Optimal conditions for imaging in scanning tunneling microscopy: Theory

The scanning tunneling microscopy (STM) feedback system is analyzed to look for the optimal conditions for measurement. The typical feedback circuit normally used in STM and the parameters involved on it are studied, and their relative importance into the loop are discussed. The analysis of the role of each parameter demonstrated the importance of a detailed knowledge of the instrument to assure that the images obtained are reliable. We obtained equations that involve the main parameters of the loop, and yield the optimal conditions for imaging taking into account stability, signal amplitude, and phase shift. Combining the stability conditions with the imaging conditions obtained in this work, we found values for the feedback parameters to perform optimal STM measurements. Moreover, with this work, we highlight the importance to include in further publications the value of the main parameters used to obtain STM images. The conclusion of our work is that in some cases (in particular atomic resolution and fractal analysis! STM users should pay more attention to the setting of the instrument. (C) 1998 American Institute of Physics. pS0034-6748(98)02411-3].