## 2 2D Material Transfer Systems
### Microscope  
The operator's need for a clear view of the working area, which varies widely from 2 \(\times\) 2 mm\({}^{2}\) for flake identification, to 500 \(\times\) 500 \(\upmu\)m\({}^{2}\) for carrying out the transfer step, and to below 100 \(\times\) 100 \(\upmu\)m\({}^{2}\) for closer inspection of the structures, necessitates the incorporation of a microscope with varying magnification objectives (5\(\times\) to 50\(\times\) Plan objectives) [102]. Objectives with large working distances and mounted on a revolver head are preferred, as they facilitate focused observation and prevent the lens from contacting with the stamp holder. A comfortable working distance required during the transfer step should be greater than 5 mm, so as to ensure enough space for the glass slide containing the stamp to be inserted. These Plan objectives are widely used by research labs and commercially available 2D transfer setups (see hq2d.com, analytical-online.com, holmarc.com) and can be obtained from reputable companies, like Zeiss, Nikon, Olympus, Mitutoyo or Leica. Whereas high-magnification (greater than 50\(\times\)) objectives are crucial for inspection, they are unsuitable for transfer due to their shallow depth of field. It must also be noted that more expensive objectives, such as the apochromatic lens, are generally not a stringent requirement for the purpose of 2D material transfer. In addition, a fast (>30 fps), high-resolution (>20 MP) digital camera, and related camera software, is essential for real-time monitoring and capturing of high-quality images throughout the transfer process. A crucial requirement for 2D material transfer is the need for independent focusing of both the stamp surface and the substrate surface. This is especially true during the moments the actual transfer is taking place. To achieve this, vertical adjustment of the objective lens is required. In typical metallurgical or inspection microscopes, the sample is focused via vertical adjustment of the sample stage, while the objective lenses remain stationary. For this reason, 2D material transfer setups work more effectively with modular microscopes designed with vertical movement of the objective lens for focusing, akin to microscopes found in probe station setups [70]. Such a setup is usually mounted on a firm stationary base with no movable sample stage, which allows the user to conveniently insert XYZ linear stages or micromanipulation accessory in the empty space between the objective lens and the base. Also helpful is the fact that the microscope arm in these setups can be detached from the base and installed on a more vibration isolated optical breadboard. While such modified (modular) microscopes from reputable manufacturers exist, and offer superior performance, more affordable alternatives (for example, MXFMS from Sunny Optical Technologies Limited, Zhejiang, China or ICM-100, from LANOPTIK Technologies Limited, Guangzhou, China) are available that are more compact and thus provide convenience for glovebox setups, a functionality that is of utmost importance for air-sensitive vdW integration. Higher quality, large working distance objectives may be installed onto these systems to improve the quality of the imaging. Additionally, stereo/zoom microscopes with single objectives and zoom functionality (see Figure 1c) serve as an effective alternative. While these systems are less costly and offer a longer working distance, they come at the expense of slightly reduced image quality. It must be noted that the simplest and most straightforward way to build a transfer system is by using a probe station (Figure 1b). Except for their bulkiness, which makes it cumbersome to load them into a glovebox, typical probe station setups are ideal as they can be quickly converted to function as a transfer system. All that is required is the appropriate linear stage for the stamp holder and a little modification to the sample stage to enable substrate heating, if this feature is required by the transfer method employed.