Conductive atomic force microscopy for routine defect characterization of two-dimensional semiconductors

Routine defect characterization is a critical capability for understanding defect-property correlations, optimizing growth of two-dimensional (2D) materials, and understanding the impact of defects on devices. High throughput optical methods for defect characterization, such as Raman spectroscopy, are useful for graphene, but are often insufficiently sensitive to defects in some other 2D materials, such as transition metal dichalcogenides (TMDs), particularly for defect densities of about 10¹² cm^-2 or less. Typical methods for directly detecting defects at the atomic scale, such as scanning transmission electron microscopy (STEM) and scanning tunneling microscopy (STM), are effective, but they are relatively slow and often require arduous sample preparation. There is a need for 2D material defect characterization techniques that are routine, fast, and reliable. Here, we show that conductive atomic force microscopy (AFM) can locate and differentiate the defects in a similar way as STM by comparing conductive AFM and STM on the same region of a flux-grown TMD crystal¹. We will also present measurements on TMD monolayers from different sources. We will share practical considerations for carrying out these measurements, such as sample preparation, tip selection, and choice of bias. We will also discuss a statistical framework for presenting defect density results and discuss situations in which these measurements are most effective. Overall, our work establishes conductive AFM as a higher-throughput alternative to STM for defect quantification that one can use as a routine characterization tool for 2D semiconductors.

(1) Xu, K.; Holbrook, M.; Holtzman, L. N.; Pasupathy, A. N.; Barmak, K.; Hone, J. C.; Rosenberger, M. R. Validating the Use of Conductive Atomic Force Microscopy for Defect Quantification in 2D Materials. ACS Nano 2023, 17 (24), 24743–24752. https://doi.org/10.1021/acsnan....

Lateral force microscopy of atomic defects in two-dimensional materials

Rapid and quantitative characterization of atomic defects in two-dimensional (2D) materials is crucial for understanding and improving 2D material performance. However, such defect metrology remains challenging due to limitations of existing characterization methods, which are generally destructive, slow, or lack the necessary sensitivity. Here, we describe the use of lateral force microscopy (LFM) to directly observe atomic defects in 2D materials¹. Through a direct comparison with conductive atomic force microscopy, we show that LFM can observe intrinsic point defects in semiconducting 2D materials. As a purely mechanic technique, LFM has the advantage of not requiring a conductive pathway, which makes it useful on insulating 2D materials and semiconducting 2D materials that are on an insulating substrate without electrical contact. We demonstrate defect measurements on hexagonal boron nitride as well as 2D semiconductors on their growth substrates and within fabricated transistors. Finally, we discuss a few limitations to be aware of and guidance on how to practically implement this technique. This work demonstrates that LFM is a simple and quantitative tool for understanding defects in 2D materials.

(1) Yang, Y.; Xu, K.; Holtzman, L. N.; Yang, K.; Watanabe, K.; Taniguchi, T.; Hone, J.; Barmak, K.; Rosenberger, M. R. Atomic Defect Quantification by Lateral Force Microscopy. ACS Nano 2024, 18 (9), 6887–6895. https://doi.org/10.1021/acsnan...

(2) Yang, Y.; Xu, K.; Peña, T.; Neilson, K.; Zheng, X.; Hoang, A. T.; Yang, K.; Hennighausen, Z.; Zhang, T.; Holtzman, L. N.; Nattoo, C. A.; Hone, J. C.; Barmak, K.; Kong, J.; Mannix, A. J.; Pop, E.; Rosenberger, M. R. Nondestructive Atomic Defect Quantification of Two-Dimensional Materials and Devices. ACS Appl. Mater. Interfaces 2026, 18 (6), 10161–10170. https://doi.org/10.1021/acsami...

C-AFM Imaging and Electronic Spectroscopy of Atomic Defects in 2D Materials

Thanks to their outstanding physical characteristics, two-dimensional (2D) materials have the potential to revolutionize next-generation electronics. 2D materials unavoidably contain atomic defects, the effects of which need to be evaluated in order to effectively utilize them in devices. Although the majority of applications utilizing 2D materials will take place under ambient conditions, conventional tools for characterizing materials with atomic resolution operate under strict environmental conditions imposed by ultrahigh vacuum (UHV). This critically limits the usefulness of the information provided by UHV-based methods such as scanning tunnelling microscopy (STM) and noncontact atomic force microscopy (NC-AFM).

Our lab demonstrated the capability of true atomic-resolution imaging via conductive atomic force microscopy (C-AFM) under ambient conditions [1]. Here, we will focus on atomic-resolution imaging of defects in various 2D electronic materials: (i) the prototypical transition metal dichalcogenide (TMD) molybdenum disulfide (MoS₂) [2], (ii) a 2D dielectric (indium oxide, InO₂) [3], and (iii) ultrathin crystals of tungsten carbide (WC), covered by monolayer graphene. We additionally demonstrate the capability of electronic spectroscopy on individual defects under ambient conditions, enabling chemical identification [4]. Our findings highlight C-AFM as a powerful tool for atomic-resolution imaging and electronic spectroscopy of defects in 2D materials under ambient conditions.

[1] S.A. Sumaiya, J. Liu, M.Z. Baykara, ACS Nano 16, 20086 (2022)

[2] B. Kumral, et al. Nature Communications 16, 7105 (2025)

[3] F. Turker, et al. Advanced Materials 38, e16133 (2025)

[4] J.R. Evans, D.A. Garibay, A.N. Kuhls, M.Z. Baykara, ACS Omega, in press (2026)

Autonomous Defects Detection & Back-Contact Free Electrical Atomic Force Microscopy in 2D Materials

Electrical scanning probe microscopy is now a cornerstone of materials characterization with impact on the broader community of materials scientists, engineers and nanotechnologists. Here, we report a rapid, generalizable pipeline that couples conductive atomic force microscopy (C-AFM) imaging with a physics-aware Machine-Learning (ML) based workflow to automatically detect, classify, and quantify defects from microscopic to mesoscopic scales in 2D materials. Second, we discuss how to overcome one of the most limiting design constraints that prevents electrical AFM adoption for in-line wafer and panel metrology, i.e., the requirement for electrical back-contact. This reliance on back-contact constitutes a significant roadblock, preventing the automated deployment of electrical AFM in complex manufacturing environments. To address the limitations imposed by physical back-contacts, we present a novel solution that replaces the mechanical connection with a low-energy electron beam focused on the sample surface near the AFM probe. We refer to this configuration as electron-beam excited AFM (EB-AFM). This approach yields results comparable to conventional techniques while unlocking applications previously inaccessible due to geometry or material constraints. Here, we demonstrate the efficacy of this strategy for contact-free electrical characterization on various systems including, as-grown, patterned and area-selected grown 2D materials.

More information coming soon

More information coming soon

More information coming soon

More information coming soon