No abstract

The development of novel photonic devices which incorporate biological materials is strongly tied to the development of thin film forming processes. Solution-based ("wet") processes when used with biomaterials in device fabrication suffer from dissolution of underlying layers, incompatibility with clean environment, inconsistent film properties, etc. We have investigated ultra-high-vacuum molecular beam deposition of surfactant-modified deoxyribonucleic acid (DNA). We have obtained effective deposition rates of ∼0.1−1 Å/s, enabling reproducible and controllable deposition of nanometer-scale films.Interest is continuing to increase 1-5 rapidly in the optical and electronic properties of DNA and other biopolymers and in related device applications. Usually, reports on these properties are either based on relatively thick films obtained by "wet" processes (such as spin-coating) techniques 6 or based on heroic efforts with single molecules. 7,8 In this paper, we report on the properties of nanometer-scale surfactantmodified DNA thin films formed by molecular beam deposition [9][10][11] (MBD). In general, polymers, unlike small molecule organic materials, do not usually lend themselves to MBD since their high molecular weight results in very low vapor pressures (and negligible deposition) up to their decomposition temperature. However, we have found that several types of complexed DNA can be deposited by MBD with subnanometer thin film control, thus opening the door to its incorporation in nanoscale devices. MBD is a thermal evaporation technique widely utilized in the fabrication of photonic devices based on compound semiconductors, where it is commonly known as molecular beam epitaxy (MBE) since the thin films have an epitaxial relationship to the substrate on which they are grown. This deposition technique takes place under high vacuum conditions, which allows the formation of a molecular beam (with a minimum of scattering) and results in deposition rates of the order of 1 Å/s for atomic or small molecule materials. The small furnace (or effusion cell) that holds the material to be evaporated is connected to the high vacuum chamber. The deposition rate is controllable with high precision over a wide range by adjusting the temperature of the effusion cell containing the material. An MBD chamber with several cells can be utilized for the sequential deposition of multiple materials for the formation of complex device structures. This in situ "dry" process in a high vacuum environment prevents the generation of defects by contamination of the materials or by particulate deposition from the environment, both of which can occur during wet processing.We have previously reported 12 on the first use of spincoated DNA complex films as electron "blocking" layers (EBL) in organic light-emitting devices (OLEDs), showing significant enhancement in both luminance and device efficiency over conventional device structures. In this paper, we report on the properties of nanometer-thin DNA-based films by the MBD technique.We...

Solutions and powders formed from salmon sperm deoxyribonucleic acid (DNA) reacted with the cationic surfactant cetyltrimethylammonium chloride (CTMA-Cl) incorporated fluorescent rhodamine molecules: anionic sulforhodamine 640 (SRh) or cationic/zwitterionic rhodamine 640 perchlorate (RhP). The role of the cationic surfactant in the interaction between rhodamine dye and DNA-surfactant molecules has been investigated in both solution and solid state using optical spectroscopy and electrophoresis. Unexpectedly, the dye molecules did not interact directly with DNA, rather the DNA double helix acted as a template for the interaction between dye molecules and CTMA in the DNA/CTMA complex. The SRh and RhP molecules yield different fluorescence characteristics with increasing DNA/CTMA amount, indicating different configurations between the CTMA ligands.

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