Engineering topics

Meyyappan, M.

Publications and source records attributed to Meyyappan, M..

At least 19 records

NASA NTRS2016

Atmospheric Pressure Plasma Jet as a Dry Alternative to Inkjet Printing in Flexible Electronics

We have developed an atmospheric pressure plasma jet printing system that works at room temperature to 50 deg C unlike conventional aerosol assisted techniques which require a high temperature sintering step to obtain desired thin films. Multiple jets can be configured to increase throughput or to deposit multiple materials, and the jet(s) can be moved across large areas using a x-y stage. The plasma jet has been used to deposit carbon nanotubes, graphene, silver nanowires, copper nanoparticles and other materials on substrates such as paper, cotton, plastic and thin metal foils.

Printable electronics↗

NASA NTRS2013

Label-Free Detection of Cardiac Troponin-I Using Carbon Nanofiber Based Nanoelectrode Arrays

A sensor platform based on vertically aligned carbon nanofibers (CNFs) has been developed. Their inherent nanometer scale, high conductivity, wide potential window, good biocompatibility and well-defined surface chemistry make them ideal candidates as biosensor electrodes. A carbon nanofiber (CNF) multiplexed array has been fabricated with 9 sensing pads, each containing 40,000 carbon nanofibers as nanoelectrodes. Here, we report the use of vertically aligned CNF nanoelectrodes for the detection of cardiac Troponin-I for the early diagnosis of myocardial infarction. Antibody, antitroponin, probe immobilization and subsequent binding to human cardiac troponin-I were characterized using electrochemical impedance spectroscopy and cyclic voltammetry techniques. Each step of the modification process resulted in changes in electrical capacitance or resistance to charge transfer due to the changes at the electrode surface upon antibody immobilization and binding to the specific antigen. This sensor demonstrates high sensitivity, down to 0.2 ng/mL, and good selectivity making this platform a good candidate for early stage diagnosis of myocardial infarction.

cardiac output↗

NASA NTRS2011

Carbon Nanotube Based Nanotechnology for NASA Mission Needs and Societal Applications

Carbon nanotubes (CNT) exhibit extraordinary mechanical properties and unique electronic properties and therefore, have received much attention for more than a decade now for a variety of applications ranging from nanoelectronics, composites to meeting needs in energy, environmental and other sectors. In this talk, we focus on some near term potential of CNT applications for both NASA and other Agency/societal needs. The most promising and successful application to date is a nano chem sensor at TRL 6 that uses a 16-256 sensor array in the construction of an electronic nose. Pristine, doped, functionalized and metal-loaded SWCNTs are used as conducting materials to provide chemical variation across the individual elements of the sensor array. This miniaturized sensor has been incorporated in an iPhone for homeland security applications. Gases and vapors relevant to leak detection in crew vehicles, biomedical, mining, chemical threats, industrial spills and others have been demonstrated. SWCNTs also respond to radiation exposure via a change in conductivity and therefore, a similar strategy is being pursued to construct a radiation nose to identify radiation sources (gamma, protons, neutrons, X-ray, etc.) with their energy levels. Carbon nanofibers (CNFs) grown using plasma enhanced CVD typically are vertical, individual, freestanding structures and therefore, are ideal for construction of nanoelectrodes. A nanoelectrode array (NEA) can be the basis for an affinity-based biosensor to meet the needs in applications such as lab-on-a-chip, environmental monitoring, cancer diagnostics, biothreat monitoring, water and food safety and others. A couple of demonstrations including detection of e-coli and ricin will be discussed. The NEA is also useful for implantation in the brain for deep brain stimulation and neuroengineering applications. Miniaturization of payload such as science instrumentation and power sources is critical to reduce launch costs. High current density (greater than 100 mA/per square centimeters) field emission capabilities of CNTs can be exploited for construction of electron gun for electron microscopy and X-ray tubes for spectrometers and baggage screening. A CNT pillar array configuration has been demonstrated, not only meeting the high current density needs but more importantly providing long term emitter stability. Finally, supercapacitors hold the promise to combine the high energy density of a battery with the high power density of capacitors. Traditional graphite electrodes have not delivered this promise yet. A novel design and processing approach using MWCNTs has shown a record 550 F/g capacitance along with significant device endurance. This supercapacitor is suitable for railgun launch application for NASA, powering rovers and robots, consumer electronics and future hybrid vehicles.

