Materials characterisation by light scattering and reflectometry

 


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Mapping

 

More information

 

 

 

The optional motorised x-y stage allows most numerical data to be obtained as surface maps or line scans. This ability is particularly useful when studying how properties vary from point-to-point over the surface of a specimen or when examining surface defects. A unique feature of the Imaging Reflectometer is the combination of data available in a single measurement. Each mapping point contains information on gloss, refractive index, macro-roughness (in two orthogonal directions) and micro-roughness. Other information is also available such as calculated gloss, gloss at various acceptance angles, reflection haze and displacement of the centroid of the reflected beam (can be used to quantify large-scale surface waviness).

 

This combination of data is very powerful. For instance, given a gloss map showing spatial variations in reflectance, one can also examine the corresponding refractive index and roughness maps to seek the cause of the gloss variations.

 

Information on applications examples may be found in the technical section or references given in the bibliography. Some illustrative examples are given below.

 

The measurement software allows several maps to be collected from regions defined on available mapping area (up to 100 x 100 mm) without operator intervention – this  allows the motorised x-y stage to be used as a limited automatic sample changer (by mounting several samples side by side on the platform) and is especially useful when collecting maps or line scans on different regions of a sample, or at different resolutions.

 

A separate program is provided for analysis and display of maps, which allows analysis to be done “off-line” while the Reflectometer is engaged in collecting data.

 

Motorised x-y stage


Vacuum platforms


 

 

 

 

 

 

 

 


 

 

These images show gloss, refractive index (RI) and macroroughness maps obtained on a coated paper showing both gloss and print mottle. Visual inspection indicates spatial correlation between gloss and RI, but relatively less with roughness. A higher RI  suggests a more compact, less porous surface. The spatial correlation suggests that the gloss variations are significantly due to point-to-point variations in surface porosity which also affects the resulting print density (Maps shows a region approx 25 x 25 mm at a resolution of 0.2 mm.)

 

Gloss map

(brighter = higher gloss)

 

RI map                            (brighter = higher RI)

 

Macroroughness map      (brighter = lower roughness)

 

 

 

 

 

                                 Gloss Map                      Macroroughness Map

                                          (brighter = higher gloss)      (brighter = Higher roughness)

Careful examination of these coloured maps, by contrast, shows a strong correlation between gloss and roughness. For these paper, there was little correlation of gloss with RI, and the conclusion is that the gloss mottle was largely due to point-to-point variations in macro-roughness over the sheet surface.

 

The maps are show in false colour. Red = high, blue = low.

 

Image analysis techniques can be used to tease out more detailed information from maps.

 

 

 

 

 

 

RI map showing density variations in a hand-drawn coating

 

10 pt text mapped in RI

 

Resolution in mapping mode is estimated to be around 0.25 mm. However, the resolution does depend on the nature of the specimen and the “contrast” between features.

 

Line scan across gate marks in injection moulded nylon

 

Line scans are a quick method of obtaining information on how properties vary over a surface. Especially useful where properties change over some boundary or in a systematic (as opposed to random) way.

 

 

 

 

 

 

 

 

 

 

 

 

© Dayta Systems Ltd 2011