Formation of Twin-Free Single Phase β-InSe Layers via Selenium Diffusion into InP(111)B Substrate.

Indium selenide, InSe, has recently attracted growing interest due to its remarkable properties, including room temperature ferroelectricity, outstanding photoresponsivity, and exotic in-plane ferroelectricity, which open up new regimes for next generation electronics. InSe also provides the important advantage of tuning the electrical properties of ultrathin layers with an external electrical and magnetic field, making it a potential platform to study novel two-dimensional physics. Yet, InSe has many different polymorphs, and it has been challenging to synthesize a single phase material, especially using scalable growth methods, as needed for technological applications.

Chemical Conversions within the Mo-Ga-C System: Layered Solids with Variable Ga Content.

Layered carbides are fascinating compounds due to their enormous structural and chemical diversity, as well as their potential to possess useful and tunable functional properties. Their preparation, however, is challenging and forces synthesis scientists to develop creative and innovative strategies to access high-quality materials. One unique compound among carbides is MoGaC.

Quantitative measurement of nanoscale electrostatic potentials and charges using off-axis electron holography: Developments and opportunities.

Off-axis electron holography has evolved into a powerful electron-microscopy-based technique for characterizing electromagnetic fields with nanometer-scale resolution. In this paper, we present a review of the application of off-axis electron holography to the quantitative measurement of electrostatic potentials and charge density distributions. We begin with a short overview of the theoretical and experimental basis of the technique.

Large positive linear magnetoresistance in the two-dimensional t electron gas at the EuO/SrTiO interface.

The development of novel nano-oxide spintronic devices would benefit greatly from interfacing with emergent phenomena at oxide interfaces. In this paper, we integrate highly spin-split ferromagnetic semiconductor EuO onto perovskite SrTiO (001). A careful deposition of Eu metal by molecular beam epitaxy results in EuO growth via oxygen out-diffusion from SrTiO.

Above 400-K robust perpendicular ferromagnetic phase in a topological insulator.

The quantum anomalous Hall effect (QAHE) that emerges under broken time-reversal symmetry in topological insulators (TIs) exhibits many fascinating physical properties for potential applications in nanoelectronics and spintronics. However, in transition metal-doped TIs, the only experimentally demonstrated QAHE system to date, the QAHE is lost at practically relevant temperatures. This constraint is imposed by the relatively low Curie temperature () and inherent spin disorder associated with the random magnetic dopants.

Direct Mapping of Charge Distribution during Lithiation of Ge Nanowires Using Off-Axis Electron Holography.

The successful operation of rechargeable batteries relies on reliable insertion/extraction of ions into/from the electrodes. The battery performance and the response of the electrodes to such ion insertion and extraction are directly related to the spatial distribution of the charge and its dynamic evolution. However, it remains unclear how charge is distributed in the electrodes during normal battery operation.

Determination of Mean Inner Potential and Inelastic Mean Free Path of ZnTe Using Off-Axis Electron Holography and Dynamical Effects Affecting Phase Determination.

The mean inner potential (MIP) and inelastic mean free path (IMFP) of undoped ZnTe are determined using a combination of off-axis electron holography and convergent beam electron diffraction. The ZnTe MIP is measured to be 13.7±0.

Carrier density modulation in a germanium heterostructure by ferroelectric switching.

The development of non-volatile logic through direct coupling of spontaneous ferroelectric polarization with semiconductor charge carriers is nontrivial, with many issues, including epitaxial ferroelectric growth, demonstration of ferroelectric switching and measurable semiconductor modulation. Here we report a true ferroelectric field effect-carrier density modulation in an underlying Ge(001) substrate by switching of the ferroelectric polarization in epitaxial c-axis-oriented BaTiO3 grown by molecular beam epitaxy. Using the density functional theory, we demonstrate that switching of BaTiO3 polarization results in a large electric potential change in Ge.

Determination of polarization-fields across polytype interfaces in InAs nanopillars.

Polarization fields within InAs nanopillars with zincblende(ZB)/wurtzite(WZ) polytype stacking are quantified. The displacement of charged ions inside individual tetrahedra of WZ regions is measured at the atomic scale. The variations of spontaneous polarization along the interface normal are related to strain at interfaces of different polytypes.

Atomic configurations at InAs partial dislocation cores associated with Z-shape faulted dipoles.

The atomic arrangements of two types of InAs dislocation cores associated by a Z-shape faulted dipole are observed directly by aberration-corrected high-angle annular-dark-field imaging. Single unpaired columns of different atoms in a matrix of dumbbells are clearly resolved, with observable variations of bonding lengths due to excess Coulomb force from bare ions at the dislocation core. The corresponding geometric phase analysis provides confirmation that the dislocation cores serve as origins of strain field inversion while stacking faults maintain the existing strain status.

Exploring aberration-corrected electron microscopy for compound semiconductors.

