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04 10-20 nano-sensor report


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A report on nano-scale sensors for next generation space based missions.

A report on nano-scale sensors for next generation space based missions.

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  • 1. National Nanotechnology Initiative Grand Challenges: Nanotechnology in Space Exploration Nanosensors and Instrumentation Vision Advances in nanotechnology are expected to enable and enhance both supporting and mission-critical technologies in the near future. These advances will be critical in meeting the challenges of new space missions in the decades to come,. The vision is to capitalize on the investment within academic, government, and industrial research circles and provide nanoscale sensors and instrumentation that enhance existing space mission capabilities while enabling new mission concepts that are prohibitive or impossible without this technology. The vision for nanosensors in space exploration covers remote sensing, vehicle health and performance, astrobiological and geochemical research, and manned space flight. With a continued investment in fundamental research and strategic development for space-based applications, nanotechnology is expected to provide important mission- critical components for next-generation aerospace and astronautical sensors and instrumentation. For the last 40 years, the microelectronics, chemical synthesis, and biological research communities have pioneered novel top-down and bottom-up manufacturing, characterization, and manipulation technologies. Operating at nanometer dimensions, the synergy of these technologies is the basis for a growing industrial revolution in nanotechnology. The potential of nanotechnology is a reduction in payload mass compared to similar Apollo era systems with a consequent increase in performance. Mission engineers developing next-generation technologies for the exploration of space should consider the potential operational improvements offered by a nanoscale approach. Following the incorporation of microelectromechanical (MEM) technology in current mission concepts over the past 25 years of academic and industrial partnerships, space missions expected to benefit from critical nanotechnology enhancements will probably have launch windows from 2015 to 2025 and beyond. It is therefore essential for current research development efforts to continue over the next 10 to 15 years with a focus on mission-enabling technologies. The envisioned return on investment falls into several areas: bulk materials production, novel sensors, standardized integration, compact biological research laboratories, next-generation vehicle sensor systems, and rapid technology infusion. Bulk Materials Production: The low-cost bulk fabrication of carbon nanotubes and other inorganic and organic nanostructures or their hybrids with selected properties will facilitate their large-scale use in sensor systems throughout the aerospace industry. Facilities will refine nanomaterials based on desired physical and electromagnetic properties. Novel Sensors: Nanoscale devices are expected to exhibit quantum phenomena at elevated temperatures. Sensor developers will therefore employ capabilities previously 1
  • 2. attainable at only very low temperatures. Nanoscale devices will necessarily operate at natural frequencies within the 100 MHz to 1 GHz range. To be viable, however, nanosensors for use in space instruments should have both higher sensitivity and a higher operating temperature than current devices. The requirement of higher sensitivity and higher operating temperature can only be met if basic research and the search for applications are vigorously pursued in tandem. Standardized Integration: The development of nanoscale interface techniques will facilitate the rapid integration of nanodevices into conventional electronics and applicable devices. The incorporation of ancillary components such as power supplies, processors, and wireless connections will reduce the number of connections between the nano- and the macroworld. A fully integrated system of sensors, processors, and network infrastructure could generate a palm-sized space probe. Compact Biological Research Laboratories: Current space missions are designed to visit the distant planets and moons of our solar system in a search for the signs of life. It is unknown whether the signature of life exists in a fossilized record, a priori chemical building blocks, or some other form, if at all. Should the signature consist of fundamental chemical components, the in-situ capability for nanoscale manipulation and analysis may be an essential research tool. Onboard, space-qualified analysis systems can provide the necessary selection criteria for subsequent sampling missions and more detailed laboratory analysis. In the search for biochemical building blocks within the solar system, nanoscale lab-on-a-chip sensors may be essential for evaluating the potential for extraterrestrial life if not also its form and function. Similar laboratory sensors should also be relevant to spacecraft environmental monitoring and control (e.g. water-quality management) and astronaut health and safety (e.g. biochemical monitoring of