Li, Jing↗

NASA NTRS2011

Nanomaterials for Electronics and Optoelectronics

Nanomaterials such as carbon nanotubes(CNTs), graphene, and inorganic nanowires(INWs) have shown interesting electronic, mechanical, optical, thermal, and other properties and therefore have been pursued for a variety of applications by the nanotechnology community ranging from electronics to nanocomposites. While the first two are carbon-based materials, the INWs in the literature include silicon, germanium, III-V, II-VI, a variety of oxides, nitrides, antimonides and others. In this talk, first an overview of growth of these three classes of materials by CVD and PECVD will be presented along with results from characterization. Then applications in development of chemical sensors, biosensors, energy storage devices and novel memory architectures will be discussed.

Koehne, Jessica E.↗

NASA NTRS2011

Nanotechnologv Enabled Biological and Chemical Sensors

Nanotechnology is an enabling technology that will impact almost all economic sectors: one of the most important and with great potential is the health/medical sector. - Nanomaterials for drug delivery - Early warning sensors - Implantable devices - Artificial parts with improved characteristics Carbon nanotubes and nanofibers show promise for use in sensor development, electrodes and other biomedical applications.

Koehne, Jessica↗

NASA NTRS2008

Biochips Containing Arrays of Carbon-Nanotube Electrodes

Biochips containing arrays of nanoelectrodes based on multiwalled carbon nanotubes (MWCNTs) are being developed as means of ultrasensitive electrochemical detection of specific deoxyribonucleic acid (DNA) and messenger ribonucleic acid (mRNA) biomarkers for purposes of medical diagnosis and bioenvironmental monitoring. In mass production, these biochips could be relatively inexpensive (hence, disposable). These biochips would be integrated with computer-controlled microfluidic and microelectronic devices in automated hand-held and bench-top instruments that could be used to perform rapid in vitro genetic analyses with simplified preparation of samples. Carbon nanotubes are attractive for use as nanoelectrodes for detection of biomolecules because of their nanoscale dimensions and their chemical properties.

Li, Jun↗

NASA NTRS2008

Carbon-Nanotube-Based Electrodes for Biomedical Applications

A nanotube array based on vertically aligned nanotubes or carbon nanofibers has been invented for use in localized electrical stimulation and recording of electrical responses in selected regions of an animal body, especially including the brain. There are numerous established, emerging, and potential applications for localized electrical stimulation and/or recording, including treatment of Parkinson s disease, Tourette s syndrome, and chronic pain, and research on electrochemical effects involved in neurotransmission. Carbon-nanotube-based electrodes offer potential advantages over metal macroelectrodes (having diameters of the order of a millimeter) and microelectrodes (having various diameters ranging down to tens of microns) heretofore used in such applications. These advantages include the following: a) Stimuli and responses could be localized at finer scales of spatial and temporal resolution, which is at subcellular level, with fewer disturbances to, and less interference from, adjacent regions. b) There would be less risk of hemorrhage on implantation because nano-electrode-based probe tips could be configured to be less traumatic. c) Being more biocompatible than are metal electrodes, carbon-nanotube-based electrodes and arrays would be more suitable for long-term or permanent implantation. d) Unlike macro- and microelectrodes, a nano-electrode could penetrate a cell membrane with minimal disruption. Thus, for example, a nanoelectrode could be used to generate an action potential inside a neuron or in proximity of an active neuron zone. Such stimulation may be much more effective than is extra- or intracellular stimulation via a macro- or microelectrode. e) The large surface area of an array at a micron-scale footprint of non-insulated nanoelectrodes coated with a suitable electrochemically active material containing redox ingredients would make it possible to obtain a pseudocapacitance large enough to dissipate a relatively large amount of electric charge, so that a large stimulation current could be applied at a micron-scale region without exhausting the redox ingredients. f) Carbon nanotube array is more compatible with the three-dimensional network of tissues. Particularly, a better electrical-neural interface can be formed. g) A carbon nanotube array inlaid in insulating materials with only the ends exposed is an extremely sensitive electro-analysis tool that can measure the local neurotransmitter signal at extremely high sensitivity and temporal resolution.

