parasitic and extrinsic capacitances. We present a quantitative analysis of the limitations imposed by probe pad parasitics on single-wall carbon nanotube transistor characterization at gigahertz frequencies. Our analysis reveals the various kinds of frequency responses that can be expected to be measured. Furthermore, we present design guidelines and a suitable device layout to achieve gain and bandwidth at gigahertz frequencies

Probabilistic Modeling of QCA Circuits Using Bayesian Networks

Abstract: To push the frontiers of quantum-dot cellar automata (QCA) based circuit design, it is necessary to have design and analysis tools at multiple levels of abstractions. To characterize the performance of QCA circuits it is not sufficient to specify just the binary discrete states (0 or 1) of the individual cells, but also the probabilities of observing these states. We present an efficient method based on graphical probabilistic models, called Bayesian networks (BNs), to model these steady-state cell state probabilities, given input states. The nodes of the BN are random variables, representing individual cells, and the links between them capture the dependencies among them. BNs are minimal, factored, representation of the overall joint probability of the cell states. The method is fast and its complexity is shown to be linear in terms of the number of cells. This BN model allows us to analyze clocked QCA circuits in terms of quantum- mechanical quantities, such as steady-state polarization and thermal ratios for each cell, without the need for full quantum-mechanical simulation, which is known to be very slow and is best postponed to the final stages of the design process. We can also estimate the most likely (or ground) state configuration for all the cells and the lowest energy configuration that results in output errors. We validate the model with steady-state probabilities computed by the Hartree-Fock self-consistent approximation (HT-SCA). Using full adder designs, we demonstrate the ability to compare and contrast QCA circuit designs with respect to the variation of the output state probabilities with temperature and input. We also show how weak spots in clocked QCA circuit designs can be found using our model by comparing the (most likely) ground-state configuration with the next most likely energy state configuration that results in output error

Characterization of heat transfer along a silicon nanowire using thermoreflectance technique

Abstract: We studied heat transfer along a silicon nanowire suspended between two thin-film heaters using a thermoreflectance imaging technique. The thermoreflectance imaging system achieved submicrometer spatial resolution and 0.1/spl deg/C temperature resolution using visible light. The temperature difference across the nanowire was measured, and then its thermal resistance was calculated. Knowing the dimension of the nanowire (115 nm in width and 3.9 /spl mu/m in length), we calculated the thermal conductivity of the sample, which is 46 W/mK. Thermal conductivity decreases with decreasing wire size. For a 115-nm-wide silicon nanowire, the thermal conductivity is only one-third of the bulk value. In addition, the transient response of the thin-film heaters was also examined using three-dimensional thermal models by the ANSYS program. The simulated thermal map matches well with the experimental thermoreflectance results.