The PP3006 CoolLok offers rapid transfer and cryo temperature observation of specimens for SEM, FIB/SEM, beamline or other suitable vacuum systems. Freezing is on-contact with the pre-cooled SEM or FIB/SEM cold stage, or specimens can be rapidly pre-frozen in slushy liquid nitrogen using the optional freezing station (24425).
Vacuum airlock and cooling gas feedthrough
Mounted onto a suitable vacuum chamber port, the CoolLok consists of a loading chamber body with built-in controls for pumping, venting and transfer. A custom-designed interface flange to the vacuum chamber and connections and fittings to the pumping system are included (see: Pumping below). The interface has cold nitrogen gas feeds to and from the microscope cold stage and cold trap. Interlocking to the microscope is included.
Specimen holders and transfer device
The compact vacuum transfer device has a bayonet fitting to a dovetail-profile specimen holder (shuttle). Standard shuttles are included, but optional holders allow a range of specimen types to be handled. If the optional freezing station is not used, then consideration needs to be given as to how specimens are mounted because liquids should not be transferred through the airlock and microscope vacuum. The 20270 shuttle with holding clips (supplied as standard) is one option or quick-drying mounting media (not supplied) can be used.
Cold stage and cold trap
A highly stable and thermally isolated nitrogen gas-cooled cold stage attaches to the SEM, FIB/SEM stage. The location and shape of the cold trap is tailored to suit the internal geometry of the microscope. Both cold stage and cold trap are capable of reaching temperatures down to -190°C with a stability of <0.5°C. For easy specimen exchange an interlocked LED chamber light is fitted.
The cold stage connects to the SEM stage using an adaptor and has a dovetail fitting to accept a cryo specimen holder (shuttle). When not in use the cold stage is uncoupled and stored within the chamber with the gas and electrical fittings connected.
Cooling dewar, trolley and controller
The cold stage and cold trap are cooled by a floor-mounted, vacuum isolated 21 litre dewar and heat exchanger assembly, which at normal operating temperatures can run for up to 24 hours between fills. The gas lines between the dewar and the SEM interface are vacuum isolated for maximum thermal efficiency.
The cooling dewar is located on a floor-mounted trolley which also houses the temperature monitor/controller for the cold stage and temperature monitor for cold trap, plus nitrogen gas flow controllers.
Rapid freezing station (24425)
With the standard CoolLok, specimen freezing is by contact with the SEM cold stage following transfer and therefore freezing rates are relatively slow. This is generally suitable for hard, non-hydrated specimens, but for liquid-based material rapid freezing is essential to reduce the detrimental effects of ice crystal growth and to allow through-vacuum transfer onto the cold stage.
For these applications the optional 24425 nitrogen slush freezing station is required. However, for many applications (especially lifesciences) cold fracturing and sputter coating are essential process steps and require the advanced capabilities of the Quorum PP3010 – a full cryo-SEM preparation system.
25852 glove box valve/airlock interface
An optional glove box valve/airlock assembly (25852) can be supplied. The airlock is connected to a glove box using a generic NW40 fitting and for most applications requires a suitable pumping system (13034 rotary pump or 2336 turbo plus diaphragm pump system). Gas connections are included. The outer face of the 25852 is designed to accept the vacuum transfer device.
Using the CoolLok
The specimen is mounted on a suitable holder (shuttle) and the transfer device fitted onto the airlock and the dead space evacuated to a set vacuum level. The gate valve is opened and the specimen guided onto the SEM stage. For transfers from other vacuum systems, or a glove box, additional interface flanges are available on request. Vacuum transfers can be made from the optional 24425 trolley-mounted nitrogen slush freezing station, if fitted.