Li, Jun↗

NASA NTRS2005

Silicon nanowire synthesis by a vapor-liquid-solid approach

Synthesis of silicon nanowires is studied by using a vapor-liquid-solid growth technique. Silicon tetrachloride reduction with hydrogen in the gas phase is used with gold serving as catalyst to facilitate growth. Only a narrow set of conditions of SiCl4 concentration and temperature yield straight nanowires. High concentrations and temperatures generally result in particulates, catalyst coverage and deactivation, and coatinglike materials.

Evaluation Studies↗

NASA NTRS2005

A Survey of the Rapidly Emerging Field of Nanotechnology: Potential Applications for Scientific Instruments and Technologies for Atmospheric Entry Probes

The field of Nanotechnology is well funded worldwide and innovations applicable to Solar System Exploration are emerging much more rapidly than thought possible just a few years ago. This presentation will survey recent innovations from nanotechnololgy with a focus on novel applications to atmospheric entry science and probe technology, in a fashion similar to that presented by Arnold and Venkatapathy at the previous workshop forum at Lisbon Portugal, October 6-9, 2003. Nanotechnology is a rapidly emerging field that builds systems, devices and materials from the bottom up, atom by atom, and in so doing provides them with novel and remarkable macro-scale performance. This technology has the potential to revolutionize space exploration by reducing mass and simultaneously increasing capability. Thermal, Radiation, Impact Protective Shields: Atmospheric probes and humans on long duration deep space missions involved in Solar System Exploration must safely endure 3 significant hazards: (i) atmospheric entry; (ii) radiation; and (iii) micrometeorite or debris impact. Nanostructured materials could be developed to address all three hazards with a single protective shield, which would involve much less mass than a traditional approach. The concept can be ready in time for incorporation into NASA s Crew Exploration Vehicle, and possible entry probes to fly on the Jupiter Icy Moons

Meyyappan, M.↗

NASA NTRS2005

Growing Aligned Carbon Nanotubes for Interconnections in ICs

A process for growing multiwalled carbon nanotubes anchored at specified locations and aligned along specified directions has been invented. Typically, one would grow a number of the nanotubes oriented perpendicularly to a silicon integrated-circuit (IC) substrate, starting from (and anchored on) patterned catalytic spots on the substrate. Such arrays of perpendicular carbon nanotubes could be used as electrical interconnections between levels of multilevel ICs. The process (see Figure 1) begins with the formation of a layer, a few hundred nanometers thick, of a compatible electrically insulating material (e.g., SiO(x) or Si(y)N(z) on the silicon substrate. A patterned film of a suitable electrical conductor (Al, Mo, Cr, Ti, Ta, Pt, Ir, or doped Si), having a thickness between 1 nm and 2 m, is deposited on the insulating layer to form the IC conductor pattern. Next, a catalytic material (usually, Ni, Fe, or Co) is deposited to a thickness between 1 and 30 nm on the spots from which it is desired to grow carbon nanotubes. The carbon nanotubes are grown by plasma-enhanced chemical vapor deposition (PECVD). Unlike the matted and tangled carbon nanotubes grown by thermal CVD, the carbon nanotubes grown by PECVD are perpendicular and freestanding because an electric field perpendicular to the substrate is used in PECVD. Next, the free space between the carbon nanotubes is filled with SiO2 by means of CVD from tetraethylorthosilicate (TEOS), thereby forming an array of carbon nanotubes embedded in SiO2. Chemical mechanical polishing (CMP) is then performed to remove excess SiO2 and form a flat-top surface in which the outer ends of the carbon nanotubes are exposed. Optionally, depending on the application, metal lines to connect selected ends of carbon nanotubes may be deposited on the top surface. The top part of Figure 2 is a scanning electron micrograph (SEM) of carbon nanotubes grown, as described above, on catalytic spots of about 100 nm diameter patterned by electron-beam lithography. These and other nanotubes were found to have lengths ranging from 2 to 10 m and diameters ranging from 30 to 200 nm, the exact values of length depending on growth times and conditions and the exact values of diameter depending on the diameters and thicknesses of the catalyst spots. The bottom part of Figure 2 is an SEM of an embedded array of carbon nanotubes after CMP.