blood, urine, etc.). Next-Generation Vehicle Sensor Systems: With future missions to the Moon and Mars, next-generation sensors must monitor the condition of critical vehicle systems and crew environments. Most current systems have limited monitoring capabilities because comprehensive sensor systems are prone to failure and require labor intensive maintenance. In general, existing sensor systems do not assist in the recertification of spacecraft following each mission. A manual inspection of flight critical hardware is an identified bottleneck in the return-to-flight process. Comprehensive diagnostics of vehicle health necessitate increased sensor reliability, durability, and coverage. Embedded or integrated sensing technologies that form a distributed vehicle nervous system are envisioned for next-generation programs. Networked sensor technologies provide in- place vehicle diagnostics along with a framework for active in-flight corrections and feedback control. With minimal size, weight, and power requirements, nanosensor networks could enable smart, self-aware vehicle designs. Embedded sensors should be stand-alone, self-calibrating, and self-regulating systems complete with signal conditioning, power, and communication capabilities. Combined with future information systems technology, embedded micro- and nanoscale sensor networks could form the critical capability needed to improve mission performance while monitoring and accommodating unexpected subsystem level failures. 2
  • 3. Rapid Technology Infusion: Novel sensors should be included early in the design phase of next-generation developments rather than as a forced-fit afterthought. Experience shows that technology managers should carefully partner nanoscale researchers and sensor systems developers with end users so new approaches can rapidly win the support of the aerospace community. It is in providing new capabilities that nanosensor technology can revolutionize future missions though savings in weight, power, volume, and performance. Major Challenges Nanoscale developers face many of the same problems addressed at the microlevel: materials, structures, and processes. Materials include thin films and novel compounds and properties. Structures are not only the layering of materials, but also the three-dimensional shape of nanocomponents and their interaction properties. Processes are the means by which materials and structures are handled in the construction of functional devices. As emphasized by Dr. Timothy Krabach (JPL), the physics of behavior for molecules and atoms at the nanoscale is poorly understood. This suggests that the nanotechnology’s full potential will be realized only when such “new” laws are established and understood. The methodology of nanoscale sensors faces several challenges in meeting the visions outlined above. Production and Refinement: The production of carbon, metal, and oxide nanotubes and structures is limited. Refinement and purification techniques are needed to select chemical, electrical, and mechanical subgroups of species produced in bulk volumes. Manipulation and Control: Nanoscale materials require similar sized handling techniques; yet these techniques must be driven at macroscale dimensions. Lithography: Reliable nanoscale deposition of materials (e.g. inks, masks or nanoindentations). Macro–Micro–Nano Integration: Bridging the gap between the macro- and nanoworld requires standardized interfaces and yet-to-be-developed tools. Wireless communication may be applicable along with networked communication infrastructures. Toxicology: Nanoscale materials must be safely stored, handled, and recycled. Standardized practices are needed to protect our communities and the environment. Robust and Reliable Architectures: The inherent anomalies of nanoscale fabrication may require greatly improved fault-tolerant designs. Radiation hardness may come from nanoscale systems’ inherent multiplicity of capability. Self-Calibrating Networks: Large sensor networks must be self-calibrating. Networking technologies must be efficient and employ error-correcting capabilities. 3
  • 4. Data Fusion: Heavily networked sensor systems may generate data fusion problems similar to the problems faced by massive data warehouses. Solutions may be found outside of typical aerospace disciplines. Current Scientific/Technical Status Working at the nanoscale, researchers have demonstrated improved devices. Workshop participants summarized current efforts and outlined areas needing improvement. Chemical Sensors: Researchers from NASA and university research facilities are concerned with sensors for emission monitoring, fuel leak detection, fire detection, and environmental detection of hydrocarbons and hydrazine. From the NASA Glenn Research Center (GRC), Dr. Gary Hunter discussed the development of sensors based on micromachining and microfabrication technology and the use of nanocrystalline materials. The performance of nanoscale sensors must match existing solutions in areas of: - Response time, sensitivity, selectivity, and stability - Power, packaging, signal conditioning, and communications - Ease of deployment, reliability, redundancy, and orthogonality The development of a lock-and-key sensing geometry at nanoscale dimensions may enable the identification of unique electrochemical