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  3. We describe methods for producing and analyzing large, thin flakes of air-sensitive two-dimensional materials. Thin flakes of layered or van der Waals crystals are produced using mechanical exfoliation, in which layers are peeled off a bulk crystal using adhesive tape. This method produces high-quality flakes, but they are often small and can be hard to find, particularly for materials with relatively high cleavage energies such as black phosphorus. By heating the substrate and the tape, two-dimensional material adhesion to the substrate is promoted, and the flake yield can be increased by up to a factor of ten. After exfoliation, it is necessary to image or otherwise analyze these flakes but some two-dimensional materials are sensitive to oxygen or water and will degrade when exposed air. We have designed and tested a hermetic transfer cell to temporarily maintain the inert environment of a glovebox so that air-sensitive flakes can be imaged and analyzed with minimal degradation. The compact design of the transfer cell is such that optical analysis of sensitive materials can be performed outside of a glovebox without specialized equipment or modifications to existing equipment. 
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  4. A method based on the tracking of the peaks of interference fringes as a function of time-dependent analyzer setting is used to detect the Pancharatnam phase of light. The advantage of this method is demonstrated by observations of the nonlinearity of the Pancharatnam phase for certain paths on Poincare sphere where the fringe visibility reduces to almost zero. We also describe variations of this experiment with structured light beams, where the Pancharatnam phase leads to linear or nonlinear rotation of flower-pattern or spiral-shape interference fringes. 
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