Transmittance and Variable Angle Reflectance of Thin Film Coatings

Thin films (10 µm or less) are a huge business, used in a wide range of modern products. Thicker “protection” films or “hard coats” are used in a variety of consumer products, such as automotive wheels, door knobs, and eye glass lenses. These thicker films are designed in a way that enables them to provide a protection layer, capable of preventing the scratching of the underlying surface and also acting as a barrier to moisture and other harmful compounds.

Most food packaging materials comprise of thin film layers, which each provide a specific function, including as UV, moisture or oxygen barriers, or as surfaces appropriate for ink adhesion and protection. Anti-reflective (AR) coatings can consist of one to many thin film layered stacks, and are present on a number of consumer products, like solar cells, cell phones, cell phones, camera lenses, eye glass lenses, and binoculars to name a few.

Most of these films must be capable of allowing light transmission and still provide the optical or physical function that they were designed to achieve. The functional characteristic of a film is influenced by its thickness. For example, AR stacks can be formed with the help of twelve layers of alternating high and low refractive index materials, with a thickness range of 10-150 nm. Controlling the thickness in the manufacturing and QA/QC stage of products can be a challenging task.

It is extremely important to effortlessly distinguish films with variable angle transmission and reflection in the design/development process, and also in the final production stage. Two UV-Vis-NIR Spectrophotometers and a wide range of accessories to suit these tasks are offered by Shimadzu. This includes the UV-3600Plus, equipped with the Variable Incident Angle Film Holder (VIAFH) and the 5-Degree Specular Reflectance stage, and the SolidSpec-3700, equipped with the Absolute Variable Angle Measurement Attachment (VAMA). The two spectrophotometers and their accessories have the potential to distinguish films in the complete spectral wavelength region, extending from the UV, via visible, and well into the NIR.

Experimental Data

Characterized below is four thin film depositions on 25 x 25 mm glass substrates. Transmission is determined in both spectrophotometers at angles of incidence of 0, 5, 15, 30 and 45°. Reflection is measured at the same angles of incidence in the SolidSpec-3700, and at a 5° angle of incidence on the UV-3600 Plus. The spectral acquisitions that have been obtained are depicted in Figures 1-4.

Sample 1 - 0 Deg (red), 5 Deg (orange), 15 Deg (green), 30 Deg (Blue), and 45 Deg (violet)

Sample 1 - 0 Deg (red), 5 Deg (orange), 15 Deg (green), 30 Deg (Blue), and 45 Deg (violet)

Figure 1. Sample 1 - 0 Deg (red), 5 Deg (orange), 15 Deg (green), 30 Deg (Blue), and 45 Deg (violet)

Sample 2 - 0 Deg (red), 5 Deg (orange), 15 Deg (green), 30 Deg (Blue), and 45 Deg (violet)

Sample 2 - 0 Deg (red), 5 Deg (orange), 15 Deg (green), 30 Deg (Blue), and 45 Deg (violet)

Figure 2. Sample 2 - 0 Deg (red), 5 Deg (orange), 15 Deg (green), 30 Deg (Blue), and 45 Deg (violet)

Sample 3 - 0 Deg (red), 5 Deg (orange), 15 Deg (green), 30 Deg (Blue), and 45 Deg (violet)

Sample 3 - 0 Deg (red), 5 Deg (orange), 15 Deg (green), 30 Deg (Blue), and 45 Deg (violet)

Figure 3. Sample 3 - 0 Deg (red), 5 Deg (orange), 15 Deg (green), 30 Deg (Blue), and 45 Deg (violet)

Sample 4 - 0 Deg (red), 5 Deg (orange), 15 Deg (green), 30 Deg (Blue), and 45 Deg (violet)

Sample 4 - 0 Deg (red), 5 Deg (orange), 15 Deg (green), 30 Deg (Blue), and 45 Deg (violet)

Figure 4. Sample 4 - 0 Deg (red), 5 Deg (orange), 15 Deg (green), 30 Deg (Blue), and 45 Deg (violet)

Results

The spectra exhibit excellent correlation between spectral acquisitions performed on the two spectrophotometers and accessories. The benefit of the SolidSpec-3700 and the VAR accessory is the need to obtain only a single baseline, which is capable of being used for any type of transmittance and reflectance angle. This saves time and cost in the whole analysis. The reflection spectra received with the SolidSpec-3700 are absolute in nature.

The UV-3600 Plus comprises of the same 3-detector design and monochromator as the SolidSpec-3700, which has the potential to provide high-quality noise reduction and higher resolution for the total spectral wavelength range. The lack of an integrating sphere in the detector system allows the UV-3600 Plus to achieve an extended analytical range to 3300 nm with optimal S/N.

Conclusion

The UV-3600 Plus and SolidSpec-3700 spectrophotometers are powerful systems with capabilities suitable for thin film characterization in both production, and research and development activities.

This information has been sourced, reviewed and adapted from materials provided by Shimadzu Scientific Instruments.

For more information on this source, please visit Shimadzu Scientific Instruments.

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