Fig 10: I-V characteristics of Au/PDNC/Al/Au junction. This shows that the molecule has rectification towards the positive bias. Current (A) M I A M I U N I V E R S I T Y C E N T E R F O R N A N O T E C H N O L O G Y Digit Design and Fabrication via E-Beam Lithography Bulk Measurements of PDNC Fig 10 : This is chemical depiction of PDNC with one side connected to a gold metal surface. This molecule will bond to the surface perpendicularly or at a very small angle. This complex will be used to bond the paddlewheel complexes at the axial positions. Summary We have successfully fabricated Cr: Au electrodes on thermally oxidized silicon wafers with repeatable gaps of 35 nm using e-beam lithography and thermal deposition. Through electro chemical synthesis, we try to close the gaps to a size of 2 or 3 nm. Bulk measurements have been completed on similar molecules With an Au/ Al-Au contact pad, asymmetric I-V curves are observed with rectification toward the positive bias. With only an Au/Au contacts, a macular wire behavior is observed A shift in the C=N Raman peak was observed when the C=N junction was made with metal We gratefully Acknowledge the support of NFS through the NER-ECS Grant For more information contact Jan Yarrison-Rice at Fabrication of Single Digit Electrodes by E-Beam Lithography for Coupled Raman Spectroscopy and Electrical Conductivity Measurements of Single Molecules Neil Smith, and Jan M. Yarrison-Rice, Physics Department, & Archana Jaiswal, Shouzhong Zou, Thomas Scott and Hongcai Zhou, Chemistry Department, Miami University In order to assemble nanoscale devices based on molecular electronics, an understanding of the basic physics and chemistry that occurs on a nanometer length scale must be gained. The objective of this research is measure the conductivity of single molecule wires with a metal-metal bonds. Ultimately, other devices, such as diodes, transistors and light activated switches, can be developed using single molecules. Note: Because of proximity effects, the 75 nm gaps closed to a distance of 30 nm Closing the Gap Fig 4: Contact pads connected with 30 μm thick gold wires to package. +V -V Fig 5: Through electrolysis, the 30 nm gaps can be closed to 1 or 2 nm with Gold-Cyanide solution Adding the Molecule [Note: Raith 150 System: 300 nm PMMA on Silicon Wafer] Fig. 2: GDSII design of digits with a 500 μm contact pads and a designed gap of 75 nm 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 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 Fig 6: The molecule on the left is Di-Di-chloro-tetra(μ2-2-mercaptopyridine)- di-rhenium(III) (abbreviated by Re2(mp)4Cl2). The molecule on the right is Di-chloro-tetra(μ2-2-mercaptopyridine)-di-platinum(III) (abbreviated by Pt2(mp)4Cl2 ). These are the two molecule which are proposed to be placed between the electrodes for the molecular transistor. Re2(mp)4Cl2 is a quadruple bond while the Pt2(mp)4Cl2 is only a single bond. Exposed Resist Silicon Dioxide PMMA Silicon Prepared Silicon Wafer Final Design Developed Resist Evaporate Metal Fig 7: This is a chemical depiction of the thiol-actate group directly connected between gold electrodes on either side and an Re2(mp)4Cl2 molecule. Fig 8: 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 nm thick. The top layer is evaporated through a mask. The top layer consists of either an Au layer or an Au/Al layer. Each contact pad is round with a diameter of 0.5 mm, and is in contact with about 5 x molecules. I-V characteristics are obtained by applying voltage to the top and bottom layers of gold. The Raman spectra are collected through the back scattering light. Gold Digits Glass Slide Au Layer (~16 nm) PDNC (~1.5 nm) Au Layer (~8 nm) Al Layer (~10 nm) v Ga /In A Fig 9: I-V characteristics of Au/PDNC/Au junctions. The I-V curve shows behavior found in many types of molecular wires. Current (A) Fig 11: Raman spectra of PDNC on Au: (1) before top electrode; (2) after 15 nm top Au layer; (3) after top Al (8 nm) + Au (10 nm) layer deposition. Both the α and γ peaks come from the benzene ring of the molecule while the β peak comes from the fluoresces of the glass slide which the sample was made on. α β γ Fig 12: Focusing on the C=N junction, a peak is observed at 2180 cm -1 (Raman line #1). Once a layer of gold was added to the top of the molecule, the peak shifted by 10 cm -1 to 2191 cm -1 (Raman line #2). The peak was further shifted when an Au/Al layer was added on top of the molecule to 2203 cm -1 (Raman Line #3) a) b)