STM UHV System

Figure 2.11 shows an overview of the UHV system that housed the Nano-graph STM-01 system and illustrates the placement of the UHV manipulator arms required to transport both the STM tip and sample within the UHV system. It was a necessity that the sample could be relocated within the UHV system so that it could be sputtered, annealed or deposited upon in separate UHV chambers to the STM system, as described in Section 2.2.3. Each manipulator arm had two specifically shaped prongs designed and built to work with both the sample hold-ers and the tip tool – one prong is shown in Figure 2.10. The rear of the prongs were screwed into a small spring-loaded plate and attached to the manipulator arm, therefore when the manipulator arm was positioned it did not put excessive force on the STM system or any other components inside the UHV system.

The front end of the UHV arm prongs were designed to fit into the two holes in the back of the sample holder (shown in Figure 2.9). The prongs slid into the sample holder up to the point where the prongs widen and the UHV arm could then manipulate the sample holder. Although only friction held the sample holder onto the UHV arm prongs, once the sample holder was rotated to unlock it from the STM system or any other UHV component there was negligible force to resist the UHV arm if it was aligned correctly.

The STM tip nut was manipulated with a bespoke ‘tip tool’ designed and constructed on-site – the tip tool is pictured in Figure 2.12. This tip tool required more delicacy with the UHV manipulator arms than for the sample holder and required the UHV arm prongs to have a wider diameter section (as shown in Figure 2.10). The wider section could fit into the two large holes in the tip tool base and once past the entrance of the tip tool base, the prongs could be rotated in both directions, but could only be removed from the tip tool when the prongs were aligned with the two large holes. Thus any frictional forces holding the tip tool in place could be overcome when the prongs were locked within the tip tool and the tip tool was then displaced in the direction of the UHV manipulator arm. This was required when the tip tool was securing a tip nut in the STM, for example.

The tip nut slotted into the end of the tip tool shaft (the opposite end to where the UHV arm prongs would fit) securely so the tip nut did not fall out, but not so securely the tip nut could not be removed from the tip tool using physical manipulation. The tip nut was shaped so that when the tip tool was rotated the tip nut would rotate, similar to how a nut or bolt would interact with the correct sized spanner. A ratchet and spring were also incorporated so the tip nut could

Figure 2.11: Nanograph STM-01 UHV system schematic (a) illustrating several chambers of the UHV system, and a photograph of the chambers (b). The fast entry load-lock (FEL) and gas handling line (GHL) chambers are also shown.

Note that the preparation chamber is in the same plane as the transfer and STM chambers but is not shown in the schematic.

Chapter 2. Experimental Techniques 39

Figure 2.12: The bespoke tip tool required to secure the STM tip nut into and out of the Nanograph STM-01 STM system and Nanomesh yoke, (a) the end of the tip tool shaft where the tip nut was held and (b) the two holes for the UHV

manipulator arm prongs which allowed the prongs to rotate with respect to the tip tool.

not be tightened excessively when it was secured on the delicate scan tube of the STM.

The tip tool base was specifically designed to fit and lock into the same com-ponents as the sample holder, as shown in Figure 2.12. Thus the tip tool could be shuttled around the UHV system via the sample holder storage sections and ma-nipulated by all the UHV manipulator arms. However, the tip tool could also pass through the opening in the STM sample holder mount when the sample holder had been removed. Whilst on a UHV manipulator arm, the tip tool would ap-proach and carefully slide onto the tip nut, then the UHV arm would be rotated anticlockwise. Once the UHV arm prongs were locked inside the tip tool, the tip tool could be rotated anticlockwise. Rotating the tip tool anticlockwise allowed the tip tool to unscrew the tip nut from the scan tube and release the tip nut – the UHV arm could then be retracted with both the tip tool and tip nut safely se-cured on the UHV arm prongs. The tip tool could then be transported around the UHV system and secured into any sample holder storage section, with the STM tip itself protected within the tip tool. The tip tool could also be removed from the system in this configuration so the STM tip could be replaced, as described later in Section 2.2.3.

Figure 2.11 illustrates the different chambers of and components within the Nanograph STM-01 UHV system, note that all chambers were separated by a gate valve except the connection between the transfer chamber and preparation chamber. Figure 2.11 also shows how the sample holders and STM tip nuts could

shown in Figure 2.13.

The Nanomesh yoke had two storage spaces for sample holders which could also fit the tip tool. These storage spaces contained grooves for the sample holder to rotate and lock when the UHV arm was removed from the sample holder, thus the sample holder would not fall out of the yoke unless there was a severe user error.