Li, Jun↗

NASA NTRS2005

Carbon Nanotubes/Nanofibers by Plasma Enhanced Chemical Vapour Deposition

Plasma enhanced chemical vapour deposition (PECVD) has been recently used for the production of vertically aligned carbon nanotubedfibers (CN) directly on substrates. These structures are potentially important technologically as electron field emitters (e.g. microguns, microwave amplifiers, displays), nanoelectrodes for sensors, filter media, superhydrophobic surfaces and thermal interface materials for microelectronics. A parametric study on the growth of CN grown by glow discharge dc-PECVD is presented. In this technique, a substrate containing thin film Ni catalyst is exposed to C2H2 and NH3 gases at 700 C. Without plasma, this process is essentially thermal CVD which produces curly spaghetti-like CN as seen in Fig. 1 (a). With the plasma generated by biasing the substrate at -6OOV, we observed that the CN align vertically during growth as shown in Fig. l(b), and that the magnitude of the applied substrate bias affects the degree of alignment. The thickness of the thin film Ni catalyst was found to determine the average diameter and inversely the length of the CN. The yield and density of the CN were controlled by the use of different diffusion barrier materials under the Ni catalyst. Patterned CN growth [Fig. l(c)], with la variation in CN diameter of 4.1% and 6.3% respectively, is achieved by lithographically defining the Ni thin film prior to growth. The shape of the structures could be varied from very straight nanotube-like to conical tip-like nanofibers by increasing the ratio of C2H2 in the gas flow. Due to the plasma decomposition of C2H2, amorphous carbon (a-C) is an undesirable byproduct which could coat the substrate during CN growth. Using a combination of depth profiled Auger electron spectroscopy to study the substrate and in-situ mass spectroscopy to examine gas phase neutrals and ions, the optimal conditions for a-C free growth of CN is determined.

Teo, K. B. K.↗

NASA NTRS2005

Electronic Transport through Self Assembled Thiol Molecules: Effect of Monolayer Order, Dynamics and Temperature

We present the charge transport and tunneling conductance of self assembled organic thiol molecules and discuss the influence of order and dynamics in the monolayer on the transport behavior and the effect of temperature. Conjugated thiol molecular wires and organometals such as terpyridine metal complexes provide a new platform for molecular electronic devices and we study their self assembly on Au(111) substrates by the scanning tunneling microscope. Determining the organization of the molecule and the ability to control the nature of its interface with the substrate is important for reliable performance of the molecular electronic devices. By concurrent scanning tunneling microscopy and spectroscopy studies on SAMs formed from oligo (phenelyne ethynelyne) monolayers with and without molecular order, we show that packing and order determine the response of a self assembled monolayer (SAM) to competing interactions. Molecular resolution STM imaging in vacuum shows that the OPES adopt an imcommensurate SAM structure on Au(111) with a rectangular unit cell. Tunneling spectroscopic measurements were performed on the SAM as a function of junction resistance. STS results show that the I-Vs are non linear and asymmetric due to the inherent asymmetry in the molecular structure, with larger currents at negative sample biases. The asymmetry increases with increasing junction resistance due to the asymmetry in the coupling to the leads. This is brought out clearly in the differential conductance, which also shows a gap at the Fermi level. We also studied the effect of order and dynamics in the monolayer on the charge transport and found that competing forces between the electric field, intermolecular interactions, tip-molecule physisorption and substrate-molecule chemisorption impact the transport measurements and its reliability and that the presence of molecular order is very important for reproducible transport measurements. Thus while developing new electronic platforms based on molecules, it is important to have a good control of the molecule-substrate interface, for the devices to perform reliably. While such a control would minimize fluctuations and dynamics in the ensemble, the real challenge is to develop device architectures that are tolerant to fluctuations, since they cannot be totally eliminated in these low dimensional soft systems. Results of temperature dependent STS measurements will also be discussed.

