Wideband low-noise optical beam deflection sensor with photothermal excitation for liquid-environment atomic force microscopy

Abstract

I developed a wideband low-noise optical beam deflection sensor with a photothermal cantilever excitation system for liquid-environment atomic force microscopy. The developed sensor has a 10 MHz bandwidth and 4.7 fm/ ͱ Hz deflection noise density in water. The theoretically limited noise performance ͑i.e., the noise level limited only by the photodiode shot noise͒ has been achieved in liquid for the first time. Owing to the wide bandwidth and the replaceable focus lens design, the sensor is applicable to cantilevers with various dimensions. The deflection noise densities of less than 7.8 fm/ ͱ Hz have been achieved in water for cantilevers with lengths from 35 to 125 m. The ideal amplitude and phase versus frequency curves without distortion are obtained with the developed photothermal excitation system. The excitation system is applicable to relatively stiff cantilevers ͑Ͼ20 N / m͒ in liquid, making it possible to obtain true atomic-resolution images in liquid. True atomic-resolution imaging of mica in water is demonstrated using the developed deflection sensor and the photothermal excitation system.

Atomic-resolution imaging in liquid by frequency modulation atomic force microscopy using small cantilevers with megahertz-order resonance frequencies

“…The AFM experiments were performed by a custom-built AFM head with an ultralow noise cantilever deflection sensor [3,29] and a photothermal excitation setup [30]. The AFM head was controlled with a commercially available AFM controller (ARC2: Asylum Research).…”

Dissolution Processes at Step Edges of Calcite in Water Investigated by High-Speed Frequency Modulation Atomic Force Microscopy and Simulation

“…Note that this performance is available only when the noise from the instruments is smaller than that from the thermal vibration of the cantilever. To meet this requirement, we developed a wideband, low noise and highly stable cantilever deflection sensor [22][23][24] , photothermal cantilever excitation system 21,24 and digital phase-locked loop (PLL) circuit 25,26 . With these improvements, we achieved thermal-noise-limited performance even with a small cantilever, as shown in Figure 1b.…”

Advanced Instrumentation of Frequency Modulation AFM for Subnanometer-Scale 2D/3D Measurements at Solid-Liquid Interfaces

“…For detecting the cantilever vibration at 3-4 MHz, the deflection sensor should have a bandwidth higher than 10 MHz. We satisfied this requirement by optimizing the circuit design of the preamplifier and the differential amplifier in the deflection sensor [51]. To achieve the thermal-noiselimited performance, the deflection noise density caused by the deflection sensor (n zs ) should be sufficiently smaller than that by the cantilever Brownian motion (n zB ).…”

“…To satisfy this requirement, we improved most of the components in our FM-AFM setup. We improved the circuit design of the cantilever deflection sensor and improved its bandwidth to ∼10 MHz [51]. We replaced the piezoelectric excitation mechanism with the photothermal excitation system and achieved over 10 MHz bandwidth [51].…”

“…We improved the circuit design of the cantilever deflection sensor and improved its bandwidth to ∼10 MHz [51]. We replaced the piezoelectric excitation mechanism with the photothermal excitation system and achieved over 10 MHz bandwidth [51]. We developed a separate-type high-speed XY sample and Z tip scanner and enabled their operation at ∼1 kHz and ∼10 kHz, respectively [53].…”