Nanoscale electrical characterization of graphene-based materials by atomic force microscopy

Abstract

Graphene, an atomically thin two-dimensional (2D) material, exhibits outstanding electrical properties and thus has been employed in various electronic devices. However, the device performance strongly depends on the structural variations present in the graphitic lattice, such as crystal domains, grain boundaries, lattice imperfections, dopants, etc., which are nanoscopic in nature. Hence, understanding the correlation between the structure and the electrical properties in the nanoscale is essential. Atomic force microscopy (AFM) techniques provide the best way to picture such relationships, which is particularly in demand for future miniaturized devices. This review article highlights the characterization of the electrical properties of graphene-based materials via AFM-based techniques such as conductive AFM, scanning Kelvin probe microscopy, electrostatic force microscopy, and piezoresponse force microscopy that is certainly beneficial for a broad research community not only working on graphene-based materials but also in the fields of other 2D materials and scanning probe microscopy. Graphical abstract

Photocurrent of Graphene/Au-Nanopillar: Near-Unity Degree of Linear Polarization

“…36,37 Since the conducting tips are employed as electrodes in the C-AFM experiments, it is possible to characterize the local transport of a nanomaterial without fabricating electrodes. 33,37 As shown in Figure 5b,c, the measured dark-state CPD (V CPD,Dark ) at the Gr layer in contact with the AuNP top is smaller than that at the suspended Gr layer. Since CPD is given by (WF tip − WF sample )/e (WF tip , the work function of the tip; WF sample , the work function of the sample; e, the electron charge), the work function of the Gr monolayer (WF Gr ) can be estimated from the CPD maps.…”

“…32−37 The most popular techniques are Kelvin probe force microscopy (KPFM) and conductive AFM (C-AFM), which can measure contact potential difference (CPD) and electric current at the sample surface, respectively. 33 Since the work function of a sample determines the CPD value, the measured CPD depends on the doping concentration of a semiconducting sample. 32−35 The sharp tip of C-AFM, with an apex radius of a few tens of nm, can achieve very high spatial resolution.…”

“…For the local current− voltage (I−V) characterizations, the C-AFM tip and AuNP worked as top and bottom electrodes, respectively. 33,37 Thus, the out-of-plane electric current across the Gr/Au interface can be measured without electrode fabrication processes. Under light illumination, two kinds of excess electrons can be generated: photogenerated electrons and SPP-induced hot electrons, as illustrated in Figure 6a.…”

“…AFM-based characterization techniques have been used to investigate the electrical properties of low-dimensional materials due to their nanoscale spatial resolution. − The most popular techniques are Kelvin probe force microscopy (KPFM) and conductive AFM (C-AFM), which can measure contact potential difference (CPD) and electric current at the sample surface, respectively . Since the work function of a sample determines the CPD value, the measured CPD depends on the doping concentration of a semiconducting sample. − The sharp tip of C-AFM, with an apex radius of a few tens of nm, can achieve very high spatial resolution. , Since the conducting tips are employed as electrodes in the C-AFM experiments, it is possible to characterize the local transport of a nanomaterial without fabricating electrodes. , …”

“…Figure b,c show the measured photocurrent data of Gr/AuNP when illuminated by TE- and TM-mode light with wavelengths of 530 and 850 nm, respectively. The estimation of the current collection area is not trivial in the case of C-AFM measurement . Thus, either the current density or the responsivity cannot be estimated for the Gr/AuNP samples.…”