Polycrystalline Grain Boundaries Research Articles

Grain Boundaries in Barium Strontium Titanate Thin Films: Structure, Chemistry and Influence on Electronic Properties

In this paper, we investigate the role of grain boundaries in polycrystalline (BaxSr1−x)Ti1+yO3+z films, grown by metal organic vapor deposition, in the accommodation of nonstoichiometry, as well as their role in the strong composition dependence of the electric and dielectric behavior observed in these films. High-spatial resolution electron energy-loss spectroscopy is used for the analysis of composition and structural changes at grain boundaries, as a function of film composition. The existence of amorphous, titanium rich, TiO2-like phases at the grain boundaries of films with large amounts of excess Ti (y ≥ 0.08) may explain the non-monotonic resistance degradation behavior of the films as a function of Ti content. However, we show that a grain boundary phase model fails to explain the strong composition dependence of the dielectric behavior. Electron energy-loss spectra indicate a distortion of the Ti–O octahedra in the grain interiors in samples with increasing Ti excess. The decrease of the dielectric constant with increasing amounts of excess Ti is therefore more likely due to Ti accommodation in the grain interiors.

Diffusion — Induced creep of polycrystalline and nanostructured metals

Kinetic mechanisms of phenomena to be induced by the diffusion on the grain boundaries in polycrystalline and nanostructured (NS) materials have been analyzed. By way of example of nickel and copper nanostructured (grain size 100÷300 nm) it was shown that the effect of diffusion induced loss of strength by creep was much observed at temperatures low than 400 K in comparison with polycrystalline condition with grain size 20 μm. It was supposed that the physical reason for the decrease in the temperature for the effect to manifest itself is much higher value of diffusion coefficients of impurities in nanostructures.

Low-energy disclination structures at grain boundaries in polycrystalline and nanocrystalline solids

Peculiarities of the splitting of grain boundary disclinations in polycrystalline and nanocrystalline solids are examined theoretically. The three basic variants of such a splitting (planar splitting, threefold star splitting, circle splitting) are considered with special attention to calculations of the energetic characteristics of these splitting processes. It is shown that the planar splitting decreases the probability of microcrack generation of grain boundaries. [Russian Text Ignored].

Electromigration transport mechanisms in Al thin-film conductors

Electromigration occurs along grain boundaries in polycrystalline thin-film conductors when the grain size is significantly larger than the conductor width. As circuit feature sizes have been reduced, microstructures have become near bamboo and alternate diffusion mechanisms must operate within the bamboo grains. In this article we examine drift velocity data to determine electromigration mechanisms in bamboo grains. We present measurements of the temperature and width dependence of the drift velocity of thin-film conductors with bamboo microstructures. The activation energy for drift is consistent with lattice diffusion in Al. There is no width dependence of the drift velocity in the range 0.6–2.7 μm, indicating a negligible flux of atoms along the conductor edges. We compare these measurements with data available for a variety of conductor microstructures, and with drift data for bulk Al. The drift velocities of conductors with bamboo microstructures obtained from a variety of sources show very good agreement, and are similar to drift velocities observed in bulk Al. We conclude that the dominant mode of electromigration in thin-film conductors with bamboo microstructures and bulk Al is the same, and occurs by lattice vacancy diffusion.

Preparation and characterization of In 4Se 3 films

Thin films of In 4Se 3 were obtained by vacuum evaporation of polycrystalline materials onto substrates at different temperatures T s . Systematic X-ray analysis was carried out and revealed that the flash evaporation technique can produce stoichiometric films for depositing polycrystalline materials of composition In 1.11Se 0.89. Optical and electrical characterizations are reported. The energy gap of In 4Se 3 films is located between 1.41 and 1.48 eV depending on the substrate temperature. A.c. and d.c. conductivities were measured as a function of T s . Amorphous films exhibit a T − 1 4 dependence of the conductivity which fits well with the Mott model with a density of localized states N(E F ) = 8.5 × 10 18 cm −3 eV −1 . The effect of annealing temperature was also investigated. Hall measurement as a function of temperature show that the predominant conduction mechanism is scattering by grain boundaries in polycrystalline In 4Se 3 films.

Origin of Grain Boundary Recombination Activity in Silicon Wafers

AbstractIn silicon bicrystals grain boundaries (GBs) become recombining after they have been annealed in argon at temperatures higher than 800°C for tens of hours. In order to verify the eventual influence of metallic elements, interstitials gold atoms are introduced in the bicrystals by diffusion (T ≤ 8000 C) from gold dots deposited far from the GB (gold could be segregated by the GB but cannot give deep levels in the grains). It is found by DLTS, EBIC contrast and LBIC scan map that the recombination strength of GBs is not changed by gold in diffusion in as grown bicrystals, while it is reduced in annealed samples. Similar results are obtained with GBs of polycrystalline wafers.It is concluded that the activation of GBs in CZ silicon bicrystals is certainly due to the segregation of a slow diffuser like oxygen, and that fast diffusers play a secondary role only.

An experimental and theoretical study of polycrystalline thin film transistor

This paper describes work undertaken to develop the Wiemer theory of thin film transistors [1] to be valid for polycrystalline semiconductors (s.c.) as well as monocrystalline s.c. A simple representation of the grain boundaries of polycrystalline s.c. as a series resistance has been proposed. A comparison of experimental and theoretical results shows good agreement between the calculated and measured values of the transistor parameters. Finally, an application of the theory has been extended to evaluate the average resistivity of the grain boundaries of polycrystalline s.c. such as InSb.

Evidence for electron diffraction by off-coincidence grain boundaries in polycrystalline lead films

Evidence for electron diffraction by off-coincidence grain boundaries in polycrystalline lead films

The propagation of cracks through grain boundaries in polycrystalline 3% silicon-iron

This paper describes experimental results on the effect of misorientation on the propagation of hydrogen-induced cleavage microcracks through grain boundaries in 3% silicon-iron. It is shown that the ability of such cracks to propagate through a boundary depends on whether or not new cleavage crack segments can be initiated in the adjacent grain, and the misorientation results are discussed in terms of suitable initiation models.