Advanced Materials for Safe, Pure Drinking Water

 

 

Adviser:

Stephanie Hooker, (303) 497-4326

email

 

Water encompasses the vast majority of the Earth, but precious little (<1 %) can be used as is. Over the next two decades, the average water supply per person will drop by a third, forcing additional reliance on purified or desalinated water supplies. Nanotechnology offers many potential benefits for improved water purification and quality control, increasing our ability to utilize brackish water sources. New membrane designs are being developed that exploit unique pore shapes and sizes; integrate nanoparticles along pore surfaces for advanced trapping and sensing; and utilize nanocomposites and nanofibers to better mimic naturally-occurring separation materials. Characterization of membrane reliability is essential for ensuring rapid commercialization of these new concepts, including both mechanical robustness and surface stability (anti-fouling). The Materials Reliability Division has extensive capabilities for mechanical characterization of small-scale structures (such as nanostructured membranes), as well as custom tools for quantifying surface interactions of nanoparticles and thin films with chemicals and biological materials. Extension of this work to interaction with specific water-borne contaminants (e.g., pharmaceuticals) is of particular interest.

 

 

 

 

Atomistic Modeling for Nanomaterials Measurements

(50.85.32.B5574)

 

Adviser:

Andrew Slifka, (303) 497-3744

email

Many disease processes involve changes in mechanical properties of tissues, cells, or extracellular matrix. The ability to measure such changes as a function of the local mechanical environment is critical for biological research. We are investigating these issues using devices from an in-house microfabrication facility that has allowed rapid turnaround of designs for measurements of fibroblasts and vascular smooth muscle cells. Our research interests include studies where a mechanical aspect is part of a biochemical pathway of interest. The design flexibility of Bio-MEMS allows measurement of single cells or small groups of cells, where intercellular signaling is key for rapid testing of pharmaceuticals, biofactors, and protein substrates as a function of cellular health. We are interested in the development of new devices, modifications of existing devices, and use of existing devices applied to important biological problems.

 

 

 

 

Adviser:

Thomas Siewert, (303) 497-3523

email

The Federal Highway Administration’s data base lists over 70,000 bridges that are structurally deficient. Another 80,000 are functionally obsolete. Given the significant cost of replacing or upgrading each one, it will be many years until the problem is solved, especially as new ones are added. This project includes a multifaceted approach to speed the process. One component is the improvement of inspection technology so the most serious issues can be clearly identified and addressed first (certainly before catastrophic failure). Another component is the development of more efficient (especially lower cost) repair technologies that will allow more bridges to be repaired each year for a given amount of funding. The third component is the streamlining of the repair or replacement process through better procedures and standards, thus minimizing the time that bridges are out of service.

 

 

 

 

Adviser:

Ward Johnson, (303) 497-5805

email

Brillouin light scattering (BLS) provides a means of characterizing acoustic waves (phonons) and spin waves (magnons) by measuring the direction and shift in frequency of inelastically scattered light. The Materials Reliability Division (Boulder) is developing new BLS metrology and modeling tools that provide information on the dynamic mechanical and/or magnetic properties of nanostructures and thin-film devices. Possible topics of research include spin-wave excitations in magnetic devices and phonons in carbon nanotubes, nanolines, and nanowires.

 

 

 

 

Adviser:

Robert Keller, (303) 497-7651

email

This research opportunity targets the development and application of methods for measuring strain with high spatial and strain resolutions in crystalline materials using electron microscopy. Applications include understanding the roles of strain localization on failure and reliability in microelectronic and optoelectronic materials. Elastic strains can be measured with an uncertainty approaching a few parts in 10,000 and spatial resolution in the range of several nanometers by means of convergent-beam electron diffraction and electron backscatter diffraction. These approaches potentially allow for determination of complete strain tensors, depending on crystal orientation, because of their inherently three-dimensional scattering. Research interests include development of new methods for measuring strain with high resolution, such as Kossel microdiffraction, as well as methods for mapping strain distributions in an automated fashion using already-established techniques. Sophisticated analysis schemes applicable to diffraction patterns must also be developed, in order to strengthen the implementation of quantitative, automated strain measurement and mapping. Our laboratory has a field emission scanning electron microscope with automated electron backscatter diffraction, a 200 kV transmission electron microscope, an atomic force microscope, optical microscopes, and a variety of systems for mechanical testing and characterization.

