Extra diffractions caused by stacking faults in cubic crystals

Electron-beam induced Mn oxidation in TEM: Insights into the heating effect of Auger excitation

Electron-beam irradiation of α-Mn triggers dramatic microstructural transformations. Transmission electron microscopy (TEM) reveals localized thinning and MnO formation within the irradiated area. Reduced thermal conductivity due to thinning suggests significant local temperature rise by electron-beam irradiation. Finite element analysis (FEA) identifies Auger excitation as the dominant heating mechanism, surging temperatures to ∼2300 K with ultrafast cooling. Our findings indicate that the oxidation of Mn under electron-beam irradiation is primarily attributed to beam heating via Auger excitation, rather than defect formation through sputtering. This conclusion is supported by the fact that the maximum energy transferable from the incident electron beam in TEM is below the minimum displacement energy for Mn.

On the origin of epitaxial rhombohedral-B4C growth by CVD on 4H-SiC

Rhombohedral boron carbide, often referred to as r-B4C, is a potential material for applications in optoelectronic and thermoelectric devices. From fundamental thin film growth and characterization, we investigate the film-substrate interface between the r-B4C films grown on 4H-SiC (0001̄) (C-face) and 4H-SiC (0001) (Si-face) during chemical vapor deposition (CVD) to find the origin for epitaxial growth solely observed on the C-face. We used high-resolution (scanning) transmission electron microscopy and electron energy loss spectroscopy to show that there is no surface roughness or additional carbon-based interlayer formation for either substrate. Based on Raman spectroscopy analysis, we also argue that carbon accumulation on the surface hinders the growth of continued epitaxial r-B4C in CVD.

On the origin of diffuse intensities in fcc electron diffraction patterns

Interpreting diffuse intensities in electron diffraction patterns can be challenging in samples with high atomic-level complexity, as often is the case with multi-principal element alloys. For example, diffuse intensities in electron diffraction patterns from simple face-centred cubic (fcc) and related alloys have been attributed to short-range order1, medium-range order2 or a variety of different {111} planar defects, including thin twins3, thin hexagonal close-packed layers4, relrod spiking5 and incomplete ABC stacking6. Here we demonstrate that many of these diffuse intensities, including [Formula: see text]{422} and [Formula: see text]{311} in ⟨111⟩ and ⟨112⟩ selected area diffraction patterns, respectively, are due to reflections from higher-order Laue zones. We show similar features along many different zone axes in a wide range of simple fcc materials, including CdTe, pure Ni and pure Al. Using electron diffraction theory, we explain these intensities and show that our calculated intensities of projected higher-order Laue zone reflections as a function of deviation from their Bragg conditions match well with the observed intensities, proving that these intensities are universal in these fcc materials. Finally, we provide a framework for determining the nature and location of diffuse intensities that could indicate the presence of short-range order or medium-range order.

Imaging and analysis of nanowires

We used vapor-liquid-solid (VLS) methods to synthesize discrete single-element semiconductor nanowires and multicomposition nanowire heterostructures, and then characterized their structure and composition using high-resolution electron microscopy (HRTEM) and analytical electron microscopy techniques. Imaging nanowires requires the modification of the established HRTEM imaging procedures for bulk material to take into consideration the effects of finite nanowire width and thickness. We show that high-resolution atomic structure images of nanowires less than 6 nm in thickness have lattice "streaking" due to the finite crystal lattice in two dimensions of the nanowire structure. Diffraction pattern analysis of nanowires must also consider the effects of a finite structure producing a large reciprocal space function, and we demonstrate that the classically forbidden 1/3 [422] reflections are present in the [111] zone axis orientation of silicon nanowires due to the finite thickness and lattice plane edge effects that allow incomplete diffracted beam cancellation. If the operating conditions are not carefully considered, we found that HRTEM image delocalization becomes apparent when employing a field emission transmission electron microscope (TEM) to image nanowires and such effects have been shown to produce images of the silicon lattice structure outside of the nanowire itself. We show that pseudo low-dose imaging methods are effective in reducing nanowire structure degradation caused by electron beam irradiation. We also show that scanning TEM (STEM) with energy dispersive X-ray microanalysis (EDS) is critical in the examination of multicomponent nanowire heterostructures.

TEM analysis of epitaxial semiconductor layers with high stacking fault densities considering artifacts induced by the cross-section geometry

Epitaxial semiconductor layers, in particular II-VI compound semiconductors with the component Se deposited on III-V semiconductor substrates like GaAs or InAs, can contain high densities of stacking faults. CdxMg(1-x)Se layers with Cd-concentrations x of 93% and 57% on InAs(0 0 1) substrates were investigated as typical representatives of this class of heterostructures. The defect structure of the layers is dominated by a high density of stacking fault (SF) pairs bound by Shockley partial dislocations with Burgers vectors b = 1/6 <1 1 2> and a stair-rod dislocation with b = 1/6 <1 1 0> at the intersection line of the pairs. Plan-view transmission electron microscopy (TEM) is generally applied to obtain information about the type, density and arrangement of the stacking faults in thin epilayers up to moderate SF densities. Cross-section TEM is more frequently carried out for thick layers and at high SF densities. It will be demonstrated by a detailed analysis of cross-section images that a careful interpretation of the observed SF morphologies is necessary due to artifacts induced by the cross-section geometry.