Ivan Puchades

Mechanism of chemical doping in electronic-type-separated single wall carbon nanotubes towards high electrical conductivity

Enhanced electrical conductivity of carbon nanotubes (CNTs) can enable their implementation in a variety of wire and cable applications traditionally employed by metals. Electronic-type-separated single wall carbon nanotubes (SWCNTs) offer a homogeneous platform to quantify the unique physiochemical interactions from different chemical dopants and their stability. In this work, a comprehensive study of chemical doping with purified commercial CNT sheets shows that I2, IBr, HSO3Cl (CSA) and KAuBr4 are the most effective at increasing the electrical conductivity of CNT films by factors between 3× and 8×. These dopants are used with electronic-type-separated SWCNT thin-films to further investigate changes in SWCNT optical absorption, Raman spectra, and electrical conductivity. The dopant effects with semiconducting SWCNTs result in quenching of the S11 and S22 transitions, and a red shift of 8–10 cm−1 of the Raman G′ peak, when compared to a purified SWCNT thin-film. The average electrical conductivity of purified semiconducting SWCNT thin-films is 7.3 × 104 S m−1. Doping increases this conductivity to 1.9 × 105 S m−1 for CSA (2.6× increase), 2.2 × 105 S m−1 for IBr (3.1×), to 2.4 × 105 for I2 (3.3×), and to 4.3 × 105 for KAuBr4 (5.9×). In comparison, metallic SWCNT thin-films exhibit only slight quenching of the optical absorbance spectra for the M11 transition, and shifts in the Raman G′-peak of less than 1 cm−1 for I2 and IBr, whereas KAuBr4 and CSA promote red shifting by 4 cm−1, and 7 cm−1, respectively, when compared to a purified control sample. The increase in electrical conductivity of metallic SWCNT thin-films is gradual and depends on the dopant. With an average value of 9.0 × 104 S m−1 for the purified metallic SWCNT thin-films, I2 doping increases the electrical conductivity to 1.0 × 105 (1.1× increase), IBr to 1.5 × 105 S m−1 (1.7×), KAuBr4 to 2.4 × 105 S m−1 (2.6×), and CSA to 3.2 × 105 S m−1 (3.5×). The time-dependent stability of the chemical dopants with SWCNTs is highest for KAuBr4, which remains in effect after 70 days in ambient conditions. The doping-enhanced electrical conductivity is attributed to the relative potential difference between the SWCNT electronic transitions and the redox potential of the chemical species to promote charge transfer. The results of this work reinforce the chemical doping mechanism for electronic-type-separated SWCNTs and provide a path forward to advance SWCNT conductors.

Enhanced Electrical Conductivity in Extruded Single-Wall Carbon Nanotube Wires from Modified Coagulation Parameters and Mechanical Processing

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 Microelectromechanical (MEMS) Device For Measuring Viscosity

A thermally actuated non-cantilever-beam microelectromechanical viscosity sensor is presented. The proposed device is based on thermally induced vibrations of a simple silicon diaphragm 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. Thermal analysis was performed utilizing temperature diodes in the silicon diaphragm to determine 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. Viscosity measurements were performed and compared to motor oil measured on a commercial cone-and-plate viscometer.

Carbon Nanotube Thin-Film Antennas

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.

An Electromagnetic MEMS Actuator for Micropumps

In this paper, design, fabrication and evaluation of an electromagnetic MEMS micropump actuator are reported. Based on MEMS technology, the proposed micropump actuator is designed and fabricated using integrated surface and bulk micromachining at the Microfabrication Facility at the Rochester Institute of Technology. A thin silicon diaphragm with a planar spiral coil ensures the desired degree of robustness and guarantees the specified volumetric changes. The magnetic force is generated due to the interaction between the magnetic field of a permanent magnet and current in the coil. The experimental results are reported

Design and Fabrication of Microactuators and Sensors for MEMS

This paper reports the results for various microelectromechanical systems, devices and structures fabricated using bulk and surface micromachined processes. These microelectromechanical systems (MEMS) are designed and fabricated at the Semiconductor Micro-Fabrication Facility Laboratory at Rochester Institute of Technology. The microactuators and sensors are designed and fabricated for proof-of-concept lab-on-a-chip systems. The experimental results, which include testing, evaluation and characterization of microelectromechanical actuators and sensors, are reported.

