Proceedings Volume 5392

Testing, Reliability, and Application of Micro- and Nano-Material Systems II

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Proceedings Volume 5392

Testing, Reliability, and Application of Micro- and Nano-Material Systems II

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Volume Details

Date Published: 21 July 2004
Contents: 7 Sessions, 28 Papers, 0 Presentations
Conference: NDE for Health Monitoring and Diagnostics 2004
Volume Number: 5392

Table of Contents

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Table of Contents

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  • Material Properties on the Nanoscale I
  • Material Properties on the Nanoscale II
  • Advanced Microscopic Techniques
  • Surfaces and Cracks
  • Composites and Interfaces
  • Applications of MEMS and Micro-electronics
  • Additional Paper
Material Properties on the Nanoscale I
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Micro/nanoscale tribological and mechanical characterization for MEMS/NEMS
Recent investigations have revealed the profound influence of adhesion, friction, and wear on the reliability of micro/nanoelectromechanical systems (MEMS/NEMS) devices. Studies of determination and suppression of these failure mechanisms are critical to improving the reliability of MEMS/NEMS. Using atomic force microscopy (AFM), researchers have developed the methodology to study the micro/nanotribological and mechanical behavior of one of the commercial MEMS -- digital micromirror devices (DMD). Surface roughness, adhesion, friction and wear properties of the contacting elements of the DMD lubricated by a self-assembled monolayer (SAM) have been extensively studied. Potential mechanism for micromirror stiction accrual has been suggested in light of the findings. In addition, the molecular level adhesion, friction, and wear performance of SAMs have been also investigated using AFM. The molecular tribological mechanisms of SAMs have been discussed to aid the design and selection of proper lubricants for MEMS/NEMS.
Nondestructive mechanical imaging of SnO2 nanobelts
Yuegui Zheng, Robert E. Geer
The relative surface contact stiffness of SnO2 nanobelts has been investigated via nondestructive ultrasonic force microscopy (UFM). The nanobelt crystal structure, as determined via transmission electron microscopy, was indexed to the tetragonal rutile structure (with lattice constants identical to those of bulk SnO2) as reported previously. The atomic Sn:O composition of the nanobelts studied was at or near 1:2. Topographic imaging studies revealed the nanobelt surface to be atomically flat with the exception of surface nano-dots, assumed to be local SnO2 crystallites. Preliminary local (10nm x 10nm) reduced modulus measurements were carried out via differential UFM on both the flat and nanodot regions of the nanobelt. Using the underlying Si substrate as a calibration standard the SnO2 modulus was estimated at 157±12 GPa, significantly lower than corresponding bulk values for any of the observed crystal orientations. We speculate this discrepancy is due in part to a combination of the aspherical probe tip and unknown adhesive properties of nanobelt, although an intrinsic reduction of the SnO2 nanobelt modulus cannot be ruled out.
Material Properties on the Nanoscale II
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Nanoscale nondestructive electric field probing in ferroelectrics, organic molecular films and near-field optical nanodevices
Lukas M. Eng, Stefan Grafstrom, Ingo Hellmann, et al.
Inspecting and tuning electric fields on the nanometer scale offers a great potential in overcoming limitations inherent in assembling nanostructures. Both optical and electronic devices may be improved in performance provided that a quantitative knowledge on the strength and orientation of local (stray) fields is gained. Here we present nanoscale investigations of functional surfaces probing the surface potential and electronic properties of ferroelectric and ultra thin organic films. We developed methodologies that are able to non-invasively track the electric field both above and below interfaces, thus providing insight also into the sample. Hence, interface dipole formation and interface charging directly shows up in potential changes revealing the donor/acceptor characteristics of molecules, as well as the surface charge screening in ferroelectrics. Such inspections are possible using conventional scanning force microscopy operated in sophisticated modes measuring the electrostatic force or the inverse piezoelectric effect. Finally, electric fields are also probed in the optical regime using near-field optical methods. Examples are shown where the strength and frequency of surace plasmon resonances become tunable due to simple nanostructuring of metallic thin films.
