Kelvin probe force microscopy is a scanning probe technique used to quantify the local electrostatic potential of a surface. In common implementations, the bias voltage between the tip and the sample is modulated. The resulting electrostatic force or force gradient is detected via lock-in techniques and canceled by adjusting the dc component of the tip–sample bias. This allows for an electrostatic characterization and simultaneously minimizes the electrostatic influence onto the topography measurement. However, a static contribution due to the bias modulation itself remains uncompensated, which can induce topographic height errors. Here, we demonstrate an alternative approach to find the surface potential without lock-in detection. Our method operates directly on the frequency-shift signal measured in frequency-modulated atomic force microscopy and continuously estimates the electrostatic influence due to the applied voltage modulation. This results in a continuous measurement of the local surface potential, the capacitance gradient, and the frequency shift induced by surface topography. In contrast to conventional techniques, the detection of the topography-induced frequency shift enables the compensation of all electrostatic influences, including the component arising from the bias modulation. This constitutes an important improvement over conventional techniques and paves the way for more reliable and accurate measurements of electrostatics and topography.

Nanoparticle superlattices produced with controllable interparticle gap distances down to the subnanometer range are of superior significance for applications in electronic and plasmonic devices as well as in optical metasurfaces. In this work, a method to fabricate large-area (∼1 cm 2 ) gold nanoparticle (GNP) superlattices with a typical size of single domains at several micrometers and high-density nanogaps of tunable distances (from 2.3 to 0.1 nm) as well as variable constituents (from organothiols to inorganic S 2− ) is demonstrated. Our approach is based on the combination of interfacial nanoparticle self-assembly, subphase exchange, and free-floating ligand exchange. Electrical transport measurements on our GNP superlattices reveal variations in the nanogap conductance of more than 6 orders of magnitude. Meanwhile, nanoscopic modifications in the surface potential landscape of active GNP devices have been observed following engineered nanogaps. In situ optical reflectance measurements during free-floating ligand exchange show a gradual enhancement of plasmonic capacitive coupling with a diminishing average interparticle gap distance down to 0.1 nm, as continuously red-shifted localized surface plasmon resonances with increasing intensity have been observed. Optical metasurfaces consisting of such GNP superlattices exhibit tunable effective refractive index over a broad wavelength range. Maximal real part of the effective refractive index, n max , reaching 5.4 is obtained as a result of the extreme field confinement in the high-density subnanometer plasmonic gaps.

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We present the design, fabrication, and characterization of an in-plane vibration sensor with frequency selective displacement amplification and differential capacitive read-out. The mechanical structure is based on six resonators with decreasing stiffness coupled in-plane. A differential capacitance attached to the last mass serves as electrical read out. Finite element and lumped element models are both presented. The devices were fabricated in a single mask silicon on insulatorbased process. The mechanical, as well as the capacitive transfer function and the pressure dependence, have been investigated experimentally and compared with simulations. The measured mean (minimum) amplification was 24 dB (16 dB) over a bandwidth of 10 kHz (3-13 kHz). While the mean amplification is pressure dependent, the minimum amplification and bandwidth show a less than 10% decrease over a wide pressure range from 6.3 to 64 mbar. The pressure dependent measurements also show that the minimum amplification is independent of the Q factor of the modes down to values of Q∼10. Both simulation and experiment show that the off-axis modes occur outside the bandwidth of the device. Along with the low cross-sensitivity of the capacitive readout (0.06%), this provides good axis selectivity despite the high number of degrees of freedom. The device can be used for detection of broadband vibration signals, e.g., for structural monitoring of infrastructure such as bridges and pipelines.

Direct views of electron clouds in atoms h-ave been observed visually and photographed by means of a two-stage holographic miscroscope based on Gabor's principle of image reconstruction. Holograms are produced with 40-kilo-volt electron radiation and decoded with an optical laser. The obviation of an objective lens makes feasible a numerical aperture of 0.37 and a resolving power exceeding 0.1 angstrom.