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Microsensors to monitor missile storage and maintenance needs

Description: Accurate assessments of reliability and condition based maintenance can only be implemented where a good understanding of ammunition stockpile condition exists. Use of miniaturized intelligent sensors provides an inexpensive means of nondestructively gaining insight into stockpile condition while keeping costs low. In the past, evaluation of ammunition lifetimes has utilized humidity, temperature, pressure, shock, and corrosion. New technologies provide the possibility of obtaining these environmental parameters, as well as a number of other indicators of propellant degradation, including NOx by utilizing a microsensor with capability for remote wireless monitoring. Micro-electro-mechanical systems (MEMS) like microcantilevers promise to revolutionize the field of sensor design. In the automobile industry, micromachined acceleration sensors are now used for triggering airbags and pressure sensors adjust the air-fuel intake ratio in the engine. By applying coatings to the sensor`s surface the behavior of the microdevice can be measurably altered to respond to chemical species as demonstrated by ORNL using microcantilevers to detect mercury vapor and humidity. Ultimately, single-chip detectors with electronics and telemetry could be developed with conceivably hundreds of individual microsensors on each chip to simultaneously monitor identify, and quantify many important chemical species for ammunition as well as measure environmental parameters.
Date: October 30, 1997
Creator: Mee, D.K.; Thundat, T.G. & Oden, P.I.
Partner: UNT Libraries Government Documents Department

Defects and their origin in thin films of (001) alkaline earth oxides

Description: MgO is used as an optical isolation layer for waveguides epitaxially grown on Si. Crystalline perfection of MgO is critical because it serves as a substrate for the single crytal, perovskite guiding layer. Imperfections in the MgO will result in imperfections in the guiding layer and lead to large optical losses for the planar waveguide structure. It is shown that the most common defect to form in thin MgO films are twin boundaries between {l_brace}111{r_brace}-type planes. Highest density of twins is observed when (001) MgO is grown directly on silicon/MgO interlayers containing Ba. Twinning is shown to accommodate the large size of Ba impurities incorporated in the MgO films through formation of internal grain boundaries and oper surface other than the growing (001) of MgO.
Date: December 31, 1995
Creator: Walker, F.J.; McKee, R.A.; Pennycook, S.J. & Thundat, T.G.
Partner: UNT Libraries Government Documents Department

Morphology and microstructure of (111) crystalline CeO{sub 2} films grown on amorphous SiO{sub 2} substrates by pulsed-laser ablation

Description: The surface morphology and microstructure of (111)-oriented CeO{sub 2} thin films, grown on amorphous fused silica (SiO{sub 2} substrates by low-energy-ion-beam assisted pulsed laser ablation, have been studied by atomic force microscopy (AFM) and x-ray diffraction (XRD). These CeO{sub 2} films are aligned with respect to a single in-plane axis despite being deposited on an amorphous substrate. There is a honeycomb-like growth morphology to the films and island-growth can be observed in thicker films. These islands, inside of which are high density of honeycomb-like clusters, are separated by a void network with {approximately}700 nm width. However, on the surface of the thinnest film ({approximately}3 nm), only very small clusters (diameter <60 nm) appear, and the boundaries of the void network are undefined, which implies that the film is just beginning to coalesce into clusters (grains). The combined AFM images and XRD pattern suggest these clusters probably are the initial seeds for the subsequent island growth. Based on these results, the growth mechanism of oriented CeO{sub 2} films on amorphous fused silica substrates is discussed.
Date: November 1, 1994
Creator: Zhu, S.; Lowndes, D.H.; Budai, J.D.; Thundat, T.; Norton, D.P. & Warmack, R.J.
Partner: UNT Libraries Government Documents Department

Piezoresistive microcantilever optimization for uncooled infrared detection technology

Description: Uncooled infrared sensors are significant in a number of scientific and technological applications. A new approach to uncooled infrared detectors has been developed using piezoresistive microcantilevers coated with thermal energy absorbing materials. Infrared radiation absorbed by the microcantilever detector can be sensitively detected as changes in electrical resistance as function of microcantilever bending. The dynamic range of these devices is extremely large due to measurable resistance change obtained with only nanometer level cantilever displacement. Optimization of geometrical properties for selected commercially available cantilevers is presented. We also present results obtained from a modeling analysis of the thermal properties of several different microcantilever detector architectures.
Date: October 1, 1996
Creator: Rajic, S.; Evans, B.M. III; Oden, P.I.; Datskos, P.G. & Thundat, T.
Partner: UNT Libraries Government Documents Department

