The PP2000 cryo-SEM series embodies design features that ensure the vacuum in all three areas is optimally clean and that specimens risk minimal exposure to contamination. The PP2000 cryo-SEM series is the result of many years’ experience of cryo techniques and vacuum and coating technologies. The instrumentation is ‘logical’, easy to understand, simple to use and maintain, and will give high quality results from a wide range of specimens.

Specimen handling, mounting and freezing

We offer a wide range of holders to suit most specimen types and can tailor holders to specific customer requirements. The standard slushy nitrogen freezer is suitable for most bulk SEM specimens. For handling pre-frozen specimens, the optional PP7465 Advanced Specimen Handling System allows specimens that have been frozen by alternative freezing methods (or stored field specimens) to be manipulated under liquid nitrogen and then transferred under vacuum into the PP2000/PP2000T preparation chamber for subsequent processing and observation.

Specimen freezing and manipulation of pre-frozen specimens

Specimen transfer: The transfer device is used to transfer frozen specimens under vacuum between the freezing device, preparation chamber and SEM cold stage. The compact, vacuum-tight design and ease of use of the PP2000/PP2000T transfer device is crucial to the success of the cryo preparation procedure. A bayonet connection to the specimen shuttle helps to ensure rapid transfer.

PP7465 Advanced Specimen Handling System option: The PP7465 allows pre-frozen specimens to be efficiently and easily transferred into the PP2000/PP2000T for subsequent processing (fracturing, sublimation, coating etc) and observation in the SEM or FIB/SEM.

Cryo preparation chamber and pumping

The PP2000T preparation chamber is attached directly to the microscope and provides preparation facilities needed for all types of specimens.

Cold stage and cold trapping: The chamber is a totally enclosed vacuum environment with integral gate valves to ensure stable, contamination-free operation. A variable temperature cold stage is mounted centrally in the chamber. Cooling is by copper conduction from an integral LN₂ dewar. The specimen stage can be cooled to below -185°C and heated to 50°C, and controlled within an accuracy of +/- 1°C. The preparation chamber is fitted with large cold traps running at close to liquid nitrogen temperature. Additionally, the inner face of the cooling dewar acts as a very efficient cold trap. Controls for specimen exchange are conveniently located on the preparation chamber, making specimen change simple, fast and reliable.

Sputter coating: A compact, low-energy sputter coater is fitted enabling high-resolution coating of platinum (Pt) (standard in the PP2000T) and other metals, including gold/palladium (Au/Pd) and iridium (Ir). Argon gas used in the sputtering process can be provided by a small cylinder of ultra-high purity (PP2000T). For non-high resolution applications standard grade argon from a cylinder can be used (PP2000). A carbon fibre evaporation head is available as an option.

High vacuum environment: The PP2000T preparation chamber is pumped by a remotely-positioned turbomolecular pumping system, conveniently located on the floor behind the SEM. Typical preparation chamber vacuums during operation are in the region of 10-5mbar or better. Positioning the turbomolecular pump away from the SEM ensures total elimination of mechanical vibration. It also means that the mass and size of the preparation chamber is kept to a minimum. The PP2000 rotary pumped model will typically operate at vacuums in the region of between 10-2mbar and 10-3mbar when cold.

Specimen manipulation and observation: A micrometer-controlled, cooled fracturing knife and cooled probe (‘wobble-stick’) allows cold specimens to be cut, fractured and manipulated. The PP2000/PP2000T preparation chamber includes a large viewing window and internal LED lighting. An optional stereo microscope (PP7424) with 10x or 20x magnification can be fitted.

SEM cold stage and cold trap (anti-contaminator): The PP2000/PP2000T cold stage attaches to the SEM stage, introducing a cold block for low temperature observation. Cooling of the stage is by pre-cooled nitrogen gas. An important and unique feature of the PP2000T/PP2000 SEM dewar system is that the SEM stage and cold trap are cooled by two separate cold gas circuits - both capable of reaching temperatures down to -192°C . This configuration means that the user can easily set up a large temperature difference between the SEM stage and the anti-contaminator, typically in the region of 40-50°C, without compromising the stability of the SEM stage.

SEM cold stage and cold trap cooling dewar: There is a choice of a small (0.6L) SEM column-mounted dewar, or large (12L) off-column dewar - the CHE2000. This is highly recommended as it will run for over nine hours without needing to be refilled and includes a pre-cooling system that allows lower grade nitrogen gas to be used, plus a heater to prevent build up of ice on the top of the dewar. The CHE2000 is typically seated behind the SEM, alongside the turbomolecular pumping system and rotary pump.

Site Requirements

NB: Site requirements will vary according to the PP2000/PP2000T package supplied. The information below is only an indication of the services required - for full Site Requirement document please contact a member of our Sales team.

Mains electricity: Ensure that a suitable mains electricity supply (110 VAC or 240 VAC, frequency 50/60Hz) is available. Check that the voltage label attached to the side of the cabinet is suitable for the local voltage and frequency. A complete PP2000/PP2000T installation will require four separate mains power outlets of 10A (240V) and 20A (110V). If the optional CHE2000 off-column dewar and/or PP7690 Film Thickness Monitor accessory is fitted, additional mains power outlets will be required. NB: PP7690 may be powered from integral interlocked output on PP7480 Control unit rear panel. Mains supply should be on a separate circuit from the SEM.

Gases: The following gas supplies are required:

Nitrogen gas - Two 250 cubic foot cylinders of dry nitrogen gas (one of which should ideally be ZERO grade <3 vpm H₂O) with regulators, to operate in the pressure range 0-15psi (0-1kg/cm^-2, 0-1 bar). The first cylinder is required for the intermittent venting and slushing functions. The second cylinder is required for cooling the SEM stage and SEM anticontaminator. NB: if the CHE2000 off-column cooling dewar is fitted, lower grade nitrogen gas can be used.

Argon gas for sputter coating - For PP2000: One 250 cubic foot cylinder of dry argon gas (ZERO grade) with regulator, to operate in the pressure range 0-15psi (0-1kg/cm^-2, 0-1 bar). For PP2000T: The system is supplied with a 1L canister of spectrographically pure argon sputtering gas, mounted directly onto the preparation chamber. This should be used for high-resolution applications.

Liquid nitrogen - During normal operation the PP2000/PP2000T will use around 12L of liquid nitrogen during a full working day. It is convenient to have a bulk storage dewar of liquid nitrogen which can be used to fill 1L/5L dewar containers for subsequently filling both dewars on the PP2000/PP2000T and the liquid nitrogen slushing chamber. The room in which liquid nitrogen is being handled or used needs to be well vented in accordance with local regulations. Suitable face masks and protective gloves are required.