Adsorption of organic molecules on surfaces of semiconductors and metals are expected as a method to produce new electronic devices.It is well-known that Nucleo-base have some characteristic; 4 species that A,C,G and T or U . It memorize genetic information by combination to make with its 4 kinds as DNA or RNA. Therefore when we can align them up on surface of semiconductor and metal, we expect to use it as a storage device to utilize memory system what DNA have like one of double chain of DNA and RNA.
Silicon combine to genetic molecules by using covalent bond and cohesive strength is stronger than that of metals. Moreover, distance between dimer on Si(001) surface is 3.8Å and nearly distance between Nucleobase 3.5Å in DNA. Therefore aligned nucleobase can be expected to use as genetic information storage similar to DNA.
In this paper, we calculated adsorption structure Adenine and Cytosine of Nucleobase on Si(001) surface using the first principles calculation. The total-energy and electronic-structure calculations are performed using the Simulation Tool for Atom TEchnology (STATE) implementation of the gradient-corrected density functional theory (DFT-GGA). The electron–ion interaction is described by non-normconserving ultrasoft pseudopotentials, allowing for the accurate quantum-mechanical treatment of first-row elements with a relatively small basis set of plane waves. We expand the electronic wave functions into plane waves up to an energy cutoff of 30 Ry.
The Si(001) surface is modeled with a periodically repeated slab. The supercell consists of 6 atomic Si layers plus adsorbed molecules and a vacuum region equivalent in thickness to 11 atomic layers. The atomic configuration of topmost five layers of the slab as well as the adsorbed molecules are allowed to relax. The Si bottom layer is saturated with hydrogen and kept frozen during the structure optimization.
We found that Adenine adsorbed on a dimer of Si(001) with alignment similar to that in DNA as shown in the figure. Thus, we can apply the adsorption of Adenine as one monolayer coverage of Adenine on Si(001) substrate. However, for Cytosine, the similar alignment is not most stable.
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