What is Grazing Incidence X-Ray Diffraction (GIXRD) Possible with BT XRD, AERIS?

What is Grazing Incidence X-Ray Diffraction (GIXRD), or low-angle incidence X-ray diffraction?

X-ray beams are typically directed at the sample at a very low incidence angle, often below 1 degree, resulting in X-rays interacting only with the top few nanometers of the material. Therefore, it produces diffraction patterns that are highly sensitive to the crystallographic characteristics of the surface area. 

In conventional X-ray diffraction (XRD), the X-rays are incident on the sample at various angles, creating diffraction patterns from a few microns deep. In contrast, GIXRD optimizes the incidence beam angle at a specific shallow penetration depth to control the volume of the material being measured. It is specially designed to avoid signals from below the surface or thin films.

We will explain how to use GIXRD for polycrystalline coating research.

Thin films, as polycrystalline coatings, are used in various applications, from biomedical coatings for medical implants and spray paint coatings on automotive steel to films deposited on electrodes within batteries or metal contacts in semiconductors, and optical coatings in displays.

The crystal phase of deposited films and the residual stress are major parameters for assessing the efficacy of deposition methods or process steps. Monitoring the integrity of the film during use is also very important to ensure long-term product success. By using Grazing Incidence X-Ray Diffraction (GIXRD), you can adjust configurations to maximize signals through coatings, thus obtaining desired outcomes and best data in cases requiring detailed studies of the crystal phase or high-speed quality control. 

50nm Thin Film of Polycrystalline Iridium on Silicon Substrate

The refractory metal iridium is widely applied in high-performance optical devices due to its high X-ray reflectivity, low oxidation rate, and high melting point. For example, iridium is researched as a material replacing gold and silver as optical coatings in high-performance telescopes.

The grain size and microstrain are good indicators of the film’s microstructure and overall quality, which can be rapidly and non-destructively monitored by observing changes in diffraction peaks. For these thin films, iridium’s diffraction peaks can be easily lost in the signal from the substrate peaks. Using grazing incidence diffraction geometry allows quick acquisition of clear and useful data (see Figure 3.1).

^85o High angle peaks of the layer, such as the 85^o peak, are so weak that they are not observable in reflection geometry but can be seen exclusively in GIXRD scans. 

Using HighScore analysis software, results for average grain size (11.1nm) and microstrain (0.585%) can be quickly obtained (see Figure 3.2).

These structural parameters help monitor and optimize the processing process to achieve the required layer performance and product quality control.

In the case of thin films and coatings, it is important to measure the residual stress of the film to understand how the stress of the layer is formed during deposition and to comprehend the final quality of the film. Thin films can sustain high stresses, and coatings can further strengthen or conversely weaken the entire component beyond the chemical protection of the component. Alternatively, thin films under excessive stress may easily crack or delaminate from the substrate. Crystallographic residual stress is a significant quality control parameter in thin film processing. Residual stress within the layers can be determined using Stress Plus [2] software with multiple {hkl} residual stress analyses (see Figure 3.3). 

Comparing conventional Bragg-Brentano data with GIXRD data in Figure 3.4 reveals that both iridium and silicon exhibit strong diffraction peaks near 69^o 2θ.  Through GIXRD scans, smaller iridium peaks are now clearly observed without being obscured by the silicon substrate peaks, and high angle peaks such as 85^o and 107^o can be more easily seen. 

Continue Reading: Aeris for Thin Films

Aeris Configured for Grazing Incidence X-Ray Diffraction

Through grazing incidence X-ray diffraction, much improved peak signals can be achieved in thin films where regular asymmetric (Bragg-Brentano) powder scans cannot provide adequate peak intensity or cause too much interference from the substrate. 

Aeris is a dedicated thin film diffractometer for routine measurements, or a versatile powder diffractometer that occasionally measures thin films. The high-performance decoupling goniometer scanning technology provides reproducible 2θ scanning at various precise incidence beam (ω) angles, ideal for grazing incidence X-ray diffraction (GIXRD) and residual stress measurements. A parallel plate collimator on the diffracted beam side transforms Aeris into a parallel beam measurement mode, providing accurate peak positioning and solving out-of-focus effects to deliver high-quality data. A comprehensive range of stage holders provides diverse sample mounting options that meet customer needs. 

The patented unique PreFIX optical mounting system allows Aeris to be quickly reconfigured to compare data from Bragg-Brentano, Transmission, and GIXRD methods. GIXRD scans can be obtained within minutes, which helps optimize data collection settings by comparing data from various incidence angles. Together with our analytical software, HighScore Plus, and Stress Plus, high-quality data showcases phase purity, crystallization, grain size, microstrain, and residual stress for a complete view of polycrystalline thin film samples.