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Tutorials

Here we offer some tutorials which show in detailed step-by-step examples how certain features of our programs are handled. The download files are zip-archives which contain in most cases a Windows help file with the tutorial, configuration files for SCOUT or Window Coating Designer and - if necessary - some data files with required spectra. If you don't know how to handle zip-files just tell us and we'll help you.

SCOUT

Tutorial 1 (Download) (Online version)

Example 1

What you learn:

Definition of a simple optical constant model, a simple layer stack and a simple infrared reflectance spectrum. Manual, visual and automatic parameter fitting.

Physical background:

The doping of semiconductors leads to free charge carriers which can be investigated by IR spectroscopy. The response of the free carriers to oscillating electric fields can be described to a good approximation by the simple Drude model. The parameters of that model relate the concentration of the charge carriers and their mobility to properties of the dielectric function. After a model parameter fit of the simulated spectrum to measured data the carrier concentration and the mobility or resistivity can be computed.

Example 2

What you learn:

Modification of an existing SCOUT configuration. Thickness determination from interference pattern analysis.

Physical background:

As we have seen in the previous example the doping level of a semiconductor can be determined from an infrared reflectance spectrum. An undoped layer on a highly doped substrate leads to optical contrast in those spectral regions which carry information on the doping, i.e. the low wavenumber range. \par At each interface the radiation is partially transmitted and reflected. The superposition of the partial waves reflected at the vacuum-epilayer interface and the epilayer-substrate interface to the total reflected wave leads to destructive and constructive interference: The spectral position of the maxima and mimina depends mainly on the thickness of the epilayer which determines the travelling time of the light waves through the epilayer and hence their phase shift. \par If we can match the simulated interference patterns with the measured ones quantitatively we will get a very reliable thickness value from the simulation.

Example 3

What you learn:

Setting up a model making use of the database of optical constants. Treating thick substrates with incoherent superposition of partial waves. Simple thickness determination in the visible spectral range.

Physical background:

For the controlled production of thin films it is very important to determine the deposition rate of the used device. The simplest way is to produce a set of films with different deposition times, find out their thickness and determine the slope of the - hopefully linear - thickness vs. time relation. In many cases the thickness of the produced films can be obtained with the help of optical spectroscopy.

Here we show a simple example, namely the determination of the deposition rate for sputtering silver on glass. The thickness is obtained analyzing measured reflectance spectra in the spectral range from 200 to 1100 nm. We will work with fixed optical constants for silver and glass that we take from the database. The only fit parameter will be the silver thickness. After the determination of the thickness for several spectra the sputtering rate can be computed.

Example 4

What you learn:

Control SCOUT_98 from outside by OLE automation. Use VisualBasic of Excel 97 as macro language to compute spectra and fill tables with spectra data. Create automatically a 3D view showing how the reflectivity of a layer stack depends on the angle of incidence of the radiation.

 

Tutorial 2 (Download) (Online version)

Example 1

What you learn:

Effective medium tutorial: Comparison of different simple effective medium approaches, making use of the Bergman representation, description of metal-insulator composites.

Physical background:

I n this example we show how the effective medium models built into SCOUT are applied. The goal is to describe the optical properties of inhomogeneous silver layers on glass in the Vis/UV spectral range (1.1 ... 5 eV). The origin of the inhomogeneities is the island growth that occurs during the first stages of the silver deposition by sputtering.

The optical properties of the silver layers can be described by a so-called effective dielectric function which is a suitable average of the dielectric functions of silver and air. But what is the 'suitable' average? The 'averaging rule' should depend on the microgeometry: If the metal islands are very far from each other there is no electric current transport in the system and the effective medium behaves like an insulator. In this case an effective medium theory should favour the vacuum component in the mixing of the two phases to the effective dielectric function. If, on the other hand, the islands would be very close to each and metallic connections have developed already, the material should appear to the outside as a conducting metal. The effective medium would not be conducting as good as pure silver, but certainly much better than vacuum. Hence the silver dielectric function should have a significant weight in the averaging for this kind of network systems.

It is shown that only with the flexible Bergman representation a satisfying description of the silver layers can be achieved. All the simple approaches (including the Bruggeman formula, known as EMA) severely fail to reproduce the experimentally found features.

 

Example 2

What you learn:

Treatment of anisotropic materials. Working with global master and slave parameters. These are new features introduced in SCOUT (version 2).

Physical background:

If the production of a technical device requires the deposition of large molecules on a substrate it might be important to know if the orientation of the molecules in the layer is random or if certain directions dominate. In the case of orientation a layer of molecules will eventually exhibit anisotropic optical properties. In such cases the molecular orientation can be determined by optical analysis. Here we show how infrared spectra of such a system can be used to determine orientation angles of the molecules.

 

CODE (Coating Designer)

Tutorial 1 (Download) (Online version)

Example 1

What you learn:

Compute technical data of coatings: Use spectrum product objects to calculate radiation losses of window panes, compute color coordinates, calculate integral transmission values. Use OLE automation to automatically investigate large numbers of thickness combinations. Use color coordinates as target values to optimize a layer stack.

Physical background:

Uncoated window panes exhibit very large radiation losses in the infrared. These can be avoided by a metal coating, usually realized by a silver layer of sufficient thickness. The decrease of transparency in the visible can be avoided by adding two more dielectric layers. The systematic investigation of this three layer coating is demonstrated in this tutuorial.


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