Ferromagnetic nanocomposite films from thermally labile nitride precursors

Description: A series of nanocomposite films containing Ni or Co nitride dispersed in a ceramic matrix of Al nitride, B nitride, or Sio nitride, were prepared by reactive sputtering of selected alloys or compounds such as Ni aluminide or Co silicide. Thermal treatment of the nitride composites in vacuum at {le}500 C leads to selective loss of N from CoN or Ni{sub 3}N to generate dispersions of the metal in the ceramic matrix. This treatment may be performed in a localized manner by means of a focused laser beam to generate microscopic features that are imaged by magnetic force microscopy. The films are potentially useful for data storage with superior chemical and mechanical stability provided by the ceramic matrix and high encoding density made possible because of the size of the magnetic particles of less than 10 nm generated in the thermal treatment. The films were characterized by chemical and physical means including FTIR, TEM, MFM, and magnetic measurements. Preliminary results on similar iron composites are also described.
Date: December 31, 1996
Creator: Maya, L.; Paranthaman, M.; Thompson, J.R.; Thundat, T. & Stevenson, R.J.
Partner: UNT Libraries Government Documents Department

Microcantilever sensors

Description: Novel sensors based on bending and resonance frequency changes of (coated silicon) microcantilevers are discussed. Adsorption-induced resonance frequency changes of microcantilevers can be due to a combination of mass loading and change of spring constant resulting from adsorption of chemicals on the surface. Cantilevers also undergo static bending due to adsorption-induced differential surface stress if the adsorption is confined to one surface. Hence cantilever deflection as well as resonance frequency change can be used as the basis for development of novel chemcal sensors.
Date: April 1, 1996
Creator: Thundat, T.; Warmack, R.J.; Oden, P.I.; Dasktos, P.G. & Chen, G.Y.
Partner: UNT Libraries Government Documents Department

New insights into the kinetics of the stress-driven 2D to 3D transition

Description: The authors have systematically investigated the morphological evolution of Ge{sub 0.5}Si{sub 0.5} strained films during post-growth annealing. The changes of the surface structure are found to follow the kinetic route of strain relaxation at different stages. A number of interesting features are revealed, which include the existence of an energy barrier to the 2D/3D transition, and a self-limiting effect in the growth kinetics of strained 3D islands. They demonstrate that the annealing approach provides a new way to grow coherent islands with uniform size.
Date: December 31, 1995
Creator: Chen, K.M.; Jesson, D.E.; Pennycook, S.J.; Thundat, T. & Warmack, R.J.
Partner: UNT Libraries Government Documents Department

Analysis of the surface structure of HFCVD diamond films

Description: Structure analysis was carried out on various surface features of diamond films using scanning electron microscopy (SEM) and atomic force microscopy (AFM). The films were grown via hot filament assisted chemical vapor deposition (HFCVD) in methane and hydrogen gas mixtures. The authors investigated the surfaces of films grown under parameters selected to produce certain textures or surface features such as penetration twins or hopper shaped faces. The SEM images of these films show that the {l_brace}100{r_brace} planes are usually flatter than the {l_brace}111{r_brace}. The {l_brace}111{r_brace} planes show interesting growth features. The ``hopper`` shaped structures were imaged in the tapping mode of the AFM, and the angles between planes and their orientations have been determined. These AFM and SEM images are presented with quantitative analyses of the exposed surfaces. Detailed quantitative information will be useful in understanding the growth of these films.
Date: July 1, 1995
Creator: Mehta, P.; Feigerle, C.S.; Clausing, R.E.; Heatherly, L. & Thundat, T.
Partner: UNT Libraries Government Documents Department

Optical and infrared detection using microcantilevers

Description: The feasibility of micromechanical optical and infrared (IR) detection using microcantilevers is demonstrated. Microcantilevers provide a simple means for developing single- and multi-element sensors for visible and infrared radiation that are smaller, more sensitive and lower in cost than quantum or thermal detectors. Microcantilevers coated with a heat absorbing layer undergo bending due to the differential stress originating from the bimetallic effect. Bending is proportional to the amount of heat absorbed and can be detected using optical or electrical methods such as resistance changes in piezoresistive cantilevers. The microcantilever sensors exhibit two distinct thermal responses: a fast one ({theta}{sub 1}{sup thermal} < ms) and a slower one ({tau}{sub 2}{sup thermal} {approximately} 10 ms). A noise equivalent temperature difference, NEDT = 90 mK was measured. When uncoated microcantilevers were irradiated by a low-power diode laser ({lambda} = 786 nm) the noise equivalent power, NEP, was found to be 3.5nW/{radical}Hz which corresponds to a specific detectivity, D*, of 3.6 {times} 10{sup 7} cm {center_dot} {radical}Hz/W at a modulation frequency of 20 Hz.
Date: May 1, 1996
Creator: Oden, P.I.; Datskos, P.G.; Warmack, R.J.; Wachter, E.A. & Thundat, T.
Partner: UNT Libraries Government Documents Department

