R. Luna, D. Runsewe, N. Austin-Bingamon, D.C. Binod, T. Betancourt, Y. Miyahara
Texas State University,
United States
Keywords: DNA, charge transfer, molecular electronics, electrostatic force microscopy
Summary:
Interest in the use of single molecules in nano-electronics has grown in recent years. Their nanometer size, unique properties, and ability to form complex structures make single molecules natural choices for the creation and innovation of future nano-devices. Of the many molecules currently being studied, DNA has emerged as a promising building block for the use in molecular nano-electronics due to its programmable nature, rapid production, and potential for charge transfer. While attempts at characterizing the electrical properties of individual DNA molecules have been previously performed, there remains disagreement among the scientific community regarding the classification of DNA molecules as an electronic material. Much of this disagreement can be attributed to the use of varying methodologies, as well as due to potential contact and deformation of the DNA molecule being probed. In this work we present a non-invasive method for characterizing charge transfer at the molecular scale using Atomic Force Microscopy (AFM). We then use this method to characterize charge-transfer across hybridized DNA molecules with gold nano particles (GNP) attached at one end. For the work herein, we measured three DNA strands, each with a distinct sequence and an increasing number of guanine-cytosine base pairs. Energy spectrums and subsequent tunneling rate values were obtained for all three strands. These tunneling rates ranged from 0.1 - 0.6 MHz with no cytosine-guanine base pairs to 1-5 MHz with increasing cytosine-guanine base pairs. The results obtained showed a clear distinction in the charge-transfer rates between all three strands, highlighting the effectiveness of the technique to individually probe different molecules. The method used involved a biased AFM tip being brought close to and oscillated near the GNP attached to the target DNA. This oscillation of the tip allows for the oscillation charging energy levels of the GNP. With proper control of the amplitude and voltage, the coulomb blockade within the GNP can be overcome, allowing single electron charging to occur across the DNA molecules. These charging events are then measured and quantified via the use of Electrostatic Force Microscopy (EFM) at cryogenic temperatures​​. Moreover, the method used herein can be used while scanning, allowing for measurement and creating of high-resolution maps of charging behavior across a given sample surface, wherein various devices could be placed. As this method relies on the single-electron charging of the nano particle attached, it can easily be adapted to study the energy structure of semiconductor nano particles.