X-Ray Refraction Topography techniques are based on Ultra Small Angle Scattering by micro structural elements causing phase related effects like refraction and total reflection at a few minutes of arc as the refractive index of X-rays is nearly unity (1x10^-5). The extraordinary contrast of inner surfaces is far beyond absorption effects. Scanning of specimens results in 2D-imaging of closed and open pore surfaces and crack surface density of ceramics and foams. Crack orientation and fiber/matrix debonding in plastics, polymers and ceramic composites after cyclic loading and hydro thermal aging can be visualized. In most cases the investigated inner surface and interface structures correlate to mechanical properties. For the exploration of Metal Matrix Composites (MMC) and other micro structured materials the refraction technique has been improved to a 3D Synchrotron Refraction Computed Tomography (SR-CT) test station. The specimen is situated in an X-ray beam between two single crystals. Therefore all sample scattering is strongly suppressed and interpreted as additional attenuation. Asymmetric cut second crystals magnify the image up to 50 times revealing nanometer resolution. The refraction contrast is several times higher than "true absorption" and results in images of cracks, pores and fiber debonding separations below the spatial resolution of the detector. The technique is an alternative to other attempts on raising the spatial resolution of CT machines. The given results yield a much better understanding of fatigue failure mechanisms under cyclic loading conditions.

Crystallinity, composition, homogeneity and anisotropy determine the mechanical properties of materials significantly, but the performance of most non-destructive techniques is too poor for measuring these micro structures as they are optimized for finding individual flaws/defects. X-ray (wide angle) Diffraction Topography by single beam scanning images molecular information at a spatial resolution of several ten micrometers even in three dimensions. Especially for the non-destructive characterization of composite materials, they provide additional capabilities by crystallographic contrast by the molecular/atomic probe. The different material phases of compounds and their molecular orientation can be imaged e.g. fibers or polymer chain orientation in composites: A sample is scanned or rotated, while only part of the scattering pattern is pointing at an X-ray detector area. Three different methods have been developed: i) planar X-ray Scanning Topography at one or more pre-selected scattering angles provides high contrast of different phases of components. ii) X-Ray Rotation Topography reveals the texture angle of composite fibers and chain polymers. iii) X-ray Diffraction Microscopy images the texture and phase distribution of transversal sections of the material. The principles of Wide Angle X-Ray Diffraction Topography are explained and examples of investigations will be presented. They combine the advantages of radiographic imaging and crystal structure information. The applied X-ray energies are much lower than in NDT radiography, which recommends preferably the application to light weight materials.

Fiber Reinforced Plastics (FRP) are increasingly applied in transportation systems (aircraft, railway, automotive) and infrastructure industries due to the good specific properties of high strength at low weight. Advanced FRP structures have to endure high mechanical and environmental loading. Therefore the durability and reliability depends much more on the micro mechanical properties as on the global strength. X-ray refraction topography is a powerful tool for the characterization of inner surfaces in materials. Applied to fiber composites the presented investigations give information about the mean diameter of the fibers, orientation and the quality of impregnation. Strong correlations were found between fiber matrix debonding and micro cracking and the stress state due to mechanical loading. Additionally a new method for a quantitative determination of transverse and shear strength in a complex laminate is presented. Therefore the X-Ray refraction technique is applied on-line during tensile load of specimens.

The direct reconstruction approach employs a new iterative procedure by collecting projected trajectory data of selected volume elements of the sample and add them partially up in a reconstruction matrix. Repetitive application solves the problem of reversing the overlap of projected trajectories without Fourier filtering. This avoids the blur effects of the classical Fourier method due to the sampling theorem. But longer computing time is required. Under optimal conditions the spatial resolution of the reconstructed image is better than that of the detector. Any set of projection angles may be selected. Limited rotation of the object yields good reconstruction of details. Projections of a partial region of the object can be reconstructed very well thus reducing the overall radiation dose in medical applications. Noisy signal data have low impact on spatial resolution. The image quality is monitored during all iteration steps and is pre-selected according to the specific requirements. DIRECTT is suitable for any tomography equipment, also in addition to conventional reconstruction or as a refinement filter.

