A STABLE SCANNING TUNNELING MICROSCOPE DESIGNED FOR INVESTIGATIONS OFORGANIC THIN-FILMS IN AIR

A new and stable scanning tunneling microscope (STM) system has been c onstructed for the investigation of thin organic films in air. The STM unit is made of Macor, which is machinable ceramic and has a small th ermal expansion coefficient and a high mechanical stiffness. Three-dim ensional coarse position adjustment (within 3 mu m) is carried out usi ng five stacked piezoelectric transducers (PZTs). A cross-type configu ration is used to prevent the thermal effect of the x- and y-direction displacement mechanism. In order to achieve high resolution, x-, y-, and z-direction displacements are performed using a tube-type PZT. The z direction of the tube PZT has a high mechanical resonant frequency of 24.4 kHz. Therefore, this STM unit is mechanically rigid, and allow s stable operation under mechanical disturbances (sound and mechanical vibration). Moreover, this STM unit can be controlled for 24 h or lon ger by using an ordinary operational amplifier, because thermal effect s are compensated. The STM system can also be used to obtain informati on on the spatially resolved local tunneling barrier height, which is sensitive to the chemical structure of the sample. The capabilities of this newly designed STM are demonstrated with experiments investigati ng the morphology and tunneling barrier height of stearic acid thin fi lms on indium-tin-oxide substrates. (C) 1997 American Institute of Phy sics.