Electronic-type-separated SWCNTs thin-films were used to demonstrate that the strength of the redox potential of dopants influences their electrical conductivity enhancement.

Single-wall carbon nanotubes (SWCNTs) synthesized via laser vaporization have been dispersed using chlorosulfonic acid (CSA) and extruded under varying coagulation conditions to fabricate multifunctional wires. The use of high purity SWCNT material based upon established purification methods yields wires with highly aligned nanoscale morphology and an over 4× improvement in electrical conductivity over as-produced SWCNT material. A series of eight liquids have been evaluated for use as a coagulant bath, and each coagulant yielded unique wire morphology based on its interaction with the SWCNT-CSA dispersion. In particular, dimethylacetamide as a coagulant bath is shown to fabricate highly uniform SWCNT wires, and acetone coagulant baths result in the highest specific conductivity and tensile strength. A 2× improvement in specific conductivity has been measured for SWCNT wires following tensioning induced both during extrusion via increased coagulant bath depth and during solvent evaporation via mechanical strain, over that of as-extruded wires from shallower coagulant baths. Overall, combination of the optimized coagulation parameters has yielded acid-doped wires with the highest reported room temperature electrical conductivities to date of 4.1-5.0 MS/m and tensile strengths of 210-250 MPa. Such improvements in bulk electrical conductivity can impact the adoption of metal-free, multifunctional SWCNT materials for advanced cabling architectures.

A thermally actuated non-cantilever-beam micro-electro-mechanical viscosity sensor is presented. The proposed device is based on thermally induced vibrations of a silicon-based membrane and its damping due to the surrounding fluid. This vibration viscometer device utilizes thermal actuation through an in-situ resistive heater and piezoresistive sensing, both of which utilize CMOS compatible materials leading to an inexpensive and reliable system. Due to the nature of the actuation, thermal analysis was performed utilizing PN diodes embedded in the silicon membrane to monitor its temperature. This analysis determined the minimum heater voltage pulse amplitude and time in order to prevent heat loss to the oil under test that would lead to local viscosity changes. In order to study the natural vibration behavior of the complex multilayer membrane that is needed for the proposed sensor, a designed experiment was carried out. In this experiment, the effects of the material composition of the membrane and the size of the actuation heater were studied in detail with respect to their effects on the natural frequency of vibration. To confirm the validity of these measurements, Finite Element Analysis and white-light interferometry were utilized. Further characterization of the natural frequency of vibration of the membranes was carried out at elevated temperatures to explore the effects of temperature. Complex interactions take place among the different layers that compose the membrane structures. Finally, viscosity measurements were performed and compared to standard calibrated oils as well as to motor oils measured on a commercial cone-and-plate viscometer. The experimentally obtained data is compared to theoretical predictions and an empirically-derived model to predict viscosity from vibration measurements is proposed. Frequency correlation to viscosity was shown to be the best indicator for the range of viscosities tested with lower error (+/-5%), than that of quality factor (+/-20%). Further viscosity measurements were taken at elevated temperatures and over long periods of time to explore the device reliability and drift. Finally, further size reduction of the device was explored.

Multiwalled carbon nanotube (MWCNT) and single-walled carbon nanotube (SWCNT) dipole antennas have been successfully designed, fabricated, and tested. Antennas of varying lengths were fabricated using flexible bulk MWCNT sheet material and evaluated to confirm the validity of a full-wave antenna design equation. The ∼20× improvement in electrical conductivity provided by chemically doped SWCNT thin films over MWCNT sheets presents an opportunity for the fabrication of thin-film antennas, leading to potentially simplified system integration and optical transparency. The resonance characteristics of a fabricated chlorosulfonic acid-doped SWCNT thin-film antenna demonstrate the feasibility of the technology and indicate that when the sheet resistance of the thin film is >40 ohm/sq no power is absorbed by the antenna and that a sheet resistance of <10 ohm/sq is needed to achieve a 10 dB return loss in the unbalanced antenna. The dependence of the return loss performance on the SWCNT sheet resistance is consistent with unbalanced metal, metal oxide, and other CNT-based thin-film antennas, and it provides a framework for which other thin-film antennas can be designed.

Metal-assisted chemical etching (MacEtch, MACE) has been heralded as a robust and cost-effective semiconductor fabrication technique that combines many advantages of wet and dry etching, while simultaneously overcoming their accompanying limitations. However, widespread use of MACE has been hindered partly due to the use of metallic catalysts such as Au that potentially introduce deep-level trap defects into Si processing. Moreover, alternative noble metal catalysts (e.g., Ag) embed an optically reflective film within the etched substrate, which can be detrimental to devices that rely on MACE-generated structures for improved light absorption. Here, a versatile process is detailed whereby carbon nanotube (CNT) composite films are used as catalysts for site-selective etching of Si(100) wafers. The so-called carbon-nanotube-assisted chemical etching (CNT-ACE) method enables solution-based and room-temperature fabrication of vertical Si micropillar arrays. Vertical etch rates (VERs) of Si samples etched by using nominally undoped CNTs and potassium tetrabromoaurate (KAuBr4)-doped CNTs are compared. Enhancement of VER from ∼28 to ∼142 nm/min is observed for KAuBr4-doped CNTs compared to undoped films, which is attributed to a shift in the catalytic film’s aggregate reduction potential toward that of pure Au. Raman spectroscopy and Auger electron spectroscopy reveal that the catalytic CNT layer is not degraded during etching. A solar-weighted reflectance (SWR) of ∼2% is measured for Si micropillar arrays with embedded CNT membranes. This represents over 94% reduction in SWR compared to bare Si and 33% reduction compared to Si micropillar arrays fabricated via conventional MACE with embedded Au catalysts. A physical model is provided for the CNT-ACE mechanisms, including additional mass transport pathways for dissolution products through the CNT film. The CNT-ACE method enables complementary metal–oxide–semiconductor (CMOS) compatible fabrication of Si micro/nanostructures for device applications including photovoltaic solar cells and photodetectors and is particularly beneficial for applications wherein nonreflective embedded contacts are desired.

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