Editorial Feature

Measuring Nanostructures Using X-Ray Diffraction

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In order to determine the properties of a material, detailed knowledge of the structures it contains at the atomic level is required. This information can be obtained using conventional X-ray diffraction (XRD) methods for ordinary materials. Using XRD, the distances between the atoms in a material can be measured with respect to the wavelength of X-rays.

In the past, several XRD techniques have been developed and applied to a wide range of materials – from simple solids to complex proteins. XRD has also been successfully used to explore the structure of nanomaterials.

X-ray Diffraction Analysis of Nanostructures

Any material exhibiting a periodic atomic order at a long range acts as a well-defined grating when irradiated with X-rays. Nanomaterials exhibit structural coherence for a length of several nanometres, which means that these materials fall between regular crystals and non-crystals.

The limited degree of structural coherence may be due to very well-defined atomic ordering or difference in atomic ordering over distances of few nanometres. The nanomaterial would act as a grating in either case thereby producing XRD patterns which provide a diffuse component and Bragg peaks.

Unlike XRD patterns of regular crystals, the XRD patterns of a nanomaterial do not exhibit a number of sharp Bragg peaks. However, the diffuse component is very strong and similar to that of non-crystal materials. The spatial characteristics of the grating can be determined by measuring the intensities and positions of the Bragg peaks and the three-dimensional arrangement of the atoms in the nanomaterials can be studied as a result.

Research on X-ray Diffraction Analysis of Nanostructures

In 2009, researchers from Japan carried out a study to characterise low crystallinity carbon materials by analysing the structure of polyparaphenylene-based carbon using high energy XRD. The results revealed the presence of basic structural units and hexagonal carbon layers in disordered materials such as polyparaphenylene carbon.

In 2012, Italian researchers used XRD methods to study the uniaxial elastic strain of individual lithographically defined SiGe nanostructures. They developed one and two dimensional nanostructures of a strained SiGe layer by mapping the reciprocal space in the nanostructures using an X-ray beam.

They also combined diffraction data and kinematic simulations of strain to obtain the ‘in plane’ and ‘out of plane’ components. The results proved that it is possible to achieve pure elastic anisotropic strain relaxation using this method, which in turn results in the conversion of biaxial strain state to uniaxial strain state.

The Future of X-Ray Diffraction

XRD is a versatile, non-destructive technique which provides detailed information on the micro and crystallographic structure and chemical composition of all types of synthesized as well as natural materials. With most of the current technologies employing materials at smaller scales, nanomaterials are being manufactured in increasing numbers.

This method has proven to be a valuable research tool for analysing nanostructures and it has attracted significant research interest over other microscopic techniques as it provides accurate information on orientation of atoms in space.

Sources and Further Reading

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