A carbon nanotube is a one-dimensional molecular wire. In this paper, we discuss some of the properties of carbon nanotubes as microwave and mm-wave antennas. We also discuss some of the conceptual issues involved with understanding the interaction of microwaves with one-dimensional quantum wires. While we focus on simple dipole antennas, our discussion applies generally to the interaction of microwaves with nano-materials, including nanotube arrays and composites.
We measure the dynamical conductance of electrically contacted single-walled carbon nanotubes at dc and ac as a function of source-drain voltage in both low and high dc bias voltage. We show a direct relationship between the ac conductance and dc conductance. We also measure the microwave conductance of 2 nanotubes in parallel and observe an anomalous frequency dependence.
We present the design, fabrication, and impedance measurements of plasma wave detectors fabricated from GaAs/AlGaAs heterostructures. The design principles will allow broadband (dc to 7 GHz) measurements of the device power coupling and responsivity as a detector, which is a "scale model" of a THz plasma wave detector. We demonstrate clear resonance behavior in the impedance spectrum.
The development of nanowire and nanotube FETs for high frequency applications faces a challenge of impedance matching, due to the inherent mismatch between the resistance quantum (≈ 25 kΩ) typical of nanodevices, and the characteristic impedance of free space (≈ 377 Ω) typical of RF circuits. One possible solution is to use parallel nanotube or nanowire FETs to decrease the input impedance, and increase the drive current. In this paper, we present our progress towards this goal using aligned arrays of nanotube FETs. Initial studies on randomly oriented CVD grown devices give mobilities of 4 cm2/V-s. These initial devices carry ≈ 0.25 mA of current. Even higher mobilities (hence very high operational frequencies up to THz) should be possible with aligned nanotube FETs.
The study of the ac properties of nano-electronic systems is still in its infancy. In this paper we present an overview of recent work aimed at advancing the understanding of this new field. Specifically, we first discuss the passive RF circuit models of one-dimensional nanostructures as interconnects. Next, we discuss circuit models of the ac performance of active 1d transistor structures, leading to the prediction that THz cutoff frequencies should be possible. We recently demonstrated the operation of nanotube transistors at 2.6 GHz. Third, we discuss the radiation properties of 1d wires, which could form antennas linking the nanoworld to the macroworld. This could completely remove the requirements for lithographically defined contacts to nanotube and nanowire devices, one of the greatest unsolved problems in nanotechnology.
We present a new technique for fabricating gold nanowires using carbon nanotubes as the template. By applying an ac voltage to an electrically contacted single walled carbon nanotube, we generate highly non-uniform ac electric fields in the vicinity of the nanotubes. These ac electric fields serve to polarize 2 nm gold nanoparticles dispersed in solution. The induced dipole moment in the nanoparticles is attracted to the high-intensity field regions at the surface of the nanotube, thus causing a gold nanowire to grow on the surface of the nanotube. Interestingly, we find gold nanowires grow even on nanotubes that are not electrically contacted but in close proximity to the electrodes. Future applications of this work may include DNA sensors based on functionalized Au nanoparticles.
The particular form of electrochemiluminescence (ECL) used for analytical assays relies upon the discovery that tris(2,2'-bipyridyl)ruthenium(II) [Ru(bpy)32+] emits a 620 nm photon when adjacent to an electrode held at about one volt relative to Ag/AgCl. This reaction occurs within nanometers of the electrode. The enormous economic investment in nanoscale lithography tools is leading to tools capable of routinely producing 32 nm features by 2009. We propose that these two technologies could be combined to produce a nanoscale microscopy system. We constructed a macroscopic test-bed and performed tests on it to explore the feasibility of such a system. We tested an ECL solution containing 1 mM Ru(bpy)32+ 0.2 mM ammonium oxalate monohydrate in a 0.1 M ammonium acetate buffer at pH 5.0. Using this solution, we found that the ECL light was most intense at an applied voltage of 1.6 Volts, that the effect had excellent reproducibility and that the time to reach maximum intensity was several seconds after applying a voltage.