Laser spectroscopical methods as Raman scattering (RS) and Photoluminescence as well as Small Angle Scattering of Xrays (SAXS) are presented as powerful tools for the efficient, nondestructive and contact-less characterization of nanoparticles of low concentration (< 1% in volume) in solids in dependence on the history of thermal treatment. The complementary determination of size distribution of CdS_xSe_1-x nanocrystallites in silicate glass filters and of arsenic precipitates in low-temperature grown GaAs layers by RS and SAXS is exemplarily presented.

X-ray imaging offers a number of unique properties that are favorable for NDE applications, including large penetration depth, elemental specificity, and relatively low radiation damage. While direct-projection type x-ray systems with a few um resolution have been widely deployed, recent advances in x-ray optics and imaging methodology have lead to lens-based x-ray microscopes with better than 60-nm resolution, and with integrated 3D imaging and material analysis capabilities. Used independently or in combination with established techniques based on visible light and electron microscopy, these new high-resolution x-ray systems introduces many attractive new capabilities for studying structures at micrometer to tens-of-nm scale.

We present a low vacuum tool for ultra high resolution scanning electron microscopy of insulators and floating conductors. Charging is stabilized by ionized gas molecules generated using an environmental secondary electron detector designed to operate within the magnetic field on an immersion objective lens. The charge stabilization mechanism yields consistent charge control that is transparent to the operator, and independent of the tasks performed during imaging. This is illustrated by series of artifact-free, high resolution images of an insulating test sample acquired as a function of magnification and scan speed, at a number of accelerating voltages. The low vacuum method is compared to the high vacuum technique of adjusting the electron beam landing energy so as to minimize charging artifacts (i.e., the "total yield" method). The low vacuum approach is less sensitive to changes in beam current density (determined by the beam current, magnification, scan speed and beam diameter) and yields higher ultimate image resolution. The resolution improvement results from effective suppression of both charge-induced defocusing of the electron beam and distortion of the scan pattern.

The authors present a new approach, fibDAC, which allows to measure and analyze deformation fields on stressed micro and nano components, which can be utilized for mechanical material characterization. The method bases on digital image correlation (DIC) algorithms applied locally to load state images captured from focused ion beam (FIB) equipment. As a result, deformation fields are determined, which occur due to loading of microsystem structures inside the focused ion beam system. A similar tool, called microDAC/nanoDAC, has been reported earlier and applies DIC techniques to SEM or AFM images. The advantages of the new fibDAC approach occur in the incorporation of specimen preparation like ion milling, ion beam surface polishing and DIC patterning as well as specimen loading by ion milling and DIC deformation measurement in a single equipment. Combining measured fields with finite element simulations or analytical solutions of the corresponding mechanical problem, relevant mechanical material properties can be evaluated. Corresponding object loading is accomplished either externally by testing modules designed for application inside the FIB equipment or by ion milling on the test specimen. As an example ion milling on specimens with residual stresses is demonstrated. Released in this way residual stresses cause object deformations nearby the milling area. Measured deformation fields by fibDAC allow to evaluate very local residual stresses. Some principal experiments illustrate the feasibility of the chosen approach. Features and challenges connected with this new method are discussed in some detail.

Several work performed at the Fraunhofer Institute IZFP Dresden on photo and particle acoustic methods is presented. It includes both, modeling activities by an explicit numerical method (CEFIT) and experimental work. The given examples of applied excitations are photons (Laser acoustics) and electrons (Scanning Electron Acoustic Microscopy, SEAM). Both, time resolved measurements by pulse excitation as well as monofrequent measurements by periodic excitation together with signal recovery (lock-in technique) are discussed.

Resonant contact atomic force microscopy (resonant C-AFM) is used to quantitatively measure the elastic modulus of polymer nanotubes and metallic nanowires. To achieve this, an oscillating electric field is applied between the sample holder and the microscope head to excite the oscillation of the cantilever in contact with the nanostructures suspended over the pores of a membrane. The resonance frequency of the cantilever with the tip in contact with a nanostructure is shifted to higher values with respect to the resonance frequency of the free cantilever. It is demonstrated that the system can simply be modeled by a cantilever with the tip in contact with two springs. The measurement of the frequency shift enables the direct determination of the spring stiffness, i.e. the nanowires or nanotube stiffness. The method also enables the determination of the boundary conditions of the nanobeam on the membrane. The tensile elastic modulus is then simply determined using the classical theory of beam deflection. The obtained results for the larger nanostructures fairly agree to the values reported in the literature for the macroscopic elastic modulus of the corresponding materials. The measured modulus of the nanomaterials with smaller diameters is significantly higher than that of the larger ones. The increase of the apparent elastic modulus for the smaller diameters is attributed to the surface tension effects. It is thus demonstrated that resonant C-AFM enables the measurement of the elastic modulus and of the surface tension of nanomaterials.