The development of aberration-corrected electron microscopes (ACEMs) has made it possible to resolve individual atomic columns ('dumbbells') with correct interatomic spacings in elemental and compound semiconductors. Thus, the latest generations of ACEMs should become powerful instruments for determining detailed structural arrangements at defects and interfaces in these materials. This paper provides a short overview of off-line ('software') and on-line ('hardware') ACEM techniques, with particular reference to characterization of elemental and compound semiconductors.

Polarization-induced charge distribution at homogeneous zincblende/wurtzite heterostructural junctions in ZnSe nanobelts.

Homogeneous heterostructural wurtzite (WZ)/zincblende (ZB) junctions are successfully fabricated in ZnSe nanobelts. Polarity continuity across the ZB/WZ interface is demonstrated. The saw-tooth-like potential profile induced by spontaneous polarization across the WZ/ZB/WZ interfaces is identified directly at the nanoscale.

Observation of hole accumulation in Ge/Si core/shell nanowires using off-axis electron holography.

Hole accumulation in Ge/Si core/shell nanowires (NWs) has been observed and quantified using off-axis electron holography and other electron microscopy techniques. The epitaxial [110]-oriented Ge/Si core/shell NWs were grown on Si (111) substrates by chemical vapor deposition through the vapor-liquid-solid growth mechanism. High-angle annular-dark-field scanning transmission electron microscopy images and off-axis electron holograms were obtained from specific NWs.

Phase-shifting electron holography for atomic image reconstruction.

Phase-shifting electron holography was used to reconstruct the object-wave function of high-spatial-frequency specimens of HgCdTe, and the requirements for precise measurements were investigated. Fresnel fringes due to the electrostatic biprism caused serious calculation errors during the phase-shifting reconstruction. Uniform interference fringes, obtained by adjusting the biprism voltage to cancel out the Fresnel fringes, were needed to minimize these errors.

Determination of the inelastic mean-free-path and mean inner potential for AlAs and GaAs using off-axis electron holography and convergent beam electron diffraction.

The mean-free-paths for inelastic scattering of high-energy electrons (200 keV) for AlAs and GaAs have been determined based on a comparison of thicknesses as measured by electron holography and convergent-beam electron diffraction. The measured values are 77 +/- 4 nm and 67 +/- 4 nm for AlAs and GaAs, respectively. Using these values, the mean inner potentials of AlAs and GaAs were then determined, from a total of 15 separate experimental measurements, to be 12.

Crystal habits and magnetic microstructures of magnetosomes in coccoid magnetotactic bacteria.

We report on the application of off-axis electron holography and high-resolution TEM to study the crystal habits of magnetosomes and magnetic microstructure in two coccoid morphotypes of magnetotactic bacteria collected from a brackish lagoon at Itaipu, Brazil. Itaipu-1, the larger coccoid organism, contains two separated chains of unusually large magnetosomes; the magnetosome crystals have roughly square projections, lengths up to 250 nm and are slightly elongated along [111] (width/length ratio of about 0.9).

Sample preparation for precise and quantitative electron holographic analysis of semiconductor devices.

Wedge polishing was used to prepare one-dimensional Si n-p junction and Si p-channel metal-oxide-silicon field effect transistor (pMOSFET) samples for precise and quantitative electrostatic potential analysis using off-axis electron holography. To avoid artifacts associated with ion milling, cloth polishing with 0.02-microm colloidal silica suspension was used for final thinning.

Reconstruction technique for off-axis electron holography using coarse fringes.

A reconstruction technique for off-axis electron holography not requiring Fourier transformation is presented. Background intensity and amplitude modulation recorded in a hologram are normalized using an envelope function, and a cosine-function image corresponding to interference fringes is retrieved from the hologram. A reconstructed phase image is then calculated from the retrieved cosine image.

Characterization of charging in semiconductor device materials by electron holography.

Quantitative analysis of electrostatic potential in semiconductor device samples using off-axis electron holography in the electron microscope is complicated by the presence of charged insulating layers. Preliminary results indicate that the behavior of p-type material near the Si-insulator interface may differ from that of n-type if the insulator is charging. Coating one side of the sample surface with carbon usually eliminates charging effects.

Habits of magnetosome crystals in coccoid magnetotactic bacteria.

High-resolution transmission electron microscopy and electron holography were used to study the habits of exceptionally large magnetite crystals in coccoid magnetotactic bacteria. In addition to the crystal habits, the crystallographic positioning of successive crystals in the magnetosome chain appears to be under strict biological control.

Conventional and back-side focused ion beam milling for off-axis electron holography of electrostatic potentials in transistors.

Off-axis electron holography is used to characterize a linear array of transistors, which was prepared for examination in cross-sectional geometry in the transmission electron microscope (TEM) using focused ion beam (FIB) milling from the substrate side of the semiconductor device. The measured electrostatic potential is compared with results obtained from TEM specimens prepared using the more conventional 'trench' FIB geometry. The use of carbon coating to remove specimen charging effects, which result in electrostatic fringing fields outside 'trench' specimens, is demonstrated.