Evaluation of interactive forces between alkaline earth metal fluoride particles and single crystal substrate using atomic force microscopy
Yi-Yang Tsai, Vijay Nalladega, Shamachary Sathish, et al.
Interactive forces between particles play an important role in diverse fields of science and technology. With the advent of Atomic Force Microscopy, investigation of interactive forces has been extended to micro and nano-scale particles with new applications. These forces are known to vary with the dimension of the particles and with the different levels of humidity. In the present paper we have investigated the interactive forces between a spherical particle probes of eutectic BaF2-CaF2 and a single crystal surface of CaF2 using an Atomic Force Microscope. The effect of humidity on the interactive forces has been examined by analyzing the force-displacement curves at controlled levels of humidity. Force distance curves obtained with two different probes, 5 μm and 17 μm in diameter, and have been examined to investigate the effect of probe dimensions. The results are discussed in view of the application of eutectic BaF2-CaF2 particles in self-lubricating coatings for aerospace applications.
Characterization of microcracks by application of digital image correlation to SPM images
Juergen Keller, Astrid Gollhardt, Dietmar Vogel, et al.
With the development of micro- and nanotechnological products such as sensors, MEMS/NEMS and their broad application in a variety of market segments new reliability issues will arise. The increasing interface-to-volume ratio in highly integrated systems and nanoparticle filled materials and unsolved questions of size effect of nanomaterials are challenges for experimental reliability evaluation. To fulfill this needs the authors developed the nanoDAC method (nano Deformation Analysis by Correlation), which allows the determination and evaluation of 2D displacement fields based on scanning probe microscopy (SPM) data. In-situ SPM scans of the analyzed object are carried out at different thermo-mechanical load states. The obtained topography-, phase- or error-images are compared utilizing grayscale cross correlation algorithms. This allows the tracking of local image patterns of the analyzed surface structure. The measurement results of the nanoDAC method are full-field displacement and strain fields. Due to the application of SPM equipment deformations in the micro-, nanometer range can be easily detected. The method can be performed on bulk materials, thin films and on devices i.e microelectronic components, sensors or MEMS/NEMS. Furthermore, the characterization and evaluation of micro- and nanocracks or defects in bulk materials, thin layers and at material interfaces can be carried out.
Positron annihilation spectroscopy to study nanoprecipitations in aluminum alloys
Norbert Meyendorf, Gunter Dlubek, Alexander Surkov
Positron Annihilation Spectroscopy has been used to study the microstructure in aluminum alloy AA7075-T6 after RRA (retrogression and re-aging) heat treatment. Nano-precipitates act as traps for thermalised positrons. The measured positron lifetime is sensitive to the local electron density at the annihilation site while the Doppler broadening of the annihilation line is sensitive to the chemical environment of the annihilation site. The combination of both methods was used to study changes of nano-precipitates, during the Retrogression and Re-aging (RRA) process. Results are compared to previous published isochronal annealing experiments of an Al Cu model alloy.
Advanced Microscopic Techniques
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Micro- and nano-NDE in the laboratory for acoustic diagnosis and quality assurance
NDE activities at the Laboratory for Acoustic Diagnosis and Quality Assurance (EADQ) Dresden are outlined. The applied methods comprise acoustic, thermal, optical and X-ray ones. Additionally, scanning probe methods (SPM) and scanning electron microscopy (SEM) are used. Combinations of different methods are especially effective. This is demonstrated for the coupling of an acoustic approach with SEM. For NDE on a micro- and nano-meter scale, preparation of appropriate test flaws and the verification of the NDE results turn out to be a challenge. To meet this challenge, we propose an approach based on focused ion beam technique.
