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CAMP Professor Sokolov investigates surface structures

CAMP Professor Igor Sokolov, from the Department of Physics at Clarkson University, is studying a variety of surface phenomena that occur at the molecular/atomic level. Much of Professor Sokolov's research involves modification and characterization of surfaces at the nanometer dimension. This work is of great importance to nanotechnology. Surface characterization generally involves Scanning Probe Microscopy (SPM), also known as Atomic Force (AFM) and Scanning Tunneling (STM) Microscopies. Brief descriptions of topics from Professor Sokolov's research are provided.

 

Atomic Structures on Crystalline Surfaces

The fast growing interest in nanotechnology increases attention to the study of materials at the molecular/atomic level. Scanning Probe Microscopy, a technique for this study, was invented fifteen years ago. It includes Scanning Tunneling Microscopy (STM) and Atomic Force Microscopy (AFM). The inventors of the STM received the Nobel Prize. Such a high regard for this technique was mainly due to its ability to directly visualize atoms. However, images can only be obtained on a conducting surface. The AFM technique, which can also be used on insulator surfaces, displays an "averaged" atomic picture which is an artifact of friction. Only five years ago, the AFM's ability to image individual atoms has been unambiguously demonstrated while scanning in an ultrahigh vacuum (UHV) in a so-called non-contact mode. However, difficulties of the UHV AFM experimental setup and lack of a clear understanding of the imaging mechanism have resulted in a limited number of successful observations by research groups. Simpler in use and broadly used commercially available AFMs, that can work in either liquid or ambient conditions in the so-called contact mode, are not known to be able to attain true atomic resolution. Recently Professor Sokolov suggested a new technique, which presumably can lead to true atomic resolution with a typical non-vacuum AFM working in liquids. The first experiments performed by Professor Sokolov have already showed its feasibility. This technique uses the electrical double layer (EDL) effect to decrease the interaction between an AFM tip and a sample below some critical value. Despite the success of the first experiments, the imaging mechanism is still not completely understood. Furthermore, experimental limitations and conditions for the use of the EDL technique have not been studied. This technique is new and no experiments in this field have yet been done in the United States. Professor Sokolov is developing the EDL technique to attain true atomic resolution on a typical commercially available AFM. His study focuses on the integral experimental and computational approaches in investigating the conditions of true atomic resolution under various imaging conditions. The computational part of this project will be done by means of atomistic computer simulations. Such a method has been successfully used to analyze 3D-force geometry in Atomic Force Microscopy. (See Figure 3.)

Figure. 3. The figure illustrates an example of attaining atomic resolution on the surface of anhydrite mineral (CaSO4) with the AFM. The right figure shows an experimental scan with a 2DFFT filtered patch in the top left corner. A scan simulation is presented in the figure to the left. As one can see, the simulated image and the experimental image are in very good agreement. Atoms of calcium, oxygen and sulfur are clearly visible.

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