CC302M Closed Cycle 15K cooling stage for SEM

Gatan is pleased to introduce a new, 15K base temperature, SEM stage module which is liquid Helium free. Gatan has partnered with a leading manufacturer of ultra-low-vibration, closed cycle cryo-coolers to achieve excellent specifications for specimen cooling in the SEM.
Specimen cooling in the SEM is often performed for Cathodoluminescence studies. For certain specimen types cryogenic temperatures close to liquid helium temperature are essential for efficient light production and for enabling better opto-electronic characterisation studies. Other applications for low cryogenic temperatures are studies of superconductivity and other electrical transport properties.

Closed cycle coolers are commonly employed in laboratory environments because of their ease of use and cost effectiveness in not requiring consumption of relatively expensive cryogen. Gatan continues to make a variety of products for SEM and TEM using liquid helium because with the optimum cryogenic technology, liquid helium provides a low base temperature, rapid cooling and good stability. However, there are circumstances where liquid helium is difficult or too expensive to procure, so a closed cycle cooling stage is desirable. Also in some clean laboratories, dewars of liquid helium are not allowed, or a simpler operating protocol is specified.

Low vibration in closed cycle cold stages has normally been associated with low cooling power and relatively high base temperatures. Gatan is pleased to announce a new product which has broken these limitations with ultra-low vibration cooling of specimens in the SEM to 15K. The CC302M is a result of a partnership between Gatan and a world-leading manufacturer of ultra-low vibration cryo-coolers.

The CC302M has a cooling module which is attached to the SEM stage. The novel design of remote clamping of the module to the SEM goniometer stage allows the SEM stage door (“drawer” type) to be withdrawn whilst maintaining the necessary short connection between the chiller and module. When attached, this short connection still allows limited XY translation of the SEM stage.

A nitrogen cooled shroud and anti contaminator is used to enable the 15K base temperature, and also reduces the cool down time. If the chiller is started from ambient, the base temperature can be achieved in approximately 135 minutes, or less if the chiller is already cold. The shroud and anti contaminator reach close to LN2 temperatures by forcing cooled, dry nitrogen gas through an internal circuit inside the microscope. This is similar to the technology Gatan uses in its LN2 cold stages and anti- contaminators. A digital temperature controller is used to control and monitor the temperature at the specimen position.

The cryo-chiller cold finger is in the SEM vacuum and supported from the SEM flange. A braid coupling thermally connects the cold finger to the specimen mount in the module. A proprietary vibration isolation technology is provided between the chiller and the cold finger. The water-cooled compressor is powered by electricity and is coupled to the chiller with flexible pipes. Although the chiller provides ultra-low vibration to the cold finger, final SEM performance will depend on site conditions.

Internal view of SEM chamber showing CC302M module detached from SEM stage, but attached to the remote clamping mechanism.

External view of CC302M showing housing for cold finger, SEM flange, and chiller support structure.

Typical Specifications. CC302M.

• Low vibration closed cycle cryostat in SEM vacuum with pneumatically driven cold head
• Flexible braid coupling to specimen mount, thermally isolated from SEM stage
• Thermal radiation shielding and anti-contaminator using liquid nitrogen cooled gas
• Heater and temperature sensor at specimen mount for digital temperature control and monitoring
• Additional heater on cold finger for faster warm up
• Module detachable from SEM stage by ex situ control
• Specimen mount temperature with LN2 cryo shield in use: 15-300K
• Specimen mount temperature without LN2 cryo shield in use: ~35K
• 3m stainless steel braided hoses. Longer lines optional
• Time to cool from ambient state of chiller: ~135 minutes
• Vibration of chiller cold finger (de-coupled from SEM). 5nm displacement.
• Vibration of specimen (dependent on microscope and site conditions)
• Standard XY translation +/16 mm
• Standard specimen mount. 10 mm radius stub
• Number of hours operation of compressor (adsorber) between servicing, 12,000
• Compressor, water-cooled, requires 3l/minute at maximum 25C. Power single phase, 17A at 208/230V

Optional

Airlock loading of specimen. Suitable for certain microscopes and airlock loading mechanisms by special request. Additional functionality may impact base temperature.
Longer braid hoses.

Higher cooling power, lower base temperature chiller units