molecular signatures. Dr. Pedro Medelius (ASRC Aerospace Corporation) reported on efforts aboard the space shuttle to improve leak detection using several compact spectrometers as an “electronic-nose.” An electronic nose experiment from JPL flew on STS-95 in 1998 ( The installation of necessary wiring adds to sensor deployment costs while increasing the risk of performance failures. A replacement for existing copper wiring approaches (i.e. conductive or organic polymers or carbon nanotubes) with more robust and reliable performance is desirable. Dr. Sudipta Seal (University of Central Florida) reviewed the performance of MEM sensors using tin oxides (SnO2) as a function of environment and nanoparticulate composition.1 Recent developments include the use of doped SnO2 nanofibers grown by Dr. Meyya Meyyappan’s group at the NASA Ames Research Center and characterized using focused ion beams and high-resolution transmission electron microscopy. Nanofibers are gaining attention because of their high surface-to-volume ratio, preferred grain orientation, and alignment of vacancies for conduction. Particulate and fiber nanostructures of SnO2 are expected to sense hydrogen at lower temperatures (25–50 C) and in more oxygen-free environments compared to existing thin-film technologies. Dr. Nicholas Prokopuk (Naval Air Warfare Center) discussed the development of nanogap architectures and amperometric techniques as nanoscale chemical sensors. 1 S. Shukla, S. Seal, L. Ludwig and C. Parrish (2004), “Nanocrystalline indium oxide doped tin oxide for low temperature hydrogen gas sensor,” Sens. Actuators B-Chemical, 97 (2-3), 256-265. 4
  • 5. Nanogap chemiresistors are based on the change in electron tunneling currents with the chemical identity of the intervening material. Nanogap sensors with gaps of 1–5 nm are created in the fabrication of nanoscale crossbar arrays, thus maximizing sensor element density. A similar approach is used for amperometric sensors where a biological key is bound to an electrode with an electron mediator. In response to a selective biomolecular reaction, an electrical current is generated. Modifying the surface of the device controls the selectivity and specificity of these sensors. Arrays of sensors can recognize patterns of analytes. Professor James Morris (Portland State) is applying his past experience with thin- film arrays of metal nanoparticles to the development of single-electron transistor (SET) sensors. Optimization in a SET structure will greatly enhance the demonstrated thin-film performances of strain gage factors in the 100s, and of ppm hydrogen sensitivity with discrimination at response times under a minute. Both examples exploit the exponential dependence of the electron tunneling current on gap width. Current research is focused on the fabrication of stable 1–2 nm islands for 77 K or room temperature operation. Integrated Nanotube Sensors: Next-generation vehicle designers envision the integration of multifunctional materials. With the broad-based acceptance of composite materials, the potential inclusion of metallic or semiconducting nanostructures appears both feasible and attractive. Based on the predicted strength-to-weight advantage, single walled carbon nanotubes (SW-CNT) are the focus of studies in the use of nanotubes to make “smart” vehicle skins able to sense mechanical strain and ambient pressures and temperatures. Dr. Anthony N. Watkins (NASA Langley) described research on the handling and mechanical characterization of SW-CNT as strain-sensitive gauges. Currently, the limited availability of nanotubes with selected properties makes large area strain-sensitive skins impractical. Initial experiments at NASA Langley have focused on developing a CNT-based strain sensor. The fabrication steps are illustrated in Figure 1. Laboratory results indicate that CNT-based strain gauges follow commercial standards when comounted to the backside of a 2023-T3 aluminum beam. Further improvements in the CNT sensor design include new dispersion techniques for the deposition of individual CNT, extending the design to an array of sensors, and allowing the creation of CNT-based sensors for other structural health parameters. Devices have been prototyped to demonstrate this approach to integrated and efficient vehicle-health management. Multifunctional structures that enable system-wide health monitoring and adaptive structures will fill the need for improved reliability and safety in next-generation vehicles. CNT Cathode X-ray Tube: Mr. Robert Espinosa (Microwave Power Technology) highlighted the use of carbon nanotubes (CNT) as cold-field emission cathodes and electron sources in X-ray tubes for hand held and portable X-ray fluorescence (XRF) spectrometers. Cold emission cathodes require less power while offering a simple, rugged design. Multiwalled CNT (MW-CNT) cathodes are grown via a thermal chemical vapor deposition process on substrates with metal catalysts. Developed jointly by Microwave Power Technology and Oxford Instruments, the current CNT tubes provide an X-ray spot less than 40 µm in diameter and are suitable for X-ray diffraction (XRD) spectrometry. 5