Design and Evaluation of a MEMS Bimetallic Thermal Actuator for Viscosity Measurements

A non-cantilever-beam micro-electro-mechanical (MEMS) based viscosity sensor is proposed. This novel vibration viscometer device utilizes thermal actuation and piezoresistive sensing. As the actuation bias is kept constant, viscosity changes can be correlated to changes in the oscillation amplitude. This proposed solution is CMOS compatible, inexpensive and reliable. This paper investigates the vertical movement of thin silicon/aluminum bimetal diaphragms with varying bimetal areas and diaphragm thickness to better understand the thermo- mechanical behavior of the proposed actuator/sensor device. Proof of concept results are presented in which the oscillation amplitude of the bimetal actuator changes when the device is immersed in media of different viscosity.

Blue cathodoluminescence from tantalum zinc oxide

We have observed cathodoluminescence (CL) at low voltages (<50 V) with a peak at /spl sim/410 nm from tantalum zinc oxide, Ta/sub 2/Zn/sub 3/O/sub 8/, (TZO). The thin films were prepared by reacting Ta with ZnO on silicon and silicon dioxide substrates at elevated temperatures (1200/spl deg/C) using rapid thermal annealing. Subsequently, the bulk phase was synthesized from the powder raw materials, ZnO and Ta/sub 2/O/sub 5/ using ceramic techniques. The resulting material shows similar CL characteristics. No charging was observed during the CL measurements, indicating a conducting nature of the material. It is observed that TZO exhibits better blue both in thin film and bulk form, as compared to conventional ZnS:Ag, a blue CRT phosphor and zinc gallate, another low voltage blue phosphor.

Emerging MEMS and nano technologies: Fostering scholarship, STEM learning, discoveries and innovations in microsystems

We report scholarship and learning activities in Rochester Institute of Technology (RIT) in areas of micro-electromechanical systems (MEMS) and nanotechnology. Microsystems may integrate microelectronics, nano and MEMS technologies and solutions. To enable integrated transformative scholarship and learning, fundamental and applied research is conducted at the state-of-the-art Microsystems Fabrication Facilities. Contributing to research in core areas of critical importance of science, technology, engineering and mathematics (STEM), undergraduate and graduate MEMS and Nanotechnology courses are developed and offered. The MEMS curriculum includes MEMS Design, MEMS Fabrication and MEMS Evaluation courses. The Nanotechnology curriculum comprises an undergraduate Nano Science, Engineering and Technology (NanoSET) course, as well as a graduate Fundamentals of Micro and Nano Engineering course. To meet overall and specific educational goals and objectives, we facilitate course and curriculum developments focusing on active learning, scholarship, effective teaching and pedagogy. These activities advance a STEM knowledge base. Our courses and educational activities positively contribute to STEM transformative developments. In order to enable learning and scholarship, faculty, professionals and students are engaged in discoveries, innovations and knowledge base generation. These attributes are achieved by means of advanced designs, analyses, fabrication and test of various MEMS and microsystems. Methods, concepts, tools and algorithms of computational and applied mathematics are used. Our research, capstone and laboratory projects enable STEM education, advance fundamental findings, facilitate research, support discoveries and enrich training. High-performance microsystems and MEMS are devised, designed, analysed, fabricated and evaluated. We advance technology readiness levels, ensure technology transfer and enable commercialization capacity.

MEMS microthrusters with nanoenergetic solid propellants

Solid propellants are used in various flight and underwater systems as well as in propulsion platforms. Micromachining, microelectromechanical systems (MEMS) and automatic dispensing of high-energy-density nanoenergetic materials are examined for current and next generation of application-specific flight and underwater platforms. The integrated MEMS-technology microthrusters with the optimized-by-design nanostructured propellants ensure the expected thrust-to-weight and thrust-to-power ratios, specific impulse, effective exhaust velocity, thrust, energy density, controlled combustion, etc. The flight-proven propulsion and micromachining technologies are suitable in a wide range of applications, such as payload delivery, stabilization, guidance, navigation, etc. Compared with mono- and bi-propellant, ion, laser, plasma, Hall-effect and other thrusters, our solution ensures fabrication simplicity, affordability, robustness, integration, compatibility, safety, etc. The experimental substantiation, evaluation and characterization of fabricated proof-of-concept devices with nanoenergetic propellants are reported.