Two high frequency photoacoustic techniques were applied to investigate the mechanical properties of two sets of thin film materials in this work. Broadband photoacoustic guided-wave method was used to measure the guided-wave phase velocity dispersion curves of nano-structured diamond-like carbon hard coatings. The experimental velocity spectra were analyzed by a nonlinear optimization approach in conjunction with a multi-layer wave-propagation model. The derived Young’s moduli using the broadband photoacoustic technique were compared with line-focus acoustic microscopy and nano-indentation tests and good quantitative agreement is found. In a second set of experiments, ultra-thin two-layer aluminum and silicon nitride thin film materials were tested using the femtosecond transient pump-probe method using high frequency bulk waves generated by the ultra-fast laser pulses. The measured moduli of silicon nitride thin layers are in the range of 270 - 340 GPa. Photoacoustic methods are shown to be suitable for in-situ and non-destructive evaluation of the mechanical properties of thin films.

Differential ultrasonic force microscopy (d-UFM) has been used to investigate the nanoscale mechanical response of multi-walled carbon nanotubes (MWNTs) synthesized via chemical vapor deposition (CVD). In contrast to earlier studies, MWNTs with relatively high numbers (~ 60) of concentric walls were investigated. Quantitative analysis of the MWNT d-UFM data utilized Si3N4 cantilevered tips and Si substrates as a calibration standard. Initial investigations of the CVD MWNTs through d-UFM revealed a surprisingly large radial indentation modulus compared to Si. Frictional force imaging (FFM) was also carried out on the MWNTs in the presence and absence of an ultrasonic vibration. A FFM contrast reversal was observed between the MWNT and the Si substrate as the static set point force of the AFM cantilever was increased. This is attributed to an increase in the local indentation of the MWNT by the Si₃N₄ tip.

A numerical model of an acoustic microscope based on the elastodynamic finite integration technique (EFIT) is presented. It allows time-domain simulations of elastic wave propagation in both, fluids and solids, and includes focusing of the incident wave field as well as scattering at defects and the fluid-solid interface taking mode converted echoes and leaky Rayleigh waves into account. The simulations can be performed for different frequencies and materials and can be used for the continuous and time-resolved mode as well as for transmission and reflection microscopy. The simulation results can be represented by time-domain signals and wave front snapshots. The formation of V(r,z) curves is also possible. In the present paper the simulations are applied to the problem of vertical cracks and spherical inclusions in a solid substrate as well as for subsurface characterization of thin coatings.

Investigation of dynamics of micro electromechanical systems (MEMS) is an important problem of engineering, technology and metrology. Specifically, recent interest in applying MEMS technology to miniaturization of relays, sensors, actuators for variety of applications requires design of appropriate testing and measurement tools for investigation of dynamic properties of those systems. Therefore, application of measurement technologies capable of detecting the dynamic properties of micro scale systems may help to understand and evaluate the functionality of those systems. The shearographic technique for the detection of the transverse displacements of micro-cantilevers with respect to the shearing direction is presented. The method is expanded upto a hybrid numerical-experimental approach and includes the generation of shearographic images of the microstructures using finite element methods. The presented analysis is based on modeling NDE shearographic method and microstructures behavior.

Some time ago a near-field optical imaging technique had been introduced (Appl. Phys. Lett. 73, 1669 (1998)), which achieves high spatial resolution and excellent sensitivity by exploiting the highly localized and mutual near-field interactions between a Au-nanosphere and a sharp Si-probe under evanescent field illumination. Specifically, the scattering of Au-nanoparticles is significantly enhanced by the presence of a sharp nanoscopic probe demonstrating that the probe acts as an efficient antenna. The present study focuses on the underlying physics of the original results by investigating more systematically nanoparticle-probe interactions: (1) The polarization pattern of the scattered field of an evanescent wave excited Si-probe is studied, which demonstrates that the probe scatters as a single dipole. (2) The enhanced scattering signal is measured as a function of sample size, which allows us to predict the signal strength for different size samples. (3) The wavelength dependence of the probe-sample scattering is investigated by exciting Au-nanospheres on (@543 nm) and off plasmon resonance (@633nm). The data shows a pronounced wavelength dependence reflecting the near-field spectrum of the Au-nanocrystals. (4) Finally, a simple, but intuitive model describing these mutual near-field interactions is presented, which explains qualitatively both the size and wavelength dependence of the enhanced scattering signals.