Introduction to EBSD analysis of micro- to nanoscale microstructures in metals and ceramics
Electron BackScatter Diffraction (EBSD) is a relatively new, scanning electron microscope-based technique used to characterize microstructures and textures in crystalline metal and ceramic materials. Advances in SEM technology, especially the development of field emission SEMs, as well as in EBSD detector design have allowed characterization at the sub-10 nm level. This paper gives a basic introduction to the EBSD technique with applications on materials with microstructures on the micron and sub-micron scale. Automated EBSD mapping at these and other resolution levels is used to study texture, individual grain orientation, crystallography-based phase identification, grain size, grain shape, strain state, grain boundary character, area percentages of multiple phases in bulk samples, crystallography of facets and failure initiation sites, and other materials characteristics. Sample sectioning and polishing are often necessary for mapping microstructures in bulk samples, however as-grown structures such as thin films and interconnects are suitable for mapping as is, and “point & shoot” type analyses may be used on other unprepared samples in conjunction with SEM imaging for phase identification and basic crystallographic orientation studies. For micron-scale devices and components, EBSD-equipped dual beam FIBs are used to select cross-sectional planes of analysis with high precision.
Raman spectroscopic investigation of stresses in microstructures of pyroelectric devices
Electronic microstructures show a great variety of geometric shapes like edges and stripes and features like columns which can cause large stress concentrations decreasing the reliability and life time of devices. Otherwise, the properties of materials e.g. ferroelectric layers, are dependent on mechanical stress. Raman spectroscopy provides the possibility to measure stresses in silicon with a spatial resolution of about 1 to 2 microns and with an accuracy of about 20 MPa using the piezo-spectroscopic effect. The frequency shift of Raman modes can be related to the mean hydrostatic stress in the material which is described by an empirical relation. Silicon dominates the microelectronic technology. The present contribution demonstrates how spectroscopic data measured on silicon in complex thin film structures can be interpreted in terms of stresses with a combined modeling of the measurement process and the stress field using the finite element method. Pyro-electric devices consisting of laterally structured lead zirconate titanate thin films and metal electrodes have been investigated. The films are deposited on silicon substrates or on poly-silicon membranes covering evacuated cavities to realize thermal isolation. Stresses in individual films and in the substrate near critical points of microstructures, e.g. at edges and near columns which carry a membrane, have been predicted theoretically by finite element calculations. A 2D finite element model was developed to describe experimental stress profiles. It was used to estimate film stresses in individual microstructures by a fitting procedure.
Barkhausen noise and eddy current microscopy: a new scanning probe technique for microscale characterization of materials
Klaus Szielasko, Sergey Lugin, Melanie Kopp, et al.
The need for an accelerated development of new materials and surfaces raises expectations in lateral homogeneity and quantitative exactness of the characteristic material properties. The interest is focused on microstructure characterization, detection of micro-imperfections and evaluation of the local distribution of residual stresses, mechanical hardness and coating thickness. These requirements meet with the development of high-resolution NDT methods such as Barkhausen Noise and Eddy Current MIcroscopy (BEMI) at IZFP. BEMI enables locally high-resolved non-destructive materials testing by means of Barkhausen noise and eddy current analysis: The sample is scanned with a miniaturized inductive probe which serves as Barkhausen noise pick-up and eddy current inductive sensor. Characteristic quantities are derived from the measured data and mapped as 2-D or 3-D images allowing the recognition of defects as small as 5 μm. The device is controlled by a modular measuring system which is split into modules for positioning, data acquisition and evaluation. Two additional software modules enable contact-less, quantitative testing of sensitive surfaces. This way, thin coatings can be characterized regarding their microstructure, thickness, internal stresses and heat-treatment condition. The efficiency of this device was demonstrated on many materials as solids stacks of several thin films. The BEMI testing device achieves an accuracy of 10 nm for the thickness of thin films on a variety of substrates.
Improved mechanical properties of metallic micro-structures
Properties of materials used in micro- and nano-technology are rather different from those of bulk material and even to lateral macroscopic extended thin films. Designing MOEMs components, it has to be clarified how functionality and reliability of the micro-devices are influenced. Suitable tools are necessary to test the materials properties on micro- and submicro-scale. The application of Al- and Ti-layers in micro-mirror devices is discussed. Attempts to control and improve their mechanical properties in accordance with the application requirements for micro-mirror devices are described.
