A refined plan-view specimen preparation technique for high-quality electron microscopy studies of epitaxially grown atomically thin 2D layers.

The structural studies of two-dimensional (2D) van der Waals heterostructures and understanding of their relationship with the orientation of crystalline substrates using transmission electron microscopy (TEM) presents a challenge in developing an easy-to-use plan-view specimen preparation technique. In this report, we introduce a simple approach for high-quality plan-view specimen preparation utilizing a dual beam system comprising focused ion beam and scanning electron microscopy. To protect the atomically thin 2D heterostructure during the preparation process, we employ an epoxy layer.

Level set simulation of focused ion beam sputtering of a multilayer substrate.

The evolution of a multilayer sample surface during focused ion beam processing was simulated using the level set method and experimentally studied by milling a silicon dioxide layer covering a crystalline silicon substrate. The simulation took into account the redeposition of atoms simultaneously sputtered from both layers of the sample as well as the influence of backscattered ions on the milling process. Monte Carlo simulations were applied to produce tabulated data on the angular distributions of sputtered atoms and backscattered ions.

Cross-sectional shape evolution of GaN nanowires during molecular beam epitaxy growth on Si(111).

We study the cross-sectional shape of GaN nanowires (NWs) by transmission electron microscopy. The shape is examined at different heights of long NWs, as well as at the same height for NWs of different lengths. Two distinct trends in the evolution of the cross-sectional shape along the NW length are observed.

Anodic TiOnanotube arrays for photocatalytic COconversion: comparative photocatalysis and EPR study.

Titania (TiO) is a widely used semiconductor for the photocatalytic decomposition of organic impurities in air, water and the conversion of COinto hydrocarbon fuel precursors. TiOin the form of nanotubes arrays is the most attractive for practical use because of the morphological advantages providing more favorable diffusion of photocatalytic reaction products and a low recombination rate of photogenerated electrons and holes. We have carried out a comparative study of the photocatalytic activity of gas-phase conversion of COto hydrocarbon products and the defect properties of multi-walled and single-walled arrays of TiOnanotubes.

Influence of Proximity to Supporting Substrate on van der Waals Epitaxy of Atomically Thin Graphene/Hexagonal Boron Nitride Heterostructures.

Combining graphene and the insulating hexagonal boron nitride (h-BN) into two-dimensional heterostructures is promising for novel, atomically thin electronic nanodevices. A heteroepitaxial growth, in which these materials are grown on top of each other, will be crucial for their scalable device integration. However, during this so-called van der Waals epitaxy, not only the atomically thin substrate itself must be considered but also the influences from the supporting substrate below it.

Complex Pore Structure of Mesoporous Zeolites: Unambiguous TEM Imaging Using Platinum Tracking.

The article proposes a new way for visualization of mesopores and quantitative evaluation of the pore structure in zeolite crystals. The approach is based on platinum tracking inside the zeolite material after its incorporation from a gaseous precursor using an electron beam prior to preparing a TEM specimen by the focused ion beam technique. The pores in mesoporous silica and purely microporous zeolite Y were visualized in TEM images in a demonstration of the capabilities of the approach.

Melting temperature of metal polycrystalline nanowires electrochemically deposited into the pores of anodic aluminum oxide.

The arrays of metallic nanowires are considered as promising precursors for 1D semiconductor nanostructures after appropriate treatment at temperatures close to the melting point. Therefore the melting behaviour of the metallic structures in oxide templates is a key parameter for the subsequent conversion process. The present paper focuses on understanding of the effect of mechanical stress generated during heating on the melting point of the metal nanowires deposited into the pores of anodic alumina.

Mesoscopic properties of interfacial ordering in amorphous germanium on Si(111) determined by quantitative digital image series matching.

For the quantitative characterization of atomic ordering in the transition region between crystalline and amorphous materials we have previously described a method based on averaging HREM images along the interface, simulation of averaged images with the use of the averaged projected potential approximation and determination of the atom arrangement by means of an iterative matching procedure for high-resolution focus series. In order to study mesoscopic properties of crystal induced ordering a fully quantitative procedure is developed in this work. For this purpose, the width of the averaging region is defined as a compromise providing necessary accuracy of calculations and desirable locality of characterization of the atom distribution.

Analysis of high resolution transmission electron microscope images of crystalline-amorphous interfaces.

For the analysis of images of homogeneous crystalline-amorphous interfaces we propose to average them along the interface obtaining the averaged interface image or the averaged intensity profile. Due to averaging, contrast components with the periodicity of the crystalline area of the image are extracted. Thus, the contrast features originating from the random overlap of the projected potentials of atoms in the amorphous layer are suppressed.

Elastic scattering of partially coherent beams of fast electrons by a crystal with a defect.

Scattering of a quasi-monochromatic electron beam by a crystal with a defect is described with the use of the mutual coherency function and the formalism of quasi-Bloch waves. An expression correlating the mutual intensity on the exit and entrance surfaces of the crystal in terms of the scattering matrix has been found. The matrix elements are determined by a system of integro-differential equations, which have been obtained without using the column approximation.