Using gold electrodes lithographically fabricated onto microscope cover slips, DNA and proteins are interrogated both optically (through fluorescence) and electronically (through conductance measurements). Dielectrophoresis is used to position DNA and proteins at well-defined positions on a chip. For the electronic manipulations, quadrupole electrode geometries are used with gaps ranging from 3 to 100 μm; AC field strengths are typically 106 V/m with frequencies between 10 kHz and 30 MHz. Nanoparticles (20 nm latex beads) are also manipulated. A technique of in situ impedance monitoring is tested for the first time to measure the conductance of the electronically manipulated DNA and proteins. The electrical resistance of DNA and proteins is measured to be larger than 40 MΩ under the experimental conditions used.
Superconductive hot-electron bolometer (HEB) mixers have been built and tested in the frequency range from 1.1 THz to 2.5 THz. The mixer device is a 0.15 - 0.3 micrometer microbridge made from a 10 nm thick Nb film. This device employs diffusion as a cooling mechanism for hot electrons. The double sideband noise temperature was measured to be less than or equal to 3000 K at 2.5 THz and the mixer IF bandwidth is expected to be at least 10 GHz for a 0.1 micrometer long device. The local oscillator (LO) power dissipated in the HEB microbridge was 20 - 100 nW. Further improvement of the mixer characteristics can be potentially achieved by using Al microbridges. The advantages and parameters of such devices are evaluated. The HEB mixer is a primary candidate for ground based, airborne and spaceborne heterodyne instruments at THz frequencies. HEB receivers are planned for use on the NASA Stratospheric Observatory for Infrared Astronomy (SOFIA) and the ESA Far Infrared and Submillimeter Space Telescope (FIRST). The prospects of a submicron-size YBa2Cu3O7-(delta ) (YBCO) HEB are discussed. The expected LO power of 1 - 10 (mu) W and SSB noise temperature of approximately equals 2000 K may make this mixer attractive for various remote sensing applications.
We report on the development of quasioptical Nb hot-electron bolometer mixers for heterodyne receivers operating at 1 THz 3 THz. The devices have submicron in-plane sizes, thus exploiting diffusion as the electron cooling mechanism. Quasioptical mixer circuits have been developed with planar double-dipole or twin-slot antennas. The measured (DSB) receiver noise temperatures are 1670 K at 1.1 THz, with an estimated mixer noise temperature of approximately equals 1060 K, and 2750 K at 2.5 THz, with an estimated mixer noise temperature of approximately equals 900 K. The IF bandwidth is found to scale as the length-squared, and bandwidths as high as 8 GHz have been measured. These results demonstrate the low-noise, broadband operation of the diffusion-cooled bolometer mixer over a wide range of far-infrared wavelengths.
We report on the first heterodyne measurements with a diffusion-cooled hot-electron bolometer mixer in the submillimeter wave band, using a waveguide mixer cooled to 2.2 K. The best receiver noise temperature at a local oscillator frequency of 533 GHz and an intermediate frequency of 1.4 GHz was 650 K (double sideband). The 3 dB IF roll-off frequency was around 1.7 to 1.9 GHz, with a weak dependence on the device bias conditions.
The role of chemical-mechanical polishing (CMP) of ILD and metal layers is increasing as device densities in the ULSI shrink. However, the advantages in film planarization gained with CMP are often offset by contaminants which are abundant in the chemical bath (known as the slurry) to which the wafers are exposed during processing. Such chemistries particularly metallic ions can adversely effect device reliability and performance if left on the wafer or ILD in large densitites. The problem we address is that of detecting such residual contaminants post-CMP on product wafers nondestructively. In this work we look at the effects of ionic residuals in ILD oxides before and after exposure to various methods of CMP. Using an optical methodology known as contact potential differentiation in which the potential across the oxide is separated out from (and compared with) a standard surface barrier measurement, we can passively examine any dramatic charge on the wafer and in the oxide as a result of this process. In this paper this technique will be demonstrated on several CMP samples illustrating the contaminant effects on CMP oxides with results compared to chemical spectroscopy.