Surfaces and Cracks
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Comparison between the atomic force microscopy and x-ray reflectivity on the characterization of the roughness of a surface
Hui-Chia Su, Ming-Zhe Lin, Tzu-Wen Huang, et al.
X-ray reflectivity and atomic force microscopy are two common tools in characterizing the surface roughness. However, the measurement results reported by these two methods were usually not consistent between each other. In this work, polished sapphire wafers with different surface roughness were prepared and measured by both methods. To understand the disagreement, a possible interpretation for X-ray reflectivity and atomic force microscopy on the characterization of the surface roughness is described. The difference in the X-ray reflectivity measurement, the X-ray beam covers a larger area of few mm2 on the sample, while the atomic force microscopy probes only a local area (around μm2). In general, the surface roughness measured by atomic force microscopy should be smoother than that obtained by X-ray reflectivity due to the convolution of tip shape of atomic force microscopy and the short wavelength of probing X-rays. However, the surface contamination of the sample and the atomic force microscopy environment complicate the measurements for both methods, especially, for these samples with root-mean-square roughness less than 1 nm.
Carbon buffer layers for smoothing substrates of EUV and x-ray multilayer mirrors
Smoothing of surfaces by thin film deposition is facilitated by methods which release hyperthermal particles on the substrate. One of these techniques is pulsed laser deposition (PLD), with high kinetic particle energies of up to several 100 eV. The concrete energy distribution of the particles can be widely influenced by the laser power density. We investigated the deposition of carbon layers by PLD on numerous substrates with rms-roughnesses between 0.15 and 0.75 nm using different laser power densities and film thicknesses. It turns out that a better smoothing can be obtained with higher laser power densities, whereby diamond-like carbon films are created. With typical thicknesses of dC = 100 nm, the rms-roughness is reduced from 0.75 nm to 0.55 nm and from 0.32 nm to 0.18 nm. Accordingly by applying smoothing carbon buffer layers, the EUV reflectance of Mo/Si multilayers on rough substrates is increased from typically 60% to > 65% on substrates with initial roughnesses of 0.75 nm.
Determination of Local Stress Intensity Factor at Crack Tip Using Image Correlation Techniques
Yi-Yang Tsai, Juergen Keller, Daniel Eylon, et al.
The extraordinary mechanical properties of high strength aluminum alloys such as AA7075-T6 are caused by coherent nanoprecipitations. These nanoprecipitations generate local stress fields and interact with moving dislocations and propagating microcracks. In this paper, image correlation techniques are used to determine the local strain and stress field in the vicinity of fatigue crack tips during the loading of compact tension (CT) specimen. The fatigue crack tip was sharpened with decreasing fatigue loading after fatigue cracks initial appearance. Images of the crack tip were taken using atomic force microscopy/ultrasonic force microscopy (AFM/UFM) and white light interference microscopy (WLIM) before and after mechanical loading of the specimen. Both techniques are applicable for measuring the out-of-plane displacement during the loading process. In addition, image correlation techniques can be used to determine the in-plane displacement resulting from mechanical loading. This information is used to calculate the local stress intensity factor in the vicinity of the crack tips.
Characterization of materials with nanoscopic filler particles by AFM techniques
Dietmar Vogel, Juergen Keller, Bernd Michel
In order to modify material properties different kind of filler particles are added to polymer matrices. Miniaturization in electronics, MEMS and photonics applications forces to reduce the size of filler particles, even to submicron and nano scale dimensions. R&D processes as well as later production quality control demand suitable tools and procedures to characterize filler particles, e.g., within polymeric composites. The authors studied different AFM based methods of particle detection and imaging. The underlying purpose was to utilize stress state micrographs of composites with filler particles for deformation measurements. The foreseen digital image correlation technique (DIC) for highest resolution deformation analysis is briefly introduced. In order to understand the impact of filler particles on the mechanical behavior, particle identification and imaging as well as deformation measurement has to be performed on the same micrographs. Main emphasis in this work is made on different imaging modes realizable with scanning probe microscopy (SPM), which can be used to image and to characterize submicron and nano scale fillers. Additionally the influence of surface finishing before the SPM imaging is analyzed, mainly the impact of focused ion beam (FIB) polishing after mechanical polishing. The examined SPM methods for filler characterization are compared to alternative tools like FIB, SEM, AFAM and Laser Scanning Microscopy (LSM).
