After spending many years working in the area of metal-on-metal crystal growth, at the Max-Planck-Institute I had a once-in-a-lifetime chance for me to investigate organic-on-metal crystal growth. This topic was the speciality and passion of my colleague, Frank Schreiber, who has since moved on to lead a very successful and large research group at the University of Tübingen, in southern Germany.
![Here is a short overview of various organic molecules that are grown as crystals and studied.](https://ritley.com/wp-content/uploads/2014/08/OMBE-1-300x211.jpg)
R-Cell. Okay, I built it, but someone else named it after me!
The bread-and-butter of crystal growth via molecular beam epitaxy (or MBE) involves a high-tech oven, specially designed for ultra-high-vacuum (or UHV) environments, known as a Knudsen cell, or more simply as a K-cell. K-cells can be used to melt or sublime metals, and with special cooling attachments such cells can even be used to evaporate materials such as gold.
![There are various ways to grow crystals of organic compounds. The method my colleagues and I used was molecular beam epitaxy, or MBE.](https://ritley.com/wp-content/uploads/2014/08/OMBE-2-300x221.jpg)
In order to carry out experiments involving the crystal growth of organic materials, we needed something similar, but with a few small differences. First, the evaporation temperatures we used were much less than that for e.g. liquid metals, hence we needed a cell that had excellent thermal conduction properties. Second, we intended to grow crystals in a portal chamber, so we didn’t want our organic sources moving around – or worse, falling out of the oven.
The solution was the so-called R-cell, shown below. Not shown is an interesting approach to keep the organic evaporant stable: glass fiber wool. Capping the alumina crucible with a small wad of glass fiber wool seemed to have two effects: it increased the surface area of the evaporant, and it ensured that during transportation, the organic material would remain in place.