Use of Langmuir Blodgett Thin Films in Tunnel Diodes for Energy Harvesting or Sensing Applications

Tunnel diodes have been found suitable for use in high frequency rectification for energy harvesting or sensing applications in structures known as rectennas. For tunneling to take place in a metal insulator metal (MIM) type assembly, an ultrathin pinhole free insulating layer must be deposited between the metal layers for the diode to operate with small turn on voltages.

Langmuir Blodgett (LB) thin film deposition is a useful technique that allows the deposition of conformal, uniform monomolecular layers with a precise control of thickness. Organic compounds such as Vinyl Stearate, 10-12 Pentacosadiynoic Acid (PDA), Arachidic Acid and Porphyrin were considered for deposition onto a Nickel film and were later topped with a small metal contact to complete the metal insulator metal diode assembly.

Optical, electrochemical and electrical characterization were performed to check the quality of deposition of the thin insulator film and to analyze its material properties. Specifically, UV spectroscopy, atomic force microscopy and infrared spectroscopy techniques were utilized for this purpose. An electrochemical study was performed with the insulating monolayers deposited using the LB method on an Indium Tin Oxide coated glass substrate.

Picoammeter measurements on the metal insulator metal junctions showed improved tunneling characteristics with fewer pinholes in the film after UV initiated  polymerization. This was possible due to the intermolecular crosslinking in the film which was induced by the UV exposure. This was confirmed with the detection of more pronounced peaks at C=C vibration frequencies.