Dholakia, Geetha↗

NASA NTRS2005

Phase-Imaging with a Sharpened Multi-Walled Carbon Nanotube AFM Tip: Investigation of Low-k Dielectric Polymer Hybrids

Phase shift tapping mode scanning force microscopy (TMSFM) has evolved into a very powerful technique for the nanoscale surface characterization of compositional variations in heterogeneous samples. Phase shift signal measures the difference between the phase angle of the excitation signal and the phase angle of the cantilever response. The signal correlates to the tip-sample inelastic interactions, identifying the different chemical and/or physical property of surfaces. In general, the resolution and quality of scanning probe microscopic images are highly dependent on the size of the scanning probe tip. In improving AFM tip technology, we recently developed a technique for sharpening the tip of a multi-walled carbon nanotube (CNT) AFM tip, reducing the radius of curvature of the CNT tip to less than 5 nm while still maintaining the inherent stability of multi-walled CNT tips. Herein we report the use of sharpened (CNT) AFM tips for phase-imaging of polymer hybrids, a precursor for generating nanoporous low-k dielectrics for on-chip interconnect applications. Using sharpened CNT tips, we obtained phase-contrast images having domains less than 10 nm. In contrast, conventional Si tips and unsharpened CNT tips (radius greater than 15 nm) were not able to resolve the nanoscale domains in the polymer hybrid films. C1early, the size of the CNT tip contributes significantly to the resolution of phase-contrast imaging. In addition, a study on the nonlinear tapping dynamics of the multi-walled CNT tip indicates that the multi-walled CNT tip is immune to conventional imaging instabilities related to the coexistence of attractive and repulsive tapping regimes. This factor may also contribute to the phase-contrast image quality of multi-walled CNT AFM tips. This presentation will also offer data in support of the stability of the CNT tip for phase shift TMSFM.

Nguyen, Cattien V.↗

NASA NTRS2004

Improvement of thermal contact resistance by carbon nanotubes and nanofibers

Interfacial thermal resistance results of various nanotube and nanofiber coatings, prepared by chemical vapor deposition (CVD) methods, are reported at relatively low clamping pressures. The five types of samples examined include multi-walled and single-walled nanotubes growth by CVD, multi-walled nanotubes grown by plasma enhanced CVD (PECVD) and carbon nanofibers of differing aspect ratio grown by PECVD. Of the samples examined, only high aspect ratio nanofibers and thermally grown multi-walled nanotubes show an improvement in thermal contact resistance. The improvement is approximately a 60% lower thermal resistance than a bare Si-Cu interface and is comparable to that attained by commercially available thermal interface materials.

Evaluation Studies↗

NASA NTRS2004

Ultrasensitive Label-free Electronic Chip for DNA Analysis Using Carbon Nanotube Nanoelectrode Arrays

