Toplayer-dependent crystallographic orientation imaging in the bilayer two-dimensional materials with transverse shear microscopy

Abstract

Nanocontact properties of two-dimensional (2D) materials are closely dependent on their unique nanomechanical systems, such as the number of atomic layers and the supporting substrate. Here, we report a direct observation of toplayer-dependent crystallographic orientation imaging of 2D materials with the transverse shear microscopy (TSM). Three typical nanomechanical systems, MoS2 on the amorphous SiO2/Si, graphene on the amorphous SiO2/Si, and MoS2 on the crystallized Al2O3, have been investigated in detail. This experimental observation reveals that puckering behaviour mainly occurs on the top layer of 2D materials, which is attributed to its direct contact adhesion with the AFM tip. Furthermore, the result of crystallographic orientation imaging of MoS2/SiO2/Si and MoS2/Al2O3 indicated that the underlying crystalline substrates almost do not contribute to the puckering effect of 2D materials. Our work directly revealed the top layer dependent puckering properties of 2D material, and demonstrate the general applications of TSM in the bilayer 2D systems.

Size-dependent strain-engineered nanostructures in MoS2monolayer investigated by atomic force microscopy

“…Figure 2(a) shows the AFM topography image of typical triangular sharp-corner MoS 2 monolayer, in which no specific features is observed within the flake. In our previous work [30,44], the FFM mode has been used to characterize the strain-induced structures. The distinctive strain-induced features were clearly observed by the FFM mode, as shown in in figure 2(b), in which the three sharp corners (marked as II) show different contrast from the central region (marked as I) of triangular MoS 2 monolayer flake.…”

Advanced atomic force microscopies and their applications in two-dimensional materials: a review

“…FFM and TSM are the derivatives of the contact mode of AFM. They maintain the normal force constant and record the lateral signal between the tip and sample surface (figure 5) [18,19,[66][67][68]. The lateral bending or twisting arises from forces parallel to the sample surface plane and acting on the AFM-tip.…”

“…Tuning the material band structure by subjecting it to strain is an important strategy to enhance the electronic device performance. Diverse methods have been proposed for introducing strain in 2D materials, including the bending of films on elastic substrates [10,11,16], stretching of films using atomic force microscope probes [17][18][19], and thermal expansion mismatch [20][21][22][23]. Our review mainly focuses on the stress application methods discussed in sections 2.1.1 and 2.1.2.…”

“…TSM characterization is useful for crystallographic orientation imaging of monolayer samples and characterization of bilayer samples, such as bilayer MoS 2 and graphene [19]. Due to the van der Walls (vdW) interactions between the top and bottom layer, the adhesion and puckering effect occur primarily between the AFM tip and top layer as the AFM tip approach, contact, and move on the top layer (figures 25(a) and (b)).…”

Twist angle-dependent work functions in CVD-grown twisted bilayer graphene probed by Kelvin probe force microscopy

“…For measuring the surface potentials and work functions, Kelvin probe force microscopy (KPFM) has proven to be an excellent technique with outstanding resolution and sensitivity. 33,34 Relevant work has been done using KPFM technology to study the relationship between the work function of stripped graphene and the number of layers. [35][36][37][38] In 2018, Robinson et al measured the surface potential between layers with different twist angles or layer thicknesses in graphene obtained by chemical vapor deposition and combined it with Raman technology to resolve different twist angles.…”