  • 6. XRD is essential for the characterization of mineral and organic crystalline structures throughout the solar system. Electron beams are also finding applications in a growing number of industrial, medical, and environmental areas (e.g. destruction of volatile hydrocarbons and biological and chemical agents). Space-related applications of CNT cathodes include purifying the air in base stations, eliminating toxic products and biological toxins, and the sterilization of materials. CNT cold-field emission cathodes are suitable for both planetary rovers and long-duration space missions. Nanotribology: As reviewed by Prof. Bharat Bhushan (Ohio State University), tribology is the study of surface interactions and encompasses the complex areas of friction, wear, lubrication, and surface characterization.2 Enabled by developments in atomic force microscope (AFM) and frictional force microscope (FFM) techniques, tribology has successfully addressed the nature of stiction, friction, and mechanical wear at the MEM scale (e.g. the characterization and improvement of digital micromirror operational performance). Comparable progress is expected as nanoelectrical mechanisms are developed and their operational characteristics are studied. For many devices that involve relative surface motions, tribological studies are essential. The AFM is the fundamental tool for quasistatic and dynamic mechanical characterization of nanostructures. AFM studies provide direct measurements of the Young’s modulus of elasticity, the fatigue strength, and the critical fracture strength on the nanoscale. Such macro- and microscale parameters are expected to differ at nanoscale dimensions. Nanotribology characterizes the high adhesion surface of monolayer depositions and gauges the effect of surface contaminants. The performance of nanoscale lubricants can be characterized under typical and extreme environments. Research efforts need to focus on key issues such as the development of high adhesion surfaces for molecule-specific receptors, low surface energy surface depositions, the perfection of fabrication processes for polymeric materials, and the hydrophobicity of surfaces. Current efforts include the development of spectroscopic techniques in conjunction with probe- based tribology. At Ohio State, laboratory studies have included the effects of oxide and diamond- like coatings, ion implantation, self-assembled monolayers, and ultrathin bonded perfluoropolyether lubricant films. The scaling effect of adhesion, friction, and wear have been measured and modeled. Additional studies have included the adhesion and friction of various lubricant films used in microfluidics and the modeling of bioadhesion for nanoscale drug-delivery devices. In the area of biomimetics, Dr. Bhushan’s laboratory has measured the surface roughness present on lotus and other leaves and characterized the surface films to understand the mechanism responsible for high hydrophobicity. Hydrophobic laboratory surfaces are now possible. AFM tips are typically made of single-crystal silicon, silicon nitride, or diamond. Recent efforts have focused on CNT as the AFM scanning probe tip. Dr. Cattien V. Nguyen (Eloret Corporation) discussed the unique mechanical properties of CNT as AFM probe tips. Existing approaches use both SW- and MW-CNT. A unique fabrication process development at NASA Ames produces very robust MW-CNT tips with a high 2 B. Bhushan (1999), Handbook of Micro/Nanotribology, 2nd ed. CRC Press, Boca Raton, Florida. 6
  • 7. aspect ratio (> 1 µm in length and 10–20 nm in diameter). In addition, a novel and simple tip sharpening technique has been developed to reduce the radius of curvature of the MW-CNT tips (radius < 5 nm). As a result, CNT tips can image high aspect ratio features with higher lateral resolution. The nanotube tips are used in a number of different scanning problem techniques—magnetic force, chemical force, semiconductor metrology, and liquid imaging of biopolymers. Select CNT tips are also electrically conductive and, so, are useful for scanning probe lithography (SPL). Operated by passing an electrical current between the CNT tip and substrate while scanning, SPL can form chemically patterned surfaces with nanometer accuracy. With SPL, the nanotube tip offers a high resolution and precise means for nanoscale material deposition and opens up many possibilities for nanoscale device fabrication. Semiconductor Quantum Dots: The stringent requirements of space applications for infrared detector arrays include high quantum efficiency, extremely low noise, ambient (radiatively cooled) operation, radiation hardness, etc. Dr. Sarath Gunapala (JPL) introduced semiconducting quantum dots (QD) as promising optoelectronic devices. Because the nanoscale carrier confinement is in all three dimensions (d ~ 20–60 nm), QD have discrete energy levels with sharp delta-function–like electron state densities, large optical nonlinearity, lower dark current (as a result of weak electron-photon coupling), and a high radiation tolerance. Unlike quantum well infrared photoconductors (QWIP), QD infrared photodetectors (QDIP) work under normally incident radiation at near- infrared (< 5 µm) wavelengths. Work at JPL in the development of site- and size-controlled semiconductor QD relied on molecular beam epitaxial (MBE) growth on GaAs substrates for suitable demonstration sensors. Although fabrication methods using self-organization (e.g. Stranski–Krastanov