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Imperfections in Crystal Structure: Point, Line and Plane Defects

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A perfect crystal, in theory, has a uniform structure with the same unit cell and lattice points throughout. However, any deviation from this periodic arrangement is known as an imperfection or defect. These defects can be categorized into three types: point, line, and plane defects.Point defects occur when there is a deviation from the ideal due to missing atoms, displaced atoms, or additional atoms. These imperfections might occur due to imperfect packing during crystallization or because of...

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Schottky defects arise when some lattice points in a crystal, such as those in NaCl, remain unoccupied, creating lattice vacancies without disturbing the overall electrical neutrality of the crystal. This defect is common in ionic crystals where the positive and negative ions are similar in size, as seen in sodium chloride and cesium chloride. The presence of Schottky defects enables the crystal to conduct electricity to a small extent through an ionic mechanism. Electric fields cause nearby...

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Non-stoichiometric defects refer to a type of defect in the crystal structure of a compound where the ratio of its constituent elements deviates from the ideal stoichiometric ratio. There are two main types of non-stoichiometric defects: metal excess defects and metal deficiency defects.Metal excess defects occur when there is a slight surplus of metal ions than what is required by the stoichiometric ratio of the compound. For example, heating a sodium chloride crystal in sodium vapor results...

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Solids in which the atoms, ions, or molecules are arranged in a definite repeating pattern are known as crystalline solids. Metals and ionic compounds typically form ordered, crystalline solids. A crystalline solid has a precise melting temperature because each atom or molecule of the same type is held in place with the same forces or energy. Amorphous solids or non-crystalline solids (or, sometimes, glasses) which lack an ordered internal structure and are randomly arranged. Substances that...

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The structure of a crystalline solid, whether a metal or not, is best described by considering its simplest repeating unit, which is referred to as its unit cell. The unit cell consists of lattice points that represent the locations of atoms or ions. The entire structure then consists of this unit cell repeating in three dimensions. The three different types of unit cells present in the cubic lattice are illustrated in Figure 1.
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Related Experiment Video

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Quantitative Atomic-Site Analysis of Functional Dopants/Point Defects in Crystalline Materials by Electron-Channeling-Enhanced Microanalysis

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Mobile point defects and atomic basis for structural transformations of a crystal surface.

I S Hwang, S K Theiss, J A Golovchenko

Science (New York, N.Y.)

|July 22, 1994

Summary

Lead atoms enable observation of atomic motions on germanium surfaces at low temperatures. This catalysis facilitates understanding of surface structural changes and phase transitions in elemental semiconductors.

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Theoretical Calculation and Experimental Verification for Dislocation Reduction in Germanium Epitaxial Layers with Semicylindrical Voids on Silicon

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Published on: July 17, 2020

Area of Science:

Surface science
Materials science
Condensed matter physics

Background:

Elemental semiconductor surface transformations usually require high temperatures (> hundreds of °C) and involve rapid atomic motions difficult to observe.
Surface dangling bonds play a critical role in mediating atomic rearrangements.

Purpose of the Study:

To investigate catalytic effects of lead atoms on germanium (Ge) surface dynamics at lower temperatures.
To elucidate the atomic mechanisms behind surface structural transformations and phase transitions on Ge(111).

Main Methods:

Utilizing a scanning tunneling microscope (STM) to observe atomic-scale motions.
Developing a detailed atomic model to explain observed phenomena.

Main Results:

A few lead atoms catalyze atomic motions on the Ge(111) surface, observable below 80 °C.
Observed mass transport and structural changes are driven by point defects (vacancy-like and interstitial-like).
The Ge(111)-c(2x8) <--> 1x1 structural phase transition near 300 °C is explained by the atomic model.

Conclusions:

Lead atoms significantly lower the temperature threshold for observing surface atomic dynamics on germanium.
The study provides atomic-level insights into surface defect dynamics and phase transitions in elemental semiconductors.
The developed atomic model successfully explains the observed catalytic effects and phase transition behavior.