A Manual Fit Session

This page describes the steps one takes when fitting 1D reflectivity data on the web application, starting at the point when one logs in the application.

After login in, click in Choose File in order to select file double_layer.txt found in directory test/data/. After selecting the file, click in Submit in order to upload the file. The file will show up in the list of uploaded files.

Click in the link click to fit. A default initial layer structure will be shown near the bottom of the model page:

The default layer structure has only one layer, limited by air and Si on both sides. The solution layer structure contains two layers with specific thickness and other properties, namely

Thus, we must include an additional layer into the default initial layer structure. We use the “+” button for that (in the below picture, enclosed in the dashed-line red circle). However, before adding a layer we must evaluate or fit the current model. Press on the Evaluate button (in the below picture, enclosed in the dashed-line purple circle)

The evaluation prints the current model curve on top of the data. The plot is located near the top of the model page. As one would expect, the initial model is a poor fit of the data:

The poor fit is of little consequence now. Let’s click in the “+” button now to add a new layer. This is the current model with two layers:

We enter the parameters of the solution layer structure into the model:

This should provide a model curve closely fitting the data. We’re going to create an initial guess for the fit starting with these optimal parameters. We just distort the two thickness parameters for layers A and B. The goal is to recover the solution thickness when we fit the model. In this case we entered initial values of 500 and 40 Angstroms for layers A and B, respectively (red circle in the below picture). Also, we removed the nearby checkmarks, indicating these are fit parameters (purple circle in the below picture). When a parameter is unchecked, a min and max range becomes available (range rectangle in the below picture). We have adjusted the ranges so that our initial guesses fall right in the middle of the ranges:

Click the Evaluate button to see how our initial guess aligns with the data. We find an “out-of-phase” fit:

We now fit the model by clicking in the Fit button. The job is submitted to the (local or remote) work server and fits results will be available once the fit job is finished. A message at the top of the page indicates this is so, with a link to display the fit:

After clicking in the link, we can inspect the fit to the data and the fit parameters

We obtain thicknesses 578.3 and 42.89 (compare to given solution parameters 577.6 and 44.75).

If so desired, we can save the fit by clicking in the save model link (red circle in the below picture):

A pop-up will confirm the model was saved:

Close the pop-up by clicking in the OK button. Then, click in the show models button (red circle in the below picture):

The model will show at the top of the list of available models:

Clicking in the pencil button (red circle in the picture above) will show the fit parameters:

This finishes the manual fit session!