With the development of the information industry, computer chips play a central role in information storage and have become highly integrated. Currently, there is increasing interest in the use of organic and polymer materials as nonvolatile memory elements.[1] Organic nonvolatile memory is a possible substitute for volatile dynamic random access memory (DRAM), which typically requires a data refresh every few milliseconds, and has the advantage of very low power consumption. However, limitations of the nanoscaled device fabrication of vapor-deposited organic resistive random access memory (ORRAM) [2] and spin-coated polymer resistive random access memory (PORAM) [3] have led to increased importance of molecular monolayer memory using organic self-assembled monolayers (SAMs). Several research groups have developed possible voltage-driven molecular memory devices possessing the advantages of fast response time and highly dense circuits over a photodriven circuit, [4] using a molecular monolayer for metal-molecule-metal (MMM) devices.[5] However, the use of molecular monolayers has been limited by low device yields, which are mainly attributed to electrical shorting, [6] especially for voltagedriven devices. As the top metal electrode is deposited onto the molecular monolayer, energetic metal atoms can degrade the SAM molecules, [7] and metal particles often penetrate the molecular monolayers to form metallic current paths.[8] To reduce the degree of electrical shorting, the following issues have been considered: the compactness and robustness of Langmuir-Blodgett (LB) films [9] and SAMs; [10] the use of bilayer SAMs; [11] a metal electrode with a nanosized surface area; [12] reduction of the surface roughness of the metal electrode;[13] a Pd nanowire [14] or single-walled carbon nanotube [15] as a substitute for the top metal electrode; and the use of a conducting polymer layer (PEDOT:PSS) [16] as a soft portion of the top metal electrode on the molecular monolayer. Although various prototype molecular monolayer memory devices, including a photodriven example, [4] have been introduced, there are very few reports on molecular monolayer nonvolatile memory (MMNVM). For the fabrication of MMNVM, the design of redox-active molecular memory SAM materials becomes a critical factor, especially for the development of a voltage-driven MMNVM that requires direct contact measurement of the memory effect through a molecular monolayer between the bottom and top electrodes. It was recently demonstrated by scanning tunneling microscopy (STM) that Ru II terpyridine complexes without alkyl chains-metal-to-ligand charge-transfer (MLCT) complexes-have a voltage-driven molecular switch in the solid-state molecular junction. [17] In the fabrication of a molecular monolayer memory device, however, the direct use of Ru II terpyridine complexes without alkyl chains results in electrical shorting. In an implementation of molecular monolayer memory circuits with high yield, it is important to reduce the electrical shorting by modifying the...

With the development of the information industry, computer chips play a central role in information storage and have become highly integrated. Currently, there is increasing interest in the use of organic and polymer materials as nonvolatile memory elements. [1] Organic nonvolatile memory is a possible substitute for volatile dynamic random access memory (DRAM), which typically requires a data refresh every few milliseconds, and has the advantage of very low power consumption. However, limitations of the nanoscaled device fabrication of vapor-deposited organic resistive random access memory (ORRAM) [2] and spin-coated polymer resistive random access memory (PORAM) [3] have led to increased importance of molecular monolayer memory using organic self-assembled monolayers (SAMs). Several research groups have developed possible voltage-driven molecular memory devices possessing the advantages of fast response time and highly dense circuits over a photodriven circuit, [4] using a molecular monolayer for metal-molecule-metal (MMM) devices. [5] However, the use of molecular monolayers has been limited by low device yields, which are mainly attributed to electrical shorting, [6] especially for voltagedriven devices. As the top metal electrode is deposited onto the molecular monolayer, energetic metal atoms can degrade the SAM molecules, [7] and metal particles often penetrate the molecular monolayers to form metallic current paths. [8] To reduce the degree of electrical shorting, the following issues have been considered: the compactness and robustness of Langmuir-Blodgett (LB) films [9] and SAMs; [10] the use of bilayer SAMs; [11] a metal electrode with a nanosized surface area; [12] reduction of the surface roughness of the metal electrode; [13] a Pd nanowire [14] or single-walled carbon nanotube [15] as a substitute for the top metal electrode; and the use of a conducting polymer layer (PEDOT:PSS) [16] as a soft portion of the top metal electrode on the molecular monolayer. Although various prototype molecular monolayer memory devices, including a photodriven example, [4] have been introduced, there are very few reports on molecular monolayer nonvolatile memory (MMNVM). For the fabrication of MMNVM, the design of redox-active molecular memory SAM materials becomes a critical factor, especially for the development of a voltage-driven MMNVM that requires direct contact measurement of the memory effect through a molecular monolayer between the bottom and top electrodes. It was recently demonstrated by scanning tunneling microscopy (STM) that Ru II terpyridine complexes without alkyl chains-metal-to-ligand charge-transfer (MLCT) complexes-have a voltage-driven molecular switch in the solid-state molecular junction. [17] In the fabrication of a molecular monolayer memory device, however, the direct use of Ru II terpyridine complexes without alkyl chains results in electrical shorting. In an implementation of molecular monolayer memory circuits with high yield, it is important to reduce the electrical shorting by modifying...