Jin He
Assistant Professor Research
Ph.D. (ASU Physics, 2005)
Home Department SMB, the Biodesign Institute
Areas of Study Molecular Electronics, Single molecule charge transport, Biomolecule imaging, Nanofludic
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Background Single-molecule conductance measurement is critical to fundamental research as well as applications like molecular electronics. From a fundamental view, this topic is essentially a continuation of several decades of electron transfer research of donor-molecule-acceptor system. From an application view, it's of great interest to explore the capabilities of molecules as building blocks in future nano-electronics. The main technique for single molecule conductance measurement is STM break junction method. Briefly, a break-junction is formed repeatedly by pushing a gold probe into the Au (111) substrate(covering molecules with sticky groups at both ends) and recording the current vs. time as the probe is withdrawn. Steps in the trace of current vs. time correspond to integer numbers of molecules trapped in the gap. Histograms are built based on thousands of such traces. The peaks in the histograms give the single molecule conductance value. Recently, I mainly studied the charge transport of Au-redox molecule-Au junctions immersed in an electrolyte using STM. A large gate field (on the order of 1V/Ǻ) can be achieved in an electrolyte because the gate voltage falls across sub-nanometer thick double layers at the electrode-electrolyte interfaces. By using electrochemical gating, we can change the alignment of electronic levels effectively. A huge conductivity enhancement was observed on studied redox molecules when the probe locally addressed a molecule which had its molecular orbital(s) aligned with the Fermi level by an electrochemical field.

Schematic of STM break junction method
team-he.jpe
Jin He
1001 S. McAllister
Tempe, AZ 85287-5

phone: 480-727-0427
fax: (480) 727-2378
email: jinhe@asu.edu
[Publication] He J, Chen F, Nuckolls C, Lindsay SM Length Dependence of Charge Transport in Oligoanilines Appl. Phys. Lett. accepted (2007)
[Publication] He J, Fu Q, Lindsay SM, Ciszek JW, Tour JM The Electrochemical Origin of Voltage-Controlled Molecular Conductance Switching J. Am. Chem. Soc., 128 (46): 14828-14835 (2006)
[Publication] Li XL, He J, Hihath J, Xu BQ, Lindsay SM, Tao NJ Conductance of Single Alkanedithiols: Conduction Mechanism and Effect of Molecule-Electrode Contacts J. Am. Chem. Soc., 128(6); 2135-2141 (2006)
[Publication] He J, Lindsay SM. On the mechanism of negative differential resistance in ferrocenylundecanethiol self-assembled monolayers J. Am. Chem. Soc.(Communication); 127(34); 11932-11933 (2005)