growth) are widely studied, site and size control of multilayered QD material has not been successful to date. Dr. Gunapala did present the latest results of QDIP grown by Stranski–Krastanov techniques. Operating at temperatures of 150 K, QDIP have shown detectivities of D* = 2 x 1010 , which is a factor of 10 higher than other uncooled sensors (e.g. silicon microbolometers). In addition, QDIP have very high carrier lifetimes. In the past several years, high density In(As)Sb QD on InP substrates have performed as distributed feedback lasers at 1.3 µm. With an area density of 4 x 1010 cm-2 , the In(As)Sb QD at room temperature emit luminescence at a wavelength of 1.7–2.3 µm. [QD lasers operating at 2 µm in continuous wave mode (cw) were demonstrated. Narrow- ridge waveguide lasers lased at up to 25 C in cw operations.] For both QD lasers and QDIP fabrication, a considerable number of challenges remain unresolved by developers: - Definition of periodic nanofeatures (< 10 µm) with E-beam lithography - Definition and control of nanofeature profiles - Transfer of nanofeatures to GaAs substrates - Preservation of nanofeatures during substrate cleaning and prior to MBE growth - Optimization of the multilayer QD structure Single-Electron Transistors: Dr. Carl Stahle re-presented developments at NASA GSFC in SET technologies. The SET can be used as a very low-noise, fast, muliplexable, 7
  • 8. readout amplifier integrated with cryogenic detectors to produce ultrasensitive, large format detector arrays for high priority NASA missions in the far-infrared and submillimeter ranges. SET are quantum-effect devices that use the quantization of charge on nanoscale islands and function as very-high-performance electrometers.3 The nanometer scale of the tunnel junction between the small metallic “island” and the source and drain is essential to the charge quantization of the SET. If the capacitance across the tunnel junctions is small enough, the current flow is blocked by charging effects and regulated by a potential applied to the capacitive gate. The response of source–drain current to gate charge is periodic, with a period equal to one electron’s gate charge. The GSFC SET operate at below 1 K with a subfemtofarad input capacitance and dissipate only picowatts of power. Figure 2 shows the fabrication and circuit schematic of a radio- frequency (RF) SET4 with its readout and multiplexing electronics. A two-channel RF- SET system has been demonstrated and a fifty-channel system is under development at GSFC. Novel Developments in Nanotechnology Several examples are highlighted from the presentations of workshop participants. Each example demonstrates the capabilities of current laboratory efforts to apply nanoscale solutions to the visions and challenges discussed above. Functionalized Nanowire Surfaces for Biochemical Characterization: Dr. Brian Hunt (JPL) described the characterization of semiconducting nanowire chemical sensors based on the change in conductance as the wire’s surface adsorbs molecules. The device acts as a chemically sensitive field-effect transistor in which the conductance change arises from the electrostatic gating or charge transfer from the attached molecule. Laboratory results have demonstrated detection limits in the picomolar to femtomolar range for a few model molecular systems.5 Nanowire molecular sensors operate at sub-nWatt power levels and can be made chemically specific with functionalized wire surfaces. Work at JPL demonstrated nanowire chemical sensors using CNT and silicon nanowires grown by chemical vapor deposition from nanoscale catalyst particles. The CNT devices are produced using lithographically patterned molybdenum electrodes followed by the definition of an iron nanoparticle catalyst region and CVD growth of the nanotubes. The resulting single-wall nanotubes have electrode gaps ranging from 100 nm to 2 µm. The Si nanowire is grown from Au nanoparticle catalysts or nm-thickness Au films followed by patterning with Ti/Au electrodes. Previous chemical sensing efforts at JPL have focused on bare, unfunctionalized nanowires for both gas and liquid phase chemical sensing. The liquid phase testing aimed at measurements of amino acids in water—a key molecule of interest in astrobiology. Preliminary conductance–time 3 T. A. Fulton and G. J. Dolan (1987), “Observation of single-electron charging effects in small junctions,” Phys. Rev. Lett. 59, 109. 4 R. J. Schoelkopf, P. Wahlgren, A. A. Kozhevnikov, P. Delsing, and D. E. Prober (1998), “The radio- frequency single-electron transistor (RF-SET): A fast and ultrasensitive electrometer,” Science, 280, 1238. 5 Hahm and Lieber (2004), Direct ultrasensitive electrical detection of DNA and DNA sequence variations using nanowire nanosensors, Nano Letters, 4, 51. 8
