We present a flexible linear optimization model for correcting multi-angle curtaining effects in plasma focused ion beam scanning electron microscopy (PFIB-SEM) images produced by rocking-polishing schemes. When PFIB-SEM is employed in a serial sectioning tomography workow, it is capable of imaging large three-dimensional volumes quickly, providing rich information in the critical 10–100 nm feature length scale. During tomogram acquisition, a “rocking polish” is often used to reduce straight-line “curtaining” gradations in the milled sample surface. While this mitigation scheme is effective for deep curtains, it leaves shallower line artifacts at two discretized angles. Segmentation and other automated processing of the image set requires that these artifacts be corrected for accurate microstructural quantification. Our work details a new Fourier-based linear optimization model for correcting curtaining artifacts by targeting curtains at two discrete angles. We demonstrate its capabilities by processing images from a tomogram from a multiphase, heterogeneous concrete sample. We present methods for selecting the parameters which meet the user’s goals most appropriately. Compared to previous works, we show that our model provides effective multi-angle curtain correction without introducing artifacts into the image, modifying non-curtain structures or causing changes to the contrast of voids. Our algorithm can be easily parallelized to take advantage of multi-core hardware.

Using transmission electron microscopy, we have analyzed dislocations in AlN nucleation layers and GaN films grown by metallorganic chemical vapor deposition (MOCVD) on the (0001) surface of epitaxially-grown 4H-SiC mesas with and without steps. For 4H-SiC substrates free of SiC surface steps, half-loop nucleation and glide parallel to the AlN/SiC interfacial plane play the dominant role in strain relief, with no mechanism for generating threading dislocations. In contrast, 4H-SiC mesa surfaces with steps give rise to regions of high stress at the heteroepitaxial interface, thereby providing an environment conducive to the nucleation and growth of threading dislocations, which act to accommodate misfit strain by the tilting of threading edge dislocations.

Standard Focused Ion Beam (FIB) lift-out methods for production of transmission electron microscopy (TEM) thin sections destroy many cubic microns of material in order to produce a single 100-nm thick section. Microtome sectioning, in contrast, allows serial sectioning of adjacent multiple 100-nm sections, without loss of materials between sections, but lacks site specificity. In order to maximize the yield of analyzable material in thin section form from valuableone-of-a kind- micron-sized samples, we have developed serial sectioning techniques that combine FIB lift-out with microtomy. In this paper, we show an example of sectioning and subsequent TEM analysis of simulated cometary residues which resemble impact craters collected during the NASA Stardust Mission. These techniques may be generalized to any one-of-a-kind sample for which preserving analyzable volume is critical, such as forensic analysis of dust particles, failure analysis and electronic device sectioning.

This paper updates recent progress made in growth, characterization, and understanding of high quality homoepitaxial and heteroepitaxial films grown on step-free 4H-SiC mesas. First, we report initial achievement of step-free 4H-SiC surfaces with carbon-face surface polarity. Next, we will describe further observations of how step-free 4H-SiC thin lateral cantilever evolution is significantly impacted by crystal faceting behavior that imposes non-uniform film thickness on cantilever undersides. Finally, recent investigations of in-plane lattice constant mismatch strain relief mechanisms observed for heteroepitaxial growth of 3C-SiC as well as 2H-AlN/GaN heterofilms on step-free 4H-SiC mesas will be reviewed. In both cases, the complete elimination of atomic heterointerface steps on the mesa structure enables uniquely well-ordered misfit dislocation arrays to form near the heterointerfaces with remarkable lack of dislocations threading vertically into the heteroepilayers. In the case of 3C-SiC heterofilms, it has been proposed that dislocation half-loops nucleate at mesa edges and glide laterally along the step-free 3C/4H interfaces. In contrast, 3C-SiC and 2H-AlN/GaN heterofilms grown on 4H-SiC mesas with steps exhibit highly disordered interface misfit dislocation structure coupled with 100X greater density of dislocations threading through the thickness of the heteroepilayers. These results indicate that the presence of steps at the heteroepitaxial interface (i.e., on the initial heteroepitaxial nucleation surface) plays a highly important role in the defect structure, quality, and relaxation mechanisms of single-crystal heteroepitaxial films.

Silicon carbide (SiC) is rapidly becoming the substrate of choice for the development of high frequency and high power electronic devices employing the III-V nitride family of materials. This heteroepitaxial growth system continues to receive considerable attention, as materials issues remain the fundamental limiters to device performance. The heteroepitaxial growth of gallium nitride (GaN) thin films on stepped and step-free 4H SiC surfaces is reported. Step-free SiC surfaces are created by mesa patterning of a SiC wafer and subsequent epitaxial growth in a process described previously. This process results in a collection of both step-free and stepped surfaces on a given sample. We have employed an established metalorganic chemical vapor deposition process to grow first a thin (1200Å) aluminum nitride (AlN) nucleation layer and then a 2 μm thick GaN thin film. We have interrupted growth at various stages of AlN and GaN growth to evaluate the growth evolution using atomic force microscopy (AFM). The results show marked differences in the manner in which the initial AlN layer deposits. Nucleation is random with elongated grains on step-free SiC surfaces, while stepped surfaces have round nuclei of uniform dimensions and a high degree of spatial correlation with the nuclei arranged in rows. These differences diminish as the AlN layer approaches the desired thickness. Growth of the GaN epilayer is also markedly different on the two types of surfaces with step-free surfaces leading to random and low density nucleation of crystallites that remain as single grains for long growth times, whereas the stepped surfaces have large numbers nuclei that rapidly grow laterally. Cross-sectional transmission electron microscopy (TEM) reveals that grain sizes are 2–3X larger on step-free surfaces.

Indium tin oxide is one of the most used transparent conducting oxides. In order to reduce the processing thermal budget and enhance compatibility of these films for such applications as transparent electrodes for solar cells and flat panel displays, lower deposition temperatures are desirable. The addition of a non-thermal energy source during deposition, in this case, a mercury lamp, has the ability to lower the required substrate temperature during processing while increasing the oxygen content of the deposited film through the added contribution of ionized species into the deposited material. We investigated the microstructure of UV-assisted pulsed laser deposited indium tin oxide films. Comparisons between the UV and non-UV films were made in order to judge the effectiveness of the UV radiation in achieving desirable properties.