  Quasi-two-dimensional (Quasi-2D) van der Waals (vdW) materials can be
mechanically or chemically exfoliated down to monolayer because of their strong
intralayer bonding and the weak interlayer vdW interaction. Thanks to this
unique property, one can often find exotic thickness-dependent electronic
properties from these quasi-2D vdW materials, which can lead to band gap
opening, emerging superconductivity, or enhanced charge density waves with
decreasing thickness. Surface-sensitive scanning tunneling microscopy (STM) can
provide direct observation of structural and electronic characteristics of such
layered materials with atomic precision in real space. However, it is very
challenging to preserve the intrinsic surfaces of air-sensitive quasi-2D
materials between preparation and measurement. In addition, vdW 2D crystals
after exfoliation are extremely hard to explore with a typical STM setup due to
their small size (< 10 {\mu}m). Here, we present a straightforward method
compatible with any STM setup having optical access: (1) exfoliating and/or
stacking layered materials in a glove box, (2) transferring them to an
ultra-high vacuum STM chamber using a suitcase without exposure to air, and (3)
navigating surface to locate exfoliated vdW 2D flakes with different
thicknesses. We successfully demonstrated that the clean surfaces of the
air-sensitive Fe$_3$GeTe$_2$ can be effectively protected from unwanted
oxidation during transfer. Furthermore, our method provides a simple but useful
way to access a specific tiny stack of layered materials without any ex-situ
fabrication processes for STM navigation. Our experimental improvement will
open up a new way to investigate air-sensitive layered vdW materials with
various thicknesses via surface-sensitive techniques including STM.
