Bespoke beamline engineering: the Diamond Sample Manipulator
The Surface and Interfaces village brings together six beamlines with a range of techniques for investigating structural, magnetic and electronic properties of surfaces and interfaces. Many of those beamlines rely on a Sample Manipulator to hold samples securely in an X-ray beam less than a tenth of a millimetre across, whilst also enabling them to move and rotate around multiple axes and rotate around each axis. The differing requirements of each beamline mean that the basic design of the Sample Manipulator is customised for each one.
Video 1: Demonstrating the the operation of Sample Manipulator.
The I09 beamline, for example, is used for studying atomic structures and electronic properties across a wide variety of surfaces and material interfaces. The Sample Manipulator on I09 makes it possible to use X-ray techniques to study monolayer adsorption and surface reconstructions in a vacuum, crystalline and non-crystalline thin films, nano-particulates, large molecules and complex organic films and magnetism and magnetic thin-films.
ARPES (Angle Resolved Photo Emission) benefits from the Sample Manipulators precise and repeatable motions, which enable the maximum flow of electrons from the sample to the analyser. Its high quality tilt motion enables data sets from different angles to be stitched together to map the crystal structure.
For some experiments the Sample Manipulator is required to ‘clean’ the sample by heating to over 1200 K (1000°C). In others, investigation of magnetic properties requires cooling the sample to below 10 K (-263°C) using liquid helium. Fast cooling, good thermal stability at cryogenic temperatures and low liquid helium usage during long experiments are all critical requirements.
Figure 1: The Sample Manipulator in situ as seen through the vacuum window.
One assembly is required to electrically isolate the sample from the support, enabling measurement of the low current pico amp (10-12 A) signal from the X-rays hitting the sample. It also needs to provide enough thermal conductivity to lower the sample temperature to a few degrees above absolute zero. The solution to this particular engineering challenge lies in single crystal sapphire, which can be manufactured using a chemical vapour deposition (CVD) method to provide thin sections of material with the thermal conductivity and high resistivity properties required.
For heating samples up to 600°C it is possible to use a resistive heating, but for higher temperatures up to 1200°C an electron beam (e-beam) heater is required. E-beam heaters use the energy of electrons to deliver energy to a small spot. Electrons are accelerated by raising the voltage of the sample to +500 volts and passing current through a tungsten coil filament in close proximity with a free path to the back of the sample holder.
All of this needs to be fitted into a space not much larger than a pocket watch. The drive parts and fasteners used are selected from the minimum size a supplier can deliver, and the Diamond’s engineers are constantly searching for specialist materials that can make seemingly impossible combinations of requirements possible. As beamline requirements evolve, so too does the Sample Manipulator. So let’s celebrate this understated engineering superhero!