AIR OPERATING ATOMIC FORCE-SCANNING TUNNELING MICROSCOPE SUITABLE TO STUDY SEMICONDUCTORS, METALS, AND BIOLOGICAL SAMPLES

A scanning tunneling (STM)-atomic force microscope (AFM) operating at ambient pressure is described. A sound-isolated chamber contains the STM-AFM unit; the chamber can be evacuated or filled with inert gas, after the sample and tip (lever) are loaded, in order to reduce contamination on the sample. The STM-AFM unit consists of two separable cylindrical supports whose lower one contains the sample holder mounted on top of a piezoelectric scanner (movements 6×6×3 μm) that is contained in a motor controlled x-y-z stage (movements 8×8×1 mm). An I/V converter preamplifier for STM operation and a laser deflection circuit for AFM operation are separately mounted inside two different top cylinders. The STM top cylinder can be changed with the AFM one without removing the sample thus giving the possibility of looking at the same sample with STM and AFM. An optical microscope that can reach 120 enlargements allows us to position the tip or the lever on particular regions of the sample through the motor drives. A completely digitized feedback circuit allows fast sample-tip (lever) approach and simultaneous acquisition of constant force and lateral force images, for AFM operation, and constant current and barrier height ones, for STM operation. The same platinum grating has been imaged with STM and AFM. InGaAs wires onto a GaAs substrate and uncoated neurons have been imaged with AFM. © 1995 American Institute of Physics.