Time-resolved electrostatic force microscopy using tip-synchronized charge generation with pulsed laser excitation

Abstract

Nanoscale observation of charge distribution and electric polarization is crucial for understanding and controlling functional materials and devices. In particular, the importance of charge dynamics is well recognized, and direct methods to observe charge generation, transfer, and recombination processes are required. Here, we describe tip-synchronized timeresolved electrostatic force microscopy. Numerical modeling clarifies that the tipsynchronized method provides temporal resolution with the timescale of the cantilever oscillation cycle. This method enables us to resolve sub-microsecond charge migration on the surface. The recombination of photo-excited carriers in a bilayer organic photovoltaic thin film is observed as a movie with a 0.3 µs frame step time resolution. Analysis of the images shows that the carrier lifetime is 2.3 µs near the donor/acceptor interface. The tipsynchronized method increases the range of time-resolved electrostatic force microscopy, paving the way for studies of nanoscale charge dynamics.

Quantitative phase‐mode electrostatic force microscopy on silicon oxide nanostructures

“…For instance, the charge distribution in finite size systems (Yalcin et al ., 2012; Roy‐Gobeil et al ., 2015; Miyahara et al ., 2017), even in the presence of spatial, compositional and energy disorder (El Khoury, 2017), can be visualized by these techniques. Local electrostatic techniques provide information on the 2D spatial distribution of charge carriers in semiconductors (Chin et al ., 2008; Musumeci et al ., 2017), nanostructures (Krauss & Brus, 1999; Cherniavskaya et al ., 2003; Marchi et al ., 2008; Borgani et al ., 2016) and devices (Pingree et al ., 2009) and, more recently, in volume (3D) (Collins et al ., 2015; Fabregas & Gomila, 2020) and in time (Araki et al ., 2019; Borgani & Haviland, 2019; Mascaro et al ., 2019). 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.…”

Visualization of Charge Migration in Conductive Polymers via Time-Resolved Electrostatic Force Microscopy

“…The frequency shift was monitored using a phase-locked loop (PLL; OC4 station, Nanonis) to measure the attractive force resulting from the electrostatic interaction between the tip and sample. A detailed explanation of this combined amplitude modulation–frequency modulation mode has been described previously . The tr-EFM experiments were conducted under vacuum (<10 –2 Pa) at room temperature.…”

“…Using a similar approach, Marohn and co-workers employed phase-kick EFM for time-resolved electrostatic force detection . Recently, we were able to obtain a video showing photoexcited carrier migration on an organic photovoltaic device with a time resolution of 0.3 μs and sensitivity of 0.3 Hz …”

Open-loop amplitude-modulation Kelvin probe force microscopy operated in single-pass PeakForce tapping mode

“…One of the main motivations for OL KPFM is the full access to the raw data, uncorrected by any measurement procedure such as the feedback loop of a real-time operation. Moreover, the limited speed response of the feedback loop can also become a great impediment in observing ultrafast phenomena at time scale of the order of microseconds or less [29][30][31][32][33].…”

“…Moreover, the finite response time of the CL feedback (of the order of milliseconds in some cases) prevents the use of CL KPFM from observing fast electrodynamic processes. Some of these impediments are addressed in OL implementations such as time-resolved electrostatic force microscopy [29,30], pump-probe KPFM [31,32], or fast free force recovery KPFM [33] that are capable of observing the dynamics of the optoelectronic response of materials and electric field-induced charge migration at time scales of the order of tens of microseconds.…”