Roughness Analysis

$images\btnroughness.gif$ Start the roughness calculation by the key symbolizing the bearing curve. The roughness analysis will then be based on the Main Image. It is also possible to calculate roughness parameters from profiles by Right Clicking in the Curve Window. For Images a large set of roughness parameters can be calculated and depending on the options defined in the Options Dialog the results may be written to files with the added extension .rgh or to the database of the ImageMet Explorer. For profiles a subset of the image parameters are calculated. For a detailed description of all roughness parameters, please consult the Reference Guide at the end of this document. Roughness parameters based on Image will have the prefix 'S' and when based on a profile the prefix 'R' is used. For example will the Roughness Average Parameter be denoted Sa and Ra for images and profiles respectively. The result file will automatically be shown in a dedicated window:

$images\rougnessdata.gif$

For convenience, the data is written in both a row and a column form in the .rgh output file. Depending on how you want to organize the data in a spreadsheet you can ignore one of the two forms. To put the data into a spreadsheet program just mark the data of interest and Copy Paste it to the spreadsheet program.

The files can be used for statistical analysis by third party programs. A definition of the different roughness parameters is found in the Reference Guide, Roughness_Parameters. In addition to the predefined roughness parameters it is possible to add your own defined parameters by use of roughness plug-ins.

The roughness analysis will also generate the bearing curve (Abbott). In the case that the Fourier Image has been calculated the Angular Spectrum, the Radial Spectrum, the Integrated Radial Spectrum and the Fractal Dimension windows are shown too, see screen dump below.

The angular spectrum and the fractal dimension are shown in Polar Plots (also called Rose Plots) with a value for all discrete angles between 0 and 180 degree.

The parameters depending on the Fourier image are only calculated when these parameters have been set on in the Options Dialog.

The fractal dimension is calculated for the different angles by analyzing the Fourier amplitude spectrum; for different angles the Fourier profile is extracted and the logarithm of the frequency and amplitude coordinates calculated. The fractal dimension D for each direction is then calculated as

D = (6 – s)/2,

where s is the slope of the Log - Log curves [John Russ]. The fractal dimension can also be evaluated from 2D Fourier amplitude spectra by application of the Log Log function. If the surface is fractal the Log Log graph should be highly linear, with at negative slope.

$images\rougness.gif$

Roughness Options

To define roughness options such as roughness parameters and graphs you want to see activate the roughness selection window by clicking on Options->Preferences and then select the Analysis section and Roughness Analysis in the list box.

$images\preferencesroughness.gif$

To select among the available roughness parameters click the Parameters button.

$images\optionsroughness.gif$

To select among the available roughness graphs/windows to appear click the Output button:

$images\preferencesroughnessoutput.gif$

Plane Correction

Many roughness parameters are extremely sensitive to plane distortions and it is therefore important to consider whether your image is affected by plane distortion and in such case how to deal with it. You can select between the following plane correction options for preprocessing images before calculating the roughness parameters:

None: If an image already have been plane corrected by use of the Plane Correction Dialog or long wave structures have been reduced by High Pass filtering using the Filter Dialog or the Fourier Dialog it may not be necessary to perform further plane correction. Another reason for setting the Plane Correction option to None is when comparing with another software packages, such as the Internet based Surface Metrology Algorithm Testing System (ISMAT) developed by NIST.

Subtract Mean: SPIP versions earlier than 4.6 did always subtract the mean before calculating the roughness parameters. It is a gentle way to assure that a high mean level does not contribute to the roughness values. However in some cases you may want to preserve the height values such that the bearing (dominating) height value is kept at zero to get at better number for the skewness, Ssk parameter. If you want to get roughness amplitude parameters comparable with SPIP versions before version 4.6 you should select this option.

Subtract 1.st Order Plane: For most images this option assures that most of the plane distortion will be removed and not influence the roughness parameters. However, for images containing, e.g., step structures it may tilt the images such that undesirable slopes are introduced on plateaus. As 1st order plane correction is the default plane correction method in the Veeco NanoScope software you should use this option if you want to compare roughness results with the NanoScope software.

The preferred unit used for the roughness parameters can also be set in the Options->Preferences dialog.