Is it possible to produce electronic components whose size does not exceed that of a single molecule? And if we manage to integrate such components into electrical circuits, will they function similarly to the conventional, large materials, or will they perhaps have special properties that will allow the creation of completely new systems?
Dr. Oren Tal, who is currently establishing his new laboratory in the Department of Chemical Physics in the Faculty of Chemistry at the Weizmann Institute of Science, believes that the correct way to answer these questions is to investigate the most basic aspects of electron conduction through individual molecules. "We are interested in understanding the basic principles of electron conduction through nanostructures. Molecules are particularly interesting nanostructures, since the structure of the molecule, the atomic composition and the nature of the bond between the atoms can be well controlled. This property allows us to study the relationship between the structure of the molecule and the behavior of the electron current passing through it. A deep understanding of the relationship between structure and conduction will allow us to control the electronic current on the nanometer scale, and may even lead, in the future, to technological breakthroughs. In addition, it is possible that during the research we will even learn new things about the world we live in", says Dr. Tal.
To study the molecules, Dr. Tal must first capture them. For this purpose, he releases molecules into the space of an empty cell (vacuum), which is cooled to a temperature of four degrees above absolute zero (269 degrees Celsius below zero). His molecule trap is made of a metal wire attached to a flexible base. When the base is pushed from below, it bends, the wire stretches and breaks at a certain point - which was weak beforehand. As a result, a space opens between the two segments of the wire, the size of which allows the entry of one molecule.
By measuring the current passing through the wire, Dr. Tal can tell if a molecule has been caught in the space between the sections of the wire (the electrodes), and check what happens to it when electrons pass through it. Since the bending base makes it possible to control the distance between the electrodes with a precision of the order of a hundredth of an angstrom (an angstrom is one-tenth of a millionth of a millimeter), the resulting molecular bridge can be stretched, and the effect of stretching on conduction and even on the molecular vibrations can be examined. In fact, the captured molecule becomes part of an electrical circuit that includes the molecule and the two electrodes. How does the molecule affect the flow of electrons in the electric circuit? Do the properties of the molecule change, or the properties of the electrodes?
The molecules in Dr. Tal's experiments bind directly to the electrodes, and in many cases, the nature of the chemical bond created has a considerable effect on the conduction properties of the molecular bridge.
In his post-doctoral research, Dr. Tal studied simple molecules, such as hydrogen water and benzene. Since then, Dr. Tal and the research students in his laboratory, Tamar Yelin and Ran Vardimon, have progressed to more complex molecules, called oligoacenes, which consist of repeating units of carbon rings. The most basic molecule in this family, benzene, is a simple ring containing six carbon atoms. The benzene molecule slides between the electrodes perpendicular to them, and during the stretching of the molecular bridge it leans on its side, so that the overlap with the electrodes is small. This movement changes the conductivity of the molecule, similar to dimming. The use of oligoacenes makes it possible to study the conditions in which the conductivity of the molecular bridge is as high as the conductivity of metal atoms.
What makes the molecular bridge a better or worse conductor? In other words, what determines the passage of electrons through it? Each molecular bridge limits the flow of electrons through it to a number of conduction channels with limited conduction capacity. Dr. Tal identifies these channels using a special method, which allows him to "listen to the noise" created as a result of returning some of the electrons to the electrode from which they came.
Another study that Dr. Tal plans to carry out in his laboratory at the Weizmann Institute of Science is related to a new field - "spintronics". Spintronics is based on the use of the electronic spin feature in addition to the charge feature, for the purpose of creating electronic devices. The spin of the electrons can be in one of two states: up or down. Spintronic devices may be very efficient in terms of energy consumption and speed of operation, and above all allow operations that cannot be performed by normal electronic devices. To develop spintron circuits, scientists must develop a controlled way to control and maintain the spin states. Dr. Tal intends to capture molecules with interesting shapes, for example molecules with chiral symmetry. He believes that the movement of electrons in a screw-like structure may, under certain conditions, give priority to the conduction of spins of a certain state.
personal
Oren Tal grew up in Moshav Ramot-Hashavim. After completing a master's degree in chemistry at the Weizmann Institute of Science, he continued to study for a PhD in the electronic engineering department at Tel Aviv University, in the field of physical electronics. In his post-doctoral research, in the physics department at Leiden University, the Netherlands, Dr. Tal began his studies dealing with the capture of single molecules, with the aim of investigating their electrical properties. "I got to know three different fields of research - chemistry, engineering and physics - which are characterized by a different way of thinking, but the basic subject of the research - conduction of electrons in molecular structures - remains the same", he says.
Dr. Oren Tal is married to Shiri, and is the father of Jonathan, three years old, and Liya, one year old. His hobbies include the Japanese martial art of Aikido, painting and music.
