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3(b). Transfer Device & Preparation Chamber

Table of Contents:

1. Introduction
2. Physical Consideration
(a) Cryogenic
(b) Environmental
3. Cryo SEM Preparation System
(a) Specimen Stub & Freezing Chamber
(b) Transfer Device & Preparation Chamber
(c) Microscope Stage (SEM) & Applications

TRANSFER DEVICE

In order to ensure good thermal contact between the specimen stub and the coldstages (Preparation chamber and SEM), it is essential to prevent the build-up of frost on the cooled specimen stub while it is transferred.

This is achieved in the K1250X System by the use of an evacuated transfer device (T.D.). The specimen stub attached to the end of the T.D. - transfer rod can be withdrawn into the chamber of the T.D. This chamber can then be evacuated, allowing the specimen stub to be moved around the K1250X system in a clean environment. Hence, the combination of a shrouded stub and an evacuated transfer device serve to eliminate contamination of the specimen surface and the specimen stub.

Transfer Device

Figure 4: Transfer Device with stub attached

PREPARATION CHAMBER

Situated alongside the freezing chamber is the preparation chamber housing a large ‘T’-shaped shrouded coldstage. During operation, this chamber is held under vacuum and the temperature of the stage is held at better than -160oC.

Access to the preparation stage (for the specimen transfer device) is via a valved port situated at the front of the Preparation Unit. This valve enables preservation of the vacuum n the preparation chamber during specimen entry. Typically transfer of the specimen from the freezing chamber to the preparation chamber takes 90 seconds; during which there is minimal specimen temperature rise (8oC).

Once fitted to the preparation stage, the stub temperature is held to that of the stage. The standard workchamber is equipped, without the need for head-change, with the following facilities:-

  • Macro fracture device for fracturing the specimen using a cooled knife with adjustable vertical feed.
  • Macromanipulator (pointed needle).
  • Sputter Coating stage with ultra-low thermal input, high resolution (magnetic deflection) sputtering. (Less than 15oC temperature rise during sputtering for 4 minutes).
  • Carbon evaporation stage, for carbon-fibre flash evaporation/carbon rod evaporation.
  • Metal evaporation (from a tungsten wire basket).
  • Etching stage (conductive heating and/or radiant heating).

Because the above facilities are constantly available during specimen preparation, a wide variety of sample types can be accommodated and different preparation regimes can be applied to the same sample.

The Preparation Unit is used totally independent of the SEM, evacuation is performed using a turbomolecular pump backed by a two-stage rotary pump. Due to the highly efficient shrouding and cold-trapping incorporated in the K1250X, diffusion pumping is not considered necessary, this is supported by operational experience.

K1250X

Figure 5: K1250X Turbo Pumped Cryogenic Preparation System with standard sputtering and carbon evaporation system shown and included.

K1250X with E-Beam Guns

K1250X with special E-Beam gun positions in vertical and 45o mode.

E-Beam Gun Tubes

Details of E-Beam gun tubes and special viewing window


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