Images and force measurements taken by an atomic‐force microscope (AFM) depend greatly on the properties of the spring and tip used to probe the sample’s surface. In this article, we describe a simple, nondestructive procedure for measuring the force constant, resonant frequency, and quality factor of an AFM cantilever spring and the effective radius of curvature of an AFM tip. Our procedure uses the AFM itself and does not require additional equipment.

Calibration of atomic‐force microscope tips

1. Introduction 2. Theoretical foundations 3. Propagation and focusing of optical fields 4. Spatial resolution and position accuracy 5. Nanoscale optical microscopy 6. Near-field optical probes 7. Probe-sample distance control 8. Light emission and optical interaction in nanoscale environments 9. Quantum emitters 10. Dipole emission near planar interfaces 11. Photonic crystals and resonators 12. Surface plasmons 13. Forces in confined fields 14. Fluctuation-induced phenomena 15. Theoretical methods in nano-optics Appendices Index.

/pdf/principles-of-nano-optics-1hz998yqo8.pdf

Principles of nano-optics

http://experimentationlab.berkeley.edu/sites/default/files/AFMImages/butt_AFM.pdf

Force measurements with the atomic force microscope: Technique, interpretation and applications

Molecular self-assembly presents a `bottom-up' approach to the fabrication of objects specified with nanometre precision. DNA
 molecular structures and intermolecular interactions are particularly
 amenable to the design and synthesis of complex molecular objects. We
 report the design and observation of two-dimensional crystalline forms
 of DNA that self-assemble from synthetic DNA double-crossover
 molecules. Intermolecular interactions between the structural units are
 programmed by the design of `sticky ends' that associate according to
 Watson-Crick complementarity, enabling us to create specific periodic
 patterns on the nanometre scale. The patterned crystals have been
 visualized by atomic force microscopy.

https://issg.cs.duke.edu/courses/spring04/cps296.4/papers/WLWS98.pdf

Design and self-assembly of two-dimensional DNA crystals

A method to determine the spring constant of a rectangular atomic force microscope cantilever is proposed that relies solely on the measurement of the resonant frequency and quality factor of the cantilever in fluid (typically air), and knowledge of its plan view dimensions. This method gives very good accuracy and improves upon the previous formulation by Sader et al. [Rev. Sci. Instrum. 66, 3789 (1995)] which, unlike the present method, requires knowledge of both the cantilever density and thickness.

/pdf/calibration-of-rectangular-atomic-force-microscope-290lry8thn.pdf

Calibration of rectangular atomic force microscope cantilevers

The adsorption of neutral molecules and ions on the surfaces of zeolites was observed in real time with an atomic force microscope (AFM). Direct imaging of the surface of the zeolite clinoptilolite was possible by using a diluted tert-butyl ammonium chloride solution as a medium. Images of the crystal in different liquids revealed that molecules could be bound to the surface in different ways; neutral molecules of tert-butanol formed an ordered array, whereas tert-butyl ammonium ions formed clusters. These absorbed molecules were not rearranged by the AFM tip when used in an imaging mode. However, when a sufficiently large force was applied, the tip of the AFM could rearrange the tert-butyl ammonium ions on the zeolite surface. This demonstration of molecular manipulation suggests new applications, including biosensors and lithography.

https://science.sciencemag.org/content/sci/247/4948/1330.full.pdf

Imaging and manipulating molecules on a zeolite surface with an atomic force microscope.

We have demonstrated that the atomic force microscope (AFM) operating in air may be used to pattern narrow features in resist in a noncontact lithography mode. A micromachined AFM cantilever with an integrated silicon probe tip acts as a source of electrons. The field emission current from the tip is sensitive to the tip-to-sample spacing and is used as the feedback signal to control this spacing. Feature sizes below 30 nm have been patterned in 65-nm-thick resist and transferred through reactive ion etching into the silicon substrate. We show that the same AFM probe used for noncontact patterning can be used to image the sample. In addition to eliminating the problem of tip wear, this noncontact system is easily adapted to multiple-tip arrays where each cantilever has an integrated actuator to adjust the probe height.

Noncontact nanolithography using the atomic force microscope

Force microscopy in liquids offers many advantages including the mitigation of capillary forces and the simulation of real environments for biological and technological processes. Noncontact force microscopy in liquids adds the advantage of probing electrical and magnetic fields above surfaces. Here we demonstrate magnetic force imaging of recorded bits on a computer hard disk in air and in liquid. A method of noncontact force microscopy (patent pending, Digital Instruments) is used in which the tip is first scanned in contact to image topography and then rescanned above the surface to image long‐range forces.Force microscopy in liquids offers many advantages including the mitigation of capillary forces and the simulation of real environments for biological and technological processes. Noncontact force microscopy in liquids adds the advantage of probing electrical and magnetic fields above surfaces. Here we demonstrate magnetic force imaging of recorded bits on a computer hard disk in air and in liquid. A method of noncontact force microscopy (patent pending, Digital Instruments) is used in which the tip is first scanned in contact to image topography and then rescanned above the surface to image long‐range forces.

Noncontact force microscopy in liquids

The atomic force microscope (AFM) has been successful imaging rigid samples with atomic resolution, but this resolution has not been matched on soft biological samples at room temperature. On many biological samples even tracking forces as small as 10−9 N distort the sample during a scan.At low temperatures proteins freeze into a single conformational state and become much more rigid. In this paper we demonstrate that it should be feasible to get atomic resolution on frozen biological samples with a low‐temperature AFM. We also show some preliminary low‐temperature AFM images of one biological sample, purple membrane.

Atomic force microscopy of biological samples at low temperature

We present atomic force microscope images of hydroxide and oxide formation on a gold surface obtained in perchloric acid electrolyte and under potential control. We find that the oxide is disordered over the Au(111) surface. Further, these images show that oxide formation on rough gold surfaces is accompanied by rapid annealing, most likely due to place exchange.

V. Elings

Papers

Imaging and manipulating molecules on a zeolite surface with an atomic force microscope.

Noncontact nanolithography using the atomic force microscope

Noncontact force microscopy in liquids

Atomic force microscopy of biological samples at low temperature

Electrochemistry on a gold surface observed with the atomic force microscope