Electrical Conductivity Measurements for Single Molecules Neil Smith, and Jan M. YarrisonRice, Physi

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Electrical Conductivity Measurements for Single
Molecules Neil Smith, and Jan M.
Yarrison-Rice, Physics Department, Miami
UniversityArchana Jaiswal, Shouzhong Zou, Thomas
Scott and Hongcai Zhou, Chemistry Department,
Miami University
MIAMI UNIVERSITY CENTER FOR NANOTECHNOLOGY
Closing the Gap
Bulk Measurements of PDNC
Digit Design and Fabrication via E-Beam
Lithography
Fig 4 Contact pads connected with 30 µm thick
gold wires to package.
Fig 7 Bulk measurements are performed by
evaporating gold on to a glass slide about 16 nm
thick. The slide is then dipped into a solution
containing the molecule paradicyanobenzene (PDNC)
to form a monolayer about 1.5 nm thick. The top
two layers are evaporated through a mask.
Fig. 1 E-Beam Lithography is a multi step
process. 1) Apply a layer of resist, about 300
nm by spinning the resist onto the wafer 2)
Expose the patterns through E-Beam lithography
3) Develop Resist 4) Metal is then evaporated
onto the wafer through a thermal evaporation
method. Chromium 20 nm thick, Gold 180 nm thick,
total thickness of 200 nm. 5) Lift-off procedure
Fig 5 Through electrolysis, the 30 nm gaps can
be closed to 1 or 2 nm with Gold-Cyanide solution
Adding the Molecule
Fig. 2 GDSII design of digits with a 500 µm
contact pads and a designed gap of 75 nm
Fig 8 Current vs Voltage shows that this
molecule has rectification. In this case we have
a a positive rectification characteristics.
Fig 3 Exposed digits with a width of 800 nm and
a gap spacing of 30 nm a) Fingers with contact
pads, b) Close-up of gap where the digits meet
Note Because of proximity effects, the 75 nm
gaps closed to a distance of 30 nm
Fig 6 A single molecule, Re2(mp)4Cl2, will be
placed between the two digits using a thiolate
for the electrical conductivity measurements.
Note Raith 150 System 300 nm PMMA on Silicon
Wafer