Evaluating of Energy Gap in Single Molecular Device

Abstract

We developed a metrology approach for single molecular device for performance analysis of molecular nanoelectronics devices to probe the energy gap in single molecular devices. Molecular Nanoelectronics technologies at early time were very immature both on technological and scientific levels. The closeness of energy of the high occupied molecular orbital - low unoccupied molecular orbital (HOMO-LUMO) energy gap was detected by electric (\(\Phi\)_B^\(\sum\)) and optic measurements (\(\Delta\)o), \(\Phi\)_B^\(\sum\) \(\approx\) \(\Delta\)o. The ‘electrical gap’, \(\Phi\)_B^\(\sum\), consists of sum of two barriers, \(\Phi\)_B^LUMO and \(\Phi\)_B^HOMO, for tunneling of electrons and holes through molecular barrier correspondingly, in devices with a different pair of electrodes at low biases and difference in work function, \(\Delta\)WF, between these metal electrodes: \(\Phi\)_B^\(\sum\) = \(\Phi\)_B^LUMO + \(\Phi\)_B^HOMO+ \(\Delta\)WF. We created and examined two devices using a pair of of gold (Au) and aluminum (Al) electrodes to find \(\Phi\)_B^HOMO (\(\Phi\)_B^Au) and \(\Phi\)_B^LUMO (\(\Phi\)_B^Al) using Simmons tunneling model. The symbols \(\Phi\)_B^LUMO and \(\Phi\)_B^HOMO signify difference in energy between HOMO and LUMO levels in a molecular system with respect to the Au and Al electrode’s Fermi level. In nanoscale devices, Comparison of \(\Phi\)_B^\(\sum\) and \(\Delta\)o can reveal the presence of electrically active molecules between electrodes.