Characterization of microscopic surface breaking cracks using the near-field intensification of nondestructive laser-generated surface waves
Optical generation and detection of surface acoustic waves provides a non-contact, remote means of characterizing microscopic surface-breaking cracks in aerospace and industrial materials. Surface ultrasonic displacement fields generated by a non-destructive, laser induced thermoelastic mechanism and detected with an interferometric probe allow for an all optical and spatially adjustable (spot-size, beam shape, beam separation) utlrasonic NDE system. Location of surface-breaking cracks is achieved through observation of a near-field intensification of the detected ultrasonic signal in the vicinity of the crack. The near-field intensification was found to be optimized by scanning both the source and detection beams with specific spatial variables. This non-contact, laser beam scanning NDE technique, allows for imaging capabilities to further enhance surface-breaking crack characterization.
Laser processing of micro-cracks for structural life extension
James L. Blackshire, Larry Dosser, Ken Hix
A considerable amount of work has recently been applied to the development of laser processing techniques for a wide variety of applications. With regard to aging aircraft, laser processing techniques could play a role in inhibiting crack growth and extending the life of structural aircraft components. The basic concept involves the application of a sharply-focused, moderate power laser beam to a local microscopic defect site that has been detected through advanced NDE techniques. The defect could be pitting corrosion site, a fretting region, or even a microcrack site. The laser would be raster-scanned across the defect, re-melting the site locally to a level where the sharp features of the defect are smoothed out, or perhaps re-melted completely to eliminate the flaw site altogether, thereby reducing stress concentration levels in the material. In order to test the feasibility of this basic concept, a series of measurements were made to study the effect of microscopic laser treatments applied to artificial defects in Al-2024-T3 aluminum and Ti-Al6-4V titanium. The major results of the study showed a moderate to significant level of fatigue life enhancement for engineered notches in the 1 mm size range. The laser treatmen approah may provide an opportunity for 'healing' structural defects in aerospace materials that would otherwise require expensive and time-consuming part replacements in aging aircraft structures.
Calibration of an electro-optical variable circular retarder with application in a nulling microellipsometer
We report on the design and calibration of a high speed electro-optical variable circular retarder (EOVCR). This retarder consists of an electro-optical variable linear retarder and two quarter-wave plates aligned at specific angles. This EOVCR provides a pure polarization rotation that is independent of the initial incoming polarization. Application of this device in a rotationally symmetric microellipsometer design is also discussed. The use of such an EOVCR eliminates the vibrational noise reported in the previously reported microellipsometer design and allows a high speed nulling detection scheme to be used, substantially improving the accuracy of microellipsometer.
Composites and Interfaces
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NDE of microstructured materials by x-ray diffraction and refraction topography
Manfred P. Hentschel, Axel Lange, K.-Wolfram Harbich, et al.
For the purpose of micro structural characterization X-ray topography reveals the spatially resolved scattering of materials and small components. It combines the advantages of radiographic imaging and the analytical information of wide and small angle X-ray scattering like phase distribution, texture, micro cracks, interfaces and pores. Scanning techniques at selected scattering conditions permit the topographic characterization of any crystalline or amorphous solid or liquid. Topographic methods and applications for the purposes of research, quality control and damage evaluation are presented.
Application of computer tomography in microelectronic packaging
Martina Speck, Klaus-Jurgen Wolter, Dietmar Daniel, et al.
