Direct measurement of surface photovoltage by AC bias Kelvin probe force microscopy

Abstract

Surface photovoltage (SPV) measurements are a crucial way of investigating optoelectronic and photocatalytic semiconductors. The local SPV is generally measured consecutively by Kelvin probe force microscopy (KPFM) in darkness and under illumination, in which thermal drift degrades spatial and energy resolutions. In this study, we propose the method of AC bias Kelvin probe force microscopy (AC-KPFM), which controls the AC bias to nullify the modulated signal. We succeeded in directly measuring the local SPV by AC-KPFM with higher resolution, thanks to the exclusion of the thermal drift. We found that AC-KPFM can achieve a SPV response faster by about one to eight orders of magnitude than classical KPFM. Moreover, AC-KPFM is applicable in both amplitude modulation and frequency modulation mode. Thus, it contributes to advancing SPV measurements in various environments, such as vacuum, air, and liquids. This method can be utilized for direct measurements of changes in surface potential induced by modulated external disturbances.

Clarification of Au dimer adsorption sites on Si (111)-7 × 7 surface by AFM/KPFM

“…The contrast between the two atoms of the Au dimer appears slightly darker compared to the Si adatoms on the Si(111)-7 × 7 surface, indicating that the Au atoms are slightly positively charged. This is consistent with the findings of contrast variation in CPD images, as explained by several studies [31][32][33][34][35][36]41].…”

Dual-heterodyne Kelvin probe force microscopy

“…Moreover, under periodic pumping, an additional frequency mixing process occurs due to the simultaneous existence of modulated potentials at ω = ω ac and ω = nω mod . In our case, the terms of interest are those resulting from the multiplication of V ac by V mod in Equation 5 (in the following we will omit the other terms, bearing in mind that they exist): (6) This can be rewritten as: (7) Finally, the other frequency mixing process (multiplication by the capacitive term, first harmonic) results in the appearance of additional spectral components in the oscillating electrostatic force, but this time there are 4 × n of them (instead of two sidebands for conventional AM-heterodyne KPFM): (8) To avoid any confusion, in the following, the sidebands will be labelled as follow:…”

“…Working under modulated illumination also allows direct SPV measurements using special modulation/demodulation schemes, such as the one recently proposed by Miyazaki and co-workers for ac-bias KPFM [6]. In addition, most time-resolved KPFM modes developed so far rely on the use of a pulsed/modulated illumination chain.…”

Understanding and decoupling the role of wavelength and defects in light-induced degradation of metal-halide perovskites

“…[14][15][16][17][18][19] Recent reports in the literature endeavor to disentangle the impact of light on the perovskite structure at the nanoscale. [20][21][22][23][24] However, up to now, a detailed model at the nanoscale of the light-induced chemical conversion/degradation of the perovskite is still lacking. Such a model could uncover unforeseen chemical processes, responsible for the intrinsic light degradation of the perovskite material and infer worthwhile strategies to mitigate them, which is exactly what we tackled in the present study.…”