developments

The development of AFM tools has been a constant throughout my career, from my beginnings at Nanotec to the present. This includes both instrumental and methodological developments. Below I show some of the most relevant examples of both types.

INSTRUMENTATION

1. High Vacuum AFM (Nanotec) 2. VF-MFM (Nanotec) 3. AFM for liquids (Nanotec) 4. AFM add-ons for electrochemistry (Nanotec)

5. AFM with bottom optical access (UAM) 6. Multiplatform AFM (UoM) 7. Nanofluidics sample holder with temperature control (UoM)

8. Variable-temperature ambient-controlled motorized Probe Station (UAM)

AFM setup for simultaneous inverted optical microscopy techniques, in particular, AFM and Total Internal Reflection Fluorescence Microscopy (TIRFM). TIRFM uses an evanescent wave to selectively illuminate and excite fluorophores in a region of the specimen immediately adjacent to a glass substrate-liquid interface. The AFM/TIRFM combination was carried out in collaboration with Prof. Julio Gómez-Herrero and Dr. Pedro J. de Pablo’s groups. The setup includes fully motorized laser and photodiode alignments, as well as tip-sample approach and optical focus. One of the main advantages of the developed setup, compared to other AFM configurations compatible with inverted optical microscopy, is an enhanced resolution thanks to improvements on the stiffness of the setup. This was achieved by minimizing the mechanical loop (the distance between the structural elements that are required to hold the probe at a fixed distance from the sample), which reduces the mechanical noise.

METHODOLOGICAL

1. Exfoliated graphite flakes soft-electrodes (UAM) 2. MFM in liquids (UAM) 3. Nanowire electrodes (UAM)

4. WSxM Flatten Plus (Nanotec) 5. Jumping Mode+ (Nanotec)

Scanning-Probe-Assisted Nanowire Circuitry (SPANC), new technique for fabricating nanoelectrodes for the characterization of electrical transport properties at the nanoscale. We use an AFM tip to manipulate gold nanowires (∼50 nm in diameter and 5 µm in length) and join them together by cold welding. This way we form highly conductive complex reconfigurable nanostructures, which allow the electrical connectivity and characterization of other nano-objects in a clean and simple way, since this technique does not require the use of polymers or chemicals.

Magnetic Force Microscopy in liquids. MFM in liquids was a challenge as a consequence of the low quality factor (Q) of the cantilever resonance characteristic of liquid measurements. This low Q results in a significant loss of sensitivity in the MFM signal. We first used commercial MFM cantilevers and, despite an expected reduction in the signal-to-noise ratio, we detected the magnetic contrast in liquid showing a good lateral resolution.

We later demonstrated that the Focused Electron Beam Induced Deposition (FEBID) of magnetic nanorods on cantilevers optimized for measurement in liquids leads to outstanding MFM performance in a liquid environment, for which no commercial alternatives are available.

In total, these findings open up new avenues for investigating biological samples in a physiological medium, a key aspect for the development of new applications in nanobiology and nanomedicine.