Apertureless-based, near-field Raman imaging holds the potential for nanoscale stress metrology in emerging Si devices. Preliminary application of near-field Raman imaging on Si device structures has demonstrated the potential for stress measurements. However, detailed investigations have not been published regarding the effect of tip radius on observed near-field enhancement. Such investigations are important to understand the fundamental limits regarding the signal-to-noise ratio of the measurement and the spatial resolution that can potentially be achieved before wide application to semiconductor metrology can be considered. Investigations are presented into near-field enhancement of Raman scattering from Si device structures using a modified near-field optical microscope (NSOM). The nano-Raman system utilizes an off-axis (45°) backscattering NSOM geometry with free-space collection optics. The spectroscopic configuration utilizes a single-bounce spectrometer incorporating a holographic notch filter assembly utilized as a secondary beam-splitter for an apertureless backscattering collection geometry. Near-field enhancement is observed for both Al- and Ag-coated probes. An inverse square power-law relationship is observed between near-field enhancement factor and tip radius.

The aerospace, automotive, and electronic industries are finding increasing need for components made from silicon carbide (SiC) and silicon nitride (Si₃N₄). The development and use of miniaturized ceramic parts, in particular, is of significant interest in a variety of critical applications. As these application areas grow, manufacturers are being asked to find new and better solutions for machining and forming ceramic materials with microscopic precision. Recent advances in laser machining technologies are making precision micromachining of ceramics a reality. Questions regarding micromachining accuracy, residual melt region effects, and laser-induced microcracking are of critical concern during the machining process. In this activity, a variety of nondestructive inspection methods have been used to investigate the microscopic features of laser-machined ceramic components. The primary goal was to assess the micromachined areas for machining accuracy and microcracking using laser ultrasound, scanning electron microscopy, and white-light interference microscopic imaging of the machined regions.

Many technical processes, e.g. in mechanical engineering, are causing acoustic emission. Acoustic emission (AE) consists of elastic waves, generated by stress changes in a solid. These waves can be detected at the surface of the solid by piezoelectric sensors. Classical methods to characterize acoustic emission signals include detecting and counting single events, describing their energy and frequency properties. The spreading conditions for acoustic waves in solids and the interference of a large number of AE sources lead to quasi-continuous signals from which no individual AE event can be extracted. This is also typical for wire sawing. If AE signals shall be used for online process monitoring, it is necessary to extract signal properties that are correlated with process changes. A common feature is the RMS value of the signal, which is correlated with the energy of AE and was found to be very sensitive to changing process conditions. Other features used are the peak values of the signal and the number of zero crossings. To get more information about the actual state of the observed process, parameters of the statistical distribution of short-time RMS like mean value, variation coefficient and skewness have been tested and their sensitivity to process changes have been investigated. An online monitor has been developed based on a hard- and software concept, adapted to process continuous acoustic emission data, with fast acquisition rates and signal processing.

Although the conventional optical lever technology typically used for scanning probe microscope applications has proven highly sensitive, accurate, and cost effective for most applications involving micromachined cantilever deflection measurements, frequency limitations and space needs limit its applicability to emerging ultrasonic-based SPM applications. Recently, the fabrication of cantilevers integrated with actuation and sensing components has opened avenues for feedback-based driving of micromachined cantilevers at higher-order resonance frequencies while sensing average deflection without the need for an optical deflection pathway for average deflection sensing. The work presented here will review recent efforts by our group in fabricating micromachined cantilevers with integrated piezoresistive deflection-sensing components combined with integrated ZnO actuation layers to induce cantilever deflection. These cantilevers are being fabricated for use in a heterodyne force microscopy system (HFM) to enable SPM imaging contrast based on viscoelastic response of a surface in contact with a micromachined tip wherein active-feedback technology is being applied to maintain ultrasonic tip excitation at higher order cantilever resonances. The first and second-pass fabrication results will be presented and reviewed regarding cantilever release and ZnO actuator (and electrode) fabrication. Dynamic response data from these structures, measured via laser Doppler vibrometery reveal the expected resonance structure for a cantilever of these dimensions.