11 research outputs found
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Detection and Characterization of Chemicals Present in Tank Waste - Final Report - 09/15/1998 - 09/14/2001
DOE has a strong commitment to the efficient and safe remediation of waste (high level radioactive waste, mixed waste, and hazardous waste) present in underground waste storage tanks. Safety issues arise from the presence of organic chemicals and oxidizers and concerns are raised about the flammability, explosivity, and the possible corrosion of storage tanks due to presence of nitrates and nitrites. Knowledge of the physical parameters and chemical and radioactive composition of waste is necessary for effective and safe tank remediation. New and improved characterization and monitoring of waste present in storage tanks is necessary. The overall goal of this project has been to develop and demonstrate novel multi-parameter micro-electro-mechanical system (MEMS) sensors based on Si and SiNx microcantilever (MC) structures that are robust and can be used to simultaneously detect the presence of target chemicals (analytes) in a mixture, radiation emitted from radioactive materials, an d the heat generated by the absorption of photons of specific wavelength by the target analytes. The mechanisms by which adsorption, photophysical, photothermal processes cause stress in MC surfaces are better understood. Methods of applying a wide variety of chemically selective coatings have been developed specifically for miniaturized MC surfaces, and the response characteristic of the cantilever were shown to be altered dramatically and predictably through incorporation of these phases on the surfaces. By addressing sensitivity and liquid matrix issues, the spectroscopic approach promises to provide an essential element of specificity for integrated sensors. We discovered early in these studies that fundamental limitations exist regarding the degree to which adsorption of analytes on smooth surfaces cause stress and this significantly limits chemi-mechanical response. To circumvent this limitation a concerted effort was made to devise and test ways to nanostructure cantilever surfaces, thereby creating new mechanisms of analyte-induced stress. Substantial improvement in chemi-mechanical response resulted from this work
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Hybrid Micro-Electro-Mechanical Systems for Highly Reliable and Selective Characterization of Tank Waste
Our multifaceted research program is aimed at the fundamental and practical development of hybrid micro-electro-mechanical-systems (MEMS) that integrates several elements of chemical selectivity and sensor function. We are developing MEMS sensors that combine chemimechanical transduction, and surface enhanced Raman spectroscopy (SERS) and radiation detection. One of our goals is to develop highly effective methods of immobilizing a wide variety of molecular and ionic recognition phases onto micromechanical surfaces. We have introduced fundamentally new modes of adsorbate-induced surface stress through nano-structuring of microcantilever surfaces; the responsivity for has increased by over two-orders of magnitude over previously existing technological approaches. Noble metal nanostructures similar to those that enhance chemi-mechanical transduction exhibit substantial Raman enhancement factors
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Hybrid Micro-Electro-Mechanical Systems for Highly Reliable and Selective Characterization of Tank Waste
The main objective of this research program is to develop robust and reliable micro-electro-mechanical sensing systems, based on microcantilevers (MCs), that can operate in liquid environments with high levels of sensitivity and selectivity. The chemical responses of MCs result from analyte-induced differential stress at the cantilever surfaces. We aim to employ various surface nanostructuring strategies that enhance these stresses and hence the degree of static bending of the cantilevers. Receptor phases as self assembled monolayers (SAMs) and thin films are being synthesized and tested to provide selectivity. Selectivity is chemically enhanced by using different phases on individual MCs in arrays and by adding a spectroscopic component, surface enhanced Raman spectrometry (SERS), in hybrid approaches to sensing. Significant progress was made in tasks that were listed in the work plan for DOE EMSP project ''Hybrid Micro-Electro-Mechanical Systems for Highly Reliable and Selective Characterization of Tank Waste''. Several project areas are listed below and discussed and referenced to our literature on the topics
Differentially Ligand-Functionalized Microcantilever Arrays for Metal Ion Identification and Sensing
Control of Membrane Permeability in Air-Stable Droplet Interface Bilayers
Air-stable droplet interface bilayers
(airDIBs) on oil-infused
surfaces are versatile model membranes for synthetic biology applications,
including biosensing of airborne species. However, airDIBs are subject
to evaporation, which can, over time, destabilize them and reduce
their useful lifetime compared to traditional DIBs that are fully
submerged in oil. Here, we show that the lifetimes of airDIBs can
be extended by as much as an order of magnitude by maintaining the
temperature just above the dew point. We find that raising the temperature
from near the dew point (which was 7 °C at 38.5% relative humidity
and 22 °C air temperature) to 20 °C results in the loss
of hydrated water molecules from the polar headgroups of the lipid
bilayer membrane due to evaporation, resulting in a phase transition
with increased disorder. This dehydration transition primarily affects
the bilayer electrical resistance by increasing the permeability through
an increasingly disordered polar headgroup region of the bilayer.
