Electron microscopy study of ion beam synthesized β-FeSi2

β-FeSi₂ embedded in a Si matrix was prepared by ion beam synthesis (IBS). Two step implantation, with energies 60 and 20 keV, of two different doses of the iron ions, 5 × 10¹⁵ and 5 × 10¹⁶ cm⁻¹, was performed. After the implantation, the samples were subjected to rapid thermal annealing (RTA) at 900 °C. The crystal structure of the resulting material was studied using cross-sectional transmission electron microscopy (XTEM), including high-resolution electron microscopy (HREM). The comparison of the XTEM images with the initial iron ions implantation profiles, simulated by SRIM (Stopping and Range of Ions in Matter) demonstrate that the process of IBS, followed by RTA, preserves the initial implantation profile, implying a negligible Fe atoms diffusion velocity in comparison with the one of the chemical reaction between Fe and Si. The XTEM images show that continuous β-FeSi₂ layers are fabricated when there is a stoichiometric region in the initial implantation profile. Fe concentration lower than the stoichiometric one in the whole implantation range results in formation of β-FeSi₂ nanocrystallites embedded in the Si matrix. The behavior of the absorption coefficient energy dependences, obtained from the optical transmittance and reflectance measurements, reflects the different crystal structures forming in the two types of samples.     

The application of focused ion beam microscopy in the material sciences

This paper describes the application of focused ion beam microscopy in the characterisation of materials. The paper is of a tutorial nature whose aim is to assist the novice user in acquiring high quality, artefact-free data. The design of FIBs is described, together with a brief background on the interactions which occur between the incident ion beam and the specimen. The use of focused ion beam microscopy in a wide range of materials science applications, including specimen preparation methods and in the generation of 3D visualisation is described.     

Transmission electron microscopy study of carbon nanophases produced by ion beam implantation

The formation of carbon nanocrystals, produced by ion implantation of carbon ions into fused SiO₂ substrates, followed by 1 h thermal annealing at 1000 °C, in an Ar + 5% H atmosphere has been studied. Combined high-resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED) have been employed for structural characterization of carbon nanophases embedded in the quartz substrate. The dependence of grain size and sample morphology of the carbon nanophases on implantation dose was studied. The carbon nanocrystals formed by the implantation for a dose of 1 × 10¹⁶ C/cm² at 320 keV have been identified as a mixture of c-diamond nanophase and a modified diamond nanophase known as n-diamond. For a higher implantation dose, 5 × 10¹⁶ C/cm², besides n-diamond, another solid carbon nanophase was observed, with a structure known as i-carbon. Following the highest implantation dose 1 × 10¹⁷ C/cm² the sample contained the i-carbon nanophase only. A least-square refinement of SAED patterns was employed for the calculation of unit-cell parameters of identified carbon nanophases.     

Characterization and inspection of microlens array by single cube beam splitter microscopy

The application of a single cube beam splitter (SCBS) microscope to micro-optics characterization is presented. The SCBS in the optical path, with a small angle between the optical axis and its central semireflecting layer, not only gives off-axis digital holograms but also provides dual-channel imaging. It is a unique and easy way to perform uniformity inspection across the entire microlens array. Experimental results on physical spherical phase compensation, single lens characterization, dual-channel imaging, and uniformity inspection are provided to demonstrate the unique properties of SCBS microscopy.     

Residual stress measurements in welded steel beam column connections by scanning acoustic microscopy

Residual stresses which arise from thermal expansion and contraction due to welding may have contributed to the brittle fracture exhibited by welded steel beam-to-column connections during the Northridge Earthquake. These residual stresses have a strong influence on crack initiation and crack propagation in the vicinity of stress concentrations (i.e., unfused backup bar in welded steel beam-to-column connections) and account for changes in the driving force for fracture. They affect material toughness by changing the constraint condition under which fracture occurs. Currently, all methods of dealing with residual stresses are hampered by the lack of a consistent means of measuring the magnitudes and distribution of these stresses. This paper describes a new acoustic microscopy technique that allows the mapping of residual stresses in welded connections with high spatial resolution. The technique is based on the sensitivity of polarized acoustic modes to local elastic anisotropy induced by stress. The technique furthermore allows the mapping of residual stresses in a tomographic way by changing the frequencies of the acoustic waves. The results reveal that the magnitude of the residual stresses is influenced by the local microstructure of the steel and the weld metal. Ductile microstructures within the weld and the heat affected zone release residual stresses by yielding, whereas brittle microstructures retain residual stresses.     

