Prof. Aviad Frydman, of the Department of Physics and member of the Nano Magnetism Center at the Institute of Nanotechnology and Advanced Materials (BINA), has succeeded in fabricating narrow metallic, superconducting and magnetic wires and ultrathin films that exhibit unique electric and magneto-resistance properties.
In addition, Frydman’s group has developed a novel method to connect a single metallic or magnetic nanoparticle to large metallic leads with the ability to control the particle-lead coupling. Such a system can be used as a single electron transistor – a device which is extremely sensitive to small currents.
The electronic properties of the above structures – attributed to the quantum phenomena that govern the behavior of materials at a very small scale – make them excellent candidates for use in nano-scale elements in future nanoelectronics such as sensors and transistors.
In order to achieve high quality thin films, Frydman and his team use the “quench-condensation” technique, i.e. evaporation on a cryo-cooled substrate under UHV conditions within the measurement apparatus. Using this method they are able to study the properties of a single metallic/superconducting/magnetic film as a function of the amount of deposited material.
This is done while keeping the sample at low temperatures and in a UHV environment without having to thermally cycle it (risking metallurgical or structural changes due to annealing) or expose it to the atmosphere. The morphology of the quench-condensed layers depends strongly on the substrate properties. For thin enough films on a non-passivated substrate (such as Si or SiO), the layer takes the form of discontinuous grains with diameters of a few nm.
Quench condensing material on a passivated substrate (which is achieved by pre-depositing a monolayer of Ge or Sb on the substrates) results in a smooth uniform layer for ultra-thin films having thicknesses of 2-3 mono-layers of material.
Using advanced e-beam lithography techniques combined with angle evaporation methods, Frydman’s group fabricates wires as narrow as 10nm. Magnetic wires exhibit unique asymmetric magneto-resistance curves (R (H)= – R (-H).
Superconducting nanowires that are exposed to an ac bias source exhibit a dc voltage drop along the wire which is anti-symmetric with magnetic field and is characterized by sample specific quasi-periodic magneto-voltage oscillations. These structures are promising candidates for magnetic field and electromagnetic radiation sensors.
Combining Atomic Force Microscope nanoscribing and nanomanipulation with electrochemical methods, Frydman’s group fabricates systems of a metallic/magnetic particle coupled to large metallic electrodes in a MOSFET geometry.
This technique enables probing the current-voltage characteristics and conductance versus gate voltage of a nanoparticle while varying its distance to the leads. The electrical characteristics are sensitive to single electrons, making these devices promising for applications such as highly sensitive transistors and sensors.
Frydman and his team focus on the study of the electrical properties of low dimensional and nano systems, with an emphasis on nano-magnetism and nano-superconductivity. They are constantly involved in the development of new techniques to fabricate miniature devices and to connect them to the macroscopic world.
Their research goals are to better understand the basic science of the electric and magneto-electric properties on the nano-scale, and to develop future applications in the field of nano-electronics.