There is a strong need for faster, cheaper, and simpler methods for nucleic acid analysis in today s clinical tests. Nanotechnologies can potentially provide solutions to these requirements by integrating nanomaterials with biofunctionalities. Dramatic improvement in the sensitivity and multiplexing can be achieved through the high-degree miniaturization. Here, we present our study in the development of an ultrasensitive label-free electronic chip for DNA/RNA analysis based on carbon nanotube nanoelectrode arrays. A reliable nanoelectrode array based on vertically aligned multi-walled carbon nanotubes (MWNTs) embedded in a SiO2 matrix is fabricated using a bottom-up approach. Characteristic nanoelectrode behavior is observed with a low-density MWNT nanoelectrode array in measuring both the bulk and surface immobilized redox species. The open-end of MWNTs are found to present similar properties as graphite edge-plane electrodes, with a wide potential window, flexible chemical functionalities, and good biocompatibility. A BRCA1 related oligonucleotide probe with 18 bases is covalently functionalized at the open ends of the MWNTs and specifically hybridized with an oligonucleotide target as well as a PCR amplicon. The guanine bases in the target molecules are employed as the signal moieties for the electrochemical measurements. Ru(bpy)3(2+) mediator is used to further amplify the guanine oxidation signal. This technique has been employed for direct electrochemical detection of label-free PCR amplicon through specific hybridization with the BRCAl probe. The detection limit is estimated to be less than approximately 1000 DNA molecules, approaching the limit of the sensitivity by laser-based fluorescence techniques in DNA microarray. This system provides a general electronic platform for rapid molecular diagnostics in applications requiring ultrahigh sensitivity, high-degree of miniaturization, simple sample preparation, and low- cost operation.

Li, Jun↗

NASA NTRS2004

Modeling of Sheath Ion-Molecule Reactions in Plasma Enhanced Chemical Vapor Deposition of Carbon Nanotubes

In many plasma simulations, ion-molecule reactions are modeled using ion energy independent reaction rate coefficients that are taken from low temperature selected-ion flow tube experiments. Only exothermic or nearly thermoneutral reactions are considered. This is appropriate for plasma applications such as high-density plasma sources in which sheaths are collisionless and ion temperatures 111 the bulk p!asma do not deviate significantly from the gas temperature. However, for applications at high pressure and large sheath voltages, this assumption does not hold as the sheaths are collisional and ions gain significant energy in the sheaths from Joule heating. Ion temperatures and thus reaction rates vary significantly across the discharge, and endothermic reactions become important in the sheaths. One such application is plasma enhanced chemical vapor deposition of carbon nanotubes in which dc discharges are struck at pressures between 1-20 Torr with applied voltages in the range of 500-700 V. The present work investigates The importance of the inclusion of ion energy dependent ion-molecule reaction rates and the role of collision induced dissociation in generating radicals from the feedstock used in carbon nanotube growth.

Hash, David B.↗

NASA NTRS2004

Low-Temperature Plasma Functionalization of Carbon Nanotubes

A low-temperature plasma process has been devised for attaching specified molecular groups to carbon nanotubes in order to impart desired chemical and/or physical properties to the nanotubes for specific applications. Unlike carbon-nanotube- functionalization processes reported heretofore, this process does not involve the use of wet chemicals, does not involve exposure of the nanotubes to high temperatures, and generates very little chemical residue. In addition, this process can be carried out in a relatively simple apparatus and can readily be scaled up to mass production.

Khare, Bishun↗

NASA NTRS2004

The Role of Plasma in Plasma Enhanced Chemical Vapour Deposition of Nanostructure Growth

Chemical vapour deposition (CVD) has become the preferred process for high yield growth of carbon nanotubes and nanofibres because of its ability to pattern growth through lithographic positioning of transition metal catalysts on substrates. Many potential applications of nanotubes such as field emitters [1] require not only patterned growth but also vertical alignment. Some degree of ali,ment in thermal CVD processes can be obtained when carbon nanotubes are grown closely together as a result of van der Waals interactions. The ali,onment however is marginal, and the van der Waals prerequisite makes growth of freestanding nanofibres with thermal CVD unrealizable. The application of electric fields as a means of ali,onment has been shown to overcome this limitation [2-5], and highly aligned nanostructures can be grown if electric fields on the order of 0.5 V/microns are employed. Plasma enhanced CVD in various configurations including dc, rf, microwave, inductive and electron cyclotron resonance has been pursued as a means of enabling alignment in the CVD process. However, the sheath fields for the non-dc sources are in general not sufficient for a high degree of ali,pment and an additional dc bias is usually applied to the growth substrate. This begs the question as to the actual role of the plasma. It is clear that the plasma itself is not required for aligned growth as references [3] and [4] employed fields through small applied voltages (3-20 V) across very small electrode spacings (10-100 microns) and thus avoided striking a discharge.

Hash, David B.↗