[33] Coleman P. (Ed.) (2000) Positron Beams and Their Applications. World Scientific.
[34] Tuomisto F. and Makkonen I. (2013) Defect identification in semiconductors with positron annihilation: Experimental and Theory. Rev. Mod. Phys. 85, 1583.
[35] Krause R., Saarinen K., Hautojärvi P., Polity A., Gärtner G. and Corbel C. (1990) Observation of a monovacancy in the metastable state of the EL2 defect in GaAs by positron annihilation. Phys. Rev. Lett. 65, 3329.
[36] Lawther D. W., Myler U., Simpson P. J., Rousseau P. M., Griffin P. B. and Plummer J. D. (1995) Vacancy generation resulting from electrical deactivation of arsenic. Appl. Phys. Lett. 67, 3575.
[37] Tuomisto F., Ranki V. and Saarinen K. (2003) Evidence of the Zn vacancy acting as the dominant acceptor in n-type ZnO. Phys. Rev. Lett. 91, 205502.
[38] Ling C. C., Lui M. K., Ma S. K., Chen X. D., Fung S. and Beling C. D. (2004) Nature of the acceptor responsible for p-type conduction in liquid encapsulated Czochraiski-grown undoped gallium antimonide. Appl. Phys. Lett. 85, 384.
[39] Khalid M., Ziese M., Setzer A., Esquinazi P., Lorenz M., Hochmuth H., Grundmann M., Spermann D., Butz T., Brauer G., Anwand W., Fischer G., Adeagbo A., Hergert W. and Ernst A. (2009) Defect-induced magnetic order in pure ZnO films. Phys. Rev. B 80, 035331.
[40] Uedono A., Ishibashi S., Watanabe T., Wang X. Q., Liu, S. T., Chen G., Sang L. W., Sumlya M. and Shen B. (2012) Vacancy-type defects in InxGa1−xN alloys probed using a monoenergetic positron beam. J. Appl. Phys. 112, 014507.
[41] Johansen K. M., Zubiaga A., Tuomisto F., Monakhov E. V., Kuznetsov A. Yu and Svensson B. G. (2011). H passivation of Li on Zn-site in ZnO: Positron annihilation spectroscopy and secondary ion mass spectroscopy. Phys. Rev. B 84, 115203.
[42] Rauch C., Makkonen I. and Tuomisto F. (2011) Identifying vacancy complexes in compound semiconductors with positron annihilation spectroscopy: A case study of InN. Phys. Rev. B 84, 125201.
[43] Watkins G. D. (1999) EPR and ENDOR studies of defects in semiconductors. Identification of Defects in Semiconductors, Stavola M. (Ed.), Semiconductors and Semimetals Vol. 51A 1, Academic Press.
[44] Loubser J. H. N. and van Wyk J. A. (1978) Electron spin resonance in the study of diamond. Rep. Prog. Phys. 41, 1201.
[45] Kennedy T. A. and Glaser E. R. (1999) Magnetic resonance of epitaxial layers detected by photoluminescence. Identification of Defects in Semiconductors, Stavola M. (Ed.), Semiconductors and Semimetals Vol. 51A 93, Academic Press.
[46] Spaeth J.-M. (1999) Magneto-optical and electrical detection of paramagnetic resonance in semiconductors. Identification of Defects in Semiconductors, Stavola M. (Ed.), Semiconductors and Semimetals Vol. 51A 45, Academic Press.
[47] Abe E. and Sasaki K. (2018) Magnetic resonance with nitrogen-vacancy centers in diamond — microwave engineering, materials science, and magnetometry. J. Appl. Phys. 123, 161101.
[48] Nardo R. L., Wolfowicz G., Simmons S., Tyryshkin A. M., Riemann H., Abrosimov N. V., Becker P., Pohl H. J., Steger M., Lyon S. A., Thewalt M. L. W. and Morton J. J. L. (2015) Spin relaxation and donor-acceptor recombination of Se+ in 28-silicon. Phys. Rev. B 92, 165201.
[49] S. Kilpeläinen, K. Kuitunen, F. Tuomisto, J. Slotte, H. H. Radamson, and A. Yu. Kuznetsov, Phys. Rev. B 81, 132103 (2000).
CHAPTER 2
Defect Physics in 2D Nanomaterials Explored by STEM/STM
JINHUA HONG∗, MAOHAI XIE†,‡ and CHUANHONG JIN∗,§
∗State Key Laboratory of Silicon Materials, School of Materials Science and Engineering, Zhejiang University, Hangzhou 310027, China
†Physics Department, The University of Hong Kong, Pokfulam Road, Hong Kong
1. Introduction
Structural disorders such as point defects (vacancies, anti-sites, interstitials, and dopants), dislocations, and grain boundaries are commonly present in crystalline materials, which play a key role in dominating the mechanical, opto/electronic, and chemical properties of the crystal materials [1–3]. For instance, the success of modern microelectronics is based on the manipulation of the charge carriers in semiconductor channels of field effect transistors through defect engineering. This helps to realize p-to-n conversion and to control the electric and optical performance of semiconductors. In general, structural defects break the translational symmetry of crystals leading to unique electronic states modifying the intrinsic electronic structure, and thereby considerably tailor the electronic, optical, magnetic, as well as the chemical/catalytic properties of crystals, as reflected by optical spectroscopy — such as ultraviolet–visible spectroscopy (UV–Vis), photoluminescence (PL) spectroscopy, X-ray absorption spectroscopy (XAS), alternating current (AC) conductance, or magnetic properties measurements.
Defect exploration, control, and engineering have always been at the heart of modern materials science and industrial applications such as traditional semiconductor microelectronics, metal refining, and catalyst design. Besides the traditional 3D solids, such a structure–property philosophy of defects remains a common but challenging issue to be explored even in low-dimensional crystal materials, such as nanocrystals, quantum dots, nanotubes, or ribbons and graphene-like two-dimensional (2D) materials. Hence, direct imaging of the defect structure will be of crucial significance to detect the localized defect state and its electronic properties. The whole picture of structure–property correlation in defects may also lead to the discovery of novel nanophysics in nanomaterials such as magnetism/spin crossover and single-atom catalysis.
In this chapter, five sections will be included in defect characterization: (1) a brief introduction of scanning transmission electron microscopy (STEM) and scanning tunneling microscopy (STM) in direct probing; (2) STEM characterization of point defects (vacancy and antisite) in 2D transition metal dichalcogenides; (3) real-time experimental observation of defects’ migration in monolayer MoS2; (4) STEM and STM/scanning tunneling spectroscopy (STS) characterization of inversion domain boundaries in molecular beam epitaxy (MBE)-grown MoSe2; (5) STEM and STS of the domains of bilayer MoSe2 to reveal the stacking band structure diversity.
2. Instrumentation and Technique
Among the available microscopy techniques for direct atom probing in real space, STEM and scanning probe microscopy (SPM) are suitable to visualize the structure of defects at the atomic scale. Both microscopic techniques can enable us in direct atomically