Mapping site-specific endonuclease binding to DNA by direct imaging with AFM

Description: Physical mapping of DNA can be accomplished by direct AFM imaging of site specific proteins bound to DNA molecules. Using Gln-111, a mutant of EcoRI endonuclease with a specific affinity for EcoRI sites 1,000 times greater than wild type enzyme but with cleavage rate constants reduced by a factor of 10{sup 4}, the authors demonstrate site-specific mapping by direct AFM imaging. Images are presented showing specific-site binding of Gln-111 to plasmids having either one (pBS{sup +}) or two (pMP{sup 32}) EcoRI sites. Identification of the Gln-111/DNA complex is greatly enhanced by biotinylation of the complex followed by reaction with streptavidin gold prior to imaging. Image enhancement coupled with improvements in the preparation techniques for imaging large DNA molecules, such as lambda DNA (47 kb), has the potential to contribute to direct AFM restriction mapping of cosmid-sized genomic DNAs.
Date: December 31, 1995
Creator: Allison, D.P.; Thundat, T.; Doktycz, M.J.; Kerper, P.S.; Warmack, R.J.; Modrich, P. et al.
Partner: UNT Libraries Government Documents Department

Triangular step instability and 2D/3D transition during the growth of strained Ge films on Si(100)

Description: We show that an activation energy barrier exists to the formation of wavy step edges due to stress-driven 2D instability. The barrier height and the barrier width depend sensitively on the surface stress anisotropy and step free energy. The large misfit strain of Ge films significantly reduces the barrier by lowering the S{sub B} step energy, inducing S{sub A} steps to undergo a triangular instability even during low temperature growth of Ge on Si(100). The step instability results in a novel arrangement of stress domains, and the interaction between the domains causes a spatial variation of surface strain with a surprisingly large influence on the energy barrier for island nucleation. Calculations indicate a dramatic enhancement in the nucleation of 3D islands at the apex regions of triangular steps, in good agreement with our experimental measurements.
Date: April 1, 1995
Creator: Chen, K.M.; Jesson, D.E.; Pennycook, S.J.; Mostoller, M.; Kaplan, T.; Thundat, T. et al.
Partner: UNT Libraries Government Documents Department

Microsensors for in-situ chemical, physical, and radiological characterization of mixed waste. 1998 annual progress report

Description: 'A widespread need exists for portable, real-time, in-situ chemical, physical, and radiological sensors for characterization of mixed wastes, groundwater, contaminated solids, and process streams. None of the currently available technologies offer a clear path to the development of sensors that are miniature, cost-effective, selective, highly sensitive with a wide dynamic range, and have the ability to work in air or liquid while providing chemical, physical, and radiological information. The objective of this research program is to conduct the fundamental research necessary to develop microcantilever-based micromechanical sensors for in-situ characterization of groundwater, sediments, and mixed wastes. Chemical selectivity will be achieved by coupling surface modification chemistry with molecular recognition agents. Physical measurements of adsorption (absorption) induced deflection (bending) and resonance frequency variation of microcantilevers can be achieved with extreme precision resulting in ppb-ppt sensitivity. Good progress has been made in the first nine months of this project. Progress has been made in three focus areas: radiation detection, detection of heavy metals in water, modification of microcantilever surfaces for chemical selectivity, and pH measurement.'
Date: June 1998
Creator: Thundat, T. G.; Warmack, R. J.; Dabestani, R.; Britt, P.; Bonnesen, P. V. & Brown, G. M.
Partner: UNT Libraries Government Documents Department

Multiple Input Microcantilever Sensor with Capacitive Readout

Description: A surface-micromachined MEMS process has been used to demonstrate multiple-input chemical sensing using selectively coated cantilever arrays. Combined hydrogen and mercury-vapor detection was achieved with a palm-sized, self-powered module with spread-spectrum telemetry reporting.
Date: March 11, 1999
Creator: Britton, C.L., Jr.; Brown, G.M.; Bryan, W.L.; Clonts, L.G.; DePriest, J.C.; Emergy, M.S. et al.
Partner: UNT Libraries Government Documents Department

Nanoscale Science, Engineering and Technology Research Directions

Description: This report describes important future research directions in nanoscale science, engineering and technology. It was prepared in connection with an anticipated national research initiative on nanotechnology for the twenty-first century. The research directions described are not expected to be inclusive but illustrate the wide range of research opportunities and challenges that could be undertaken through the national laboratories and their major national scientific user facilities with the support of universities and industry.
Date: January 1, 1999
Creator: Lowndes, D. H.; Alivisatos, A. P.; Alper, M.; Averback, R. S.; Jacob Barhen, J.; Eastman, J. A. et al.
Partner: UNT Libraries Government Documents Department