 

 

 

Adviser:

Lawrence Robins, (303) 497-6794

email

Localized stresses control or influence the operation of a wide range of microelectronic and optoelectronic devices, from strain engineered microprocessor chips to planar and nanowire semiconductor structures for solid-state lighting. Manufacturers and users of these devices require new stress mapping metrologies with 10 nm to 100 nm lateral resolution. Tip-enhanced Raman spectroscopy (TERS), based on local enhancement of the Raman scattering by surface plasmons of a nanoscopic metal tip placed in a focused laser beam, has shown great promise for extending Raman measurements to dimensions below 100 nm. The application of TERS to stress mapping, or other types of materials characterization, has been impeded by poor reproducibility of the near-field enhancement with present-day tip fabrication methods, limited knowledge of the effect of tip shape and microstructure on the near-field optical properties, and tip damage due to tip-sample contact during the measurement. We are developing TERS instrumentation to address these critical limitations, utilizing side-illumination optics that enables inspection of opaque samples and a shear-force nanopositioning mode that minimizes tip-sample contact. In addition, structural characterization of probe tips (e.g., by TEM), and modeling of the effect of tip shape and microstructure on the surface plasmon enhancement, will facilitate fabrication of tips optimized for our TERS system. This project offers the opportunity for a highly motivated researcher, preferably with a background in near-field optics, plasmonics, or Raman spectroscopy, to make a significant impact on development of a new and important metrology.

 

 

Adviser:

Thomas Siewert, (303) 497-3523

email

Our nation’s current infrastructure is under increasing threats both from the natural aging of structures (e.g., pipelines, buildings, ships) and from intentional attacks. Our objective is to develop improved techniques to predict and correct such problems. This project focuses on issues for structural materials (i.e., steel and castings) and fabrication and inspection technology. Our staff has expertise in mechanical testing (strength, impact toughness, and fatigue), welding, and some types of nondestructive evaluation. We have laboratories with mechanical test systems with load capacities spanning the N to MN range, the master impact machines used to verify performance to ASTM Standard E 23, scanning and transmission microscopes, and a metallurgical examination laboratory.

 

 

 

 

Adviser:

Thomas Siewert, (303) 497-3523

email

As the country moves toward alternate fuels (especially ethanol and butanol blends), our fuel storage and distribution systems are being exposed to new chemical environments. Already, increased levels of stress corrosion cracking have been identified in some piping and storage systems. We need to develop more data now, so designers can select optimal materials for new pipelines and decide whether additional protection is needed on repurposed pipelines and tanks (those originally designed for other service). This project involves developing new materials test procedures to screen for compatibility issues in existing systems and to evaluate remediation techniques (liners, coatings, and additives).

 

 

 

 

Adviser:

Thomas Siewert, (303) 497-3523

email

The rapid growth in hydrogen-fueled vehicle projects across the country suggests that we need to be planning large-scale, yet safe and economical distribution systems. While tube trailers and rail cars may meet the short-term needs, pipelines are recognized as one of the ultimate solutions. Unfortunately, most property data bases are based on past generations of material production technology. This project involves developing new materials test techniques to provide designers and researchers with improved measures of materials performance for future pipelines that are both safe and efficient.

 

 

 

 

Advisers:

Timothy Quinn, (303) 497-3480

email

 

Andrew Slifka, (303) 497-3744

email

Mechanical response of cells and tissues is at the heart of many disease mechanisms and these effects can be exploited for diagnosis and treatments of disease. However, biological materials offer unique challenges for mechanical measurements as they are anisotropic, nonlinear, viscoelastic, and continually adapting to their environment. We are currently developing a suite of custom tools to measure the responses of biological materials to various mechanical stimuli. Such responses include changes in strength, elasticity, biological response, and adhesion. We use BioMEMS platforms, optical traps, custom bioreactors, inflation tests, ultrasonics, and traditional material testing machines to provide mechanical input and to measure mechanical response. We also have facilities for cell culture and optical and electron microscopy.

 

 

 

 

Adviser:

Andrew Slifka, (303) 497-3744

email

The pulmonary arteries remodel to become stiffer with the onset of pulmonary hypertension and the consequence of this remodeling continues to be investigated. In a recent study, a measure of compliance was found to be the single strongest predictor of mortality among patients with idiopathic pulmonary arterial hypertension. A test system to measure the mechanical properties of these membrane-like arteries, based on the bubble test, has been designed and built at NIST, and the tools for analyzing the accumulated data are in place. Measuring the mechanical properties of pulmonary arteries in rat and mice models will contribute to research programs at a nearby medical center on the development, diagnosis, and treatment of pulmonary hypertension. We seek a candidate interested in tissue mechanics, who would continue this program in collaboration with physicians and scientists at the medical center and who would conduct the tests, providing the data for a number of research programs that require well-defined perturbations to the established test procedures.

