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ABSTRACT:We report on the nonvolatile memory characteristics of a bistable organic memory (BOM) device with Au nanoparticles (NPs) embedded in a conducting poly-(N-vinylcarbazole) (PVK) colloids hybrid layer deposited on flexible poly(ethyleneterephthalate) (PET) substrates. Transmission electron microscopy (TEM) images show the Au nanoparticles distributed isotropically around the surface of a PVK colloid. The average induced charge on Au nanoparticles, estimated using the C-V hysteresis curve, was large, as much as 5 holes/NP at a sweeping voltage of (3 V. The maximum ON/OFF ratio of the current bistability in the BOM devices was as large as 1 Â 10 5 . The cycling endurance tests of the ON/OFF switching exhibited a high endurance of above 1.5 Â 10 5 cycles, and a high ON/OFF ratio of ∼10 5 could be achieved consistently even after quite a long retention time of more than 1 Â 10 6 s. To clarify the memory mechanism of the hole-mediated bistable organic memory device, the interactions between Au nanoparticles and poly(Nvinylcarbazole) colloids was studied by estimating the density of states and projected density of state calculations using density functional theory. Au atom interactions with a PVK unit decreased the band gap by 2.96 eV with the new induced gap states at 5.11 eV (HOMO, E 0 ) and LUMO 4.30 eV and relaxed the HOMO level by 0.5 eV (E 1 ). E 1 at ∼6.2 eV is very close to the pristine HOMO, and thus the trapped hole in E 1 could move to the HOMO of pristine PVK. From the experimental data and theoretical calculation, it was revealed that a low-conductivity state resulted from a hole trapping at E o and E 1 states and subsequent hole transportation through Fowler-Nordheim tunneling from E 1 state to Au NPs and/or interface trap states leads to a high conductivity state.

Two-dimensional (2-D) metal chalcogenides have received great attention because of their unique properties, which are different from bulk materials. A challenge in implementing 2-D metal chalcogenides in emerging devices is to prepare a well-crystallized layer over large areas at temperatures compatible with current fabrication processes. Tin monosulfide, a p-type layered semiconductor with a high hole mobility, is a promising candidate for realizing large-area growth at low temperatures because of its low melting point. However, tin sulfides exist in two notable crystalline phases, SnS and SnS2. Therefore, it is imperative to control the oxidation state of Sn to achieve a pure SnS film. Here, the synthesis of SnS thin films by atomic-layer-deposition (ALD) is demonstrated using bis­(1-dimethylamino-2-methyl-2-propoxy)­tin­(II) and H2S as Sn and S sources, respectively, over a wide temperature window (90–240 °C). Impurities such as carbon, oxygen, and nitrogen were negligibly detected. The morphological evolution of plate-like orthorhombic SnS grains was observed above 210 °C. Moreover, properties of thin film transistors and gas sensors using SnS films as the active layers were investigated. The SnS ALD process would provide promising opportunities to exploit the intriguing properties of the 2-D metal chalcogenides for realizing emerging electronic devices.

The functionalization of two-dimensional electron gas (2DEG) at oxide interfaces can be realized integrating 2DEG with multifunctional oxide overlayers by epitaxial growth. Using a ferroelectric Pb(Zr0.2 Ti0.8 )O3 overlayer on 2DEG (LaAlO3 /SrTiO3 ), we demonstrate a model system of the functionalized 2DEG, where electrical conductivity of 2DEG can be reversibly controlled with a large on/off ratio (>1000) in a non-volatile way by ferroelectric polarization switching.

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