Dual beam light profile microscopy: a new technique for optical absorption depth profilometry

Light profile microscopy (LPM) is a recently developed technique of optical inspection that is used to record micrometer-scale images of thin-film cross-sections on a direct basis. In single beam mode, LPM provides image contrast based on luminescence, elastic, and/or inelastic scatter. However, LPM may also be used to depth profile the optical absorption coefficient of a thin film based on a method of dual beam irradiation presented in this work. The method uses a pair of collimated laser beams to consecutively irradiate a film from two opposing directions along the depth axis. An average profile of the beam's light intensity variation through the material is recovered for each direction and used to compute a depth-dependent differential absorbance profile. This latter quantity is shown from theory to be related to the film's depth-dependent optical absorption coefficient through a simple linear model that may be inverted by standard methods of numerical linear algebra. The inverse problem is relatively well posed, showing good immunity to data errors. This profilometry method is experimentally applied to a set of well-characterized materials with known absorption properties over a scale of tens of micrometers, and the reconstructed absorption profiles were found to be highly consistent with the reference data.     

Material sensitive scanning probe microscopy of subsurface semiconductor nanostructures via beam exit Ar ion polishing

Whereas scanning probe microscopy (SPM) is highly appreciated for its nanometre scale resolution and sensitivity to surface properties, it generally cannot image solid state nanostructures under the immediate sample surface. Existing methods of cross-sectioning (focused ion beam milling and mechanical and Ar ion polishing) are either prohibitively slow or cannot provide a required surface quality. In this paper we present a novel method of Ar ion beam cross-section polishing via a beam exiting the sample. In this approach, a sample is tilted at a small angle with respect to the polishing beam that enters from underneath the surface of interest and exits at a glancing angle. This creates an almost perfect nanometre scale flat cross-section with close to open angle prismatic shape of the polished and pristine sample surfaces ideal for SPM imaging. Using the new method and material sensitive ultrasonic force microscopy we mapped the internal structure of an InSb/InAs quantum dot superlattice of 18 nm layer periodicity with the depth resolution of the order of 5 nm. We also report using this method to reveal details of interfaces in VLSI (very large scale of integration) low k dielectric interconnects, as well as discussing the performance of the new approach for SPM as well as for scanning electron microscopy studies of nanostructured materials and devices.     

Imaging the surface stress and vibration modes of a microcantilever by laser beam deflection microscopy

There is a need for noninvasive techniques for simultaneous imaging of the stress and vibration mode shapes of nanomechanical systems in the fields of scanning probe microscopy, nanomechanical biological and chemical sensors and the semiconductor industry. Here we show a novel technique that combines a scanning laser, the beam deflection method and digital multifrequency excitation and analysis for simultaneous imaging of the static out-of-plane displacement and the shape of five vibration modes of nanomechanical systems. The out-of-plane resolution is at least 100 pm Hz?1/2 and the lateral resolution, which is determined by the laser spot size, is 1-1.5 μm. The capability of the technique is demonstrated by imaging the residual surface stress of a microcantilever together with the shape of the first 22 vibration modes. The vibration behavior is compared with rigorous finite element simulations. The technique is suitable for major improvements in the imaging of liquids, such as higher bandwidth and enhanced spatial resolution.     

Application of focused ion beam (FIB) microscopy to the study of crack profiles

Focused ion beam (FIB) microscopy is used to form an image similar to that formed in a conventional scanning electron microscope (SEM), but with greatly enhanced grain contrast due to the use of a primary ion beam as opposed to a beam of primary electrons as found in the SEM. In addition, by increasing the current of the positively charged gallium ion beam, it can be used as a precision, essentially stress-free milling machine on a scale of tens of nanometres to several hundred microns. In this paper, the application of FIB microscopy to the study of crack profiles is reported. Samples of a Grade 448 (X-65) pipeline steel were cyclically loaded in a dilute simulated groundwater solution of near neutral pH. Cracks that initiated on these samples were imaged in plan view and were locally cross-sectioned using a high-current focused gallium ion beam at different locations along the cracks. Samples were then tilted in situ to permit imaging of the crack profile, the grain structures around the crack tip and accurate measurement of the crack depth using the same ion beam at lower currents. The transgranular crack path and other microstructural features associated with crack development were clearly illustrated, and crack aspect ratio (depth/length) could be obtained. The capability of the FIB for enhanced imaging of grain structures, combined with its precision-sectioning capability, make it a novel new tool for the study of cracks.     