 

 

 

 

Adviser:

David Read, (303) 497-3853

email

We are developing techniques for mechanical characterization of materials for micro- and nanoscale electronic interconnects, thin films for MEMS/NEMS, and future device components such as molecular electronics. The objective is to provide materials data and develop novel test methods that enable device designers and manufacturers to produce reliable products and to make useful projections of their service life. The approach is to test specimens of the exact size and condition in which they occur in electronic packages. Techniques to fabricate and test freely suspended metal thin films are in place. We have tested microtensile specimens as small as 2 x 0.5 x 180 micrometers. We are relating microtensile results to results of instrumented indentation tests and to fatigue life under thermomechanical cycling driven by high amplitude alternating current. Research focuses on improving measurements; testing a wider range of materials including polymers and dielectrics; testing smaller specimens by utilizing advanced microscopy techniques such as atomic force microscopy, scanning electron microscopy, and transmission electron microscopy; and relating observed behavior to material micro- and nanostructure.

 

 

 

 

Adviser:

Robert Keller, (303) 497-7651

email

Our goal is to understand at the microstructural level the physical processes controlling interconnect reliability, and the phenomena of electromigration and stress-limiting barriers to the continuously decreasing geometries of interconnects in microelectronic devices. Further, with the incorporation of new materials systems, multilevel structures, and the associated interfaces, the detailed effects of thermal- and current-induced stresses, as well as their interactions are largely unknown on a local scale. Research includes microstructural measurement methods as applied to interconnect systems, studies of microstructural changes occurring during processing or service, design of standard test structures and methods, effects of local microstructural variations on interconnect behavior, characterization and effects of local residual stresses, and development of lifetime prediction models. Our laboratory has a field emission scanning electron microscope with an automated electron backscatter diffraction analysis system, a 200 kV transmission electron microscope, a scanned probe microscope, optical microscopy capabilities, image processing and analysis equipment, and an apparatus for dc and ac electromigration testing.

 

 

Adviser:

Robert Keller, (303) 497-7651

email

This opportunity focuses on the development and application of microsystems for the evaluation of materials properties under conditions where conventional test methods cannot provide sufficient information about mechanical behavior. We have interest in application of microsystems technology to the development of test methods: (1) for the evaluation of micro- and nanoscale materials, where material dimensions are comparable to the size of microstructural features that control behavior, (2) for the evaluation of material behavior in harsh environments that make conventional testing extremely hazardous, and (3) amenable to in situ testing of properties such as fatigue, creep, and fracture toughness in conjunction with electron microscopy, x-ray diffraction, and scanned probe microscopy. This opportunity will involve design, development, and fabrication of various MEMS-based testing systems. Access to two NIST fabrication facilities allows for rapid design, (hands-on) fabrication, and rework. Testing and evaluation facilities includes in-house microscopy (light optical, SEM, TEM, scanned probe) and x-ray diffraction, as well as access to other world-class NIST facilities.

 

 

 

 

Adviser:

Vinod Tewary, (303) 497-5753

email

The objective of this project is to develop multiscale Green’s function and ab-initio quantum mechanical methods for modeling strains in strained silicon (s-Si). This research would supplement the active experimental work in our group for development of measurement tools needed for the strain engineering of silicon. Strain engineering of silicon is becoming increasingly important in the fabrication of high performance devices. Strained silicon has significantly improved carrier mobility and reduced power consumption, enabling higher switching speeds. Strained silicon can be made by introducing layers of germanium in a silicon lattice or by depositing silicon on Si1-xGex, which introduces strains in the silicon lattice and can be manipulated to increase the carrier mobility. The performance of the s-Si based devices is sensitive to the strains, and the presence of point defects, surfaces, and interfaces. An important problem in the design of s-Si based devices is that it has not yet been possible to measure all components of strain in the finished device. It is, therefore, necessary to have reliable theoretical models for calculating the full three-dimensional strain field in s-Si with and without the lattice defects. A reliable model for s-Si must give the local atomistic distortion in the lattice as well as strains in the entire solid. The model must account for the local discrete structure of the lattice including nonlinear effects where necessary. It should also account for the presence of extended defects such as surfaces and interfaces in the solid. We have already developed multiscale Green’s functions for nanostructures such as quantum dots and nanowires. This research would address an even more challenging problem of combining the Green’s function technique with ab-initio calculations and applying the technique to a practical problem of contemporary industrial interest.

