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A unique in situnanoindentation stage has been built and developed at the National Center for Electron Microscopy in Berkeley, CA. By using piezoceramic actuators to finely position a 3-sided, boron-doped diamond indenter, we are able to image in real time the nanoindentation induced deformation of thin films. Recent work has included the force-calibration of the indenter, using silicon cantilevers to establish a relationship between the voltage applied to the piezoactuators, the displacement of the diamond tip, and the force generated.In this work, we present real time, in situTEM observations of the plastic deformation of Al thin films grown on top of lithographically-prepared silicon substrates. The in situnanoindentations require a unique sample geometry (see Figure 1) in which the indenter approaches the specimen normal to the electron beam. in order to meet this requirement, special wedge-shaped silicon samples were designed and microfabricated so that the tip of the wedge is sharp enough to be electron transparent.

GaN and related wide band gap semiconductor alloys have received considerable attention over the past several years because of their utility in short wavelength opto-electronic and high power / high frequency devices. In most cases, GaN alloys are grown heteroepitaxially on (0001) single crystal sapphire. Due to the high lattice mismatch between GaN and sapphire, typical dislocation densities in these films vary from as high as 1010cm-2to, at best, 108cm-2. Hollow core dislocations - also known as nanopipes - are also frequently observed. The presence of high defect densities is widely believed to limit the performance of GaN based electronic devices, especially the lifetime of commercially important blue and green laser diodes.In this work, we present real time, in-situTEM observations of the formation mechanism of nanopipes in single crystal GaN.

The mechanical behavior of metallic thin films on silicon plays a crucial role in the performance and reliability of microelectronic devices. A substantial body of research has focused on experimental methods for determining the mechanical properties of these systems as well as their response to thermomechanical stimuli. Of particular interest is a fundamental understanding of the how these films respond to the thermal expansion stresses that develop during typical microelectronic device fabrication steps.In this work, we present a series of real time in-situtransmission electron microscopy observations of the thermomechanical response of a model metal film on silicon system. Physical vapor deposition of approximately 50 nm of aluminum onto a clean Si substrate held at 280 °C results in the creation of an epitaxial bicrystalline film with two variants of Al (110) oriented grains. In order to observe a large, uniform area during in-situTEM thermal cycling, the Si substrate used was a SIMOX structure composed of 300 nm of Si (001) over 370 nm of buried SiO2).

When acquiring energy-filtered TEM (EFTEM) images of a crystalline material, the detrimental effects of diffraction contrast can often be seen in raw energy-filtered images (EFI) (i.e., pre-edge and post-edge images), jump-ratio images and elemental maps as residual diffraction contrast. Residual diffraction contrast occurs in raw EFI because of plural scattering (i.e., inelastic-elastic and elastic-inelastic electron scattering) and in jump-ratio images and elemental maps because background removal procedures often are unable to completely account for intensity changes due to dynamical effects (elastic scattering) that occur between pre-edge and post-edge images acquired at different energy losses.It is demonstrated in these experiments that, when examining a planar interface, EFTEM images have increased compositional contrast and decreased residual diffraction contrast when the sample is oriented so that the interface is parallel to the electron beam, but not directly on a zone axis.

The rate of heteroepitaxial strain relaxation via misfit dislocation introduction is strongly limited by the kinetics of dislocation nucleation, propagation and interaction. Here we describe real-time observations of the interaction between moving threading dislocations and pre-existing interfacial misfit dislocations using in-situtransmission electron microscopy. This was accomplished both during in-situobservations of the heteroepitaxial growth process using a modified ultrahigh vacuum TEM (UHV-TEM) equipped with chemical vapor deposition capabilities, as well as during in-situanneals of metastable structures grown by molecular beam epitaxy.In Figure 1, we present our UHV-TEM observations of the epilayer thicknesses and compositions at which dislocation interactions result in blocking of the propagating threading segment, and compare these with the theoretical predictions of Freund and those of Schwarz and Tersoff. Our results show that dislocation blocking can significantly affect the overall rate of strain relaxation in these structures. This is important, as blocked threading segments introduce undesired band gap states into electronic devices and can act as easy diffusion paths for impurities and dopants.