Robust All-Carbon Molecular Junctions on Flexible or Semi-Transparent Substrates Using “Process-Friendly” Fabrication

Abstract

Large area molecular junctions were fabricated on electron-beam deposited carbon (eC) surfaces with molecular layers in the range of 2-5.5 nm between conducting, amorphous carbon contacts. Incorporating eC as an interconnect between Au and the molecular layer improves substrate roughness, prevents electromigration and uses well-known electrochemistry to form a covalent C-C bond to the molecular layer. Au/eC/anthraquinone/eC/Au junctions were fabricated on Si/SiOx with high yield and reproducibility and were unchanged by 10(7) current-voltage cycles and temperatures between 80 and 450 K. Au/eC/AQ/eC/Au devices fabricated on plastic films were unchanged by 10(7) current density vs bias voltage (J-V) cycles and repeated bending of the entire assembled junction. The low sheet resistance of Au/eC substrates permitted junctions with sufficiently transparent electrodes to conduct Raman or UV-vis absorption spectroscopy in either reflection or transmission geometries. Lithographic patterning of Au/eC substrates permitted wafer-scale integration yielding 500 devices on 20 chips on a 100 mm diameter wafer. Collectively, eC on Au provides a platform for fabrication and operation of chemically stable, optically and electrically functional molecules on rigid or flexible materials. The relative ease of processing and the robustness of molecular junctions incorporating eC layers should help address the challenge of economic fabrication of practical, flexible molecular junctions for a potentially wide range of applications.

Photocurrent, Photovoltage, and Rectification in Large‐Area Bilayer Molecular Electronic Junctions

“…Figure D displays the average JV behavior collected under vacuum of the four MJ structures in the present study with the observed RR values ( RR  | J −3.5 V / J +3.5 V |) of the bilayer MJs. All JV curves were observed to be similar to those previously reported, independent of scan rate in the bias region studied, and stable for at least thousands of JV scans. The bilayer JV curves require larger applied bias to achieve current densities similar to the single‐layer MJs due mainly to increased thickness.…”

“…Figure C displays a schematic energy level diagram for the bilayer BTB–AQ molecular device under zero bias showing the highest occupied (HOMO) and lowest unoccupied molecular orbitals (LUMO) of the BTB and AQ bilayer MJs (estimated with Gaussian 09 [B3LYP/6‐31G(d)] for the free molecules) with the electron beam deposited carbon (eC) electrode contacts. The eC Fermi levels are assumed equal to −4.8 eV versus vacuum, as determined previously …”

“…Absorbance spectra of AQ, BTB, AQ–BTB, and BTB–AQ are shown in Figure A for nonpatterned quartz/Cr 4 /Au 25 /eC 10 substrates to determine the single and bilayer optical absorption. The single layer of AQ exhibits a main absorption peak centered at 259 nm and a second smaller peak at 336 nm, while single layers of BTB exhibit strong absorption at 360 nm with a small feature at 257 nm. Absorption spectra of the AQ–BTB and BTB–AQ bilayers reveal two bands characteristic of the main peak of BTB and AQ, respectively, suggesting successful incorporation of both substituents in the bilayer with weak intermolecular electronic coupling.…”

“…A) UV–vis absorbance of Au/eC modified with AQ (red curve), BTB (blue curve), AQ–BTB (black curve), and BTB–AQ (green curve) after subtraction of substrate spectra . B) PC yield versus wavelength of molecular junctions containing AQ (red curve), BTB (blue curve), AQ–BTB (black curve), and BTB–AQ (green curve).…”

A Rotaxane Scaffold Bearing Multiple Redox Centers: Synthesis, Surface Modification and Electrochemical Properties

“…[1,2] Controlling the directionality of electron transfer inside or between macromolecules while keeping at the same time af ast signal transduction remains however ac hallenge. [1,2] Controlling the directionality of electron transfer inside or between macromolecules while keeping at the same time af ast signal transduction remains however ac hallenge.…”