1/<i>f</i> Noise Scaling Analysis in Unipolar-Type Organic Nanocomposite Resistive Memory

We studied noise characteristics of a nanocomposite of polyimide (PI) and phenyl-C61-butyric acid methyl ester (PCBM) (denoted as PI:PCBM), a composite for the organic nonvolatile resistive memory material. The current fluctuations were investigated over a bias range that covers various intermediate resistive states and negative differential resistance (NDR) in organic nanocomposite unipolar resistive memory devices. From the analysis of the 1/<i>f</i>^γ type noises, scaling behavior between the relative noise power spectral density <i>S̃</i> and resistance <i>R</i> was observed, indicating a percolating behavior. Considering a linear rate equation of the charge trapping–detrapping at traps, the percolation behavior and NDR could be understood by the modulation of the conductive phase fraction φ with an external bias. This study can enhance the understanding of the NDR phenomena in organic nanocomposite unipolar resistive memory devices in terms of the current path formation and the memory switching

Electric Stress-Induced Threshold Voltage Instability of Multilayer MoS₂ Field Effect Transistors

We investigated the gate bias stress effects of multilayered MoS₂ field effect transistors (FETs) with a back-gated configuration. The electrical stability of the MoS₂ FETs can be significantly influenced by the electrical stress type, relative sweep rate, and stress time in an ambient environment. Specifically, when a positive gate bias stress was applied to the MoS₂ FET, the current of the device decreased and its threshold shifted in the positive gate bias direction. In contrast, with a negative gate bias stress, the current of the device increased and the threshold shifted in the negative gate bias direction. The gate bias stress effects were enhanced when a gate bias was applied for a longer time or when a slower sweep rate was used. These phenomena can be explained by the charge trapping due to the adsorption or desorption of oxygen and/or water on the MoS₂ surface with a positive or negative gate bias, respectively, under an ambient environment. This study will be helpful in understanding the electrical-stress-induced instability of the MoS₂-based electronic devices and will also give insight into the design of desirable devices for electronics applications

Interface-Engineered Charge-Transport Properties in Benzenedithiol Molecular Electronic Junctions via Chemically p‑Doped Graphene Electrodes

In this study, we fabricated and characterized vertical molecular junctions consisting of self-assembled monolayers of benzenedithiol (BDT) with a p-doped multilayer graphene electrode. The p-type doping of a graphene film was performed by treating pristine graphene (work function of ∼4.40 eV) with trifluoromethanesulfonic (TFMS) acid, producing a significantly increased work function (∼5.23 eV). The p-doped graphene–electrode molecular junctions statistically showed an order of magnitude higher current density and a lower charge injection barrier height than those of the pristine graphene–electrode molecular junctions, as a result of interface engineering. This enhancement is due to the increased work function of the TFMS-treated p-doped graphene electrode in the highest occupied molecular orbital-mediated tunneling molecular junctions. The validity of these results was proven by a theoretical analysis based on a coherent transport model that considers asymmetric couplings at the electrode–molecule interfaces

Electrical and Optical Characterization of MoS₂ with Sulfur Vacancy Passivation by Treatment with Alkanethiol Molecules

We investigated the physical properties of molybdenum disulfide (MoS₂) atomic crystals with a sulfur vacancy passivation after treatment with alkanethiol molecules including their electrical, Raman, and photoluminescence (PL) characteristics. MoS₂, one of the transition metal dichalcogenide materials, is a promising two-dimensional semiconductor material with good physical properties. It is known that sulfur vacancies exist in MoS₂, resulting in the n-type behavior of MoS₂. The sulfur vacancies on the MoS₂ surface tend to form covalent bonds with sulfur-containing groups. In this study, we deposited alkanethiol molecules on MoS₂ field effect transistors (FETs) and then characterized the electrical properties of the devices before and after the alkanethiol treatment. We observed that the electrical characteristics of MoS₂ FETs dramatically changed after the alkanethiol treatment. We also observed that the Raman and PL spectra of MoS₂ films changed after the alkanethiol treatment. These effects are attributed to the thiol (−SH) end groups in alkanethiols bonding at sulfur vacancy sites, thus altering the physical properties of the MoS₂. This study will help us better understand the electrical and optical properties of MoS₂ and suggest a way of tailoring the properties of MoS₂ by passivating a sulfur vacancy with thiol molecules