Transmission electron microscopy convergent beam measurement of S-phase volume fraction in Al---Li---Cu---Mg---Zr alloy (8090)

A statistical study of S-phase particle distribution in thin foils, measuring foil thickness by a transmission electron microscopy convergent beam technique, has shown the change of S-phase average length and volume fraction by varying treatments prior to artificial aging. The investigation shows that the average length and volume fraction of S-phase particles increases with increasing degrees of predeformation in the Al---Li---Cu---Mg---Zr alloy studied.     

Theoretical and experimental study of nanopore drilling by a focused electron beam in transmission electron microscopy

Sub-10 nm nanopores drilled by a focused electron beam in a transmission electron microscope are widely used in solid-state nanopore devices for DNA translocation. However, there still remains much controversy surrounding the drilling mechanism. In order to explain the drilling of nanopores by electrons, we undertook a theoretical consideration of the energy transfer from the fast electrons to the solid through such mechanisms as elastic and inelastic scattering. According to the calculations based on the scattering cross-section, the direct atomic displacement cross-section induced by elastic scattering increases with increasing incident electron energy, while the ionization cross-section and temperature increment decrease. We performed nanopore drilling in a Si3N4 membrane using two different electron energies, 200 and 300 kV, to identify the drilling mechanism. The dependence of the nanopore drilling on the incident electron energy was well matched with the direct atomic displacement.     

X-ray photoelectron spectroscopy and conducting atomic force microscopy investigations on dual ion beam sputtered MgO ultrathin films

Ultrathin films of MgO (~ 6 nm) were deposited on Si(100) using dual ion beam sputtering in different partial pressures of oxygen. These thin films were characterized by X-ray photoelectron spectroscopy (XPS) for chemical state analysis and conducting atomic force microscopy for topography and local conductivity map. No trace of metal Mg was evidenced in these MgO films. The XPS analysis clearly brought out the formation of oxygen interstitials and Mg(OH)₂ primarily due to the presence of residual water vapors in the chamber. An optimum value of oxygen partial pressure of ~ 4.4 × 10^− 2 Pa is identified with regard to homogeneity of film and stoichiometry across the film thickness (O:Mg::0.93-0.97). The local conductivity mapping investigations also established the film homogeneity in respect of electrical resistivity. Non-linear local current-voltage curves revealed typical tunneling characteristics with barrier width of ~ 5.6 nm and barrier height of ~ 0.92 eV.     

Mechanical,atomic force microscopy and focussed ion beam studies of isotactic polystyrene/titanium dioxide composites

Composites of isotactic polystyrene with different loading of titanium dioxide were prepared by melt mixing in a Brabender Plasticorder at a rotor speed of 60 rpm at 180 °C. Mechanical properties of the composites were measured by various techniques and most of the properties were found to be increasing with filler loading. Tapping mode atomic force microscopy was used to study the surface characteristics of the composites. Various AFM analytical parameters like power spectral density, roughness analysis and section analysis were measured. The mechanical properties of the composites were correlated with analytical data obtained from the AFM studies. The focused ion beam technique was also used to characterize the dispersion of the filler in the polymer matrix.     

Singular solutions in elasticity

Summary General solutions of the time-independent equations of motion for linear elasticity with couplestresses are studied. The completeness of a displacement potential similar to theGalerkin-Somigliana representation is proved. The fundamental singular solution of the field equations is defined with the aid of the reciprocal work theorem.

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Zusammenfassung Allgemeine Lösungen der zeitunabhängigen Bewegungsgleichungen der linearen Elastizität mit Momentenspannungen werden studiert. Die Vollständigkeit eines Verschiebungspotentials, ähnlich dem vonGalerkin-Somigliana, wird bewiesen. Die singuläre Grundlösung der Feldgleichungen wird mit Hilfe des verallgemeinertenBettischen Reziprozitätssatzes definiert.