Dual tunneling-unit scanning tunneling microscope for practical length measurement based on reference scales

A new setup of dual tunneling-unit scanning tunneling microscope (DTU STM) has been developed that can realize simultaneous calibration between test s ample images and standard reference scales. The crystalline lattices and pe riodic grating features are employed as such scales for practical length me asurements, respectively, in the nanometer and the micron orders. The DTU S TM consists of a reference unit and a test unit horizontally set in paralle l to eliminate Abbe's errors. Their probe tips are attached to one single X Y scanner on the same surface, while the reference and test sample holders are open. As the tips scan over the sample surfaces, two images with the sa me lateral size are simultaneously acquired. Line lengths in the test image could be measured by counting the number of crystalline lattices or gratin g patterns in the reference side. Two vertical impact drive mechanisms were applied to coarsely positioned samples in the Z direction. Another two imp act drive mechanisms were employed to the horizontal drive sample holders a s to automatically position the samples in the lateral plane. We present a brief discussion about the concept and setup of the DTU STM. Some compariso n results using crystalline lattices and grating patterns, respectively, as reference scales for length calibration are provided. Experiments show a s atisfactory matching between the two tunneling units when covering a wide s can range from 5 nm to 10 mum. With its new setup, the DTU STM is confirmed to be a more accurate device for practical length measurement even when me asuring comparatively large and heavy samples. (C) 2000 American Vacuum Soc iety. [S0734-211X(00)04706-5].