Sample Manipulation

There are two requirements that the sample manipulation system, which controls the physical position of the sample, must fulfill. Firstly, due to the physical size of the sample chamber and the requirement for the measurements to be performed under a high magnetic field, the sample must be extended forward (into the flared section discussed in section 3.5) beyond the sample chamber. Also, fine control of the vertical and horizontal positions is also required and will be discussed further is section 3.8.2. Secondly, the process of loading and unloading samples into the sample chamber must be accomplished while maintaining high vacuum. This is commonly referred to as a load-lock system and involves the addition of a smaller vacuum chamber referred to as the load-lock chamber. The components of this system are shown in figure 3.26 and will be discussed in the following paragraphs.

Jason

Roberts

Thesis

June

3.7. The Sample Stage Hardware 83

The terminating flange of the beamline is fitted with a Thermionics Northwest Inc. xyzθsample manipulator, model FM103-1.53-2-2-12/LM/HMP, which fulfils the first requirement of the sample manipulation system. This is a two stage piece of apparatus which allows the horizontal and vertical position to be adjusted

±25 mm from the central position, while allowing 3600 (914 mm) of travel along the axis of the beam. This is shown in the retracted position in figure 3.26, though the forward position is shown partly transparent. The θ stage, which allowed rotation of the sample, was removed to allow a wider tee to be fitted at the rear of the manipulator to alleviate problems encountered in the high voltage system. Inside the vacuum chamber, the end of the manipulator is fitted with a gold coated sample holder mounted using ceramic rods. This provides electrical isolation, allowing the sample to be biased. The design of the sample manipulator and holder includes the capability to add control of the sample temperature while the measurements are being conducted. However, hardware for this functionality has yet to be designed.

The load-lock chamber is mounted to one of the horizontal flanges of the sample chamber. This is a small four way cross chamber separated from the sample chamber by an MDC 23

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gate valve, referred to as the Sample Chamber Gate Valve (SCGV). Opposite this valve in the load-lock chamber is a Ferrovac magnetic transporter, model FD40, referred to as the load-lock arm. This is mounted using an MDC heavy duty, off axis port aligner, allowing the angle of the load-lock arm to be varied during sample manipulation. In order to allow access to the load-lock chamber a hinged door, aptly named the load-lock door, is fitted to the load-lock chamber. Due to the frequency with which this door is used, it seals with a rubber o-ring rather than a copper gasket. The final port in the load-lock chamber leads, through the Sample Chamber Load Lock Valve (SCLLV), to the sample chamber roughing pump detailed previously. The final valve in the system (not shown in figure 3.26) is the Sample Chamber Roughing Valve (SCRV) which can be used to isolate the low pressure side of the turbomolecular pump from the remainder of the roughing system. This prevents the turbomolecular pump from being exposed to high pressures when evacuating the load-lock chamber with the roughing pump. A discussion of the operation of the valves detailed here can be found in section 3.8.3. While figure 3.26 shows the components discussed here to scale, a simplified layout of the pumping arrangement can be seen in figure 3.30.

Jason

Roberts

Thesis

June

JR To Roughing

Pump (via SCLLV) Load LockDoor Sample Manipulator

SCGV

Load Lock Arm Load Lock

Chamber

High Voltage Can

Forward Sample Position

Sample Carousel ExB Plates

Figure 3.26: Shown here is a top view of the sample chamber with its com- ponents labelled. The details of the sample manipulation system can be seen as well as the internal components of the high voltage system.

In addition to the load-lock chamber, a sample carousel is mounted to the downward flange of the sample chamber. This is controlled using a second Fer- rovac magnetic transporter and is capable of holding up to eight samples to streamline the loading or unloading process.

The three valves discussed here, as well as the BGV, are controlled by the beamline computer through a custom made TTL interface. This interface con- tains twelve channels, with channels one through four being used to control the valves discussed (more detail can be found in table 3.3). In addition, channel nine is utilised by the high voltage system (discussed in the following section) and channels ten through twelve are used to control the three roughing valves associated with the turbomolecular pumps of the trap stage.

Associated with the sample manipulation hardware already outlined, are five micro-switches; these allow the state of the system to be determined by the beamline computer. Of these switches, three are used to determine the location of the sample manipulator, one is used to identify when the load-lock arm is fully retracted and the final switch indicates when the load-lock door is closed. In addition to these micro-switches, the valve states are also determined by the beamline computer using magnetic reed switches. These states, in conjunction with access to the two pressure gauges of the sample stage, allow the operation of the load-lock chamber to be almost fully automated (with the exception being the manipulation of the sample blocks).

Jason

Roberts

Thesis

June

3.7. The Sample Stage Hardware 85