  • 9. measurements of electrically gated nanotube sensors were made as the concentrations of three different amino acid solutions were varied. These experiments showed clear differences in the conductance for arginine, aspartic acid, and tryptophan. Further studies are under way to optimize the sensitivity via adjustment of the device gate voltage and to understand the effect of pH. Initial measurements suggest that even unfunctionalized nanotubes may be useful in amino acid sensing. Efforts to functionalize Si/SiO2 surfaces for the detection of biomolecules used oxysilane chemical links to attach biotin as a model receptor. Chemically specific reactions with the model target molecule streptavidin, labeled with a Au nanoparticle, were verified with AFM and SEM measurements. Functionalized nanowire surfaces may eventually enable chemically specific sensing of a variety of different molecules in nanowire sensor arrays. Chirally specific sensing of biomolecules is attractive as a potential indicator of extraterrestrial life. Nanoscale mapping of chemical heterogeneity: Dr. Tinh Nguyen (National Institute of Standards and Technology) described the on-going development of techniques for providing the mapping of surfaces at nanoscale resolutions using chemically functionalized conventional AFM probes or a chemically modified CNT. By manipulating the relative humidity (RH) of the tip-sample environment, AFM tips can image nanoscale hydrophilic and hydrophobic regions for the investigation of self- assembled monolayers and polymer blend samples. Thiol chemistry created CH3 and COOH functionalized AFM tips. Using a NIST-patented humidity chamber, the functionalized AFM tips generated high-contrast images of hydrophilic and hydrophobic regions with RH values of > 50%. At high RH levels, AFM imaging could detect the minor difference in polar surface energies between different surface chemical domains. Mechanical Resonators: Professor Nick Melosh (Stanford) presented an interesting alternative to electrochemical-based detection methods for gas- and liquid-phase analytes. As with any mechanical system, the length and stiffness of a structure implies a natural resonance frequency. For metallic nanowires 20 nm in length under stochastic excitation, the resultant natural frequency of vibration is in the range of 100–200 MHz and can be detected as a magnetic-field induced voltage. The adsorption of individual molecules causes a measurable change in the natural frequency. In a viscous liquid, the natural frequency will also change as molecules adsorb to the wire’s surface with a resultant change in the viscous damping coefficient. For a typical protein of 8 nm in diameter, the change in viscous drag is approximately 2%. Laboratory measurements indicate that nanoscale mechanical resonators can detect three proteins with 99% confidence. This detection method has been found to be linear up to an adsorption of 3,000 proteins. Such a resonant sensor is attractive for micro fluidic systems and is also orthogonal to electrochemical sensing techniques. Nanorheostats: Dr. John Cumings (Stanford) emphasized the emerging use of transmission electron microscopy as a powerful tool for studying the dynamic properties of nanoscale devices. TEM studies have uncovered important and subtle effects in device operation such as structural changes, chemical sensitivities, electromagnetic fields, and heat flow. Dr. Cumings’ work focused on a novel in-situ nanomanipulation probe for 9
  • 10. handling MW-CNT. TEM imaging demonstrated the telescopic extension of MW-CNT using the in-situ probe. Laboratory measurements have determined the friction forces between nanotube surfaces and the variation in nanotube electrical resistance with extension. As indicated, the MW-CNT can potentially serve as a nanoscale rheostat. Research efforts have demonstrated the wealth of information available through TEM studies of nanodevices. Nanofluidic, Size-Exclusion Chromatography: The search for life on other planetary bodies will require extremely miniature, low power instruments capable of detecting microbial forms in unknown states (extant, dormant, extinct, or fossilized) with unknown chemical building blocks and in unknown concentrations. Dr. Sabrina Feldman (NASA ARC), working with engineers and scientists from JPL, is developing a nanofluidic lab- on-a-chip based upon the principles of size-exclusion chromatography (SEC) that may provide information on the geochemical and biological history of soil, ice, and water samples through the identification and quantification of polar and nonpolar macromolecular compounds. The molecular separation of SEC is based on the characteristic elution times of molecules traveling through microcolumn channels with thousands of nanoscale features. SEC is a standard technique on Earth for studying humus, oils, bitumen, and other organic substances in soil and sediment samples. Organic macromolecule separation using SEC requires only that molecules differ in diameter and avoids the second-guessing with regard to missing classes of organic molecules. Nano- SEC offers significant advantages when compared with instruments designed to detect target classes of organic compounds because nano-SEC can provide definite and interpretable information even if the organic macromolecule development followed a different path on other planetary bodies. The conventional SEC column is packed with silica or polymer beads with dimensions of 10 µm and average pore sizes of 10–1000 nm. Dr. Feldman’s proposed instrument is well suited for the separation and analysis of complex mixtures with an unknown chemical state using either aqueous or organic solvents. Macromolecules can be formed through abiotic and biotic processes. On other planets, their discovery may provide clues about ancient organic in-fall from