In nondestructive testing (NDT) of microelectronic components many applications using X-ray radiography are well established. This method is based on the attenuation of radiation intensities of x-rays transmitting an object. Computer tomography (CT), however, is a visualization method which is based on reconstructing three-dimensional models from several two-dimensional X-ray projections of the object. It is only recently used for NDT because it is more expensive and time consuming than conventional X-ray imaging. Nevertheless, there are applications where simple radiography provides only poor results because of superimposed object layers. This article discusses NDT specific problems of CT such as beam hardening and shows some microelectronic applications benefiting from CT as well as examples where modifications of the standard CT procedure are necessary to gain depth information about the object. This so called limited angle tomography reaches a higher image resolution than CT when flat modules are tested.
Mechanical wave propagation at phase and material interfaces of microstructures
Jacqueline Vollmann, Dieter M Profunser, Jozefien Goossens, et al.
When a mechanical stress pulse, which is propagating in an elastic medium, encounters a material- or phase interface, which generally represents a change of the acoustic impedance, it is split up into a part which propagates further into the new material and another part which is reflected. The amplitude ratio of the reflected and the transmitted part is governed by the normalized difference of the acoustic impedances only, provided that the impedance change is a pure step function in space. If the acoustic impedance change is broadened spatially, the ratio of the transmitted and reflected part becomes frequency dependent and the effect can therefore be used for filter-, damping-, acoustic isolation-, and/or spectrum analysis purposes or for a quantitative analysis of the interface. The effect is of growing importance for micro- and nanostructures since the relative size of interface layers is generally larger than in macroscopic structures. Oxidation or diffusion processes might lead to 'smooth' acoustic interface layers which are characterized by gradually varying mechanical properties like density, Young's- and shear moduli, which need to be quantified by nondestructive in-depth profiling methods.
Acoustic Emission (AE) of fiberglass insulation material
In order to develop an effective and accurate way to monitor and control the quality of fiberglass products, Acoustic Emission (AE) signals, generated during compression of fiberglass samples, were studied and analyzed using neural network based pattern recognition software. Distinguishable patterns were found in samples manufactured under different conditions and compositions, which resulted in different product quality. AE waveform features, such as absolute energy, average frequency, duration, and rise time were analyzed and the features showed strong dependence on the sample tested. This made sample classification possible and definitive and therefore a classifier was developed and applied to data collected from additional test samples. Finally, an AE system for the evaluation of fiberglass insulation was designed and built. It is expected that the developed system will be used as a quality control tool in industrial production of fiberglass insulating material. In this paper we will discuss the AE data collection and analysis, classifier development, and give an overview of the inspection system developed.
Continuum simulation of adhesive-adherend interface layers for USNDE
R. Yerikalapudy Vasudeva, Gopinathan Sudheer
Characterization of effective interfacial properties in adhesive joints is one of the major challenges in NDE. The interlayer between the adhesive and the adherend is typically of the order of 1μm and even over this distance -- it is realized -- the interlayer could be a function of depth depending on adhesive penetration and pore formation on adherend surface affecting the ultimate bond strength. The thinness of this complex region is taken advantage of in the present work to treat it as a continuum with different length scales at micro and macro levels. The dispersion-attenuation of leaky guided waves is simulated to facilitate USNDE of this region.
Nondestructive ultrasonic characterization of multilayer coatings
Saeed Uzzaman, Mohammad Khobaib, Jochen P. Hoffmann, et al.
Acoustic Microscopy is used to study the structure and properties of polymer coatings. In a multi-layer coating system, the reflection of an ultrasonic signal takes place at each interface. For thin coatings, the reflected signals from different interfaces superimpose and appear as a single reflected signal. The amplitude and the fine structure of the reflected signal depend on the material properties of the sample. To separate the reflected signal from different interfaces of the multi-layer coatings, the pulse length has to be shorter than the time of flight of the ultrasonic pulse through each layer. However, usually ultrasonic pulses are longer. The approach used here is to model the acoustic signal for different interfaces and compare the model signal with the signal recorded from the degraded coating. Due to thermal and environmental effect, the properties like acoustic impedance, density and thickness of the polymer coatings will change with time. This results in minor modifications of the shape of the reflected signal from a degraded coating. By using a calibrated scale for different kinds of coating properties, coating characteristics can be determined. This paper will discusses the application of the above method to characterize the degradation of aircraft coatings.
