Sean N. Natoli

Redox-Active Molecular Nanowire Flash Memory for High-Endurance and High-Density Nonvolatile Memory Applications

In this work, high-performance top-gated nanowire molecular flash memory has been fabricated with redox-active molecules. Different molecules with one and two redox centers have been tested. The flash memory has clean solid/molecule and dielectric interfaces, due to the pristine molecular self-assembly and the nanowire device self-alignment fabrication process. The memory cells exhibit discrete charged states at small gate voltages. Such multi-bit memory in one cell is favorable for high-density storage. These memory devices exhibit fast speed, low power, long memory retention, and exceptionally good endurance (>10(9) cycles). The excellent characteristics are derived from the intrinsic charge-storage properties of the protected redox-active molecules. Such multi-bit molecular flash memory is very attractive for high-endurance and high-density on-chip memory applications in future portable electronics.

Engineering Chemically Exfoliated Large‐Area Two‐Dimensional MoS2 Nanolayers with Porphyrins for Improved Light Harvesting

Molybdenum disulfide (MoS2 ) is a promising candidate for electronic and optoelectronic applications. However, its application in light harvesting has been limited in part due to crystal defects, often related to small crystallite sizes, which diminish charge separation and transfer. Here we demonstrate a surface-engineering strategy for 2D MoS2 to improve its photoelectrochemical properties. Chemically exfoliated large-area MoS2 thin films were interfaced with eight molecules from three porphyrin families: zinc(II)-, gallium(III)-, iron(III)-centered, and metal-free protoporphyrin IX (ZnPP, GaPP, FePP, H2 PP); metal-free and zinc(II) tetra-(N-methyl-4-pyridyl)porphyrin (H2 T4, ZnT4); and metal-free and zinc(II) tetraphenylporphyrin (H2 TPP, ZnTPP). We found that the photocurrents from MoS2 films under visible-light illumination are strongly dependent on the interfacial molecules and that the photocurrent enhancement is closely correlated with the highest occupied molecular orbital (HOMO) levels of the porphyrins, which suppress the recombination of electron-hole pairs in the photoexcited MoS2 films. A maximum tenfold increase was observed for MoS2 functionalized with ZnPP compared with pristine MoS2 films, whereas ZnT4-functionalized MoS2 demonstrated small increases in photocurrent. The application of bias voltage on MoS2 films can further promote photocurrent enhancements and control current directions. Our results suggest a facile route to render 2D MoS2 films useful for potential high-performance light-harvesting applications.

Stepwise Synthesis of Bis-Alkynyl CoIII(cyclam) Complexes under Ambient Conditions

Reported herein is a new synthetic method for the synthesis of Co(III)(cyclam) bis-alkynyls (cyclam = 1,4,8,11-tetraazacyclotetradecane) under aerobic conditions. Upon the treatment of AgOTf in acetonitrile, complex trans-[Co(cyclam)(C2C6H4NMe2)Cl]Cl (1) was converted to trans-[Co(cyclam)(C2C6H4NMe2) (NCMe)](OTf)2 (2), and 2 was in turn reacted with HC2Ar under weakly basic conditions to afford the novel bis-alkynyls trans-[Co(cyclam)(C2C6H4NMe2)(C2Ar)](OTf) (Ar = C6H4NMe2 (3) and C6F5 (4)) in reasonable yields. Voltammetric analysis revealed a modest NMe2/NMe2 coupling across the Co-alkynyl backbone in 3, while DFT calculations identified the HOMO in 3 as the superexchange pathway for such coupling.

Turning a New Leaf on Metal-TMC Chemistry: Ni(II)(TMC) Acetylides.

Novel [Ni(TMC)C≡CY](+)-type compounds 1-4 [TMC = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane; Y = SiMe3 (1), Si(i)Pr3 (2), Ph (3), and C2H (4)] have been synthesized and characterized. Single-crystal X-ray diffraction studies revealed that these compounds adopt a distorted square-pyramidal geometry, with the acetylide ligand occupying the apical position and a RSRS isomer for the TMC ligand. The room temperature magnetic properties of 1-4 are consistent with an S = 1 ground state, as corroborated by CASSCF and density functional theory calculations, which indicate that the singly occupied molecular orbitals are d(z(2)) and d(x(2)-y(2)).

Correction to Redox-Active Molecular Nanowire Flash Memory for High-Endurance and High-Density Nonvolatile Memory Applications.

where q is the elementary charge, N is the total charge stored in the redox centers, CRedox is the total capacitance arising between the redox centers and the metal gate, CAlO is the capacitance of the Al2O3 layer, εAlO is the dielectric constant of Al2O3, L is the channel length, tAlO‐out and tAlO‐in are the distances from the center of Si nanowire to the outside and inside surfaces of the Al2O3 layer. We neglect the contribution of the molecular component between the redox center and the Al2O3 because it is only about 0.5 nm, which is significantly shorter than the Al2O3 (25 nm). The charge density calculated for the ferrocene molecular flash memory is around 4.97 × 10 cm−2, which is still comparable to the results obtained from the capacitor structure. The overall charge density of the Ru2 SAM calculated with the same equation by using the ΔVth at the second charged state is around 5.74 × 10 cm−2. Even though this charging density is about 20% of the coverage density of Ru2 molecules obtained from the cyclic voltammetry measurement, effective memory characteristics have still been achieved. The conclusions of the original work are not affected. The authors regret this mistake. Addition/Correction