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Quantitative Electrical Measurements


Discussion T e ResiScope mode for AFM resistance measurements provides an unprecedented range, spanning ten decades from 10 2 to 10 12 ohms. Because of the system confi guration, the current between the sample and probe is limited, minimizing current leakage and local oxidation. Typically conductive AFM techniques only use amplifi ers to measure a current with a constant bias applied. T e ResiScope module is confi gured to auto-calibrate when the system is started, using internal precision resistors as references. No other system has this capability. T e Soſt ResiScope mode is the only commercial system providing quantitative electrical characterization on soſt or compliant samples. Other systems would require a higher force and cause damage. In the Soſt ResiScope mode, the tip is held at a point long enough to make an electrical measurement so that the data is quantitative. It is also semi-oscillating so the sample is not damaged. Using the Nano-Observer AFM with the ResiScope module, data is acquired with a constant and controlled force while taking quantitative resistance and current measurements.


Conclusions


Quantitative resistance and current data can be measured using a ResiScope module with a Nano-Observer AFM. T e ResiScope overcomes previous limitations of electrical AFM measurements including friction interference, lack of quanti- tative measurements, diffi culties measuring soſt materials, and limited resistance range. Because the current between the sample and probe is limited, the conductive probe is protected from


high-current damage. Soſt or compliant samples cannot be imaged successfully in contact mode, whereas the Soſt ResiScope mode for electrical characterization can image these materials. Hard samples were imaged to confi rm that data from the standard and Soſt ResiScope modes are equivalent. A soſt polymer was imaged and measured to illustrate the eff ectiveness of the Soſt ResiScope mode. It is also possible to take multiple measurements simultaneously or consecutively when the ResiScope and Nano-Observer AFM are used in combination. Analyses of multiple measurements provide an excellent illustration of why there are diff erent AFM imaging modes. Topography imaging alone does not always provide the answers that researchers need, and the data oſt en do not correlate to the material properties. For these reasons, advanced imaging and Soſt ResiScope modes have been developed to provide quanti- tative data on a variety of surfaces.


Acknowledgements T anks for fruitful discussions and data from Louis Pacheco at Concept Scientifi c Instruments.


References [1] G Binnig et al ., Phys Rev Letters 56 ( 1986 ) 930 – 33 . [2] RC Barrett and CF Quate , J Appl Phys 70 ( 5 ) ( 1991 ) 2725 – 33 .


[3] U Hartmann , Journal of Magnetism and Magnetic Materials 157 ( 1996 ) 545 – 49 .


[4] M Nonnenmacher et al ., Appl Phys Lett 58 ( 1991 ) 2921 – 23 . [5] S Gunes et al ., Chem Rev 107 ( 2007 ) 1324 – 38 .


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