 

 

 

 

Adviser:

Donna Hurley, (303) 497-3081

email

In this work, we seek to understand the mechanical properties of polymers and polymer-based composites at micro- and nanometer length scales. Research involves new techniques based on atomic force microscopy (AFM). Other tools such as instrumented (nano-) indentation, SEM, and conventional AFM are used to obtain complementary information. Potential project areas include AFM methods to measure viscoelastic properties; techniques to determine the glass transition temperature in ultrathin films; evaluating the role of the interphase in polymer-based nanocomposites; and understanding the effect of nanoscale mechanical properties on device reliability.

 

 

 

 

Adviser:

Timothy Quinn, (303) 497-3480

email

The engineering of functionally competent tissue depends on the biochemical and mechanical environment in which the tissue-engineered construct develops. We are currently developing custom bioreactors with integrated measurement systems that can be used to optimize tissue-engineered constructs. In conjunction with collaborators at the University of Colorado, we are conducting demonstration experiments with constructs of poly(ethylene glycol)-based hydrogel with embedded chondrocytes as well as adult mesenchymal stem cells to develop functional cartilage. Bioreactors are being developed that can provide mechanical stimulation as well as online measurements of the mechanical properties and quality of the constructs. The online measurements include mechanical testing and ultrasonic measurements that will target the quantity of the extracellular matrix. A scanning electrochemical microscope is being developed to assess the permeability of scaffolds and metabolic rates of cells growing on them. Heuristic algorithms will also be developed to optimize the constructs. Possible topics could focus on the scaffold, the bioreactor, the biology of the construct, and/or the heuristic optimization.

 

Adviser:

Timothy Quinn, (303) 497-3480

email

Osteoporosis is projected to affect 20 million Americans by 2020. Dual energy X-ray absorptiometry (DXA) is the most widely used modality to assess bone mineral density (BMD) for evaluating bone health and predicting fracture risk. Currently, there are no standard methods for calibrating machines made by different manufacturers. During a scan to determine BMD two different X-ray energies are used in hopes of account for the absorption of the soft tissue around the bone. The Surgeon General has called for a reduction in the uncertainty in DXA measurements so that physicians can better diagnose and treat diseases related to bone health. This project involves designing, manufacturing, and testing phantoms to mimic the X-ray absorption of the body across the range of expected physiologies. Modeling of the system complimented with measurements could also be used to quantify the uncertainties in the measurement and design best practices for making DXA measurements. Topics for research include material design and selection based on X-ray absorption models, material testing, phantom geometry, and net shape manufacturing.

 

 

 

Quality Assurance of Carbon Nanotubes and Other Nanoparticles

 

 

Adviser:

Stephanie Hooker, (303) 497-4326

email

 

Determining the purity and homogeneity of nanomaterials is necessary to ensure that the performance advantages associated with these new materials are realized in the final product. However, quality control techniques are in their infancy for nanomaterials, with conventional analytical methods either pushed to their resolution limits or providing only an average indicator of material quality. We are developing new screening tools based on quartz crystal microbalances (QCMs) as high-resolution alternatives to conventional thermo-gravimetric analysis. These devices have the potential to offer rapid inspection of chemical purity and consistency for sub-microgram specimens (including, but not limited to, carbon nanotubes). Spin coating, dip coating, and spray deposition are currently used to apply thin films to the crystal surfaces, which are then heated to decompose the constituents. Because the measurements require little time or material to perform, statistical homogeneity within a given batch of nanotubes can quickly be determined, as well as variability between different batches or due to purification, functionalization, dispersion, or coating processes. Projects are sought to further refine and improve the measurement technique; demonstrate alternative miniaturized platforms (e.g., via MEMS fabrication or surface acoustic wave sensors) to further increase sensitivity; and integrate other measurement approaches (e.g., optical characterization) for more extensive materials analysis.

