Analysis of Air and Moisture Sensitive Substances by Thermogravimetric Analysis - METTLER TOLEDO

Analysis of Air and Moisture Sensitive Substances by Thermogravimetric Analysis

How can air- and moisture sensitive substances be analyzed by thermal analysis without the substances decomposing beforehand? The solution is to install the TGA in a glove box. In this article, we show how this was done and describe some results from our current research.

 

Introduction

An important part of our research is concerned with the synthesis of suitable precursors for the deposition of thin films or nanostructured 1D and 2D materials by gas phase deposition, the so-called Metal Organic Chemical Vapor Deposition (MOCVD) process.

This technique was first developed in the 1970s. Since then it has become an important method for producing many kinds of films ranging from metals and semiconductors through to ceramic oxides and nitrides and hard materials. We are mainly interested in the preparation of binary semiconductor material films (aluminum antimonide, AlSb; gallium antimonide, GaSb; zinc nitride Zn3N2) and carbide- and nitride-based hard materials such as aluminum nitride (AlN) or titanium carbide (TiC). To prepare them, we use special liquid and solid precursors whose elementary composition at the molecular level corresponds to that of the desired material. The precursor thus contains the elements of the film in a single compound in which the elements are bound together via stable chemical bonds.

In addition, the compounds contain organic ligands that kinetically stabilize the metal organic precursor. In this case, one refers to single molecule or single source precursors. In the MOCVD process, the precursor is first vaporized, typically in the pressure range 10-3 to 1013 mbar, and then thermally decomposed on a suitable substrate.

An important requirement for a precursor is that it can be vaporized without decomposition. Information about its thermochemical properties such as vaporization temperature, vapor pressure, and stability in the gas phase is therefore essential.

Thermogravimetric analysis (TGA; possibly in combination with DSC) is a technique in which the change in mass of a sample is measured while the sample is heated according to a defined temperature program in a defined (inert or reactive gas) atmosphere. It is therefore a very important method for the identification of suitable precursors.

The metal organic precursors we use are however highly sensitive to the presence of air and moisture. This makes them more difficult to measure in a TGA instrument. A particular difficulty is for example how to fill the crucible and how to insert it into the measuring cell under oxygen- and moisture-free conditions.

 

TGA/DSC 1 in the Glove Box

We therefore decided to install a suitable TGA/DSC instrument in a glove box so that the precursors could be handled under protective gas under inert conditions (exclusion of moisture and oxygen).



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Conclusions

Thermogravimetric analysis is an important analytical technique for obtaining initial information about the thermal behavior of new metal organic precursors for the MOCVD process.

The substances described are very sensitive and it is essential to perform the measurements under defined inert conditions and the strict exclusion of air and moisture.

The modular design of the METTLER TOLEDO TGA/DSC 1 makes it ideal for use in a glove box.


Analysis of Air and Moisture Sensitive Substances by Thermogravimetric Analysis | Thermal Analysis Application No. UC345 | Application published in METTLER TOLEDO Thermal Analysis UserCom 34