We have demonstrated Schottky diodes using semiconducting single-walled nanotubes (s-SWNTs) with titanium Schottky and platinum Ohmic contacts for high-frequency applications. The diodes are fabricated using angled evaporation of dissimilar metal contacts over an s-SWNT. The devices demonstrate rectifying behavior with large reverse bias breakdown voltages of greater than -15 V. To decrease the series resistance, multiple SWNTs are grown in parallel in a single device, and the metallic tubes are burnt-out selectively. At low biases these diodes showed ideality factors in the range of 1.5 to 1.9. Modeling of these diodes as direct detectors at room temperature at 2.5 terahertz (THz) frequency indicates noise equivalent powers (NEP) potentially comparable to that of the state-of-the-art gallium arsenide solid-state Schottky diodes, in the range of 10(-13) W/ radical Hz.

We describe the fabrication and characterization of a nanoelectromechanical (NEM) switch based on carbon nanotubes. Our NEM structure consists of single-walled nanotubes (SWNTs) suspended over shallow trenches in a SiO(2) layer, with a Nb pull electrode beneath. The nanotube growth is done on-chip using a patterned Fe catalyst and a methane chemical vapor deposition (CVD) process at 850 degrees C. Electrical measurements of these devices show well-defined ON and OFF states as a dc bias up to a few volts is applied between the CNT and the Nb pull electrode. The CNT switches were measured to have speeds that are 3 orders of magnitude higher than MEMS-based electrostatically driven switches, with switching times down to a few nanoseconds, while at the same time requiring pull voltages less than 5 V.

Microfluidic diaphragm valves and pumps capable of surviving conditions required for unmanned spaceflight applications have been developed. The Pasteur payload of the European ExoMars Rover is expected to experience temperatures ranging between -100 degrees C and +50 degrees C during its transit to Mars and on the Martian surface. As such, the Urey instrument package, which contains at its core a lab-on-a-chip capillary electrophoresis analysis system first demonstrated by Mathies et al., requires valving and pumping systems that are robust under these conditions before and after exposure to liquid samples, which are to be analyzed for chemical signatures of past or present living processes. The microfluidic system developed to meet this requirement uses membranes consisting of Teflon and Teflon AF as a deformable material in the valve seat region between etched Borofloat glass wafers. Pneumatic pressure and vacuum, delivered via off-chip solenoid valves, are used to actuate individual on-chip valves. Valve sealing properties of Teflon diaphragm valves, as well as pumping properties from collections of valves, are characterized. Secondary processing for embossing the membrane against the valve seats after fabrication is performed to optimize single valve sealing characteristics. A variety of different material solutions are found to produce robust devices. The optimal valve system utilizes a membrane of mechanically cut Teflon sandwiched between two thin spun films of Teflon AF-1600 as a composite "laminated" diaphragm. Pump rates up to 1600 nL s(-1) are achieved with pumps of this kind. These high pumping rates are possible because of the very fast response of the membranes to applied pressure, enabling extremely fast pump cycling with relatively small liquid volumes, compared to analogous diaphragm pumps. The developed technologies are robust over extremes of temperature cycling and are applicable in a wide range of chemical environments.

X-ray photoelectron spectroscopy (XPS) has been used to investigate the reaction of YBa2Cu3O7−x films with solutions of HF, HCl, Br2, HBr, I2, and HI in absolute ethanol (EtOH). The XPS core level and x-ray excited Auger spectra from untreated and halogen-treated surfaces are used to identify surface species by comparison with XPS data from the literature and with XPS spectra from more than 20 Y, Ba, and Cu halides, oxides, hydroxides, and carbonates measured in this work. XPS measurements on a number of these materials are being reported for the first time. Treatment of films with HF/EtOH results in the formation of an oxyfluoride with Y:Ba:Cu relative concentrations of 1:4:3. Additional features in the XPS spectra from HF-treated films are also consistent with the formation of CuF, a compound which does not exist in bulk form. Treatment of films with HCl/EtOH results primarily in the formation of BaCl2 (∼75%), with smaller amounts of YCl3, CuCl, and CuCl2. Treatment of films with Br2/EtOH or HBr/EtOH results in the formation of YBr3, BaBr2, and CuBr with relative concentrations 1:4:3. YBa2Cu3O7−x films were found to have no discernible reaction with I2/EtOH solutions, but treatment of films with HI/EtOH results in the formation of CuI on the surface.

We have developed high-current density field emission sources using arrays of multiwalled carbon nanotube bundles. The field emission behavior of a variety of lithographically patterned array geometries was investigated and the arrays of 1-μm and 2-μm-diameter nanotube bundles spaced 5μm apart (edge-to-edge spacing) were identified as the most optimum combination, routinely producing 1.5–1.8A∕cm2 at low electric fields of approximately 4V∕μm, rising to >6A∕cm2 at 20V∕μm over a ∼100-μm-diameter area. We have found that the field emission performance depends strongly on the bundle diameter and interbundle spacing and such arrays perform significantly better in field emission than ordered arrays of isolated nanotubes or dense, continuous mats of nanotubes previously reported in literature.