comets or meteorites as well as about the presence of extant or extinct life. Nanopore Gating of Single Molecules: Professor Holger Schmidt (University of California at Santa Cruz) discussed a new approach to fabricating integrated optical sensors for ultrasmall liquid or gaseous sample volumes. Hollow-core antiresonant reflecting optical waveguides6 and nanopores are combined to achieve single-molecule sensitivity and selectivity. Using a focused ion beam, individual nanopores are etched with diameters of < 60 nm. Such nanoscale pores act as gates for selective introduction of individual molecules into fluidic waveguides for the study of optical properties and resonant photonic states. Changes in the ionic current blockade as molecules pass through pore openings allow one to electrically distinguish individual biomolecules. By combining these nanopores with integrated optics, the optical properties of molecules can be simultaneously studied using standard spectroscopic techniques (e.g. fluorescence, 6 D. Yin, H. Schmidt, J. P. Barber, and A. R. Hawkins (2004), "Integrated ARROW waveguides with hollow cores," Optics Express, 12, 2710. 10
  • 11. molecule-specific Raman scattering). The current research seeks to integrate the gating and sensing technology in a lab-on-a-chip design. Electrophoretic Nanofabrication: Benjamin Sullivan outlined ongoing research with Dr. Michael Heller at the University of California San Diego on the development of microelectronics arrays for the electrophoretic and dielectrophoretic control and assembly of nanoscale components. The fabrication of homogeneous and precisely functionalized nanocomponents on a manufacturing scale is both difficult and expensive. While self- assembly at the nanoscale is possible under certain limited conditions (based on biological models), trying to use self-assembly alone to create viable higher-order integrated devices maybe be a somewhat naïve approach. Developed for genomic research and DNA diagnostic applications, CMOS microarray devices generate configurable electric field geometries for the surface transport of charged reagent and analyte molecules (DNA, RNA, oligonucleotide probes, amplicon antibodies, proteins, enzymes, nanoparticles, and micrometer-sized semiconductor devices). Laboratory demonstrations of electric field assisted self- assembly illustrate the potential for nanoscale fabrication using this approach. Other methods do not provide as precise a control of nanoscale structures. In addition, electrophoretic and dielectrophoretic methods can control how functional groups (chemical ligand, proteins, DNA, etc.) are arranged around core nanostructures. Current efforts will allow different nanocomponents to be assembled in a precise manner to create more heterogeneous higher-order nanostructures. Because these processes must be carried out in highly parallel formats, it will be imperative to create detailed mechanical models of the interactions of the nanocomponents so that experimental parameterization can drive programmed assembly. The success of electric field directed self-assembly at the nanoscale depends on the development of stable, homogeneous micro- and nanoelectrode array platforms that can carry out the assisted, highly parallel assembly of components. Goals The goal of nanosensors and instrumentation production is the demonstration of solutions that employ the novel properties of nanoscale materials. Pushing toward smaller feature sizes will also necessitate innovation for integration between the nano- and microscales. With an example provided by Dr. Paul Drzaic (Alien Technology Corp.), fluidic self or assisted assembly may provide an important construct for bridging the multiple size scales involved in nanoscale technology integration. New materials will require an improved understanding and control of the fabrication processes. In addition, developments in fault tolerant architectures needed for nanoscale structures are likely to prove beneficial in the harsh radiative environment of space. The use of heavily instrumented systems is likely to create a data fusion problem. Engineers can gain considerable structural and performance insight through visualization and analysis tools that fuse data from differing sensor systems. As a similar problem has arisen in the earth observing systems community, a comparable tool set drawing upon 11
  • 12. existing solutions will be needed to represent the housekeeping data from next-generation vehicles. Goals for the next 5–10 years - Continued demonstration of mission-enabling solutions employing nanotechnology o New materials  Band-gap engineered semiconductors  Electron-phonon decoupling  Radiation shielding improvements o Improved passive components  Fatigue resistant wiring  High density capacitors o Improvement in device performance  Sensitivity, selectivity, weight, power, volume - Development of novel approaches o Fault-tolerant architectures  Reduced sensitivity to radiation  Enhanced durability and reliability  Monitoring and predicting failures o Distributed sensor networks  “Lick and stick” technology  Improved integration and coverage  Feedback control and monitoring o Sensor self-calibration - Control of the fabrication process o Necessary tools still under development  Fluidic self-assembly  Template pattern control  Electrostatic assisted assembly - Standardized micro–nano integration Goals beyond 10 years - Leveraging the nano–bio–info convergence o Habitat and well-being monitors for astronauts o Search for and characterization of life on other worlds - Development of biomimetic systems capable of self-assembly, repair, and regulation. o Complex natural mechanisms for locomotion and the efficient conversion and storage of energy. Barriers and Solutions 12
