The researchers worked with an organic light-emitting diode (OLED, organic light-emitting diode) operated by a simple and tiny circuit of microscopic size connected to a layer of organic material with a thickness of a single molecule located between a positive electrode and a negative electrode.
![A single layer of organic molecules connects a positive electrode to a negative electrode in a molecular junction of an organic light-emitting diode [Courtesy: Alexander Shestopalov/University of Rochester]](https://www.hayadan.org.il/images/content3/2014/05/shestopalov_nanodevice.jpg)
Chemical engineering professor Alexander Shestopalov of the University of Rochester has done just that and in doing so succeeded in advancing the science signal one more step closer to the development of nanoscale electrical circuits. "Until now, scientists have not been able to reliably direct the transfer of an electric charge from one molecule to another," says the researcher. "However, that's exactly what we had to do when we were working on electronic circuits that were one or two molecules thick."
The researchers worked with an organic light-emitting diode (OLED, organic light-emitting diode) operated by a simple and tiny circuit of microscopic size connected to a layer of organic material with a thickness of a single molecule located between a positive electrode and a negative electrode. Updated research papers have shown that it is difficult to control the current passing through such a tiny circuit between two electrodes. The solution, as explained by the researchers in an article published in the scientific journal Advanced Material Interfaces, was to add an additional, inert layer of molecules.
The inert (inactive) layer consists of a straight chain of organic molecules. On this layer are aromatic molecules (rings) that function as a wire for the conduction of electrons. The inert layer actually functions like the plastic covering found in electrical wires that insulates and separates the wires carrying live electricity from their surroundings. Since the lower layer is not able to react with the layer adjacent to it, the electronic properties of the entire array are determined solely by the upper layer.
The two-layer arrangement also gave the researchers the ability to adjust the degree of control over the passage of the charges. By changing the functional groups - those units of atoms that replace the hydrogen atoms in the molecule and determine the characteristic chemical reactivity of the molecule - the researchers were able to more precisely control the rate at which the electron flow passes between the electrodes and the upper layer of the organic molecules.
In the field of molecular electronic devices, certain functional groups accelerate the transfer of charges, while others delay the rate. With the help of adding the inert layer, the researchers were able to reduce the chemical interference of the upper layer, and as a result, achieve the exact and required charge transfer rate by changing the nature of the functional group.
For example, an organic light emitting diode may require a faster rate of charge transfer in order to maintain a defined level of luminescence, while a biomedical injection device may require a slower rate in delicate or variable procedures.
Although the researchers managed to overcome a significant setback, much work remains before bilayer molecular electronic devices can become a practical product. The next failure is the level of stability of the device. "The system we developed breaks down quickly at high temperatures," says the lead researcher. "We need to develop stable standards for years, a task that will continue for a long time."