 

 

 

Advisers:

Andrew Slifka, (303) 497-3744

email

 

Sustained vasoconstriction is a hallmark of pulmonary hypertension and contributes to other pulmonary and systemic arterial diseases. A potential target for abnormal vasoconstriction is the smooth muscle cell. The strength and duration of smooth muscle contraction is highly dependent on a complex network of intracellular regulatory mechanisms including the small GTPase Rho and its effector, Rho-associated kinase (Rho-kinase)/ROK/ROCK. There are two general approaches for exploring the relationships between the mechanical properties of smooth muscle cells and their environment. In one case, a controlled mechanical environment is provided and the biological response is monitored. In the other case, a controlled biochemical environment is provided and mechanical response is measured. Using either approach single cells and/or bulk tissues can be considered for evaluation. Biomechanical reactors, MEMS test platforms, and optical tweezers can be modified to meet the needs of the project. General study areas for this project include the following: (1) studying the stress-strain characteristics (and possibly adhesion) of smooth muscle cells when interfering with the function of ROCK and its substrates by the use of dominant interfering mutants of each of its known targets, which will be expressed by adenoviral and/or lentiviral gene delivery; and (2) studying signaling events initiated by mechanical forces in smooth muscle cells. This would include the evaluation of signaling mechanisms controlling the expression of genes that impact on smooth muscle function. t of a new and important metrology.

 

 

 

 

 

Advisers:

Andrew Slifka, (303) 497-3744

Grady White, (303) 497-4638

email

As the US population ages, the use of active implantable medical devices (AIMDs) will increase to counteract hearing loss, chronic pain, Parkinson’s disease, cardiac arrhythmia, and other conditions. AIMDs are medical devices that have an implanted component and have electronic circuits that perform a function within the body. While these AIMDs play an enormous role in maintaining quality of life, if the device fails the consequence can severely compromise the patient’s quality of life, at best, or causing death, at worst. Many environmental conditions must be considered when evaluating reliability and lifetimes (e.g., cyclic loading, corrosive environments, inflammatory response of the body, electromagnetic fields, different pressure environments (from diving to climbing Everest), diagnostic and therapeutic radiation, and impacts). The processing and transportation conditions, prior to implantation, offer many other potential hazards to device reliability. We seek a candidate to investigate how the combined effects of certain use conditions compromise device reliability. Another aspect of the program is to develop models to predict device lifetimes.

 

 

 

 

Adviser:

Stephanie Hooker, (303) 497-4326

email

Nanoparticles, including carbon nanotubes and other high-aspect-ratio nanomaterials, are of interest for a vast array of biomedical applications, including drug delivery, high-contrast bioimaging, electrophysiological recording, neural/retinal prosthetics, and reinforced tissue engineering scaffolds, among many others. While the integration of nanotechnology with the biomedical field holds great promise, there are significant challenges that must be addressed before widespread innovation, development, and implementation of nanostructures in the health care industry can occur. NIST’s Materials Reliability Division is particularly interested in the issue of nanomaterial degradation due to mechanical, thermal, and chemical stresses encountered in-vivo. Development of new methods to evaluate, verify, and predict changes in particle surfaces; coatings; functionalized layers; physical and electrical contacts; and other interfaces are of particular interest. Quantifying the impact of such changes on the effectiveness of the nanostructure, its interaction with the surrounding cells and tissue, and its overall biocompatibility are also needed.

 

 

Adviser:

Timothy Quinn, (303) 497-3480

email

Product innovations that use nanoparticles are rapidly expanding in many sectors of the world economy with their incorporation into a wide range of products including cosmetics, pharmaceuticals, polymer composites, clothing, and microelectronics. However, effective and accepted methods to quickly and thoroughly assess nanoparticle toxicity are not yet developed. Traditional cell culture toxicity studies are fast, but have limited applicability because they usually do not mimic the important components of the biological system. Whole animal studies are expensive, slow, and increasingly unpopular. Additionally, in whole animal experiments, it is difficult to correctly dose and then later find the nanoparticles. In this program, we are developing three-dimensional scaffolds that will be seeded with nanoparticles and have encapsulated cells in order to provide an intermediate alternative to screen the nanoparticles for effects on cell health. The three dimensional scaffold allows the cells to grow in a state that is closer to in vivo conditions than typical two dimensional culture. Projects in this program could include scaffold development, the effects of scaffolds on normal cell physiology, nanoparticle imaging using targeted antibodies, and nanoparticle surface chemistry and its interaction with the scaffold and with the cells.