  • 13. - Leveraging the concurrent development among industrial, academic, and government research centers. - Continued funding for focused research on critical enabling technologies - Sensor networks requiring data fusion technologies o Leveraging software developed for the analysis of earth observing data - Organized and systematic investigations of physics bridging the micro-, nano-, and subnanoscales. Conclusions Nanotechnology offers considerable promise in the development of novel sensors and as an important component of next-generation instrumentation. Clearly, new technology faces obstacles within the risk-averse aerospace community. The high cost of missions dictates the use of reliable and flight-proven hardware. Under these conditions, the incorporation of new technology is always a challenge. Program managers must carefully weight the risks against the benefits of newly developed technical solutions. Without exception, managers are best advised to partner nanotechnology developers with system-wise engineers for the incorporation of novel solutions and the satisfaction of end users. The risks for novel sensors employing innovations in nanoscale engineering are offset by the potential for improvements in the areas of reliability, sensitivity, and selectivity along with savings in mass, volume, and power. In addition, our need to understand the mechanics of cellular operations will also drive the development of nanoscale technology. Engineers working at the nanoscale seek to mimic the designs of biological systems. Indeed, life itself is an existence proof of nanoscale possibilities while remaining an enigmatic engine of mystery. As future NASA missions attempt to identify the signs of life on the surface of Mars and the moons of Jupiter, nanoscale devices are expected to play a key role in analyzing the nature of any complex molecules uncovered. On Earth, developments in genetic testing have reshaped our understanding of nature’s tree of life. Should life exist elsewhere in the solar system, the thrust to understand the origin and function of extraterrestrial samples may provide the largest impetus for developments in space-based nanoscale techniques, sensors, and instrumentation. 13
  • 14. Figures A B C D A B C D Figure 1 CNT-based strain sensor developed at NASA Langley Research Center. A) optical micrograph showing large circuit elements defined using photolithography; B) AFM topography image detailing deposited and aligned CNT bundles spanning the alignment electrodes with the measurement electrodes defined; C) aluminum beam instrumented with a flexible CNT-based strain sensor and mounted in a single axis load frame; and D) results from the CNT strain sensor (blue) compared with a standard strain gage (red) mounted on the backside of the aluminum beam. 14
  • 15. (a) (b) (c) Figure 2 (a) Scanning electron micrograph of a SET with 0.5 fF input gate fabricated at GSFC. Inset shows 60 nm x 60 nm tunnel junctions connecting source and drain leads to SET island. (b) Schematic of RF readout and multiplexing system. (c) Substrate for RF-SET fabrication showing 16 RF inductors Li located along top and bottom of 8 x 10 mm chip. 15
  • 16. 16 Contributors This report was formulated from the presentations and discussions of the participants in the Nanosensors and Instrumentation break-out session at the NNI Grand Challenge Workshop on Nanotechnology in Space Exploration held in San Jose CA on August 23– 25, 2004. Please refer to the individual presenters and participants list in the Contributors section of this document as points of contact for further information on their work. Co-Chairs Sean C. Casey, PhD, USRA Pedro Medelius, PhD, Aerospace Corp. Peter Shu, NASA GSFC Benny Toomarian, PhD, JPL Mary Zeller, PhD, NASA GRC Presenters Steve Arnold, PhD, Polytechnic Univ. David Bartine, PhD, NASA KSC David Blake, PhD, NASA ARC Bharat Bhushan, PhD, Ohio State John Cumings, PhD, Stanford Univ. Paul Drzaic, PhD, Alien Tech. Sabrina Feldman, PhD, NASA ARC Sarath Gunapala, PhD, JPL Brian Hunt, PhD, JPL Gary Hunter, PhD, NASA GRC Tim Krabach, PhD, JPL Brook Lakew, PhD, NASA GSFC Nick Melosh, PhD, Stanford Univ. Jim Morris, PhD, Portland State Cattien Nguyen, PhD, Eloret Tinh Nguyen, PhD, NIST Nicholas Prokopuk, PhD, NavAir Holger Schmidt, PhD, UC Santa Cruz Sudipta Seal, PhD, Univ. of Florida Calvin Shipbaugh, PhD, Rand Corp. Joseph Stetter, PhD, Trans. Tech Benjamin Sullivan, UC San Diego S. K. Sundaram, PhD, PNN Lab Neal Watkins, PhD, NASA LaRC Participants Robert Espinosa, Microwave Power Technology Jam Farhoomand, TechnoScience Michael Freier, NanoConsulting Michael Heller, PhD, UC San Diego Brock Hinzman, SRI Jim Hurd, NanoScience Exchange Carl Ruoff, PhD, JPL Philippe Sarrazin, PhD, CheMin N. B. Singh, PhD, Westinghouse Electric Bo Varga, NanoSIG Robert Wilbur, San Jose State Univ.