Grazing incidence x-ray diffraction

Grazing incidence X-ray diffraction (GIXRD) is a version of X-ray diffraction (XRD) used to determine the crystal structure, lattice parameters, and physical properties of thin films and coatings. GIXRD can characterize materials with thin layers of crystalline matter and is often used in product development and quality control in different industries.

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What is grazing incidence X-ray diffraction?

Grazing incidence XRD (GIXRD) is a modification of the X-ray diffraction (XRD) analytical method. With XRD, the properties of the crystallographic structure (i.e. crystal structure) of crystalline material can be determined. When an XRD analysis using conventional scanning methods is performed on thin, 1-1000 nanometers thick films in a film stack, it generally produces a weak signal from the surface layer and an intense signal from the lower layer of the sample making it difficult to examine the top layer. One way to avoid this intense signal from the substrate and instead get a stronger signal from the film on the surface is to perform the X-ray scanning with a fixed grazing angle of incidence of the X-ray beam. This method is known as grazing incidence X-ray diffraction (GIXRD). GIXRD has the same operating principle as XRD but it is able to measure the crystal structure and particle level properties of thin films and coatings. You can find more information about the working principles of XRD from our XRD method page.

How to properly adjust the incident angle of the X-rays?

In GIXRD, the incident angle of the X-ray beam hitting the sample is adjusted relative to the critical angle of the reflected X-rays in the same way as in X-ray reflectivity (XRR), with which the structural properties of thin films can be determined. The critical angle of the reflected X-ray beam is unique for every material and is generally very small. The higher the incident angle relative to the critical angle of the material, the deeper the X-rays go down into the material. Therefore, if the incident angle of the X-rays rises above the critical angle, the depth of the penetrating X-rays increases rapidly, but when the incident angle is smaller than the critical angle, the X-rays go through the sample only a few nanometers.

The surface sensitivity of GIXRD

Because of the phenomenon related to the critical angle, grazing incidence XRD can measure the crystal structure of thin films and coatings by using small enough incident angles of the X-ray beam. Below the critical angle of the surface material, only an evanescent wave of the reflected X-rays is established for a short distance and the wave is exponentially damped. Therefore, the reflections in the diffraction pattern are only coming from the surface structure in GIXRD. However, the incident angle is usually chosen to be slightly above the critical angle of the material in order to obtain a total reflection of the whole surface layer. Still, the penetration of the X-ray beam into the bulk material is prevented and limited only to the surface layer, making the diffraction phenomenon surface sensitive. Because the overlapping peaks in the diffractogram coming from different depths of the sample are avoided with GIXRD, it makes the examination of thin surface films in film stacks much easier. GIXRD also amplifies the weak diffraction signal coming from ultra-thin films and thus optimizes the intensity of the reflected X-rays. In conclusion, GIXRD is a method that combines the best of two techniques: the analysis of crystal structure (XRD) and the examination of thin films (XRR).

What are grazing incidence XRD analyses used for?

Thanks to its surface sensitivity, GIXRD is a powerful tool for many purposes related to research, product development, quality control, and failure analysis of surfaces, thin films, layers, and coatings. The result of GIXRD is a diffractogram, which is a graph from which important information about the crystal structure of the sample is obtained.

The crystal structure, lattice parameters as well as crystallite size, and strain of inorganic and hybrid organic-inorganic thin films and coatings can be examined with GIXRD. Because electronic and optical properties strongly depend on the particle level structure of the compounds in the coating material, GIXRD analysis can be very helpful during the product development process. Also, the changes in the crystal structure of the surface after different treatments are possible to distinguish. Different surface layers can be identified based on their diffraction patterns because every substance produces its own kind of diffraction pattern and thus diffractogram. Also the phases present at the surface of the sample, in thin films of multilayered film stacks or passivation layers can be identified. 

Suitable samples for GIXRD

The samples used in GIXRD can be film stacks having multiple thin films or substrates with thin coatings. The layer examined has to be solid crystalline material meaning that it must have a regular crystal structure in order for the diffraction to occur. Amorphous materials can also be examined with GIXRD but only a little amount of information can be obtained from them.

Suitable sample matrices

  • Film stacks consisting of multiple thin layers
  • Materials with thin coatings
  • Solid and crystalline materials
  • Alloys
  • Ceramics
  • Polymers
  • Minerals
  • Zeolites

Ideal uses of GIXRD

  • Examination of the crystal structure and particle level properties of thin films
  • Industrial research and product development of materials for example in metallurgy
  • Material identification
  • Quality control
  • Failure and defect analyses, such as internal stress measurements
  • Optimization of production processes

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Frequently asked questions

What is GIXRD commonly used for?

GIXRD is used especially in materials science, but also in many other fields of industry to investigate thin films in film stacks and coatings on different substrates. With GIXRD, the crystal structure of a film or a coating can be determined, and thus information on how the actual structure of the layer differs from the ideal one is obtained. The structural properties of the film, such as grain size, lattice parameters, strain, preferred orientation of the particles, and phase composition are possible to determine with this method. Because GIXRD can be applied to examining the internal stresses and defects of the layer, it can be a helpful tool in research and product development as well as in quality control when manufacturing materials. Identification of thin films is also a commonly used application of GIXRD.

What are the limitations of GIXRD?

In GIXRD, the distances are in the range of nanometers, which means that the films examined have to be very thin, usually less than 5 nanometers. However, the thickness of individual films in a film stack can not be determined with GIXRD so the approximate thickness of the film is needed to know in advance. For this purpose, X-ray reflectometry (XRR) is a suitable method.

Only samples consisting of crystalline matter can be examined with GIXRD. The method also works out for amorphous matter, but the amount of information obtained from it remains small. If the sample consists of many different crystalline components, the diffractogram may be too complex to analyze the repeating unit cells or particles of the material.

When a layer of unknown material is wanted to identify properly, the layer should be homogenous or its composition should be consistent. Identification of the material also requires a reference data library. 

What kind of samples can be analyzed with GIXRD?

The samples used in GIXRD have to be thin films or coatings with thicknesses of less than 5 nanometers. The individual films can be part of a film stack consisting of multiple different layers.

In order for the diffraction to occur, the X-rays have to scatter from a regular array of particles that have a long-range order in the material. This is why the sample material has to be solid and preferably crystalline. The material can be either inorganic or hybrid organic-inorganic.

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