Massively parallel cantilever-free atomic force microscopy

Wenhan Cao,Keith A Brown,Nourin Alsharif,Yuhuang Wang,Alice E White,Zhongjie Huang

doi:10.1038/s41467-020-20612-3

Wenhan Cao, Keith A Brown + Show 4 more

Open Access

https://doi.org/10.1038/s41467-020-20612-3

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Abstract

Resolution and field-of-view often represent a fundamental tradeoff in microscopy. Atomic force microscopy (AFM), in which a cantilevered probe deflects under the influence of local forces as it scans across a substrate, is a key example of this tradeoff with high resolution imaging being largely limited to small areas. Despite the tremendous impact of AFM in fields including materials science, biology, and surface science, the limitation in imaging area has remained a key barrier to studying samples with intricate hierarchical structure. Here, we show that massively parallel AFM with >1000 probes is possible through the combination of a cantilever-free probe architecture and a scalable optical method for detecting probe–sample contact. Specifically, optically reflective conical probes on a comparatively compliant film are found to comprise a distributed optical lever that translates probe motion into an optical signal that provides sub-10 nm vertical precision. The scalability of this approach makes it well suited for imaging applications that require high resolution over large areas.

Highlights

Resolution and field-of-view often represent a fundamental tradeoff in microscopy
Combining contact mechanics and an analytical estimate for specular reflection off a tilted surface, we developed a model of this effect, which we term a distributed optical lever (Supplementary Fig. 1 and Supplementary Information)
By designing distributed optical levers to measure the deformation of each probe, we show that scanning probes can be parallelized as a path to improving the throughput of Atomic force microscopy (AFM) imaging

Summary

Introduction

Resolution and field-of-view often represent a fundamental tradeoff in microscopy. Atomic force microscopy (AFM), in which a cantilevered probe deflects under the influence of local forces as it scans across a substrate, is a key example of this tradeoff with high resolution imaging being largely limited to small areas. Optically reflective conical probes on a comparatively compliant film are found to comprise a distributed optical lever that translates probe motion into an optical signal that provides sub-10 nm vertical precision The scalability of this approach makes it well suited for imaging applications that require high resolution over large areas. To address the limited throughput inherent to serial patterning, a cantilever-free architecture has been explored, in which an array of probes rests on a compliant film on a rigid surface[21–24]. While this architecture endows the probes with the compliance needed for gentle probe–sample contact and a scalability affording up to millions of probes, the force-sensing capability afforded by the cantilever is lost. The high-throughput nature of this system makes it promising for application in fields where both high resolution and large areas are important, such as integrated circuit metrology, optical metasurface characterization, and multi-scale studies of biological tissue

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