Electrostatic imaging of encapsulated graphene

Abstract

Devices made from two-dimensional (2D) materials such as graphene and transition metal dichalcogenides exhibit remarkable electronic properties of interest to many subdisciplines of nanoscience. Owing to their 2D nature, their quality is highly susceptible to contamination and degradation when exposed to the ambient environment. Protecting the 2D layers by encapsulation between hexagonal boron nitride (hBN) layers significantly improves their quality. Locating these samples within the encapsulant and assessing their integrity prior to further processing then becomes challenging. Here we show that conductive scanning probe techniques such as electrostatic force and Kelvin force microscopy makes it possible to visualize the encapsulated layers, their charge environment and local defects including cracks and bubbles on the sub-micrometer scale. Our techniques are employed without requiring electrical contact to the embedded layer, providing valuable feedback on the device's local electronic quality prior to any device etching or electrode deposition. We show that these measurement modes, which are simple extensions of atomic force microscopy, are perfectly suited for imaging encapsulated conductors and their local charge environments. Supporting Information

Quantitative phase‐mode electrostatic force microscopy on silicon oxide nanostructures

“…These techniques were proven useful in studying the localization of trapped charges in thin films (Silveira & Marohn, 2004; Chen et al ., 2005a; Chen et al ., 2005b; Muller & Marohn, 2005), quantum dots (Tevaarwerk et al ., 2005) and nanotubes (Chin et al ., 2008); to measure the resistance at metal–semiconductor interfaces and grain boundaries in operating devices (Annibale et al ., 2007); to relate electrical properties, such as dielectric permittivity (Gramse et al ., 2009; El Khoury et al ., 2016; Fumagalli et al ., 2018), conductivity (Castellano‐Hernández & Sacha, 2015; Aurino et al ., 2016), piezoelectricity (Moon et al ., 2017) and percolation pathways (Barnes & Buratto, 2018), directly to the organization of the material at the mesoscopic length scales. Charge distribution in supramolecular architectures (Dabirian et al ., 2009; Borgani et al ., 2014; Garrett et al ., 2018), biomolecules (Gil et al ., 2002; Cuervo et al ., 2014; Dols‐Perez et al ., 2015; Lozano et al ., 2018; Lozano et al ., 2019), living organism (Esteban‐Ferrer et al ., 2014; Van Der Hofstadt et al ., 2016a; Van Der Hofstadt et al ., 2016b) and 2D materials (Collins et al ., 2013; Miyahara et al ., 2015; Shen et al ., 2018; Altvater et al ., 2019) was recently addressed with these techniques. The information obtained can be used as input for the design and optimization of device layouts, and ultimately for the simulation of functional devices and circuits.…”

Photoelectrical Properties Investigated on Individual Si Nanowires and Their Size Dependence

“…In the second lifted pass (the tip was lifted high enough to neglect the phase shift induced by van der Waals force), a DC bias was applied between the tip and the sample and the phase shift signal determined by the electrical force gradient was detected. The detailed operation principles could be found in previous studies [ 45 , 46 ]. Pt/Cr-coated tips (Multi75E-G, Budget Sensors, radius approximately 25 nm) were applied in all electrical measurements and all experiments were performed in a flowing N 2 ambient.…”

Photoelectrical properties investigated on individual Si nanowires and their size dependence

“…In the second lifted pass (the tip was lifted high enough to neglect the phase shift induced by van der Waals force), a DC bias was applied between the tip and the sample and the phase shift signal determined by the electrical force gradient was detected. The detailed operation principles could be found in previous literatures [41,42]. Pt/Cr-coated tips (Multi75E-G, Budget Sensors, radius approximately 25 nm) were applied in all electrical measurements and all experiments were performed in a flowing N2 ambient.…”