Applications of MEMS and Micro-electronics
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Real-time visualization of bridge structural response through wireless MEMS sensors
Hung-Chi Chung, Tomoyuki Enomoto, Kenneth Loh, et al.
This study investigates the reliability and accuracy of wireless micro-electromechanical-system (MEMS)-type sensors in application of bridge structural vibration monitoring. With wireless capabilities added onto the developed sensors, it becomes unnecessary for engineers to connect enormous lengths of cables in order to measure vibration on bridges for instance. We investigated two types of MEMS accelerometers: the ADXL 202E and the Silicon Design 2210. To prove the validity of measuring acceleration by using these devices with wireless communication, we succeeded on measuring a pedestrian bridge's vibration under excitation loads in the center of span. The result had been compared with the traditional cabled sensor, PCB 393C. The wireless sensors were showed to be effective and much affordable to carry out the monitoring missions in situ.
Development of GMR eddy current sensors for high-temperature applications and imaging of corrosion in thick multilayer structures
Detection and quantification of corrosion damage in aircraft structures is essential for condition based maintenance strategies and for the extension of the life of the aircraft. The eddy current technique was found to be one of the most favorable methods for the determination of thickness loss due to corrosion because this technique is capable of detecting corrosion in several layers of a multi-layer structure. A limitation for the eddy current technique is the eddy current penetration depth. Decreasing the analyzing frequency can increase the eddy current penetration depth. Giant Magneto Resistive sensors are highly sensitive magnetic field sensors, they have better signal to noise ratio for very low frequencies than conventional coils systems. Moreover these sensors are very efficient over a broad frequency range. Hence they allow the use of the multi-frequency concept for multi-layer structures of higher thickness. Images of corrosion damage can be generated separately for different layers of a multi-layer structure by using deep penetrating GMR based eddy current probes and data acquired from the multi-frequency eddy current testing. This paper describes the design of deep penetrating GMR based eddy current probes and their application for generating images of corrosion in different layers with the help of a MAUS scanner.
High-resolution nondestructive evaluation at the Center for Materials Diagnosis
The paper will give a brief overview on techniques that have been developed or are in progress for high resolution characterization of materials at the Center for Materials Diagnostics, University of Dayton. Acoustic microscopy is used to characterize coating systems and localized defects like corrosion pits. Significantly higher resolution is provided by Ultrasonic force microscopy, which allows the imaging of elastic inhomogenities in materials for example, studying nano-grain structures in copper films and nano precipates in aluminum alloys. Several optical high-resolution techniques have been developed or are in progress. These include interferometric imaging of the response of acoustic MEMS transducers, imaging of acoustic wave structures and early detection of crack initiation. Microellipsometric and NSOM imaging techniques are in development for imaging of surface structures significantly smaller than the optical wavelength. White light interference microscopy is frequently used to characterize surface topography with nanometer resolution for example, to quantify fretting damage or stress fields in front of fractures.
Additional Paper
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Materials characterization of micro-devices
During the design of ever smaller sized micro-systems, the question appears how much the properties of the materials used differ from those of bulk material and even to laterally extended thin films. The aim of this paper is to analyze mechanical behavior of micro-structured metallic systems like Cu- and Al- interconnections in microelectronic devices or metallic components in micro-opto-electro-mechanical systems (MOEMS). Using atomic force microscopy (AFM) several features like roughness, grain size and dimension accuracy of the materials could be measured for the initial state and in-situ during thermo-mechanical load. For that purpose, meander like line structures produced in CMOS technology as well as special structures fabricated by laterally resolved ion beam sputtering by a focused ion beam equipment (FIB) were used for bending tests. Additionally the elastic and plastic deformation of the lines can be assessed nondestructively by the change of the line resistance measured with high precision. The analysis of the experimental results reveals abnormal plastic-elastic mechanical properties of metallic systems of micro- and sub-micrometer dimension. Practical consequences are discussed concerning the reliability of metallic interconnects, the quality of micro-mirror materials as well as a new approach of micro-material tailoring by surface treatment.