Temperature and relative humidity are conveniently tunable parameters
for controlling the stability and composition of airDIB membranes
while still allowing for operation in ambient environments
Control of Membrane Permeability in Air-Stable Droplet Interface Bilayers
Air-stable droplet interface bilayers
(airDIBs) on oil-infused
surfaces are versatile model membranes for synthetic biology applications,
including biosensing of airborne species. However, airDIBs are subject
to evaporation, which can, over time, destabilize them and reduce
their useful lifetime compared to traditional DIBs that are fully
submerged in oil. Here, we show that the lifetimes of airDIBs can
be extended by as much as an order of magnitude by maintaining the
temperature just above the dew point. We find that raising the temperature
from near the dew point (which was 7 °C at 38.5% relative humidity
and 22 °C air temperature) to 20 °C results in the loss
of hydrated water molecules from the polar headgroups of the lipid
bilayer membrane due to evaporation, resulting in a phase transition
with increased disorder. This dehydration transition primarily affects
the bilayer electrical resistance by increasing the permeability through
an increasingly disordered polar headgroup region of the bilayer.
Temperature and relative humidity are conveniently tunable parameters
for controlling the stability and composition of airDIB membranes
while still allowing for operation in ambient environments
Bimaterial microcantilevers as a hybrid sensing platform
Microcantilevers, one of the most common MEMS structures, have been introduced as a novel sensing paradigm nearly a decade ago. Ever since, the technology has emerged to find important applications in chemical, biological and physical sensing areas. Today the technology stands at the verge of providing the next generation of sophisticated sensors (such as artificial nose, artificial tongue) with extremely high sensitivity and miniature size. The article provides an overview of the modes of detection, theory behind the transduction mechanisms, materials employed as active layers, and some of the important applications. Emphasizing the material design aspects, the review underscores the most important findings, current trends, key challenges and future directions of the microcantilever based sensor technology
Assessment of laser tracking and data transfer for underwater optical communications
We report on an investigation into optical alignment and tracking for high bandwidth, laser-based underwater optical communication links. Link acquisition approaches (including scanning of narrow laser beams versus a wide-angle ‘beacon’ approach) for different underwater laser-based communications scenarios are discussed. An underwater laserbased tracking system was tested in a large water flume facility using water whose scattering properties resembled that of a turbid coastal or harbour region. The lasers used were state-of-the-art, temperature-controlled, high modulation bandwidth gallium nitride (GaN) devices. These operate at blue wavelengths and can achieve powers up to ~100 mW. The tracking performance and characteristics of the system were studied as the light-scattering properties of the water were increased using commercial antacid (Maalox) solution, and the results are reported here. Optical tracking is expected to be possible even in high scattering water environments, assuming better components are developed commercially; in particular, more sensitive detector arrays. High speed data transmission using underwater optical links, based on blue light sources, is also reported
Synthesis of Hexagonal Boron Nitride Monolayer: Control of Nucleation and Crystal Morphology
Monolayer
hexagonal boron nitride (hBN) attracts significant attention due to
the potential to be used as a complementary two-dimensional dielectric
in fabrication of functional 2D heterostructures. Here we investigate
the growth stages of the hBN single crystals and show that hBN crystals
change their shape from triangular to truncated triangular and further
to hexagonal depending on copper substrate distance from the precursor.
We suggest that the observed hBN crystal shape variation is affected
by the ratio of boron to nitrogen active species concentrations on
the copper surface inside the CVD reactor. Strong temperature dependence
reveals the activation energies for the hBN nucleation process of ∼5
eV and crystal growth of ∼3.5 eV. We also show that the resulting
h-BN film morphology is strongly affected by the heating method of
borazane precursor and the buffer gas. Elucidation of these details
facilitated synthesis of high quality large area monolayer hexagonal
boron nitride by atmospheric pressure chemical vapor deposition on
copper using borazane as a precursor